Ichnology of the Lower Miocene Chenque Formation, Patagonia, Argentina: animal - substrate interactions and the Modern Evolutionary Fauna
Noelia B. Carmona1, Luis A. Buatois2, María Gabriela Mángano2 and Richard G. Bromley3
1Laboratorio de Geología Andina. Centro Austral de Investigaciones
Científicas. CONICET. B. Houssay 200, 9410 Ushuaia.
Tierra del Fuego. Argentina. carmonanb@yahoo.com.ar
2Department of Geological Sciences. University of Saskatchewan.
114 Science Place. Saskatoon. SK S7N 5E2, Canada.
3Department of Geography and Geology. University of Copenhagen.
Øster Voldgade 10. 1350 Copenhagen K. Denmark.
Abstract. The lower Miocene Chenque Formation of Patagonia contains superbly preserved and diverse ichnofaunas, including the ichnogenera Asterosoma, Balanoglossites, Chondrites, Gastrochaenolites, Gyrolithes, Helicodromites, Macaronichnus, Nereites, Ophiomorpha, Palaeophycus, Phycosiphon, Planolites, Protovirgularia, Rhizocorallium, Rosselia, Schaubcylindrichnus, Scolicia, Siphonichnus, Skolithos, Spongeliomorpha, Taenidium, Teichichnus, and Thalassinoides. Wave-influenced open-marine deposits are characterized by intense bioturbation, complex tiering structures and a very high diversity. Restricted, brackish-water, tide-dominated deposits display lesser degrees of bioturbation, less complex tiering structures and lower ichnodiversity. Both marginal- and open-marine deposits are commonly punctuated by discontinuity surfaces delineated by firmground ichnofaunas. The complex tiering structure of open marine ichnofaunas shows the development of a finely partitioned infaunal niche and an increment in bioturbation by the Neogene, which is consistent with trends revealed by body fossils. However, further expansion of the Cenozoic ichnologic database is necessary in order to evaluate the role of evolutionary and latitudinal controls.
Resumen. Icnología De La Formación Chenque (Mioceno Inferior), Patagonia, Argentina: Interacciones Sustrato-Animal y La Fauna Evolutiva Moderna. La Formación Chenque (Mioceno temprano) se caracteriza por presentar icnofaunas extremadamente diversas, que incluyen los icnogéneros Asterosoma, Balanoglossites, Chondrites, Gastrochaenolites, Gyrolithes, Helicodromites, Macaronichnus, Nereites, Ophiomorpha, Palaeophycus, Phycosiphon, Planolites, Protovirgularia, Rhizocorallium, Rosselia, Schaubcylindrichnus, Scolicia, Siphonichnus, Skolithos, Spongeliomorpha, Taenidium, Teichichnus y Thalassinoides. Los depósitos marinos normales con influencia de oleaje se caracterizan por presentar un intenso grado de bioturbación, el desarrollo de estructuras de escalonamiento muy complejas y una alta icnodiversidad. Por el contrario, los depósitos restringidos, de aguas salobres, dominados por mareas, presentan un menor grado de bioturbación, una estructura de escalonamiento menos compleja y una menor icnodiversidad. Tanto los depósitos marinos marginales como los marinos abiertos presentan icnofaunas características de sustratos firmes, las cuales delimitan superficies de discontinuidad. La compleja estructura de escalonamiento observada en las icnofaunas marinas normales refleja el desarrollo de una fina partición del ecoespacio infaunal y un incremento en la bioturbación durante el Neógeno, lo cual concuerda con las tendencias globales reflejadas a partir del registro de cuerpos fósiles. Sin embargo, se requiere un mayor número de estudios sobre icnofaunas cenozoicas para discriminar entre controles evolutivos y latitudinales.
Key words. Trace fossils; Miocene; Chenque Formation; Patagonia; Shallow marine.
Palabras clave. Trazas fósiles; Mioceno; Formación Chenque; Patagonia; Marino somero.
Introduction
Lower Miocene deposits of the Chenque Formation, outcropping in the southeast of Chubut and northeast of Santa Cruz provinces, Argentina, contain extremely abundant and diverse trace fossils. Although the body fossils and sedimentary facies of this formation have received considerable attention (Frenguelli, 1929; Feruglio, 1949; Expósito, 1977; Cione, 1978; Bellosi, 1987, 1995; Bellosi and Barreda, 1993; Paredes, 2002; del Río, 2002), its ichnology has not yet been analyzed. Only recently, some papers provided information on some of these well-preserved trace fossil assemblages (Carmona et al., 2002; Buatois et al., 2003a; Carmona and Buatois, 2003; Carmona, 2005; Carmona et al., 2006). Therefore, the main purposes of this paper are: (1) to describe and illustrate the trace fossils of the Chenque Formation, (2) to evaluate their paleoecology and ethology, and (3) to briefly discuss the paleoenvironmental distribution of the trace fossils and their significance with respect to secular changes in bioturbation linked to the development of the Modern Evolutionary Fauna.
Geological setting
The Chenque Formation crops out in the San Jorge Basin, Central Patagonia, Argentina (figure 1) and consists mainly of shallow-marine deposits bearing abundant and diverse invertebrate body fossils and trace fossils. The Chenque Formation comprises five shallowing-upward depositional sequences (figure 2), deposited during the Leonense (26-21 Ma) and Superpartagoniense (19-18 Ma) Atlantic transgressions (Bellosi, 1987, 1995). The age of the Chenque Formation is based on the sequence stratigraphic framework (Bellosi, 1990a; Bellosi and Barreda, 1993), dinoflagellates (Palamarczuk and Barreda, 1998; Barreda and Palamarczuk, 2000a,b), pollen and spores (Barreda, 1996; Barreda and Palamarczuk 2000a,b), foraminifers (Bertels and Ganduglia, 1977), vertebrates (Caviglia, 1978; Cione, 1978), and isotope dating (Riggi, 1979; Bellosi, 1990b). The first two sequences are dominated by sandy, muddy, and tuffaceous shoreface deposits, with abundant body fossils (specially oysters and other mollusks), and dominance of shoreface environments, while the upper sequences of this formation (sequences III-V), are sandier, with less abundant body fossils and ichnofossils, reflecting deposition in restricted, marginal-marine, tide-influenced environments (Bellosi, 1987, 1995, 2000; Bellosi and Barreda, 1993).
Figure 1. Map showing the distribution of the Chenque Formation
and the studied localities / mapa de distribución de la Formación Chenque, mostrando la ubicación de las localidades estudiadas.
Figure 2. Sequences of the Chenque Formation and proposed depositional
environments (modified from Bellosi and Barreda,
1993). This study focused on sequences I-III (marked with grey
shadow) / secuencias de la Formación Chenque y diferentes ambientes depositacionales propuestos (modificado de Bellosi y Barreda, 1993). El presente estudio se centró en el análisis de las secuencias I-III (marcadas con color gris).
Field work was especially concentrated on deposits outcropping on the Atlantic coast of Chubut and Santa Cruz provinces, because these deposits show the best preservation of trace fossils and the highest ichnodiversity. Trace fossils were analyzed at 14 localities (figure 1), the majority of which consist of vertical cliff sections and extensive horizontal surfaces that represent the abrasion platform exposed during low tide. Superb preservation allows threedimensional reconstructions of the trace fossils. The analyzed localities include deposits belonging mostly to the lower sequences (I-III) which, as mentioned above, record the highest abundance and diversity of biogenic structures of this formation.
Systematic ichnology
This section focuses on the systematic description
of the trace fossils identified in the Chenque
Formation. Trace fossils were mainly studied in the
field, and ichnotaxonomic analysis was complemented
with drawings, photographs and collected specimens,
which are housed at the Collection of Paleontology
of Invertebrates of CADIC (Centro Austral de
Investigaciones Científicas), Ushuaia, Argentina. Ichnotaxa
are arranged alphabetically, and their analysis
includes a brief discussion about ichnotaxonomy,
environmental and stratigraphic range, and probable
ethology of the tracemaker.
The majority of the specimens were identified at
ichnospecific level. However, some ichnofossils
show morphological variation that makes it difficult
to assign them to defined ichnospecies. In addition,
some beds contain abundant biogenic structures
that intersect with complex cross-cutting relationships,
a fact that further complicates identification
of ichnofossils. In these cases, open nomenclature is
used. Table 1 summarizes additional information
about the recognized ichnogenera in the Chenque
Formation.
Table 1. Ichnogenera identified in the Chenque Formation. Information includes environmental distribution, stratigraphic range, ethology and probable trace makers / icnogéneros identificados en la Formación Chenque. La tabla incluye información sobre la distribución ambiental, rango estratigráfico, etología y posibles organismos productores.
Ichnogenus Asterosoma von Otto, 1854
Asterosoma isp. A Figure 3.1-2
Figure 3. 1-2, Asterosoma isp. A. 1, Bedding plane view, Playa Las Cuevas. 2, Cross-section view and Schaubcylindrichnus coronus (Sch),
Punta Delgada. 3-4, Asterosoma isp. B. 3, Specimen showing predominantely horizontal bulbs, Caleta Olivia. 4, Cross-section view,
Cerro Hermitte. 5, Balanoglossites isp. in the tuffaceous beds, Punta Delgada. The arrow indicates the presence of apparent scratch ornament. 6, Chondrites isp. reworking previous trace fossils, Playa Las Cuevas. 7-8, Gyrolithes isp., bedding plane view, Punta Delgada.
In 7, the fill of Gyrolithes isp. is reworked by pale Chondrites isp. (Ch). In 8, two specimens of Gyrolithes isp. (Gy) indicated by arrows
/ 1-2, Asterosoma isp. A. 1, Vista en planta, Playa Las Cuevas. 2, Vista en sección de Asterosoma isp. A y Schaubcylindrichnus coronus (Sch), Punta Delgada. 3-4, Asterosoma isp. B. 3, Vista en planta de un ejemplar mostrando predominio de bulbos horizontales, Caleta Olivia. 4, Vista en sección, Cerro Hermitte. 5, Balanoglossites isp. en depósitos tobáceos, Punta Delgada. La flecha indica la presencia de aparente ornamentación. 6, Chondrites isp. retrabajando estructuras biogénicas previas, Playa Las Cuevas. 7-8, Gyrolithes isp., vista en planta, Punta Delgada. En la figura 7, el relleno de Gyrolithes isp. se encuentra retrabajado por Chondrites isp. (Ch) claros. En la figura 8 se indican con flechas dos especimenes de Gyrolithes isp. (Gy).
Description. Horizontal and subhorizontal bulbs
arranged radially or in a fan-like manner. The fill of
the bulbs comprises concentrically laminated sediment
enclosing a central to subcentral tube. Bulb diameter
is 15-25 mm and maximum length is 200 mm.
The concentric structures are composed of mud and
very fine-grained sand. Intersection of bulbs is commonly
observed in cross section. Preserved as full relief.
Remarks. The bulb walls of some Cretaceous (Otto,
1854) and Jurassic (Schlirf, 2000) occurrences show
longitudinal furrows or striae. In the Miocene specimens
identified as Asterosoma isp. A, however, this
feature was not recognized, probably because their
external surface is not visible. They also lack the typical
tapering of the bulbs, and associated shafts (e.g.
Bromley and Uchman, 2003) were not observed. Specimens
of Asterosoma isp. A resemble Asterosoma radiciforme
von Otto, 1854 for its radial or star-like orientation
of the bulbs. However, poor definition of the
general morphology and absence of views of the external
surfaces of the bulbs preclude ichnospecific assessment.
Localities. Playa Las Cuevas, Punta Delgada and Rada Tilly.
Asterosoma isp. B Figure 3.3-4
Description. Subvertically arranged bulbs, showing
concentric lamination and subcentral inner tube.
Bulbs do not overlap and generally taper at their distal
ends. Bulb diameter is commonly 25-30 mm and
length is 90-200 mm. Preserved as full relief.
Remarks. Asterosoma isp. B differs from Asterosoma
isp. A in having a subvertical arrangement of the
bulbs and tapering ends. At only one locality (roadcut
on National Route 3), do the bulbs show furrows
on their external surfaces. However, these specimens
are preserved as concretions and this preservation
could have caused the irregularities and striae seen
on their surfaces. Therefore, this feature probably
should not be regarded as a character reflecting the
original morphology of this trace fossil. Asterosoma
isp. B differs from A. radiciforme von Otto, 1854 by the
radial and horizontal arrangement of the bulbs in the
latter. These specimens also differ from A. ludwigae
Schlirf, 2000 by the subvertical orientation of the
bulbs and absence of the typical ramification of this
ichnospecies (Schlirf, 2000).
Localities. Caleta Olivia, Cerro Antena, Cerro Hermitte and roadcut on National Route 3.
Ichnogenus Balanoglossites Mägdefrau, 1932
Balanoglossites isp. Figure 3.5
Description. Connected U-shaped burrows, 15-19
mm wide. Maximum depth observed is approximately
140 mm. Some specimens have tunnels with
smaller diameters that form blind ends, diverging
from the principal U-shaped burrow. Striations occur
on the wall of some specimens. Burrows are passively
filled with sand. Preserved as full relief.
Remarks. Specimens of Balanoglossites isp. from the
Chenque Formation differ from the type specimens
in the presence of tunnels that go downward and laterally
from the main burrow. In contrast, specimens
from the Middle Triassic of Poland and Germany
show ramifications that diverge from the U-shape
burrow in an upward direction (Kazmierczak and
Pszczólkowski, 1969).
The studied specimens of Balanoglossites isp. resemble
Diplocraterion parallelum var. arcum (Ekdale
and Lewis, 1991) in overall morphology of the
causative burrow. However, absence of spreiten distinguishes
Balanoglossites isp. from D. parallelum. In addition,
the ichnogenus Balanoglossites characteristically
has ramifications, which are absent in D. parallelum.
Kazmierczak and Pszczólkowski (1969) observed
that the material from the Middle Triassic of Poland
presents net outlines and smooth walls without any
evidence of bioglyphs. These authors also suggested
that the tracemakers were not able to live in consolidated
or firm substrates and suggested emplacement
in a soft substrate instead based on the deformation
observed in some of the burrows. In contrast, specimens
of Balanoglossites from the Chenque Formation
rework a tuffaceous substrate that was firm at the
time of colonization. This interpretation is supported
by the presence of bioglyphs (figure 3.5), the net outline
and the ichnofauna associated with Balano-
glossites isp. Furthermore, Knaust (1998) described
Balanoglossites in association with the boring Trypanites
in hardgrounds, suggesting a firm, pre-cementation
substrate for Balanoglossites.
Locality. Punta Delgada.
Ichnogenus Chondrites von Sternberg, 1833
Chondrites isp. Figures 3.6-7, 4.5, 5.10
Figure 4. 1-3, Gastrochaenolites ornatus. 1, Lateral view of several specimens with the internal casts and external moulds of the bivalve
tracemakers. 2, Lateral view, showing in the upper portion the bivalve cast well preserved. 3, Basal view of several specimens showing
different sizes. 4-5, Helicodromites mobilis. 4, Bedding plane view with H. mobilis reworking Scolicia isp. (Sc). Thalassinoides isp. (Th)
is in the upper right corner. 5, Helicodromites mobilis reworked by Chondrites isp. (Ch). 6-7, Macaronichnus segregatis, Caleta Olivia. 6, Bedding plane view of M. segregatis. This trace fossil constitutes a dominant element in these beds. 7, Cross section view of M. segregatis (Ma). 8, Palaeophycus tubularis, Cerro Hermitte / 1-3, Gastrochaenolites ornatus. 1, Vista lateral de varios especimenes de G. ornatus con los moldes internos y secundarios de los bivalvos productores. 2, Vista lateral, mostrando en la porción superior, el molde secundario del bivalvo productor con excelente preservación. 3, Vista basal de varios ejemplares de diferentes tamaños. 4-5, Helicodromites mobilis. 4, Vista en planta de H. mobilis retrabajando Scolicia isp. (Sc). Thalassinoides isp. (Th) en el extremo superior derecho. 5, Helicodromites mobilis retrabajado por Chondrites isp. (Ch). 6-7, Macaronichnus segregatis, Caleta Olivia. 6, Vista en planta de M. segregatis. Esta traza fósil constituye un elemento dominante en estos estratos. 7, Vista en sección de M. segregatis (Ma). 8, Palaeophycus tubularis, Cerro Hermitte.
Figure 5. 1-2, Nereites missouriensis preserved in the interface between sandy and muddy beds, Caleta Olivia. 3-5, Ophiomorpha nodosa. 3, 4, Cerro Hermitte. In 3, well developed pellets and sandy filling. In 4, pellets have been weathered out, leaving empty spaces
along the vertical shaft. 5, Specimen from Playa Alsina, showing a thick wall and the fill mainly composed of coarse sand and bioclastic
fragments. 6-10., Ophiomorpha isp., Punta Delgada. 6 and 7 correspond to vertical sections of Ophiomopha isp. In 6, the arrow indicates
the apparent bilobate morphology of pellets. In 7 the characteristic conical morphology of the pellets is visible. 8, Cross section of Ophiomorpha isp., showing greater development of those pellets located on the roof of the burrow. The arrow indicates the absence of
pellets on the floor. 9, Specimen at the turnaround point, showing that ramifications form sharp angles. 10, Ophiomorpha isp. in oblique
section, showing specimens of Chondrites isp. (Ch) reworking its fill / 1-2, Nereites missouriensis preservado en la interface arena fango, Caleta Olivia. 3-5, Ophiomorpha nodosa. 3, 4, Cerro Hermitte. En 3, ejemplar de O. nodosa con pellets bien desarrollados y relleno arenoso. En 4, los pellets no se preservaron, dejando espacios vacíos a lo largo del tubo vertical. 5, Especimen de Playa Alsina, mostrando una pared gruesa y relleno principalmente compuesto por arenas gruesas y fragmentos bioclásticos. 6-10, Ophiomorpha isp., Punta Delgada. Las figuras 6 y 7 muestran secciones verticales de Ophiomorpha isp. En 6, la flecha indica la morfología aparentemente bilobada de los pellets. En 7 se puede reconocer la morfología cónica características de estos pellets. 8, Sección de Ophiomorpha isp. mostrando mayor desarrollo de los pellets en el techo de la excavación. La flecha indica la ausencia de pellets en la base. 9, Vista en planta de un ejemplar de Ophiomorpha isp. con ramificaciones formando ángulos rectos. 10, Ophiomorpha isp. en un corte oblicuo, mostrando especimenes de Chondrites isp. (Ch) retrabajando su relleno.
Description. A tree-like system of tunnels that
branch downward. Width of tunnels constant within
each specimen (1.0-1.8 mm). Angle of branching
commonly less than 45º. Almost all specimens show
second-order branches. Color of the sediment fills always
different from the color of the host rock.
Preserved as full relief.
Remarks. The studied specimens differ from the ichnospecies
Chondrites intricatus by commonly having
slightly curved branches and tube diameters larger
than 1 mm. The slightly curved branches resemble C.
targionii (Brongniart, 1828), although in this ichnospecies,
tunnels are commonly a few millimeters
wide (Uchman, 1999). Chondrites patulus Fischer-
Ooster, 1858 has simple branches perpendicular to
the primary stems (Uchman, 1999) and C. recurvus
(Brongniart, 1823) shows branches arising only from
one side of the masterbranch, bending in a single direction.
These characteristics allow the distinction of
both C. recurvus and C. targionii from the studied
specimens. Chondrites isp. also differs from C. caespitosus
(Fischer-Ooster, 1858) by the dense and short
winding branches that characterized the latter.
Finally, these specimens differ from C. stellaris
Uchman, 1999 in the smaller size and radiating
branching of the latter (Uchman, 1999). Tunnel fill of
Chondrites isp. may be either lighter or darker than
the host rock (figure 3.6).
Localities. Playa Alsina, Playa Las Cuevas, Punta Borja, Punta Delgada and Rada Tilly.
Ichnogenus Gastrochaenolites Leymerie, 1842
Gastrochaenolites ornatus Kelly and Bromley, 1984 Figure 4.1-3
Specimens. CADIC PI 39-45.
Description. Clavate structures with bioglyphs in
their deeper portions. Diameters of the main chambers
are highly variable (2-25 mm). When the neck is
preserved, specimens are up to 95 mm long. The bioglyphs
show two preferred orientations: oblique and
parallel to bedding. Some specimens have a small,
shallow subcentral depression at their base.
Remarks. The presence of bioglyphs relates these lower
Miocene specimens to the ichnospecies Gastrochaenolites
ornatus. This feature distinguishes Gastrochaenolites
ornatus from the other ichnospecies of
Gastrochaenolites (e.g. G. ampullatus Kelly and
Bromley, 1984, G. cor Bromley and D'Alessandro,
1987, G. dijugus Kelly and Bromley, 1984, G. lapidicus
Kelly and Bromley, 1984, G. orbicularis Kelly and
Bromley, 1984, G. cluniformis Kelly and Bromley,
1984, G. turbinatus Kelly and Bromley, 1984 and G.
torpedo Kelly and Bromley, 1984).
The studied specimens were constructed in a
firm, tuffaceous substrate and are connected to the
boundary surface between the continental Sarmiento
Formation and the shallow-marine Chenque Formation
(Carmona et al., 2006). Although the studied
specimens were emplaced in firm substrates and the
ichnogenus Gastrochaenolites was primarily defined
to designate clavate borings developed in hard substrates
(Kelly and Bromley, 1984), these specimens
are assigned to this ichnogenus because their morphology
is identical to the specimens constructed in
lithified substrates (Carmona et al., in press).
Localities. Astra, Infiernillo and West of Bahía Solano.
Ichnogenus Gyrolithes de Saporta, 1884
Gyrolithes isp. Figure 3.7-8
Description. Vertical, unbranched spiral burrows.
Width of the burrows is 45-65 mm and radius of the
whorls is 69-95 mm. Whorls sinistrally coiled and
wall structure commonly consisting of a thin muddy
layer (1-2 mm) or with few, irregularly distributed
conical pellets. Preserved as full relief.
Remarks. Specimens from the Chenque Formation
have the diagnostic characteristics proposed by
Bromley and Frey (1974) for this ichnogenus.
However, the studied specimens clearly differ from
the type ichnospecies Gyrolithes davreuxi of Saporta,
1884, from G. saxonicus (Häntzschel, 1934) and from G. krymensis Vialov, 1969 by their larger size, orientation
of the whorls and characters of the wall. In addition,
incomplete preservation of these specimens
precludes an ichnospecific designation. Preservation
restricted to bedding planes also precludes measurement
of height of the burrows and height of the
whorls.
Specimens of Gyrolithes isp. form a dense aggregation,
covering approximately a surface of 2 m2. Some
burrows have been reworked by Chondrites isp.
(figure 3.7). The same characteristic was observed in
the fillings of Ophiomorpha isp., which occur in the same
bed with Gyrolithes isp. These observations, and
the presence of sparsely distributed conical pellets in
the Gyrolithes specimens, support the idea that these
two ichnogenera were produced by the same organism.
Mayoral and Muñiz (1993) also recorded intergrading Gyrolithes and Ophiomorpha in Late Miocene-
Pliocene deposits of Huelva. Hester and Prior (1972)
interpreted that these intergradations could represent
adaptative responses of the organisms to live in
substrates with differences in cohesiveness, building
Ophiomorpha-like burrows in sandier substrates and
Gyrolithes-like burrows in muddier deposits.
Locality. Punta Delgada.
Ichnogenus Helicodromites Berger, 1957
Helicodromites mobilis Berger, 1957 Figures 4.4-5, 7.2
Description. Horizontal spiral burrows, with pale fill
contrasting with the host-rock. Diameter of tubes
with two different sizes; smaller specimens are 2.6-
3.2 mm wide and larger ones are 5.4-9.8 mm wide.
Length is highly variable and some structures reach
up to 300 mm long. Distance between successive
whorls is 10-13 mm in the smaller specimens and 26-
29 mm in the larger examples. Preserved as full relief.
Remarks. Analysis of the specimens from the Chenque
Formation indicates a relationship between tube
diameters and the distance between successive
whorls. In all the studied specimens this relationship
is 0.2-0.3, suggesting that specimens of Helicodromites
mobilis were constructed by the same organism and
that differences in sizes reflect ontogenetic variations.
Tiering analysis shows that the Helicodromites
tracemaker was a relatively deep bioturbator, cutting
almost all the other biogenic structures in these deposits,
being only reworked by Chondrites isp. (figure
4.5).
Localities. Playa Las Cuevas and Punta Delgada.
Ichnogenus Macaronichnus Clifton and Thompson, 1978
Macaronichnus segregatis Clifton and Thompson, 1978 Figure 4.6-7
Description. Predominately horizontal or sub-horizontal,
cylindrical trace fossil that interpenetrates
randomly. Diameter is 4-6 mm. Trace fossil fill lighter
than the host rock. It occurs gregariously. Preserved
as full relief.
Remarks. Pemberton et al. (2001) and Gingras et al.
(2002b) mentioned that modern polychaetes produce
structures similar to the ichnospecies Macaronichnus
segregatis, ingesting sand to consume bacteria and organic
material attached to the grains, and excreting
the clean sand that fills the core of the burrow
(Pemberton et al., 2001).
Macaronichnus segregatis segregatis differs from the
other three ichnosubspecies by its randomly interpenetrating
burrow configurations (Bromley et al., in
press). The specimens from the Chenque Formation
are straight or slightly curved and in some cases, approaching
the morphology of M. s. lineiformis show
interpenetrations producing "false branchings" (sensu
D'Alessandro and Bromley, 1987). In the Chenque
Formation M. segregatis is the dominant ichnotaxon
in deposits that also contain vertical components of
Ophiomorpha nodosa.
Localities. Caleta Olivia, Playa Alsina and Punta Delgada.
Ichnogenus Nereites MacLeay, 1839
Nereites missouriensis (Weller, 1899) Figure 5.1-2
Description. Predominantely horizontal, winding to
meandering trace fossil with a dark, central tunnel
and lateral lobes of reworked, paler sediment.
Measured on horizontal surfaces, the diameter is 5.2-
6.5 mm, and the central tunnel, composed of alternating
muddy and sandy laminae, is 3.0-4.0 mm wide.
Maximum length observed is 64 mm. On vertical sections,
the same measurements were 5.5-6.9 mm and
2.2-2.5 mm respectively. The thin lateral lobes are not
clearly visible in horizontal sections, especially if
there is a dense association of structures, but they are
much clearer in vertical section, where they resemble
giant Phycosiphon. Preserved as epirelief.
Remarks. Proportions between width of central
channel and the reworked zone fall within the
range proposed by Uchman (1995) for Nereites missouriensis.
This ichnospecies differs from Nereites
cambrensis (Murchinson, 1839) in the absence of
lanceolate lateral lobes and from Nereites imbricata Mángano, Buatois, West and Maples, 2000, by
having transverse scalariform ridges (Mángano et
al., 2002) instead of the imbricated subspherical
pads characteristic of the latter. Nereites missouriensis
is also distinguished from N. irregularis (Schafhäutl, 1851) by having the central backfilled
tunnel and the envelope zone of similar thickness,
and also by the absence of coiled, closely packed
meanders, typical of the last ichnospecies
(Uchman, 1998).
Locality. Caleta Olivia and Playa Las Cuevas.
Ichnogenus Ophiomorpha Lundgren, 1891
Ophiomorpha nodosa Lundgren, 1891 Figure 5.3-5
Description. Large burrow systems, with vertical
and horizontal components, having walls composed
of dense, regularly or irregularly distributed ovoid
pellets. Branching T- and Y-shaped. The fill is passive
and diameter range is 20-40 mm. Maximum depth
observed is approximately 640 mm. Preserved as full
relief.
Remarks. The studied specimens show the diagnostic
characteristics of Ophiomorpha nodosa, although
they show some variations in size, three-dimensional
configuration and pellet composition in the different
specimens studied. For example, in the upper
deposits of Playa Alsina locality specimens are composed
principally of vertical components, with large
and ovoid pellets (approximately 7.5 mm wide).
These pellets are muddy and form a continuous
wall. Burrow diameter is approximately 40 mm and
the fill is composed of alternating muddy and sandy
laminae with bioclast fragments (figure 5.5). In other
localities (e.g. roadcut on National Route 3; Cerro
Antena and Cerro Hermitte), the specimens are
smaller, reaching diameters up to 25 mm (figure
5.3).
Localities. Caleta Olivia, Cerro Antena, Cerro Chenque, Cerro Hermitte, Cerro Viteau, Infiernillo, Playa Alsina, Punta Borja, Rada Tilly and roadcut on National Route 3.
Ophiomorpha isp. Figures 5.6-10, 6.7
Figure 6. 1-2, Phycosiphon incertum. 1, Cross section view, Punta Delgada. 2, Cross section, Caleta Olivia. 3, Abundant Planolites beverleyensis,
Cerro Viteau. 4, Protovirgularia isp., Caleta Olivia. Epichnial preservation in a muddy layer. 5, Cross section view of Rhizocorallium isp. in the upper tuffaceous deposit from Punta Delgada. Arrows indicate specimens of Thalassinoides isp. (Th). 6-8, Rosselia socialis. 6, R. socialis in tidal channel deposits, showing erosive truncation (indicated by arrows), Cerro Hermitte. 7, Rosselia socialis, reworked by Ophiomorpha isp. in its basal portion. Rada Tilly. 8, Rosselia socialis, Caleta Olivia. The specimen shows erosive
truncation (indicated by the arrow), and renewed building up of the structure / 1-2, Phycosiphon incertum. 1, Vista en sección, Punta Delgada. 2, Vista en sección, Caleta Olivia. 3, Abundantes especímenes de Planolites beverleyensis, Cerro Viteau. 4, Protovirgularia isp., Caleta Olivia. Preservación epicnia en un sustrato pelítico. 5, Vista en sección de Rhizocorallium isp. en el nivel tobáceo superior de Punta Delgada. Las flechas señalan ejemplares de Thalassinoides isp. (Th). 6-8, Rosselia socialis. 6, R. socialis en depósitos de canales mareales, mostrando truncamiento erosivo (indicado por flechas), Cerro Hermitte. 7, Especimen de R. socialis retrabajado por Ophiomorpha isp. en su porción basal, Rada Tilly. 8, Rosselia socialis, Caleta Olivia. Este ejemplar muestra truncamiento erosivo (indicado por la flecha), y nuevo crecimiento de la estructura biogénica.
Figure 7. 1, Schaubcylindrichnus coronus, showing closely bundled tubes. 2, Schaubcylindrichnus freyi, Helicodromites mobilis (He), Scolicia isp. (Sc) and Planolites beverleyensis (Pl), Playa Las Cuevas. 3-5, Scolicia isp., Playa Las Cuevas. 3, Upper bedding plane view
of Scolicia isp. with its possible tracemaker (spatangoid echinoid). 4, Cross section of Scolicia isp. showing its two drain tubes (dt) at
the base of the trace fossil. 5, Bedding plane view of a deposit completely reworked by Scolicia isp. These specimens are commonly associated
with the body fossils of their tracemakers. 6, Cross section of Siphonichnus eccaensis associated to Thalassinoides suevicus (Th),
Playa Alsina. 7, Specimen of Spongeliomorpha isp., Playa Alsina. The arrow indicates the scratch ornament (so) sculpted in the firm host
sediment / 1, Schaubcylindrichnus coronus, mostrando el agrupamiento ceñido de los tubos. 2, Schaubcylindrichnus freyi, Helicodromites mobilis (He), Scolicia isp. (Sc) y Planolites beverleyensis (Pl), Playa Las Cuevas. 3-5, Scolicia isp., Playa Las Cuevas. 3, Vista en planta de Scolicia isp. con su posible organismo productor (equinodermo espatangoideo). 4. Vista en sección de Scolicia isp. mostrando los dos canales de drenaje (dt) en la parte basal de la traza fósil. 5, Vista en planta de un nivel completamente retrabajado por Scolicia isp. Comúnmente estas estructuras biogénicas se encuentran asociadas a los cuerpos fósiles de sus organismos productores. 6, Vista en sección de Siphonichnus eccaensis asociado a Thalassinoides suevicus (Th), Playa Alsina. 7, Ejemplar de Spongeliomorpha isp., Playa Alsina. La flecha señala los bioglifos (so) generados en un sustrato firme.
Description. Burrow systems having T- and Y-shaped
branches, characterized by the presence of conical
pellets, with a square base facing to the interior of
the burrow. Some pellets apparently have a bi-conical
morphology. Although size of pellets is variable
(5-11 mm width and 4.0-11.5 mm height), most commonly
they are 8-10 mm wide and 7-9 mm high.
Pellets are regularly arranged in the walls. Burrows
are 40-100 mm wide and the fill is passive. Preserved
as full relief.
Remarks. These specimens were described in detail
by Carmona and Buatois (2003) and are classified at
the ichnogeneric level because the overall morphology
of the pellets distinguishes this material from
all formally defined ichnospecies of Ophiomorpha.
These Lower Miocene specimens differ from the
ichnospecies Ophiomorpha nodosa by the absence of
ovoid pellets and by having a more regular distribution
in the walls. These specimens differ from
Ophiomorpha annulata (Ksiazkiewicz, 1977) because,
although having the elongate section of the pellets
oriented perpendicular to the long axis of the burrows,
they are not smooth in their external surface.
Ophiomorpha irregulaire Frey, Howard and Pryor,
1978 may have elongated conical, ovoid or mastoid
pellets, irregularly distributed on burrow walls and
a characteristic "meander maze" morphology (e.g.
Bromley and Ekdale, 1998; Pedersen and Bromley,
2006). However, the specimens from the Chenque
Formation show a much more organized distribution
of the pellets than O. irregulaire, and we consider
that this character is diagnostic. Ophiomorpha
puerilis Gibert, Netto, Tognoli and Grangeiro, 2006,
is characterized by having distinctive elongated
round-ended fecal pellets, which are absent in the
specimens of Ophiomorpha isp. described here.
Finally, Ophiomorpha borneensis Keij, 1965 is characterized
by regularly distributed bilobate pellets
(Frey et al., 1978), similar to the examples from the
Chenque Formation. However, these bilobate pellets
are rounded and not conical as in the studied
material. In summary, the overall morphology of
the pellets distinguishes Ophiomorpha isp. from all
formally defined ichnospecies of Ophiomorpha and
we consider that these lower Miocene burrows
could correspond to a new ichnospecies of Ophiomorpha
and will be further analyzed elsewhere.
Localities. Punta Delgada and Rada Tilly.
Ichnogenus Palaeophycus Hall, 1847
Palaeophycus heberti (de Saporta, 1872) Not figured
Description. Straight to slightly curved, inclined to
horizontal smooth-walled burrows. Wall lining is
relatively thick (1.5-2.5 mm). Tube diameter remains
constant along the burrows (6-10 mm).
Maximum length observed is 33 mm. Preserved as
full relief.
Remarks. Some of these specimens are similar in
burrow diameter and lining width to Schaubcylindrichnus
Frey and Howard, 1981 and they commonly
occur in the same beds. This ichnospecies differs
from Palaeophycus tubularis by having a thicker lining
and differs from other ichnospecies of Palaeophycus
(e.g. P. striatus Hall, 1852 or P. alternatus Pemberton
and Frey, 1982) by the absence of ornamentations or
annulations.
Localities. Playa Alsina, Playa Las Cuevas and Punta Delgada.
Palaeophycus tubularis Hall, 1847 Figure 4.8
Description. Straight to slightly sinuous, horizontal,
smooth, thinly lined burrows. Width is 4-7 mm and
maximum length observed is 50 mm. Burrow lining
is 0.5-1.0 mm thick. Burrow fill is massive and similar
to the host rock. Preserved as full relief.
Remarks. Palaeophycus tubularis is the type ichnospecies of Palaeophycus. This ichnospecies has a thinner
wall lining than P. heberti and is distinguished
from other ichnospecies of Palaeophycus (e.g. P. striatus)
by the absence of striae and annulations.
Localities. Cerro Hermitte, Playa Las Cuevas, Punta Delgada and Rada Tilly.
Ichnogenus Phycosiphon Fischer-Ooster, 1858
Phycosiphon incertum Fischer-Ooster, 1858 Figure 6.1-2
Description. Spreite trace fossils formed by recurving
U-lobes in bedding planes. In cross section, the
dark core is 3.7-4.7 mm wide whereas the surrounding
pale mantle is 1.3-1.8 mm wide. Preserved as full
relief.
Remarks. The studied specimens do not clearly
show the presence of spreiten, but show the pale
mantle and the general configuration of Phycosiphon
incertum and, therefore, they are assigned to this ichnospecies.
The analyzed specimens are similar in
preservation to those studied by Uchman (1995,
Plate 8, Fig. 7 and 8).
Localities. Caleta Olivia, Playa Alsina, Playa Las Cuevas, Punta Delgada and Rada Tilly.
Ichnogenus Planolites Nicholson, 1873
Planolites beverleyensis (Billings, 1862) Figures 6.3, 7.2
Description. Relatively large, unlined, smooth,
straight to slightly curved structures, oriented predominantely
horizontally. Diameter is 4-7 mm.
Maximum length observed is 50 mm. Some specimens
possess diagenetic halos. Preserved as full relief.
Remarks. These specimens differ from Planolites annularis
Walcott, 1890 in the absence of annulations characteristics
of that ichnospecies. Planolites beverleyensis
also differs from P. montanus Richter, 1937 by its larger
size, better defined boundaries and by being more
continuous along the bedding plane. Absence of small
striae distinguishes these specimens from Planolites
terraenovae Fillion and Pickerill, 1990.
Localities. Caleta Olivia, cerro Antena, cerro Chenque, cerro Hermitte, cerro Viteau and roadcut on National Route 3.
Planolites montanus Richter, 1937 Not figured
Description. Relatively small horizontal to subhorizontal,
unlined structures, 3-5 mm wide and 25-50
mm long. Burrow fill is massive and lighter than host
rock. Preserved as full relief.
Remarks. These specimens differ from Planolites beverleyensis
in their small size and more curved course.
Localities. Playa Alsina, Playa Las Cuevas, Punta
Delgada and Rada Tilly.
Ichnogenus Protovirgularia M'Coy, 1850
Protovirgularia isp. Figure 6.4
Description. Predominantly horizontal trace fossil
characterized by the presence of closely spaced, Vshaped
ornamentation along the structure. If the internal
structure is preserved, it is formed by successive
sediment pads. Specimens are 7-18 mm wide
and the maximum length observed is 188 mm. Traces
are mostly straight, locally curved. The chevron ornamentation
is variable in morphology, being closely
spaced and having a defined morphology in some
specimens while showing an irregular outline in others.
In epichnial specimens, chevron patterns are
formed mainly by mud, although in endichnial
preservations they are formed of alternating sandy
and muddy packets.
Remarks. The analyzed Protovirgularia isp. shows a
wide morphologic variability, probably related to
differences in substrate consistency. Mángano et al.
(2002 and references therein) mentioned morphological
variations of Protovirgularia in Carboniferous
deposits from Kansas, and attributed them to
substrate properties and position of the bivalve
within the substrate. The specimens from the Chenque
Formation are preserved as endichnia and, more
rarely, as epichnia. Some specimens show affinities
with Protovirgularia dichotoma M'Coy, 1850, based
on the morphology of the chevron markings
and a few specimens have a Lockeia-like structure at
the beginning or end of the locomotion structures,
a characteristic that could relate this material to
Protovirgularia rugosa (Miller and Dyer, 1878). However,
the endichnial and epichnial preservations
do not allow to clearly observe the morphology of
the chevron patterns and, therefore, it is not possible
to classify this material at ichnospecific level.
Locality. Caleta Olivia.
Ichnogenus Rhizocorallium Zenker, 1836
Rhizocorallium isp. Figure 6.5
Description. U-shaped burrows having a spreite, oriented
oblique to the bedding plane. Diameter of the
limbs is approximately 5-7 mm and total width of the
structure is 40-80 mm. Limbs are filled with sand.
Preserved as full relief.
Remarks. These specimens resemble Rhizocorallium
jenense Zenker, 1836, in their oblique orientation and
their general morphology (a simple U-shaped burrow).
However, absence of a bedding plane view precludes
assignement of this material to a defined ichnospecies.
Abundance of specimens of Rhizocorallium
isp. is low to moderate, being restricted only to a
tuffaceous level in the Punta Delgada locality.
Locality. Punta Delgada.
Ichnogenus Rosselia Dahmer, 1937
Rosselia socialis Dahmer, 1937 Figure 6.6-8
Description. Vertical to inclined funnel-shaped burrow
with a central tube filled with sandy sediment,
surrounded by concentric muddy lamination. Size is
highly variable; diameter is 30-100 mm and length is
50 to 400 mm. Specimens showing erosional truncations
are common. Preserved as full relief.
Remarks. Rosselia socialis differs from R. chonoides
Howard and Frey, 1984 by the absence of spiral
swirls of sediment and from R. rotatus McCarthy,
1979 by having concentric lamination and lacking of
helicoid structures in the backfill, which are produced
by the rotational movement of the central
tube in R. rotatus (Fillion and Pickerill, 1990). Alternatively,
Uchman and Krenmayr (1995) synonymized
R. rotatus with R. socialis, considering that
features of R. rotatus constitute intraspecific variations
of R. socialis related to high-energy environments.
Wide variations in length and diameter found in
the studied specimens may be related to variable environmental
conditions. Specimens of Rosselia socialis
are isolated or form crowded clusters. The isolated
specimens show a vertical orientation in the finegrained
deposits of the lower shoreface, whereas an
inclined orientation is typical in sandier tidal channel
deposits (figure 6.7 and 8).
Figure 8. 1, Taenidium isp., bedding plane view, Playa Las Cuevas. 2-3, Cross section views of Teichichnus rectus, Caleta Olivia. 4-5, Teichichnus zigzag, Playa Las Cuevas. 4, Oblique cross-section of T. zigzag. 5, Bedding plane view of T. zigzag and associated trace fossils. 6, ?Teichichnus isp., showing the causative burrow with arcuate filling, Rada Tilly. 7-8, Thalassinoides suevicus. 7, Cerro Chenque,
note the large size of this structure and its development in the horizontal plane. 8, High abundance of T. suevicus, Playa Alsina. 9, Bedding plane view of Thalassinoides isp., Punta Borja, showing apparent Y-ramification pattern. The boundary of this structure is not
clearly visible and the filling seems to correspond to the arcuate passive type / 1, Taenidium isp., vista en planta, Playa Las Cuevas. 2-3, Vista en sección de Teichichnus rectus, Caleta Olivia. 4-5, Teichichnus zigzag, Playa Las Cuevas. 4, Sección oblicua de T. zigzag. 5, Vista en planta de T. zigzag y trazas fósiles asociadas. 6, ?Teichichnus isp., mostrando el tubo causativo con relleno arqueado, Rada Tilly. 7-8, Thalassinoides suevicus. 7, Ejemplar del Cerro Chenque. Note el gran tamaño de esta estructura y el desarrollo que presenta en el plano horizontal. 8, Gran abundancia de T. suevicus, Playa Alsina. 9, Vista en planta de Thalassinoides isp., Punta Borja, mostrando aparentemente un patrón de ramificación en Y. El límite de este ejemplar no se distingue claramente y el relleno parece corresponder al tipo pasivo arqueado.
Localities. Caleta Olivia, cerro Antena, cerro Chenque, cerro Hermitte, cerro Viteau, Infiernillo, Playa Las Cuevas, Punta Borja, Punta Delgada, Rada Tilly and roadcut on National Route 3.
Ichnogenus Schaubcylindrichnus Frey and Howard, 1981
Schaubcylindrichnus coronus Frey and Howard, 1981 Figures 3.2, 7.1
Description. Oblique to horizontal bundles of congruent,
pale-lined tubes. Diameter is 5.9-6.6 mm and
lining is 1.3-1.6 mm thick. Tubes are mainly circular
in cross-section and some specimens show cross-cutting
relationships between successive tubes. Exterior
surfaces of the tubes are smooth, without ornamentation.
Preserved as full relief.
Remarks. Schaubcylindrichnus coronus is characterized
by the presence of closely-packed bundles of tubes,
this feature being the main difference between
this ichnospecies and S. freyi (Miller, 1995). Number
of tubes in each specimen is variable, although commonly
they comprise 3-4 tubes. Schaubcylindrichnus
coronus also differs from S. formosus Löwemark and
Hong, 2006, by being smaller and by the absence of
interconnections and ramifications in the central part
of the sheaves, typical of this last ichnospecies.
Localities. Playa Las Cuevas, Punta Delgada and Rada Tilly.
Schaubcylindrichnus freyi Miller, 1995 Figure 7.2
Description. Vertical to oblique burrows, rarely subhorizontal,
and having a pale lining. The burrows
form loose bundles. Diameter is highly variable (4.5-
12.0 mm), although tubes from the same specimens
maintain a constant diameter. Lining is 0.8- 2.0 mm
thick. Some specimens show flattened tubes. Preserved
as full relief.
Remarks. The specimens from the Chenque Formation
form loose bundles, which is distinctive of
Schaubcylindrichnus freyi and allow differentiation
from S. coronus and S. formosus. In addition, these
specimens are smaller than S. formosus (Löwemark
and Hong, 2006).
The analyzed specimens from the Chenque
Formation show a wide size range. Miller (1995) considered
that size variations observed in specimens of
S. freyi are related to grain size. He concluded that in
coarsening-upward sequences, the basal deposits
with finer-grained sediments contain the largest specimens,
while in the upper coarser-grained deposits,
the specimens of S. freyi show variable sizes. His conclusion
is consistent with the relations observed in
the Chenque Formation (e.g. in Playa Las Cuevas and
Punta Delgada localities).
Recently, Nara (2006) considered Schaubcylindrichnus
freyi as a junior synonym of S. coronus. This
author analyzed the type material of these two ichnospecies
and concluded that except for their mode
of occurrence, size and construction of the tubes are
similar in both ichnospecies. However, we consider
that our material should be included in S. freyi because
it displays the morphological characters of this
ichnospecies, being clearly distinguished from specimens
of S. coronus.
Localities. Caleta Olivia, Playa Alsina, Playa Las Cuevas, Punta Delgada and Rada Tilly.
Ichnogenus Scolicia de Quatrefages, 1849
Scolicia isp. Figures 4.4, 7.2-5
Description. Horizontal, sinuous or meandering
trails with a bilobate backfill and two parallel strings
located at the base. The strings are 7-8 mm wide and
are interpreted as traces of drain canals. The region
between these canals is slightly concave upward. In
cross section, burrow outline is normally oval to
somewhat square, 42-44 mm wide and 20-22 mm
high. Preserved as full relief.
Remarks. The studied specimens were not assigned
to any defined ichnospecies of Scolicia because these
are distinguished by characters present on their bases,
which are observed only in hypichnial preservations.
In longitudinal section, some specimens have a
small V-shaped depression in the upper part of the
backfill, being similar in morphology to the Laminites
preservational variant as illustrated by Plaziat and
Mahmoudi (1988, figure 3). The backfill is invariably
composed of alternate sandy and muddy laminae.
Localities. Playa Alsina, Playa Las Cuevas, Punta Borja, Punta Delgada and Rada Tilly.
Ichnogenus Siphonichnus Stanistreet, Le Blanc Smith and Cadle, 1980
Siphonichnus eccaensis Stanistreet, Le Blanc Smith and Cadle, 1980 Figure 7.6
Description. Vertical structures containing a backfill
of concave-downward menisci. The laminae that
form the backfill are cut through centrally by a vertical
tube, filled with pale, massive sand. In bedding
plane view, burrow diameter is 20-28 mm and central
tube diameter is approximately 9-11 mm.
Remarks. In bedding plane views, specimens of
Siphonichnus have a rounded transverse cross-section.
This feature distinguishes this ichnogenus from
aggradational Lingulichnus, which are characterized
by having an elliptical transverse cross-section (Zonneveld
and Pemberton, 2003). Most of the specimens
of Siphonichnus eccaensis show a straight vertical orientation,
although some examples may present a
slightly sinuous course. Stanistreet et al. (1980) postulated
that siphon length of the bivalve tracemakers
should be equal to the length of backfill laminae. In
their material, the minimum length proposed is 12.5
cm. However, the specimens from the Chenque
Formation are longer, recording a maximum length
of 35 cm, which renders the bivalve model unlikely.
Alternatively, this may record the increase in burrowing
depth by bivalves that resulted from the
Mesozoic Marine Revolution.
Localities. Playa Alsina, Playa Las Cuevas, Punta Borja, Punta Delgada and Rada Tilly.
Ichnogenus Skolithos Haldemann, 1840
Skolithos linearis Haldemann, 1840 Not figured
Description. Simple, vertical tubes. Diameter is 3-4
mm and length of complete specimens is 200-350
mm. The majority of specimens are preserved as
fragments. Burrow fill is sandy and the walls are
thinly lined by fine sediment. Preserved as full relief.
Remarks. The specimens of Skolithos linearis are associated
with sandy deposits. The wall of these specimens
is commonly affected by diagenesis, enhancing
their visibility. Skolithos lineraris is associated with
Ophiomorpha nodosa, suggesting moderate to high energy
conditions.
Locality. Cerro Chenque.
Skolithos verticalis (Hall, 1843) Not figured
Description. Vertical to inclined, straight to slightly
curved tubes. Diameter is 2.3-4.0 mm and length is
50-70 mm. Burrow fill is finer-grained than the host
rock and is mainly composed of massive mud.
Preserved as full relief.
Remarks. This ichnospecies is poorly represented in
the studied deposits. However, in those localities
where it was observed, the abundance of structures
was relatively high, being dominant and forming
monospecific associations.
Diameters obtained from the studied specimens
of Skolithos verticalis are coincident with the values
from the Paleozoic examples studied by Fillion and
Pickerill (1990), although the Miocene specimens are
longer. Skolithos verticalis is distinguished from S. linearis
because the former is smaller and shorter. They
also differ in the type of fill, being muddy in S. verticalis
and mainly sandy in S. linearis.
Localities. Playa Alsina and roadcut on National Route 3.
Ichnogenus Spongeliomorpha de Saporta, 1887
Spongeliomorpha isp. Figure 7.7
Description. Burrow with an ornament of short
ridges covering the surface of the structure. Burrow
diameter is 25 mm. Burrow fill is massive, composed
of sandy sediment. Preserved as full relief.
Remarks. The studied specimen constitutes a burrow
fragment and therefore it was not possible to
identify the general morphology of the structure,
precluding ichnospecific assessment. The short
scratches are oriented mainly parallel to the axis
of the burrow. This specimen is distinguished
from Spongeliomorpha sublumbricoides (Azpeitia
Moros, 1933), S. orviense (Ksiazkiewicz, 1977), S.
milfordiensis Metz, 1993 and S. carlsbergi (Bromley
and Asgaard, 1979), these ichnospecies having
obliquely oriented scratch ornament (D'Alessandro
and Bromley, 1995). It also differs from
Spongeliomorpha sicula D'Alessandro and Bromley,
1995, in the absence of longitudinally extended
ridges and ovoid chambers. These specimens are
also distinguished from S. chevronensis Muñiz and
Mayoral, 2001, by the absence of regularly distributed,
oblique ridges, and from S. sinuostriata Muñiz and Mayoral, 2001, by lacking the long and
sinuous scratch ornament that characterizes this
ichnospecies.
Localities. Infiernillo and Playa Alsina.
Ichnogenus Taenidium Heer, 1877
Taenidium isp. Figure 8.1
Description. Cylindrical and unlined sinuous trace
fossils, 10-15 mm wide. Length is variable, generally
80-100 mm. Fill consists of meniscate segments alternately
composed of fine- and coarse-grained sediments.
Preserved as full relief.
Remarks. The taxonomic status of Taenidium is uncertain
because the type material is lost and at its
type locality no true specimens of Taenidium have
been subsequently found. The name Taenidium is
provisionally adopted here, pending a comprehensive
review of meniscate ichnofossils.
Taenidium isp. from the Chenque Formation commonly
occurs in intensely bioturbated beds. This
high bioturbation does not allow clear observations
of the relevant morphologic characteristics and,
therefore, precludes ichnospecific designation.
Specimens found in Playa Las Cuevas and Rada Tilly
localities show hemispheric menisci, similar to those
described for T. barretti (Bradshaw, 1981). However,
specimens of T. barretti have a more constant diameter
than the specimens from the Chenque Formation.
These specimens also differ from Taenidium crassum
Bromley, Ekdale and Richter, 1999 by the absence of
parabolic- or chevron-like menisci that characterize
this ichnospecies (Bromley et al., 1999).
Localities. Playa Las Cuevas and Rada Tilly.
Ichnogenus Teichichnus Seilacher, 1955
Teichichnus rectus Seilacher, 1955 Figure 8.2-3
Description. Horizontal to slightly inclined, unlined,
simple structures, with a retrusive spreite. Causative
burrow is 17.5-27.3 mm in diameter and the length of
the spreite is up to 200 mm. In lateral view, the specimens
are mainly horizontal or they can display a
flattish U-shape. Preserved as full relief.
Remarks. Schlirf (2000) observed that Late Jurassic
specimens from the Boulonnais, France, have the
causative burrow rarely preserved. This kind of
preservation is commonly observed in the majority
of the studied specimens, except those from Caleta
Olivia where T. rectus displays excellent causative
burrows in cross section (e.g. figure 8.3).
Localities. Caleta Olivia, Playa Las Cuevas, Punta Delgada and Rada Tilly.
Teichichnus zigzag Frey and Bromley, 1985 Figure 8.4-5
Description. Teichnichnus having a spreite showing
not only a vertical migration vector, but also a lateral
vector, producing a zig-zag pattern. Width of the
spreite is 15-40 mm, a range that exceeds the diameter
of the causative burrow (10-12 mm). Size and
morphology of the specimens are highly variable.
The causative burrow fill is preferentially sandy,
while the dark spreite laminae are muddy. Preserved
as full relief.
Remarks. This ichnospecies differs from the other
defined ichnospecies of Teichichnus by the zig-zag
pattern of the spreiten. In the original diagnosis of
this ichnospecies, Frey and Bromley (1985) considered
that the spreite observed in these structures typically
shows an arcuate course, developed in the vertical
plane. However, they also mentioned that in
some specimens the spreite course is horizontal, as is
the case of specimens from the Chenque Formation.
Frey and Bromley (1985) suggested that the general
morphology of T. zigzag could correspond to a shallow
U-shaped burrow. In Playa Las Cuevas locality,
the specimens of T. zigzag are well preserved and
they are only reworked by Chondrites isp.
Locality. Playa Las Cuevas.
?Teichichnus isp. Figure 8.6
Description. Large horizontal structures with a
retrusive spreite and a terminal, passively filled tube.
Some specimens seem to branch. Spreite height is 60-
70 mm and maximum length observed is 550 mm.
Preserved as full relief.
Remarks. The analyzed specimens are asigned to
Teichichnus with doubts, because they apparently present
ramifications, making interpretation of the threedimensional
morphology of these trace fossils uncertain.
In cross-section, the specimens are similar to
large Techichnus rectus (with dimensions resembling
T. pescaderoensis Stanton and Dodd, 1984, an ichnospecies
considered to be a junior synonym of T. rectus
by Fillion and Pickerill, 1990, and Schlirf and
Bromley, 2007). However, the apparent branching
pattern seen in the bedding plane view prevents assignment
of this material to the ichnospecies T. rectus.
These structures also resemble Teichichnus patens
Schlirf (2000) because this ichnospecies presents ramifications.
However, the Miocene material differs
from T. patens in the more clearly defined morphology
and constant diameter of the branches of the latter.
Structures similar to those found in the Chenque
Formation were observed in lower Miocene deposits
from Las Grutas, Patagonia, Argentina (Olivero,
pers. com., 2005). These specimens show a comparable
general morphology, although the lithologic constrast
is greater in these deposits, allowing identification
of some features such as possible scratch traces.
These specimens from Las Grutas are interpreted as
having been constructed by decapods (Olivero, pers.
com., 2005).
Localities. Rada Tilly.
Ichnogenus Thalassinoides Ehrenberg, 1944
Thalassinoides suevicus (Rieth, 1932) Figures 7.6, 8.7-8
Description. Predominantly horizontal, passively filled, large and regularly branching, cylindrical burrow systems. Diameter is 60-120 mm. T-shaped and Yshaped bifurcations are common. Swellings occur at branching points. In horizontal components, maximum observed length is 1.5 m. Preserved as full relief. Remarks. The studied specimens present lengths and diameters larger than those mentioned for other specimens of T. suevicus (e.g. Frey and Bromley, 1985). The burrows display T-shaped and Y-shaped ramifications. These specimens differ from Thalassinoides paradoxicus (Woodward, 1830) in having ramifications more regularly arranged and in the presence of predominantly horizontal components.
Localities. Cerro Chenque, Playa Alsina, Playa Las Cuevas and Punta Delgada.
Thalassinoides isp. Figures 4.4, 8.9
Description. Large burrow systems with horizontal
and vertical components. Diameter is highly variable
(17-76 mm). Passive fill is mainly composed of structureless
sand or subhorizontal, alternating muddy
and sandy laminae. Preserved as full relief.
Remarks. In many of the studied deposits, the
specimens assigned to Thalassinoides isp. are incompletely
preserved, mainly consisting of short fragments;
branching points are not observed. This partial preservation precludes ichnospecific identification.
The fill of Thalassinoides isp. is mainly sandy, except
in those deposits interpreted as tidal flat facies,
where the fill consists of alternating sandy and muddy
laminae, most likely reflecting tidal cyclicity. In
some cases, burrows are reworked by Chondrites isp.
and Phycosiphon incertum.
Localities. Astra, Caleta Olivia, cerro Antena, cerro Hermitte, Infiernillo, Playa Las Cuevas, Punta Delgada, Rada Tilly and West of Bahía Solano. Structures produced by the bivalve Atrina Figure 9.1-3
Figure 9. 1-3, Equilibrium structures of Atrina, Caleta Olivia. 1-2, Close-up views of two different specimens, with the body fossils of
their tracemakers at the end of the structures, and also showing the traces left by the byssal threads (indicated by arrows). 3, General
view of the equilibrium trace fossils. 4-5, Concave upward structures from Caleta Olivia. These biogenic structures are probably feeding
traces of rays / 1-3, Estructuras de equilibrio de Atrina, Caleta Olivia. 1-2, Vista detallada de dos ejemplares que presentan los cuerpos fósiles de los organismos productores preservados al final de las estructuras. Note también las marcas dejadas por el biso (indicadas con flechas). 3, Vista general de las estructuras de equilibrio. 4-5, Estructuras cóncavas observadas en depósitos de Caleta Olivia. Estas trazas fósiles son comparables a estructuras de alimentación de rayas.
Description. Large vertical to slightly oblique, V-shaped
spreiten structures. Vertical length is variable (120-240
mm). Maximum length observed is 500 mm. The Vshaped
spreite is always retrusive. Commonly, the
shells of the bivalve tracemakers are preserved at the
upper end of the structures. Exceptionally preserved
specimens display some pale, very thin sandy threads,
radiating from the basal part of these trace fossils.
Remarks. These biogenic structures represent equilibrichnial
trace fossils produced by Atrina bivalves during
their upward movement, in response to aggradational
events. The retrusive backfill is composed of alternating
sandy and muddy V-shaped laminae. The
thin sandy structures that radiate from the basal part of
the ichnofossils are interpreted as the traces left by the
byssal threads of these bivalves (figures 9.1 and 2).
Preservation of these specimens is restricted to vertical
sections, so bedding plane views are not available.
These equilibrium trace fossils co-occur with specimens
of Teichichnus rectus in the same beds.
Hanken et al. (2001) defined the ichnogenus Scalichnus
to include large, vertically oriented, bottleshaped
structures, formed during retrusive and pro-
trusive movement of the bivalve Panopea. As in the
case of the trace fossils generated by Atrina in the
Chenque Formation, Scalichnus is also regarded as an
equilibrichnial trace fossil. However, this ichnogenus
differs from the present material by its general sacklike
morphology and its thick lining.
Locality. Caleta Olivia. Large, concave-upward structures Figure 9.4-5
Description. Concave upward structures, 250-320
mm wide in the upper portion and 80-100 mm in the
lower portion. Cross sections of these structures generally
show asymmetric U-profiles, with one slope
steeper than the other. Fill differs markedly from the
host rock. Preserved as full relief.
Remarks. The specimens observed in these Miocene
deposits resemble biogenic structures generated by
rays while feeding, assigned to the ichnogenus
Piscichnus Fiebel, 1987. The ichnogenus Piscichnus
was originally defined by Fiebel (1987) to include shallow
depressions interpreted as nesting traces produced
by bony fishes. In his original description,
Fiebel (1987) recognized only one ichnospecies,
Piscichnus brownii. Later, Gregory (1991) described a
new ichnospecies of Piscichnus, P. waitemata, to include
pits much deeper and more cylindrical than P.
brownii. Piscichnus waitemata also cut the internal
structure of the substrate and is interpreted as formed
by hydraulic jetting generated by rays while feeding
(Gregory, 1991). Although the specimens from the
Chenque Formation are similar to Piscichnus, the low
abundance of structures and the absence of bedding
plane views preclude a definite assignment.
Locality. Caleta Olivia.
Environmental distribution of trace fossils The Chenque Formation comprises shallowmarine deposits (figure 2), encompassing both open marine and marginal marine environments (Bellosi, 1987, 1995, Buatois et al., 2003a, Carmona, 2005). In turn, tide-dominated marginal marine successions include both estuarine and deltaic deposits. Some of these deposits are truncated by surfaces that are associated with erosional exhumation of the substrate (firmgrounds). Table 2 summarizes the occurrence of trace fossils in the different localities.
Table 2. Occurrence of trace fossils in the Chenque Formation. X indicates the presence of the different ichnotaxa. Localities: AS: Astra,
BS: West of Solano Bay, CA: Cerro Antena, CC: Cerro Chenque, CH: Cerro Hermitte, CO: Caleta Olivia, CRN: roadcut on National Route
3, CV: Cerro Viteau, IN: Infiernillo, LC: Playa Las Cuevas, PA: Playa Alsina, PB: Punta Borja, PD: Punta Delgada, RT: Rada Tilly / Ocurrencia de las trazas fósiles en la Formación Chenque. La X indica la presencia de los diferentes ichnotaxones. Localidades: AS: Astra, BS: Oeste de Bahía Solano, CA: Cerro Antena, CC: Cerro Chenque, CH: Cerro Hermitte, CO: Caleta Olivia, CRN: corte de la Ruta Nacional 3, CV: Cerro Viteau, IN: Infiernillo, LC: Playa Las Cuevas, PA: Playa Alsina, PB: Punta Borja, PD: Punta Delgada, RT: Rada Tilly.
Open marine environments
Open marine successions include upper, middle
and lower shoreface deposits. Lower shoreface deposits
are recognized in the Playa Las Cuevas, Rada
Tilly and Punta Delgada localities. These deposits
consist of thoroughly bioturbated very fine-grained
silty sandstone. Only locally parallel lamination and
discrete shell layers are observed. Trace fossils are
abundant and diverse. These lower shoreface deposits
are characterized by the presence of the archetypal
Cruziana ichnofacies (Buatois et al., 2003a).
Common elements include Chondrites isp., Phycosiphon
incertum, Thalassinoides suevicus, Teichichnus
zigzag and T. rectus, Palaeophycus heberti, Scolicia isp.,
Helicodromites mobilis, Nereites missouriensis,
Planolites montanus, Schaubcylindrichnus coronus and
S. freyi, Taenidium isp., Asterosoma isp. A, and Rosselia
socialis.
In the Rada Tilly and Punta Delgada localities, a
slight upward increase in grain size and the presence
of elements of the Skolithos ichnofacies suggest progressive
shallowing and deposition in a middle
shoreface environment. This ichnofauna is dominated
by Ophiomorpha isp. and Asterosoma isp. A. Subordinate
elements comprise Thalassinoides suevicus,
Phycosiphon incertum, Schaubcylindrichnus freyi,
Chondrites isp., Scolicia isp., Rosselia socialis,
Palaeophycus heberti, Palaeophycus tubularis, Planolites
montanus and Teichichnus rectus. This trace fossil suite
is interpreted as a proximal expression of the
Cruziana ichnofacies.
Upper shoreface deposits are recognized in the
upper interval of the Playa Alsina section. These deposits
consist of glauconitic sandstones with trough
cross-stratification and planar lamination. The trace
fossil suite represents the Skolithos ichnofacies, and is
characterized by heavily lined, deeply penetrating
vertical structures such as Ophiomorpha nodosa, and
mobile intrastratal deposit feeding burrows, such as
Macaronichnus segregatis.
Tide-dominated estuarine environments
Estuarine deposits occur at Cerro Antena, Cerro
Chenque, Cerro Hermitte, Cerro Viteau, and the
roadcut on National Route 3. At almost all of these
localities, intertidal flat and subtidal sandbar and
channel deposits are present. The intertidal flat deposits
mainly consist of heterolithic beds with a low
to moderate degree of bioturbation and well preserved
physical sedimentary structures. Depositfeeder
trace fossils, such as Asterosoma isp. B and
Planolites beverleyensis, are dominant components of
these assemblages.
The subtidal sandbar and channel deposits display
planar and trough cross bedding. The observed
ichnodiversity is low to moderate and monospecific
assemblages are common. Macaronichnus segregatis,
Ophiomorpha nodosa and Rosselia socialis dominate this
ichnofauna.
Overall, these characteristics (e.g. low to moderate
ichnodiversity, monospecific associations, generally
small sizes, presence of an impoverished Cruziana-
Skolithos ichnofacies) suggest a stressful environment,
affected by salinity fluctuations. The Chenque
estuarine ichnofauna is similar to other brackish-water
estuarine ichnofaunas described from the fossil
record (e.g. Pemberton and Wightman, 1992; Mac-
Eachern and Pemberton, 1994; Mángano and Buatois,
2004b; Buatois et al., 2005).
Tide-dominated deltaic environments
Tide-dominated deltaic deposits occur in outcrops
from the Caleta Olivia locality. Two main subenvironments
are recognized: prodelta and deltafront,
stacked forming a progradational coarseningupward
succession. The prodelta is characterized by
lenticular and wavy-bedded heterolithic strata, with
abundant synaeresis cracks. These deposits typically
display low to moderate bioturbation intensities, although
a high degree of bioturbation occurs locally.
The trace fossil assemblage is dominated by deposit
feeder structures, such as Planolites beverleyensis, Teichichnus rectus and Phycosiphon incertum; subordinate
and rare elements include Asterosoma isp. B,
Nereites missouriensis, Rosselia socialis, Schaubcylindrichnus
freyi, and Thalassinoides isp. This assemblage
is considered a stressed expression of the archetypal
Cruziana ichnofacies.
The delta-front succession shows two main facies
representing distal to proximal deposits. The distal
delta-front facies consists of flaser-bedded, heterolithic
muddy sandstone, almost completely obliterated
by equilibrium trace fossils of Atrina.
Subordinately, Teichichnus rectus, Thalassinoides isp.
and Schaubcylindrichnus freyi are also present. Proximal
delta-front facies are sand-dominated with thin
siltstone interbeds. The trace fossil suite is dominated
by large Rosselia socialis and Macaronichnus segregatis
in the sandier beds, whereas Nereites missouriensis
and Protovirgularia isp. are commonly associated
to the mud drapes blanketing the sandstone foresets.
The intensity of bioturbation is commonly low, although
some intervals may show relatively higher
values. The trace fossil suite found in the delta-front
facies corresponds to an impoverished expression of
the proximal Cruziana ichnofacies.
The described ichnofaunas show features typical
of deltaic environments (MacEachern et al., 2005).
These include alternation of unburrowed and bioturbated
intervals, juxtaposition of stressed and relatively
diverse suites, opportunistic colonization of
substrates and suppression of the Skolithos ichnofacies.
Firmground surfaces
Firm substrates with development of the Glossifungites
ichnofacies are recognized at Astra, West of
Solano Bay and Infiernillo. At these localities the
Glossifungites ichnofacies develops on the boundary
surface between the Sarmiento Formation and the
Chenque Formation and contains Gastrochaenolites ornatus
and Thalassinoides isp. (Carmona et al., 2006).
This suite occurs in a co-planar surface that results
from amalgamated lowstand and transgressive erosion.
Firm substrates containing the Glossifungites ichnofacies
also occur in the lower interval of the Playa
Alsina section and in the upper part of the Punta Delgada
section. Thalassinoides suevicus, Siphonichnus eccaensis
and Spongeliomorpha isp. are present in Playa
Alsina, while Thalassinoides suevicus, Balanoglossites
isp. and Rhizocorallium isp. dominate in the Punta
Delgada firmground. These two surfaces correspond
to transgressive surfaces of erosion. At both sections,
the surfaces are overlain by conglomeratic lags and
the trace fossil suites show dominance of suspension
feeder structures. However, at the Playa Alsina section,
the presence of Siphonichnus eccaensis (a deposit
feeding structure) may suggest emplacement of the
discontinuity surface in a more distal setting than
that recorded in the Punta Delgada section (see
MacEachern and Burton, 2000, and Pemberton et al.,
2004).
Finally, a third example of the Glossifungites ichnofacies
is recorded in the upper interval of the Playa
Las Cuevas section, where post-omission Thalassinoides
isp. penetrate deeply into the upper interval of
the lower shoreface deposits, from the overlying regressive
surface of marine erosion (Buatois et al.,
2003a). This surface probably records rapid shallowing
during a forced regression.
The Chenque ichnofauna and the Modern Evolutionary Fauna
Secular changes in bioturbation through the
Phanerozoic, based on comparative ichnologic analysis
are receiving increasing attention in recent years
(e.g. Thayer, 1983; Uchman, 2004; Buatois et al., 2005).
Comparisons of the ichnofauna from the Chenque
Formation with other Mesozoic and Cenozoic shallow-
marine trace fossil assemblages reveal some similarities,
mainly in trace fossil composition, although
differences in tiering structure and partitioning of the
infaunal niche are evident also. Cretaceous siliciclastic
shallow-marine ichnofaunas are well known and
have been analyzed in detail in a number of studies
(Howard and Frey, 1984; Frey and Howard, 1990;
MacEachern and Pemberton, 1992). Some characteristics
and patterns identified in these studies (e.g. the
composition of archetypal Cruziana ichnofacies in the
lower shoreface settings) are similar to those recognized
in the Chenque Formation.
The ichnology of Cenozoic shallow-marine deposits
is comparatively less documented (especially
for the Paleogene). However, a number of studies
serve for comparison (e.g. Ting et al., 1991; Pickerill et
al., 1996; Uchman and Krenmayr, 2004; Uchman and
Gazdzicki, 2006). Early Eocene, shallow-marine ichnofaunas
are known from the La Meseta Formation,
Seymour (Marambio) Island, Antarctica (Uchman
and Gazdzicki, 2006). These authors documented an
ichnoassemblage consisting of Diplocraterion, Lockeia,
Polykladichnus, Teichichnus, Scolicia, Ophiomorpha, Parataenidium,
Protovirgularia, Rhizocorallium, Skolithos
and Taenidium; and considered that these deposits accumulated
in a foreshore-offshore environment. In a
previous study of this ichnofauna, Porebski (1995)
suggested that the low ichnodiversity observed
could be indicating lowered salinity conditions.
Nevertheless, Uchman and Gazdzicki (2006) consid-
ered that although fluctuations in salinity were possible,
the presence of trace fossils produced by stenohaline
organisms (e.g. Scolicia) indicates that the
salinity was normal, at least locally. In addition,
these authors mentioned that the ichnodiversity
recorded in the La Meseta Formation is not different
from that documented in other Cenozoic shallowmarine
formations. However, the present study
shows a higher ichnodiversity for the Lower Miocene,
fully-marine deposits of the Chenque Formation.
Uchman and Krenmayr (2004) analyzed Lower
Miocene ichnofaunas from Austria that are compositionally
very similar to those from the Chenque Formation.
These authors described some characteristics
that were also identified in the Chenque Formation
(e.g. presence of isolated Rosselia specimens in highenergy,
tide-dominated deposits, identification of
Macaronichnus- or Teichichnus-monospecific ichnofabrics;
occurrence of Macaronichnus in thin sandstone
beds of mud dominated successions).
Furthermore, these authors identified the presence of
Macaronichnus-Ophiomorpha ichnofabrics in relation
to subtidal sandbar facies. This ichnofabric has been
previously described from Jurassic and Eocene deposits
of NW Europe by Pollard et al. (1993).
However, the tiering structure in some open-marine
facies from the Chenque Formation (e.g. in Playa Las
Cuevas and Punta Delgada; see Buatois et al., 2003a,
b) reveals a greater complexity than that recorded by
the Austrian ichnofaunas. Notably, the tiering structure
of the Austrian ichnofaunas closely resembles
that of the tide-dominated, deltaic ichnofaunas from
the Chenque Formation (e.g. Caleta Olivia), which is
consistent with the abundance of tidal indicators in
the example documented by Uchman and Krenmayr
(2004).
Studies in Middle Miocene to Late Pliocene deposits
from Taiwan (Ting et al., 1991) have also
shown similarities in trace fossil composition with
the Chenque Formation. In particular, lithofacies C
from Taiwan is similar to the lower shoreface facies
studied in the Playa Las Cuevas, Rada Tilly and
Punta Delgada localities. Lithofacies C is characterized
by a high degree of bioturbation, with complete
homogenization of the beds, and dominance of
Zoophycos isp., Scolicia isp., Thalassinoides paradoxicus
and Ophiomorpha nodosa. However, the study from
Taiwan does not provide information about tiering
structure, and therefore, it cannot be further compared
to the ichnofauna from the Chenque Formation.
Pickerill et al. (1996) studied the ichnologic content
of the Pliocene Bowden Formation from Jamaica
and recognized the dominance of deposit-feeder
structures (e.g. Chondrites isp., Planolites isp.,
Phycosiphon incertum, Teichichnus rectus). This ichnofauna
characterizes low-energy and low sedimentation
rates in a relatively deep-water environment
(Pickerill et al., 1996). Comparison between this
Pliocene ichnofauna and that from the Chenque
Formation suggests that the former is less diverse
and has a more simple tiering structure, and indicates
that the Bowden ichnofauna may illustrate a
transition between a distal Cruziana ichnofacies and a
Zoophycos ichnofacies.
Modern ichnofaunas seem to have been well established
in shallow-marine, open environments
since the Mesozoic. This is particularly well exemplified
in the Chenque Formation, where finely
tuned climax communities display vertical niche
partitioning and a remarkable use of the infaunal
ecospace. For example, in the lower shoreface deposits
analyzed, up to six ichnoguilds and nine
tiers have been recognized (Buatois et al., 2003b).
This tiered ichnocoenosis includes vagile, depositfeeder
structures that produce a mottled texture in
the shallowest tiers, a Thalassinoides-Asterosoma-
Rosselia ichnoguild that includes semi-vagile, deposit-
feeder traces in the shallow tiers, a
Schaubcylindrichnus-Palaeophycus ichnoguild consisting
of vagile, suspension- and deposit-feeder
structures in the middle tiers, a Scolicia-
Phycosiphon-Helicodromites-Teichichnus-Taenidium
ichnoguild comprising vagile, deposit-feeder structures
in the middle tiers, a Thalassinoides ichnoguild
that consists of stationary, deposit-feeder structures
in the deep-tiers, and a Chondrites ichnoguild
that includes non-vagile, deposit-feeder or chemosymbiont
structures in the deepest tiers. This complex
tiering structure reflects a higher partitioning
of the infaunal niche and represents a departure
with respect to Mesozoic and Paleogene ichnofaunas
in siliciclastic settings, being only equivalent to
the tiering structure documented for Cretaceous
chalk of northern Europe (Ekdale and Bromley,
1984) and southern United States (Frey and
Bromley, 1985). During the Mesozoic, the development
of the Modern Evolutionary Fauna led to important
ecological changes in marine communities
(Sepkoski, 1990). Some of these changes involved
the acquisition of additional ecologic guilds that
were not present in the Cambrian and Paleozoic
Evolutionary Faunas, particularly with respect to
the exploitation of the deep infaunal ecospace
(Thayer, 1983; Bambach, 1983; Sepkoski, 1990). The
complex tiering structure found in the Chenque
Formation shows the development of a finely partitioned
infaunal niche and an increment in bioturbation
by the Neogene. This is consistent with
trends revealed by body fossils, which show that by
the late Cenozoic, marine paleocommunities have a
much greater representation of infaunal organisms
and higher proportion of motile animals than mid-
Paleozoic communities (Bush et al., 2007).
Paleoclimatic significance
Recent research is starting to explore the importance
of latitudinal and climatic controls on shallowmarine
ichnofaunas (e.g. Aitken et al., 1988; Mángano
et al., 2002; Goldring et al., 2004; Pemberton et al.,
2006; Gingras et al., 2006). Aberhan et al. (2006) noted
that the proliferation of deep burrowers seems to be
most evident in mid and high latitudes. Bush et al.
(2007) also recognized a greater proportion of deep
infauna in temperate Cenozoic paleocommunities
than in tropical Cenozoic assemblages. Interestingly,
the mid-latitude Chenque ichnofauna reveals a
dominance of deep burrowers when compared with
the ichnologic data available for Cenozoic low-latitude
shallow-marine settings, further supporting the
pattern reflected by the body fossil record.
Goldring et al. (2004) suggested that Cenozoic and
Pleistocene occurrences of echinoid and crustacean
burrows present a climatic control and recognized
three latitudinal zones for shallow-marine settings: a
tropical and subtropical zone (with occurrences of
pellet-forming thalassinideans and burrowing echinoids),
a temperate zone (with echinoid burrows and
Thalassinoides, but not Ophiomorpha), and an arctic
zone (where neither group is present).
The lower Miocene Chenque Formation was
formed in mid latitudes and its body fossil content
suggests temperate to cold climates. Both Ophiomorpha
and Scolicia are abundant in the lower shoreface deposits,
these occurrences being anomalous to the latitudinal
division suggested by Goldring et al. (2004).
Consequently, further expansion of the Cenozoic ichnologic
database is required in order to discriminate
between latitudinal and evolutionary controls.
Acknowledgments
Valuable exchange with participants of the Ichnia 2004 field trip is greatly acknowledged, particularly J. de Gibert, R. Netto, D. Knaust, A. Uchman and A. Wetzel. B. Aguirre-Urreta, E. Olivero, J.J. Ponce, D. Lazo, M.I. López Cabrera, M. Nara, L. Löwemark, D. Martinioni and N. Pearson provided useful feedback. J.J. Ponce, M.S. Alvarez, E. Bellosi and J. Paredes helped in the field. Alvar Sobral is thanked for preparation of thin sections and polished slabs. We thank A. Uchman and M. Verde for their detailed reviews and suggestions. Financial support for this study was provided by the Antorchas Foundation, a Doctoral Grant from the Argentinean Research Council (CONICET) and an International Association of Sedimentologists Postgraduate Grant Scheme to Carmona, PIP-CONICET 5100, Natural Sciences and Engineering Research Council (NSERC) Discovery Grants 311727-05 and 311726-05 awarded to Mángano and Buatois, respectively, and University of Saskatchewan Start-up funds to Buatois.
References
1. Aberhan, M., Kiessling, W. and Fürsich, F.T. 2006. Testing the role of biological interactions in the evolution of mid-Mesozoic marine benthic ecosystems. Paleobiology 32: 259-277.
2. Aitken, A.E., Risk, M.J. and Howard, J.D. 1988. Animal-sediment relationships on a subarctic intertidal flat, Pangnirtung Fiord, Baffin Island, Canada. Journal of Sedimentary Research 58: 969- 978.
3. Asgaard, U., Bromley, R.G. and Hanken, N-M. 1997. Recent firmground burrows produced by a upogebiid crustacean: palaeontological implications. Courier Forschungsinstitut Seckenberg 210: 23-28.
4. Azpeitia Moros, F. 1933. Datos para el estudio paleontológico del Flysch de la Costa Cantábrica y de algunos puntos de España. Boletín del Instituto Geológico y Minero de España 53: 1-65.
5. Baldwin, C.T. and McCave, I.N. 1999. Bioturbation in an active deep-sea area: implications for models of trace fossil tiering. Palaios 14: 375-388.
6. Bambach, R.K. 1983. Ecospace utilization and guilds in marine communities through the Phanerozoic. In: M.J.S. Tevesz and P.L. McCall (eds.), Biotic Interactions in Recent and Fossil Benthic Communities, Plenus Press, New York, pp. 719-746.
7. Barreda, V. 1996. Bioestratigrafía de polen y esporas de la Formación Chenque, Oligoceno tardío?- Mioceno temprano de las provincias de Chubut y Santa Cruz , Patagonia, Argentina. Ameghiniana 33: 35-56.
8. Barreda, V. and Palamarczuk, S. 2000a. Palinoestratigrafía del Oligoceno tardío-Mioceno, en el área sur del Golfo San Jorge, provincia de Santa Cruz, Argentina. Ameghiniana 37: 103-117.
9. Barreda, V. and Palamarczuk, S. 2000b. Estudio palinoestratigráfico del Oligoceno tardio-Mioceno en las secciones de la costa patagónica y plataforma continental argentina. Serie de Correlación Geológica 14: 103-138.
10. Bellosi, E.S. 1987. [Litoestratigrafía y Sedimentación del "Patagoniano" en la Cuenca San Jorge, Terciario de Chubut y Santa Cruz. Universidad de Buenos Aires, Tesis Doctoral. 252 pp. Unpublished.].
11. Bellosi, E.S. 1990a. Discontinuidades en la sedimentacion litoral "patagoniana" de la Cuenca San Jorge (Terciario medio). 3º Reunión Argentina de Sedimentología (San Juan), Actas 1: 372- 377.
12. Bellosi, E.S. 1990b. Formación Chenque: registro de la transgresión patagoniana en la Cuenca San Jorge. 11° Congreso Geológico Argentino (San Juan), Actas 2: 57-60.
13. Bellosi, E.S. 1995. Paleogeografía y cambios ambientales de la Patagonia central durante el Terciario medio. Boletín de Informaciones Petroleras (B.I.P.). Tercera época. Año 11, 44: 50-83.
14. Bellosi, E.S. 2000. Facies mareales regresivas en cortejos de nivel alto: depósitos estuáricos o deltaicos? Un caso en el Mioceno de Patagonia, Argentina. 2º Congreso Latinoamericano de Sedimentología y 8º Reunión Argentina de Sedimentología (Mar del Plata), Resúmenes: 45.
15. Bellosi, E.S. and Barreda, V.D. 1993. Secuencias y palinología del Terciario medio en la Cuenca San Jorge, registro de oscilaciones eustáticas en Patagonia. 12º Congreso Geológico Argentino y 2º Congreso de exploración de Hidrocarburos (Mendoza), Actas 1: 78-86.
16. Benton, M.J. 1982. Trace fossils from the Lower Palaeozoic oceanfloor sediments of the Southern Uplands of Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 73: 67-87.
17. Berger, W. 1957. Eine spiralförmige Lebesspur aus dem Rupel der bayrischen Beckenmolasse: Neues Jahrbuch für Geologie, und Paläontologie, Monatshefte 1957: 538-540.
18. Bertels, A. and Ganduglia, P. 1977. Sobre la presencia de foraminíferos del Piso Leoniano en Astra (Provincia del Chubut). Ameghiniana 14: 308.
19. Billings, E. 1862. New species of fossils from different parts of the Lower, Middle and Upper Silurian rocks of Canada. In: Palaeozoic Fossils, 1. 1861-1865. Geological Survey of Canada Advance Sheets, pp. 96-168.
20. Bradshaw, M.A. 1981. Paleoenvironmental interpretations and systematics of Devonian trace fossils from the Taylor Group (Lower Beacon Supergroup), Antarctica. New Zealand Journal of Geology and Geophysics 24: 615-652.
21. Bromley, R.G. 1996. Trace Fossils. Biology, Taphonomy and Applications. Chapman & Hall, London, 361 pp.
22. Bromley, R.G. 2004. A stratigraphy of marine bioerosion. In: D. McIlroy (ed.), The application of ichnology to palaeoenvironmental and stratigraphic analysis, Geological Society Special Publication 228: 455-479.
23. Bromley, R.G. and Frey, R.W. 1974. Redescription of the trace fossil Gyrolithes and taxonomic evaluation of Thalassinoides, Ophiomorpha and Spongeliomorpha. Bulletin of the Geological Society of Denmark 23: 311-335.
24. Bromley, R.G. and Asgaard, U. 1975. Sediment structures produced by a spatangoid echinoid: a problem of preservation. Bulletin of the Geological Society of Denmark 24: 261-281.
25. Bromley, R.G. and Asgaard, U. 1979. Triassic freshwater ichnocoenosis from Carlsberg Fjord East Greenland. Palaeogeography, Palaeoclimatology and Palaeoecology 28: 39-80.
26. Bromley, R.G. and D'Alessandro, A. 1987. Bioerosion of the Plio- Pleistocene transgression of southern Italy. Rivista Italiana di Paleontologia e Stratigrafia 93: 379-442.
27. Bromley, R.G. and Ekdale, A.A. 1998. Ophiomorpha irregulaire (trace fossil): redescriptiom from the Cretaceous of the Book Cliffs and Wasatch Plateau, Utah. Journal of Paleontology 72: 773-778.
28. Bromley, R.G. and Uchman, A. 2003. Trace fossils from the Lower and Middle Jurassic marginal marine deposits of the Sorthat Formation, Bornholm, Denmark. Bulletin of the Geological Society of Denmark 52: 185-208.
29. Bromley, R.G., Ekdale, A.A. and Richter, B. 1999. New Taenidium (trace fossil) in the Upper Cretaceous chalk of northwestern Europe. Bulletin of the Geological Society of Denmark 46: 47-51.
30. Bromley, R.G., Uchman, A., Milàn, J. and Hansen, K.S. Rheotactic macaronichnus, and human and cattle trackways in Holocene beachrock, Greece: reconstruction of paleoshoreline orientation. Ichnos. (In press).
31. Brongniart, A.T. 1823. Observations sur les fucoids. Société d'Histoire Naturelle de Paris, Mémoires 1: 301-320.
32. Brongniart, A.T. 1828. Histoire des végétaux fossiles ou recherches botaniques et géologiques sur les végétaux renfermés dans les diverses couches du globe, volume 1. G. Dufour & E. d'Ocagne, Paris, 136 pp.
33. Buatois, L.A., Mángano, M.G. and Sylvester, Z. 2001. A diverse deep-marine ichnofauna from the Eocene Tarcau Sandstone of the Eastern Carpathians, Romania. Ichnos 8: 23-62.
34. Buatois, L.A., Bromley, R.G., Mángano, M.G., Bellosi, E. and Carmona, N.B. 2003a. Ichnology of shallow marine deposits in the Miocene Chenque Formation of Patagonia: complex ecologic structure and niche partitioning in Neogene ecosystems. Publicación Especial de la Asociación Paleontológica Argentina N° 9: 85-95.
35. Buatois, L.A., Bromley, R.G., Carmona, N.B., Mángano, M.G. and Bellosi, E. 2003b. Tiering structure and ichnoguilds from Miocene lower shoreface deposits, Playa Las Cuevas, Patagonia, Argentina. 7º International Ichnofabric Workshop (Basel), Abstract Book: 15.
36. Buatois, L.A., Gingras, M.K., MacEachern, J., Mángano, M.G., Zonneveld, J.-P., Pemberton, S.G., Netto, R.G. and Martin, A.J. 2005. Colonization of brackish-water systems through time: Evidence from the trace-fossil record. Palaios 20: 321-347.
37. Buckman, J.O., 1997. An unusual new trace fossil from the Lower Carboniferous of Ireland: Intexalvichnus magnus. Journal of Paleontology 71: 316-324.
38. Bush, A.M., Bambach, R.K. and Daley, G.M. 2007. Changes in theoretical ecospace utilization in marine fossil assemblages between the mid-Paleozoic and late Cenozoic. Paleobiology 33: 76-97.
39. Carey, J. 1979. Sedimentary environments and trace fossils of the Permian Snapper Point Formation, southern Sidney Basin. Journal of the Geological Society of Australia 25: 433-458.
40. Carmona, N.B. 2005. [Icnología del Mioceno marino en la Región del Golfo San Jorge. Universidad de Buenos Aires, Tesis Doctoral. 250 pp. Unpublished.].
41. Carmona, N.B. and Buatois, L.A. 2003. Estructuras biogénicas de crustáceos en el Mioceno de la cuenca del Golfo San Jorge: implicancias paleobiológicas y evolutivas. Publicación Especial de la Asociación Paleontológica Argentina N° 9: 97-108.
42. Carmona, N.B., Paredes, J.M., Buatois, L.A. and Mángano, M.G. 2002. Trazas fósiles y arquitectura de cuerpos sedimentarios en ambientes dominados por mareas, Formación Chenque, Mioceno inferior, provincia de Chubut. 9º Reunión Argentina de Sedimentología (Córdoba), Resúmenes: 61.
43. Carmona, N.B., Ponce, J.J., Mángano, M.G. and Buatois, L.A. 2006. Variabilidad de la icnofacies de Glossifungites en el contacto entre las Formaciones Sarmiento (Eoceno-Oligoceno) y Chenque (Mioceno temprano) en el Golfo San Jorge, Chubut, Argentina. Ameghiniana 43: 413-425.
44. Carmona, N.B., Mángano, M.G., Buatois, L.A. and Ponce, J.J. 2007. Bivalve trace fossils in an early Miocene discontinuity surface in Patagonia, Argentina: Burrowing behavior and implications for ichnotaxonomy at the firmground-hardground divide. Palaeogeography, Palaeoclimatology, Palaeoecology 255: 329- 341.
45. Caviglia, C. 1978. Discusión de la edad del denominado "Piso Patagoniano" sobre la base de la presencia de cetáceos. 7° Congreso Geológico Argentino (Buenos Aires), Actas 2: 385-392.
46. Cione, A.L. 1978. Aportes paleoictiológicos al conocimiento de la evolución de las paleotemperaturas en el área austral de América del Sur durante el Cenozoico. Aspectos zoogeográficos y ecológicos conexos. Ameghiniana 15: 183-208.
47. Clifton, H.E. and Thompson, J.K. 1978. Macaronichnus segregatis - a feeding structure of shallow marine polychaetes. Journal of Sedimentary Petrology 48: 1293-1302.
48. Crimes, T.P., García-Hidalgo, J.F. and Poiré, D.G. 1992. Trace fossils from Arenig flysch sediments of Eire and their bearing on the early colonization of deep seas. Ichnos 2: 61-77.
49. Corner, G.D. and Fjalstad, A. 1993. Spreite trace fossils (Teichichnus) in a raised Holocene fjord-delta, Breidvikeidet, Norway. Ichnos 2: 155-164.
50. D'Alessandro, A. and Bromley, R.G. 1987. Meniscate trace fossils and the Muensteria-Taenidium problem. Palaeontology 30: 743- 763.
51. D'Alessandro, A. and Bromley, R.G. 1995. A new ichnospecies of Spongeliomorpha from the Pleistocene of Sicily. Journal of Paleontology 69: 393-398.
52. Dahmer, G. 1937. Lebensspuren aus dem Taunusquarzit und den Siegener Schichten (Unterdevon). Preussische Geologische Landesanstalt, Jahrbuch 1936: 523-539.
53. del Río, C. 2002. Moluscos del Terciario Marino. In: M.J. Haller (ed.), Geología y Recursos Naturales de Santa Cruz. Relatorio del 15º Congreso Geológico Argentino (El Calafate), 2-9: 495-517.
54. Driese, S.G. and Dott, R.H. 1984. Model for Sandstone-Carbonate "Cyclothems" based on Upper Member of Morgan Formation (Middle Pennsylvanian) of Northern Utah and Colorado. American Association of Petroleum Geologists Bulletin 68: 574-597.
55. Dworschak, P.C. 2000. On the burrows of Lepidophthalmus louisianensis (Schmitt 1935) (Decapoda: Thalassinidea: Callianassidae). Senckenbergiana maritima 30: 99-104.
56. Dworschak, P.C. and Rodrigues, S. de A. 1997. A modern analogue for the trace fossil Gyrolithes: burrows of the thalassinidean shrimp Axianassa australis. Lethaia 30: 41-52.
57. Ekdale, A.A. and Bromley, R.G. 1984. Comparative ichnology of shelf-sea and deep-sea chalk. Journal of Paleontology 58: 323-332.
58. Ekdale, A.A. and Lewis, D.W. 1991. Trace fossils and paleoenvironmental control of ichnofacies in a late Quaternary gravel and loess fan delta complex, New Zealand. Palaeogeography, Palaeoclimatology, Palaeoecology 81: 253-279.
59. Ekdale, A.A. and Bromley, R.G. 2001. Bioerosional innovation for living in carbonate hardgrounds in the Early Ordovician of Sweden. Lethaia 34: 1-12.
60. Ehrenberg, K. 1944. Ergänzende Bemerkugen zu den seinerzeit aus dem Miozän von Burgschleinitz beschriebenen Gangkernen und Bauten dekapoder Krebse. Paläontologische Zeitschrift 23: 354-359.
61. Expósito, E.S. 1977. [Estratigrafía del Terciario marino de Astra, provincia de Chubut. Universidad de Buenos Aires. Trabajo Final de Licenciatura FCEN. 70 pp. Unpublished.].
62. Feruglio, E. 1949. Descripción Geológica de la Patagonia II. Yacimientos Petrolíferos Fiscales. Buenos Aires.
63. Fiebel, C.S. 1987. Fossil fish nests from the Koobi Fora Formation (Plio-Pleistocene) of northern Kenya. Journal of Paleontology 61: 130-134.
64. Fillion, D. and Pickerill, R.K. 1990. Ichnology of the Upper Cambrian? to Lower Ordovician Bell Island and Wabana groups of eastern Newfoundland, Canada. Palaeontographica Canadiana 7, 119 pp.
65. Fischer-Ooster, C. von. 1858. Die fossilen Fucoiden der Schweizer Alpen, nebst Erörterung über deren geologisches Alter. Huber und Companie, Bern, 74 pp.
66. Frenguelli, J. 1929. Descripción de algunos perfiles en la zona petrolífera de Comodoro Rivadavia. Boletín de Informaciones Petroleras 59: 575-605.
67. Frey, R.W. and Howard, J.D. 1981. Conichnus and Schaubcylindrihnus: redefined trace fossils from the Upper Cretaceous of the Western Interior. Journal of Paleontology 55: 800-804.
68. Frey, R.W. and Bromley, R.G. 1985. Ichnology of American chalks: the Selma Group (Upper Cretaceous), western Alabama. Canadian Journal of Earth Science 22: 801-828.
69. Frey, R.W. and Howard, J.D. 1990. Trace fossils and depositional sequences in a clastic shelf setting, Upper Cretaceous of Utah. Journal of Paleontology 64: 803-820.
70. Frey, R.W., Howard, J.D. and Pryor, W.A. 1978. Ophiomorpha: its morphologic, taxonomic and environmental significance. Palaeogeography, Palaeoclimatology, Palaeoecology 23: 199-229.
71. Fürsich, F.T. 1974. Ichnogenus Rhizocorallium. Paläontologische Zeitschrift 48: 16-28.
72. Gibert, J.M. de, Netto, R.G., Tognoli, F.M.W. and Grangeiro, M.E. 2006. Commensal worm traces and possible juvenile thalassinidean burrows associated with Ophiomorpha nodosa, Pleistocene, southern Brazil. Palaeogeography, Palaeoclimatology, Palaeoecology 230: 70-84.
73. Gingras, M.K., Pemberton, S.G., Saunders, T. and Clifton, H.E. 1999. The ichnology of modern and Pleistocene brackish-water deposits at Willapa Bay, Washington: Variability in estuarine settings. Palaios 14: 352-374.
74. Gingras, M.K., Räsänen, M.E., Pemberton, S.G. and Romero, L.P. 2002a. Ichnology and sedimentology reveal depositional characteristics of bay-margin parasequences in the Miocene amazonian foreland basin. Journal of Sedimentary Research 72: 871- 883.
75. Gingras, M.K., MacMillan, B., Balcom, B.J., Saunders, T. and Pemberton, S.G. 2002b. Using magnetic resonance imaging and petrographic techniques to understand the textural attributes and porosity distribution in Macaronichnus-burrowed sandstone. Journal of Sedimentary Research 72: 552-558.
76. Gingras, M., Dashtgard, S.E. and Pemberton, S.G. 2006. Latitudinal (climatic) controls on neoichnological assemblages of modern marginal-marine depositional environments. AAPG 2006 Annual Convention (Houston), Abstract: 38.
77. Goldring, R., Pollard, J.E. and Taylor, A.M. 1991. Anconichnus horizontalis: a pervasive ichnofabric-forming trace fossil in post- Paleozoic offshore siliciclastic facies. Palaios 6: 250-263.
78. Goldring, R., Cadée, G.C., D'Alessandro, A., Gibert, J.M. de, Jenkins, R. and Pollard, J.E. 2004. Climatic control of trace fossi distribution in the marine realm. In: D. McIlroy (ed.), The application of ichnology to palaeoenvironmental and stratigraphic analysis, Geological Society Special Publication 228: 77-92.
79. Gregory, M.R. 1991. New trace fossils from the Miocene of Northland, New Zealand, Rosschachichnus amoeba and Piscichnus waitemata. Ichnos 1: 195-206.
80. Haldemann, S.S. 1840. Supplement to number one of "A monograph of the Limniades, and another freshwater univalve shells of North America", containing descriptions of apparently new animals in different classes, and the names and characters of the subgenera in Paludina and Anculosa. Private publication, 3 pp.
81. Hall, J. 1843. Geology of New York. Part 4. Survey of the Fourth Geological District. Carroll and Cook, Albany, 683 pp.
82. Hall, J. 1847. Palaeontology of New York. Volume 1. State of New York, 338 pp.
83. Hall, J. 1852. Palaeontology of New York. Volume 2. Containing descriptions of the organic remains of the Lower Division of the New York System (equivalent in part to the Lower Silurian rocks of Europe). C. van Benthuysen, 362 pp.
84. Hanken, N.-M., Bromley, R.G., and Thomsen, E. 2001. Trace fossils of the bivalve Panopea faujasi, Pliocene, Rhodes, Greece. Ichnos 8: 117-130.
85. Häntzschel, W. 1934. Schraubenformige und spiralige Grabgänge in turonen Sandsteinen des Zittauer Gebirges. Senckenbergiana 16: 313-324.
86. Häntzschel, W. 1975. Trace fossils and problematica. In: C. Teichert (ed.), Treatise on Invertebrate Paleontology, Part W, Miscellanea. Supplement 1. Geological Society of America and University of Kansas Press, Lawrence, 269 pp.
87. Heer, O. 1877. Flora Fossilis Helvetiae. Die vorweltliche Flora der Schweiz. J. Wünster & Co. 182 pp.
88. Hester, N.C. and Pryor, W.A. 1972. Blade-shaped crustacean burrows of Eocene age: a composite form of Ophiomorpha. Bulletin of the Geological Society of America 83: 677-688.
89. Howard, J.D. and Frey, R.W. 1975. Regional animal-sediment characteristics of Georgia estuaries. Senckenbergiana Maritima 7: 33-103.
90. Howard, J.D. and Frey, R.W. 1984. Characteristics trace fossils in nearshore to offshore sequences, Upper Cretaceous of eastcentral Utah. Canadian Journal of Earth Sciences 21: 200-219.
91. Jensen, S. 1997. Trace fossils from the Lower Cambrian Mickwitzia sandstone, south-central Sweden. Fossils & Strata 42: 1-111.
92. Kazmierczak, J. and Pszczólkowski, A. 1969. Burrows of Enteropneusta in Muschelkalk (Middle Triassic) of the Holy Cross Mountains, Poland. Acta Palaeontologica Polonica 14: 299-318.
93. Keighley, D.G. and Pickerill, R.K. 1994. The ichnogenus Beaconites and its distinction from Ancorichnus and Taenidium. Palaeontology 37: 305-337.
94. Keij, A.J. 1965. Miocene trace fossils from Borneo. Paläontologische Zeitschrift 39: 220-228.
95. Kelly, S.R.A. and Bromley, R.G. 1984. Ichnological nomenclature of clavate borings. Palaeontology 27: 793-807.
96. Knaust, D. 1998. Trace fossils and ichnofabrics on the Lower Muschelkalk carbonate ramp (Triassic) of Germany: tool for high-resolution sequence stratigraphy. Geologische Rundschau 87: 21-31.
97. Kotake, N. 1991. Packing process for the filling material in Chondrites. Ichnos 1: 277-285.
98. Ksiazkiewicz, M. 1977. Trace fossils in the flysch of the Polish Carpathians. Palaeontologia Polonica 36: 1-200.
99. Leymerie, M.A. 1842. Suite de mémoire sur le terrain Crétacé du département de l'Aube. Mémoires de la Société Géologique de la France 5: 1-34.
100. Löwemark, L. and Hong, E. 2004. A new ichnospecies of Schaubcylindrichnus in Miocene sandstones from Northeastern Taiwan. 1º International Congress on Ichnology Ichnia 2004 (Trelew), Abstract book: 47-48.
101. Löwemark, L. and Hong, E. 2006. Schaubcylindrichnus formosus isp. nov. in Miocene sandstones from the Northeastern Taiwan. Ichnos 13: 1-10.
102. Lundgren, S.A.B. 1891. Studier öfver fossilförande lössa block. Geologiska Föreningens i Stockholm 13: 111-121.
103. MacEachern, J.A. and Pemberton, S.G. 1992. Ichnological aspects of Cretaceous shoreface succession and shoreface variability in the Western Interior seaway of North America. In: S.G. Pemberton (ed.), Application of Ichnology to Petroleum Exploration. A Core Workshop. Society of Economic Paleontologists and Mineralogists 17: 57-84.
104. MacEachern, J.A. and Pemberton, S.G. 1994. Ichnological aspects of incised valley fill systems from the Viking Formation of the Western Canada Sedimentary Basin, Alberta, Canada. In: R. Boyd, B.A. Zaitlin and R. Dalrymple (eds.), Incised valley systems- Origin and sedimentary sequences. Society of Economic Paleon_tologists and Mineralogists Special Publication 51: 129-157.
105. MacEachern, J.A. and Burton, J.A. 2000. Firmground Zoophycos in the Lower Cretaceous Viking Formation, Alberta: a distal expression of the Glossifungites ichnofacies. Palaios 15: 387- 398.
106. MacEachern, J.A., Bann, K.L., Bhattacharya, J.P. and Howell, C.D. Jr. 2005. Ichnology of deltas: Organism responses to the dynamic interplay of rivers, waves, storms, and tides. In: Giosan, L. and Bhattacharya, J.P. (eds.), River Deltas - Concepts, Models and Examples. Society of Economic Paleontologists and Mineralogists Special Publication 83: 49-85.
107. MacLeay, W.S. 1839. Note on the Annelida. In: R.I. Murchinson, The Silurian System, 2: 699-701, J. Murray (London).
108. Mägdefrau, K. 1932. Über einige Bohrgänge aus dem unteren Muschelkalk von Jena. Paläontologische Zeitschrift 14: 150-160.
109. Mángano, M.G. and Buatois, L.A. 2004a. Reconstructing Early Phanerozoic intertidal ecosystems: ichnolog of the Cambrian Campanario Formation in northwest Argentina. Fossils & Strata 51: 17-38.
110. Mángano, M.G. and Buatois, L.A. 2004b. Ichnology of Carboniferous tide-influenced environments and tidal flat variability in the North American Midcontinent. In: D. McIlroy (ed.), The application of ichnology to palaeoenvironmental and stratigraphic analysis. Geological Society, London, Special Publication 228: 157-178.
111. Mángano, M.G., Buatois, L.A., West, R.R. and Maples, C.G. 2000. A new ichnospecies of Nereites from the Carboniferous tidalflat facies of eastern Kansas, USA-Implications for the Nereites- Neonereites debate. Journal of Paleontology 74: 149-157.
112. Mángano, M.G., Buatois, L.A., West, R.R. and Maples, C.G. 2002. Ichnology of Pennsylvanian equatorial tidal flat. The Stull Shale Member at Waverly, Eastern Kansas. Kansas Geological Survey, Bulletin 245. 133 pp.
113. Maples, C.G. and Suttner, L.J. 1990. Trace fossils and marine-nonmarine cyclicity in the Fountain Formation (Pennsylvanian: Morrowian/Atokan) near Manitou Springs, Colorado. Journal of Paleontology 64: 859-880.
114. Mayoral, E. and Muñiz, F. 1993. Consideraciones paleoetológicas acerca de Gyrolithes. Comunicaciones de las IX Jornadas de Paleontología (Málaga, 1993), Actas: 18-22.
115. McCarthy, B. 1979. Trace fossils from a Permian shoreface-foreshore environment, eastern Australia. Journal of Paleontology 53: 345-366.
116. M'Coy, F. 1850. On some genera and species of Silurian Radiata in the Collection of the University of Cambridge. Annals and Magazine of Natural History 2: 270-290.
117. Metz, R. 1993. A new ichnospecies of Spongeliomorpha from the Late Triassic of New Jersey. Ichnos 2: 259-263.
118. Miller, S.A. and Dyer, C.B. 1878. Contributions to paleontology no. 1. Journal of the Cincinnati Society of Natural History 1: 24-39.
119. Miller, W., III. 1995. "Terebellina" (= Schaubcylindrichnus freyi ichnosp. nov.) in Pleistocene outer-shelf mudrocks of northern California. Ichnos 4: 141-149.
120. Muñiz, F. and Mayoral, A. 2001. El icnogénero Spongeliomorpha en el Neógeno superior de la Cuenca del Guadalquivir (Área de Lepe-Ayamonte, Huelva, España). Revista Española de Paleontología 16: 115-130.
121. Murchinson, R.I. 1839. The Silurian System. London, John Murray, 768 pp.
122. Myrow, P.M. 1995. Thalassinoides and the enigma of Early Paleozoic open-framework burrow systems. Palaios 10: 58-74.
123. Nara, M. 1995. Rosselia socialis: a dwelling structure of a probable terebellid polychaete. Lethaia 28: 171-178.
124. Nara, M. 2006. Reappraisal of Schaubcylindrichnus: a probable dwelling/feeding structure of a solitary funnel feeder. Palaeogeography, Palaeoclimatology, Palaeoecology 240: 439-452.
125. Nicholson, H.A. 1873. Contributions to the study of the errant annelids of the older Paleozoic rocks. Royal Society of London. Proceedings 21: 288-290.
126. Otto, E. von. 1854. Additamente zur Flora des Quaderbigerbiges in saschsen. G. Mayer (Leipzig). Part 2: 53 p.
127. Palamarczuk, S. and Barreda, V. 1998. Bioestratigrafía en base a quistes de dinoflagelados de la Formación Chenque (Mioceno), Provincia del Chubut, Argentina. Ameghiniana 35: 415-426.
128. Paredes, J.M. 2002. Asociaciones de facies y correlación de las sedimentitas de la Formación Chenque (Oligoceno-Mioceno) en los alrededores de Comodoro Rivadavia, Cuenca del Golfo San Jorge, Argentina. Revista de la Asociación Argentina de Sedimentología 9: 53-64.
129. Pedersen, G.K. and Bromley, R.G. 2006. Ophiomorpha irregulaire, rare trace fossil in shallow marine sandstones, Cretaceous Atane Formation, West Greenland. Cretaceous Research 27: 964- 972.
130. Pemberton, S.G. and Frey, R.W. 1982. Trace fossil nomenclature and the Planolites-Palaeophycus dilemma. Journal of Paleontology 56: 843-881.
131. Pemberton, S.G. and Wightman, D.M. 1992. Ichnological characteristics of brackish water deposits. In: S.G. Pemberton (ed.), Applications of ichnology to petroleum exploration - A core workshop. Society of Economic Paleontologists and Mineralogists, Core Workshop 17: 141-167.
132. Pemberton, S.G., Spilla, M., Pulham, A.J., Saunders, T., MacEachern, J.A., Robbins, D. and Sinclair, I.K. 2001. Ichnology and Sedimentology of shallow to marginal marine systems: Ben Nevis and Avalon Reservoirs, Jeanne d`Arc Basin. Short Course Volume 15, Geological Association of Canada, 343 pp.
133. Pemberton, S.G., MacEachern, J.A. and Saunders, T.D.A. 2004. Stratigraphic applications of substrate-specific ichnofacies: delineating discontinuities in the rock record. In: D. McIlroy (ed.), The application of ichnology to palaeoenvironmental and stratigraphic analysis. Geological Society, London, Special Publication 228: 29-62.
134. Pemberton, S.G., MacEachern, J.A., Bann, K.L., Gingras, M.K. and Saunders, T.D.A. 2006. High-latitudinal versus low-latitude: capturing the elusive signal using trace fossil suites from the ancient record. AAPG 2006 Annual Convention (Houston, 2006), Abstract: 84.
135. Pickerill, R.K., Keighley, D.G. and Donovan, S.K. 1996. Ichnology of the Pliocene Bowden Formation of Southeastern Jamaica. Caribbean Journal of Science 32: 221-232.
136. Plaziat, J.-C. and Mahmoudi, M. 1988. Trace fossils attributed to burrowing echinoids: a revision including new ichnogenus and ichnospecies. Geobios 21: 209-233.
137. Pollard, J.E., Goldring, R. and Buck, S.G. 1993. Ichnofabrics containing Ophiomorpha: significance in shallow-water facies interpretation. Journal of the Geological Society 150: 149-164.
138. Poiré, D.G. and Matheos, S.D. 1994. Icnofacies de Trypanites and Glossifungites en la Formación Picún Leufu (Cretácico), Cuenca Neuquina, Argentina. Su significado sedimentológico y paleoambiental. 5º Reunión Argentina de Sedimentología (San Miguel de Tucumán), Actas: 235-240.
139. Porebski, S.J. 1995. Facies architecture in a tectonically-controlled incised-valley estuary: La Meseta Formation (Eocene) of Seymour Island, Antactic Peninsula. In: K. Birkenmajer (ed.), Geological results of the Polish Antarctic expeditions. Part 11. Studia Geologica Polonica 107: 7-97.
140. Quatrefages, M.A. de. 1849. Note sur la Scolicia prisca (A. de Q.), annélide fossile de la craie. Annales des Sciences Naturelles 3, Zoologie 12: 265-266.
141. Richter, R. 1937. Marken und Spuren aus allen Zeiten. I-II. Senckenbergiana 19: 150-169.
142. Rieth, A. 1932. Neue Funde spongeliomorpher Fucoiden aus dem Jura Schwabens. Geologische und palaeontologische. Abhandlungen 19: 257-294.
143. Riggi, J. 1979. Nuevo esquema estratigráfico de la Formación Patagonia. Revista de la Asociación Geológica Argentina 34: 1-11.
144. Rindsberg, A.K. and Gastaldo, R.A. 1990. New insights on the ichnogenus Rosselia (Cretaceous and Holocene, Alabama). Journal of the Alabama Academy of Sciences 61: 154.
145. Saporta, G. de. 1872-1873. Paléontologie francaise ou description des fossiles de la France. 2 série Végétaux. Plantes Jurassiques. G. Masson, Paris 1: 506.
146. Saporta, G. de. 1884. Les organismes problématiques des anciennes mers. Masson. 100 pp.
147. Saporta, G. de. 1887. Nouveaux documents relatifs aux organismes problématiques des anciennes mers. Société Géologique de France, Bulletin 3: 286-302.
148. Schafhäutl, K.E. 1851. Geognostische Untersuchungen des südbayerischen Alpengebirges. Literarisch-artistische Anstalt, München, 208 pp.
149. Schlirf, M. 2000. Upper Jurassic trace fossils from the Boulonnais (northern France). Geologica et Palaeontologica 34: 145-213.
150. Schlirf, M. and Bromley, R.G. 2007. Teichichnus duplex n. isp., new trace fossil from the Cambrian and the Triassic. Beringeria 37: 133-141.
151. Seilacher, A. 1955. Spuren und Fazies im Unterkambrium. In: O.H. Schindewolf and A. Seilacher (eds.). Beiträge zur Kenntnis des Kambriums in der Salt Range (Pakistan). Akademie der Wissenschaften und der Literatur zu Mainz, mathematisch- naturwissenschaftliche Klasse, Abhandlungen 10: 373-399.
152. Seilacher, A. and Seilacher, E. 1994. Bivalvian trace fossils: A lesson from actuopaleontology. Courier Forschungs Institut Senckenberg 169: 5-15.
153. Sepkoski, J.J. Jr. 1990. Evolutionary faunas. In: D.E.G. Briggs and P.R. Crowther (eds.), Palaeobiology: A synthesis, Blackwell Scientific Publications, Oxford, pp. 37-41.
154. Stanistreet, I.G., Le Blanc Smith, G. and Cadle, A.B. 1980. Trace fossils as sedimentological and palaeoenvironmental indices in the Ecca Group (Lower Permian) of the Taansvaal. Transactions of the Geological Society of the South Africa 83: 333- 344.
155. Stanton, R.J. Jr., and Dodd, J.R. 1984. Teichichnus pescaderoensis - New ichnospecies in the Neogene shelf and slope sediments, California. Facies 11: 219-226.
156. Sternberg, K.M.G., von. 1833. Versuch einer geognostischbotanischen Dartsellung der Flora der Vorwelt. Fleischer, Leipzig 5-6: 1-80.
157. Thayer, C.W. 1983. Sediment-mediated biological disturbance and the evolution of the marine benthos. In: M.J.S. Tevesz and P.L. McCall (eds.), Biotic interactions in Recent and fossil benthic communities, Plenum, New York, pp. 479-625.
158. Ting, H.-H., Huang, C.-Y. and Wu, L.-C. 1991. Paleoenvironments of the Late Neogene Sequences along the Nantzuhsien River, Southern Taiwan. Petroleum Geology of Taiwan 26: 121-149.
159. Tchoumatchenco, P. and Uchman, A. 2001. The oldest deep-sea Ophiomorpha and Scolicia and associated trace fossils from the Upper Jurassic-Lower Cretaceous deep-water turbidite deposits of SW Bulgaria. Palaeogeography, Palaeoclimatology, Palaeoecology 169: 85-99.
160. Uchman, A. 1995. Taxonomy and palaeoecology of flysch trace fossils: The Marnoso-arenacea Formation and associated facies (Miocene, Northern Apennines, Italy). Beringeria 15: 1-115.
161. Uchman, A. 1998. Taxonomy and ethology of flysch trace fossils: revision of the Marian Ksiazkiewicz collection and studies of complementary material. Annales Societatis Geologorum Poloniae 68: 105-218.
162. Uchman, A. 1999. Ichnology of the Rhenodanubian flysch (Lower Cretaceous - Eocene) in Austria and Germany. Beringeria 25: 65-171.
163. Uchman, A. 2004. Phanerozoic history of deep-sea trace fossils. In: McIlroy, D. The application of ichnology to palaeoenvironmental and stratigraphic analysis. Geological Society Special Publication 228: 125-139.
164. Uchman, A. and Krenmayr, H.G. 1995. Trace fossils from Lower Miocene (Ottnangian) molasse deposits of Upper Austria. Paläontologische Zeitschrift 69: 503-524.
165. Uchman, A. and Krenmayr, H.G. 2004. Trace fossils, ichnofabrics and sedimentary facies in the shallow marine Lower Miocene Molasse of Upper Austria. Jahrbuch der Geologischen Bundesanstalt 144: 233-251.
166. Uchman, A. and Gazdzicki, A. 2006. New trace fossils from the La Meseta Formation (Eocene) of Seymour Island, Antarctica. Polish Polar Reseach 27: 153-170.
167. Vialov, O.S. 1969. Screw-like motion of Arthropoda from Cretaceous deposits of the Crimea. Paleontologicheskiy Sbornik 6: 105-109.
168. Walcott, C.D. 1890. Descriptive notes of new genera and species from the Lower Cambrian of Olenellus Zone of North America. United States National Museum Proceedings 12: 33-46.
169. Weller, S. 1899. Kinderhook faunal studies. I. The faunal of the vermicular sandstone at Northview, Webster County, Missouri. Transactions of the Academy of Science St. Louis 9: 9-51.
170. Wetzel, A. 2002. Modern Nereites in the South China Sea- Ecological Association with redox conditions in the sediment. Palaios 17: 507-515.
171. Woodward, S. 1830. A synoptic table of British organic remains. XIII + 50 p. London & Norwich.
172. Zenker, J.C. 1836. Historich-topographisches Taschenbuch von Jena und seiner Umgebung besonders in naturwissenschaftlicher und medicinischer Beziehung. Wackenhoder, Jena, 338 pp.
173. Zonneveld, J.-P. and Pemberton, S.G. 2003. Ichnotaxonomy and behavioral implications of lingulide-derived trace fossils from the Lower and Middle Triassic of Western Canada. Ichnos 10: 25-39.
174. Zonneveld, J.-P., Gingras, M.K. and Pemberton, S.G. 2001. Trace fossil assemblages in a Middle Triassic mixed siliciclastic-carbonate marginal marine depositional system, British Columbia. Palaeogeography, Palaeoclimatology, Palaeoecology 166: 249-276.
Recibido: 3 de octubre de 2006.
Aceptado: 27 de noviembre de 2007.