Resumo

MANGANO, María Gabriela  e  BUATOIS, Luis Alberto. Estratigrafía y ambiente de sedimentación de la Formación Suri en los alrededores del Río Chaschuil, Ordovícico del Sistema del Famatina, noroeste argentino. Rev. Asoc. Argent. Sedimentol. [online]. 1994, vol.1, n.2, pp.143-169. ISSN 1853-6360.

The Suri Formation (Arenig-Llanvirn) records part of the infill of the Famatina Basin. It was originally defined by Harrington (in Harrington & Leanza, 1957), and later used by subsequent workers. However, no stratigraphic type section was provided. Recent research at Chaschuil (northern Famatina System) suggests that the Suri Formation displays more lithologic variability than formerly thought. Detailed stratigraphic information allows us to distinguish three members within this unit (from base to top): Vuelta de las Tolas, Loma del Kilómetro and Punta Pétrea members. Type sections are described for each of these stratigraphic units with representative faunas. The Vuelta de Las Tolas Member consists of silicified siltstones and mudstones punctuated by erosive-based, channelized volcanic conglomerates and breccias. This unit represents deposition in a slope apron setting dominated by episodic processes. No diagnostic fossils were detected, but stratigraphic relationships indicate an age not younger than early Arenig. The Loma del Kilómetro Member consists of mudstones, tuffaceous, massive, graded, wave-rippled and hummocky cross-stratified sandstones, and interbedded siltstones. This member records sedimentation within a narrow shelf affected by storms and volcaniclastic debris flows. The Loma del Kilómetro Member hosts an invertebrate fauna, which includes trilobites, braquiopods, bivalves and gastropods. Evidence suggests a middle to late Arenig age, but an early Llanvirn age cannot be completely disregarded. The Punta Pétrea Member consists of thick packages of breccias, tuffs and tuffaceous sandstones. It represents the progradation of a fan delta associated with an increased volcanic activity. This member contains an invertebrate fauna dominated by articulate brachiopods. Although fossils provide no definite age, stratigraphic relationships suggest that the Punta Pétrea Member is not older than early Llanvirn. In the study area, syndepositional volcanism is recorded from the Suri Formation, which displays interbedded andesite and basandesite lavas within the Vuelta de Las Tolas and Punta Pétrea members. Postdepositional magmatism is evidenced by the presence of dacite and riodacite dykes, sills and surface intrussives, affecting the sedimentary succession. In turn, the volcanosedimentary succession and the surface intrussives are intruded by granitoid rocks. The suggested threefold stratigraphic scheme reflects more accurately the lithological and paleoenvironmental variability of the Suri Formation and provides a general framework for future sedimentologic and paleontologic studies.

Palavras-chave : Stratigraphy; Sedimentary environments; Suri Formation; Famatina Basin; Ordovician.

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