Neoproterozoic to Lower Palaeozoic successions of

Authors: Udo Zimmermann Daniel G Poiré Lucía Gómez Peral

Publish Date: 2010/08/28

Volume: 100, Issue: 2-3, Pages: 489-510

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Abstract

The Cryogenian to Uppermost Ediacaran successions of the Tandilia System Sierras Bayas Group and Cerro Negro Formation in centraleastern Argentina is exceptional because of its unmetamorphosed and nearly undeformed character its sediment provenance trend and the absence of any identified glacial deposit and the deposition of warm water carbonates We decipher a dramatic change in the basin evolution from smallscale depositional areas during the Neoproterozoic to a larger basin related to an active continental margin throughout the Uppermost Ediacaran The base of the succession is represented by immature detritus of alkaline composition Villa Mónica Formation but towards the top of this formation the material is sorted and reworked nonetheless still reflecting in its detritus the local rocks The clastic deposition is interrupted by diagenetic overprinted dolomites The unconformable overlying quartzarenitic Ediacaran Cerro Largo Formation reworked the Cryogenian Villa Mónica Formation and contains mainly felsic granitic and metamorphic basement material of slightly wider variety while the dominant alkaline geochemical signature in rocks of the Villa Mónica Formation disappears Based on diagenetic petrographic and sedimentological data we can interpret the unconformity representing a longer time of erosion The Cerro Largo Formation shows a transition to mudstones and the heterolithic facies of the Olavarría Formation The top of the Sierras Bayas Group is represented by limestones Loma Negra Formation which are discordantly overlain by the Uppermost Ediacaran Cerro Negro Formation The latter displays detrital material derived from a continental arc mafic and felsic sources Several arcrelated geochemical proxies Th/Sc  08 Zr/Sc  10 La/Sc  2 Ti/Zr  20 are recorded in the sediment detritus as are syndepositional pyroclastites The absence of volcanic material in the underlying rocks allows proposing that the Cerro Negro Formation is related to an active continental margin fringing Gondwana “Terra Australis Orogen” as a retroarc or retroarc foreland basinFieldwork was supported by funds of the CONICET and Cemento Avellaneda SA wherefore DGP and LPG are thankful XRF analyses were executed at the University of Johannesburg Statoil and Marathon Norge supported other analytical work We are grateful to S Siegesmund and MAS Basei to be invited to this special volume We thank VA Janasi and an anonymous reviewer for their very helpful and thoughtful comments which improved the manuscript

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