Petrographic, mineralogical and geochemical characterization of fine-grained rocks of the Pilmatué Member (Upper Valanginian-lower hauterivian) of the Neuquén Basin (Argentina): Implications for siliciclastic input, carbonate productivity and redox conditions. (October 2020)

• Record Type: Journal Article
• Authors: Remírez, Mariano N.; Spalletti, Luis A.; Isla, Manuel F.
• Is Part Of: Journal of South American earth sciences. Volume 102(2020)
• Publication Date: 2020-10
• Subjects: Black shales -- Offshore deposits -- Mixed siliciclastic-carbonate systems -- Neuquén basin; Geology -- Latin America -- Periodicals; Earth sciences -- Latin America -- Periodicals; Geology -- Antarctica -- Periodicals; Earth sciences -- Antarctica -- Periodicals; Geology -- Caribbean Area -- Periodicals; Earth sciences -- Caribbean Area -- Periodicals; Géologie -- Amérique latine -- Périodiques; Sciences de la terre -- Amérique latine -- Périodiques; Géologie -- Antarctique -- Périodiques; Sciences de la terre -- Antarctique -- Périodiques; Géologie -- Caraïbes (Région) -- Périodiques; Sciences de la terre -- Caraïbes (Région) -- Périodiques; Earth sciences; Geology; Antarctica; Caribbean Area; Latin America; Periodicals; 550.5
• DOI: 10.1016/j.jsames.2020.102663
• Languages: English
• ISSNs: 0895-9811

Abstract

Abstract: Petrographic, mineralogical and geochemical analyses of mixed siliciclastic-carbonate offshore deposits of the Pilmatué Member (Neuquén Basin) were carried out to define two scenarios for deposition: a confined ramp setting (CRS) and an open ramp setting (ORS). The CRS involves marly to carbonate-rich fine-grained mudstones, mostly laminated and non-bioturbated, enriched in redox proxies and depleted in rare earth elements (REE). The ORS comprises abundant siliciclastic-rich mudstones, mostly coarser-mudstones, depleted in redox proxies and with REE pattern similar to the PAAS. These variations are explained through fluctuations in carbonate productivity/terrigenous input, and changes in the circulation pattern of the basin. Within the CRS, high carbonate productivity would be favored due to the general greenhouse condition for the Early Cretaceous and the scarcity of terrigenous supply, related to the landward migration of the shoreline and low effectiveness of sediment distribution by marine currents. Furthermore, high organic matter productivity should lead to an oxygen-depletion close to the sediment-water interface. Instead, increasing sediment supply and dissolved oxygen in the ORS is related to shoreline progradation in the south and the consequent installation of across shelf flows that allowed vertical water circulation and the oxygen replenishment in benthic environment. Highlights: Sedimentary processes of an offshore mixed siliciclastic-carbonate system are presented. Anoxic to euxinic conditions are linked to high carbonate and organic productivity. Black shales deposition in mixed systems is tightly related to the siliciclastic input and carbonate productivity. Multiscale analysis of fine-grained rocks provide ground-truth to the shallow-marine, sequence-stratigraphic framework.