Palaeoenvironmental conditions for the preservation of organic matter during the late Hauterivian in the Neuquén Basin (Western Argentina)

LESCANO, MARINA; TUNIK, MAÍSA; ERRA, GEORGINA; OMARINI, JULIETA; CAMPETELLA, DÉBORA; BREA, FABIÁN; MARTINEZ, MATHIEU; ODINO-BARRETO, ANDREA LORENA; GARBÁN, GRONY; AGUIRRE-URRETA, BEATRIZ

MARINE AND PETROLEUM GEOLOGY

ELSEVIER SCI LTD

Año: 2020 vol. 120

0264-8172

The Agua de la Mula Member of the Agrio Formation, comprises marine deposits accumulated in a mixed carbonate-siliciclastic outer ramp during the late Hauterivian. An innovative multi-proxy study that includes sedimentological, geochemical and paleobiological data from the El Portón section were combined in order to constrain the environmental context.Two major sedimentary cycles have been recognised (TST-HST) reflecting the position of both distal and proximal sediments within the depositional system. The distal outer ramp deposits (FA1) are predominantly characterised by carbonate-bearing mudstones, with TOC content up to 4.43 wt% TOC (average 1.62 wt%) and Type II marine-derived amorphous organic matter. The high TOC could be reflecting enhanced bioproductivity during periods of decreased salinity as mirrored by peaks of Micrantholithus, and reduced dilution by siliciclasticmaterial in a distal setting. Conversely, the proximal outer ramp succession (FA2) shows a higher siliciclastic pattern, along with the terrestrial organic matter signal (Type II-III kerogen) and TOC content around 1 wt% (average 1.05 wt%). In this interval primary production is associated with more stable conditions and stratified water, as reflected in peaks of Nannoconus. These conditions allowed a greater diversity and high abundances of calcareous nannofossil assemblages.