A late eocene-early Oligocene transgressive event in the Golfo San Jorge basin: Palynological results and stratigraphic implications

Abstract

A new Cenozoic dataset in the subsurface of the South Flank of the Golfo San Jorge Basin (Santa Cruz province) allowed to identify a non-previously recognized transgressive event of late Eocene to early Oligocene age. Below of a marine succession containing a dinoflagellate cyst assemblage that characterizes the C/G palynological zone of the Chenque Formation (early Miocene), a 80-110 m thick marine succession contains a palynological assemblage integrated by Gelatia inflata, Diphyes colligerum and Reticulatosphaera actinocoronata supporting the occurrence of a marine incursion in the M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT basin during the Eocene-Oligocene transition (EOT). The new lithostratigraphic unit -here defined as El Huemul Formation -covers in sharp contact to the Sarmiento Formation, and become thinner from East to West; the unit has been identified in about 1,800 well logs covering up to 3,500 km 2 , and its subsurface distribution exceed the boundaries of the study area. The El Huemul Formation consists of a thin lag of glauconitic sandstones with finingupward log motif, followed by a mudstone-dominated succession that coarsening-upward to sandstones, evidencing a full T-R cycle. Preservation of the El Huemul Formation in the subsurface of the South Flank has been favored by the reactivation of WNW-ESE late Cretaceous normal faults, and by the generation of N-S striking normal faults of PaleoceneEocene age. Flexural loading associated to igneous intrusions of Paleocene?-middle Eocene age also promoted the increase of subsidence in the South Flank of the basin prior to the transgression.

Stratigraphic architecture and paleosols as basin correlation tools of the early Paleogene infill in central–south Patagonia, Golfo San Jorge Basin, Argentinean Patagonia

“…The earliest Cenozoic infill of the GSJB is characterized by a nearhorizontal succession of marine and continental sedimentary rocks deposited in a passive margin setting in an extensional context (e.g., Figari et al, 1999;Foix et al, 2008Foix et al, , 2012, exceeding the Cretaceous boundaries of the Chubut Group basin (Foix et al, 2015). This infill starts with the marine-estuarine deposits of the Salamanca Formation, which correspond to an Atlantic transgression that flooded the Eastern Sector of the basin during the Danian (Fig.…”

“…1B), the Salamanca Formation outcrops start with the Glauconítico and Fragmentosa deposits, which are followed by the estuarine deposits of the Banco Verde and the pedogenized swamp deposits of the Banco Negro Inferior (BNI) (Feruglio, 1949;Andreis et al, 1975;Legarreta et al, 1990;Legarreta and Uliana, 1994;Raigemborn, 2008;Raigemborn et al, 2010Raigemborn et al, , 2014Foix et al, 2015;Ruiz et al, 2017, this volume). The Río Chico Group in this area comprises the low-sinuosity fluvial systems of the Las Violetas Formation, the moderate-to high-sinuosity fluvial systems of the Peñas Coloradas Formation, and the moderate-to high-sinuosity fluvial systems of the Las Flores Formation (Feruglio, 1949;Andreis et al, 1975;Legarreta et al, 1990;Legarreta and Uliana, 1994;Raigemborn, 2008;Krause, 2009;Raigemborn et al, 2010Raigemborn et al, , 2014Krause and Piña, 2012;Foix et al, 2013Foix et al, , 2015. Foix et al (2013Foix et al ( , 2015 related the first of these fluvial architectures to a high aggradation rate, and to a low aggradation rate to the latter, and attributed both styles to variations in subsidence rates and sedimentary supply, assuming a constant climate across the Golfo San Jorge Basin.…”

“…The Río Chico Group in this area comprises the low-sinuosity fluvial systems of the Las Violetas Formation, the moderate-to high-sinuosity fluvial systems of the Peñas Coloradas Formation, and the moderate-to high-sinuosity fluvial systems of the Las Flores Formation (Feruglio, 1949;Andreis et al, 1975;Legarreta et al, 1990;Legarreta and Uliana, 1994;Raigemborn, 2008;Krause, 2009;Raigemborn et al, 2010Raigemborn et al, , 2014Krause and Piña, 2012;Foix et al, 2013Foix et al, , 2015. Foix et al (2013Foix et al ( , 2015 related the first of these fluvial architectures to a high aggradation rate, and to a low aggradation rate to the latter, and attributed both styles to variations in subsidence rates and sedimentary supply, assuming a constant climate across the Golfo San Jorge Basin. The Las Violetas and Peñas Coloradas formations show a lateral stratigraphic relationship (Raigemborn et al, 2010;Krause et al, 2017).…”

“…2). The area hosts abundant sedimentological and paleopedological data (Feruglio, 1949;Andreis et al, 1975;Legarreta et al, 1990;Martínez, 1992;Legarreta and Uliana, 1994;Matheos et al, 2001;Iglesias, 2007;Raigemborn, 2008;Raigemborn et al, 2009aRaigemborn et al, , b, 2010Raigemborn et al, , 2014Raigemborn et al, , 2018aKrause et al, 2010aKrause et al, , b, 2017Krause and Piña, 2012;Foix et al, 2013Foix et al, , 2015Clyde et al, 2014;Woodburne et al, 2014;Comer et al, 2015;Ruiz et al, 2017Ruiz et al, , 2020Lizzoli et al, 2018;Zucol et al, 2018), at which recently was added a temporal resolution (Clyde et al, 2014;Krause et al, 2017). The Salamanca Formation and the lowermost Río Chico Group have been recently correlated with globally recognized sea-level events, highlighting the role of fluctuating sea level as a primary control (e.g., Clyde et al, 2014;Comer et al, 2015).…”

“…The Salamanca Formation and the lowermost Río Chico Group have been recently correlated with globally recognized sea-level events, highlighting the role of fluctuating sea level as a primary control (e.g., Clyde et al, 2014;Comer et al, 2015). On the other side, outcrops and subsurface data of the Salamanca Formation and the Río Chico Group at the North Flank of the basin have been related to changes in accommodation space and to differential subsidence across the basin (Foix et al, 2013(Foix et al, , 2015. However, up to date, no large-scale (i.e., basin-scale) stratigraphic architectural correlation, including paleosols and relationships within the sequence stratigraphic context of both the Salamanca Formation and the Río Chico Group, have hitherto been carried out.…”