Clay minerals of the Vaca Muerta Formation, Neuquén Basin (Argentina): distribution and origin

CAPELLI, I.; SCASSO, R.A.; KIETZMANN, D.A.; CRAVERO, M.F.; SPANGENBERG, J.; ADATTE, T.

Congreso; IAS 35th Meeting of Sedimentology; 2021

The Vaca Muerta Fm (VMFm) is an organic-rich, marine succession deposited during the Tithonian-Berriasian in the Neuquén Basin, Argentina. Due to its high total organic carbon content (TOC) which may reach up to 12 wt.%, the VMFm is considered as an outstanding unconventional hydrocarbon shale reservoir but very little is known about its clay mineralogy. In the framework of an integral study of the VMFm the 470 °C).The clay mineralogy analysis of the VMFm suggests that smectite was progressively transformed to I/S during burial, in agreement with the OM maturation trend. The difference reported in the clay mineralogy of Zapala and Malargüe is related to the provenance of the sediments. The smectite observed in Zapala section was developed through weathering of volcanogenic soils of the North Patagonian Massif, located in the southeast of the basin. Conversely, the kaolinite, illite and probably smectite present in the Malargüe section were formed through the weathering of acidic rocks (rhyolites/dacites) of the San Rafael Block, placed to the northeast of the basin. In spite of the different provenances, changes of the relative abundance of the clays in each section (e.g., kaolinite/illite ratio) suggest two periods of enhanced humidity in the hinterlands (early Tithonian and early Berriasian), separated by a period of more arid conditions (late Tithonian) in agreement with the Tethyan paleoclimatic reconstructions.Three variables regulate the clay mineralogy of the VMFm: the intensity of burial diagenesis, the provenance of the sediments and the paleoclimate prevailing in the hinterlands. Burial diagenesis andthe provenance are the variables with more influence in the final clay mineralogy, whereas the paleoclimatic conditions in the hinterlands regulate the relative abundance of the clays in each section.