LAUSR

Abstract The Tithonian Vaca Muerta Formation (500 m-thick marine carbonates) in the Pampa de Tril area is a potential unconventional hydrocarbon reservoir but earlier studies rarely focused on its diagenetic history. It constitutes the upper part of the lower Mendoza Group in the Neuquen Basin, western Argentina. Petrographic examinations reveal four generations of calcite (C1, C2, Cb and C3). The microbial lime mudstone (C1, The Ce (Ce/Ce*)SN and La (La/La*)SN anomalies of Cb and C3 are consistent with precipitation under reducing conditions of deep burial settings. The Vaca Muerta carbonates are enriched in organic matter (up to 12%) that fills the pores but permeability is insignificant.