KEROGEN CHARACTERIZATION OF THE VACA MUERTA FORMATION (TITHONIAN–VALANGINIAN), AT MALLÍN QUEMADO AND PUERTA CURACO, NEUQUÉN BASIN, CENTRAL-WEST PATAGONIA, ARGENTINA. PALYNOFACIES AND GEOCHEMICAL APPROACH

This contribution integrates palynofacies, organic geochemical and sedimentological analyses to characterize the depositional environment and the kerogen properties related to the hydrocarbon source potential of the Vaca Muerta Formation at the Mallín Quemado Norte (MQN) and Puerta Curaco (PC), Neuquén Basin, Argentina. Thirty-five outcrop samples were analyzed for palynofacies and total organic carbon (TOC). At MQN, five palynofacies types and sedimentological evidence suggest deposition mainly in an outer shelf marine environment with a variable continental input. At PC, three palynofacies types and sedimentological observations point to accumulation mainly in an outer ramp marine environment with minimal to moderate terrigenous input. Depositional processes involve an interplay of suspension settling from the water column (marine snow) and buoyant plumes, followed by reworking of the seafloor by bottom currents and sediment gravity flows. Under identical hydrodynamic flow conditions, equidimensional phytoclasts respond better to transport sorting than blade-shaped. The first documentation of high-relief organic spheres (HROS) in this unit points to redox oscillation between sulfidic and ferruginous anoxic microenvironments during early diagenesis. Low HROS percentages and crypto-bioturbated strata suggest that bottom waters were not strictly anoxic. Organic carbon preservation may be partly related to the role of extracellular polymeric substances as an organic matter encapsulator. The kerogen aligns with type III-IV, and TOC values are mainly high (MQN: up to 4.69%; PC: 4.9–10.4%). Although an over-mature state cannot be entirely ruled out (highly dark palynological matter), the poor preservation of the kerogen suggests a negligible hydrocarbon potential.