BURIAL, TEMPERATURE AND MATURATION HISTORY OF THE AUSTRAL AND WESTERN MALVINAS BASINS, SOUTHERN ARGENTINA, BASED ON 3D BASIN MODELLING

V.F. Sachse^{1,2 *}, Z. Anka^1,4, R. Littke², J.F. Rodriguez³, B. Horsfield¹ and R. di Primio^1,5

¹ GFZ German Research Centre for Geosciences, Helmholtz Centre Potsdam, Germany.

² Energy and Minerals Resources (EMR), Institute of Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University, Germany.

³ Petrobras Argentina S.A., Argentina.

⁴ present address: TOTAL Exploration - New Ventures, Paris, France.

⁵ present address: Lundin Norway AS, PO Box 247, N-1326 Lysaker, Norway.

^* Corresponding author, email: victoria.sachse@emr.rwth-aachen.de

This paper presents a numerical petroleum systems model for the Jurassic-Tertiary Austral (Magallanes) Basin, southern Argentina, incorporating the western part of the nearby Malvinas Basin. The modelling is based on a recently published seismo-stratigraphic interpretation and resulting depth and thickness maps. Measured vitrinite reflectance data from 25 wells in the Austral and Malvinas Basins were used for thermal model calibration; eight calibration data sets are presented for the Austral Basin and four for the Malvinas Basin. Burial history reconstruction allowed eroded thicknesses to be estimated and palaeo heat-flow values to be determined. Six modelled burial, temperature and maturation histories are shown for well locations in the onshore Austral Basin and the western Malvinas Basin. These modelled histories, combined with kinetic data measured for a sample from the Lower Cretaceous Springhill Formation, were used to model hydrocarbon generation in the study area. Maps of thermal maturity and transformation ratio for the three main source rocks (the Springhill, Inoceramus and Lower Margas Verdes Formations) were compiled. The modelling results suggest that deepest burial occurred during the Miocene followed by a phase of uplift and erosion. However, an Eocene phase of deep burial leading to maximum temperatures cannot be excluded based on vitrinite reflectance and numerical modelling results. Relatively little post-Miocene uplift and erosion (approx. 50-100 m) occurred in the Malvinas Basin.

Based on the burial- and thermal histories, initial hydrocarbon generation is interpreted to have taken place in the Early Cretaceous in the Austral Basin and to have continued until the Miocene. A similar pattern is predicted for the western Malvinas Basin, with an early phase of hydrocarbon generation during the Late Cretaceous and a later phase during the Miocene. However, source rock maturity (as well as the transformation ratio) remained low in the Malvinas Basin, only just reaching the oil window. Higher maturities are modelled for the deeper parts of the Austral Basin, where greater subsidence and deeper burial occurred.

Keywords: Basin modelling, petroleum system, hydrocarbon generation, maturity, erosion, Austral Basin, Malvinas Basin, Argentina, South America

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