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Diagenesis of Neogene Strata in the Victoria Land Basin, Antarctica: Towards an Understanding of Reservoir Quality in Polar Settings

Abstract

Previous studies conducted in the Victoria Land Basin (VLB), Antarctica have focused primarily on the stratigraphy, paleontology, and sedimentology of the area. Less attention has been given to the burial history of the succession, including the nature and distribution of subsurface fluids and their significance with regard to diagenesis and porosity evolution. Because of this, some aspects of the burial, structural, and hydrologic history of the VLB remain unresolved. This petrographic study documents the presence and characteristics of carbonate cement phases through the Cenozoic succession of the VLB and explores relationships between the distribution of cements and sandstone type, associated sequence stratigraphic systems tracts, depth, and paleoclimate. Point counting was conducted to determine percentages of cement, porosity, matrix, and grains. The results display a general pattern of increasing cement abundance and decreasing porosity with depth. Increasing depth also shows a pattern in cement morphologies, with poikilotopic and blocky cements more abundant below 700 mbsf. In addition, an increase in cement abundance related to these morphologies is proportional to a decrease in porosity. Porosity appears to be higher in highstand systems tract sands, whereas, lowstand systems tract lithologies tend to have porosity values less than 5%. Findings indicate that paleoclimate also plays a major role in controlling diagenesis and determining porosity values. Low porosity values due to cement occlusion occur in samples representing the coldest climate regimes, with extremely low values corresponding to Upper and Lower Miocene. Low porosity values are also attributed to an abundance of fine-grained matrix in conjunction with lesser amounts of cement in AND-2A samples representing high latitude temperate glacial regimes. High porosity values were found in deltaic sands deposited under high latitude temperate glacial regimes with distant wet-based glaciers. The highest values of porosity in AND-2A correspond to the warmest period of the Miocene. Notwithstanding processes associated with progressive burial, strong correlations between climatic regime and the distribution of porosity and cement point towards climate and sea level variations as the major controls on burial diagenetic processes.