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Quantitative Outcrop Characterization of System Scale Axis to Margin Changes in Stratigraphic Architecture and Static Connectivity of Transgressive Fluvial Deposits, Eocene Escanilla Formation, Ainsa Basin, Spain


Transgressive fluvial strata are deposited during an overall landward migration of the shoreline. Few studies have focused on transgressive fluvial strata, especially those deposited in high-accommodation settings. The Escanilla Formation of the Ainsa Basin contains world-class outcrops of fluvial strata deposited during transgression in a high-accommodation setting. This study uses outcrop data to document system scale vertical and lateral variations in stratigraphic architecture, net-sand content, and static connectivity in this setting. Data from stratigraphic columns, interpreted photopanels, and geologic maps of depositional facies and sand body locations are used to document temporally and spatially varying characteristics including, lithology, grain size, sedimentary structures, lithofacies, architectural elements, net-sand content, stratal boundaries, and static connectivity of channel bodies. These data are used to construct longitudinal and lateral cross sections that document the location of the paleoshoreline, distribution of floodplain and channel deposits, and changes in net-sand content and static connectivity. Key axis-to-margin patterns in the fluvial system are an increase in the proportion of channel-fill and splay stories, and channel-belt elements at the expense of floodplain fine stories, and an increase in net-sand content, channel-belt element size, modal grain size, and static connectivity from the margin to the axis of the system. The axis of the system contains the best reservoir quality strata and potential for static connectivity. Key vertical changes in the fluvial system are an upward increase in channel-belt element size, net-sand content, modal grainsize within channel-belt elements, and static connectivity. Data provided herein provide insight into high accommodation, transgressive fluvial deposits and can be used to reduce uncertainty in the interpretation of subsurface data, provide input to constrain rules-based forward stratigraphic models, and provide input to constrain reservoir models in transgressive fluvial systems.