SALINITY VARIATIONS AS AN INDICATOR OF FLUID FLOW IN THE LOWER ELLESMERIAN SEQUENCE, NORTH SLOPE, ALASKA

Previous studies have shown the existence of a topographically driven recharge system in the North Slope foreland basin, Alaska. Fluids are recharged in the uplifted Brooks Range to the south and southeast and flow topographically to areas of discharge proximal to the North Slope coastline. The Lower Ellesmerian Sequence represents the lowest most flow pathway in the stratigraphic sequence. Limestones and dolomites of the Lisburne Group and sands and shales of the Endicott Group represent laterally extensive pathways for flow.

Salinities calculated from spontaneous potential response in the Lower Ellesmerian range from less than 10 gL^-1 to over 150 gL^-1. Low salinities calculated for the Lower Ellesmerian indicate the displacement of connate marine waters by topographic flow throughout the history of the North Slope foreland basin. Flushing of connate waters likely occurred during the Pennsylvanian through Permian and in the Early Cretaceous when Lower Ellesmerian sediments were subaerially exposed on topographic highs such as the ancestral Barrow Arch. Flow direction during this time was likely in a north to south (present day) orientation due to the reversal of topographic gradient that existed early in the history of the basin.

Present day fluid flow in the Lower Ellesmerian likely exists. Active or very recent fluid flow may be the case for structures proximal to the southeast Brooks Range where outcropping Lower Ellesmerian sediments act as recharge points. Salinities of less than 12 gL^-1 have been calculated from log data and verified by water samples from oil and gas wells in the area. Active fluid flow in these structures is indicated by variations in temperature and hydraulic head. Salinity cross sections show thrust faults associated with the southeast Brooks Range acting as barriers to flow.