Preliminary Investigation of Linkages Between Arctic Pingos and Subsurface Stratigraphy

This NASA-SETI supported study investigates the distribution of pingos (elliptically-shaped ice-rich topographic mounds) across 2300 square kilometers of the central coastal plain of Arctic Alaska in relation to the shallow geological framework that exists immediately beneath them. Pingos in the central North Slope of Alaska are classified as being of the closed or hydrostatic type. Their genesis is often assigned to freezing and cryogenic uplift of near-surface saturated thaw lake sediments that are exposed as lakes are drained and/or become choked with sediments. Although thaw lakes appear rather ubiquitous across the study area, pingos do not. Pingo distributions can be categorized as either clusters of elements or as relatively dispersed. Spatial statistical analysis reveals that pingo distribution is non-random and clustered. The analysis also took into account that pingo distribution is a function of preferential preservation between modern rivers channels that cross the study area. Pingo distributions and frequency were tested in relation to the location and type of stratigraphic and sedimentological features that characterized the shallow subsurface across the study area. Subsurface interpretation was derived mostly from oil well wireline logs. Gamma ray logs for more than 160 wells were used to define, correlate and assess the connectivity and conductivity of shallow and near-surface stratigraphic units between wells. Assessed also were major facies changes and the type and locations of subsurface structures such as major basement-to-surface faults and folds. The surface and near-surface truncation and subcropping of tilted, alternating units of permeable coarse-grained and confining fine- grained units were also mapped in relation to pingo locations. Preliminary and intriguing findings will be presented which contribute to the hypothesis that pingo genesis, location, and variations in morphology could be, in part, linked to a well-documented and active subsurface geohydrologic system. This system is characterized by multiple stacked hydrocarbon-, saline- and freshwater-rich reservoirs. Processes include fault reactivation and basin subsidence that drive episodic basin expulsion, and upward migration and mixing of deep basin and phreatic fluids along basin margins. Endpoints of the system include demonstrable gas hydrates deposits that occur below and within the permafrost, and documented seepage of hydrocarbons and groundwater at the surface. Our hypothesis entertains the idea that closed pingos might also be endpoints of the petroluem system as basin and phreatic fluids migrate vertically within a thick and leaky permafrost interval along faults and tilted reservoir sand-rich units, which intersect and differentially charge frozen near-surface sedimentary units. Future field-based sampling and geophysical studies may shed additional light on this model's application for pingo genesis and resource exploration on Mars.