LAKE EVOLUTION IN THE HARTFORD BASIN

The Triassic-Jurassic rift system in eastern North America was formed by the breakup of Pangaea. The sedimentary fill and lava flows of these rift basins are collectively known as the Newark Supergroup. Stratigraphy and sedimentary evolution of one of these rift basins, the Hartford Basin, spanning Connecticut and Massachusetts, is still being refined because exposure is sparse and fault patterns make simple correlation difficult across the basin. Four sedimentary formations with three interbedded basalt lava flows include from oldest to youngest: New Haven Arkose, Talcott, Shuttle Meadow, Holyoke, East Berlin, Hampden, and Portland. Evolution of lake types through time and the influence of both climate and tectonics are interrupted in this basin by basalt flows. These flows could potentially rearrange local drainage patterns, impact accommodation space, and possibly lower or raise sill heights resulting in localized hydrologic changes. It is not clear that volcanic flows did influence the change of lake types through time. The lake-type sequence-stratigraphic model of Bohacs, Carroll, and others predicts an evolution of a fluvial to overfilled lacustrine environment, then to a balanced-filled and an underfilled lacustrine environment and back through balanced-filled lacustrine to fluvial conditions as accommodation space increases then decreases in an evolving rift. The New Haven Arkose is interpreted as fluvial sediments while the lower portion of the Shuttle Meadow contains an overfilled lake deposit. The upper part of the Shuttle Meadow to the middle of the Portland represent balanced-filled lake deposits with the upper Portland as fluvial facies. No thick evaporite deposits are preserved to indicate an underfilled lake deposit; however, the preservation of underfilled evaporites may be problematic in hydrologic situations where closed drainage conditions only applies to surface flow, not groundwater flow. Paleosol features of the upper Shuttle Meadow versus those of the East Berlin and Portland point to changing hydrologic and groundwater conditions in the Hartford Basin. Even the driest conditions could not generate evaporites because subsurface flow of groundwater was not closed. Lake conditions changed independently of the basalt flows as represented by the facies changes in the Shuttle Meadow Formation.