SEQUENCE STRATIGRAPHY AND DEPOSITIONAL CONTROLS OF CONTINENTAL STRATA: EXAMPLE FROM THE JURASSIC EAST BERLIN FORMATION, HARTFORD BASIN, CONNECTICUT

Depositional sequences of continental strata often respond more to tectonic- and climate-controlled changes in sediment and water supply than to changes in accommodation associated with base level rise or fall. This can lead to significantly different stratal architecture when compared to typical marine sequence stratigraphic models. The Jurassic East Berlin Formation of the Hartford Basin contains alternating playa and perennial lake deposits that have been interpreted to reflect deposition controlled by cyclic changes between arid and more humid climates. Furthermore, the basin appears to have had a closed paleohydrology, isolating it from the effects of changes in relative sea level.

Unlike typical marine sequences that exhibit prograding and retrograding facies geometries associated with fluctuations in relative sea level, facies changes in the East Berlin Formation are aggradational in nature. Vertical shifts between playa and perennial lake facies occur abruptly and simultaneously across the entire basin without evidence of lateral facies shifts, and are interpreted to be related to changes in climate. Therefore, identification of sequence and parasequence boundaries in the East Berlin Formation relies on the interpretation of climate cycles that control depositional facies, a practice that is more difficult than using observable stratal terminations such as onlap and downlap. Key facies that indicate changes in water and sediment input (such as lake mudstone and sheet flood sandstone) or long periods of limited sedimentation (such as paleosols) become the main criteria for sequence recognition. These concepts were used to develop a sequence stratigraphic framework for the continental strata in the East Berlin Formation, and reveal that climate and paleohydrology (surface and groundwater), rather than tectonics, exerted the most fundamental controls on facies distribution.