Lacustrine and Playa Facies in the Early Jurassic East Berlin Formation Exposed in the Dinosaur State Park Core, Hartford Basin, Connecticut

A core from the upper portion of the East Berlin Formation near Dinosaur State Park (DSP core) contains an interval of perennial lake strata bounded above and below by playa and alluvial plain strata that were deposited in the rifted Hartford Basin (Connecticut) during the Early Jurassic. The core, totaling thirteen meters in length, is located 3.6 km from the Eastern Border Fault, and contains strata not typically exposed this close to the basin edge. Strata in the core are divided into five depositional facies, including black shale and gray mudstone (interpreted to be perennial lake and lake margin environments), rippled and laminated reddish-brown siltstone and pedogenically-altered reddish-brown siltstone (interpreted to be playa and arid alluvial plain environments), and white cross-bedded sandstone. The sandstone is interbedded with both perennial lake and alluvial plain facies, and represents sediment brought into the basin by relatively unconfined flows.

The DSP core can be correlated to an outcrop exposed in Cromwell, Connecticut, located 3.2 km further into the basin. The stratigraphic interval preserved in the DSP core thins by two meters over that distance, and contains more numerous (and thicker) cross-bedded sandstone beds. The sandstone facies is independent of other facies in the core, but only occurs within the playa and alluvial plain facies in the Cromwell outcrop. During arid climatic periods, sand is transported into the center of the basin through unconfined flows. During humid climates, sand is trapped adjacent to the basin's edge as a result of increased subaqueous accommodation associated with expanding perennial lakes. In addition, the DSP core contains perennial lake facies in four stratigraphic parasequences, while the outcrop has lake facies in only two parasequences, indicating that the core location adjacent to the Eastern Border Fault provides a more complete depositional record of the perennial lake environment.