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The Lower Jurassic East Berlin Formation of the Hartford Group (Newark Supergroup), located in the Hartford Basin (Connecticut and Massachusetts), is an alluvial and lacustrine half-graben succession deposited in a semi-arid climate. The formation mainly comprises massive red mudstones, reddish rippled siltstones and shales with minor gray-green mudrocks and shales, black shales, and sheet sandstones. The red mudstones, which contain desiccation cracks up to 1m deep and pedogenic features, are interpreted as fossil vertisols. Like modern analogs in central Australia, these paleosols produced abundant sand-sized mud aggregates that were transported as bedload, and are still recognizable within sandy facies, but were obscured by compaction in the mudstones. Thus, although overwhelmingly muddy, the alluvial system is interpreted as a bedload-dominated distal alluvial plain to sandflat. Sheet sandstones comprise trough cross-stratified sandstone overlain by lineated planar-laminated sandstone or rippled siltstone; all are attributed to sheetfloods, some of which entered the lake.

Lacustrine deposits are represented by stratified gray-green mudrocks and black shales. Sedimentologic, petrologic, and ichnologic evidence all indicate a saline lacustrine paleoenvironment. The lake deposits are associated with disrupted shales that are interpreted as playa sediments. Disrupted shales, interbedded with massive mudstones, show similar vertisol development to the playa muds. The lack of prominent shoreline deposits and large-scale deltaic features is attributed to frequent lake-level fluctuations, which caused extensive migration of the lake shore across distal parts of the uniformly sloping alluvial plain. Major changes in lake level through time in the Hartford Basin are attributed to climatic influences, whereas changes in hydrologie drainage appear to be related to tectonic activity.

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