SEDIMENTOLOGICAL AND STRATIGRAPHIC INTERPRETATION OF CROSS-BEDDED SANDSTONE IN THE JURASSIC EAST BERLIN FORMATION, HARTFORD BASIN, CONNECTICUT

The Lower Jurassic East Berlin Formation from the Hartford Rift Basin (Connecticut and Massachusetts) contains conspicuous white sandstone beds that usually occur in reddish-brown playa facies and have been interpreted to represent sheet flood deposits within an overall arid environment. The occurrence of this sandstone facies has been previously interpreted to indicate increased water and sediment flux into the basin during arid times, and was used to recognize parasequence and sequence boundaries. The sandstone is absent in perennial lake facies over most of the basin. However, a core taken in Rocky Hill, CT, a few kilometers from the basin's border fault, preserves beds of cross-bedded and plane-bedded sandstone (up to 1 meter thick) within both perennial lake facies (black shale and gray siltstone/shale) and playa facies (rippled red siltstone and pedogenically altered siltstone). In addition, the sandstone in this core makes up a higher percentage of the overall section than it does at more distal locations.

This study demonstrates that the cross-bedded sandstone occurs within both playa and perennial lake facies, and may not be a unique proxy for sediment and water flux into an arid playa environment. Flood-transported sands deposited during times of predominantly arid climate are easily transported far into the basin interior over relatively flat playa topography. However, during more humid climate episodes, the sand is trapped near the margin of perennial lakes, in proximal parts of the basin. This suggests that sand transport into the basin occurs during times of both arid and more humid climates. Furthermore, it allows us to identify more parasequences within perennial lake facies near the border fault than further within the basin, where the similarity of facies hinders parasequence recognition.