A LAKE - MARGIN HOT SPRING DEPOSIT: THE COE LIMESTONE (JURASSIC), HARTFORD BASIN, CT

The Hartford Basin is comprised of Triassic-Jurassic sediments and continental flood basalts deposited during rifting of Pangaea. Alluvial fans, fluvial-playa red beds, and lacustrine sequences are characteristic of arid/wet cycles dominated by a monsoonal climate. Limestone deposits within the Hartford Basin are spatially limited and generally associated with lacustrine paleoenvironments. Limestone exposed in Plainville, CT has been identified as of lacustrine origin based on infilling of rhyzolith structures.

The Coe Quarry Limestone, North Branford, CT represents a dissimilar carbonate facies compared with the typical finely laminated gray lacustrine sequences. Textures represented include cellular tufa, micritic travertine and finely laminated cellular tufa, algal/bacterial tufa, limy sandstone, siliceous tufa, and micritic/banded travertine. Interpretation by others suggest either a hot-spring (Steinen at al, 1987) or algal reef (Cornet, 1999) origin for the Coe Quarry limestone. The now inaccessible quarry is in the vicinity of the Eastern Border Fault, stratigraphically lies within the Shuttle Meadow Formation and is juxtaposed to brecciated and dolomitized Talcott Basalt.

Samples from the Coe Quarry were analyzed petrographically and under cathodoluminescence. Identifying relict textures and the presence of Fe and/or Mg –rich void fill generations may provide insight regarding fluid chemistry during primary and diagenetic processes. These methods were used to confirm a hot-spring origin for the Coe Limestone, and to reveal its possible affinity to another lake-margin hydrothermal spring deposit located to the south (Coron, 2007).