PETROGRAPHY OF THE COE LIMESTONE, SHUTTLE MEADOW FM. (JURASSIC), SOUTHERN HARTFORD BASIN, CT

One of 16 syn-rift basins comprising the Central Atlantic Magmatic Province (CAMP), the Hartford Basin is infilled with early Jurassic flood basalts interbedded with arkosic sandstones, mudstones and conglomerates. Monsoonal seasons are represented in sedimentary facies by pedogenic horizons and alluvial deposits. Limestone deposits are ubiquitous within the basin. A deposit in Durham, CT, at a location previously quarried by the Coe family was originally interpreted as a hot spring deposit (Steinen et al., 1987; Krynine, 1950). The now inaccessible deposit stratigraphically lies within the Shuttle Meadow Formation and is juxtaposed to brecciated and dolomitized Talcott Basalt.

Detailed petrographic examination and cathodoluminescence have revealed previously unrecorded textures that support interpretation of the Coe Limestone deposit as a sublacustrine seep. Hydrologic changes including subaerial exposure, fluctuations in salinity, and meteoric mixing have been identified. Textural findings include fossiliferous facies not previously identified, suggesting alkaline or freshwater conditions. Pedogenic fabrics represented in various lithologies include skewed planar matrices within a muddy, clotted groundmass, infilling of vugs/fenestrals with silt- to sand-sized detritus, corroded grains, and baroque dolomitic spar fill within fractures and fenestrals. Other mineralogical constituents include iron oxide pseudomorphs, spherulites of microcrystalline quartz/chalcedony, and anhydrite.