STRATIGRAPHY OF THE LOWER SHUTTLE MEADOW FM. (JURASSIC), LAMENTATION MTN., MERIDEN-BERLIN, CT

During the Late Triassic-Early Jurassic, 4-7 km of alluvial fan-fluvial -playa redbeds, and gray/black lacustrine sediments accumulated, alternating with three phases of tholeiitic basalt extrusions in a subtropical half-graben at 25⁰N paleolatitude. The so-called Hartford Basin is one of 16 exposed synrift basins that extend for more than 2000 km from eastern Canada into the southeastern United States. Widespread lacustrine sequences occur within three formations in the basin: the New Haven, Shuttle Meadow and Portland Formations.

A previously undescribed nearly 30 foot-thick section of the lower Shuttle Meadow (“Durham Member”) can be subdivided into three gradational sections representing fluctuating lake conditions from under-filled to balanced-filled to under-filled again, as the lake margin facies expanded at the expense of the profundal area. The lowermost beds are fluvio-lacustrine arkosic mudstones and siltstones (6.8 ft.), displaying ripple marks, cross-bedding and mudcracks. This passes upwards into 2.5 ft. of carbonate-rich mottled sandstones and mudstones, culminating in calcareous dark gray mudstones of the profundal facies, which continue into a 6.5.foot-thick section of siliciclastic laminated mudstones with framboidal pyrite. Intercalated with these dark gray mudstones are several indurated mixed clay layers from 0.25 to 1.25 inches thick. These clay layers host hematite pseudomorphs (after pyrite) and hematite spherules which could have formed from fluid interaction with tephra from the adjacent volcanic center. Overlying the dark gray mudstones are 13.1 feet of alternating fissile micaceous arkosic siltstones and gray mudstones with additional clay layers (8.3 ft.) and dark red micaceous arkosic siltstones with mudcracks (4.5 ft.).

The sequential organization of the basin-fill succession is directly influenced by syndepositional tectonics and climate fluctuations, whereas the lateral variation in the lacustrine sequence architecture, supported by stratigraphic analysis and a preliminary chemostratigraphic framework, is due to the localized sediment supply, varied topography, differential subsidence, and the chemistry of fluid influx.