ORIGIN AND CHARACTERISTICS OF MUD- AND DEBRIS-FLOW DEPOSITS IN THE SHUTTLE MEADOW FM., SOUTHERN HARTFORD BASIN, CT

Criteria for recognition and distinction of sediment-water flows have primarily been based on rheologic flow properties, sediment concentration, flow velocity and/or the morphology of the deposits. Distinguishing among hyperconcentrated flows, slurry or debris flows, and granular flows within the geologic record of the Hartford synrift basin has been complicated by numerous unroofing events and penecontemporaneous and later faulting, making identification of and proximity to source areas and recognition of fan architectural elements difficult.

Five units within the Talcott-Shuttle Meadow transition or within the basal Shuttle Meadow Formation have been mapped, described and petrographically analyzed from four locations in Middlesex County. These deposits fall within facies Gmm, Gmg, Gci, and Gcm (Miall, 1978, 2010). Sharp, predominantly non-erosive bases, thick defined units, unstratified, unsorted, with inverse and normal grading, rough imbrication and/or sub-vertical clast orientation imply debris flow transport, and argue against reworked debris flow or stream origin. Of the five units studied, one is mappable as a lahar and two are hydrothermally altered due to proximity to volcanic centers. Another is a mid-fan flow, proximal to the Eastern Border Fault.

The overall sequential organization of the basin-fill succession reflects syndepositional tectonic control, climatic influence, and variation in sequence architecture due to source unroofing (localized sediment supply), differential subsidence, and to interaction with the volcanic complexes.