HIGH RESOLUTION STRATIGRAPHY OF THE DEEP RUN SHALE MEMBER (MOSCOW FORMATION) ACROSS THE FINGER LAKES OF NEW YORK: A REINTERPRETATION OF BASIN AXIS DEPOSITION

The Middle Devonian Deep Run Shale Member is an east-west trending muddy siltstone, which accumulated predominately during a marine transgression across a shallow shelf and also within a basinal trough, which marked the northern arm of the Appalachian Basin. Our field research has allowed us to map two new regionally widespread units within the Deep Run Shale Member; a 1 m thick, lower fossiliferous layer herein designated the Kipp Road Bed, and a 4 -15 m thick, sparsely fossiliferous upper unit herein designated the Willard siltstone interval. Furthermore, previously undescribed Ludlowville-Moscow sections along the west shore of present-day Seneca Lake revealed additional beds, which may have been deposited only in the central trough prior to Deep Run time. We currently interpret these deposits to lie above the Jaycox (uppermost Ludlowville Fm.) and to be localized, early phases of the Tichenor (Moscow Fm), which represent partial closure of the sequence boundary unconformity that floors the Moscow Fm.

Species diversity and abundance is high in the Kipp Road Bed but decreases basinward due to increased bathymetry as well as increased turbidity. Moreover, low species diversity and scarcity in the Willard interval reflects rapid rates of sediment accumulation in association with variably intense bioturbation and with maximum inferred water depths. Only a few widely scattered very thin shell-rich horizons occur within the Willard interval and indicate a temporary slowing of sedimentation. The excellent fossil preservation in these shell-rich horizons as well as many taxa found in-situ suggests a renewal of rapid burial. At the very top of the Willard siltstone an erosional surface developed, presumably resulting from shallowing sea levels. Sediments were truncated both east and west of the central trough prior to the deposition of the Menteth, thereby ending the accumulation of the siliciclastics of the Deep Run Shale Member.