CORRELATION OF HIGH ORDER CYCLES IN A MIDDLE DEVONIAN MARINE-PARALIC TRANSITION: HAMILTON GROUP, EASTERN NEW YORK STATE

The upper Middle Devonian (Givetian) Hamilton Group of New York State stretches from the shores of Lake Erie in the west to the Catskill Front in the east, encompassing facies deposited in deep, anoxic basin to shallow, storm-dominated shelf and continental flood plain settings. The Moscow Formation, upper-most unit of the Hamilton Group, is subdivisible into five smaller-scale packages of rock representing high-order cycles of sea level oscillation. The larger cycles have previously been correlated across the basin, with some variation, from Lake Erie in the west to about Hamilton in the east. Recent detailed tracing of marker beds, has demonstrated that even small-scale cycles can be correlated over 100 km farther eastward to Milford and Schenevus, eastern Otsego Co., Summit, western Schoharie Co., and eventually to outcrops along the Schoharie Valley. Along this transect, the section thickens from about 75 m to 150 m and facies change rapidly recording changes from distal shelf, to shallow shelf, shoreface, and finally to estuarine-fluvial environments. Despite these changes, general patterns of sea level oscillation cycles can be discerned even in the eastern-most outcrops. Dark shale horizons of western, basinal sections correlate with shaly marine tongues that onlap marginal marine sands. Correlation of small scale cycles within the Moscow Formation, has also elucidated the stratigraphic positions of different levels of the famous "Gilboa Forest" Lagerstätten. Stumps of the progymnosperm Eospermatopteris were buried in life position by massive sands and eventually rotted and were filled-in with sand to form molds. The stumps are interpreted to occur at the boundaries of the small scale sea level cycles, i.e. flooding surfaces within the middle Moscow Formation. Continental red-beds of the Manorkill Formation had previously been interpreted as correlative to the upper portion of the Moscow Formation. However, recent stratigraphic work demonstrates that the red-beds actually come in above the uppermost cycles of the Moscow Formation and thus apparently are correlative with the lower/middle Tully Formation. This interpretation accords with evidence that the middle Tully represents a major shallowing in the basin during the late Givetian.