Book Description
Organic-carbon-rich shales of the Burket Member, Harrell Formation, were deposited at the toe and basinward of a series of alternately prograding and backstepping clinothems associated with the proto-Catskill Delta complex centered in or around western Susquehanna and Wyoming Counties, Pennsylvania. Distribution of organic-carbon-rich facies was controlled by changes in the delta complex driven by variations in rates of creation of accommodation and by a persistent topographic high centered in the area of western McKean and eastern Warren counties, Pennsylvania. Specifically, I interpret the middle and upper Tully Ls., the Burket Mbr., and the upper Harrell Fm. as comprising a single third order depositional sequence with the lower Tully Ls. being deposited during the falling stage of the preceding third order sequence. The middle Tully LS. represents the lowstand systems tract (LST), whereas the upper Tully Ls. and basal portion of the Burket Mbr. were deposited during the transgressive systems tract (TST). The upper portion of the Burket Mbr. was deposited during the highstand systems tract (HST) and the upper Harrell Fm. was deposited during the falling stage systems tract (FSST). The regional extent of parasequence sets, systems tracts, and the inferred depositional sequences, along with correlations with large scale transgressive sequences in other basins, suggest that base-level fluctuations were largely the result of allogenic forcing -- eustacy, climate, or regional thermal uplift or subsidence -- rather than autogenic forcing. Geochemical analysis suggests that bottom water conditions were oxic to suboxic at the time of Tully Ls. deposition but that conditions had become anoxic to euxinic by the time of Burket Mbr. deposition.
