Paper No. 87-18
Presentation Time: 9:00 AM-5:30 PM
A SEQUENCE STRATIGRAPHIC INTERPRETATION OF THE ALLEGHENY GROUP (LATE MOSCOVIAN) IN THE DISTAL APPALACHIAN BASIN
New highway construction has exposed a complete section of the Allegheny Group in southeastern Ohio. The study site is located in the backbulge region of the Alleghanian Orogeny where total accommodation was low. Detailed facies analysis of six measured sections was used to divide the interval into 9 sequences that vary from 2 to 15 m in thickness. Transgressive Systems Tracts vary in composition from marine shales and mudstones to coal to fluvial sandstones. Highstand Systems Tract deposits consist primarily of interbedded laminated mudstones, thin fine-grained sandstones and coal seams overlying gleyed paleosols. Sequence boundaries were placed at the top of paleosol profiles and base of incised fluvial sandstones. The vertical pattern of grain size and of sandstone bed thickness were used to infer locations of the MFS horizons. Marine limestones are absent at the study site, although they are present within this interval to the north and south of the study. The composition of the sequences varies from a single fluvial sandstone body to a complex assemblage of marine to lacustrine mudstones, sandstones and coal. Fluvial sandstones comprise entire sequences near the base and top of the section. The variation in facies patterns and sequence thickness within the section, and between this location and other locales along strike reported in the literature, is interpreted to be primarily a function of allogenic glacial-eustatic sea level changes. The allogenic driver was modified to varying degrees by autogenic processes, such as channel avulsion during Highstands, that shifted channel locations between sequences. Fluvial incision during times of Falling Stage and Lowstand resulted in the erosion of some or all of underlying sequences, the formation of paleosols on interfluves, and the amalgamation of fluvial sandstones.