A SEQUENCE STRATIGRAPHIC MODEL FOR NONMARINE STRATA OF THE MID-LATE PENNSYLVANIAN CONEMAUGH FORMATION, CENTRAL APPALACHIAN BASIN

Sequence stratigraphic studies of fluvial successions are hindered by rapid lateral facies changes and inability to distinguish time-significant surfaces. The recognition of widespread mature paleosols as interfluvial sequence boundaries (IFSBs) between incised valley fills (IVFs) has led to significant progress in this area. A total of 2,251 m of strata was measured and described at 65 outcrops through the lower 80-100 m of the Conemaugh Formation in central West Virginia. The lack of persistent coals or marine units hindered attempts of previous workers at high resolution stratigraphic correlation in this area. In this study, paleosol bounded packages of dominantly terrestrial strata in Kanawha, Lincoln, Roane Counties are correlated with similar packages containing marine units downdip to the north and west in Braxton, Cabell, Wayne Counties. IVFs occur in association with each paleosol-bounded cycle and consist of multistory fluvial and upper estuarine channel-fills. Initial stages of IFSB paleosol development occurred on interfluves during FSST and LST under well-drained, oxidizing conditions and strongly seasonal climate forming calcic vertisols and aridosols. Sediment bypassing allowed for prolonged pedogenesis over 10s to 100s of ky. Gleying and local histosol development occurred during TST caused by rising water table due to rising sea level and wetter, less seasonal climate. Microconchid limestones, typically overlying thick calcic vertisols (IFSBs), formed under lacustrine, palustrine, and brackish intertidal conditions; the top of this facies represents a maximum flooding surface. Overlying coarsening-upward bay and lake fill sequences formed during the HST.

Sea-level/base level was the primary control on high frequency variations in accommodation space within the low gradient, coastal plain fluvial systems during the development of the fourth-order cyclothems. Striking parallels in scale and internal architecture occur between downdip, marine-cored cyclothems and their updip ‘nonmarine’ cyclothem equivalents in central West Virginia. This study underscores the importance of regionally developed paleosols and microconchid limestones as valuable tools in stratigraphic correlation and in sequence stratigraphic studies.