ABSTRACT: High-Resolution Sequence Stratigraphic Analysis of Fluvio-Deltaic Cyclothems: The Pennsylvanian Breathitt Group, East Kentucky

DAVIES, H., Shell Research, Rijswijk, The Netherlands, M. BURN, University of Kentucky, Lexington, KY, and M. C. BUDDING and H. WILLIAMS, Shell Research, Rijswijk, The Netherlands

The Carboniferous Appalachian basin of the eastern United States is a classic study area for fluvio-deltaic sequences. Many of the early detailed deltaic facies models were first developed in this region. Large-scale road-cut exposures and extensive continuous coring records make eastern Kentucky unparalleled as an area in which to study the architectural organization of fluvio-deltaic sequences.

A study area of 1000 sq. kilometers was chosen, within which some 600 cored well logs and a major highway were present. Detailed facies recognition work at outcrop was complemented by subsurface facies mapping.

Three-dimensional mapping of sediment body geometries revealed that the 125 m thick Four Corners Formation principally comprises three facies associations organized into cyclic, fining-upward sequences of 20-50 m thickness, which extend for >70 km in depositional dip sections.

These sequences are interpreted to be initiated by lowstand fluvial entrenchment generating incised valleys. The subsequent fining-upward sequence records deposition of a retrograding fluvio-deltaic system during relative sea level rise. Proximal fluvio-distributary channels filled incised valleys, and were succeeded by a retrogressive lower delta plain system.

In sequence stratigraphic terms these cyclic deposits form high-frequency sequences with the incised valleys defining Sequence Boundaries, and the subsequent valley-fill and delta plain facies making up the Lowstand Systems Tract. The marine facies are predominantly

Transgressive Systems Tract deposits with the general paucity of Highstand deposits reflecting the depth of lowstand incision.

In summary, the application of sequence stratigraphic techniques to the Carboniferous sequences of eastern Kentucky highlights the importance of relative sea level changes, and provides a rationale for facies organization in fluvial-dominated delta systems.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)