Paleodepositional Environments, Diagenesis, Paleocurrent Flow Dynamics, and Reservoir-Quality Sands of Alexander Formation

Peter J. Hatgelakas

The Alexander formation is a distal marine turbidite sand deposited off the Catskill delta system. Supporting evidence for this interpretation can be found through study of a core from the heart of the field and from regional facies work across the northern half of West Virginia. The Alexander is somewhat unique among flysch turbidite deposits of the Appalachian basin, which affects the strategy for its development.

There is an interrelationship between depositional facies and reservoir characteristics for these distributary deposits of the Catskill cone. No evidence was found relating structural influences to reservoir quality or production. The effects of diagenesis on production, and the relationship of diagenesis to facies, are clearly demonstrated through SEM work. Detailed mapping of the Alexander sandy silts reveals geometries of terminus bars and traction carpets that may be used as templates for biased contouring elsewhere.

The presence of authigenic clays within the sands and silts was found to be crucial to the preservation of permeability in the reservoir. Because of the parallel overlying succession of turbidity flows, dipmeters can be used to predict channel course and position.

Gaps in sand accumulations along current paths suggest that self-ignition was a prevalent phenomenon of these turbidity flows. Can these gaps in the traction carpet be related to paleotopographic changes in slope on the clinoform?

Regional mapping of the Alexander sands demonstrates an intricate dendritic pattern of turbidity flows and provides a clue to the network and form of paleocurrents in this epicontinental Devonian sea.

AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.