Adverse Effects of Crevasse-Splay Deposits in an Appalachian Coal Mine, Eastern Kentucky

Stephen F. Greb

Facies analysis of highwall exposures, roof and pillar information, and 56 core descriptions indicate that a series of narrow, bifurcating paleochannels and associated sheet sandstones in an eastern Kentucky coal mine were deposited by at least three crevasse-splay and overbank flooding events that occurred during and immediately following peat accumulation in a fluviolacustrine flood-basin environment.

The proximal crevasse facies is channel-form, dominantly gray, very fine to fine-grained sandstone exhibiting ripple-drift, current-ripple, and small-scale trough cross-bedding, abundant micaceous laminae, and common disseminated plant and stem debris.

The proximal crevasse channels grade laterally, and are incised into distal splay sandstones, shales, claystones, and coal riders. Sandstones of the distal splay facies are gray, sheet form to wedge shaped, shaly to very fine grained, and exhibiting ripple-drift, irregular, and massive bedding, disseminated and well-preserved plant and stem fossils, micaceous concentrations, coal spar, and rooting structures. Shales of the distal splay facies are gray and laminated, with abundant, well-preserved plant and stem fossils, sideritic nodules, claystone, and coal laminae.

Economic problems resulting from the crevasse-splay facies include (1) multiple washouts of the coal seam, (2) increased parting thickness and frequency, (3) split wedges in the coal seam, and (4) significant roof stability problems.

Large roof falls in the crevasse-splay (stackrock) roofs result from (1) thin bedding of facies, (2) rapid lateral and vertical changes of facies, (3) internal bedding weaknesses, such as fossil plant and micaceous concentrations, sideritic nodules, and coal spar, (4) thin coal riders and streaks in the roof, and (5) slickensided shale beneath sandstone channels.

Mapping the crevasse-splay facies may help to predict coal quality and roof stability problems in unmined areas.

AAPG Search and Discovery Article #91041©1987 AAPG Eastern Section Meeting, Columbus, Ohio, October 7-10, 1987.