The Brentwood Memberof the Bloyd Formation conformably overlies the Prairie Grove Member, Hale Formationin the type Morrowansuccession of northwestern Arkansas. At its type locality, the Brentwoodis separated fromthe underlying PrairieGroveMemberby nearly 6 m of dark shale. Away fromthis area, the shale thins rapidly and the Hale-Bloydboundary may be placed withdifficulty. At some localities east of type section, the boundary is thought to be erosional rather than the more typical gradational contact. TheBrentwoodconsists of discrete carbonate bodies separated by dark shales. The carbonates consist principally of open shelf deposits, such as crinozoan biosparites and oolites. All carbonate lithologies contain varying amounts of fine to mediumgrained, rounded, quartz sand. Regionally, the BrentwoodMember becomes more shaly to the west of its type locality and loses the quartz sand content in its carbonate lithologies. To the east, the Brentwoodshales becomeless prominent and quartz sandstone intervals characterize the succession. TheWoolsey Memberoverlies the BrentwoodMemberand consists of light to dark, argillaceous shales with occasional sandstones, carbonates, and a thin coal. Thecoal is confined essentially to Washington and northern Crawfordcounties and never exceeds 45.7 cm. The shales are thought to be of terrestrial origin, but marine fossils and thin limestones in the lowerpart of typical Woolsey strata indicate a transitional change withinthe member rather than at its base. In contrast, the detrital fraction of the upper Brentwoodcarbonates seem to decrease rather than increase towards the Woolsey contact. To the west of the type area, the Woolsey gives rise to marineshales and carbonates. To the east, the Woolsey is equivalent to a thick, quartz pebble-bearing sandstone of fluvialorigin. The top of the Woolsey Memberis a regional unconformity withthe overlying DyeShaleMember, Bloyd Formation.
Thomas A. McGILVERYand, Charles E. Berlau
Journal of the Arkansas Academy of Science