Paper No. 266-6
Presentation Time: 9:15 AM
STORM DEPOSITS ON A MUDDY, OUTER SHELF, BRENTWOOD LIMESTONE MEMBER, BLOYD FORMATION MORROWAN (PENNSYLVANIAN) NORTHWEST ARKANSAS
Sedimentation on an outer shelf setting was controlled by strong tropical storms during late Morrowan (Early Pennsylvanian) time. Storm deposits are exposed in the Brentwood Member of the Bloyd Formation in the northern Boston Mountains of northwest Arkansas. The outer shelf setting was a site of mud and silt sedimentation adjacent to a shallow inner shelf carbonate environment. The storm sequences were produced by strong shore-directed, unidirectional currents during the initial phase of storm activity. The storm surge eroded shallow channels into the existing outer shelf muds and transported terrigenous mud into the inner shelf carbonate environments. The return flow transported skeletal fragments and terrigenous mud into the outer shelf environments producing a storm sequence in previously eroded channels. A complete storm sequence reflects initial bottom currents of high competency that declined through time and were succeeded by wave generated oscillatory flow. Skeletal debris was incorporated into hummocky cross strata as unidirectional currents were replaced by oscillatory flow. The storm succession consists of an erosion surface followed by a basal pebble conglomerate, massive grainstone and packstone, whole fossil wackestone, hummocky stratification and a swell-lag of platy crinoid calyx plates. As storm activity ceased, fair weather deposits of outer shelf mud blanketed the storm sequences.