Inhomogeneities, Paleomorphology, and Architectural Elements in Shoal Deposits of Salem Limestone (Mississippian) in Southern Indiana

Todd A. Thompson, Mark A. Brown

The shoal deposits (building-stone facies) of the Salem Limestone are renowned for their uniform texture and composition. Despite this apparent homogeneity, new stone-cutting techniques are exposing a hierarchy of sedimentary structures and bounding surfaces that previously were not recognized. The most significant features are hardgrounds along third-order bounding surfaces. The hardgrounds package distinct depositional events and define mesoforms. The mesoforms are interpreted as sand waves similar to the bed forms described from the modern Bahama Banks.

In the Dark Hollow quarry near Oolitic, Indiana, a single sand wave (2.5 m thick) consists of (1) a bar core characterized by planar cross-stratified grainstone with horizontal set boundaries, (2) bar slip-face wedges composed of cosets of trough cross-stratified grainstone, and (3) bar-drape deposits consisting of massive and burrowed grainstone. The bar-drape deposits are interpreted as hardgrounds and mark the stabilized and reactivated surfaces of the mesoform. The sand wave is linear and trends northwest-southeastward. Paleocurrent measurements indicate a northeasterly (landward) transport direction perpendicular to the long axis of the sand wave. The sand wave was dominated by storm events as indicated by the pervasive unidirectional paleocurrent trend in the large-scale cross-b ds and by the packaging of depositional events by hardgrounds.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.