ABSTRACT

Carboniferous rocks between the Lower Elkhorn and Whitesburg coals near Pikeville, Kentucky are interpreted as products of lower delta plain sedimentation. Excellent exposure permits study of these deposits in the third dimention; a view which can only be inferred in modern deltaic systems.

The principal depositional elements of the Pikeville lower delta plain deposits (like those of the Mississippi River delta plain) are 1) interdistributary bays, 2) distributary mouth bar sands, 3) crevasse splays and, 4) distributary and splay channel fills. Interdistributary bays consist of thick sequences of fine grained sediment, coarsening upward from silty shales to siltstones and are overlain by distributary mouth bar sands or splay sandstones and silty sandstones. Distributary mouth bars consist of fine to medium grain sandstones with small scale crossbeds and multiply scours. Splay deposits, which form by crevassing the main distributary are gradational in size from a small shoal to a distributary mouth bar. Natural levee deposits account for only a small part of the sequence. Channel fills of both distributary and splay channels are uniformly fine grained.

The lower delta plain deposits near Pikeville are similar to those of the Mississippi in that; interdistributary bay sequences gradationally coarsen vertically upward and laterally into sands of distributary mouth bars; the dominate type of channel fill is abandoned fill; levee deposits are irregular but comparable in size and are frequently crevassed by numerous splays. These deposits differ with respect to overall grain size, scale of bays, distributary mouth bars and channels. The wide variation in size of Carboniferous Pikeville splays does not occur in the modern Mississippi. The significant differences between the Carboniferous and Mississippi deltaics are due to tectonic setting (location on the continental plate), type of subsidence and proximity to the source area.