Due to the strategic location of Kentucky, being bisected as it is by the Cincinnati arch and containing within its boundaries the southern end of the Central Interior basin, the western border of the Appalachian basin, the northern flank of the Ozarks-extended, and the northern tip of the Mississippi embayment, it was necessary to go beyond the confines of the state into the deeper parts of these various basins of sedimentation in order to gain some real clues about the depositional history during the early and middle Paleozoic. Instead of working from unconformity to unconformity, an attempt was made to find the basins of continuous deposition and thus work from the most complete sections onto the structures where the section is shortest. For that reason the Appalachian basin on the east flank of the Cincinnati arch was chosen as a place to begin the report, where sedimentation was continuous during late Ordovician and early Silurian. The great unconformity at that time, so far as the area under discussion is concerned, was related to the Ozark stable area. The Cincinnati arch became effective as a subsea barrier to clastic deposition during the early Silurian, and during the late Silurian was a positive feature which actually contributed detrital material to the early Devonian being deposited in the basins on either side. This is the first time the Cincinnati arch as such can be demonstrated to have played an active part in geological history. The seas retreated only from the broad arch area at this time and sedimentation was continuous in the southern part of the Illinois basin, southward across Tennessee and presumably thus into open sea, a broadened and enlarged Mississippi embayment. Deposition was continuous also in the Appalachian basin and the Michigan basin where evaporites were formed back of the Cincinnati arch barrier during much of the Silurian and well into the Devonian. The report ends within the basin of continuous deposition between Devonian and Mississippian, that is, within the thick black shale sequence on the western border of the Appalachian basin. End_Page 1------------------------------ The pattern of sedimentation is illustrated by isopachous maps of the Silurian and Devonian and of the various components of these systems, and with facies indicated. It was necessary to suggest minor changes in correlation in some instances, a particular instance being the suggestion that the Helderberg is open-sea facies of the upper part of the Salina evaporite, but in many instances small details of correlation which have been troublesome in the past fall into line with this interpretation.
An attempt has been made to correlate the subsurface Devonian and Silurian strata in the western Kentucky basin with equivalent beds in the generally distant outcrops. Samples from about forty wells were studied, zoned on the basis of general lithology and insoluble residues, and a tentative correlation of these zones with the outcrop material suggested. The formations recognized at the surface in southern Illinois can be traced into the subsurface in western Kentucky. The absence of the Decatur and upper Brownsport of the Tennessee Silurian from the sections high on the flank of the Cincinnati arch, and their presence on the west side of the basin indicates some post-middle Silurian and pre-Devonian uplift and erosion. The Kentucky Lower and lower Middle Devonian strata may represent the seaward facies of the Arkansas and Texas novaculites as thickening toward the southwest suggests that the source of the thick cherts and dolomites was in that direction. Post-Hamilton warping of the basin, perhaps as a result of relative east-west uplift occasioned by movement of the Nashville dome, served to cut off the southern end of the syncline. This resulted in the preservation of a complete section of Lower and Middle Devonian in the deepest part, and the stripping of the Hamilton and most of the Onondaga from the east, south, and west sides. All or nearly all of the Devonian sediments were removed from the region high on the Cincinnati arch side of the basin, from Hardin County south to Barren County, before deposition of the Chattanooga shale.
'%3e%3cpath fill='%23001489' d='M0 0v6h9V0z'/%3e%3cpath fill='%23e03c31' d='M0 0v3h9V0z'/%3e%3cg stroke='%23fff' stroke-width='2'%3e%3cpath id='d' d='m0 0 4.5 3L0 6m4.5-3H9'/%3e%3cuse xlink:href='%23b' stroke='%23ffb81c' clip-path='url(%23c)'/%3e%3c/g%3e%3cuse xlink:href='%23d' fill='none' stroke='%23007749' stroke-width='1.2'/%3e%3c/g%3e%3c/svg%3e)
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
