Carbonate Stratigraphy Of The Lower Part Of Slade Formation (Mississippian) And The Soft-Sediment Deformation In The St. Louis Member, Kentucky, USA

This dissertation aims to make explanations on two problems from the carbonate of the lower part of Slade Formation in northeastern and east-central Kentucky, USA: (1) possible origin of the peculiar dolomitic bodies and associated soft sediment deformation structures, and (2) coupling of the stratigraphy of the lower part of Slade Formation and tectonics.On the basis of previous studies and descriptions of geological phenomena, it is concluded that the dolomitic bodies and the temporally equivalent“Big Sinking bed”deformation were formed in a paleo-earthquake, possibly at Richard magnitude 7.3, during the hiatus between the St. Louis and Ste. Genevieve deposition. The co-seismic activity along the Locust Branch Fault Trend is the most probable trigger of the soft sediment deformation, although the Jinks Fault Trend possibility can not be totally excluded.The favorable lithology for the formation of dolomitic bodies is the St. Louis subunit B which consists of interbedded limestone and shale. The lens shape of the dolomitic bodies was related to the extension on the upper part of the Acadia forebulge induced by lithospheric flexure, and resembles the forming mechanism of Boudinage structure. During the earthquake, the cyclic stress liquefied the mud component but not the limestone, and the alternative compression and stretching made the mud into a high energy flow that flew parallel to bedding or lamination or penetrated the weakness of the limestone beds; the repeated shear of mud flow along the broken part of the limestone generated the round ends of the bodies at the outcrop scale.Dolomitization of the bodies was secondary and selective. Cyclic shear over the unliquefied and overconsolidated limestone, at undrained condition, resulted in fracture zone or fracture network, which induced much higher permeability in the limestone than rocks surrounding. The high permeability was favorable for high Mg2+ fluid flowing through and thus for selective dolomitization.With the measured sections and facies analysis, the possible migrating Ouachita forebulge that reactivated basement faults was presented here to explain the stratigraphy of the lower part of Slade Formation, including St. Louis, Ste. Genevieve, Warix Run and Mill Knob Members. During the St. Louis deposition, which was before the Ouachita orogeny, limestones deposited onlapping the top of the Renfro Member in a gentally dipping ramp environment. In early Chesterian, the Ouachita orogeny along southeast Laurentia incepted, and thrust sheets loaded on and flexured the Laurentia lithosphere. As the loading advancing craton-ward, a peripheral forebulge as wide as 300km formed and covered the study area, and migrated northward. During Ste. Genevieve deposition, forebulge crest migrated to the area between Glencairn Fault Trend and Locust Branch Fault Trend, where was uplifted and did not receive Ste. Genevieve oolitic shoal deposits. Then, the forebulge crest migrated to the north and located between Glencairn Fault Trend and Kentucky River Fault System, where was uplifted and few Warix Run sediments deposited; and the former uplifted area during Ste. Genevieve deposition and the area to the to the north of the Kentucky River Fault System was depressed relatively and accommodated major part of the Warix Run tidal Channel deposits. Afterwards, during the Mill Knob deposition, the forebulge crest shifted to the north of the Kentucky River Fault System; with the sea-level lowstand, the interplay of the forebulge crest and Waverly Arch kept the Mill Knob tidal-flat deposits away from the core part of the arch. Thereafter, the forebulge crest migrated out of the study area to the north. After all, the spatio-temporal stratigraphic characteristics of the lower part of Slade formation reflected the interaction of tectonic activities and eustasy.