Large-scale Tectonic Controls on the Origin of Paleozoic Dark-shale Source-rock Basins

Eustatic and far-field tectonic control on the development of an intra-platform carbonate-shoal complex: upper tongue of the Tanglewood Member, Upper Ordovician Lexington Limestone, central Kentucky, U.S.A.

“…Because the basement is inhomogeneous and rife with brittle deformation left over from older episodes of lithospheric tension and compression (Fig. 4), these dislocations remain zones of weakness that can be reactivated when exposed to new stresses (Ettensohn and Lierman, 2012). Hence, the apparent reactivation of such structures during deposition of the Lexington Limestone, when other causes are absent (Ettensohn et al, 2002a), is inferred to have been caused by large-scale Taconian compressional and tensional stresses, or far-field forces, impelled westward along a network of old basement dislocations during coeval orogeny.…”

“…Middle and early Late Ordovician (Darriwilian and early Sandbian) parts of the orogeny were concentrated at the Virginia promontory in the Blountian tectophase and had little effect in Kentucky, but as the orogeny migrated northeastward due to diachronous, scissors-like convergence, orogeny became concentrated at the New York promontory in the Late Ordovician (late Sandbian-Katian; midlate Caradoc; Chatfieldian-early Edenian) Taconic tectophase (Ettensohn, 1991). Intense deformational loading at this promontory not only generated a deep foreland basin that filled with dark shales, but also apparently reactivated many Iapetan and older basement structures through far-field forces to generate the Lexington Platform and structures related to the Tanglewood buildup (Ettensohn et al, 2002a;Ettensohn and Lierman, 2012) (Figs. 1 and 4).…”

Testing Tectonostratigraphic Hypotheses of the Blountian Phase of the Taconic Orogeny in the Southern Appalachians through an Integrated Geochronological and Sedimentological Study of Ordovician K-Bentonites and Quartz Arenites

“…Standard collisional tectonic models show molasse sediments consisting of fine to coarse continental clastic sedimentary rocks being derived from eroding tectonic highlands and then deposited in an adjacent foreland basin during later stages of orogenic activity [52], when waning tectonism is accompanied by a decline in explosive volcanism like that which was responsible for the tephras that are now the K-bentonites. The molasse sediments that accumulated as the Blountian tectophase was ending include red mudrocks (Figure 3) of the Moccasin, Bays, and Greensport formations [53], as well as the distinctive sandy to pebbly quartz arenites [15,33,[54][55][56].…”

Subsurface Relationships between the Sebree Trough and Carbonate-Siliciclastic Mixing in the Upper Ordovician Lexington-Trenton and Point Pleasant-Utica Intervals in Ohio, USA, using Multivariate Statistical Well Log Analysis

“…In the deepening seas, the presence of upwelling into-and the restricted nature of-the Sebree Trough generated epicontinental, quasi-estuarine circulation patterns that fostered the development of a stratified water column; the dysaerobic and anaerobic conditions being reflected in the dark, organic-rich shales of the Point Pleasant and Utica formations (Kolata et al 2001;Ettensohn et al 2002;Ettensohn 2010;Ettensohn and Lierman 2015). At the same time, coeval dark shales from the Martinsburg, Reedsville, and Antes formations, and from the Utica Group of New York, expanded across adjacent parts of the Appalachian foreland basin (Ettensohn 2008;Ettensohn and Lierman 2012). The nature and origin of the dark shales filling the Sebree Trough in Illinois, Indiana, Kentucky, and southwestern Ohio are relatively well-known (Kolata et al 2001;Ettensohn et al 2002;McLaughlin and Brett 2007;Young et al 2016); however, in the rest of this paper, these relationships for the dark Point Pleasant and Utica shales will be examined throughout the remaining parts of Ohio.…”