D. Jeffrey Over

Conodonts and the Devonian-Carboniferous boundary in the upper Woodford Shale, Arbuckle Mountains, south-central Oklahoma

The Woodford Shale of south-central Oklahoma was deposited in an offshore, quiet-water, oxygen-poor setting on the southern margin of North America in assocation with other dark organic-rich shales of the Upper Devonian–Lower Carboniferous black-shale facies. The basal Woodford was deposited unconformably over lower Paleozoic carbonate strata as a south-to-north transgressive unit during the Frasnian and early Famennian. Black shales and cherts lie directly above the basal beds. Phosphatic shales in the upper Woodford contain a conodont succession characterized by three distinct environmentally controlled faunas. The lower fauna is characterized by Palmatolepis gracilis ssp., Branmehla inornata, Bispathodus stabilis , and Pseudopolygnathus marburgensis trigonicus , indicative of the Late Devonian Lower expansa Zone to Upper praesulcata Zone. The middle fauna, which spans the Devonian–Carboniferous (D/C) boundary, is characterized by Polygnathus communis communis and species of Protognathodus . On the Lawrence uplift the D/C boundary is disconformable, as indicated by the absence of Protognathodus kockeli before the first occurrence of Siphonodella sulcata . Light-colored phosphate laminae and beds, indicative of erosion and nondeposition, and a change in biofacies from an offshore palmatolepid–bispathodid fauna to a more nearshore, palmatolepid–polygnathid–protognathodid fauna indicate higher energy conditions and a lowering of sea level associated with the boundary interval. In the eastern Arbuckle Mountains the D/C boundary is apparently conformable, marked by a green shale interval containing a Protognathodus fauna. Species of Siphonodella , indicative of an offshore setting, characterize the third and youngest fauna. The Early Carboniferous sulcata , Lower duplicata , and Upper duplicata Zones are recognized in the upper Woodford. The Woodford Shale is conformably overlain by the “pre-Welden Shale’ and its equivalents, or unconformably overlain by the lower Caney Shale (Osagean?–Meramecian) in the northern outcrop regions and the Sycamore Formation (late Osagean?–Meramecian) in the southern Arbuckle Mountains.

CONODONTS FROM THE UPPER OLENTANGY SHALE (UPPER DEVONIAN, CENTRAL OHIO) AND STRATIGRAPHY ACROSS THE FRASNIAN–FAMENNIAN BOUNDARY

Abstract The Upper Olentangy Shale of Ohio, a green pyritic shale interbedded with thin dark gray shale beds, disconformably overlies the lithologically similar Middle Devonian Lower Olentangy Shale. The muds were deposited in a quiet offshore environment on the distal margin of the Appalachian Basin during the Late Frasnian through Early Famennian. The Upper Olentangy Shale contains abundant and diverse conodonts of MN Zone 13 and the Middle triangularis Zone. The Frasnian-Famennian boundary is 4–8 cm below the base of the Huron Shale at the Olentangy Shale type section in Delaware, Ohio. The boundary interval is a green shale containing a mixed highest Frasnian (e.g., Palmatolepis bogartensis, P. linguiformis) and lowest Famennian (e.g., P. delicatula, P. subperlobata, P. triangularis) conodont fauna. An ash horizon, pyritic bed, finely laminated dark shale, and a thin green-blue shale comprise the upper 3 cm of the Olentangy, and contain a conodont fauna indicative of the Middle triangularis Zone.

Protosalvinia Dawson and Associated Conodonts of the Upper Trachytera Zone, Famennian, Upper Devonian, in the Eastern United States

Abstract Protosalvinia first occur in association with conodonts of the Upper trachytera Zone and below the Three Lick Bed in the Ohio Shale and the Ellicott Shale of the central and northern Appalachian Basin, as well as in the Clegg Creek Member of the New Albany Shale of the Illinois Basin. In the Chattanooga Shale of the southern Appalachian Basin, Protosalvinia are found no lower than the Upper marginifera Zone or associated with obviously reworked conodonts in the Middle expansa Zone. Regionally Protosalvinia are associated with a disconformity and may be found with conodonts of the Lower expansa Zone.

Chapter 4 Sedimentary fill of the late devonian flynn creek crater: a hard target marine impact

Abstract The 3.6 km wide Flynn Creek crater in north-central Tennessee was produced by an asteroid that struck a flatlying succession of Ordovician carbonates. The crater is filled by a basal breccia and Late Devonian Chattanooga black shale. Conodonts in shallow water lag deposits that overlie the Ordovician succession in the region indicate lower Frasnian flooding of the area. The continuous stratigraphic record in the crater spans impact and post-impact deposits; the recovery of shallow water components and lower Frasnian conodonts in initial marine deposits above the crater fill breccia indicate that marine sedimentation commenced immediately after impact and that the impact occurred in shallow water. Most recent radiometric calibrations of Devonian conodont zones suggest that the impact occurred around 382 Ma. Stratigraphy and sedimentary features suggest the following sequence of events: (1) shallow water impact duringthe early Frasnian; (2) formation of basal breccia as a fallback deposit; (3) deposition of graded breccia as displaced water rushed back into the crater; (4) ejecta washed back into the crater by storm-induced waves and currents; (5) accumulation and preservation of black shale first in the crater, and also as sea level rose outside the crater. Because the target rocks were lithified carbonates, the Flynn Creek crater has the morphologic characteristics of a subaerial impact. The sediment fill, however, reflects the shallow marine setting of the impact site.

Johnognathus huddlei Mashkova, an element in the apparatus of Distomodus staurognathoides (Walliser); Conodonta (Silurian)

The genus and species Johnognathus huddlei Mashkova, 1977, is synonymized with Distomodus staurognathoides (Walliser, 1964) on the basis of common occurrence, similar morphology, and the discovery of a complete S element of D. staurognathoides with a posterior process developed into a platform that is identical in morphology to specimens referred to J. huddlei .

Geochemical Signatures of Some Devonian Black Shales

Shales from two geographical locations but of the same age (Devonian) were compared in this study. Given that the depositional geochemical environment may be similar, it remains to be seen in if there is a possible unique geochemical signature that can globally unite all black shales of similar origin. Samples from the Oatka Creek Formation (USA) and Batu Gajah Shale (Malaysia) showed similar trends in terms of their absorbance at 465 and 665 nm. Since the E4 and E6 absorbance values are similar, it is believed that the supply of organics and the diagenetic history could have been very similar. The preliminary results suggest further that the similarity in the individual values of the E4 and E6 absorbances as well as the E4/E6 ratios may well serve as a unique geochemical signature for such black shales from the Devonian.