Interpreting and correlating epeiric sea sequences is key to understanding ancient marine environments. As a result, eNd, d13C and Sm/Nd profiles are developed as tools for interpreting epeiric sea carbonates. Previously, eNd and d13C profiles in epeiric sea carbonates have been used to study changes in the Nd isotope balance and C-cycle of adjacent ocean water. Instead, eNd, d13C and Sm/Nd profiles of Ordovician Midcontinent carbonates of North America demonstrate that fluctuations in sea level and depth are driving local changes in the eNd, d13C and Sm/Nd composition of epeiric seawater. <p> Dissolved Nd derived from the Transcontinental Arch, Taconic Highlands and the Iapetus Ocean determine the eNd composition of Midcontinent seawater. As sea level fluctuated, submergence of the Arch and an influx of Iapetus ocean waters adjusted the Nd isotope balance of epeiric seawater. As a result, eNd profiles can be used to track the submergence history of the Late Ordovician Midcontinent. Comparison of stratigraphic variations in carbonate Sm/Nd ratios with sea level curves, conodont paleoecology, and the eNd profiles also suggests that variations in Sm/Nd ratios are related to changes in depth. However, processes effecting Sm/Nd ratios in epeiric seas may be varied and require further investigation. <p> Sea level fluctuations and the waxing and waning of cool, nutrient rich, oxygen poor Iapetus waters onto the craton adjusted productivity and organic carbon burial rates on the Ordovician Midcontinent. Close to the Transcontinental Arch sea level rise caused an increase in organic carbon burial and productivity, while close to the Sebree Trough, and the influx of Iapetus waters, sea level rise caused a decrease in organic carbon burial and productivity. Differences in local C-cycling across a single epeiric sea encourage caution when using d13C profiles from epeiric sea carbonates to track changes in the C-cycle of adjacent oceans. <p> Because of their connection to sea level fluctuations, variations in the eNd, d13C and Sm/Nd profiles can also used to correlate Ordovician Midcontinent carbonates. However, the ability to correlate coeval strata using these profiles is limited by changes in depositional environment across the craton, which cause excursions to be absent, dampened, or magnified.

Interpreting and correlating epeiric sea sequences is key to understanding ancient marine environments. As a result, eNd, d13C and Sm/Nd profiles are developed as tools for interpreting epeiric sea carbonates. Previously, eNd and d13C profiles in epeiric sea carbonates have been used to study changes in the Nd isotope balance and C-cycle of adjacent ocean water. Instead, eNd, d13C and Sm/Nd profiles of Ordovician Midcontinent carbonates of North America demonstrate that fluctuations in sea level and depth are driving local changes in the eNd, d13C and Sm/Nd composition of epeiric seawater. <p> Dissolved Nd derived from the Transcontinental Arch, Taconic Highlands and the Iapetus Ocean determine the eNd composition of Midcontinent seawater. As sea level fluctuated, submergence of the Arch and an influx of Iapetus ocean waters adjusted the Nd isotope balance of epeiric seawater. As a result, eNd profiles can be used to track the submergence history of the Late Ordovician Midcontinent. Comparison of stratigraphic variations in carbonate Sm/Nd ratios with sea level curves, conodont paleoecology, and the eNd profiles also suggests that variations in Sm/Nd ratios are related to changes in depth. However, processes effecting Sm/Nd ratios in epeiric seas may be varied and require further investigation. <p> Sea level fluctuations and the waxing and waning of cool, nutrient rich, oxygen poor Iapetus waters onto the craton adjusted productivity and organic carbon burial rates on the Ordovician Midcontinent. Close to the Transcontinental Arch sea level rise caused an increase in organic carbon burial and productivity, while close to the Sebree Trough, and the influx of Iapetus waters, sea level rise caused a decrease in organic carbon burial and productivity. Differences in local C-cycling across a single epeiric sea encourage caution when using d13C profiles from epeiric sea carbonates to track changes in the C-cycle of adjacent oceans. <p> Because of their connection to sea level fluctuations, variations in the eNd, d13C and Sm/Nd profiles can also used to correlate Ordovician Midcontinent carbonates. However, the ability to correlate coeval strata using these profiles is limited by changes in depositional environment across the craton, which cause excursions to be absent, dampened, or magnified.

The Middle-Ordovician Simpson group, deposited in a shallow epicontinental sea, is composed of a sequence of interbedded limestone, shale, and smaller amounts of sandstone. By means of electric and radioactivity logs the group is divided into eight zones traceable across Pecos County, except for its absence, over the Fort Stockton uplift area, caused by post-Simpson erosion. Each zone thins persistently eastward toward the Texas Peninsula, which separated the West Texas basin from the Oklahoma basin of deposition. A northwestward increase in sand content of each zone indicates that the source area for the sand was to the northwest. In Pecos County oil is produced from the Simpson at present in only a small north-central area. / text

Anticosti Island, located in Eastern Canada, displays one of the most complete, best exposed, and most fossiliferous carbonate successions spanning the Ordovician-Silurian (O/S) Boundary in the World. This study develops a new high-resolution framework for the post End-Ordovician extinction strata (~ 260 m thick) exposed in coastal outcrops and recovered from a continuous drill core (La Loutre #1), both located in the western part of the island. In total, eight facies, all associated with a storm-dominated carbonate system, were recognized and organized into a multi-order depositional cycles. A new high resolution isotopic curve with more than 300 data points from well-preserved bulk micrite samples covers the late Hirnantian to Early Aeronian time interval and corresponds to the upper Ellis Bay, Becscie, Merrimack and lower Gun River formations. Two distinct positive carbon isotope excursions are present in the late Hirnantian part of the Ellis Bay Formation (+5‰) and in the lower Aeronian part of the Gun River Formation (+2‰). These positive isotopic carbon excursions provide a distinctive chemostratigraphic signature for regional and global correlations with other O/S sections. Like the Quaternary δ18O marine signal, our δ18O record is largely coupled with multi-order cyclic facies changes. This study demonstrates the importance of glacio-eustasy following the End-Ordovician glacial maxima as one of the primary factors controlling the stratigraphic architecture of paleotropical neritic carbonates during the Early Silurian.

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Middle and Upper Ordovician strata in the southernmost Appalachians document initial collision along the southeastern margin of Laurentia during the Blountian orogeny, an early phase of the Taconic orogeny. Coeval drowning and exposure of different parts of the former platform and variations in stratal architecture have been attributed to tectonic and depositional loading along the collisional margin. Stratigraphic correlations, using a bentonite-graptoliteconodont time framework, a palinspastic map, and a map of subsurface basement structures, suggest that basement-fault reactivation, flexural subsidence, and eustasy variously controlled uplift, subsidence, and deposition at different sites within the peripheral foreland basin. This dissertation documents how pre-existing structures in the continental margin and interior affected subsidence, deposition, diagenesis, and composition of foreland strata, and deformation in tectonic loads. Stratigraphic correlations document an early episode of basementfault inversion in the distal foreland, and heterogeneous subsidence and provenance patterns in the middle and proximal foreland. Abrupt variations in depth of erosion of passive-margin strata and in thickness of distal foreland deposits coincide with the boundaries of the intraplate Birmingham graben. Inversion of the former graben increased the magnitude of erosion on inverted upthrown blocks; increased tectonic subsidence in adjacent blocks; supplied chert and quartz detritus to shallow-marine carbonate depocenters; and facilitated influx of meteoric water to aquifers in shallow-marine limestones. Tectonic subsidence of middle and proximal foreland deposits reflects local irregularities in the foreland subsidence and different rates of migration of the flexural wave along strike. Differential subsidence between embayments and promontories may have caused reactivation of transverse basement faults. Relief produced by reactivation of transverse basement faults and flexural normal reactivation of basement faults may provide sources for local conglomerates interbedded with deep-water shales. Differences in orogenicbelt deformation are reflected in provenance analyses that suggest exposure of dominantly feldspar-bearing basement rocks in the orogenic belt adjacent to the promontory and exposure of basement rocks and sedimentary cover in the orogenic belt adjacent to the embayment. Results of this study reveal the importance of considering the effects of pre-existing structures in the interpretation of along- and across-strike variations of foreland strata. Therefore, geodynamic modeling of the Blountian foreland basin needs to consider along-strike variations in the geometry of tectonic loads and reactivation of different basement structures.