Lithostratigraphy of the upper Turinian – lower Chatfieldian (Upper Ordovician) foreland succession, and a U–Pb ID–TIMS date for the Millbrig volcanic ash bed in the Ottawa Embayment

Three stages of carbonate-platform development are preserved in the upper Turinian – lower Chatfieldian succession of the Ottawa Group in the Ottawa Embayment and represent deposition along the Late Ordovician Taconic foreland interior of paleo-southern Laurentia. Compared with contemporary stratigraphy in the adjacent northern Appalachian (southern Ontario, New York state) and western Quebec basins, the intermediate Stage 2 succession, which brackets the Turinian–Chatfieldian boundary, preserves embayment-specific stratigraphic patterns. These include: (i) dramatic west-to-east thickening of the upper Turinian Watertown Formation that defines differential subsidence along the present axis of the embayment, (ii) post-Watertown base-level fall defined by appearance of shoreface siliciclastics, (iii) early Chatfieldian marine transgression represented by the proposed L’Orignal Formation that is coeval with but lithologically distinct from the Selby Formation in the northern Appalachian Basin, and (iv) platform segmentation that resulted in a depositional mosaic of shallow banks (Rockland Formation) and equivalent deeper water mico-seaways (lower Hull Formation). The latter event immediately follows accumulation of the Millbrig bentonite, here dated at 453.36 ± 0.38 Ma. Bracketing these local stratigraphic patterns are the bounding stages (1 and 3) represented by the upper Turinian Lowville Formation and middle Chatfieldian Hull Formation, respectively, that contain facies attributes in common with the adjacent basins and characterize inter-regional depositional systems of first warm, then cooler oceanographic conditions. Stage 2 identifies a structurally controlled transition between these end-member stages: a far-field response in the foreland interior, localized along the axis of a late Precambrian fault system, to contemporary change in subsidence rates and tectonomagmatic events along the Laurentian margin.

Geomechanical characterization of a caprock-reservoir system in the Northern Appalachian Basin: Estimating spatial variation of in situ stress magnitude and orientation

Assessing the mechanical integrity of the caprock-reservoir system is necessary to evaluate the practical storage capacity for geologic [Formula: see text] storage. We used a combination of well-log and experimental data to estimate the statistical distribution (mean and variance) of rock mechanical properties of Cambrian-Ordovician strata within the Northern Appalachian region of Ohio and studied their heterogeneity throughout the study area. Empirical correlations between static-dynamic moduli of carbonate and sandstone formations of the Northern Appalachian Basin were developed. The state of stress (the orientation and magnitude of the maximum horizontal stress) for caprock and reservoir formations in the Cambrian-Ordovician sequence was determined at multiple well locations to understand the regional variability of these properties throughout the study area. The maximum horizontal stress ([Formula: see text]) azimuth was estimated from image logs for six wells and S-wave anisotropy data for five wells. The [Formula: see text] magnitude was estimated by analytical and numerical modeling of stresses around the wellbore calibrated to the occurrence of wellbore breakouts and drilling-induced fractures in three wells as a function of depth. The results of assessing the [Formula: see text] magnitude and stress regime in the caprock and reservoirs in the Cambrian-Ordovician sequence using rock mechanical data acquired in this study, well-log data, and drilling data indicate that both parameters vary throughout the study area. In this work, we determined how integrating different types of data from multiple wells allowed us to estimate mechanical properties and characterize the spatial variability (laterally and vertically) of in situ stress for Cambrian-Ordovician caprock and reservoirs throughout the study area. A combination of different methods — numerical, analytical, and stress polygon — is used to estimate the in situ stress magnitude, especially [Formula: see text], regionally on a formation-by-formation basis. The results of this work can be used to improve our understanding the complex nature of stress in the Northern Appalachian Basin.