Triassic Taylorsville Basin, Virginia, USA: Comparative Thermal History and Organic Facies Within the Early Mesozoic Eastern North American Lacustrine Rift Basin System

摘要

The Late Triassic Taylorsville basin is an onshore continental rift basin along the US Central Atlantic margin. The basin is one member of the early Mesozoic North American rift basin system that trends north-south from the southern US into maritime Canada and has formed within a wide rift zone between Early Triassic collapse of the Appalachian orogen and Jurassic initiation of Atlantic sea floor spreading. The basin, mostly buried under the Cretaceous and younger Atlantic Coastal Plain, is a half-graben having a western border fault. It was a target of conventional exploration drilling >25 years ago, although recent interest is in unconventional gas exploitation. Difference in kerogen type, basement and advective heat flow, and stratigraphic/hydrologic architecture among the Late Triassic-Early Jurassic rift basins is predictable when paleolatitude, paleoclimate,and position within the late Paleozoic Appalachian orogen are considered. For example, the Taylorsville basin, which formed in a humid equatorial climate, is a gas-prone overfilled-lake-type basin, in contrast to the temperate oil-prone balanced- to underfilled Newark rift-lake basin. Downhole vitrinite reflectance data and maturation modeling show that the Taylorsville basin, along the axis of Appalachian metamorphism/orogenic collapse, experienced long-term elevated heat flow modified by synrift gravity-driven cross-basin fluid flow (40-55°C/km), compared to the off-axis Newark basin （≤35°C/km）. Postrift structural inversion resulted in variable (<1 to >3 km) erosion of Taylorville synrift strata. Duration of sedimentation modeling suggests basin synrift sedimentation likely ended before the Jurassic, unlike sister basins to the north with extant earliest Jurassic formations.