The onset of mid-Carboniferous glacio-eustasy: Sedimentologic and diagenetic constraints, Arrow Canyon, Nevada

Abstract

The Devonian–Permian Late Paleozoic Ice Age (LPIA) has been considered the longest-lived and most widespread ice age of the past half billion years. However, it is increasingly clear that the LPIA consisted of several discreet icehouse times punctuated by warmer periods of glacial minima. This paper documents the timing and dynamics of a transition between two climate modes: from the greenhouse that characterized most of the Visean (Osagean and Meramecian) to the icehouse that characterized the late Visean and Serpukhovian (Chesterian). This transition is archived in the stratigraphy and early diagenetic history of an equatorial ramp exposed in the Arrow Canyon Range, southeastern Nevada. Visean (Osagean and Meramecian) rocks of the Yellowpine and lower Battleship Wash formations consist of shallow subtidal to intertidal carbonates with little to no evidence of significant subaerial exposure. Just above the Meramecian–Chesterian (late Visean) boundary, two significant exposure horizons are developed on subtidal limestones. Fenestral peritidal limestones and the absence of evaporites indicate a relatively humid Visean climate. The contact between the early Serpukhovian upper Battleship Wash Formation and late Serpukhovian Indian Springs Formation is unconformable, consisting of > 3 stacked exposure surfaces; locally, these exposure horizons are amalgamated, creating “missed beats” that are evident only by diagenetic overprints. The overlying Indian Springs Formation contains a significant detrital siliciclastic component, abundant evidence for exposure of subtidal facies, and well-developed Vertisols, Argillisols, and Protosols, suggesting a seasonal sub-humid to semi-arid climate. Exposure horizons developed on subtidal limestones continue to cap m-scale carbonate cycles upward into the Bashkirian (Morrowan) Bird Spring Formation. Integrated stratigraphic, sedimentologic, and diagenetic characteristics suggest that glacio-eustasy began near the Meramecian–Chesterian boundary (within the late Visean). Anomalously thin early Chesterian strata suggest significant missing time at early Chesterian exposure horizons, likely due to growth of late Visean ice. Inferred sea-level fluctuations increased in amplitude in the late Serpukhovian, when the platform was repeatedly exposed and then flooded to depths near storm wave-base (> 10–50 m). Coeval Tethyan and Euramerican stratigraphic and isotopic records also document the onset of glacio-eustasy during late Visean (basal Chesterian) time. Climatically sensitive soils and sediments indicate a sub-humid to semi-arid seasonal climate prevailed across western equatorial Pangaea during the Serpukhovian (late Chesterian), suggesting the presence of monsoonal circulation.