Magnetic polarity stratigraphy and paleolatitude of the Triassic–Jurassic Blomidon Formation in the Fundy basin (Canada): implications for early Mesozoic tropical climate gradients

Abstract

A magnetic polarity stratigraphy is established for a continuously cored 360 m thick section of the entire cyclical lacustrine sequence and part of the sandy fluvial and eolian basal sequence of the Late Triassic Blomidon Formation in the Fundy basin in Nova Scotia (Canada). In conjunction with published results for the Newark and Dan River basins, the Fundy basin record allows us to precisely map the spatio–temporal distribution of climate-sensitive continental lithofacies along a paleolatitudinal transect in eastern North America corresponding to the tropics of Pangea in the Late Triassic. Indicators of high humidity such as coals and black shales tend to occur within 5° of the paleoequator and eolian dunes and other evidence of aridity occurs within 10° of the paleoequator. Although steep, the latitudinal climate gradient in the interior of the Pangea supercontinent is not that different from the average modern zonal variation in the balance of evaporation to precipitation even though the distribution of continents was radically different and there is no evidence of continental ice sheets in the Late Triassic. We suggest that the common perception of a dry paleoequator in the Triassic is largely an artifact of observational bias because compilations of paleoclimate proxies usually have spatio–temporal resolutions that are inadequate to delineate narrow zonal climate belts, giving an aliased impression of ancient climate.