Fluvial response to paleo-equatorial climate fluctuations during the late Paleozoic ice age

The Maritimes Basin of Atlantic Canada preserves a 12-km-thick stratigraphic succession deposited within a low-latitude, predominantly continental setting during the late Paleozoic. This paper examines the utility of using such successions for paleoclimate analysis, with specific reference to changes in fluvial style. Modern rivers in the subhumid and semiarid tropics preserve a suite of features that are distinct from those in humid and arid environments. These features include an abundance of sedimentary structures formed under Froude transcritical to supercritical flow conditions and the presence of in situ vegetation growing within the channel environment. This fluvial style is indicative of prolonged low-flow conditions punctuated by intense precipitation events in a strongly seasonal climatic setting. Fluvial channel bodies within the Maritimes Basin preserve a remarkably similar style compared with these modern systems, suggesting that a subhumid, strongly seasonal paleoclimate was the dominant imprint on parts of the preserved successions. Strongly seasonal deposits are concentrated within four discrete stratigraphic intervals (E1–E4), ranging in duration from 2 to 6 m.y. These intervals are correlated across the entire basin and between basins characterized by markedly different tectonic regimes, which suggests that a coherent regional climate signal is recorded. Intervals are separated by deposits characteristic of humid and arid river systems, and the alternation between these different fluvial styles implies that several pronounced, long-term changes in precipitation and runoff regimes occurred during the Carboniferous within the region. Furthermore, these intervals broadly coincide with major periods of Southern Hemisphere glaciation, which suggests that glaciation had a profound and controlling effect on paleotropical climate.