A NOVEL METHODOLOGY TO EXAMINING THE SEDIMENT ACCUMULATION HISTORY OF TERRESTRIAL BASINS: APPLICATION TO THE UNESCO WORLD HERITAGE JOGGINS FOSSIL CLIFFS, NOVA SCOTIA, CANADA

During the Late Paleozoic Ice Age (LPIA), the fault-bounded equatorial Cumberland basin (CB) experienced rapid subsidence, accumulating km-thick fluvial sedimentary units from two highlands to the NW and SE. Major variations are recorded in the drainage of paleosols exposed at the UNESCO Joggins Fossil Cliffs, ranging from oxidized and well-drained soils with strongly developed vertic features, to highly reduced organic-rich mudstones suggesting water-saturation for extended periods and overall poor soil development. Although halokinetic subsidence of the CB is known to have been operative during deposition of these units, previous research favored glacio-eustatic processes. New results suggest that tectonic subsidence of the CB during the LPIA was a more important driver of fluvial sedimentation than previously thought. A threshold autoregressive (TAR) model was applied to a series of 474 Fluvial Aggradational Cycles (FAC) on the entire Joggins and the lower portion of the overlying Spring Hill Mine Formations. Results suggest a random distribution of the data, contradicting the hypothesis that fluvial sedimentation was mainly driven by glacio-eustatic cycles. Additionally, it suggests that more than one mechanism controlled fluvial deposition based on the thickness of FACs, the soil and sand content of individual FACs, and the soil-to-sand ratio of FACs. Repetitive thinner FACs (< 1.9m) show a more cyclic distribution and have a higher soil content, with a faintly predictable behavior repeated every third FACs. On the other hand, thicker FACs show a random distribution, and usually contain a higher sand proportion. Thicker FACs are interpreted to represent sudden deepening of the CB caused by spikes of halokinetic dissolution in the substratum allowing for a drop in base level and increased reworking of coarser sediments, while thinner FACs likely represent short episodes of relative tectonic stability allowing climatic forcing to be the main driver of fluvial sedimentation with deposition of finer particles on the overbank. We propose that this novel methodology will provide a better constraint on the sediment accumulation history of terrestrial basins when applied to conformable sedimentary successions, and more accuracy to linking paleosol development to climatic processes.