CLIMATIC VS TECTONIC CONTROL ON SOIL DRAINAGE FLUCTUATIONS: USING ALLUVIAL STRATIGRAPHY CONCEPTS AT JOGGINS FOSSIL CLIFFS, NOVA SCOTIA, CANADA

During the Late Paleozoic Ice Age (LPIA), the fault-bounded equatorial Cumberland basin was experiencing 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, drab mudstones rich in organic remains and suggesting water-saturation for extended periods and overall poor soil development. Such drainage fluctuations can be explained by either climatic or tectonic causes (i.e., halokinetic processes occurring in the substratum during sediment deposition). Thick conformable alluvial successions such as at Joggins are particularly good candidates for alluvial stacking analyses, and provide useful information regarding the sediment accumulation history of terrestrial basins. Fluvial Aggradational Cycle (FAC) analysis of the Joggins and overlying Spring Hill Mine Formations show an interesting pattern of relatively cyclic increases/decreases in accommodation space in the basin, interrupted by short-lived, very sharp accommodation space increases. Sharp accommodation space gains coincide well with soils having experienced important water-saturation and organic matter preservation, indicating abnormally rapid deepening of the basin and enhanced water-ponding impeding soil drainage processes. During periods of relatively steady and cyclic sedimentation history, paleosols range from well drained to poorly drained, and likely reflect effects of seasonal fluctuations and long-term climatic trends related to expansion and contraction of the Gondwanan Ice Sheets (GIS). During periods of GIS expansion, the InterTropical Convergence Zone (ITCZ) narrowed towards the equator, allowing development of more humid climatic conditions and impeding soil drainage processes. During periods of GIS contraction, the ITCZ covered a wider area, allowing better-developed soil drainage processes and overall greater soil development. We propose that the study of alluvial stacking pattern at Joggins provides useful insights regarding long-term climatic trends during the LPIA, as well as a better understanding of the regional tectonic history of the area.