CLIMATE OR WATER BUDGET? WHAT DO PALEOSOLS REALLY TELL US ABOUT THEIR DEPOSITIONAL ENVIRONMENT: CASE OF JOGGINS, NS, CANADA

During the late Paleozoic ice age, the fault-bounded equatorial Cumberland Basin of Nova Scotia experienced rapid halokinetic subsidence, driving deposition of km-thick fluvial sedimentary units. Recent research has shown that halokinetic subsidence was a more important driver of alluvial sedimentation than previously thought and interfered with climatic patterns controlling sedimentation in many other Carboniferous sedimentary basins. Major variations are recorded in the paleosols exposed at the Joggins Fossil Cliffs, suggesting alternating conditions between well-drained floodplain environments and water saturation associated with overall poor soil development throughout the depositional history of these units. Micromorphological descriptions of paleosols over a 66-meter continuous interval indicate that these units experienced alternating drainage conditions from extensive water-ponding characterized by gley, gray-green reduced paleosols with abundant partially preserved organic remains and early diagenetic siderite nodules; to better-oxidized red paleosols showing evidence of well-developed vertic properties and precipitation of pedogenic calcium carbonate nodules indicating gradual lowering of the water-table and increased drainage. Whole-soil bulk geochemistry analysis indicates that there is little geochemical differentiation between these stratigraphic units. Additionally, paleoclimatic reconstructions using pedotransfer functions systematically yield similar MAT and MAP estimates regardless of the soil profile considered, confirming that paleosols were not exposed long enough on the land surface to equilibrate with the atmosphere and record the dominant climatic conditions at the time of soil development. These results raise interesting concerns regarding the paleopedological features that develop in soil profiles as well as the type of information that they provide. Our results suggest that soils will develop pedogenic features relating to water availability rather than climate following sediment deposition and early pedogenesis. Conversely, soil geochemistry requires very long stable soil exposure on the land surface in order to provide information that can be related to dominant climatic trends at the time of deposition and development.