Interaction of climate and tectonics upon alluvial architecture: Late Carboniferous-Early Permian sequences at the southern margin of the Pennine Basin, UK

Late Carboniferous (mid to late Westphalian D) to Early Permian strata of south Staffordshire, English Midlands were deposited on the margins of a foreland basin (Pennine Basin) during a period of increasing climatic aridity. Approximately 300–500 m of grey and red-bed alluvial sediments contain five vertically stacked facies associations, each with characteristic stratal architecture and palaeosols. ccession exhibits three orders of cyclicity. First order cycles (100–150 m thick) resulted from tectonic activity in the hinterland. Second order cyclicity, reflected in three regionally extensive, dekametre-scale, upward-fining packages resulted from isostatic readjustment of the source area. Third order, autocyclic responses caused metre- to dekametre-scale, upward-fining and upward-coarsening trends. ics and climate were interdependent and their combined effects led to deposition of first order cycles or sequences. Cycle 1 was deposited largely upon a poorly drained alluvial plain; caliches within the interfluves indicate relatively high evapotranspiration rates. Heavy mineral data suggest a distant source. Cycles 2 and 3 reflect a switch to a local source. This was probably due to the combined effects of hinterland tectonism and increasing aridity. The latter led to fluvial inefficiency and increasing input from local drainage basins. The change in climate and source area resulted in variable sand/mud ratios and depositional styles for each cycle. ition of the influence of tectonics and climate in fluvial sedimentation means that the resultant genetic alluvial sequence architecture has a predictive function. In the absence of good biostratigraphical markers, this can be used in correlation and predicting sequence architecture in adjacent areas.