Using Pb isotopic composition of detrital feldspars to infer sites of sub-glacial erosion from the Weddell Sea, Antarctica

Pb isotopic compositions of individual feldspars, sourced from the Recovery Glacier catchment and deposited at the front of the Filchner Ice Shelf, indicate that major provenance shifts have occurred since the last glacial maximum (LGM). Compositions of near modern Late Holocene ice-rafted feldspars from marine sediments match the compositions of rock units inferred to comprise the areas where today ice velocity, bed roughness and shear stresses are high. These regions likely eroded bedrock and were the primary sources for the ice-rafted feldspar because signals from areas where ice velocity is high but bed roughness and shear stress are low were not recorded. Compositions from tills deposited since the LGM differ only subtly from the more recently deposited ice-rafted feldspar and suggest similar sources for the feldspar. Till deposited during or prior to the LGM contain feldspar with strikingly different Pb isotopic compositions to those from the younger sediments. These compositions are not known from any rock exposure and indicate a very different source region. Candidate areas exist in the hinterland of the Recovery Glacier catchment area. These data indicate how very different provenance signals can result from erosion in different areas within large glacial Antarctic catchment areas. An important implication of this finding is that, shifts in provenance do not necessarily correlate with episodes of ice sheet instability.