On the Provenance of Freshwater Pulses in the Gulf of Mexico During the Last Deglaciation: the Contribution of Associated Terrigenous Inputs

The clay mineralogy and grain-size of sediments deposited during the deglaciation in the Orca basin (Gulf of Mexico) show that three different sedimentary regimes took place during that period : the early deglaciation (20 to 13 ka) is characterized by (1) a terrigenous-dominated sedimentation, reflecting the high detrital contribution of the illite and chlorite-rich Great lakes area towards the Gulf of Mexico, interrupted by (2) repetitive fine-grained smectite-rich events (SR) originating from the northwestern Mississippi River watershed area, whereas the last part of the record (after 13 ka) shows a reduced detrital vs. carbonated sedimentation and an additional contribution from a kaolinite and illite-rich southern province. The comparison of the respective timing of the SR with the Laurentide ice-sheet meltwater history -recorded in d18O of planctonic foraminifera from the Gulf of Mexico- and with the modelled chronology of deglacial drainage reveals that the SR occur simultaneously with the major meltwater floods. The comparison of potential source areas for the SR detrital supply (based on recently published clay mineral distribution maps on land) and the Laurentide margin evolution (as depicted by continental studies) provides additional constrains on the dominant melting areas. In addition, the mineralogical characteristics of the peculiar meltwater episode associated with the Heinrich-1 cold climatic event help pinpoint its provenance (Great Lakes area vs. northwestern Mississippi province). The decreased contribution of terrigenous supply associated with changing provenance after 13 ka suggest strong modifications of both the continental hydrography in relation with the Lake Agassiz history and of the connection between the Orca basin and the Mississippi delta due to rising sea-level. This study shows that combining clay mineralogy and grain-size characteristics of sediments deposited in the Orca basin offers a unique opportunity to link the reconstructed continental glacial history, the modelled drainage patterns, and the marine record of meltwater flows in the Gulf of Mexico.