The Mississippi Embayment, North America: a first order continental structure generated by the Cretaceous superplume mantle event

The Mississippi Embayment of North America, a northward extension of the Gulf of Mexico coastal plain, is a southwestward-plunging trough containing similar to1.5 km of Cretaceous and Cenozoic sediments. The Embayment is underlain by the early Paleozoic Mississippi Valley graben basement fault complex. Previous authors have attributed Embayment subsidence to the opening of the Gulf of Mexico. However, the Embayment subsided 60 million years after cessation of the sea-floor spreading in the Gulf. We have previously argued that the Mississippi Embayment formed as a result of the westward passage of faulted crust (Mississippi Valley graben) over the Bermuda hotspot in mid-Cretaceous. More recently published age data clarify age progressive (northwest-to-southeast) mid-Cretaceous volcanism that crosses the Mississippi Embayment, beginning similar to115 Ma in eastern Kansas and ending similar to65 Ma in central Mississippi. This line of volcanism coincides with the predicted Bermuda hotspot path and has isotopic signatures consistent with a mantle hotspot source. We propose that during mid-Cretaceous, the weak crust of the Mississippi Valley graben complex was uplifted 1-3 km as it passed over the Bermuda plume, and this upland was eroded. As the Mississippi Valley graben complex moved west of the hotspot, it subsided, and the eroded region became a topographic low that filled with fluvio-marine sediments, the Mississippi Embayment. Supporting evidence for mid-Cretaceous uplift and erosion of the Embayment region includes: (1) an angular unconformity on pre-Late Cretaceous rocks with similar to2 km eroded at mid-Cretaceous along the hotspot path; (2) a broad anticline in the Embayment at mid-Cretaceous (revealed by unfolding the down-warped basal Late Cretaceous unconformity); (3) exhumation and weathering of mid-Cretaceous plutons before burial by Late Cretaceous sediments; and (4) a mid-Cretaceous change in the northern part of the Gulf of Mexico sedimentation from a continuous carbonate platform to a large influx of deltaic clastics. We now suggest that magmatic activity and pronounced uplift in the Mississippi Valley graben region may have been a result of increased hotspot flux of the typically weak Bermuda hotspot during the Cretaceous superplume, mantle event (similar to120-80 Ma). (C) 2002 Elsevier Science Ltd. All rights reserved.