2000 GSA Annual Meeting -- Reno, Nevada
Author(s): COX, Randel Tom, and VAN ARSDALE, Roy B., Geological Sci. Dept, 402 Smith, Univ. of Memphis, Memphis, TN 38152, email@example.com
Keywords: superplume, Mississippi, Embayment, Bermuda, hotspot
The Mississippi Embayment (ME), a first-order feature on the geologic map of North America, is a southwestward-plunging trough with up to 1.5 km of Cretaceous and Cenozoic sediments. The ME, a northward extension of the Gulf of Mexico coastal plain, is underlain by the early Paleozoic Mississippi Valley graben (MVG) basement fault complex. Previous authors have attributed ME subsidence to opening of the Gulf of Mexico. However the ME subsided 60 million years after cessation of sea-floor spreading in the Gulf. We have previously argued that the ME formed as a result of the westward passage of faulted crust (MVG) over the Bermuda hotspot in mid-Cretaceous. Age progressive (west-to-east) mid-Cretaceous volcanism in southern North America, beginning ~115 Ma in eastern Kansas and ending ~65 Ma in central Mississippi, crosses the ME. This line of volcanism coincides with the Bermuda hotspot track reconstruction and has isotopic signatures consistent with a mantle hotspot source. We propose that during mid-Cretaceous, the weak crust of the MVG complex was uplifted 1 to 3 km as it passed over the Bermuda plume, and this upland was eroded. As the MVG complex moved west of the hotspot plume, it subsided, and the eroded region became a topographic low that filled with fluvio-marine sediments, the ME. Supporting evidence for mid-Cretaceous uplift and erosion of the ME region includes: 1) an angular unconformity on pre-Late Cretaceous rocks with ~2 km eroded at mid-Cretaceous along the hotspot track; 2) a broad anticline in the ME 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 northern Gulf of Mexico sedimentation from a continuous carbonate platform to a large influx of deltaic clastics. We now suggest that pronounced uplift of the MVG region associated with Bermuda hotspot volcanism may have been a result of an increased hotspot flux during the superplume interval (~120 to 65 Ma). Thus, the Mississippi Embayment may be an effect of the Cretaceous superplume.
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