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ABSTRACT

From a multidisciplinary study that utilized high-resolution seismic and a variety of analytical data from four continuously-cored boreholes, we have identified six major (and many minor) sequence boundaries and maximum flooding surfaces associated with the oxygen isotope stages 14 to 1 (since 500 KY BP) within the Late Pleistocene shelf margin Lagniappe delta complex in the NE Gulf of Mexico. We discuss here in detail a portion of the delta complex that prograded seaward for several tens of miles during the last, fourth-order, glacial-interglacial cycle since 125 KY BP. A well-developed calcareous-rich interval deposited during the isotope stage 5 (125-70 KY BP) underlies this portion of the delta complex. The delta complex consists of many lobes that were deposited during the several, fifth-order, sealevel drops within the falling stage and during the maximum lowstand-early sealevel rise of the cycle. We have recognized one main fourth-order sequence boundary that resulted from the erosion of an incised valley during the maximum lowstand of sealevel, and several, fifth-order sequence boundaries that were created during the minor sealevel drops within the falling stage. The incised valley-fill deposits consist of distributary channel deposits, bay-head deltas and estuarine deposits that were subsequently transgressed during the Holocene sealevel rise. This transgressive surface forms the base of isotope stage 1. On the whole, the isotope 5 to 1 stage interval of the Lagniappe Delta can be divided into four systems-tracts—highstand, falling stage, lowstand-early rise and transgressive.

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