Completed Subtask: Investigations of Millenial-Scale Forcing on Stratigraphic and Sedimentary Response to Latest Quaternary of the Central Mississippi River Delta Plain

Subtask Leader: Mark Kulp - Pontchartrain Institute for Environmental Sciences (PIES), University of New Orleans, Louisiana

Aim

The relationship between stratigraphic and sedimentary characteristics of strata within large deltaic depocenters will provide important contributions towards understanding temporal variations in sediment supply, sea-level change, and substrate subsidence. Data of these types also simultaneously provide the opportunity to understand how coastal depositional systems respond to allochthonous and authochothonous forcing factors such as sediment supply and sea-level change. An array of research has shown that during the latest Quaternary the NGOM region has been affected by relative sea-level change and variable sediment supply as the Earth's climate transitioned from glacial conditions to interglacial conditions similar to those that prevail today.

In this sense, the shallow Mississippi River delta system, and its extant geologic and geomorphic architecture, has recorded portions of the change and the overall evolution that has occurred along the north-central Gulf of Mexico since the initial sea-level rise that accompanied the most recent deglaciation. The magnitude and frequency of past changes in environmental forcing factors (such as sea-level change) and associated depositional responses (such as frequency of avulsions) provides an opportunity to better understand modern ecosystem response to ongoing and anticipated future changes arising from similarly operating modern variables.

Although numerous studies within the last 100 years have addressed much of the NGOM shallow deltaic and coastal geology, ongoing questions exist regarding the rates, magnitudes and direction of late Quaternary sea-level change. Specifically, significant changes in the texture of sediments supplied to the Mississippi River delta depocenter may have occurred, and the chronology and distribution of marine flooding and successive progradation following the late Wisconsin sea-level lowstand is poorly defined. In general, there has been a relative lack of information that associates the lower alluvial valley and early Holocene deltaic plain with more updip stratigraphy. Such information would be the basis for developing a truly regional framework within which to gauge the relative role of aforementioned variables in coastal-deltaic systems.

Approach

The primary goal of this subtask is to investigate the latest Quaternary sedimentary systems of the delta plain and the depositionally linked alluvial valley. The final product of this effort will be an evaluation of the system evolution within spatially and temporally variable regimes of tectonic motion, drainage basin maturation, relative sea-level change and sediment supply.

Accomplishments

The focus of the first year award was to develop an inventory of available stratigraphic data, to map the distribution of deltaic and fluvio deltaic strata overlying the late Wisconsin unconformity within the incised valley fill of the central alluvial valley. During the period of award the research was specifically dominated by establishing a database of relevant lithostratigraphic data and mapping major stratigraphic horizons and lithosomes that have been previously identified but not regionally correlated within the alluvial valley. The approach involved the establishment of several cross sections for the alluvial valley capturing the architecture (e.g. distribution, thickness, and sedimentary character) of Holocene depocenters overlying the latest Wisconsin unconformity and depocenters within the lower alluvial valley. This effort has resulted in the development of several regional stratigraphic cross sections that can aid in identifying major transgressive or regressive surfaces as well as the distribution of primary fluvial depocenters. The distribution and development of discrete lithosomes is currently being used to document geomorphic changes resulting from RSL as well as inputs to numerical isostatic compensation models to resolve the affect of sediment loading on regional subsidence patterns.

Publications

Manuscripts

Abstracts and Presentations