Rapid and widespread response of the Lower Mississippi River to eustatic forcing during the last glacial-interglacial cycle

Abstract

The Lower Mississippi Valley provides an exceptional fi eld example for studying the response of a continental-scale alluvial system to upstream and downstream forcing associated with the large, orbitally controlled glacialinter glacial cycles of the late Quaternary. However, the lack of a numerical chronology for the widespread Pleistocene strata assemblage known as the Prairie Complex, which borders the Holocene fl oodplain of the Lower Mississippi River, has so far precluded such an analysis. Here, we apply optically stimulated luminescence (OSL) dating, mainly on silt-sized quartz from Prairie Complex strata. In total, 27 OSL ages indicate that the Prairie Complex consists of multiple allostratigraphic units that formed mainly during marine isotope stages 7, 5e, and 5a. Thus, the aggradation of the Prairie Complex is strongly correlated with the sea-level highstands of the last two glacialinterglacial cycles. Fluvial incision during the sea-level fall associated with the MIS 5a-MIS 4 transition extended as far inland as ~600 km from the present-day shoreline, testifying to the dominant downstream control of fl uvial stratigraphic architecture in the Lower Mississippi Valley. In addition, the short reaction time of the Lower Mississippi River suggests that large fl uvial systems can respond much more rapidly to allogenic forcing than is commonly believed.

Influence of water and sediment supply on the stratigraphic record of alluvial fans and deltas: Process controls on stratigraphic completeness

“…The first pertains to using the stratigraphic record to answer questions that are unrelated to the interworkings of the sediment transport system, for example a chemical signal useful as a regional or global climate proxy that is fixed to deposited sediment [ Fike et al ., ; Maloof et al ., ]. The second pertains to using the stratigraphic record to extract information regarding the processes and products of a sediment transport system [ Mohrig et al ., ; Jerolmack and Sadler , ; Shen et al ., ]. Our experimental results suggest that the magnitudes of Q w and Q s impact these two types of records in different ways.…”

Delta growth and river valleys: the influence of climate and sea level changes on the South Adriatic shelf (Mediterranean Sea)

“…Depending on the amount of sediment available and on the efficiency of the river systems associated, incised valleys may respond to a base level rise by a fill entirely formed by fluvial aggradation; in this case no accommodation space is left for estuarine or shallow marine sediments (the Brazos, Rio Grande and Colorado incised valleys in Gulf of Mexico are an example, Simms et al, 2006). Although river systems may respond "instantaneously" to eustatic forcing (Shen et al, 2012), when rapid base level rise is not balanced by fluvial aggradation because of low sediment supply, accommodation space remains available and is later exploited by non-continental deposits; in these cases the incised valley may be progressively filled by backstepping brackish to open marine facies . Under such conditions, the incision may represent the only accommodation space left in a shallow-marine setting protected from marine reworking that can be exploited by sand to fine-grained sediments, if available.…”

Buffered, Incomplete, and Shredded: The Challenges of Reading an Imperfect Stratigraphic Record

“…The reason for this, as shown through numerical modeling by Snow and Slingerland (), is that while full adjustment to a new steady state (response) is well estimated by T eq , fluvial adjustment begins immediately [sensu Bull, ; Duller et al, ] after a perturbation in forcing conditions (Figures and ). As topography approaches a new steady state, it does so asymptotically (Allen, ; Duller et al, ) suggesting that this transient response has the potential to be stored in strata (e.g., Shen et al, ), if operative over long enough timescales, even if full adjustment has not been reached.…”