Fluvial Response to Climate and Sea–Level Change: An Example of Falling Stage and Lowstand Fluvial Deposition from the Late Quaternary Trinity River Incised Valley, Texas Gulf Coast

The issue of fluvial response to climate and sea–level change has been the focus of many studies. The creation of incised valleys by fluvial incision and deposition throughout the falling stage and lowstand of sea level records a critical link between source and sink by acting as a buffer to external controls.

Recently acquired optically stimulated luminescence dates from the Wisconsin age falling–stage and lowstand fluvial Deweyville deposits along the Trinity River in Texas provided insight to their timing of deposition and allogenic controls on fluvial processes. Incision and valley widening through lateral channelbelt migration of the High, Middle, and Low Deweyville fluvial terraces were constructed and subsequently preserved during the most rapid eustatic fall of sea level within the Wisconsin glacial period from the latter portion of Oxygen Isotope Stage (OIS) 3 through OIS 2, 35–24ka, 26.6–23ka, and 23.2–18.8ka respectively. Timing of channelbelt activity correlates well with increased sedimentation rates recorded downdip in basin four of the Brazos–Trinity slope system.

In addition, previously conducted research using discharge retrodiction equations inferred much greater discharges and precipitation as the primary cause of the larger paleo–channel dimensions of the glacial age Deweyville units found along the Gulf of Mexico. Reconstructed paleo–hydrology of the Trinity river using planform properties along with channel slope and sediment size yield contrasting results to these earlier studies.

Comparisons of available ages of Deweyville deposits along rivers entering the Gulf of Mexico suggest out of phase timing relationships of lateral channelbelt migration within the lower coastal plain. This is due to the different boundary conditions of each system and how allogenic forcing mechanisms produce variations in discharge, sediment supply, and affect the long profiles of fluvial systems as they extended across the shelf due to base–level lowering.