The impact of long-term and short-term sea level changes on the evolution of the Wisconsinan-Holocene Trinity/Sabine incised valley system, Texas continental shelf

[摘要] Over 1,000 km of high resolution seismic profiles and nearly 200 piston cores, vibracores, and geotechnical boring descriptions were interpreted to document the evolution of the Trinity/Sabine incised valley system.Long-term sea level fluctuations (20 ky duration and 50 m amplitude) produced coeval coastal plain and fluvial terrace sequences, as sea level fell from the $partialsp{18}$O stage 5e highstand $approx$120 kyBP to the stage 2 lowstand $approx$20 kyBP. The geometry of the offlapping coastal sequences matches well the shape of $partialsp{18}$O curves. The stage 5e condensed section/downlap surface is regionally correlatable, and ties to $partialsp{18}$O analysis of wells at the Louisiana shelf margin. The Trinity/Sabine incised valley began forming $approx$110 kyBP, and was continually reoccupied as sea level fell, leaving a complex architecture of incised fluvial terraces along the valley margin.Short-term sea level changes (less than a thousand years duration and 5 to 10 m in amplitude) influenced valley-fill deposition during the stage 1 transgression. Parasequences comprised of linked upper bay facies and tidal facies aggrade to base level during periods of sea level stillstand. Rapid sea level rises are manifested as flooding surfaces which bound these parasequences. Parasequences within the Trinity/Sabine valley are observed at $-$36 m (PS I), $-$29 m (PS II), $-$20 m (PS III), and $-$14 m (PS IV). Tentative ages for the parasequences are PS I $>$9,200 yBP, PS II 9,200 to 8,600 yBP, PS III 8,600 to 6,800 yBP, and PS IV 6,800 to 2,800 yBP.The rate of sea level rise affected valley-fill facies architecture by controlling accommodation. Rapid, large sea level rises enhance deposition and preservation of lower bay and tidal facies. Steps in the bayline surface may reflect periods of bayhead delta progradation. The large shelf sand banks (e.g., Sabine and Heald Banks) formed during stillstands, but were extensively reworked and then isolated during subsequent sea level rise.

[发布机构] Rice University

[效力级别] Geophysics