LATE QUATERNARY EVOLUTION OF THE WAVE–STORM-DOMINATED CENTRAL TEXAS SHELF

2004 ◽  
pp. 271-287 ◽  
Author(s):  
BRENDA J. ECKLES ◽  
MICHELLE L. FASSELL ◽  
JOHN B. ANDERSON
Keyword(s):  
Late Quaternary ◽  
Central Texas

Late quaternary alluvial stratigraphy of a low-order tributary in central texas, USA and its response to climate and sediment supply

2004 ◽  
Vol 62 (3) ◽  
pp. 289-300 ◽  
Author(s):  
Lee Nordt
Keyword(s):  
Late Quaternary ◽  
Base Flow ◽  
Sediment Supply ◽  
Sediment Storage ◽  
Climate Conditions ◽  
Fort Hood ◽  
Stratigraphic Framework ◽  
Central Texas ◽  
High Base ◽  
Low Order

This paper presents the first comprehensive late Quaternary alluvial stratigraphic study of a low-order tributary in central Texas, using Cowhouse Creek as a case study. The late Pleistocene Jackson (JA) alluvium forms the elevated T2 terrace. The entrenched Holocene valley is filled with the buried Georgetown (GT) alluvium (approximately 11,000 to 8000 14C yr B.P.) and associated Royalty paleosol, and the surficially exposed Fort Hood (FH) alluvium (approximately 7000 to 5000 14C yr B.P.) and West Range (WR) alluvium (approximately 4200 to 600 14C yr B.P.) forming the broad T1 terrace. The Ford (FO) alluvium (<600 14C yr B.P.) forms the modern T0 floodplain entrenched into T1. Conditioned by cooler and wetter climates, Cowhouse Creek was characterized by relatively high base flow and low sediment supply during deposition of the JA and GT alluvium. Appreciable upland soil erosion ensued during the middle Holocene in response to warmer climate conditions, resulting in widespread valley filling by the FH alluvium. Deposition of the late Holocene WR and F0 alluvium was characterized by diminished sediment storage during relatively stable climate conditions. The temporal alluvial stratigraphic framework of the bedrock-confined Cowhouse Creek valley is out of phase with the alluvial sequence in the larger Brazos River valley.

Late Quaternary Vegetation and Climate Changes in Central Texas Based on the Isotopic Composition of Organic Carbon

1994 ◽  
Vol 41 (1) ◽  
pp. 109-120 ◽  
Author(s):  
Lee C. Nordt ◽  
Thomas W. Boutton ◽  
Charles T. Hallmark ◽  
Michael R. Waters
Keyword(s):  
Organic Carbon ◽  
Late Pleistocene ◽  
Plant Biomass ◽  
Late Quaternary ◽  
Stable Carbon Isotope ◽  
Climatic Conditions ◽  
Significant Shift ◽  
Alluvial Deposits ◽  
The Past ◽  
Central Texas

AbstractStable carbon isotope analysis of organic carbon in alluvial deposits and soils of three streams in central Texas reveals significant shifts in the ratio of C3 to C4 plant biomass production during the past 15,000 yr. These temporal changes in vegetation appear to be in response to changes in climate. During the late Pleistocene, C4 plants comprised only about 45 to 50% of the vegetative biomass in this area, suggesting that conditions were cooler and wetter than at any time during the past 15,000 yr. The time between 11,000 and 8000 yr B.P. is interpreted as transitional between late Pleistocene conditions and warmer and drier Holocene conditions based on a slight increase in the abundance of C4 plant biomass. During the middle Holocene, between approximately 6000 and 5000 yr B.P., mixed C3/C4 plant communities were replaced almost completely by C4-dominated communities, indicating prairie expansion and warmer and drier climatic conditions. By 4000 yr B.P., the abundance of C4 plant biomass decreased to levels similar to the early Holocene transitional period, suggesting a return to cooler and wetter climatic conditions. No significant shift in the ratio of C3 to C4 productivity has occurred during the last 4000 yr, except for a slight increase in the abundance of C4 plant biomass around 2000 yr B.P. The results of this investigation correlate well with other regional late Quaternary climatic interpretations for central and north Texas, the Southern Plains region, and with other portions of the Great Plains.

Late Quaternary Floodplain History of the Brazos River in East-Central Texas

1995 ◽  
Vol 43 (3) ◽  
pp. 311-319 ◽  
Author(s):  
Michael R. Waters ◽  
Lee C. Nordt
Keyword(s):  
Late Quaternary ◽  
Thick Layer ◽  
Soil Formation ◽  
Coarse Grained ◽  
Vertical Accretion ◽  
Brazos River ◽  
East Central ◽  
Central Texas ◽  
History Of ◽  
Quaternary History

AbstractThe floodplain along a 75-km segment of the Brazos River, traversing the Gulf Coastal Plain of Texas, has a complex late Quaternary history. From 18,000 to 8500 yr B.P., the Brazos River was a competent meandering stream that migrated from one side of the floodplain to the other, creating a thick layer of coarse-grained lateral accretion deposits. After 8500 yr B.P., the hydrologic regime of the Brazos River changed. The river became an underfit meandering stream that repeatedly became confined within narrow and unstable meander belts that would occasionally avulse. Avulsion occurred four times; first at 8100 yr B.P., then at 2500 yr B.P., again around 500 yr B.P., and finally around 300 yr B.P. The depositional regime on the floodplain also changed after 8500 yr B.P., with floodplain construction dominated by vertical accretion. Most vertical accretion occurred from 8100 to 4200 yr B.P. and from 2500 to 1250 yr B.P. Two major and three minor periods of soil formation are documented in the floodplain sequence. The two most developed soils formed from 4200 to 2500 yr B.P. and from around 1250 to 500 yr B.P. These changes on the floodplain appear to be the result not of a single factor, but of the complex interplay among changes in climate, sediment yield, and intrinsic floodplain variables over time.

Evidence for the silicate source of relict soils on the Edwards Plateau, central Texas

2007 ◽  
Vol 67 (2) ◽  
pp. 275-285 ◽  
Author(s):  
M. Jennifer Cooke ◽  
Libby A. Stern ◽  
Jay L. Banner ◽  
Lawrence E. Mack
Keyword(s):  
Isotope Composition ◽  
Late Quaternary ◽  
Soil Formation ◽  
Clay Content ◽  
Element Geochemistry ◽  
Edwards Plateau ◽  
Quaternary Climate ◽  
Limestone Bedrock ◽  
Central Texas ◽  
Del Rio

AbstractRelict soils provide insights into Quaternary soil formation and erosion on the Edwards Plateau of central Texas and into soil-forming processes in karst terranes. Late Quaternary climate-driven soil erosion produced a mosaic of thick and thin soils on the Edwards Plateau landscape. Thick soils on uplands of the Edwards Plateau are interpreted to be relicts of a formerly more extensive soil cover that was eroded during the late Pleistocene to middle Holocene. The relict, thick soils are silicate-rich and most commonly overlie the relatively silicate-poor Cretaceous Edwards Limestone, which supports the idea that the thick soils did not form from weathering of the underlying limestone. Other potential sources of silicates for the relict soils include dust, alluvial sediments, and the Del Rio Clay, a stratigraphically higher but locally eroded clay-rich unit. Here we investigate the geographic distribution, texture, clay-sized mineralogy, rare earth element geochemistry, and neodymium isotope composition of the relict soils. We have found that the relict, thick soils are deeply weathered soils that occur dominantly over the Edwards Limestone and have a high clay content and a neodymium isotope composition that is similar to that of the Del Rio Clay. Thus, we propose that in situ weathering of the Del Rio Clay, along with partial weathering of the upper portion of the underlying Edwards Limestone produced thick chert- and clay-rich soils over resistant limestone. In areas like the Edwards Plateau, where pure limestones are interbedded with clay-rich strata, the overlying clay-rich strata must be considered as a possible silicate source to soils on pure limestone bedrock.

C4 Plant Productivity and Climate-CO2 Variations in South-Central Texas during the Late Quaternary

2002 ◽  
Vol 58 (2) ◽  
pp. 182-188 ◽  
Author(s):  
Lee C. Nordt ◽  
Thomas W. Boutton ◽  
John S. Jacob ◽  
Rolfe D. Mandel
Keyword(s):  
Late Pleistocene ◽  
Mississippi River ◽  
Late Quaternary ◽  
Plant Productivity ◽  
Glacial Meltwater ◽  
The Holocene ◽  
Global Circulation ◽  
South Central ◽  
Central Texas ◽  
Ecophysiological Responses

AbstractA continuous record of organic carbon δ13C from a buried soil sequence in south-central Texas demonstrates: 1) strong coupling between marine and adjacent continental ecosystems in the late Pleistocene as a result of glacial meltwater entering the Gulf of Mexico and 2) ecosystem decoupling in the Holocene associated with a reduction of meltwater and a shift in global circulation patterns. In the late Pleistocene, reduction in C4 plant productivity correlates with two well-documented glacial meltwater pulses (∼15,000 and 12,000 14C yr B.P.), indicating a cooler-than-present adjacent continental environment. Increased C4 production between 11,000 and 10,000 14C yr B.P. suggests that the Younger Dryas was a warm interval responding to the diversion of glacial meltwater away from the Mississippi River. With waning meltwater flow, C4 productivity generally increased throughout the Holocene, culminating in peak warm intervals at ∼5000 and 2000 14C yr B.P. Shifts in the abundances of C3–C4 plants through the late Quaternary show no correlation to ecophysiological responses to atmospheric CO2 concentration.

Architecture of Radiolitid Rudist (Mollusca) Shell-Wall Structures and its Phylogenetic Implications

1975 ◽  
Vol 33 ◽  
pp. 686-687
Author(s):  
David H. Sturm ◽  
Bob F. Perkins
Keyword(s):  
Phylogenetic Relationships ◽  
Outer Wall ◽  
Shell Microstructure ◽  
Shell Wall ◽  
Wall Structures ◽  
Phylogenetic Implications ◽  
Cellular Wall ◽  
Superfamily Analysis ◽  
Central Texas

Each of the seven families of rudists (Mollusca, Bivalvia, Hippuritacea) is characterized by distinctive shell-wall architectures which reflect phylogenetic relationships within the superfamily. Analysis of the complex, calcareous, cellular wall of the attached valve of the radiolite rudist Eoradiolites davidsoni (Hill) from the Comanche Cretaceous of Central Texas indicates that its wall architecture is an elaboration of the simpler monopleurid rudist wall and supports possible radiolite-monopleurid relationships.Several well-preserved specimens of E. davidsoni were sectioned, polished, etched, and carbon and gold coated for SEM examination. Maximum shell microstructure detail was displayed by etching with a 0.7% HC1 solution from 80 to 100 seconds.The shell of E. davidsoni comprises a large, thick-walled, conical, attached valve (AV) and a small, very thin, operculate, free valve (FV) (Fig. 1a). The AV shell is two-layered with a thin inner wall, in which original structures are usually obliterated by recrystallization, and a thick, cellular, outer wall.

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