Texas Gulf Coastal Plain Research Articles

Distribution of rare earth and other critical elements in lignites from the Eocene Jackson Group, Texas

Coal is increasingly evaluated as a source of rare earth elements (REEs) in the United States to address the overreliance on imported REEs. The objective of this study was to assess the distribution of REEs in lignites from selected mining areas in the Texas Gulf Coastal Plain region. Thirty-one archived lignite and rock samples previously collected by the U.S. Geological Survey were analyzed for their rare earth element and critical mineral content. These include samples from one core (5400 and 5500 lignite horizons) and two opencast lignite mines (Gibbons Creek 3500 and 4500 horizons, and San Miguel horizons A to D) in the Eocene Jackson Group of the Texas Gulf of Mexico Coastal Plain. Some lithologies in the Gibbons Creek 3500 and 4500 lignite-bearing sections have high total rare earth, yttrium (Y), and scandium (Sc) (REYSc) values, up to 7800 ppm (ash basis) REYSc. The lignite lithologies show an enrichment in rare earths, [samarium (Sm) through gadolinium (Gd)]. The basal Gibbons Creek 3500 lignite bench shows a heavy rare earth element enrichment pattern resembling that often seen in peats through high volatile A bituminous coals. The 5500 lignite sequence, overlying the latter lignite sections, shows a light rare earth enrichment. The San Miguel lignite benches have heavy rare earth enrichments with a negative europium (Eu) anomaly.

Vegetation History and Estuarine Ecology of the Texas Gulf Coastal Plain in Relation to Climate and Sea-Level Changes According to Three Pollen Cores

The vegetation history of the Texas Gulf Coastal Plain in the Holocene is considered according to pollen evidence from three coring sites where both terrestrial and marine ecology are reconstructed. These pollen sites record oscillations in the limit of the Southeastern US Forest zone in relation to climate changes, with a major, southward migration of the forest limit and expansion of the range limit of Betula nigra being recorded in the 6th millennium BP and a northward migration in the 4th millennium BP. The appearance of Rhizophora pollen also indicates increased tropical influence in the Middle Holocene. Moreover, changes in the salinity profiles of estuaries are reconstructed in relation to broader coastal environmental changes, such as sea-level oscillations and the formation of barrier islands, with a major sea-level transgression phase being recorded in the 4th millennium BP and still-stand conditions after the 3rd millennium BP. These vegetation changes are finally compared to occupational evidence of prehistoric humans in the Central Texas Gulf Coastal Plain region in relation to ecological factors. Here, human occupation of the coastal zone is correlated with afforestation, the proliferation of pecan and the emergence of low-salinity estuaries.

Prestack simultaneous inversion for delineation of the Lower Wilcox erosional remnant sandstone beneath the Texas Gulf Coastal Plain: A case study

The Lower Wilcox lowstand sand deposits encased between two sequence boundaries along the Texas Gulf Coastal Plain are of good reservoir quality and usually gas productive. However, the sedimentation is sparsely scattered within such a depositional environment and it is hard to predict by qualitative interpretation methods. Simultaneous inversion of elastic parameters such as P-impedance, S-impedance, and density by the integration of prestack data and well logs allows us to quantitatively characterize the reservoirs and to distinguish them from the surrounding rocks. We have used prestack simultaneous inversion of the elastic parameters for delineation of the gas reservoir in an active field with limited log availabilities. For wells that are missing sonic and density logs, we estimate the parameters using the time-average equation (TAE) and Gardner’s equation, respectively. The shear wave velocity estimation methods are tested and compared using the measured log value. The estimation results are verified using well-log correlations in adjacent wells. Rock-physics analyses on wells are conducted to find the optimal elastic parameters for characterizing the gas-bearing sand. We successfully delineate the reservoir using the crossplot of VP/ VS versus S-impedance values. The inversion results are quality controlled by a producing well in the reservoir zone, and probability maps of each lithology are calculated by the probability density function. Our results from the Lower Wilcox Formation indicate that simultaneous inversion based on the estimated parameters using TAE is feasible, and the gas-bearing reservoirs can be recommended with high confidence.

Quantifying the Impacts of Land-Use and Climate on Carbon Fluxes Using Satellite Data across Texas, U.S.

Climate change and variability, soil types and soil characteristics, animal and microbial communities, and photosynthetic plants are the major components of the ecosystem that affect carbon sequestration potential of any location. This study used NASA’s Soil Moisture Active Passive (SMAP) Level 4 carbon products, gross primary productivity (GPP), and net ecosystem exchange (NEE) to quantify their spatial and temporal variabilities for selected terrestrial ecosystems across Texas during the 2015–2018 study period. These SMAP carbon products are available at 9 km spatial resolution on a daily basis. The ten selected SMAP grids are located in seven climate zones and dominated by five major land uses (developed, crop, forest, pasture, and shrub). Results showed CO2 emissions and uptake were affected by land-use and climatic conditions across Texas. It was also observed that climatic conditions had more impact on CO2 emissions and uptake than land-use in this state. On average, South Central Plains and East Central Texas Plains ecoregions of East Texas and Western Gulf Coastal Plain ecoregion of Upper Coast climate zones showed higher GPP flux and potential carbon emissions and uptake than other climate zones across the state, whereas shrubland on the Trans Pecos climate zone showed lower GPP flux and carbon emissions/uptake. Comparison of GPP and NEE distribution maps between 2015 and 2018 confirmed substantial changes in carbon emissions and uptake across Texas. These results suggest that SMAP carbon products can be used to study the terrestrial carbon cycle at regional to global scales. Overall, this study helps to understand the impacts of climate, land-use, and ecosystem dynamics on the terrestrial carbon cycle.

U-Pb detrital zircon geochronology of the Upper Paleocene to Lower Eocene Wilcox Group, east-central Texas

Arrival of Laramide uplift sediments to the Texas Gulf Coastal Plain and northwestern Gulf of Mexico during the early Paleogene is recorded in strata of the Wilcox Group as a significant increase in sediment accumulation and with the appearance of 65–52 Ma detrital zircons that correspond with the timing of late Laramide uplift. New U-Pb dating of detrital zircons by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) for samples obtained from the Lower Paleocene Tehuacana Member through the Lower Eocene Queen City Formation in east-central Texas identifies the Hooper Formation of the Wilcox Group as the oldest stratigraphic unit to contain 65–52 Ma ages. Late appearance of 65–52 Ma detrital zircons in the Hooper Formation is correlated with unroofed Laramide magmatic intrusions or nearly syndepositional volcaniclastic sources; whereas older detrital zircons are inferred to be derived primarily from sedimentary cover and basement rocks exposed during uplift of Laramide blocks. Potential source region and Gulf Coastal Plain detrital zircon data support a relatively similar paleodrainage area and sediment sources for east-­central Texas Tehuacana Member to Carrizo Formation and central Louisiana Wilcox Group data, and for east-central Texas Queen City Formation and central Louisiana middle-upper Claiborne Group data. South Texas Wilcox Group data contrast with data from these samples and support a different paleodrainage area and sediment sources for the south Texas region. We propose that headwaters sourced from southeastern Wyoming to the southern Rocky Mountain region delivered sediments to east-central Texas and central Louisiana during the Paleocene to Middle Eocene. Pronounced Mesoproterozoic and Neoproterozoic detrital zircons in the lower Claiborne Group of east-central Texas and the middle-upper Claiborne Group of central Louisiana are attributed to new or unroofed recycled sediments with Grenvillian age detrital zircons incorporated from the Ouachita region and other proximal locations in the preexisting paleodrainage area. The inferred paleodrainage area for east-central Texas and central Louisiana includes most of the Rocky Mountain Laramide uplift blocks, has a southern boundary separating it from a south Texas paleodrainage, and an eastern boundary roughly coincident with the Mississippi embayment, which separates it from Appalachian Mountains drainages.

Lithospheric structure of the Texas‐Gulf of Mexico passive margin from surface wave dispersion and migrated Ps receiver functions

AbstractThe seismic velocity structure beneath Texas Gulf Coastal Plain (GCP) is imaged by migrating Ps receiver functions with a seismic velocity model found by fitting surface wave dispersion. We use seismic data from a linear array of 22 broadband stations, spaced 16–20 km apart. A Common Conversion Point (CCP) stacking technique is applied to earthquake data to improve the S/N ratios of receiver functions. Using an incorrect velocity model for depth migration of a stacked CCP image may produce an inaccurate image of the subsurface. To find sufficiently accurate P and S‐velocity models, we first apply a nonlinear modeling technique to fit Rayleigh wave group velocity dispersion via Very Fast Simulated Annealing. Vs ranges from 1.5 km/s in shallow layers of the GCP to 4.5 km/s beneath the Llano uplift and just outboard of the Balcones Fault Zone (BFZ). The BFZ is characterized by slow velocities that persist to nearly 100 km depth. In the stacked image, the largest amplitude positive‐polarity event ranges from the surface, at the Llano uplift, to a maximum depth of ∼16 km beneath Matagorda Island. We attribute this event to the sediment‐basement contact, which is expected to produce a large impedance contrast. Another large‐amplitude and positive‐polarity event at ∼35 km depth, which likely marks the Moho, disappears outboard of the Luling Fault Zone. The disappearance of the Moho beneath the GCP may be due to serpentinization of the upper mantle, which would reduce the impedance contrast between the lower crust and upper mantle dramatically.

Sp receiver function imaging of a passive margin: Transect across Texas's Gulf Coastal Plain

The Gulf Coast of Texas has been the subject of intensive geological and geophysical investigation in pursuit of hydrocarbons but studies that penetrate beyond the upper crust are limited to a few refraction profiles and regional surface wave investigations. The passing of EarthScope's Transportable Array has facilitated regional investigations of the lithosphere but its 70-km station spacing does not allow many important tectonic features to be imaged. A broadband seismic transect across the Texas Gulf Coastal Plain was therefore performed in order to image deep structure beneath this passive margin and the transition to the neighboring craton. A 2D Sp receiver function common conversion point (CCP) stacked image produced for this transect reveals several discontinuities in the sub-crustal lithosphere.The region nearest the shoreline is underlain by an anomalous ∼18 km thick low velocity layer that produces a strong negative pulse in the Sp receiver functions. The drop in velocity is too large to be due to any reasonable change in Fe or Mg content but could be produced by partial melt or mantle hydration. It is unlikely that partial melt would still be found in a 160–180-year-old passive margin, such as the Gulf Coast, but hydration, possibly introduced by a through-going Balcones fault system, and resulting serpentinization could produce the observed anomaly.An event with negative polarity appears at a depth of ∼110 km, which we interpret to be the lithosphere–asthenosphere boundary (LAB). Thermal variations alone would not produce a sufficiently sharp discontinuity to be imaged by Sp converted phases. Recent shear-wave splitting studies revealed unusually large delay times in this region, along with fast polarization directions that differ from measurements on the Laurentian craton. Large delay times may imply significant flow, which could also produce frictional heating, due to shearing, and partial melt, which would steepen the velocity gradients.An additional layer is bounded by discontinuities at 145–165 km depth (with negative polarity) and 185–205 km depth (with positive polarity). The appearance of these discontinuities suggests that the mantle beneath the LAB is more complicated here than elsewhere and that the transition from lithosphere to asthenosphere occurs over a broad (85–100-km-thick) depth interval.

Mineralogy and Geochemistry of the Main Glauconite Bed in the Middle Eocene of Texas: Paleoenvironmental Implications for the Verdine Facies

The Main Glauconite Bed (MGB) is a pelleted greensand located at Stone City Bluff on the south bank of the Brazos River in Burleson County, Texas. It was deposited during the Middle Eocene regional transgression on the Texas Gulf Coastal Plain. Stratigraphically it lies in the upper Stone City Member, Crockett Formation, Claiborne Group. Its mineralogy and geochemistry were examined in detail, and verdine facies minerals, predominantly odinite, were identified. Few glauconitic minerals were found in the green pelleted sediments of the MGB. Without detailed mineralogical work, glaucony facies minerals and verdine facies minerals are easily mistaken for one another. Their distinction has value in assessing paleoenvironments. In this study, several analytical techniques were employed to assess the mineralogy. X-ray diffraction of oriented and un-oriented clay samples indicated a clay mixture dominated by 7 and 14Å diffraction peaks. Unit cell calculations from XRD data for MGB pellets match the odinite-1M data base. Electron microprobe analyses (EMPA) from the average of 31 data points from clay pellets accompanied with Mössbauer analyses were used to calculate the structural formula which is that of odinite: Fe3+ 0.89 Mg0.45 Al0.67 Fe2+ 0.30 Ti0.01 Mn0.01) Σ = 2.33 (Si1.77 Al0.23) O5.00 (OH)4.00. QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) data provided mineral maps of quantitative proportions of the constituent clays. The verdine facies is a clay mineral facies associated with shallow marine shelf and lagoonal environments at tropical latitudes with iron influx from nearby runoff. Its depositional environment is well documented in modern nearshore locations. Recognition of verdine facies clays as the dominant constituent of the MGB clay pellets, rather than glaucony facies clays, allows for a more precise assessment of paleoenvironmental conditions.

Estimating Shorebird Populations During Spring Stopover in Rice Fields of the Louisiana and Texas Gulf Coastal Plain

Abstract.— Migrating shorebird populations using approximately 2% of Louisiana and Texas Gulf Coastal rice fields were surveyed during spring migration (March–May of 1997 and 1998) using biweekly stratified random surveys conducted at 50 roadside survey points and approximately 30,000 shorebirds were observed. Shorebird counts were extrapolated and almost 1.4 million birds in 1997 and over 1.6 million birds of 31 species in 1998 were estimated to use rice field habitat for stopover sites in Louisiana and Texas. Greater than 50% of the estimated North American populations were estimated to use rice field habitats for five species, including a species of concern, Buff-breasted Sandpiper (Tryngites subruficollis) at 187%. Because of predictability of suitable rice field habitat acreage, timing of field preparation and water availability, coastal rice prairies are identified as critical spring migration stopover sites.

Stable Isotope Study of Hunter-Gatherer-Fisher Diet, Mobility, and Intensification on the Texas Gulf Coastal Plain

The Gulf Coastal Plain of Texas was populated by hunter-gatherers from the Early Archaic (ca. 7000 B.P.) through to the Late Prehistoric period (ca. A.D. 700-1400). In order to characterize past dietary adaptations along the coast and further inland, stable isotopes of carbon and nitrogen were analyzed in preserved bone from 198 individuals from mortuary sites. In addition, 140 samples of faunal bone were analyzed to elucidate the stable isotope ecology for each region. The results indicate long-term stability in dietary adaptations with regional variation among coastal, riverine, and inland groups, including an early and, substantial, use of freshwater and marine resources. There is also evidence for constrained mobility and increasing use of plant resources within regions as populations increased in size and density.

A large range extension and molecular phylogenetic analysis of the monotypic North American aquatic gastropod genus Cincinnatia (Hydrobiidae)

The freshwater gastropod genus Cincinnatia (Hydrobiidae: Nymphophilinae) contains a single species, C. integra (Say, 1821), which is distributed across much of eastern North America from the Great Lakes region to the Texas Gulf Coastal Plain. Here we use morphological and molecular evidence to evaluate the taxonomic status of a Cincinnatia population that was recently discovered in an upper reach of the Rio Panuco basin (northeastern Mexico) c. 700 km distant from its most closely proximal congeners. The Panuco basin population cannot be consistently differentiated from C. integra by its shells, although it differs from previously reported material of this species in several details of reproductive anatomy. The Panuco basin population differs from specimens from the type locality area and five other populations of C. integra by 1.5–2.6% mtCOI sequence divergence, but was no more differentiated than most of the other populations and was not consistently resolved as a monophyletic subunit of Cincinnatia using these molecular data. Based on this evidence we treat this population as belonging to C. integra pending a more comprehensive study of morphological and genetic variation across the broad geographic range of this species. This new record represents a large range extension not only for Cincinnatia, but also for the entire North American nymphophiline radiation, whose previously recorded southern limit was the Cuatro Cienegas basin in Coahuila.

Adult Stature and Health Among Early Foragers of the Western Gulf Coastal Plain

Female and male skeletal remains from early cemetery sites on the Western Gulf Coastal Plain of North America were analyzed to assess secular changes in stature across time. Sample populations consisted of hunter-gatherers and date from the Middle Archaic (3000-1500 B.C.), the Late Archaic (1500 B.C.-A.D. 600), and the Late Prehistoric (A.D. 600-1500) time periods. Results display a slight decline in average statures between the Middle and Late Archaic, but a more than 2.5 cm increase in stature from the Late Archaic to the Late Prehistoric. All populations achieved at least 94.9 percent of modern adult statures. Compared with historically documented nineteenth-and twentieth-century populations, prehistoric Texas foragers enjoyed a level of nutrition greater than that of nineteenth-century working class Europeans, Caribbean slaves, and twentieth-century hunter-gatherers. Average estimated statures were comparable with upper class nineteenth-century Europeans. Results of the study are consistent with the archeological consensus that the prehistoric hunter-gatherers of the Texas Gulf Coastal Plain practiced a conservative but highly successful hunting and gathering subsistence strategy.

Morphology and stratigraphy of the late Quaternary lower Brazos valley: Implications for paleo-climate, discharge and sediment delivery

A shallow coring and geophysical logging program has recorded the sedimentary fill of the Brazos River valley in the Texas Gulf Coastal Plain. Thermoluminescence dates together with new and recalibrated published radiocarbon dates show the valley fill to include extensive, sandy, buried falling stage and lowstand Oxygen Isotope Stage (OIS) 3 and 2 deposits. These alluvial deposits are punctuated by numerous paleosoil horizons that record alternating periods of cutting, bypass and accumulation. Maximum valley incision and two periods of terrace formation preceded marine lowstand conditions, suggesting significant discordance between preserved fluvial and classical marine system tracts. The latest Pleistocene incision and fill history appears related to cycles of increased discharge and incision, followed by system equilibration and terrace formation. Analysis of the Brazos River incised valley and its contained paleochannels indicates that latest Pleistocene mean annual discharge was as much as four times greater than that of today. This magnitude of discharge in the Brazos would require a two-fold increase in precipitation across the drainage basin. Such an increase is comparable to the present day measured positive El Niño winter precipitation anomaly across the region. Paleochannel geometries and the stratigraphic and sedimentologic data from this investigation support the hypothesis that periods of high-amplitude, El Niño-like climatic perturbations characterized the late Quaternary climate of the south-central and southwestern U.S. This period of high discharge coincides, at least in part, with late OIS 3 progradation of the Brazos delta to the shelf margin, OIS 3 and 2 valley incision across the Texas shelf, and concomitant sand bypass to intraslope basins beyond the shelf edge.

The M. W. Burks Site (41WD52): A Late Caddo Hamlet in Wood County, Texas

While attempting to locate and evaluate prehistoric Caddo archaeological sites in the Dry Creek watershed, Wood County, Texas, that had been originally recorded by A. T. Jackson and M. M. Reese in 1930, the M. W. Burks site (41WD52) was discovered by James E. Bruseth and Bob D. Skiles in June 1977. The site is in the Forest Hill community, about 5 km north of Quitman, Texas, in the East Texas Pineywoods and Gulf Coastal Plain. It is on a small rise in the uplands overlooking a small intermittent drainage that is an unnamed tributary of Little Dry Creek. The landowner, Mr. M. W. Burks, had resided in this part of Wood County since the 1920s, and recalled where A. T. Jackson and crew had spent time excavating the J. H. Reese (41WD2) site. He mentioned that while putting in a fence on his property in the early 1960s, adjacent to the property where the Reese site is located, he had found some pottery sherds in one of the post holes. Bruseth and Skiles placed a small shovel test next to this fence post hole, and a large articulated red-slipped Ripley Engraved carinated bowl was encountered at 65 em below the surface (bs) in tan sand E-horizon deposits. This find demonstrated that the Burks site contained both intact archaeological deposits as well as an apparently undisturbed Late Caddo Titus phase burial or cemetery. Bruseth, Skiles, and Perttula followed up this work with more intensive investigations in the spring and fall of 1978. This research was carried on as an adjunct to the ongoing (and final season of) archaeological work being conducted by Bruseth and Perttula at Lake Fork Reservoir on Lake Fork Creek, a few miles to the west of the Burks site. Our purpose in carrying out archaeological research at the Burks site was to examine in more detail the spatial character of a Late Caddo Titus phase settlement, and also obtain information on the material culture remains (especially the ceramics) made and used by the Caddo peoples that lived at the Burks site some 400-500 years ago.

Pedogenic processes and domain boundaries in a Vertisol climosequence: evidence from titanium and zirconium distribution and morphology

The occurrences of titanium (Ti) and zirconium (Zr) within eight Vertisols formed in a climosequence on the Upper Beaumont Formation of the Texas Gulf Coastal Plain were investigated in order to determine processes responsible for Ti and Zr redistribution during pedogenesis. Discontinuities defined by significant shifts in particle size distribution and the content (in volume percent) of Zr are present at 160 to 260 cm depth in each pedon. The discontinuities are interpreted to be functional boundaries, i.e., physico-chemical expressions of pedogenic domains, between an upper soil domain dominated by open-system pedogenesis and a lower, more closed-system domain dominated by chemical weathering. The depth at which the functional boundary occurs is dependent on physical and hydrogeochemical influences, which are largely a function of available water. Soil materials above the discontinuities are slightly coarser textured and enriched in Zr, whereas below the sediments are finer textured and have lower and more constant Zr contents. The Zr is associated almost exclusively with zircon and Zr contents correlate positively to the weight percent sand+coarse silt, with negligible Zr present in the <20 μm size fraction. By comparison, Ti occurs preferentially in the <20 μm size fraction and there are no marked discontinuities in Ti contents with depth. Scanning electron microscopy (SEM) of individual zircon and rutile grains show predominantly physical damage to zircons, whereas rutile grains appear to have been affected predominantly by chemical weathering. Thus, different processes dictate Ti and Zr content and distribution in these Vertisols, although both elements are often considered immobile in weathering profiles. Profile volume loss/gain (i.e., soil strain, ε), a mass-balance calculation that assumes Zr or Ti immobility during pedogenesis, indicate ε Zr values nearly four times greater than ε Ti. Large values of ε Zr within the upper soil domains are due primarily to sand and coarse silt additions to the Vertisols and preclude use of Zr as a basis of mass-balance calculations in these soils, despite its relative chemical stability. By comparison, Ti is generally conserved within the clay-rich soil profiles and is therefore better suited for mass-balance calculations of volume change and mobile element translocation during pedogenesis.

Distinguishing climate and time in the soil record: Mass-balance trends in Vertisols from the Texas coastal prairie

Research Article| April 01, 2003 Distinguishing climate and time in the soil record: Mass-balance trends in Vertisols from the Texas coastal prairie Cynthia A. Stiles; Cynthia A. Stiles 1Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37996-1410, USA Search for other works by this author on: GSW Google Scholar Claudia I. Mora; Claudia I. Mora 1Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37996-1410, USA Search for other works by this author on: GSW Google Scholar Steven G. Driese; Steven G. Driese 1Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37996-1410, USA Search for other works by this author on: GSW Google Scholar Amelia C. Robinson Amelia C. Robinson 1Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37996-1410, USA Search for other works by this author on: GSW Google Scholar Geology (2003) 31 (4): 331–334. https://doi.org/10.1130/0091-7613(2003)031<0331:DCATIT>2.0.CO;2 Article history received: 05 Jul 2002 rev-recd: 18 Dec 2002 accepted: 20 Dec 2002 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Cynthia A. Stiles, Claudia I. Mora, Steven G. Driese, Amelia C. Robinson; Distinguishing climate and time in the soil record: Mass-balance trends in Vertisols from the Texas coastal prairie. Geology 2003;; 31 (4): 331–334. doi: https://doi.org/10.1130/0091-7613(2003)031<0331:DCATIT>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Mass-balance relationships of 10 major elements in a Vertisol climosequence and chronosequence formed on alluvial terraces on the Texas Gulf Coastal Plain indicate that the soils develop characteristic element translocation patterns in response to climatic forcing and reach mass-flux equilibrium within a relatively short period of time. Vertisols within the climosequence (age 35 ka, 800–1500 mm mean annual precipitation [MAP]) approach a net mass flux of ∼−16% (±3%) of parent element contents, corresponding to a weathering flux of −1.0 × 10−3 to −1.3 × 10−3 g cm−2 yr−1, when MAP exceeds 900 mm. Net mass-flux assessments in a Vertisol chronosequence (0.4–35 ka, 1000 mm MAP) show that this equilibrium is achieved within 5–6 k.y. Below 900 mm MAP, positive net mass fluxes indicate that Vertisol profiles are gaining material (at a rate of 0.2 × 10−3 g cm−2 yr−1). Vertisols forming in drier MAP areas approach equilibrium with climate by different mechanisms and at different rates, compared to their wetter counterparts, and may not be as sensitive to millennial-scale climate shifts. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Pedogenic iron-manganese nodules in Vertisols: A new proxy for paleoprecipitation?

The total Fe content of pedogenic iron-manganese (Fe-Mn) nodules taken from a Vertisol climosequence on the Texas Gulf Coastal Plain correlates with mean annual precipitation (MAP, r 2 = 0.92). No significant trend of total Fe (FeTOT) with depth was noted in profiles. Using the regression developed from modern Vertisol data, FeTOT contents of Paleozoic paleo-Vertisol Fe-Mn nodules yielded MAP regimes comparable to previously inferred paleoenvironmental interpretations. Paleoprecipitation estimates derived from Fe-Mn nodules for an uneroded, Late Mississippian paleo-Vertisol are very close to estimates determined from a depth to pedogenic carbonate horizon (DCH) proxy determined from the modern Vertisol climosequence. The lack of soil depth dependence of the Fe-Mn nodule proxy provides a consistent paleoprecipitation estimate even in eroded paleo- Vertisols and, in combination with the DCH, may be useful in determining original paleosol thickness.

Houston Area Geoarcheology: A Framework for Archeological Investigation, Interpretation, and Cultural Resource Management in the Houston Highway District

This report represents an examination of geoarcheological issues affecting a six county area in the vicinity of Houston, Texas. The study area includes Harris, Montgomery, Waller, Fort Bend, Brazoria, and Galveston counties (Figure 1), which collectively make up the Houston District, a regional administrative entity of the Texas Department of Transportation (TxDOT). This study represents the first phase of a district-focused geoarcheological program being implemented at TxDOT, with similar studies of other districts to follow . It is intended to familiarize archeologists working in the region with relevant geoarcheological issues, thus serving as a resource for researchers involved in prospection, assessment, and interpretation of prehistoric archeological sites. Although the focus of investigation is on the six counties making up the Houston District, most of the issues addressed are equally applicable to adjacent areas of the upper Texas Gulf Coastal Plain.

Abstract: Importance of Falling Stage Fluvial Deposition: Quaternary Examples from the Texas Gulf Coastal Plain and Western Europe&amp;nbsp;

Abstract: Importance of Falling Stage Fluvial Deposition: Quaternary Examples from the Texas Gulf Coastal Plain and Western Europe&amp;nbsp;

Abstract: Current Thinking on Late Quaternary Alluvial Successions of the Texas Gulf Coastal Plain&amp;nbsp;

Abstract: Current Thinking on Late Quaternary Alluvial Successions of the Texas Gulf Coastal Plain&amp;nbsp;