Steven G. Driese

Middle to Late Paleozoic Atmospheric CO2 Levels from Soil Carbonate and Organic Matter

The stable carbon isotope compositions of ancient soil carbonate and coexisting soil organic matter indicate that atmospheric CO2 levels decreased by a factor of 10 during the middle to late Paleozoic era. Proxy measurements of CO2 were made by application of a soil carbonate CO2 paleobarometer to a suite of paleosols that share key physical and chemical characteristics. The estimates agree with theoretical models that imply that a decrease in Paleozoic atmospheric CO2 levels was associated with afforestation of the land surface by terrestrial plants and with global climate change leading to the extensive Permo-Carboniferous glaciation.

The Buttermilk Creek Complex and the Origins of Clovis at the Debra L. Friedkin Site, Texas

A large artifact assemblage dating to 15,000 years ago lies beneath a Clovis assemblage in central Texas. Compelling archaeological evidence of an occupation older than Clovis (~12.8 to 13.1 thousand years ago) in North America is present at only a few sites, and the stone tool assemblages from these sites are small and varied. The Debra L. Friedkin site, Texas, contains an assemblage of 15,528 artifacts that define the Buttermilk Creek Complex, which stratigraphically underlies a Clovis assemblage and dates between ~13.2 and 15.5 thousand years ago. The Buttermilk Creek Complex confirms the emerging view that people occupied the Americas before Clovis and provides a large artifact assemblage to explore Clovis origins.

Mass-balance reconstruction of a modern Vertisol: implications for interpreting the geochemistry and burial alteration of paleo-Vertisols.

Abstract Utilizing identical sampling and analytical techniques, the morphological and chemical characteristics of a modern Vertisol (Houston Black series, central Texas) can be directly compared with an Upper Mississippian paleo-Vertisol from the Appalachian basin (Pennington Formation, east-central Tennessee). Mass-balance reconstructions suggest retention of primary pedochemical patterns in the paleo-Vertisol, including patterns of soil volume change (strain) and transport functions (translocations) of many major and trace elements. Retention of primary pedochemical patterns suggests that Vertisols constitute nearly closed systems during burial diagenesis. Chemical and mineralogical changes associated with burial diagenesis of the paleo-Vertisol include oxidation of organic carbon (OC), illitization of smectites, dehydration and recrystallization of Fe–Mn oxyhydroxides, and dolomitization of pedogenic calcite. Significant differences in the chemical behavior of gilgai microhigh and microlow pedons in modern Vertisols have implications for interpretation of geochemical data obtained from paleo-Vertisols. Overall wetter soil conditions and variable redox potential under gilgai microlows promote greater depths of leaching and mobility of redox-sensitive trace elements, including Co, Cr, Cu, Mn, Ni, and V. Gilgai microhighs behave as evaporative “wicks” that draw moisture and soluble phases towards the soil surface, resulting in precipitation of metal hydrosylate complexes and sulfates (gypsum) at the capillary fringe and shallower depths of leaching and fixation of trace elements. Paleoprecipitation estimates from paleosols, based on the depth to the top of the pedogenic carbonate horizon, should therefore utilize field, petrographic and geochemical data for characterizing maximum depths of leaching, loss or gain of exchangeable bases, and calcification, rather than relying solely upon field data.

Paleopedology and Paleohydrology of a Volcaniclastic Paleosol Interval: Implications for Early Pleistocene Stratigraphy and Paleoclimate Record, Olduvai Gorge, Tanzania

ABSTRACT A cumulative red paleosol interval developed on volcaniclastic parent material under semiarid conditions in Olduvai Gorge, Tanzania. It contains a complex history of pedogenesis that was affected by: (1) episodic pyroclastic and debris-fan processes and (2) episodic expansions and contractions of an adjacent alkaline lake and the associated fluctuations in the water table. The paleosol interval is 130-320 cm thick, represents 25 ka of the 50 kyr duration of lowermost Bed II, and is defined by early Pleistocene ( 1.75 Ma) Tuffs IF and IIA. The paleosol interval records a paleocatena related to both landscape and drainage--the slope position on a pyroclastic fan relative to an alkaline lake, the proximity to freshwater wetlands, and the position of water table. Biogenic paleosol structures include grass and sedge root traces, zeolite rhizocretions, and soil fauna (termite and ant) traces. Abundant pedogenic features sensitive to soil moisture conditions, including redoximorphic mottles in the paleosol matrix, Fe oxide glaebules, grain and pore coatings, illuviated clay grain and pore coatings, and vadose siliciclastic and zeolite crystal silt, record episodic water-table fluctuations. The geochemistry of whole-rock samples distinguishes two parent materials (early low Ti/Zr, weathered volcaniclastic sediment; and late high Ti/Zr, tuffaceous sediment), which represent two distinct pedogenic phases. The Lower Paleosol developed at both sites, whereas the Upper Paleosol developed only at the upslope site. Mass-balance calculations indicate greater weathering, higher Eh and pH, and greater zeolite precipitation at the upslope site than at the downslope site. These relationships are compatible with the upslope site having had a lower overall water table and better-drained conditions than the downslope site, which had a higher water table and poorly drained conditions. The Lower Paleosol provides evidence of a fluctuating water table consistent with a wetter climate followed by a prolonged arid period. The Upper Paleosol began to form after a return to wetter conditions and ended under arid conditions. The position of the Olduvai Subchron, C2n (1.942-1.785 Ma) in Bed I, directly beneath the paleosol interval, is used to make a tentative correlation at 1.75 Ma with global climate (dust) records (wet/dry cycles).

Carbon dioxide in the Paleozoic atmosphere: Evidence from carbon-isotope compositions of pedogenic carbonate

Stable carbon-isotope compositions of pedogenic carbonate occurring in three clay-rich vertic paleosols within Paleozoic red-bed successions in central Pennsylvania provide a record of past pedogenic environments and can be used to estimate CO{sub 2} pressure (P{sub CO{sub 2}}) of the Paleozoic atmosphere. The {delta}{sup 13}C values of carbonate nodules from paleosols in the deltaic lower Bloomsburg Formation (Upper Silurian) reflect the contribution of carbon from marine groundwater or fossils, coupled with low biological activity. The {delta}{sup 13}C values of carbonate rhizocretions from stratigraphically high paleosols in the Bloomsburg Formation, and in the alluvial Catskill (Upper Devonian) and Mauch Chunk (Upper Mississippian) Formations, suggest an extensive C{sub 3} flora and significant contribution of atmospheric CO{sub 2}. Paleozoic atmospheric CO{sub 2} levels inferred from {delta}{sup 13}C of pedogenic carbonate are significantly higher than present levels.

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

Abstract 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 Profile volume loss/gain (i.e., soil strain, e), a mass-balance calculation that assumes Zr or Ti immobility during pedogenesis, indicate eZr values nearly four times greater than eTi. Large values of eZr 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.

Vertisol Carbonate Properties in Relation to Mean Annual Precipitation: Implications for Paleoprecipitation Estimates

Previous publications combining the properties of multiple soil orders show that depth to carbonate (DTC) increases systematically between 350 and 1000 mm of mean annual precipitation (MAP). We hypothesize that carbonate in Vertisols (clay‐rich, shrink‐swell soils) respond differently to water flux than other soil orders because of lower permeability. To test this hypothesis, we compiled soil description and characterization data from multiple published sources across a late Pleistocene climosequence of the coast prairie of Texas to assess the relationship between MAP (700–1400 mm) and DTC. The DTC of carbonate nodules represents an index of accumulation and the DTC of calcium carbonate equivalent (total carbonate <2.0 mm diam.) an index of leaching. The DTC for 1%, 2%, and 5% abundances were assessed using regression analysis. The R2 values were highest for the DTC of 2% nodules and of 1% calcium carbonate equivalent in Vertisol microlows. Surprisingly, relatively high R2 values were calculated for regression between MAP and DTC in Vertisol microhighs, whereby the relationship is expressed as a parabolic curve and DTC is shallowest in the central part of the climosequence where gilgai expression is greatest. When compared with previous MAP‐DTC relationships, it is clear that Vertisols retain carbonate into rainfall isohyets exceeding 1400 mm, >400 mm higher than the preservation of carbonate in other soil orders. When replotted, the use of DTC to estimate paleoprecipitation with previous equations underestimates MAP in a Mississippian paleo‐Vertisol microlow by approximately 32% at a DTC of 100 cm for 5% nodules. Other paleosol proxies also project greater rainfall than previous DTC equations in this paleo‐Vertisol.

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.

Preservation of a Paleo-vertisol and an Estimate of Late Mississippian Paleoprecipitation

ABSTRACT A Late Mississippian paleosol satisfying all of the morphological criteria required for classification of Holocene Vertisols provides quantitative paleoclimate information, in addition to the now commonplace interpretation of precipitation seasonality based on the presence of vertic features. Paleoprecipitation was estimated using the empirical relationship between depth to pedogenic carbonate horizon in Quaternary soils. Burial compaction, erosional truncation, and high paleoatmospheric CO2 concentration, all factors that complicate paleoprecipitation estimates, are unusually well constrained for this paleosol. Allowing for 10% compaction, the paleosol had a pre-burial depth of 100 cm for the pedogenic carbonate horizon, yielding a mean annual paleo-precipitation estimate f 648 ± 141 mm. This is comparable to the mean annual precipitation for Brownsville, Texas, where similar soils are found today. A dolomicrite crust, developed in gilgai microlows, is well preserved in the paleo-Vertisol. Higher Late Mississippian paleotemperatures and rates of evapotranspiration associated with a lower-latitude paleogeography for central Tennessee during the Late Mississippian may explain in part why Holocene coastal Vertisols in the Brownsville region lack surficial crusts similar to that of the paleo-Vertisol. We qualitatively define the Late Mississippian climate of central Tennessee as semiarid.

Very large plant and root traces from the Early to Middle Devonian: Implications for early terrestrial ecosystems and atmospheric p(CO2)

Plant and root traces from the Fort Prevel Member of the Battery Point Formation (late Early Devonian, Emsian), Gaspe Bay, Quebec (Canada), are larger and more complex than previously postulated for land plants of this time. The traces are preserved as clay- and silt-lined casts in or near growth position and provide evidence that early vascular land plants achieved substantial stature (2–3 m) and were capable of deep rooting (to nearly 1 m). The root traces and alluvial deposits in which they occur suggest increased landscape stabilization and root system and paleosol morphologies that were influenced by a water-stressed, episodically energetic environment. Early Devonian plants of such large stature may have been partly responsible for initiation of a steep decline in atmospheric p (CO 2 ), through organic carbon burial and accelerated terrestrial weathering.