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CO 2 CONCENTRATIONS IN VERTISOLS: SEASONAL VARIABILITY AND SHRINK–SWELL DANIEL O. BREECKER AND JUNYEON YOON Department of Geological Sciences, The University of Texas at Austin, 1 University Station C1100, Austin, Texas 78712, USA e-mail: breecker@jsg.utexas.edu LAUREN A. MICHEL Department of Geology, Baylor University, One Bear Place #97354, Waco, Texas 76798, USA TAKELE M. DINKA Soil and Crop Sciences Department, Texas A&M University, 2474 TAMU, College Station, Texas 77843, USA STEVEN G. DRIESE, JASON S. MINTZ, AND LEE C. NORDT Department of Geology, Baylor University, One Bear Place #97354, Waco, Texas 76798, USA KATHERINE D. ROMANAK Bureau of Economic Geology, The University of Texas at Austin, Austin, Texas 78712, USA AND CRISTINE L.S. MORGAN Soil and Crop Sciences Department, Texas A&M University, 2474 TAMU, College Station, Texas 77843, USA ABSTRACT: The paleosol–carbonate CO 2 barometer is widely accepted to be the most reliable method for reconstructing Earth’s atmospheric CO 2 concentrations in deep time. Currently, the largest source of error in atmospheric CO 2 calculated using the paleosol barometer originates from uncertainty in soil CO 2 concentrations during soil carbonate formation. Many of the paleosols used for CO 2 reconstruction were formed in clay-rich alluvium and have vertic properties, which may influence soil CO 2 .We hypothesized that the cracking during drying of shrink–swell clays results in rapid CO 2 escape and low soil CO 2 concentrations. We tested our hypothesis by monitoring soil cracking and the concentration of CO 2 in the pore spaces of surface Vertisols (the Houston Black and Heiden series fine, smectitic, thermic Udic Haplusterts). Crack porosity of soils was estimated by measuring soil subsidence, and CO 2 was measured in syringe samples collected from soil gas wells. During the period of study, pore-space CO 2 concentrations at ~1-m soil depth varied by two orders of magnitude, from 10% during water-saturated conditions to
GROUNDWATER-FED WETLAND SEDIMENTS AND PALEOSOLS: IT’S ALL ABOUT WATER TABLE GAIL M. ASHLEY Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey 08854, USA e-mail: gmashley@rci.rutgers.edu DANIEL M. DEOCAMPO Department of Geosciences, Georgia State University, Atlanta, Georgia 30302, USA JULIA KAHMANN-ROBINSON Department of Geology, Baylor University, One Bear Place #97354, Waco, Texas 76798, USA AND STEVEN G. DRIESE Department of Geology, Baylor University, One Bear Place #97354, Waco, TX 76798, USA ABSTRACT: Wetlands are continental depositional environments and ecosystems that range between ephemerally wet to fully aquatic habitats, and, thus, the character of a wetland soil is directly related to the position of the water table over seasonal and longer timescales. The sediment and paleosol records of wetlands are products of a unique setting that can be both exposed to the atmosphere and water-saturated at the same time. Wetlands tend to occupy low-gradient portions of the landscape in places where the phreatic zone is at least ephemerally exposed at the surface, and hydrophytic vegetation has an opportunity to colonize. Groundwater-fed wetlands are an end member of a continuum of waterlogged environments and are associated with localized groundwater discharge (GWD); e.g., springs and seeps that can sustain permanent saturation. Research has tended to follow one of two parallel tracks: sedimentology or pedology. An objective of this paper is to bring these two separate lines of inquiry closer together. The signature of wetland pedogenesis includes redoximorphic features, enhanced hydrolytic alteration or dissolution of soluble phases, and preservation of biotic indicators of wetland habitats. Histosols (peats) and other hydric soils (indicated by gley color and reduced minerals like pyrite and siderite) are common in sites with a permanently high water table and anaerobic conditions. Illuvial clays, in contrast, record episodes in which wetlands dry out and drainage improves sufficiently for these features to form. A case study from Holocene-age Loboi Swamp, Kenya, illustrates the importance of integrating field observations and laboratory analyses. Wetland conditions were observed through thin section micromorphology, mineralogy, bulk geochemistry, and macro- and microfossils. The record of Loboi Swamp is characterized by the juxtaposition of features indicating episodes of soil saturation alternating with those indicating desiccation. In order to extract the most information recorded in groundwater-fed wetlands, soils and sediments should be studied as part of the larger spatial and climatic frameworks in which they occur.
Page 2 and 3: New Frontiers in Paleopedology and
Page 4 and 5: A SHORT HISTORY AND LONG FUTURE FOR
Page 8 and 9: SOIL AND LANDSCAPE MEMORY OF CLIMAT
Page 10 and 11: PALEOCLIMATIC APPLICATIONS AND MODE
Page 12 and 13: ALLUVIAL STACKING PATTERN ANALYSIS
Page 14 and 15: PROGRADING DISTRIBUTIVE FLUVIAL SYS
Page 16 and 17: SOIL DEVELOPMENT ON MODERN DISTRIBU
Page 18 and 19: A PEDOSTRATIGRAPHIC APPROACH TO NON
Page 20 and 21: oth higher temperatures and an inte
Page 22: EARLY CAMBRIAN HUMID, TROPICAL, COA

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