Holocene Pedogenesis in Fluvial Deposits of the Conejos River Valley, Southern Colorado

Relatively few geomorphic studies have examined Holocene-aged soils developed in alluvial deposits in the Rocky Mountains. Here, we present a soil morphological investigation from a suite of fluvial terraces in the glaciated portion of the Conejos River Valley, southern Colorado. The surficial geology of 25 km of the glacial valley was mapped in detail. Within three separate sub-reaches (Platoro, Lake Fork and South Fork) a total of thirteen soil pits and exposures were excavated and described on alluvial deposits. Soil samples were analyzed for particle size and extractable iron. Soil horizonation (A/C to A/B/2C), structure (fine sub angular to medium angular blocks), clay content of the B horizon (8.0% to 22.8%) and Feo/Fed (0.39 to 0.80) illustrate trends with relative terrace deposit age in individual sub-reaches. However, only Feo/Fed ratios displayed similar rates of development between all sub-reaches highlighting the usefulness of this metric for determining accurate rates of pedogenesis and relative age for Holocene-aged deposits in sub-alpine environments. Results indicate that clay content and structure developed in alluvial deposits of similar ages vary between sub-reaches. Clay contents were found to be lower in the Platoro sub-reach (e.g. 13.1% at Platoro and 20.0% at South Fork on Qt1 deposits). This variation is attributed to heterogeneity in the nature of the inherited parent material and potential variability in aeolian dust contributions throughout the Holocene

Systematic Approach to Identifying Deeply Buried Archeological Deposits

This project is designed to assist cultural resource specialists involved in Nebraska Department of Transportation (NDOT) and the Federal Highway Administration (FHWA) project planning and development. The goal was to develop Geographic Information System (GIS) data layers that spatially delineate different landform-sediment assemblages (LSAs) and depict the associated geologic potential for buried cultural deposits in select watersheds in Nebraska. The Nebraska Buried Sites GIS resource will allow planners and cultural resource specialists to determine whether future project areas are likely to be free of deeply buried sites or whether subsurface exploration is necessary

Using the factors of soil formation to assess stable carbon isotope disequilibrium in late Pleistocene (MIS 3) buried soils of the Great Plains, North America

The stable carbon isotope composition of both soil organic matter (SOM) and pedogenic carbonate are widely used as paleoenvironmental proxies. This study utilizes δ13C analyses to reconstruct bioclimatic change from a series of buried soils in the central Great Plains of North America that developed between ca. 44–24 ka. Results revealed a paradoxical isotopic disequilibrium between the isotopic composition of bulk SOM (δ13CSOM) and pedogenic carbonate (δ13Ccarb). Specifically, Δ13C values are 0.1 to 6.3 per mil greater than the highest expected equilibrium value of 17 per mil in the Bk horizons. In contrast, Δ13C values are 0.1 to 4.8 per mil lower than the lowest expected equilibrium value of 14 per mil in the Ak horizons. A soil-forming factor approach was utilized to establish multiple working hypotheses regarding the influence of climate, vegetation, parent material, and time on the observed isotopic disequilibrium. Of the various hypotheses presented, we suggest that the following most likely explain the observed isotopic disequilibrium. The greater-than-expected Δ13C values in the Bk horizons most likely reflects seasonal bias in pedogenic carbonate formation, resulting in an apparent C4-biased signal. The lower-than-expected Δ13C values in the Ak horizons remains perplexing. The most likely explanation is that detrital carbonate contributions affected the δ13Ccarb record or that the δ13Ccarb and δ13CSOM records are asynchronous. Overall, it appears that different factors have affected the δ13CSOM and δ13Ccarb records independently and therefore results of this study highlight the importance of assessing pedogenic carbonates for isotopic equilibrium as well as the need to understand past environmental conditions (i.e., soil-forming factors) when interpreting isotopic trends

Mississippian Stratigraphic Nomenclature Revisions in Kansas

This paper reviews proposed Mississippian nomenclature changes in Kansas and outlines the changes to Zeller (1968) that have been adopted by the Kansas Geological Survey. The Sedalia Dolomite is changed to the Sedalia Formation and the Northview Shale is changed to Northview Formation due to lateral lithology changes. The Short Creek Oolite Member as originally defined and described by Smith and Siebenthal (1907) at the type section in Kansas is reinstated. The Cowley Formation as originally defined and described by Lee (1940) in Kansas is reinstated. The Ste. Genevieve Limestone is placed as the basal formation of the Chesteran Stage

Quaternary Stratigraphy and Stratigraphic Nomenclature Revisions in Kansas

This paper outlines Quaternary nomenclature changes to Zeller (1968) that have been adopted by the Kansas Geological Survey (KGS). The KGS formally recognizes two series/epochs for the Quaternary: the Holocene and Pleistocene. Pleistocene stage/age names Kansan, Aftonian, Nebraskan, and Yarmouthian are abandoned and replaced with the broader term "pre-Illinoian." Formation names Bignell, Peoria, Gilman Canyon, and Loveland are maintained for loess units. Formation names for the following alluvial lithostratigraphic units are abandoned: Crete, Sappa, Grand Island, Fullerton, and Holdrege. The Severance Formation is adopted as a new lithostratigraphic unit for thick packages of late Pleistocene alluvium and colluvium in Kansas. The DeForest Formation is accepted as a valid lithostratigraphic unit for deposits of fine-grained Holocene alluvium in Kansas. Formation names Iowa Point, Nickerson, and Cedar Bluffs for glacial tills and Atchison and David City for glaciofluvial deposits are abandoned. The Afton and Yarmouth Soils are abandoned as pedostratigraphic units, whereas the Sangamon Geosol and Brady Geosol are maintained

Systematic Approach to Identifying Deeply Buried Archeological Deposits

This project is designed to assist cultural resource specialists involved in Nebraska Department of Transportation (NDOT) and the Federal Highway Administration (FHWA) project planning and development. The goal was to develop Geographic Information System (GIS) data layers that spatially delineate different landform-sediment assemblages (LSAs) and depict the associated geologic potential for buried cultural deposits in select watersheds in Nebraska. The Nebraska Buried Sites GIS resource will allow planners and cultural resource specialists to determine whether future project areas are likely to be free of deeply buried sites or whether subsurface exploration is necessary

https://dot.nebraska.gov/media/4yaemfil/m100-nebraska-buried-archeological-sites-phase-ii.pdf

This project developed a GIS to assist with the identification of deeply buried archeological sites in alluvial settings across Nebraska with the exception of the Sandhills region. Soil survey data, previous geoarcheological investigations, landform position, and other information was used to rank the potential of any stream valley setting as low, low-moderate, moderate-high, or high potential to contain buried soils (paleosols). While the presence of buried soils does not necessarily translate to presence of buried archeological sites, the potential for such sites is far greater in paleosols. The GIS can be used by NDOT and other agencies with statutory historic preservation obligations, to identify tracts on proposed construction projects that might require deep mechanical testing (backhoe or coring) in search of buried archeological properties

Forces Driving Late Pleistocene (ca. 77-12 ka) Landscape Evolution in the Cimarron River Valley, Southwestern Kansas

This study presents stratigraphic, geomorphic, and paleoenvironmental (δ13C) data that provide insight into the late Pleistocene landscape evolution of the Cimarron River valley in the High Plains of southwestern Kansas. Two distinct valley fills (T-1 and T-2) were investigated. Three soils occur in the T-2 fill and five in the T-1 fill, all indicating periods of landscape stability or slow sedimentation. Of particular interest are two cumulic soils dating to ca. 48–28 and 13–12.5 ka. δ13C values are consistent with regional paleoenvironmental proxy data that indicate the prevalence of warm, dry conditions at these times. The Cimarron River is interpreted to have responded to these climatic changes and to local base level control. Specifically, aggradation occurred during cool, wet periods and slow sedimentation with cumulic soil formation occurred under warmer, drier climates. Significant valley incision (~ 25 m) by ca. 28 ka likely resulted from a lowering of local base level caused by deep-seated dissolution of Permian evaporite deposits

Pliocene paleoenvironments in the Meade Basin, Southwest Kansas, USA

Terrestrial paleoenvironmental reconstructions from the Pliocene Epoch (5.3-2.6 Ma) of the Neogene Period are rare from the North American continental interior, but are important because they provide insight into the evolutionary context of modern landscapes and ecological systems. Pliocene marine records indicate that global climate was warmer and atmospheric pCO2 was higher than pre-industrial conditions, spurring efforts to understand regional climate and environmental variability under conditions potentially analogous to future warming scenarios. In this study, we investigate sedimentary environments and paleoclimate conditions from the Meade Basin of southwest Kansas, a moderately sized basin formed from dissolution and withdrawal of deep evaporites. Pliocene intervals of the Meade Basin have yielded classic faunal assemblages representing the early to middle Blancan North American Land Mammal Age (∼ 4.5-3.2Ma).We reconstruct the paleoenvironments using a multidisciplinary approach of lithofacies analysis, paleopedology, and ichnology. The stratigraphic interval we examined is bounded by large-scale, fluvial trunk channels that show paleocurrent trends to the south-southwest-tangential to modern drainages-likely due to local halotectonic subsidence during the Neogene. The stratigraphic interval between these fluvially dominated phases consists of palustrine landscapes with temporally and laterally variable subaqueous and subaerial facies. Paleosols are abundant; however, most pedotypes are poorly to variably drained, and so their elemental compositions do not reflect local climate state. The few mature, oxidized, and relatively well-drained paleosols observed contain elemental signatures consistent with subhumid climate conditions. Frequent and recursive ponding events are discerned through the tiering of burrows (Camborygma ISP.) similar to those produced by modern freshwater decapod crustaceans (i.e., crayfish). The drivers of these flooding events are most likely episodic halotectonic subsidence and groundwater discharge, though influence from intervals of relatively wetter climate cannot be ruled out. By the late middle Pliocene, landscapes returned to fluvially dominated environments as sedimentation began to outpace accommodation. Our results collectively indicate that climate was likely wetter than modern conditions in the early to middle Pliocene in the western Great Plains, contrary to forecasts for the region under current pCO2-driven warming