ABSTRACT Presence of an A horizon in paleosols is important for taxonomic classification, interpreting pedogenic processes, and reconstructing paleoenvironments. However, identifying the A horizon in buried contexts is challenging because of potential erosion during burial and post-burial diagenesis. Thus, 745 master horizons from 299 training pedons were analyzed to develop indicators for identifying buried A horizons and non-A horizons. Indicators of A horizons include < 12% organic carbon or < 24% LOI, ped diameters ≤ 1 cm, platy peds, or > 2% root traces in sandy substrates. Non-A horizon indicators represent properties of the O, E, transitional (e.g., AB), B, or C horizons. Together, the indicators yield the highest proportion of true positives for classification of known A horizons and true negatives (TN) for classification of known non-A horizons in the database (∼ 80 to 90% success rate). Confusion-matrix statistics show that the classification performance of the indicators are optimized when considering sensitivity, specificity, precision, and accuracy. In addition, there were no significant differences (z-test) in the performance of the indicators between the training pedons and 30 validation pedons. Testing the indicators on buried Quaternary paleosol sequences demonstrates that most A horizons survive the burial process in alluvial settings, giving confidence in their potential preservation in lithified paleosols of deeply buried contexts. Applying the indicators to selected Quaternary and lithified Miocene through Permian buried paleosols with previously assigned master horizons altered some pedogenic and climate interpretations. Examples are given of problematic buried paleosols for further testing of the indicators.

Deciphering the characteristics and drivers of depositional cyclicity has long been a focus of research for sedimentary successions deposited during the late Paleozoic ice age (LPIA). In this study, we integrate stratigraphic and stable isotopic data to better understand the paleoclimatic, paleoceanographic, and tectonic processes influencing patterns of accumulation for Middle Pennsylvanian to lowermost Permian Paradox Basin sediments. The succession records a long-term transition from predominantly marine to fully continental deposition, extending beyond the marine-dominated Middle Pennsylvanian succession that has been the primary focus of prior cyclostratigraphic studies within the Paradox Basin. Conodont apatite records an average δ18O of 19.0‰ (VSMOW), whereas lingulide and ichthyolith δ18O values are on average 2.0 to 2.5‰ lower than coeval conodont samples. Stratal stacking pattern analysis provides an assessment of changing facies proportions within meter-scale depositional cycles and an associated minimum sea level estimate through time. A third-order accommodation trend (∼1–3 Myr) was detected with three transgressive-regressive cycles. The δ18O of limestone micrite covaries with this third-order trend, most likely due to meteoric diagenesis during episodic subaerial exposure of the shallow carbonate platform. Biogenic apatite δ18O trends are difficult to explain solely via changing paleoclimate or glacial volume, and we find changing salinity, coupled with local sea surface temperature, to be the most likely explanation for long-term trends. In the absence of clear evidence for changing glacial volume from biogenic apatite δ18O, we interpret a tectonic origin for the three third-order accommodation cycles identified within Middle Pennsylvanian to lowermost Permian Paradox Basin sediments.

The Chalbi Desert, located in eastern Africa, is a significant but overlooked archive of the Pleistocene and Holocene periods that could add insight into investigations on human evolution. We revisited southeastern Chalbi Desert landforms between the towns of Kargi and Maikona to improve the chronostratigraphy and provide paleoenvironmental context. Direct U-series and electron spin resonance dating of various fossil teeth recovered from a deflated dune (Qzs) landform at the Farre locality return a mean age of ∼545 ka, which is compatible with biostratigraphic inferences. While this numerical age result should probably be regarded as mostly indicative given the existing uncertainty on the environmental dose rate evaluation, the data set available nevertheless strongly suggests a Middle Pleistocene age for at least some of the fauna. Sedimentology, luminescence, and 14 C dating further suggest that this Qzs landform and its contents were modified by alluvial fan development and weathering during denudation in a proximal fan setting through the late Pleistocene into the Holocene. The Qzs landform currently experiences aeolian additions, erosion, and salt-affected soil development in an arid climate. Pedogenic carbonate isotope geochemistry suggests that deflated sand dunes were covered by woody grasslands during Marine Isotope Stage (MIS) 4 and 3 pluvials, consistent with nearby fan progradation constrained at >35 ka. The desert experienced increased hydrologic activity during late Pleistocene and African humid period pluvials, as evidenced by additional optically stimulated luminescence and 14 C dating from fan, dune, and playa contexts. The last significant pluvial episode ended after 4.4 ± 0.3 cal ka BP, which coincides with the final regression of nearby Lake Turkana. This study extends the chronology of Quaternary sediments in the Chalbi Desert to the Middle Pleistocene and offers paleoenvironmental insights into the conditions experienced by Middle Stone Age tool users in the region.

The perudic, udic, ustic, xeric and aridic are taxonomically-defined soil moisture regimes (SMRs) derived from values of mean monthly precipitation (MMP), mean monthly potential evapotranspiration (MMPET), and soil water holdingcapacity to estimate intervals during which the soil control section is dry or moist. However, estimating the SMR in buried paleosols (herein paleosols) is problematic because standard paleoclimate proxies only yield mean annual precipitation (MAP) and mean annual temperature (MAT). Consequently, we analyzed 299 pedons from three United States Department of Agriculture-Natural Resource Conservation Service (USDA-NRCS) datasets and developed indicators for identifying the SMR using MAP and MAT alone. Results show that pedons with a perudic SMR occur in areas where MAP >2200 mm, reflecting monthly soil water surplus. The boundary separating the four udic (moist) and four ustic (moist/dry) subregimes is defined by MAP and MAT ranging from >300 to 2200 mm and from <= 8 to >22 degrees C, respectively. The aridic SMR has two subregimes where MAP <400 mm when MAT >8-22 degrees C and <= 600 mm when MAT >22 degrees C. The crygel soil temperature regime (STR) occurs when MAT is <= 8 degrees C and MAP is <= 300 mm, while the xeric SMR is not included here. Because of uncertainties associated with the MAP and MAT paleo-proxies, we employed a fuzzy logic model to classify the dominant SMR and then partial memberships of adjacent SMRs. When applied to paleosols buried in Ordovician to Pleistocene sediments, the reconstructed SMRs improved taxonomic placement and inferences about pedogenic processes and plant fidelity.

Studies of ancient drylands can enhance our understanding of ecosystem responses to changing climate, but reconstructing deep-time dryland environments using paleosols is challenging because these fossil soils are often weakly developed and many proxies are not equilibrated to past climate. Paleosols from the uppermost Honaker Trail Formation and lower Cutler beds (Rico and Halgaito Formations) span the Pennsylvanian-Permian transition within the Paradox Basin of southeast Utah (USA) and are an ideal setting to explore dryland paleoenvironments. Integration of bulk oxide, micro-XRF, and stable isotopic data allows for assessments of paleoclimate, provenance, and pedogenic processes. Ti/Al ratios track a broadly consistent provenance while Ti/ Zr trends follow allochthonous dust contributions, possibly indicating a shift in paleowinds near the Rico-Halgaito boundary that is supported by Ti/Zr and Zr/Hf ratios from within-zircon analysis. Carbon isotopic data suggest pedogenic carbonate formation under conditions of low soil productivity while modeled MAP estimates reveal an average of 409 mm/yr +/- 209. Evaluation of MAT and MAP relationships suggests that Inceptisols identified within this study could represent ancient Aridisols. We conclude that dry climatic conditions promoted an unstable landscape for the region encompassing the study interval while also precluding hydrolysis and leaching, resulting in weakly developed paleosols with abundant carbonate features and red coloration. These findings are consistent with other work from the region, pointing to dry conditions and shifting paleowinds within paleoequatorial Pangea during the Pennsylvanian-Permian transition.

The lower Cutler beds (i.e., Rico and Halgaito formations) and uppermost Honaker Trail Formation represent the final phase of Paradox Basin sediment fill during the latest Pennsylvanian to Permian and Late Paleozoic Ice Age. Outcrop exposures in the San Juan River canyon near Mexican Hat, Utah, record mixed marine and coastal-plain deposition across the southwestern shelf of the Paradox Basin. The succession was deposited downwind of a major eolian erg and near the probable terminus of an alluvial fan complex derived from the Uncompahgre Uplift, which bounded the Paradox Basin to the northeast. The coastal plain siliciclastics are commonly described as glacially derived "loess." However, fine-grained sediments were more likely derived from eolian processes similar to those of modern temperate to subtropical dryland settings due to the paleogeographic position relative to an eolian erg. Paleosols consist of paleoEntisols, paleoInceptisols, and a paleoVertisol and provide clear evidence of a predominantly arid to semiarid climate including pedogenic carbonate, eolian-derived detrital carbonate, and minerals consistent with weak chemical weathering. A new cyclostratigraphic approach centered around discontinuity-bounded alluvial units is applied to investigate continental depositional cyclicity. The stratal succession provides evidence for possible third-order wetter-drier paleoclimatic shifts based on assessment of facies proportions, alluvial grain-size trends, and inferred depositional processes. Paleosol attributes suggest generally dry conditions during this time, but alluvial grain-size trends, resulting from sediment dispersal via fluvial and eolian processes, may suggest shorter-lived periods of increased precipitation, thus highlighting the complicated nature of precipitation patterns for paleoequatorial Pangea before establishment of the Pangean monsoon.

While woody root structures, such as bald cypress (Taxodium distichum) "knees," can act as conduits of methane (CH4), little has been done to explain variation from this flux pathway. We captured spatial (i.e., across knee surface, within sites, between sites) and temporal dynamics of CH4 from knees, and built empirical models to predict the contribution of knees to net CH4 fluxes. Knee and soil CH4 fluxes were measured across seasons within the lower Mississippi Alluvial Valley in a main channel (semi-permanently flooded), side channel (seasonally flooded), and a reservoir edge (artificially flooded). Knees were a net source of CH4 across all seasons, even during periods of soil CH4 uptake. During periods of high knee CH4 efflux, fluxes varied across the knee surface, decreasing with height from the ground. Knee CH4 fluxes at the main and side channels decreased during a severe drought and increased similar to ten-fold in summer and two-fold in winter following flooding events. At the reservoir edge, knee fluxes differed between the controlled draw up and draw down at the same water level, likely due to differences in temperature and oxygen availability. Knee CH4 fluxes were positively correlated with water level (measured from subsurface wells, above similar to-70 cm in the soil profile) and subsurface temperature, but the strength of the relationships differed across geomorphic positions. Cypress knees appear to be an important contributor to wetland CH4 efflux and accounting for the density of knees is needed to upscale their fluxes and better understand their ecosystem contribution.

The Gona Paleoanthropological Research Project area in the Afar Region of Ethiopia arguably contains one of the most complete records of archaeological sites anywhere in the world, from the earliest Oldowan dated to 2.6 Ma, to the Later Stone Age (LSA) dated to ca. 12-7 Ka. This makes Gona an ideal place to examine long-term trends in hominin-environment interaction. We revisited archaeological and hominin fossil sites at Gona and characterized the fossil soils using paleopedology and found evidence of paleo-Fluvisols, -Cambisols and -Vertisols. Greater than 70% of those archaeological sites spanning Oldowan to the Later Stone Age are found in buried paleosols with A-C and A-Bk-C paleosol profiles resembling modern-day Fluvisols or Fluvic Cambisols. Fluvisol morphology shows presence of bedding, incipient soil structure development and overprinting after burial. Stratigraphy and lithofacies show that these paleo-Fluvisols were proximal to the ancestral Awash River (Type I depositional system) or a distal fan channel (Type II depositional system). These data suggest that soil burial rates were rapid due to proximal flooding, where this would be a primary factor inhibiting soil development. This style of sedimentation and weathering resembles a narrow (5-10 m width) strip of land in a modern-day channel shelf and bar setting, separating the river from the adjacent gallery forest. A review of the literature shows that the frequent association of artifacts with paleo-Fluvisols may be prevalent throughout eastern Africa and indicates a long history of hominin reliance on a riverine ecosystem edge, proximal stream water and gallery forest resources within broader river valleys. The few older archaeological sites (e.g., Oldowan and Acheulian) found in/on more well-developed paleosols at Gona are an exception to this rule. These latter sites may hint at different land-use patterns and thus differing trajectories of hominin-environmental interactions. Because most paleosol studies at Gona and elsewhere in eastern Africa use paleo-Vertisols or other more well-developed calcareous soils to reconstruct paleoenvironment, there is a potential spatial and temporal decoupling between those well-studied paleosols and the more weakly-developed ones where archaeology is found.

Identifying paleosols with aquic conditions is essential for understanding the evolution and distribution of ancient wetland systems. Yet there are no guidelines for paleopedologists for writing field descriptions to target properties that indicate wetness. Here we provide field indicators for aquic conditions modified from the U.S. Soil Taxonomy based on organic materials, matrix color, and iron redoximorphic features. These field-based soil morphological properties have been correlated to numerous hydrological monitoring stations. The universal indicators presented here were developed from four of the eleven mineral soil orders and are the most conservative for identifying aquic conditions across paleosol types. If aquic conditions are not met with these indicators, others are provided for specific taxonomic orders where it is difficult to form or observe aquic indicators; for example, iron rich paleo-Oxisols. Strategies are provided to help separate paleosol properties that may be diagenetically altered from those representing environmental conditions during soil formation prior to burial. The aquic indicators were tested 102 paleosols showing that more than one-fourth were originally mis-identified. However, testing of a stratigraphic succession of two paleosol studies indicated that between 25 and 50 % failed to meet the interpretations of the original investigators. Testing also showed the difficulty of identifying aquic conditions in seasonally wet paleosols, but the indicators provide consistency in how those decisions were made. The aquic condition criteria may be applied to paleosols classified by any taxonomic scheme. This is a first approximation and will require further testing of the indicators provided here.

There is a gap in our understanding of if and how bottomland forest type will affect long-term nutrient cycling and loss. This study aims to determine how different forests affect soil hydrologic variability and whole-soil P loss in a humid-subtropical setting. We used replicate-sampling and measured soil physical, chemical, and miner-alogical properties at 12 sites in two forest ecosystems, post oak (Quercus stellata) and cherry bark oak (Quercus pagoda) in Clarks River National Wildlife Refuge in Western Kentucky. We hypothesize that wetting-drying events in redox soils of forested bottomlands can cause positive feedback in whole-soil P loss. Trees with greater P demand (e.g., post oak) take up more water creating more frequent and pronounced episodes in swelling and shrinking of expandable clays. Repeated swelling and shrinking of clays occlude the surface of Fe-Mn oxides from further adsorption of P in acidic soil. This can lead to greater loss or plant uptake of available P. Our results show (i) a significant difference in mean whole-soil P loss between the oak species with more loss in soils underlying the post oak forest, and (ii) a difference in the total P found in the sap-and heartwood of the two oak species. Soil analysis reveals that the clay mineralogy of the post and cherry bark oak sites are similar, and thus, may only play a minor role in governing the whole-soil P loss difference. However, the leaf data analysis suggests that the post oak site could be P and nitrogen-limited, while the cherry bark is only nitrogen limited. Our study shows that differences in the oak forest ecosystem may affect the long-term balance in water and nutrient uptake and may alter the redistribution of nutrients in the canopy and the underlying soils.

The Busidima Formation in the Afar region, Ethiopia, spans the Quaternary and records the cultural evolution of the genus Homo. Yet, the Middle Pleistocene to Holocene fluvial environments in which early humans lived are undersampled in eastern Africa. This paper examines the stratigraphy, geochronology and paleoenvironments of the newly designated Odele Member of the uppermost Busidima Formation (<152 thousand years ago (ka)), which has received little attention despite representing a critical period in the evolution of early Homo sapiens and its migration out of Africa. The Odele Member is 40-50 m thick and is dated using tephrochronology, radiometric, luminescence, and electron spin resonance techniques. The member spans 151 to 7 ka, defined at the base by the widespread Waidedo Vitric Tuff (WAVT, 151 +/- 16 ka modeled age and 95.4% credible interval - C.I.). There are two prominent erosional unconformities in the Odele Member, a lower one after the WAVT deposition with a modeled 95.4% C.I. range of 124-97 ka; and an upper one involving widespread alluvial fan incision commencing between 21.7 and 12.9 ka. The uppermost Odele Member also contains black, organic-rich mats, redox features, reed casts, and freshwater gastropods marking wetter conditions during the terminal Pleistocene and Early Holocene. A black, fine-grained relict soil coeval with the Halalalee paleosol bounds the top of the Odele Member and has mollic and vertic properties, weathering since similar to 12 ka. These incision events and prominent paleosol development near/at the top of the Busidima Formation document Middle to Late Pleistocene Awash River incision to its present-day course. Paleo-rainfall estimates suggest that the Early Holocene-age Halalalee paleosol weathered under a climate with mean annual rainfall 10-15% higher than today. A compilation of radiocarbon ages from aquatic gastropods, carbonized wood and charcoal from the upper Odele Member shows wetter and possibly more vegetated conditions during late marine isotope stage (MIS) 3 and the African Humid Period (AHP) that are tightly coupled with precession-driven summer insolation maxima. These key findings suggest that periods of incision, aggregation, and landscape stability in the Odele Member have an orbital precession pacing. The Odele Member revises upward the age of the Busidima Formation to 7 ka, showing that it spans into the Holocene and now includes Middle and Later Stone Age archaeological traditions. (c) 2023 Elsevier Ltd. All rights reserved.