Projects

Learn more about projects in the Stinchcomb Lab.

Holocene

Modern mineral-soil wetlands and the carbon cycle

In collaboration with Murray State University and University of Arkansas, we are exploring controls on the soil methane cycle in mineral-soil wetlands in western Kentucky. The Stinchcomb Lab at University of Memphis is focusing on how soil properties influence methane dynamics, especially the key nutrient, phosphorus. (DoE funding, DE-SC0022228)

(ABOVE) Time series plot shows methane flux at the soil surface in two forests (CBO = cherry bark oak; PO = post oak) over portions of the 2022 and 2023 field seasons. Note that the soil ecosystem acts as a methane sink during the summer (forest growth). During the late winter/early spring, there is some indication that the CBO soil may act as a methane source.

The role of oak species in long-term soil P loss in a humid river bottomland

How do functional traits by tree species influence nutrient cycles? This study, funded through the USGS (104b), KWRRI, and DoE, used a replicate soil sampling approach to examine P loss in soils underlying forest stands dominated by cherry bark oak (moist soil) and post oak (drought tolerant species).

We used a combination of moisture, temperature, and salinity based sensor measurements along with dendrochemistry and mass-balance soil geochemistry to quantify the plant-soil P cycle. Image shows Ben Ferguson and Bassil El Masri installing a solar panel to power our soil moisture sensors.

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.

The petrographic images show soil Fe-Mn nodules that vary by forest stand. Specifically, there is variation in the frequency of oriented clay along the exterior of the nodule. We think this may be linked to soil wet-dry cycling, shrink-swell clays and the limiting of P through adsorption onto the Fe-Mn nodules. This process 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.

Stinchcomb, G.E., El Masri, B. and Ferguson, B., 2023. The role of oak species in long-term soil P loss in a humid river bottomland. Catena, 227, p.107125.

Changes in landscape, labor and livelihood during the Post-Classic and Colonial periods in the Tuxtlas, Mexico

In collaboration with Murray State University (Dr. Marcie Venter) and University of Kentucky (Dr. Chris Pool), we are reconstructing the past environments and site formation of late Post Classic and Colonial period sites at the foot of the Tuxtla Mountains (NSF BCS 2050496). Learn more by watching video below.

An excavation unit wall at the Post Classic Mazapa archaeological site, Veracruz, Mexico. The horizons contained numerous lithic and pottery fragments (e.g., right of soil tape at ~28 cm below the surface). A buried Post Classic plaza floor is centered at 60 cm below the surface (Cu horizon).

This wall was sampled extensively and included bulk samples for (isotopic) geochemical and mineralogical analyses, and oriented samples for petrographic analysis. Preliminary results show that the soil layers have a near-neutral to slightly acidic pH and enhanced magnetic susceptibility along the Cu horizon (buried plaza floor). Preliminary stable isotopic measurements on soil organic carbon along nearby landforms suggest a mixture of C3 and C4 plants along the surface. These data are consistent with previous work and conversion of pasture to sugarcane (C4) fields.

(ABOVE) Image showing a portion of the Post Classic Mazapa archaeological site that contains mounds, plaza floors, and a ballcourt. Our 2022 field campaign included a survey of soils along this archaeological site and along nearby upland, hillslope, and fluvial landforms adjacent to the Tecolapan River.

Pleistocene

Fluvial response to Quaternary hydroclimate in eastern Africa: Evidence from Gona, Afar, Ethiopia

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 work 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.

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 10e15% 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.

G.E. Stinchcomb, J. Quade, N.E. Levin et al. Quaternary Science Reviews 309 (2023) 108083.

Figure 11 from Stinchcomb et al. (2023). Wet environment indicators during the middle and late Pleistocene and African Humid Period intervals of the Odele Member. (A) Marine Isotope Stages (MIS) from Lisiecki and Raymo (2005). Also shown is the timing of the Younger Dryas (YD e dashed vertical lines) and African Humid Period (AHP e blue rectangle). (B) General geologic features of the Odele Member discussed in the text, including: Lower Odele Member Unconformity (LOMU), Fw bedded and pedogenically modified black mud (gray shade with wetland symbol) and the Upper Odele Member Unconformity (UOMU). (C) Wet climate intervals from Lake Tana, Ethiopia (Lamb et al., 2018). (D) Radiocarbon summed-probability distributions of aquatic gastropods and black mat charcoal from Gona. These two proxies are inferred to be wet-climate indicators (see Discussion for details). Vertical gray bars denote more frequent wet environments at Gona, based on these summed-probability distributions. The age ranges of the gray bars (cal. yr BP) are shown at the top of figure. Also, note the general timing of the Bahaku and Halalalee paleosols discussed in text. (E) List of Gona archaeological sites with known ages. See Fig. 1 for archaeological site locations and Table 5 for age estimates. (F) June 21 insolation curve for 11 N (Laskar et al., 2004). (G) Frequency histograms showing the % of records with wet indicators from northern Africa (Shanahan et al., 2015). (H) Fe-counts from the MS27PT Nile marginal delta core in the Mediterranean Sea as a proxy for discharge from the Blue Nile (Bastian et al., in review; Revel et al., 2010) (I) Radiocarbon summed-probability distributions of aquatic gastropods and charcoal from paleosols from Ziway-Shala lake system are shown (Gillespie et al., 1983; Benvenuti et al., 2002). (J) Water levels from Lake Abhe (Gasse, 2000).

Revisiting Farre (GfJo2): A Middle Pleistocene Open-Air Site in the Chalbi Desert, Eastern Africa, and Its Implications for Paleoenvironment and Archaeology

The Chalbi Desert, located in eastern Africa, is a significant but often overlooked archive of the Pleistocene and Holocene periods. The region's paleoenvironment and archaeology have not been thoroughly investigated, but one of the most extensive Middle Pleistocene open-air sites, Farre (GfJo2), has recently been revisited and studied alongside other geological sites.

Our on-going work shows that Farre is a lag on a deflated interdune surface that experiences aeolian additions, erosion, and salt-affected soil development in an arid climate. Pedogenic carbonates suggest that Farre was covered by woody grassland vegetation during MIS-4 and MIS-3 pluvials, consistent with nearby alluvial fan progradation constrained at >35 ka. Our work is revealing new insights into the paleoenvironment and archaeology of the Chalbi Desert, emphasizing the need for further research in this area.

Paleosols of hominin archaeological sites at Gona, Afar Depression, Ethiopia

The Gona Paleoanthropological Research Project area in the Afar Region of Ethiopia arguably contains the most complete record of archaeological sites anywhere in the world, from the earliest Oldowan dated to 2.6 Ma, up to Later Stone Age dated to ca. 12-7 Ka. This makes Gona an ideal place to examine long-term trends in hominin-environment interaction. We revisited archaeological sites at Gona and characterized the paleopedology and found evidence of paleo-Fluvisols and -Vertisols. Detailed paleosol characterization is underway.

Image of modern Entisol along the banks of the Awash River. This soil has a thin, ochric epipedon overlying a rooted, bedded sand.

Miocene

Late Miocene to Pliocene environments & climate at the Lothagam fossil site in northern Kenya

Early Miocene environments & climate in eastern Africa

We are collaborating with researchers from several universities (NSF FRES 2021591) to study the role of tectonics and climate on Miocene ecosystems and evolution in eastern Africa. Two field campaigns (2022-23) have yielded >30 detailed paleosol descriptions and ~200 samples for geochemical, mineralogical and petrographic analyses. Results from these efforts are forthcoming.

Preliminary results:

Saslaw, M., Liutkus-Pierce, C., Stinchcomb, G., Shedroff, S., Uno, K., Tweedy, R., Beck, C., Feibel, C., Miller, E., Henkes, G., 2022, Soil Carbonate Clumped Isotope Temperatures and Paleoenvironmental Interpretations from the Miocene of the Turkana Basin, East Africa: Geological Society of America Abstracts with Programs. Vol 54, No. 5, 2022, doi: 10.1130/abs/2022AM-382365

Stinchcomb, G. E., Liutkus-Pierce, C. M., Beck, C., Saslaw, M., Shedroff, S., Minya, A., Winget, M., Tweedy, R., Rowan, C. M., Mana, S., Feibel, C., Henkes, G., Uno, K., 2022, Early Miocene Climate and Landscape Change Inferred from Paleosols at Loperot, West Turkana, Kenya: Geological Society of America Abstracts with Programs. Vol 54, No. 5, 2022, doi: 10.1130/abs/2022AM-383126

Lidar model of a Late Oligocene/Early Miocene fossil tap root in a calcareous and vertic paleosol from Nakwai, Turkana Basin, Kenya (outcrop vertical length = 1 m). Credit goes to Aggrey Minya for discovery and Mae Saslaw (Stony Brook U) for this incredible reconstruction. Move the model with your mouse so you can gain different perspectives of the root trace.

The calcite-cemented sand that fills the root channel is more erosion resisitant than the surrounding matrix, creating the positive relief that is evident in outcrop and in the scan.

Cretaceous - Paleogene

Revisiting the K-Pg boundary along the Mississippi Embayment, western Kentucky

We are revisiting a Cretaceous-Paleogene (K-Pg) sedimentary section in western Kentucky to determine the nature of this stratigraphic boundary and the depositional environments. The K-Pg boundary was previously identified at the site based on pollen, but a detailed sedimentological framework remains lacking for the succession and therefore inhibits interpretation of the nature of the boundary. A combination of stratigraphy and sedimentology are being used to characterize the section in detail.

Petrographic image of large quartz grain with planar deformation features (plane-polarized light image).

Close up view of of large quartz grain with planar deformation features (cross-polarized light image). This is evidence of shock metamorphism likely related to the K-Pg impact.

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