Gail M. Ashley

Gail M. Ashley
Rutgers, The State University of New Jersey | Rutgers · Department of Earth and Planetary Sciences

PHD University of British Columbia Vancouver Canada

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166
Publications
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Publications

Publications (166)
Article
Kisima Ngeda (KN), a spring on the northern margin of saline Lake Eyasi, Tanzania, sustains an Acacia-Hyphaene palm woodland and Typha swamps, while the surrounding vegetation is semi-desert. To study the vegetation changes associated with this spring, which represents a plausible modern analog for the fossil springs documented in the nearby paleoa...
Chapter
Springs are ecosystems influenced by the exposure of groundwater at the Earth's surface. Springs are abundant and have played important, highly interactive ecological, cultural, and socio-economic roles in arid, mesic, and subaqueous environments throughout human evolution and history. However, springs also are widely regarded as being highly threa...
Article
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The Critical Zone (CZ) as visualized in 1998 was a way to integrate the research of the four scientific spheres (lithosphere, hydrosphere, biosphere and atmosphere) at the surface of Earth and to study the linkages, feedbacks and record of processes. Rather than closeting studies by a variety of disciplines into their respective pigeonholes the CZ...
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Plain Language Summary Lake sediments contain a rich archive of information about past climate change. Clay minerals in such sediments, in particular, can potentially provide important insight into changes in humidity and aridity in the terrestrial environment by recording changes in precipitation as reflected in lake salinity. Until now, the clima...
Article
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Freshwater limestones are uncommon in the sedimentary record of the East African Rift System. Recent research in the Olduvai Basin, Tanzania has revealed an extensive carbonate unit ~ 1.8 Ma in age that varies spatially in thickness, petrography, trace element and rare earth geochemistry, C and O isotope values and freshwater microfossils. Five dis...
Article
The sedimentary and biological material preserved in wetlands in semi-arid regions provide a rich repository of paleoclimate and paleoecological archives. These records reflect an underutilized, but typically ignored paleoenvironmental resource in semi-arid settings. The results presented here demonstrate that groundwater-fed wetlands constitute a...
Article
The sedimentary and biological material preserved in wetlands in semi-arid regions provide a rich repository of paleoclimate and paleoecological archives. These records reflect an underutilized, but typically ignored paleoenvironmental resource in semi-arid settings. The results presented here demonstrate that groundwater-fed wetlands constitute a...
Article
Hominins evolved in Africa during a period of overall regional cooling, drying and increasingly variable climate. Despite prevailing regional aridity since the mid-Miocene, data show that early hominins Sahelanthropus tchadensis, Orrorin tugenensis, and Ardipithecus ramidus lived in environments made of mosaics of grasslands, mixed grasslands, wood...
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Dongodien (GaJi4) is a sequence of sub-lacustrine, beach, and sub-aerial lake margin sediments of the Galana Boi Formation at Koobi Fora, Lake Turkana, Kenya. The sediments accumulated under a climate of increasing aridity in the latter African Humid Period. The section contains two archaeologically rich beds (Horizons B and A). Here, we present ne...
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Water is a fundamental resource, yet its spatiotemporal availability in East Africa is poorly understood. This is the area where most hominin first occurrences are located, and consequently the potential role of water in hominin evolution and dispersal remains unresolved. Here, we show that hundreds of springs currently distributed across East Afri...
Data
Supplementary Figures and Supplementary Tables
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The paleoclimatic framework of human evolution is central to the study of human origins. Olduvai Gorge, Tanzania, has a rich paleontological record, including four hominin species. We analyzed 177 mudstone samples from a lacustrine section, supported by a new high-resolution geochronology, to track changes in paleolake water chemistry. Six peaks in...
Article
We have analyzed the phytolith content of 37 samples from the paleosol capped by Tuff IC dated 1.84 Ma within Middle Bed I at Olduvai Gorge, Tanzania. Samples were obtained from different trenches sampling an area of about 25 ha to document the paleovegetation associated with the abundant faunal remains and hominin artifacts in FLK, AMK, PTK and DS...
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Playa lake systems tend to be overlooked archives of paleoenvironmental change due to the likelihood of a short and intermittent record of deposition. Groundwater-fed wetlands associated with these climate-sensitive playas, however, preserve changes in hydrologic budget and are thus valuable archives for semiarid regions. This study examines the pa...
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The availability of plants and freshwater shapes the diets and social behavior of chimpanzees, our closest living relative. However, limited evidence about the spatial relationships shared between ancestral human (hominin) remains, edible resources, refuge, and freshwater leaves the influence of local resources on our species' evolution open to deb...
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Few proxies exist to identify aridity in the depositional record, even though drylands cover ~30% of the modern continental surface. New exposures in a siliciclastic and carbonate sequence in an arid to hyperarid basin at Olduvai Gorge, Tanzania provide a unique multi-proxy record of a 1.85 Ma landscape that was exploited by early humans. The 2 m t...
Conference Paper
Full-text available
Olduvai Gorge is located in northern Tanzania (3°S, 35.35°E) on the Serengeti Plain and on the margin of the East Africa Rift System. Seventy-nine sediment samples were collected during the 2015 field season from a 6-meter high section of lacustrine sediment (~1.9-1.86 Ma). Samples were collected at ~15 cm intervals from 50 cm to 580 cm. The purpos...
Conference Paper
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Paleoenvironmental reconstructions are critical to fully understanding paleoclimate change and hominin evolution. Authigenic clays have been identified as a potential proxy for paleoclimate change because Mg-rich clays form in saline and alkaline conditions. With these minerals as a proxy, we can identify fluctuations between saline and freshwater...
Article
Paleosols record paleoclimatic processes in the Earth's Critical Zone and are archives of ancient landscapes associated with archeological sites. Detailed field, micromorphologic, and bulk geochemical analysis of paleosols were conducted near four sites at Olduvai Gorge, Tanzania within the same stratigraphic horizon as the Zinjanthropus (Paranthro...
Article
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The Olduvai Basin (3° S), situated just west of the East African Rift System in northern Tanzania, contains a two-million-year record of paleoclimate and paleoenvironmental change, as well as a rich archive of vertebrate paleontology (including hominins). Milankovitch precession cycles ( ∼ 20 kyr) regulate the mean annual precipitation (250-700 mm/...
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Groundwater is essential to modern human survival during drought periods. There is also growing geological evidence of springs associated with stone tools and hominin fossils in the East African Rift System (EARS) during a critical period for hominin evolution (from 1.8 Ma). However it is not known how vulnerable these springs may have been to clim...
Article
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Olduvai Gorge, Tanzania contains a rich record of Pleistocene paleoclimate and paleoenvironment, as well as an abundance of paleontological and archaeological data. The 2.2 Ma of volcaniclastic infill can be divided into time-slices using dated tuffs. Sediments were deposited in a semi-arid, closed rift basin containing a shallow saline–alkaline la...
Article
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The multi component FLK North archaeological site was discovered over 50 years ago, and its inter-pretation has been highly controversial since. Explanations of the dense bone and stone tool accumu-lation range from a site on a featureless lake margin that is dominantly anthropogenic in origin to a site near a freshwater wetland that is dominated b...
Article
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Olduvai Gorge, Tanzania is known for its fossil and cultural record of early hominins. The archaeological records are typically found within pedogenically modified sediments, thus the interpretation of paleosols provides important paleoenvironmental context information. The Gorge contains a rich and diverse record of paleosols that vary spatially a...
Article
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Recent excavations in Level 4 at BK (Bed II, Olduvai Gorge, Tanzania) have yielded nine hominin teeth, a distal humerus fragment, a proximal radius with much of its shaft, a femur shaft, and a tibia shaft fragment (cataloged collectively as OH 80). Those elements identified more specifically than to simply Hominidae gen. et sp. indet are attributed...
Article
FLK North is one of the densest concentrations of fossils found in Olduvai Gorge. A recent taphonomic re-evaluation of the collection excavated by Leakey at the site suggests that it was a palimpsest in which most of the animals were accumulated and modified by carnivores. The lithic tools therefore seem to have an independent depositional history...
Article
From excavation at FLK North levels 1–2 in 1960–1962, Mary Leakey reported approximately 1200 Oldowan artifacts and 3300 large mammal fossils as a hominin "living floor". Preliminary taphonomic analysis by Bunn seemed supportive, based on the presence of some cut-marked bones, the concentration of several dozen bovid individuals, and the relative a...
Article
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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...
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The role of savannas during the course of early human evolution has been debated for nearly a century, in part because of difficulties in characterizing local ecosystems from fossil and sediment records. Here, we present high-resolution lipid biomarker and isotopic signatures for organic matter preserved in lake sediments at Olduvai Gorge during a...
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Water and its influence on plants likely exerted strong adaptive pressures in human evolution. Understanding relationships among water, plants, and early humans is limited both by incomplete terrestrial records of environmental change and by indirect proxy data for water availability. Here we present a continuous record of stable hydrogen-isotope c...
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Meat-eating was an important factor affecting early hominin brain expansion, social organization and geographic movement. Stone tool butchery marks on ungulate fossils in several African archaeological assemblages demonstrate a significant level of carnivory by Pleistocene hominins, but the discovery at Olduvai Gorge of a child's pathological crani...
Article
Recent excavations at FLK North (Olduvai Gorge, Tanzania) have produced new information on the orientation of archaeological materials at various levels of the site. This information includes the uniform distribution of material azimuths, which contrasts with previous inferences of highly patterned orientations of materials in the Bed I archaeologi...
Article
Laser-induced breakdown spectroscopy will be used by the ChemCam instrument on the Curiosity rover to obtain chemical analyses of the martian surface. Surficial and deeper hydrothermal processes on Mars have produced a diverse family of chemical and clastic sedimentary lithologies from primary igneous rocks through physical and chemical transport,...
Article
Hominin evolution took place in Africa during the Plio-Pleistocene and climate change is thought to be a factor, with Africa experiencing a general cooling and increasing aridification over the last several million years. Today, the climate of the East African Rift Valley of Kenya is characterized as semi-arid with evapotranspiration four times pre...
Article
The Holocene was time of dramatic climate change in East Africa, shifting from wetter climate in the Early–Mid Holocene (∼10–5ka) to drier climates in the Late Holocene, followed by a slight reversal at <1ka. The Holocene was a time of cultural change from hunter-gatherer and fishing to pastoralism. Recent excavations along the eastern shores of La...
Article
LIBS will be used by the ChemCam instrument on MSL to obtain chemical analyses. This study examines accuracies that result from using combinations of different rock types and minerals in the training set used for calibration by multivariate analysis.
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The stratigraphic record of 137Cs activity levels found in Pitt Lake, British Columbia, mimics the radioactive fallout values for 137Cs and 90Sr recorded in milk from the adjacent Fraser Valley. The Pitt Lake record closely parallels the fallout values obtained in England, Alabama, and Lake Michigan. The presence of 137Cs in Pitt Lake sediments is...
Article
Paleoclimate studies increasingly apply the hydrogen isotopic composition of individual biomarkers as a proxy for the composition of environmental waters. However, the environmental, physical and ecologic influences on hydrologic signatures are complex. Here, we separate the influences of climate and physiology on the hydrogen isotopic compositions...
Article
The 1959 discovery of the hominin fossil Zinjanthropus boisei brought the world's attention to the rich records at Olduvai Gorge, Tanzania. Subsequent excavations of archaeological level 22 (FLK Zinj) Bed I uncovered remains of Homo habilis and a high-density collection of fossils and Oldowan stone tools. The occurrence of this unusual collection o...
Article
Renewed excavations at FLK Zinj and its surrounding landscape have yielded valuable information regarding its paleoecological situation and the prehistoric behavioral function of the site. The density of materials at the main cluster of the site excavated by Leakey contrasts with the bone and lithic scatters surrounding the site. The location of FL...
Article
The phytolith content of 10 samples collected immediately under Tuff IF (~ 1.785 Ma) at FLK N and other surrounding localities (~ 2 km²) provides a direct botanical evidence for woody vegetation in the eastern margin of Olduvai Gorge during uppermost Bed I time. Observation and counting of 143 phytolith types (5 to >150 μ) reveal dense but heteroge...
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Recent work at FLK North (FLK N) has unearthed a new archaeological assemblage recovered with precise control of its stratigraphic position. In the present work, the technological study of the new lithic sample is described. The results show the co-occurrence in the same site of different technological behaviors. At FLK N, hominins were involved in...
Article
The records of early hominins are commonly localized both temporally and spatially even in archaeologically rich basins like Olduvai Gorge, Tanzania. The FLK North site was discovered in 1960, but the reason for the exact location of this dense concentration of fossils and stone tools on a lake-margin flat has not been explained. We present new geo...
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Recent field work at Olduvai Gorge (Tanzania) using sedimentary geology, in particular high-resolution paleoenvironmental reconstruction and isotope geochemistry, has revealed that freshwater was in proximity to a number of the rich fossil sites in Beds I and II (similar to 2.0-1.0 Ma). This paper presents the first geological evidence for springs...
Article
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Lithological and biological features of a fossiliferous tufa in the Kapthurin Formation, Baringo, Kenya, reveal the presence of a lush wetland in a semi-arid environment during the Middle Pleistocene (ca 500 ka) in this portion of the East African Rift Valley. Four geological sections, each between 3 m and 8 m in thickness, exposed over a distance...
Chapter
This paper examines the effect of tide-induced flow reversals on sediment transport and channel morphology in the riverine–estuarine transition zone of the Raritan River, New Jersey, U.S.A. The Raritan (drainage area 2862 km²) has a mean annual discharge of 52 m³ sec⁻¹, and is about 100 km long, with the lower 26 km being tidally affected. There ar...
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An interdisciplinary study of the geologic and archaeological records of a 50 ky year period at the Plio-Pleistocene boundary in Olduvai Basin (Tanzania) revealed that a small groundwater-fed wetland was a consistent focus of hominin activity during periods of climate change (wet/dry cycles). Paleoenvironmental analysis of sedimentary records from...
Article
An inventory of Loboi swamp was undertaken to determine the macrophyte diversity and distribution. A total of 36 vascular plant species in 13 families were recorded, with Cyperaceae forming over 30% of macrophytes. Two vegetation zones were observed, characterised by the presence of Typha and papyrus. The Typha zone, comprising over 70% of the swam...
Article
Studies of African faunal evolution suggest intensified mammalian speciation and migration during the Plio- Pleistocene (c. 1.85 Ma) was triggered by regional aridification and high-amplitude climate variability. Marine sedimentological and stable isotopic studies indicate a changing moisture balance in East Africa during this time was paced by orb...
Article
The East African Rift (EAR) system may be a good Earth analogue for martian surface sediments. Seventeen EAR samples were probed with a remote LIBS instrument designed to replicate the ChemCam instrument at a 9 m standoff distance.
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A wide range of rhizoliths occurs around the margins of Lake Bogoria, Kenya. These include root casts, moulds, tubules, rhizocretions, and permineralised root systems. These rhizoliths are variably composed of opaline silica, calcite, zeolites (mainly analcime), fluorite, and possibly fluorapatite, either alone or in combinations. Some rhizoliths a...
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The lithostratigraphy at the Pliocene-Pleistocene boundary exposed in Olduvai Gorge, East Africa, was used to determine the duration and cause of climate variations (wet-dry periods). The area has rich paleontological and archaeological records, and the time interval is a critical period in human evolution. Five episodes of lake expansion and contr...
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Paleosol carbonates from trenches excavated as part of a landscape-scale project in Bed I of Olduvai Gorge, Tanzania, were analyzed for stable carbon and oxygen isotopic composition. The approximately 60,000-year interval ( approximately 1.845-1.785 Ma) above Tuff IB records evidence for lake and fluvial sequences, volcanic eruptions, eolian and pe...
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Over the past two and a half decades, new techniques for studying climate change, applied especially to deep-sea drill core records, have driven the development of environmental forcing hypotheses of human evolution. These hypotheses link specific climate transitions in the Neogene (23 to 2 million years ago) or changes in Neogene climate variabili...
Article
The East African Rift Valley is characterized as an arid to semi-arid region, with several large, well studied, alkaline lakes; within the region, freshwater wetlands persist. These wetland systems, locally are important sources of freshwater. They also provide overlooked important paleoclimate archives, as the fragile ecology of these wetlands can...