Eolian chronology reveals causal links between tectonics, climate, and erg generation

The onset and intensification of eolian activity mark climatic transitions that promote wide-scale aridification, recorded by the generation and preservation of massive sand deposits. Evaluating the impact and implications of such repositories on Earth systems requires knowledge about the timing of their emplacement and the mechanisms responsible for their generation, which remain highly uncertain. Here we provide time constraints for the establishment of the Kalahari Erg, which is the largest continuous body of sand on Earth. We apply cosmogenic nuclide dating of sand from the Kalahari Desert combined with numerical modeling to determine when sand was introduced into the interior of southern Africa. Through the consideration of several scenarios, we show that major events of eolian sand transport and accumulation occurred between ~2.5 and 1 Myr ago. This substantial activity, which significantly altered environmental settings, corresponds to regional, continental, and global scale morphotectonic and climatic changes that contributed to the mass production and widespread dispersion of sand. These changes substantially altered existing habitats, thus constituting a crucial milestone for hominin evolution and migration throughout the African continent during the Pleistocene.

Tabun Khara Obo impact crater, Mongolia: Geophysics, geology, petrography, and geochemistry

ABSTRACT Tabun Khara Obo is the only currently known impact crater in Mongolia. The crater is centered at 44°07′50″N and 109°39′20″E in southeastern Mongolia. Tabun Khara Obo is a 1.3-km-diameter, simple bowl-shaped structure that is well visible in topography and clearly visible on remote-sensing images. The crater is located on a flat, elevated plateau composed of Carboniferous arc-related volcanic and volcanosedimentary rocks metamorphosed to upper amphibolite to greenschist facies (volcaniclastic sandstones, metagraywacke, quartz-feldspar–mica schist, and other schistose sedimentary rocks). Some geophysical data exist for the Tabun Khara Obo structure. The gravity data correlate well with topography. The −2.5–3 mGal anomaly is similar to that of other, similarly sized impact craters. A weak magnetic low over the crater area may be attributed to impact disruption of the regional trend. The Tabun Khara Obo crater is slightly oval in shape and is elongated perpendicular to the regional lithological and foliation trend in a northeasterly direction. This may be a result of crater modification, when rocks of the crater rim preferentially slumped along fracture planes parallel to the regional structural trend. Radial and tangential faults and fractures occur abundantly along the periphery of the crater. Breccias occur along the crater periphery as well, mostly in the E-NE parts of the structure. Monomict breccias form narrow (<1 m) lenses, and polymict breccias cover the outer flank of the eastern crater rim. While geophysical and morphological data are consistent with expectations for an impact crater, no diagnostic evidence for shock metamorphism, such as planar deformation features or shatter cones, was demonstrated by earlier authors. As it is commonly difficult to find convincing impact evidence at small craters, we carried out further geological and geophysical work in 2005–2007 and drilling in 2007–2008. Surface mapping and sampling did not reveal structural, mineralogical, or geochemical evidence for an impact origin. In 2008, we drilled into the center of the crater to a maximum depth of 206 m, with 135 m of core recovery. From the top, the core consists of 3 m of eolian sand, 137 m of lake deposits (mud, evaporites), 34 m of lake deposits (gypsum with carbonate and mud), 11 m of polymict breccia (with greenschist and gneiss clasts), and 19 m of monomict breccia (brecciated quartz-feldspar–mica schist). The breccias start at 174 m depth as polymict breccias with angular clasts of different lithologies and gradually change downward to breccias constituting the dominant lithology, until finally grading into monomict breccia. At the bottom of the borehole, we noted strongly brecciated quartz-feldspar schist. The breccia cement also changes over this interval from gypsum and carbonate cement to fine-grained clastic matrix. Some quartz grains from breccia samples from 192, 194.2, 196.4, 199.3, 201.6, and 204 m depth showed planar deformation features with impact-characteristic orientations. This discovery of unambiguous shock features in drill core samples confirms the impact origin of the Tabun Khara Obo crater. The age of the structure is not yet known. Currently, it is only poorly constrained to post-Cretaceous on stratigraphic grounds.

The empirical correlation between shear wave velocity and penetration resistance for the eolian sand deposits in the city of Olmos-Peru

Shear wave velocities (Vs) and the number of blows of SPT (N) are parameters that are generally recorded in a geotechnical exploration campaign, in the literature there are several publications on the empirical correlations between N y Vs in different types of soil, the first studies being attributed to Japanese researchers in the 60s and 70s. North Peruvian pipeline was built on a recent quaternary eolian deposit, so a research area in Olmos near to the structure was used for tests. In the geotechnical research campaign were carried out in an arrangement multi-channel and standard penetration test in order to obtain Vs and N respectively. The correlations in this publication are for eolian sand deposits that can potentially be used in other regions with similar characteristics. The correlations presented are; N₆₀ - Vs considering and incorporating into the model the influence of the effective overload.

Seismic response to paleo-sand dunes in the Nugget Sandstone Formation, southwestern Wyoming

We have analyzed a 3D seismic survey acquired for a carbon sequestration project on top of the Moxa Arch in southwestern Wyoming. We observed a zone of discontinuous reflectors on vertical slices of seismic amplitude volume, whereas, the northwest–southeast lineations were observed on the time slices. We performed a seismic to well tie that suggested that the lineations occur within the Nugget Sandstone. The Nugget Sandstone is an eolian sandstone deposit of Early Jurassic age, deposited as a subtropical dune field, and equivalent to the Navajo Sandstone of southwestern Utah. Petrophysical analysis indicates that the Nugget Sandstone is dominated by clean sandstone (70%–80%), whereas evaporites, including halite and anhydrite, are present in certain zones. Previous outcrop studies on the Navajo Sandstone indicate the wind direction to be predominantly northeast–southwest. Seismic attributes, including coherence and curvature, displayed on stratal slices within the Nugget Sandstone interval indicate the presence of lineations in the northwest–southeast direction with irregular spacing. These lineations are approximately perpendicular to the inferred dominant wind direction. We computed the dominant wind direction from the average azimuth of the lineations as seen on the curvature attribute in the Nugget Sandstone interval. Geological feature: Eolian sand dunes with interdunal evaporites Seismic appearance: Parallel lineations with irregular spacing on seismic attribute horizon slices Alternative interpretations: Canyons at continental slopes; slope failures Features with a similar appearance: Marine bars; contourites Formation: The Nugget Sandstone — equivalent to the Navajo Sandstone Age: Early Jurassic Location: Moxa Arch, Wyoming Seismic data: Obtained by the University of Wyoming with U.S. DOE funding Contributors: Dhruv Agrawal, Brady Lujan, Sumit Verma, Shuvajit Bhattacharya, and Subhashis Mallick Analysis tools: Coherence and curvature attributes; seismic inversion; petrophysical inversion

Onset of permanent Taklimakan Desert linked to the mid-Pleistocene transition

The initial occurrence of desert landscape or eolian sand dunes is thought to have occurred long before the Pleistocene, and desertification was subsequently enhanced under cold, dusty glacial conditions. However, when and how the desert landscape persisted during both glacial and interglacial periods, defined as “permanent” desert here, remain elusive. Here, we present carbonate carbon isotope and grain-size records from the Tarim Basin, western China, revealing a detailed desertification history for the Taklimakan Desert. Our records demonstrate that after desiccation of episodic lakes at ca. 4.9 Ma, alternations of eolian sand dunes and fluvial and playa-like conditions persisted for a long period until 0.7 Ma in the Tarim Basin. The onset of permanent desert landscape around 0.7–0.5 Ma occurred concurrently with the climatic reorganization across the mid-Pleistocene transition. The occurrence of mountain glaciers on the Tibetan Plateau and atmospheric circulation changes may have controlled the formation and extreme aridification of the permanent desert in inland Asia since the mid-Pleistocene transition.

Preliminary Map Showing Quaternary Geology of the Mooresville East 7.5-Minute Quadrangle, Indiana

The Mooresville East 7.5-minute quadrangle is situated near the maximum limit of Wisconsin Episode glacial deposits in northeastern Morgan County. Till and outwash of Wisconsin Episode age and Holocene alluvium are the dominant surficial materials in the quadrangle. Wisconsin Episode eolian sand, loess, and colluvium are also present, with eolian sand and colluvium being adjacent to the West Fork White River valley and loess blanketing Wisconsin Episode till and outwash. Holocene (post-glacial) alluvium is found in the West Fork White River and White Lick Creek valleys and tributaries. Mississippian Borden Group bedrock controls many aspects of the surficial geology of the southeastern sector of the quadrangle. For much of this area, bedrock controls the topography and is less than 20 ft below the ground surface. It is mantled on the summits and shoulders of interfluves mainly by Wisconsin till and minor amounts of sand and gravel (outwash) and eolian sand. The depth to bedrock (Borden Group) is greater along the trend of the modern West Fork White River valley, with depths greater than 100 ft. This bedrock paleovalley is filled with mainly Wisconsin Episode outwash (sand and gravel), and the paleovalley was a major path for meltwater in central Indiana during the Wisconsin Episode, from around 27,000 to 19,000 years ago. The Wisconsin Episode maximum limit lies just outside the quadrangle boundary to the south and east. The Laurentide Ice Sheet reached its maximum limit 24,000 years ago, based on radiocarbon dating of organics within till at the terminal moraine in the adjacent Cope quadrangle. Evidence for a readvance of the ice sheet is found in the Mooresville East quadrangle, which occurred 21,700 years ago; the southern limit of the readvance runs through the central part of the quadrangle, just south of State Highway 144.

An Early Iron Age Camp of Reindeer Hunters in the Bolshezemelskaya Tundra, Nenets Autonomous Okrug

This study outlines the fi ndings of excavations at More-Yu II—a site in the northern Bolshezemelskaya tundra. The habitation layer with numerous charcoal lenses was discovered inside the layer of buried soil overlain by eolian sand. Most fi nds are ceramics and animal bones. Arrowheads, o rnaments, tools, and ritual items are very rare. On the basis of palynological and faunal analyses, environmental changes from the sub-boreal warming until the end of the sub-Atlantic period are reconstructed. The temperature regime during the formation of cultural deposits was unstable. The principal subsistence strategy was reindeer hunting. The age of reindeer suggests that habitation periods coincided with cold seasons. Radiocarbon dates generated from reindeer bones point to the Early Iron Age. The camp dwellers were native reindeer hunters inhabiting the tundra belt of northeasternmost Europe. Ceramics representing the More-Yu type belong to the early stage of the Subarctic Pechora culture. They mark the Arctic component that became part of the n orthern Glya denovo population, abruptly changing the Finno-Permic culture of the taiga part of the Pechora basin in northern Urals.