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Sedimentary Deposits (sedimentary + deposit)

Distribution by Scientific Domains

Earth and Environmental Science	80%

Selected Abstracts

Australasian microtektites and associated impact ejecta in the South China Sea and the Middle Pleistocene supereruption of Toba

METEORITICS & PLANETARY SCIENCE, Issue 2 2006
Billy P. Glass
Unmelted ejecta were found associated with the microtektites at this site and with Australasian microtektites in Core SO95,17957,2 and ODP Hole 1144A from the central and northern part of the South China Sea, respectively. A few opaque, irregular, rounded, partly melted particles containing highly fractured mineral inclusions (generally quartz and some K feldspar) and some partially melted mineral grains, in a glassy matrix were also found in the microtektite layer. The unmelted ejecta at all three sites include abundant white, opaque grains consisting of mixtures of quartz, coesite, and stishovite, and abundant rock fragments which also contain coesite and, rarely, stishovite. This is the first time that shock-metamorphosed rock fragments have been found in the Australasian microtektite layer. The rock fragments have major and trace element contents similar to the Australasian microtektites and tektites, except for higher volatile element contents. Assuming that the Australasian tektites and microtektites were formed from the same target material as the rock fragments, the parent material for the Australasian tektites and microtektites appears to have been a fine-grained sedimentary deposit. Hole 1144A has the highest abundance of microtektites (number/cm2) of any known Australasian microtektite-bearing site and may be closer to the source crater than any previously identified Australasian microtektite-bearing site. A source crater in the vicinity of 22° N and 104° E seems to explain geographic variations in abundance of both the microtektites and the unmelted ejecta the best; however, a region extending NW into southern China and SE into the Gulf of Tonkin explains the geographic variation in abundance of microtektites and unmelted ejecta almost as well. The size of the source crater is estimated to be 43 ± 9 km based on estimated thickness of the ejecta layer at each site and distance from the proposed source. A volcanic ash layer occurs just above the Australasian microtektite layer, which some authors suggest is from a supereruption of the Toba caldera complex. We estimate that deposition of the ash occurred ,800 ka ago and that it is spread over an area of at least 3.7 times 107 km2. [source]

Late Bronze Age paleogeography along the ancient Ways of Horus in Northwest Sinai, Egypt

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2008
Stephen O. Moshier
The northwest Sinai contained the eastern frontier of New Kingdom Egypt during the Late Bronze Age. The ancient Pelusaic branch of the Nile Delta influenced the environmental setting of this region at that time. Fortresses were built along the coastal byway through the study area known as the Ways of Horus to protect Egyptian-held territory from immigrants and intruders from Canaan and the Mediterranean Sea. Building on previous geomorphic studies in the region, this paper presents the results of field investigations of Holocene sedimentary deposits, aided by satellite photography, used to create a paleogeographic map that places archaeological sites in their proper environmental context. CORONA satellite photographs from the late 1960s reveal surface features that have been obscured by more recent agricultural development in the region. Canals dug for an agricultural project provided easy access to the shallow subsurface for mapping the extent of Holocene sediments representing barrier coast, lagoon, estuarine, fluvial, and marsh depositional environments. © 2008 Wiley Periodicals, Inc. [source]

ESR isochron dating analyses at Bau de l'Aubesier, Provence, France: Clues to U uptake in fossil teeth

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 7 2001
Bonnie A.B. Blackwell
At Bau de l'Aubesier, Provence, Mousterian artifacts and human teeth occur in inhomogeneous ("lumpy") sedimentary deposits that include bone and tooth fragments and extensive burnt horizons. Electron spin resonance (ESR) isochron analyses of mammal teeth, which use multiple subsamples with different U concentrations, can measure the external dose rate experienced by the tooth regardless of reworking and sedimentary dose rate changes. Isochron analyses do depend on the U uptake model assumed, but can also identify teeth that have experienced secondary U uptake or leaching. Using 11 teeth from six archaeological layers, the isochrons demonstrate that at least three teeth have experienced secondary uptake. For eight teeth, the U uptake has apparently not followed strictly early (EU), linear (LU), or recent uptake (RU), but more closely approximates LU-RU. Comparing volumetrically averaged sedimentary geochemistry with thermoluminescent dosimetry suggests that fossil tissues in the sediment have also experienced LU-RU uptake. LU-RU uptake can explain standard ESR ages that underestimate the true fossil age. © 2001 John Wiley & Sons, Inc. [source]

Archaeogeophysical study on the site of Tell Toukh El-Qaramous, Sharkia Governorate, East Nile Delta, Egypt

ARCHAEOLOGICAL PROSPECTION, Issue 1 2003
H. Ghazala
Abstract The archaeological site of Tell Toukh El-Qaramous, which is located to the south of Abu Kebir, Sharkiya Governorate, was subjected to detailed geophysical studies using magnetic vertical gradient and geoelectric resistivity survey. The success of these surveys depends on the contrast in the physical properties between the dominant sedimentary deposits (clays and sands) and the buried archeological constructions. The area of study occupies about 80 acres at present. It was subjected firstly to a regional geophysical survey to discover the subsurface conditions above one of the most important military fortress that had been constructed to be vanguard of the eastern entry to Egypt during the Ptolemaic age (323,30 BC). Detailed gridded magnetic (0.5 m grid interval) and geoelectric resistivity surveys (2 m grid interval) were also carried out at a selected site of about 50 × 100 m according to the recommendations of the archaeologists who periodically carried out excavation of the archaeological remains. Such surveys could help mapping of the anomalous features that probably reflect the buried archaeological remains. The integrated results of the magnetic gradient images obtained as well as apparent resistivity maps for depths ranges from 1 to 5 m gave fascinating results. The results indicate that the Tell-Toukh El-Qaramous has been built on a buried sand gezira. Also, groups of ancients walls made of mud bricks and some interesting locations of archeological buried artefacts have been delineated. Both the magnetic and resistivity data supported each other and are in good agreement for the same locations of archeological interest. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Paleoproterozoic, High-Metamorphic, Metasedimentary Units of Siberian Craton

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2009
Lena URMANTSEVA
Abstract: Sensitive, high-resolution ion microprobe zircon U,Pb ages of Paleoproterozoic, high-grade, metasedimentary rocks from the south-western part of the Siberian Craton are reported. Early Precambrian, high-grade complexes, including garnet,biotite, hypersthene,biotite, and cordierite-bearing gneisses compose the Irkut terrane of the Sharyzhalgay Uplift. Protoliths of studied gneisses correspond to terrigenous sediments, ranging from greywacke to shale. The paragneiss model Nd ages of 2.4,3.1 Ga indicate Archean-to-Paleoproterozoic source provinces. Zircons from gneisses show core-rim textures in cathodoluminescence (CL) image. Round or irregular shaped cores indicate detrital origin. Structureless rims with low Th/U are metamorphic in origin. The three age groups of detrital cores are: ,2.7, ,2.3, and 1.95,2 Ga. The ages of metamorphic rims range from 1.86 to 1.85 Ga; therefore, the sediments were deposited between 1.95 and 1.86 Ga and derived from Archean and Paleoproterozoic source rocks. It should be noted that Paleoproterozoic metasedimentary rocks of the Irkut Block are not unique. High-grade metaterrigenous sediments, with model Nd ages ranging from 2.3 to 2.5 Ga, are widely distributed within the Aldan and Anabar Shields of the Siberian Craton. The same situation is observed in the North China Craton, where metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 to 2.1 Ga (Wan et al., 2006). All of these sedimentary units were subjected to Late Paleoproterozoic metamorphism. In the Siberian Craton, the Paleoproterozoic sedimentary deposits are possibly marked passive margins of the Early Precambrian crustal blocks, and their high-grade metamorphism was related to the consolidation of the Siberian Craton. [source]