Deposits In Central Asia Research Articles

TO CORRELATE OR NOT TO CORRELATE--THAT IS NOT THE QUESTION ANYMORE! CONTINENTAL LATE JURASSIC TO EARLY CRETACEOUS SUPRAREGIONAL CORRELATION BASED ON FRESHWATER TO BRACKISH-WATER OSTRACODES

On several occasions at paleontology-, geology-, and stratigraphy-related meetings during the past years, I noticed that many colleagues, even micropaleontologists, are not (anymore!) aware of the fundamental application potential of pre-Quaternary, fresh- and brackish-water ostracode fossils. Ostracodes, aquatic crawling or swimming microcrustaceans with a calcified bivalved shell and high fossilization potential, have rarely been considered as a major tool in biostratigraphy, fading mostly into the background compared to other fossil groups in the marine realm. In the continental realm, however, ostracodes are often the most common and abundant fossils, whether in freshwater or saline deposits. Yet, supraregional and intercontinental biostratigraphy based on aquatic organisms sounds absurd. It is not, however! Fresh- and brackish-water ostracodes have developed different strategies and mechanisms to facilitate their adaptation to temporary habitats and dispersal in such settings. Recent fresh- and brackish-water ostracodes, just as did their fossil counterparts, have a high potential to be passively distributed over long distances and across migration barriers by wind and larger animals, particularly owing to the desiccation- and freeze-resistant resting eggs of major groups (e.g., Horne and Martens, 1998) and, therefore, are a strong candidate for biostratigraphic application. Dealing with biostratigraphy of Lower Cretaceous continental deposits, it is important to understand that in most regions, except western Europe, we are not necessarily talking about high-resolution biostratigraphy. For example, many publications to-date on such deposits in Central Asia, South America, and Africa only provide an age of Early Cretaceous without further subdivision, and no attribution to stages. In the North American Western Interior foreland basin, Lower Cretaceous continental deposits are widely regarded to be of pre-middle Albian age, or to range from Aptian to Albian, sometimes Barremian–Albian in age (e.g., Cobban and Reeside, 1952; Peck, 1959; Mateer et al., 1992; Dyman et al. 1994; Way et …

End-Permian to mid-Triassic termination of the accretionary processes of the southern Altaids: implications for the geodynamic evolution, Phanerozoic continental growth, and metallogeny of Central Asia

The Altaids is one of the largest accretionary orogenic collages in the world with the highest rate of Phanerozoic continental growth and significant metallogenic importance. It is widely accepted that subduction-related orogenesis of the Altaids started in the late Precambrian and gradually migrated southward (present coordinates). However, it is uncertain when and how the building of the Altaids was finally completed. Based on structural geology, geochemical, geochronological, and paleomagnetic data, this paper presents late Paleozoic to early Mesozoic accretionary tectonics of two key areas, North Xinjiang in the west and Inner Mongolia in the east, together with neighboring Mongolia. The late Paleozoic tectonics of North Xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of Siberia and its final amalgamation with the passive margin of Tarim, which may have lasted to the end-Permian to early/mid-Triassic. In contrast, in Inner Mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of Siberia and the northern active margin of the North China craton, which may have lasted to the mid-Triassic. The final products of the long-lived accretionary processes in the southern Altaids include late Paleozoic to Permian arcs, late Paleozoic to mid-Triassic accretionary wedges composed of radiolarian cherts, pillow lavas, and ophiolitic fragments, and high-pressure/ultrahigh-pressure metamorphic rocks. Permian Alaskan-type zoned mafic-ultramafic complexes intruded along some major faults of the Tien Shan. We define a new Tarim suture zone immediately north of the Tarim craton that is probably now buried below the Tien Shan as a result of northward subduction of the Tarim block in the Cenozoic. The docking of the Tarim and North China cratons against the southern active margin of Siberia in the end-Permian to mid-Triassic resulted in the final closure of the Paleoasian Ocean and terminated the accretionary orogenesis of the southern Altaids in this part of Central Asia. This complex geodynamic evolution led to formation of giant metal deposits in Central Asia and to substantial continental growth.

THE PALEOZOIC SEDIMENTS OF THE FERGANA BASIN: THEIR POTENTIAL FOR OIL AND GAS

The Paleozoic deposits of Central Asia, including the Fergana basin, are considered by most investigators to be basement rocks, strongly deformed and highly metamorphosed, and as such to offer no prospects for discovering significant deposits of oil or gas. However, up till now, the Paleozoic sediments of the Fergana basin, or for that matter of the whole of Central Asia, have not been studied specifically from the aspect of their possible petroleum content, although there are many positive examples in the area. The author has made an attempt to analyze the composition and the structural-textural features of these sediments in order to determine the reservoir properties of the rocks and the possible accumulation of hydrocarbons in them. Geochemical, lithological, petrographic, and geological data are described. The author asserts that the data point to the Karatau-Guzan-Korachatyr zone, a deep trough with thick Paleozoic clastic and carbonate sequences which contain organic matter, to a certain degree transformed into liquid and gaseous hydrocarbons, as the primary target for drilling to test the petroleum prospects of the Paleozoic sediments. 10 references, 1 figure.

Oxygenisotope features of cassiterites from tin-ore deposits of Central Asia

(1979). Oxygenisotope features of cassiterites from tin-ore deposits of Central Asia. International Geology Review: Vol. 21, No. 8, pp. 937-944.

Loess deposits associated with deserts

The division of loess deposits into warm/desert and cold/glacial is well entrenched in the literature. The nature and distribution of glacial loess are well accounted for but doubts have been cast on the existence of a true desert loess, i.e. a loess consisting of silt particles actually formed in a desert region. It appears that the loess deposits in Central Asia and North China were formed from silt particles transported out of adjacent deserts — but the particles themselves had their origins in glacial grinding and cold weathering processes in the adjacent mountains. Thus the deserts close to mountainous areas tend to have associated loess deposits. Deserts which are not particularly associated with mountains, e.g. the Sahara and Australian deserts, do not have large loess deposits nearby. Some loess deposits in the Persian/Arabian Gulf region have been observed which consist of silt-sized carbonate particles; a separate division of carbonate loess is proposed. Large scale silt formation is still one of the consequences of glacial action, however it is apparent from recent studies of quartz clasts that glacial grinding is not such an exclusive quartz silt producer as was once proposed. Much coarse-silt-sized quartz is produced directly by weathering of igneous rocks, but there appears to be little doubt that the vast majority of the silt particles for the loess deposits of the world were formed as a consequence of glacial action and cold weathering — and this includes the deposits in Central Asia and North China. Die Gliederung von Lößablagerungen unter Bedingungen eines warmen Wüsten— und eines kalten Glazialklimas ist in der Literatur weit verbreitet. Die Eigenschaften und die Verteilung von glazialem Löß sind hinreichend beschrieben, dagegen wird die Existenz von echtem Wüstenlöß angezweifelt, d.h. von Löß, der aus Schluffpartikeln besteht, die tatsächlich in einem Wüstengebiet gebildet worden sind. Es scheint, daß die Lößablagerungen in Zentralasien und Nordchina aus Schluffen gebildet wurden, die aus den benachbarten Wüsten herantransportiert wurden. Die Schluffpartikel selbst jedoch entstanden durch Frostverwitterung und glazigenem Abrieb in den benachbarten Gebirgen. Deshalb sind Wüsten in der Nähe von Gebirgen gewöhnlich mit Lößablagerungen verbunden. Wüsten, die nicht mit ausgedehnten Gebirgen vergesellschaftet sind, z.B. die Sahara und die Australischen Wüsten, haben keine großen Lößvorkommen in ihrer Nähe. Im Bereich des Persisch-Arabischen Golfes sind Lößablagerungen beobachtet worden, die aus Kalkpartikeln von Schluffgröße bestehen; daher wird eine getrennte Benennung in Karbonatlöß vorgeschlagen. Schluffbildung im großen Stil ist immer noch eine Folge kaltklimatischer Morphodynamik. Aus neueren Untersuchungen von Quarzpartikeln geht jedoch hervor, daß glazigener Abrieb keineswegs so ausschließlich Quarzschluff produziert wie früher angenommen wurde. Ein großer Teil der groben Quarzschluffe wird direkt durch Verwitterung der Tiefengesteine erzeugt. Doch scheint es wenig zweifelhaft, daß die überwïegende Mehrheit der Schluffpartikel der Lößvorkommen der Erde als Folge glazialer Bedingungen und der Frostverwitterung gebildet wurde — dies schließt die Ablagerungen in Zentralasien und Nordchina ein.

Physicochemical conditions of endogene processes in copper-molybdenum deposits in Central Asia

The evolution of mineral-forming solutions in copper-molybdenum deposits of Kuznetsk Alatau, Eastern Transbaikalia, and Middle Asia is considered on the basis of the study of gas-liquid inclusions in minerals of different stages and mineral assemblages. The data permit estimation of the temperature, the state of aggregation, the composition, and the pressure of the solutions at various stages. K-feldspathization was caused by gaseous solutions at 730 degrees to 400 degrees C and pressures over 1,400 atm. Argillic and sericitic rocks formed from near-critical and liquid solutions at 430 degrees to 320 degrees C. Silicification took place in a wide temperature range between 800 degrees and 200 degrees C that varied in state of aggregation from gaseous to critical to liquid. The principal ore deposition occurred from liquid solutions enriched in carbon dioxide at 400 degrees to 200 degrees C. Essential differences can be shown in the chemical composition of the solutions forming various deposits. Solutions from deposits of Kuznetsk Alatau are essentially fluoride during the early stages and fluoride-carbonate rich at later stages. Those of Eastern Transbaikalia deposits are rich in chloride at early stages, chloride and carbonate at later stages. Those of Middle Asia deposits are rich in chloride.

Typomorphism of mineral parageneses of native bismuth in rocks and deposits of Central Asia

Typomorphism of mineral parageneses of native bismuth in rocks and deposits of Central Asia

Sonic aerosol filtering devices: Abboud, H.I., US Patent 3, 413, 781 (3 December 1968) (Filed 15 August 1966) (1259)

Loess deposits in Central Asia provide an important record of regional climate and environmental change. However, in contrast to the intensively investigated loess deposits on the Chinese Loess Plateau (CLP), loess sediments in the Ili Basin of eastern Central Asia are poorly understood. Based on field investigation and existing literature, this paper presents a preliminary study of the distribution, strata and composition of the Ili loess. The distribution of the Ili loess is clearly controlled by topographic and geomorphic conditions, mainly in the river terraces, low uplands, and slopes of the Tianshan Mountains. The thickness of the loess varies from several meters to over two hundred meters. To characterize the Ili loess composition, the authors analyzed its grain size, geochemistry, X-ray diffraction pattern and heavy mineral assemblage. Grain size analyses reveal that the Ili loess consists predominantly of silt (4–63 μm) with a minor proportion of sand, which is coarser than the loess of the CLP and suggests a nearby provenance. The bulk mineral components of the Ili loess are dominated by quartz and feldspar with minor amounts of calcite, chlorite, mica, dolomite and hornblende. More than 20 types of heavy minerals were observed with major components of amphibole, magnetite and epidote. The major elements of the Ili loess are characterized by high abundance of SiO2, Al2O3 and CaO and minor amounts of Fe2O3, MgO, Na2O and K2O. Compared to the CLP loess, the Ili loess is relatively rich in Na2O and displays higher Na2O/Al2O3 ratios, suggesting weak weathering. The distribution patterns of REEs indicate that both the Ili loess and CLP loess are of typical upper crustal composition, with enrichment in LREE, negative Eu anomalies, and depletion of HREE. Both the heavy mineral assemblage and geochemistry indicate that the local bedrock of the Ili Basin may have contributed only a little to the loess sediments.

Composition of subsurface waters in certain mercury-antimony deposits in Central Asia

In the Khaydarkan and the Karasu ore fields, mercury is present in outcropping subsurface waters (fractions of one microgram per liter), and is enriched significantly in sediments of the springs. The fig content of waters circulating in carbonate rocks is higher, almost by a whole order of magnitude, than in aluminosilicate rocks. The waters are of the HCO3 and SO4 type, low in Na and Cl, at pH 5 to 6. 5, T. S. at 200 to 600 ppm; traces of Sb, As, Zn, Cu, Sr, Ba, others are present. -- V. P. Sokoloff.

Riphean and Cambrian of central Asia

Mountain structures of Central Asia are made up largely of Riphean and,Cambrian deposits that are continuous and consistent over thousands of kilometers. It is quite probable that a discrete tectonic belt existed in the Urals, Central Asia, and North China in the Riphean and Cambrian. The Riphean is late Precambrian and Early Cambrian. Shatskiy assigned a type of Riphean locality in the F3askirian Urals. Riphean deposits of Central Asia begin with well-sorted quartz sands (metamorphosed to quartzites), locally ferruginous. Ripple marks and mudcracks indicate a shallow environment. The quartzites are locally interbedded with shales, siltstones and carbonates. Thick conglomerates at the base of the Riphean are present only farther east, in the Utaishan and Taihangshan, eastern Shansi. Still farther east, in the Liaotung Peninsula and North Korea, the basal conglomerates are absent or restricted. The boundary, between Riphean,and older rocks is definitely known only from transition regions between troughs an...

Selenium in palaeogene deposits of Central Asia

Selenium in palaeogene deposits of Central Asia