Discovery of Early Proterozoic Carbon Isotope Shifts

The authors have detailedly and systematically studied the carbon isotopic composition of Early Proterozoic carbonate rocks. Samples which are all dolomicrite were taken from the Jianancun, Daguandong and Huaiyincun Formations of the Hutuo Group in Wutai County Shanxi Province, North China. A total of 209 samples were analysed for their carbon isotope compositions, and the mean sampling interval was 6.9 m. Carbon isotope analysis clearly shows δ13C shifts at the boundary between the Jian'ancun Formation and Daguandong Formation and near the boundary between the Daguandong Formation and Huaiyincun Formation. Like carbon isotope shifts at the Cretaceous-Tertiary, Permian-Triassic and Precambrian-Cambrian boundaries, the discovery of δ13C shifts in the Early Proterozoic has important significance in further studies on Early Proterozoic biotic evolution, regional and global stratigraphic correlation, and carbon geochemical cycles.     

An Early Tertiary Vertebrate Fauna from Yuauchü

In the Yuanchü-Mienchih border along the Huangho,a very promis-ing early Tertiary basin was known and first reported by Andersson.~1The fauna was later described by Zdansky.~2 Although most of the formsdescribed are in bad condition of preservation,this basin represents so     

New Early Cambrian Chordates from Haikou, Kunming

Two new chordates, Cathaymyrus haikouensis Luo et Hu sp. nov. and Zhongxiniscus intermedius Luo et Hu gen. et sp. nov. are studied in this paper. Both display numerous S-shaped myomeres on their trunk. C. haikouensis shows a long and slim body similar to that of Cathaymyrus diadexus Shu et al., Zhongxiniscus approaches to Myllokunmingia and Haikouichthys in the dorsal fin, but differs in the myomeres. Zhongxiniscus may be the intermediate form between Cathaymyrus and Myllokunmingia and Haikouichthys.     

Remobilization of Iodine in Marine Sediments During Early Diagenesis

Based on the sedimentary geochemical studies of the Antarctic Ocean and the various geochemical parameters available,this paper deals with the process of emobilization of iodine in marine sediments during early diagenesis.The results showed that the process is not always controlled completely by organic matter as was expected previously.On average the adsorption and oxide phases of iodine account respectively for 23% and 32% of the total in continental-shelf and hemipelagic surficial sediments.Chemical analysis has revealed that the upward diffusion flux and redox conditions would play an important role in the concentration of iodine in the surface sediments.And the species of iodine in the surfial sediments characteristic of high I/Corg ratios would bepredominated by the oxide and adsorption phases.As experimentally evidenced,it is the early diagenetic remoibilization of iodine associated with the oxide and adsorption phases that led to the decrease of I/Corg with increasing depth.Calculations suggested that the diffusion flux of iodine from the deep parts of te sedimentary columum upwards is on the same order of magnitude as the deposition flux of it from sea water.This may be one of the important factors leading to the depletion of iodine in sedimentary rocks.On the basis of the above discussion and calculations the author has proposed a model for the remobilization of iodine in marine sediments during early diagenesis.     

Ediacaran–Early Ordovician paleomagnetism of Baltica: A review

The Ediacaran–Early Ordovician interval is of great interest to paleogeographer's due to the vast evolutionary changes that occurred during this interval as well as other global changes in the marine, atmospheric and terrestrial systems. It is; however, precisely this time period where there are often wildly contradictory paleomagnetic results from similar-age rocks. These contradictions are often explained with a variety of innovative (and non-uniformitarian) scenarios such as intertial interchange true polar wander, true polar wander and/or non-dipolar magnetic fields. While these novel explanations may be the cause of the seemingly contradictory data, it is important to examine the paleomagnetic database for other potential issues.This review takes a careful and critical look at the paleomagnetic database from Baltica. Based on some new data and a re-evaluation of older data, the relationships between Baltica and Laurentia are examined for ~ 600–500 Ma interval. The new data from the Hedmark Group (Norway) confirms suspicions about possible remagnetization of the Fen Complex pole. For other Baltica results, data from sedimentary units were evaluated for the effects of inclination shallowing. In this review, a small correction was applied to sedimentary paleomagnetic data from Baltica. The filtered dataset does not demand extreme rates of latitudinal drift or apparent polar wander, but it does require complex gyrations of Baltica over the pole. In particular, average rates of APW range from 1.5° to 2.0°/Myr. This range of APW rates is consistent with ‘normal’ plate motion although the total path length (and its oscillatory nature) may indicate a component of true polar wander. In the TPW scenario, the motion of Baltica results in a back and forth path over the south pole between 600 and 550 Ma and again between 550 and 500 Ma. The rapid motion of Baltica over the pole is consistent with the extant database, but other explanations are possible given the relative paucity of high-quality paleomagnetic data during the Ediacaran–Cambrian interval from Baltica and other continental blocks.A sequence of three paleogeographic maps for Laurentia and Baltica is presented. Given the caveats involved in these reconstructions (polarity ambiguity, longitudinal uncertainty and errors), the data are consistent with geological models that posit the opening of the Iapetus Ocean around 600 Ma and subsequent evolution of the Baltica–Laurentia margin in the Late Ediacaran to Early Ordovician, but the complexity of the motion implied by the APWP remains enigmatic.     

Changchun symposium on Metallogeny of the Early Precambrian in China

According to the international geological correlation ploject 91, the Chinese working group is in duty bound to hold a symposium on mdtallogeny of the early Precambrian in China. with the help of Changchun College of geology this sgmposium was held between the 10th and 13th April, 1982 in Changchun.     

Biomarker signatures from Neoproterozoic–Early Cambrian oil,western India

The Neoproterozoic–Early Cambrian time is the cradle of multicellular, eukaryotic life and thereafter metazoan life started populating the planet. Biomarkers, which record the chronicles of biotic events on Earth, have been investigated using gas chromatography–mass spectrometry from a suite of nine oil samples extracted from oil stained sediments and a crude oil of Neoproterozoic–Early Cambrian age from Bikaner-Nagaur Basin, western India. The biomarker distribution is characterized by high concentration of both tricyclic terpanes and pentacyclic hopanes. The predominance of C₂₉ regular sterane over C₂₇ and C₂₈ steranes indicates green algal contribution and may imply the prominence and diversification of the same algal group. The low pristane/phytane ratio and occurrence of substantial quantity of gammacerane, monomethyl 2-methyl-2-(2,4,8-trimethyltridecyl) chroman and 1,1,7,8-tetramethyl-1,2,3,4 tetrahydrophenanthrene are indicative of stratified water column as well as anoxic and enhanced salinity condition of the environment of deposition. This paper reports for the first time the presence of methyltrimethyltridecyl chromans (MTTCs) from Neoproterozoic–Early Cambrian time. Putative C₁₉ norsteranes, probably indicative of sponge input, are recorded in the studied samples and also reported from other infracambrian oils and sediments. Normal alkanes (n-C₁₇ and n-C₁₈) and isoprenoids (pristane and phytane) are highly depleted in δ¹³C. The overall biomarker distribution and carbon isotope data of oils from Bikaner-Nagaur Basin show similarities with those of other infracambrian oils like Huqf oils from Oman and Baykit High oils from eastern Siberia.     

Early Mesozoic Basin-Mountain Coupling Mechanism and Basin Geodynamics of East China

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An obliquity-controlled Early Pleistocene river terrace record from Western Turkey?

Investigation of the Pleistocene sequence of the Gediz River, Western Turkey, has revealed a record of Early Pleistocene river terraces. Eleven terraces spanning the interval from 1.67 to 1.245 million years ago (MIS 59–37) are preserved beneath basaltic lava flows. The high number of terraces over this short time period reflects high-frequency sedimentation/incision cycles preserved due to the fortuitous combination of relatively high uplift rates (0.16 mm yr⁻¹) and progressive southwards valley migration. Comparison of this record with ODP967 from the Eastern Mediterranean Basin suggests a link between the production of terraces and obliquity-driven 41,000 year climate cycles in the Early Pleistocene.     

Study of the Early and Middle Triassic Lower Yangtze Sea Basin

The Early and Middle Triassic primary lower Yangtze sea basin was formed before the Yangtze and Sino. Korean blocks collided and were assembled. showing the characteristics of an open continental shelf.continental margin sea. In order to provide evidence useful for oil and gas exploration in the studied region, this paper centres on the features of the sediments and their facies framework in the basin and the sedimentation parameters such as the deposition rate, palaeotemperature, palaeosatinity, palaeodepth of water and palaeocurrents of the basin.     

Coevolution of Brachiopod Paleobiogeography and Tectonopaleogeography during the Early–Middle Permian

A comprehensive compilation and systematic analysis of known early and middle Permian brachiopod faunas shows that the early Permian brachiopod faunas comprise three realms, six regions, and eleven provinces, while those of the middle Permian comprise three realms, four regions, and eight provinces. A comparison and analysis of brachiopod faunal patterns reveal a coevolution between global brachiopod paleobiogeography and tectonopaleogeography during the early–middle Permian. Although temperature/latitude is the main factor controlling the formation of three realms, tectonopaleogeographic factors determine the temperature/latitude in which the continents were located. The ‘continental barrier' of Pangea, as a ‘central axis' continent, divided the three realms into six regions, which indicates that the formation of biogeographic regions was controlled mainly by the tectonopaleogeographic factors. The evolution of tectonopaleogeography was sometimes a long-term process, so that the biogeographic regions(or provinces) controlled by tectonopaleogeography displayed relative stability. Shifts in the nature of biogeographic provinces(e.g., from cool water to warm water, and vice versa), extensions or narrowing of geographical ranges, and recombinations of some provinces were all related to regional tectonic evolution. The study of the coevolution between brachiopod paleobiogeography and tectonopaleogeography not only accounts for the formation mechanisms of brachiopod paleobiogeographic patterns during the early–middle Permian, but also provides evidences for the locations and configurations of oceans and plates(blocks) during this period.     

Cretaceous–Early Cenozoic Geodynamics of the Olyutorka–Kamchatka Accretionary Zone

Doklady Earth Sciences - Within the Olyutorka–Kamchatka accretionary zone, several terranes of an island-arc, marginal-sea, and oceanic nature are distinguished. The igneous complexes of...     

Keivy Paraschists (Archean–Early Proterozoic): Nanobacteria and Life

Nanobacteria, buried in situ, were discovered in the Early Precambrian paraschists (Keivy, Kola Peninsula). It is suggested that occurrence of nanobacteria indicates that a biological factor played a role in the formation of enclosing rocks.     

Geological events of the Late Cretaceous–Early Paleogene in Western Kamchatka

The age ranges of Upper Cretaceous lithotectonic complexes of Western Kamchatka—terrigenous Kikhchik, volcanic Irunei, and terrigenous Omgon—are analyzed to reveal their almost simultaneous deposition. The pre-Cenozoic settings of these complexes are reconstructed. Based on analysis of the composition and structural features of Late Cretaceous lithotectonic complexes and on correlation of events, the Late Cretaceous paleogeography is reconstructed. It is found that the formation of the contemporary structure of the studied region would have required significant displacement of the volcanic Irunei complex from west to east and the terrigenous Omgon complex from north to south. It is concluded that the Western Kamchatka continental block (minor lithospheric plate) was independent in the Late Cretaceous.     

New Paleomagnetic Data on the Devonian–Early Carboniferous Strata in Tuva

Doklady Earth Sciences - New paleomagnetic data on the Devonian and Early Carboniferous rocks in Tuva have been obtained. Component analysis of magnetization has been carried out. Coordinates of...     

A New Ornithocheirid from the Early Cretaceous of Liaoning Province, China

Based on a nearly complete skeleton with skull from the Early Cretaceous of Liaoning Province, a new ornithocheirid pterosaur: Boreopterus cuiae gen. et sp. nov. is erected. Boreopterus cuiae is different from other pterosaurs preserved with skulls known from the western Liaoning Province and its neighboring areas. Tiffs new oterosaur has more and larger teeth than those in other ornithocheirids. Its anterior nine pairs of teeth are larger than other teeth. The fourth pair of upper and lower teeth are slightly larger than the third pair. Overall, Boreopterus cuiae shows much small range of tooth size variation than Anhanguerapiscator and Coloborhynchus robustus. The new taxon shares with other ornithocherids in having a relatively large size of the third and fourth pairs of teeth.     

The Origin of the Early Proterozoic Kuandian Complex: Evidence from Geochemistry

The Kuandian Complex is scarcely preserved Early Proterozoic volcanic suite, formed2.3-2.4 Ga ago. It is located in an Early Proterozoic mobile belt bounded by the ArchaeanRangrim and Ryonggang Blocks of the northeastern Sino-Korean Craton. The Complex ismainly made up of amphibolites, gneisses, leucoleptite, leptite and layered granite. Petrologicaland geochemical studies show that the protoliths of the Complex are mainly assoctations ofbimodal volcanics and anorogenic granites. The Kuandian amphibolites are depleted in Nb, Ta,P and Ti, and enriched in LILE, e.g. K, Rb and Cs, with pronounced depletion of Sr relative toNd and Pb; La/Nb ratios are higher than 1(1.75 to 5.18). The trace element patterns of theamphibolites are similar to continental flood basalts formed by the Gondwana break-up, suchas those in South Karoo and Tasmania, which shows continental contamination. ε_(Nd) valuesranging from 0.70 to 1.94 of the Kuandian amphibolites and the relationships between Nb/Yband La/Yb suggest that contamination of basaltic magma happened in the mantle, rather thanalong the conduit. Isotope ratios of ~(208)Pb/~(204)Pb, ~(207)Pb/ ~(204)Pb, ~(206)Pb/~(204)Pb, ~(143)Nd/~(144)Ndand ~(87)Sr/~(86)Sr indicate that the magma was derived from a contaminated mantle source likeDMM or a mixture of DMM and EM2. The Kuandian Complex has Dupal anomaly, as is thecase with some continental basalts in the south hemisphere, e.g. in South Karoo and Tasmania.Petrochemical modelling proposes that the Kuandian gneiss, granite, and amphibolite camefrom the same parental magma, being products of strong fractional crystallization. Protoliths ofthe Kuandian Complex were formed in extensional tectonic setting during the transition fromcontinental crust to oceanic crust. The formation of the Kuandian Complex indicates that 2.3or 2.4 Ga ago tectonic evolution of the Sino-Korean craton was different from that of otherwell-studied Precambrian cratons, e.g. the North American shield, European platform andAustralian continent in that strong volcanic eruption resulted in its accretion. Besides, the con-taminated magma source with a Dupal anomaly for the Complex indicates that crust-mantleconvection whose scale was similar to that of the present plate tectonics had occurred at leastbefore the formation of the Kuandian Complex (2.3-2.4 Ga B.P).