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Wang X.-F.,Wuhan Institute of Geology and Mineral Resources
Palaeoworld | Year: 2015

The morphology of the pseudoplanktonic crinoid Traumatocrinus from the early Late Triassic (Carnian) Xiaowa Formation of Guanling County (South China, Guizhou Province) is described based on articulated and disarticulated material. Juvenile individuals of less than 10. mm crown height with 20 isotomously branching arms prove the encrinid ancestry of the family Traumatocrinidae. However, even the smallest individuals have five large interradials. Endotomous branching commences at crowns of slightly more than 10. mm at the outer arms of the rays. All brachial articulations are ligamentary (granosyzygies). The assignment of the Chinese material to one of the nominal species of Traumatocrinus is still left open. The diagnosis of the genus Traumatocrinus is emended. Traumatocrinus lived attached to driftwood and was widespread across the Palaeo-Tethys. In contrast to its benthic encrinid ancestors, Traumatocrinus fixed its distal column with countless anastomosing radicular cirri to its substrate, preferentially to the ends of the driftwood logs. Depending on the state of the hypothesized mutable collagene tissue, the columns are preserved in straight positions or curved like a rope. Crowns are preserved in star position with radially splayed arms or in lateral bell position with the cup disrupted in interbrachial position. As usual in black shales, the exposed upper sides of the crinoids are in a more or less progressive state of decomposition whereas the embedded lower sides are intact. © 2015 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. Source

Deng X.,Wuhan University | Deng X.,Wuhan Institute of Geology and Mineral Resources | Wu K.B.,Wuhan University | Yang K.G.,Wuhan University
Science China Earth Sciences | Year: 2013

The Shigujian pluton is a gneissic quartz monzonite located in Tiantangzhai area in central part of the Dabie orogen. Anisotropy of magnetic susceptibility (AMS) data show that most magnetic foliations dip steeply to southeast. About 85% of sampling points dip from 40° to 90°. Magnetic foliations are generally parallel to the foliations measured in the field. The pluton has NWW-SEE trending lineations in the southeast and NE-SW trending lineations in central part and north, but the lineations plunge to SW in central part and to NE in the north. All plunges are moderate. The anisotropy degree (P) is between 1.065 and 1.532 and the shape parameter (T) is between 0.005 and 0.694. A Flinn diagram of the magnetic fabrics shows that the value of K is less than 1. The analysis of AMS suggests that the pluton was emplaced and deformed under a SE-NW compressional stress regime. The analysis of quartz C-axis fabrics indicates that the pluton was deformed under compressional stress and deformation temperatures range from 400 to 500°C. Microstructures indicate that the pluton is deformed in near solidus conditions and the pluton is a synkinematic intrusion. The emplacement of the Shigujian granite is inferred to have taken place syntectonically. The zircon U-Pb dating of the granite suggests that the pluton was intruded at 141±2.3 Ma. By synthesizing all data, it seems that the Shigujian pluton was emplaced in a compressional environment and the transformation time of the Dabie orogen from compression to extension took place after 141 Ma. The structural evolution of the Dabie orogen was controlled by the Pacific tectonic domain when the Shigujian pluton was emplaced, whereas the adjacent Tiantangzhai complex massif is the result of an extensional environment. © 2013 Science China Press and Springer-Verlag Berlin Heidelberg. Source

Ding L.-X.,Wuhan University | Ding L.-X.,Wuhan Institute of Geology and Mineral Resources | Ma C.-Q.,Wuhan University | Li J.-W.,Wuhan University | And 4 more authors.
Lithos | Year: 2011

The NWW-striking Qinling Orogen formed in the Triassic by collision between the North China and Yangtze Cratons. Triassic granitoid intrusions, mostly middle- to high-K, calc-alkaline, are widespread in this orogen, but contemporaneous intrusions are rare in the southern margin of the North China Craton, an area commonly considered as the hinterland belt of the orogen. In this paper, we report zircon U-Pb ages, elemental geochemistry, and Sr-Nd-Hf isotope data for the Laoniushan granitoid complex that was emplaced in the southern margin of the North China Craton. Zircon U-Pb dating shows that the complex was emplaced in the late Triassic (228±1 to 215±4Ma), indicating that it is part of the post-collisional magmatism in the Qinling Orogen. The complex consists of, from early to late, biotite monzogranite, quartz diorite, quartz monzonite, and hornblende monzonite, which span a wide compositional range, e.g., SiO2=55.9-70.6wt.%, K2O+Na2O=6.6-10.2wt.%, and Mg# of 24 to 54. The biotite monzogranite has high Al2O3 (15.5-17.4wt.%), Sr (396-1398ppm) and Ba (1284-3993ppm) contents and relatively high La/Yb (mostly 14-30) and Sr/Y (mostly 40-97) ratios, but low Yb (mostly 1.3-1.6ppm) and Y (mostly14-19ppm) contents, features typical of adakitic rocks. The quartz monzonite, hornblende monzonite and quartz diorite have a shoshonitic affinity, with K2O up to 5.58wt.% and K2O/Na2O ratios averaging 1.4. The rocks are characterized by strong LREE/HREE fractionation in chondrite-normalized REE pattern, without obvious Eu anomalies, and show enrichment in large ion lithophile elements but depletion in high field strength elements (Nb, Ta, Ti). The biotite monzogranite (228Ma) has initial 87Sr/86Sr ratios of 0.7061 to 0.7067, εNd(t) values of -9.2 to -12.6, and εHf(t) values of -9.0 to -15.1; whereas the shoshonitic granitoids (mainly 217-215Ma) have similar initial 87Sr/86Sr ratios (0.7065 to 0.7075) but more radiogenic εNd(t) (-12.4 to -17.0) and εHf(t) (-14.1 to -17.0). The Sr-Nd-Hf isotope data indicate that the rocks were likely generated by partial melting of an ancient lower continental crust with heterogeneous compositions, as partly confirmed by the widespread presence of early Paleoproterozoic inherited zircons. Mafic microgranular enclaves (MMEs), characterized by fine-grained igneous textures and an abundance of acicular apatites, are common in the Laoniushan complex. Compared with the host rocks, they have lower SiO2 (48.6-53.7wt.%) and higher Mg# (51-56), Cr (122-393ppm), and Ni (24-79ppm), but equivalent Sr-Nd isotope compositions, indicating that the MMEs likely originated from an ancient enriched lithospheric mantle. The abundance of MMEs in the granitoid intrusions suggest that magma mixing plays an important role in the generation of the Laoniushan complex. Collectively, it is suggested that the Laoniushan complex was a product of post-collisional magmatism related to lithospheric extension following slab break-off. Formation of the adakitic and shoshonitic intrusions in the Laoniushan complex indicates that the Qinling Orogen had evolved into a post-collisional setting by about 230-210Ma. © 2011 Elsevier B.V. Source

Li X.,Wuhan Institute of Geology and Mineral Resources | Li X.,Nanjing University | Cai Y.,Nanjing University
Cretaceous Research | Year: 2013

We have used diffuse reflectance spectroscopy to investigate the colouration mechanisms of hematite in Cretaceous Oceanic Red Beds (CORBs). Data for samples of CORBs from the Chuangde section in Tibet, Vispi Quarry section in Italy, and Core 12X of Ocean Drilling Program Hole 1049C in the North Atlantic were compared with calibration datasets obtained for hematite in different crystalline forms (kidney and specular hematite) and calcite matrix. Spectra for hematite in either pure form or in calibration datasets show that the centre of the reflection peak shifts to a longer wavelength and depth (D) decreases as the crystallinity of the hematite increases. Compared with specular hematite, the presence of just 0.5% of kidney hematite can cause a much deeper absorption peak and greater redness value, which indicates that kidney hematite has a higher colouration capacity than specular hematite. However, both kidney and specular hematite exhibit a good correlation between the redness value for each calibration dataset and the absorption peak depth. In all three studied sections, hematite is the main iron oxide mineral responsible for colouration. Spectral features such as absorption peak depth and peak centre reveal that hematite crystallinity gradually decreases from red shale to limestone to marl. Based on a spectral comparison of red shale in the Chuangde section before and after citrate-bicarbonate-dithionite (CBD) treatment, we found that two forms of hematite are present: a fine-grained and dispersed form, and a detrital form. The former is relatively poorly crystalline hematite, which has a much stronger colouration capacity than the detrital form. In the Vispi Quarry section and Core 12X of ODP Hole 1049C, a good correlation between the absorption peak depth of hematite and redness value indicates that the red colouration is caused by hematite of similar crystallinity in each section. © 2013 Elsevier Ltd. Source

Cheng L.,Wuhan Institute of Geology and Mineral Resources | Chen X.-H.,Wuhan Institute of Geology and Mineral Resources | Shang Q.-H.,CAS Institute of Vertebrate Paleontology and Paleoanthropology | Wu X.-C.,Canadian Museum of Nature
Naturwissenschaften | Year: 2014

The Luoping fauna (Anisian, Middle Triassic) is probably the oldest of Triassic faunas in Guizhou-Yunnan area, China. The reptilian assemblage is comprised of ichthyosaurs, a number of sauropterygians (pachypleurosaur-like forms), saurosphargids, protorosaurs, and archosauriforms. Here, we report on a peculiar reptile, newly found in this fauna. Its dentition is fence or comb-like and bears more than 175 pleurodont teeth in each ramus of the upper and lower jaws, tooth crown is needle-like distally and blade-shaped proximally; its rostrum strongly bends downward and the anterior end of its mandible expands both dorsally and ventrally to form a shovel-headed structure; and its ungual phalanges are hoof-shaped. The specializations of the jaws and dentition indicate that the reptile may have been adapted to a way of bottom-filter feeding in water. It is obvious that such delicate teeth are not strong enough to catch prey, but were probably used as a barrier to filter microorganisms or benthic invertebrates such as sea worms. These were collected by the specialized jaws, which may have functioned as a shovel or pushdozer (the mandible) and a grasper or scratcher (the rostrum). Our preliminary analysis suggests that the new reptile might be more closely related to the Sauropterygia than to other marine reptiles. © 2014 Springer-Verlag Berlin Heidelberg. Source

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