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Yu W.,Wuhan University | Yu W.,University of Cincinnati | Algeo T.J.,Wuhan University | Algeo T.J.,University of Cincinnati | And 6 more authors.
Precambrian Research | Year: 2017

Sturtian cap carbonate deposits, previously unknown in South China, are documented in this study from the base of the Datangpo Formation in the Nanhua Basin (Guizhou Province). The age of these deposits is constrained by an LA-ICP-MS U-Pb zircon age of 662.7 ± 6.2 Ma from the overlying Mn-shale layer, which is approximately coeval with the termination of the Sturtian glaciation globally. The newly discovered cap carbonates are composed of massive, laminated, pisolitic, and sandy dolomites, and formed subtidally on the summits of horsts within the Nanhua Basin. Two δ13Ccarbprofiles (from the JJS-1 and ZK01 sections) show positive shifts of 4–5‰ from the base to the top of the cap carbonates with a ∼2‰ offset between the profiles. These features suggest both a large global perturbation as well as local influences on carbonate carbon isotopes during the Sturtian deglaciation, which is consistent with aspects of both the Snowball Earth and gas hydrate destabilization hypotheses for the origin of cap carbonates. The newly discovered cap carbonates are inferred to be correlative with rhodochrosite (Mn-carbonate)-bearing deposits of the basal Datangpo Formation in adjacent grabens of the Nanhua Basin. This correlation is based on (1) the equivalent stratigraphic positions of the cap carbonates and Mn-deposits, both of which are found at the base of the Datangpo Formation, and (2) consistent U-Pb dates of 667–663 Ma for tuff layers interbedded with these deposits at two locales. The Mn-deposits show significantly higher TOC content (1–3% vs <0.7%) and more negative δ13Ccarbvalues (−10.5 to −5.5‰ vs −4.0 to +2.5‰) than the cap carbonates. The upsection trend toward higher δ13Ccarbin the cap carbonates may reflect increases in marine productivity and the burial rate of organic carbon following the Sturtian glaciation. Despite coeval formation, the dolomitic cap carbonates deposited on horsts and the Mn-carbonate sediments deposited in grabens are heterogeneous facies with different formation mechanisms. © 2017 Elsevier B.V.

Wang X.,Wuhan University | Jiao Y.,Wuhan University | Du Y.,Wuhan University | Ling W.,State Key Laboratory of Geological Process and Mineral Resources | And 6 more authors.
Journal of Geochemical Exploration | Year: 2013

The rare earth element (REE) behavior and the related Ce anomalies of two profiles in bauxite of the Xinmo Syncline from Wuchuan-Zheng'an-Daozhen (WZD) area (Northern Guizhou, China) have been studied. The bauxite has diaspore as its main ore mineral, with lesser amounts of boehmite. Clay minerals, including kaolinite, chlorite, illite and smectite, are a minor mineral constituent. Furthermore, a significant Ce-bearing mineral parisite (Ce2Ca(CO3)3F2) is found near the bottom of the profiles. The bauxites have flat HREE (Er-Lu) shape relative to NASC, with variable weak depletion to weak enrichment patterns of LREE (La-Nd) and MREE (Sm-Ho) across the profiles. Strong positive Ce-anomalies (normalized to NASC) are also noticeable in the uppermost part of the profiles. Mass balance calculations suggest that an obvious fractionation exists among different REE and LREE are more mobile than HREE during the leaching process. In addition, the samples collected along a vertical profile show that a downward increase for the REE concentration and a remarkable enrichment of REE are found at the basement of the bauxite deposits. A similar downward increase trend is also observed in the values of LaN/YbN and GdN/YbN. The above characteristics show that the REE losses caused by leaching decreased gradually from the top to the bottom of the profile. The higher mobility of LREE in the profile might be due to differences in the stabilities of the original REE-bearing minerals during leaching process. The REE enrichment at the basement of bauxite deposits is attributed to the increase of pH around the parent rock as well as the presence of mineral ligands during bauxitization. The value of [Ce/Ce*]NASC decreased downwards, and increased again near the bottom of the profile. The positive Ce-anomaly in the uppermost part of the profile has been attributed to the redox change of Ce3+ to Ce4+ and the consequent precipitation of cerianite (CeO2). A decrease in the oxidation state downwards causes the decrease of the value of [Ce/Ce*]NASC. The formation of parisite near the bottom of the profile leads up to the increase in the value of [Ce/Ce*]NASC again. The precipitation of parisite may occur via reactions between the fluoride complexes (CeF2+ or CeCO3F0) and Ca2+ and HCO3 -. © 2013 Elsevier B.V.

Chen R.,Guizhou University | Bi K.,Guizhou Bureau of Geology and Mineral Exploration and Development
Chinese Journal of Geochemistry | Year: 2011

The karst area accounts for 61. 9% of the total area in Guizhou Province, which gives rise to a fragile environment and backward economy. Comparative studies on the element contents of rock and soil and agriculture production in both carbonate area and non-carbonate area have been made to establish factors leading to low output and poor quality of agricultural products in the karst area. The result shows that there is an apparent lack of nutrient elements in carbonate rocks. The trace element contents of carbonate rocks are only 3532. 27×10-6, but those of non-carbonate rocks are 10894. 21×10-6. The available element contents in cultivated soil delivered from carbonate rocks are merely 101. 4×10-6, but those from non-carbonate rocks are 326. 05×10-6. The available element contents and total element contents in cultivated soil delivered from non-carbonate rocks are 3 times higher than those from carbonate rocks. Besides, high-quality agricultural products such as rice, potato and tea are mainly produced in the non-carbonate area. It is indicated that the low output and quality of agricultural products are caused by the above-mentioned low trace element contents and poor agricultural environment. Therefore, a new method of mineral nutrients compensation has been put forward, which is very effective to raise the load-bearing capacity of agricultural environment, agricultural output and quality of agricultural products. © 2011 Science Press, Institute of Geochemistry, CAS and Springer-Verlag Berlin Heidelberg.

Yu W.,Wuhan University | Yu W.,University of Cincinnati | Algeo T.J.,Wuhan University | Algeo T.J.,University of Cincinnati | And 7 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2016

The Neoproterozoic Datangpo Formation of the Nanhua Basin in South China records interglacial sedimentation between the ~ 720–660-Ma Sturtian and ~ 654–635-Ma Marinoan glaciations. The lower part (1st Member) of this formation contains manganese-rich deposits that represent a mixture of two main components, Mn-carbonates and Mn-bearing aluminosilicates (clay minerals). The Mn-carbonate component is characterized by high La/Sc ratios, high initial 87Sr/86Sr ratios, and low initial εNd(t) values, and the siliciclastic component by low La/Sc ratios, low initial 87Sr/86Sr ratios, and high initial εNd(t) values. The likely source of the non-radiogenic siliciclastic material is weathering of Neoproterozoic continental flood basalts on the Yangtze Block. Discriminant plots show that the Mn-ore samples have compositions consistent with at least partial derivation from hydrothermal sources. Mn-carbonate deposition was the result of reactions between aqueous Mn and sedimentary organic matter during early diagenesis that led to elevated Mn2 + concentrations and alkalinity in sediment porewaters. Based on these observations, we propose a new metallogenic model for the Datangpo Formation manganese deposits. During the Sturtian glaciation, the anoxic Nanhua Basin accumulated abundant dissolved Mn, a substantial fraction of which was derived from hydrothermal sources. When glaciation ended and a redox-stratified water column developed in the basin with an oxic surface layer and an anoxic deep layer, the accumulated dissolved Mn precipitated as Mn-oxides on the basin floor during episodic ventilation events. After co-burial with organic-rich sediments, these Mn-oxides were reduced during organic matter oxidation, which led to the formation of secondary Mn-carbonates (rhodochrosite) through increases in sediment porewater Mn2 + and in alkalinity via microbial sulfate reduction and microbially mediated Mn reduction. © 2016

Ma X.,Wuhan University | Yang K.,Wuhan University | Li X.,Inner Mongolia Chifeng Bureau of Land and Resources | Dai C.,Guizhou Academy of Geological Surveying | And 2 more authors.
Canadian Journal of Earth Sciences | Year: 2016

The Jiangnan Orogeny generated regional angular unconformities between the Xiajiang Group and the underlying Sibao Group in the western Jiangnan Orogen along the southeastern margin of the Yangtze Block in southeast Guizhou, South China. Laser ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS) U–Pb zircon dating of two samples of the Motianling granitic pluton yielded U–Pb zircon ages of 826.2 ± 3.4 and 825.5 ± 6.1 Ma, with an average age of 825.6 ± 3.0 Ma, which is considered the minimum depositional age of the Sibao Group. The U–Pb ages of the youngest detrital zircon grains from the Sibao Group and the Xiajiang Group yielded average ages of 834.9 ± 3.8 and 794.6 ± 4.2 Ma, respectively. The depositional age of the Sibao Group can be constrained at 825–835 Ma, and deposition of the Xiajiang Group did not begin before ca. 800 Ma. These results suggest that the Jiangnan Orogeny, which led to the assembly of the Yangtze and Cathaysia blocks, ended at 795–835 Ma on the western segment of the Jiangnan Orogen. The detrital zircon distribution spectrums of the Sibao and Xiajiang groups suggest a provenance from Neoproterozoic basement sedimentary sequences along with a mixture of local Neoproterozoic subduction-related felsic granitoids, distant plutons from the western Yangtze Block and eastern Jiangnan Orogen, and recycled materials from the interior of the Yangtze Block. By comparing the basin evolution histories and magmatic and metamorphic events along the continental margins of the Rodinia supercontinent, it is proposed that the South China Block might have been located at the periphery, adjacent to North India and East Antarctica, rather than in the interior of Rodinia in Neoproterozoic time. © 2016.Can. J. Earth Sci. all right reserved.

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