Clay mineralogical characteristics at the Permian–Triassic Shangsi section and their paleoenvironmental and/or paleoclimatic significance - Archive ouverte HAL Access content directly
Journal Articles Palaeogeography, Palaeoclimatology, Palaeoecology Year : 2017

Clay mineralogical characteristics at the Permian–Triassic Shangsi section and their paleoenvironmental and/or paleoclimatic significance

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Abstract

High–resolution clay mineralogical investigations were conducted on the Permian–Triassic (P–Tr) carbonate– and siliceous rocks from the Shangsi section, South China. The clay mineralogy is dominated by illite and illite/ smectite mixed–layers (I/S) throughout the sampled section with subordinate chlorite and vermiculite emerging from bed 24 (approaching the End–Permian mass extinction horizon–EPME) onwards. Positive correlations of clay fraction with mainly land–derived TiO2 and magnetic susceptibility (MS) indicate a primary continental origin of the clay minerals. Rock–Eval pyrolysis analysis, palynomorph coloration, scanning electron microscope (SEM) and Transmission ElectronMicroscope (TEM) observations, all suggest that the rocks experienced thermal diagenesiswhichmainly promotes illitization processes of smectite clay mineralswhile discrete clayminerals are merely affected. Despite this diagenetic effect, clayminerals still carry valuable paleoenvironmental and paleoclimatic information in the Shangsi section. The overall illitic composition of the clayminerals and nearly absence of kaolinite suggest a general semi–arid condition during the P–Tr interval. Appearance of chlorite frombed 24 onwards suggests further aridification compared to the Late Permian. Occurrence of vermiculite frombeds 24–28 in association with abundant volcanogenic materials, most negative δ13Ccarb values as well as enhanced soil– derivedmoretane abundance, suggests catastrophic soil erosion and likely soil acidification during the P–Tr transition in the source area(s) in relation with the active volcanism in that time. Further, decrease of chemical weathering and increase of physical weathering are indicated by increased input of primary clay minerals such as chlorite, a better illite crystallinity and increase of Al2O3/TiO2 ratios. A climate cooling period corresponding to the Clarkina changxingensis–Clarkina deflecta conodont zone to the lower Clarkina zhangi conodont zone is indicated by higher abundance of illite, lower terrigenous TiO2, MS and Al2O3/TiO2 in comparison with the overlying uppermost Permian strata.
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hal-01371554 , version 1 (26-09-2016)

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Guozhen Xu, Jean-François Deconinck, Qinglai Feng, François Baudin, Pierre Pellenard, et al.. Clay mineralogical characteristics at the Permian–Triassic Shangsi section and their paleoenvironmental and/or paleoclimatic significance. Palaeogeography, Palaeoclimatology, Palaeoecology, 2017, 474, pp.152-163. ⟨10.1016/j.palaeo.2016.07.036⟩. ⟨hal-01371554⟩
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