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Provenance Analysis And Lithofacies Palaeogeographic Characteristics Of Xujiahe Formation In Middle Of Sichuan Basin

Posted on:2012-02-09Degree:MasterType:Thesis
Country:ChinaCandidate:C HuFull Text:PDF
GTID:2210330338967772Subject:Geology
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Sichuan basin is a polycycle sedimentary basin in Yangtze paleo-plates.Indosinian orogeny in late Triassic directly influenced and controlled the tectonicframework of Sichuan basin. The provenance thing of Sichuan basin had always beena hot point, since there were several orogens around the basin. Based on two methods,including sedimentary attribute analytical method and geochemistry analytical method,this article researched the provenance of Xu 2 member, Xu 4 member, and Xu 6member in middle of Sichuan basin. Finally, compiled lithofacies paleographic mapbased on the provenance analysis. The main achievements are as follows:1. According to the analysis and identification of thin sections, sandstone typesof Xujiahe formation of Sichuan basin in upper Triassic were mainly lithic quartzsandstone, followed with lithic sandstone and feldspathic lithic sandstone. Thecontent of quartz sandstone was relatively minor, only found in Huaying Xikou andHechuan Tanba. Based on the identification of sandstone clastic components, thequartz was mainly monocrystal quartz, followed with polycrystal quartz. Feldsparsin sandstone were mainly plagioclase and microcline. Lithic fragments were mainlymetamorphic rock, followed with sedimentary rock, and minor magmatic rock.2. The provenance areas of Xu 2 member, Xu 4 member and Xu 6 member hadsome differences by using Dickinson triangle chart. The main provenance area of Xu2 member was Kangdian ancient land in southwest of Sichuan basin, andE'mei-Washan ancient land in south of Sichuan basin. The Micangshan-Dabashanuplift and Xuefeng ancient land only affected the south and east of research area.Provenance area of Xu 4 member was maily E'mei-Washan ancient land in south ofSichuan basin. Combined with the tectonic framework coursed by late Indosinianorogeny, the author deduced the provenance area of Xu 6 member was stillE'mei-Washan ancient land in south of Sichuan basin.3. On basis of geochemistry analytical method, the REE elemental partition ofXu 2 member was familiar with Xu 4 member. The primary materials were from upper crust. Distribution pattern of Xu 6 member was obviously different from thefirst two, it indicated that the provenance of Xu 6 member was different from Xu 2and Xu 4 member. According to the trace elements characters, the source rocks of Xu2 and Xu 4 were mainly sedimentary rock and granite, Xu 6 member was mainlysedimentary rock. From Xu 2 member to Xu 6 member, the mainland island convertedto active continental margin tectonic setting.4. Lithofacies paleographic map of Xujiahe formation in upper Triassic had beencompiled. The middle of Sichuan basin was mainly shore-shallow lake deposition,sometimes developed the braided fluvial river delta front. The variation tendency ofstratoisohypse in each period and the direction of provenance might be confirmed.
Keywords/Search Tags:Sichuan basin, middle of Sichuan basin, Xujiahe formation, provenance, Sedimentary facies and Palaeogeography
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