學術資源整合系統-相關推薦

 
作者Ming-Shiou Jeng;Horng-Sheng Mii;Song-Chuen Chen;Shih-Wei Wang
出版日期201806
著作名稱A Preliminary Study on the Cold-Seep Carbonates of the Maanshan Formation, Hengchun Peninsula, Taiwan =臺灣恆春半島馬鞍山層中冷泉碳酸鹽岩之初步研究
刊名Collection and Research
31
頁數9-23
主題地質
關鍵字cold-seep carbonates, Maanshan Formation, stable isotope, hydrocarbon seepage, Hengchun Peninsula
摘要This study examined the origin of distinctive carbonate-cemented rocks observed in borehole core BH-6, drilled at Dingtanzi, Hengchun Peninsula, southern Taiwan. We focused on the underlying strata of reefal limestone which could be divided into mudstone and conglomerate lithofacies in ascending order. The former belongs to the Maanshan Formation, which mainly consists of unconsolidated mudstone and irregular carbonate-cemented mudstone nodules. The conglomerate lithofacies mainly consists of well-rounded granule- to cobble-sized lithic grains and shows a matrix to clast-supported fabric. The lithology of those lithoclasts mainly comprises carbonate-cemented mudstone and well-lithified calcareous sandstone, and is thought to be eroded from carbonate-cemented mudstone of the Maanshan Formation. The facies change from the underlying mudstone upward into conglomerate is abrupt, suggesting results of bottom scouring. In total, eight and 12 mudstone subsamples were respectively prepared from rocks of the mudstone lithofacies and conglomerate lithofacies. In addition, one coral sample was selected from each of the conglomerate and reefal limestone lithofacies to test for burial diagenesis of carbonates. Moreover, 11 floats obtained from a preliminary field survey conducted in 2012 were also included in this study. These collection sites are located near or at the Maanshan Formation outcrops, all of which are most likely derived from the Maanshan Formation as a result of human activities in this area. These rocks occurred as pipe-like, thin- to medium-bedded, massive carbonate-cemented mudstone. In total, 19 subsamples for analyses were prepared from these field collections. Based on XRD analyses of the 39 subsamples, the two coral skeletons are considered to be pristine and are possibly Holocene in age, which should be excluded from subsequent discussions. δ13C values of 37 subsamples were all negative and ranged from -31.8‰ to -6.7‰ V-PDB. δ18O values of 11 subsamples were negative (-8.4‰ to -0.4‰ V-PDB), whereas 26 subsample carbonates yielded 18O-enriched data (+0.9‰ to +7.5‰ V-PDB). According to the isotopic compositions, two borehole core subsamples fell within the range of temperate meteoric diagenesis. Most of the δ13C values of 35 subsamples (-31.8‰ to -7.5‰ V-PDB) indicated that their carbonates had possibly precipitated from deep thermogenic hydrocarbon seepages. As a whole, δ18O values of cold-seep carbonates previously collected from the Kenting Mélange were more negative than those of this study. This study documents the first discovery of cold-seep carbonates from the Maanshan Formation.
全文Full Text
DOI10.6693/CAR.201803_(31).0002
系統號NO000005089

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