Devonian-Carboniferous transition containing a Hangenberg Black Shale equivalent in the Pho Han Formation on Cat Ba Island, northeastern Vietnam
Devonian-Carboniferous transition containing a Hangenberg Black Shale equivalent in the Pho Han Formation on Cat Ba Island, northeastern Vietnam
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DOI：
10.1016/j.palaeo.2014.03.021
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发表时间：
2014-06
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通讯作者：
T. Komatsu;S. Kato;Kento Hirata;R. Takashima;Yukari Ogata;M. Oba;H. Naruse;P. Tạ;Phong Nguyen;H. T. Dang;T. N. Doan;H. H. Nguyen-H.;S. Sakata;K. Kaiho;P. Königshof
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作者：
T. Komatsu;S. Kato;Kento Hirata;R. Takashima;Yukari Ogata;M. Oba;H. Naruse;P. Tạ;Phong Nguyen;H. T. Dang;T. N. Doan;H. H. Nguyen-H.;S. Sakata;K. Kaiho;P. Königshof
在越南东北部的Cat Ba岛，泥盆纪到石炭纪的转换(D-C)主要由斜坡型碳酸盐岩夹在Pho han组中的黑色页岩层(1-176层)组成，是古特提斯东部为数不多的D-C转换记录之一。层序的三个主要相是相1(白灰到灰灰岩和泥灰岩的交替)、相2(钙灰岩，115B层)和相3(暗灰色灰岩和富有机碳的黑色页岩的交替，层115C-120和126-129)。法门期最新牙形刺组合OFS。在113-115c层中识别出多齿红藻、细掌藻、乙状掌藻和多齿红藻。第105-112层通常含有扩张棕榈藻、纤细棕榈藻和细小棕榈藻。乙状结肠。119层产生了基底石炭纪指数牙形齿沟管藻。在116-118层中，有柱状拟毛虫和拟毛类等立足类。是富有机碳的深灰色灰岩中的特征物种。1相以生物碎屑、颗粒状和碎屑内砾岩和包岩为特征，含有大量的正常级配和交错纹层，代表风暴波基面以上的深层斜坡碳酸盐岩。相2为典型的覆盖在海侵面上的滞后沉积。相3由富含有机碳的黑色页岩和少量冲刷充填的生物碎屑岩、颗粒岩和碎屑内填充岩组成，可能代表碳酸盐斜坡周围的边缘盆地平原环境。富含有机碳的黑色页岩和深灰色包岩(相3)蚀变无生物扰动迹象，有机碳含量高(0.18~5.73wt.%)。在海侵滞后沉积(从相2的115B层到相3的下部的115C-120层)内的一个小序列相当于汉根堡黑色页岩(S，L)。由于115B-120层没有生物扰动的证据和高TOC含量，解释为在缺氧-缺氧条件下堆积的115B-120层。
On Cat Ba Island in northeastern Vietnam, the Devonian to Carboniferous (D–C) transition consists mainly of ramp carbonates intercalated with black shale beds (Beds 1 to 176) in the Pho Han Formation and is one of the few records of the D–C transition of the eastern Paleotethys. The three main facies of the sequence are Facies 1 (alternations of whitish gray to gray limestone and marl), Facies 2 (calcirudite, Bed 115b), and Facies 3 (alternations of dark gray limestone and organic-carbon-rich black shale, Beds 115c–120 and 126–129). The latest Famennian (Siphonodella praesulcataSubzone) conodont assemblage ofS. praesulcata,Palmatolepis gracilis,Palmatolepis sigmoidalis, andRhodalepis polylophodontiformiswas recognized in Beds 113–115c. Beds 105–112 commonly containPalmatolepis expansa,P. gracilis, andP. sigmoidalis. Bed 119 yielded a basal Carboniferous index conodontSiphonodella sulcata. In Beds 116–118, solenoporids such asPseudochaetetes elliottiandParachaetetessp. were characteristic species in organic-carbon-rich dark gray limestone.Facies 1 is characterized by bioclastic, peloidal, and intraclastic grainstone and packstone containing massive normal grading and cross-laminations, and is interpreted to represent deep ramp carbonates above storm wave base. Facies 2 is represented by typical lag deposits overlying a transgressive surface. Facies 3 comprises organic-carbon-rich black shale and minor scour-filling bioclastic, peloidal, and intraclastic packstone, and may represent a marginal basin plain environment surrounding a carbonate ramp. The alternations of organic-carbon-rich black shale and dark gray packstone (Facies 3) show no evidence of bioturbation and have high TOC contents (0.18–5.73 wt.%). A minor succession within the transgressive lag deposits (from Bed 115b of Facies 2 to Beds 115c–120 in the lower part of Facies 3) is equivalent to the Hangenberg Black Shale (s. l.) in the middle part of theSiphonodella praesulcatatoSiphonodella sulcatazones, because Beds 115b–120 characterized by no evidence of bioturbation and high TOC contents are interpreted to be accumulated in anoxic to dysoxic conditions.