Lower Triassic mixed carbonate and siliciclastic setting with Smithian-Spathian anoxic to dysoxic facies, An Chau basin, northeastern Vietnam
Lower Triassic mixed carbonate and siliciclastic setting with Smithian-Spathian anoxic to dysoxic facies, An Chau basin, northeastern Vietnam
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DOI：
10.1016/j.sedgeo.2013.10.009
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发表时间：
2014-03-01
影响因子：
2.8
通讯作者：
Sone, Masatoshi
中科院分区：
文献类型：
--
作者：
Komatsu, Toshifumi;Naruse, Hajime;Sone, Masatoshi
在越南东北部的安州盆地，奥伦尼克阶（下三叠统）阶段包括混合碳酸盐岩和硅质碎屑浅海到边缘盆地沉积物，延伸至华南南盘江盆地南部。上谅山组以硅质碎屑相为主，由受风暴和波浪影响的浅海和斜坡沉积物组成。上覆和相互交错的 Bac Thuy 组由潮坪、波浪影响的碳酸盐台地、斜坡和边缘盆地平原沉积物组成。潮滩沉积物主要由透镜状、波状层状或薄层状碳酸盐岩组成，含有干燥裂缝和波纹，表明存在双向古水流。台地碳酸盐岩以波状波纹、鲕鱼为特征，海相软体动物和微体化石丰富；软体动物化石组合主要包含史密斯菊石，例如 Owenites koeneni。斜坡沉积物的特点是石灰岩角砾岩和滑塌层。边缘盆地平原沉积物由经典浊积岩层、少量石灰岩角砾岩以及含有斯巴斯蒂亚菊石提罗沸石和钶沸石的半远洋泥岩和泥灰岩组成。浊积岩组可能代表了边缘盆地平原的锋面张开环境。这些Olenekian碳酸盐岩和硅质碎屑岩相是典型的海侵层序。Smithian-Spathian边界和Smith晚期的缺氧至缺氧相的特点是富含有机质的深灰色灰岩和泥岩沉积物，夹层在斜坡到边缘盆地平原相的序列中，主要由重力流和半远洋沉积物组成。富含有机物的沉积物没有显示出生物扰动的证据，并且其特征是动物群多样性低。盆地边缘平原沉积物中的碎屑明显来自西部；因此，硅质碎屑重力流的古水流方向大致为向东。皇冠版权所有 (C) 2013 由 Elsevier B.V. 出版。保留所有权利。
In the An Chau basin in northeastern Vietnam, the Olenekian (Lower Triassic) stage comprises mixed carbonate and siliciclastic shallow marine to marginal basin deposits that extend into the southern Nanpanjiang basin in South China. The upper Lang Son Formation, which is dominated by siliciclastic facies, is composed of storm- and wave-influenced shallow marine and slope deposits. The overlying and interfingering Bac Thuy Formation consists of tidal flat, wave-influenced carbonate platform, slope, and marginal basin plain deposits. The tidal flat deposits are composed mainly of lenticular, wavy-bedded, or thin flat-bedded carbonates containing desiccation cracks and ripples that are indicative of bidirectional paleocurrents. The platform carbonates are characterized by wave ripples, ooids, and abundant marine mollusks and microfossils; the molluscan fossil assemblage primarily contains Smithian ammonoids such as Owenites koeneni. The slope deposits are characterized by limestone breccia and slump beds. The marginal basin plain deposits consist of classical turbidite beds, minor limestone breccia, and hemipelagic mudstone and marl containing the Spathian ammonoids Tirolites and Columbites. The turbidite sets may represent frontal splay environments in the marginal basin plain. These Olenekian carbonate and siliciclastic fades are typical of a transgressive succession.The Smithian-Spathian boundary and the anoxic to dysoxic facies of the latest Smithian are characterized by organic-rich dark gray limestone and mudstone deposits intercalated in the succession of slope to marginal basin plain fades, which are composed mainly of gravity flow and hemipelagic deposits. The organic-rich deposits show no evidence of bioturbation and are characterized by low-diversity fauna. Clastics in the marginal basin plain deposits were apparently supplied from the west; hence, the paleocurrent direction of the siliciclastic gravity flows was approximately eastward. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.