Permian–Triassic boundary microbialites at Zuodeng Section, Guangxi Province, South China: Geobiology and palaeoceanographic implications
Permian–Triassic boundary microbialites at Zuodeng Section, Guangxi Province, South China: Geobiology and palaeoceanographic implications
复制标题
广西左邓剖面二叠纪—三叠纪边界微生物岩：地球生物学和古海洋学意义
DOI：
10.1016/j.gloplacha.2017.02.011
复制
发表时间：
2017-05
影响因子：
3.9
通讯作者：
Mao Luo
中科院分区：
文献类型：
--
作者：
Yuheng Fang;Zhong-Qiang Chen;Stephen Kershaw;Hao Yang;Mao Luo
中国南部田东县左登剖面二叠系-三叠系(P-Tr)界线层中一层以前不为人知的微生物层，其下部由薄的叠层岩(最大厚度为5厘米)组成，其余6米为血栓岩。与该地区其他地点一样，左登微闪岩在二叠纪晚期的生物碎屑灰岩和微闪岩之间存在明显的不规则接触。叠层石由低浮雕的柱状和宽阔的穹顶几何形状组成，含有微弱的纹层。血栓岩在抛光的块状中表现为稀疏的深色蚀变微生物组构和浅色间隙沉积物的不规则混合物。大量的微问题钙质微生物结构保存在叠层石的深色叠层区域和血栓岩中的疏松区域(即钙质微生物部分，而不是间隙沉积物)中，并垂直于叠层石层。每个个体都有密集排列的节段，形成柱状到扇形的结构。叠层岩和血栓岩中的石榴石个体略有不同，但很容易与其他P-Tr界面微生物岩中的Gakhumella和Renalcis类化石区分开来，因为它们的尺寸较小，没有分枝的柱状物，排列密集，呈拱形。Renalcids通常具有较大的身体尺寸和分枝，分叶轮廓。叠层石中还观察到丝鞘聚集体，它们都是一个方向的。Gakhumellaas和丝鞘聚集体可能都是光合作用的藻类，这可能在左登微生物群的形成中起到了重要作用。其他钙质微生物为球体，叠层石和血栓石中共识别出五种形态类型：(1)无外鞘的闪光方解石球体，(2)被薄薄的闪光方解石鞘包裹的大的闪光方解石核，(3)被薄薄的闪光方解石鞘包裹的大的泥晶框体集合体核(细菌团状球体)，(4)包裹着薄的微晶鞘的泥晶框体集合体的大核，以及(5)被粗粒的、辐射的真水射线包裹的小的闪光核。由于中国南部地区的区域退缩，左登微生物岩下的不规则接触被解释为陆上曝露面。左登微闪岩的消亡可能是由于海平面的快速上升，因为它们生长在相对较浅的海洋条件下，并被含有远洋牙形刺的泥质石灰岩覆盖。此外，微生物岩上方的硅质碎屑含量增加，表明随着海侵的进行，可能与气候有关的风化作用增加。
A previously unknown microbialite bed in the Permian–Triassic (P–Tr) boundary beds of Zuodeng section, Tiandong County, Guangxi, South China comprises a thin (5 cm maximum thickness) stromatolite in the lower part and the remaining 6 m is thrombolite. The Zuodeng microbialite has a pronounced irregular contact between the latest Permian bioclastic limestone and microbialite, as in other sites in the region. The stromatolite comprises low-relief columnar and broad domal geometries, containing faint laminations. The thrombolite displays an irregular mixture of sparitic dark coloured altered microbial fabric and light coloured interstitial sediment in polished blocks. Abundant microproblematic calcimicrobe structures identified here asGakhumellaare preserved in dark coloured laminated areas of the stromatolite and sparitic areas in thrombolites (i.e. the calcimicrobial part, not the interstitial sediment) and are orientated perpendicular to stromatolitic laminae. EachGakhumellaindividual has densely arranged segments, which form a column- to fan-shaped structure. Single segments are arch-shaped and form a thin chamber between segments.Gakhumellaindividuals in the stromatolite and thrombolite are slightly different from each other, but are readily distinguished from theGakhumella- andRenalcis-like fossils reported from other P–Tr boundary microbialites in having a smaller size, unbranching columns and densely arranged, arch-shaped segments. Renalcids usually possess a larger body size and branching, lobate outlines. Filament sheath aggregates are also observed in the stromatolite and they are all orientated in one direction. BothGakhumellaand filament sheath aggregates may be photosynthetic algae, which may have played an important role in constructing the Zuodeng microbialites. Other calcimicrobes in the Zuodeng microbialite are spheroids, of which a total of five morphological types are recognized from both stromatolite and thrombolite: (1) sparry calcite spheroid without outer sheaths, (2) a large sparry calcite nucleus coated with a thin sparry calcite sheath, (3) a large nucleus of micrite framboid aggregates rimmed by a thin sparry calcite sheath (bacterial clump-like spheroids), (4) a large nucleus of micrite framboid aggregates coated with a thin micritic sheath, and (5) a small sparry nuclei rimmed by coarse-grained, radiated euhedral rays. The irregular contact beneath the Zuodeng microbialites is interpreted as a subaerial exposure surface due to regional regression in South China. The demise of the Zuodeng microbialites may have been due to rapid rise in sea-level because they grew in relatively shallow marine conditions and are overlain by muddy limestones containing pelagic conodonts. Also siliciclastic content increases above the microbialite, suggesting a possible climate-related increase in weathering as the transgression progressed.
登录
查看更多内容
影响因子：
--
作者：
G. Hughes
通讯作者：
G. Hughes
影响因子：
12.1
作者：
A. Woods
通讯作者：
A. Woods
影响因子：
1.8
作者：
S. Kershaw;Li Guo;A. Swift;Jiasong Fan
通讯作者：
S. Kershaw;Li Guo;A. Swift;Jiasong Fan
牙形刺白牙冠中的稀土元素模式：最近二叠纪生物危机期间火山灰大量输入的证据？
影响因子：
3.9
作者：
Gao, Shan;Zhou, Lian;Hu, Zhaochu;Liu, Yongsheng
通讯作者：
Liu, Yongsheng
华南二叠纪—三叠纪边界附近微生物岩中微贝类的古生态学
影响因子：
1.5
作者：
Yongbiao Wang;Weiquan Ou;Wei Liao;Xi Mei
通讯作者：
Xi Mei