安徽巢湖平顶山下三叠统牙形石生物地层序列   总被引：6，自引：2，他引：4  

赵来时童金南  左景勋 《地球科学》2003,28(4):414-418

简要介绍安徽巢湖平顶山下三叠统牙形石生物地层研究的最新成果.对平顶山西坡剖面112.8 m厚的下三叠统地层所采集的286件牙形石样品, 经处理后获得2 870余枚牙形石样本, 经鉴定共有11属51种.这些属分别是Hindeodus, Isarcicella(?), Neogondolella, Neospathodus, Platyvillosus, Cratognathodus, Parachirognathus, Pachycladina, Ellisonia, Aduncodina和Cornudina.牙形石生物地层从老到新可划分为9个牙形石带: (1)Hindeodus typicalis- Neogondolella planata带; (2)Neogondolella krystyni带; (3)Neospathodus kummeli带; (4)Neospathodus dieneri带; (5)Neospathodus n. sp. C- Neospathodus n.sp. D带; (6) Neospathodus waageni带; (7)Neospathodus n.sp. M带; (8)Neospathodus eotriangularis带; (9) Neospathodus abruptus- Neospathodus homeri带.牙形石的组合面貌基本可与国内外其他地区牙形石带相对比.但其中牙形石(2), (3), (5), (7), (8)带为巢湖地区首次建立.在下三叠统菊石带控制下所建立的连续的牙形石分带对全球的三叠系阶的对比具有十分重要的意义. 关键词: 牙形石; 牙形石生物地层; 下三叠统; 安徽巢湖.   相似文献   

The subduction of the Paleo‐Pacific Plate to the Jiamusi Block: Evidence from the Early Mesozoic sedimentary rocks of the eastern Jiamusi Block     

Zhongjie Xu  Jintao Kong  Rihui Cheng  Jianbo Zhou 《Island Arc》2020,29(1)

In order to provide references of the subduction process of the Paleo‐Pacific Plate beneath the Jiamusi Block, this paper studied the clastic rocks of the Nanshuangyashan Formation using modal analysis of sandstones, mudstone elements geochemistry, and detrital zircon U–Pb dating. These results suggest the maximum depositional age of the Nanshuangyashan Formation was between the Norian and Rhaetian (206.8 ±4.6 Ma, mean standard weighted deviation (MSWD) = 0.17). Whole‐rock geochemistry of mudstone indicates that source rocks of the Nanshuangyashan Formation were primarily felsic igneous rocks and quartzose sedimentary rocks, which were mainly derived from the stable continental block and a magmatic arc. Detrital zircon analysis showed the Nanshuangyashan Formation samples recorded four main age groups: 229–204 Ma, 284–254 Ma, 524–489 Ma and 930–885 Ma, and the provenances were attributed to the Jiamusi Block and a Late Triassic magmatic arc near the study area. Furthermore, the eastern Jiamusi Block was a backarc basin, affected by the subduction of the Paleo‐Pacific Plate in the Late Triassic, but the magmatic arc related to the subduction near the study area finally died out due to tectonic changes and stratigraphic erosion.  相似文献   

西秦岭上三叠统海底扇沉积环境特征与模式          下载免费PDF全文

张晓宝  方国庆 《地质科学》1996,31(2):154-162

利用浊积岩相、相组合和组合序列分析方法,将西秦岭上三叠统浊积岩系划分为B、C、D、E、G等5个浊积岩相;水道、越岸沉积、舌状体-水道过渡带、舌状体、盆地平原等5个相组合;盆地平原→舌状体和盆地平原→舌状体→舌状体-水道过渡带→水道等2个组合序列。研究结果表明研究层段属海底扇沉积环境,并具有浊流搬运斜坡较陡,冲刷作用强烈;堆积地形平缓,为盆底扇;巳扇体规模较小,水道与舌状体相连等特征。基于上述分析,建立了海底扇的沉积模式。  相似文献   

Giant sector-collapse structures (scalloped margins) of the Yangtze Platform and Great Bank of Guizhou,China: Implications for genesis of collapsed carbonate platform margin systems     

Daniel J. Lehrmann  Marcello Minzoni  Paul Enos  Caroline Kelleher  Leanne Stepchinski  Xiaowei Li  Jonathan L. Payne  Meiyi Yu 《Sedimentology》2020,67(6):3167-3198

Sector-collapse structures ranging up to 27 km wide with up to 7.7 km bankward erosion (scalloped margins) and linear escarpments occur along the east-north-east-trending, south-facing margins of the Yangtze Platform and Great Bank of Guizhou. Exposure of one of the structures on the rotated limb of a syncline displays the geometry in profile view. Declivities range from 65° to 90° in the upper wall and decrease asymptotically to the toe. Catastrophic collapses of the margins in both platforms occurred during the late Ladinian as constrained by the ages of strata truncated along the margins and the siliciclastic turbidites that onlap collapse structures. Middle Triassic Anisian and Ladinian platform-edge reef facies and platform-interior facies were truncated along both the Yangtze and Great Bank of Guizhou margins. Lower Triassic facies were also truncated along the Great Bank of Guizhou margin. Gravity transport during the main episodes of collapse occurred as mud-rich debris-flows and as mud-free hyper-concentrated flows. Clasts, several to tens of metres and, exceptionally, hundreds of metres across, were transported to the basin. Following collapse, talus, carbonate turbidites and periplatform-mud accumulated at the toe of slope. Shedding of skeletal grains and carbonate mud indicates active carbonate factories at the margin. Preserved sections of the margins demonstrate that the platforms evolved high-relief, accretionary escarpments prior to collapse. High-relief, without buttressing by basin-filling sediments, predisposed the margins to collapse by development of tensile strain and fracturing within the margin due to the lack of confining stress. The linear geometry of margins and active tectonics in the region supports tectonic activity triggering the collapse. Collapse is thus interpreted to have been triggered by fault movement and seismic shock. Comparison with other systems indicates that evolution from high-relief accretion to tectonic collapse of largely lithified margins resulted in large sector-collapse structures and deposition of a coarse, generally mud-poor breccia apron.  相似文献   

Controls on carbonate platform architecture and reef recovery across the Palaeozoic to Mesozoic transition: A high-resolution analysis of the Great Bank of Guizhou     

Brian M. Kelley  Daniel J. Lehrmann  Meiyi Yu  Adam B. Jost  Katja M. Meyer  Kimberly V. Lau  Demir Altiner  Xiaowei Li  Marcello Minzoni  Ellen K. Schaal  Jonathan L. Payne 《Sedimentology》2020,67(6):3119-3151

Carbonate platforms spanning intervals of global change provide an opportunity to identify causal links between the evolution of marine environment and depositional architecture. This study investigates the controls on platform geometry across the Palaeozoic to Mesozoic transition and yields new stratigraphic and palaeoenvironmental constraints on the Great Bank of Guizhou, a latest Permian to earliest Late Triassic isolated carbonate platform in the Nanpanjiang Basin of south China. Reconstruction of platform architecture was achieved by integrating field mapping, petrography, biostratigraphy, satellite imagery analysis and δ¹³C chemostratigraphy. In contrast to previous interpretations, this study indicates that: (i) the Great Bank of Guizhou transitioned during Early Triassic time from a low-relief bank to a platform with high relief above the basin floor (up to 600 m) and steep slope angles (preserved up to 50°); and (ii) the oldest-known platform-margin reef of the Mesozoic Era grew along steep, prograding clinoforms in an outer-margin to lower-slope environment. Increasing platform relief during Early Triassic time was caused by limited sediment delivery to the basin margin and a high rate of accommodation creation driven by Indosinian convergence. The steep upper Olenekian (upper Lower Triassic) slope is dominated by well-cemented grainstone, suggesting that high carbonate saturation states led to syndepositional or rapid post-depositional sediment stabilization. Latest Spathian reef initiation coincided with global cooling following Early Triassic global warmth. The first Triassic framework-building metazoans on the Great Bank of Guizhou were small calcareous sponges restricted to deeper water settings, but early Mesozoic reef builders were volumetrically dominated by Tubiphytes, a fossil genus of uncertain taxonomic affinity. In aggregate, the stratigraphic architecture of the Great Bank of Guizhou records sedimentary response to long-term environmental and biological recovery from the end-Permian mass extinction, highlighting the close connections among marine chemistry, marine ecosystems and carbonate depositional systems.  相似文献   

右江盆地中三叠世碎屑岩地球化学特征及其物源分析∶以贵州册亨地区为例     

陈兴  彭成龙  陈建书  吴开彬  张德明  王文明  龚桂源  邓贵标  骆珊 《高校地质学报》2020,26(6):639-655

右江盆地中三叠世充填了一套巨厚的复理石沉积，岩性为细砂岩、粉砂岩、泥岩及其过渡岩石，其独特的沉积特征颇受国内外地质学界关注，但目前对该套碎屑岩的物源尚有争议。文章通过对册亨地区中三叠世碎屑岩开展详细的岩石学和地球化学分析，结果显示：碎屑岩成分成熟度与结构成熟度都较低，具近源沉积特征。SiO₂（平均为58.49%）含量较低，变化范围较大，说明石英含量较低；Al₂O₃（平均为12.46%）含量较高，说明粘土矿物及长石含量较高；Al₂O₃/SiO₂的比值平均为0.22，与杂砂岩（0.20~0.23）一致，说明碎屑岩成熟度较差，亦具近源沉积特征；CaO（平均为7.83%）含量较高，说明含碳酸盐类物质较多。微量元素表现为富集Rb、Th、La、Nd、Hf和Pb以及相对亏损P、Ti、Sr、Nb和Ta的特点，稀土元素具有ΣREE变化范围大，轻稀土富集，Eu亏损的特点。主量、微量和稀土元素分析表明，碎屑岩的源岩以长英质岩石为主，并有少量中性岩及石英质沉积岩的混入；源区构造背景以大陆岛弧为主，兼有被动大陆边缘及活动大陆边缘特 征。化学蚀变指数（CIA）值为53.93~74.80，均值为65.12。通过CIA以及Th/U比值，表明碎屑岩源区主要经历了中等化学风化作用。  相似文献   

藏东类乌齐地区晚三叠世基性岩浆作用与构造意义     

陈言飞  张泽明  陈宣华  田作林  邵兆刚  康东艳  江媛媛 《岩石学报》2020,36(9):2701-2713

羌塘地体东部类乌齐地区是龙木措-双湖古特提斯洋和班公湖-怒江特提斯洋的叠加控制区域，该地区三叠纪的岩浆活动同时受两个大洋演化的影响，导致该地区岩浆岩的构造属性尚不明确。本文对类乌齐地区吉塘岩群内出露的变辉长岩的岩石学、锆石U-Pb年代学和Lu-Hf同位素以及岩石地球化学进行了研究。LA-ICP-MS锆石U-Pb测年结果显示变辉长岩结晶年龄为212~206Ma（晚三叠世）。岩石富集LREEs、Th，亏损Nb、Ta、Zr、Hf和Ti，表现出典型的岛弧火山岩的地球化学特征，较低的ε_Hf（t）值（-10.6~-3.2）表明岩浆来自中元古代岩石圈地幔部分熔融或富集地幔，较高的Th和LREEs含量以及Th/Yb和Th/Nb比值表明岩浆源区有不同程度俯冲沉积物的加入。结合区域上前人的研究成果，本文认为类乌齐地区变辉长岩是形成在班公湖-怒江特提斯洋向北俯冲在羌塘地体下的大陆弧背景下。  相似文献   

大兴安岭中部乌兰浩特地区花岗岩锆石U-Pb年龄、地球化学特征及构造意义     

张海华  李永飞  张健  苏飞  郑月娟  卞雄飞  张德军 《现代地质》2020,34(3):483-493

对内蒙古乌兰浩特地区出露的花岗岩侵入体进行LA-ICP-MS锆石U-Pb定年和岩石地球化学研究,以探讨该区花岗岩形成时代、成因类型和区域构造演化。结果显示,其锆石²⁰⁶Pb/²³⁸U年龄的加权平均值为(214.4±2.6) Ma,反映岩体的结晶年龄为晚三叠世。岩石主量元素具高硅、高碱、富钾,贫钙、贫镁及低钛的特征;稀土元素配分曲线呈“海鸥式”较弱的右倾分布特征,具有强烈的Eu负异常;微量元素Rb、Th、Zr、Y和Yb含量较高,Ba、Sr含量较低,岩石具有高的Rb/Sr 、Rb/Nb 值,显示为低 Sr、高 Yb 型花岗岩的特征。综合分析显示花岗岩形成的压力较低,应为减薄地壳物质熔融的产物。综合区域构造演化和K₂O-Na₂O、(Zr+Nb+Ce+Y)-(Na₂O+K₂O)/CaO、SiO₂-TFeO/MgO、(Y+Nb)-Rb、(Yb+Ta)-Rb、Nb-Y-Ce图解分析,认为该岩体形成于造山后伸展构造背景,研究区由中三叠世的碰撞造山构造体制向晚三叠世造山后伸展构造体制转变,同时西伯利亚板块和华北板块的碰撞时限持续到中三叠世。  相似文献   

右江盆地中三叠统细碎屑岩地球化学特征及其对物源区、构造背景的指示     

赵东杰  王学求 《大地构造与成矿学》2020,(2):311-324

右江盆地位于华南板块西南缘与印支板块的结合部位,于中三叠世沉积了一套以细碎屑岩为主的巨厚浊积岩。研究区中三叠统细碎屑岩的主量、微量和稀土元素分析表明,细碎屑岩以杂砂岩和岩屑砂岩为主,其源岩来自大陆上地壳,物源区岩石类型主要为长英质沉积岩和火成岩,岩石风化程度中等偏高,构造背景为大陆岛弧和活动大陆边缘。综合细碎屑岩稀土元素特征及前人对该区中三叠统古流向和碎屑锆石U-Pb年代学研究,认为中三叠统碎屑物来源复杂,云开地区、江南造山带和越北地块是主要的物源区。  相似文献   

湖北早三叠世鱼龙前肢化石新材料及对比讨论     

邹亚锐  赵璧  陈刚  李姜丽  程龙  阎春波  谭秋明 《地质学报》2020,94(4):1017-1026

杨钟健和董枝明曾在1972年指出中国发现的早三叠世鱼龙Chaohusaurus geishanensis与欧洲的Grippia前肢和头部相似,具有系统关系。但后来中国该时代鱼龙类化石大多前肢特化或不完整,难以进一步对比研究。本文记述了湖北下三叠统嘉陵江组中发现的2件较完整的鱼龙前肢化石新材料,对中国的古老鱼龙类相关信息进行了补充。通过形态学对比,认为湖北被归入Chaohusaurus的早三叠世鱼龙前肢总体特征与同属的Ch.geishanensis接近而与Ch.chaoxianensis有明显差别,而且其以相对较大的个体、间中骨挤压变形以及豌豆骨发育等特征表现出与Grippia、Utatsusaurus、Parvinatator等其他早三叠世鱼龙类前肢的相似性。据此分析推测,早三叠世鱼龙类可能存在两个演化方向。即在二叠纪末大灭绝(EPME)事件后不久,鱼龙类起源并在奥伦尼克期出现分化,一部分个体相对较大、前肢未特化、运动能力较强的鱼龙类实现了跨区交流,另一些个体相对较小、前肢特化、运动能力较弱的鱼龙类则成为地方性(东特提斯区)的独立演化分支。但两者之间的系统发生关系以及Chaohusaurus的单系性还有待进一步研究揭示。  相似文献