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81.
在综合分析区域地质背景、铜矿床基本特征、主要控矿因素、找矿标志的前提下,对该区寻找铜矿的前景提出了看法,指出宁芜北段今后寻找铜矿应侧重斑岩型铜矿,提出了皇姑山等地区可作为今后寻找铜矿的重点地段及今后找矿的工作建议。 相似文献
82.
The Tandilia Belt in northeast Argentina includes a Neoproterozoic sequence of sediments (Sierras Bayas Group), in which the Cerro Largo Formation, ca. 750 Ma in age, forms a siliciclastic, shallowing upward succession of subtidal nearshore to tidal flat deposits. Trace fossils Palaeophycus isp. and Didymaulichnus isp. have been described from the upper part of this succession. Specific sedimentary structures consisting of round-crested bulges, arranged in a reticulate pattern, and networks of curved cracks are associated with the trace fossils. These structures are considered to be related to epibenthic microbial mats that once colonized the sediment surface. They reflect stages of mat growth and mat destruction, if compared to analogous structures in modern cyanobacterial mats of peritidal, siliciclastic depositional systems. Also the trace fossils are interpreted as mat-related structures, partly forming components of networks of shrinkage cracks, partly representing the upturned and involute margins of shrinkage cracks or circular openings in desiccating and shrinking, thin microbial mats.
The definition of Didymaulichnus miettensis Young as a Terminal Proterozoic trace fossil is questioned, and it may be considered to interpret the ‘bilobate’ structure as the upturned, opposite margins of microbial shrinkage cracks which have been brought back into contact by compaction after burial. 相似文献
83.
A geological study of the hitherto poorly described Neoproterozoic Gifberg Group, with emphasis on lithogeochemistry and O, C and Sr isotopic composition of the carbonate-dominated Widouw Formation (Vredendal Outlier, westernmost South Africa) revealed that the entire group is an equivalent of the relatively well constrained Port Nolloth Group in the external, paraautochthonous part of the Pan-African Gariep Belt further north. Thus, the Vredendal Outlier can be regarded as the southern extension of the Port Nolloth Zone. Two diamictite units are recognised in the Vredendal Outlier, which can be correlated respectively with the c. 750 Ma Kaigas Formation diamictite and the 583 Ma, syn-Gaskiers Numees Formation diamictite in the Gariep Belt proper. The dominating carbonate unit in the studied area is post-glacial with respect to the older of the two diamictite units. The combined textural, structural and geochemical evidence suggests that parts of the variably dolomitised limestone succession represent former evaporite beds. Sedimentation in a restricted, very shallow and proximal basin led to a wide range in C isotope ratios (δ13CPDB from − 4.2 to + 4.8‰), very high Sr concentrations (derived from original anhydrite) and initial 87Sr/86Sr ratios that are significantly higher (0.70785) than those of coeval seawater. As C and Sr isotopes are commonly used for chemostratigraphic correlation, and high Sr concentrations in Neoproterozic carbonates are often interpreted as evidence of former aragonite, the findings of this study should be used as warning against uncritical use of geochemical and isotopic parameters for describing ancient seawater composition. Thus C and Sr isotope ratios alone in Neoproterozoic carbonates may be less powerful proxies of ancient seawater composition, and high Sr contents are not necessarily indicative of an “aragonite sea”, as previously inferred. 相似文献
84.
Takeshi Ohno Tsuyoshi Komiya Yuichiro Ueno Takafumi Hirata Shigenori Maruyama 《Gondwana Research》2008,14(1-2):126
We measured both mass-dependent isotope fractionation of δ88Sr (88Sr/86Sr) and radiogenic isotopic variation of Sr (87Sr/86Sr) for the Neoproterozoic Doushantuo Formation that deposited as a cap carbonate immediately above the Marinoan-related Nantuo Tillite. The δ88Sr and 87Sr/86Sr compositions showed three remarkable characteristics: (1) high radiogenic 87Sr/86Sr values and gradual decrease in the 87Sr/86Sr ratios, (2) anomalously low δ88Sr values at the lower part cap carbonate, and (3) a clear correlation between 87Sr/86Sr and δ88Sr values. These isotopic signatures can be explained by assuming an extreme greenhouse condition after the Marinoan glaciation. Surface seawater, mixed with a large amount of freshwater from continental crusts with high 87Sr/86Sr and lighter δ88Sr ratios, was formed during the extreme global warming after the glacial event. High atmospheric CO2 content caused sudden precipitation of cap carbonate from the surface seawater with high 87Sr/86Sr and lighter δ88Sr ratios. Subsequently, the mixing of the underlying seawater, with unradiogenic Sr isotope compositions and normal δ88Sr ratios, probably caused gradual decrease of the 87Sr/86Sr ratios of the seawater and deposition of carbonate with normal δ88Sr ratios. The combination of 87Sr/86Sr and δ88Sr isotope systematics gives us new insights on the surface evolution after the Snowball Earth. 相似文献
85.
86.
2005年在河南西峡含恐龙蛋层中首次发现介形虫化石,产自红山水库-丹水剖面上白垩统赵营组下段64层,是以Eucypris-Mongolocypris-Cypridea-Talicypridea为特征的介形虫化石组合,由12属20余种组成.其中Talicypridea是中国、蒙古和东亚晚白垩世最典型的化石,在非洲刚果及南美阿根廷的晚白垩世地层中也有分布,因此赵营组的时代无疑应归属为晚白垩世.赵营组介形虫化石的新发现,为地层的划分对比、沉积环境的演变和盆地的演化研究提供了重要的依据. 相似文献
87.
88.
山东莒南地质公园发现小型兽脚类恐龙
足迹化石Minisauripus 总被引:2,自引:0,他引:2
在山东省莒南地质公园内发现6个小型恐龙足迹化石,被归入足迹属Minisauripus。化石产于下白垩统大盛群田家楼组.时代为早白垩世巴列姆(Barremian)-阿普特期(Apdan)。5个较大,长约6cm,产于下部“主”层面上,其中4个组成2节行迹:1个较小,长约3cm,位于“主”层面30cm之上的上部层面上。山东Minisauripus的特征是:足迹个体小(长3.1~5.6cm,宽2.0~3.7cm),三趾型,略不对称;足迹纵长,各趾近平行,趾垫较清晰;趾末端较钝,但爪迹较尖。Ⅲ趾比Ⅳ趾略长,而Ⅳ趾比Ⅱ趾略长且窄。此外,步幅较长,足长与步长之比约为10:1。与四川、韩国Minisau却淞不同之处是:足迹个体较大,长约是它们的2倍。继中国四川和韩国之后,山东是Minisau而淞在全球的第三个发现点。 相似文献
89.
90.
辽东南地区晚中生代地层发育不甚完全,具有两期盆地叠合演化的特征,即早中侏罗世和早白垩世两个演化阶段,经历了2次伸展裂陷和2次挤压反转。在详细研究辽东南地区各盆地岩石地层序列、生物化石组合特征、年代地层格架以及区域地层对比的基础上,讨论了盆地的演化阶段和演化规律,指出是古太平洋板块向东亚大陆边缘不同方向的俯冲与走滑,以及来自北方西伯利亚板块的持续碰撞挤压的联合构造应力场制约了中国东北地区晚中生代盆地的裂陷过程和构造反转的演化,进而为揭示华北克拉通晚中生代岩石圈演化的动力学机制提供参考依据。 相似文献