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211.
Trace fossils of Beaconites type are found abundantly and widely in the Old Red Sandstone magnafacies of the British Isles, particularly in fluviatile deposits, where they occur in or closely associated with channel sandstones. Because of their giant size, however, terminations to the sediment-filled burrows are almost impossible to detect, and it has hitherto been uncertain whether the Beaconites organism dwelt in or near active rivers, or merely colonized the sandy deposits at their abandoned sites. At Llanstephan in southwest Wales B. antarcticus is preserved in a laterally accreted sandstone, a unique example of the trace fossil being truncated by an erosion surface cut during the sideways growth of a presumed point bar. The Beaconites organism is therefore thought to have lived in and near active river channels, where a moist environment was provided. 相似文献
212.
辽西阜新北部原建平群大理岩系中微古植物化石的发现及其意义 总被引:3,自引:1,他引:2
在辽西阜新北部原建平群大理岩系中发现了大量的微古植物化石,经鉴定有5个属,其组合时代为中元古代。这些微古植物化石的发现为确定这些大理岩形成时代提供了可靠证据,并对进一步探讨华北板块北缘古大陆边缘构造演化及整个东北亚地区的前寒武纪地质具有重要意义。 相似文献
213.
Puncoviscana folded belt in northwestern Argentina: testimony of Late Proterozoic Rodinia fragmentation and pre-Gondwana collisional episodes 总被引:1,自引:0,他引:1
R. H. Omarini R. J. Sureda H.-J. Götze A. Seilacher F. Pflüger 《International Journal of Earth Sciences》1999,88(1):76-97
Stratigraphic correlations and tectonic analysis suggest that the Puncoviscana fold belt of northwestern Argentina was an
intracontinental basin with bimodal igneous suites that formed in connection with the breakup of the Rodinia supercontinent
(at ∼800 Ma). Several lines of evidences point to an initial lithosphere rupture, possibly induced by a rising mantle plume.
The earliest synrift igneous products are represented by ultra-potassic dykes and alkaline lava flows of high LREE/HREE and
low Zr/Nb–Y/Nb ratios. The dyke emplacements and the initiation of rifting were probably synchronous. They pass laterally
and upwards (middle part of the Puncoviscana succession) into basalts of alkaline transitional character (OIB-like source).
The distinctive chemical feature of these lavas are very similar to the source of oceanic island basalts; thus, they are thought
to represent a magmatism associated with the rift and rift-drift transition stage. During this stage of rifting probably true
oceanic crust was formed. The upper part of the Puncoviscana sequence, Late Precambrian/Lower Cambrian in age, comprises a
thick and monotonous sequence of pillow lavas, massive basaltic flows and minor volcanic breccias and hyaloclastites. These
lavas exhibit MORB trace element characteristics with high FeOt and TiO2, low K2O and P2O5, flat light REE spectra, little or no depletion in Nb and Ta. This volcanism consists of the major and latest effusive episode
from the Puncoviscana basin which was slightly modified by subduction processes. The geodynamical model proposed for the generation
of these volcanic rocks could have been developed in two stages. In the first stage the volcanic event is compatible with
a progressive opening of a continental rift leading to formation of a mature oceanic basin. In contrast, the second stage
shows the effects of a completed Wilson cycle including a primitive volcanic arc which continued until the accreted Cuyania-Arequipa-Belen-Antofalla
(CABA) terrane against the proto-Gondwana western borderland of the Amazonian shield (∼535 Ma).
Received: 23 December 1997 / Accepted: 9 December 1998 相似文献
214.
215.
CENOZOIC SEDIMENTARY SEQUENCE IN THE KUMUKULI BASIN, XINJIANG AND NEW EVIDENCE ON LATE QUATERNARY UPLIFT OF THE QINGHAI—TIBETAN PLATEAU 相似文献
216.
风暴沉积的遗迹学研究 总被引:5,自引:0,他引:5
遗迹化石正在证明其在鉴别和解释事件地层中的作用。风暴沉积含有一套混合的、与能量水平变化相适应的遗迹化石组合,两种不同的遗迹群落反映变化着的行为方式对生物所移居的两种连续的,但是单个性质不同的生境所作出的反应:常住的或平常天气的遗迹群落可以作为一种稳定的底栖群落的代表,在这一群落里单个的居群达到或接近它们的承载能力;而周期性产生的风暴遗迹群落则代表着在一种不稳定的、生态环境恶化的、机械控制的环境下繁盛的机会主义生物的群落。典型的陆源碎屑的风暴沉积中的遗迹群落可以加拿大艾伯塔上白垩统卡迪组中的遗迹群落为例,而碳酸盐风暴沉积中的遗迹群落则可以中国华北地台东部上寒武统崮山组中的碳酸盐风暴沉积序列中的遗迹群落为例,本文详细介绍这两种类型的成因及结构、构造特点。 相似文献
217.
豫西鲁山洛峪口组宏观藻类的发现及地质意义 总被引:6,自引:1,他引:5
本文报道在华北地台南缘豫西鲁山下汤九女洞剖面洛峪群洛峪口组下部灰绿色粉砂质页岩中发现可靠的宏观碳质印膜化石,包括Chuaria,Shouhsienia,Tawuia,Ovidiscina等属。通过同国内外已发现的前寒武纪宏观藻类资料广泛对比,并结合其他化石资料的综合分析,对华北地台南缘晚前寒武纪地层对比及新元古代地层格架进行探讨。 相似文献
218.
山东聊城地区隐伏的晚古生代含煤地层发育,其中晚石炭—早二叠世太原组灰岩中富含类化石。由三灰、七灰、十灰共鉴定出化石11属45种,自上而下可建立1个类组合带(Pseudoschw agerina带),2个类组合亚带(Triticites paramontiparus亚带;Pseudofusulina firma-Rugosofusulina complicata亚带),该地区所产类组合与华北其他地区及国外相关组合具可比性,Pseudoschw agerina带的时代为早二叠世早期。 相似文献
219.
ZHANG Zhifei HAN Jian ZHANG Xingliang LIU Jianni SHU DeganEarly Life Institute Key Laboratory for Continental Dynamics of the Ministry of Education Northwest University Xi''an Shaanxi E-mail: zhangelle@sina.com.cn Wang Si''en Xie Guanglian 《《地质学报》英文版》2003,77(3):288-293
The Chengjiang Lagerstatte has been celebrated for prolific soft-bodied fossils. Based on specimens recently excavated in the Chengjiang Lagerstatte by the Early Life Institute, Northwest University, Diandongia pista Rong, 1974, is directly revealed to be a pediculate brachiopod, assigned to the Family Botsfordiidae, as is further confirmed by the exceptionally preserved vascular system including dorsal and ventral mantle canals. These specimens described herein exhibit some peculiarities, notably the extremely thin and long pedicles, which suggest that Diandongia is epifaunal rather than burrowing brachiopod. A study of this group of animals indicates that they may be vital to understand the relationship between the lingulids and the remaining brachiopods, and the character evolution of the early Cambrian brachiopods. 相似文献
220.