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91.
The intramontane basins of the Betic Cordilleras (SE Spain) formed subsequent to the main phase of orogenic deformation during the middle Miocene in a close genetic relation to the Trans-Alboran Shear zone. Left lateral movements along a local branch (Carboneras fault zone, CF; strike NE–SW) of this zone played a major role in controlling the formation and dynamics of the Nijar-Carboneras Basin. To the south of the fault, a major phase of strike-slip faulting is recorded during the late Tortonian. The expression of this event is the Brèche Rouge de Carboneras (BRC), which seals a deep denudational surface on top of dislocated fault blocks formed by volcanics of the Cabo de Gata complex and early Tortonian shallow marine calcarenite. The sedimentary facies of this widely distributed unit in the Carboneras-Subbasin mirror the submarine topography and the distribution of the fault zones. Along strike-slip fault zones, autoclastic breccias and neptunian dikes preferentially oriented NW–SE and NE–SW occur, which are interpreted to represent the near-surface expression of the faults. Red limestone forms the groundmass of the autoclastic breccia and infills of neptunian dikes, which exhibit multiple phases of opening of fissures, gravitational sedimentary infill, lithification, and renewed creation of cracks. Steep relief, probably along fault scarps, was mantled by epiclastic volcanic conglomerate with a red carbonate matrix. Well-lithified coarse skeletal limestone rich in planktonic foraminifera formed pavements along sediment starved rocky surfaces in deep water. Laterally, within topographic depressions, the pavement limestone grades into thick accumulations of skeletal rudstone composed of fragmented azooxanthellate corals and stylasterid hydrozoans, which were concentrated by powerful bottom currents and gravitiy flows. Within the shallow water zone of dip slope ramps, cross-bedded calcarenite and calcirudite formed. Based on textures, fabrics and biota, rocks of the BRC were grouped into nine genetic lithofacies which document cryptic, deep-aphotic and shallow-photic environments typical of a sediment starved extensional basin. 相似文献
92.
Given the difficulty of separating the three Picea species—P. glauca, P. mariana, and P. rubens (white, black, and red spruce)—in the pollen record, little is known about their unique histories in eastern North America following deglaciation. Here we report the first use of a classification tree analysis (CART) to distinguish pollen grains of these species. It was successfully applied to fossil pollen from eight sites in Maine and one in Massachusetts. We focused on the late glacial/early Holocene (14,000 to 8000 cal yr B.P.) and the late Holocene (1400 cal yr B.P. to present)—the two key periods since deglaciation when Picea has been abundant in the region. The result shows a shift from a Picea forest of P. glauca and P. mariana in the late glacial to a forest of P. rubens and P. mariana in the late Holocene. The small number of P. rubens grains identified from the late glacial/early Holocene samples (<5%) suggests that that species was either absent or rare at most of the sites. The occurrence and distribution of the three species do not reveal any geographic or temporal trend during late glacial time, but the data suggest that they were distributed in local patches on the landscape. The results of this study indicate that the recent population expansion of Picea (1000 to 500 cal yr B.P.) was likely the first time since deglaciation that P. rubens was abundant in the region. 相似文献
93.
Charles E Schweger 《Quaternary Research》2003,60(1):44-49
Pollen analysis at two sites, correlated by the presence of the 190,000 yr-old Sheep Creek tephra, documents fluctuations in vegetation and climate consistent with this date and indicates that the records span marine oxygen isotope stage 7 and the stage 6/7 transition. Dawson Cut, near Fairbanks, Alaska, provides a 5.2-m-long pollen record of interglacial boreal forest succeeded by shrub tundra and then forest/tundra. Ash Bend, Stewart River, central Yukon, provides a 9.5-m-long record of interglacial boreal forest succeeded by forest/tundra, shrub tundra, and herbaceous tundra. The replacement of forest at both sites by more open or tundra vegetation indicates warm interglacial conditions giving way to cold and arid climate. It is not clear whether stage 7 was warmer than the present. The warm-cool-warm climate oscillation evident at both sites may correlate to Lake Baikal substages 7a, 7b, and 7c. Sheep Creek tephra fell on forest/tundra vegetation. 相似文献
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Vijaya 《Cretaceous Research》1997,18(6):833-847
Palynofloras have been examined from infra- and intertrappean sediments of the Panchet and Rajmahal Formations in the Domra Sub-basin of the Damodar Basin, West Bengal, India. Three distinct palynological assemblages are identified and referred to the following palynozones: (i)Lundbladispora–Verrucosisporites(506.60–505.00 m, late Early Triassic, (ii)Murospora florida(501.65–422.20 m. Late Jurassic, Kimmeridgian–Tithonian), and (iii)Cicatricosisporites australiensis(342.00–229.6 m. Early Cretaceous, Tithonian–Berriasian). The first occurrences ofCallialasporites turbatusandC. dampieriare at 501.65 m.Callialasporitesis a dominant element of the succeeding assemblages from the Panchet Formation and indicates a Jurassic age. The FAD ofCicatricosisporites australiensisandC. augustusat 342.00 m, and inconsistent occurrences ofAequitriradites spinulosus,Crybelosporites stylosusin the overlying sediments indicate Jurassic–Cretaceous transition. 相似文献
96.
略论塔里木古生代盆地演化 总被引:11,自引:0,他引:11
依据所处板块构造位置和地球动力学环境,提出塔里木古生代盆地演化经历了震旦—泥盆纪和石炭—二叠纪两个完整的开合旋回。第一旋回自震旦纪开始张裂形成大陆裂谷,寒武—奥陶纪伸展为被动大陆边缘,志留—泥盆纪俯冲消减,泥盆纪晚期碰撞闭合,时间跨度达400Ma以上。第二旋回表现为石炭—二叠纪弧后拉张—弧后造山事件,延续仅约100Ma。 相似文献
97.
北淮阳金寨—苏仙石地区中生代花岗岩类岩石学及地球化学特征 总被引:4,自引:4,他引:4
位于大别山北麓的北淮阳金寨—苏仙石地区广泛发育花岗岩类侵入岩,同位素年龄为140~97Ma,时代属J3—K1。根据侵入岩的地质、岩石学和岩石地球化学特征,将本区侵入岩划分为3个超单元(包括10个单元)和3个独立单元,分属中性岩和酸性岩两大类,岩石类型有闪长岩、二长岩和花岗岩等。根据岩石化学的判别结果,侵入岩均属亚碱性系列中的钙碱性岩石,并属于普通型和钾质型 相似文献
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99.
100.
本文介绍了GIS的基本概念原理,分析了应用GIS处理地质信息的可行性和优越性,并以在河北晚古生代岩相古地理研究中的应用为实例,介绍了应用GIS处理分析地质信息的一般方法。最后分析了GIS处理地质信息方面还存在的一些问题,笔者认为,随着GIS技术及其基础学科的不断发展,GIS在处理地质信息方面将显示出更大的潜力 相似文献