首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 0 毫秒
1.
A unique late Quaternary lacustrine deposit has been discovered recently on the Missouri Coteau of North Dakota. A diverse, extremely well-preserved biota of more than 160 species has been recovered primarily from an organic mud deposited about 9500 years before the present. The lacustrine body shallowed gradually as the climate became drier.  相似文献   

2.
3.
4.
Newman WS  March S 《Science (New York, N.Y.)》1968,160(3832):1110-1112
Isobases constructed from recently published data are strikingly parallel to both the edge of the continental shelf off the northeastern United States and the Fall Zone. Our analyses suggest that the downwarping recorded by these isobases may be explained by Daly's hypothesis of a collapsing peripheral or marginal "bulge."  相似文献   

5.
Oxygen isotopic, radiocarbon, and micropaleontological analysis of deep-sea cores from the northeastern Gulf of Mexico identify an episode of rapid ice melting and sea-level rise at about 9600 years B.C. This age coincides, within the limits of all errors, with the age of the Valders ice readvance and with the age assigned by Plato to the flood he describes.  相似文献   

6.
Major negative oxygen isotopic anomalies in planktonic foraminifera are associated with deep-sea anoxic mud layers (sapropels) deposited 9000 and 80,000 years ago in the eastern Mediterranean. The isotopic depletion in surface-dwelling foraminifera is significantly greater than in mesopelagic foraminifera. This difference in isotopic response suggests that surface-water salinities were drastically reduced during times of sapropel formation, possibly as the result of meltwater runoff from the Fennoscandian ice sheet into the eastern Mediterranean by way of the Black and Aegean seas.  相似文献   

7.
Analyses of lignin oxidation products and pollen for an 11-meter core from Lake Washington provide independent but similar reconstructions of the late Quaternary vegetation in the Puget Lowland. An exception is in sediments of the late Pleistocene where pollen percentages and influx values suggest conifer forest whereas lignin compositions suggest a treeless source region. This dissimilarity appears to result from different major provenances: eolian transport of pollen to the lake from adjacent or downstream drainage basins as opposed to fluvial transport of lignified plant debris only from the Lake Washington drainage basin.  相似文献   

8.
A moth egg assignable to the family Noctuidae (Lepidoptera) is described from 75-million-year-old sediments from Martha's Vineyard, Massachusetts. This sample, which extends the fossil record of this farnily and modern heteroneuran moths back to the Cretaceous, may provide insight into the coevolution of moths and flowering plants, as well as have implications for the evolution of bats.  相似文献   

9.
10.
Uranium-lead data indicate that the high-pressure granulitic and charnockitic nuclei within the medium-grade metamorphic complex of the Peruvian coastal area must be related to an orogenic event 2 x 10(9) years ago. As in western Africa and Brazil, this old granulitic basement is reworked by Late Precambrian orogeny. Its presence along the Peru-Chile Trench must be taken into account in interpreting the anomalously high strontium isotopic ratios of recent calc-alkaline volcanism.  相似文献   

11.
在宁夏引黄灌区的生态及生产条件下,研究了北方11个大豆品种在大田种植条件下的生育表现及产量性状,结果表明:参试的11个品种均能正常成熟,生育期在122~142 d,每667 m2折合产量在131.86~415.39 kg之间;品种晋遗52每667 m2折合产量最高、为415.39 kg,冀豆20每667 m2折合产量最低、为131.86 kg,而对照铁丰31每667 m2折合产量为332.44kg.较对照增产的品种有晋遗52、沈农00-5011、晋遗51,其他品种较对照均减产.辽09品-31的百粒重表现为30.2 g、冀豆17单株粒数达到309个,均可以作为优势性状在大豆遗传育种研究中加以利用.  相似文献   

12.
13.
Magnitude of the 2010 Gulf of Mexico oil leak   总被引:1,自引:0,他引:1  
To fully understand the environmental and ecological impacts of the Deepwater Horizon disaster, an accurate estimate of the total oil released is required. We used optical plume velocimetry to estimate the velocity of fluids issuing from the damaged well both before and after the collapsed riser pipe was removed. We then calculated the volumetric flow rate under a range of assumptions. With a liquid oil fraction of 0.4, we estimated that the average flow rate from 22 April 2010 to 3 June 2010 was 5.6 × 10(4) ± 21% barrels/day (1.0 × 10(-1) meter(3)/second), excluding secondary leaks. After the riser was removed, the flow was 6.8 × 10(4) ± 19% barrels/day (1.2 × 10(-1) meters(3)/second). Taking into account the oil collected at the seafloor, this suggests that 4.4 × 10(6) ± 20% barrels of oil (7.0 × 10(5) meters(3)) was released into the ocean.  相似文献   

14.
15.
16.
Condie KC 《Science (New York, N.Y.)》1967,155(3765):1013-1015
Geochemical studies of Wyoming Precambrian graywackes derived from continental crust older than 3.2 x 10(9) years indicate that their source area was at least as highly differentiated as most younger Precambrian crust. The composition of this early crust (approximately that of calcium-rich granite) is not unlike that of the 2.5 to 3.2 x 10(9) year old North American crust. Limited geochemical data suggest that the composition of North America may not have changed significantly during the last 3.0 to 3.5 x 10(9) years.  相似文献   

17.
18.
19.
20.
A few leafy gymnosperm shoots were found in Eocene deposits of southeastern North America. Similar fossil material from Tertiary deposits in North America has been identified as Taxodium, Taxites, and Sequoia. This new fossil material is not related to these genera but belongs to Podocarpus section Stachycarpus. This is the first fossil record of this section in North America.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号