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1.
Lower Miocene microfossils occur in basaltic glass in two dredge hauls from the crestal area of the Mid-Atlantic Ridge near 30 degrees N. From the ridge and adjoining abyssal hills 43 pre-Pleistocene cores were identified, including one Cretaceous and four Eocene. Dredgings and cores now available suggest that the upper layer of the crust of the ridge is constructed of layers of interbedded sediments and basalt flows. The data rule out the possibility of large-scale continental drifting or spreading of the ocean floor since the Lower Miocene. 相似文献
2.
Larsen HC Saunders AD Clift PD Beget J Wei W Spezzaferri S;ODP Leg Scientific Party 《Science (New York, N.Y.)》1994,264(5161):952-955
Glacial till, glaciomarine diamictites, and ice-rafted detritus found in marine cores collected off the shore of southeast Greenland record multiple Late Cenozoic glaciations beginning in the Late Miocene. Distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast Greenland margin. Glaciers advanced to the sea during several intervals in the Pliocene and Pleistocene. North Atlantic glaciation may have nucleated in southern Greenland rather than further north because of the high mountains and the high levels of precipitation in this region. 相似文献
3.
C C Black 《Science (New York, N.Y.)》1967,156(771):62-64
The multituberculate Parectypodus lovei has been found in late Eocene rocks in Montana, together with 11 other mammal species similar to those found in the late Eocene Tepee Trail Formation in Wyoming.The multituberculate and six other species are unknown in rocks of equivalent age or of middle Eocene age elsewhere.It is suggested that the known middle Eocene faunas are all taken from a similar ecological situation and do not reflect the true diversity of middle Eocene life. Middle Eocene faunas of different ecological aspect may be recovered from sediments along, and in, the mountain fronts of northwestern Wyoming. 相似文献
4.
Several mechanisms have been proposed to explain the high levels of plant diversity in the Neotropics today, but little is known about diversification patterns of Neotropical floras through geological time. Here, we present the longest time series compiled for palynological plant diversity of the Neotropics (15 stratigraphic sections, 1530 samples, 1411 morphospecies, and 287,736 occurrences) from the Paleocene to the early Miocene (65 to 20 million years ago) in central Colombia and western Venezuela. The record shows a low-diversity Paleocene flora, a significantly more diverse early to middle Eocene flora exceeding Holocene levels, and a decline in diversity at the end of the Eocene and early Oligocene. A good correlation between diversity fluctuations and changes in global temperature was found, suggesting that tropical climate change may be directly driving the observed diversity pattern. Alternatively, the good correspondence may result from the control that climate exerts on the area available for tropical plants to grow. 相似文献
5.
Late Miocene fossil hominid teeth recovered from Ethiopia's Middle Awash are assigned to Ardipithecus kadabba. Their primitive morphology and wear pattern demonstrate that A. kadabba is distinct from Ardipithecus ramidus. These fossils suggest that the last common ancestor of apes and humans had a functionally honing canine-third premolar complex. Comparison with teeth of Sahelanthropus and Orrorin, the two other named late Miocene hominid genera, implies that these putative taxa are very similar to A. kadabba. It is therefore premature to posit extensive late Miocene hominid diversity on the basis of currently available samples. 相似文献
6.
Simpson GG 《Science (New York, N.Y.)》1970,168(3929):361-362
The age of a New Zealand specimen generally believed to represent the oldest known penguin, hitherto considered early Eocene (Heretaungan), has been restudied by the New Zealand Geological Survey and is early Miocene. The oldest known penguins are from the late Eocene. The reported great range of a single species, Palaeeudyptes antarcticus, from late Eocene to late Oligocene or early Miocene (Kaiatan to Waitakian) is not acceptable. Dating of some other specimens is less precise than previously reported. 相似文献
7.
More than 50 cores ranging in age from Pliocene to Lower Miocene have been recovered from the East Pacific Rise. Near the crestal regions the sediment cover is thin or lacking, and only Pleistocene sediments were recovered. On the flanks, the sediment thickness increases and pre-Pleistocene sediments are encountered. This pattern of increasing age and increasing sediment thickness away from the axis of the rise is in agreement with that predicted for spreading of the ocean floor. 相似文献
8.
巨蚓科蚯蚓是我国的主要蚯蚓类群,运用分子系统学方法研究其系统发育具有重要价值。本研究采用测定的线粒体COI、12S与16S基因序列,分析其序列特征,构建了广东黑石顶自然保护区的巨蚓科蚯蚓的最大似然树与贝叶斯树,确定该区域物种间的分子系统发育关系,明确远盲蚓属与腔蚓属均非单系群。研究还基于松散分子钟估算了不同物种之间的分化时间。该保护区的巨蚓科祖先进行物种分化起于始新世中期[42.88百万年前(Ma)],其腔蚓属蚯蚓约起源于中新世前期。 相似文献
9.
Hathaway JC Poag CW Valentine PC Manheim FT Kohout FA Bothner MH Miller RE Schultz DM Sangrey DA 《Science (New York, N.Y.)》1979,206(4418):515-527
The first broad program of scientific shallow drilling on the U.S. Atlantic continental shelf has delineated rocks of Pleistocene to Late Cretaceous age, including phosphoritic Miocene strata, widespread Eocene carbonate deposits that serve as reflective seismic markers, and several regional unconformities. Two sites, off Maryland and New Jersey, showed light hydrocarbon gases having affinity to mature petroleum. Pore fluid studies showed that relatively fresh to brackish water occurs beneath much of the Atlantic continental shelf, whereas increases in salinity off Georgla and beneath the Florida-Hatteras slope suggest buried evaporitic strata. The sediment cores showed engineering properties that range from good foundation strength to a potential for severe loss of strength through interaction between sediments and man-made structures. 相似文献
10.
Estimation of average Cenozoic sedimentation rates for the Atlantic, Indian, and Pacific oceans indicates global synchronous fluctuations. Paleocene-early Eocene and late Eocene-early Miocene rates are only a fraction of middle Eocene and middle Miocene-Recent rates. These changes must reflect significantly different modes of continental weathering, which may be due to alternate states of atmospheric circulation marked by reduction of global precipitation. 相似文献
11.
Bandy OL 《Science (New York, N.Y.)》1963,142(3597):1290-1292
Planktonic foraminiferal trends across the Miocene-Pliocene boundary in the Philippines suggest that sections of eight deep-sea cores reported to be Pliocene are actually latest Miocene, and that a marked extinction of discoasters in the deep-sea cores is due to an unconformity, separating Miocene and Pleisto-cene sediments, representing a time gap of some 10 million years of Pliocene time. 相似文献
12.
Schoell M Schouten S Damsté JS de Leeuw JW Summons RE 《Science (New York, N.Y.)》1994,263(5150):1122-1125
The difference in carbon-13 ((13)C) contents of hopane and sterane biomarkers in the Monterey formation (Naples Beach, California) parallels the Miocene inorganic record of the change in (18)O (delta(18)O), reflecting the Miocene evolution from a well-mixed to a highly stratified photic zone (upper 100 meters) in the Pacific. Steranes (delta(13)C = 25.4 +/- 0.7 per mil versus the Pee Dee belemnite standard) from shallow photic-zone organisms do not change isotopically throughout the Miocene. In contrast, sulfur-bound C(35) hopanes (likely derived from bacterial plankton living at the base of the photic zone) have systematically decreasing (13)C concentrations in Middle and Late Miocene samples (delta(13)C = -29.5 to -31.5 per mil), consistent with the Middle Miocene formation of a carbon dioxide-rich cold water mass at the base of the photic zone. 相似文献
13.
The morphology of complex deposits of Pleistocene sediments covering the upper continental slope between Lindenkohl Canyon and South Toms Canyon results from both depositional and erosional processes. Small slump or slide features were detected primarily on the flanks of canyons or valleys and were observed to occur only within Pleistocene-aged sediments. Eocene to Miocene sediments are exposed over much of the mid- and lower slope in this area. 相似文献
14.
Riedel WR 《Science (New York, N.Y.)》1967,157(3788):540-542
In sediments west of the East Pacific Rise between the equator and 20 degrees N, Eocene microfossils are recorded no farther east than 134 degrees W; Oligocene, no farther east than 125 degrees W; while Miocene and Pliocene occurrences extend closer to the crest of the rise. This distribution may result from post-Eocene spreading of the sea floor here averaging about 8 centimeters per year. 相似文献
15.
Kanfoush SL Hodell DA Charles CD Guilderson TP Mortyn PG Ninnemann US 《Science (New York, N.Y.)》2000,288(5472):1815-1818
Records of ice-rafted detritus (IRD) concentration in deep-sea cores from the southeast Atlantic Ocean reveal millennial-scale pulses of IRD delivery between 20,000 and 74,000 years ago. Prominent IRD layers correlate across the Polar Frontal Zone, suggesting episodes of Antarctic Ice Sheet instability. Carbon isotopes (delta(13)C) of benthic foraminifers, a proxy of deepwater circulation, reveal that South Atlantic IRD events coincided with strong increases in North Atlantic Deep Water (NADW) production and inferred warming (interstadials) in the high-latitude North Atlantic. Sea level rise or increased NADW production associated with strong interstadials may have resulted in destabilization of grounded ice shelves and possible surging in the Weddell Sea region of West Antarctica. 相似文献
16.
近年来在中国范围内频繁发生洪涝灾害,长江中下游地区为重灾区之一,洪水环流对江河湖岸不同地形产生冲刷作用,是长江决堤右岸多于左岸及大堤决口常始于堤面的主要原因,为了有铲抑制洪流的破坏作用,对长江沿岸的生态环境等进行了调查,结果表明,长江中下游地区沿江胡岸分布的适于营造护岸植的植物近１００种,其中具抗洪作用的优树种１２种,据此提出了因地制宜选用适合树种,营造防洪护堤防护林的减灾措施。 相似文献
17.
Klasik JA 《Science (New York, N.Y.)》1975,189(4203):631-632
The high-temperature forms of cristobalite and tridymite have been found occurring in a Middle Eocene, radiolarian-rich claystone. Evidence indicates that these crystals formed at low temperature and were chemical precipitates. Scanning electron microscopy, energy-dispersive x-ray analysis (microprobe), and x-ray diffraction provided the data upon which the determinative mineralogy was based. 相似文献
18.
The relation between the partial pressure of atmospheric carbon dioxide (pCO2) and Paleogene climate is poorly resolved. We used stable carbon isotopic values of di-unsaturated alkenones extracted from deep sea cores to reconstruct pCO2 from the middle Eocene to the late Oligocene (approximately 45 to 25 million years ago). Our results demonstrate that pCO2 ranged between 1000 to 1500 parts per million by volume in the middle to late Eocene, then decreased in several steps during the Oligocene, and reached modern levels by the latest Oligocene. The fall in pCO2 likely allowed for a critical expansion of ice sheets on Antarctica and promoted conditions that forced the onset of terrestrial C4 photosynthesis. 相似文献
19.
Wilf P Cúneo NR Johnson KR Hicks JF Wing SL Obradovich JD 《Science (New York, N.Y.)》2003,300(5616):122-125
Tropical South America has the highest plant diversity of any region today, but this richness is usually characterized as a geologically recent development (Neogene or Pleistocene). From caldera-lake beds exposed at Laguna del Hunco in Patagonia, Argentina, paleolatitude approximately 47 degrees S, we report 102 leaf species. Radioisotopic and paleomagnetic analyses indicate that the flora was deposited 52 million years ago, the time of the early Eocene climatic optimum, when tropical plant taxa and warm, equable climates reached middle latitudes of both hemispheres. Adjusted for sample size, observed richness exceeds that of any other Eocene leaf flora, supporting an ancient history of high plant diversity in warm areas of South America. 相似文献
20.
Lower Eocene flowers with Pistillipollenites macgregorii pollen represent the earliest megafossil evidence of the Gentianaceae. The Paleocene occurrence of P. macgregorii, the fossil's modern floral structure, and suggested trends in the evolution of pollen in the Gentianaceae indicate a considerably earlier origin for the family. Floral morphology typical of bee-pollinated flowers provides the earliest, albeit indirect, fossil evidence of bees. 相似文献