Stable isotope enrichment in paleowaters of the southeast atlantic coastal plain, United States

Paleowaters from the Floridan aquifer system in the southeastern Atlantic coastal plain have higher D/H and (18)O/(16)O ratios than local Holocene ground water. Maximum delta(18)O enrichments in ground water having adjusted radiocarbon ages of 20,000 to 26,000 years are 0.7 to 2.3 per mil. The trend in isotopic enrichment in paleowaters is the reverse of that normally observed in continental glacial age ground water. Dissolved nitrogen and argon concentrations indicate, however, that the average recharge temperature was 5.3 degrees C cooler than that today. The data indicate cool conditions in the southeast Atlantic coastal plain during the last glacial maximum, with recharge limited primarily to late summer tropical cyclones and hurricanes.     

Micropaleontological evidence for increased meridional heat transport in the north atlantic ocean during the pliocene

The Middle Pliocene ( approximately 3 million years ago) has been identified as the last time the Earth was significantly warmer than it was during the Last Interglacial and Holocene. A quantitative micropaleontological paleotemperature transect from equator to high latitudes in the North Atlantic indicates that Middle Pliocene warmth involved increased meridional oceanic heat transport.     

Transform faulting and growth of the gulf of california since the late pliocene

Seismic-reflection and magnetic profiles over more than 6000 kilometers suggest that spreading of the sea floor on the East Pacific Rise, at the mouth of the Gulf of California, began to broaden a proto-gulf about 4 million years ago. Movement occurred, on transform faults, offsetting the rise and other centers of crustal growth within the gulf, and translated the end of the peninsula about 200 kilometers to the northwest. Thick pelagic sediments on the east flank of the rise indicate that there was a lapse of spreading by crustal growth between 4 and 10 million years ago.     

Diversity and extinction of tropical american mollusks and emergence of the isthmus of panama

The gradual closure of the Panamanian seaway and the resulting environmental change stimulated an increase in Caribbean molluscan diversity rather than the mass extinction hypothesized previously on the basis of inadequate data. Upheaval of molluscan faunas did occur suddenly throughout tropical America at the end of the Pliocene as a result of more subtle, unknown causes. There is no necessary correlation between the magnitude of regional shifts in abiotic conditions and the subsequent biological response.     

A pleistocene sand sea on the alaskan arctic coastal plain

A ridge and thermokarst-basin landscape that is strikingly portrayed in Landsat winter imagery consists of large Pleistocene dunes that have been modified by younger eolian activity and thermokarst processes. This is the most extensive area of large stabilized dunes yet reported in the North American Arctic; the landscape is of particular interest because it has been proposed as a first-order analog for martian fretted terrain. Recognition of the large dunes permits a new interpretation for linear and curvilinear trends visible in Landsat summer imagery.     

Fossil peccary from the pliocene of South Africa

Pecarichoerus africanus, new species, from Langebaanweg, Cape Province, is the first fossil peccary to be described from Africa and represents the youngest record of the peccary family in the Old World.     

Evolutionary implications of pliocene hominid footprints

Hominid footprints discovered at the Pliocene (3.6 to 3.8 million years ago) site of Laetoli in northern Tanzania represent the earliest evidence of bipedalism in human evolution. This new evidence emphasizes the mosaic pattern of human evolution.     

Opaline sediments of the southeastern coastal plain and horizon a: biogenic origin

Scanning electron microscope techniques show that Eocene opaline claystones (fuller's earth and buhrstone) of the Atlantic and Gulf Coastal Plain, deposits long considered volcanic in origin, are actually highly altered diatomites formed as transgressive facies in normal marine continental shelf environmnents. These findings are in agreement with a biogenic origin for time-equivalent horizon A and A deep-sea cherts of the North Atlantic and Caribbean.     

Quaternary climates and sea levels of the u.s. Atlantic coastal plain

Uranium-series dating of corals from marine deposits of the U.S. Atlantic Coastal Plain coupled with paleoclimatic reconstructions based on ostracode (marine) and pollen (continent) data document at least five relatively warm intervals during the last 500,000 years. On the basis of multiple paleoenvironmental criteria, we determined relative sea level positions during the warm intervals, relative to present mean sea level, were 7 +/- 5 meters at 188,000 years ago, 7.5 +/- 1.5 meters at 120,000 years ago, 6.5 +/- 3.5 meters at 94,000 years ago, and 7 +/- 3 meters at 72,000 years ago. The composite sea level chronology for the Atlantic Coastal Plain is inconsistent with independent estimates of eustatic sea level positions during interglacial intervals of the last 200,000 years. Hydroisostatic adjustment from glacial-interglacial sea level fluctuations, lithospheric flexure, and isostatic uplift from sediment unloading due to erosion provide possible mechanisms to account for the discrepancies. Alternatively, current eustatic sea level estimates for the middle and late Quaternary may require revision.     

Thermal structure of the deep pacific ocean in the early pliocene

The thermal structure of the Pacific Ocean between water depths of about 1 and 4.5 kilometers is estimated from the oxygen isotopic ratio of benthonic foraminifera from deep-drilled and piston cores of early Pliocene age (about 3 to 5 million years ago). The ratio of oxygen-18 to oxygen-16 in the early Pliocene at each site varies by an average of only +/- 0.12 per mil (1 standard deviation). A plot of the oxygen isotopic ratio against modern bottom-water temperature is adequately fit by a line having a slope of - 0.26 per mil per degree Celsius (the equilibrium temperature dependence of calcite-water fractionation), suggesting that the temperature gradient of the Pacific Ocean during the early Pliocene was similar to that of today.     

Dinoflagellates: fossil motile-stage tests from the upper cretaceous of the northern new jersey coastal plain

Fossil dinoflagellate tests have been considered to represent encysted, nonmotile stages. The discovery of flagellar porelike structures and probable trichocyst pores in the Upper Cretaceous genus Dinogymnium suggests that motile stage tests are also preserved as acid-resistant, organic-walled microfossils.     

Viscosity of the atlantic ocean bottom

Two profiles across the Mid-Atlantic Ridge were analyzed to determine viscosity values. Viscous creeping of bottom features due to gravitational stress was assumed, as was sea floor spreading at a rate of 2 centimeters per year. Values obtained agreed well with previous results obtained on the Fennoscandian Uplift, despite great differences in the horizontal dimensions of the bottom relief.     

基于SDI校正指数的滨海平原盐渍化生态风险评价

为了研究滨海平原区土壤盐渍化风险情况,本研究以黄骅市为研究区,将Landsat 8夏季遥感影像获得的SDI（盐渍化植被监测指数）校正指数作为生态终点,采用相关性分析法筛选土壤生产潜力和土壤健康方面指标,最终选取含盐量、电导率及有机质、K⁺、Na⁺、Mg²⁺、SO₄^2-、Cl^-含量8个指标,借助SDI指数标准化校正的灰色关联度法构建盐渍化生态风险评价模型,对滨海平原区盐渍化生态风险进行定量评价及空间分析。结果表明：研究区内盐渍化生态风险值介于0.24~0.73,均值高达0.42,其中99.25%的区域处于中度及以上盐渍化生态风险水平,整体上土壤生态风险较高,呈现东部沿海高、西部平原低的趋势;盐渍化生态风险评价在空间上与土壤含盐量、土壤电导率较为相似,因此,土壤含盐量及电导率对盐渍化生态风险评价起主导作用。研究区内盐渍化生态风险及评价因子的空间分布可为生态环境、农业健康持续发展、地下水的限采禁采、土壤改良和盐渍化防治提供参考依据。     

Crustal plates in the central atlantic

Various people have proposed that North and South America are a part of a gigantic crustal plate within which little differential movement is taking place. Considerations of the size of this postulated plate and the pattern of seismicity around the Caribbean indicate that it is in fact two plates, separated in the region between the Lesser Antilles and the Mid-Atlantic Ridge. Many of the offsets of the Mid-Atlantic Ridge opposite the Caribbean are the result of differential spreading rates and the westward continuations of the fracture zones extending from these offsets are active left-lateral faults.     

Monoplacophora in the South atlantic ocean

Occurrence of Neopilina off the southeastern tip of South America may indicate rather widespread distribution of this abyssal group, under favorable conditions, throughout the seas of the world.     

Jurassic sandstone from the tropical atlantic

The oldest sediment yet sampled from the abyssal margins of South America, late Jurassic (or possibly very early Cretaceous) shallow-water, coarse-grained, calcareous sandstone containing palynomorphs and mollusk prisms, was recovered from a depth of 4400 meters on the seaward scarp of the Demerara Plateau. The sandstone was deposited in a shallow, late Jurassic epicontinental sea after the initial stages of rifting when the newly created Atlantic began to founder.