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51.
Jeremy C. Stalker Rene M. Price Victor H. Rivera-Monroy Jorge Herrera-Silveira Sara Morales Jorge A. Benitez David Alonzo-Parra 《Estuaries and Coasts》2014,37(6):1376-1387
Oxygen isotopes and strontium concentrations were used as geochemical tracers to discern the sources of water to Celestún Lagoon, a small subtropical estuary on the western side of the Yucatán Peninsula of Mexico. Celestún Lagoon is underlain by karstified limestone with numerous locations where groundwater is observed discharging directly to the lagoon. In this study, samples of groundwater, lagoon surface water, and seawater (SW) were collected in April 2008 and June 2009 and analyzed for salinity, stable isotopes of oxygen, and strontium (Sr2+) concentrations. These geochemical tracers were used in two tertiary mixing models to calculate the relative ratio inputs of fresh groundwater, brackish groundwater, and SW to the lagoon. Two sources of groundwater were found to contribute to the surface water in the lagoon; one fresh and the other brackish with an average salinity of 19 psu. The fresh groundwater had an oxygen isotopic signature (δ18O) and strontium concentration (Sr2+) of δ18O?=?-3.30‰ and Sr2+?=?0.03 mmol/l, respectively. The brackish groundwater observed in the northern end of the lagoon add a dissimilar oxygen isotopic signature and Sr2+ concentration of δ18O?=?3.01‰ and Sr2+?=?0.12 mmol/l, respectively. Local SW had an isotopic oxygen signature and Sr2+ concentration between the two fresher sources (δ18O?=?1.40‰, Sr2+?=?0.09 mmol/l). The lagoonwide results of the two tracer mixing models (δ18O and Sr2+) agreed well (within 5 %) and indicated a ratio of brackish groundwater–fresh groundwater– SW of 31 %–26 %–43 % (±5 %) for the Sr2+ model and 35 %–25 %–40 % (± 5 %) for the δ18O model. Brackish groundwater is dominant in the northern portion of the lagoon, while SW dominates the southern portion. Fresh groundwater discharge is a significant contributor of water along the entire eastern boundary of the lagoon where mangrove forests are the dominant vegetation. 相似文献
52.
This paper outlines evidence from Pakefield (northern Suffolk), eastern England, for sea‐level changes, river activity, soil development and glaciation during the late Early and early Middle Pleistocene (MIS 20–12) within the western margins of the southern North Sea Basin. During this time period, the area consisted of a low‐lying coastal plain and a shallow offshore shelf. The area was drained by major river systems including the Thames and Bytham. Changes in sea‐level caused several major transgressive–regressive cycles across this low‐relief region, and these changes are identified by the stratigraphic relationship between shallow marine (Wroxham Crag Formation), fluvial (Cromer Forest‐bed and Bytham formations) and glacial (Happisburgh and Lowestoft formations) sediments. Two separate glaciations are recognised—the Happisburgh (MIS 16) and Anglian (MIS 12) glaciations, and these are separated by a high sea level represented by a new member of the Wroxham Crag Formation, and several phases of river aggradation and incision. The principal driving mechanism behind sea‐level changes and river terrace development within the region during this time period is solar insolation operating over 100‐kyr eccentricity cycles. This effect is achieved by the impact of cold climate processes upon coastal, river and glacial systems and these climatically forced processes obscure the neotectonic drivers that operated over this period of time. © British Geological Survey/Natural Environment Research Council copyright 2005. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd. 相似文献
53.
54.
Slab melt as metasomatic agent in island arc magma mantle sources, Negros and Batan (Philippines) 总被引:2,自引:0,他引:2
Fernando G. Sajona Rene C. Maury Gaëlle Prouteau Joseph Cotten Pieree Schiano Hervé Bellon Laure Fontaine 《Island Arc》2000,9(4):472-486
Abstract Two new cases of association of adakites with ‘normal’ island arc lavas and transitional adakites are recognized in the islands of Batan and Negros in northern and central Philippines, respectively. The Batan lavas are related to the subduction of the middle Miocene portion of the South China Sea basin along the Manila trench; those of Negros come from the almost aseismic subduction of the middle Miocene Sulu Sea crust along the Negros trench. The occurrence of the Batan adakites is consistent with previous findings showing adakitic glass inclusions within minerals of mantle xenoliths associated with Batan arc lavas. The similarity of adakite ages (1.09 Ma) and that of the metasomatized xenoliths (1 Ma) suggests that both are linked to the same slab‐melting and metasomatic event. Earlier Sr, Pb and Nd‐isotopic studies, however, also reveal the presence of an important sediment contribution to the Batan lava geochemistry. Thus, the role played by slab melts, assumed to have mid‐ocean ridge basalts‐like (MORB) isotopic characteristics, in enriching the Batan subarc mantle is largely masked by the sediment input. The Negros adakites are present only in Mount Cuernos, the volcanic center nearest to the Negros trench. Batch partial melting calculations show that the Negros adakites could be derived from a garnet amphibolitic source with normal‐MORB (N‐MORB) geochemistry. This is supported by the MORB‐like isotopic characteristics of the Mount Cuernos lavas. The volcanic rocks from the other volcanoes consist of normal arc and transitional adakitic lavas that have slightly higher Sr‐ and Pb‐isotopic ratios, probably due to slight sediment input. Mixing of adakites and normal arc lavas to produce transitional adakites is only partly supported by trace element geochemistry and not by field evidence. The transitional adakites can be modeled as partial melts of an adakite‐enriched mantle. Trace element enrichment of non‐adakitic lavas could reflect the interaction of their mantle source with uprising slab melts, as metasomatic mantle minerals scavenge certain trace elements from the adakitic fluids. Therefore, in arcs beneath which thick (up to 2 km) continent‐derived detrital sediments are involved in subduction, like in Batan, the sediment signature can overwhelm the slab melt input. In arcs like Negros where slow subduction could cause a more efficient scraping of thinner (approximately 1 km) detrital sediments, the contribution of slab melts is easier to detect. 相似文献
55.
Assessment of long-range kinematic GPS positioning errors by comparison with airborne laser altimetry and satellite altimetry 总被引:3,自引:0,他引:3
Long-range airborne laser altimetry and laser scanning (LIDAR) or airborne gravity surveys in, for example, polar or oceanic
areas require airborne kinematic GPS baselines of many hundreds of kilometers in length. In such instances, with the complications
of ionospheric biases, it can be a real challenge for traditional differential kinematic GPS software to obtain reasonable
solutions. In this paper, we will describe attempts to validate an implementation of the precise point positioning (PPP) technique
on an aircraft without the use of a local GPS reference station. We will compare PPP solutions with other conventional GPS
solutions, as well as with independent data by comparison of airborne laser data with “ground truth” heights. The comparisons
involve two flights: A July 5, 2003, airborne laser flight line across the North Atlantic from Iceland to Scotland, and a
May 24, 2004, flight in an area of the Arctic Ocean north of Greenland, near-coincident in time and space with the ICESat
satellite laser altimeter. Both of these flights were more than 800 km long. Comparisons between different GPS methods and
four different software packages do not suggest a clear preference for any one, with the heights generally showing decimeter-level
agreement. For the comparison with the independent ICESat- and LIDAR-derived “ground truth” of ocean or sea-ice heights, the
statistics of comparison show a typical fit of around 10 cm RMS in the North Atlantic, and 30 cm in the sea-ice region north
of Greenland. Part of the latter 30 cm error is likely due to errors in the airborne LIDAR measurement and calibration, as
well as errors in the “ground truth” ocean surfaces due to drifting sea-ice. Nevertheless, the potential of the PPP method
for generating 10 cm level kinematic height positioning over long baselines is illustrated. 相似文献
56.
Mineral Paragenesis of the Lepanto Copper and Gold and the Victoria Gold Deposits, Mankayan Mineral District, Philippines 总被引:5,自引:0,他引:5
Rene Juna R. CLAVERIA 《Resource Geology》2001,51(2):97-106
Abstract: Mineral paragenesis of the alteration, ore and gangue minerals of the Lepanto epithermal copper‐gold deposit and the Victoria gold deposit, Mankayan Mineral District, Northern Luzon, Philippines, is discussed. The principal ore minerals of the Lepanto copper‐gold deposit are enargite and luzonite, with significant presence of tennantite‐tetrahedrite, chalcopyrite, sphalerite, galena, native gold/electrum and gold‐silver tellurides. Pervasive alteration zonations are commonly observed from silicification outward to advanced argillic then to propylitic zone. The ore mineralogy of the Lepanto copper‐gold deposit suggests high fS2 in the early stages of mineralization corresponding to the deposition of the enargite‐luzonite‐pyrite assemblage. Subsequent decrease in the fS2 formed the chalcopyrite‐tennantite‐pyrite assemblage. An increase in the fS2 of the fluids with the formation of the covellite‐digenite‐telluride assemblage caused the deposition of native gold/electrum and gold‐silver tellurides. The principal ore minerals of the Victoria gold deposit are sphalerite, galena, chalcopyrite, tetrahedrite and native gold/electrum. The alteration halos are relatively narrow and in an outward sequence from the ore, silica alteration grades to illitic‐argillic alteration, which in turn grades to propylitic alteration. The Victoria gold mineralization has undergone early stages of silica supersaturation leading to quartz deposition. Vigorous boiling increased the pH of the fluids that led to the deposition of sulfides and carbonates. The consequent decrease in H2S precipitated the gold. Gypsum and anhydrite mainly occur as overprints that cut the carbonate‐silica stages. The crosscutting and overprinting relationships of the Victoria quartz‐gold‐base metal veins on the Lepanto copper‐gold veins manifest the late introduction of near neutral pH hydrothermal fluids. 相似文献
57.
Andreas Beha Rene O. Thomsen Ralf Littke 《International Journal of Earth Sciences》2008,97(5):1087-1100
In this study a 2D basin model has been built along a transect crossing the Horn Graben in WNW-ESE direction. The aim of the investigation was to improve the understanding of the thermal evolution of the basin and its influence on possible petroleum systems. The 2D model of the subsurface is based on one seismic line and data from two exploration wells. Both wells TD’ed in Triassic sediments. The updoming of the Ringkøbing-Fyn High began during Late Carboniferous–Early Permian. At the end of the Permian the Horn Graben became active due to regional extension. The subsequent sedimentation history from Triassic to date is well recorded by well reports. A matter of debate has been whether or not significant amounts of Pre-Permian sediments exist in this area of the North Sea. Since organic material rich Paleozoic sediments serve as source rocks in widespread areas of North Germany and the southern North Sea it would be of great importance to know whether the same deposits exist in the Horn Graben. Nielsen et al. (Bull Geol Soc Denmark Copenhagen 45:1–10, 1998) introduced a model, which shows Paleozoic sediments covering the basement at a maximum depth of 6.5 km. Assuming, Paleozoic sediments are underlying the Permian salt deposits there should be an active petroleum system present. The 2D model includes the Paleozoic source rock and tries to explain why two exploration wells have not found petroleum. 相似文献
58.
Rene Westerholt Bernd Resch Franz-Benjamin Mocnik Dirk Hoffmeister 《International journal of geographical information science》2018,32(3):571-600
Spatial variance is an important characteristic of spatial random variables. It describes local deviations from average global conditions and is thus a proxy for spatial heterogeneity. Investigating instability in spatial variance is a useful way of detecting spatial boundaries, analysing the internal structure of spatial clusters and revealing simultaneously acting geographic phenomena. Recently, a corresponding test statistic called ‘Local Spatial Heteroscedasticity’ (LOSH) has been proposed. This test allows locally heterogeneous regions to be mapped and investigated by comparing them with the global average mean deviation in a data set. While this test is useful in stationary conditions, its value is limited in a global heterogeneous state. There is a risk that local structures might be overlooked and wrong inferences drawn. In this paper, we introduce a test that takes account of global spatial heterogeneity in assessing local spatial effects. The proposed measure, which we call ‘Local Spatial Dispersion’ (LSD), adapts LOSH to local conditions by omitting global information beyond the range of the local neighbourhood and by keeping the related inferential procedure at a local level. Thereby, the local neighbourhoods might be small and cause small-sample issues. In the view of this, we recommend an empirical Bayesian technique to increase the data that is available for resampling by employing empirical prior knowledge. The usefulness of this approach is demonstrated by applying it to a Light Detection and Ranging-derived data set with height differences and by making a comparison with LOSH. Our results show that LSD is uncorrelated with non-spatial variance as well as local spatial autocorrelation. It thus discloses patterns that would be missed by LOSH or indicators of spatial autocorrelation. Furthermore, the empirical outcomes suggest that interpreting LOSH and LSD together is of greater value than interpreting each of the measures individually. In the given example, local interactions can be statistically detected between variance and spatial patterns in the presence of global structuring, and thus reveal details that might otherwise be overlooked. 相似文献
59.
Rene P. Schwarzenbach Richard H. Bromund Philip M. Gschwend Oliver C. Zafiriou 《Organic Geochemistry》1978,1(2):93-107
The occurence and temporal variations of a variety of low to medium polarity organic compounds in the volatility range bracketed by n-heptane and n-octadecane have been studied in seawater from a station in Vineyard Sound, Massachusetts, and from a tidal creek in Sippewisset Marsh, Massachusetts. The closed-loop vapor phase stripping method of Grob and Zürcher (J. Chromatogr., v. 117, p. 285–294), high resolution glass capillary gas chromatography, and gas chromatography-mass spectrometry were used. Approximately 50 compounds were found at ≥ 2 ng/kg; most were recovered at less than 10 ng/kg, while the 20 ng/kg level was only rarely exceeded by a few components. The total material recovered was 0.2–1.0 μg organic carbon equivalent/kg seawater. The major compound classes found were normal alkanes, alkenes, aromatic and alkylaromatic hydrocarbons, n-aldehydes, dimethyldisulfide and dimethyltrisulfide, and a few halogenated hydrocarbons. The preliminary results suggest that both biogenic and anthropogenic sources were representted. Also, air-sea gas exchange and other physical processes may be important non-biological sinks. 相似文献
60.