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1.
The purpose of the study is to better understand the relationship between organic matter optical properties and the presence of potentially large oil and gas accumulations in Arctic Canada. The type and thermal maturity of the dispersed organic matter of the Mesozoic formations in the southern Sverdrup Basin, Melville Island, have been studied using organic petrology and Rock-Eval pyrolysis.All types of organic matter are present in the strata of Mesozoic age. Hydrogen-rich liptinite is dominated by alginite (Botryococcus and Tasmanites), dinoflagellate cysts and amorphous fluorescing matrix. Sporinite, cutinite, resinite and liptodetrinite made up the lesser hydrogen-rich exinite. Vitrinite reflectance in Cretaceous sediments ranges from 0.36 to 0.65% Ro; in Jurassic sediments it ranges from 0.40 to 1.0% Ro and in the Triassic from 0.45 to 1.30% Ro, showing an overall increase with depth of burial.Cretaceous sediments of the Deer Bay Formation are thermally immature and contain organic matter of terrestrial origin. The Upper Jurassic shales of the Ringnes Formation contain predominantly organic matter of liptinitic and exinitic origin with a considerable vitrinitic input. At optimum maturation levels, potential source beds of this formation would have a good hydrocarbon-generating potential. The hydrocarbon potential, however, would be limited to the generation of gases due to the leanness of the source rocks. Parts of the Lower Jurassic Jameson Bay Formation are organic-rich and contain a mixed exinitic/vitrinitic organic matter, Botryococcus colonial algae but visible organic matter is dominated by high plant remains (mainly spores). The Schei Point Group shales and siltstones contain organic matter of almost purely marine origin, whereas the predominantly higher plant-derived organic matter found in the Deer Bay, Jameson Bay and partly in the Ringnes formations have higher TOC. Among the Schei Point Group samples, the Cape Richards and Eden Bay members of the Hoyle Bay Formation are richer in TOC (>2.0%) than the Murray Harbour Formation (Cape Caledonia Member). This may reflect differences in the level of maturity or in the depositional environment (more anoxic conditions for the former).Regional variations in the level of thermal maturity of Mesozoic sediments in Sverdrup Basin appear to be a function of burial depth. The Mesozoic formations thicken towards the basin centre (NNE direction), reflecting the general pattern of increasing thermal maturity north of Sabine Peninsula. However, the regional thermal-maturation pattern of the Mesozoic is not solely a reflection of the present-day geothermal gradient, which indicates that anomalous zones of high geothermal gradient may have existed in the past, at least since when the Mesozoic sediments attained maximum burial depth. The contour pattern of the regional variation of maturity at the base of numerous Triassic formations is similar to that of the structural contours of the Sverdrup Basin, indicating that present-day maturation levels are largely controlled by basin subsidence.  相似文献   

2.
Examples of the three volcanic rock types, wyomingite, orendite and madupite from the Leucite Hills have been examined with the electron microprobe. The results show that leucite is non-stoichiometric as predicted byCross (1897), having an excess of potassium and silicon, and that the only feldspar found, a sanidine, contains up to 18 percent of the iron-feldspar molecule. The co-existing phlogopite, diopside and olivine together with the groundmass amphibole are all highly magnesian. Of the varied accessory minerals, priderite (K2Ti8O16) and wadeite (K4Zr2Si6O18) have been identified and analyzed together with ubiquitous apatite and perovskite, both of which contain rare earths in abundance. Comparative mineralogical data has been obtained on a few representative specimens from West Australia and on the jumillite from Spain.The new rock analyses together with the existing data from the Leucite Hills show the rare but characteristic molecular excess of potassium over aluminium; this excess is considered to account for the ahsence of the iron-titanium oxides in the orendites and wyomingites, and of course for the unusual composition and species of the minerals. Exploratory melting experiments show that these potassic lavas have a comparable melting range to magnesian basalts, and a crustal origin is thereby considered precluded. There is no evidence that sialic contamination contributed notably to the composition of the oversaturated orendites and wyomingites, and their relationship by any process of crystal fractionation to the undersaturated madupite is obscure. The generation of madupite could be achieved by crystal fractionation at high pressure of a liquid derived by partial fusion of mantle material.  相似文献   

3.
Bedload is moved down the East Fork River in distinct wavelike pulses that have the form of composite dune fields The moving material consists mostly of coarse sand and fine gravel The wavelengths of the pulses are about 500–600 m, a distance that is predetermined by the pattern of stoage of bed sediment in the river during low water As the river discharge increases, the bed sediment is scoured from the storage areas, and it is moved onto and across the interventing riffles As the river discharge decreases, the bed sediment is scoured off the riffles and moved into the next storage area downstream Each successive pulse of water discharge sets into motion a wave of bedload that continues to move unitil it reaches the next storage area  相似文献   

4.
黄永高 《地质与勘探》2020,56(4):732-744
通甸地区地处三江特提斯兰坪盆地铅-锌-铜-银巨型矿集区东北部,具有寻找沉积岩型铅锌矿的前景。在通甸地区开展了1∶5万水系沉积物地球化学测量,以进一步指导铅锌矿勘察工作。确定了Pb、Zn和Ag等15种单元素异常范围,揭示了不同成因类型组合元素的分布特征及规律,圈定了21处地球化学综合异常。通过化探异常查证,识别出两条铅锌矿(化)体,经分析检测,Pb含量为1.93%~2.01%,Zn含量为0.48%~12.22%。研究表明,三合洞组(T3sh)碳酸盐岩和与其上下地层接触部位是区内重要的矿源层。结合异常分布规律、异常查证结果以及成矿地质背景进行综合评价,优选AS05甲1综合异常区为最佳铅锌找矿靶区,为通甸地区深入开展矿产勘查提供参考和依据。  相似文献   

5.
Relations between wind speed, sediment flux and dune morphology were measured for two reversing dunes situated in the south-western part of the Silver Peak dunefield in Clayton Valley, west-central Nevada. The larger dune was 120 m in length with a height of 12.5 m and the smaller dune 80 m long and 6 m high. Both dunes were sharp crested, aligned approximately E-W perpendicular to the dominant wind direction, and had slightly concave stoss profiles. Twenty-seven rotating cup anemometers were placed (0.3 m elevation) along N-S transects on each of the dunes. At each anemometer site a passive wedge-shaped sediment trap was used to measure sediment flux. Amplification of wind speed was observed towards the crest on the stoss side of both dunes with speed-up factors (ucrest/Ubase) ranging from 1·50–3·19, with a corresponding increase in sediment flux by 1–2 orders of magnitude. In general, the ratio of crest flux to base flux (qc/qt,) increased with increasing incident basal wind speed on both dunes. Direct measurements of the stoss slope variation in sediment flux relative to the dune crest are in good agreement with Owen's transport model. Friction speed (u) was approximated from near surface (0·3 m) point wind speed. Although not all assumptions of the Owen model are upheld, the modified model performance is sufficiently robust to predict short-term variation in stoss sediment flux on the study dunes. Improved models that adequately account for variation in sediment flux under changing air flow and transport conditions are necessary for the prediction of longterm evolution of dunes. In this regard, further progress in model development will require increased understanding of the spatial and temporal variability of airflow and the short term response of sediment flux to these flow conditions.  相似文献   

6.
Geochemical stream sediment survey in Winder Valley, Balochistan, Pakistan   总被引:1,自引:0,他引:1  
A pilot scale geochemical survey of sediments from the Winder Stream (SW Pakistan) and its tributaries was carried out. The Winder Stream mainly receives sediment from the southern extensions of the Mor and Pab Ranges in the District of Lasbela (Balochistan). In these two mountain ranges, rocks from Jurassic to Cretaceous age are exposed. Rocks of the Ferozabad Group comprise of carbonates and siliciclastics of Lower–Middle Jurassic age and occupy the dominant part of the Mor Range. These strata host syngenetic and epigenetic Zn–Pb–Ba mineralizations of Stratiform Sediment-Hosted (SSH) and Mississippi Valley Type (MVT) deposits.Quantitative estimates of mobile and immobile elements were made from active stream sediments of the Winder stream and its tributaries. The samples were analyzed for Ag, Zn, Pb, Cu, Ni, Co, V, Mn, Fe and Ba using atomic absorption spectroscopy. The abundance of these elements is discussed in relation to local geological conditions such as bedrock, climate, weathering, mobility and pH of the dispersing waters. A number of Zn anomalies have been distinguished in the study area. Kharrari (Zn, 360 ppm), Sand (Zn, 340 ppm) and Draber (Zn, 210 ppm) are demarcated as new areas for Zn mineralization. The present study also indicates prospects of Ag, Cu and V in the rocks of the Mor Range.Relationships between various elements have been identified from scattergrams and reflect genetic associations. Whereby the positive correlation between Cu–Zn (0.55, n=18) and Cu–Pb (0.63) is related to possible sulphide mineralization.  相似文献   

7.
8.
 Proposed groundwater withdrawals in the San Luis Valley of Colorado may lower the water table in Great Sand Dunes National Monument. In response, the National Park Service initiated a study that has produced a generalized conceptual model of the hydrologic system in order to assess whether a lowering of the water table might decrease the surface flow of lower Medano Creek. Based upon information obtained during the drilling of several boreholes, there appear to be five important hydrostratigraphic units underlying lower Medano Creek within the upper 30 m of the ground surface: 1. a perched aquifer overlying an aquitard located between about 5 and 6 m below the ground surface; 2. the aquitard itself; 3. an unconfined aquifer located between the upper and lower aquitards; 4. an aquitard located between about 27 and 29 m below the ground surface; and 5. a confined underlying the lower aquitard. Because the areal extent of the aquitards cannot be determined from the borehole data, a detailed conceptual model of the hydrogeologic system underlying lower Medano Creek cannot be developed. However, a generalized conceptual model can be envisioned that consists of a complex system of interlayered aquifers and leaky aquitards, with each aquifer having a unique hydraulic head. Water levels in the perched aquifer rise rapidly to their annual maximum levels in response to the arrival of the flow terminus of Medano Creek during the spring runoff event, and the location of the flow terminus is directly dependent upon the discharge of the creek. Water levels in the deeper, non-perched aquifers do not appear to fluctuate significantly in response to the arrival of the flow terminus, demonstrating that it is unlikely that the proposed groundwater withdrawals will decrease the surface flow of lower Medano Creek. Received: 27 December 1995 · Accepted: 20 February 1996  相似文献   

9.
Stratigraphically limited intervals from the Lower Eocene Willwood Formation contain laterally extensive carbonaceous shales and ribbon sandstone networks associated with channel avulsion. We present data from one such interval that documents the avulsion sequence. Vertical sections measured along the outcrop of this interval are similar and comprise a basal carbonaceous shale overlain by fine-grained deposits on which weakly developed, hydromorphic paleosols formed. The paleosols enclose and are locally incised by ribbon sandstones, some of which cut down to and partly through the carbonaceous shale. The ribbons have width/thickness ratios between 3 and 13. Some ribbons cluster at a particular stratigraphic level, which, together with paleocurrent trends, suggests that they formed channel networks. Sections are capped by yellow-brown paleosols showing moderate pedogenic development. We suggest that the carbonaceous shales developed in low-lying topogeneous swamps in distal portions of the floodplain far from the trunk channel. Such a location set limits on the sediment that they received. The mudrocks with weakly developed paleosols and associated ribbon sandstones are interpreted as crevasse-splay complexes resulting from avulsion of the trunk river. The ribbon sandstones represent ancient feeder channels of the avulsion complex. The rapid influx of avulsion deposits appears to have been crucial to preserving the organic material, and this study reveals an important and as yet uncharacterized link between trunk channel processes and the accumulation of organic-rich deposits in distal alluvial swamps. Similar deposits are found in other stratigraphic units in the Rocky Mountain region, and the development of these and other organic-rich deposits should be reassessed in terms of channel avulsion.  相似文献   

10.
The spatial analysis of geochemical data has several environmental and geological applications. The present study investigated the regional distribution of Al, Ba, Ca, Ce, Co, Cr, Cu, Fe, K, La, Li, Mg, Mn, Na, Ni, Pb, Sc, Th, Ti, U, V, and Zn elements in stream sediment samples from New Mexico State. These elements were studied in order to integrate them with geological and environmental characteristics of the area. Data are used from 27,798 samples that were originally collected during the national uranium resource evaluation (NURE) Hydrogeochemical and stream sediment reconnaissance (HSSR) program in the 1970s. The original data are available as U.S. Geological Survey Open-File Report 97-492. The study used a variety of data processing and filtering techniques that included univariate, bivariate, factor analyses and spatial analyses to transform the data into a useable format. Principal component analysis and GIS techniques are applied to classify the elements and to identify geochemical signatures, either natural or anthropogenic. The study found that the distribution of the investigated elements is mainly controlled by the bed rock chemistry. For example, along the Rio Grande rift and Jemez lineament a strong association between Co, Cr, Cu, Fe, Ni, Sc, Ti, V and Zn was observed and indicates that elements distribution in the area controlled by the mafic factor. The rare earth elements (REE) factor which is consists of Ce, La and U, also has strong, localized, clusters in the felsic centers in New Mexico.  相似文献   

11.
Rocks enriched in iron oxide and mafic silicates are commonly present as minor volumes of Proterozoic anorthosite complexes. In the Laramie Range, Wyoming, anorthositic rocks, gabbros, and iron oxide ore have been chemically analyzed to determine if the spatial association is a result of genetic relationships between the rock types.Variations in abundances of REE, Th, Sc, and Sr in whole-rock and in mineral separates from anorthositic rocks provide evidence for the presence of trapped intercumulus liquid. Initial 87Sr/86Sr ratios in apatites separated from iron oxide ore (0.70535±0.00004) are analogous to initial 87Sr/86Sr ratios in Laramie Range anorthosite (0.70531 and 0.70537). In addition, REE abundances in calculated parental liquids for both anorthositic rocks and iron ore are similar, providing further evidence for a comagmatic relationship.Trace element and textural characteristics of spatially associated Laramie Range gabbros indicate that they are not mixtures of the trapped liquid and cumulus components which formed anorthositic rocks. It is suggested that gabbros are early differentiation products of a high-Al gabbroic magma which subsequently crystallized large volumes of plagioclase to produce the anorthosite massif.  相似文献   

12.
金杖子地区位于冀东-辽西金成矿带,区内矿产资源丰富,成矿地质条件优越。本文在1∶25000水系沉积物测量工作的基础上,结合该区地质特征和成矿地质条件,对该地区10种元素的地球化学特征、离散程度及综合异常特征进行研究,圈定综合异常3处,为进一步的地质勘查工作提供了依据。  相似文献   

13.
The Permian Park City Formation consists of cyclically bedded subtidal to supratidal carbonates, cherts and siltstones. Early diagenesis of Park City Formation carbonates occurred under the influence of waters ranging from evaporative brines to dilute meteoric solutions and resulted in evaporite emplacement (syndepositional nodules and cements), as well as dolomitization, silicification and leaching of carbonate grains. Major differences are seen, however, in the diagenetic patterns of subsurface and surface sections of Park City Formation rocks. Subsurface samples are characterized by extensively preserved evaporite crystals and nodules, and preserve evidence of significant silicification (chert, chalcedony and megaquartz) and minor calcitization of evaporites. In outcrop sections, the evaporites are more poorly preserved, and have been replaced by silica and calcite and also leached. The resultant mouldic porosity is filled with widespread, very coarse, blocky calcite spar. These replacements appear to be multistage phenomena. Field and petrographic evidence indicates that silicification involved direct replacement of evaporites and occurred during the early stages of burial prior to hydrocarbon migration. Siliceous sponge spicules provided a major source of silica, and the fluids involved in replacement were probably a mixture of marine and meteoric waters. A second period of replacement and minor calcitization is inferred to have occurred during deep burial (under the influence of thermochemical sulphate reduction), although the presence of hydrocarbons probably retarded most other diagenetic reactions during this time interval. The major period of evaporite diagenesis, however, occurred during late stage uplift. The late stage replacement and pore-filling calcites have δ13C values ranging from 0·5 to -25·3%, and δ18O values of -16·1 to -24·30 (PDB), reflecting extensive modification by meteoric water. Vigorous groundwater flow, associated with mid-Tertiary block faulting, led to migration of meteoric fluids through the porous carbonates to depths of several kilometres. These waters reacted with the in situ hydrocarbon-rich pore fluids and evaporite minerals, and precipitated calcite cements. The Tosi Chert appears to have been an even more open system to fluid migration during its burial and has undergone a much more complex diagenetic history, as evidenced by multiple episodes of silicification, calcitization (ferroan and non-ferroan), and hydrocarbon emplacement. The multistage replacement processes described here do not appear to be restricted to the Permian of Wyoming. Similarly complex patterns of alteration have been noted in the Permian of west Texas, New Mexico, Greenland and other areas, as well as in strata of other ages. Thus, multistage evaporite dissolution and replacement may well be the norm rather than the exception in the geological record.  相似文献   

14.
Characterizing stream erosion in any steep mountain landscape is arduous, but the challenge level increases when the stream flows through a glaciated catchment frequently modified by hillslope debris.Glacial landforms and stochastic mass wasting in alpine systems may interfere with sediment delivery to downstream sites where detrital sediments are often collected to represent upstream bedrock sources.To use detrital sediments as indicators of erosion, we need to understand potential sediment accumulation in flat glaciated reaches or behind rockfall barriers. This study investigates the stream channel in Garnet Canyon, a glaciated catchment located in the central Teton Range, to describe hillslope coupled channel morphology and the subsequent effects on sediment transport throughout the catchment.Stream cross-section surveys and sediment size measurements of the surface bedload were collected in the field within a glacially flattened segment of Garnet Canyon. Calculations of shear stress conditions allowed evaluation of the importance of mineral densities on potential grain entrainment. The length of the Garnet Canyon stream observed in this study was coupled with hillslope deposits. Critical shear stresses were sufficient to move gravel-sized sediments through all sections when calculated with quartz mineral density and through most sections when applying apatite mineral density. These results verify the application of detrital sediments to evaluate erosion rates or spatial bedrock sources because snowmelt stream flow efficiently moves entrained sediment past glacially reduced slopes and potential talus barriers.  相似文献   

15.
Aeolian limestones are widespread in the Quaternary record and have been identified in outcrops and cores of late Palaeozoic strata. These rocks have been interpreted as a low latitude signal of glacio-eustatic sea level fluctuations and have not been previously reported from the Mesozoic or from other episodes of earth history generally believed to have been non-glacial. Numerous lenticular bodies of cross-stratified oolite lie near the contact between the lower and upper members of the mudstone-dominated lower Sundance Formation (Middle and Upper Jurassic) in the Bighorn Basin of north-central Wyoming, USA. The lenses, up to 12 m thick, contain sedimentary structures diagnostic of aeolian deposition. Inversely graded laminae within thick sets of cross-strata were deposited by climbing wind ripples. Adhesion structures and evenly dispersed lag granules are present in flat-bedded strata at the bases of several of the oolite bodies. Thin sections reveal abundant intergranular micrite of vadose origin. The lenses appear to represent virtually intact, isolated aeolian bedforms that migrated across a nearly sand-free deflation surface. When the Sundance Sea transgressed the dunes, a thin (<1 m thick), wave-rippled, oolite veneer formed on the upper surface of the aeolianite. Previous workers, primarily on the basis of sedimentary structures in the veneer, interpreted the oolite lenses as tidal sand bodies. The dunes provide clear evidence of widespread subaerial exposure on the crest and north flank of the Sheridan Arch. This structural high was delineated by previous workers who demonstrated thinning of pre-upper-Sundance Formation strata and localized development of ooid shoals. Ooids that formed in shoals on the windward (southern) side of the palaeohigh were exposed and deflated during lowstand. Thin, scour-filling ooid grainstone lenses that crop out in the southern part of the study area represent remnants of the marine beds that sourced the aeolianites. Farther north (down-wind), oolitic dunes prograded over thinly laminated lagoonal silts. When relative sea level began to rise, the uncemented dunes were buried under fine-grained marine sediment as the lee side of a low-relief island was inundated.  相似文献   

16.
Soil chronofunctions are often quasilinear, but those relationships may be only gross, fortuitous generalizations that ignore changes in soils resulting from climatic and other cyclic external influences that govern soil formation or soil degradation. In the Rocky Mountains, soil development has been extensively used to estimate the age of sediments, but the number of soils is usually few, and large ranges in values for soil data may be dismissed as “normal variation.” In a detailed study of soils in the Wind River Range and Wind River Basin, characteristics of near-surface horizons do not follow age trends. However, the underlying carbonate-bearing horizons do have age-related characteristics. This “soil paradox” may be related to glacial–interglacial cycles in which (1) wind erodes near-surface horizons and then provides new parent material and (2) cryoturbation disrupts carbonate horizons, remobilizing carbonate and changing carbonate morphology but with only minimal loss of carbonate from the soil.  相似文献   

17.
The fluvio-tidal transition of suspended sediment in terms of mineralogy and composition in the Loire River drainage basin, the largest French river basin, was investigated in the fluvial zone at Montjean and in the tidal zone at Mauves-Thouaré, for a complete seasonal cycle. At Montjean, where the river experiences unidirectional flow, the composition and mineralogy (especially clays and clay minerals) of river suspended material (RSM) are governed by the river discharge, upstream contributions, climatic conditions and microbiological activities. However, due to reversing tidal and river currents at Thouaré, in the zone of tidal dynamics, these relations are changed. In the downstream direction sand and clay content in the RSM decrease while the silt content increases. Among clay minerals, between these two observation stations, montmorillonite remains constant, kaolinite diminishes, and the other minerals increase downstream. Combustible material (organic) and nitrate (NO3) contents in the RSM increase whereas the phosphate (PO43-) and CaCO3 contents decline considerably during transport. At the head of the tidal zone, where the river flow encounters the tidal influence, there is a relatively stationary water mass (tidal slack) where sands, clays, phosphate, carbonate and silica are deposited by physical and chemical processes. Physical sedimentation takes place by simple gravitational deposition (sands), and by sorting and complicated differential settling (clays); chemical sedimentation takes place by precipitation (calcite-CaCO3; apatite-Ca5 (PO4)3 (OH,F,Cl); coagulation of dissolved silica-SiO2) in connection with seasonal algal bloom and eutrophic events.  相似文献   

18.
Testate amoebae are increasingly used for environmental monitoring as well as paleoenvironmental reconstructions. Paleoecological interpretations of testate amoebae assemblages depend on the understanding of the ecological processes operating today. We then ask the question of the link between testate structure and its environment. This study analyses both the grain size and mineralogical assemblage of tests of common species belonging to the genus Centropyxis and Difflugia. It is concluded that grain size is a limiting factor for test construction, whereas mineral composition is not. Hence, when analyzing agglutinated testate amoebae for paleoenvironmental reconstructions, it should be taken into account the mean grain size of the sediment. A non-appropriate grain-size probably inhibits the development of a testate amoebae specific assemblage.  相似文献   

19.
 A series of water samples from Steamboat Creek, Nevada, was analyzed for total mercury concentrations. Concentrations from these waters were 40 to 60 times higher than the pristine mountain streams entering the creek. The major source of the mercury entering Steamboat Creek is probably from gold/silver processing that took place in the 1860s. Received: 10 March 1997 · Accepted: 2 September 1997  相似文献   

20.
Salt marshes play a significant roll in the marine and coast ecological systems. They can function as a sink for pollutants that would otherwise be harmful to the environment. Our investigation is mainly focused on clay mineralogy of the salt marsh sediment, metal associations in the environment of the modern (centennial) salt marsh sediment and possible relation between these metal associations and clay minerals involved. The studied salt marsh is located in the Skalingen Peninsula, West Denmark. About 85 percent of the deposited materials, including the heavy metals, was imported from the North Sea while only a small quantity of the materials was transported through the Varde River whose mouth is located about 10 km from the salt marsh, at the opposite side of the lagoon. A 25 cm high monolithic profile of the salt marsh sediment was collected and was cut into 1-cm slices. The rate of sediment accumulation, detailed grain size distribution, clay mineralogy, dating of the profile (^210Pb and ^137Cs), content of organic matter as well as 17 metals: K, Ca, Ti, Mn, Fe, V, Cr, Co, Ni, Cu, Zn, Br, Rb, Sr, Y, Zr, Nb were investigated. Principal components and factor analyses demonstrated strong positive loadings for most of the studied metals, fine grain fractions as well as organic matter, indicating a close relation among these components. Mn, Fe, Ni, Cu, Zn, Rb were found best correlated to the clay fraction (〈2 microns), which comprises primarily illite, kaolinite, minor chlorite and lesser smectite/illite mixed layer.  相似文献   

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