The Lower Devonian Jauf Formation in Saudi Arabia is an important hydrocarbon reservoir. However, in spite of its importance as a reservoir, published studies on the Jauf Formation more specifically on the reservoir quality (including diagenesis), are very few. This study, which is based on core samples from two wells in the Ghawar Field, northeastern Saudi Arabia, reports the lithologic and diagenetic characteristics of this reservoir. The Jauf reservoir is a fine to medium-grained, moderate to well-sorted quartz arenite. The diagenetic processes recognized include compaction, cementation (calcite, clay minerals, quartz overgrowths, and a minor amount of pyrite), and dissolution of the calcite cements and of feldspar grains. The widespread occurrences of early calcite cement suggest that the Jauf reservoir lost a significant amount of primary porosity at a very early stage of its diagenetic history. Early calcite cement, however, prevented the later compaction of the sandstone, thus preserving an unfilled part of the primary porosity. Based on the framework grain–cement relationships, precipitation of the early calcite cement was either accompanied or followed by the development of part of the pore-lining and pore-bridging clay cement. Secondary porosity development occurred due to partial to complete dissolution of early calcite cements and feldspar. Late calcite cement occurs as isolated patches, and has little impact on reservoir quality of the sandstones.In addition to calcite, several different clay minerals including illite and chlorite occur as pore-filling and pore-lining cements. While the pore-filling illite and chlorite resulted in a considerable loss of porosity, the pore-lining chlorite may have helped in retaining the porosity by preventing the precipitation of syntaxial quartz overgrowths. Illite, which largely occurs as hair-like rims around the grains and bridges on the pore throats, caused a substantial deterioration to permeability of the reservoir. Diagenetic history of the Jauf Formation as established here is expected to help better understanding and exploitation of this reservoir. 相似文献
Washovers, dune scarps and flattened beach profiles with concentrations of coarse-grained sediment or heavy minerals are the diagnostic geological signatures of large storms on barriers today. It is clear that storms are a major force driving transgressive barriers onshore, but what is not as well understood is the role these powerful erosive events play in the evolution of prograding barriers. Application of ground-penetrating radar (GPR) and a combination of coring techniques have significantly improved our ability to image barrier architecture. Results of these studies reveal a more complex evolution than previously recognized. It is now possible to precisely locate and map storm deposits within prograded barrier lithosomes.
A comprehensive study of northern Castle Neck, Massachusetts was performed using 15 km of GPR surveys, a 120-m-long seismic line, 11 cores, and several radiocarbon dates. Storm-related layers are the most prominent horizons contained in the barrier stratigraphy. The geometry and sedimentology of these layers closely resembles those of a present-day post-storm beach. Twenty closely spaced, curvilinear heavy mineral layers imaged in the landward portion of the barrier suggest that the Castle Neck barrier was heavily influenced by storms during its initial phase of progradation beginning 4000 years BP. Approximately 1800 years BP, two intense storms impacted the coast depositing two extensive coarse-grained units. These layers mimic the flat-lying sand and gravel deposits that occur in front of a nearby eroding till outcrop following major storms. The great number of storm deposits in the early history of Castle Neck is related to either a period of greater storm activity and/or a slow rate of barrier progradation. The occurrence and preservation of these earlier storm layers are likely a product of the exposure of nearby drumlins resulting in greater availability of iron oxide and ferromagnesian sands. The supply of heavy-mineral sands has gradually diminished as the barrier prograded and the proximal drumlin source was buried by beach and dune sands. 相似文献
Soil contamination by heavy metals has been an increasingly severe threat to nature environment and human health. Efficiently investigation of contamination status is essential to soil protection and remediation. Visible and near-infrared reflectance spectroscopy (VNIRS) has been regarded as an alternative for monitoring soil contamination by heavy metals. Generally, the entire VNIR spectral bands are employed to estimate heavy metal concentration, which lacks interpretability and requires much calculation. In this study, 74 soil samples were collected from Hunan Province, China and their reflectance spectra were used to estimate zinc (Zn) concentration in soil. Organic matter and clay minerals have strong adsorption for Zn in soil. Spectral bands associated with organic matter and clay minerals were used for estimation with genetic algorithm based partial least square regression (GA-PLSR). The entire VNIR spectral bands, the bands associated with organic matter and the bands associated with clay minerals were incorporated as comparisons. Root mean square error of prediction, residual prediction deviation, and coefficient of determination (R2) for the model developed using combined bands of organic matter and clay minerals were 329.65 mg kg−1, 1.96 and 0.73, which is better than 341.88 mg kg−1, 1.89 and 0.71 for the entire VNIR spectral bands, 492.65 mg kg−1, 1.31 and 0.40 for the organic matter, and 430.26 mg kg−1, 1.50 and 0.54 for the clay minerals. Additionally, in consideration of atmospheric water vapor absorption in field spectra measurement, combined bands of organic matter and absorption around 2200 nm were used for estimation and achieved high prediction accuracy with R2 reached 0.640. The results indicate huge potential of soil reflectance spectroscopy in estimating Zn concentrations in soil. 相似文献
With a mean annual flow of 5.9×1011m3yr–1 and sediment load of 1600x1012gyr–1 the Ganges river ranks second and third, respectively, in terms of water flow and sediment load among the world's rivers. Considering the enormous sediment transport by Ganges to the Bay of Bengal, a study was conducted on the size distribution and mineral characteristics of the suspended sediments of the Ganges river and is reported here. Most of the sediment load has a size range between <4–5.75 ). The sediments are mostly medium to coarse silt and are poorly sorted. Mica dominates among the clay minerals, followed by chlorite, vermiculite, kaolinite, and smectite. Due to differences in geology, smectite becomes a major clay mineral in downstream rivers. At Calcutta, the clay mineral transport in millions of tons per year is 18,464, 8000, and 2147, for mica, smectite, and chlorite, respectively. 相似文献
The basin-fill aquifers of the Western U.S. contain elevated concentrations of arsenic in the groundwater due to ancient volcanic deposits that host arsenic minerals. Microcosms were constructed using two oxidized sediments and, by contrast, a reduced sediment collected from a shallow basin-fill aquifer in the Cache Valley Basin, Northern Utah to evaluate the fate of geologic arsenic under anoxic conditions. Sequential extractions indicated the primary arsenic host mineral was amorphous iron oxides, but 13%–17% of the total arsenic was associated with carbonate minerals. Arsenic was solubilized from the sediments when incubated with groundwater in the presence of native organic carbon. Arsenic solubilization occurred prior to iron reduction rather than the commonly observed co-reactivity. Arsenic(V) associated with carbonate minerals was the main source of arsenic released to solution and redistributed onto less soluble minerals, including FeS and siderite as defined by chemical extraction. Arsenic reduction occurred only in the site-oxidized sediments. The addition of a carbon and energy source, glucose, resulted in enhanced arsenic solubilization, which was coupled with iron reduction from the site-oxidized sediments. Adding glucose promoted iron reduction that masked the role of carbonate minerals in arsenic solubilization and retention as observed with incubation with groundwater only. 相似文献
Non-fuel marine minerals are reviewed from the perspective of resources and their value as active analogs that can advance understanding of types of ancient ore deposits that formed in marine settings. The theory of plate tectonics is the largest influence in expanding our vision of marine minerals and in developing our understanding of geologic controls of mineralization in space and time. Prior to the advent of plate tectonics, we viewed the ocean basins as passive sinks that served as containers for particulate and dissolved material eroded from land. This view adequately explained marine placer deposits (heavy minerals and gems), aggregates (sand and gravel), and precipitates (phosphorites and manganese nodules). Although numerous sites of placer mineral deposits are known on continental shelves worldwide, current activity pertains to diamond mining off southwestern Africa, tin mining off southeastern Asia, and intermittent gold mining off northwestern North America, which are all surpassed economically by worldwide recovery of marine sand and gravel, in turn dwarfed by offshore oil and gas. With the advent of plate tectonics, plate boundaries in ocean basins are recognized as active sources of mineralization in the form of hydrothermal massive sulfide deposits and proximal lower-temperature deposits hosted in oceanic crust (mafic at ocean ridges and felsic at volcanic island arcs), and of magmatic Ni–Cu sulfide, chromite and PGE deposits inferred to be present in the oceanic upper mantle–lower crust based on their occurrence in ophiolites. Some 300 sites of hydrothermal active and relict mineralization, most of them minor, are known at this early stage of seafloor exploration on ocean ridges, in fore-arc volcanoes, at back-arc spreading axes, and in arc rifts; deposits formed at spreading axes and transported off-axis by spreading are present in oceanic lithosphere but are virtually unknown. The TAG (Trans-Atlantic Geotraverse) hydrothermal field in the axial valley of the Mid-Atlantic Ridge (latitude 26° N) is considered to exemplify a major Volcanogenic Massive Sulfide (VMS) deposit forming at a spreading axis. The most prospective of these occurrences lie within the 200 nautical mile (370 km)-wide Exclusive Economic Zone (EEZ) of the nations of the volcanic island arcs of the western Pacific where metal content of massive sulfides (Ag, Au, Ba, Cu, Pb, Sb, Zn) exceeds that at ocean ridges. Plate tectonics early provided a framework for mineralization on the scale of global plate boundaries and is providing guidance to gradually converge on sites of mineralization through regional scales of plate reorganization, with the potential to elucidate the occurrence of individual deposits (e.g., Eocene Carlin-type gold deposits). Investigation of the spectrum of marine minerals as active analogs of types of ancient mineral deposits is contributing to this convergence. Consideration of questions posed by Brian Skinner (1997) of what we do and do not know about ancient hydrothermal mineral deposits demonstrates the ongoing advances in understanding driven by investigation of marine minerals. 相似文献
Stratigraphic offsets in the peak concentrations of platinum-group elements (PGE) and base-metal sulfides in the main sulfide
zone of the Great Dyke and the precious metals zone of the Sonju Lake Intrusion have, in part, been attributed to the interaction
between magmatic PGE-bearing base-metal sulfide assemblages and hydrothermal fluids. In this paper, we provide mineralogical
and textural evidence that indicates alteration of base-metal sulfides and mobilization of metals and S during hydrothermal
alteration in both mineralized intrusions. Stable isotopic data suggest that the fluids involved in the alteration were of
magmatic origin in the Great Dyke but that a meteoric water component was involved in the alteration of the Sonju Lake Intrusion.
The strong spatial association of platinum-group minerals, principally Pt and Pd sulfides, arsenides, and tellurides, with
base-metal sulfide assemblages in the main sulfide zone of the Great Dyke is consistent with residual enrichment of Pt and
Pd during hydrothermal alteration. However, such an interpretation is more tenuous for the precious metals zone of the Sonju
Lake Intrusion where important Pt and Pd arsenides and antimonides occur as inclusions within individual plagioclase crystals
and within alteration assemblages that are free of base-metal sulfides. Our observations suggest that Pt and Pd tellurides,
antimonides, and arsenides may form during both magmatic crystallization and subsolidus hydrothermal alteration. Experimental
studies of magmatic crystallization and hydrothermal transport/deposition in systems involving arsenides, tellurides, antimonides,
and base metal sulfides are needed to better understand the relative importance of magmatic and hydrothermal processes in
controlling the distribution of PGE in mineralized layered intrusions of this type. 相似文献