Статті в журналах з теми "Salt pans (Geology) Australia"

A taxonomic account of the genus Monocarpus and its only species, M. sphaerocarpus, is presented. The species was initially discovered on salt pans in Western Australia, and only later, in southern Africa. It is extremely rare and the structure of the minute thalli is difficult to determine, also to describe and to illustrate. As far as could be determined, no SEM micrographs o f the thalli and spores have been published before, nor has the capsule wall been illustrated.

In China, pre-Quaternary solid potash deposit has only been discovered in the Simao Basin, and the Lower Cretaceous Mengyejing (MYJ) Formation (Fm.) is the productive layer of potash deposit. In this study, we investigated the clay conglomerates which are distributed in upper and lower members of the potash-bearing salt rock layer. We analyzed the relative contents of major elements (Al2O3, Fe2O3T, MgO, CaO, Na2O, K2O) and trace elements (B, Ba, Co, Cr, Cu, Ga, Mn, Ni, Rb, Sr, V, Zn, Zr) in the samples. The results show that MgO and CaO in the major elements are rich relative to Post Archean Australian Shale (PAAS), whose average enrichment factor values of the MgO (EFMgO) is 2.61 and CaO (EFCaO) is 4.57, and the others major elements are relatively minor; trace elements (B, Ga, Mn, Zr) are rich relative to PAAS, and the others trace elements are minor relative to PAAS. The study of paleogeographic conditions using various parameters shows that the paleoclimate is generally dry and hot during the period of clay conglomerate deposition, but it was warm and humid in certain periods; the main sedimentary environment is weak oxidation condition with strong oxidation conditions in individual periods; the average value of paleosalinity is ~21‰, and the highest is no more than ~92‰. The significance of the paleogeographic characteristics of MYJ Fm. to potash mineralization are as follows: (1) they indicates that the clay conglomerates of MYJ Fm. are not clastic sediments in brine formed by seawater, because the paleosalinity of clay conglomerates deposition period is obviously lower than that of seawater; (2) MYJ potassic salt ore is not formed by evaporation and concentration of seawater in clay conglomerates in the sedimentary basin, because there is no carbonate rock and sulfate rock of corresponding scale after the deposition of clay conglomerates in the basin; (3) clay conglomerates of MYJ Fm. were deposited in continental shallow water basin; (4) the matter source of potash minerals is deep marine strata; (5) in the MYJ Fm. sedimentation period, deep source salt moved to the surface under the background of extensional structure, and the subsequent sedimentary clastic rock formed a protective layer of potash-bearing rock, thus completing the “deep source and shallow mineralization” metallogenic process.

ABSTRACT This study documents the growth of a megaflap along the flank of a passive salt diapir as a result of the long-lived interaction between sedimentation and halokinetic deformation. Megaflaps are nearly vertical to overturned, deep minibasin stratal panels that extend multiple kilometers up steep flanks of salt diapirs or equivalent welds. Recent interest has been sparked by well penetrations of unidentified megaflaps that typically result in economic failure, but their formation is also fundamental to understanding the early history of salt basins. This study represents one of the first systematic characterizations of an exposed megaflap with regards to sub-seismic sedimentologic, stratigraphic, and structural details. The Witchelina diapir is an exposed Neoproterozoic primary passive salt diapir in the eastern Willouran Ranges of South Australia. Flanking minibasin strata of the Top Mount Sandstone, Willawalpa Formation, and Witchelina Quartzite, exposed as an oblique cross section, record the early history of passive diapirism in the Willouran Trough, including a halokinetically drape-folded megaflap. Witchelina diapir offers a unique opportunity to investigate sedimentologic responses to the initiation and evolution of passive salt movement. Using field mapping, stratigraphic sections, petrographic analyses, correlation diagrams, and a quantitative restoration, we document depositional facies, thickness trends, and stratal geometries to interpret depositional environments, sequence stratigraphy, and halokinetic evolution of the Witchelina diapir and flanking minibasins. Top Mount, Willawalpa, and Witchelina strata were deposited in barrier-bar-complex to tidal-flat environments, but temporal and spatial variations in sedimentation and stratigraphic patterns were strongly influenced from the earliest stages by the passively rising Witchelina diapir on both regional (basinwide) and local minibasin scales. The salt-margin geometry was depositionally modified by an early erosional sequence boundary that exposed the Witchelina diapir and formed a salt shoulder, above which strata that eventually became the megaflap were subsequently deposited. This shift in the diapir margin and progressive migration of the depocenter began halokinetic rotation of flanking minibasin strata into a megaflap geometry, documenting a new concept in the understanding of deposition and deformation during passive diapirism in salt basins.

Abstract The aeolian regime of the 100 km wide, hyperarid Namib Desert has been sporadically punctuated by the deposition of fluvial sediments generated during periods of higher humidity either further inland or well within the desert from Late Oligocene to Late Holocene. Four new Late Cenozoic formations are described from the northern Skeleton Coast and compared with formations further south: the Klein Nadas, Nadas (gravels, sands), Vulture’s Nest (silts) and Uniab Boulder Formations. The Klein Nadas Formation is a trimodal mass-flow fan consisting of thousands of huge, remobilised, end-Carboniferous Dwyka glacial boulders, many >3 m in length, set in an abundant, K-feldspar-rich and sandy matrix of fine gravel. Deluge rains over the smallest catchments deep within the northern Namib were the driving agent for the Klein Nadas Fan, the termination of which, with its contained boulders, rests on the coastal salt pans. These rains also resulted in catastrophic mass flows in several of the other northern Namib rivers. The Uniab Boulder Formation, being one, consists only of huge free-standing boulders. Gravelly fluvial deposition took place during global interglacial and glacial events. The Skeleton Coast Erg and other smaller dune trains blocked the rivers at times. The low-energy, thinly bedded silt deposits of the central and northern Namib are quite distinctive from the sands and gravels of older deposits. Their intermittent deposition is illustrated by bioturbation and pedogenesis of individual layers. Published offshore proxy climatological data (pollens, upwelling, wind, sea surface temperatures) point to expansion of the winter-rainfall regime of the southern Cape into southwestern Angola during strong glacial periods between the Upper Pleistocene and Holocene. In contrast to deposition initiated by short summer thunder storms, we contend that the silt successions are river-end accumulations within which each layer was deposited by runoff from comparatively gentle winter rains that lasted several days.

The Officer Basin described in this paper includes four Proterozoic to Lower Palaeozoic sub-basins (Gibson, Yowalga, Lennis, Waigen) which extend in a northwest to southeast belt across 200 000 sq. km of central Western Australia. These sub-basins are bounded by Archaean to Proterozoic basement blocks and are almost entirely concealed by a veneer of Permian and Cretaceous sediments. Depth to magnetic basement locally exceeds eight kilometres.Until recently, information on the sub-surface geology was limited to shallow levels, based on the results of a petroleum exploration campaign in the 1960s and the work of State and Federal Geological Surveys. In 1980, the Shell Company of Australia was awarded three permits (46 200 sq. km) covering the Yowalga and Lennis Sub-basins. The results of 4700 km of seismic data and three deep wildcat wells, combined with gravity, aeromagnetic, Landsat, outcrop and corehole information, has led to a better understanding of the regional subsurface geology.The Lennis Sub-basin appears to contain Lower to Middle Proterozoic sediments, whereas the Yowalga Sub- basin is primarily an Upper Proterozoic to Lower Cambrian sequence which comprises a basal clastic section, a middle carbonate and evaporite sequence and an upper clastic section. Widespread Middle Cambrian basalts cap the Upper Proterozoic to Lower Cambrian prospective sequence. Late Proterozoic uplift resulted in salt- assisted gravity tectonics leading to complex structural styles, especially in the basin axis.Despite oil shows, organic matter in the oil and gas generation windows and reservoir-quality sandstones with interbedded shales, no convincing source rocks or hydrocarbon accumulations have yet been located. The area remains, however, one of the least explored basins in Australia.

Abstract. Dryland salinity poses a major threat to agricultural production in the wheatbelt of Western Australia and much time and effort is expended on understanding the mechanisms which cause it and on developing techniques to halt or reverse its development. Whilst the location of much dryland salinity can be explained by its topographic position, a significant proportion of it cannot. This study investigated the hypothesis that major faults in the Yilgarn Craton represented in aeromagnetic data by intense curvilinear lows explained the location of areas of dryland salinity not explained by topography. Moreover, the causal mechanisms that might underpin a spatial relationship between major faults and dryland salinity were sought. In one fourth order catchment, nearly 85% of the salinity that was not explained topographically was within 2km of the centre line of a major fault, the remaining 15% being in the other 12km of the catchment. Three groups of similar third order catchments in the western wheatbelt of Western Australia were also investigated; in each case the catchment that was underlain by a major fault had dryland salinity an order of magnitude more than the unfaulted catchment(s). This evidence demonstrates a strong spatial association between major faults and the development of dryland salinity. Other evidence suggests that the underlying mechanism is hydraulic conductivity 5.2 to 2.9 times higher inside the fault zone compared to outside it and shows that geomorphology, salt store, regolith thickness, and degree of clearing are not the underlying mechanisms. In one of the groups of catchments, it has been calculated that an amount of recharge, significant in relation to recharge from rainfall, was entering from an adjacent catchment along a major fault. The paper concludes that geological features such as major faults affect the development of dryland salinity in the wheatbelt of Western Australia because of permeability differences in the regolith and therefore computer models of salinity risk need to take these differences into account. Techniques need to be developed to map, quickly and relatively cheaply, the geology-related permeability differences over wide areas of the landscape.

The Garden Park National Natural Landmark (GPNNL) is north of Cañon City, Colorado, and encompasses all of the major historical dinosaur quarries of the Upper Jurassic Morrison Formation in this area. The formation there can be divided into the lower redefined Ralston Creek Member and an upper unnamed member. The Morrison Formation is bracketed below by the J-5 unconformity and above by the K-1 unconformity. The Ralston Creek Member is composed of up to 55 m of arkosic conglomerate, sandstone, siltstone, and gypsum conformably underlying the unnamed member. Fossil fishes previously used to infer a Middle Jurassic age are non-diagnostic. A diplodocid skeleton 4 m above the J-5 unconformity from the west-adjacent Shaws Park, and a radiometric date of 152.99 + 0.10 Ma from the Purgatoire River area demonstrate that the Ralston Creek rightly belongs in the Morrison Formation and correlates with the Tidwell and Salt Wash Members on the Colorado Plateau. The Ralston Creek was deposited in a broad playa complex analogous to those of central Australia and here called the Ralston Creek boinka. Groundwater flux played an important role in gypsum deposition in gypsisols and playa lakes. The overlying unnamed member in the GPNNL can be subdivided on the west side of Fourmile Creek into a lower part composed largely of mudstone with many thin, discontinuous channel sandstone beds, and a thicker upper part containing more persistent tabular sandstone beds; this subdivision does not occur east of Fourmile Creek. Several thin limestone beds occur in the Ralston Creek Member and in the lower part of the unnamed upper member. The limestone contains fresh water ostracods and aquatic mollusks indicating a lacustrine origin. However, these fauna are apparently stunted and the ostracod valves closed indicating periodic hypersaline conditions. All detrital rocks in the Morrison Formation at Garden Park are composed of varying amounts of quartz, potassic feldspar, and the clay minerals illite, smectite, and kaolinite. Mapping of the clay minerals in the unnamed member reflect various paleosols throughout the mudstone interval, including protosols and argillisols. At the top of the formation, a sandstone previously assigned to the Morrison is reassigned to the overlying Cretaceous Lytle Formation based on similar weathering characteristics, mineral content, and fabric. Thus, the K-1 unconformity between the Morrison and overlying Lytle rests on the uppermost occurrence of the Morrison Formation mudstone-sandstone-limestone complex and beneath the blocky, cliff-forming Lytle Formation.

The Garden Park National Natural Landmark (GPNNL) is north of Cañon City, Colorado, and encompasses all of the major historical dinosaur quarries of the Upper Jurassic Morrison Formation in this area. The formation there can be divided into the lower redefined Ralston Creek Member and an upper unnamed member. The Morrison Formation is bracketed below by the J-5 unconformity and above by the K-1 unconformity. The Ralston Creek Member is composed of up to 55 m of arkosic conglomerate, sandstone, siltstone, and gypsum conformably underlying the unnamed member. Fossil fishes previously used to infer a Middle Jurassic age are non-diagnostic. A diplodocid skeleton 4 m above the J-5 unconformity from the west-adjacent Shaws Park, and a radiometric date of 152.99 + 0.10 Ma from the Purgatoire River area demonstrate that the Ralston Creek rightly belongs in the Morrison Formation and correlates with the Tidwell and Salt Wash Members on the Colorado Plateau. The Ralston Creek was deposited in a broad playa complex analogous to those of central Australia and here called the Ralston Creek boinka. Groundwater flux played an important role in gypsum deposition in gypsisols and playa lakes. The overlying unnamed member in the GPNNL can be subdivided on the west side of Fourmile Creek into a lower part composed largely of mudstone with many thin, discontinuous channel sandstone beds, and a thicker upper part containing more persistent tabular sandstone beds; this subdivision does not occur east of Fourmile Creek. Several thin limestone beds occur in the Ralston Creek Member and in the lower part of the unnamed upper member. The limestone contains fresh water ostracods and aquatic mollusks indicating a lacustrine origin. However, these fauna are apparently stunted and the ostracod valves closed indicating periodic hypersaline conditions. All detrital rocks in the Morrison Formation at Garden Park are composed of varying amounts of quartz, potassic feldspar, and the clay minerals illite, smectite, and kaolinite. Mapping of the clay minerals in the unnamed member reflect various paleosols throughout the mudstone interval, including protosols and argillisols. At the top of the formation, a sandstone previously assigned to the Morrison is reassigned to the overlying Cretaceous Lytle Formation based on similar weathering characteristics, mineral content, and fabric. Thus, the K-1 unconformity between the Morrison and overlying Lytle rests on the uppermost occurrence of the Morrison Formation mudstone-sandstone-limestone complex and beneath the blocky, cliff-forming Lytle Formation.

Climate change induced sea-level rise (SLR) is on its increase globally. Regionally the lowlands of China, Vietnam, Bangladesh, and islands of the Malaysian, Indonesian and Philippine archipelagos are among the world’s most threatened regions. Sea-level rise has major impacts on the ecosystems and society. It threatens coastal populations, economic activities, and fragile ecosystems as mangroves, coastal salt-marches and wetlands. This paper provides a summary of the current state of knowledge of sea level-rise and its effects on both human and natural ecosystems. The focus is on coastal urban areas and low lying deltas in South-East Asia and Vietnam, as one of the most threatened areas in the world. About 3 mm per year reflects the growing consensus on the average SLR worldwide. The trend speeds up during recent decades. The figures are subject to local, temporal and methodological variation. In Vietnam the average values of 3.3 mm per year during the 1993-2014 period are above the worldwide average. Although a basic conceptual understanding exists that the increasing global frequency of the strongest tropical cyclones is related with the increasing temperature and SLR, this relationship is insufficiently understood. Moreover the precise, complex environmental, economic, social, and health impacts are currently unclear. SLR, storms and changing precipitation patterns increase flood risks, in particular in urban areas. Part of the current scientific debate is on how urban agglomeration can be made more resilient to flood risks. Where originally mainly technical interventions dominated this discussion, it becomes increasingly clear that proactive special planning, flood defense, flood risk mitigation, flood preparation, and flood recovery are important, but costly instruments. Next to the main focus on SLR and its effects on resilience, the paper reviews main SLR associated impacts: Floods and inundation, salinization, shoreline change, and effects on mangroves and wetlands. The hazards of SLR related floods increase fastest in urban areas. This is related with both the increasing surface major cities are expected to occupy during the decades to come and the increasing coastal population. In particular Asia and its megacities in the southern part of the continent are increasingly at risk. The discussion points to complexity, inter-disciplinarity, and the related uncertainty, as core characteristics. An integrated combination of mitigation, adaptation and resilience measures is currently considered as the most indicated way to resist SLR today and in the near future.References Aerts J.C.J.H., Hassan A., Savenije H.H.G., Khan M.F., 2000. Using GIS tools and rapid assessment techniques for determining salt intrusion: Stream a river basin management instrument. 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Tidal channels comprise a peculiar and dynamic environment. This paper aims to recognize the sedimentary distribution and composition of a tidal channel located in a semi-arid climate area in order to understand the sedimentary dynamics of the region. This region has economic and environmental importance considering that several activities are developed in the area such as; salt industry and aquaculture with shrimp farming. The results and discussion presented here on the Barra Grande Port tidal channel are based on 43 superficial samples distributed in the area, in which we analyzed the grain-size distribution and the calcium carbonate and organic matter contents. The data enabled the characterization and compartmentalization of the tidal channel on five sections and the interpretation of the sedimentary dynamics of the area. The sections present an important variation in the composition and selection. The section 1 is located in supratidal zone while sections 02, 03, 04 and 05 are in intertidal zone. The grain-size mean has a tendency to decrease toward the end of the channel as well as the gravel percentage, and the carbonate and organic matter contents. Differently, the mud content and the sorting increase toward the end of the channel and the skewness becomes more positive. In a general way, the carbonate content is high throughout the tidal channel ranging from 20 to 98% while the organic matter content is low ranging from 0 to 3%. This sedimentary distribution occurs due to the development of a hydraulic dam on section 3, causing a morphological growth of this sand bar, which acts as a natural hydraulic dam, hampering the access of the tide and consequently reducing the effectiveness of the transport, resulting in the deposition of fine sediments in the sheltered areas of the channel (sections 04 and 05). The high temperatures and low rainfall of the tropical hot semi-arid climate allowed the development of carbonate sedimentation as well as the development of anthropic activities such as salt extraction in artificial salt pans which may have influenced the low levels of organic matter.

AbstractIn this contribution, I discuss the putative link of mantle plumes with selected categories of mineral systems. Continental rifting and break-ups can be induced by the upwelling of mantle plumes, also resulting in the generation of a wide range of mineral deposits. These include magma-associated ores, anorogenic igneous events responsible for iron oxide–copper–gold (IOCG) deposits, carbonatites and hydrothermal-induced mineralization, as well as hydrocarbons, salt domes, petroleum and gas, and several mineral systems in continental passive margins. Amongst the magma-associated mineral systems, the Ni–Cu–platinum group element (PGE), Fe–Ti–V and Cr deposits are the economically most important, such as those of the Bushveld Igneous Complex in South Africa. Anorogenic magmas are generally alkaline and associated with IOCG mineral systems, as exemplified by the giant Olympic Dam and similar deposits in South America. Carbonatites are considered as a distal effect of hotspot mantle plumes, as shown by Mount Weld in Australia, which may be related to the Bushveld Superplume. Plume-related thermal anomalies are the principal factor for the inception of hydrothermal circulation and the genesis of a wide range of hydrothermal mineral systems in rift-related tectonic settings. These include large-scale sedimentary-rock-hosted metalliferous ores, such as sedimentary exhalative (SEDEX) deposits. A modern example of is provided by the Red Sea brine pools. Some key examples are presented in this paper.