摘要:

ABSTRACTThe carbonate platforms of the Wetterstein Formation of the Eastern Alps (Drau Range and Northern Calcareous Alps) show a distinct facies zonation of reefs and lagoons. While some lagoonal areas were episodically emerged and formed lagoonal islands, others remained permanently flooded. The scale of near surface, meteoric or marine diagenesis was related to this lagoonal topography. At shallow burial depth, cementation was dominated by altered marine solutions, which additionally caused recrystallization of metastable constituents of the sediment and earlier marine cements (high magnesian calcite, aragonite) connected with a carbon and oxygen isotopic change to more negative values.Deeper burial cementation shows a succession with two types of saddle dolomite and three types of blocky calcite. Carbon and oxygen isotopic values of these cements show a trend towards more negative values from the first to the last generation, in the following succession: clear saddle dolomite—zoned blocky calcite—cloudy saddle dolomite—post‐corrosion blocky calcite—replacive blocky calcite. Fluid inclusion studies of the carbonate cements are interpreted to indicate a deeper burial temperature development that first increases from 175 to 317°C, followed by a temperature decrease to 163–260°C, and subsequent increase up to 316°C, whereby the samples of the Drau Range always show the lowest values. Calculations of the isotopic composition of the water, from which the carbonate cements were precipitated, yielded positive δ18O values from 6.66 to 17.81%o (SMOW), which are characteristic for formation and/or metamorphic waters. Also, the isotopic compositions of the palaeofluids probably changed during deeper burial diagenesis, following the temperat

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1995.tb02099.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe Neogene Humboldt (Eel River) Basin is located along the north‐eastern margin of the Pacific Ocean within the Cascadia subduction zone. This sedimentary basin originated near the base of the accretionary prism in post‐Eocene time. Subduction processes since that time have elevated strata in the south‐eastern portion of the basin above sea level. High‐resolution chronostratigraphic data from the onshore portion of the Humboldt Basin enable correlation of time‐equivalent lithofacies across the palaeomargin, reconstruction of slope‐basin evolution, and preliminary delineation of climatic and tectonic influence on lithological variation. Emergent basin fill is divided into five lithofacies which clearly document shoaling of the inner trench slope from deep‐water environments in early Miocene time to paralic environments in Pleistocene time. The oldest strata consist of hemipelagic mudstones and minor debris‐flow breccias deposited in a deep‐water setting during elevated sea level. These strata are overlain by glauconite‐rich, fine‐grained turbidites which heralded an increasing influx of terrigenous detritus. Water depths shoaled earlier in the eastern basin area as the palaeoshoreline prograded seaward. Turbidite deposition ceased in the eastern basin area at about 2‐2 Ma, whereas 22 km to the west, turbidite deposition continued until about 1‐8 Ma. Lithofacies at the western study site change abruptly across a middle Pleistocene unconformity from outer shelf to paralic deposits. In the east, a more complete Pleistocene section records transition from outer to inner shelf, beach and fluvial environments.The Humboldt Basin lithofacies sequence is overprinted by eustatic control of sediment source. Comparison of sediment character with palaeoceanographic conditions indicates dominance of hemipelagic facies during periods of elevated sea level in the middle Miocene and early Pliocene when depocentres were isolated from terrigenous sediment. Glauconite‐rich facies were mobilized from an upper slope setting following these periods of elevated sea level and redeposited in a deep‐marine environment. Pleistocene shoreline lithofacies display glacio‐esutatic control of depositional environment by recording several cycles of nearshore to fluvial progressions.General models of accretionary prism behaviour and trench‐slope basin evolution are compatible with the overall coarsening‐upward lithofacies sequence filling the Humboldt Basin. Early structural barriers precluded deposition of terrigenous material except from locally derived debris flows; subsequent shoaling and burial of deactivated thrust‐folds enabled turbidity flows to reach the basin floor.However, late‐stage tectonism apparently controlled the onset of coarse‐grained deposition in this sequence. Significant sand‐rich turbidite deposition began in the middle Pliocene, synchronous with tectonic uplift of the southern basin margin. Conversely, cessation of turbidite deposition in the eastern basin area in latest Pliocene time was synchronous with growth of anticlinal structures which again blocked widespread dispersal of turbidity flows. This middle Pliocene to Holocene period of crustal shortening is synchronous with continued reduction in spreading rate along the southern Juan de Fuca ridge, and probably reflects partial coupling between the subducting litho

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1995.tb02100.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe Early to Middle Cambrian Red Heart Dolomite and lower Arthur Creek Formation of the southern portion of the Georgina Basin, Australia, is an entirely dolomitized succession of shallow‐water evaporitic mudflat and deeper‐water subtidal lithologies. Three types of dolomite have been identified and are interpreted as: (1) syndepositional dolomite; (2) regional replacement dolomite; and (3) void‐filling dolomite (cement). Syndepositional dolomite, derived from saline pore fluids developed in a sabkha environment, is a minor dolomite type with very fine crystal mosaics and has a mottled, non‐zoned cathodoluminescence. The widespread regional replacement dolomite ranges from fine‐ to medium‐crystalline forming mainly planar‐s and non‐planar‐a crystal mosaics, and displays blotchy, mottled, non‐zoned cathodoluminescence. Void‐filling dolomite commonly forms planar‐s to planar‐e, medium to very coarse crystal mosaics. Rare non‐planar‐c, very coarsely crystalline saddle dolomite also exists. Void‐filling dolomite has a successively zoned cathodoluminescence pattern from non‐, to brightly, to dully luminescent.Geochemically, the syndepositional dolomite has δ18O (PDB) values ranging between − 5.3 and − 8.6%o. Regional replacement dolomites exhibit a wide range of δ18O values from − 3.3 to − 10.9%owhereas void‐filling dolomite has δ18O values ranging from − 10.8 to − 14.3%o. All three dolomite types have similar δ13C (PDB) values, in the range between +1.7 and −1.7%o.Three initial dolomitization episodes are interpreted: (1) a sabkha stage, forming the syndepositional dolomite and dolomitizing the evaporitic mudflat lithologies; (2) a brine‐reflux stage, replacing the subtidal lithologies; and (3) a burial stage, forming the void‐filling dolomite type. Final dolomite stabilization occurred during burial, at elevated temperatures, in the presence of basinal fluids, resulting in progressive recrystallization and stabilization of the earlier‐formed syndepositional and replacement dolomites. Both textural and geochemical evolution should be taken into account when studying the origin of dolomites, based on their present geochemical composition.Sulphates are represented by very fine‐crystalline syndepositional anhydrite in association with the syndepositional dolomite, and coarse to very coarse anhydrite cement. Evaportic mudflat (sabkha) and burial environments are inferred for the origin of the former and the latter anhydrite types, respectively. Evaporite dissolution breccias, indicative of the former

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1995.tb02101.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe Middle Miocene evaporites in the Red Sea rift were deposited within a complex system of fault‐bounded basins that were episodically active during sedimentation. Such a tectonic framework is known to be highly favourable to resedimentation processes. An offshore petroleum well in the north‐western Red Sea has cored, below a massive salt unit, an anhydrite‐bearing succession which provides an excellent opportunity to study the processes of gravity induced redeposition of Ca‐sulphates in a deep basin. Anhydrite deposits, interbedded with siliciclastic layers and thin halite layers, are composed of resedimented facies ranging from fine‐grained laminated sediments to coarse‐grained breccias. The components derive from the reworking of shelf sediments deposited initially in shallow water to supratidal settings on the surface and edges of structural highs bordering depressions: proximal siliciclastic deposits with interstitial anhydrite (cement patches, nodules) or gypsum and dolostones with early diagenetic anhydrite facies (nodular, chicken‐wire) formed in sabkha conditions, interstitially grown gypsum crystals and subaqueous gypsum crusts precipitated in hypersaline ponds, and diatom‐rich oozes formed in marine, shallow‐water conditions. The homogeneity of the stable isotope composition and petrography of sulphates argue for the initial crystallization of Ca‐sulphates within brines of the same origin and in closely interconnected sedimentary settings. The unconsolidated sediments redeposited as slope‐foot accumulations were carried both as anhydrite (nodules, soft masses, various fragments, individual grains or crystals released by disintegration of large masses) and gypsum (crystalline aggregates or single crystals) later converted to anhydrite during burial. Layers of chaotic breccia are interpreted as the result of seismic events, whereas the fine‐grained deposits could be related to redistribution by nepheloid layers of suspensions of finer grains released by disintegration of the soft anhydrite masses during downslope transport, or of insitudeposits removed

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1995.tb02102.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe size distribution of river bed material plays an important role in the study of fluvial hydraulic processes. It is not always easy to sample the river bed material for the determination of its size distribution, but knowledge of the frequency distribution and of bed material sizes can be used to predict its size distribution. Therefore, data on bed material size distributions of 63 streams from 10 different countries have been analysed to determine the frequency distribution which can be best fitted to them. The log normal distribution cannot be fitted to the bed material mixtures when the entire range of sizes is considered. The method of power transformation is found to normalize these mixtures. Relationships have been proposed between the parameters of the normalization and the stream slope. These relations can be used to predict the size distribution of the river bed material.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1995.tb02103.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe Uhangri Formation forms part of the Cretaceous sedimentary sequence deposited in a series of inland basins in the south‐western Korean Peninsula. It comprises an approximately 400‐m‐thick epiclastic sequence of conglomerate, (gravelly) sandstone, cherty mudstone and black shale. The entire sequence can be represented by 16 distinctive sedimentary facies organized into four facies associations.Facies association I is characterized by thick homogeneous brownish siltstone, wedge‐shaped disorganized conglomerate and thinly interlayered gravelly sandstone units. The siltstone units were formed by large floods submerging the alluvial fan fringe (floodplain), whereas the conglomerate and gravelly sandstone units were deposited by sheetfloods and debris flows. Facies association II consists of stratified conglomerate — gravelly sandstone, laminated sandstone and sandstone/siltstone couplets which form fining‐upward cycles. Some facies units are low‐angle trough cross‐bedded and show broad channel geometries. This association represents subaqueous delta lobes fed by high‐ and low‐concentration turbidity currents in the distal delta realm. Facies association III is characterized, by wedged conglomerate and gravelly sandstone facies with interfingered massive sandstone bounded by scoured bases. It represents a delta front where distributary channels and mouth bars are dominant. Facies association IV consists of laterally continuous sequence of laminated black shale, crudely stratified sandstone and convoluted sandstone/cherty mudstone. This facies association is suggestive of depositional processes controlled by chemical equilibrium resulting from an interaction between density inflows and lake water. The cherty mudstone resulted from inorganic precipitation from siliceous solution provided by acidic volcanism.The Uhangri sequence generally shows a fining‐upward trend with a transition from alluvial fan fringe, coarse‐grained subaqueous delta, to shallow lake. The retrogradation was probably due to continuous subsidence related to continental rifting in the o

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1995.tb02104.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTSequence stratigraphic interpretation of paralic successions is complicated by the complex interfingering of marine and continental strata. The successions may also include terrestrial extensions of marine parasequences and completely independent lacustrine parasequence analogues. Failure in recognizing the possible interbeddding of these two independent parasequence types may lead to construction of sequence stratigraphic schemes based on incompatible data sets. We have studied a Lower Jurassic paralic section from the Baltic island of Bornholm, situated in the Tornquist Zone, which demarcates the transition from the stable Precambrian Baltic Shield to the subsiding Danish Basin and Danish‐Polish Trough. The Hettangian‐Sinemurian Sose Bugt Member (Rønne Formation) of Bornholm includes lacustrine, fluvial and restricted marine, estuarine deposits reflecting the basin‐margin position. Biostatigraphic resolution is poor and a sequence stratigraphic interpretation of the paralic succession is far from straightforward. A multidisciplinary approach including facies analysis, recognition and lateral trading of key surfaces, palynostratigraphy, palynofacies, coal petrography, palaeopedology, clay mineralogy and source rock geochemistry is applied in order to obtain a high degree of precision in the interpretation of the paralic facies. In this way four sequences are recognized in the overall backstepping lacustrine to estuarine succession. Marine and marginal marine parasequences are distinguished from their purely lacustrine analogues, and an internally consistent sequence stratigraphic scheme is proposed. This is compared and tentatively correlated with fossiliferous marine sediments in the Danish Basin and with published eustatic cycle

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1995.tb02105.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTA continuum mechanics model for the gravitational compaction of sediments is derived by assuming that the sediments are normally pressured and in a one‐dimensional state of stress. Sediment strength is characterized in terms of effective stress laws adopted from soil mechanics. The model is a relatively simple mathematical formula that gives the porosity as a function of burial depth. The shape of the porosity profile is controlled by two mechanical parameters, the compression index and the void ratio at an effective stress of 100 kPa. The model was verified by analysing the porosity—depth data of oozes and chalk from the Ontong Java Plateau, gathered during Leg 130 of the Ocean Drilling Program. The mechanical parameters of the sediments were estimated using a least‐squares method to fit the theoretical profile to the porosity data. The theoretical profile described accurately the ooze porosity data over depth ranges of 100 m or more. However, over smaller length‐scales of 10–50 m there were systematic deviations between the theoretical porosity values and the ooze porosity data. The porosity deviations correlated with variations in the mean grain size of the sediments, due in part to changes in the foraminifera abundance. In the case of the oozes, the estimated mechanical parameters were consistent with published values obtained from one‐dimensional compression tests. In contrast, the estimated mechanical properties for the chalks differed from published values. The chalk porosities were lower than could be explained by mechanical compaction. This explanation is supported by the compressional (P‐wave) velocity data. In the chalk sections, the P‐wave velocity increases more rapidly with burial depth than it does in the ooze sections, suggesting that sediment elastic properties are increasing due to interp

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1995.tb02106.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1995.tb02107.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1995.tb02108.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY