共查询到20条相似文献，搜索用时 546 毫秒
1.
P. B. Kabanov 《Stratigraphy and Geological Correlation》2009,17(5):493-509
General classifications of Phanerozoic carbonate facies and controlling them factors are reviewed. Three principal carbonate
factories distinguished by W. Schlager (2000, 2003) are the tropical shallow-water, the cool-water, and the mudmound factories.
The general term for facies associations in the first factory is photozoan carbonates. The cool-water factory encompasses
environments producing heterozoan carbonate facies. The mudmound factory is a non-actualistic sedimentary system producing
mound-shape buildups of non-skeletal microbial micrites (also termed automicrites). The benthic carbonate production is controlled
by light, bottom temperature, eutrophication, siliciclastic influx, and the evolution of marine ecosystems. The cyclic alternation
of skeletal associations (“biofacies”) formed under the control of high-amplitude sea level changes is exemplified by the
Moscovian (Carboniferous) epeiric carbonates of the East European Craton. Three principal biofacies associations in this example
are bryonoderm extended (heterozoan), staffellid-syphonean (photozoan). and Meekella-Ortonella (intertidal flat to stagnant
lagoon). 相似文献
2.
The nature of Phanerozoic carbonate factories is strongly controlled by the composition of carbonate‐producing faunas. During the Permian–Triassic mass extinction interval there was a major change in tropical shallow platform facies: Upper Permian bioclastic limestones are characterized by benthic communities with significant richness, for example, calcareous algae, fusulinids, brachiopods, corals, molluscs and sponges, while lowermost Triassic carbonates shift to dolomicrite‐dominated and bacteria‐dominated microbialites in the immediate aftermath of the Permian–Triassic mass extinction. However, the spatial–temporal pattern of carbonates distribution in high latitude regions in response to the Permian–Triassic mass extinction has received little attention. Facies and evolutionary patterns of a carbonate factory from the northern margin of peri‐Gondwana (palaeolatitude ca 40°S) are presented here based on four Permian–Triassic boundary sections that span proximal, inner to distal, and outer ramp settings from South Tibet. The results show that a cool‐water bryozoan‐dominated and echinoderm‐dominated carbonate ramp developed in the Late Permian in South Tibet. This was replaced abruptly, immediately after the Permian–Triassic mass extinction, by a benthic automicrite factory with minor amounts of calcifying metazoans developed in an inner/middle ramp setting, accompanied by transient subaerial exposure. Subsequently, an extensive homoclinal carbonate ramp developed in South Tibet in the Early Triassic, which mainly consists of homogenous dolomitic lime mudstone/wackestone that lacks evidence of metazoan frame‐builders. The sudden transition from a cool‐water, heterozoan dominated carbonate ramp to a warm‐water, metazoan‐free, homoclinal carbonate ramp following the Permian–Triassic mass extinction was the result of the combination of the loss of metazoan reef/mound builders, rapid sea‐level changes across Permian–Triassic mass extinction and profound global warming during the Early Triassic. 相似文献
3.
Alkaline lakes like the hydrothermally affected lake Specchio di Venere (Pantelleria Island, Central Mediterranean) are typical geological settings harbouring calcified microbial mats. The present work is focused on the discrimination between biotic and abiotic processes driving carbonate precipitation in this lake, using hydrochemical, mineralogical and isotopic data. Hydrochemical analyses demonstrate that the lake is nearly 10−fold supersaturated with regard to aragonite and seasonally reaches hydromagnesite supersaturation. Microscopic observations depict organosedimentary laminated structures consisting of microbial communities and aragonitic precipitates, which are rather disseminated in pores than directly linked to microorganisms. Oxygen isotopic data indicate that authigenic carbonate crystallisation from evaporating water is the dominant precipitation process, further suggested by the absence of textural evidence of diagenetic processes. Conversely, the observed δ13C values reflect an influence of extracellular polymeric substances (EPS) on carbon fractionation during the precipitation process, due to the selective sequestration of 12C in the biomass. The above considerations suggest that at lake Specchio di Venere the carbonate precipitation is mainly of inorganic nature, but a minor role played by biologically influenced processes in microbial mats is not excluded. 相似文献
4.
The carbonate factories, their controlling factors and their palaeoecological and sedimentological signals recorded in sedimentary successions are key elements for understanding the evolution of carbonate platform systems. Luis Pomar has dedicated most of his academic life to the study of carbonate rocks and carbonate factories. The idea for this special issue to celebrate Pomar’s career arose during a session at the 34th International Association of Sedimentologists meeting held in Rome, entitled ‘Understanding carbonate factories through palaeoecological and geochemical signals’. The proposal encountered great response among participants, and additional contributions followed an email invitation to other specialists. This issue contains a variety of papers on carbonate sedimentology and carbonate factories. Here, an introduction that contextualizes the papers and key concepts discussed in this thematic issue is provided. It reviews Luis Pomar’s major achievements in carbonate sedimentology and discusses the evolution of the concept of the carbonate factory and the series of palaeoecological and sedimentological signals used to characterize the wide spectrum of carbonate depositional systems found in the natural world. 相似文献
5.
Tertiary syntectonic carbonate platform development in Indonesia 总被引：2，自引：0，他引：2
Cenozoic tropical carbonate sedimentation was strongly influenced by local and regional tectonics in SE Asia. This paper outlines the evolution of the syntectonic Eocene to middle Miocene Tonasa Formation of South Sulawesi, evaluating controls on sedimentation, facies distribution and sequence development. Development of a facies model for this Cenozoic tropical carbonate platform provides a meaningful analogue for similar, less well‐studied SE Asian carbonates, which commonly comprise targets for hydrocarbon exploration. This study also has considerable implications for the study of syntectonic carbonates, controls on carbonate sedimentation, carbonate platform development in backarc areas and SE Asian tectonics. Detailed facies mapping, logging, petrographic and biostratigraphic analyses indicate that the Tonasa Formation was deposited initially as part of a transgressive sequence in a backarc setting. By late Eocene times, shallow‐water carbonates were being deposited over much of South Sulawesi forming a widespread (100‐km long) platform area. Shallow‐water sedimentation continued unabated in some areas of the platform until the middle Miocene. Elsewhere, active normal faulting resulted in fault‐block platforms, with local subaerial exposure of footwall blocks and the formation of basinal graben in adjacent hangingwall areas. Platform‐top facies were aggradational and dominated by larger benthic foraminifera. Low‐angle slopes, particularly hangingwall dip slopes, were characterized by the development of ramps. Faults, controlled in part by pre‐existing structures, were periodically active and formed steep escarpment margins. Variable regional subsidence strongly influenced the development of the Tonasa Carbonate Platform, whereas platform‐wide effects caused by regional eustacy have not been identified. Computer modelling of the Tonasa Platform confirms that the accommodation space and sedimentary geometries observed can be produced by block faulting and regional subsidence alone. Modelling also reveals that regional subsidence and extension, oblique to the main stretching direction, were low on the margins of the backarc basin. Shallow‐water accumulation rates for this foraminifera‐dominated tropical carbonate platform were an order of magnitude lower than those for modern warm‐water platforms dominated by corals or ooids. 相似文献
6.
During the late Miocene, the Guadalquivir Basin and its satellite basin, the Ronda Basin, were under Atlantic cool-water influence. The aim of our study is to develop a sequence stratigraphic subdivision of the Ronda Basin fill and to provide models for the cool-water carbonates. The Upper Miocene of the Ronda Basin can be divided into three depositional sequences. Sequence 1 is early Tortonian, Sequence 2 late Tortonian to earliest Messinian, and Sequence 3 Messinian in age. The sediments were deposited in a ramp depositional system. Sequence 1 is dominated by conglomerates and marls. In Sequence 2 and Sequence 3, carbonate deposits dominate in the inner ramp whereas siliciclastics preferentially occur in the middle and outer ramp. Bryomol carbonate sediments occur in all sequences whereas rhodalgal carbonates are restricted to Sequence 3. In bays protected from siliciclastic influx, rhodalgal deposits formed under transgressive conditions. A bryomol factory occurs in zones of continuous siliciclastic supply. This distribution results from facies partitioning during the flooding of the Ronda Basin, which has a rugged and irregular relief. Embayments were protected from siliciclastic influx and provided regions with less hydraulic energy. 相似文献
7.
The southeastern coastal plain of South Australia contains a spectacular and world-renowned suite of Quaternary calcareous eolianites. This study is focused on the provenance of components in the Holocene, actively forming sector, of these carbonate eolian deposits. Research was carried out along seven transects across a lateral distance of 120 km from ～30 m water depth offshore across the beach and into the dunes. Offshore sediments were acquired via grab sampling and SCUBA. Results indicate that dunes of the southern Lacepede and Bonney coasts are composed of siliciclastic particles (mainly quartz), relict allochems, Cenozoic and limestone pieces, but dominated by Holocene invertebrate and calcareous algal biofragments. The most numerous grains are from molluscs > benthic foraminifera ≥ coralline algae, > echinoids and > bryozoans. Most of these particles originate in carbonate factories such as macroalgal forests, rocky reefs, seagrass meadows and low-relief sea-floor rockgrounds. Incorporation of Holocene carbonate skeletons into coastal dunes, however, depends on a combination of: (1) the addition of infauna from intertidal and nearshore environments; (2) the physical characteristics of different allochems and their ability to withstand bioerosion, fragmentation and abrasion; (3) the character of the wave and swell climate; and (4) the nature of eolian transport. Most eolian dune sediment is derived from nearshore and intertidal carbonate factories. This is well illustrated by the abundance of robust infaunal bivalves that inhabit the nearshore sands and virtual absence of bryozoans that are common as sediment particles in offshore water depths >15 m. Importantly, the calcareous eolianites in this cool-water, open-platform carbonate setting are not simply an allochthonous reflection of the offshore marine shelf factories, but more a product of autothonous shallow nearshore–intertidal skeletal production and modification. These findings explain the preponderance of mollusc fragments and lack of bryozoans in similar older Pleistocene calcareous eolianites up to ca 1 million years old across ～2000 km of southern Australia with implications for the older rock record. 相似文献
8.
Upper Ordovician (Caradocian) carbonates of eastern North America were deposited along the Iapetus continental margin and record a transition from warm- to cool-water settings despite this margin having been within the southern hemisphere tropical belt. This event has been documented from Virginia (USA) to southern Québec (Canada) although, not previously from areas close to the palaeoequator. Field, petrographic and major element geochemistry data have been gathered from the poorly-known Upper Ordovician carbonate succession outcropping in the Lac Saint-Jean outlier in central Québec. The succession consists of a lower siliciclastic formation (Tremblay) overlain by three limestone formations (Simard, Shipshaw and Galets) and capped by shales (Pointe-Bleue Shale). From macro- and microfaunal evidence, carbonate sedimentation occurred during the late Caradoc and is younger than the early- to mid-Caradoc carbonate succession present farther south. Relative sea level fluctuations recorded in the sediments suggest an overall sea level rise briefly halted by a minor end-Caradocian sea level fall. The lower limestone formation (Simard) consists of muddy sediments with algal-coral-stromatoporoid boundstones; green algae are abundant. This unit reflects low energy sedimentation on a shallow warm-water carbonate ramp colonized by a diverse chlorozoan fauna. The upper limestone formation (Galets) is typified by coarse-grained bioclastic sediments punctuated by numerous phosphate-rich hardgrounds with evidence for high energy shallow marine conditions. Faunas were dominated by crinoids and bryozoans. This unit represents high energy sedimentation on a cool shallow water carbonate ramp colonized by a brynoderm faunal association. Between both units, a deeper marine (outer shelf) limestone formation (Shipshaw) was developed. In the Lac Saint-Jean area, a transition from warm- to cool-water carbonate ramps occurred in latest Caradoc times and is litho- and biofacies-wise, similar to what is documented for lower Caradocian limestones present farther south. Upwelling of nutrient-rich cool bottom oceanic waters was a probable cause for this transition. 相似文献
9.
Analysis of water and associated carbonate precipitates from a small, warm-spring travertine system in SW Colorado, USA, provide an example of the: (i) great variability of the geochemical parameters within these dynamic systems, and (ii) significance of the microenvironment in controlling mineralogy and morphology of carbonate precipitates. Waters emerged from the springs highly charged in CO2, with an initial pCO2 of 1.2 × 105 Pa. Degassing of the CO2 from the waters decreased the pH from 6.1 to 8.0, resulting in an increase of 8%‰ in δ13C values downflow in the total CO2 in solution and an increase in the ISAT from 2.1 to as high as 63 times supersaturation with respect to calcite. Due to changes in the stable isotopic composition of the waters downflow as well as changes in the degree of supersaturation, stable isotopic analyses range greatly from locale to locale within this small system. Near the spring vents, at relatively low ISAT levels, well-developed rhombohedra of calcite formed as biotically induced precipitates around diatom stalks and other algae as well as abiotic crusts. In contrast, near the distal end of the system, very high ISAT levels were reached and resulted in the precipitation of skeletal-dendritic crystals of calcite on copper substrates, floating rafts of laterally linked hemispheres of aragonite crystals, and bimineralic carbonate-encrusted bubbles. Microenvironmental parameters control the mineralogy and habit of these precipitates. 相似文献
10.
11.
The Eocene represents the last greenhouse interval before Present. The maximum warming during the early Eocene was followed by a long-term cooling trend culminating in the Antarctica glaciation at the base of the Oligocene. Superimposed on this long-term cooling trend there is a prominent transient warming event known as the middle Eocene climatic optimum (MECO) occurring during the early Bartonian. The carbonate ramp succession cropping out in the Argentina Valley (Maritime Alps) offers new insights on the evolution of shallow water realms during this time interval. This ramp displays two main facies belts, middle and outer ramp. The middle ramp is recorded by larger benthic foraminifer floatstone to rudstone, passing to Solenomeris branches and nodule floatstone to rudstone evolving to branching coralline algal floatstone. The outer ramp is dominated by bioturbated marly wackestone to packstone alternating with larger benthic foraminifer floatstone with a silty matrix. The investigated ramp was affected by continuous dispersion and reworking of the skeletal components as other Tethyan Eocene ramps. During the Eocene, the Alpine foreland was influenced by fine terrigenous input controlling the trophic conditions and promoting seawater stratification and the development of a strong pycnocline, for which many perturbations could propagate as internal waves. The reworking of skeletal components of the ramp has been ascribed to the action of internal waves. The switch of carbonate production from a carbonate factory dominated by larger benthic foraminifera to a factory in which the encrusting foraminifer Solenomeris was the main carbonate producer biota, is indicative of a radical change in palaeoenvironmental conditions affecting the early Bartonian. The acme of Solenomeris often coincided with the crisis of carbonate producers during intervals of an evident deterioration of environmental conditions. In this case the acme is probably related to the adverse conditions linked to the (MECO) warming event. Finally, the drowning of the nummulitic ramp has been caused by light reduction for the photo-dependent biota due to progressively increasing depth linked to flexural subsidence of the foreland plate, and minor efficiency of the aphotic carbonate factory. 相似文献
12.
塔中隆起海相碳酸盐岩大型凝析气田成藏特征与勘探 总被引：3，自引：0，他引：3
多次资评与勘探实践表明塔中隆起成藏条件优越,海相碳酸盐岩油气资源丰富,奥陶系油气藏集中赋存于上奥陶统礁滩体与下奥陶统风化壳储层中,缝洞系统控制了大型凝析气藏纵向多套叠置-横向准层状分布规律。多学科、动静态一体化研究表明,形成塔中海相碳酸盐岩大型凝析气田主力烃源岩为寒武-奥陶系两套碳酸盐岩,原油具有明显的混源特征,天然气主要来源于中-下寒武统高成熟度原油裂解气。奥陶系海相碳酸盐岩凝析气藏是古油藏在喜山期被寒武系来源的原油裂解气气侵的结果,经历了三期成藏过程,即中晚加里东期、晚海西期原油充注,喜山期注气。两套烃源岩长期供烃是形成塔中奥陶系海相碳酸盐岩大型凝析气田的物质基础,构造作用、岩溶作用是形成了塔中奥陶系多套优质碳酸盐岩储集体的主控因素,断裂、不整合面、缝洞发育带构建的网状油气输导体系是塔中海相碳酸盐岩复式聚集混源成藏的重要保障。塔中奥陶系海相碳酸盐岩具备10亿吨当量的油气资源潜力。 相似文献
13.
The formation of calcite, aragonite, dolomite, hydromagnesite, and nesquehonite in speleothems of a small cave within dolostone may be compared with the formation of these carbonate minerals in much larger environments in which evaporation exceeds precipitation (salt lakes, tropical lagoons, sebkhas etc...). In all cases the formation and diagenetic alteration is mainly governed by the Mg/Ca-ratio of the solutions, from which precipitation (or transformation) takes place.The certain occurrence of monohydrocalcite in the speleothems and in technical incrustations lead to the conclusion, that this very rare mineral precipitates from solutions which are transported as aerosols. 相似文献
14.
Hydrothermal mixing,carbonate dissolution and sulfide precipitation in Mississippi Valley-type deposits 总被引：1，自引：0，他引：1
A large number of Mississippi Valley-Type (MVT) deposits are located within dissolution zones in carbonate host rocks. Some genetic models propose the existence of cavities generated by an earlier event such as a shallow karstification, that were subsequently filled with hydrothermal minerals. Alternative models propose carbonate dissolution caused by the simultaneous precipitation of sulfides. These models fail to explain either the deep geological setting of the cavities, or the observational features which suggest that the dissolution of carbonates and the precipitation of minerals filling the cavities are not strictly coeval. We present a genetic model inspired by the textural characteristics of MVT deposits that accounts for both the dissolution of carbonate and precipitation of sulfides and later carbonates in variable volumes. The model is based on the mixing of two hydrothermal fluids with a different chemistry. Depending on the proportion of the end members, the mixture dissolves and precipitates carbonates even though the two mixing solutions are both independently saturated in carbonates. We perform reactive transport simulations of mixing of a regional groundwater and brine ascending through a fracture, both saturated in calcite, but with different overall chemistries (Ca and carbonate concentrations, pH, etc). As a result of the intrinsic effects of chemical mixing, a carbonate dissolution zone, which is enhanced by acid brines, appears above the fracture, and another zone of calcite precipitation builds up between the cavity and the surrounding rock. Sulfide forms near the fracture and occupies a volume smaller than the cavity. A decline of the fluid flux in the fracture would cause the precipitation of calcite within the previously formed cavities. Therefore, dissolution of carbonate host rock, sulfide precipitation within the forming cavity, and later filling by carbonates may be part of the same overall process of mixing of fluids in the carbonate host rock.Editorial handling: C. Everett 相似文献
15.
海相碳酸盐的沉淀方式被认为与水体氧化还原条件密切相关,即太古宙至古元古代缺氧的铁化海水中碳酸盐沉淀抑制剂Fe2+和Mn2+强力抑制灰泥在水柱中成核,但允许文石直接在海底生长,从而导致大量文石以海底沉淀方式产出,而新元古代适度的氧化海水则有利于灰泥以水柱沉淀方式形成。然而,碳酸盐沉淀方式的长期变化还可能受控于其他因素,其与海水氧化还原条件之间的关系还需要通过大量具体实例来验证。针对上述科学问题,笔者选择碳酸盐沉淀方式尚处于过渡时期的华北中元古界碳酸盐岩为研究对象,开展碳酸盐沉淀方式及与之对应的氧化还原条件研究。结果表明,华北高于庄组三段(约1.56 Ga)、雾迷山组四段下部(约1.48 Ga)和铁岭组二段(约1.44 Ga)发育大量灰泥水柱沉淀,其Ⅰ/(Ca+Mg)值较高(普遍大于0.5 μmol/mol)、Ce负异常(低至0.8),指示适度氧化的条件;而高于庄组四段下部(约1.55 Ga)和雾迷山组二段中部(约1.50 Ga)则发育大量纤维状文石海底沉淀,其Ⅰ/(Ca+Mg)值约为0,指示次氧化至缺氧的环境。因此,本研究首次用大量实例证实了前寒武纪海水氧化还原条件对碳酸盐沉淀方式的重要调控作用,并且后者可作为海水氧化还原条件分析的重要指标,适用于高效开展长序列、多剖面的低氧背景下前寒武纪碳酸盐岩地层的氧化还原条件分析。 相似文献
16.
Claire E. Reymond Konny‐Sebastian Zihrul Jochen Halfar Bernhard Riegl Alexander Humphreys Hildegard Westphal 《Sedimentology》2016,63(4):940-958
Strongly influenced by seasonal and interannual (i.e. El Niño‐Southern Oscillation) upwelling, the equatorial setting of the Galápagos Archipelago is divided into well‐defined temperature, nutrient and calcium carbonate saturation (Ωaragonite) regions. To understand the relationship between oceanographic properties and sediment grain associations, grain size, carbonate content and components from sea floor surface samples were analysed, representing the main geographical regions of the Galápagos Archipelago. The shallow‐water rocky reefs of the Galápagos Archipelago are characterized by mixed carbonate–siliciclastic slightly gravelly sands. Despite minor differences in carbonate content, major differences exist in the distribution and composition of key carbonate producing biota. Halimeda is absent and benthic foraminifera occur in extremely low abundance. The western side of the Galápagos Archipelago is strongly influenced by nutrient‐rich, low‐Ωaragonite, subtropical water, which generates a heterozoan carbonate biofacies in a tropical realm resembling cold‐water counterparts (i.e. serpulid, echinoderm, gastropod, barnacle and bryozoan‐rich facies). The Central East region is composed of a transitional‐heterozoan biofacies. Biofacies observed in the northern region have an increased occurrence of tropical corals, albeit with a minor overall contribution to the carbonate components. Although the temperature gradient would allow for a broader distribution of photozoan biofacies, the increased nutrient concentration and related reduced light penetration from the upwelled waters favour heterozoan carbonate factories, mimicking cool‐water, deeper or higher latitude environments. The recent sedimentary record of the Galápagos Archipelago presents a range of tropical heterozoan carbonate communities, responding to more than simply latitude or temperature but a much more complex mixture of physical, evolutionary and geological processes. 相似文献
17.
长期以来,海相碳酸盐沉积物被广泛认为是温暖浅海沉积环境中的产物,然而近年来国外研究表明,在冷水陆架环境中,也可以形成规模的碳酸盐沉积,即冷水碳酸盐岩。通过对大量文献的调研,综述了冷水碳酸盐岩的概念、地质特征、沉积模式等方面的研究进展,并展望了该研究领域未来的发展方向。研究表明,冷水碳酸盐沉积是指在(古)纬度约30°~35°以上的温带及寒带地区、温度约20℃以下的沉积水体中,或是在富营养的寒冷上升流水体中形成的碳酸盐沉积物或岩石,其沉积特征与暖水碳酸盐岩不同。冷水碳酸盐沉积物中的生物颗粒组合以底栖有孔虫、软体动物、苔藓虫等异养生物和钙质红藻为主,缺乏造礁珊瑚和钙质绿藻以及鲕粒、集合颗粒等非骨架颗粒,而且沉积物中灰泥基质含量较少,矿物成分以方解石为主,氧同位素较重,胶结作用弱,以破坏性成岩作用为主。冷水碳酸盐沉积形态以缓坡为主,波浪磨蚀和再沉积作用较强。古代冷水碳酸盐岩的沉积特征、识别标志及其作为储层的油气资源潜力尚处于探索阶段,仍需进一步深入研究。 相似文献
18.
WONSUCK KIM BRUCE W. FOUKE ANDREW L. PETTER TERRENCE M. QUINN CHARLES KERANS FRED TAYLOR 《Sedimentology》2012,59(6):1677-1694
A mathematical model of carbonate platform evolution is presented in which depth‐dependent carbonate growth rates determine platform‐top accumulation patterns in response to rising relative sea‐level. This model predicts that carbonate platform evolution is controlled primarily by the water depth and sediment accumulation rate conditions at the onset of relative sea‐level rise. The long‐standing ‘paradox of a drowned platform’ arose from the observation that maximum growth rate potentials of healthy platforms are faster than those of relative sea‐level rise. The model presented here demonstrates that a carbonate platform could be drowned during a constant relative sea‐level rise whose rate remains less than the maximum carbonate production potential. This scenario does not require environmental changes, such as increases in nutrient supply or siliciclastic sedimentation, to have taken place. A rate of relative sea‐level rise that is higher than the carbonate accumulation rate at the initial water depth is the only necessary condition to cause continuous negative feedbacks to the sediment accumulation rates. Under these conditions, the top of the carbonate platform gradually deepens until it is below the active photic zone and drowns despite the strong maximum growth potential of the carbonate production factory. This result effectively resolves the paradox of a drowned carbonate platform. Test modelling runs conducted with 2·5 m and 15 m initial sea water depths at bracketed rates of relative sea‐level rise have determined how fast the system catches up and maintains the ‘keep‐up’ phase. This is the measure of time necessary for the basin to respond fully to external forcing mechanisms. The duration of the ‘catch‐up’ phase of platform response (termed ‘carbonate response time’) scales with the initial sea water depth and the platform‐top aggradation rate. The catch‐up duration can be significantly elongated with an increase in the rate of relative sea‐level rise. The transition from the catch‐up to the keep‐up phases can also be delayed by a time interval associated with ecological re‐establishment after platform flooding. The carbonate model here employs a logistical equation to model the colonization of carbonate‐producing marine organisms and captures the initial time interval for full ecological re‐establishment. This mechanism prevents the full extent of carbonate production to be achieved at the incipient stage of relative sea‐level rise. The increase in delay time due to the carbonate response time and self‐organized processes associated with biological colonization increase the chances for platform drowning due to deepening of water depth (> ca 10 m). Furthermore this implies a greater likelihood for an autogenic origin for high‐frequency cyclic strata than has been estimated previously. 相似文献
19.
Understanding how carbonate factories influence platform evolution is either based on qualitative conceptual models or quantitative numerical stratigraphic forward models. This study establishes new production depth profiles for four Cenozoic carbonate factories and uses two-dimensional stratigraphic forward models to explore how interactions between sediment production and transport within carbonate systems influence carbonate platform development. Newly established production/depth profiles are used to model photozoan and heterozoan carbonate grain associations, and the associated carbonate producing factories, and results are compared with well-studied outcrop successions. Sediment production from photozoan and heterozoan grain associations is also equalized, so that the total sediment production is the same but the depth/production profiles retain their distinctly different form. Thus, the effect of the different production profiles can be assessed. Ramps form when sediment diffusional transport rates are high relative to production rates and flat-top steep-margin platforms form when sediment diffusional transport rates are low relative to production rates, whether they are photozoan or heterozoan grain associations. The control exerted by sediment production and transport is expressed as a sediment transport–production ratio where transport ratio is a diffusional sediment transport in two-dimensions and production ratio is the total sediment production rate which is the product of a production profile that varies in depth and laterally. The transport–production ratio is a key control on the evolution and geometry of carbonate platforms. This is the case with different production profiles (both euphotic and oligophotic) and in mixed grain-size and mixed transport-rate systems. Carbonate producing factories significantly influence the rate of sediment production, the depth distribution of sediment production (production profiles), as well as the type of grain sizes produced (influencing resistance to erosion). Thus, different types of carbonate grain associations, and the associated carbonate producing factories, can produce the critical differences between carbonate platform geometries. 相似文献
20.
Sedimentological investigation of the late Paleoproterozoic (Orosirian) Vempalle Formation of the Cuddapah Basin, Dharwar craton, India, reveals three facies association that range from supratidal to deep subtidal. Sedimentary rocks of this succession are dominated by heterolithic carbonate mudstone, intraformational carbonate conglomerate, and a variety of columnar, domal, and stratiform microbialite facies. Deposition occurred in an extensional regime during development of a low-gradient ramp, where the distribution of microbialite facies is distinctly depth-partitioned. A gradual increase in synoptic relief of columnar stromatolites through the section, and the upward transition from stratiform to columnar microbialites, record a prolonged marine transgression with little or no influx of terrigenous detritus. Siliciclastic influx along the northeastern side of the shelf reflects the redistribution of topographic highs concomitant with large scale volcanic activity. Redistribution of topographic highs eventually led to progradation of peritidal facies and shutting down of the carbonate factory. Earthquake-induced ground shaking and voluminous volcanism experienced by this platform point to the reactivation of a deep-seated mantle-plume that resulted in thermal doming of the Dharwar crust prior to the onset of Cuddapah deposition. Isotopic and elemental chemistry of a selection of Vempalle Formation carbonate rocks record elevated Mn2+ and Fe2+ concentrations and depleted carbon isotope values in inner ramp lagoonal facies, relative to more open marine stromatolitic facies. Patterns of isotopic and elemental variation suggest the presence of geochemically distinct water masses—either within the water column or within substrate pore fluids—that resulted from a combination of globally low marine oxygenation and restricted oceanographic circulation in inner ramp environments. These data suggest that, even in the aftermath of Early Paleoproterozoic oxygenation, that ocean chemistry was heterogeneous and strongly affected by local basin conditions. 相似文献