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1.
Assemblages of miospores and dinoflagellate cysts encounterd in core samples three boreholes drilled in southern Iraq an Aptian-mid Albian age-range for the Zubair Formation, the largest oil reservoir in southern Iraq and neighbouring Kuwait. Four types of palynofacies have been identified, and are interpreted to indicate delta top swamp and marsh, delta front, prodelta and marine platform environments respectively. Amorphous matter comprises more than 50% of the organic component of some of the palynofacies in the upper part of the Zubair Formation. The rocks with which they are associated are highly rated as a potential source of liquid hydrocarbons. Those deposits yielding less than this (down to 12%) are considered to have moderate potential.  相似文献   

2.
Palynological and palynofacies analyses were carried out on some Cretaceous samples from the Qattara Rim-1X borehole, north Western Desert, Egypt. The recorded palynoflora enabled the recognition of two informal miospore biozones arranged from oldest to youngest as Elaterosporites klaszii-Afropollis jardinus Assemblage Zone (mid Albian) and Elaterocolpites castelainii–Afropollis kahramanensis Assemblage Zone (late Albian–mid Cenomanian). A poorly fossiliferous but however, datable interval (late Cenomanian–Turonian to ?Campanian–Maastrichtian) representing the uppermost part of the studied section was also recorded. The palynofacies and visual thermal maturation analyses indicate a mature terrestrially derived organic matter (kerogen III) dominates the sediments of the Kharita and Bahariya formations and thus these two formations comprise potential mature gas source rocks. The sediments of the Abu Roash Formation are mostly dominated by mature amorphous organic matter (kerogen II) and the formation is regarded as a potential mature oil source rock in the well. The palynomorphs and palynofacies analyses suggest deposition of the clastics of the Kharita and Bahariya formations (middle Albian and upper Albian–middle Cenomanian) in a marginal marine setting under dysoxic–anoxic conditions. By contrast, the mixed clastic-carbonate sediments of the Abu Roash Formation (upper Cenomanian–Turonian) and the carbonates of the Khoman Formation (?Campanian–Maastrichtian) were mainly deposited in an inner shallow marine setting under prevailing suboxic–anoxic conditions as a result of the late Cenomanian and the Campanian marine transgressions. This environmental change from marginal to open (inner shelf) basins reflects the vertical change in the type of the organic matter and its corresponding hydrocarbon-prone types. A regional warm and semi-arid climate but with a local humid condition developed near/at the site of the well is thought to have prevailed.  相似文献   

3.
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4.
Serikagni Formation (lower–middle Miocene) was studied at four outcrop sections within Sinjar Anticline, Para (the western plunge), Jaddala, Sinjar, (Southern limb), and Noaniaa (Northern limb) of Sinjar Mountain, which is part of foothill zone in northwest Iraq. This formation is composed of Globigerina limestone, marly limestone intercalated with marl, deposited in quiet, deep marine environment. Palynological analyses and the percentages of palynological matter were determined. Palynofacies analysis was recorded for paleoenvironmental interpretation. Mineralogical investigations and petrographical analyses were done. Geochemical analyses for the determination of the major constituents (CaO, MgO, and I.R.),the secondary constituents (SiO2, Al2O3, Fe2O3, Na2O, K2O, and trace elements (Sr, Mn, Cu, Zn, Co, Cr, Pb) in the rock samples were accomplished. The calcite is the predominant mineral which is mostly of micrite types as well as spary calcite. The insoluble residue (I.R.) has negative correlation with the carbonate percentages in the rock formation as observed by the XRD analyses. Clay minerals show low occurrence represented by palygorskite, montmorillonite, and sepiolite. Geochemical differences can be noticed between the limy and marly facies constituting the same formation. Differences are also observed between the geochemistry and mineralogy of the four studied localities such as the relatively more pure limestone in Jaddala and Para sections than Sinjar and Noaniaa sections which indicate the higher percentages of marly limestone. This is believed to be due to the geographic location of these sections within the main depositional environment, as well as the consequences of sea level fluctuation. Two palynofacies (PF-1) and (PF-2) were identified. Palynomorphs are more numerous with high percentages (>80%) of amorphous organic matter (AOM) is present in the PF-1. The lithological association of this palynofacies is limestone and marly limestone. This palynofacies 1, indicate the deep marine depositional environment. The second palynofacies (PF-2) reflect low quantities (less than 40%) of AOM, with increase of phytoclasts (translucent-type) to more than 30% and the miospores (small spores and pollen grains) to more than 20%. The lithological association of this palynofacies is marl and marly limestone. This palynofacies 2, indicate the nearshore and shallow marine depositional environment.  相似文献   

5.
Three exploration wells were selected near Mosul city (Az-29, Bm-15, and Kd-1) to study the palynozones and hydrocarbon generation potential of the Upper Triassic Baluti and Kurrachine Formations. This study was completed in two phases: The first was a study of palynofacies and their paleoenvironmental indications, degree of preservation, diversity of palynomorphs, and organic maturity of the rocks according to palynomorphs’ color using a refracted light microscope. More than 80 slides of organic matter were used for this study. Four palynofacies were tentatively recognized. (1) The first palynofacies is diagnostic of the Baluti Formation in the Az-29 and Kd-1 wells; (2) The second palynofacies appeared at different depths in the Kurrachine Formation in three wells. (3) The third was only found between the depths of 4,534 to 4,685 m in the well Az-29. (4) The fourth was only found between 3,500- and 3590-m depth in the well Bm-15. A distal coastal marine environment is suggested for the Baluti Formation and restricted lagoonal environment for the Kurrachine Formation. The second phase used organic geochemical analyses to confirm the suggested paleoenvironmental and hydrocarbon generation material. Three techniques were used, namely total organic carbon, pyrolysis, and pyrolysis gas chromatography, on more than 35 samples from different depths in three wells. The analyses proved that a sufficient quantity of organic matter occurs that and has suitable maturity for hydrocarbon generation potential of oil and gas.  相似文献   

6.
The study of palynomorphs and calcareous nannofossils from the Albian–Campanian Napo Group in the Pungarayacu 30 well in the Subandean Zone of Ecuador has led to a new biostratigraphic framework revealing the existence of several hiatuses for this area. The palynological and palynofacies data are used together with other fossils and lithological evidence to define a sequence stratigraphic framework. The distribution of palynomorphs and palynofacies indicates a strong terrestrial input for the lower part of the Napo Group (Napo Basal and Lower Napo formations). In the upper part (Middle and Upper Napo formations), terrestrial input is reduced and a restricted marine environment with several dysoxic–anoxic intervals can be inferred. The hydrocarbons present in the well studied have traditionally been regarded as locally sourced. However, several lines of evidence (TAS, Tmax and VR) prove the immature stage of the source rock in this borehole as well as in a larger area.  相似文献   

7.
Quantitative analyses of palynomorph assemblages, particulate organic matter (kerogen), and total organic carbon (TOC) have been made on samples of the Albian–Cenomanian Kharita and Bahariya formations encountered in the Abu Gharadig-5 well, Western Desert, Egypt. Two assemblage palynozones are defined: Assemblage Zone A (Kharita Formation) of late Albian–early Cenomanian age and Assemblage Zone B (Bahariya Formation) of early–middle Cenomanian age. Palynofacies of the Kharita Formation suggest that sedimentation of these strata took place in a warm, shallow, nearshore-marine environment. The deposition of the lower Bahariya Formation took place initially in similar conditions but subsequently further offshore in somewhat deeper water of the inner shelf. The relatively high percentage of Ephedripites, Afropollis and elaterate pollen in both formations indicates an arid climate. The Kharita Formation yields kerogen types III and IV whereas the assemblages recovered from the Bahariya Formation contain types II and III. The TOC is generally between 0.42 and 0.65% in the Kharita Formation, while it ranges between 0.42 and 0.80% in samples of the Bahariya Formation. The spores and pollen grains are pale in colour; hence little source potential for hydrocarbons is indicated.  相似文献   

8.
This paper presents the integrated results of palynofacies and geochemical analyses in Turonian carbonate strata from the Sergipe Basin, Brazil. Forty-three outcrop samples were analyzed from sections of the Cotinguiba Formation in the Votorantim and Rita Cacete quarries. Our results allow for the characterization of the organic matter and interpretation of the environments of deposition. Together with the existing geochemical data, the results allow for recognition of oxic and dysoxic intervals and inferences pertaining to local oceanographic conditions to explain these environmental changes. The palynofacies groups are dominated by marine palynomorphs and amorphous organic matter (AOM), with minor amounts of terrigenous palynomorphs and phytoclasts. The total organic carbon (TOC) and δ13C ratio are directly correlated with the dominant palynofacies elements, particularly AOM. The upper section in Rita Cacete quarry has the most complete data set, and the TOC, δ13C and marine-derived AOM in this section tend to decrease upsection and serve to differentiate the oxic and dysoxic intervals. The sections also contain abundant, low-diversity dinoflagellate assemblages composed primarily of Trichodinium boltenhagenii, Cribroperidinium? muderongense, Canningia reticulata and Xenascus plotei. The palynofacies and dinoflagellate assemblages indicate deposition in shallow marine to outer neritic environments. The dysoxic events are recognized by an increase in TOC and δ13C, high amounts of AOM, an abundance of the low-diversity dinoflagellate assemblages and the lowest amounts of terrestrial components. The changes in marine productivity seem to be related to periods of low-intensity upwelling, which likely decreased the levels of dissolved oxygen in the basin.  相似文献   

9.
In recent years it has become clear that many shallow‐marine heterolithic and mudstone‐dominated successions are deposited as mud belts forming part of subaqueous deltas that are related to major fluvial sources either upstream or along shore. Here the Havert Formation is presented as an ancient example of this kind of system. The Havert Formation in the south‐western Barents Sea represents shelf margin clinoforms consisting predominantly of heterolithic deposits. Sediments were mainly derived from the east (Ural Mountains), but a smaller system prograded northward from Fennoscandia. The Havert Formation holds a lot of interest due to: (i) its stratigraphic position, directly above the Permo–Triassic boundary and contemporaneous to the emplacement of the Siberian Traps; (ii) the fact that it represents the first siliciclastic input in the south‐western Barents Sea and it shows interaction between Uralian‐derived and Fennoscandian‐derived sediments; and (iii) its hydrocarbon potential. This study is focused on a detailed sedimentological analysis of cored intervals of the (Ural‐derived) Havert Formation, in combination with seismic interpretation, well‐log correlations and palynological analysis of the Havert and overlying Klappmyss formations. The cored intervals belong to the shelf environment of the Havert shelf‐margin clinoforms (300 to 500 m thick). This sedimentological analysis distinguishes six facies associations, spanning from tidally‐influenced channels at the shoreline to mud‐rich subaqueous platform and foresets of the subaqueous delta. Seismic lines and well‐log correlations show the larger‐scale evolution of the Ural‐derived Havert Formation, characterized by episodes of low‐accommodation and high‐accommodation. The palynological analyses provide the first detailed study of the Havert Formation in the Nordkapp Basin, revising its depositional age in the region as Induan to early Olenekian (Smithian). Furthermore, they strengthen the environmental interpretation; palynofacies present on the shelf record flora of tidally‐influenced coastal plains, whereas the palynofacies in the deep‐water slope contain only amorphous organic matter.  相似文献   

10.
Twenty-eight samples from the Bahariya Formation of the Salam-17 Well in the north Western Desert were palynologically investigated. These samples are of Cenomanian age. Fair diversity and fair to moderately preserved palynomorph assemblage has been recovered. Among them, the dinoflagellate cysts showed very poor diversity and abundance. Four miospore zones have been informally identified in the lower Cenomanian. Various palynofacies criteria, adopted from previous publications (e.g. relative particle abundance data, brown to black wood ratio, equi-dimensional to lath-shaped black wood ratio, average size of phytoclasts and spores/pollen ratio) are applied as alternative indicators to monitor the proximal–distal trends instead of the marine palynomorphs-based parameters. The method can be applied in the Egyptian Western Desert to overcome the rarity and absence of dinoflagellate cysts in the recovered organic residues. The palynofacies study of the section demonstrates a predominantly regressive phase, characterized by deltaic, distributary or tidal channels, interrupted by short-lived marine incursions. The palynofacies trends within the studied succession indicate six genetic sequences informally described as Genetic Stratigraphic Sequences A through F.  相似文献   

11.
We studied upper Albian to Turonian shallow-marine shelf deposits (Ajlun Group) of west central Jordan along a NNE-SSW running transect. The carbonate-dominated succession includes few siliciclastic intercalations, claystones and shales, and can be subdivided into five formations. The Naur, Fuheis and Hummar Formations of upper Albian to upper Cenomanian age represent shallow subtidal to supratidal platform environments. The uppermost Cenomanian to middle Turonian Shueib Formation includes deeper water deposits of the inner/mid-shelf and locally TOC-rich black shales. Shallow-marine platform environments once again dominate the Wadi As Sir Formation (middle-upper Turonian). A new multibiostratigraphic framework is based on ammonites (mainly of the middle Cenomanian rhotomagense Zone to the middle Turonian woollgari Zone) and calcareous nannofossils (biozones CC 9–CC 11), supplemented by benthic and planktonic foraminifers and ostracods. It forms the base of a sequence stratigraphic subdivision, containing eight sedimentary sequences (S1–S8), which are separated by four Cenomanian sequence boundaries (CeJo1–CeJo4) and three Turonian sequence boundaries (TuJo1–TuJo3). This scheme allows the correlation of the platform succession from distal to proximal shelf areas in contrast to previous correlations using lithologic units. Furthermore, comparisons between the platform successions and sequence patterns of west central Jordan and those from neighbouring areas allow to differentiate local, regional, and global controlling factors of platform development within the study area.  相似文献   

12.
Two geochemical types of volcanic ash are recognized in the Redkino Horizon of the East European Platform based on the systematics of trace elements. The first type developed in the northeastern area of the platform is characterized by Ni/Cr and Ce/Yb ratios typical of the silicic tephra of recent volcanic eruptions in the Kuril–Kamchatka and Aleutian island-arc systems. The respective ratios in ash of the second type are typical of volcanics from the lower Vendian Berestovets Formation. Depletion of the upper Vendian pelites of the East European Platform in Ca, Sr and P (relative to the PAAS) indicates the continental chemical weathering of provenance.  相似文献   

13.
The Cenomanian–Turonian carbonate-dominated lithofacies of Israel reflect a complex interplay between tectonics, sea-level change, and palaeoecology. Improved correlation based on revision of the bio- and chronostratigraphic framework has enabled the establishment of a sequence-stratigraphic model comprising five sequences delineated by four sequence boundaries, in the Late Cenomanian–Early Coniacian interval. The Late Cenomanian–Turonian succession begins with prograding, highstand, carbonate-platform deposits of the first sequence. Interruption of progradation and drowning of this platform took place within the Late Cenomanian guerangeri Zone (=the vibrayeanus Zone in Israel), resulting in a drowning unconformity which is regarded as a Type 3 sequence boundary (labelled CeUp). The drowning is attributed in part to extinctions in the rudist-dominated biofacies (e.g., Caprinidae), which led to reduced carbonate production and enhanced the impact of the sea-level rise. Similar drowning of Tethyan platforms around the C/T boundary has been linked to the establishment of coastal upwelling and consequent eutrophication. Outer ramp hemipelagic facies (Derorim and the Lower Ora formations) replaced the platform carbonates, thickening substantially southwards in the Eshet-Zenifim Basin of southern Israel. Along the ancient continental slope (Mediterranean coastal plain) evidence of this drowning is obscured by submarine erosion, while in central and northern Israel the drowned section is represented by condensation or a hiatus, reflecting an elevated, sediment-starved sea-floor. A carbonate platform dominated by rudistid shoals (‘Meleke’ Member; Shivta Formation) was re-established in the Judean hills and northern Negev during the middle part of the Turonian coloradoense Zone (local zone T4). Later, during kallesi Zone times (T7), the platform facies prograded southwards towards the Eshet-Zenifim intra-shelf basin. The drowning succession and overlying resurrected carbonate platform are topped in central and southern Israel by a pronounced Type 1 sequence boundary (Tu1) between the kallesi (T7) and ornatissimum (T8) zones (Middle Turonian). In central Israel and northern Negev the sequence boundary is overlain by lowstand deposits of the ‘Clastic Unit’ and by the transgressive and highstand inner to mid-ramp deposits of the Nezer and Upper Bina formations. In the southern Negev the sequence boundary is overlain by lowstand and transgressive systems tracts of mixed carbonates, siliciclastics, and localized evaporites (Upper Ora Formation), and then by mid to inner ramp carbonates of the Gerofit Formation. The latter represents a very high rate of accumulation, indicating rapid, continued subsidence balanced by platform growth. The Tu2 sequence boundary of the Late Turonian is expressed in the southern Negev by a shift from inner ramp carbonates of the Gerofit Formation to outer ramp chalky limestones of the Zihor Formation, indicating localized drowning. The succeeding Co1 sequence boundary again indicates localized drowning of the prograding highstand deposits of the Zihor Formation (‘Transition Zone’) overlain by Lower Coniacian transgressive deposits of the upper part of the Zihor Formation. All of these third-order sequences are expressed in southern Israel, where the rate of subsidence was in balance with sea-level fluctuations. In contrast, the Judean Hills and eastern Galilee areas have a more incomplete succession, characterized by hiatuses and condensation, because of reduced subsidence. More distal areas of continuous deep-water deposition in western Galilee and the coastal plain failed to record the Middle Turonian lowstand, while a longer term, second-order sequence spanning the entire Late Cenomanian–Early Coniacian interval, is present in the Carmel and Yirka Basin areas.  相似文献   

14.
滇西耿马四排山地区地质新认识   总被引：5，自引：3，他引：5  
滇西耿马四排山地区弄巴组（原南皮可组上部）盛产化石抱粉，通过５０多块样品的分析，获得了晚泥盆世末（Ｒｅｔｉｓｐｏｒａｌｅｐｉｄｏｐｈｙｔａ）叶至早石炭世早期（Ｇｒａｎｄｉｓｐｏｒａｓｐｉｃｕｌｉｆｅｒａ）孢粉组合。它们可以与西欧同期孢粉进行对比，并能部分地与澳大利亚同期孢粉对比。因原南皮河组岩性复杂，已经被刘本培等（１９９３）改为南皮河群。本文对原南皮河组上部地层进行了研究并命名为弄巴组，其时代为晚泥盆世末至早石炭世。通过抱粉相分析和野外沉积标志的观察以及对孢粉比较学的研究，从而获得了对该套地层沉积相和植物古地理方面的新认识。  相似文献   

15.
The Ilam Formation (Santonian–Campanian in age), part of the Bangestan Group, is disconformably overlain by the Sarvak Formation and underlain by the Gurpi Formation in the Tang-E Rashid, Peyon area, Izeh (Zagros), southwest of Iran.Facies analyses indicate that the Ilam carbonates formed in four microfacies belts: tidal flat, lagoon, shoal and open marine, in a platform ramp environment. Major and minor elements and carbon and oxygen isotope values were used to determine the original carbonate mineralogy of the Ilam Formation. Petrographic evidence and elemental and oxygen and carbon isotope values indicate that aragonite was the original carbonate mineralogy in the Ilam Formation. The elemental and isotopic compositions of the Ilam carbonates also illustrate that they have stabilized in the marine phreatic environment. Variations of Sr/Ca and δ18O values versus Mn suggest that diagenetic alteration occurred in a closed system. Temperature calculation based on the oxygen isotope value of the least-altered sample indicates that the very early shallow burial fluid temperature was around 28 °C.Recognition of the exact boundary between the Ilam and Sarvak Formations is difficult, due to similar lithologies and the absence of the Surgah Formation in the study area. However, elemental and oxygen and carbon isotope analysis were used to determine the boundary between these formations. The δ18O and δ13C values, along with elemental results, clearly indicate a subaerial exposure surface, below which meteoric diagenesis affected the sediments.  相似文献   

16.
Our organic facies model of a platform environment is based on the analysis of (1) total organic carbon, (2) visual protokerogen types and hydrogen indices of the sediments, (3) sediment mineralogy and grain size, and (4) reef patterns, water circulation, and relief of the adjacent land.TOC values are lowest on reefs and outer platforms (0.2%); intermediate in sediments fringing carbonate islands (0.5–2.0%), on sea-grass meadows (0.5–0.7%), and in forereef lagoons (0.1–0.7%); highest in inner platform lagoons (0.5–5.0%) and mangrove swamps (2.7–3.5%). Paniculate organic matter comprises structured terrestrial, marine, and amorphous types. On average, terrestrial material accounts for 28% of OM in Puerto Rico and 12% in Belize. The mean hydrogen index of the sediment is 355 (mg hydrocarbons/g TOC) in Puerto Rico and 719 in Belize.This study indicates that TOC values are mainly related to platform subenvironment, while OM types are controlled by distance from the shoreline. Organic facies dominated by structural terrestrial OM occur closer to the shore, whereas toward the shelf margin marine and amorphous OM contents increase.  相似文献   

17.
Vase-shaped microfossils (VSMs) are described from the Ediacaran Doushantuo phosphorites (ca. 599–584 Ma) of Guizhou Province, South China. They are morphologically attributed to two genera and three species, and thus expand our knowledge of the Neoproterozoic protozoans in the Weng'an biota. They resemble to the VSMs from the Lower Cambrian pre-trilobitic Kuanchuanpu Formation of southern Shaanxi Province in terms of the microstructures and chemical composition of the fossil walls. Microscopic observations indicate that the VSMs from both the Weng'an biota and the Kuanchuanpu Formation are preserved in either single-layered or multi-layered walls, and composed of calcium phosphate in chemical composition. The present fossils also share similarities, in size and general contour, to the VSMs previously described from the Gaojiashan Member, middle part of the Dengying Formation (ca. 551–542 Ma) in southern Shaanxi. The discovery of the VSMs from the Doushantuo phosphorite is an important contribution to the Weng'an biota, and may throw much light on the early evolution and diversification of protozoans during Precambrian–Cambrian interval.  相似文献   

18.
Palynological and palynofacies analyses were carried out on some middle–upper Cretaceous samples from the El-Noor-1X borehole, northern Western Desert, Egypt. Palynological age has lead to a refinement of the original ages suggested by the drilling company. Upper Albian–Lower Cenomanian, Upper Cenomanian, and Turonian–Coniacian were recognized. The palaeoenvironment was interpreted on the basis of the ecological preferences of the palynomorphs. It was fluctuating between marginal to inner-middle shelf environment. Distribution of araucaroid pollen and xerophytes suggests that arid or semi-arid paleclimate prevailed during the deposition of the studied sediments. A warm tropical palaeoclimate is suggested on the basis of abundance of hygrophilous plants. Based on the recovered palynological organic matter, two palynofacies were recognized: palynofacies A for the Bahariya Formation, which suggests kerogen type III, and palynofacies B for the upper Bahariya and Abu Roash Formations, which suggests kerogen type IX. Data gathered from the theoretically estimated vitrinite reflectances, which are based on spore/pollen coloration, and visual pterographic kerogen analysis are used to define the source rock potentialities of the studied sediments.  相似文献   

19.
The exposed Cretaceous shelf succession of the Cauvery Basin, southeastern India, has provided a world-class record of mid and Late Cretaceous invertebrates, documented in a substantial literature. However, the lithostratigraphy of the succession has been little studied and previously subject to a range of nomenclature. It is revised here, on the basis of intensive regional mapping, to stabilize the definition and nomenclature of lithostratigraphic units. The Uttattur Group is restricted in outcrop to the Ariyalur district and divided into the Arogypapurum Formation (new; Albian), Dalmiapuram Formation (late Albian), and Karai Formation (late Albian–early Turonian) for which the Odiyam and Kunnam Members are recognized. The Trichinopoly Group follows unconformably and is also restricted in outcrop to the Ariyalur district. It is divided into the Kulakkalnattam Formation (Turonian) and Anaipadi Formation (late Turonian–Coniacian). The Ariyalur Group is more widely distributed. In the Ariyalur district, the Sillikkudi Formation (Santonian–Campanian) and its Kilpaluvari Member, the Kallakurichchi Formation (early Maastrichtian), the Kallamedu Formation (mid and Late Maastrichtian) and the Niniyur Formation (Danian) are recognized. The sequence in the Vriddhachalam area consists of the Parur and Patti formations (Campanian), Mattur Formation (late Campanian–earliest Maastrichtian) and Aladi Formation (Maastrichtian). For the Pondicherry district, the Valudavur and Mettuveli formations (Maastrichtian) and Kasur and Manaveli formations (Paleocene) comprise the succession. The interpreted depositional environments for the succession in the Ariyalur district indicate four eustatic cycles in the mid and Late Cretaceous and earliest Tertiary: late Albian–early Turonian, late Turonian–Santonian, Campanian, Maastrichtian, and Paleocene. Overall the Cauvery Basin sequence is arenaceous and relatively labile in terms of framework grain composition, and contrasts with the pelitic assemblage developed on the west Australian margin from which eastern India separated in the Early Cretaceous (Valanginian). The difference is ascribed to palaeoclimate as controlled by palaeolatitude. For the Late Cretaceous, the Cauvery Basin drifted north on the Indian plate from 40 to 30°S. This zone is inferred to constitute Southern Hemisphere horse latitudes for Late Cretaceous time, characterized by an arid climate, physical weathering and the production of labile sands. By contrast, the west Australian margin of matching tectonic history remained in a high palaeolatitude (>40°S) throughout the Late Cretaceous, experiencing a pluvial climate, the dominance of chemical weathering and the production of clays.  相似文献   

20.
采用微相分析的方法,对新疆阿合奇地区晚石炭世—早二叠世哈拉奇组和康克林组碳酸盐岩的微相类型和沉积环境进行了研究,发现两地层单元具有不同的岩石结构、颗粒组分及生物化石组合微相特征。哈拉奇组沉积粒度相对较细,泥质含量较高,生物碎屑相对较少,可划分出5种微相类型和5种次一级微相类型;康克林组生物种类丰富,个体保存较完整,颗粒组分出现了较多鲕粒、核形石等,亮晶胶结普遍,泥级组分相对较少,可划分出6种微相类型和8种次一级微相类型。根据微相类型组合特征和野外沉积构造,认为哈拉奇组碳酸盐岩主要形成于深水陆棚和台地斜坡2种沉积环境,其次为台地边缘浅滩和开阔台地沉积,总体反映较深水沉积环境;康克林组碳酸盐岩主要形成于台地边缘浅滩、开阔台地和局限台地3种沉积环境,反映沉积环境水体相对较浅。  相似文献   

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