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1.
Past geomorphological models assume that erosion of sediments from old mountain belts occurred at a relatively constant rate, based on comparatively uniform isostatic adjustment caused by unloading. Late Miocene strata of the south‐eastern United States provide an example of pulsed tectonism resulting in a surge in siliciclastic sediment production and transport. Regional tectonism (uplift of the southern Appalachian Mountains) and climatic conditions during the Late Miocene resulted in the long‐distance (up to 1000 km) fluvial transport of coarse siliciclastic sediments onto a stable carbonate platform in southern Florida. The sediments are unusual in that they are significantly coarser than marine‐transported sands in southern Florida, with discoidal quartz and quartzite clasts up to 40 mm in diameter locally present, and have relatively high potassium feldspar contents (up to 16% in some sample fractions), whereas feldspar is rare in modern Florida beach sands. It is suggested that previously documented rejuvenation of the southern Appalachian Mountains during the Middle to Late Miocene time, coupled with the Messenian sea‐level low, generated the increased rate of sediment production and necessary hydraulic gradient to allow rapid transport of coarse sediments. Tectonic influence on the river pathway in Florida, as well as in the southern Appalachian Mountains, may have maintained the river on the narrow carbonate platform. The Florida Platform during the Late Miocene must also have had a sufficiently wet climate to cause episodic transport of the coarse sediments. Siliciclastic sediment transport on the Florida Platform during the Late Miocene greatly differed from Pleistocene to modern conditions, which are dominated by the transport of fine‐grained sands by longshore marine processes.  相似文献   

2.
Abstract

The oldest rocks in the Western Highlands of New Guinea are granite and metamorphic rocks, and these are unconformably overlain by an incomplete marine succession of Permian, Upper Jurassic, Cretaceous, Eocene, Oligocene and Miocene sediments with a maximum thickness of 34,000 ft. The sedimentary succession in the east of the region is much thicker than in the west. Jurassic seas transgressed from the east. Studies of the faunas and petrology of the sediments show that the western part of the region was out of range of the sources of Cretaceous vulcanism and slow pelagic sedimentation continued into the Lower Miocene. By the Middle Miocene a volcanic island arc had developed in the vicinity of the Lai Syncline and the sediments are of shallow-water type, rich in volcanic debris.

Both sediments and basement were folded into a number of anticlines and synclines at the end of the Pliocene. Vigorous erosion was followed by extensive Pleistocene vulcanism in the west. Pleistocene glaciation occurred in the Bismarck Range down to about 13,000 feet above sea-level.  相似文献   

3.
The Argillite Sequence located at the base of the sedimentary cover on the continental slope of the Sea of Japan was studied by petrographic, palynological, and X-ray diffraction methods. Two spores-pollen complexes were distinguished in it: the Late Oligocene reflecting cooling and the Early Miocene corresponding to initiated warming. The data obtained indicate that the sequence is composed of terrigenous silty-clayey sediments that accumulated in shallow coastal-marine settings. The global sea-level rise at the Early-Middle Miocene transition, combined with the regional tectonic processes, determined the basin deepening, owing to which the argillite sequence was overlain by thick Middle Miocene diatomaceous-clayey sediments. Due to tectonic movement along existing faults in the terminal Late Miocene, the argillite sequence occurring initially at depths of at least 400–500 m was locally exhumed to the basin bottom.  相似文献   

4.
A detailed analysis of depositional history of Miocene sediments and various effects which are governed for creation of accommodation space as well as the processes of sedimentation inherent to the depositional system at that period is described in this work. The early Miocene clastic sediments are deposited in prograding environment where sediment supply exceeds the accommodation space available. The accommodation space created due to basin subsidence and source area upliftment due to local and regional tectonic activity in the basin. In the early Miocene time, the Assam shelf major transgression occurred and several minor transgression followed. There was wide spread deposition of the fluvial Tipam sandstones. In Miocene time due to thrust loading and flexure subsidence, accommodation space was created for deposition of the sediments. The Tipam Sandstone is deposited by cyclic deposition of fining upward sequence in a fluvial to brackish water environment of braided river processes. The mechanism of braided rivers is also discussed in which it laterally expanded, leaving sheet like or wedge — shaped deposits of channel and bar complexes preserving only minor amounts of flood plain material.  相似文献   

5.
Relics of a thick, widely spread, fluvial sequence of Early Miocene age are scattered throughout southern Israel, eastern Sinai, the Dead Sea Rift Valley and the western margins of the Jordanian Plateau. These relics are mainly preserved in structural lows, karstic systems, and abandoned stream valleys. The paleogeography of this fluvial system was reconstructed based on the relations between the sequence remnants and the main structural and morphological features of the southeastern Levant region.Three sedimentary associations were identified in the Miocene sequence: a lower part dominated by locally derived clastic sediments; a thicker middle part, composed mostly of far-field allochthonous clastic sediments; and an upper part composed of local as well as allochthonous sediments. The two lower parts are regionally distributed whereas the upper part is syn-tectonic and confined to the Dead Sea basin and the Karkom graben in the central Negev. The composition of the far-field allochthonous sediments points to a provenance of Precambrian crystalline rocks of the Arabo-Nubian massif that were exposed along the uplifted shoulders of the Red Sea Rift as the upper drainage basin of the fluvial system. The diverse mammal remains found in this fluvial sequence suggest a complex of savanna, forests and fluvial habitats similar to those of present East Africa, with monsoon-type rains, which were the dominant water source of the rivers.The thickness of the Miocene sequence in the central Negev is at least 1700 m, similar to that of the subsurface sequence encountered in the Dead Sea basin. This similarity suggests that both were parts of an extensive subsiding sedimentary basin that developed between the Neo-Tethys and the uplifted margins of the Red Sea.The relations between the reconstructed pre-depositional landscape of southern Israel during the Early Miocene and the overlying fluvial sequence indicate that the entire area was buried under several hundred meters of fluvial sediments, reflecting a subsidence of the northern margins of the African continent (Arabian plate) before its breakup and the splitting of the Sinai–Israel subplate by the Dead Sea Transform.During the early Middle Miocene the subsidence was inversed as the mountainous backbone of Israel was uplifted. The uplift triggered a large scale denudation that removed the thick Early Miocene fluvial sequence from the Negev and transported the eroded sediments northwestward toward the eastern Mediterranean basin. Additional uplift during the late-Middle Miocene was associated with entrenchment of the Be’er Sheva Valley between the Judea Mountains in the north and the Negev Highlands in the south. This valley was flooded by the sea during the Late Miocene.We suggest that the formation of the Early Miocene subsiding basin at the northern edge of the Arabian sub-plate predated the breakup of the Arabian plate by the DST. The inversion of the subsiding regime, which led to the establishment of the Negev Highlands seems to be intimately related to the detachment of the Sinai–Israel sub-plate from the Arabian plate during the Middle Miocene.  相似文献   

6.
Phosphates are present on the surface of the Mio-Pliocene unconformity in the Otway, Port Phillip and Gippsland basins of south-east Australia. The phosphates occur as lenticular lag deposits and include reworked phosphatic intraclasts, vertebrate bone and teeth. In situ phosphatized burrows are also found in sediments of Late Miocene and Early Pliocene age. The phosphatic intraclasts on the unconformity are interpreted as reworked phosphatized burrows derived from latest Miocene sediments (6 to 5 Ma). The phosphatization of these intraclasts is temporally related to the unconformity. The timing of phosphogenesis coincides with a period of transgression across the south-east Australian margin following Late Miocene uplift. This transgression is responsible for initial marine erosion of the underlying Miocene sequence, creation of a period of very slow sedimentation that was favourable to phosphate formation and subsequent deposition of the latest Miocene through to Pliocene sediments. The continental weathering of the uplifted highlands adjacent to the sedimentary basins, global phosphorus enrichment in the Late Miocene oceans and localized upwelling may all have contributed to phosphatization in south-eastern Australia.  相似文献   

7.
Fine-grained lacustrine, riverine and ash-fall sediments of the Shooting Iron Formation, whose late Pliocene age is established by Blancan gastropods and vertebrates, yield a pollen flora that is essentially similar in composition to the modern pollen rain in the Jackson Hole area. The Pliocene assemblage suggests a climate like that of the Jackson valley and foothills today. These spectra also resemble a Pliocene pollen flora from Yellowstone Park dated at ∼ 2.02 Ma. However, the underlying Miocene Teewinot sediments differ by containing pollen of four exotic deciduous hardwoods (Tertiary relicts) that suggest a summer-moist climate, unlike that of today. The Shooting Iron sediments lie with an angular unconformity on and above the Miocene lake sediments of the Teewinot Formation. Both of these deposits probably preceded the main uplift of the Teton Range based on the absence of Precambrian clasts in the Tertiary valley deposits. Because the Pliocene floras were modern in aspect, a Plio-Pleistocene transition would be floristically imperceptible here. The sequence denotes a protracted period of relative stability of climate during Teewinot time, and a shift in vegetational state (summer-wet trees drop out) sometime between the latest Miocene and latest Pliocene. The Pliocene spectra suggest a dry, cooler climate toward the end of Shooting Iron time.  相似文献   

8.
In the past15 years,the Cenozoic calcareous nannofossilsin the East China Sea were biostratigraphically studied duringthe extensive offshore petroleum exploration in a number ofbasins on the shelf of the East China Sea.A number of Pale-ocene to Quaternary nannofossil zones were recognized basedon the nannofossils from m any offshore wells (SBMGS,1989,1985 ) .These previous studies indicated a lot of biostratigraphicproblems,resulting in difficulties in the understanding of afurther detail…  相似文献   

9.
This work presents a clarified stratigraphic scheme of the Miocene sediments of the Fore-Urals and the territory of Bashkortostan. As a result of the work carried out, the regional stratigraphic divisions of the Miocene of the Fore-Urals were described and stratotypes and reference sections were established for the first time. The stratigraphic scheme of the Miocene sediments includes the sequences of the Lower (the upper part of the Tyulganskian Formation, Kuyurgazinskian and Voroshilovskian formations), the Middle-Upper (Ushkatlinskian Formation) and the Upper (the lower sub-formation of the Tchebenkovskian Formation) Miocene. In addition, the stratigraphic scheme developed was correlated with those of the Urals, the Russian Plain and the Lower Volga Region. The scheme is based on the data obtained from study of sediments, analysis of paleontological and lithological data, and summary of literary and library materials, which allowed us to elucidate in detail the Miocene events in the Fore-Urals.  相似文献   

10.
南海北部深水区沉积物稀土元素特征及其物源指示意义   总被引：1，自引：0，他引：1  
对南海北部白云深水区沉积物稀土元素的研究表明,渐新世至中新世的物源发生较大变化。渐新世时期,白云深水区不同区域稀土元素的分布特征差异明显,表明沉积物物源不同。深水区北部沉积物主要来自古珠江物源区,深水区东、西部沉积物中含有较多中基性火山物质,南部则主要包含基性火山物质,说明当时南海北部地区构造活动较强,存在较多火山活动,火山活动由北向南基性成分增多。渐新世末的白云运动使南海北部深水区产生强烈持续沉降,造成陆架坡折带北移,白云深水区从渐新世浅海陆架环境演化为中新世陆坡深水环境,中新世期间沉积物主要来自深水区北部的珠江三角洲物源,深水区东部存在东沙隆起源区,而深水区南部沉积物在中新世仍受到基性火山活动的影响。  相似文献   

11.
The International Ocean Discovery Program (IODP) Expedition 367/368 reported massive Upper Miocene deep-sea turbidite in the northern South China Sea basin. The Upper Miocene turbidite sand-bodies at Site U1500 were examined with detrital zircon U-Pb dating to conduct the source-to-sink analysis. This study shows that the U-Pb age spectrums of Site U1500 sample are similar to those detrital zircons from the Miocene Qiongdongnan Basin and the Pearl River Mouth Basin. Multidimensional scaling (MDS) plot also shows that the turbidite sand-bodies at Site U1500 are closely related to the sediments in the Pearl River Mouth Basin and Qiongdongnan Basin. It is likely that the thick deep-sea turbidite succession in the deep-water basin of northern South China Sea was formed by a mixed provenance pattern during the late Miocene. On the one hand, terrigenous sediments from the west of the South China Sea were transported along the Central Canyon to the eastern South China Sea deep-sea basin in the form of turbidity current. On the other hand, terrigenous sediments were also transported from the Pearl River through the slope canyon system to the northern South China Sea in the form of gravity flow . Those mixed sediments from two different source areas have collectively deposited at the deep-sea basin and thus, give rise to turbidite sequence of hundred meters. Provenance analysis of the thick turbidites sand-bodies in the deep-sea basin is of great significance to the profound understanding of the tectonic evolution, filling processes, provenance evolution, and the palaeogeographic characteristics of the Cenozoic basins of the South China Sea.  相似文献   

12.
IODP367/368航次在南海北部深海盆地多个站位发现上中新统厚达数百米的大规模深海浊积岩。采用碎屑锆石U-Pb年龄谱系分析方法对U1500站上中新统浊积砂体进行源汇对比分析。研究结果表明U1500站上中新统浊积岩碎屑锆石年龄谱系与其西侧琼东南盆地和北侧珠江口盆地中新世沉积物特征类似。多维排列分析(MDS)结果也显示,该站位样品与珠江口盆地、琼东南盆地沉积物关系密切,表明南海北部深海盆地内厚达数百米的上中新统浊积砂体为南海北部物源和南海西部物源混合堆积形成。南海西部陆源输入物质以浊流搬运的方式,沿中央峡谷从西到东搬运至南海东部深海盆地;南海北部珠江物源以重力流的形式,经南海北部陆坡峡谷搬运至深海盆地中,两种来源的沉积物在深海盆地发生混合沉积,形成U1500站厚达数百米的浊积砂体。南海北部深海盆地厚层浊积砂体物质来源的准确识别,对深刻理解南海新生代盆地的构造演化、沉积物充填过程、物源演变以及古地理特征均具有重要意义。  相似文献   

13.
This study investigates the δ13C values of Middle Miocene–Modern drift deposits and periplatform sediments in the Maldives and compares these data with the global δ13C values derived from bulk oceanic sediments and foraminifera. This comparison reveals that while the δ13C values of the early Miocene periplatform sediments in the Maldives appear to track the global record of δ13C values, including increases associated with the Oligocene–Miocene boundary as well as the variations within the Monterey Event, the correlation with the Monterey Event may be coincidental. It is suggested that variations in δ13C values do not reflect changes in oceanic dissolved inorganic carbon, but instead pulses of sediment arising from platform progradation that contribute carbonates with elevated δ13C values derived from the adjacent shallow‐water atolls. This conclusion is supported both by correlations between the seismic sequence architecture and the δ13C values which document progradation of 13C‐rich platform sediments, and also by the continuation of the interval of 13C‐rich sediments past the end of the Monterey Event at 13 Ma within the drift.  相似文献   

14.
新生代西昆仑隆升的地层学和沉积学记录   总被引：16，自引：2，他引：16  
金小赤  王军等 《地质学报》2001,75(4):459-467
西昆仑北坡的新生代沉积在很大程度上良好地记录了新生代西昆仑的隆升过程。区域性不整合面和沉积界面记录了隆升的阶段性；沉积环境变化反映了山体和盆地在格局上的变化；沉积物厚度、粒度变化显示了隆升的幅度和速率。就西昆仑的情况看，海相环境（塔里木海湾）由晚白垩世持续到渐新世，尽管此时海湾已退缩到西部。在此期间，形成了石膏层、瓣鳃类介壳灰岩和杂色砂泥质沉积。中新世全面出现了陆相沉积。中新世2000－3000m的沉积厚度表明了相对较高的隆升速率。从中新世后期开始的厚达2000－3000m的磨拉石沉积，其粒度向上加大，显示从中新世后期到早更新世隆升速率高而且是加速的。磨拉石沉积被早更新世的一次强烈的构造脉动所打断，它使磨拉石沉积和较老的沉积在许多地方高角度向盆地方向倾斜甚至直立、倒转。水平盖在磨拉石和更老地层之上的中－晚更新世河流和冲积扇机粗粒沉积是重新隆升的标志，亦可视为磨拉石沉积的继续。由昆仑山流向塔里木盆地的河流将中－上更新统及更老沉积切割50－100m以上，表明全新世以来的隆升速率是相当高的。  相似文献   

15.
We report results of an integrated study of volcanosedimentary rocks of the Middle-Late Miocene Dzhilinda Formation consisting of the prevolcanic sedimentary Lower Dzhilinda and volcanosedimentary Upper Dzhilinda subformations. The section was studied in three wells drilled near Lake Mukhal (Khoigot paleovalley, Vitim upland). The Dzhilinda sediments contain ubiquitous Alveolophora jouseana (Moiss.) Moiss. typical of Miocene environments. Deposition occurred in two main stages represented by different water (diatoms) and land (spores and pollen) plant communities. The upsection successive changes in diatom species are attendant with changes in pollen and spore assemblages. The K-Ar ages of lavas indicate that the mostly sedimentary lower section of the Dzhilinda Formation deposited between 12 and 14 Ma and the more volcanic upper section, with a lacustrine lens at base, formed at about 10.8–9.5 Ma. The isotope dating of volcanic rocks agrees with the ages inferred from the diatom and spore-pollen analyses. The prevolcanic Lower Dzhilinda subformation deposited during the Middle Miocene climate optimum. The stratigraphy, lithology and facies of sediments suggest that the Dzhilinda deposition was associated with the development of a deep freshwater lake in the conditions of active tectonism and volcanism.  相似文献   

16.
阿尔金山脉新生代剥露历史——前陆盆地沉积记录   总被引：8，自引：1，他引：7  
新疆且末县江尕勒萨依盆地位于阿尔金山脉的北西山前,其内连续沉积了中生代一新生代地层。盆地内古新统一始新统为河流相沉积;渐新统至中新统为山麓河流相灰色砾岩和棕色砂岩;上新统为山麓洪积相砾岩夹泥岩;下更新统全为砾岩层。岩性组合特征及其砂岩碎屑、砾石组分变化规律,反映出阿尔金山脉的新生代剥蚀历史：古近纪早、中期,阿尔金山脉的地形高差小,古生界双峰式火山岩首先被剥蚀;至渐新世末一中新世早期,山脉高差加大,基底元古宇开始出露地表被剥蚀;中新世末期,山脉高差进一步加大,剥蚀速率加快;至第四纪早期西域砾岩开始沉积时,地形高差加剧,中、古元古界开始暴露被剥蚀。区域资料分析表明,阿尔金山脉在新生代具有多期次阶段性隆升的特征,存在3期次快速隆升事件：渐新世末一中新世早期、中新世晚期(大约8Ma)和第四纪早期。  相似文献   

17.
The 85°E Ridge extends from the Mahanadi Basin, off northeastern margin of India to the Afanasy Nikitin Seamount in the Central Indian Basin. The ridge is associated with two contrasting gravity anomalies: negative anomaly over the north part (up to 5°N latitude), where the ridge structure is buried under thick Bengal Fan sediments and positive anomaly over the south part, where the structure is intermittently exposed above the seafloor. Ship-borne gravity and seismic reflection data are modelled using process oriented method and this suggest that the 85°E Ridge was emplaced on approximately 10–15 km thick elastic plate (Te) and in an off-ridge tectonic setting. We simulated gravity anomalies for different crust-sediment structural configurations of the ridge that were existing at three geological ages, such as Late Cretaceous, Early Miocene and Present. The study shows that the gravity anomaly of the ridge in the north has changed through time from its inception to present. During the Late Cretaceous the ridge was associated with a significant positive anomaly with a compensation generated by a broad flexure of the Moho boundary. By Early Miocene the ridge was approximately covered by the post-collision sediments and led to alteration of the initial gravity anomaly to a small positive anomaly. At present, the ridge is buried by approximately 3 km thick Bengal Fan sediments on its crestal region and about 8 km thick pre- and post-collision sediments on the flanks. This geological setting had changed physical properties of the sediments and led to alter the minor positive gravity anomaly of Early Miocene to the distinct negative gravity anomaly.  相似文献   

18.
The Iraqi territory could be divided into four main tectonic zones; each one has its own characteristics concerning type of the rocks, their age, thickness and structural evolution. These four zones are: (1) Inner Platform (stable shelf), (2) Outer Platform (unstable shelf), (3) Shalair Zone (Terrain), and (4) Zagros Suture Zone. The first two zones of the Arabian Plate lack any kind of metamorphism and volcanism.The Iraqi territory is located in the extreme northeastern part of the Arabian Plate, which is colliding with the Eurasian (Iranian) Plate. This collision has developed a foreland basin that includes: (1) Imbricate Zone, (2) High Folded Zone, (3) Low Folded Zone and (4) Mesopotamia Foredeep.The Mesopotamia Foredeep, in Iraq includes the Mesopotamia Plain and the Jazira Plain; it is less tectonically disturbed as compared to the Imbricate, High Folded and Low Folded Zones. Quaternary alluvial sediments of the Tigris and Euphrates Rivers and their tributaries as well as distributaries cover the central and southeastern parts of the Foredeep totally; it is called the Mesopotamian Flood Plain. The extension of the Mesopotamia Plain towards northwest however, is called the Jazira Plain, which is covered by Miocene rocks.The Mesopotamia Foredeep is represented by thick sedimentary sequence, which thickens northwestwards including synrift sediments; especially of Late Cretaceous age, whereas on surface the Quaternary sediments thicken southeastwards. The depth of the basement also changes from 8 km, in the west to 14 km, in the Iraqi–Iranian boarders towards southeast.The anticlinal structures have N–S trend, in the extreme southern part of the Mesopotamia Foredeep and extends northwards until the Latitude 32°N, within the Jazira Plain, there they change their trends to NW–SE, and then to E–W trend.The Mesozoic sequence is almost without any significant break, with increase in thickness from the west to the east, attaining 5 km. The sequence forms the main source and reservoir rocks in the central and southern parts of Iraq. The Cenozoic sequence consists of Paleogene open marine carbonates, which grades upwards into Neogene lagoonal marine; of Early Miocene and evaporitic rocks; of Middle Miocene age, followed by thick molasses of continental clastics that attain 3500 m in thickness; starting from Late Miocene. The Quaternary sediments are very well developed in the Mesopotamia Plain and they thicken southwards to reach about 180 m near Basra city; in the extreme southeastern part of Iraq.The Iraqi Inner Platform (stable shelf) is a part of the Arabian Plate, being less affected by tectonic disturbances; it covers the area due to south and west of the Euphrates River. The main tectonic feature in this zone that had affected on the geology of the area is the Rutbah Uplift; with less extent is the Ga’ara High.The oldest exposed rocks within the Inner Platform belong to Ga’ara Formation of Permian age; it is exposed only in the Ga’ara Depression. The Permian rocks are overlain by Late Triassic rocks; represented by Mulussa and Zor Hauran formations, both of marine carbonates with marl intercalations. The whole Triassic rocks are absent west, north and east of Ga’ara Depression. Jurassic rocks, represented by five sedimentary cycles, overlie the Triassic rocks. Each cycle consists of clastic rocks overlain by carbonates, being all of marine sediments; whereas the last one (Late Jurassic) consists of marine carbonates only. All the five formations are separated from each other by unconformable contacts. Cretaceous rocks, represented by seven sedimentary cycles, overlie the Jurassic rocks. Marine clastics overlain by marine carbonates. Followed upwards (Late Cretaceous) by continental clastics overlain by marine carbonates; then followed by marine carbonates with marl intercalations, and finally by marine clastics overlain by carbonates; representing the last three cycles, respectively.The Paleocene rocks form narrow belt west of the Ga’ara Depression, represented by Early–Late Paleocene phosphatic facies, which is well developed east of Rutbah Uplift and extends eastwards in the Foredeep. Eocene rocks; west of Rutbah Uplift are represented by marine carbonates that has wide aerial coverage in south Iraq. Locally, east of Rutbah Uplift unconformable contacts are recorded between Early, Middle and Late Eocene rocks. During Oligocene, in the eastern margin of the Inner Platform, the Outer Platform was uplifted causing very narrow depositional Oligocene basin. Therefore, very restricted exposures are present in the northern part of the Inner Platform (north of Ga’ara Depression), represented by reef, forereef sediments of some Oligocene formations.The Miocene rocks have no exposures west of Rutbah Uplift, but north and northwestwards are widely exposed represented by Early Miocene of marine carbonates with marl intercalations. Very locally, Early Miocene deltaic clastics and carbonates, are interfingering with the marine carbonates. The last marine open sea sediments, locally with reef, represent the Middle Miocene rocks and fore reef facies that interfingers with evaporates along the northern part of Abu Jir Fault Zone, which is believed to be the reason for the restriction of the closed lagoons; in the area.During Late Miocene, the continental phase started in Iraq due to the closure of the Neo-Tethys and collision of the Sanandaj Zone with the Arabian Plate. The continental sediments consist of fine clastics. The Late Miocene – Middle Pliocene sediments were not deposited in the Inner Platform.The Pliocene–Pleistocene sediments are represented by cyclic sediments of conglomeratic sandstone overlain by fresh water limestone, and by pebbly sandstone.The Quaternary sediments are poorly developed in the Inner Platform. Terraces of Euphrates River and those of main valleys represent pleistocene sediments. Flood plain of the Euphrates River and those of large valleys represent Holocene sediments. Residual soil is developed, widely in the western part of Iraq, within the western marginal part of the Inner Platform.  相似文献   

19.
The middle Miocene continental fluvial sediments of the Sangaredi Group in the western districts of the Futa Jallon-Mandingo bauxite-bearing province were initially more widespread. Their thickness in the axial zones of the main drainage systems (Paleocogon, Paleotomine, etc.) attained 150 m. The lower, early Miocene steps of topography formed during the first phase of regional neotectonic evolution were buried beneath these sediments by the end of middle Miocene. The sediments of the Sangaredi Group underwent substantial epigenetic alteration in the glei geochemical setting with removal of iron and bleaching. At the second stage of neotectonic uplifting and dissection, this low-Fe and high-Al protolith was again affected by lateritic weathering with formation of unique sedimentary-lateritic bauxites. The underlying bedrock was also affected by bleaching and lateritization with formation of high-quality infiltration-metasomatic bauxites with geliform cryptocrystalline structure and massive porcelainlike or oolitic texture. Both classes of bauxites are high-quality and of great economic importance.  相似文献   

20.
Integrated geoscientific datasets have contributed to an understanding of the Tertiary palaeovalleys once draining the Gawler Craton. Systematic investigations of both the shape and depth of the channels are based on interpretations from field exposures, a compendium of geological and drilling data, computer modelling of ancient landscapes, topographic and evaluated digital elevation models, remote sensing imagery, magnetics, seismic, gravity, airborne and transient electromagnetics, and radiometrics. Physical property contrasts that exist between the channel sediments and the underlying bedrock, for example, can be differentiated by geophysical methods to locate the incised‐valley thalweg. Evidence from sedimentology is combined with evidence from other geological and geophysical characteristics to arrive at a general reconstruction of palaeovalley architecture and history. The palaeovalleys were originally incised into the weathered pre‐Tertiary landscape of mostly weathered basement, and Tertiary fluvial, lacustrine, estuarine and even marine sediments accumulated during the Eocene and Miocene. Marine influence extended at least 100 km up the palaeovalleys during at least three major transgressions in the Eocene and Miocene intervals. Major sedimentary phases occurred in the Paleocene to Early Eocene, Middle to Late Eocene, Oligocene to Early Miocene, and Middle Miocene to Early Pliocene times.  相似文献   

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