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1.
华亭矿区延安组形成于河流、湖泊三角洲-湖泊沉积体系,其中以湖泊三角洲平原占优势,其沉积相有河流相、冲积扇相、湖泊三角洲相、湖泊相.煤系沉积初期,以河流及冲积扇沉积为主,沉积中期则以湖泊三角洲沉积为主,晚期以湖泊环境为主,延安组各煤层大多是在湖泊三角洲平原上泥沼化形成的. 相似文献
2.
3.
为查明唐山西部平原区晚新生代以来松散堆积物的沉积演化特征,依托鸦鸿桥幅1∶5万区域地质调查工作,对唐山西部PZK14孔进行色度、粒度、视电阻率测井、自然伽马测井等研究,划分沉积相并计算各时段的沉积速率,结果表明: 该地区新生代晚期主要发育湖泊相、三角洲相和河流相。早更新世初始发育三角洲相,随着气候转暖,古滦河冲积扇退积,三角洲相转变为河流相; 早更新世中—晚期,发育3个湖泊-三角洲相沉积旋回; 中更新世发育一个湖泊-三角洲相沉积旋回; 晚更新世初沉积了巨厚的湖相层,随着气候转冷,渤海湾沿岸海侵结束,湖盆开始萎缩,转变为河流相; 全新世则以河间洼地沉积为主。沉积速率-年龄曲线表明: 第四纪以来构造作用对该地区沉积速率控制较弱,气候为影响沉积相发育的主要因素。第四纪各个时期的沉积速率均较快,奥杜威极性亚时(1.95~1.77 Ma)沉积速率最大,约为194.0 m/Ma; 2.52~1.95 Ma沉积速率最小,约为111.2 m/Ma。研究成果对恢复该区域古地理演化、水工环地质勘查等具有重要意义。 相似文献
4.
In East Africa, the feedback between tectonic uplift, erosional denudation and associated possible climate changes is being studied by a multidisciplinary research group, ‘Riftlink’. The group's focus is the Albertine Rift, the northern part of the western branch of the East African Rift System, and in particular the rising Rwenzori Mountains that stretch along the border of the D.R. Congo and Uganda. Major questions relate to the timing of the formation of the Rwenzori Mountains, and whether the height of these mountains (> 5000 m) relates to rift movements in Neogene times, or represents an old basement block that formed a topographic high long before. Though, at first, research concentrated on the eastern (Ugandan) part of the Albertine Rift and Rwenzori Mountains, it has now moved further to the west to the D.R. Congo. A first field‐campaign, covering the area from northern Lake Edward along the rift shoulder up to the Blue Mountains at Lake Albert, was conducted in summer 2009, in cooperation with the Ruwenzori State University of Butembo. Here, we present a brief overview of the field‐campaign, with impressions gathered on the morphology and geology of the study area. 相似文献
5.
Alluvial-fan-carbonate facies with evaporites, Eocene Guarga Formation, Southern Pyrenees, Spain 总被引：1，自引：0，他引：1
ENNO NICKEL 《Sedimentology》1982,29(6):761-796
Continental carbonates of the basal part of the Guarga Formation, Upper Eocene, have been studied in the field and in the laboratory. Both geographic pattern and vertical sequences served as a basis for sedimentary models. The pattern reveals that carbonate deposition was greater in the western part of the Tremp-Graus Basin than in the eastern part. Studies of slabs and thin sections suggest high energy deposition in the eastern part of the basin and low energy deposition in the western part. Gross lithology, petrography, and faunal/floral associations indicate sedimentary environments which include calcimorphic palaeosoils, caliche nodule zones, solid caliche nodule zones, caliche crusts, fluvial carbonates, paludal carbonates, and pond/lake carbonates. Distribution pattern of the carbonate bodies and lithologies seem to be controlled by alluvial-fan processes. They are typical fining-upward sequences in the sense of Collinson (1978) which furthermore can be assigned to a channel-bound group and a succession independent of fluvial channels. Referring to fan-physiography the sequences can be subdivided into fluvial proximal interchannel, fluvial distal interchannel, lacustrine distal interchannel, nearshore lacustrine-paludine, and lacustrine offshore carbonate facies. The two last categories are distal alluvial plain and/or fan-edge associations. The presence of especially charophyte oogonia adjacent to pseudomorphs of lenticular gypsum in the lacustrine carbonates of the western Tremp-Graus Basin indicates that their depositional environment was that of shallow lakes with alternating salinities. Diagenetic alterations consist of three major phenomena: (a) general cementation of the carbonates by low-Mg calcite, (b) pseudomorphs of lenticular gypsum, and (c) silification. The relationship of gypsum and silica diagenesis to the regional distribution of lacustrine carbonates suggests early diagenetic processes for their formation. Gypsum pseudomorphs are small and are found to be replaced by Fe-calcite throughout the whole area, or are large and replaced preferentially by silica in the west only. There is experimental evidence (Cody, 1979) that distribution of gypsum morphology and crystal sizes can be related to increased salinities and increased organic production in the west. Chert-gypsum fabrics from that area resemble the ‘silex nectique’ of Cayeux (1929). The occurrence of this noteworthy type of chert together with length-slow chalcedony is an indication of relatively early silification of the gypsum. It is suggested that the sediments containing the silicified lenticular gypsum hosted brines of partly marine origin which alternately became brackish or fresh. An attempt was made to check the influence of evaporation during carbonate deposition by determining the stable isotope composition of the carbonates and of the chert. The data show no distinct variations with respect to the presumed palaeoenvironments. The ranges in the carbonates (δ13C ? 5,0 to ?7,9; δ18 O ?4,5 to ?7,7) fit among the data given in the literature. The values derived from chert (δ18O 26,9 to 31 SMOW) support a concept of alternating salinities. Distribution of carbonate lithofacies indicate a systematic change in sedimentation from fluvial/ephemeral to permanent lacustrine from east to west. Diagenetic alterations suggest an increase of salinities of pore waters in the same direction. In addition the lacustrine limestones in the west were due to frequent changes in pore-water salinity. Similar sequences lacking subtidal and/or lagoonal fossil associations but including pseudomorphs of carbonate and chert after lenticular gypsum were described from the Lower Purbeckian of Dorset (West, 1964, 1975, 1979), and from the Tertiary of the Paris Basin (Fontes, 1968). Guarga limestone environments of especially the western Tremp-Graus Basin probably resembled the modern semi-arid ephemeral saline lakes in Australia (Burne, Bauld & De Dekker, 1980). Gypsum precipitation in these environments can be compared to the one in modern sabkhas from the Mediterranean coast of Egypt (West, Ali & Hilmy, 1979; Ali West & Hilmy, 1980). 相似文献
6.
江汉盆地马王庙地区古近系新沟嘴组下段沉积相及其演化 总被引：1，自引：0，他引：1
通过对岩石学特征、沉积构造、沉积层序和测井相等的综合分析表明,江汉盆地马王庙地区古近
系新沟嘴组下段发育三角洲-湖泊沉积体系,包括三角洲平原、三角洲前缘、前三角洲、滨浅湖和膏盐湖等亚
相类型。在沉积相类型识别的基础上,根据单因素分析多因素综合作图法,编制了马王庙地区新沟嘴组下段各
油组地层等厚图、砂岩等厚图、砂地比等值线图和典型单井优势相投影图等单因素图件。综合分析各单因素图,
绘制了马王庙地区新沟嘴组下段Ⅰ、Ⅱ和Ⅲ共３个油组的沉积相图,并探讨了其沉积相平面展布特征和演化规
律：古近纪新沟嘴组下段沉积时期,研究区的物源来自北东和北西方向,并分别向南西和南东方向展布,依次
发育三角洲平原-三角洲前缘-前三角洲亚相,其中以三角洲前缘的水下分流河道和席状砂微相最为发育;两
支三角洲砂体周围为滨浅湖沉积。自Ⅲ油组到Ⅱ、Ⅰ油组沉积时期,研究区水体经历了由浅变深再变浅的过程;
Ⅲ油组和Ⅱ油组沉积时期,三角洲砂体分布面积广,储集层发育较好。 相似文献
7.
Thermal and exhumation history of the central Rwenzori Mountains, Western Rift of the East African Rift System, Uganda 总被引：2，自引：1，他引：1
F. U. Bauer U. A. Glasmacher U. Ring A. Schumann B. Nagudi 《International Journal of Earth Sciences》2010,99(7):1575-1597
The Rwenzori Mountains (Mtns) in west Uganda are the highest rift mountains on Earth and rise to more than 5,000 m. We apply
low-temperature thermochronology (apatite fission-track (AFT) and apatite (U–Th–Sm)/He (AHe) analysis) for tracking the cooling
history of the Rwenzori Mtns. Samples from the central and northern Rwenzoris reveal AFT ages between 195.0 (±8.4) Ma and
85.3 (±5.3) Ma, and AHe ages between 210.0 (±6.0) Ma to 24.9 (±0.5) Ma. Modelled time–temperature paths reflect a protracted
cooling history with accelerated cooling in Permo-Triassic and Jurassic times, followed by a long period of constant and slow
cooling, than succeeded by a renewed accelerated cooling in the Neogene. During the last 10 Ma, differentiated erosion and
surface uplift affected the Rwenzori Mtns, with more pronounced uplift along the western flank. The final rock uplift of the
Rwenzori Mtns that partly led to the formation of the recent topography must have been fast and in the near past (Pliocene
to Pleistocene). Erosion could not compensate for the latest rock uplift, resulting in Oligocene to Miocene AHe ages. 相似文献
8.
利用数十口井的电性、岩性及分析化验资料，将柴达木盆地西部地区古近纪与新近纪沉积相划分为七种相和亚相：洪积锥、水下冲积扇、河道和泛滥平原、滨湖、浅湖、较深湖和三角洲。沉积相的空间展布概括起来分为三大带：（1）阿尔金山前西段陡坡带洪积锥-水下冲积扇-扇三角洲-河道和泛滥平原-湖相 (2)阿尔金山前中段陡坡带洪积锥-水下冲积扇-湖相；（3）昆仑山前洪积锥-河道和泛滥平原-三角洲相。沉积相不仅影响着碎屑岩的成分和结构，而且也影响其物性与含油性。由洪积锥到水下冲积扇，到河道和泛滥平原，到三角洲，到湖相，石英和胶结物含量逐渐升高，岩屑和杂基含量逐渐降低，分选及磨圆变好，颗粒的粒级变细。浅层以河道和泛滥平原及三角洲相的物性最好，深层以三角洲相的物性最好，次为冲积扇，湖相最差。碎屑岩的油气富集以河道、泛滥平原和三角洲相最好，滨浅湖相油气富集最差。 相似文献
9.
The Mt Isa Rift Event is a Palaeoproterozoic intracontinental extension event that defines the beginning of sedimentation into the Isa Superbasin in the Western Fold Belt, Mt Isa terrane. In the mildly deformed Fiery Creek Dome region, on the northwest flanks of the Mt Isa Rift, elements of the Mt Isa Rift Event rift architecture are preserved without being intensely overprinted by later deformation. In this region two discrete generations of northwest‐dipping normal faults have been identified. Early generation normal faults were active during the deposition of fluvial and immature conglomerate and sandstone of the Bigie Formation. Renewed rifting and the development of late‐generation normal faults occurred during deposition of shallow‐marine sandstone and siltstone of the lower Gunpowder Creek Formation. Differential uplift between tilt blocks formed an array of spatially and temporally discontinuous synrift unconformities on the crests of uplifted tilt blocks. Applying the domino model yields ～28% crustal extension for the entire Mt Isa Rift Event. Northwest‐striking transverse faults facilitated differential displacement along normal faults and formed boundaries to normal fault segments, creating smaller depositional compartments along half‐graben axes. Three large domes were formed during laccolith emplacement. These domes produced palaeogeographical highs that divided the region into sub‐basins and were a source for the coarse fluvial synrift sequences deposited during the early Mt Isa Rift Event. The basin architecture in the Fiery Creek Dome region is consistent with northwest‐southeast‐directed extension. 相似文献
10.
Toru Tamura Yoshiki Saito Sotham Sieng Bunnarin Ben Meng Kong Im Sim Sokuntheara Choup Fumio Akiba 《Quaternary Science Reviews》2009,28(3-4):327-344
Modern deltas are understood to have initiated around 7.5–9 ka in response to the deceleration of sea-level rise. This episode of delta initiation is closely related to the last deglacial meltwater events and eustatic sea-level rises. The initial stage of the Mekong River delta, one of the world's largest deltas, is well recorded in Cambodian lowland sediments. This paper integrates analyses of sedimentary facies, diatom assemblages, and radiocarbon dates for three drill cores from the lowland to demonstrate Holocene sedimentary evolution in relation to sea-level changes. The cores are characterized by a tripartite succession: (1) aggrading flood plain to natural levee and tidal–fluvial channel during the postglacial sea-level rise (10–8.4 ka); (2) aggrading to prograding tidal flats and mangrove forests around and after the maximum flooding of the sea (8.4–6.3 ka); and (3) a prograding fluvial system on the delta plain (6.3 ka to the present). The maximum flooding of the sea occurred at 8.0 ± 0.1 ka, 2000 years before the mid-Holocene sea-level highstand, and tidal flats penetrated up to 20–50 km southeast of Phnom Penh after a period of abrupt ～5 m sea-level rise at 8.5–8.4 ka. The delta progradation then initiated as a result of the sea-level stillstand at around 8–7.5 ka. Another rapid sea-level rise at 7.5–7 ka allowed thick mangrove peat to be widely deposited in the Cambodian lowland, and the peat accumulation endured until 6.3 ka. Since 6.3 ka, a fluvial system has characterized the delta plain, and the fluvial sediment discharge has contributed to rapid delta progradation. The uppermost part of the sedimentary succession, composed of flood plain to natural-levee sediments, reveals a sudden increase in sediment accumulation over the past 600–1000 years. This increase might reflect an increase in the sediment yield due to human activities in the upper to middle reaches of the Mekong, as with other Asian rivers. 相似文献
11.
The infill of the Neuquén Basin recorded the Meso-Cenozoic geological and tectonic evolution of the southern Central Andes being an excellent site to investigate how the pattern of detrital zircon ages varies trough time. In this work we analyze the U–Pb (LA–MC–ICP–MS) zircon ages from sedimentary and volcanic rocks related to synrift and retroarc stages of the northern part of the Neuquén Basin. These data define the crystallization age of the synrift volcanism at 223 ± 2 Ma (Cerro Negro Andesite) and the maximum depositional age of the original synrift sediments at ca. 204 Ma (El Freno Formation). Two different pulses of rifting could be recognized according to the absolute ages, the oldest developed during the Norian and the younger during the Rhaetian–Sinemurian. The source regions of the El Freno Formation show that the Choiyoi magmatic province was the main source rock of sediment supply. An important amount of detrital zircons with Triassic ages was identified and interpreted as a source area related to the synrift magmatism. The maximum depositional age calculated for the Tordillo Formation in the Atuel-La Valenciana depocenter is at ca. 149 Ma; as well as in other places of the Neuquén Basin, the U–Pb ages calculated in the Late Jurassic Tordillo Formation do not agree with the absolute age of the Kimmeridgian–Tithonian boundary (ca. 152 Ma). The main source region of sediment in the Tordillo Formation was the Andean magmatic arc. Basement regions were also present with age peaks at the Carboniferous, Neoproterozoic, and Mesoproterozoic; these regions were probably located to the east in the San Rafael Block. The pattern of zircon ages summarized for the Late Jurassic Tordillo and Lagunillas formations were interpreted as a record of the magmatic activity during the Triassic and Jurassic in the southern Central Andes. A waning of the magmatism is inferred to have happened during the Triassic. The evident lack of ages observed around ca. 200 Ma suggests cessation of the synrift magmatism. The later increase in magmatic activity during the Early Jurassic is attributed to the onset of Andean subduction, with maximum peaks at ca. 191 and 179 Ma. The trough at ca. 165 Ma and the later increase in the Late Jurassic could be explained by changes in the relative convergence rate in the Andean subduction regime, or by the shift to a more mafic composition of the magmatism with minor zircon fertility. 相似文献
12.
二连盆地吉尔嘎朗图凹陷是一个陆相断陷聚煤盆地,下白垩统赛汉塔拉组是其主要含煤地层,作者利用岩心、钻孔资料对其岩相类型、沉积相、层序地层及聚煤作用特征进行研究。(1)赛汉塔拉组主要由砂砾岩、砂岩、粉砂岩、泥岩、碳质泥岩及厚层褐煤组成,发育扇三角洲平原相、扇三角洲前缘相、辫状河三角洲平原相、辫状河三角洲前缘相、滨浅湖相,分别属于扇三角洲沉积体系、辫状河三角洲沉积体系和湖泊沉积体系。(2)识别出2种层序界面:不整合面和下切谷冲刷面,将赛汉塔拉组划分为2个三级层序。从层序Ⅰ到层序Ⅱ,煤层厚度逐渐增大,聚煤作用逐渐增强。(3)在滨浅湖环境下厚煤层主要形成于湖侵体系域早期,在扇/辫状河三角洲环境下厚煤层主要形成于湖侵体系域晚期,煤层厚度在凹陷中部最大,向西北和东南方向均变小。聚煤作用明显受基底沉降作用影响,可容空间增加速率与泥炭堆积速率相平衡,从而形成了区内巨厚煤层。 相似文献
13.
Massimiliano Ghinassi 《Sedimentary Geology》2007,202(4):677-701
This study focuses on the lowstand and early transgressive systems tracts of a basin-fill sequence of lower Pliocene nearshore deposits in the Val d'Orcia Basin of the Northern Apennines, Italy. The basin at that time was a semi-enclosed marine embayment, and, in the study area, its margin was subject to highly variable subsidence along the depositional strike, attributed to a decrease in tectonic displacement. The nearshore succession in the more rapidly-subsiding segment of the basin is around 20 m thick, comprising three storeys of laterally-stacked Gilbert-type delta lobes overlain by a shoal-water delta, whereas the nearshore succession in the adjacent, more slowly-subsiding segment, is up to 9 m thick. This succession is characterised by alternation of shoreface and offshore deposits, moderately wave-worked and covered by shoal-water deltaic facies.These coeval nearshore successions consist of several transgressive-regressive cyclothems. The development and lateral variation of the cyclothems was controlled by the local subsidence rate and coastal topographic gradient. Some of the cyclothems are considered to be higher-order sequences and others to be parasequences, with the former passing laterally into the latter in the area where the sea-level fall was countered by fast local subsidence. Some of the bounding surfaces are of limited lateral extent, with two parasequences passing laterally into a single one.Coastal topography controlled particularly the thickness of transgressive deposits. In the low-gradient setting of a delta plain, the relative sea-level rises caused major landward shifts of the shoreline and reduced fluvial sediment supply, with the formation of a transgressive lag in sediment-starved conditions. In the high-gradient coastal setting of the non-deltaic zone, the shoreline shift was minimal and had relatively little impact on local sediment supply, which promoted an accretionary transgression.At the end of the lowstand stage, the rate of sediment accumulation in the non-deltaic nearshore zone was lower, allowing the onset of subsequent transgression to be recorded considerably earlier than in the deltaic nearshore zone. This diachroneity suggests that facies criteria alone may not necessarily be a reliable basis for the recognition of systems tract boundaries. 相似文献
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15.
Thomas Christian Brachert Gerhard B. Brügmann Dieter F. Mertz Ottmar Kullmer Friedemann Schrenk Dorrit E. Jacob Immaculate Ssemmanda Heinrich Taubald 《International Journal of Earth Sciences》2010,99(7):1663-1675
The Neogene was a period of long-term global cooling and increasing climatic variability. Variations in African-Asian monsoon
intensity over the last 7 Ma have been deduced from patterns of eolian dust export into the Indian Ocean and Mediterranean
Sea as well as from lake level records in the East African Rift System (EARS). However, lake systems not only depend on rainfall
patterns, but also on the size and physiography of river catchment areas. This study is based on stable isotope proxy data
(18O/16O, 13C/12C) from tooth enamel of hippopotamids (Mammalia) and aims in unravelling long-term climate and watershed dynamics that control
the evolution of palaeolake systems in the western branch of the EARS (Lake Albert, Uganda) during the Late Neogene (7.5 Ma
to recent). Having no dietary preferences with respect to wooded (C3) versus grassland (C4) vegetation, these territorial, water-dependant mammals are particularly useful for palaeoclimate analyses. As inhabitants
of lakes and rivers, hippopotamid tooth enamel isotope data document mesoclimates of topographic depressions, such as the
rift valleys and, therefore, changes in relative valley depth instead of exclusively global climate changes. Consequently,
we ascribe a synchronous maximum in 18O/16O and 13C/12C composition of hippopotamid enamel centred around 1.5–2.5 Ma to maximum aridity and/or maximum hydrological isolation of
the rift floor from rift-external river catchment areas in response to the combined effects of rift shoulder uplift and subsidence
of the rift valley floor. Structural rearrangements by ~2.5 Ma within the northern segment of the Albertine Rift are well
constrained by reversals in river flow, cannibalisation of catchments, biogeographic turnover and uplift of the Rwenzori horst.
However, a growing rain shadow is not obvious in 18O/16O signatures of the hippopotamid teeth of the Albertine Rift. According to our interpretation, this is the result of the overriding
effect of evaporation on 18O/16O responding to aridification of the basin floor by a valley air circulation system through relative deepening of the valley.
On the other hand, a synchronous arid pulse is not so clearly recorded in palaeosol data and mammalian fauna of the eastern
branch of the EARS. This discrepancy indicates that rift mesoclimates may represent an underestimated aspect in previous palaeoclimate
reconstructions from rift valley data and represent a clear limitation to attempts at global climate reconstructions. The
results of this study also suggest that using 18O/16O data as a proxy to rain shadow evolution must take into account relative basin subsidence to properly document mountain
range uplift. 相似文献
16.
A siliciclastic-dominated succession (～11 m thick) underlying Harrat Rahat, belonging to the Miocene–Pliocene Bathan Formation is recently exposed at Al-Rehaili area, North Jeddah, Saudi Arabia. It covers a wide spectrum of grain sizes varying from clay-rich mudstones to cobble grade conglomerate and consists of a variety of facies vary from fluvial to marginal and open lacustrine deposited in a half-graben basin formed along the eastern margin of the extensional Red Sea Basin. Field-based sedimentologic investigation enables to identify ten facies grouped into three facies associations (A–C). The depositional history is subdivided into two stages. The first stage represents deposition in gravel to sand-dominated fluvial system sourced from a southern source and grade northward into lacustrine delta and open lacustrine setting. The second stage on the other hand includes deposition of fluvial channels running in E–W direction with attached bank sand bar. Sequence stratigraphic interpretations of the lacustrine deposits enable to identify three unconformity-bounded sequences (SQ1–3). The basal sequence is incomplete, consisting of three aggradationally to progradationally stacked delta plain and delta front parasequences. The second sequence is sharply and erosively overlying a red paleosol bed that defines the upper boundary of the first sequence. It includes two system tracts; upward-fining and deepening lacustrine offshore mudstones of the transgressive system tracts unconformably overlain by red paleosol of the regressive systems tracts. The top of this sequence is delineated at the sharp transgressive surface of erosion at the base of delta mouth bar deposits of sequence 3. Changes in the accommodation and sedimentation rates by basin subsidence under the influence of tectonics and sediment compaction and loading as well as climatic oscillation between semi-arid to arid conditions were the major controls on the fluvio-lacustrine sedimentation and their facies distribution. Tectonic reorganization of the drainage system resulted in the formation of E–W flowing fluvial streams in the second stage. 相似文献
17.
塔里木盆地库车坳陷与塔西南坳陷的白垩系沉积厚度大,岩石类型多,既有碎屑岩,又有蒸发岩和碳酸盐岩。沉积相类型丰富,包括海相、海陆交互相和陆相,并以陆相碎屑岩沉积为主。库车坳陷与塔西南坳陷在早白垩世虽为分隔性的沉积盆地,但其陆相碎屑沉积具有几乎相同的特征：均以冲积沉积体系发育为主,相带分布和储层发育具有明显的相似性。对应山前断陷盆地的不对称性,冲积扇-扇三角洲、辫状河三角洲沉积体系发育在靠近山前的陡坡一侧,正常河流三角洲沉积体系发育在湖盆缓坡一侧。冲积扇-扇三角洲沉积体系由冲积扇、扇三角洲平原、扇三角洲前缘等构成,辫状河三角洲沉积体系由辫状河三角洲平原、辫状河三角洲前缘等构成。储层主要发育于扇三角洲或辫状河三角洲的辫状河道、水下分流河道及分流河口砂坝中,在库车坳陷和塔西南坳陷都形成了优质的储集岩。砂体厚度大,分布广,储集条件好。冲积沉积体系的普遍发育预示了白垩系储集岩在盆地内的分布可能是十分广泛的。近年在喀什凹陷、英吉苏凹陷相继取得的勘探成果大大拓宽了其勘探领域,白垩系正逐渐成为盆地内主要的勘探目的层之一,展现了良好的勘探前景。 相似文献
18.
D. Koehn M. Lindenfeld G. Rümpker K. Aanyu S. Haines C. W. Passchier T. Sachau 《International Journal of Earth Sciences》2010,99(7):1633-1642
New structural and seismologic evidence from the Rwenzori Mountains, Uganda, indicate that continental rifts can capture and rotate fragments of the lithosphere while rift segments interact, in a manner analogous to the interaction of small-scale fractures. The Rwenzori Mountains are a basement block within the western branch of the East African Rift System that is located at the intersection of two rift segments and is apparently rotating clockwise. Structural data and new seismological data from earthquake epicentres indicate a large-scale, 20-km-long transsection fault is currently detaching the Rwenzori micro-plate on its northern margin from the larger Victoria plate (Tanzania craton), whereas it is already fully detached in the south. We propose that this fault develops due to the rotation of the Rwenzori block. In a numerical model we show how rift segment interaction, block rotation and the development of transsection faults (faults that cut through the Rwenzori Mountains) evolve through time. The model suggests that uplift of the Rwenzori block can only take place after the rift has opened significantly, and rotation leads to the development of transsection faults that connect two rift segments, so that the block is captured within the rifts. Our numerical model suggests that the majority of the uplift has taken place within the last 8 Ma. 相似文献
19.
RICARDO NÉSTOR MELCHOR 《Sedimentology》2007,54(6):1417-1446
Well‐exposed Triassic rift strata from the Ischigualasto–Villa Unión Basin (NW Argentina) include a 80 to ca 515 m thick lacustrine‐dominated package that can be correlated across a half‐graben using key stratigraphic surfaces (sequence boundaries, lacustrine flooding surfaces and forced regressive surfaces). The characteristics of the synrift lacustrine fill in different parts of the half‐graben have been examined and the mechanisms controlling sedimentation inferred. A variety of sedimentary environments are recognized including; volcaniclastic floodplain, mildly saline lake and playa lake, offshore lacustrine, delta front to fluvial‐dominated and wave‐dominated deltas, distributary and fluvial channel, and interdistributary bay. The succession can be divided into four stratigraphic sequences (SS1 to SS4), the oldest of which (SS1) contains volcaniclastic, fluvial and saline lake deposits; it is thickest close to the western border fault zone, reflecting more rapid subsidence here. Accommodation exceeded sediment and water input during SS1. The second and third sequences (SS2 and SS3) mark the onset of widespread lacustrine sedimentation, reflecting a balance between accommodation creation and water and sediment fluxes. Sequences SS2 and SS3 are represented by offshore meromictic lacustrine and deltaic deposits, the latter mostly sourced from the flexural and southern axial margins of the half‐graben. The presence of stacked parasequences bound by lacustrine flooding surfaces is related to climatically induced lake‐level fluctuations superimposed on variable rates of subsidence on the controlling rift border fault zone. The youngest sequence (SS4) is represented by the deposits of littoral lacustrine and shallow shelf deltas distinguished by a change in lithofacies, palaeocurrents and sandstone composition, suggesting a switch in sediment supply to the footwall margin to the NW. The change in the sediment source is related to reduced footwall uplift, the possible presence of a relay ramp and/or supply from a captured antecedent drainage network. During SS4, the rate of creation of accommodation was exceeded by the sediment and water discharge. The stratigraphic evolution of lacustrine strata in the half‐graben was mainly controlled by tectonic processes, including subsidence rate and the growth and evolution of the border fault zone, but changing climate (inducing changes in water balance and lake level) and autocyclic processes (delta lobe switching) were also important. 相似文献
20.
David J. Went 《Sedimentology》2020,67(1):330-363
Lower Palaeozoic fluvial systems tend to be more sand-prone than those of later eras and the nature of coastal environments less certain. Field studies are presented that characterize the fluvial to marine transition over a distance of 80 km, in the Lower Cambrian of the Cotentin Peninsula, northern France. The sedimentary rocks are divided into six facies associations which represent deposition in proximal fluvial, distal fluvial, delta plain, delta front, pro-delta and offshore carbonate bank environments. The basin fill is sandstone-dominated and subdivided into three stratigraphic intervals. A 200 to 300 m thick basal interval contains very coarse-grained fluvial sandstones deposited during a relative sea level lowstand. An overlying interval, 250 to 1500 m thick, is a facies mosaic. Fluvial strata in the north-west pass laterally south-east into deltaic and shallow marine pro-delta sediments. The delta front deposits show repetitively stacked, upward-coarsening parasequences, 8 to 10 m thick, which reflect the repeated progradation of lobate, fluvially-dominated deltas onto a shallow marine shelf. The deltas formed following marine transgression and accumulated during a period of gradually rising relative sea level. An upper unit, 130 m thick, containing offshore stromatolitic and oolitic limestones, caps the study interval and represents deposition during a relative sea level highstand. The fluvial and delta distributary channel sandstones of the middle unit contain <1% mudstone. The cohesionless substrate determined that deltaic distributaries were predominantly braided in character and subject to common bifurcations which resulted in an ordered diminution of channel size and competence in a seaward direction. Terminal distributary channels show evidence of migratory levées and mouth-bars and consistently delivered fine to medium-grained sand to the delta front. The study highlights an example of pre-vegetation deltaic sedimentation that was hydraulically organized and predictable, despite being fed by braided fluvial systems with high levels of peak discharge. 相似文献