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1.
The Moodies Group in the Dycedale Syncline, Barberton Greenstone Belt consists of a 100–130 m-thick upward-fining succession that exhibits a transition from fluvial to tide-modified sedimentation. A basal, 10–30 m-thick conglomerate–sandstone interval of alluvial origin is overlain by stacked upward-fining, decimeter- to meter-scale cycles within which three facies are recognized: 1) conglomerate lag; 2) cross-bedded sandstone; and 3) interlaminated sandstone–siltstone and mudstone. Within the cycles, the abundance of mudstone drapes increases upwards. Structureless conglomerates and cross-beds lacking mudstone drapes record braided-alluvial processes. In contrast, cross-beds with mudstone drapes and interlaminated sandstone–siltstone and mudstone are products of flows modified by various tidal beats. Sand and/or silt transport took place during the ebb and flood stages and mudstone accumulated during slack water phases. Alternating thick–thin laminations reflect dominant and subordinate, twice-daily tides. Thicker groupings of foresets and thicker intervals of vertically stacked sandstone–siltstone and mudstone laminations are interpreted as spring tide deposits whereas thinner groupings of foresets and thinner laminations record neap tides. Desiccated mudstone drapes on foresets indicate that bedforms rarely were locally exposed during some portion of the tidal cycle. Abundant exposure structures in the interlaminated sandstone–siltstone and mudstone facies indicate that the cycles are upward shoaling. The stacked upward-fining cycles are attributed to alternating subaerial exposure and fluvial influx followed by marine inundation, probably related to absolute sea level fluctuations. Lack of high-order vegetation on the Archean landscape promoted rapid lateral migration or avulsion of tidally influenced fluvial channels.
The association of facies within the 100–130 m-thick upward-fining succession is comparable to Holocene and ancient paleovalley fills characterized by basal alluvial gradational upwards into estuarine facies. However, in the absence of vegetation, the land–ocean interface in the Archean probably consisted of laterally extensive fan or braid deltas rather than point sources of sediment characteristic of most modern rivers. The abrupt up-section change from syntectonic, high-energy, alluvial–fluvial flash flood deposits to tide-influenced sedimentation implies a proximal source that provided sediment to a shoreline influenced by strong tidal action. Possible Holocene analogues are orogenic settings such as the Canterbury Plains of New Zealand, the Indo-Gangetic Plains of India and strike-slip settings such as the Gulf of Aqaba but all three examples lack a direct transition to tidally influenced sedimentation. 相似文献
2.
During the Carboniferous Period the Yarrol and New England Orogens comprised an active depositional margin east of cratonised parts of Australia. Patterns of deposition within the orogens were probably controlled by dextral shear systems believed responsible for tectonism and the positions of the various depositional elements (volcanic chain, shelf, slope and basin, pull‐apart troughs and graben), and global changes in sea level. These patterns are illustrated by a series of non‐palin‐spastic palaeogeographic reconstructions. In the Early Carboniferous, similar patterns of deposition existed within the western volcanic chain, marine shelf, and eastern slope and basin provinces of both orogens. Sediments were deposited in two cycles. They range from volcanic fluvial and marine sandstone to siltstone, mudstone and turbidites. Complex depositional patterns within shelfal regions are shown in detailed palaeogeographic reconstructions. This uniform pattern changed during the latest Visean and Namurian, with the uplift of the New England Arch, subsidence of a non‐marine graben (Werrie Trough) to the west, and development of a new shelf in the east. The Werrie Trough received volcanics as well as fluvial and glacigene sediments, and the shelf marine sandstone and siltstone. The Yarrol Orogen was unaffected by tectonism but there was a change in provenance. Late in the Carboniferous the Yarrol Orogen was restructured by the intrusion of granitoids into the former volcanic chain, and development of the Yarrol and North D'Aguilar Troughs as probable pull‐apart basins. In the New England Arch, deformation and metamorphism were followed by intrusion of S‐type granitoids. A comparable episode of deformation and metamorphism affected the southeastern part of the Yarrol Orogen at the end of the Carboniferous Period. This partial cratonisation of the mobile zone was a prelude to widespread basin formation during the Permian Period. 相似文献
3.
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
4.
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
5.
The Hunghae Formation, SE Korea: Miocene debris aprons in a back-arc intraslope basin 总被引：1，自引：0，他引：1
ABSTRACT During early to middle Miocene times a sudden opening of the Ulleung (Tsushima) back-arc basin in the East Sea (Sea of Japan) led to the development of intraslope basins along the rifted southwestern margin (southeast Korea). Abrupt subsidence resulted in the deposition of the 200 m thick Hunghae Formation (middle Miocene), a sand/mudstone sequence that can be divided into five facies. Facies I (sand and mudstone couplet) and II (coarse sand) are turbiditic in origin, as evidenced by massive, graded, crudely-layered and parallel-laminated sand beds. Facies III (homogeneous mudstone) is characterized by various lignite and plant fragments, clastic and biogenic grains that are randomly oriented, suggestive of hemipelagic deposition. Facies IV (chaotic deposit) is characterized by the disruption of beds, the presence of isolated siltstone blocks (or balls) and large clasts in the muddy matrix, indicative of retrogressive rockfall and slide/slump. Facies V (conglomerate) is of debris flow origin, as evidenced by clast- and matrix-supported features, floating large clasts and absence of traction structures. Individual facies are organized into two types of facies association: (1) homogeneous mudstone (facies III) associated randomly with the rest (facies I, II, IV and V), indicative of hemipelagic and episodic sediment-gravity flow processes, respectively; (2) conglomerate (facies V), coarse sand (facies II) and sand/mudstone couplet (facies I), representing the flow transformation from debris flow to high- and low-concentration turbidity currents. These facies associations are similar in many respects to modern and ancient debris (or slope) aprons found elsewhere. Numerous isolated slide/slump blocks, wedged conglomerates with armoured mudstone balls, discontinuous lignite-containing sand/mudstone beds, chaotic structure and growth faults suggest that the deposition occurred on a steep slope (intraslope basin) off coalescing fan-deltas, mainly by unchannellized sediment-gravity flows. Ancient deposits with irregular facies sequences can be viewed as debris-apron systems, which provide alternatives to submarine-fan models in many clastic basins with a line rather than point source. 相似文献
6.
金宝屯盆地是一中生代内陆盆地。含煤地层为上侏罗统协尔苏组,主要由灰绿色、灰色砾岩和砂岩,灰黑色、黑色细砂岩和粉砂岩、泥岩及灰白色中—粗砂岩组成,平均厚110m。区内不同沉积环境,出现在盆地演化的不同阶段和盆地的不同部位。下部砾岩段沉积期以冲积扇环境为主;含煤段沉积期为冲积扇-河流-湖泊环境组合;成煤后演化为曲流河环境;上部砂岩砾岩段沉积期以辫状河沉积为主。聚煤作用发育于盆地中的湖泊分布区,发生于盆地快速沉降之后的整体稳定、缓慢沉降阶段的早期,煤层直接覆于湖相厚层泥岩之上。盆地仅经历了一个快—慢沉降旋回,煤层的形成受控于这种“无振荡聚煤作用”。 相似文献
7.
Dr. Satyendra M. Casshyap 《International Journal of Earth Sciences》1975,64(1):610-640
Regional patterns of sandstone distribution were examined in the coal-bearing Bochumer Formation with the help of fence diagrams and isolith (thickness) maps. In addition, isolith maps and cross-sections were drawn for some well defined sandstone bodies, like Dickebank sandstone (Lower), Röttgersbank sandstone (Middle), and Matthias sandstone (Upper), and sand-mud ratio maps were prepared, on which isolith contours showing the total thickness of coal were superimposed. Most sandstone bodies are oriented west-southwest; they are elongate, straight to sinuous, show bifurcation and branching, and closely resemble sand-bodies designated as belt and dendroid. The area with greater thickness (50 m or more) of sandstone and poorer in mudstone (sand-mud ratio > 1.0) is linearly distributed to the north in the Lower unit, but shifts toward the south in the Middle and Upper units. Interrelationship between certain stratigraphic variables was investigated statistically, and it is concluded that the total thickness of strata or net subsidence of the basin exhibits direct relationship with the number and thickness of sandstone, rooty bed, and coal. A synthesis of integrated results reveals that the sediments of the Bochumer Formation were transported to and across the basin down the regional paleoslope toward west-southwest, and partly toward northwest; that it was a longitudinal marginal basin; and that the depositional environment consisted mainly of a high-constructive delta plain, in which distributary and tributary channels and their subenvironments including natural levees and coal-forming swamps developed and migrated constantly across the plain to give rise to characteristic interbedded (cyclic) sequence. 相似文献
8.
9.
The Salvan‐Dorénaz Basin formed during the Late Palaeozoic within the Aiguilles‐Rouges crystalline basement (Western Alps) as an asymmetric, intramontane graben elongated in a NE–SW direction and bounded by active faults. At least 1700 m of fluvial, alluvial fan and volcanic deposits provide evidence for a strong tectonic influence on deposition with long‐term, average subsidence rates of > 0·2 mm yr?1. The early basin fill was associated with coarse‐grained alluvial fans that were dominated by braided channels (unit I). These issued from the south‐western margin of the basin. The fans then retreated to a marginal position and were overlain by muddy floodplain deposits of an anastomosed fluvial system (unit II) that drained towards the NE. Deposition of thick muds resulted from a reduction in the axial fluvial gradient caused by accelerated tectonic subsidence. Overlying sand‐rich meandering river deposits (unit III) document a reversal in the drainage direction from the NE to the SW caused by synsedimentary tectonism, reflecting large‐scale topographic reorganization in this part of the Variscides with subsidence now preferentially in the W and SW and uplift in the E and NE. Coarse‐grained alluvial fan deposits (unit IV) repeatedly prograded into, and retreated from, the basin as documented by coarsening‐upward cycles tens of metres thick reflecting smaller scale tectonic cycles. Volcanism was active throughout the evolution of the basin, and U/Pb isotopic dating of the volcanic deposits restricts the time of basin development to the Late Carboniferous (308–295 Ma). 40Ar/39Ar ages of detrital white mica indicate rapid tectonic movements and exhumation of the nearby basement. In unit I, youngest ages are close to that of the host sediment, but the age spectrum is wide. In unit II, high subsidence and/or sedimentation rates coincide with very narrow age spectra, indicating small, homogeneous catchment areas. In unit III, age spectra became wider again and indicate growing catchment areas. 相似文献
10.
为了深入认识河流相储层分布规律,通过地层对比、沉积相、主控断裂特征等分析对饶阳凹陷留北地区新近系河流相砂体展布特征及影响因素进行了研究.结果表明:饶阳凹陷新近系各超短期旋回的砂体在平面上呈带状展布,砂体主要延伸方向与边部控洼断层大致平行.留北地区的NE向及NEE向主控断裂在新近纪仍表现为继承性生长的特征,受NE及NEE向近平行于盆地轴向的盆缘继承性主控断裂的影响,在下降盘形成大致平行于其轴向的河谷洼地、斜坡或山脊复合古地貌体系,断层上盘发育的沉降中心沿轴向延伸,地层厚度呈NE向展布.盆缘断层附近发育高梯度扇体或河流沉积,以沉积物的横向搬运体系为主.远离物源区,在主控断层下降盘,来自短轴物源的横向河流或冲积扇的影响变弱,河流向着轴向倾斜下端方向(最大斜坡方向)改道,汇聚形成轴向搬运沉积体系,平行于主要断层边界走向的方向延伸. 相似文献
11.
The cyclic arrangement of lithofacies of the Karharbari Formation of the Damuda Group from a part of the Talchir Gondwana
basin has been examined by statistical techniques. The lithologies have been condensed into five facies states viz. coarse-,
medium-, fine-grained sandstones, shale and coal for the convenience of statistical analyses. Markov chain analysis indicates
the arrangement of Karharbari lithofacies in form of fining upward cycles. A complete cycle consists of conglomerate or coarse-grained
sandstone at the base sequentially succeeded by medium-and fine-grained sandstones, shale and coal at the top. The entropy
analysis categorizes the Karharbari cycles into the C-type cyclicity, which is essentially a random sequence of lithologic
states. Regression analysis undertaken in the present study indicates the existence of sympathetic relationship between total
thickness of strata (net subsidence) and number and average thickness of sedimentary cycle and antipathic relationship between
number and average thickness of sedimentary cycle. These observations suggest that cyclic sedimentation of the Karharbari
Formation was controlled by autocyclic process by means of lateral migration of streams activated by intrabasinal differential
subsidence, which operated within the depositional basin and the channels carrying coarse grade clastic sediments, which make
the cycles thicker, tend to be more common in the areas of maximum subsidence. Clastic sediments issued from the laterally
migrating rivers interrupted the cyclic sedimentation of the Karharbari Formation in many instances. 相似文献
12.
13.
The Upper Jurassic Guará Formation comprises an 80–200 m thick continental succession exposed in the western portion of the Rio Grande do Sul State (Brazil). It comprises four distinct facies associations: (i) simple to locally composite crescentic aeolian dune sets, (ii) aeolian sand sheets, (iii) distal floodflows, and (iv) fluvial channels. The vertical stacking of the facies associations defines several 5–14 m thick wetting-upward cycles. Each cycle starts with aeolian dune sets followed by aeolian sand sheets deposits and culminating in either fluvial channels or distal flood strata. Within some cycles, aeolian sand sheets are absent and fluvial deposits rest directly above aeolian dune facies. The transitions from one facies association to another are abrupt and marked by erosive surfaces that delineate distinct episodes of sediment accumulation. The origin of both the wetting-upward cycles and the erosive surfaces was controlled by the ground-water table level, dry sand availability and aeolian and fluvial sediment transport capacity variations, related to climatic fluctuations between relatively arid and humid conditions. Preservation of the fluvial–aeolian deposits reflects an overall relative water table rise driven by subsidence. 相似文献
14.
The 400 m of Blomidon redbeds accumulated in a semi-arid rift valley in the subtropics. At St Mary's Bay, these redbeds are 64% sandy mudstone (playa mudflats), 25% graded beds (sandflats at the toes of alluvial fans), 10% fissile claystone (playa lakes), and 1% channel sandstone (stream channels). Flash floods in mountains south of the valley flowed down alluvial fans to spread out to the north-east as sheet flows on sandflats and playa mudflats. Deceleration of the sheet flows deposited graded beds 2–83 cm in thickness on the sandflats and thin layers of mud on the playas. Nine sequences, consisting of arrangements of six lithologies, compose 90% of the graded beds. In order of decreasing abundance, these are: ripple cross-laminated siltstone → horizontally laminated mudstone; fining-upward, ripple cross-laminated siltstone; ripple cross-laminated sandstone → horizontally laminated mudstone; cross-bedded sandstone horizontally laminated mudstone; ripple cross-laminated sandstone → ripple cross-laminated siltstone; rippledrift cross-laminated siltstone horizontally laminated mudstone; fining-upward, ripple-drift cross-laminated siltstone; cross-bedded sandstone → ripple cross-laminated siltstone; and cross-bedded sandstone → ripple cross-laminated siltstone → horizontally laminated mudstone. The sheet flows, perhaps up to 1 m in depth, had a high concentration of suspended load. Deposition was dominantly during lower flow regime conditions and moderate to rapid flow deceleration. There are 32 thinning and fining-up cycles where a sandflat package of graded beds is transitionally followed by a playa package of sandy mudstone. The cycles range in thickness from 1·3 to 13·3 m, averaging 4·6 m. Each cycle is initiated by avulsion to a new active channel network on a fan. Gradual abandonment of the channel network produces the thinning and fining-up cycle. The cycles are grouped in three 60–70 m fining-up megacycles. Upwards within each megacycle, the packages of sandy mudstone compose a progressively larger proportion of the cycles. Each megacycle evidently was initiated by a brief period of tectonic movement on the border faults that produced greater relief of the highlands relative to the valley floor. Subsequent erosion gradually lowered the relief to yield a fining-up megacycle. 相似文献
15.
《Quaternary Science Reviews》2007,26(22-24):2758-2782
The paper discusses the Quaternary evolution of the Danube and Tisza rivers and their main tributaries in the context of evolution of the entire Pannonian Basin, which is Europe's largest intramontane basin, within the Alp–Carpathian orogen. The palaeo-drainage reconstruction of the Pannonian Basin for the pre-Quaternary period is outlined in connection with the gradual regression of Lake Pannon since the Late Miocene. Deltas of rivers that entered the basin from the northwest and northeast were gradually transformed into extended alluvial plains; thus, the earliest possible ancestor of the Danube coming southeastwards from the Alps could be as old as Late Miocene. By the Pliocene the whole Lake Pannon was infilled. The former extensional basin formation was replaced by a compresional stress field, which resulted in an uplift of the marginal flanks and late-stage subsidence anomalies. The increasing relief led to the formation of the Quaternary drainage pattern. The actively subsiding young basins were filled by fluvial sediments, transported by the Danube and Tisza river systems from the uplifting mountains. Between the subsiding regions of the Little and Great Plains, the Danube has formed an antecedent valley with terrace staircases between the uplifting sections of the Transdanubian Range and the North Midmountains. The formation of the terraces is attributed to periodic climate changes during the Pleistocene combined with differences in the uplift rate. The paper gives a complex overview of the classical chronology of the six terraces based on various data sources: mostly dating of loess/paleosol sequences, travertines, aeolian sand, and tephra strata overlying the fluvial sediments, complemented by scattered vertebrate faunal data and archaeological evidence directly from the terrace sediments.The Quaternary drainage pattern evolution of the Great Plain, with a strong tectonic control, is discussed in detail. Rivers originating from the uplifting marginal areas were drawn towards the subsiding depressions which served as local base level. Changes in subsidence rates in space and time throughout the Quaternary resulted in the evolution of a complex drainage pattern. A special emphasis is placed on the Late Pleistocene–Holocene development of the Middle–Tisza region and the Körös basin, where the Berettyó–Körös Rivers form an eastern tributary system of the Tisza River. A comparative evaluation of these two areas is especially relevant, as they provide insights into large-scale Late Pleistocene avulsion of the Tisza River. OSL dating, complemented with inferred transport directions determined from heavy mineral analysis of fluvial sediments in the Körös basin, has revealed an ancient large meandering river system that can be identified with the palaeo-Tisza, which was flowing along a tectonically controlled depression during the Late Pleniglacial. Successions in the Middle Tisza region have allowed differentiation between the older channels of the palaeo-Bodrog River and the Sajó–Hernád alluvial fan and the younger meander belts of the new course of the Tisza. In the Tisza system, changes in river style (braided to various scales of meandering) show correspondence to millennial-scale climate changes of the last 25 ka, while in the Körös basin the effects of tectonics are overprinted onto the regional climatic signals. 相似文献
16.
The Lower Cretaceous (Albian) upper Blairmore Group is part of a thick clastic wedge that formed adjacent to the rising Cordillera in south-western Alberta. Regional transgressive intervals are superimposed on the overall regressive succession. Alluvial conglomerates, sandstones and mudstones were deposited in east-north-eastward draining fluvial systems, orientated transverse to the basin axis. Five facies associations have been identified: igneous pebble conglomerate, thick sandstone, interbedded lenticular sandstone and mudstone, thick mudstone with thin sandstone interlayers, and fossiliferous sandstone and mudstone. The facies associations are interpreted as gravelly fluvial channels, sandy fluvial channels, sand-dominated floodplains, mud-dominated floodplains, and marine shoreline deposits, respectively. Five types of palaeosols are recognized in the upper Blairmore Group based on lithology, the presence of pedogenic features (clay coatings, root traces, ferruginous nodules, slickensides, carbonate nodules) and degree of horizonization. The regional distribution of the various types of palaeosols enables a refinement of the palaeoenvironmental reconstruction permitting an assessment of the controls on floodplain evolution. In source-proximal areas, palaeosol development was inhibited by high rates of sedimentation. In source-distal locations, poor drainage resulting from high watertables, low topography and lower rates of sedimentation also inhibited palaeosol development. The best-developed palaeosols (containing Bt horizons) occur in intermediate alluvial plain positions (tectonic hinge zone) where the floodplains were most stable due to a balance between sedimentation, erosion and subsidence rates. Extrapolating from the upper Blairmore Group suggests that the tectonic hinge zone of continental foreland basins can be established by palaeosol analysis. At the hinge zone, soil development is controlled primarily by climate and tectonics and their effect on sediment supply, whereas closer to the palaeoshoreline, relative sea level fluctuations, resulting in poor drainage, may have a more significant influence. 相似文献
17.
José López-Gómez Alfredo Arche Henar Vargas Mariano Marzo 《Sedimentary Geology》2010,223(3-4):320-333
The stratigraphy of a sedimentary basin is mainly the result of the long-term response of a depositional surface to prolonged subsidence. However, the real nature of interrelations between fluvial architecture and subsidence is still unknown. Herein, we present new data on these relationships by combining the results of detailed sedimentological field work with data acquired through automated forward modelling and backstripping for the alluvial Permian and Triassic sediments of the SE Iberian Ranges. Using this methodology, we determined tectonic subsidence of the basin by means of backstripping analysis and crust and lithospheric mantle stretching factors (δ and β, respectively) using forward modelling technique. Results indicated that a configuration of two individual and independent layers during lithospheric subsidence for each tectonic phase fit better for this time of the studied basin evolution than the assumption of subsidence due to a single layer spanning the whole lithosphere.For this study, we simplified fluvial geometries as two main types: isolated (I) and amalgamated (A), with subtypes in each case. Different order bounding surfaces (b.s.) were distinguished in the field, although we only selected those affecting the whole basin under study. These included those b.s. of clear tectonic origin, ranging from individual basin boundary-fault pulses produced over periods of approximately 1 My to those arising from major tectonic events, such as the beginning of extension in the basin, causing major changes in basin geometry over periods of 3–5 My.The comparison of δ and β values and fluvial geometries for each identified tectonic phase in the basin evolution, revealed some possible relationship between subsidence and fluvial geometry: Sections showing the most varied fluvial architectural geometries, including ribbon and nested forms, were related to higher β and δ stretching factors values indicating tectonic phases of greater stretching and subsidence. When both stretching factors were similar and close to 1, fluvial geometry was basically reduced to amalgamated geometry type. Wider ranging of fluvial geometries was associated with stages of basin development in which crust and upper mantle activities differed, that is, showing larger differences of β and δ stretching factors values. The related slope changes are proposed as the main surface control of fluvial styles.Combination of subsidence with other possible controlling factors such as avulsion rate, climate or budget of sediments, gives rise to the definitive alluvial architecture of a basin. 相似文献
18.
Electronic computers have enabled the quantitative relationships between stratigraphic variables to be calculated for a sequence of Namurian (E1 zone) cycles deposited in a differentially subsiding basin east of Stirling. Despite their limitations, coefficients of correlation and linear regression equations provide a relatively simple means of expressing the relationships between critical variables and so provide a useful way in which various cyclically deposited sequences can be compared. All possible pairs chosen from eleven variables are investigated, including the total number and average thickness of cycles, total number of coals and total thicknesses of coal, sandstone and shale. These six variables all tend to show a linear relationship with total thickness of strata and hence net subsidence. A second part of this paper, to be published later, will examine the relationships between variables in more detail, using the technique of factor analysis. 相似文献
19.
Shallowing‐upward, decametre‐scale, Palaeoproterozoic iron formation cycles in northern Wisconsin record the combined effects of tectonism and changing oceanographic conditions on a storm‐dominated shelf. Cycles consist of a lower unit of laminated, Fe‐ and Si‐rich chemical mudstone that is transitional into an upper unit dominated by trough cross‐stratified chert grainstone. Grainstone lenses become progressively thicker upwards in cycles with the largest at cycle tops, where they are sharply overlain by a unit of slumped chemical mudstone. The cycles developed through progradation when offshore‐directed storm currents transported chert sand intraclasts that were formed in nearshore settings into middle and distal shelf environments. Abrupt subsidence events, probably resulting from normal faulting associated with extensional tectonism, repeatedly terminated chert grainstone accumulation and may also have generated the slumped units at cycle boundaries. The episodic storm currents are also interpreted to have transported biologically oxygenated waters from the shallow‐water, inner shelf into otherwise anoxic bottom waters of the strongly stratified distal shelf. The consequence of such transport and mixing was rapid deposition of chemical mud, mainly as precipitated Fe‐oxide. In many cases, the resultant decrease in Fe2+ in the water column, together with pelagic inorganic precipitation of SiO2 and rainout of terrigenous clays, resulted in submillimetre‐ to millimetre‐thick, chemically graded laminae. The concomitant decreasing Fe2+/Mn2+ ratio also led to increasing Mn‐compound precipitation and enrichment in the upper portions of some chemically graded layers. 相似文献
20.
Raymond V. Ingersoll 《Sedimentary Geology》1978,21(3):205-230
The Upper Cretaceous part of the Great Valley Sequence provides a unique opportunity to study deep-marine sedimentation within an arc-trench gap. Facies analysis delineates submarine fan facies similar to those described from other ancient basins. Fan models and facies of Mutti and Ricci-Lucchi allow reconstruction of the following depositional environments: basin plain, outer fan, midfan, inner fan, and slope. Basin plain deposits are characterized by hemipelagic mudstone with randomly interbedded thin sandstone beds exhibiting distal turbidite characteristics. Outer fan deposits are characterized by regularly interbedded sandstone and mudstone, and commonly exhibit thickening-upward (negative) cycles that constitute depositional lobes. The sandstone occurs as proximal to distal turbidites without channeling. Midfan deposits are characterized by the predominance of coarse-grained, thick, channelized sandstone beds that commonly are amalgamated. Thinning-upward (positive) cycles and braided channelization also are common. Inner fan deposits are characterized by major channel-fill complexes (conglomerate, pebbly sandstone, and pebbly mudstone) enclosed in mudstone and siltstone. Positive cycles occur within these channel-fill complexes. Much of the fine-grained material consists of levee (overbank) deposits that are characterized by rhythmically interbedded thin mudstone and irregular sandstone beds with climbing and starved ripples. Slope deposits are characterized by mudstone with little interbedded sandstone; slumping and contortion of bedding is common. Progressions of fan facies associations can be described as retrogradational and progradational suites that correspond, respectively, to onlapping and offlapping relations in the basin. The paleoenvironments, fan facies associations, and tectonic setting of the Late Cretaceous fore-arc basin are similar to those of modern arc—trench systems. 相似文献