Unincised fluvial and tide-dominated estuarine systems from the Mesoproterozoic Lower Tombador Formation,Chapada Diamantina basin,Brazil

The Mesoproterozoic Lower Tombador Formation is formed of shallow braided fluvial, unconfined to poorly-channelized ephemeral sheetfloods, sand-rich floodplain, tide-dominated estuarine, and shallow marine sediments. Lowstand braided fluvial deposits are characterized by a high degree of channel amalgamation interbedded with ephemeral, intermediate sheetflood sandstones. Sand-rich floodplain sediments consist of intervals formed by distal sheetflood deposits interbedded with thin layers of eolian sandstones. Tide-dominated estuarine successions are formed of tide-influenced sand-bed braided fluvial, tidal channel, tidal sand flat and tidal bars. Shallow marine intervals are composed of heterolithic strata and tidal sand bars. Seismic scale cliffs photomosaics calibrated with vertical sections indicate high lateral continuity of sheet-like depositional geometry for fluvial–estuarine successions. These geometric characteristics associated with no evidence of incised-valley features nor significant fluvial scouring suggest that the Lower Tombador Formation registers deposition of unincised fluvial and tide-dominated systems. Such a scenario is a natural response of the interplay between sedimentation and fluctuations of relative sea level on the gentle margins of a sag basin. This case study indicates that fluvial–estuarine successions exhibit the same facies distributions, irrespective of being related to unincised or incised-valley systems. Moreover, this case study can serve as a starting point to better understand the patterns of sedimentation for Precambrian basins formed in similar tectonic settings.     

Architecture of vertically stacked fluvial deposits,Atane Formation,Cretaceous, Nuussuaq,central West Greenland

Excellent exposures of thick, multistorey, fluvial deposits from the deltaic Atane Formation on south‐east Nuussuaq, central West Greenland, show the architecture of up to 100 m thick continuously aggrading fluvial depositional complexes. The succession comprises vertically stacked channel belt sandstones separated by thin floodplain deposits, with little to no incision between storeys. Architectural elements and palaeocurrent patterns of channel deposits indicate deposition in large, relatively stable, low‐sinuosity rivers, probably located within an incised valley. Gradual transitions from channel to floodplain deposits accompanied by a gradual change from floodplain to spillover sand suggest avulsion on the floodplain as a possible mechanism for the vertically alternating channel and floodplain deposits. Despite its relative proximity to contemporaneous sea‐level (ca 35 km upstream from the palaeo‐shoreline) the depositional complex is entirely non‐marine. The aggrading nature of the deposits suggests a continuously rising base level coupled with a high and steady sediment supply. Vertical alternations between floodplain and channel deposits may be forced by subtle interruptions in this balance or autocyclic mechanisms on the floodplain. This study provides an example of aggrading lowstand/non‐marine transgressive systems tract deposits.     

Formation of braided river floodplains, Waimakariri River, New Zealand

Floodplains along the braided gravel-bed Waimakariri River are discontinuous although generally extensive landforms composed predominantly of gravel bars capped with vertically accreted fines. In order of importance, three mechanisms lead to floodplain formation. River bed abandonment by lateral migration of the braid-train initiates the formation of the largest floodpiains, which usually occur downstream of tributary fans and valley bedrock spurs. In the headwater reaches, localized river bed aggradation during high magnitude events leads to floodplain formation by producing a surface resistant to erosion by lesser events due to either the coarse nature of the deposit, or by its elevation over the river bed, or both. The least important mechanism initiating floodplain development is localized river or channel incision. A six stage model is proposed for the sequential development of floodplains on the Waimakariri River from: (i) active river bed; (ii) stabilizing bar; (iii) incipient floodplain; (iv) established floodplain; (v) mature floodplain; and to (vi) terrace. Two mechanisms, lateral migration by the braid-train and reactivation of abandoned channels within floodplains, operating separately or in combination, are responsible for floodplain reworking and their relatively young age (<250 years). Clearly, braided rivers can construct substantial areas of well developed floodplain.     

辫状河流演变过程与机理的研究进展

辫状河流属于冲积河流的主要类型,对流水地貌景观、水生栖息地和河流开发与生态保护具有重要科学意义。根据辫状河流演变过程与机理的国内外研究进展,对定义与形态特征进行综合描述,并给出常用的形态表征方法与参数。总结辫状河流的4种野外地形观测方法以及水槽试验和数值模型的应用,比较它们的适合范围;描述辫状河流的不同形态单元的组成,列举沙洲形成、汊道调整与横向迁移、岸滩侵蚀、河漫滩淤积等基本演变规律;对比分析水流功率、床沙粒径、泥沙补给、滨河植被、河谷宽度等影响辫状河流形态动力学过程的主要控制因素;指出青藏高原不同空间尺度辫状河流的形成原因、形态特征和演变规律是河流动力学的重要研究方向。     

A simulation model of alluvial stratigraphy

The quantitative model presented simulates the development of a two-dimensional alluvial sedimentary succession beneath a floodplain traversed by a single major river. Several inter-related effects which influence the distribution of channel-belt sand and gravel bodies within overbank fines are accounted for. These are (a) laterally variable aggradation, (b) compaction of fine sediment, (c) tectonic movement at floodplain margins, and (d) channel avulsion. Selected experiments with the model show how the interconnectedness and areal density of channel-belt deposits decrease with increasing floodplain width/channel-belt size, mean avulsion period, and channel-belt aggradation rate. Separation of stream patterns based on interconnectedness and channel deposit density is difficult. Tectonic movements do not have a significant influence upon the successions unless a preferred direction of tilting is maintained (half-graben). Then channel-belt deposits showing offlap tendencies tend to cluster adjacent to the active floodplain margin, leaving dominantly fine-grained alluvium to accumulate on the inactive side. Individual channel-belt deposits thicken during aggradation, although a self-regulating limit to such thickening is likely to operate. ‘Multistorey’features resulting from aggradation may be difficult to tell apart from those arising through superposition of distinct channel-belt deposits of avulsive origin.     

Late Quaternary stratigraphic development in the lower Luni,Mahi and Sabarmati river basins,western India

This study reviews the Quaternary alluvial stratigraphy in three semi-arid river basins of western India i.e., lower Luni (Rajasthan), and Mahi and Sabarmati (Gujarat alluvial plains). On the basis of OSL chronologies, it is shown that the existing intra-valley lithostratigraphic correlations require a revision. The sand, gravel and mud facies are present during various times in the three basins, however, the fluvial response to climate change, and the resulting facies associations, was different in the Thar desert as compared to that at the desert margin; this makes purely lithostratigraphic correlations unviable. It is further shown that the rivers in the Thar desert were more sensitive to climate change and had small response times and geomorphic thresholds as compared to the desert-margin rivers. This is illustrated during the early OIS 1, when the Luni river in the Thar desert was dynamic and showed frequent variations in fluvial styles such as gravel bedload braided streams, sand-bed ephemeral streams and meandering streams, all followed by incision during the early Holocene. The coeval deposits in Sabarmati, however, only show a meandering, floodplain-dominated river. Late Quaternary alluvial deposits in these basins unconformably overlie some older deposits that lack any absolute chronology. Based on the facies types and their associations, and the composition and architecture of the multistoried gravel sheets in the studied sections, it is suggested that older deposits are of pre-Quaternary age. This hypothesis implies the presence of a large hiatus incorporating much of the Quaternary period in the exposed sections     

Natural hazards in the Ghaghara River area, Ganga Plain, India

The Ganga Plain is one of the most densely populated regions of the world due to its fertile soil and availability of water. The rivers of this plain are the lifeline for millions of people of this vast alluvial plain. All rivers of this plain are characterized by narrow channel confined within wide valley. Continuously increasing pressure of population on this plain has led to the intensification of settlement even into the valley of the river. This unplanned expansion has enhanced the damage due to flooding during high-discharge period and lateral erosion during low-discharge period. Flooding and lateral erosion are identified as fluvial hazards in the Ghaghara River area. Extensive studies have been carried out on flooding, but not much attention has been paid to the phenomenon of lateral erosion. However, it has been observed that lateral erosion is an independent fluvial hazard that operates during low-discharge period. Low degree of compaction due to the presence of sandy and silty facies in the river valley deposits, mass movement, palaeocurrent pattern, and fractures initiates and enhances the lateral erosion. The present paper deals with the fluvial hazards in the Ghaghara River area.     

Quaternary stratigraphy of the Koratallaiyar-Cooum basin,Chennai

In this paper we present Quaternary stratigraphy of the area around Chennai based on archaeological findings on the ferricrete surface, geomorphological observations supplemented by radiocarbon dating. The coastal landscape around Chennai, Tamil Nadu, has preserved ferruginised boulder gravel deposits, ferricretes and fluvial deposits of varying thickness. The area studied is approximately 150 km east to west and 180 km north to south with a broad continental shelf towards the seaward. Several rivers enter the Bay of Bengal along its shores like the Koratallaiyar, Cooum and the Adyar. Precambrian charnockite and Upper Gondwana sandstone and shale bedrock rim the shelf margin. For the most part, the Upper Pleistocene-Holocene fluvial sediments overlie an erosion surface that has cut into older Pleistocene sediments and ferricrete surface. Incised valleys that cut into this erosion surface are up to 5–6 km wide and have a relief of at least 30 m. The largest valley is that cut by the Koratallaiyar River. Holocene sediments deposited in the incised valleys include fluvial gravels, early transgressive channel sands and floodplain silts. Older Pleistocene sediments are deposited before and during the 120-ka high stand (Marine isotope stage 5). They consist of ferricretes and ferricrete gravel formed in nearshore humid environments. Muddy and sandy clastic sediments dated to the ca. 5 ka highstand suggest that the climate was semi arid at this time with less fluvial transport. The coarsening up sequence indicates deposition by high intensity channel processes. Pedogenic mottled, clayey silt unit represents an important tectonic event when the channel was temporarily drained and sediment were sub aerially exposed. Uplift of the region has caused the local rivers to incise into the landscape, forming degradation terraces.     

River floodplain relocations and the abandonment of Aborigine settlements in the Upper Amazon Basin: A historical case study of San Miguel de Cunibos at the Middle Ucayali River

Lathrap introduced the concept of lateral channel migration of the meandering rivers as a potential factor for human community dynamics in the Upper Amazon. Nevertheless, the dynamics considered by Lathrap is restricted to particular floodplains. He payed no attention to a large scale fluvial phenomenom: the sudden river relocations (avulsion), which also profoundly affected the Upper Amazon cultures. We present here a historical case study analyzing a river floodplain avulsion at the Middle Ucayali River during the late 1700s, causing the abandonment of a settlement called San Miguel de Cunibos and probably leading to the massive migration of the Cunibos Indians. Furthermore, we argue that similar situations have frequently occurred during the human history of the Upper Amazon, and thus these fluvial phenomena should be taken into consideration in future archaeological and ethnohistorical studies. © 1996 John Wiley & Sons, Inc.     

从端点走向连续:河流沉积模式研究进展述评

从河道类型的划分、河床演变与河型转换、河道沉积与河流砂体的建筑结构要素、河漫滩沉积、季节性河流与分支河流体系、河流沉积相模式、河流沉积学研究技术与方法等方面对国内外河流沉积模式的研究进展进行了综述,认为近十年来河流沉积学的理论和方法都发生了重要的变化。地貌学家、沉积学家和工程师认识到河道形态是连续可变的,而不是只有4~40多个端点类型。河床的演变受河床比降、流量变幅、河岸沉积物粒度构成、气候、植被以及构造沉降速率等多方面的影响。垂向剖面分析法难以对古河流类型做出正确的判断,运用建筑结构要素分析法重建河道内大型底形的地貌形态是河型判别和河流相模式重建的正确方法。河漫滩是河流沉积事件记录最为齐全的部位,对河漫滩、天然堤和泛滥平原沉积层序的研究能够揭示更多古河流沉积过程以及古环境、古气候和古生物方面的信息。对季节性河流、受季风强烈影响地区的河流、以及不同气候带河流所发育的独特沉积构造和建筑结构要素的研究不断增加。分支河流体系的概念得到越来越多的应用,但也得到不少质疑。我国学者应当注重对现代河流地貌形态和沉积过程的观察,把河床演变学的定量方法与沉积学的观点、理论和资料相结合,利用露头、三维地震资料和探地雷达技术建立河流砂体内部建筑结构信息数据库,加强对古河流河漫滩和泛滥平原的沉积过程、特征及其控制因素的研究,加强对不同构造和气候条件下河流沉积的差异性研究,不断发展河流沉积学研究技术,加强河流沉积学实验室建设和研究队伍建设,加强国际交流与合作,使我国河流沉积学为国家经济社会发展提供更加有力和有效的支撑,为推动国际河流沉积学发展做出中国人自己的贡献。     

Braided rivers within an arid alluvial plain (example from the Lower Triassic,western German Basin): recognition criteria and expression of stratigraphic cycles

Based on a detailed sedimentological analysis of Lower Triassic continental deposits in the western Germanic sag Basin (i.e. the eastern part of the present‐day Paris Basin: the ‘Conglomérat basal’, ‘Grès vosgien’ and ‘Conglomérat principal’ Formations), three main depositional environments were identified: (i) braided rivers in an arid alluvial plain with some preserved aeolian dunes and very few floodplain deposits; (ii) marginal erg (i.e. braided rivers, aeolian dunes and aeolian sand‐sheets); and (iii) playa lake (an ephemeral lake environment with fluvial and aeolian sediments). Most of the time, aeolian deposits in arid environments that are dominated by fluvial systems are poorly preserved and particular attention should be paid to any sedimentological marker of aridity, such as wind‐worn pebbles (ventifacts), sand‐drift surfaces and aeolian sand‐sheets. In such arid continental environments, stratigraphic surfaces of allocyclic origin correspond to bounding surfaces of regional extension. Elementary stratigraphic cycles, i.e. the genetic units, have been identified for the three main continental environments: the fluvial type, fluvial–aeolian type and fluvial/playa lake type. At the time scale of tens to hundreds of thousands of years, these high‐frequency cycles of climatic origin are controlled either by the groundwater level in the basin or by the fluvial siliciclastic sediment input supplied from the highland. Lower Triassic deposits from the Germanic Basin are preserved mostly in endoreic basins. The central part of the basin is arid but the rivers are supplied with water by precipitation falling on the remnants of the Hercynian (Variscan)–Appalachian Mountains. Consequently, a detailed study of alluvial plain facies provides indications of local climatic conditions in the place of deposition, whereas fluvial systems only reflect climatic conditions of the upstream erosional catchments.     

Facies and architectural element analysis of a meandering fluvial succession: The Permian Warchha Sandstone, Salt Range, Pakistan

The 30 to 155 m thick Early Permian (Artinskian) Warchha Sandstone of the Salt Range, Pakistan is a conglomerate, sandstone and claystone succession within which seven lithofacies types (Gt, St, Sp, Sr, Sh, Fl and Fm) occur in a predictable order as repeated fining-upward cycles. Common sedimentary structures in the conglomerates and sandstones include planar and trough cross-bedding, planar lamination, soft sediment-deformed bedding, compound cosets of strata with low-angle inclined bounding surfaces and lags of imbricated pebbles. Structures in the finer-grained facies include desiccation cracks, raindrop imprints, caliche nodules and bioturbation. Groups of associated facies are arranged into nine distinct architectural elements (channels, gravel bars, sandy bedforms, downstream and laterally accreting barforms, sand sheets, crevasse splays, levees, floodplain units and shallow lakes), which is consistent with a fluvial origin for the succession. The types of architectural elements present and their relationship to each other demonstrate that the Warchha Sandstone preserves a record of a meandering river system that drained the northern margin of Gondwanaland. The dominance of fine-grained (floodplain) facies over gravel-grade (channel-base) facies and the widespread occurrence of large-scale lateral accretion elements supports the interpretation of a high-sinuosity, meandering fluvial system in which channel bodies accumulated via the lateral accretion of point bars but in which the active channels covered only a small part of a broad floodplain at any time instant. Although the regional and temporal distribution of these deposits is complex, in broad terms the lower part is dominated by stacked, multistorey channel bodies, whereas single-storey channel elements isolated in abundant fine-grained floodplain deposits dominate the middle and upper parts of the formation.     

Exhumed channel sandstone networks within fluvial fan deposits from the Oligo-Miocene Caspe Formation, South-east Ebro Basin (North-east Spain)

The Oligo‐Miocene Caspe Formation corresponds to the middle fluvial facies of the wider Guadalope‐Matarranya fluvial fan, located in the South‐east Ebro foreland basin (North‐east Spain). At the time of the Caspe Formation deposition, this sector of the Ebro basin underwent a very continuous, moderate sedimentation rate. Lithofacies comprise deposits from channellized and unchannellized flows. Channellized flow lithofacies form multi‐storey ribbon‐like sandstone bodies that crop out as extensive sandstone ridges belonging to exhumed channel networks. Width/thickness ratios of these channel‐fill bodies average close to six. Sinuosity is usually low (most common values around 1·1), although it can be high locally (up to 2). Thicknesses range from a few metres to 15 m. Unchannellized flow lithofacies form tabular bodies that can be ascribed to overbank deposits (levées, crevasse splays and fine‐grained floodplain deposits) and also to frontal lobes, although recognition of this last case requires exceptional outcrop conditions or geophysical subsurface studies. The unchannellized flow lithofacies proportion ranges from 75% to 97·8%. Methods applied to this study include detailed three‐dimensional architectural analysis in addition to sedimentological analysis. The architecture is characterized by an intricate network of highly interconnected ribbon‐like sandstone bodies. Such bodies are connected by three kinds of connections: convergences, divergences and cross‐cuttings. Although the Caspe Formation lithofacies and architecture resemble anastomosed channels (low topographic gradient, high preservation potential, moderate aggradation rate, high lateral stability of the channels, dominance of the ribbon‐like morphologies and high proportion of floodplain to channel‐fill sediments), an unambiguous interpretation of the channel networks as anastomosed or single threaded cannot be established. Instead, the observed architecture could be considered as the product of the complex evolution of a fluvial fan segment, where different network morphologies could develop. A facies model for aggrading ephemeral fluvial systems in tectonically active, endorheic basins is proposed.     

The anatomy of exhumed river-channel belts: Bedform to belt-scale river kinematics of the Ruby Ranch Member,Cretaceous Cedar Mountain Formation,Utah, USA

Many published interpretations of ancient fluvial systems have relied on observations of extensive outcrops of thick successions. This paper, in contrast, demonstrates that a regional understanding of palaeoriver kinematics, depositional setting and sedimentation rates can be interpreted from local sedimentological measurements of bedform and barform strata. Dune and bar strata, channel planform geometry and bed topography are measured within exhumed fluvial strata exposed as ridges in the Ruby Ranch Member of the Cretaceous Cedar Mountain Formation, Utah, USA. The ridges are composed of lithified stacked channel belts, representing at least five or six re-occupations of a single-strand channel. Lateral sections reveal well-preserved barforms constructed of subaqueous dune cross-sets. The topography of palaeobarforms is preserved along the top surface of the outcrops. Comparisons of the channel-belt centreline to local palaeotransport directions indicate that channel planform geometry was preserved through the re-occupations, rather than being obscured by lateral migration. Rapid avulsions preserved the state of the active channel bed and its individual bars at the time of abandonment. Inferred minimum sedimentation durations for the preserved elements, inferred from cross-set thickness distributions and assumed bedform migration rates, vary within a belt from one to ten days. Using only these local sedimentological measurements, the depositional setting is interpreted as a fluvial megafan, given the similarity in river kinematics. This paper provides a systematic methodology for the future synthesis of vertical and planview data, including the drone-equipped 2020 Mars Rover mission, to exhumed fluvial and deltaic strata.     

Recognition and significance of sharp‐based mouth‐bar deposits in the Eocene Green River Formation,Uinta Basin,Utah

Sandstone bodies in the Sunnyside Delta Interval of the Eocene Green River Formation, Uinta Basin, previously considered as point bars formed in meandering rivers and other types of fluvial bars, are herein interpreted as delta mouth‐bar deposits. The sandstone bodies have been examined in a 2300 m long cliff section along the Argyle and Nine Mile Canyons at the southern margin of the Uinta lake basin. The sandstone bodies occur in three stratigraphic intervals, separated by lacustrine mudstone and limestone. Together these stratigraphic intervals form a regressive‐transgressive sequence. Individual sandstone bodies are texturally sharp‐based towards mudstone substratum. In proximal parts, the mouth‐bar deposits only contain sandstone, whereas in frontal and lateral positions mudstone drapes separate mouth‐bar clinothems. The clinothems pass gradually into greenish‐grey lacustrine mudstone at their toes. Horizontally bedded or laminated lacustrine mudstone onlaps the convex‐upward sandstone bars. The mouth‐bar deposits are connected to terminal distributary channel deposits. Together, these mouth‐bar/channel sandstone bodies accumulated from unidirectional jet flow during three stages of delta advance, separated by lacustrine flooding intervals. Key criteria to distinguish the mouth‐bar deposits from fluvial point bar deposits are: (i) geometry; (ii) bounding contacts; (iii) internal structure; (iv) palaeocurrent orientations; and (v) the genetic association of the deposits with lacustrine mudstone and limestone.     

Response of a mountain‐foreland fluvial system to an advancing ice sheet,southern Poland

In this paper, fluvial deposits of Middle Pleistocene age in the mountain‐foreland area of southern Poland (Eastern Sudetes and Western Carpathians) are studied in order to document the evolution of fluvial systems during the coldest stages of glacial periods when the Scandinavian Ice Sheet advanced far to the south. The focus is on fluvial response to climate change and glacial impact on river system behaviour. Also considered is the tectonic uplift of the mountain part of river catchments and its potential influence on the style of fluvial sedimentation in the fore‐mountain area. Three drainage basins that were active during the Elsterian and Saalian glaciations are investigated. Facies analyses are carried out on thick successions of braided river deposits covered with till or glaciolacustrine sediments, which result in a reconstruction of the fluvial activity synchronous with the ice‐sheet advance. The results suggest that fluvial activity declined prior to ice‐sheet advance into the fore‐mountain area. This climatically induced change is directly recorded in alluvial successions by upward‐decreasing bed thicknesses and grain sizes. River longitudinal profiles were shortened in front of the advancing ice sheet. The base level of the studied rivers, created by the ice‐sheet margin, rose in parallel with glacial advance. As a result, the successive reaches of rivers (degradational, transitional, aggradational) underwent shortening and moved upstream within the catchments. Moreover, tectonically induced local increases of river slopes may have influenced the depositional processes.     

Facies and basin architecture of the Late Carboniferous Salvan-Dorénaz continental basin (Western Alps, Switzerland/France)

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.     

Recognizing products of palaeoclimate fluctuation in the fluvial stratigraphic record: An example from the Pennsylvanian to Lower Permian of Cape Breton Island,Nova Scotia

Tectonics and climate are the major extrinsic upstream controls on both the external and internal architectures of fluvial channels. While the role of tectonics has been well‐documented, the role of climate has received less attention. Because both tectonics and climate can produce similar stratigraphic architectures, the ability to recognize and differentiate these has major ramifications for the interpretation of fluvial stratigraphy. The Pennsylvanian to Permian succession of the Maritimes Basin complex on Cape Breton Island is ca 5 km thick, and is composed of predominantly non‐marine strata deposited within a series of depocentres characterized by different subsidence regimes. Basins in the west are transtensional depocentres characterized by episodic fault movement. In contrast, basins in the east were formed during prolonged periods of passive thermal subsidence. The stratigraphy is composed of four second‐order sequences (A to D), each 5 to 10 Myr in duration. These sequences are composed of amalgamated fluvial channel deposits that fine upwards into extensive mud‐dominated floodplain deposits with isolated fluvial channel bodies. A spectrum of fluvial styles is recorded within the study area including perennial, perennial/intermittent and ephemeral. Four stratigraphic intervals (E1 to E4) are recognized in which the deposits of strongly seasonal perennial/intermittent fluvial deposits are predominant. These intervals, 2 to 6 Myr in duration, are correlated across the study area between basins with differing tectonic regimes and do not correlate with a particular position in second‐order sequences. This suggests that climate exerted the dominant influence on the formation of these intervals and can be differentiated from tectonic imprints. While the tectonic regime of a particular basin exerted a fundamental control on the external architecture, a coherent record of climate change is recognized in the internal architecture of fluvial units. This study demonstrates that tectonic and climatic controls can be recognized and differentiated in vertical successions by evaluating the changes in fluvial architecture.     

断陷盆地拗陷期河流层序样式及其地貌响应:以渤海湾盆地沙垒田凸起区新近系明化镇组下段为例*

对于断陷盆地拗陷期远离滨岸的河流而言,其层序划分是层序地层学研究的难点。本研究在已有钻测井、岩心及地震资料分析基础上,以渤海湾盆地沙垒田凸起区新近系明化镇组下段(简称“明下段”)作为研究对象,将其划分为1个完整的三级层序、4个四级层序(即SQm1-SQm4)。沉积间断面、宽浅下切谷及复合连片砂体是该地区河流层序界面重要的识别标志。每个四级层序均由低可容空间和高可容空间体系域组成。地震地貌学定量分析表明,低可容空间体系有利于低弯度河流(辫状河、低弯度曲流河)发育,高可容空间体系域有利于中高弯度河流发育。新增可容空间和沉积物供给速率的变化对于河流不同体系域的砂体样式具有重要控制作用。