摘要:

ABSTRACTSyn‐rift sediments in basins formed along the future southern continental margin of the Jurassic Tethys ocean, comprise, in the eastern Alps of Switzerland, up to 500 m thick carbonate turbidite sequences interbedded with bioturbated marls and limestones. In the fault‐bounded troughs no submarine fans developed; in contrast, the fault scarps acted as a line source and the asymmetric geometry as well as the evolution of the basin determined the distribution of redeposited carbonates.The most abundant redeposits are bio‐ and lithoclastic grainstones and packstones, with sedimentary structures indicating a wide range of transport mechanisms from grain flow to high‐ and low‐density turbidity currents. Huge chaotic megabreccias record catastrophic depositional events. Their main detrital components are Upper Triassic shallow‐water carbonates and skeletal debris from nearby submarine highs.After an event of extensional tectonism, sedimentary prisms accumulated in the basins along the faults. Each prism is wedge‐shaped with a horizontal upper boundary and consists of a thinning‐ and fining‐upward megacycle. Within each megacycle six facies associations are distinguished. At the base of the fault scarp, an association of breccias was first deposited by submarine rockfall and rockfall avalanches. A narrow, approximately 4000 m wide depression along the fault was subsequently filled by the megabreccia association, in which huge megabreccias interfinger with thin‐bedded turbidites and hemipelagic limestones. The thick‐bedded turbidite association covered the megabreccias or formed, farther basinward, the base of the sedimentary column. Within the thick‐bedded turbidites, thinning‐ and fining‐upward cycles are common. The overlying thin‐bedded turbidite association shows nearly no cyclicity and the monotonous sequence of fine‐grained calciturbidites covers most of the basin area. With continuous filling and diminishing sediment supply, a basin‐plain association developed comprising fine‐grained and thin‐bedded turbidites intercalated with bioturbated marls and limestones. On the gentle slopes opposite the fault escarpment, redeposited beds are scarce and marl/limestone alternations as well

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1987.tb00576.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTThis paper describes the sedimentation style associated with the basal Carboniferous transgression in southern Ireland and the influence which this event had on the palaeogeography of the region. The transgression as marked by the base of the Carboniferous succession is shown to represent one of several genetically related transgressive pulses which commenced during the Late Devonian. At this time an east‐west trending graben, the South Munster Basin, developed in southern Ireland. This was initially a non‐marine depositional site in which sediment was derived from the north and west. Subsidence and eustatic sea‐level rise resulted in a marine transgression which proceeded in a rhythmic style resulting in a number of transgressive‐stillstand pulses. The first transgressive pulse (T1) advanced in a westerly direction along the basin axis resulting in the development of an epicontinental‐like sea. The shoreline remained essentially static along the northern basin margin initially until a second transgressive pulse (T2) resulted in expansion of the marine area. The latter proceeded by gradual northward erosive advance of a barred coastal area as far as the northern basin margin where the stability of the bounding platform halted its progress. Erosion of the barrier shoreface was insufficient to destroy all the backbarrier lagoonal deposits which are preserved as a thin transgressive diachronous unit which grades northwards to a coastal alluvial plain.Immediately preceding the basal Carboniferous transgression (T3), a shallow, wave‐dominated, storm‐influenced shelf sea occupied the basinal area. Two sublittoral sand bar complexes developed on the shelf under the influence of shore‐parallel current regimes, apparently derived from source areas located on either side of the epicontinental seaThe basal Carboniferous transgression took place in two pulses. The first (T3a) resulted in a rapid reduction in sand supply to the shelf and deposition of clay. The barrier shoreline responded by erosively retreating across the lagoon, leaving a transgressive lag in its wake. Its northwards advance was, however, limited due to the relative stability of the northern platform. Sand supply to the shelf was completely terminated in the second pulse (T3b) and the barrier rapidly migrated erosively across the northern platform for a considerable distance such that the coastal plain is overlain by a thin transgressive lag. This transgressive phase was immediately followed by shoreline stillstand and progressive shallowing of the shelf. An open sandy shelf developed on which offshore sand bars accumulated under a storm and wave dominated regime. Clay deposition continued in the deeper part of the basinal area but was eventually terminated as the shelf sands prograded centripetally into the basin.The main factor that controlled the style of the overall transgression was an interplay between eustatic sea level rise and basin subsidence. The rate of relative sea‐level rise together with the effect of differential subsidence and fluvial input from the north appear to have diminished with time. The rate at which successive transgressive pulses advanced northwards shows an overall pro

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1987.tb00577.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTThe Upper Cretaceous (Campanian) Kenilworth Member of the Blackhawk Formation (Mesaverde Group) is part of a series of strand plain sandstones that intertongue with and overstep the shelfal shales of the western interior basin of North America. Analysis of this section at a combination of small (sedimentological) and large (stratigraphical) scales reveals the dynamics of progradation of a shelf‐slope sequence into a subsiding foreland basin.Four major lithofacies are present in the upper Mancos and Kenilworth beds of the Book Cliffs. A lag sandstone and channel‐fill shale lithofacies constitutes the thin, basal, transgressive sequence, which rests on a marine erosion surface. It was deposited in an outer shelf environment. Shale, interbedded sandstone and shale, and amalgamated sandstone lithofacies were deposited over the transgressive lag sandstone lithofacies as a wave‐dominated delta and its flanking strand plains prograded seaward.Analysis of grain size and primary structures in Kenilworth beds indicates that there are four basic strata types which combine to build the observed lithofacies. The fine‐ to very fine‐grainedgraded strataof the interbedded facies are tempestites, deposited out of suspension by alongshelf storm flows (geostrophic flows). There is no need to call on cross‐shelf turbidity currents (density underflows) to explain their presence. Very fine‐ to fine‐grainedhummocky strataare likewise suspension deposits created by waning storm flows, but were deposited under conditions of more intense wave agitation on the middle shoreface.Cross‐stratasets in this region are bed‐load deposits that accumulated on the upper shore‐face, in the surf zone.Lag strataare multi‐event, bed‐load deposits that are the product of prolonged storm winnowing. They occur on transgressive surfaces. While the graded beds are tempestites in the strict sense, all four classes of strata are storm deposits.The distribution of strata types and their palaeocurrent orientations suggests a model of the Kenilworth transport system driven by downwelling coastal storm flows, and probably by a northeasterly alongshore pressure gradient. The stratification patterns shift systematically from upper shoreface to lower shoreface and inner shelf lithofacies partly because of a reduction in fluid power expenditure with increasing water depth, but also because of progressive sorting, which resulted in a decrease in grain size in the sediment load delivered to successive downstream environments.The Kenilworth Member and an isolated outlier, the Hatch Mesa lentil, constitute a delta‐prodelta shelfdepositional system.Their rhythmically bedded, lenticular, sandstone and shale successions are a prodelta shelf facies, and may be prodelta plume deposits. Major Upper Cretaceous sandstone tongues in the Book Cliffs are underlain by erosional surfaces like that beneath the Blackhawk Formation, which extend for many tens of kilometres into the Mancos shale. These surfaces are the boundaries of Upper Cretaceousdepositional sequences.The sequences are large‐scale genetic stratigraphic units. They result from the arranging of facies into depositional systems; the depositional systems are in turn stacked in repeating arrays, which constitute the depositional sequences. The anatomy of these fo

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1987.tb00578.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The deposits comprising ‘valley‐side fans’ in a small intermontane basin of the Southern Alps are classified as debris flow, water‐laid, intermediate and mixed deposits on the basis of particle size and clast orientation characteristics. Five varieties of debris flow deposit are identified including unimodal and bimodal ‘mudflow gravels’. The fans comprise mainly unimodal mudflow gravels which although apparently similar to the mudflow gravels described from montane and periglacial environments are coarser, have less silt and clay and are better sorted than the mudflow deposits described from semiarid alluvial fans. Additions of airborne silt and fine sand to the fan catchments during later stages of fan building gave rise to bimodal debris flow deposits which appear similar to gravels described from cold‐climate fans in Tasmania and classed as water‐laid deposits. Braided stream deposits were added to the depositional sequence towards the closing stages of fan building indicating that the fan had become ‘wetter’. In many places, however, the youngest Pleistocene fan deposits are silt‐rich mixtons reflecting a pea

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1987.tb00579.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTLate Pleistocene morainic sequences around Dundalk Bay, eastern Ireland, were deposited in a variety of shallow, glaciomarine environments at the margins of a grounded ice lobe. The deposits are essentially ice‐proximal delta‐fan and ‐apron sequences and are divided into two lithofacies associations. Lithofacies association 1 occurs as a series of morainal banks formed at the southern margin of the ice lobe in a body of water open to influences from the Irish Sea. The morainal banks consist mainly of diamictic muds deposited from turbid plumes and by ice‐rafting with minor occurrences of turbidites, cross‐bedded gravels (subaqueous outwash) and massive boulder gravels (high‐density debris flows). Lithofacies association 2 was deposited in a narrow arm of the sea at the north‐eastern margin of the ice lobe. The deposits consist mainly of a series of coalescing, ice‐proximal Gilbert‐type fan deltas which are interbedded distally with tabular and lens‐shaped subaqueous deposits. The latter are mainly ice‐rafted diamictons, debris‐flow deposits and subaqueous sands and gravels. Both lithofacies associations are draped by diamictons formed by a combination of rain‐out, debris flow and traction‐current activity. At a few localities the upper parts of the sequence have been sheared by minor oscillations of the ice sheet margin.These sequences form part of an extensive belt of glaciomarine deposits which border the drumlin swarms of east‐central Ireland. Lithostratigraphic variability is partially related to the arrival of large volumes of debris at the ice lobe margin when the main lowland ice sheet surged during drumlin formation. Complex depositional continua of this type lack any major erosional breaks and should not be used either as climatic proxies or f

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1987.tb00580.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTStatistical size distribution and scanning electron microscopic studies of suspended sand grains in the Loire River at Montjean, France were carried out over a period of a year (hydrological cycle) to discern seasonal variations. The sand fraction in suspension is better sorted during winter (average mean = 0.69 mm, median = 0.65–0.95 mm, sorting value, σ= 1.1–1.35) and is dominated by quartzo‐feldspathic minerals. During summer, on the contrary, this fraction is rich in mica minerals and is poorly sorted (average mean = 1.21 mm, median = 0.33–0.95 mm, sorting value, σ= 1.4–2.0). The grain size of the coarser fraction shows a tendency to increase with river discharge up to an optimum discharge of about 1000 m3s‐1and thereafter decreases.Scanning electron photomicroscopy of quartz grains from the suspended sand population indicates that both mechanical and chemical features occur. The former (conchoidal fractures, mechanical fractures and breakage) dominate in the samples collected near the water surface during winter floods and the latter (solution pits, vermicular features, silica flowers, neogene silica and diatoms) in the samples from the bottom during low summer flows. During summer, chemical action takes place on sediments prior to or upon their deposition. Sediments that are resuspended during winter floods undergo mainly physical processes (attrition/abrasion). Mixed surface features are, therefore, observed during average and low river discharge. Inheritance of these surface features from the source area is, however, not completely excluded.Thus, the history of quartz grains in suspension can be reconstructed from SEM exoscopic studies: therefore, it can be proposed that the fluvial quartz grain surface textures result from a combination of alternating chemical and physi

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1987.tb00581.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1987.tb00582.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1987.tb00583.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Books review in this article:Recognition of Fluvial Depositional Systems and their Resource Potential—SEPM Short Course No 19, by R. M. Flores, F. G. Ethridge, A. D. Miall, W. E. Galloway&T. D. FouchSedimentology of Gravels and Conglomerates, ed. by Emlyn H. Koster&Ron J. SteelQuaternary Geology and Environment in China, ed. by Liu Tung‐sheng et al., China Ocean PressCoastal and Estuarine Sediment Dynamics, by Keith R. DyerReview of Jurassic sedimentary evolution and nappe emplacement in the Argolis Peninsula (Peloponnesus, Greece), by Peter O. BaumgartnerAn Introduction to Carbonate Sediments and Rocks, by Terence P. ScoffinRoles of Organic Matter in Sediment Diagenesis, ed. by D. L. GautierDeep Ocean Sediment Transport, ed. by A. R. M. Nowell and C. D. Holli

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1987.tb00584.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1987.tb00585.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY