摘要:

ABSTRACTLarge scale sedimentary structures present in the Upper Turonian to Santonian chalks of Haute Normandie (northern France) represent the remains of a carbonate bank complex which formerly extended over an area of at least 1500 km2. Cliff exposures along the Channel coast from St Valéry‐en‐Caux to Cauville and along the Seine from Sandouville to Lillebonne show sections of banks up to 50 m high and 1500 m across, their internal structures picked out by hardgrounds, nodular chalks and horizons of burrow flint.Associated with banks are slump sheets up to 20 m thick, slump scars, sedimentary breccias, injection phenomena and faults contemporaneous with sedimentation. Later diagenetic features include extensive dolomitization and silicification.These structures compare closely with the Waulsortian banks of the Palaeozoic, and bryozoan bioherms known from the Upper Cretaceous and Palaeocene of Denmark. Frame‐building, sediment trapping and stabilizing organisms are absent, and bank development and stabilization was probably due to a plant covering, either algal or of marine angiosperms. Banks generated much of their own sediment, whilst a pelagic constituent (calcareous nannofossils and Foraminiferida) is also present.The distribution of the bank complex is related to a basement controlled swell area, whilst the life of the complex was limited to a relatively shallow water, regressive episode in the predominantly transgressive Upper Cretaceous history of the region.Les falaises littorales du Pays de Caux comprises entre Antifer et St Valèry‐enCaux, et les affleurements de la basse vallée de la Seine permettent d'observer des formations du Turonien supérieur‐Sénonien inférieur qui présentent des stratifications irrégulières soulignées par de nombreux hardgrounds, des horizons de craie noduleuse et des cordons de silex. Ces structures sont identifiées à des accumulations de calcilutite et calcarénite sous forme de bancs sous‐marins dont la hauteur peut atteindre 50 m et qui couvrent une surface supérieure à 1500 km2; ils apparaissent au‐dessus de hardgrounds subhorizontaux qui indiquent un haut‐fond régional stable. Des glissements sous‐marins sont associés à ces bancs et engendrent des niveaux avec des déformations souples atteignant 20 m d'épaisseur. Des brèches apparaissent localement et contiennent des blocs basculés de hardgrounds fragmentés lors du glissement; on y observe aussi de petites failles intrasédimentaires et des phénomènes d'injection. Aucun organisme constructeur ou capable de piéger et retenir le sédiment n'a été observé. La stabilisation de ces bancs serait due à une couverture végétale (algues ou angiospermes marines) dont on sait qu'elle peut disparâitre sans laisser de trace lors de la fossilisation. La croissance de ces bancs serait réalisée par un apport de sédiment comprenant une part de nourrissage autochtone comme cela existe pour les bancs récents en eau

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01780.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

ABSTRACTFacies relationships in Pleistocene braided outwash deposits in southern Ontario demonstrate the presence of a large braid bar with adjacent side channel. The core of the bar is up to 6 m high, and consists of crudely horizontally stratified gravels. Downstream from the core is the bar front facies, consisting of large gravelly foresets up to 4 m high, rounded off in many places by reactivation surfaces. Upstream from the core is the bar stoss side facies consisting of several sets (individually up to 35 cm thick) of tabular cross‐bedding, arranged in coarsening‐upward sequences. The stoss side—core—bar front relationships are continuously exposed in one 400 m long quarry face which is cut almost parallel to the palaeoflow direction. A transverse quarry face shows the side channel facies, which consists of trough cross‐bedded sands. Gravel layers can be seen to finger from the main gravelly bar into the sandy side channel, but they do not reach the base of the channel. This surprising relationship indicates that gravel moved only in the topographically higher parts of the system. After deposition in the side channel, and growth upstream and downstream from the bar core, the entire system aggraded. Crudely horizontally stratified, and imbricated gravel sheets were laid down as a bar top facies.Grain size analyses indicate strongly bimodal distributions, implying that much of the sand in the spaces between pebbles and boulders filtered in after the gravel had been deposited. This interpretation is strengthened by velocity calculations—mean velocities in excess of 300 cm/s would be needed to roll the gravel as bed load, but at such a velocity, a large amount of sand would be transported entirely in suspension.In a final section of the paper, our results are combined with other work on braided systems in an attempt to formulate a more general f

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01781.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

ABSTRACTThe separated valves of bivalve molluscs, certain gastropods, and many brachiopods closely resemble the regular geometrical form known as the shell. The packing concentration of natural accumulations of such organic shells may be placed within bounds with the aid of packing models making use of ordered arrangements of equal geometrical shells, either conical, cylindrical or spherical. The low packing concentrations, comparable with 0·1–0·2, indicated by these models are confirmed by experiments using the shells of four common British species of bivalve or gastropod mollusc. Packings of these shells have a substantial intrinsic strength, and experimentally appear able to support without failing sedimentary overburdens equivalent to loads comparable with 1000 kg mass/m2. The observed and predicted low packing concentrations suggests that natural shell beds can hold relatively very large amounts of pore fluids or mineral cements. The resistance to compaction of the packings means that the high original porosities of natural shell beds have a good chance of being permanently preser

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01782.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

ABSTRACTSurface textures of quartz sand grains from several glacial environments at the Feegletscher, Switzerland examined by means of scanning electron microscopy are described. The difference between supraglacial and subglacial material is very slight. At the moment the interpretation of these textures must be done with care until the full statistical relation to environments can be ascertained. This does not necessarily invalidate earlier investigations although it does mean that glacial and extraglacial environments in the vicinity of glaciers are apparently not distinguishable. Examination of surface precipitation features suggests a sequence of events which can be used to help discriminate between different ages of deposits in an area. A similarity between some of the surface debris from moraine samples and those seen in loess and quickclay deposits is also suggested.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01783.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

ABSTRACTA tidal inlet system with an outer tidal, delta, situated between two barrier islands along the north coast of Holland was studied for size and shape sorting. With size data different sand types can be distinguished and in individual samples distinct grain populations can be recognized in some cases. Graphs of shape values, plotted against the size intervals of samples also reveal the presence of different grain populations, together with their genetical significance.The following conclusions could be drawn.There is no sand transport directly from island to island. Sand up to 400 μm enters the tidal inlet, is sorted out in the tidal flat area and partly re‐enters the sea via the outer tidal delta. On the delta, the sediment is split up again in different populations. A lag deposit is left behind on the frontal part of the delta. The rest of the sand either re‐enters the tidal inlet cycle or contributes to the beach building of the next island. In the offshore environment, sand movement by wave‐induced currents is restricted to the shallow zone. In deeper water, part of the sediment is relatively immobile and has preserved inherited characteristics from the early Holocene transgressive phase. In front of Ameland, fossil barrier‐face deposits‐are present, off Schiermonnikoog the sea floor contains old tidal channe

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01784.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

RÉSUMÉLes ressources en mineral de fer du bassin de Bretagne‐Anjou proviennent essentiellement de quatre couches de mineral sédimentaire situées dans le grès armoricain (Arénig). Les paragenèses les plus fréquentes réunissent le quartz, la magnétite, la sidérite et des silicates (bavalite, stipnomélane). La paragenèse à hématite et la paragenése à pyrite sont plus rares. L'étude pétrographique permet en outre de définir deux types de minerais: un type à allochems et un type sans allochems.L'examen des variations de paragenèses et de puissance des couches de minerai permet de reconstituer en partie l'histoire de la sédimentation ferrifère: le fer est mis en solution sur les reliefs cadomiens émergés. Lors de la transgression paléozoïque le fer parvient dans le bassin de sédimentation qui est peu profond et encombré d'iîles et de hauts‐fonds. Suivant les conditions locales le fer précipite alors soit sous ses formes oxydées (magnétite, hématite), soit sous ses formes réduites (bavalite, sidérite, pyrite). Les facteurs essentiels de la différenciation des paragenèses sont l'épaisseur de la tranche d'eau, l'agitation de l'eau et la teneur du sédiment en matiére organique. Dans certains cas un phénomène de concrétionnenment au sein du sédiment donne naissance aux allochems qui peuven

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01785.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

ABSTRACTRotating drum experiments on the repose angles of mixtures of glass spheres have shown that φr(angle of shear) is strongly influenced by the proportions of the mixture. It was found that φrreached a peak value for the minimum porosity mixture; where the pore spaces between the large particles were just filled with small material; which was attributed to increased dilatation on the shear plane during avalanching. The geomorphic significance of these observations, in terms of slope development, is discussed.Secondly, the results of the experiments showed that, although more constant than φi(limiting angle of repose), φrwas subject to some variation. Thus φr, as measured in a rotating drum, is not a true constant and can not be exactly analogous to φ'cv(angle of internal sliding friction at constant volume) as measured in a shearbox test—as has been previously suggested. It is tentatively suggested that at least some of the variability in φris attributable to the magnitude of the immediately preceding value of φi, in that an unusually high value of φi, favours a lower value of φrdue to the greater amount of kinetic energy released

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01786.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01787.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY