摘要:

ABSTRACTTidal inlets, narrow, comparatively deep gaps between barrier islands, are channels through which tidal currents flow vigorously as the water enters and leaves the backbarrier lagoons, bays, and intertidal flats and marshes. Many geologists have compared tidal inlets to river channels and have speculated that if an inlet shifts laterally, it should deposit a distinctive sequence of sediments, analogous to the point‐bar sequence left by a meandering stream channel.Fire Island Inlet, located 56 km east of New York City, has migrated WSW at a mean rate of 64 m/year during the period 1825–1940. Waves approaching the coast, predominantly from the southeast, have shifted sediment along the shore toward the WSW. Deposition of sediment on the east side of the inlet has forced the tidal currents to erode the west side of the inlet, thus causing lateral migration.Because hydraulic conditions vary from the channel floor to the subaerial part of the spit which is present on the ENE side of the channel, sedimentary structures and textures vary systematically with depth. We have determined the various sedimentary environments associated with the modern Fire Island Inlet, sampled and described the sediments from these environments, and have collected samples from corings made on that part of Fire Island through which the inlet has migrated.On the basis of our studies, we propose an inlet sequence which is formed by the lateral migration of a tidal inlet. The sequence includes five major units, as follows on p. 492.The sediments belonging to various units in this sequence have been identified in four borings made on those parts of Fire Island through which the Fire Island Inlet has migrated since 1825.This sequence should be applicable to other inlets also. We think that the boundary between deep channel and shallow channel units remains relatively fixed at −4.5 m, whereas the thickness of the deep channel unit is determined by the depth range between −4.5 m and the total depth of the inlet. Hence, the main source of variation in the inlet sequence will be the thickness of the deep‐channel unit.Most of the sediments of the inlet sequence are incised below mean low water; hence they will almost certainly be preserved in the geologic record, even if all other associated sediments from barrier environments located above mean low water are not preserved. Because of the great variability possible in rates of lateral migration of inlets along the shore compared with the rates of barrier displacement perpendicular to the shore, inlet sediments may be preserved as elongate lenses, or as widespread blankets. The shape of inlet deposits reveals much about the behaviour of barriers during a submergence. Hence, inlet sediments should shed new light on sediments of the continental shelves and on basal transgressive sands in the geolog

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01788.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

ABSTRACTSediments in the valley sandurs of Markarfljot and Landmannalaugar accrete in complex lateral (transverse) bars. Directional structures within the bars are more variable in orientation than the channels which contain them. This greater variability is mainly due to the diversification of the flow, at the low stage, as it moves through the accretion topography of the sandur. Different directional structures preferentially record different stages of the flow: imbrication and lineation form mainly in response to the high flow stage, and have a low degree of dispersion; cross‐stratification records the low stage of flow, and has a wide dispersion. Cross‐stratification is produced in four main ways: by small deltas, by megaripples, by ripple topped bars, and by migrating accretionary bar banks. Small deltas form at low flow stage; accretionary banks at h

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01789.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

ABSTRACTA total of about 1100 well‐distributed samples of suspended matter in surface waters off the length of eastern Asia are available. From these samples, 180 were selected for detailed examination of the non‐combustible fraction using optical and electron microscopy along with computer methods of particle measurement and counting. The results showed that, generally, all major components of the suspended matter are most abundant in the nearshore belt (combustible fraction, mineral grains of silt size, skeletal debris, and clay minerals), the result of mechanical transport of detrital sediment and chemical transport of nutrients from the land. Mineral grains of silt size average about 2%, skeletal debris plus clay minerals—23%, and combustible organic matter—75% of total sample weights, but the last two categories vary over a wide range depending upon geographical positions of the samples. Most evident is an oceanward decrease in percentage and concentration of the total noncombustible fraction and an oceanward increase in median diameter of the mineral

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01790.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

ABSTRACTPiston cores 7 m and 6.5 m long were collected from Lakes Zug and Zurich respectively. Radiocarbon age determinations, pollen assemblage zones and varve counts indicate dates of 5000–6000 years B.P. (Zug), and 12,000–13,000 years B.P. (Zurich) for the base of the cores. Declination of the magnetic remanence varies through 70° and inclination varies through 30°. Although the correlation with the geomagnetic secular variation curve covering the last 15,000 years as determined from Lake Windermere, England (Creeret al., 1972) is not precise, the results suggest that Lake Zug and Lake Zurich sediments have been recording the broad outline of past secular variations of the earth's magnetic field. Since intensity of magnetization and susceptibility correlate markedly with lithology, a detailed sediment stratigraphy is presented. The amount and texture of the detrital input appears to be a controlling factor for the natural magnetic remanence. Intensity varies from 90 μG in zones of organic, sulphide pigmentation and those with ultra‐fine laminations to 0.8 μG in impure lacustrine chalk. Susceptibility ranges from 9 μG/Oe in laminated, fine‐grained glacially derived muds to 0.5 μG/Oe in impure lacustrine chalk. Intensity of magnetization also varies systematically within individual turbidites with lowest values in the coarse‐grained, basal fractions. Slumped beds were identified on the basis of erratic anomalies in magnetic declination and inclinati

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01791.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

ABSTRACTA sequence of irregular nodular limestones in the Silurian of northern New Brunswick appear to have undergone early marine lithification. Nodules and crusts formed soon after deposition in the argillaceous lime sediments by sporadic diagenetic precipitation of calcium carbonate and were subsequently modified by differential compaction and minor flowage.While lack of both borings and encrusting organisms on the nodules indicates they were not ‘hard grounds’, computed porosities at the time of lithification based on the ratio of carbonate to insoluble residues suggest lithification depths within a few tens of feet of the sediment‐water interface. Consideration of the availability of calcium carbonate suggests lithification very close to the sediment su

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01792.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

ABSTRACTInterdistributary bay sedimentation is dominated by flood‐generated incursions from the distributaries. There are three processes by which sediment‐laden flood waters can be transferred to the bay: overbank flooding, crevassing and avulsion. These processes combine to produce a family of sedimentary sequences, the majority of which are small‐scale coarsening upwards sequences representing infilling of the bay. Subordinate related sequences include those of small‐scale (crevasse) channels and larger scale (distributary) channels. Spits or beaches at the mouth of open interdistributary bays produce larger scale, wave‐dominated coarsening upwards sequences.A model of bay sedimentation concerning a recently initiated (hypothetical) distributary is presented. Four phases of sedimentation (overbank flooding, crevasse splay, minor mouth bar—crevasse channel couplets and avulsion) characterize the history of the distributary, and it is postulated that the phases are genetically related to alluvial ridge

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01793.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

ABSTRACTClastic features in recent halite deposits are observed along the beaches of an artificially dammed part of the Dead Sea. These features include halite oolites (termed halolites in this paper) and ripples.Halite precipitates initially either at the brine surface or on the floor. It is suggested that moderate increase of wave agitation shifts the balance towards brine‐surface crystallization, and keeps the growing halite grains in constant motion. In this way rippled structures are formed. A further increase of wave energy leads to the growth of coated halite grains.The accumulation of the various halite grains along the beach, to form soft rippled floor and oolitic beach ridge is brought about during shoreward winds.During calm periods the bulk of the halite crystallizes directly on the floor. It develops into a hard crust which assumes the morphology of the substrate, including the ripple form

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01794.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.tb01795.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.tb01796.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Book reviewed in this article:The Persian Gulf.Edited by B. H. Purser.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1974.tb01797.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY