摘要:

ABSTRACTA detailed survey of the upper and middle Nova Scotian continental slope at 42°50′N and 63°30′W indicates a complex morphology dominated by mass movements on various scales and an immature turbidity current channel. The range of sediment facies is diverse including hemipelagic and turbidite muds, turbidite sands and gravelly sandy muds of debris flow origin. Deformed units, interpreted as slump deposits are also observed. Several facies associations, related to discrete morphological environments, are recognized. Thick turbidite sand units with minor intervening mud beds are characteristic of the high‐relief uppermost slope and channel margin. Thinner turbidite sands, deformed slump beds and various mud facies are associated with small‐scale, hummocky mid‐slope topography. Sand beds are more abundant in the depressions than on intervening hummocks indicating the preferred transport paths of small turbidity currents. At the lower end of the main turbidity current channel, frequent turbidite sand beds with relatively minor mud beds are deposited on a depositional lobe. In areas unaffected by mass movements, alternating bioturbated mud and sandy muds make up the core sequences. A local model of sedimentation is proposed for this area and illustrates that simple models of continental slope sedimentation only apply to a limited range

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1984.tb00861.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

ABSTRACTA high‐resolution side‐scan sonar survey of the lake bed off the Keweenaw Peninsula, Lake Superior, demonstrates that bottom currents are affecting lake bed morphology at depths up to 240 m. Numerous lineations which run parallel to the shore appear to be sand ribbons. A field of sedimentary furrows which occurs in one area demonstrates the long‐term directional stability of the near‐bottom flow. Large (100–300 m in diameter, 2–5 m deep), unusual ring‐like or arcuate depressions are common throughout the western half of Lake Superior. These rings themselves do not appear to have been formed by bottom currents, but may have developed as water was released by the rapid compaction of glacial sediments which underlie the lake bed. Off the Keweenaw Peninsula the forms of the rings have been modified by bottom currents. The bottom currents which have modified the lake bed are probably generated when storms cross the lake at times when it is poor

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1984.tb00862.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

ABSTRACTA regional programme of continuous seismic (boomer) profiling in the central Great Barrier Reef Province has identified a widespread shallow seismic discontinuity (reflector A) which is interpreted as the pre‐Holocene surface.Nine seismic facies units are distinguished primarily on the basis of the seismic records, but also with the aid of additional criteria such as location and surface sediment types. Two units underlie reflector A and are pre‐Holocene. These units are interpreted as: (a) Permo‐Carboniferous bedrock, and (b) Pleistocene/? Tertiary sediments, consisting of both shelf‐wide terrigenous units, and carbonate mounds and platforms under present reefs. Seven units are post‐glacial and overlie reflector A. These units are interpreted as: (c) fluvial/estuarine channel fill, (d) relict delta‐front deposits, (e) relict transgressive veneer, (f) coastal coarse and (g) fine deposits, (h) modern reef and (i) reef talus.In general post‐glacial sediment cover is very thin and in many places on the mid‐shelf the pre‐Holocene units crop out. Substantial post‐glacial accumulations are limited to protected coastal embayments and to o

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1984.tb00863.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

ABSTRACTThe compositional variability shown by sands of present continental margins was determined through conventional microscopic techniques. This allowed the establishment of a descriptive classification of deep‐sea terrigenous sands based on a restricted number of commonly used parameters. The fundamental sand types include: (1) QF suite—sands in which quartzose and/or feldspathic grains predominate. Carbonate‐L‐bearing sands (on average richer in lithics) occur within this suite. (2) QL suite—in which quartzose and/or lithic grains predominate. Little compositional diversification is apparent within this suite. (3) FL suite—in which lithic and/or feldspathic grains predominate. Two compositional members can be identified based on the K‐feldspar/plagioclase ratio. (4) LV suite—consists of sands in which volcanic grains largely dominate the lithic types. Vitric and serpentine sands occur within this suite.The suites are related to distinct source‐area types defined as follows: (1) cratonic block; (2) sedimentary orogenic belt; (3) volcanic orogenic belt; (4) volcanic arc.Some sands cannot be easily assigned to a single compositional suite because petrologic parameters overlap with an adjacent suite. Suchcritical compositionsare commonly arkosic. Using roundness of the framework components, it is possible to define a category identified asmatured sands,which are greatly enric

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1984.tb00864.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

ABSTRACTIntertidal sandwaves in the Minas Basin and Cobequid Bay, Bay of Fundy, occur under a wide range of conditions (mean grain size 0.274‐1.275 mm; velocity strength index (V1)0.46‐3.34; and velocity symmetry index (V2) 0.011‐0.294), and they vary from symmetrical to strongly asymmetrical in cross‐section. Heights and wavelengths average 0.81 and 37.9 m respectively. They are straight to weakly sinuous and laterally continuous in plan, occasionally show crestal branching reminiscent of wave ripples, and are commonly skewed relative to the strongest currents because of differential migration rates along their length. The average migration rate is 0.11 m/tidal cycle. Megaripples occur on each sandwave crest, at least during spring tides, but the areal extent, sinuosity and size of the megaripples increases as the dominant current speed increases. The megaripples have heights averaging 24% of the sandwave height, are oriented perpendicular to the fastest dominant currents, and have life spans of several tidal cycles. They are believed to be in quasi‐equilibrium with the sandwaves and play a key role in sandwave dynamics and internal structure formation: periods of lee face steepening and rapid forward migration (megaripple crest at sandwave brink) alternate with times of non‐deposition or erosion and slowed or reversed migration (trough at brink).Dominant‐current cross‐bedding predominates in the two intergradational varieties of translation structure observed:Inclined Cross‐Bedding—decimetre‐scale cross‐beds separated by gently inclined (9° average) erosional surfaces; andLarge‐Scale Foresets—cross‐beds with thicknesses greater than half the sandwave height, interrupted by weakly erosional to conformable discontinuity surfaces. These are overlain by a vertical growth or repair structure,Complex Cross‐Bedded Cosets, that consists of nearly equal volumes of dominant‐ and subordinate‐current cross‐beds stacked without a preferred set‐boundary dip. The translation structures correspond well to forms predicted by Allen (1980a, fig. 8) but the inclined set boundaries and discontinuity surfaces (master bedding planes) are produced by megaripple troughs rather than by current reversals. Consequently, Allen's regime diagram is unable to predict structure occurrences. The repair structures suggest that ‘curvature‐related mass‐transport’ (Allen, 1980a, b) is important in tidal sandwave maintenance, although it is not

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1984.tb00865.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

ABSTRACTThe concentration and composition of suspended particulate matter (SPM) were measured weekly for a period of one year in the flood front waters traversing a muddy tidal flat. SPM concentrations were lowest in the winter when portions of the tidal flat were covered with ice, and biological activity was minimal. In contrast, the summer months had the highest SPM concentrations which reflected increased bottom resuspension.The two main sources of SPM were suspended matter carried in from offshore on the flooding tide and resuspendedin situbottom sediments. The offshore source was characterized by low SPM concentrations, coarse textures, and a high content of protein and chlorophyll ‘a’. Samples taken during resuspension events (storms/showers) had high SPM concentrations, finer textures, and were enriched in dead detrital organic material (phaeophytin). At any one time the SPM was primarily an admixture of these two sources.The highest SPM measurements were taken during storm events, with rainfall seeming to play a dominant physical role in aiding resuspension. SPM concentrations, textures, and compositions collected during the storms closely approximated SPM measurements made over newly dug ‘clam f

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1984.tb00866.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

ABSTRACTDetailed lithostratigraphical, palynological and14C analyses have served to reconstruct the palaeoenvironment during two main, mid‐Holocene, regional phases of increased fluvial clay and sand deposition in the Rhine/Meuse deltaic plain. The investigated location lies in a broad area transitional to the upstream fluviatile and the downstream marine (lagoon/tidal flat) deposition zones. The palaeoenvironment appears to have been extensive, permanent open water intersected by the wooded natural levees of many small river channels. The term fluviolagoon is proposed for this typical environment, as illustrated here by three‐dimensional oblique landscape drawings. A present‐day example is found in the Magdalena river deltaic plain, Col

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1984.tb00867.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

ABSTRACTLake Hazar lies within a small pull‐apart basin along the East Anatolian Transform Fault in south‐eastern Turkey. Deltas are formed where streams debouch into the low‐energy lacustrine environment. The facies constituting the deltas include delta plain debris flow, braided stream, and marginal lacustrine deposits; delta front foreset and mouth bar deposits; prodelta and lacustrine deposits. The facies are spatially restricted with sharp transitions. Facies sequences and relationships indicate two distinct styles of deltaic sedimentation. Fan deltas with a tripartite structure characteristic of Gilbert‐type deltas comprise the marginal drainage system and form along the basin margins. Mouth bar deltas develop where the axial drainage system of the basin debouches into the lake. The distribution of the two deltaic types is thought to be a function of gradient and controlled by position relative to faults within th

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1984.tb00868.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

ABSTRACTThe Jafurah sand sea of the Eastern Province of Saudi Arabia extends along the Arabian Gulf coastline from Kuwait in the north to the Rub Al Khali in the south, a distance of about 800 km. Sand drifts southward to south‐eastward from regions of high wind energy in the north to low wind energy in the south.The aeolian landscape is zoned, with areas of deflation, transport and deposition from north to south. Drift rates in the zone of transport, near Abqaiq, range from 2 m3m‐w‐1yr‐1on sabkhas, to 29 m3m‐w‐1yr‐1on the crests of dunes. Average drift rates of approximately 18 m3m‐w‐1yr‐1observed during the study can cause about 1 m of accumulation per 5500 yr in a 100 km zone of deposition downwind, not including the bulk transport represented by the forward advance of dunes. Dune advance ranged from 23 m (2.9 m high dune) to 3 m (23 m high dune) during April‐October 1980.The study area consists of dune, interdune, sand sheet and siliciclastic sabkha terrains, each of which is characterized by differing drift rates, and differing rates of erosion or deposition. Sedimentation occurs by lateral movement of dunes and interdunes, and vertical accretion by sa

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1984.tb00869.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Book reviewed in this article:Stable Isotopes in Sedimentary Geology, by M. A. Arthur, T. F. Anderson, I. R. Kaplan, J. Veizer and L. S. Land.Geomorphological Field Manual, by V. Gardiner and R. Dackombe.Sediments aragonitiques et leur genèse, by J. P. Loreau.Tomkeieff Dictionary of Petrology, ed. by E. K. Walton, B. A. Randall, M. H. Battey,&S. I. Tomkeieff.Environmental Oceanography. An introduction to the behaviour of coastal waters, by T. Beer

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1984.tb00870.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY