摘要:

From work on two Upper Carboniferous formations in southwest England, three morphologically distinct types of ripple‐drift cross‐lamination have been recognised. Type 1 is characterised by strong erosion of laminae on the stoss (or up‐current) side of the ripples, and absence of grading. Type 3 is characterised by an absence of erosion on the stoss sides, concentration of mud in the ripple troughs and an upward gradual decrease in grain size and amplitude of rippling. Type 2 is an intermediate form with some characteristics in common with types 1 and 3. An examination of the illustrated literature has shown that types 1 and 3 occur frequently, and that type 2 has not pre‐ viously been recorded.It is suggested that type 1 is formed in fluvial and shallow water environments at times of net deposition of sediment, and that type 3 is formed by deposition from a tur‐ bidity current. Type 2 suggests hydrodynamic conditions intermediate between fluvial or shallow water traction currents, and turbidity currents.Since all current ripples move forwards, or “drift”, it is suggested that the term “ripple‐drift” should be used to describe ripple cross‐lamination where the ripples can be seen to climb onto the stoss slope of the ripple immediately downstream, there having been a net deposition, and not merely a forw

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1963.tb01212.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

On the southwest coast of Florida a shoreline reentrant t Cape Roma D forms Greater Gullivan Bay. Evidence is available which suggests that the reentrant may be structurally controlled. The bay lies between the Cape Romano shoals to the north and the irregular, low energy, mangrove ridge shorelinz of the Ten Thousand Islands to the southeast.Two main currents affect the area. One, the longshore current from the north, enters the bay through the shoals, whereas the other, a tidal current, enters from the south, proceeds through the mangrove island archipelago and sweeps down the bay and back out to the open Gulf.Regionally the sediment becomes coarser seaward, a reflection of the fine material of the mangrove island shoreline and of the coarse shell material on the shelf beyond the shoals. In specific parts of the area such as the bay, shoals, islands and shelf, size of the detritus is relatively constant. The mean grain size of the carbonate, however, is variable. Sorting of the bottom sediment is best over the shoals and in the bay indica‐ ting the location of the most effective currents.Per cent carbonate is lower in the bay sediments than in any other part of the region. A similar situation exists for the organic matter. The average per cent of organic matter in the sediments is about the same as that 011 the shelf.In the lee of the shoals, at the head of the bay and in the bays of the lagoonal chain current activity is low, and a mixed sediment of quartz sand, not whole shells, silt and clay appears to be accumulating. The lower bay, because of the turbulent ebbing of the tidal current, is, in general, receiving only quartz sand. Furthermore, the shoals appear to be moving shorewar

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1963.tb01213.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

The paper deals with sedimentary structures in shallow‐water Precambrian deposits of Lower Torridonian age in the island of Skye in northwestern Scotland. The structures described include irregular lamination, ripple bedding, festoon bedding and structures produced by local erosion and reworking. Evidence of penecontemporaneous disturbance thought to be due to the movements of quicksands is briefly referred to. Variations in lithology and structure within the succession are attributed to local differences in conditions within a possible environment of sedimentation in an intertidal zone with off‐shore sandba

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1963.tb01214.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Nineteen shales from the continental Belly River Formation and sixteen shales from the marine Wapiabi Formation were studied by X‐ray diffraction and fluorescence methods. The diffraction data indicate that dolomite and Mite are present in signifi‐ cant amounts only in the Wapiabi. Feldspar and 12 Å and 14 Å clays are more abundant in the continental shales. The marine shales are enriched in K, Ca, Rb and Zr. The continental shales are higher than marine shales in Sr and Mn. The Rb/K is higher in the marine shales, the Sr/Ca is lower than in the continental s

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1963.tb01215.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Physiographic features and depositional history of the sediments forming the bed and banks of the lower 200 miles of the Mississippi River are summarized. From mile 200‐ 160 the river is scouring into coarse substratum sands, between miles 160 and 80 into Pleistocene clays, and between mile 80 and 0 chiefly into prodelta and interdistributary clays. Point‐bar accretion averages 500 acres per river mile in the uppermost segment, 200 acres per river mile in the middle segment, and 30 acres per river mile in the lower‐ most segment. The occurrence of bends caused by faulting or formed during seaward growth of the delta, and the occasional existence of coarse materials in the path of the stream are significant factors in the initiation of meanders. The composition of the bed and banks, and the length of channel occupation are important in the rate and extent of migration. Migration of the river between miles 0 and.160 has been and should continue to be very

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1963.tb01216.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

An anomalous increase of pore volume with increasing depth in the range 0—1,900 ft. occurs in fine‐grained sediments along the east side of the San Joaquin Valley of Cali‐ fornia. Several possible causes for the anomaly were inferred from a literature search and from study of the core samples. Statistical analyses of the core sample data suggest the principle causes to be variations in particle size, the diatom‐skeleton content, and the type of exchangeable cation adsorbed by the clay‐mineral constituents of the

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1963.tb01217.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

In a vast region in Scandinavia, a monotonous and extremely slow deposition of anaerobic mud persisted through the Late Cambrian. After a long time with no or very little sedimentation, deposition was recommenced in the Early Ordovician at an equally slow rate, but with calciumcarbonate as the main component. pH at the bottom was so low that the deposition of the carbonate in the long run only just outweighed the solution, which occurred frequently and sometimes during long periods. By oscil‐ lating solution and precipitation in the pores, lime mud could set into limestone on the sea‐bed. By more definite phases of solution, most of the limestone could be reduced to a marl bed with remains of undissolved limestone. Single limestone beds formed over such marl were apt to glide and deform into anticlines, which rose from the sea‐ bottom to heights up to 20 cm. These folds were rarely destroyed mechanically, which speaks for a tranquil bottom environment. Their crests were, however, cheinically corroded in the same way as discontinuity surfaces, which were also formed at many intervals. The processes by which the discontinuity surfaces were formed never affected a fold mechanically. The corrosion of the fold crests and of the discontinuity surfaces took place on the bottom of the sea, at safe distance from the surface. The corrosion was most frequently associated with the formation, and maintenance, of a glauconite skin. The abundance of preserved fold structures indicates that the region was relatively deep under the sea for most of the Early Ordovician. Later on, already in the middle‐Late Arenigian, the sea may have become shallower. The findings are extrapolated, with some probable interpretations and new observations, to include a hypothetical explanation for the passage from black shale to limestone

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1963.tb01218.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY