摘要:

ABSTRACTThe Otekura Formation (Early Jurassic,Pseudaucellazone) at Sandy Bay comprises part of a 10+ km thick, regressive, forearc shelf and slope sequence, the Hokonui facies belt of the Rangitata Geosyncline. The Otekura Formation is dominantly fine grained, being mostly mudstone, silty mudstone and siltstone. The sediments are volcanogenic throughout. The upper 150 m of the formation contains two 20 m thick, channelized bodies of medium‐thick bedded sandy flysch, each associated with thin bedded muddy flysch interpreted as overbank turbidites. Directional indicators within the channel sequence indicate emplacement from the south‐southwest. In contrast, rare turbidites that occur below the channel sequence, within the background mudstone sediment, were emplaced from the east, i.e. at right angles to the channelized flows. The immediately overlying Omaru Formation contains more abundant macrofossils, intraclastic conglomerates, and appreciable amounts of traction‐emplaced cross‐bedded sand. Bioturbated calcareous siltstones with anin situmolluscan fauna follow (Boatlanding Formation), and are of shelf origin. The Omaru Formation is therefore interpreted as a shelf‐slope break deposit, and the Otekura Formation as an upper slope facies.Reconnaissance studies indicate that the Otekura Formation is underlain by several kilometres of dominantly fine grained, deep water slope sediments, containing occasional sand and conglomerate filled channels similar to those here described in detail from the Otekura Formation. Such channels are inferred to form when a mass‐transported sand, derived from failure higher on the slope, ploughs erosively into the sea floor. After their incision, the channels served for a short time as conduits for downslope transport of sediment, the redeposited deposits of which are found filling each channel. Both channel fills at Sandy Bay are capped by thin‐bedded turbidites inferred to have overspilled from similar channels nearby

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00925.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTTen samples from a Late Messinian section measured at Capo Rossello, a few hundred metres laterally from and stratigraphically immediately below the Miocene/ Pliocene boundary stratotype, have been investigated by various techniques: carbonate content, grain‐size analysis, loss on ignition, clay mineral composition, frequency of euryhaline ostracods. Two lithological sub‐units. with different palaeoenvironmental implications, are recognized. Both sub‐units were deposited after the termination of evaporitic conditions, and immediately after deposition of an ash fall tuff. The lower unit is theCongeriamarl which yields the ‘lago‐mare’faunal assemblage, the autochthony of which is supported by biometrical analysis ofCyprides agrigentina, indicating brackish, shallow‐water conditions with Paratethyan affinities, and the upper, the Arenazzolo, a thin sandy unit indicating a higher energy environment whose duration is estimated at some thousand years. Marine faunas yielded by the Arenazzolo are interpreted as allochthonous. Sedimentary structures suggest a littoral setting at the edge of the lake, or a delta lobe.The main environmental change occurs at the base of the immediately overlying Trubi Formation, where open marine conditions indicative of oceanic depths mark the termination of the Messinian sa

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00926.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTKamloops Lake in central British Columbia is a deep, intermontane lake fed by the strong and seasonally variable flows of the Thompson River. Considerations of lake‐river interaction, supported by physical and geological evidence, suggest that sediment transport and deposition within the lake is controlled by three interdependent but distinct processes: delta progradation at the lake‐river confluence which results in delta topset and foresee bedding; sediment density surges originating along the delta face which result in turbidite sequences lakeward from the base of the delta; and dispersal by the interflowing river plume which, due to Coriolis effects, results in a higher sedimentation rate and greater fraction of coarser material along the right‐hand side (Northern Hemisphere) of the lake in the direction of

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00927.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTField observations are made of the formation of backwash ripples on the beach face, formed by undular hydraulic jumps generated by backwash down the beach face colliding with wave bores. Measured ripple wavelengths range from set averages of 48 to 70 cm. Within a particular set of ripples the spacing tends to decrease in the offshore direction. These observations are compared with laboratory experiments where undular jumps are generated in a flume, and with a computer simulation model which calculates both the flow within an undular hydraulic jump and the resulting sediment transport which gives rise to the backwash ripples. The computer model involves a numerical solution of the Bousssinesq equations which govern the fluid flow, and sediment transport equations which relate the sand transport rate to the local mean flow velocity. The model permits a study of the detailed time‐history of the undular jump development and the formation of the backwash ripples and shows good agreement with the field observations of backwash ripples, predicting an offshore decrease in their spacings. The laboratory experiments showed a similar result so long as the Froude number of the supercritical flow before the jump occurs is small (c. 1–4). Small differences between the computer model and experiments arose principally from the neglect of internal friction and surface tension in the mo

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00928.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTMirrol Trough of the northeast Atlantic contains five NNE‐SSW trending,en echelon, turbidite‐filled basins deeper than 5500 m, each ranging from 4 to 10 km in width and 19 to 65 km in length. Trough deposition has consisted mainly of turbidites from adjacent hills and ridges as indicated by the physiography of the region, sediment isopach map, the nature of the sediments in the trough, and benthic foraminiferal depth indicator species. The sedimentation rate on abyssal hills and ridges, as deduced from palaeomagnetic evidence, is 1.36 cm/103years. Using this sedimentation rate, it is estimated that Mirrol Trough subsided relative to the surrounding area and began receiving sediments between 8.3 and 11.5 m.y. ago; and the deposition of the most recent turbidite has occurred sometime between 29,000 and 44,000 years b.p. Tilting of the base of the most recent turbidite with respect to the basin floor is observed, and this is attributed to relative sinking of the eastern margin of the trough after the deposition of the most recent turbid

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00929.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTAn extensive sequence of small patch‐reefs occurs within the middle member of the Upper Coralline Limestone Formation (Upper Miocene) in western Malta. In the lower horizons of the Tal Pitkal Member these structures are lensoidal in cross section and are surrounded by coarse flanking biosparites. Towards the top of the member they become more irregular in form. Extensive biostrome developments occur in association with the later structures but unlike the patch‐reefs they were killed off periodically by episodes of exposure.The resistance of these structures to wave action is verified by the presence of extensive mollusc borings both in patch‐reefs and biostromes. The initial binders within both structures are considered to be stromatolitic algae. Early diagenetic rims were also precipitated around allochems and added further strength to the frame work. Within this framework pelleted micrites accumulated which contrast strongly with the sparite cements of the flanking sediments.The organic framebuilders were finally killed off by a particularly strong episode of submarine erosion, with the subsequent establishment of an oolite shoal over the entire r

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00930.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTIn the Borrego Desert (California) and in the Sinai Desert (Israel) laminated, microbially mediated carbonate crusts have been found and analysed biologically and mineralogically, and further studied with scanning electron microscope methods combined with energy dispersive X‐ray analyses. All morphological and biological features of the extant crusts justify the term ‘desert stromatolite’, a term applied to stromatolites from desert regions which form under permanent exposure to the atmosphere. These stromatolites are never covered by standing water, and running water (heavy rainfall) covers them for only a few hours during the year. Carbonate deposition is achieved principally by the cyanobacteriumPleurocapsasp. which exhibits characteristic yet different stages of calcification. Calcification occurs in the sheaths of single cells (including baeocytes) as well as in mature colonies. The specificity for calcification inPleurocapsa sp. is disc

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00931.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTFragments of echinoderms in the Karaisali Limestone (Miocene) of the Adana Basin, Turkey, show large syntaxial overgrowths which are restricted mostly to their undersides, whilst the upper surfaces are covered by micrite. Although this pendant style of the overgrowths is reminiscent of vadose zone ‘gravitational cement', they appear to have formed in the open voids of sediments in the marine environment, simultaneously with, as well as after, the internal deposition of micrit

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00932.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00933.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00934.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY