ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1983.tb00645.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1983.tb00646.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTWidespread evaporitic sulphate horizons occur in the frequently dolomitic Mercia Mudstones (Upper Triassic) of the English Midlands. The mudstones were deposited on an extensive peneplain which had areas of upstanding minor relief (Charnwood Massif, Derbyshire—Pennines, London Platform). Horst and graben structures formed during the early and middle Triassic, controlled late Triassic sedimentation rates and peneplain slope directions. A stable isotope study (S,C,O) of the sulphates and dolomites of the Trent Formation indicates that during the deposition of the lower Fauld Member grabens such as the Need wood Basin in Staffordshire and areas marginal to a graben such as Newark in Nottinghamshire had a marine brine regime with minor continental input. Using constraints applied by sulphate concentrations of modern waters in arid environments, the ratio of volume of marine input to volume of continental input lay between 3:1 and 4:1. The horst area (East Leake, Nottinghamshire) was strongly influenced by continental brines which derived sulphate from the exposed Carboniferous Hathern Anhydrite Series. A predominantly continental brine regime existed across the whole area during deposition of the overlying Hawton Member. Periodic marine influxes gave rise to thin sulphate horizons whilst continental run‐off was occasionally sufficient to form temporary lakes. The Blue Anchor Formation (Rhaetian) was deposited in a lacustrine environment with waters of mixed marine and continental origin. Salinities were lower than those of the preceding Trent Formation bri

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1983.tb00647.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTThe middle member of the Loma del Toril formation (Kimmeridgian‐Lower Tithonian, Intermediate units, Betic Cordillera) consists of up to 250 m of resedimented carbonate material. Three units have been distinguished. The lower, Unit A, is composed of conglomerates that are interpreted as deposited in a major valley on the lower slope of a basin margin. Unit B, calcarenites with some conglomerate intercalation, is interpreted as distributary channel deposits and Unit C, calcarenites, as the result of poorly developed depositional lobes of a submarine fan. The three units form a recessional sequence. They cannot be related to a transgression because the Kimmeridgian‐Lower Tithonian in the Prebetic zone, where epicontinental sediments exist, is clearly regressive. The upper member of the Loma del Toril formation, made up of pelagic limestones with sporadic calcarenites or even thin conglomerate intercalations, is best interpreted as a basin plain facies. Lateral facies relationships suggest that down‐faulting of the basin floor controlled the development of the fan. The scarce occurrence of turbidite beds in the basin plain facies, the prevailing channelized facies and the obvious lack of overbank deposits, suggest a transport system of low efficiency, with fan deposition at the base of slope. The underlying Jurassic strata cropping out along fault scarps, coeval carbonate shelf material, and upper slope deposits were the main sources of turbiditic resediments. With respect to basin morphology sedimentary processes and fan geometry, this Jurassic turbidite basin can be compared with the modern California continental borderland. Ancient analogues have been described by Reinhart (1977) and Price (

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1983.tb00648.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTWeathering simulations carried out using a climatic cabinet have demonstrated that diurnal temperature and humidity variations typical of those occurring in warm desert environments are ineffective in causing static breakage of quartz dune sand and polymineralic regolith sand grains. Wetting and drying combined with temperature variations was also found to be a relatively ineffective weathering process. These results suggest that ‘crack tip’ processes are insignificant where mineral grains are not subject to static loading. Sodium sulphate weathering was found to cause slight damage to quartz dune sand grains and major damage to first cycle regolith grains. Feldspars and mica in the regolith sands were more susceptible to salt action than quartz. Salt weathering of the regolith sands produced substantial quantities of silt in the size range typically found in natural loess depos

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1983.tb00649.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTSurface sediments, cores and seismic reflection profiling delineate sedimentary environments and processes of sedimentation in Lake Tekapo. Sedimentation is dominated by the Godley River which forms an extensive delta in the northern third of the lake. Delta growth accounts for 55% of annual sediment deposition. In winter sandy muds are deposited at the top of the delta slope, where they may move under gravity as a surficial slide. Oversteepening of the upper slope also generates deep seated failures. The entire 20 km2of delta slope is subjected to rotational slumping which episodically reworks large volumes of sediment. Down the delta slope sedimentation rates decrease, surface sediments get finer and varves become better developed.In the lake basin sediments are parallel bedded varves, which contain typical winter‐summer annual cycles as well as minor, non‐annual flood varves. Annual varve thickness and semi‐annual varve frequency are determined by variations in the discharge of the Godley River. Sedimentation in the basin accounts for 40% of the budget and sedimentation rates decrease with distance from the delta, except at the distal end of the basin, where turbid underflows are stopped by the rising lake floor. Beyond the basin, sedimentation rates decrease abruptly. Coriolis deflection of inflowing river water increases sedimentation rates down the eastern shore. The remaining 5% of the sediment is deposited on the lateral slopes and shoulders where sediments form a thin muddy veneer over basement, which occasionally slumps to the basin

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1983.tb00650.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTThe Upper Triassic (Carnian?) Molteno Formation in the main Karoo (Gondwana) Basin, South Africa forms a northerly thinning, intracratonic clastic wedge comprising sandstones, shales and coals occurring within thick (up to 140 m) laterally persistent fining‐upward sequences. These sequences were deposited by braided streams draining an alluvial plain which may have been built on to the distal slopes of alluvial fan complexes of glacial outwash type. Geometric relations between sequences indicate three phases of tectonic activity. The lowermost fining‐upward sequence in the south accumulated against a rising mountain front; cessation of movement and an eastward shift in the main locus of tectonism and sedimentation was followed by renewed uplift and basinwide progradation of the second fining‐upward sequence adjacent to a fault‐block granite terrain located close to the present south‐east coastline of South Africa. This is believed to be the granite at the eastern end of the Falkland Island Plateau, an interpretation consistent with its position on most continental reconstructions and the fracture zone marking its northern scarp face. Faulting is attributed to the first phase of extension prior to continental breakup. The sourceward recession and lack of gross fining‐upward trends shown by the uppermost fining‐upward sequences is accounted for by limited back‐faulting of the still active basin margin. Cessation of activity and further basin margin recession occurred with deposition of the overlying floodplain deposits (Elliot Formation) which were distal equivalents of the braided

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1983.tb00651.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTPebbly sediments of the shallow marine Abrioja fan‐delta show pockets (bowl‐shaped structures, partly filled with pebbles) and pillars (elongate structures, filled with sand and pebbles). These structures are most abundant in pebbly sediments deposited on a steep slope (ca.25°‐10°) and are absent in conglomerates deposited on a slope ofca. 6° and less, although they are present in the pelitic top of these beds.The pocket and pillar structures are interpreted as fluid escape structures originating from local liquefaction and fluidization, processes which are favoured by rapid deposition, rapid sediment accumulation, the presence of less permeable layers and an immature sediment texture.These conditions are met in conglomeratic fan‐deltas, which have steep slopes with immature sediments. It is concluded that the presence of fluid escape structures in conglomeratic sediments may indicate a steep depositi

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1983.tb00652.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTThe pelagic sediments of the Semail Ophiolite are depositionally overlain by ophiolite‐derived sediments of the Zabyat Formation, dominated by matrix‐supported rudites, with subordinate arenites and lutites. The detritus was locally derived from the ophiolite, in a deep marine environment indicated by both underlying and overlying pelagic carbonates. The Zabyat rocks are restricted to fault zones in the ophiolite which were active during emplacement. They are interpreted as debris shed from the sub‐vertical fault zones during the initial disruption of the Semail ocean floor, prior to the final emplacement on to the Arabian continental margin. This interpretation places constraints on possible mechanisms of ophiolite emplac

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1983.tb00653.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTAn account of stream meandering and river morphology is given for five experiments, each having different conditions at the wetted perimeter of the channel.On the basis of the present experiments, it is proposed thata necessary (but insufficient) condition for the formation of stream meandering is an appropriately small ratio of total bank shear force to total bed shear force, both per unit length downstream. In mathematical form, the criterion is expressed byτsand τsare an average bank stress and bed stress, respectively, andpsandpbb are an average bank wetted perimeter and bed wetted perimeter of a half‐channel, respectively. The value of α is evaluated by Kinoshita's (1957) experiment and others.It is also found that the flow pattern, channel morphology and sand waves on the bed are dependent upon the boundary conditions at the wetted perim

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1983.tb00654.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY