摘要:

ABSTRACTOn the Boso Peninsula, southeast of Tokyo, individual turbidite layers have been traced over about 38 km with the aid of tuff marker‐beds.Sandstones are generally much more variable in thickness than the interbedded mudstones, showing lenticular shapes with great lateral continuities up to 30 km or more. But the latter have greater extents than the former, forming extensive sheets with a slight upslope thickening. Most sandstones show vertical and lateral grading, while mudstones gradually coarsen upslope. Sandstones have a variety of sedimentary structures typical of turbidites, whereas mudstones are virtually devoid of them throughout. Sandstones contain intensely abraded shallow‐water fauna in contrast with mudstones with well‐preserved deep‐water fauna. Thus, mudstones are mostly of hemipelagic origin, and turbiditic mudstones, if present, are of negligible amounts.In general, individual sandstone beds are much more variable in thickness on the upstream side than on the downstream side. This is probably because of the existence of some minor channels and the adjacent levee‐like embankments on the upslope side. At the base of thicker sandstone beds local penecontemporaneous erosion has usually taken place, giving rise to a few minor channels bordered by small levee‐like embankments on both sides. The downslope side of the largest channel is commonly flanked by the greatest embankment that is coincident with the thickest part of each sandstone layer. Sandstones in the minor channels and levee‐like embankments contain a lot of mud lumps torn out of the substratum, which decrease in size and amount and improve in roundness with increasing distance from the channels. In general, thicker sandstones show Boumaabcdesequences around the thickest part. Boumad‐division and convolution are developed preferentially on the downstream side of the thickest part. With decreasing bed thickness laterally, the complete depositional sequences arc successively replaced by Boumabcde, thencde, and de sequences downslope, while by Boumabc/cand thenc/esequences upslope.The facies transition of the horizon studied probably represents a section extending from the downslope end of the channelized portion of a suprafan to the outer portion with a

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb01914.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTAlluvial fans of the last glacial age in the lower Derwent Valley in southeastern Tasmania were built by debris flows and stream flows. The deposits were derived from periglacial and nivational slope mantles at the highest altitudes in the fan catchments, and from regolith of uncertain affinities at the lowest elevations. The apical and middle parts of the fans commonly consist of coarse‐grained debris flow and water‐laid deposits, while the distal deposits are predominantly water‐laid sheetflood silts and clays. Channels are important in the proximal parts of the fans and are mostly filled with water‐laid sediments, less commonly by debris flow deposits. A first approximation to the mean velocity of the last stage of debris flow in a channel is between 4 m/sec and 6 m/sec. A group of ‘water‐laid’ sediments shows very poor separation of particle sizes, and two explanations have been offered for these sediments. Firstly, the large quantities of unsorted debris available from the catchments produced moderately well‐sorted slurries, or, secondly, openwork stream gravels were infiltrated by later water flows charged with fines. The streams crossing the fans also produced water flows with relatively low suspended sediment concentrations resulting in reasonably good sorting. The debris flows and ‘water‐laid’ muddy sediments cannot be distinguished using CM plots. The debris flows display considerable variation in thickness and grain‐size characteristics, which is attributable to properties inherent i

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb01915.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTSandstone mounds occur in some shallow marine heterolithic deposits from the Late Precambrian Stangenes Formation (N. Norway) and the Cambro‐Ordovician Crozon Formation (N. W. France) and Cabos Series (N.W. Spain). The sediments displaying the mounds accumulated in partially protected tidal flat/ lagoonal environments immediately before and during major transgressions.The mounds are erosional features typically occurring on the tops of sheet sandstones (ca. 50–500 mm thick) some of which may have a storm washover origin. Mound genesis related to periodic emergence and late stage run‐off is supported by their intimate association with mudcracks and other very shallow water features (e.g. bidirectional current‐formed structures, wave ripples, ladder and interference patterns, mudflakes, etc.). Variation in mound morphology suggests that post‐depositional dissection began as elongate ridge‐gully couplets with secondary erosion of the ridge flanks leading to the development of more characteristic hemispherical geometries. Emergence may have been a function of tidal fluctuations and/or subsidence of storm surge events.Facies sequences point to the repeated filling of these inshore environments by storm washovers superimposed on ambient tidal conditions which possibly resulted from the progressive decay of beach barriers during tr

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb01916.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTSix grades of near uniformly sized silica solids (ranging in median size from 15 μm to 160 μm) were sedimented in various natural aqueous electrolytes. The influence of surface forces on these silica‐electrolyte systems was then inferred from measurements of the packing coefficient, C, of each sediment. It was found that the packings were uninfluenced by surface chemical forces when the grade size was greater than about 100 μm. For smaller grades immersed in naturally concentrated aqueous electrolytes, C was found to decrease from an initial value of about 0·50, and this was explained by the onset of surface chemical attractive forces. For smaller grades immersed in pure water, C was found to increase to a maximum of 0·58. Three explanations for this phenomenon, namely a difference in shape with grade size, a decrease in intensity of deposition, and the onset of surface chemical repelling forces were examined and the latter explanation seemed the most probable. Measurements of the angle of repose for the sediments also showed the influence of surface chemical repelling as well as attractive forces in fine silica solids. The results may be used to aid interpretation of the fabric and stability of pre‐lithified sedimenta

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb01917.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTA study of septarian concretions from late Cretaceous shale sequences of Texas and northern Mexico reveals complex burial‐exhumation histories. First generation concretions and pre‐fossilized moulds formed in silty clays before significant compaction occurred. Syneresis cracks developed and were filled by length slow fibrous calcite with a decrease in iron content toward the centre of each vein; in some cases this was succeeded by growth of equant or bladed calcite. Subsequent erosion of enclosing sediment caused collapse and break up of concretions, leaving fragments and some unbroken concretions exposed to encrustation and boring on the sea floor. These were subsequently buried and enclosed in a second generation of concretions, which also developed syneresis cracks. The calcite that filled these latter cracks was generally bladed (sometimes followed by equant calcite) and contains more iron toward the centre of the vein. Differences between the calcite filling first and second generation septarian veins indicates changing diagenetic regimes during burial in the marine environment, without a major shift in diagenetic conditions, such as the introduction of meteoric waters. These conclusions have significant implications to cementation in ancient limestones, which show textural and chemical sequences similar to those present in the septarian concretions descri

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb01918.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTClinoptilolite, a zeolite of the heulandite group, occurs commonly in sediments as an authigenic mineral. In the Middle Eocene of southern Israel, it constitutes from a few per cent up to 80 per cent of the insoluble residue of the chalks and limestones. It is associated with opal C‐T, montmorillonite and palygorskite. These chalks and limestones overlie the Danian‐Palaeocene Taqiya marls which also contain a well‐established clay mineral sequence consisting of opal C‐T, montmorillonite, palygorskite, sepiolite, and clinoptilolite.This paragenesis of minerals is shown to be typical of the Upper Cretaceous to Eocene times. It is world‐wide, occurs in deep‐sea sediments as well as in shallow water sediments, and results from the abundance of silica which probably reflects a warmer climate during this time period.The concentration of magnesium in the sea‐water and its ratio to the other cations seem to determine which authigenic silicate w

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb01919.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

ABSTRACTThe surface textures of fine sand particles from the Deep Sea Drilling Project Leg 39 have been studied via scanning electron microscopy. A large portion of the coarsest fraction of these grains from deep sea cores were formerly fragments of larger sand‐sized grains that had been mechanically broken. Surface textures characteristic of previous aeolian and subaqueous environments were preserved in fragments broken from the original larger grain surfaces, thus making palaeo‐environmental reconstruction possible.Previously, characteristic mechanical markings had not been observed on deep sea sands; the momentum of grain to grain collisions with respect to fine sands is generally insufficient to initiate mechanical break

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb01920.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb01921.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb01922.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

History of the Earth Sciences during the Scientific and Industrial Revolutions with Special Emphasis on the Physical Geosciences.By D. H. Hall.Stromatolites.Edited by M. R. Walter.Calcareous Algae. Developments in Paleontology and Stratigraphy, Vol. 4.By John L. Wray.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1977.tb01923.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY