ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01772.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTConcretions from Upper Cambrian sediments in South Wales can be divided into two groups of different ages. An early group (type) are characterised by the association of septarian structures and deformed laminae; whilst later (type Ha) concretions developed both cone‐in‐cone structures and parallel laminae.Determinations of the cement content of individual concretions revealed centrifugal variations related to the porosity changes within the sediment during concretionary growth. Growth oftype‐Iconcretions began in sediment of approx. 70% porosity and continued until compaction had reduced the porosity to less than 40%. Later,type‐IIaconcretions began growth in sediment of approx. 30–40% porosity and experienced only slight compaction over their growth spans.Liassic concretions from a prolific concretionary horizon in Dorset developed parallel laminae, but grew early in the absence of compaction (type IIIb) concretions at this horizon grew within the sediment during a pause in deposition.Evidence is described for distinguishing between concretions formed in systems open or closed to seawater. It is concluded that Cambrian concretions grew in closed systems, but the early Liassic concretions may have developed in a partially open system.A model is offered to explain the closed system growth of prolific concretionary horizons. The Cambrian concretions often proliferated along 2–3 cm thick siltstone units, which it is suggested were more permeable than the surrounding mudstones and therefore became pore‐water migration paths. Along these migration paths concretionary growth may have relieved the supersaturation of mobil

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01773.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTDistribution and size of the reefs in the Wenlock Limestone (Mid‐Silurian, Wenlock area) indicate that the most suitable site for growth was at the seaward fringe of the reef belt. The reef development increased through time as clay‐mineral concentration reduced. Many reefs colonized small mounds of coarse crinoidal debris but growth also started on soft muddy substrates. The Wenlock structures have similar characteristics to modern patch reefs: they are small—the average width is 12 m and the thickness 4.5 m—and roughly oval in section. During growth reef surfaces were gently convex and reached heights of between 50 cm and 3 m above the sea bed.The organic framework of all reefs examined consisted of massive and branching tabulate corals, stromatoporoids, branching rugose corals and bryozoans; with stromatolites, laminar corals and stromatoporoids and bryozoans playing the role of reef binders. Most reef builders grew contiguously and are preserved in growth position. Biotic zoning within reefs was not detected. Biomicrites accumulated in interstices near the surface of the reef at the time of, and just shortly after, organic growth. The sea was probably less than 30 m deep and extreme shallowing at the close of the Wenlockian terminated reef development. However, reefs were not broken up by wave or current action. The inter‐reef sediments, which were deposited at the same rate as reef growth, are predominantly argillaceous crinoidal biomicrites alternating with thin shale bands. Very few beds of reef‐derived talus occur (Fig. 13–15). High influxes of clay minerals—especially bentonites—brought about local reef death.Diagenetic processes of dissolution, recrystallisation and compaction greatly modified the original fa

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01774.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTHalite lying above the potash‐rich interval of the Permian Upper Evaporite Group of northeast Yorkshire, England, is intimately associated with fine red clastics in such a way as strongly to suggest that the former originated by nucleation and growth within the latter. It is inferred that this process took place in distal sediments of a mature basin‐margin plain, probably in a belt subject to repeated inundation caused by periodic large‐scale expansions and contractions of an extensive basin‐centre playa. Such an environment is consistent with the generally shallow‐water to continental origin of the underlying Carnallitic Marl and the overlying Permian Upper Marls, and contrasts with the deep‐basin depositional model customarily applied to the Zechstein

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01775.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTSeveral observations on Jurassic and Cretaceous clastic rocks of west Siberia may be important not only for oil and gas exploration but also for other fields of interest:1The sand and silt percentage of the sections and the sand grain‐size increase in structural uplifts. This points to synsedimentary initiation of the present structures.2The percentage of convexo‐concave grain contacts increases with depth, this increase is greater below a depth of 2,300 m.3The percentage of wedge‐shaped grain contacts is higher in the water‐bearing sandstones from the same depth.4In the clay matrix of water‐bearing sandstones, kaolinite is widespread, whereas mixed‐layer minerals (montmorillonite‐hydromica) prevail in oil‐bearing sandstones. The quantitative evaluation of these and other investigations proved a relatively young oil accumulation and a still younger gas accumulation in the area under consideration. The older oils differ chemically from the younger ones.5The clay cover of oil‐ and gas‐bearing structures proved to contain less silt content and sand flasers than the clay cover of water‐bearing structures. It is suggested, that the sandy and silty clays were not effective in trapping the hydrocarbon accumulations, mainly because of stronger jointing (when compared to pure clays). With increasing depth, the content in expanded layers decreases in these clays. At the same time, the number of joi

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01776.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTThe Miocene “molasse” of Digne (subalpine chain) is studied in the profile along the Bramefan torrent. Gross lithological and paleontological contents, textures, structures and sole marks are described. All the types of sole marks are present (cf. the Plates), as in turbidites, but they point sometimes to opposite current directions on the same sole. Large‐scale (decimeter to meter) cross‐stratification is frequent. Graded bedding is very scarce. These observations do not indicate turbidites.These coarse‐bedded, well‐sorted sediments are interpreted as high‐energy deposits. Bird tracks and Mya in living position suggest a beach environment.Some “molasse” formations of Rumania and Spain are then discussed, especially with reference to MANGIN (1962) who shows, near a photograph of the Liedena formation, a picture of bird tracks from Barles: this example comes from the abovementioned Digne molasse, and is not an argument for the occurrence of such tracks in a new

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01777.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTGrain‐size distributions of sand samples by means of a Benthos Rapid Sediment Analyzer were determined, using SCHLEE'S (1966) fall times. The results were compared with analysis of the same samples by sieving. The Rapid Sediment Analyzer (RSA) consistently overestimated the mean diameter of fine samples and underestimated the diameter of coarse samples relative to sieving. Since we used a wider settling column and a smaller sample weight than did Schlee, we infer that the differences were due to weaker grain interaction effects in our analyzer. Thus, by using Schlee's fall times, we overcompensated for these effects. We conclude that the “new grain parameter” of fall velocity (SENGUPTA and VEENSTRA, 1968) is indeed valuable. MIDDLETON'S (1967) psi transform is more convenient than the analogous phi transform in that it yields Middle‐ton sand classes of 0 to 5 psi, as compared to Wentworth‐Krumbein sand classes of ‐1 to 4 phi. However, use of fall velocity does not completely obviate the need to determine grain diameter, since this is the most expedient criterion with which to correct fall velocity to standard fa

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01778.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

ABSTRACTTextural parameters of seventeen thin sections cut from specimens of neritic units of the Thorold and Grimsby Sandstones (Silurian), were examined. The interrelationships of grain orientation, grain size and grain elongation were found to be as follows:1The interrelationships among the textural parameterswithineach sample indicate that the coarser grains (0.24–0.39 mm) are more elongated and their orientations tend to cluster within few preferred orientational classes.2The interrelationships among the samples, within the same stratigraphic section, whose grain size averages range between the fine to the very fine sand grades, indicate that the average coarser grained samples have non‐preferred grain orientations.3Samples having a wider range (large measured dispersion) of grain sizes and elongations, tend to have weaker preferred grain orientations.4The type of grain orientation distribution in each sample appears to be more strongly related to themaximumvalues and measuredvariabilities, than average values of grain size and elongation.5Utilizing a multiple regression methodology, it is found that the values of thevector magnitudes per centof the preferred grain orientation distributions are best predicted if only the averages and standard deviations of grain elongations are taken into considerat

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1971.tb01779.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY