摘要:

ABSTRACTVertical sequence analysis within 1500‐2500 m thick coarse‐grained coalfield successions allows six sedimentary associations to be distinguished. These are interpreted in terms of depositional environments on, or related to alluvial fans which fringed a fault bounded source region. (i) Topographic valley and fanhead canyon fills: occurring at the bases of the coalfield successions and comprising sporadically reddened, scree, conglomeratic thinning and fining upward sequences, and fine‐grained coal‐bearing sediments. (ii) Alluvial fan channels: conglomerate and sandstone filled. (iii) Mid‐fan conglomeratic and sandstone lobes: laterally extensive, thickly bedded (1‐25 m) and varying from structureless coarse conglomerates and pebbly sandstones, to stratified fine conglomerates and cross‐bedded sandstones. (iv) Interlobe and interchannel: siltstones, fine‐grained sheet sandstones, abundant floras, thin coals and upright trees. (v) Distal fan: 10 cm‐1.5 m thick sheet sandstones which preserve numerous upright trees, separated by silt‐stones and mudstones with abundant floras, and coal seams. The sheet sandstones and normally arranged in sequences of beds which become thicker and coarser or thinner and finer upwards. These trends also occur in combination. (vi) Lacustrine: coals, limestones, and fine‐grained, low‐energy, regressive, coarsening upward sequences.Proximal fan sediments are only preserved in certain basal deposits of these coalfields. The majority of the successions comprise mid and distal alluvial fan and lacustrine sediments. Mid‐fan depositional processes consisted of debris flows and turbulent streamflows, whilst sheetfloods dominated active distal areas. A tropical and seasonal climate allowed vegetation to colonize abandoned fan surfaces and perhaps resulted in localized diagenetic reddening. Worked coals, from 10s cm‐20 m thick, occur in the distal fan and lacustrine environments.These alluvial fan deposits infill‘California‐like’basins developed and preserved along major structural zones. In many of their characteristics, in particular the occurrence of thinning and fining, and thickening and coarsening upward sequences and megasequences, these sediments have similarities to document

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1978.tb02076.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

ABSTRACTPetrographic studies of Tertiary and Pleistocene caliche from the western Mediterranean show some unusual calcite structures. These structures were designatedMicrocodium elegansGlück 1912. New data are presented which question earlier interpretations with regard to the origin of this structure. The new discovery ofMicrocodiumin Recent soils extends its stratigraphic range into the Holocene. Retention of fine detail in Recent samples, revealed by light microscopy and SEM, has suggested an origin hitherto unconsidered, calcification of mycorrhizal associations. Ancient and RecentMicrocodiumfabrics are compared; sufficient preservation of ultrastructure in the Ancient indicates a homologous origin.Environmental, stratigraphic and palaeoecological significance ofMicrocodium is discussed: correct recognition indicates existence of a palaeosol, and hence is a valuable criterion for recognition of continental conditions, cessation of sedimentation, subaerial exposure, and time‐equivalent horizons. In particular.Microcodiumis a characteristic component of caliche in the western Mediterranean. A review of the literature suggests that its presence may have been overlooked or misinterpreted in other parts of the world and, thus, may be more widespread than hitherto suspected.This study, in its embryonic stage of development. illumines the potential importance of biolithogenesis within terrestial carbonat

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1978.tb02077.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

ABSTRACTThe87Sr/86Sr ratios and strontium concentrations for thirty‐three samples of marine carbonate rocks of Middle Triassic to Early Jurassic age have been determined. The samples were collected from four measured sections in the areas of Val Camonica in northern Italy. The strontium concentrations vary from 40 to 7000 ppm. Most of the samples are calcitic limestones containing less than 10% of non‐carbonate residues. Dolomitic samples and those containing appreciable non‐carbonate residues have significantly diminished strontium concentrations.87Sr/86Sr ratios of the carbonate phases of these rocks appear to be unaffected by dolomitization and by the presence of non‐carbonate minerals. The average87Sr/86Sr ratios of the formations vary systematically in a stratigraphic sense. The ratio increased from Early Anisian to Early‐Middle Ladinian, declined during Late Ladinian and Carnian, rose again during the Norian and then declined throughout the Late Norian (Rhaetian), Hettangian, Sinemurian and Pliens‐bachian ages. The average87Sr/86Sr ratios, relative to 0.7080 for the Eimer and Amend standard, are: Anisian: 0.70805 ± 00019; Early Ladinian: 0.7085 ± 0.00038; Late Ladinian: 0.70791 ± 0.00013; Carnian: 0.70776 ± 0.00015; Norian and Rhaetian: 0.70791 ± 0.00014; Hettangian: 0.70762 ± 0.00021; Sinemurian: 0.7070 ± 0.00038; Pliensbachian: 0.7070 ± 0.00015. These variations reflect changes in the isotopic composition of Sr entering the oceans in early Mesozoic time due to varying rates of weathering and erosion of young volcanic rocks (low87Sr/86Sr) and old granitic rocks (high87Sr/86Sr). The data presented in this report contribute to a growing body of information regarding the changes that have occurred in the87Sr/86Sr ratio of the oceans

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1978.tb02078.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

ABSTRACTThe upper part of the Riley Formation, Cambrian of central Texas, is primarily composed of a sequence of thoroughly trough cross‐stratified deposits. The dominant lithologies range from fossiliferous glaucarenite to highly glauconitic bio‐sparrudite. These cross‐stratified deposits accumulated within a tidal inlet and associated lagoonal tributary and distributary channels. Tidal inlet‐fill strata are underlain by shallow, open marine oosparites and biomicrites and are overlain by parallel bedded glaucarenites which accumulated as part of a barrier island complex. The parallel bedded deposits exhibit large scale, gently inclined strata, ripple cross‐stratification, and a minor amount of vertical burrows.Some glaucarenite units within the tidal inlet‐fill have local concentrations of skeletal material, primarily trilobite carapaces. These concentrations are most abundant in the bottoms of troughs. Cementation by bladed to fibrous spar between the carapaces has resulted in the nodular appearance of these skeletal accumulations. Calcite clasts, with relict evaporite textures, occur within the carbonate nodules and surrounding glaucarenite. These clasts were eroded from the shallow subsurface of the barrier island as the tidal inlet migrated. The presence of the former evaporite clasts attest to an arid climate at the time of thei

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1978.tb02079.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

ABSTRACTIn the Kokkinovrakhos Formation of central Greece, poorly sorted, grain supported, lithoclastic carbonate rudites, megabreccias and olistoliths are associated with accumulations of fine‐grained laminated carbonates. The laminae frequently exhibit grading and are interpreted as turbidity current deposits. The coarser grained rudites and megabreccias were also redeposited but were probably transported downslope by sliding and rolling, i.e. they are rock‐fall deposits. Olistoliths were emplaced into deeper water by sliding. The fine‐grained sediments of the laminated facies appear to have accumulated in pockets on an uneven sea floor during episodes of minimal rock fall activity. The sedimentary association is similar to that described from some modern fore‐reef environments and is possibly characteristic of accumulations of sediment on, or near to, steep slopes adjacent to carbonate platforms, when episodes of tectonic activity lead to the shearing off and transport downslope of masses of well‐cemented shallow marine c

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1978.tb02080.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

ABSTRACTThe log‐probability plots of some shallow to deep Atlantic sediments are analysed and compared with simulated mixtures of log‐normal populations. The plots consist characteristically of two smoothly connected segments which display different slopes. The point of maximum curvature (PMC) between the two segments is shown to reflect the granulometric parameters (mean and sorting) and quantitative proportions of two mixed overlapping populations. This understanding is contrary to the concept which relies heavily on the break points of cumulative plots as indicating truncation of grain size distributions and therefore reflecting hydrodynamic processes.The particular behaviour of the cumulative plots from the Atlantic indicates fining of the two component populations with depth and distance from the shore, accompanied by an increasing dominance of the finer population. This behaviour is compatible with sorting processes which operate in sediments transported through individual grain movements, rather than through mass transportation or turbidity curre

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1978.tb02081.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

ABSTRACTAbundance fluctuations ofAmphisteginain the upper 4–5 cm of a few small cores from the Gulf of Elat look somewhat like rainfall fluctuations in the hinterland. To correlate the two patterns, a sedimentation rate of 2.2–3.3 mm/year must be assumed. A similar rate is obtained from estimates of annual production ofAmphisteg

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1978.tb02082.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY