ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01602.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01603.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTWe have reconstructed the depositional environment of the gypsum‐carbonate‐shale sequence that comprises the Upper Permian Bellerophon Formation of the southeastern Alps in northern Italy. This formation, which reaches a maximum thickness of 600 m, is roughly divided into two facies: (a) a lower dolomite‐gypsum facies, and (2) an upper micritic‐skeletal limestone facies. It directly overlies, with transitional contact, a thick red‐bed sequence (alluvial fanglomerates, fluviatile sandstones and flood‐plain siltstones) and is sharply overlain by Lower Triassic calcarenites (oolites, grapestones, pellets, flat‐pebble conglomerates).The lower evaporite facies rocks are found in well‐defined cycles, each of which, from bottom to top, consists of (A) thin‐bedded, worm‐burrowed, vuggy ‘earthy’ micritic dolomite, (B) massive to poorly laminated dark grey to black sandy dolomite carrying isolated gypsum nodules, (C) layered (thin‐bedded) nodular gypsum (commonly with ‘enterolithic’ folds) with fragmented partings of dolomite, and (D) massive ‘chicken‐wire’ nodular gypsum. At Passo di Valles, just east of Predazzo, and 50 km from the basin margin, we measured forty‐six consecutive complete cycles, with an average thickness of 3 m per cycle.We interpret the cyclic sequence as having been deposited in a prograding shallow lagoon—sabkha complex. The worm‐burrowed ‘earthy’ dolomite mud accumulated in a shallow hypersaline subtidal lagoon. The black sandy dolomite was an ‘intertidal’ sand‐flat devoid of algal mats and constantly churned by burrowers (likely crustaceans). As the shoreline prograded lagoonward evaporative concentration of the groundwater induced diagenetic growth of anhydrite nodules (now gypsum) within the porous sandy dolomite. The layered nodular and ‘chicken‐wire’ gypsum of the cycle cap is an extreme product of such displacive intra‐sediment growth of anhydrite (now gypsum) above the water table of a completely exposed sabkha, such as is found in the Persian Gulf today.We have observed the same cyclically arranged lithologies in two other evaporite sequences in Italy: the Triassic Raibl Formation of the Southern Alps and the Upper Triassic Burano Formation of the central Apennines. We suggest that this mode of deposition is likely a very common one for

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01604.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTMagnesian calcite is an important sedimentary component in the deep‐sea sediments of the eastern Mediterranean Sea, comprising an average of 20–50% of the carbonate fraction in most areas. The lack of any obvious biogenic source, plus similarities with magnesian‐rich lutites from the Red Sea and deep‐sea cements from other areas suggest that this magnesian calcite was precipitated inorganically.Although the exact mode of precipitation is not understood at present, it probably occurred at the water‐sediment interface under elevated salinity and temperature conditions, such as those present in the modern eastern Mediterranean. Precipitation did not occur during periods of lower temperatures and/or salinities such as during the stagnant conditions caused by the influx of fresh waters from melting Pleistocene glaciers.The eastern Mediterranean magnesium‐rich sediments appear to represent an intermediate stage between normal deep‐sea sediments and those from the warm hpyersaline Red Sea. Normal deep‐sea carbonates are composed almost entirely of biogenic calcite, whereas the Red Sea magnesian calcite alternates with layers of aragonite that were precipitated under elevated salinity and temperature conditions brought about by lowered stan

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01605.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTThe objective of this study is to locate as closely as possible the sites of strontium, magnesium, sodium, and potassium in modern aragonitic corals, specifically whether these cations are adsorbed, or are substituted in the carbonate lattice or are incorporated in organic components. In addition to locating the sites of each of these four elements we wanted to find out quantitatively how much of each element occurs at each site. The experiments in this study are based on thedissolutionrate of aragonite in distilled water and on thesubstitutionof strontium and magnesium by calcium and sodium. Special attention has been given to the occurrence of strontium, magnesium, sodium, and potassium in the organic components of the corals.The main site for strontium in the corals is in the aragonite lattice. Twenty‐five per cent of the total magnesium occurs in adsorbed sites and in organic compounds. The rest of the magnesium may be located in the aragonite lattice, but it is easily removed by repeated leaching or by replacement with calcium ions. Another possibility is that magnesium may occur in a dispersed mineral phase more soluble than aragonite because magnesium was released at a higher Mg to Ca ratio than is found in the solid coral; also because no local concentration of magnesium could be detected with an electron microprobe. About 12% of the total sodium is in adsorbed sites and is included in the organic compounds. The rest of the sodium might be in the lattice replacing calcium, but the low total exchange capacity is not enough to provide the needed charge balance. Another possibility is that sodium is located in a proposed mineral phase. Potassium is in adsorbed sites and incorporated in the organic compounds to an extent greater than all the other elements studied (30% of the total potassium), but again the evidence suggests that the remaining potassium is in a proposed mineral phase.Calcite is detected on the surfaces of aragonite corals after 5 months in thesubstitutionexperiment. The change of argonite to calcite took place after the inhibitor magnesium was exchanged from the surface sites and replaced by calcium.The organic compounds in corals contain small amounts of strontium, magnesium, sodium and potassium. Strontium is preferentially enriched in the organic compounds over magnesiu

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01606.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTDuring the early Upper Jurassic, widespread deep‐sea radiolarites were deposited in most parts of the Northern Limestone Alps. In the formation described (Tauglboden‐Schichten), these pelagic sediments interfinger with local‐source clastic material. Depending on the topography and the kind of material, either slides and slumps, mudflows, grain flows or turbidity currents operated and formed slump‐folded beds, mud‐flow breccias, fluxoturbidites or turbidites.A breccia had been traced over an area of 20 km2. Its variation is described in terms of lithological columns, bed thicknesses, maximum grain sizes and grain orientations. It forms a tongue‐shaped body, which was probably a part of a submarine fan. The fluxoturbidites of the proximal area grade distally on three sides into turbidites within 3–5 km.The clastic material consists of marls and limestones of Rhaetian and Jurassic age. It was probably derived from a tectonically uplifted palaeo‐high by an interplay of tectonics and gravity. The clastics were deposited on submarine fans bordering this high.In its lithology the formation closely resembles certain marginal facies of

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01607.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTThe basal unit of this flysch sequence consists of about 700 m of rhythmically interlayered red and green claystone intercalated with feldspathic sandstone and lithic conglomerate. Chemical analyses show that both types of claystones have approximately the same Fe2O3content (8%).The presence within green claystone of inarticulate brachiopods, thin laminations of phosphate and pyrite, coupled with a high Mn content (Fe/Mn : 27) together with the composition of the chlorites, suggest that green mud was deposited slowly in a marine environment under reducing conditions. The hematite content of red claystone averages 4%. The Fe/Mn is high (71), and the clay fraction contains chamosite in addition to chlorite and illite. These characteristics favour a paralic oxidizing environment for the red muds.Rapid resedimentation of red sediment from a paralic environment into the green lithotope, rather than a lateral variation of facies, is suggested by: (1) the distribution of the two hemirhythms in the stratigraphic column, (2) the presence in the red hemirhythm of large slump structures, contorted laminations, and pebbly claystone, and (3) by the internal sedimentary structures of the coarse fraction.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01608.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTThe flysch of Paleocene to Eocene age outcropping in an almost unbroken cliff section at the Playa de San Telmo, Zumaya, North Spain, has been the subject of a quantitative sedimentological analysis. It is inferred that sedimentation commenced with deposition of a limestone‐red shale sequence below wave base and continued with proximal and then distal turbidite sandstones deposited in what may have been a gradually deepening trough. The trough was probably oriented approximately east‐west, parallel to the subsequent main tectonic trend. Sediment transport within the trough appears to have been essentially axial, with calcareous and siliceous sand derived from the east, but some siliceous sand was also laterally transported mainly from a land mass to the north.The sediments contain an abundant and varied suite of trace fossils. Thus, with the depositional environment already defined sedimentologically, it was possible to critically examine the relationship between facies, trace fossil distribution and possible water depth. The facies variations were shown to be reflected in a changing ichnofauna. Spreite such asZoophycosandRhizocoralliumwere present in limestones apparently deposited not far below wave base. These traces are replaced by rosetted, winding and meandering forms in the more proximal turbidite facies. In the more distal facies spiral and patterned trace fossils appear, winding and meandering forms are common butZoophycos, Rhizocoralliumand rosetted traces are absent. It is inferred that these changes reflect faunal distribution on the sea floor rather than preservational fact

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01609.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTPyrenean debris dispersed in relation to the Miocene tectonic phase filled the northern part of the Ebro basin. In the studied area (50 km south of Pamplona) the Miocene sediments are represented by fluviatile sequences consisting of flood basin and point‐bar deposits forming fining‐upward cycles.The point‐bar character of part of these sediments is not only evidenced by the internal sedimentary structures, but also by the fact that the corresponding meander bends, about 200 m in radius, are clearly visible on aerial photographs. In this way a unique opportunity is given to compare directly the vertical profile and the surface pattern of ancient small size point bars.The internal structure consists of many imbricated and concentrically arranged bundles corresponding to the accretional topography of the point bar. The separation planes between the bundles are erosional and dip toward the channel axis. The internal structure of each bundle is festoon mega‐cross‐stratification whose direction points toward the convex bank, away from the channel axis. The resulting structure resembles the Epsilon cross‐stratification of Allen (1965a) and its origin is the same as postulated by Allen for this kind of cr

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01610.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

ABSTRACTThe experimental evaporation of brine in shallow vessels shows that layered halite can form by the overgrowth of crystals in mats that have foundered from their initial position of growth at the brine‐air interface; by the upward and lateral growth of crystals that have nucleated on the floor; and by the overgrowth on detrital halite. Each of these processes, and its resultant crystal fabric, is described in relation to the environmental factors which influence it.The fabrics of primary halite crystals in layered halite‐rock and associated deposits from the Lower Keuper Saliferous Beds of the Cheshire Basin are described and compared with those of the experimentally produced halite. Some of the ancient halite‐rock may be matched with floor‐nucleated crystals, and some with detrital halite; none can be shown to have grown from foundered mats. The halite‐rock is regarded as having formed in shallow brine bodies, perhaps only a few centimetres deep, but of unknown extent, whilst the presence of planar solution or deflation surfaces at the top of the layered units, and disruptions in bedding similar to buckled salt‐crust structures, point to periodic and perhaps prolonge

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1973.tb01611.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY