Sedimentology

MACK, GREG H.

doi: 10.1111/j.1365-3091.1978.tb00321.xpmid: N/A

ABSTRACT A greater than 50% decrease in the percentage of labile light minerals occurs between the non‐marine Cutler Formation (Permian) and its facies equivalent, the marine Cedar Mesa Sandstone, in the vicinity of Moab, Utah. Both the Cutler and Cedar Mesa Formations were derived from crystalline rocks of the Uncom‐pahgre Mountains under semi‐arid to arid climatic conditions. Furthermore, diagenesis had little effect on the light‐mineral fraction. Therefore, the significant change in mineralogy where the fluvial Cutler beds grade into the littoral marine Cedar Mesa deposits can be directly related to active reworking of detritus in the shallow marine environment. Less coarse perthitic alkali feldspar, twinned plagioclase, undulose mono‐crystalline quartz, and polycrystalline quartz in the Cedar Mesa with respect to the Cutler suggest that compositional maturation was produced by breakage of mechanically weaker grains during grain‐to‐grain collisions. Furthermore, the end products of compositional modification by shallow marine processes may be sufficiently different from those produced by weathering and dilution from sedimentary source rocks to allow evaluation of the relative effects of these processes on the origin of compositionally mature ancient sandstones.

MARTINI, I. PETER; SAGRI, MARIO; DOVETON, JOHN H.

doi: 10.1111/j.1365-3091.1978.tb00322.xpmid: N/A

ABSTRACT The Antola Formation of Upper Cretaceous age crops out extensively in the Northern Apennines and consists of graded units of calcareous sandstones, sandstones, marlstones, and shales. It can be subdivided into the Cerreto, Antola Marlstone, Bruggi, and S. Donato Members on the basis of bed thicknesses and percentage of shales. Although the whole formation is interpreted as a deep‐sea basin plain deposit, the members constitute lateral facies subdivisions which range from proximal, thick‐bedded turbidities that show a prevalence of thinning upward cycles in bed thicknesses to distal turbidites that show predominantly thickening upward cycles and have a high percentage of shale. Repetitive patterns in the lithological sequence of the turbidite association are generally distinctive and are satisfactorily described as first order Markov chains. Only the Antola Marlstone Member has an additional second order Markov property. Imaginary eigenvalues of the transition probability matrices of all but the Bruggi Member demonstrate a strong cyclic character in the lithologic ordering within the formation. The behaviour of the Antola Marlstone and of the Bruggi may reflect the influence of a secondary ophiolitic intra‐basinal source of clastics that contributed sandy turbidites and olistostromes. Systematic long‐term variations in the sequence of bed thickness development in some sections of the Antola Formation are often subtle and equivocal, and pose special problems in interpretation. Fourier analysis was applied to the task of partitioning fundamental wavelengths from “background noise” introduced by essentially random depositional processes. In all members there is (1) strong short‐term wavelength of two to three beds indicative of alternating thin and thick beds and judged to be typical of turbidite sequences; (2) an intermediate wavelength ranging from about five beds (proximal facies), eight beds (distal) to nine beds (very distal), which have both thinning and thickening upward trends, interpreted respectively as valley fill due to shifting talwegs of low density turbidity currents, and to progradational, flat turbidite lobes; (3) a poorly defined long‐term wave‐length of from thirty to greater than sixty beds that may be related to an unspecified trend in the evolution of the sedimentary basin. Phase angles associated with the coniputed power spectra give indications as to the asymmetry (thickening or thinning upward) or symmetry of the representative units.

CANT, DOUGLAS J.; WALKER, ROGER G.

doi: 10.1111/j.1365-3091.1978.tb00323.xpmid: N/A

ABSTRACT The South Saskatchewan River has a long term average discharge of 275 m3/sec, with flood peaks in the range of 1500 to 3800 m3/sec. South of Saskatoon, the four major types of geomorphological elements recognised are channels, slipface‐bounded bars, sand flats and vegetated islands and floodplains. Major channels are 3‐5 m deep, up to 200 m wide, and flow around sand flats which are 50‐2000 m long, and around vegetated islands up to 1 km long. At areas of flow expansion, long straight‐crested cross‐channel bars form. During falling stage, a small part of the crest of the cross‐channel bar may become emergent, and act as a nucleus for downstream and lateral growth of a new sand flat. The dominant channel bedforms are dunes, which deposit trough cross bedding. Cross‐channel bars deposit large sets of planar tabular cross bedding. Sand flats that grow from a nucleus on a cross‐channel bar are mostly composed of smaller planar tabular sets, with some parallel lamination, trough cross‐bedding, and ripple cross‐lamination. A typical facies sequence related to sand flat growth would consist of in‐channel trough cross‐bedding, overlain by a large (1‐2 m) planar tabular set (cross‐channel bar), overlain in turn by a complex association mostly of small planar tabular cross‐beds, trough cross‐beds and ripple cross‐lamination. By contrast, a second stratigraphic sequence can be proposed, related only to channel aggradation. It would consist dominantly of trough cross‐beds, decreasing in scale upward, and possible interrupted by isolated sets of planar tabular cross‐bedding if a cross‐channel bar formed, but failed to grow into a sand flat. During final filling of the channel, ripple cross‐lamination and thin clay layers may be deposited. In the S. Saskatchewan, these sequences are a minimum of 5 m thick, and are overlain by 0.5‐1 m of silty and muddy vertical accretion deposits.

HAY, R. L.; REEDER, R. J.

doi: 10.1111/j.1365-3091.1978.tb00324.xpmid: N/A

ABSTRACT Pedogenic calcretes are closely associated with Pliocene to Holocene wind‐worked deposits of volcanic ash in the Olduvai and Ndolanya Beds of northern Tanzania. The typical profile with calcrete consists of an unconsolidated sediment layer, an underlying laminar calcrete, and a lowermost massive calcrete. The laminar calcrete is a relatively pure limestone, whereas massive calcrete is aeolian tuff cemented and replaced by calcite. An Olduvai calcrete profile can develop to a mature stage in only a few thousand years. Carbonatite ash was the dominant source for most of the calcite in the calcretes. Replacement was a major process in formation of the massive calcretes, and oolitic textures have resulted from micrite replacing pelletoid clay coatings around sand grains. Phillipsite and possible other zeolites were extensively replaced in the massive calcretes. Replacement of clay by micrite in the Olduvai calcretes is accompanied by dissolution or leaching of phengitic illite and the formation of clay approaching the composition of halloysite or kaolinite. In the upper calcrete of the Ndolanya Beds, montmorillonite was altered to a kaolinite‐type mineral and to dioctahedral chlorite. Authigenic dolomite, zeolite, and dawsonite in the Olduvai calcretes probably received at least some of their components from replaced materials.

SCHLAGER, W.; JAMES, N. P.

doi: 10.1111/j.1365-3091.1978.tb00325.xpmid: N/A

ABSTRACT Carbonate ooze in the deep troughs between the Bahama Banks is a mixture of pelagic and bank‐derived material. It consists of aragonite, calcite and magnesium calcite in a ratio of about 3:2:1. Where exposed in erosional cuts at the sea floor, this ooze lithifies within 100,000 years and is transformed into calcite micrite of only 3.5‐5 mol % MgCO3. Where buried, the ooze maintains its original composition for at least 200,000‐400,000 years and remains unlithified for tens of millions of years. Quite unexpectedly, the path of sea‐floor diagenesis of peri‐platform ooze was found to be the same as that of freshwater diagenesis. Most of the aragonite is leached, pteropod shells often leaving cement‐lined moulds behind; magnesian calcite recrystallizes and loses magnesium; polyhedral calcite of 2‐4 μm size appears as cement. The setting and the carbon‐oxygen isotope ratios rule out any freshwater influence. Carbon isotope ratios remain heavy, oxygen ratios shift towards equilibrium with the cold bottom water. The calcite cement has 3.5‐5 mol % MgCO3 and can be interpreted as the least soluble form of calcite emerging from alteration at the sea floor or, alternatively, as a direct precipitate from cold sea water. The change in the composition of calcite cements with water depth supports the second interpretation. In the Bahamas and elsewhere in the world ocean, magnesium in calcite cements decreases from the warm surface waters down to 700‐1200 m, i.e. the boundary between intermediate and cold deep‐water masses. Below this level, calcite prevails and magnesian calcite and aragonite cements are restricted to semi‐enclosed seas with exceptionally warm bottom waters.

DAVIES, PETER J.; BUBELA, B.; FERGUSON, JAMES

doi: 10.1111/j.1365-3091.1978.tb00326.xpmid: N/A

ABSTRACT Field and laboratory studies suggest that different types of ooids form during quiet and agitated water conditions. Both types have been synthesized in the laboratory. Quiet water types exhibit a radial orientation of carbonate crystals, whereas in those formed in agitated conditions, a tangential orientation is prevalent. Successful laboratory formation of quiet water ooids was accomplished in supersaturated seawater solutions containing humic acids. Negative results were obtained from strictly inorganic solutions, and from those containing simple amino acids, single proteins, mixtures of proteins or mucopolysaccharides, soil and sediment extracts. Partly successful results were obtained using an organic extract from Bahamian ooids. The organic parameters most important in quiet water ooid formation are molecular weight, the presence of carboxyl groups and an ability to participate in hydrophobic/hydrophilic interactions, all of which are critical to membrane formation. Membranes form concentric shells which act as growth surfaces for carbonate and also induce the periodicity in carbonate precipitation. Ooids exhibiting a tangential orientation of batten‐like crystals have been synthesized under conditions of agitation, supersaturation and without the intervention of organic processes during the precipitation. Complete growth may be divided into agitation, resting and sleeping stages In the agitation stage, quartz nuclei induce an inorganic, heterogeneous nucleation from a supersaturated solution, which finally ceases as a result of Mg2+ and possibly H+ poisoning of the carbonate surfaces. No further precipitation occurs until the crystal surfaces are reactivated by removal of Mg2+ and H+ during the resting stage. Following a series of agitation and resting stages, precipitation is inhibited by a degree of poisoning which is not totally removed during the resting stage. For further growth, a new substrate is required and is provided by the development of organic membranes around the grains. This occurs when the grains are buried in the subsurface, the period of organic growth constituting the sleeping stage. Only 2% of an ooid's life is spent growing in the agitated environment, while 95% of its life is spent accreting organic membranes in the subsurface. Our experimental work indicates that ooids of Bahamian type are inorganic precipitates. The tangential arrangement of battens is the result of suspension in an environment where the degree of turbulence is sufficient to induce grain to grain contact of sufficient strength and frequency to inhibit any crystal growth other than tangential. The role of organics is to provide a substrate for further growth after precipitation has slowed to a point when no further accretion is occurring.

doi: 10.1111/j.1365-3091.1978.tb00327.xpmid: N/A

Book Reviewed in this article: The Fiuviai System, by S. A. Schumm. The Evolution of North America by Phillip B. King Studies in Paleo‐Oceanography, edited by William W. Hay Paleogeographic Provinces and Provinciality, edited by Charles A. Ross Tectonics and Sedimentation, edited by William R. Dickinson