摘要:

SummaryA description is given of the sedimentary structures and pebble orientations of two braided rivers, the Durance and Ardkhe, whose origin, hydrology, mineralogy, and mechanical composition are already well known.Microtopographic measurements indicate uneven bedding planes. Macrostructures of the deposits show many channel or festoon laminations alternating with bar deposits, showing parallel bedding or oblique, foreset laminations.Oblique laminations (foreset lamination) occur mainly at the downstream ends of the bars along the upstream side of steep concave banks of channels running obliquely to the general valley trend.Pebbles, gravel, and coarse sand dominate over silty deposits which occur as the top layer of the flood plain and occasionally as channel fill. These silty deposits (loams) are very sandy and contain many irregular current ripple marks, distinguishing them from the heavy clay deposits of the flood plain of meandering rivers.Graded bedding is rare. Structures resembling the flute casts and load casts of turbidity currents have been observed but are uncommon. Irregular current ripple marks of horseshoe shape and erosion flow marks parallel to the current direction are common.The average orientation of the long axis of cobbles, pebbles, and coarse sand grains is normal to the current direction. The inclination of flat pebbles is upstream. Points aiding in discrimination between deposits of braided rivers and of turbidity currents are given in Table II.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1962.tb00453.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

SummaryThree methods for the determination of the free energy A F, of the reaction,are discussed: the method of two triple points, that of combining solubility products and that of combining dissociation pressure curves.The first method, although thermodynamically well founded, fails by irreversibility, and by the third method data of sufficient accuracy are unlikely.The solubility products (L) necessary for the second method may be derived either from solubility or from pH measurements, the results being in good agreement. For dolomite,L25D= (1.26 ± 0.24) · 10‐17is the average of values from the experiments described in this paper and these of Kramer(1959). The mean value obtained from the solubility and the pH data is Δ F1°= 1720 ± 280 cal.; forLM25the two values 3.43 · 1.3 · and 1.3 · 10‐7have been found i

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1962.tb00454.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

SummaryBeds of fairly pure to impure dolomite, varying in thickness from 1 mm to 1 ft., occur widely throughout a large part of the Salt Flats of the Great Salt Lake Desert in Western Utah. Most of the sediments studied evidently formed within the past few tens of thousands of years (as dated by C14methods), during late Lake Bonneville and Recent time. Alternating dark and light layers of dolomite, carbonate‐bearing clays, and clays make up the upper few feet of sediment that was sampled. Dark layers however, are significantly higher in silicates plus SiO2, content and have approximately twice as much Mg2+as the light layers. The writers suggest that the process of dolomite‐formation was hastened by elevated temperatures, occasioned by solar absorption through a saltcrust “window” over the salt pans. Results of this study indicate that the dolomite is possibly of secondary origin (replacement type). Enough information is not available at this time in order to determine the duration of diagenetic dolomitization in terms of days, weeks or years, nor is it known if the diagenetic alteration of calcite to dolomite occurred at the sediment‐water interface or after burial (or both at differe

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1962.tb00455.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

SummaryA number of illustrations are presented, which show some characteristics of the reefs occurring in the Upper Visby and Hogklint Beds of Gotland. These series should probably be correlated with the uppermost Llandoverian and Lower Wenlockian. Reef growth took place as the water became progressively shallower. There are no reefs in the lower part of the Upper Visby Beds, which consist of marl with limestone Ienses, and was formed in relatively deep water. No reefs occur in the uppermost Hogklint, which consists of an algal limestone formed in very shallow water.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1962.tb00456.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY