摘要:

ABSTRACTNew formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles. A low‐air‐density wind tunnel was used to extend the range of previous investigations and to separate the effects of Reynolds number and interparticle forces of cohesion. The new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the Earth, Mars, and Ve

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1982.tb01713.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

ABSTRACTWhere bedforms migrate during deposition, they move upward (climb) with respect to the generalized sediment surface. Sediment deposited on each lee slope and not eroded during the passage of a following trough is left behind as a cross‐stratified bed. Because sediment is thus transferred from bedforms to underlying strata, bedforms must decrease in cross‐sectional area or in number, or both, unless sediment lost from bedforms during deposition is replaced with sediment transported from outside the depositional area. Where sediment is transported solely by downcurrent migration of two‐dimensional bedforms, the mean thickness of cross‐stratified beds is equal to the decrease in bedform cross‐sectional area divided by the migration distance over which that size decrease occurs; where bedforms migrate more than one spacing while depositing cross‐strata, bed thickness is only a fraction of bedform height.Equations that describe this depositional process explain the downcurrent decrease in size of tidal sand waves in St Andrew Bay, Florida, and the downwind decrease in size of transverse aeolian dunes on the Oregon coast. Using the same concepts, dunes that deposited the Navajo, De Chelly, and Entrada Sandstones are calculated to have had mean heights between several tens and several hundred

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1982.tb01714.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

ABSTRACTThe aragonitic molluscs and lime‐mud of the Pennsylvanian Buckhorn asphalt (Deese Group) of southern Oklahoma precipitated calcium carbonate in oxygen and carbon isotopic equilibrium with ambient sea‐water. In addition, δ18O values indicate that the pelecypods precipitated their shells during the warmer months of the year. The coiled nautiloids probably precipitated their shells in the warm surface water and throughout the year. For the orthocone nautiloids, the δ18O values suggest that they precipitated their shells in deeper/cooler water.The low‐Mg calcite brachiopods of the Mississippian Lake Valley Formation of New Mexico precipitated shells in oxygen and carbon isotopic equilibrium with ambient sea‐water.The δ18O and δ13C values of the Buckhorn and Lake Valley faunas, in conjunction with other published results, suggest that Carboniferous sea‐water was, on a average, depleted in δ18O by 1·5 ± 2‰, PDB, relative to Recent sea‐water. However, the δ13C value of +2.6 ± 2‰, PDB, for average Carboniferous sea‐water is similar to that of Recent ocean water.Early diagenetic alteration of metastable carbonates probably occurs in a meteoric‐sea‐water mixing zone. In this zone the oxygen and carbon isotopic compositions of these components are increased by about 2‐4‰,

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1982.tb01715.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Book Reviewed in this article:Sandstone Depositional Models for Exploration for Fossil Fuels, 2nd edn, by George de Vries Klein.Soil Erosion, ed. by M. J. Kirkby and R. P. C.Economic Geology and Geotectonics, ed. by D. H. Tarling.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1982.tb01716.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY