ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00335.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTThis address reminisces and reflects on a subject in which I have been involved for more than twenty years: the effect of depositional processes on various parameters of the size‐frequency distribution of sands. Movements of air and water generally separate particles by their sizes; the distribution of sizes relates to (1) the availability of different sizes of particles in a parent material, (2) processes operating where the sediments are deposited, particularly the competency of flow, and (3) concentrations of particles in suspension. Differences in size‐frequency distributions among sands correlate with various origins, that is with their terminal depositional environments. Reminiscences in this address express my personal experience, both its up and downs, in advocating the study of this relationship, particularly in applying the method of moments on the basis of the concept that one statistical function expresses the characteristics of the population of particles.This address re‐emphasizes some points made in previous studies (Friedman, 1961, 1962b, 1967) on the interrelationship between textural parameters and depositional processes for beach, dune, and river sands and then complements and supplements data which have not been presented before. These new data are grouped on scatter plots for sands of various origins. Finally, this address displays on maps regional trends of process‐induced changes in size distributions of populations of particles in sands of four different settings: (1) a beach‐dune setting, as exemplified by Padre Island, Texas, on the shores of the Gulf of Mexico; (2) a point‐bar setting in the Arkansas River of Oklahoma; (3) a continental shelf‐slope setting in the Gulf of Mexico off Louisiana, Mississippi, and Alabama; and (4) a continental shelf setting of the western Atlantic Ocean off New Jersey.This address concludes with the observation that the distribution of particles in sands will be influenced by the conditions that determine what happens in the depositional environment, hence statistical parameters that define the size‐frequency distribution may be related to fo

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00336.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTThe Ringwood evaporite is part of the 900 m.y. old Bitter Springs Formation, a warm‐water shallow‐marine sequence of stromatolitic dolomite and limestone, microfossiliferous chert, red beds, quartzite, and evaporites. The evaporite at Ringwood comprises two parts: (i) a lower 127 m characterized by brecciated pyritic bituminous dolomite, together with smaller amounts of dolomite‐gypsum breccia, friable chloritic dololutite, coarsely crystalline anhydrite, and satin‐spar gypsum; and (ii) an upper 133 m which is similar except that bituminous dolomite forms only one bed, and the characteristic rock‐type is dolomite‐gypsum breccia. The evaporite is overlain by limestone breccia and massive stromatolitic limestone, interpreted as an algal reef. Gypsum is secondary after anhydrite, and the ratio of gypsum to anhydrite increases upwards. The evaporite shows none of the features of a sabkha or desiccated deep ocean basin deposit, and instead is interpreted as the filling of a barred basin which was cut off from the ocean by growth of an algal barrier reef. As circulation became restricted, bituminous dolomite deposited in the lagoon behind the reef, together with pyrite from the destruction by anaerobic bacteria of algal debris derived from the reef. With continued evaporation, brine concentration increased and gypsum precipitated. Occasional dust storms contributed wind‐blown clay to the deposit. The barrier reef transgressed diachronously across the evaporite lagoon, and was eventually drowned when normal marine conditions became established. Burial of the evaporite to about 7000 m beneath the succeeding sediments of the Amadeus Basin converted gypsum to anhydrite, and formed chlorite by reaction of clay with dolomite. Late Palaeozoic tectonism folded and brecciated the rocks, and was followed by erosion which eventually exposed the evaporite to ingress of meteoric water. Hydration of anhydrite to gypsum ensued, the reaction becoming less complete with increasing depth from the g

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00337.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTGrain‐size frequency distributions of suspended loads at different flow velocities and over sand beds of four different grain‐size patterns were studied in a laboratory flume. The proportion of bed material which went into suspension increased with decrease of grain‐size in each case, but the modes of the suspended loads occurred in the size classes intermediate between the coarsest and the finest. With increase of flow velocity, as also with decrease of the bed's mean grain‐size, the total amount of material in suspension markedly increased, mainly due to addition of particles to the medium size classes.The coarsest grains in the bed resisted erosion due to their weight, whereas the finest ones were either not available in sufficient quantities or resisted erosion due to their homogeneity. The finest of the erodible grains which were abundantly available in bed were therefore, lifted up in large quantities. This size sorting took place at or near the bed surface and was closely related to the process of bed form migration.Large accumulation of medium sized particles in suspension at high velocities led to lognormal grain‐size distributions when the nature of the bed (source) material was suitable. At lower velocities, or over other types of bed materials, the phi (log)‐probability plots of cumulative grain‐size distributions of the suspended loads resolved into a number of straight lines. Mixtures of linear segments on phi‐probability graphs therefore, need not necessarily indicate different modes of sediment transportation, as is commonly believed, but might reflect the conditions of flow and the nature of the

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00338.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTThe two main methods of estimating palaeoslope direction from slump structure orientation data are reviewed. The mean axis method takes the downslope direction as the perpendicular to the mean slump fold axis. The separation are method estimates the downslope direction by the bisector of a planar separation angle between groups of slump folds with opposite downplunge asymmetry. The advantages and disadvantages of each method are considered in detail, by reference first to idealized slump fold distributions and then to a compilation of sixty natural slump fold axis distributions, mostly from published data.Among the advantages of the mean axis method are the ease of deriving confidence limits for estimates and its applicability where fold asymmetry data are unavailable. The main advantage of the separation are method is its validity for strongly skewed fold axis samples. The statistical robustness of the mean axis method, however, due to its reliance on average properties of data, makes it more generally reliable than the separation arc method which depends on extreme properties of data. A procedure for determining palaeoslope directions is suggested which reflects the respective strengths of the two methods.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00339.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTIt was observed that a monolayer of glass beads which were scattered sparsely on a rigid plane floor grew into regular waves of particles under oscillatory water flow. The relative displacement of two nearby particles due to viscous fluid forces seems to be responsible for the initiation of these particle waves. It was also observed that the similar particle waves were formed on the initially flat surface of a thick sand bed and subsequently developed into oscillatory sand ripples of a common type. On the basis of these observations, it is suggested that the particle waves may be the basic cause of the initiation of general ripple marks under oscillatory flow.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00340.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTSand ridges along the coast of northern Brittany contain alternating beds of coarse and fine to medium sand 4–10 m above normal reach of highest spring tides. They were deposited in the Holocene, largely during the last centuries, by sand charged storm surges. Deformation structures at many levels in these beds have amplitudes of 2–25 cm. Fine‐grained beds were folded in a manner that suggests relative competency of transmitting horizontally directed stress. Coarse‐grained beds, by yielding, permitted folding to die out vertically. It is suggested that a transitional zone existed between the storm surge and the underlying sediment. This zone consisted of a mixture of water and sand. Deformation occurred at the moment movement in this zone was arrested. Comparison with published data on deformed bedding indicates that the described structures may be environment s

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00341.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTThe late (?) Miocene non‐marine to paralic Guayabo Group in northeastern Colombia and adjacent Venezuela contains as many as thirty‐four thin (to 15 cm) goethitic and chamositic oolites and ooid‐bearing sandstones in 1080 m of section. This eastward prograding deltaic complex consists mainly of chert‐rich litharenite in fluvial, distributary channel, and shoreline facies, and of montmorillonite mudstone in floodplain and interdistributary embayment facies. Within this framework the oolites are restricted to a paralic association that developed during episodes of waning detrital sedimentation when distributary abandonment was followed by minor transgression across mudflats.Most of the multilayered and symmetrical ooids are composed of goethite, rarely with a small amount of chamosite. These are essentially spherical; many of the chamosite‐rich ones have been plastically deformed. Goethitic ooids resemble those in a thin layer accumulating in brackish Lake Chad, central Africa. Chamositic ooids have affinities with those accumulating in a sea loch in western Scotland. Each of these examples is associated with detrital (silicate) sedimentation, apparently developed directly from colloidal ferric oxide and silicate precursors, and affords no evidence that primary aragonitic ooids were later placed by ironbearing oxide

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00342.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTMoulds after aragonite fossils from two Upper Ordovician limestones in the Oslo Region are filled with well sorted clastic fine sand. The fossil moulds are thought to have been formed by selective dissolution of aragonite shell material by fresh water in the vadose zone. Internal sedimentation post‐dates precipitation of a thin veneer of iron poor drusy calcite cement, but predates precipitation of ferroan blocky calcite cement. These age relationships and the texture of the fine sand suggests sedimentation in semiconsolidated sediment in the vadose zone of an island during early emergenc

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00343.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

ABSTRACTFor a petroleum geologist knowledge of the density of the distribution of subsurface Cretaceous reefs is a matter of practical interest. Hence, the discovery in the Judean Desert of Israel, near the western margin of the Dead Sea, of an exhumed sea bottom below an erosional unconformity is of particular interest, because it reveals the original distribution of such reefs, and thus may provide a clue to their subsurface distribution. In this desert, newly described Turonian (Upper Cretaceous) reefs are the dominant geomorphic features, as in their original habitat on the Cretaceous sea bottom. These reefs can be traced on aerial photographs: they are generally 5‐15 m in diameter and 1‐2.5 m in vertical dimension. Generally, reefs occur within 100‐200 m of one another; in many places they are less than 50 m apart. The shapes of the patch or pinnacle reefs are almost circular, as are those occurring in the Edwards Limestone (Comanchean, Lower Cretaceous) in central Texas (Roberson, 1972).The hard, resistant, ring‐like outer rims of these exposed reefs weather out as raised rims. A central depression within such structures consists, in places, of Senonian soft chalky or friable material that has been interpreted as a diagenetic product of the vadose zone. The massive reef core consists of porous dolomite. The flanking strata which dip away from the reef core at angles of approximately 15‐25° are composed of a probable original grainstone which has been diagenetically changed to a micri

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1979.tb00344.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY