Showing papers in "Sedimentology in 1966"

A review of grain‐size parameters

Abstract: SUMMARY This paper comprises a review of the many graphical and mathematical techniques that have been proposed for the statistical summary of grain-size data. Satellitic problems, such as laboratory techniques, choice of size scales, and interpretation, are only considered briefly.

Structures of dunes at white sands national monument, new mexico (and a comparison with structures of dunes from other selected areas)1

Abstract: SUMMARY The type, scale, and relative abundance of sedimentary structures in four kinds of dunes at White Sands National Monument, New Mexico, were determined by examination of vertical sections on walls of trenches cut through the dunes both in a windward direction and at right angles to this direction. Analysis of cross-stratification in all dunes examined indicated certain common features: sets of cross-strata mostly are medium- to large-scale; nearly all laminae dip downwind at high angles (not uncommonly at 30°-34°); most bounding surfaces between sets of cross-strata are nearly horizontal on the upwind side, but have progressively steeper dips to lee, downwind; and individual sets of cross-strata tend to be thinner and the laminae flatter near the top than at the bottom of a dune in vertical section. Sparse but distinctive structural features that are characteristic of the four types of dunes are varieties of contorted bedding, rare ripple laminae, and either local scour-and-fill bedding, or festoon bedding. Other structures, apparently limited to either one or two types of dunes, are the concave-downward foresets in some parabolic dunes; the low-angle reverse dips of upwind strata on high transverse dunes; and the almost horizontal laminae which represent apparent dip in sections normal to wind direction in dome-shaped and transverse dunes. Describing cross-stratification in terms of three dimensions, dune structure at White Sands consists dominantly of the tabular planar sets, with units thickest near the dune base, thinner above. To a lesser extent the sets are of simple (non-erosion) tabular form and relatively uncommonly, of the trough type. Wedge planar forms are scarce. The planar forms characteristically are of two classes in nearly equal proportions: those in which bounding surfaces are virtually horizontal and those in which they dip at moderate to high degree. A brief comparison is made between the structures of dunes that are characteristic of one effective wind direction, as at White Sands, and certain others formed by winds of two or more directions. Seif dunes of Libya, reversing dunes of the San Luis Valley, Colorado, and star dunes in Saudi Arabia are discussed as examples of complex dunes formed by multi-directional winds.

The angle of repose for a single grain on a fixed rough bed

Abstract: SUMMARY The angle of repose under water is experimentally determined for a single particle on a fixed rough bed. The effect of grain shape, size and sorting of the bed and ratio of particle diameter to average bed grain diameter are taken into account. An empirical equation is given for predicting angle of repose as a function of the above factors. The accuracy of fit of this equation is quite good. Several other conclusions drawn for the case of a single grain on a fixed rough bed are: 1Angle of repose increases with decrease in size, departure from sphericity and increased angularity. 2Angle of repose increase with decrease in sorting. 3A single angle of repose for sand size grains is not valid. Variation ranges from nearly 90° to less than 20°, depending on the values of the factors given above.

On bed forms and palaeocurrents

Abstract: SUMMARY Bed forms arise by interaction between a fluid flow and the sediment transported over or close to the bed. The geometry of bed forms is two-dimensional or three-dimensional. Two-dimensional bed forms generate two-dimensional internal sedimentary structures and are adjusted to two-dimensional flow-vector fields. Three-dimensional bed forms generate three-dimensional internal sedimentary structures and are adjusted to three-dimensional flow-vector fields. Many shallow-water flow systems observable today are each characterised by flow-vector fields of unequal rank, and hence are hierarchically structured. Hierarchies of bed forms and internal structures which parallel the hierarchies of flow-vector fields can also be established in the case of these flow systems. A single type of bed form or internal structure from an hierarchically structured flow system cannot specify that system fully with regard to either its directional or flow-dynamic characteristics. An approach to palaeocurrent analysis that is more flexible and comprehensive than previously attempted may therefore be desirable.

Matrix of turbidites: experimental approach

Abstract: SUMMARY The matrix (< 40 μ) of turbidites forms a possible clue to the density of turbidity currents and the origin of the graywacke matrix. Experiments in a circular flume provide a mechanism to study the relation between composition of suspensions at various speeds and their deposits. There is a close analogy to the lower part of turbidity currents. The lutum content of samples with median diameters greater than 400 or 500 μ is found to correspond to the suspended load of the pore water. The higher value for finer deposits can be recalculated to suspension concentration by use of the “sedimentation factor”. Hence, each turbidite carries, as it were, a sample of its depositing current. The lutum content depends not on the ratio of sand to lutum in the current, as tacitly assumed by many authors, but mainly on the ratio lutum to water, although also influenced by velocity. The average lutum density of coarser recent deep-sea sands is 1-2%. This indicates turbidity currents with 5-10% lutum by weight (density 1.03–1.07). The sand must be added to ascertain the current density. In first approximation turbidity currents tend to have densities at their nose of 1.1–1.2, but higher and much lower values also occur. The maximum original lutum percentage of coarse turbidites is below 10%. Higher values are very scarce and are due to post-depositional mixing, or we are dealing with slides. However, in fine-grained turbidites there is more matrix up to 20% for a median of 100 p. Hence, coarse graded marine graywackes with 20 or more per cent matrix are presumably weakly metamorphic turbidites, that originally held the same modest amount of lutum as recent turbidites of the same grain size. The Trask sorting of the experimental deposits is very good, like the average of natural turbidites. Most cumulative curves of turbidite grain-size analyses on arithmetic probability paper show a characteristic bend in fine sand or silt sizes.

Morphology, internal structure, and origin of glauconite pellets

Abstract: SUMMARY Glauconite pellets exhibit considerable variety in morphology and internal structure. Recognized morphological types are: (1) ovoidal or spheroidal; (2) tabular or discoidal; (3) mammillated; (4) ellipsoidal; (5) vermicular; (6) composite; and (7) fossil casts, internal molds, or replacements. Types of internal structures include: (1) random microcrystalline, (2) oriented microcrystalline, (3) micaceous, (4) organic (?) replacements, (5) coatings on detrital grains, and (6) fibroradiated rims. These characteristics can be used to interpret the origin and/or subsequent history of pellet types. Suggested origins include: (1) chemical precipitation, (2) expansion and alteration of detrital mica, (3) alteration of fecal pellets, (4) alteration of clay fillings of fossil tests, (5) mechanical aggregation, and (6) chemical replacement. Not all glauconite pellets exhibit diagnostic characteristics with regard to their genesis. Original morphologies may be obscured by abrasion (reworking) prior to final burial. Internal structures may be changed by recrystallization or other diagenetic processes. It is concluded that glauconite pellets have multiple origins. They can form from several different parent materials and by several different processes. Frequently, however, characteristics which might reveal the original nature of the pellets have been lost during reworking and diagenesis. Inasmuch as glauconite occurrences differ in kind and variety of pellets, recognition of pellet types and their distribution is potentially useful for stratigraphic correlation or environmental determinations.

Boron in clays and estimation of paleosalinities

Abstract: SUMMARY Experiments on the uptake of boron by some clays from artificial sea-water solutions at room temperatures show that the uptake is proportional to the concentration in solution, and takes place in relatively short time. The uptake process can be described by the Freundlich adsorption equation, with the constants in the equation, k and b, varying from one clay to another. Additional factor which apparently promotes the boron adsorption by clays is the occurrence of a sodium-borate complex in saline waters. The boron concentrations in a sequence of marine Cretaceous sediments derived from a fairly localized source area show variation much greater than can be accounted for by a model which assumes (1) nearly constant boron concentration in illitic-montmorillonitic clays prior to their deposition in the sea, and (2) changes in the boron concentration in solution as may be expected under slight variations in sea water of near “normal” salinity. Differences in the properties of clay-mineral polymorphs, in predepositional histories of the clays, and possible adsorption from interstitial waters, render inconsequential the estimates of the boron concentrations in the waters at the time of deposition.

Some flume experiments with a fine silt

Abstract: SUMMARY Four flume experiments have been performed in which the behaviour was investigated of a bed of fine silt under running water with and without an excess of material introduced into suspension. In the presence of excess material, bed features were formed in the tangential stress range 0.1 < θ < 0.4, and the bed was found to remain plane in the ranges 0 < θF < 0.1 and 0.4 < θF < 1.3. In the absence of excess material the stable condition over the entire range appeared to be that of the plane bed. Dual values of the threshold stress for grain movement were postulated to explain these results, and a relationship has been found between the magnitude of the tangential stress and the upstream slope of the features.

Sedimentary characteristics and climatic analysis of easterly dust storms in the negev (israel)

Abstract: SUMMARY Sedimentary and meteorological characteristics of easterly dust storms causing severe damage in the Negev in November 1958 are analysed. Though the heavy storm originated in weather conditions outside of the affected area, the intense dustiness was of a more local nature. The sedimentological character of the dust indicates that the largest portion was of local origin, picked up by the turbulent current in the loess area of the northern Negev on its passage westward. Total quantity of sediment transported in the Beersheba Basin is estimated to be 10–20 million tons. The analysis of climatic data and of sedimentary characteristics of several other dust samples indicates that though severe dust storms can produce dramatic effects in transporting and deposition of aeolian dust, the rare occurrence of easterly dust storms does not make it likely that they were responsible for the import of aeolian sediments found in the northern Negev.

Zeolites in Sedimentary Rocks, with Reference to the Depositional Environments and Zonal Distribution

Abstract: SUMMARY The authors have studied alterations of Cenozoic and Mesozoic pyroclastic rocks of Japan, which contain several kinds of zeolites in abundance. This paper summarizes zeolites in sedimentary rocks, with reference to the depositional environments and zonal distribution, by a survey of the literature in addition to the authors’ data. The zonal distribution of zeolites is recognized in buried sedimentary rocks as follows: The zeolites in syngenetic or early diagenetic origin depend strongly upon a specific sedimentary environment. Phillipsite occurs largely in pelagic sediments of the younger geologic age. Analcime is found in saline-lake and terrestrial sediments in a warm, rather arid region, frequently associated with phillipsite, chabazite and natrolite. The zeolites are not influenced by the sedimentary environments but depend upon the depth of burial, i.e., increasing temperature and pressure. Most of clinop- tilolite, mordenite and erionite, forming at a relatively shallow depth, occur only as an alteration product of acidic to intermediate volcanic glass and cement of the post- Jurassic pyroclastic rocks. Laumontite, forming at a greater depth, on the other hand, is widely distributed in the pre-Pliocene various sedimentary rocks.

Evolution of zircons in sedimentary and metamorphic rocks

Abstract: SUMMARY Zircons have been studied in the sedimentary rocks of the Sparagmite Group (Eocambrian) and their metamorphic associates from the Trondheim area and the adjacent regions in Norway and Sweden. The majority of zircon population (type B) has been formed in the sediments by authigenesis. Another authigenic associate is rutile. The authigenic zircons have irregular, round and ellipsoidal habits. In metamorphic rocks the same grains show a greater tendency of euhedrism, forming drum-like crystals with acute (331) pyramids and short prisms. Authigenic zircons are usually clear and transparent but some grains may show cloudy appearance. A few other grains (type A) with different habit and many inclusions appear to be of detritai nature. Dissolution of a metamictized zircon population in the source rock is possible in many ways. An important possibility is the dissolution of zircons in alkaline solution. Carbonated lime-rich waters or other acidic solutions could be equally effective. Zirconates, so formed, are transported to the basin of deposition as colloidal particles or as ionic complexes. The authigenic process is visualized as a deposition of the zirconates by adsorption or by precipitation as zirconium hydroxide, possibly due to change in the Eh and pH in the environment. The hydrated oxide subsequently reacts with silica to form metastable hydrozircon. In course of time hydrozircon dehydrates and becomes a normal zircon. Numerous growths have been noted and are classified genetically into (l) late authigenic growths, and (2) growths syngenetic with metamorphism. The shape of the host grain usually controls the final shape of the overgrown grain. There is some effect of metamorphism on the morphology of the authigenic zircons. In view of the characters of the newly generated zircons, the use of shape, size, zoning and such other parameters of zircons in petrogenetic problems, has to be retested to ensure its reliability. Rather than being a mineral of igneous derivation only, zircon is from three parentages: igneous, authigenic and metamorphic. It is argued that the persistence of the authigenic zircons should be greatest because of very low concentration of radioactive elements.

Sedimentation in a Meandering ESTUARY1

Abstract: SUMMARY Sand is being deposited in a meandering estuary separating Sapelo and Blackbeard Islands, Georgia, in the channel of the estuary and on two point bars associated with meanders. Sand is being eroded by the meandering channel from slightly lithified Pleistocene and unconsolidated Holocene strandline deposits, and is being redeposited by the ebb tidal currents. The estuary-channel deposits are coarse grained and their grain-size decreases down ebb current from the source outcrops. The point bars are elongated in the direction of the ebb current, and increase in grain-size from their crests downward as they grade into the channel deposits. Festoon cross-bedding and ripple marks on the point bars record the ebb direction, while elongate plant fragments are preferentially oriented normal to the bar elongation (current). Horizontally stratified muds and muddy sands are being deposited behind the bars, and contain a rich fauna (primarily annelids, arthropods, and molluscs). However, the fauna is represented in the deposits more by burrows and disturbed stratification than by preserved organisms. The sands of the bars and channel are biologically less productive, but the bioclastic content of the sediment is high.

Formulation and use of fluorescent tracer coatings in sediment transport studies

Abstract: SUMMARY Commercially available, daylight and near-ultraviolet fluorescent, colored dyes can be used in long- or short-lived surface coatings on coarse sediments. Such tracer coatings make possible day- or nighttime visual and quantitative determination of river or beach sediment transport. Testing of five commercial coatings led to formulation of two additional coatings. A wide selection of dye colors is available for use in four coating mixtures. All coatings are insoluble in fresh or saline water. Single-application coating thicknesses range between 0.0003 and 0.0024 inches. Still air drying time at room temperature for separated particles varies from 40 seconds to 14 minutes depending on coating mixture used. Volume production of marked particles in the field is possible. Extensive sediment sampling in particle transport studies possibly may be eliminated by measuring visible light emission from coated particles under nearultraviolet excitation. A battery operated, portable photometer was assembled from a light cell, linear amplifier, and metering circuit. Laboratory calibration indicates that 5% differences in areal concentration of marked particles at given sampling locations can be determined. Color coded sizes of fluorescent sand and gravel were used in a test of foreshore sediment transport pattern over a single tidal cycle. Initial trajectory (minimum transport angle) of particles moved by beach drifting is approximately equal to deep water angle of wave approach relative to the shoreline. Angular magnitude of the dispersion zone for each group of particles seems to be a function of particle size and point of introduction on the foreshore. Minimum average transport velocity of particles was 0.42 ft./min under test conditions.

Some applications of theory and experiment to the study of bedding genesis

Abstract: SUMMARY The origin of many sedimentation units deposited in granular cohesionless materials can be rationally explained by utilizing the concept of the profile of equilibrium. This basic concept can be formally expressed in terms of the variables, or groups of variables, that characterize a sediment transport system. A change in one or more variables or a shift in local base level will generally cause a shift in the spatial position of the profile, resulting in either aggradation or degradation. As shown by flume experiments, the rate of shift of the profile is a critical factor in bedding genesis. A relatively large and rapid upward shift of the profile results in the deposition of a tabular or wedge-shaped unit of cross-bedding, i.e., a laboratory delta. On the other hand, a gradual upward shift of the profile results in the deposition of a sequence of horizontal bedding that is commonly associated with intercalations of ripple or dune cross-bedding. For the intermediate case of a moderately rapid shift of the profile, the depositional sequence includes trough units and poorly-defined tabular units of cross-bedding with numerous intercalations of horizontal bedding. The concept of the profile of equilibrium therefore provides a rationale for considering the depositional framework for sedimentary structures produced by current flow.

Textural Classification of Sediments

Abstract: SUMMARY In the light of present-day requirements and the author's personal experience, existing systems of nomenclature and classification of sediments on a textural basis need revision. A system is proposed that is based on a three end-member relationship involving sand-, silt- and clay-size particles. The construction, nomenclature and application proposed, fulfils the purpose of a classification because it is simple, easily remembered, practical, has wide application, is needed; and above all it groups sediments into useful categories that make communication more effective and easier.

Air and Sand Movements to the Lee of DUNES1

Abstract: SUMMARY The large and extensive transverse and barchane dunes of coastal South West Africa are strongly oriented under the influence of predominantly southerly winds. During periods of strong winds (40–50 miles/h) deposition occurs on the lee slope in three ways: (1) sand is blown over the crest of the dune and falls on the lee slope; (2) rapid deposition near the dune crest results in periodic slumps and slides down the lee slope; (3) eddy currents developed to the lee of the dune pick up sand from the surface downwind from the dune and transport it to the lee slope. The size and strength of the lee eddy is surprising. With winds in the 40–50 miles/h range frequent gusts lift fine sand from the downwind surface to a height of several feet. Less frequently sand is picked up from a low position on the lee slope and redeposited higher on the slope. The addition of material to the lee slope by the eddy is much less volumetrically than the contribution directly over the dune crest from the windward direction; however, with strong winds the removal and transportation of sand from the area downwind of the lee slope back to the lee slope appears to be important in the deflation of this surface. The width of the area influenced by the lee eddy during strong winds is about equal to the height of the dune. Observations in low dunes from 1 to 20 ft. high at Sapelo Island, Ga., U.S.A., confirm the presence of a well developed eddy to the lee of these dunes during strong and moderate winds (20–50 miles/h).

Bed thickness and grain size: graded beds

Abstract: SUMMARY Data from Ordovician and Tertiary turbidites and from the Hekla ash fall show good correlation between bed thickness and grain size. Most of the thicker beds are coarser grained. The relation between bed thickness and grain size in graded beds can be explained by a theory which uses a sedimentation formula based on the decay law of turbulence in the deposition zone of a turbidity current.

Environmental significance of sand dikes

Abstract: SUMMARY Sand dikes that have been found in Recent desert sediments are described, and an explanation of their origin is presented. The Recent dikes are compared with ancient ones of Permian age.

Correlation of some atlantic turbidites

Abstract: SUMMARY A study of six gravity cores from an abyssal plain at the western side of the Madeira-Cape Verde Basin shows that individual turbidites can extend over a distance of at least 35 miles (65 km) in this area of final turbidity current deposition. Cores from the continental rise include relatively thinner turbidites; evidence from one of these indicates some local erosion of the sea floor: this apparently did not exceed 15 cm (as represented in the core).

Application of theory to an atlantic turbidity-current path

Abstract: SUMMARY Some results of turbidity-current theory are applied to analyses of turbidite layers in cores from the route of a large turbidity current of sheet-flow type. Novel features are that current velocity is estimated from the sediment sizes deposited, and the lateral spreading of the current is considered. An approximate quantitative picture of the current is obtained. It is compared with the turbidity current which caused the Grand Banks cable breaks.

Size differentiation in a cross-stratified unit

Abstract: SUMMARY Careful sampling of the constituent laminae of cross-stratified units and their subsequent mechanical analyses have revealed a rhythmic pattern of size differentiation. The cross-strata have been analysed in terms of our existing knowledge of the mechanics of layering in granular sediments. The concept of “elementary rhythm-unit” has been introduced and the genesis of a cross-stratified unit has been reviewed in terms of the growth and interplay of the elementary rhythm-unit.

Non-greywacke “turbidite” sandstones in the welsh geosyncline

Abstract: SUMMARY In contrast with the commonly accepted notion regarding ancient turbidites, non-greywacke sandstones are not uncommon in the typically graded turbidite facies of the Cambrian and Silurian sediments in north Wales. The sandstones are the arkosic and lithic types of PETTIJOHN (1957) or the feldspathic and lithic arenites of GILBERT (1954) and occur at the bottom of graded beds when the grain size tends to be above medium grade. Petrological features suggest that debris forming the sandstones in north Wales was not significantly modified during transportation and original provenance characters are well preserved. The occurrence of such sandstones implies that: (1) the current concept of ancient graded greywackes in the turbidite facies should be revised; (2) non-greywacke sandstones in ancient turbidites are comparable in petrological features to recent deep-sea sands; (3) these sandstones are important in connection with the origin of the clay matrix in greywacke.

The booming sand of korizo, sahara, and the squeaking sand of gower, s. wales: a comparison of the fundamental characteristics of two musical sands

Abstract: SUMMARY The occurrence of the rare phenomena of a booming sand is recorded and an account given of its behaviour in the field. Its sedimentological properties are compared with those of a squeaking sand from the seashore. Both sands are moderately to wellsorted, and show similar roundness and sphericity. The desert sand is silent, whereas the seashore sand can be made to emit a noise in the laboratory. The marked distinction between the sands lies in the mechanical analyses based on the number frequency of grains, rather than on the weight frequency. A “body-centred cubic” packing has been proposed for the desert sand and a “rhombic” packing for the seashore. Shear-box tests on the disturbed sands appear to support the hypothesis of two different modes of packing. The source of the characteristic booming sound is discussed, but it is suggested that an explanation is more likely to be forthcoming from field investigation than from small-scale laboratory studies.

The Internal Paleogene Flysch of the Eastern Carpathians: Paleocurrents, Source Areas and Facies Significance

Abstract: SUMMARY After a brief review of the structure, the stratigraphy and the facies of the Rumanian eastern Carpathians flysch zone, the authors analyse the main paleocurrent directions on the internal facies of the paleogene flysch. The most important and numerous currents were longitudinal and came into the flysch trough from an outlet area situated in the Carpathian arc region. For this reason it is inferred that the principal source of detrital material was represented by the Pannonian–Transylvanian internal massif. The crystalline core of the eastern Carpathians furnished only a small quantity of clastics, which were transported into the trench by means of transversal, relatively weak currents. The role of different structural elements (platforms, cordilleras, internal massifs) in providing detrital material is briefly discussed. Finally, an attempt is made to outline the paleogeographic evolution of the eastern Carpathians during the Paleogene.

Temperature effect on precipitation of calcium carbonate from calcium bicarbonate solutions and its application to cavern environments

Abstract: SUMMARY Solutions of calcium bicarbonate were allowed to lose carbon dioxide and evaporate to dryness under controlled temperature conditions. With filtered solutions prepared from spar calcite, precipitates were 100% calcite in the 2° to 100°C temperature range. When, in analogous experiments, coralline aragonite was the starting material, the precipitates were 100% calcite. Essentially the same was true when carbonate rocks from karst areas were used to prepare the experimental solutions. An artificially prepared mixture (maximum crystal size of about 7 u) of 70% aragonite and 30% calcite was also used in the study. The precipitates from this starting material were apparently affected by seed nuclei which passed through the filter. The stability of calcium carbonate seed nuclei appears to vary with temperature. Natural calcium bicarbonate solutions from caves yielded only calcite at 25°C. Calcite should be the dominant or only polymorph of CaCO3 formed by the loss of carbon dioxide and evaporation of natural calcium bicarbonate solutions if temperature is the controlling factor. Since appreciable amounts of aragonite are found in many cave deposits, factors other than temperature must influence the polymorphs formed. POBEGUIN (1955) proposed that rapid evaporation and slow diffusion of solutions favor aragonite. If so, layers of aragonite and calcite in speleothems may reprsent alternate wet and dry paleoclimates. During these periods, rate of introduction of solution and rate of evaporation would change markedly.

Sediment size distribution profile on the continental shelf off new jersey1

Abstract: SUMMARY A series of samples from the continental shelf off New Jersey reveals a continuous surface layer of fine sand overlying a variety of sediment type. Ripples and shell debris suggest the fine sand is reworked and is in adjustment with the present shelf environment.

Fluviatile run-off as a factor in the primary dispersal of submarine gravels in foveaux strait, new zealand

Abstract: SUMMARY Dispersal patterns, based upon the frequency distribution of rock types in the submarine gravels of Foveaux Strait, indicate a connection between the gravels and the present terrestrial drainage systems to the north and south of the Strait. It is inferred that the submarine gravels were initially deposited as fluviatile sediments during a former period of low sea-level. It is further suggested that the significant factor regulating the proportions of the various rock types was not distance from the periphery of the present marine environment or the proximity or relief of the source areas. More important were the actual sizes of the water catchment and source areas on opposite sides of the Strait.

The surf “break”: key to paleogeography?

Abstract: SUMMARY Ancient geosynclinal coastal deposits, preserved and exposed for present-day examination, probably represent interior—and hence protected—shores, and were therefore characterized by low-to-moderate breaker energy levels, as is the modern Gulf of Mexico. Modern low-energy beach sand size distributions are distinguished by an inflection, here called the surf “break”, formed by a winnowing or statistical filtering process, by the breakers, in the finer sizes. The result is a two-segment curve having an intersection in many cases not far from 1.5 phi. If the energy level is very low, a tail of fines may be added, producing a three-segment curve having two inflection points. Along high energy beaches, the surf “break” occurs at such large grain sizes that it cannot be preserved in sand; whether or not it can be recognized in gravel is not known. Ancient sandstones which represent the breaker zone, along a low-to-moderate energy coast, should also exhibit the surf “break”. The Lyons Sandstone, a known Permian beach deposit, provides an example. Other examples are cited. Any useful indicator of the shoreline position, in lithified rocks, should have three characteristics: ease of recognition, high reliability, and strong probability of preservation. The surf “break” scores reasonably well on all three points. Hence it may be an important key to paleogeography. Nevertheless, there still remains a question inasmuch as certain river sands have similar inflections. Whether these kinks were inherited from near-by, but older, beach deposits, or were formed by stream action, is not known. The reliability of the surf “break” is estimated at 80% or better, except for the case where near-shore sands, of whatever age, are reworked briefly by running water.

Relationship between longitudinal and transversal currents in the paleogene of the tarcau valley (eastern carpathians)

Abstract: SUMMARY In the Paleogene of the Tarca Valley (Rumania) the largest part of the thick-bedded and coarse-grained material was supplied by longitudinal paleocurrents from a distant source. The longitudinal supplies were independent of the lateral ones.

An unusual sedimentary structure indicative of shallow water conditions in the grès armoricain of finistère (france)

Abstract: SUMMARY The communication describes dome-like masses of sand apparently developed by gully erosion on the upper surfaces of Ordovician sandstones. The similarity of these structures to the minor topography of tidal marshes is noted, and it is suggested that similar processes may be responsible.