Fine-grained Detritus Research Articles

Braided fluvial sedimentation in the lower paleozoic cape basin, South Africa

Lower Paleozoic braided stream deposits from the Piekenier Formation in the Cape Province, South Africa, provide information on lateral and vertical facies variability in an alluvial plain complex influenced by a moderate to high runoff. Four braided stream facies are recognized on the basis of distinct lithologies and assemblages of sedimentary structures. A lower facies, dominated by upward-fining conglomerate to sandstone and mudstone channel fill sequences, is interpreted as a middle to lower alluvial plain deposit with significant suspended load sedimentation in areas of moderate to low gradients. These deposits are succeeded by longitudinal conglomerate bars which are attributed to middle to upper alluvial plain sedimentation with steeper gradients. This facies is in turn overlain by braid bar complexes of large-scale transverse to linguoid dunes consisting of coarse-grained pebbly sandstones with conglomerate lenses. These bar complexes are compared with environments of the Recent Platte River. They represent a middle to lower alluvial plain facies with moderate gradients and no significant suspended load sedimentation or vegetation to stabilize channels. These bar complexes interfinger basinward with plane bedded medium to coarse-grained sandstones interpreted as sheet flood deposits over the distal portions of an alluvial plain with low gradients and lacking fine-grained detritus or vegetation.

Spring Peas from New York State: Nucleation and Growth of Fresh Water Hollow Ooliths and Pisoliths

ABSTRACT Delicate hollow spheroids (1 to 2 mm) composed of radially fibrous calcite occur in, and on the surface of, calcareous travertine being deposited from water of the Orenda Spring, Saratoga Springs, New York State. Field observations suggest that spheroids form by the precipitation of calcite on the surface of water droplets that contain newly formed bubbles of CO2. Although many of the spheroids subsequently disintegrate, some grow by the addition of laminae consisting of radial bundles of fibrous calcite, commonly separated by thin (? seasonal) laminae of fine-grained calcite and detritus. These spheroids are either incorporated into laminar travertine sheets or grow by successive increments into fresh-water ooliths and pisoliths with both a concentric and a radial structur .

Cyclic Sedimentation of the Solor Church Formation (Upper Precambrian, Keweenawan) Southeastern Minnesota

ABSTRACT The Solor Church Formation of Late Keweenawan (Late Precambrian) age occurs in the subsurface of southeastern Minnesota where it comprises an integral part of the St. Croix horst, the major structure that underlies the northern part of the Midcontinent Gravity High. The formation consists of intercalated red intraformational conglomerate, sandstone, siltstone, mudstone/shale, and lesser amounts of limestone. The clastic rocks were derived from a dominantly basaltic terrane much like that which now flanks and underlies the formation. The limestones have a limited distribution and consist of admixed oolites and various kinds of intraclasts indurated by a sparry cement or a micritic groundmass. Two kinds of sedimentary cycles, each characterized by fining-upward attributes, are recognized in the Solor Church Formation. (1) Minor cycles, 3-50 ft thick, which consist of a sandstone/conglomerate facies overlain by a siltstone/mudstone facies. Each minor cycle contains a vertical succession of primary structures and textures indicative of alluvial sedimentation. (2) Major cycles, which may be as great as 600 ft thick, are characterized by a systematic increase, stratigraphically upward, in the amount of mudstone relative to sandstone. This fining upward trend reflects a more or less systematic increase in the thickness of the fine-grained facies, whereas the thickness of the coarse-grained facies in each minor cycle remains more or less constant. As the proportion of siltstone mudstone increases, there is a corresponding decrease in the apparent grain size of the sand- and silt-size detritus. Each major cycle is terminated by an abrupt decrease, over a short vertical distance, in the relative amount of fine-grained detritus and a corresponding increase in the amount of sandstone. The Solor Church Formation most likely was deposited by rivers flowing on an alluvial plain; in each minor cycle the conglomerate and sandstone were deposited in a migrating channel, whereas the mudstone and limestone were deposited on inter-channel flood plains and in shallow lakes. The general increase upward in the amount of silt and clay implies that the upper part of each major cycle was dominated by overbank or inter-channel deposition rather than channel deposition Thus, each major cycle records a progressive change toward a quasi-equilibrium balance between rate of subsidence and rate of infilling. However, the sudden reappearance of abundant conglomerate and sandstone, at the base of the succeeding major cycle, indicates an abrupt increase in the rate at which materials were upplied to the system. It is inferred that these abrupt changes record periods of tectonism during the evolution of the St. Croix horst.

Sedimentation in Malaysian High-Tide Tropical Delta: ABSTRACT

The Klang-Langat delta empties into the Straits of Malacca at 3° N. lat. along the west coast of the Malay Peninsula. Both the delta and its catchment basin are located in the wet tropics with mean annual rainfall ranging from 80 to 140 inches. The subaerial delta occupies about 160 square miles. Wave energy levels along this coast are low to moderate; the range of mean spring tides is 15 feet. Tidal processes dominate sediment dispersal patterns and control delta form. An extensive tongue-shaped sand bank or shoal (Angsa Bank) is down-drift from the delta. The subaerial delta displays a maze of criss-crossing tidal channels separating mangrove islands. Although the system has the configuration of an estuary, it is in reality a complex delta of the Klang and Langat R vers. Six major environments and facies are recognized in the active delta. The most seaward of these consists of well-sorted medium-grained sand deposited on extensive shoals or banks. Sorting reflects intensity of tidal currents. Local concentrations of shell and transported organic debris also are characteristic. This marine sand forms the bulk of the subaqueous delta deposits. Fringing the subaerial delta are broad low tidal flats composed of irregular-bedded, fine-grained sand, silt, and clay. Networks of small tidal creeks dissect the flats; shellfish and other burrowing organisms abound. Bottom sediment in major tidal channels is predominantly clayey sand with local concentrations of shell and transported organic debris. Mangrove-covered islands constitute most of the active subaeria delta. Although organic production is high, it is overshadowed by fine-grained detritus resulting in accumulation of organic clay, rather than peat. On the margins of the islands small sandy accretion beaches border channel mouths. Central parts of large islands and back-swamp areas between major channels in the older parts of the delta are occupied by large fresh-water jungle-covered swamps. These are the sites of woody peat accumulations which attain thickness of 20 feet or more. End_of_Article - Last_Page 459------------

General Theory of Epeiric Clear Water Sedimentation

Shallow marine sedimentation is described in contrast to oceanic, coastal deposition. Shallow marine sedimentation occurs in non-oceanic epeiric seas where great width of shelves, their low order of slopes (less than one foot per mile), and extreme shallowness of the waters on them are sufficient in themselves to restrict or eliminate circulation. Oceanic, coastal deposition occurs where steep bottom slopes are the rule and where waves and tides extend to the shore. Three marine, hydraulic energy zones, which are in effect environments of deposition, are thought to occur in epeiric seas: (1) a hundreds-of-miles wide, low-energy zone prevailing in the open sea beneath wave depth where marine currents are the only form of hydraulic energy acting upon the bottom (Zone X); (2) an intermediate, high-energy belt, tens-of-miles wide, beginning where waves first impinge upon the sea floor and thus expend their kinetic energy upon the bottom, extending landward to the limit of tidal action (Zone Y); (3) an extremely shallow, low-energy zone, tens- to hundreds-of-miles wide, occurring landward of Zone Y in which there is little circulation of water, where tides are essentially wanting, and in which the only wave action is that produced by local storms (Zon Z). Reasons are given to show that in epeiric seas, which have received no invasion of terrigenous clastics (clear water), sediments formed in Zone Y are basically of biogenic origin, are sand-size or coarser, and are those most likely to become well-winnowed primary reservoirs; that those sediments formed in Zone Z are primarily fine-grained and tight, and are generally of chemical origin; that Zone X contains sediments which are mainly fine-grained detritus from Zone Y. During a marine transgression, as each sedimentation zone migrates toward shore, it overlaps older sediments which earlier were deposited in an environment similar to the one then prevailing in the zone adjoining landward. In this manner, an ascending sequence of sediments, deposited under conditions of progressively less restricted circulation, the same as the pattern extending at a single time from land to sea, is established. During regression, each sedimentation zone migrates seaward, so that the ascending sequence of sediments is deposited under progressively more restricted conditions, and is the same as the one reaching at a single time from sea to land. Thus, in a regressive sequence, a rock type found on top of another would also occur landward from it; during transgression, ts position would be seaward. This process of continuous sedimentary overlap, as the sea advances and retreats, is the principle which explains cyclic sedimentation. It is noted that the age of geologic formations (lithofacies) becomes progressively younger in the direction of migration, emphasizing the necessity for time control. Two examples are presented together with further discussion which points out how the regular sedimentary patterns may be altered by barriers (such as reefs), by climate, and by degree of bottom slope; and how an analysis of both the normal and altered patterns may be used for exploration and grading purposes.

Cretaceous and Paleocene of Santa Lucia Range, California

Cretaceous and Paleocene of Santa Lucia Range, California