Ancient Alluvial Deposits Research Articles

Origin of fluvial grain-size trends in a foreland basin; the Pocono Formation on the central Appalachian Basin

ABSTRACT A widely recognized phenomenon of modern and ancient river systems is downstream decrease in grain size. Over the past two decades, theoretical formulations, observations of modern rivers, flume studies, and numerical models have significantly increased our understanding of sediment transport in mixed-grain-size river systems. These have established that downstream fining in modern and ancient rivers can be attributed to a combination of selective sorting, abrasion rate, and accumulation rate. However, no detailed multiple-grain-size sediment transport model has been used to address how much subsidence rate, sediment flux, water discharge, hydraulic geometry, and the mechanics of sediment transport influence grain-size distribution and facies belt development in ancient fluvial systems. We have combined the results of recent empirical and theoretical studies with a multiple-grain-size sediment transport model (MIDAS) to test the sensitivity of downstream fining trends to those controlling mechanisms. Our results demonstrate that subsidence and sediment feed rate are the most important mechanisms controlling downstream fining trends in a foreland basin if the evolution of hydraulic geometry is known. To illustrate the application of this result, we have replicated the textural trends of the Mississippian upper Pocono Formation and Burgoon Sandstone of Pennsylvania. This methodology can be applied to constrain plausible values of accumulation and subsidence rate for ancient alluvial deposits and enhances our ability to interpret paleohydraulic conditions from such facies in a foreland basin.

Relationship of soil properties to parent material and landscape position in eastern Madre de Dios, Peru

Properties of soils in the eastern part of Madre de Dios, Peru, were characterized and related to landscape position and parent material texture. Level uplands, dissected side slopes and recent flood plains dominate the topography in this region. Soil textures vary from clayey to sandy, depending on the texture of sedimentary materials from which each pedon formed. Parent material textural variation is a result of differences in the energy of the meandering rivers that deposited the ancient alluvium. Fourteen soil profiles were described and sampled in the field and analyzed in the laboratory. Data for eight soil profiles representative of the region are presented here. The profiles include soils formed in both sandy and fine-textured parent materials and soils with moisture status ranging from well drained to poorly drained. Soil moisture conditions vary with position on the landscape, such that as distance from streams increases, average depth to the fluctuating water table decreases. Redoximorphic features are present in all mineral soils. The average depth to redoximorphic features is least in locations furthest from streams. Soils in landscape positions that are poorly or somewhat poorly drained contain significant amounts of plinthite. In all soils, kaolinite is the dominant mineral in the <0.2 μm fraction, while quartz is the dominant mineral in very fine and fine sand fractions. All soils have low cation exchange capacity (CEC), low base saturation, and acid pH. Coarse-textured spodic soils with well developed zones of iron and organic matter translocation are formed in recent sand deposits of flood plains of 2nd-order streams. Organic soils are found in the wetlands associated with flood plains of some 3rd-order streams. Most properties of these soils appear to be controlled by the textures of their sedimentary parent materials and by their position on the landscape. The soils classify as Paleustults, Plinthaquults, Kandiustults, Placaquods and Troposaprists according to Soil Taxonomy. New subgroups of Paleustult are proposed.

Holocene flood-plain soil formation in the southern lower Mississippi Valley: Implications for interpreting alluvial paleosols

Holocene Mississippi River flood-plain soils in central Louisiana provide important insights on alluvial pedogenesis in an aggradational setting, insights that are useful for interpreting alluvial paleosols. The flood-plain soils are younger than ca. 5400 yr B.P. and are grouped into two categories: (1) meander belt and (2) backswamp soils. Meander belt soils are Entisols, Inceptisols, and Alfisols developed on point-bar ridges and natural levee crests; they consist of 3–5-m-thick, brown, silty and sandy, moderately well drained profiles with multiple parent materials, common yellow-brown and gray mottles, and a few iron and calcite nodules. Backswamp soils are Vertisols formed in flood-plain depressions away from active and abandoned Mississippi River channels and consist of up to 10-m-thick, gray, clayey, poorly drained profiles that have abundant yellow-brown mottles, iron and calcite nodules, gypsum accumulations, and slickensides. The thickness of the soils and the presence of multiple parent materials show that as the flood-plain aggrades, concurrent or alternating episodes of sedimentation and pedogenesis produce cumulative profiles. Profile thickness is more closely related to sediment accumulation rates than to the depth of chemical weathering, and the cumulative nature of the soils explains the difficulty of recognizing discrete paleosol profiles in many ancient alluvial deposits. Comparisons of soils formed on the three youngest Holocene Mississippi River meander belts (Saucier and Snead, 1989) show that the soils record episodes of meander belt growth, abandonment, and relocation. Meander belt 1 soils form as the active meander belt develops and consist of either vertically stacked Entisols or a single Inceptisol. The soils contain few calcite nodules and form over intervals of a few hundred years. Meander belt 2 soils are Alfisols, lack free carbonates, and form over intervals of a few thousand years following meander-belt abandonment and soil leaching. Meander belt 3 soils are Alfisols or Vertisols that contain common calcite nodules, and the profiles are developed in 1 to 2 m of backswamp mud that overlies meander-belt silt and sand. The mud inhibits profile leaching and leads to poor drainage and calcite precipitation. This change in soil hydrology complicates interpretations of the effects of time on meander-belt soil development. Backswamp soils are strongly influenced by seasonal episodes of soil wetting and drying, as demonstrated by the gray colors and the abundance of mottles, nodules, and slickensides in the soils. The distribution of calcite nodules in the backswamp and meander-belt soils is more closely related to seasonal water-table position than to mean annual precipitation, which suggests that not all calcic paleosols in ancient alluvial deposits represent semiarid or arid climates. Slickensides attest to seasonal rainfall, but the composition of the backswamp soils primarily reflects source-area lithology and depositional influences, rather than the effects of chemical weathering. In general, these soils provide an incomplete record of the humid subtropical climate of Louisiana. Although short-term sediment-accumulation rates decrease away from Mississippi River channels, the backswamp soils are not better developed (i.e., more mature) than the meander-belt soils, because poor drainage and slow but continuous sedimentation inhibits weathering. Collectively, these observations suggest that flood-plain soils that developed in aggradational settings, such as that of the Mississippi River flood plain, are best suited for interpreting depositional and hydrologic histories of ancient alluvial deposits, rather than paleoclimates.

Origin of Ancient Alluvium on the Eastern Highland Rim in Tennessee

Origin of Ancient Alluvium on the Eastern Highland Rim in Tennessee

Vegetation and soil analysis of topo-sequences in the Orinoco Llanos

Two contiguous topo-sequences in the Orinoco Llanos were analyzed. The results indicated that the relief functioned differentially in the two environmental situations involving ancient alluvium from the Guarico River covered by the Trachypogon savannas and a swamp palm community, and recent alluvium from the Orituco River covered by a seasonal gallery forest, a seasonally flooded palm savanna, and a seasonally flooded herbaceous savanna. In the soil catena (first topo-sequence), the dissected relief (via the water table) determined a lack of a dry season for the swamp palm community. On the other hand, relief in the second topo-sequence (via precipitation and run-off) prolonged the effects of the wet season on the seasonally flooded palm and the herbaceous savanna. The described vegetation were found to occupy distinct soil types. However, all the studied soils were highly infertile, the swamp palm community being the extreme case. The collection of vascular plants in the communities included 515 species, distributed in 93 families. The seasonal gallery forest presented the highest species richness with 243 species, whereas the lowest value was found in the swamp palm community (79). Comparisons of the life form spectra indicated that the Teroculmi and Teroherbae were common in all communities and both possessed a tolerant-dormant stage which allowed for their survival under stressful conditions. Chorological-ecological analysis of the data indicates that the flora of the Orinoco savannas seems to have different species sources with high affinity to the nearby systems.

Parent Materials and Stratigraphy of a Doline in the Valley and Ridge Province

AbstractA variety of contrasting parent materials have been preserved within a ridgetop doline in the Valley and Ridge Province of eastern Tennessee. These materials, related to current and past slope processes, were differentiated based on morphologic properties. Matrix color and texture and the nature and content of chert fragments were particularly important in this discrimination. The doline rim was host to several distinct parent materials, including: (i) Copper Ridge residuum, (ii) mixed ancient alluvium and colluvium, and (iii) ancient toeslope colluvium. Mass wasting and fluvial processes emplaced these “ancient” materials, which currently have no source area, during the late Pliocene or early Pleistocene. The doline sideslopes contain parent materials composed of stacked layers of cherty colluvium that are late Pleistocene and Holocene in age. These colluvial deposits were derived from upslope residual and “ancient” toeslope colluvial soils via recent mass wasting. Parent materials in the doline center have a completely different morphologic character than upslope deposits. A silty material, possibly late‐Wisconsinan loess eroded into this doline during the Holocene, is devoid of chert fragments. These materials have been sorted and deposited by active slope wash and originated from either locally derived loess deposited on upper doline sideslopes, the A and E horizons of soils located upslope, or both. At 1.3 m these silty materials rest directly on a buried A horizon (2Ab) that has been radiocarbon dated to 9170 ± 140 years before present (YBP). Beneath this buried surface, alternating layers of thick noncherty and thin cherty silt loam materials represent cycles of late Quaternary landscape stability and instability.

Estimating rates of calcrete formation and sediment accretion in ancient alluvial deposits

AbstractThe use of calcrete horizons as a means of assessing rates of sediment accretion in ancient alluvial sequences is reviewed. Any attempt to use such horizons in quantifying ancient alluvial deposition must appreciate that accurate data on rates of formation of Quaternary calcretes are limited. Such data show considerable variations in the rates and no reliable data exist at all for some calcrete types. The abundance of calcretes in the geological record warrants a new initiative to improve our understanding oftheir origins and rates of formation.

Reconstruction of asphalt shaft waterbars of contraction joints of sections of the powerhouse at the lower Kama hydroelectric station

The Lower Kama hydroelectric station on the Kama River, the foundation of which is composed of ancient alluvial river deposits, is a typical run-of-river hydrostation with respect to design and layout. The 486-mtong powerhouse, 71-m-long overflow dam, and earth dam form a single barrier. The powerhouse is combined with outlets and is divided into eight sections. Two vertical units are located in each section. The sections are separated by 30-cm-wide contraction joints. The cavity of the contraction joints between sections is sealed on the upstream and downstream sides by asphalt shaft waterbars Nos. 12 and 14, the design of which is shown in Figs. 1 and 2. The rooms of the powerhous along the joints are sealed by contour {elastic) waterbars. The shaft waterbars along the foundation slab of the sections are connected to horizontal asphalt waterbars of a U-shaped profile. On the upstreamside a spare shaft is made in the joint for the possibility of making asphalt waterbar No. 13. The cavity of the joint during normal operation is filled with water to elevations corresponding to the lower pool levels and elevation of the bypass (pipe d = 100 mm), which provides discharge of water seeping into the joint into the lower pool, bypassing shaft waterbar No. 14. The capacity of the bypass when k = 1 m is 1 ma/min. During temporary operation of the hydrostation at an intermediate reservoir elevation of 62 m considerable leaks into the joint were observed, in connection with which the water levels for a number of joints exceeded the design. This led to complications in operating the equipment, including flooding of the cable galleries. Attempts to heat the asphalt waterbars by an electrical heating system embedded in the waterbar structure did not yield positive results as a consequence of breaks in the circuit of the heating electrodes during Construction works. In 1983 the Kama Hydroelectric Station Construction Association {Kamges~nergostroi) turned to the Institute for Special Operations (Gidrospetsproekt) and the State All-Union Trust for Reinforcement of Foundations and Structures (Gidrospetsstroi) with the request to give recommendations and to perform repair and restoration works on the shaft waterbars in order to provide the design water level in the cavity ofthesectionjoin ts.

Pure gypsum separates from "dirty" evaporites

Interpretation of paleochannel patterns from ancient alluvium involves reconstruction of sinuosity and degree of braiding. It is emphasized here that the geometry, flow, and sedimentary processes of the different channel patterns form a continuum, such that similarities between their deposits are more significant than differences. While many commonly cited sedimentary criteria for distinguishing channel patterns are shown to be invalid, the following are considered useful: 1) proportion of channel fills relative to lateral-accretion deposits, which increases with degree of braiding; 2) mean grain size of channel fills relative to lateral-accretion deposits, which decreases with increasing sinuosity; 3) paleocurrent variance, which may indicate sinuosity; and 4) bankfull discharge, slope, and width/depth of paleochannels throughout the channel belt, as long as they can be quantitatively reconstructed from channel-bar and channel-fill deposits. Utilization of these criteria requires examination of completely preserved sections of channel belts and overbank deposits in large outcrops. Presently existing facies models do not convey the diversity of different channel types and facies; those that are not three-dimensional and lack scales and paleocurrent information are of limited value.

Using Paleosols to Elucidate Episodic Sedimentation in Alluvial Rocks: ABSTRACT

Ancient alluvial deposits are believed to be incomplete because flood-plains undergo relatively infrequent episodes of sedimentation for which the cumulation of time is geologically limited. However, many alluvial sequences contain superposed paleosols that preserve not only the record of deposition but also the geologically lengthier record of nondeposition and nonerosion. The only time that is not represented in an alluvial sequence with paleosols is that time represented by sediments and paleosols that have been eroded. Erosion can reflect channel migration, which produces coarse sediment filled scours and is a process common to both degrading and aggrading fluvial systems. In contrast, deep and laterally extensive scours, filled dominantly by fine sediments, are evide ce for lengthy periods of degradation. This second type of scour, whose recognition End_Page 275------------------------------ is enhanced by color differences between paleosols developed on the scoured and scour-fill deposits, is a valuable indicator of climatically and/or tectonically controlled base level changes in continental basins. Because paleosols preserve the record of nondeposition and nonerosion and are useful in identifying periods of degradation, their analysis is essential to reconstructing the complete geologic history of alluvial sediments. End_of_Article - Last_Page 276------------

Critical Appraisal of Fluvial Facies Models: ABSTRACT

Interpretation (and subsequent prediction) of the lithofacies geometry of ancient river-channel deposits requires full understanding of the formative processes. This is ideally gained by linking channel geometry and hydraulics with sediment erosion, transport, and deposition, using generalized (quantitative) physical models. Such models exist for high-stage deposition in single curved channels of simple planform: they are capable of approximating the three-dimensional variation of mean grain size and internal structure of point-bar deposits in channels with differing geometries and flow characteristics. However, such models cannot presently predict processes operating on point bar tops (e.g., sheet floods, chute channel and bar formation, scroll bars, flow separation zone ) or the nature of low-flow deposits. Lateral lithofacies variation due to meander-loop evolution and cutoff is also inadequately understood. Generalized physical models of braided and anastomosed river deposition are particularly poorly developed, and need urgent attention. Single-channel and braided rivers can be distinguished on the basis of their water discharge, slope, width/depth ratio, and sinuosity; quantitative analysis of ancient alluvium is required for reconstruction of these parameters. Although braided river deposits should typically have a high proportion of coarse-grained channel fills relative to lateral accretion deposits, coarse-grained channel fills are also common in sinuous rivers with cutoffs. It appears that presently available qualitative facies models do not adequately represent the range of lithofacies geometries expected from different kinds of rivers, and therefore do not allow thorough and uneq ivocal interpretation of paleochannel geometry, flow characteristics, and evolution. End_of_Article - Last_Page 429------------

Premiers résultats de recherches géomorphologiques dans le piémont de Thèbes (Haute-Egypte)

Abstract. Geomorphological field works in Thebes aera (Upper Egypt) bring evidence of 3 stepped « glacis d'ablation » topped with thin alluvial quaternary covers. Each of them shows an alluvial unit made of local material (limestone, chert) overlying unconformably an alluvial unit which contains a number of allochtonous pebbles (quartz) carried by a streamflood coming from the South. The analysis of relationships between these units and the geomorphological features suggest that local Pluvials would be contemporaneous with the Southern ones during the Quaternary times. The discovery of very archaic tools included into the most ancient alluvium established the precocity of Human life along the large vallery where the Nile flows presently. It strengthened the preliminary idea of a powerful streamflood draining waters from Southern humid countries in this valley very early in Quaternary times.

THE NATURE AND GENESIS OF CERTAIN ARIDISOLS IN KENYA

SummaryIn the semi‐arid Kenya lowlands, strongly contrasting soil units associated with specific positions in the landscape have developed on various ancient alluvial deposits. The soil pattern may be explained by the differential truncation of a previously solodized plateau. These contrasting soil sequences give rise to associated vegetation catenas.Necessary adaptations are applied to the 7th Approximation soil classification, thereby introducing one new Great Group (Halorthid) and several new subgroups (natric grumustert, natric grumaquert, and typic halorthid).

The study of pollen spectra from recent and ancient alluvium

Studies by Soviet palynologists on spore-and-pollen spectra of Recent and Holecene alluvium have indicated that: ( 1) spore-and-pollen spectra of river deposits generally correspond to the zonal type of the vegetation cover at the point of sampling and are comparable to the spore-and-pollen spectra of lake and bog deposits; ( 2) the run-off direction and facies character, as well as other factors of the deposits studied affect the formation of spore-and-pollen spectra; ( 3) the distribution of spores and pollen grains redeposited from older deposits is governed by only a small number of factors. A comparison of palynological data from old alluvial deposits with the results of geological investigations shows that an intimate relation exists between the vertical distribution of the sediments and past changes of climate and vegetation. A study of the specific features of alluvium accumulation in mountains, piedmont and plain areas demands: ( 1) a close correlation of palynological and geological-geomorphological data; ( 2) a selection of the most promising areas and sequences; ( 3) repeated traverses of terraces along transverse profiles; ( 4) an exact recording in the sequence of all traces of lengthy intervals or substantial washouts of the deposits; and ( 5) a separate interpretation of the results for each facies.

Presence de l'Halitherium dans l'Oligocene du Poitou

Abstract A reworked skull fragment of Halitherium sp. found in ancient alluvial deposits of an abandoned channel of the Clain river in Poitou, France, may represent a variation or mutation of H. schinzi. Its Oligocene age confirms the presence of Oligocene deposits in the region. The Tertiary so-called lacustrine deposits of the region have generally been assigned a variety of ages ranging from Lutetian (Eocene) to Aquitanian (Oligo-Miocene).

A RECONNAISSANCE CLASSIFICATION OF THE SOILS OF THE SOUTH TURKANA DESERT

Summary Development of the Soil Pattern As an outcome of an ecological reconnaissance this account provides a record of the occurrences of two major regional types, a system of consolidated sand dunes and derived sands, referred to here as the Chestnut Sands, and a wide assortment of stony truncated ‘desert pavement’ soils or soil remnants described as Stone Mantles. The latter involve areas both of basement complex and of lava origin. Briefer observations are also given on other soils of lesser extent, including flash‐flood, alluvial and lacustrine deposits.Although a present‐day desert or semi‐desert, the south Turkana region bears the stamp of successive erosion cycles, which have largely influenced its soil pattern. Modified remnants of the original end‐Tertiary surface are probably discernible in the higher‐lying stone mantles about the central hill ranges (Section 2, Introd.). Residual stone mantles of this class appear to be the last truncated remnants of an ancient soil cover. Ancient alluvial and lacustrine deposits, the former of conjectured and the latter of established Pleistocene age, have provided the material for other stone mantle areas (Section 2 (b)). The present surface of all these has been affected by more recent erosion and deflation.On top of these several types of stone mantle, or the stony soils from which they originated, seems to have been deposited the deep mantle of the Chestnut Sands, blanketing at one time the greater part of the Turkana plain. These dune sands are regarded as a mainly aeolian drift, deposited during a period of active arid erosion, though their materials may have been derived from older surfaces (Section I, Introd.). They must be subsequent to the deposits which they overlie, and may possibly be compared with the Goz or Kordofan Sands of the Sudan, which have been very tentatively referred to the late Pleistocene (Andrew, 1948).As with the Goz Sands, the dunes of the Chestnut Sands presumably became fixed under less arid conditions. Finally, in common with the rest of the Turkanalandscape, they have been subjected to the present régime of brief seasonal flash‐flood erosion and intervening wind action. Their formerly extensive dune structure has been greatly modified and from many areas they appear to have been removed wholesale. The redeposited Chestnut Sands, the flash‐flood deposits and sandy riverine alluvia are the outcome of this latest phase of erosion. At the same time tracts of comparatively recent lacustrine sands and possible deltaic silts (Section 4 (b) have been left in the east of the region as a result of the progressive retreat of Lake Rudolf.The influence of the resulting soil pattern on the vegetation of the region is very briefly indicated, with reference more particularly to the principal shrub components.

Remaniements dans les alluvions anciennes de l'Oise a Cergy (Seine-et-Oise)

Abstract Mineralogic and granulometric study of the ancient alluvial deposits of the Oise at Cergy, Seine-et-Oise, France, shows that their sandy portion is derived mainly from local Bartonian (Eocene) sands which formerly covered Lutetian structural surfaces to a greater extent than at present.

Faune et morphologie des alluvions anciennes de l'Ornain et de l'Ante

Abstract The ancient alluvial deposits of the Ornain and Ante river valleys, Meuse region, France, are characterized by the presence of a mixed fauna and detrital material whose morphology indicates deposition in an extremely wet period during which there was extensive gullying and erosion.

On the Origin of the Auriferous Conglomerates of the Gold Coast Colony (West Africa)

abstract This paper gives an account of a recent journey from Adjah Bippo to the Ankobra Junction in the Gold Coast Colony. A range of clay-slate hills is succeeded for 6 miles by flat ground in which diorite was found, and that by a lofty hill in which clay-slate dipping east occurs. The Teberibie range with reefs of conglomerate, and a second range with similar reefs, were crossed. Gold-bearing alluvia are briefly described, and the gold is supposed to have come from the hills. The Adjah Bippo, Tarkwa, and Teberibie formations are considered to be part of a syncline. Certain auriferous conglomerates, and others presumed to be identical with them, are thought to be ancient alluvial deposits.

XXIX.—On the Geology of the Thracian Bosphorus.

During a short residence at Constantinople, in March 1836, I made some researches into the geology of its vicinity. A very cursory examination sufficed to show, that the district was unexplored, and that the brief geological remarks, which exist in the works of other travellers, are very unsatisfactory. I therefore communicate my observations to the Society, in the hope that, though slight, they may serve as a guide to those geologists who may hereafter be induced to explore this interesting district*. The formations in the neighbourhood of the Bosphorus may be classed as follows:— 1. Silurian schist and limestone. 2. Igneous rocks. 3. Tertiary limestone. 4. Ancient alluvium. 1. Silurian Schist and Limestone. This formation occupies both sides of the Bosphorus for about three quarters of its length, and extends thence towards the W.N.W. and E.S.E., to an unascertained distance in Europe and Asia. It may probably form a great part of the Balcan range, of which the hills above the Bosphorus are a continuation. The formation may be described as a mass of argillaceous schist, compact brown sandstone, and compact dark blue limestone, passing into each other by insensible gradations. The argillaceous schist predominates greatly over the other two rocks, and frequently exhibits an oblique or slaty cleavage. The whole formation bears a close analogy to the lower Silurian and upper Cambrian series, exhibited in Wales and Devonshire. From its resemblance to the type of northern Europe, Andreossy* and an American traveller† referred it to the transition series on