Distal Floodplain Research Articles

Taphonomy of a late Cretaceous mammal-bearing microvertebrate assemblage from the Deccan inter-trappean beds of Naskal, peninsular India

Abstract Taphonomic analysis of a microvertebrate assemblage from the late Cretaceous Deccan inter-trappean sequence of Naskal, peninsular India, is undertaken to infer the taphonomic factors involved in the accumulation of bones at a time predaceous avians and large mammals were non-existent. Approximately 1 ton of matrix was screen washed and a large number (> 9100) of isolated skeletal remains of fish, amphibians, turtles, lizards, snakes, crocodiles, mammals and dinosaurs, in addition to pelecypods, ostracodes, gastropods and charophytes were recovered. Different mechanisms are postulated for the initial accumulation of the fauna. Whereas scavenging activity played no significant role in the accumulations, hydraulic sorting was responsible for accumulation of the terrestrial and semi-aquatic component of the fauna. The wide distribution of bone fragments, presence of pre-burial fractures on some of the bones and the occurrence of the assemblage in a thin, calcareous palaeosol unit indicate that the vertebrate remains accumulated rapidly as a consequence of a prolonged, drought-induced, mass mortality event and were subjected to subaerial exposure. The study concludes that the Naskal assemblage accumulated in a distal floodplain lake, which served as a natural death trap, on whose banks terrestrial and other animals might have gathered in search of food and water during a prolonged drought and perished subsequently due to the desiccation of the lake.

Dynamics of iron and calcium carbonate redistribution and palaeohydrology in middle Eocene alluvial paleosols of the southeast Ebro Basin margin (Catalonia, northeast Spain)

Abstract Paleosols in the alluvial middle Eocene of the Ebro Basin exhibit both the redistribution of iron (groundwater and surface-water gley) and calcium carbonate. The hydrological dynamics are reconstructed through gley features and location of carbonate accumulation. Together, these allow a sophisticated analysis of the (seasonal) palaeohydrology of ancient sedimentary environments. This analysis is performed on paleosols developed in marginal and distal floodplain and delta plain deposits derived from the southeast Ebro Basin margin. The most proximal part of the floodplain sediments had moderate, mainly vadose calcite redistribution with surface-water gleying, and fairly deep groundwater. The more distal sediments have stronger calcite redistribution, both of vadose and surface-water gley environments. These were frequently overprinted by groundwater-related calcite, indicating shallow and fluctuating groundwater. In the most distal alluvial sediments, both calcite redistribution and further soil formation were weak, while groundwater was shallow.

Wasatchian-Bridgerian (Eocene) paleoecology of the western interior of North America: changing paleoenvironments and taxonomic composition of omomyid (Tarsiiformes) primates.

Many changes in mammalian faunas occurred across the early (Wasatchian) to middle (Bridgerian) Eocene boundary as documented in the fossil record from the Western Interior of North America. One of the more striking changes took place within the tarsiiform primate family Omomyidae. In the early Eocene, omomyids were dominated, both in abundance and diversity, by the subfamily Anaptomorphinae. In the middle Eocene, the subfamily Omomyinae dominated in abundance, while both subfamilies were nearly equally diverse. Examination of a series of paleoecological indicators including leaf-margin analysis, cenogram analysis, ecological diversity analysis of trophic structure, the distribution and development of ancient soil horizons (paleosols), and the distribution of lacustrine and fluvial facies in the Bighorn and southern Green River basins of Wyoming reveals factors that may have influenced the composition of omomyid primates. Subtle but important changes occurred in paleoclimates with mean annual temperatures reaching Cenozoic maximums at the end of the Wasatchian into the early Bridgerian. Both land mammal ages were typified by subtropical, closed forested conditions, but the Bridgerian was probably more humid and wetter than the Wasatchian. Paleohabitats most commonly sampled in the Wasatchian of the Bighorn Basin are proximal and distal floodplains, while those of the Bridgerian in the southern Green River Basin are lake margins and proximal floodplains. Changes in paleoclimate may have triggered a wave of omomyine immigration near the end of the Wasatchian with omomyines entering into habitats previously occupied by anaptomorphines. Lake margin and proximal floodplain habitats are those most commonly occupied by omomyines in the Bridgerian with anaptomorphines being more common in basin margin and distal floodplain areas not commonly sampled. Omomyine immigration and sampling of differing paleohabitats are two possible explanations for the changes documented in omomyid diversity and abundance.

Floodplains and paleosols of Pakistan Neogene and Wyoming Paleogene deposits: a comparative study

Abstract Comparative study of fossil-bearing fluvi' deposits in the Eocene Willwood Formation of northern Wyoming and the Miocene Chinji Formation of northern Pakistan indicate how tectonic and climatic processes operating at different scales controlled physical and chemical features of floodplain environments and affected preservation of the paleontological record. The architecture of Willwood Fm. floodplain deposits represents a combination of avulsion-belt sediment packages and overbank sediments that formed alluvial ridges. The architecture of the Chinji Fm. floodplain deposits was controlled by widely distributed crevasse-splay deposition and floodplain topography. Similarities in individual paleosol-bounded overbank sequences from the two formations indicates that the internal structure of such deposits can be independent of channel belt proximity to areas of aggradation. Chinji Fm. paleosols have little vertical zonation and show no consistent pattern of lateral change in relation to major channels, while overbank paleosols in the Willwood Fm, exhibit considerable soil horizon development and a pattern of increasing maturity from alluvial ridge to distal floodplain. The “pedofacies model” of Bown and Kraus (1987) based on such lateral trends in the Willwood paleosols is not applicable to the Chinji Fm. Plant and animal fossils are abundant in the Willwood overbank deposits, with vertebrate remains concentrated in paleosol A horizons. Plant remains are rare in the Chinji Fm. and vertebrate fossils occur primarily in channel fills rather than in paleosols. These differences relate to contrasting patterns of floodplain deposition and to levels of oxidation that controlled penecontemporaneous recycling of organic material, particularly in paleosols. Different large-scale climatic and tectonic controls on temperature and rainfall, water table fluctuations, and soil biota are proposed to account for the differences in organic preservation. Large and small-scale environmental processes also affected spatial and temporal resolution of the organic record, resulting in important differences in the paleoecological and evolutionary information that can be reconstructed from the two sequences.

Paleocene mammals and faunal analysis of the Chappo Type Locality (Tiffanian), Green River Basin, Wyoming

ABSTRACT The Chappo Type Locality in southwestern Wyoming has produced an extensive Tiffanian (late Paleocene) mammalian fauna. Thirty-three genera and 39 species of mammals are represented at Chappo, including three newly recognized taxa, a ?lipotyphlan insectivore Palaeoryctes cruoris, sp. no v., an erinaceomorph insectivore Cedrocherus aceratus, sp. nov., and an arctocyonid condylarth Lambertocyon gingerichi, sp. nov. Comparison with other middle and late Tiffanian localities suggests that Chappo represents a transitional Ti3–Ti4 fauna. The presence of mature paleosol horizons at Chappo indicates deposition on a distal floodplain. Faunal analysis (including body size distribution, trophic structure, and taxonomic diversity) indicates that the Chappo sample consists of small- to medium-sized mammals dominated by omnivores and insectivores. The relatively low frequency of frugivores indicates less forested, more open conditions. Diversity indices suggest that middle Tiffanian mammalian diversity was only...

Origin, architecture, and paleoecology of the early Eocene continental ichnofossilScaphichnium hamatum— integration of ichnology and paleopedology

Ichnofossils and alluvial paleosols from the lower Eocene Willwood Formation of the Bighorn Basin in northwest Wyoming documents the origin and paleoecology of the ichnofossil Scaphichnium hamatum as well as provide insight on changes in paleosol hydrology and development through time. In the Willwood Formation, 5. hamatum occurs as a discrete hamate (hook‐shaped) to lunate meniscate burrow with a lower bulbous termination in assemblages that range from a few to hundreds of individuals. The burrows are concentrated within the Bg horizon (gleyed B horizon) of hydromorphic paleosols representing distal floodplain settings. Until recently, the architect responsible for its construction was unknown. Comparisons with modern examples of insect nests and burrows suggests that the architect of S. hamatum was a beetle of the family Scarabaeidae and that nest construction occurred during periods characterized by relatively dry soil conditions and lowered water tables. Interpretations of the trace fossil succession,...

Sedimentology and Ichnology of Floodplain Paleosurfaces in the Beaufort Group (Late Permian), Karoo Sequence, South Africa

Floodplain paleosurfaces are depositional surfaces that were exposed on ancient floodplains and have been preserved in the rock record. Three types of floodplain paleosurfaces have been recognised in the Late Permian Beaufort Group strata of the southwestern Karoo Basin of South Africa. They occur in sedimentary sequences which represent point bar, proximal floodplain, and distal floodplain facies. The distribution of paleosurfaces in the Beaufort strata was ultimately controlled by flash-floods which transported sand out of the large meandering river channels into the floodplains. Preservation of the vertebrate and invertebrate traces was enhanced by a silty-clay veneer that accumulated on the sand surfaces during waning flood

Vertebrate Taphonomy of Late Permian Floodplain Deposits in the Southwestern Karoo Basin of South Africa

The predominantly fluvial strata of the Late Permian Beaufort Group in the southwestern Karoo Basin contain numerous fossils of therapsid reptiles. This study investigates the taphonomy of these fossils and the sedimentology of the floodplain deposits in which they are most commonly preserved. Taphonomic assessment of 329 in itu fossils along 3 cliff exposures included data on disarticulation, bone weathering, attitude of skulls, bone color, type of perimineralization and degree of pre-fossilization damage. This led to the recognition of 6 «taphonomic pathways» along which bones entered the rock record. Three floodplain facies, channel-bank, proximal floodplain and distal floodplain, that were previously defined on sedimentological and pedological criteria also have taphonomically discrete attritional bone assemblages

Preservational, paleoecological, and evolutionary patterns in the Wyoming-Montana Paleogene and Siwalik Neogene records

The Paleocene to early Eocene sequence of Wyoming-Montana and the Miocene to Pleistocene Siwalik record of Pakistan are exceptionally long, continental sequences, each containing a rich and well documented fossil record, especially of mammals. The two sequences are broadly similar in tectonic setting and sedimentary environment, in duration and facies changes, and in diversity of fossils. Each contains a paleoclimatic record in stable isotopes and, in the Paleogene, floras. Comparison of these two sequences has focused our attention on the interaction of tectonic, climatic, sedimentologic, and taphonomic factors that produce a particular fossil record and on the co-occurring ecological and evolutionary changes that result in a historical series of biotas, each the product of local and global events.In the Paleogene record, the geographic scope of the record encompasses much of the floodbasin, and the spatial distribution of paleoenvironments formed fairly straightforward gradients from channel to distal floodplain. The Siwalik record has a smaller window onto a larger, heterogeneous fluvial system often with multiple, contemporaneous river systems that differ in magnitude. The spatial distribution of paleoenvironments was a mosaic without long proximal to distal gradients. In both records, major facies changes are correlated with striking changes in fossil productivity.The overall pattern of fossil preservation by depositional environment differs substantially in the two areas. The Siwalik sequence has a greater variety of depositional environments that produce fossils throughout the section. The primary productive environment in the older part of the Paleocene record declined in productivity upsection, while a previously unproductive facies became the major source of fossils. Much of the record represents attritional accumulation in each area, but a significant portion is transported. The taphonomic processes that created fossil concentrations led to better taxonomic resolution for most Paleogene localities than in most Siwalik localities.In each record, both aquatic and terrestrial components of the vertebrate faunas are correlated with facies. Since facies varied in productivity over time, some changes in faunal composition may have resulted from change in the prevalence or productivity of particular facies. At least one faunal turnover coincided with major facies changes in each sequence.For mammals in each record, immigration rather than speciation in situ was the primary means of appearance of new species. Episodes of immigration were not closely followed by extinctions of resident species. Mean species longevity appears to have been more than twice as great in the Neogene than in the Paleogene record. Changes in faunal composition and species richness occurred during times of global climatic change; causal connections are still being explored. Changes in species richness did not track changes in relative abundance of taxa or changes in size within lineages or faunas. In terms of guild structure, the herbivore guild had high relative generic diversity through most of both sequences. The Paleogene record had a more even distribution of taxa in the five principal guilds, while the Siwalik record was heavily dominated by the herbivore guild. Size distributions differed substantially, reflecting the early and late windows into the mammalian radiation, rather than sampling bias.

The anatomy of an early Dinantian terraced floodplain: palaeo‐environment and early diagenesis

ABSTRACTThe lowermost Carboniferous rocks in the Cockburnspath area of east Berwickshire (southern Scotland) are interpreted as coastal floodplain sediments. A lower mudstone‐dominated unit is composed of silty mudstones and shales with subordinate sandstones and argillaceous ferroan dolomites (cementstones). These are interpreted as distal floodplain sediments with periodic crevasse‐splay deposition. The dark grey colour of the mudrocks suggests deposition in reducing conditions, probably in floodplain lakes. Most of the cementstones are concretionary, some with septarian cracks, suggesting an early diagenetic origin. An immature palaeosol suggests periodic pedogenesis under improved drainage. A synsedimentary erosion surface indicates incision of a valley into the floodplain, presumably in response to base‐level lowering.An upper sandstone‐dominated unit starts with fine‐grained rippled sandstones, cut by small channel sandstones. These are interpreted as floodplain lake deposits fed by crevasse channels. A distinctive conglomerate with cementstone clasts, wood fragments and fish remains is interpreted as a major overbank deposit, dumped into a pre‐existing floodplain lake. A bivalve fauna was established in the overlying mudstones, followed by a thin limestone with a restricted marine fossil assemblage, showing that seawater flooding of the lakes occurred at times.Mudrocks throughout the sequence contain no pyrite, except for the marine band which has an organic‐carbon/sulphur ratio and degree of pyritization value typical of marine sediments. The concretionary cementstones have δ13C values around —4 to —6%0/00 PDB which are interpreted as indicative of anaerobic oxidation of organic matter. The combined geochemical data suggest a significant involvement of iron reduction in cementstone formation, although the δ13C values are ambiguous in assessing the relative involvement of methanogenesis and methane oxidation. Limited seawater inundation of the floodplains might have supplied magnesium and calcium ions for dolomite formation assuming that any H2S derived as a result of sulphate reduction was oxidized by iron reduction. Alternatively a weathering source for solutes might have been involved.

Usefulness of palynomorph concentrations in distinguishing Paleogene depositional environments in Wyoming (U.S.A.)

Canonical variates analysis of palynomorph taxon concentrations in 50 samples from five Paleogene depositional facies (pond, crevasse splay, swamp, swamp margin, distal floodplain) in the Bighorn Basin, Wyoming (U.S.A.) separates the samples by facies. The major separation is based on taxa with higher concentrations in the pond and swamp than in other facies (e.g., Deltoidospora, Sparganiaceaepollenites, Taxodiaceae, Alnus). Other separations are produced by low concentrations of Arecipites, Pandaniidites and Ulmipollenites in the crevasse splay and by Taxodiaceae, Sparganiaceaepollenites and Corylus low in the floodplain. Concentrations of particular taxa can therefore be useful indicators of particular depositional environments.

Paleomagnetic Isochrons, Unsteadiness, and Uniformity of Sedimentation in Miocene Intermontane Basin Sediments at Salla, Eastern Andean Cordillera, Bolivia

Fine-scaled stratigraphic data are combined with chronologic information provided by paleomagnetic stratigraphy to document and analyze chronostratigraphic variability of the Salla Beds, a sequence of distal floodplain and lacustrine intermontane basin sediments within the eastern Andean cordillera of Bolivia. Unsteadiness in sediment accumulation is identified using a conceptual model of episodic accumulation in which simulated accumulation histories are constructed using estimated rates for various fluvial facies and taking into account gaps in deposition and possible effects of erosion. Variability in the Salla Beds is compared to that in sequence of Miocene fluvial sediments in northern Pakistan to evaluate controls on spatial and temporal stratigraphic variability. Sedimentation in the Salla sequence was generally steady over short time scales, but over longer intervals infrequent carbonates, associated with unusually long hiatuses, served to reduce the net sediment accumulation rate. In the Chinji sequence of Pakistan, unsteady accumulation evolved into a pattern of steadier sediment accumulation as recurring cycles of unsteadiness were superimposed on the overall sequence. The controls on sediment accumulation over time in these two sequences may be similarly related to the presence and extent of atypical and infrequent events of deposition, non-deposition, or erosion that exert a significant effect on net sediment accumulation. The discrepancy of short-term episodic and long-term net stratigraphic accumulation rates in both these sequences suggests that the decrease in net sediment accumulation rate with increasing time reflects the superimposed effects of different levels of local geomorphic and extrabasinal controls.

Lateral and vertical variations in pedogenesis and other early diagenetic phenomena, Middle Jurassic Ravenscar Group, Yorkshire

SUMMARY The effects of early diagenetic processes are widespread in shallow marine and non-marine (deltaic) sediments of the Ravenscar Group. These can be related to both lateral variations in ground water chemistry within the original depositional environment on the lower coastal plain, and to the introduction of sea water into the non-marine sediments and of fresh water into the marine sediments. In the non-marine sediments lateral (catena) variations in soil profiles can be related to floodplain aggradation and abandonment. Near the major channel sands in the Saltwick Formation at Whitby West Cliff, a ganister and seatearth formed in elevated and well drained sediments that were frequently flushed with fresh water. In more distal floodplain areas, ground-waters were influenced by fresh water, but remained generally suboxic, as a result of which siderite cementation occurred. The influence of meteoric water is indicated by the isotopic composition of the cements that formed ( δ 13 C PDB −3.7 to −9.6 ‰, δ 18 O PDB −6.0 to −8.5 ‰). Rhombic siderite cemented the sands, and siderite nodules formed in both sands and shales. Siderite spheruliths formed within more distal soil horizons (such as the Long Nab Member at Crook Ness) where bacterial processes dominated the supply of bicarbonate into the ground water, and in non-marine sediments on abandoned and subsiding delta lobes. Bacterial influence is reflected in the more negative carbon isotopic composition relative to that of the nodules ( δ 13 C PDB −16.2 ‰, δ 18 O PDB −3.5 ‰). Sea water was introduced onto the floodplain locally, providing sulphate ions that were reduced and incorporated into the pyrite that precipitated in the siderite soil horizons. In the marine Millepore Bed sediments at Yons Nab early diagenetic, possibly aragonite, fringes formed on bioclasts and ooliths. These were subsequently deformed by the weight of overburden following renewed progradation. Grain-to-grain contact dissolution and kaolinite precipitation occurred as the fresh groundwater invaded these marine carbonates from the prograding delta above.

Palynological Facies Fossils in Nonmarine Environments in the Paleogene of the Bighorn Basin

Palynomorphs occur as lithofacies fossils among depositional environments of the uppermost Paleocene to lowermost Eocene sediments of the central Bighorn Basin in Wyoming. Carbonaceous sediments occur within the predominantly red-bedded sequences and they contain lithofacies interpretable as deposition in ponds, crevasse splays, reduced distal floodplains, swamp margins, and clastic swamps. The palynomorph content of these lithofacies, primarily from a limited stratigraphic interval, is shown by canonical variates analysis to be made up of distinct palynologic assemblages. These assemblages differ primarily in abundance of taxa present rather than their presence or absence. The ponds are particularly distinguished by high numbers of reworked marine dinoflagellates, algal zygospores (Tetraporina), bisaccate gymnosperm pollen, and low numbers of Alnus and Taxodiaceae. The levee/crevasse splay contains high numbers of some bisaccate pollen types, pteridophyte spores, and locally high quantities of Alnus. The reduced floodplain contains abundant bisaccate pollen and pteridophyte spores, Platycaryapollenites, and Taxodiaceae. Swamp margin samples are distinguished by high numbers of Cycadopites and locally high numbers of Plicatopollis and Alnus. The swamp is dominated by pollen of Taxodiaceae and Alnus as well as high numbers of Sparganiaceaepollenites, with locally high numbers of Pistillipollenites. Pond deposits are generally more numerous and contain a richer palynoflora, however, the occurrence of the important Paleocene-Eocene boundary taxon Platycaryapollenites occurs in swamp and neighboring facies about 200 m below its first occurrence in pond facies. Thus, lithofacies distribution effects can affect the accuracy of biostratigraphic interpretations. INTRODUCTION

完新世における豊平川扇状地とその下流氾濫原の形成過程

The Toyohira River has formed an alluvial fan during the Holocene. The author studied the Toyohira River alluvial fan and distal floodplain from the viewpoint of the fan-delta complex deposited through a river system. A series of lobes was found on the distal part of the Toyohira River alluvial fan. These lobes consisted of bed load gravels and natural levee deposits. The stratigraphy of the fan deposit and marginal alluvium was studied based on 14C datings and geological sections. The Holocene evolution of the Toyohira River alluvial fan and its distal floodplain can be summarized as follows (Fig. 7). During the latest Pleistocene, the Toyohira River formed a fan-delta system at the lower sea level of the last glacial age, As the sea level rose, in the early Holocene, the Toyohira River formed a confined fan delta in the western part of the bay mouth, dissecting the Pleistocene fan in the upper part of the fan-delta system. In the late Holocene, after the sea level had risen to the present stage, the Toyohira River shifted its channel gradually eastwards, and buried a lagoon confined by the Momijiyama barrier. This channel shift was accompanied by lateral erosion at the fan head, and with the formation of lobes distal to the fan. Such alluvial fan construction means that the Holocene fan surface of the Toyohira River was formed by two separate processes, erosion and deposition, independently (Fig. S). During the late Holocene, the Toyohira River alluvial fan has developed not continuously, but episodically, as is suggested by an extraordinarily large-scale lobe of ca. 3, 500y.P. P. The geomorphic process controlling such episodic fan development is not clarified.

Integration of Channel and Floodplain Suites, I. Developmental Sequence and Lateral Relations of Alluvial Paleosols

ABSTRACT The lower Eocene Willwood Formation of the Bighorn Basin, northwest Wyoming, consists of about 770 m of alluvial rocks that exhibit extensive mechanical and geochemical modifications resulting from Eocene pedogenesis. Willwood paleosols vary considerably in their relative degrees of maturity; maturity is defined as stage of development as a function of the amount of time required to form. Five arbitrary stages are proposed to distinguish these soils of different maturities in the Willwood Formation. Stage 1 soils, the least mature, are entisols; stage 2 and stage 3 soils are intermediate in maturity and are probably alfisols; and stage 4 and stage 5 soils, the most mature, are spodosols. These stages are not only time-progressive elements of an in situ maturation sequence for W llwood soil formation, but, in the lateral dimension, they are also usually distributed sequentially. Study of Willwood paleosols indicates that an inverse relationship exists between soil maturity and short-term sediment accumulation rate. The least mature Willwood paleosols formed in areas of relatively high net rates of sediment accumulation on 1) channel, levee, and crevasse-splay sediments of the proximal alluvial ridge, and 2) deposits filling large and small paleovalleys formed by major episodes of gullying (lowered baselevels). In contrast, the fine-grained sediments of the distal floodplain, where net sediment accumulation rates were relatively low, experienced development of much more mature soils. Soils of intermediate maturities occur in the order of their stage on intervening proximal floodplain and distal alluvial ridge sediments. Adjacent bodies of sedimentary rock that differ in their ancient soil properties because of distance from areas of relatively high sediment accumulation are denoted by the new term pedofacies. The remarkable sequence of paleosols in the Willwood Formation clearly illustrates several important principles of soil-sediment interrelationships in aggrading alluvial systems that have broad application to other deposits. This is especially true in view of the widespread distribution of paleosols in nearly all ancient fluvial rocks. Further study of Willwood paleosols will not only enable precise lateral correlation of coeval alluvial sediments, and thereby fluvial sedimentary events, from the distal to the proximal realms of the floodplain but will also contribute to increasingly informative evaluations of the nature, tempo, and mode of alluvial succession.

Eocene sheetflood systems and transitional fan‐deltas, Southern Pyrenees, Spain

AbstractThe Eocene Monllobat and Castigaleu Formations in the Southern Pyrenees consist of continental and shallow marine deposits respectively. The Monllobat Formation contains conglomerate sheets with sandstone tails, symmetrical channel fills with wings and various types of lobes, accreted laterally in channels as well as by progradation. These deposits are intercalated in large amounts of flat‐bedded silt and mudstone with mottling and caliche.The high energy alluvial flow, which deposited these sediments, was initially at right angles to the axis of the elongated basin, becoming near parallel to the axis distally. The deposits are less gravelly distally. Upstream wide, gravelly braidplains were developed. Gravel lobes and muddy sheetfloods prograded over the distal floodplain. Meandering rivers were restricted to a marginal position in the sheetflood environment.The Castigaleu Formation consists of mudstone with intercalations of sandstone. Lobes of conglomerate and sandstone dominate the contact zone with the Monllobat Formation. Flat sandstone layers with tabular cross beds and parallel lamination and massive sandstone beds are distributed throughout the other parts.The lobes were formed at the coastline during high energy inflow in the marine basin. Flow deceleration caused the deposition of the coarsest load at this site, building a wedge with an inclined front during major aggradation and progradation. The other deposition types originated during hyperpycnal inflow in a marine environment. Massive sandstones originated partly because of bioturbation. Reworking by physical marine processes did not occur. Synsedimentary tectonics determined the type of sedimentation at times.

Shallow-Water Clastic Sediments of Great Blue Formation and Manning Canyon Shale, Oquirrh Basin, Utah: ABSTRACT

An east-west belt of clastic sediments in the Mississippian Great Blue Formation and Manning Canyon Shale thickens and coarsens westward and contains terrestrial plant and palynomorph assemblages. These clastic sediments were derived from the Antler highlands in central Nevada. The depositional axis of the clastic belt or proto-Oquirrh basin is probably related to a basement weakness that controlled the east-west-trending Uinta basin. The geometry of the belt is illustrated by isopach maps and cross sections. An isopach map of the total Mississippian clastics in eastern Nevada and Utah and an east-west cross section through the Oquirrh basin demonstrate that the clastics thicken and coarsen westward and indicate a western source. A north-south cross section illustrates ho the clastic sediments were restricted to the east-west clastic belt. In contrast to previous interpretations that assumed that the clastic sediments were shed westward from the craton into deep water, field evidence suggests that they were shed eastward from the rising Antler mountains into very shallow water. Terrestrial plants preserved in shales and sandstones of the Great Blue Formation and the Manning Canyon Shale suggest that the clastic sediments were deposited in a transitional environment such as lagoons, distal flood plains, and deltas. Palynomorph assemblages in the shales lack marine forms and also indicate shallow-water deposition. In addition, surface gamma-ray patterns of measured sections are typical of transitional facies sequences such as deltas and nearshore environments. End_of_Article - Last_Page 934------------

Paleoenvironmental Control of Accumulation and Quality of Upper Freeport Coal Bed (Allegheny Formation, Middle Pennsylvanian), Castleman Coalfield, Maryland: ABSTRACT

The upper Freeport is generally a thick, widespread coal bed in the north-central Appalachian basin. It is a principal bed mined in the Castleman coalfield, Garrett County, Maryland, as delineated on a new geologic map of the coalfield. In the northern part of the coalfield, the upper Freeport is 21-48 in. (53-122 cm) thick and thickens toward the northwest, where the ash and sulfur contents are generally 7-10 wt. % and less than 1.5 wt. %, respectively. This coal bed thins southward and eastward and is absent from a large area in the central part of the coalfield, where its position is occupied by a carbonaceous claystone or flint clay. Toward the south and east, the upper Freeport coal bed generally contains 12-15 wt. % ash and 1.5-6.2 wt. % sulfur. Lithofacies analysis of the floor rocks and their lateral equivalents indicates deposition of the upper Freeport coal bed in floodplain swamps. Limestone and limy claystone floor rocks in the northwest represent distal floodplain lake deposits. Where the coal is unminable or absent to the south, proximal overbank floodplain shale, siltstone, and silty claystone grade laterally into channel sandstone. The gradation of thin coal into carbonaceous claystone to the south indicates increased oxidation and shoaling in a well-drained swamp. There, the coal has the highest ash and sulfur contents, which probably reflect the influx of detritus and iron-rich clays. Thus, the upper Freeport is thickest and has the lowest ash and sulfur contents where the paleoenvironment was a poorly drained, di tal floodplain swamp. End_of_Article - Last_Page 1924------------

Depositional Control of Aquifer Characteristics in Alluvial Fans, Fresno County, California

Research Article| August 01, 1979 Depositional Control of Aquifer Characteristics in Alluvial Fans, Fresno County, California David Cehrs David Cehrs 1U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, Water Management Research, Fresno, California 93726 Search for other works by this author on: GSW Google Scholar Author and Article Information David Cehrs 1U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, Water Management Research, Fresno, California 93726 Publisher: Geological Society of America Received: 20 Oct 1978 Revision Received: 04 Apr 1979 Accepted: 18 Apr 1979 First Online: 02 Mar 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 1979 The Geological Society of America, Inc. GSA Bulletin (1979) 90 (8_Part_II): 1282–1309. https://doi.org/10.1130/GSAB-P2-90-1282 Article history Received: 20 Oct 1978 Revision Received: 04 Apr 1979 Accepted: 18 Apr 1979 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David Cehrs; Depositional Control of Aquifer Characteristics in Alluvial Fans, Fresno County, California. GSA Bulletin 1979;; 90 (8_Part_II): 1282–1309. doi: https://doi.org/10.1130/GSAB-P2-90-1282 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Three coalescing alluvial fans, the high alluvial fans of the San Joaquin and Kings Rivers and the intervening compound alluvial fan of intermittent streams (Page and LeBlanc, 1969), and their distal flood plains from the surficial and shallow subsurface deposits (100 m thick) of central Fresno County (Fig. 1). These deposits extend from the foothills of the Sierra Nevada to the axis of the San Joaquin Valley 58 km away. Physically they resemble the smaller, semiarid-region alluvial fans found in western Fresno County (Bull, 1964a, 1964b), but they lack the extensive debris-flow (mud-flow) deposits found in the western fans. The central Fresno County alluvial fans consist of vertical and lateral accretion deposits derived from meandering streams. Within these fan—flood-plain deposits, aquifer properties change in a specific downfan sequence. From available data on sediment in surface exposures, cores and well logs, and ground-water information, a description of the relationship between the observed aquifer characteristics and the depositional system of the fans is given here.GEOLOGIC SETTINGThe Fresno alluvial fans are part of a continuum of fans along the east side of the San Joaquin Valley. The present fans are the most recent of a sequence of Cenozoic sedimentary deposits that in the axis of the San Joaquin Valley are more than 4,000 m thick (Hackel, 1966). They contain Pleistocene and Holocene deposits of lacustrine, marsh, and fluvial origins. Much of the sedimentary and depositional history of this sequence is the result of the Pleistocene climate and associated glaciations. These valley-fill sediments provide a record of tectonism and erosion of the Sierra Nevada during Late Cretaceous to Paleocene time and during renewed uplift in late Miocene—early Pliocene time. This renewed uplift was responsible for the present elevation and tilting of the Sierra Nevada and for the depth of incision of the major rivers into the batholith (Bateman and Wahrhaftig, 1966). This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.