Swamp Deposits Research Articles

Genetic Sequences and Unconformities in Shallow Marine to Fluvial Depositional Systems, Mesaverde Group, North-Central Wyoming

Continuous exposures of the Mesaverde Group (Campanian) in the Bighorn basin area, Wyoming, were utilized to establish regional facies architecture and to test sequence stratigraphic concepts along and perpendicular to the general trend of the shoreline of the Western Interior Cretaceous Seaway. Sections along the west flank of the basin begin with stacked seaward stepping, wave dominated beach sandstones that are fed by widely spaced river systems. These sandstones grade eastward into storm influenced intercalated shale/sandstone beds of the lower shoreface-shelf transitional zone. Bioturbated lower and upper shoreface deposits are often truncated by a laterally continuous erosion surface and overlain by coastal swamp and channel deposits, suggesting a regional regressive unconformity. The overlying fluvial units exhibit a distinct transition in architecture from single and multistoried, lens-shaped, avulsion-controlled, low sinuosity channel bodies to single-storied sheets of high sinuosity channels that consist exclusively of gently dipping, heterolithic lateral accretion units. The uppermost depositional sequence of the Mesaverde is the Teapot Sandstone, a conspicuous multistoried sheet sandstone that consists of laterally amalgamated, vertically stacked low to high sinuosity channels. Floodplain sediments are only represented by shale rip-up clasts in channel lags. Laterally persistent ferricrete horizons, containing plant impressions, are time significant surfaces withinmore » the Teapot and indicate a rhythmic pattern of sedimentation, nondeposition, and pedogenesis. The base of the Teapot unconformably overlies weathered lower shoreface sandstone along the east flank of the Bighorn basin and thus represents a regional sequence boundary.« less

Sedimentation-calcrete cycles in the Mesozoic Red formations from the central High atlas (Telouet area), Morocco

In the Telouet-Ighrem area (southern side of the central High Atlas, Morocco) the Mesozoic “Couches Rouges” or red formations are composed of conglomerates, sandstones and siltstones organized into upward-fining sequences locally capped by swamp deposits. Epigenetic calcretes developed within these formations, subsequent to indeindependent of the initial sedimentation. Several types occur, controlled mainly by the permeability and structures of the original sediment: nodules, prismatic pillars, small columns, etc. These carbonate bodies appear in field sections as metric to plurimetric, commonly overhanging, lenses or beds. Siliceous micro-features are locally associated with the carbonate accumulations. These calcretes are the result of polyphase epigenetic processes among which surface weathering in a semi-arid context is predominant. During the wet season, carbonates in the upper part of the profile dissolve and migrate downwards. By the end of the wet season and the beginning of the dry season solute concentration occurs which induces hydrolysis of quartz and silicates (including clay minerals). During the dry season palygorskite develops and carbonates are precipitated. These pedogenic processes may have succeeded localized and ephemeral palustrine processes related to observed lateral water circulation or to an exposed water-table, the latter being particularly sensitive to exceptional events (e.g. heavy rainfall) in this type of climate. The accumulation of detrital deposits followed by the epigenetic wrocesses which occur according to the sometimes partial sequence of calcitization-palygorskitization-dolomitization-silicification, characterize “sedimentation-calcretization cycles”. The thickness of the carbonate bodies depends on the stability of the environment, which is probably controlled by climate and tectonics (Michard, 1976; Jenny et al., 1981; Jacobshagen, 1988). A new insight is thus provided on the Mesozoic palaeogeography of the central High Atlas.

The geology of selected peat-forming environments in temperate and tropical latitudes

The geology of selected peat-forming environments in temperate and tropical latitudes

Quaternary pollen analysis in the arid zone of Australia: Dalhousie Springs, Central Australia

Sediment sequences from sites in Central Australia, one of the more arid parts of the world, have only recently been investigated for their Quaternary fossil pollen content and results from such research have not previously been published. This paper reports preliminary results from one of the sites being currently investigated, Dalhousie Springs, a major group of Great Artesian Basin mound springs in northern South Australia, where organic swamp deposits are associated with artesian spring outflows. These sediments are extremely unusual in this arid environment and offer both a unique opportunity to examine aspects of the late Quaternary vegetational history in the arid zone of Australia and a novel approach to arid region Quaternary environment studies. Results from this site primarily reflect the local swamp history of the last 2000 years or so; inferred vegetation changes largely represent changes in water flow from the spring feeding this swamp and the consequential growth of the swamp. These results demonstrate the potential for using spring-related sediments in the application of pollen analysis in the study of arid land palaeoenvironments.

Palynology of Pohehe Swamp, northwest Wairarapa, New Zealand: a study of climatic and vegetation changes during the last 41,000 years

In Pohehe Swamp, adjacent to the eastern edge of the Northern Tararua Range, sediments up to 4.5 m thick yielded abundant palynomorphs. They were present through most of the sequence but fewer at depths between 1.2 m and 1.6 m. Dating controls were provided by Aokautere Ash at 22.6 ±.0.23 ka bp, 1.9 m below the surface; a radiocarbon date of ≥. 36 ka bp on wood, 3.7 m below the surface; and the superposition of the swamp deposits on Eketahuna Gravels (c. 70 ka bp). The palynological sequence indicates four distinct floras in chronological sequence. (1) Between 41 ka and 24 ka bp, a regional Nothofagus menziesii (silver beech) forest with grassland in exposed areas, an estimated timber line at c. 500 m and a cool climate; (2) between 24 ka and 13 ka bp, grassland with shrubs in a cold climate; (3) between 13 ka and 10 ka bp a podocarp forest with a variable distribution of grass and shrubs during fairly rapid warming of climate; (4) Between 10 ka and 5 ka bp a well developed podocarp broadleaf forest growi...

Geochemical Indicators of Subsidence in Sediment, Terrebonne Coastal Plain, Louisiana: ABSTRACT

ABSTRACT Sediments comprising the Terrebone Coastal Plain consist primarily of clays, silts, and peats that fill the depressions between alluvial ridges created by former Mississippi River courses. These sediments are subsiding at variable rates. Depositional history, sedimentation rates, and environment of deposition affect both the types and abundances of diagenetic products found in deltaic sediments. Early diagenesis influences the geotechnical properties of these coastal plain deposits and their local subsidence rates. Diagenetic mineralogy and elemental geochemistry therefore offer clues to understanding some of the variability associated with subsidence in the lower deltaic plain. To determine relationships between geochemical features and subsidence rates samples were collected from undisturbed 12.5 cm diameter borings where subsidence rates had been determined by radiocarbon dating. Diagenetic features in these samples were identified using X-ray radiography and later examined more closely using light and electron microscopy, X-ray diffraction, and various chemical methods of testing. Results show that diagenetic minerals consist of carbonates (siderite, calcite, dolomite, and rhodochrosite), iron/manganese oxides, iron sulfides, and vivianite. Of these, siderite and calcite are most abundant. Siderite occurs as diffuse, lenticular nodules in fine-grained sediments (Figure 1, A), while calcite occurs as irregular, equidimensional nodules in a variety of sediments (Figure 1, B) and as inclusions in siderite nodules. Iron/manganese oxides occur as small nodules in well-drained swamp and levee deposit (Figure 1, C), while iron sulfides (primarily pyrite) occur as individual crystals and as framboidal agreegates and mats lining rootlets and filling cells (Figure 1, D and E). Vivianite is found as small, ring-shaped inclusions in poorly-drained swamp deposits (Figure 1, F). In general, nodular siderite and other carbonates as well as pyrite are higher in the fine-grained swamp and lacustrine clays of the upper/middle deltaic plain environments where sediment compaction and subsidence rates are considerably lower than rapidly deposited lower delta and marine deposits. Prodelta clays, for example, contain less varieties and lower abundances of diagenetic inclusions than their freshwater fine-grained counterparts. Oxidized sediments of well-drained swamp and natural levee deposits which contain goethite, iron oxides, manganese oxides, and carbonates are stabilized early in their depositional history and therefore do not lend themselves to rapid volume reduction associated with dewatering and compaction. Elemental concentrations can also be interpreted to reflect relative diagenetic activity in the sediments. These preliminary results indicate that close examination of diagenetic mineralogical and geochemical features can provide valuable information concerning the subsidence history of delta plain areas. End_Page 1-------------------------- FIGURE 1. [Grey Scale] A. Radiograph showing lenses of siderite. Diameter of the core = 12.5 cm. B. Radiograph showing calcite nodules. Diameter of the core = 12.5 cm. C. Radiograph showing iron oxide nodules. Diameter of the core = 12.5 cm. D. Radiograph showing pyrite filling rootlets (some siderite is also present as diffuse bands and nodules throughout the core). Diameter of the core = 12.5 cm. E. Transmission-reflection light micrograph showing pyrite filling cell. Length of bar = 10 µm. F. Radiograph showing vivianite in root channel. Diameter of the core = 12.5 cm. End_of_Record - Last_Page 2---------

Preservation of Daily Tidal Cycles and Stacked Alluvial Swamp Deposits: Depositional Response to Early Compaction of Buried Peat Bodies: ABSTRACT

The character of the clastic depositional environments represented in the lower Mary Lee coal zone of the Pennsylvanian Pottsville Formation in the Warrior basin Alabama (tidally influenced mud flats and alluvial swamps) was controlled by the compaction of buried peat bodies. The lowest mineable coal in the Mary Lee coal zone, the Jagger, is overlain by laminated shale and sandstone exhibiting pronounced cycle bedding. This bedding records daily tidal cyclicity in the form of sand-mud couplets. These correspond to flood-current deposition of the coarser fraction followed by fallout of the finer grained fraction during ensuing slack-water periods. These couplets are cyclically bundled-sandier bundles corresponding to spring tides and muddier bundles to neap tides (lamination counts suggest a 24-30-day cycle). The clastic sequence above the overlying Blue Creek coal is characterized by a series of stacked alluvial swamp horizons. These can be identified by autochthonous fossil plants and pedological features indicative of gleyed paleosols. Catastrophic flooding buried and preserved these horizons. The rapid, early compaction of the buried Jagger and Blue Creek peat bodies created accommodation space that allowed both the preservation of tidalites in the Jagger coal to Blue Creek coal interval and the stacking of alluvial swamp paleosols abovemore » the Blue Creek seam. Carboniferous peats were comprised of highly compressible plant parts and hence, were sensitive to sediment loading. Once the peat bodies had compressed to a certain extent, stability of the overlying sediment surface created conditions amenable to resumption of peat accumulation.« less

Phytogeographic patterns and continental configurations during the Permian Period

Abstract The climatic influences on vegetation in the present world can serve as an excellent model for the Permian, there being approximately the same level of floral differentiation and the same relatively cold polar regions. Accordingly, a system of present day climatically defined biomes, developed by Walter, is adapted herein for palaeophytogeographic purposes. There are ten biomes altogether which range from the tropical 'everwet' (biome 1) to the polar 'glacial' (biome 10). Biome 1 is represented by the tropical rainforests of the Cathaysian province sensu stricto which was populated by the arborescent lycopods and sphenophytes, and the Gigantopterids which are interpreted as lianas (vines). This is flanked by the lower diversity 'summerwet' biome 2, the Atlantic Province, a zone which today is characterized by savanna vegetation, and in the Permian was represented by the pteridosperm Callipteris and the primitive conifers. Biome 3 was effectively 'abiotic' and is expressed geologically by evaporite belts. The 'winterwet' or Mediterranean climate of today (biome 4) was not well developed in the Permian, or perhaps just not well preserved, but I attribute some low diversity floras of Kazakhstan to this biome. Biome 5, the 'warm temperate' biome is well developed in both hemispheres, and, like biome 1, is characterized by high diversity floras and abundant swamp deposits. Not surprisingly, the biome 5 floras have been mistaken for biome 1 with which they are transitional in the modern world and with which they share similar climatic conditions. In the Permian Angaran Realm, the Pechora Province represents this biome, while the Austroafroamerican Province is the Gondwanan equivalent. Often, biome 5 floras have been simply termed 'mixed'. Proceeding poleward across the 'hard frost line', the cool temperate floras of biome 6 were populated by diverse herbaceous sphenophytes and deciduous trees (the cordaitids of Angara and the similarly diverse glossopterids of Gondwana). Areas in the temperate zone that were remote from moisture sources are assigned to biome 7 and are only known in the southern hemisphere by some aeolian deposits in Argentina. The 'cold temperate' biome 8 is a low diversity equivalent of biome 6, and has been given the name Gangamopteris Flora in the southern hemisphere. The 'tundra' environment, biome 9, and the truly glacial deposits, biome 10, are known only from the southern hemisphere.

CECROPSIS LUCULENTUM GEN. ET SP. NOV.: EVIDENCE FOR HETEROSPOROUS PROGYMNOSPERMS IN THE UPPER PENNSYLVANIAN OF NORTH AMERICA

An anatomically preserved specimen of a woody, heterosporous pteridophyte has been discovered in Upper Pennsylvanian peat‐forming swamp deposits of eastern Ohio. The fossil is described as Cecropsis luculentum gen. et sp. nov. It consists of a protostelic shoot tip with helically‐arranged vegetative leaves, sporophylls and adaxial eusporangia. The stele is marginally mesarch, with five cauline protoxylem strands that produce leaf‐trace protoxylem in a helix that approaches 2/5. Dense wood surrounds the protostele. Secondary tracheids have reticulate bordered pitting on all walls. Rays are uniseriate and 1–2 cells high. Vegetative leaves are 2–3 cm long and are pinnately‐dichotomously branched into terete lobes. Sporophylls are somewhat more extensively webbed, with clusters of sporangia located above vascularized receptacles. Sporangia are sessile and globose, with a terminal dehiscence slit. Megasporangia and microsporangia appear to be intermixed. Most are empty, but a small number contain either fragments of bean‐shaped microspores with asymmetrical trilete sutures, or a single radial and trilete megaspore. The presence of gymnospermous protoxylem architecture and wood in this heterosporous pteridophyte place it within the circumscription of the Progymnospermopsida. However, features of the stele, leaves, sporangia, and extreme heterospory indicate that it does not conform to a presently recognized order. The Pennsylvanian occurrence and unique features of Cecropsis leave open to question whether it is phylogenetically, or only phenetically related to other members of the Progymnospermopsida.

Late Quaternary vegetation history and climatic change in the eastern Orange Free State, South Africa

Sixty-nine pollen spectra from three sites with alluvial and swamp deposits and 12 spectra representing the modern vegetation in the eastern Orange Free State and Drakensberg areas, provide evidence about the Late Quaternary environmental history of Clarens. Factor analysis is used to compare pollen data between sites. Stepwise changes in the vegetation at Clarens are indicated, relating to changes in climatic variables during the Late Pleistocene and Holocene. The earliest palaeo-environmental indications recorded immediately north of Clarens are of humid grassland with strong fynbos and swampy conditions ca. 23 000 years BP, followed by progressively cooler, drier conditions ca. 22 600 to 19 000 years BP. Grass in the vegetation became more prominent between ca. 18 000 and 17 000 years BP. Shrubby grassland with some fynbos elements occurred in the Little Caledon Basin ca. 13 000 years BP, under slightly warmer conditions which were relatively moist, probably also during winters. Podocarpus forests developed in distant mountain ravines but together with fynbos elements, declined before 10 700 years BP, possibly under the influence of slightly warmer conditions and growing seasonal contrasts. The Holocene record is incomplete, starting apparently with grassland indications for warm conditions, and ending with subhumid, markedly seasonal conditions and local swamp development as found along the Little Caledon River.

886215 Use of cone penetrometer testing to investigate sand fill subsidence beneath highways : Yilmaz, R; Horsnell, M R In: Use of In Situ Tests is Geotechuical Engineering (papers to the Conference, Blacksburg, 23–25 June 1986)P1178–1188. Publ New York: ASCE, 1986 (ASCE Geotechnical Special Publication No 6)

During construction of Interstate I-10 between Baton Rouge and LaPlace, Louisiana, highly organic swamp deposits were excavated and replaced with hydraulically pumped river sand. The main objective of the study reported was to evaluate the subsurface conditions and investigate the reason(s) for sand fill subsidence at cross-drain locations, utilizing the electric cone penetration test during the site investigation. Numerous conclusions were drawn from the study with the major factor for subsidence being loosely compacted sand at the cross-drain locations. It was demonstrated that the electric cone penetration test was a valuable quality control tool and should be utilized both immediately after construction, as well as in checking time related effects in subsidence and compaction studies.

Early Diagenesis of Interdistributary Basin Sediments--Atchafalaya Basin, Mississippi Delta Complex: ABSTRACT

Terrigenous clays, silts, and organic sediments are filling the topographic depressions between alluvial ridges that partition the Mississippi River's deltaic plain. As compared to many other deltaic deposits, these sediments are accumulating slowly and are therefore impacted early in their depositional history by organisms and diagenesis. Early emplacement of numerous diagenetic products suggests the possibility that minerals that survive later diagenesis may be used as indicators of early depositional conditions, a useful approach for studying ancient sequences. To better understand these relationships, samples from six undisturbed 5-in. (12.7-cm) diameter borings (to 152 ft (96 m) long) have been examined using x-ray radiography, light and electron microscopy, and x-ray diffraction analysis. The maximum C/sub 14/ age of these sediments is 8200 y.B.P. Early diagenetic minerals identified using these methods include iron oxides, pyrite, siderite, a variety of other carbonates, vivianite, and gypsum. Iron oxides occur primarily in well-drained swamp and levee deposits, associated with permeable pathways in the sediments. Pyrite is found throughout most borings and is associated with organic-rich zones and organic fragments. It occurs as individual octahedral crystals, framboidal aggregates, and mats. Crystals commonly line rootlets and fill cells. Siderite occurs primarily in lake sediments and lake deltas asmore » diffuse lenticular masses. The shapes of siderite masses appear to be controlled by bedding characteristics. SEM examination indicates that manganese is present and that there are numerous inclusions of CaCO/sub 3/ and quartz. The CaCO/sub 3/ contains various amounts of magnesium, and diffractograms indicate dolomite in some places. Vivianite is common as radial aggregates in organic-rich, poorly drained swamp deposits. Finally, gypsum occurs as radial aggregates associated with very organic-rich zones.« less

A Depositional Model of the Antelope Coal Field, Powder River Basin, Wyoming

ABSTRACT The Anderson and Canyon coal seams are the main seams at the Antelope coal field in the south-central Powder River Basin. Each seam splits into multiple and thinner coal seams to the southwest in the study area. The strata underlying the Canyon coal seam suggest that the area of the Antelope coal field was a poorly drained swamp that developed into a well-drained swamp with minor small channels. The area further changed to a poorly drained swamp which initiated peat accumulation in the Canyon coal swamp. The lithologies, sedimentary structures, and isopach maps of the Canyon seam partings indicate that crevasse splaying, lacustrine conditions, and small crevasse-channel development produced the observed splits in the Canyon coal seam. Distal overbank deposits occur at the top of the C nyon seam and at the base of the Anderson seam; well-drained swamp deposits and crevasse splay, lake, lacustrine delta, and small channel-fill deposits occur between the coal seams. The Anderson coal seam represents another development of a poorly drained swamp where peat accumulation was significant. The rocks overlying the Anderson seam represent a combination of the environments mentioned above, with deposits from lakes and well-drained swamp environments dominating. The coal-beating sediments were deposited in paludal and tributary subsystems along the northern margin of the Wright delta. Deposition of the Canyon and Anderson coal seams and associated parting lithologies may have occurred when a river system or parts of that system underwent anastomosis. The coal swamp in which the Anderson seam was deposited was destroyed when the anastomosed character of the river system ended or the anastomosed river system shifted westward. This may reflect a relative change in the rate of subsidence within the basin.

Seismic Facies Analysis of Delta-Plain Coals from Camrose, Alberta, and Lacustrine Coals from Pictou Coalfield, Nova Scotia

Facies models of two coalfields in Canada have been developed through seismic facies analysis. Fluvial-deltaic Upper Cretaceous coals near Camrose, Alberta, are characterized by hummocky, subparallel, high-amplitude reflections that are laterally continuous over distances of several kilometers. Deposition in an extensive delta-plain swamp is inferred. Coals of Pennsylvanian age in the Pictou coalfield, Nova Scotia, occur in two distinct seismic facies. Parallel to subparallel, relatively continuous reflections are interpreted to define a basinal facies comprising thick coals and lacustrine sediments. Basinal margin facies contain a greater abundance of variable clastic sediments and are recognized by discontinuous, subparallel to chaotic reflections. Further improvements n stratigraphic analysis will require synthetic seismograms to analyze individual reflections in terms of the thickness and separation of seams, and to enable interseam multiples to be recognized.

La formation des Calcaires et Lignites de Sigonce (Oligocène moyen, bassin de Forcalquier, Alpes-de-Haute-Provence): Datation à l'aide des mammifères; reconstitution des milieux de dépots

A section in the “Calcaires et Lignites de Sigonce” formation is described. Sedimentological study shows a swamp deposit. The collected Rodents and Insectivores teeth indicate a Middle Oligocene age (Antoingt level). Consequently, the Sigonce lignite and the basis of the Viens (Apt basin) and Bois d'Asson (Manosque trench) formations are correlated.

Holocene rate of slip and tentative recurrence interval for large earthquakes on the San Andreas fault, Cajon Pass, southern California

Abstract Detailed mapping of the San Andreas fault zone where it crosses Cajon Creek, southern California, has revealed a number of late Quaternary deposits and geomorphological features offset by the fault. Radiocarbon dates from alluvial and swamp deposits provide a detailed chronology with which to characterize the activity of the San Andreas fault. Four independent determinations of the slip rate on the San Andreas fault yield an average rate of 24.5 ± 3.5 mm/yr for the past 14,400 years. The similarity of the four values, which span different intervals of time from 5900 to 14,400 years ago, suggest that the slip rate has been constant during this period. The slip rate confirms that the San Andreas fault is accumulating slip faster than any other fault in the plate boundary, throughout California. Also, the sum of the slip rates on the San Andreas (24.5 mm/yr) and the San Jacinto (10 mm/yr) faults south of their junction is the same as the San Andreas north of their junction (35 mm/yr). An excavation provided evidence for at least two and up to four earthquakes that caused rupture on the fault between 1290 and 1805 A.D., and tentative evidence for six earthquakes in about the last 1000 years. Both lines of evidence imply an average recurrence interval for large earthquakes of about 1 to 2 centuries. Combined with the historic record, this investigation indicates that the last major earthquake at Cajon Creek was probably at the beginning or middle of the 18th century. While the record at Cajon Creek may suggest that the next major earthquake on the San Andreas fault is overdue, the data can be interpreted to indicate that the recurrence interval for earthquakes on the San Andreas south of the 1857 rupture is 3 to 4 centuries and that the anticipated event should not be expected until the next century.

Stratigraphy and Palynology of the Upper Lewis Shale, Picture Cliffs Sandstone, and the Lower Fruitland Formation (Upper Cretaceous) near Durango, Colorado

The stratigraphy and palynology of Upper Cretaceous units (upper Lewis Shale, Pictured Cliffs Sandstone, and lower Fruitland Formation) were investigated near Durango, Colorado, on the northern rim of the San Juan basin. This investigation: (1) confirms an interdeltaic depositional setting for these formations in the study area, (2) provides new biostratigraphic data for the Upper Cretaceous rocks on the northern rim of the San Juan basin, and (3) indicates a mostly freshwater origin for the Carbonero coal bed at the base of the Fruitland Formation. The upper Lewis Shale was deposited in lower offshore to upper offshore marine environments. The Pictured Cliffs Sandstone records a major regression on the western margin of the Late Cretaceous sea. The northeastward regression was not one steady event but a series of superimposed transgressive pulses. The depositional environments identified in the Pictured Cliffs Sandstone are upper offshore, shoreface, foreshore, and backshore. The lower part of the Fruitland Formation represents a coastal swamp deposit which developed just landward of the Pictured Cliffs Sandstones. The Carbonero coal bed lies at the base of the Fruitland Formation. At one location, a small tidal channel developed and inundated the local swamp environment. Ten Late Cretaceous palynomorph guide fossils were identified in the Lewis Shale, Pictured Cliffs Sandstone, and Fruitland Formation. The palynomorphs of the Lewis Shale and Pictured Cliffs Sandstone are a marine assemblage. The Fruitland Formation contains a terrestrial assemblage of pollen and spores. Trudopollis meekeri, Kuylisporites scutatus, and cf. Myrtaceoipollenites are a late Campanian Stage palynomorph assemblage in the Fruitland Formation. These findings refute the recent interpretation of a late Maestrichtian age for the Fruitland Formation. The palynological results obtained in this research can be used for correlation and mapping of interbasin and intrabasin sedimentary facies.

Lower Cantabrian basin margin deposits in NE Leon, Spain—a model for valley‐fill sedimentation in a tectonically active, humid climatic setting

ABSTRACTBasal Stephanian deposits of early Cantabrian age infill a deeply incised fossil topography at the western edge of the post‐Leonian basin of NE Leon. Seven low sinuosity palaeovalleys, trending NNW–SSE range in depth of incision from 25 to 450 m. The fill is composed of: (i) Red bed succession: a proximal alluvial valley‐fill association of debris flow and stream deposits in which seven mesosequences and two fining upwards megasequences are recognized on the basis of maximum clast sizes. (ii) Grey bed succession: two megasequences are distinguished. The lower megasequence comprises distal alluvial valley‐fill deposits (sheet sandstone, lacustrine, swamp deposits). The upper megasequence comprises a mid‐fan association of debris flow and interlobe/floodplain deposits.The palaeovalleys are considered in the context of previously described palaeovalleys and fill. These are categorized according to the degree of tectonic control and climatic setting.The lower Cantabrian examples may serve as a model for valley‐fill sedimentation in a tectonically active area and a humid climatic setting.

Stratigraphy and Economic Potential of Castle Gate Area, Carbon County, Utah: ABSTRACT

Unexcelled exposures of the coal-bearing Blackhawk Formation near Castle Gate, Utah, provide a cross section of sediments deposited by wave-dominated deltas along the western shoreline of the Cretaceous Interior seaway. Four sandstone tongues resulted from deltaic sedimentation, each overlain by thick coal. A clear genetic relationship exists between the occurrence of coal and geometries of paleoshorelines and fluvial channels. Coals are thickest where underlain by thin shoreface sandstones, and they pinch out abruptly against beach-ridge sandstones responsible for swamp proliferation. Fluvial channels subsequently cut wide swaths in swamp deposits normal to shoreline trends. Commonly, thick coals of different seams occur together, as the compaction of vegetation controll d subsequent swamp accumulation. Excellent exposures and considerable subsurface data provide the details necessary to construct a predictive exploration model useful in the Cretaceous coals of the central Rockies. Cretaceous deltaic deposits also create hydrocarbon potential, as three facies associated with Blackhawk deposition produce ideal stratigraphic relationships for hydrocarbon accumulation. Porous delta-front sandstones interfinger with the underlying organic-rich marine shale of the Mancos formation. Shale and siltstone of the flood plain then cap the sandstone. Hydrocarbons derived from the marine shale or from associated coal may accumulate in porous sands of stream channels or in mouth-bar or beach-ridge deposits of the delta front. A clear understanding of deltaic sedimenta ion, provided by analysis of the Blackhawk model, could aid in predicting the occurrences of similar subsurface sandstones. End_of_Article - Last_Page 947------------

Paleogeographic controls of coal accumulation, Cretaceous Blackhawk Formation and Star Point Sandstone, Wasatch Plateau, Utah

Analysis of sequences, associations, and relationships of facies in the Upper Cretaceous Blackhawk Formation and Star Point Sandstone in the Wasatch Plateau, Utah, leads to inferences regarding the paleogeographic controls affecting the accumulation of coals in delta–barrier-island complexes. Progradation, lateral shifting, and abandonment of these complexes created four major landward-thinning tongues of the upper sandstone bed of the Star Point Sandstone that extend into the lowermost Blackhawk Formation. Each tongue of the Star Point Sandstone trends northwest to southeast, subparallel to the general orientation of the Late Cretaceous paleoshoreline, and represents accretion-ridge, distributary-channel, and mouth-bar sandstones. The accretion-ridge or barrier-island sandstones grade landward into coastwise lagoonal and back-barrier swamp deposits, which, in turn, merge with bayhead deposits of short-headed streams. These deposits grade laterally into delta-plain deposits that consist of major distributary channels which crosscut the coastwise lagoons. Two coal populations were formed in this paleogeographic setting: delta-plain and back-barrier coals. Delta-plain coals formed as thin to thick, discontinuous bodies. Back-barrier coals are thicker and more laterally continuous. They parallel depositional strike and accumulated in swamps on surfaces of infilled lagoons. Here, the swamps were sites of accumulation of thick coals and were influenced by abandonment of associated deltaic barrier-island complexes. Successive offlap events resulted in accumulation of the Hiawatha coal, not as a single continuous bed, but as a series of discontinuous, related coal bodies.