Lower Delta Plain Research Articles

SOURCE POTENTIAL OF UPPER TRIASSIC FLUVIO-DELTAIC SYSTEMS OF THE EXMOUTH PLATEAU

The fluvio-deltaic rocks of the Upper Triassic Mungaroo Formation of the Exmouth Plateau contain abundant organic material in the form of both coal seams and dispersed fragments. Several thousand metres of these sediments lie within the oil generation window (0.5 to 1.3 per cent R̅O max vitrinite), but they have commonly not been considered as source rocks for oil because the organic matter is of terrestrial origin. Increasing acceptance of plant material as a source for oil warrants an assessment of the oil generating potential of the Mungaroo Formation.The maceral composition of organic matter is dependent on the depositional environment. The large-scale uniformity of environments (mostly lower delta plain) in the Mungaroo Formation leads to a similarity in the organic matter, with an approximate composition of 90 per cent vitrinite in the coals and 50 per cent vitrinite, 20 per cent exinite and 30 per cent inertinite for the dispersed organic matter (DOM). The exception to this is organic material from the alluvial plain environment, where the coal has a vitrinite content of 60 per cent and the dispersed organic matter has a composition of 20 per cent vitrinite, 20 per cent exinite and 60 per cent inertinite.A quantitative assessment of the oil-generating potential of the organic matter based on maceral composition, vitrinite reflectance and volume of coal and dispersed organic matter was made for a range of time-rock units. On this basis, the Carnian-Ladinian and Carnian sequences have the best source potentials.On the basis of vitrinite reflectance measurements, it appears that the Mungaroo Formation has been generating oil since late in the Triassic or early in the Jurassic, through to the Tertiary. Lack of suitable seals during the early generative phase may have permitted some oil to escape. However, significant oil generation has occurred subsequent to the deposition of the younger Mesozoic sequences, when trapping and sealing were more effective.

Early Campanian Coastal Progradational Systems and Their Coal-Forming Environments, Wyoming to New Mexico: ABSTRACT

Ammonite zones (Baculites obtusus-Scaphites hippocrepis) in the marine facies associated with the Mesaverde Formation in the Bighorn basin, Wyoming, Star Point Sandstone and Blackhawk Formation in the Wasatch Plateau, Utah, and the Point Lookout Sandstone, Menefee Formation, and Crevasse Canyon Formation in the Gallup coalfield, New Mexico, indicate that these formations were deposited during early Campanian time (80-84 Ma). The coal-forming environments of these early Campanian formations were located landward of wave-reworked coastal sand complexes of progradational systems along the western margin of the Cretaceous seaway from Wyoming to New Mexico. The Mesaverde coals accumulated in swamps of the lower delta plain and coeval interdeltaic strandplain environments. The Star Point-Blackhawk coals accumulated in swamps of the lower delta plains of laterally shifting, prograding deltas and associated barrier ridge plains. The Point Lookout, Menefee, and Crevasse Canyon coals formed in swamps of the lower delta plain and infilled lagoons behind barrier islands. Although the common coal-forming environments of these progradational systems are back barrier and delta plain, the former setting was the more conducive for accumulation of thick, laterally extensive coals. Economic coal deposits formed in swamps built on abandoned back-barrier platforms that were free of detrital influx and marine influence. Delta-plain coals tend to be lenticular and laterally discontinuous and thus uneconomic. The early Campanian coal-forming coastal-plain environments are analogous to modern peat-forming environments along the coast of Belize, Central America. Deltaic sediments deposited along the Belize coast by short-headed streams are reworked by waves into coastal barrier systems. End_of_Article - Last_Page 855------------

The taphonomy of land plants in the orinoco delta: A model for the incorporation of plant parts in clastic sediments of late carboniferous age of euramerica

The Orinoco Delta in eastern Venezuela is an excellent modern analog for Upper Carboniferous depositional environments in terms of climate, physiography, sedimentology, and the presence of morphological analogs for Upper Carboniferous plants. Processes resulting in the incorporation of plant parts in sediment were studied to assess the effects of transport and deposition on plant parts preserved as compressions in clastic strata of Late Carboniferous age. Sub-environments of the delta (e.g. levee, point bar, clastic swamp, and distributary channel) were cored and the contained plant matter described in terms of its distribution in sediment, preservational state, and relationship to living vegetation. Several experiments were performed to assess the role of tidal and fluvial transport of plants parts. We reached the following conclusions from the study: (1) Aerial parts of plants are buried relatively close to their site of growth but rarely in the actual soils in which the plants lived. (2) Plant parts are preferentially preserved in areas with slightly higher rates of sedimentation. (3) Natural levees are dry for half a year and any aerial parts of plants buried in levee deposits during floodstage oxidize during that time. Bioturbation by roots also contributes to the destruction of plant matter. Thus, levee sediments are virtually devoid of aerial parts of plants. (4) Tidal processes are as significant as annual flooding in forming plant-bearing deposits in the lower delta plain. (5) No storm-generated deposits are known in the Orinoco Delta, indicating that non-storm deposition is important for the generation of clastic deposits which contain plant parts.

Stratigraphic Framework and Petroleum Potential of Northeastern Baltimore Canyon Trough, Mid-Atlantic Outer Continental Shelf

Geologic data from 29 wells in the Baltimore Canyon Trough were released to the public as of 1982, and provide sufficient information for establishing Upper Jurassic through Cenozoic rock-stratigraphic units. Most of the units are lithologically similar to formations on the Scotian Shelf and are, therefore, considered in this study to be the Scotian Shelf homotaxial equivalents. The oldest rocks penetrated by exploratory wells in the Baltimore Canyon Trough are of Late Jurassic age and are correlative to the Scotian Shelf Mohawk, Mic Mac, and Abenaki Formations. The Mohawk(?) sandstone and Mic Mac shale equivalents in the Baltimore Canyon Trough represent lower delta plain to predominantly prodelta environments, and the Abenaki-equivalent limestone represents a shelf-margin carbonate buildup. Delta progradation continued during the Early Cretaceous, and lower delta-plain and delta-front sand and shale, equivalent to the Scotian Shelf Missisauga Formation, were deposited. A destructional phase of the delta is represented by the Naskapi equivalent, a calcareous shale. Inundation by the sea was incomplete, however, and channel and distributary-mouth-bar sands (Logan Canyon equivalent) were deposited. A final marine transgression began during the Late Cretaceous and resulted in the deposition of mudstone, which is considered equivalent to the Sco ian Shelf Dawson Canyon Formation. Marine conditions prevailed through much of the remainder of the Cretaceous and Cenozoic in both the Scotian Shelf and Baltimore Canyon Trough areas. Lithologic similarities between Cenozoic units of the Scotian Shelf and Baltimore Canyon Trough are less significant. Although both basins exhibit an upward increase in sand content, the Scotian Shelf Cenozoic strata are more sandy than those in the Baltimore Canyon Trough. In ascending order, the Baltimore Canyon Trough Cenozoic section consists of the uppermost Dawson Canyon equivalent, a chalk unit, a mudstone unit, an unconsolidated sand unit, and an uppermost clay unit. Stratigraphic traps may be present in the Baltimore Canyon Trough Upper Jurassic and Lower Cretaceous deltaic sandstones and shelf-margin carbonates. The deltaic units contain channel and distributary-mouth-bar sandstones, which may be potential reservoirs. Seals may be formed by lateral and vertical contacts against the prodelta, interdistributary bay, and marine shales. The Abenaki stratigraphic-reef trend provides another potential target. Source rocks, reservoir rocks, and traps may be associated with the trend, but its potential can only be defined by future drilling.

DEFOSITIONAL FRAMEWORK AND DIAGENESIS OF THE LATE PERMIAN GAS RESERVOIRS OF THE BONAPARTE BASIN

Late Permian sandstones form the reservoir of the Tern and Petrel gas fields in the offshore Bonaparte Basin. The producing reservoirs of the Petrel field were deposited in various environments associated with a major northwesterly trending deltaic system. The producing sands in the Tern field were deposited in the shoreface environment of a barrier-bar system.The reservoir quality of the sands is controlled by the diagenesis, which is facies dependent. In the Petrel field, sandstones deposited in the upper delta plain and along the shoreline are clean, medium-to coarse-grained and highly quartzose but have very low porosity and permeability due to extensive quartz diagenesis. However, sands deposited in delta front and lower delta plain environments are medium to fine grained, argillaceous and have fair to good reservoir potential. In these sands, the dispersed clays formed coats and rims on quartz grains during early diagenesis and inhibited quartz overgrowth. In the Tern field, sands of the upper shoreface have poor reservoir quality due to early calcite cementation. However, finer-grained sandstones of the lower shoreface facies have good reservoir quality. The porosity in these sands is mainly primary and preserved due to low carbonate and high clay content. The processes of quartz and calcite cementation which drastically reduced the reservoir quality of the coarse-grained sands occurred early and were influenced by the texture of the sands and probably also by the chemical character of the formation waters.

Paleocene Lignite Deposits of Southwest Alabama: ABSTRACT

In southwest Alabama, lignite having economic potential occurs in the Oak Hill Member of the Naheola Formation. This middle Paleocene lignite generally consists of a single bed of 1-14 ft (0.5-4 m) in thickness and is the most extensive lignite in the southwest Alabama region. The Oak Hill lignite deposit accumulated in lower delta plain coastal marshes in interchannel areas behind a barrier system. The source area for the deltaic sediments was probably to the west and/or northwest of Choctaw County, Alabama. The lignite occurs in a clay-dominated sequence. Oak Hill interdistributary bay ripple-laminated clays are interbedded with ripple-laminated, crevasse splay sands generally less than 15 ft (5 m) thick. The glauconitic sands of the overlying Coal Bluff Marl Member of he Naheola Formation represent times of marine encroachment into the interchannel basin area. Lignite having subeconomic value at present occurs in the upper part of the Tuscahoma Sand. This upper Paleocene lignite is irregular in its outcrop pattern and apparently is not represented over extensive areas. It is locally persistent with one or more beds less than 3 ft (1 m) thick. The Tuscahoma may contain up to 6 lignite seams that may exceed a total thickness of 5 ft (1.5 m). These lignite beds were deposited in lower delta-plain coastal marshes adjacent to high constructive deltaic bar finger sands. Tuscahoma marsh clays are interbedded with ripple-laminated and cross-bedded bar finger sands. The Tuscahoma Sand is overlain by the Bashi Marl Member of the Hatchetigbee Formation. The Bashi contains a diverse lower Eocene marine fossil assemblage. End_of_Article - Last_Page 502------------

Sedimentology of an ordovician fan delta complex, Western Libya

The Ordovician Haouaz Formation in the western-central Gargaf Arch of western Libya provides a well-exposed example of an ancient fan delta system. The Haouaz sequence consists of delta front deposits overlain by subaqueous distributary channels with intervening distributary mouth shoals and swash bars. This delta front complex is abruptly and erosively overlain by braided fluvial and distributary channels of the lower deltaic plain. Lower deltaic plain deposits may show reworking by wave swash processes in the upper portion, indicating marine destructive phases of delta building. This process is attributed to diminished or absent detrital influx allowing wave reworking of the deltaic plain margin. These reworked deposits may in turn be overlain by thin transgressive marine shelf sequences, also formed during periods of minimal detrital influx. The lower deltaic plain may also pass upward into an upper deltaic plain and alluvial plain environment.

Modern Mahakam Delta, Indonesia: Sand Distribution and Geometry in Mixed Tide and Fluvial Delta: ABSTRACT

A core study was made of a mixed, tide and fluvial, low-wave delta formed in the humid tropics. Little subsurface data were previously available for this type of delta, in which morphology and sediment distribution reflect both fluvial and tidal characteristics. The delta plain is a tidal marsh, with bioturbated organic clays, incised by separate networks of distributary and tidal channels. In contrast to the mud-filled meandering tidal channels, distributaries are linear and filled with sand accumulating as lateral accretion bars. Distributaries form narrow ribbons of channel-fill sands of variable thickness (5 to 11 m), eroded or superimposed onto underlying delta front clays and sands. Facies and vertical sequences are fluvial, erosive based and fining-up in the upper delta plain, and tidal and coarsening-up in the lower delta plain. The lack of fluvial levees and splays reflects the tidal influence in the distributaries. On the delta front, sand occurs as numerous bars, forming a spectrum of distinct types which reflect the local river-tide ratio. Major distributaries form thick (7 m) localized arcuate mouth bars, while off smaller distributaries, triangular middle ground bars occur, forming more sheet-like, thinner sand bodies. In areas of low river input, tidal ridges predominate. The bars are separated by organic clay, but lateral coalescence and stacking can locally increase sand continuity. Sequences are coarsening-up, and facies show tidal and marine characteristics. A general seaward bar thickening exists owing to the more distal position of the thicker arcuate bars; this results in a vertical bar thinning-up progradational sequence. Seaward of the delta front bars, prodelta sediments composed of massive clays form the base of a 50-m thick regressive sequence composed of multiple bar deposits, followed and incised by sandy distributary fills. Sedimentation rates range between 0.2 and 1.3 cm per year-1. End_of_Article - Last_Page 889------------

Lithostratigraphy of Shell 272-1 and 273-1 Wells: Implications as to Depositional History of Baltimore Canyon Trough, Mid-Atlantic OCS: GEOLOGIC NOTE

Upper Jurassic gray and red-brown shale, sandstone, and coal are the oldest strata penetrated by the Shell 272-1 and 273-1 wells, located approximately 66 mi (106 km) southeast of Atlantic City, New Jersey, in the northwest part of the Baltimore Canyon Trough. The Lower Cretaceous section consists of gray shale that is overlain by a sequence of thick-bedded sandstones interbedded with thin-bedded shales. The Upper Cretaceous section is dominated by slightly calcareous mudstone, but also contains a Coniacian to Campanian sandstone. The Cenozoic section is mainly mudstone and overlying unconsolidated sand. Seven major lithologic units were established and correlated to the COST B-2 and B-3 wells. The depositional environments of the Upper Jurassic rocks range from an upper delta plain facies penetrated in the two Shell wells and the B-2 well to a back-reef facies penetrated in the B-3 well. The Lower Cretaceous strata, in a vertical sequence, consist of upper delta plain, lower delta plain, interdistributary bay and/or marginal marine, and distributary-mouth-bar deposits. A Cenomanian sandstone penetrated in the B-3 well is the youngest indicator of deltaic deposition; marine strata dominate the remainder of the Upper Cretaceous and Cenozoic.

Cretaceous-Tertiary Versus Carboniferous Depositional Settings--Factors Affecting Coal Parameters: ABSTRACT

Recent studies in the coal measures of the Carboniferous, Cretaceous, and Tertiary have shown that one of the most critical determinants of seam parameters is the depositional environment of the coal and enclosing strata. Although some of the differences between the Cretaceous-Tertiary and Carboniferous coals can be explained by their different ages and depth of burial (Btu, moisture content), many of the coal parameters (thickness and continuity, sulfur and trace-element content, ash content, roof and floor conditions) can be attributed to their depositional setting and the effect of energy conditions in the depositional basin on the environments of peat accumulation. Because of the wave energy in the western Cretaceous seaway, many of the deltas have sandstones that were reworked into interchannel areas from contemporaneous distributary mouth bars. These delta-front sheet sandstones formed platforms upon which widespread coals developed. In contrast, the most laterally continuous Carboniferous coals of the Appalachians accumulated in the upper reaches of the lower delta plain. Because of the low wave energies at the delta front, the only sites for coals to amass were on the levee and splay deposits adjacent to distributary channels which were separated by large interdistributary bay sequences. Previous studies have related the sulfur content of coals to the occurrence of marine and brackish roof rock. Western coals are considered to be lower in sulfur than eastern coals. Since a significant part of the western reserves are in fluvially related Tertiary coals while most of the low-sulfur fluvial coals of the Appalachian Carboniferous have already been mined, this statement is true in generalities. However, the Cretaceous-Tertiary coals of the west that developed in marginal marine environments are as high in sulfur as the Appalachian Carboniferous coals that accumulated in similar environments. End_of_Article - Last_Page 724------------

The Alsands Project--A Challenge in Petroleum and Mining Geology: ABSTRACT

A third mining operation in the Athabasca oil sands area of northern Alberta is planned by the Alsands Project Group, a consortium of nine petroleum companies. The group is considering the use of large draglines to excavate oil sands from an open pit mine. This project contemplates separation of the bitumen and sand by a hot water process, followed by upgrading to synthetic crude oil. Production will begin in 1986; when design capacity of 140,000 b/d (22,250 m3/d) is reached, this project will supply over 10% of Canada's forecast crude producibility. The bitumen occurs in a 300 ft (90 m) sequence of unconsolidated sands and clays of the Lower Cretaceous McMurray Formation, at or near the surface. A thin veneer of Recent and Pleistocene aeolian and glacial deposits overlie the McMurray. Devonian carbonates and evaporites occur below the Cretaceous. McMurray deposition took place in a mesotidal, coastal environment. The lowermost sands are fluvial, upper delta plain, overlain by tidal channel and tidal flat sands and muds of the lower delta plain. Some marine barrier bars and beaches have been identified. The highest bitumen saturations occur in the fluvial and tidal channel sands. However, the lowermost sands are frequently water saturated under artesian conditions. The rugged paleotopography of the Devonian erosional surface has s gnificantly influenced the depositional pattern of the overlying McMurray. This relief is, in part, due to the solution of Middle Devonian salt beds, with subsequent collapse of the overlying units. This complex sequence of depositional patterns, varying lithologies, and fluid contents, combined with salt tectonics, has created the need for detailed geological and geotechnical studies to interface with mining engineering in developing a viable mine plan. End_of_Article - Last_Page 960------------

Carboniferous Lower Delta-Plain Sedimentation: ABSTRACT

Carboniferous Lower Delta-Plain Sedimentation: ABSTRACT

MEDICAL GEOGRAPHICAL STUDY ON SCHISTOSOMIASIS JAPONICA

Schistosomiasis japonica is one of the famous endemic disease found in east and southeast Asia. It has been a preventing factor against the social and economical development in the endemic areas. From the above reason this disease can be taken up as a subject of regional study from the view point of medical geography. In this paper the writers pointed out, as the first step of their study, a remarkable ubiquity of this disease, and examined some factors controlling its distribution. This disease is caused by a pathological complex of three factors-human being, intermediate host (a species of snail named Oncornclania hupcnsis nosophora) and Schistosorna japonicum. It is empirically well known that the most important factor among them is the snail. Taking into account the relation between ecological characters of the snail revealed by papers hitherto reported, and environmental conditions in each endemic area, the writers investigated the topography and soil as controlling factors delimiting the distribution of the disease. The results are as follows: I. The distribution of the disease is limited only to four or five localities in Japan. II. Landf orms of the habitats are classified into following three types, with reference to the landform classification of flood areas. They are: (1) Lower deltaic plain; lowlands formed by fine materials such as silt and clay, on which flood water stands deeply for a long period. To this type belong the main endemic areas, i.e. a greater part of the middle basin of the River Chikugo, the Kannabe basin, and basins of the River Tone and the River Arakawa. (2) Lower alluvial fan ; lands which may be flooded by heavy rain, but the water drains soon after the rain. A part of the basin of the River Chikugo and a greater part of the Kofu basin are classified as this type. (3) Upper alluvial fan; the surface slope is relatively steep and is well drained, having never experienced recent flood. This type is thought to be of an unusual case. A part of the fan formed by the River Midai in the Kofu basin is the only example. Thus, in brief, many of the land surfaces of the endemic areas are of the first type, with only a few exceptions. Or, in other word, the distribution pattern of the endemic areas of this disease can be well explained through landform division map by flood-type. However, the largest and the most marked endemic area of Japan, the Kofu basin, is classified as the second or the third type, suggesting that the flood topography alone may not explain the dis tribution of the disease. III. By observing in detail each topographic unit of the endemic areas where the snail inhabits are maldistributed, it was found that an important factor affecting such micro land conditions might be the soil. However no precise data concerning the soil of the endemic areas has been shown by the previous reports on this disease. The writers tried to breed snails in the laboratory for the purpose of clarifying soil characters which have influence upon the inhabitation of the snail. Soil samples used for the investigation were collected in many localities ; not only in the Kofu basin but in other plains and basins of Kanto and Chubu districts. In them were included artificially mixed soil materials with special texture. Experimental items were: separation of particle-size (by ASK method), measurement of soil texture, determination of humus contents (by Tiurin method) and investigation of differences caused by soil parent materials. The results obtained are as follows: (1) Remarkable differences in the numbers of newly hatched snails and in speed of growth and survival rates of youngs were found among samples from, each locality. Especially a sample collected in KOf u habitats showed to be the most suitable for the snail life.

Pennsylvanian Delta Patterns and Petroleum Occurrences in Eastern Oklahoma

Data from modern deltas have made it possible to interpret the origin of the Pennsylvanian sandstone in northeastern Oklahoma. Objective criteria from cores and outcrops used to define specific areal and vertical depositional patterns include: (1) vertical patterns of sedimentary structures, bedding, and grain size; (2) clay mineralogy and detrital clasts; (3) trace fossils; and (4) detailed analysis of textures. The historical development of a delta provides the insight for interpreting the depositional patterns observed in ancient deltaic sandstone bodies. The processes of progradation and maturation are used to develop a four-dimensional deltaic model. Six subdivisions are distinguishable: (1) lower alluvial plain; (2) upper deltaic plain; (3) lower deltaic plain; (4) subaqueous sand sheet; (5) marginal basin; and (6) marginal depositional plain. The lower alluvial plain is characterized by stream meandering, point bars, and confined channel flow. Stream gradients are reduced in the upper deltaic plain, distributary bifurcation occurs, and marsh, natural levee, and floodplain deposition is predominant. Development of the lower deltaic plain is controlled by crevassing of natural levees, tid s, and floods. The subaqueous sand sheet is characterized by shallow water currents. It is modified by progradation and commonly replaced by deltaic-plain environmental units. The marginal basin and depositional plain are produced by longshore drift and reflect a balance between subsidence, sediment supply, and wave energy. These environmental units may be modified or replaced by other deltaic elements. This model has been applied to the Bluejacket-Bartlesville sandstone of eastern Oklahoma. This stratigraphic interval was selected because of its importance as an oil reservoir, the large amount of available subsurface data, and the simplicity of the stratigraphic and structural framework. Lower and Middle Pennsylvanian sediments were deposited during an overall transgression, but the transgression is marked by extensive regressions. These are widespread sandstone sheets generally underlain and overlain by marine shales or limestones. The sandstones are distributed over thousands of square miles, but locally they are lenticular. Each regression is in response to the outbuilding of sediment under static sea level conditions. The supply of sediment is genetically related to a single river system, and deltaic patterns related to this system can be traced through Morrowan, Atokan, and Desmoinesian strata.

Deltaic Environments: ABSTRACT

Deltas are zones of interaction between fluvial and marine processes, and their deposits are transitional between terrestrial-alluvial and open-marine sediments. Initial inspection of a deltaic sedimentary wedge suggests the presence of a hopelessly complex interfingering sequence of beds; however, closer examination reveals an orderly arrangement of environmentally determined facies. In vertical sequence predictable progradational and transgressive sequences can be recognized and related to cyclic growth and deterioration of the delta system. Areal distribution of facies can be related best to three major components of the delta: the upper deltaic plain, lower deltaic plain, and subaqueous delta. Marginal deltaic basins and marginal deltaic plains also may be developed a appendices to the delta. Within this gross framework distinctive facies assemblages are recognizable, reflecting different environmental conditions in both modern and ancient deltas; i.e., the assemblage of environments and resulting lithofacies and biofacies within any major component is different in each delta and depends on such factors as climate, tectonic activity, nature and quantity of transported load, tidal influence, sea-state conditions, etc. With this working concept it is no longer essential to search for modern analogs to each deltaic sequence found in ancient rocks, but rather a flexible delta model may be developed which will accommodate all variations in nature and intensity of processes acting on the delta. Utilizing such a process-form model, examples of modern delt ic facies and ancient rock counterparts can be analyzed. End_of_Article - Last_Page 712------------