Lacustrine Turbidites Research Articles

ABSTRACT: Temporal Swing in Carboniferous Lacustrine Turbidite Paleocurrents, Crackington-Bude and Ross-Gull Island Formations, England and Ireland: Record of Continental Drift across Equator (Coriolis Switch)?

ABSTRACT: Temporal Swing in Carboniferous Lacustrine Turbidite Paleocurrents, Crackington-Bude and Ross-Gull Island Formations, England and Ireland: Record of Continental Drift across Equator (Coriolis Switch)?

Alternating marine and lacustrine sedimentation during late Quaternary in the Gulf of Corinth rift basin, central Greece

The Gulf of Corinth in central Greece has a maximum depth of about 900 m and is separated from the open sea by the Rion Strait, with a sill depth of 62 m marked by an extensive submarine terrace. During eustatic sea-level lowstands, the Gulf of Corinth was a lake. Under lacustrine conditions, stratified sediments accumulated in the deep-water basins and turbid underflows from rivers eroded the basin slopes. As the sea level rose, marine waters flooded the Gulf and deltas prograded across the shelves. In shallow-water areas, two key reflectors termed Z and X are terrace surfaces, commonly erosional, which mark the base of the overlying deltaic sequences. In deep-water basins, Z and X mark the top of the acoustically stratified sediments interpreted as lacustrine turbidites; reflectors Y and W mark the base of these stratified intervals and overlie acoustically transparent sections similar to the Holocene section. The last lacustrine conditions in the Gulf (Z to Y) were during isotopic stage 2 and terminated about 12 000 yr ago. Age estimates based on sedimentation rates suggest that the X to W interval corresponds to the stage 4 lowstand of sea level. In the western Gulf of Corinth, shoreline transgressive surfaces corresponding to minor transgressions in stage 5 and to major transgression at the end of stage 6 are recognised. This seismic stratigraphy permits a detailed interpretation of the history of the Gulf of Corinth in the past hundred thousand years. It also provides a general model for sedimentation in rift basins in which marine and lacustrine sediments alternate.

Hydrocarbons in rift basins: the role of stratigraphy

Hydrocarbon occurrence and distribution in rift basins is largely a product of the stratigraphic succession in the syn and postrift phases of basin evolution. Most of the known reserves of recovera...

Trace fossil analysis of lacustrine facies and basins

Abstract Two ichnofacies are typical of lacustrine depositional systems. The Scoyenia ichnofacies characterizes transitional terrestrial/nonmarine aquatic substrates, periodically inundated or desiccated, and therefore is commonly present in lake margin facies. The Mermia ichnofacies is associated with well oxygenated, permanent subaqueous, fine-grained substrates of hydrologically open, perennial lakes. Bathymetric zonations within the Mermia ichnofacies are complicated by the wide variability of lacustrine systems. Detected proximal–distal trends are useful within particular lake basins, but commonly difficult to extrapolate to other lakes. Other potential ichnofacies include the typically marine Skolithos ichnofacies for high-energy zones of lakes and substrate-controlled, still unnamed ichnofacies, associated to lake margin deposits. Trace fossils are useful for sedimentologic analysis of event beds. Lacustrine turbidites are characterized by low-diversity suites, reflecting colonization by opportunistic organisms after the turbidite event. Underflow current beds record animal activity contemporaneous with nearly continuous sedimentation. Ichnologic studies may also help to distinguish between marine and lacustrine turbidites. Deep-marine turbidites host the Nereites ichnofacies that consists of high diversity of ornate grazing traces and graphoglyptids, recording highly specialized feeding strategies developed to solve the problem of the scarcity of food in the deep sea. Deep lacustrine environments contain the Mermia ichnofacies, which is dominated by unspecialized grazing and feeding traces probably related to the abundance and accessibility of food in lacustrine systems. The lower diversity of lacustrine ichnofaunas in comparison with deep-sea assemblages more likely reflects lower species diversity as a consequence of less stable conditions. Increase of depth and extent of bioturbation through geologic time produced a clear signature in the ichnofabric record of lacustrine facies. Paleozoic lacustrine ichnofaunas are typically dominated by surface trails with little associated bioturbation. During the Mesozoic, bioturbation depth was higher in lake margin facies than in fully lacustrine deposits. While significant degrees of bioturbation were attained in lake margin facies during the Triassic, major biogenic disruption of primary bedding in subaqueous lacustrine deposits did not occur until the Cretaceous.

Abstract: Geometry and High-Resolution Stratigraphy of Aptian Lacustrine Turbidites - Alagoas Rift Basin, Brazil

Abstract: Geometry and High-Resolution Stratigraphy of Aptian Lacustrine Turbidites - Alagoas Rift Basin, Brazil

Sedimentological responses to basin initiation in the Devonian of East Greenland

ABSTRACTThe Devonian of East Greenland comprises a thick sequence of continental clastic sediments infilling an extensional basin. West of the main basin bounding fault (Western Fault Zone) are scattered outliers of Devonian conglomerate which accumulated in small basins such as found on the island, Ella Ø. The Ella Ø Basin formed by extensional movement along the Narhval Sund Fault accompanied by the formation of a prominent bedding parallel detachment surface which was subsequently modified by sub‐aerial exposure to become the unconformity surface. Mapping of this unconformity surface shows major vertical relief. A thick sequence of conglomerate occurs on Ella Ø, which, close to its exposed basal unconformity, has three lacustrine beds intercalated within it. Detailed analysis of one lake unit shows it to have significant lateral variation. At proximal localities it largely comprises lacustrine turbidites, whereas more distal locations were within a stratified lake. The interpreted sequence of events on Ella Ø is an interval of fluvial sedimentation followed by rapid drowning of the topography with lacustrine sediments onlapping onto basement. After an interval of deeper lacustrine sedimentation including laminites, the lake shallowed, the lithology changed to limestone and the lake dried out. Conglomerate deposition then recommenced. Maximum lake water depth of 100 m is estimated following correction (7°) for post‐Devonian rotation, both determined using the distribution of lacustrine sediments on the unconformity surface. The preferred mechanism for flooding of the Ella Ø Basin is episodic flooding of the entire basin system. Lacustrine sediment preservation results purely from its deposition amongst topography at the edge of the active fluvial system. In such fluvial systems lacustrine sediments may be part of the normal sedimentary cycle but were almost always removed by reworking.

Trace fossils from Jurassic lacustrine turbidites of the anyao formation (Central China) and their environmental and evolutionary significance

The Lower Jurassic Anyao Formation crops out near Jiyuan city, western Henan Province, central China. It is part of the infill of the nonmarine early Mesozoic Jiyuan‐Yima Basin. In the Jiyuan section, this unit is about 100 m thick and consists of laterally persistent, thin and thick‐bedded turbidite sandstones and mudstones displaying complete and base‐or top‐absent Bouma sequences, and thick‐bedded massive sandstones. The Anyao Formation records sedimentation within a lacustrine turbidite system developed in a pull‐apart basin. Processes involved include high and low density turbidity currents, sometimes affected by liquefaction or fluidization. Facies analysis suggests that this succession is formed by stacked aggradational turbidite lobes. The absence of thick mudstone packages indicates that background sedimentation was subordinate to high frequency turbidite deposition. The Anyao Formation hosts a moderately diverse ichnofauna preserved as hypichnial casts on the soles of thin‐bedded turbidite sands...

Reservoir architecture of syn-rift lacustrine turbidite systems, early Cretaceous, offshore South Gabon

Abstract The Lucina Formation of offshore South Gabon comprises deep lacustrine facies deposited in an early Cretaceous rift lake. Both channellized and non-channellized turbidite sandbodies occur enclosed in deep-lacustrine mudstones. These sandbodies provide reservoirs in the Lucina and Lucina West Marine fields. Dramatic changes in sandstone body thickness occur from SW to NE across the strike of the rift lake. This was a consequence of the confinement of high-density sandy turbidity currents in fault-related lake-floor depressions. Limited palaeoccurrent data from orientated core indicate sediment transport from the SW towards the NE. This represents supply from the ramp margin of the lake towards the fault system bounding the lake along its northeastern margin. The modern Lake Malawi provides an analogue in terms of genetic elements and sediment distribution patterns. In addition, ancient marine turbidite systems such as those of the Oligo-Miocene fill of the Tertiary Piedmont Basin, Northwest Italy, provide insights into the relationships between topography in the receiving basin and sandbody geometries.

Vagorichnus, a new ichnogenus for feeding burrow systems and its occurrence as discrete and compound ichnotaxa in Jurassic lacustrine turbidites of Central China

A new ichnogenus, Vagorichnus, is figured and described from Jurassic lacustrine turbidites of the Anyao Formation, Henan Province, Central China. Vagorichnus consists of complex burrow systems composed of discontinuous curved to meandering segments in which irregular networks are formed. The ichnospecies V. anyao covers burrow systems characterized by constricted and irregularly annulated segments, and ridge‐like knobs. Although traces are preserved as hypichnial ridges on the sole of turbidite sandstones, several lines of evidence indicate that these ichnofossils record the activity of a post‐event infauna. Vagorichnus occurs as discrete and compound ichnotaxa. In the latter case, it grades into Gordia and Tuberculichnus. Vagorichnus is interpreted as invertebrate feeding structures (Fodinichnia).

Rift Border System: The Interplay Between Tectonics and Sedimentation in the Reconcavo Basin, Northeastern Brazil

A geometric and depositional model is proposed to explain the tectonic and sedimentary evolution of the main border of the Reconcavo basin. The architecture of the rift margin is characterized by a rift border system constituted by (1) a master fault, (2) a step, and (3) a clastic wedge. This footwall-derived clastic wedge is interpreted as alluvial fans and fan deltas composed of conglomerates that interfinger with hanging-wall strata. The analysis of the vertical distribution of coarse-grained components of this wedge suggests that its composition is geographically controlled, and no regular inverted stratigraphy is commonly described for this type of succession. During an initial lacustrine phase, turbidites accumulated farther from and parallel to the rift margin. The mapping of marker beds that bound these lacustrine turbidite deposits may be used to infer major periods of clastic influx and, therefore, to correlate with periods of fault-related subsidence or climatic fluctuations in the depositional basin and erosion of the sediment source area. Periods of limited back-faulting and basin expansion toward the main border are distinguished through patterns of progradation and aggradation indicating progressive retreat of the rift border and younging in the footwall direction. The overall evolution of the rift border seems to be related to extension, block rotation, hanging-wall subsidence, and footwall uplift associated with the initial master fault, with limited propagation of faults away from the basin into the footwall.

The volcanic, sedimentologic, and paleolimnologic history of the Crater Lake caldera floor, Oregon:Evidence for small caldera evolution

Apparent phreatic explosion craters, caldera-floor volcanic cones, and geothermal features outline a ring fracture zone along which Mount Mazama collapsed to form the Crater Lake caldera during its climactic eruption about 6,850 yr B.P. Within a few years, subaerial deposits infilled the phreatic craters and then formed a thick wedge (10-20 m) of mass flow deposits shed from caldera walls. Intense volcanic activity (phreatic explosions, subaerial flows, and hydrothermal venting) occurred during this early postcaldera stage, and a central platform of subaerial andesite flows and scoria formed on the caldera floor. Radiocarbon ages suggest that deposition of Iacustrine hemipelagic sediment began on the central platform about 150 yr after the caldera collapse. This is the minimum time to fill the lake halfway with water and cover the platform assuming present hydrologic conditions of precipitation and evaporation but with negligible leakage of lake water. Wizard Island formed during the final part of the 300-yr lake-filling period as shown by its (1) upper subaerial lava flows from 0 to -70 m below present water level and lower subaqueous lava flows from -70 to -500 m and by (2) lacustrine turbidite sand derived from Wizard Island that was deposited on the central platform about 350 yr after the caldera collapse. Pollen stratigraphy indicates that the warm and dry climate of middle Holocene time correlates with the early lake deposits. Diatom stratigraphy also suggests a more thermally stratified and phosphate-rich environment associated respectively with this climate and greater hydrothermal activity during the early lake history. Apparent coarse-grained and thick-bedded turbidites of the early lake beds were deposited throughout northwest, southwest, and eastern basins during the time that volcanic and seismic activity formed the subaqueous Wizard Island, Merriam Cone, and rhyodacite dome. The last known postcaldera volcanic activity produced a subaqueous rhyodacite ash bed and dome about 4,240 yr B.P. The late lake beds with base-of-slope aprons and thin, fine-grained basin-plain turbidites were deposited during the volcanically quiescent period of the past 4,000 yr. Deposits in Crater Lake and on similar caldera floors suggest that four stages characterize the postcaldera evolution of smaller (≤10 km in diameter) terrestrial caldera lake floors: (1) initial-stage caldera collapse forms the ring fracture zone that controls location of the main volcanic eruptive centers and sedimentary basin depocenters on the caldera floor; (2) early-stage subaerial sedimentation rapidly fills ring-fracture depressions and constructs basin-floor debris fans from calderawall landslides; (3) first-stage subaqueous sedimentation deposits thick flat-lying lake turbidites throughout basins, while a thin blanket of hemipelagic sediment covers volcanic edifices that continue to form concurrently with lake sedimentation; and (4) second-stage subaqueous sedimentation after the waning of major volcanic activity and the earlier periods of most rapid sedimentation develops small sili-ciclastic basin base-of-slope turbidite aprons and central basin plains. Renewed volcanic activity or lake destruction could cause part or all of the cycle to repeat.

Lacustrine Turbidite Deposits in the Lower Portion of the Green River Formation, Monument Butte Field, Uinta Basin, Utah: ABSTRACT

Lacustrine Turbidite Deposits in the Lower Portion of the Green River Formation, Monument Butte Field, Uinta Basin, Utah: ABSTRACT

The Lower Cretaceous Tectonosequence of the Reconcavo Basin, Northeast Brazil-Sediment Accumulation Rates and Depositional History of the Most Prolific Hydrocarbon-Producing Rift Basin in Brazil

The Lower Cretaceous tectonosequence represents a major chronostratigraphic element defined for the Reconcavo Basin. It encompasses a time span of ca. of 24 m.y. (Berrasian to Barremian) and its associated sedimentary record reaches thicknesses of over 5000 m. Hydrocarbon production within the tectonosequence is mainly associated with synrift lacustrine turbidite and fluvio-deltaic reservoirs. Biostratigraphy is based on nonmarine ostracods, which permits the subdivision of the tectonosequence into eight time intervals (biozones and subzones) i.e., from NRT 002.2 to NRT 009. Estimates on sediment accumulation rates were based on the analysis of 93 wells. During initial rifting, accumulation rates were low (0.2-0.3 m/1,000 yr) due to the relative low sedimentary input to the basin, possibly related to an immature drainage system. Lacustrine sedimentation prevailed during this period (NRT 002.2 through NRT 004). During middle rifting, accumulation rate values are similar to or slightly higher than those related to early rifting. These values may reflect an increase in the depositional area and changes in the hydrological characteristics of the lake, oscillating from close to open conditions. During middle rift, fluvio-deltaic and lacustrine deposition prevailed. Late rift sedimentation is characterized by the highest accumulation rate values observed for the tectonosequence, reaching up tomore » 1.4 m/1000 yr. These high values are associated with fluvial sedimentation and suggest: (1) an efficient drainage system feeding into the basin, (2) removal of structural barriers that might have hampered fluvial systems to reach the basin, and (3) tectonism renewal, which increased topographic differences between source area and depositional basin. Analysis of the sediment types found within the tectonosequence suggests hot, wet climate during early rifting, and dry, arid climatic conditions during late rifting.« less

Geology and sedimentology of the Upper Devonian Escuminac Formation, Québec, and evaluation of its paleoenvironment: lacustrine versus estuarine turbidite sequence

The Escuminac Formation of-the Upper Devonian Miguasha Group at the western end of Chaleurs Bay, Québec, famous for its fossil fish fauna, is a turbidite sequence whose environment of deposition has been a matter of debate. Interpretations vary with different authors between lacustrine or brackish to coastal marine. It is possibly of estuarine origin. Its total stratigraphic thickness of 117 m has been divided into eight lithostratigraphic units on the basis of vertical changes in sands tone: shale ratio. A lacustrine setting is feasible in view of the association with fluvial formations below (Fleurant Formation) and above (Bonaventure Formation), although these are separated by a disconformity or an angular unconformity from the Escuminac. The lack of any shelly marine invertebrate fauna is negative evidence indirectly favoring a lacustrine origin. Periodically stagnant bottom-water conditions evidenced by the preservation of laminites are compatible with a lake environment. The fossil fish fauna, however, contains elements which point toward brackish or marine environments. Geochemical evidence also seems to support brackish conditions, although it is not clear to what extent the geochemical signature may have been inherited from older marine detrital clays. A silled estuary would best accommodate the different lines of evidence, but poses problems of fitting into the broadscale paleogcographic picture of the Upper Devonian Old Red Continent.
 
 RÉSUMÉ
 La Formation d'Escuminac du Groupe de Miguasha du Dévonien supérieur, dans la partie ouest de la baie des Chaleurs, Québec, célèbre pour sa faune de poissons fossile, est une séquence de turbidites dont l'environnement de déposition a fait l'objet de discussions. Les interprétations varient suivant les différents auteurs entre lacustre ou saumatre à marin côtier. C'est possiblement d'origine estuarienne. Son épaisseur totale de 117 m a été divisée en huit unités lithostratigraphiques sur la base de variations verticales dans le rapport grès:shale. Un milieu lacustre est possible en regard de l’association avec les formations fluviatiles en-dessous (Formation de Fleurant) et au-dessus (Formation de Bonaventure), bien qu'elles soient séparées de l’Escuminac par une inconformité ou une discordance angulaire. L'absence de toute faune marine invertébrée à coquille est un argument négatif favorisant indirectement une origine lacustre. Des conditions d'eau de fond périodiquement stagnante, indiquées par la préservation de laminites, sont compatibles avec un environnement de lac. La faune de poissons fossile, cependant, contient des éléments qui pointent vers des environnement saumatres ou marins. Les données géochimiques semblent aussi appuyer des conditions saumâtres, bien qu'il ne soit pas clair jusqu'à quel point la signature géochimique ait pu être héritec d'argiles marines plus anciennes. Un estuaire endigué accomoderait le mieux les diverses données, mais rencontre des difficultés à s'incrire dans le cadre paléogéographique à grande échelle du continent Old Red du Dévonien supérieur.
 
 [Traduit par la journal]

Hydrocarbon Implications of Karoo Supergroup Turbidites and Tectonics in Northern Zimbabwe

Field research in the relatively unstudied Lower Zambezi trough of northernmost Zimbabwe and adjacent Zambia and Mozambique has revealed a sedimentary tectonic history unlike other Karoo basin (Late Carboniferous to Early Jurassic) of the region. This presents a much better setting for petroleum deposits than has been found in those other areas. Aerial photo interpretation and reconnaissance geophysical data show strike-slip folds and faults at the surface and subbasins up to 10 km deep. This contrast with other Karoo basins, which are of a half-graben genesis, is further evident in the sedimentary sequences of the Lower Zambezi basin complex. Lacustrine turbidites occur in the Lower Karoo Kondo Pools Formation. Upper fan facies of a restricted active margin subaqueous fan system are found in limited outcrops in an accommodation zone uplift between the two subbasins. The overlying units are classical Karoo alluvial layers, but intercalated with a higher frequency of unconformities. Syndepositional and postdepositional deformation includes thrust faulting and detachment. Hydrocarbon potential is enhanced by three virtues that are lacking in other parts of southern Africa. Distal facies to those seen in exposures of the Kondo Pools Formation subaqueous fans should be rich in sapropelic mudstone, the source rock so elusivemore » elsewhere. Second, basin depth is sufficient for thermal maturity. Finally, the tectonic regime was conducive to the formation of convex as well as unconformity traps. Mobil Oil is in the midst of an exploration program that may capitalize on these factors.« less

Concepts for Future Exploration for Submarine Fan and Turbidite System Reservoirs: ABSTRACT

With the emphasis of future petroleum exploration in deeper water and on frontier plays, submarine fan and turbidite systems will be major reservoir targets. Successful exploration and development of these reservoirs will be largely controlled by world oil prices, politics, markets, and drilling and producing technologies. Present economics require large reserves when targeting deep water or when drilling remote regions of countries that require large capital expenditures for pipelines and development. Future techniques for successful exploration and production of turbidite reservoirs will include (1) successful application of sequence stratigraphy in identifying reservoirs, (2) new play concepts for exploring synclinal low areas, and (3) the expanded use of three-dimensional seismic surveys. Lacustrine turbidites in rift, wrench, and successor basins are good potential targets because of their association with good source rocks/seals. Reservoirs occur at the base of deltaic clinoforms interbedded with source locks or along actively subsiding fault scarps. Many of these basins are extremely large, but the distribution of source rocks may be limited, making the potential reserves in these systems highly variable. Submarine fans associated with Cenozoic deltas remain an active deep water play. Turbidite reservoirs, deposited within bathymetric lows and localized basins on the slope created by saltmore » and shale diapirism, occur in areas such as the northern Gulf of Mexico, continental margin of Nigeria, and Mackenzie Delta/Canadian Beaufort Sea. Other prospective Cenozoic delta-related margins include those associated with the Amazon, Indus, Ganges-Bramapuhtra, and Mahakam Deltas. The tremendous exploration successes in the deep-water Campos basin illustrate the great potential in passive margins. Targets are subtle and influenced by depositional topography controlled by growth faults, and shale and salt diapirs.« less

Paleoclimatic significance of the lacustrine Carboniferous deposits in northwest Argentina

The origin and probable paleoclimatic significance of Carboniferous lacustrine deposits in northwest Argentina are discussed. These rocks are developed extensively throughout northwestern Argentina, but are described in the present paper only from the region of the Sistema del Famatina. Five lithofacies have been identified: (A) laminated siltstones and claystones; (B) thinly interbedded mudstones and sandstones; (C) interlayered mudstones and sandstones with sole structures (flute marks and tool marks); (D) conglomerates and fine sandstones; (E) sandstones and diamictites. These lithofacies are interpreted as lacustrine deposits formed during the final episode of the Carboniferous glaciation. Lithofacies A originated as a suspension-load deposit in the central and intermediate parts of the lake; the presence of dropstones in this lithofacies suggests coeval ice-rafting processes. Underflow currents probably formed lithofacies B, and lacustrine turbidites lithofacies C. Lithofacies D and E were deposited in marginal environments and represent in some cases shoreline bars and small deltas. The age of the lacustrine episode is deduced from paleobotanical information. Both palynological and megafloristic data suggest that these deposits were formed during the middle Carboniferous. A palynological assemblage dominated by Cristatisporites-like spores characterizes these sediments.

Lacustrine Siliciclastic Rocks and Hydrocarbons: ABSTRACT

Siliciclastic rocks formed from sediments deposited in lake basins are source and reservoir units for large accumulations of oil and gas in North and South America, Africa, and Asia. Lacustrine strata of China consist primarily of siliciclastic units; those of Brazil, Angola, and Cabinda are principally of siliciclastic rocks with abundant carbonate beds; those of the United States consist of at least 50% carbonate rock. The sediments were deposited in, or peripheral to, ancient stratified lakes of a variety of ages, which for millions of years maintained a size comparable to that of modern inland seas. In siliciclastic fine-grained beds formed at the depositional center of these large lakes, values of organic carbon commonly average 3% or less. Those sequences of carbonate strata developed in open-lacustrine depositional settings commonly contain greater than 25% organic carbon. However, porosity values are generally very low in reservoir beds associated with the carbonate source rocks (generally cemented with carbonate minerals) relative to those associated with claystone source rocks. The world's largest lacustrine oil and gas fields are developed in depositional systems with very thick sequences of open-lacustrine clay mudstone that contain relatively low values (generally 3% or less) of organic carbon. In these fields, hydrocarbons migrated from a thick central core of claystone into peripheral and overlying lacustrine and alluvial sandstones at relatively shallow burial depths and prior to significant compaction and cementation of the beds. Siliciclastic rocks form the principal reservoir units in most of the world's ancient petroliferous lacustrine depositional systems. Lacustrine turbidite, bar, and deltaic sandstones are important reservoir units in Brazil, Africa, China, and the United States. Although nonmarine reservoir rocks are commonly described as being of a lacustrine origin, many were formed from sediment deposited at the edge of the lake or in settings well removed from the lake. A principal reservoir facies in the Uinta basin, Utah, is composed of siliciclastic beds that developed as the basal parts of coalesced fluvial channels at the fluctuating margin of Paleocene and Eocene Lake Uinta. Oil-bearing strata in some Chinese basins are channel-fill sandstones formed from sediment deposited in moderately sinu us streams on an alluvial plain several kilometers from the lacustrine shoreline. Depositional models of siliciclastic lacustrine rocks constructed to aid in the exploration and exploitation of indigenous hydrocarbon accumulations should be sensitive to type, richness, and thermochemical maturation of organic matter developed and preserved in the lake. Because siliciclastic open-lacustrine beds in many of the large petroliferous lake basins commonly contain relatively small amount of organic matter, thick sequences of such strata may be required to generate large accumulations of oil. Known accumulations are largest where migration has been to porous and permeable beds at relatively shallow burial depths. End_of_Article - Last_Page 462------------

Character of Ancient Petroliferous Lake Basins of the World: ABSTRACT

The principal oil- and gas-bearing lacustrine rocks in the world were formed from sediments deposited in or peripheral to ancient stratified lakes, of a variety of ages, which for millions of years maintained a size comparable to that of modern inland seas. In these lake systems, both lipid and woody organic matter were developed and preserved in large quantities. The lacustrine rock system commonly constitutes a depositional complex that includes indigenous hydrocarbon source, reservoir, and trap units. Lacustrine strata of China consist primarily of siliciclastic rocks; those of Brazil, Angola, and Cabinda are principally of siliciclastic rocks with abundant carbonate units; those of the End_Page 1680------------------------------ United States consist of at least 50% carbonate rock. Hydrocarbon resources of lacustrine depositional systems are greatest in the People's Republic of China (several billion barrels of recoverable oil). Hydrocarbon resources are also significant in the ancient lake basins of Brazil, Angola, Cabinda, and United States. Currently developed Chinese oil fields in nonmarine rocks are primarily in structural traps, those of South America and Africa are in combination structural and stratigraphic traps, whereas those of the United States are principally in stratigraphic traps. Available data suggest that hydrocarbons in the more deeply buried strata are contained in secondary pores which received oil or gas subsequent to significant episodes of cementation and/or compaction, and dissolution of minerals. Reservoir rocks with abundant primary porosity are most commonly preserved at relatively shallow burial depths, and many are intercalated with immature source units. Primary pores contain hydrocarbons that have migrated to reservoirs from mature source rocks (more deeply buried?). In China, oil is recovered in great quantities from sandstones with abundant primary porosity, particularly in those basins with high geothermal gradients. The oil apparently migrated to the primary pores from nearby source beds which reached thermochemical maturation at relatively shallow depths of burial and before significant early cementation and compaction of the sandstone units. Matrix porosity and permeability in sandstone units are best developed and preserved in those rocks composed of chemically stable minerals and few labile grains. Fluid-pressure gradients may be abnormally high in those lacustrine systems that have reached the stage of thermochemical maturation. In these cases, oil and/or gas are generated and expelled in quantities great enough to locally increase fluid pressures faster than pressure is released to adjoining rocks. Abnormally high fluid-pressure gradients in lacustrine units also occur in those impermeable hydrocarbon-bearing strata that have apparently been elevated at a rapid rate. In such a system, equilibration between fluid pressures in beds of low matrix permeability in the deep subsurface and permeable beds near the surface is restricted. In both cases, fractured overpressured rocks of low matrix permeability may yield oil and/or gas from pools whose boundaries are not restricted to loc l structures. Rather, they are restricted by relatively permeable beds that have provided access to the surface for pressure and fluid release (and invasion of water). Local avenues of permeability in overpressured rocks are greatest along natural, open fractures. Although reservoir rocks for fields developed in lake basins are commonly described as being of a lacustrine origin, others were formed from sediment deposited at the edge of a lake or in settings well removed from a lake. Principal reservoir rocks in the Uinta basin, Utah, represent the basal parts of coalesced fluvial channels formed at the fluctuating margin of lake Uinta. Red-colored oil-bearing strata in some Chinese fields whose reservoir rocks are channel-fill sandstones formed from sediment deposited on an alluvial plain several kilometers from the lacustrine shoreline. Lacustrine turbidite, bar, and deltaic rocks are important reservoirs in Brazil, Africa, United States, and China. Petroliferous sedimentary rocks formed in lake basins are known over much of the world where th y contain many billion barrels of recoverable oil and offer the promise of more. End_of_Article - Last_Page 1681------------

Lacustrine turbidites in the Green River Formation, northwestern Colorado

Research Article| May 01, 1981 Lacustrine turbidites in the Green River Formation, northwestern Colorado John R. Dyni; John R. Dyni 1U.S. Geological Survey, Denver Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar James E. Hawkins James E. Hawkins 2U.S. Bureau of Mines, Denver Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information John R. Dyni 1U.S. Geological Survey, Denver Federal Center, Denver, Colorado 80225 James E. Hawkins 2U.S. Bureau of Mines, Denver Federal Center, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1981) 9 (5): 235–238. https://doi.org/10.1130/0091-7613(1981)9<235:LTITGR>2.0.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation John R. Dyni, James E. Hawkins; Lacustrine turbidites in the Green River Formation, northwestern Colorado. Geology 1981;; 9 (5): 235–238. doi: https://doi.org/10.1130/0091-7613(1981)9<235:LTITGR>2.0.CO;2 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 SocietyGeology Search Advanced Search Abstract A preliminary study of drill cores of blebby and streaked oil shale from the Green River Formation (Eocene) in the deep northern part of the Piceance Creek Basin, Colorado, shows sedimentary structures that suggest deposition by turbidity currents. This type of oil shale composes about one-half of the oil-shale deposits at the saline depocenter of Eocene Lake Uinta where it is interbedded with the well-known laminated type of oil shale described previously in the literature.Episodic and rapid deposition by lake-bottom currents of large amounts of carbonate-silicate sediments that formed high-grade oil shale is a new concept for the origin of a major part of the Green River oil-shale deposits. In contrast, the laminated oil shale, as previously described, accumulated very slowly as thin varves in a chemically stratified lake under stagnant conditions. 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.