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1.
Ground Penetrating Radar (GPR) surveys were conducted on Mesoproterozoic eolian, fluvial, deltaic, estuarine, and shallow marine successions in the Chapada Diamantina Basin. The subsurface continuation of facies and facies architecture exposed on road cuts was imaged using the GPR signal of a 400-MHz antenna penetrating 8 m in depth, even with mudstone intervals. Reflection patterns in the GPR profiles that were compared with photo mosaics of outcrops and supporting data from vertical sections and gamma ray logs, reveal sedimentary, stratigraphic, and structural features, such as sedimentary structures, the external geometry of architectural elements, stratigraphic surfaces, folds and tension gashes. The patterns most likely reflect the response from low-weathered, non-porous muscovite-illite-rich mudstone and quartzarenite sandstone in which authigenic and detrital illite and sericite are prevalent clay minerals.Measured vertical sections and radar stratigraphy indicate high-frequency cyclic successions of estuarine and shoreface intervals are present at the base of the Tombador Formation. The shoreface intervals are composed of heterolithic strata and offshore tidal bars deposits. The heterolithic shoreface strata exhibit tabular geometry that can be easily identified throughout the outcrop and in the subsurface. Such intervals represent the end of high-frequency transgressive cycles, and hence they are potential candidates for including the maximum flooding surfaces and for defining genetic sequences. Therefore, GPR proved to be an independent method for studying facies architecture and the establishment of a high-resolution stratigraphic framework even in the Precambrian. 相似文献
2.
Mapping geological details and interpreting three-dimensional geometries in a highly heterogeneous outcrop such as the exposure at Big Rock Quarry has been a continuous challenge especially because high vertical cliffs make access to most of the rocks difficult for direct geological observations. Previous interpretations of facies architecture were derived from gamma-ray profiles, a core and measurements made on two-dimensional photomosaics. This paper represents the first attempt of three-dimensional interpretation of the geometry and facies pattern of the Jackfork nested channel complex deposited at the base-of-slope.Examination of the photo real model of the outcrop with assigned lithologies allowed extraction of accurate 3-D qualitative, as well as quantitative (channel dimensions) geometric information. This facilitated interpretation and reconstruction of the submarine channel complex architecture making possible correlations of strata exposed on the two sides of the quarry.Most of the exposed vertically and laterally stacked channels are large, aggradational with well-defined axial regions overlain by matrix-supported breccia which grades upward into amalgamated sandstones. The thickness of the sandstone decreases toward the southeastern end of the quarry where more shale is present. The channel infill consists of thin-bedded sandstones interlayered with shale which overlain the breccia. The upper part of the quarry is made up of smaller, lateral migrating channels.Significant channel width and thickness variation can be recognized at outcrop scale. Thirty-eight identified channels are characterized by a relatively low aspect ratio (4:1 to 32:1) with channel dimensions ranging from 25 m to 314 m wide and 2 m-24 m deep. Bed thickness distributions of various facies show that the sandstone comprises a significant proportion (83%) of the total channel thickness, while shale and breccia represent about 8%, and 17% respectively. This yields a high net-to gross ratio of more than 80%.Compared to previous reconstructions our 3-D photo real model is more accurate and it can be used to calibrate simulation of processes in deep-water environments. 相似文献
3.
Using photomosaics and measured sections, this outcrop study characterizes facies- to sandbody-scale heterogeneity in the fluvial and coastal-plain deposits of the Blackhawk Formation of the Wasatch Plateau, Utah, USA, as an outcrop analog for the fluvial tight-gas reservoirs of the adjacent greater western Rocky Mountain basins as well as for conventional fluvial reservoirs elsewhere. Analysis on eight contiguous, vertical cliff-faces comprising both depositional-dip- and -strike-oriented segments provides field-validation and calibration of the entire range of fluvial heterogeneity, where: 1) large-scale heterogeneity (10's of m vertically and 100's of m laterally) is associated with stacking of channelized fluvial sandbodies encased within coastal-plain fines, 2) intermediate-scale heterogeneity (1's of m vertically and 10's of m laterally) is related to type and distribution of architectural elements like bar-accretion and crevasse-splay units within individual sandbodies, and 3) small-scale heterogeneity (10's of cm vertically and 1's of m laterally) is attributed to facies spatial variability within individual architectural elements.At a reservoir-scale (∼6 km strike-transect), impact of these heterogeneities has resulted in potential stratigraphic compartmentalization in varied patterns and scales within and among three zones, which have similar lateral extents. Distinct vertical or lateral compartmentalization, contrasting net-to-gross pattern, width-constraint by either large- or intermediate-scale heterogeneity, disparity in communication between principal reservoir compartments by intermediate-scale heterogeneity, and reservoir-quality segregation to barrier styles rendered by small-scale heterogeneity are documented in an array of trends. These intriguing trends are challenging to correlate across the reservoir-scale dataset, contributing to multiple, analogous exploration and production uncertainties. For improved tight-gas exploration and production strategy of the western Rocky Mountain basins, study results were also used in developing potential predictive tools: 1) thickness threshold of individual channelized sandbody favoring multiple well intersection, 2) aspect ratio in performing probabilistic sandbody-width estimation, and 3) prediction of sandbody amalgamation using underlying coal thickness. 相似文献
4.
5.
This study integrates newly acquired stratigraphic data, geologic mapping, and paleocurrent data to constrain the stratigraphic evolution of the oldest channel-lobe complex in the Upper Cretaceous Cerro Toro Formation in the Silla Syncline area of the Magallanes Basin, termed the Pehoe member. The Pehoe member ranges in thickness from 60 m in the north to at least 410 m farther down system and comprises three separate divisions (A, B, and C). A lower conglomerate unit and an upper one, termed Pehoe A and C divisions respectively, represent the fill of major incised submarine channels or channel complexes. These are separated by stratified sandstone of the Pehoe B division, representing a weakly confined lobe complex, either transient or terminal.The integration of new data with observations from previous studies reveal that the three main coarse-grained conglomerate and sandstone members in the Cerro Toro Formation in the Silla Syncline include at least seven distinct submarine channels or channel complexes and two major lobe complexes. The thinning and disappearance of these units along the eastern limb of the syncline reflect confinement of the flows to a narrow trough or mini-basin bounded to the east by a topographic high. This confinement resulted in unidirectional paleocurrents to the south and southeast in all deposits. Changes in depositional geometries are interpreted as reflecting changes in sediment supply and relative confinement. Submarine channels were from 700 m to 3.5 km wide and occupied a fairway that was 4-5 km wide. Flows moving south and southeast in this mini-basin probably crossed the eastern topographic high south of the present exposures and joined those moving southward along the axis of the foreland basin at least 16 km to the east. 相似文献
6.
《Marine and Petroleum Geology》2003,20(6-8):691-710
The Pab Formation consists of deltaic and turbiditic sediments which were deposited during the Late Maastrichtian on the Indo-Pakistani passive margin. The margin geometry has been restored in the Pab Range from a regional transect 120 km long. Two superposed turbiditic systems onlap the slope carbonates and completely pinch-out southward. The lowest turbiditic system (Lower Pab) is a sand-rich basin floor fan, which consists of sand-rich channel complexes distally passing to lobes northward. This basin floor fan is overlain by a mud-rich slope fan formed during the subsequent sea-level rise, which drowned the shelf. The upper turbiditic system (Upper Pab) is a sand-rich slope fan, formed during the progradation of a deltaic system in the shelf setting. It consists of prograding tabular lobes passing upward to conglomeratic channels, and thins out northwards. The Lower Pab turbiditic system consists of three channel complexes (LP1, 2, 3) organised in a backstepping succession. Each channel complex has a multi-storey internal architecture, resulting from the amalgamation of several individual turbiditic channels. Five major facies associations have been determined in the LP3 channel complex. FA-1 corresponds to polygenic and monogenic debris-flows, FA-2 to high-density gravelly or sandy turbidites, FA-3 to by-pass deposits, FA-4 to thin-bedded turbidites (spill-over lobes and levees) and FA-5 to hemipelagites. The downstream evolution of the LP3 channel complex can be studied from canyon to mid-fan settings. Where it is confined in the canyon, the channel complex is 50 m thick and 1 km large, and shows a high sand/shale ratio. The development of overflow deposits is limited and occurs only at the top of the channel complex. At the canyon mouth, the channel complex is still deeply incised but overflow deposits start to expand laterally as a result of the decreased confinement. By-pass facies here are well-developed, and are related to hydraulic jump processes. In the mid-fan setting, the channel complex widens and the sand/shale ratio decreases. Erosion at the channel base is less developed, whereas internal and external levees are well-developed. Spill-over lobes form the last stage of the channel complex infill. The internal geometry of the channel complexes is a result of a complex interaction between lateral confinement, by-pass and lateral migration processes. 相似文献
7.
《Marine and Petroleum Geology》2007,24(6-9):529-539
Submarine channel deposits are recognised as the primary heterogeneity within the turbidite systems that host them, with channel fill heterogeneities being considered secondary. An investigation of channel fill heterogeneities was conducted on Oligocene turbidites of the Grès du Champsaur, Hautes Alpes, SE France, which was deposited in a sub-basin within the Alpine peripheral foreland basin. Here, a series of erosional channels are exposed in mountainous terrain. Maximum channel widths are in the order of 1000 m, and depths of the order of 100 m. The channels can be traced along axis for at least 6 km. Mapping of channel facies revealed three orientations of fill heterogeneity expressed as: (1) upward variations in the character of vertically stacked fill sequences, (2) lateral variability, and (3) the occurrence of downstream dipping and stacking units forming the uppermost parts of channel fill. Vertically expressed heterogeneities are thought to have developed via the gradual reduction in the efficiency of channelised flow, leading to a progressive reduction in scour and the deposition of overall thinning and fining upwards sequences. Lateral heterogeneity is related to the development of downstream-oriented elongated scour and fill facies. Downstream-dipping heterogeneity is represented by a series of several metre-scale downstream-dipping low-angle clinoforms thought to be related to final infill of the negative channel bathymetry by a migrating front of sand that would have formed part of a downstream-migrating sheet to channel transition in plan view. Both first and second orders of channel heterogeneity may control the reservoir performance of channel prone turbidite sequences. Preferred-orientation channel facies heterogeneities are thought to affect potential hydrocarbon recovery through their impact on permeability anisotropy within the confines of the channel. 相似文献
8.
《Marine and Petroleum Geology》2007,24(6-9):504-514
Forward seismic models of two ‘seismic scale’ outcrops of different style channel systems have been made to investigate their seismic signature. These two outcrops illustrate the geometric end members of channel stacking architecture in response to low- and high-accommodation space. The Eocene Nohut Tepe channel system of the Elaziğ Basin in eastern Turkey was deposited in an area of high accommodation resulting in an aggradational geometrical offset stacking of channels up against a slope. The Eocene Ainsa II Channel system of the Tremp-Pamplona Basin in the Spanish Pyrenees was deposited in an area of low accommodation resulting in a tabular, compound sheet geometry, with amalgamated channel bodies separated by clay drapes.Depth models were drawn from outcrop photos and converted to impedance models by assigning acoustic impedance properties to the sand filled channels and surrounding and interbedded mud and clay layers. These were the input for the forward seismic models, which constructed various frequency synthetic seismic sections of the two outcrops. Analysis of the outcrop synthetic seismic identified three distinct reflection configurations. Type I is characterised by a strong black peak and white trough reflection, which is due to a discrete channel body. Type II is characterised by multiple offset, time ‘stepped’ black peak reflections that are underlain by one continuous, strong white trough reflection, which is due to offset stacked channel bodies. Type III is characterised by strong black peaks which onlap an underlying, continuous white trough reflection, caused by the lateral amalgamation of channel bodies.These three types of reflection configurations observed on the outcrop synthetic seismic can also be found on actual seismic from channelised turbidite systems, which aids in interpreting channel stacking architecture, accommodation space prediction and depositional styles from the actual seismic data. Channel stacking architecture is clearly an important aspect which needs to be considered when making channel system interpretations based on seismic data. 相似文献
9.
S.S. Flint D.M. HodgsonA.R. Sprague R.L. BruntW.C. Van der Merwe J. FigueiredoA. Prélat D. BoxC. Di Celma J.P. Kavanagh 《Marine and Petroleum Geology》2011,28(3):658-674
The Laingsburg depocentre of the SW Karoo Basin, South Africa preserves a well-exposed 1200 m thick succession of upper Permian strata that record the early filling of a basin during an icehouse climate. Uniformly fine-grained sandstones were derived from far-field granitic sources, possibly in Patagonia, although the coeval staging and delivery systems are not preserved. Early condensed shallow marine deposits are overlain by distal basin plain siltstone-prone turbidites and volcanic ashes. An order of magnitude increase in siliciclastic input to the basin plain is represented by up to 270 m of siltstone with thin sandstone turbidites (Vischkuil Formation). The upper Vischkuil Formation comprises three depositional sequences, each bounded by a regionally developed zone of soft sediment deformation and associated 20-45 m thick debrite that represent the initiation of a major sand delivery system. The overlying 300 m thick sandy basin-floor fan system (Unit A) is divisible into three composite sequences arranged in a progradational-aggradational-retrogradational stacking pattern, followed by up to 40 m of basin-wide hemipelagic claystone. This claystone contains Interfan A/B, a distributive lobe system that lies 10 m beneath Unit B, a sandstone-dominated succession that averages 150 m thickness and is interpreted to represent a toe of slope channelized lobe system. Unit B and the A/B interfan together comprise 4 depositional sequences in a composite sequence with an overall basinward-stepping stacking pattern, overlain by 30 m of hemipelagic claystone. The overlying 400 m thick submarine slope succession (Fort Brown Formation) is characterized by 10-120 m thick sand-prone to heterolithic packages separated by 30-70 m thick claystone units. On the largest scale the slope stratigraphy is defined by two major cycles interpreted as composite sequence sets. The lower cycle comprises lithostratigraphic Units B/C, C and D while the upper cycle includes lithostratigraphic Units D/E, E and F. In each case a sandy basal composite sequence is represented by an intraslope lobe (Units B/C and D/E respectively). The second composite sequence in each cycle (Units C and E respectively) is characterized by slope channel-levee systems with distributive lobes 20-30 km down dip. The uppermost composite sequence in each cycle (Units D and F respectively) are characterised by deeply entrenched slope valley systems. Most composite sequences comprise three sequences separated by thin (<5 m thick) claystones. Architectural style is similar at individual sequence scale for comparable positions within each composite sequence set and each composite sequence. The main control on stratigraphic development is interpreted as late icehouse glacio-eustasy but along-strike changes associated with changing shelf edge delivery systems and variable bathymetry due to differential substrate compaction complicate the resultant stratigraphy. 相似文献
10.
《Marine and Petroleum Geology》2007,24(6-9):406-433
Several laterally offset and aggradational sinuous submarine channels are contained within a 54 km long segment of the Benin-major Canyon. Axial channel deposits produce high amplitude reflections on three-dimensional (3-D) seismic profiles. Some seismic reflections have U- or V-shaped cross-sectional motifs that were correlated with confidence along linear to meandering paths for distances up to 70 km. They are referred to here as channel-forms (CFs), and are believed to be the axial parts of submarine channels preserved during overall channel floor aggradation. A total of 15 separate CFs were mapped allowing thalweg-gradients, dimensions, and morphology to be studied spatially and through time, providing insight into how submarine canyons fill. Their planform geometry evolved predominantly in a stepwise fashion through alternating periods of cut-and-fill, but more gradual channel migrations are also observed. The largest offsets in successive channel floor position occur after periods of significant vertical CF fill (‘thalweg plugging’—with deposits commonly consisting of lower amplitude, transparent to chaotic seismic reflections). The passage of erosive flows after such periods of fill caused abrupt shifts in channel position, particularly at meander bends, with increased potential for the formation of pseudo meander loop cut-offs. Significant spatial differences in the stacking architecture of CFs are attributed to local slope deformation and perhaps also to a recent channel avulsion just west of the study area. Abrupt channel straightening in the western study area coincides with a period of increased valley-gradient associated with amplification of an underlying anticlinal fold. The youngest CFs in this area show limited aggradation and are characterized by repeated episodes of headward erosion causing knickpoint migration as the recent channel floor tried, unsuccessfully, to establish a smooth graded depth profile. This is in stark contrast to the time-equivalent predominantly aggradational CFs in the eastern study area that show a progressive increase in sinuosity through time. 相似文献
11.
Isaac Channel 3 is a rare outcrop example of a perpendicular cut through a sinuous deep-water channel, and also where levee deposits formed on opposite sides of the channel are well exposed. Strata flanking the outer- and inner-bend margin of the channel show important differences in lithofacies, architecture and association with channel-fill strata. Proximal outer-bend levee deposits are sand-rich (N:G up to 0.68) and comprise medium- to thick-bedded, Ta-d turbidites interstratified with thinly-bedded, Tcd turbidites. The thicker-bedded deposits show lateral variation in grain size and thickness over hundreds of meters whereas thin-bedded strata thin and fine negligibly over similar distances. The distal outer-bend levee (up to 700 m laterally away from the channel) consists predominantly of thin-bedded turbidites interstratified with up to 5 m thick coarse-grained splay deposits. In contrast to the outer-bend, the inner-bend levee deposits are significantly more mud-rich (N:G as low as 0.15) and consist mostly of thin-bedded, Tcd turbidites with less common thicker-bedded, Ta-d turbidites. Lateral thinning and fining trends associated with these less common thicker-bedded deposits occur more rapidly than their outer-bend counterparts.Erosion associated with lateral migration of the channel axis produced a sharp contact along the outer-bend channel margin causing coarse-grained channel-fill deposits to be in erosional contact with levee deposits. This suggests that the crest of the outer-bend levee was elevated above the channel floor and produced a channel margin upon which channel-fill strata onlapped. Positive topography is interpreted to have developed by overspilling processes that deposited abundant sand on the outer-bend levee while the majority of the flow continued through the channel bend and bypassed to areas further downslope. In contrast, some thick-bedded, amalgamated channel-fill deposits in the axial channel area grade laterally over 140 m into thinly-bedded turbidites on the inner-bend levee. The lack of channel-fill on lap relationships implies that topography along the inner bend was sufficiently subtle that at least some flows were able to expand laterally and over the overbank area without becoming separated from the main throughgoing channel flow.Stratal relationships observed in Isaac Channel Complex 3 suggests three main episodes of channel-levee growth that were each initiated by a period of increased levee relief followed by channel filling and distal levee deposition. This consistent depositional history points to the regular variations, in both time and space, of sediment transport and deposition in a deep-marine sinuous channel-levee system. 相似文献
12.
The Middle to Upper Jurassic Todagin assemblage in northwestern British Columbia, Canada, was deposited in the Bowser Basin above arc-related rocks of the Stikine terrane. Sedimentary structures indicate that a variety of gravity flow processes were involved in transport and deposition in deep-water slope environments. At Mount Dilworth, laterally continuous and channelized turbidites are interbedded with and overlain by mass-transport deposits in which sedimentary clasts are supported in a mudstone matrix. More than 50% of the succession consists of mass-transport deposits, indicating significant slope instability. A 300 m thick mass-transport complex exposed near the top of the succession is interpreted to result from tectonic activity, which triggered a major change in sediment supply from a local source area. At Todagin Mountain, a channel complex displays three successive channel-fills with associated overbank sedimentation units. Mass-transport deposits are rare, and confined to channel axes. Channels 1 and 2 are characterized by 40-50 m thick, ungraded pebble clast-supported conglomerate while the uppermost Channel 3 contains graded beds and occasional traction structures. The gradual change from erosive and amalgamated channel deposits at the base, to more aggradational channels at the top, is related to elevation of the equilibrium profile. Creation of accommodation favored aggradation on the mud-dominated slope succession and construction of well-developed channel-levee systems. The vertical succession exposed at Todagin Mountain is consistent with normal progradation of the slope under high sedimentation rates. In the Mount Dilworth area, extensional faulting associated with development of the restricted Eskay rift in the early Middle Jurassic produced a dissected basement above which the Todagin assemblage was deposited. These structures were inverted during collision of the Stikine and Cache Creek terranes, and likely played a major role in the stratigraphic evolution of the deep-water architectures. 相似文献
13.
《Marine and Petroleum Geology》2003,20(6-8):649-676
High-resolution multichannel 2-D and 3-D seismic data, primarily from upper fan reaches of near-seafloor channel-levee systems on the Niger Delta slope and in the Arabian Sea, reveal a high level of detail and architectural complexity. Several architectural elements are common to each system examined in this study. They include inner levees, outer levees, erosional fairways, channel-axis deposits, rotational slumps blocks, and mass transport deposits. Although the scale of individual systems varies significantly, similarities in first-order architectural elements and their configurations suggest that common depositional processes are involved regardless of scale differences.Most of the channel-levee systems examined in this study are characterized by a basal erosional fairway that is bordered by outer levees of varying thickness. Together these elements define the base and margins of the channel-belt, where channel-axis deposits and inner levees are the dominant architectural elements. Vertical, sub-vertical, and lateral stacking patterns of sinuous and/or meandering channels create seismic facies that range from narrow to wide zones of high amplitude reflections (HARs) with chaotic to continuous and shingled to horizontal reflections. Some HARs appear as isolated or stacked asymmetric to symmetric u- and v-shaped reflections, referred to here as channel-forms. Channel-belts evolve within the confines of the scalloped erosional fairway walls (flanked by outer levee), and are similar in morphology to meander-belts in fluvial systems, but commonly have a greater component of vertical aggradation. Detailed study of one particular channel-levee system on the Niger Delta slope shows a period of incision followed by three distinct phases of channel development during its aggradational history. Each fill phase corresponds to a different channel stacking architecture, planform geometry, and nature of terrace development, with important implications for reservoir architecture. In some cases, multiple phases of inner levee growth are observed, each intimately linked to the channel migration and aggradation history. Channel sinuosity evolves dynamically, with some meander loops undergoing periods of accelerated meander growth at the same time that others show little lateral migration. 相似文献
14.
E. Schwarz G.D. VeigaL.A. Spalletti J.L. Massaferro 《Marine and Petroleum Geology》2011,28(6):1218-1241
The Berriasian-Valanginian Springhill Formation of the Austral Basin of southern South America comprises fluvial to marine deposits. In order to interpret depositional systems and unravel the stratigraphic architecture of this unit in the southern region of the basin (Tierra del Fuego Province, Argentina), 500 m of cores combined with well-log data from 41 wells were studied. Facies associations corresponding to fluvial (A1-A6), estuarine (B1-B5) and open-marine (C1-C4) depositional environments were identified. These facies associations succeed each other vertically across the entire study area (6800 km2) forming a ∼120-m-thick transgressive succession. This unit filled a north-south-oriented valley system, developed in the underlying Jurassic volcanic complex.Lowstand fluvial deposits of the first stage of the valley-system fill occur in downdip segments of the system above a sequence boundary (SB). These fluvial deposits are overlain by coastal-plain and tide-dominated estuarine strata across an initial transgressive surface (ITS). In the northern sector the earliest valley infill is characterized by a transgressive fluvial succession, overlying a merged SB/ITS that is probably time-equivalent of marginal-marine deposits of the southern sector. The fluvial strata in the north are overlain by wave-dominated estuarine deposits. A drastic change to open-marine conditions is marked by a marine flooding surface, with local evidence of marine erosion (FS-RS). Open-marine strata are thin (<10 m) and dominated by lower-shoreface and offshore-transition deposits. They are capped by a younger flooding surface (FS), which represents the onset to offshore conditions across the study area due to a continuous long-term transgression that persisted until the Barremian.Although the interpreted depositional systems and stratigraphic architecture of the Springhill Formation resemble transgressive incised-valley-fill successions, the greater thickness and larger size of the Springhill valleys suggest inherited rift topography rather than valley development during a relative sea-level fall. 相似文献
15.
The Lower Cretaceous succession of the northwestern Barents Shelf: Onshore and offshore correlations
The Lower Cretaceous succession in the Barents Sea is listed as a potential play model by the Norwegian Petroleum Directorate. Reservoirs may occur in deep to shallow marine clastic wedges located in proximity to palaeo-highs and along basin margins. In addition, shelf-prism-scale clinoforms with high amplitude anomalies in their top- and bottomsets have been reported from reflection seismic but they have never been drilled. In Svalbard, the exposed northwestern corner of the Barents Shelf, Lower Cretaceous strata of shelfal to paralic origin occur, and includes the Rurikfjellet (Valanginian–Hauterivian/lowermost Barremian), Helvetiafjellet (lower Barremian–lower Aptian) and Carolinefjellet formations (lower Aptian–middle Albian). By combining sedimentological outcrop studies and dinocyst analyses with offshore seismic and well ties, this study investigate the link between the onshore strata and the offshore clinoforms. Age-vise, only three (S1–S3) of the seismic sequences defined in the offshore areas correlate to the onshore strata; S1 correspond to the Rurikfjellet Formation, S2 to the Helvetiafjellet Formation and the lower Carolinefjellet Formation, and S3 to the upper Carolinefjellet Formation. Offshore, all three sequences contain generally southward prograding shelf-prism-scale clinoforms. A lower Barremian subaerial unconformity defines the base of the Helvetiafjellet Formation, and its extent indicates that most of the Svalbard platform was exposed and acted as a bypass zone in the early Barremian. Onshore palaeo-current directions is generally towards the SE, roughly consistent with the clinoform accretion-direction towards the S. The local occurrence of a 150 m thick succession of gravity flow deposits transitionally overlain by prodelta slope to delta front deposits in the Rurikfjellet Formation, may indicate that shelf-edges also developed in Svalbard. The late Hauterivian age of theses deposits potentially highlights the inferred offlapping nature of the Lower Cretaceous strata as they predate the lower Barremian unconformity, and thus record a hitherto unknown regression in Svalbard. The presence of the lower Barremian subaerial unconformity in Svalbard, the general southeastward palaeo-current directions, and the age-equivalent clinoform-packages south of Svalbard, suggests that the onshore and offshore strata is genetically linked and was part of the same palaeo-drainage system. 相似文献
16.
Seismic data and sediment cores collected offshore from the Sanaga River and Nyong River mouths were used to analyse a loose mantle of yellow to reddish sandy gravel with a range of fluvial and deltaic characteristics cropping out in the middle part (25–65 m water depth) of the continental shelf of Cameroon. Contrary to most of the Atlantic shelves, where the lowstand systems tract was destroyed by erosion, we found 80–120 ms (60–90 m) of sediment mainly in the middle part of the shelf, which correspond credibly to MIS 2–4. Fluvial paleodrainage systems are preserved beneath the shelf and individual filled channels with planar infillings were mapped that cross the shelf along two surfaces of erosion. These incisions suggested westerly and northwesterly drainage shifts during presumed lowered base level. The presence of closely spaced channel fills suggests repeated avulsion of a single stream during a long-lasting sub-aerial erosion period. The seismic facies of these Pleistocene deposits distinguish themselves clearly from well-stratified older strata showing deformation (Pliocene) or intense folding (Miocene). The orientation of the paleovalleys appears strongly controlled by the N60°E trending cross faults within Mesozoic–Cenozoic strata. 相似文献
17.
An understanding of the paleoenvironment and the main sedimentary processes behind preserved deposits is crucial to correctly interpret and represent lithofacies and facies associations in geomodels that are used in the hydrocarbon industry, particularly when a limited dataset of cores is available. In this paper a fairly common facies association is discussed containing massive sands - here defined as thick (>0.5 m) structureless sand beds devoid of primary sedimentary structures, or with some faint lamination - deposited by mass failures of channel banks in deep fluvial and estuarine channels. Amongst geologists it is generally accepted that liquefaction is the main trigger of large bank failures in sandy subaqueous slopes. However, evidence is mounting that for sand deposits a slow, retrogressive failure mechanism of a steep subaqueous slope, known as breaching, is the dominant process. A model of breaching-induced turbidity current erosion and sedimentation is presented that explains the presence of sheet-like massive sands and channel-like massive sands and the sedimentary structures of the related deposits. Sheet-like packages of spaced planar lamination that are found together with massive sand bodies in deposits of these environments are identified as proximal depositional elements of breach failure events. The model, acquired from sedimentary structures in deposits in the Eocene estuarine Vlierzele Sands, Belgium, is applied to outcrops of the Dinantian fluvial Fell Sandstone, England, and cores of the Tilje and Nansen fms (Lower Jurassic, Norwegian Continental Shelf). The possible breach failure origin of some other massive sands described in literature from various ancient shallow water environments is discussed. Breach failure generated massive sands possibly also form in deep marine settings. The potentially thick and homogeneous, well-sorted sand deposits bear good properties for hydrocarbon flow when found in such an environment. However, in case of deposition in an estuarine or fluvial channel, these sand bodies are spatially constricted and careful facies interpretation is key to identifying this. When constructing a static reservoir model, this needs to be considered both for in-place volume calculations as well as drainage strategies. 相似文献
18.
Bioturbated sediments recording distal expressions of paralic depositional environments are increasingly being exploited for hydrocarbons in the super-giant Pembina Field (Cardium Formation), Alberta, Canada. These strata were previously considered unproductive due to limited vertical and horizontal connectivity between permeable beds. In these “tight oil” plays (0.1–10 mD), pressure decay profile permeametry (micropermeability) data indicate that sand-filled burrows provide vertical permeable pathways between bioturbated and parallel-laminated sandstone beds in the central, northeast and northwest parts of the field. This relationship enables the economic exploitation of hydrocarbons via horizontal drilling and multi-stage hydraulic fracturing. As the exploitation of bioturbated strata progresses in the Pembina Field, additional primary targets are being sought out, and horizontal waterflooding is being considered in areas where horizontal wells exist. Proximal to historical produced conventional targets, reservoir analyses indicate that areas where the bioturbated facies average permeability lies between 0.35 mD and 0.85 mD and sandstone isopach thicknesses are between 0.25 m and 2.5 m should be targeted in east-central Pembina.Micropermeability values enable correlation of bulk permeability from plugs and full-diameter samples to the heterogeneous permeability distributions in intensely bioturbated strata. Bulk and micropermeability data are graphically compared, and permeability distributions are mapped across the field. Using isopach thickness of bioturbated facies, production data, and permeability data, “sweet spots” are identified for placement of effective waterfloods.Production information for recently drilled horizontal wells in the Pembina Field demonstrate that bioturbated muddy sandstones and sandy mudstones in paralic environments can be economically exploited when sand-filled burrows provide connectivity between sand beds. However, well performance within these poorly understood unconventional tight oil plays can better be predicted with an in-depth characterization of their facies and complex permeability heterogeneities. Based on our results, it is clear that micropermeability analysis can be effectively employed to differentiate between economic and sub-economic plays, identify areas with high effective permeability, and high-grade areas for enhanced oil recovery schemes. 相似文献
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The large-scale stratigraphic architecture of forced regressive deposits has been documented in many previous studies. Bed-scale facies architectural analyses of these deposits, however, are still very limited. The Cretaceous Ferron “Notom Delta” in southern Utah, U.S.A. contains a 20 km dip-oriented exposure of a stepped, forced regressive systems tract. The main focus of this paper is to reconstruct the paleogeography and depositional history of the systems tract based on detailed stratigraphic and facies architectural analysis using 23 geological sections, photomosaics, and walking out of beds.Internally, the systems tract consists of 6 parasequences, 11f to 11a from the oldest to the youngest. During the progradation of parasequences 11f to 11b the paleoshorelines were wave-dominated, as indicated by the abundance of HCS and/or SCS beds, wave-ripple cross-laminated beds, and the occurrence of diverse and robust ichnological suites attributable to the Skolithos and Cruziana Ichnofacies. Progradation of the wave-dominated shorelines resulted in more homogeneous and laterally continuous sand bodies. From 11b to 11a, however, there is a distinct change in paleoshoreline regime from wave-dominated to tide-influenced as indicated by the common occurrence of tidal facies in 11a, including: (1) lenticular, wavy, and flaser bedding and bidirectional dipping cross strata; (2) reactivation surfaces, double-mud drapes, and ripple cross lamination with opposing dips at the toe of large dune-scale cross sets; (3) inclined heterolithic strata (IHS) and sigmoidal bedding with tidal rhythmites; and (4) cyclic vertical variation in facies and bed thickness and the common occurrence of sand-mud couplets. These tide-influenced facies show overall lower bioturbation intensity (BI 0-3). Progradation of the tide-influenced shoreline results in more heterolithic delta-front facies. Tidal and/or tidal-fluvial channels further dissect delta-front sandstones, forming more isolated sand bodies.Data from this study, as well as previous work, show that width and thickness of the forced regressive parasequences are small, typically less than 5 km and 20 m respectively. In subsurface studies, identifying and correlating such small-scale parasequences using sparse data involve significant uncertainties. A combination of the diagnostic features indicating forced regression and different data sets is essential to better constrain the geometry and architecture these small-scale bodies. 相似文献