Sediment Accommodation Research Articles

Late Quaternary sedimentation and palaeohydrology in the Acre foreland basin, SW Amazonia

Our study explores the geohydraulic history of the Acre retroarc foreland basin by gathering both spatial and temporal information from the upper 400 m of sediments. We also inquire into controls on sediment accommodation space as well as on stream vs. lacustrine domination.The Acre basin is located in south‐west Amazonia, proximal to the Serra do Divisor which demarcates the eastern edge of the Andean fold–thrust belt. Radiocarbon ages from a range of materials indicate that the upper 50–250 m of the Solimôes Formation accumulated during the past 50 000 years. Both surficial and drill‐core sediment records show lacustrine–fluvial transitions throughout the Late Quaternary. These shifts in depositional environments are in response to episodic changes in hydrological conditions as well as to geodynamic activity, such as subsidence. Juxtaposition of lacustrine and fluvial systems in the vertical Acre basin record mimics the regional‐scale trends in the modern, upper and middle Solimôes–Amazon floodplains.In the Acre basin record lacustrine successions are characterized by increasing calcium contents up‐section. This is also manifested, in the upper portions of lacustrine sequences outcropping at the surface, as alternating clastic and calcareous layers. The up‐section increase in carbonate content is related to increasing salinities brought about by drier hydrodynamic conditions. Desiccation cracks are typically infilled with gypsum as are cavities of fossils in bone‐beds. The latter represent isolated ponds in which the original fauna died as aridity intensified and waters became increasingly saline.Modern trunk river systems in the Acre basin flow from south‐west to north‐east with tributaries entering from the south‐west, suggesting the influence of a domino‐style, basement, fault regime. Fault or, at least, fracture control on stream channels is also suggested throughout the greater Amazon basin in the orthogonal dispositions and asymmetric terrace systems of trunk rivers as well as of major tributaries.

The Evolution of Allochthonous Salt Along a Megaregional Profile Across the Northern Gulf of Mexico Basin

Sequential restorations of a north-south megaregional cross section across the north-central Gulf of Mexico Basin from east-central Louisiana to the abyssal plain define a dynamic, complex history of sedimentation, salt flowage, and salt evacuation. Proprietary composite seismic profiles (590 km), 33 wells, and published depth-to-basement maps were used to constrain the section in depth. Thirteen sequential structural restorations, incorporating both decompaction and isostatic subsidence (thermal and tectonic), were then constructed from the Late Cretaceous to the Holocene. The restorations highlight and constrain a protracted history of deformation that is primarily controlled by gravity and the progradation of Cenozoic sediments over salt. Early stages of the tectonic history of the northern Gulf of Mexico Basin were related to differential thermal subsidence resulting from Early-Middle Jurassic rifting. During the Cenozoic, the evolution of the basin was dominated by the influx of large clastic depocenters, which caused the basinward evacuation of autochthonous Jurassic salt. Salt extrusion from the autochthonous layer was accomplished by inclined salt bodies, which flowed into salt glaciers or sheets near the sea floor. Evacuation of allochthonous salt layers provided significant sediment accommodation, and unusually thick sedimentary sections were deposited, such as the Terrebonne Trough of southern Louisiana (3-7 km of Miocene strata). Salt sheet formation and evacuation occurred progressively basinward through time in response to basinward shifts of major Cenozoic sedimentary depocenters. As a salt sheet neared complete evacuation, the underlying autochthonous salt layer would begin to evacuate, providing additional sediment accommodation that caused autochthonous salt flowage basinward, and the formation of the next allochthonous salt sheet basinward of the depocenter. The area of autochthonous salt progressively decreased through time and currently represents at most 45% of its maximum along this transect. The total area of salt through time was more stable, with variations of only 30% from its maximum. This relationship is a function of lateral salt flow into and out of the plane of section, and possible salt dissolution. The restorations indicate that very little translation or extension (1.46%) occurred at the autochthonous salt level during the evolution of the basin. The majority of translation or extension occurred above allochthonous salt sheets (25%) and was compensated laterally by salt flow. Displacements above allochthonous salt sheets were driven by gravitational instabilities caused by the slope gradient.

Abstract: Variation in Sediment Supply and accommodation in Sedimentary Basins: Implications for Sequence Development

Abstract: Variation in Sediment Supply and accommodation in Sedimentary Basins: Implications for Sequence Development

Abstract: Eustatically-Driven, Mississippi River Holocene Delta-Switching as Part of Global Highstand Process

ABSTRACT Climatic and sea level oscillations (of approximately one meter range and millennial periodicity) that influence delta-switching are documented, especially for northern temperate latitudes. Proxies for climate include 14C fluxes, elevation of tree lines and archeological positions of seaports. Occurrence of the Little Ice Age, beginning in the early 1300s, is documented by historical records and by the commencement of the Belize Delta. A complex of synergistic processes combine to create the existent Holocene sedimentation patterns. The processes include climate, rate and type of sediment inputs, sea level position, sediment accommodation space, whether the continental margin is active or passive, oceanographic western boundary intensification occurrence and its impact on local meteorology and influence on vegetation and rates of weathering, and along which atmospheric cells (Hadley, Ferrel, or Polar) deposition is/has occurred. These ten inputs can impact Holocene transgressive and highstand deposition. The intensity of these inputs varies with the strength of the climatic cycle, be it fifth order (~103 year), sixth order (~102 year and multiples thereof), and seventh order (~101 year and multiples thereof) oscillations. Each oscillation has impact on the erosion, transportation and deposition continuum. The main objectives of this study include input description and quantification, as ranges, and delineation of process equations. The inputs provided by historical data such as river flow, rainfall, temperature and sea level change yield a basis for extrapolating to prehistoric times. A Holocene description applies to similar highstand phases of the Pliocene-Pleistocene.

Abstract :Principles of Shoreline Migration: the Interplay between Sediment Supply and Accommodation Space

Abstract :Principles of Shoreline Migration: the Interplay between Sediment Supply and Accommodation Space

Abstract :Sediment Accommodation Regions: Fragmentation of a Subsiding Shelf

Abstract :Sediment Accommodation Regions: Fragmentation of a Subsiding Shelf

Tectonic variation in the Dniepr-Donets Basin from automated modelling of backstripped subsidence curves

The multiphase rift evolution of the Dniepr-Donets (DD) Basin is analysed by 1D backstripping and tectonic modelling of 66 stratigraphic sections, mostly from well data, distributed throughout the basin. The backstripping results illustrate strong temporal and lateral variations in tectonic subsidence. It is minor during an ‘inceptive’ pre-rift phase (Givetian-early Frasnian; 380.8-370 Ma) and does not show clear spatial correlations within the DD Basin framework. The main rift phase (Frasnian-Famennian; 370-362.5 Ma) corresponds to an acceleration in subsidence rates with tectonic subsidence up to 1500 m along the basin axis, displaying a slight increase from the northwest to the southeast. Strong lateral variations perpendicular to the basin axis reflect the effects of major basin border faults. A rift phase in the Visean (345-340 Ma) is characterised by relatively minor subsidence (up to about 500 m, except for some wells in the southeast), following a stage of extremely low rates of deposition in the earliest Carboniferous. The end of this rift phase can be taken to mark the onset of convex subsidence patterns in the later Carboniferous and Permian, typical in shape of post-rift thermal subsidence, but significantly increasing in magnitude from northwest to southeast in the basin. This trend shows no one-to-one relationship with Late Devonian syn-rift subsidence. The tectonic subsidence curves have been modelled using lithospheric stretching assumptions allowing different stretching factors for the crustal and sub-crustal lithosphere and the incorporation of finite and multiple stretching phases. A numerical technique was developed that automatically finds best fit stretching parameters for part or all of the tectonic subsidence data, given the specification of onset and duration of the various rifting events. Maps of the 1D modelling results display intrabasinal variations in terms of timing and magnitude of rifting. The results indicate that the observed spatial and temporal variations of tectonic subsidence in the DD Basin, specifically the increasing ratio of Carboniferous to Late Devonian subsidence from northwest to southeast, cannot be explained by either a uniform or depth-dependent stretching model adopting only a single Frasnian-Famennian rift phase. A two-phase model, in which a significant part of Carboniferous tectonic subsidence is related to Visean rift activity, strongly dominated by sub-crustal lithospheric attenuation, provides a satisfactory fit to the data although the tectonic implications of such a model are not easily reconcilable by independent constraints. A semi-quantitative investigation of the possible role of withdrawal of underlying Devonian salt during the Carboniferous to produce additional post-Devonian rift phase sediment accommodation space suggests that the effects of such a mechanism could be significant but that they are unlikely to preclude the necessity of the Visean rifting event to explain the Carboniferous basin evolution.

Foreland basin systems

A foreland basin system is defined as: (a) an elongate region of potential sediment accommodation that forms on continental crust between a contractional orogenic belt and the adjacent craton, mainly in response to geodynamic processes related to subduction and the resulting peripheral or retroarc fold‐thrust belt; (b) it consists of four discrete depozones, referred to as the wedge‐top, foredeep, forebulge and back‐bulge depozones – which of these depozones a sediment particle occupies depends on its location at the time of deposition, rather than its ultimate geometric relationship with the thrust belt; (c) the longitudinal dimension of the foreland basin system is roughly equal to the length of the fold‐thrust belt, and does not include sediment that spills into remnant ocean basins or continental rifts (impactogens).The wedge‐top depozone is the mass of sediment that accumulates on top of the frontal part of the orogenic wedge, including ‘piggyback’ and ‘thrust top’ basins. Wedge‐top sediment tapers toward the hinterland and is characterized by extreme coarseness, numerous tectonic unconformities and progressive deformation. The foredeep depozone consists of the sediment deposited between the structural front of the thrust belt and the proximal flank of the forebulge. This sediment typically thickens rapidly toward the front of the thrust belt, where it joins the distal end of the wedge‐top depozone. The forebulge depozone is the broad region of potential flexural uplift between the foredeep and the back‐bulge depozones. The back‐bulge depozone is the mass of sediment that accumulates in the shallow but broad zone of potential flexural subsidence cratonward of the forebulge. This more inclusive definition of a foreland basin system is more realistic than the popular conception of a foreland basin, which generally ignores large masses of sediment derived from the thrust belt that accumulate on top of the orogenic wedge and cratonward of the forebulge.The generally accepted definition of a foreland basin attributes sediment accommodation solely to flexural subsidence driven by the topographic load of the thrust belt and sediment loads in the foreland basin. Equally or more important in some foreland basin systems are the effects of subduction loads (in peripheral systems) and far‐field subsidence in response to viscous coupling between subducted slabs and mantle–wedge material beneath the outboard part of the overlying continent (in retroarc systems). Wedge‐top depozones accumulate under the competing influences of uplift due to forward propagation of the orogenic wedge and regional flexural subsidence under the load of the orogenic wedge and/or subsurface loads. Whereas most of the sediment accommodation in the foredeep depozone is a result of flexural subsidence due to topographic, sediment and subduction loads, many back‐bulge depozones contain an order of magnitude thicker sediment fill than is predicted from flexure of reasonably rigid continental lithosphere. Sediment accommodation in back‐bulge depozones may result mainly from aggradation up to an equilibrium drainage profile (in subaerial systems) or base level (in flooded systems). Forebulge depozones are commonly sites of unconformity development, condensation and stratal thinning, local fault‐controlled depocentres, and, in marine systems, carbonate platform growth.Inclusion of the wedge‐top depozone in the definition of a foreland basin system requires that stratigraphic models be geometrically parameterized as doubly tapered prisms in transverse cross‐sections, rather than the typical ‘doorstop’ wedge shape that is used in most models. For the same reason, sequence stratigraphic models of foreland basin systems need to admit the possible development of type I unconformities on the proximal side of the system. The oft‐ignored forebulge and back‐bulge depozones contain abundant information about tectonic processes that occur on the scales of orogenic belt and subduction system.

Implied basement-tectonic control on deposition of Lower Carboniferous carbonate ramp, southern Cordillera, Canada

cambrian (Kanasevich et al., 1969) and preThe Mount Head embayment is a regional downwarp along the west coast of Lower Middle Devonian (Norris and Price, 1966; Carboniferous western Canada that developed by differential subsidence, which we recog- Benvenuto and Price, 1979). nize from lithostratigraphic and biostratigraphic patterns. Palinspastic restoration of the Mount Head embayment illustrates that subsidence domains are geometrically coincident with previously identified tectonic elements of the autochthonous basement. Thus, it ap- METHODS pears that basement-tectonic elements controlled sediment accommodation and accumu- Geologic observations were recorded on lation within the Mount Head embayment. The overall shape of this embayment is probably palinspastically restored maps and cross setinherited from the arcuate shape of the Late Proterozoic cratonic rift margin. Within the tions and to basement-tectonic Mount Head embayment, several northeast-southwest-trending Archean and Proterozoic domains defined on aeromagnetic and gravbasement-tectonic elements intersect the autochthonous cratonic margin at high angles. ity maps (Brandley, 1993). The palinspastic Carboniferous piano-key-like structural reactivation of these tectonic elements produced base map is modified from Gibson,s (1985) oriented trends of differential subsidence that partitioned the Mount Head embayment into map of displacement vectors for Jurassic two subbasins (Crowsnest and Kananaskis depocenters) separated by a more positive area rocks. The magnitudes of the vectors were (Highwood high). Moreover, our data imply that Precambrian basement structure noted by others under the Plains and Rocky Mountain fold and thrust belt continued across the altered to reflect displacements at the MisRocky Mountain trench to the west, and that tectonic control on sedimentation noted by sissippian level documented by Bally et al. others for Precambrian and pre-Middle Devonian rocks extends clearly into overlying (1966), Price (1981), and Price and Fermor Carboniferous deposits. (1985), university theses, and Geological Survey of Canada maps and sections across

Depositional setting and sequence stratigraphic implications of the Upper Sinemurian (Lower Jurassic) sandstone interval, North Celtic Sea/St George’s Channel Basins, offshore Ireland

Abstract The Upper Sinemurian sandstone is a primary reservoir target in the North Celtic Sea/St George’s Channel Basins. Based on core examination, analysis of gamma ray logs, and interpretation of possible sandbody geometry from well log correlations and seismic character, a marine shelf depositional setting has been interpreted for the Upper Sinemurian sandstone on the northern margin of the North Celtic Sea/St George’s Channel Basins. Burrows observed in the cored interval are typical for a marine shelf depositional setting. Wavy, low-angle cross-bedding, reactivation surfaces and truncated cross-bedding suggest deposition by storm-driven, surging geostrophic currents in this setting. Examination of gamma ray logs through the Upper Sinemurian sandstone indicates that it coarsens and cleans upwards and can be divided into at least three units based on changes in curve patterns. Similar log patterns and sedimentary structure sequences in core and outcrop have been observed in elongate single and coalescing shelf ridges in the Ordovician of the eastern Williston Basin in Canada and the USA, in the Cretaceous of Wyoming and Colorado, and the Middle and Upper Jurassic of the North Sea. As will be discussed, the shelf ridge interpretation for some of these examples is controversial, with some workers suggesting an alternative incised shoreface interpretation. These examples range in thickness from 10 to 130m (33 to 425 ft). The 60+m (200+ ft) thickness of the Upper Sinemurian sandstone is well within this range. Such thicknesses suggest that ridge development (sand supply) kept up with basin subsidence. Thus, based on core data, gamma ray log curve examination, and comparisons to other sub-surface and surface examples, the Upper Sinemurian sandstone is interpreted as a series of complex elongate single and coalescing shelf sand ridges. Interpretation of recently acquired seismic data and sequence stratigraphic analysis of the Lower and Middle Jurassic section indicates that the Upper Sinemurian sandstone is part of a series of stacked sequences. These sequences result from increases in sediment accommodation space due to episodes of basin subsidence and their corresponding relative sea-level rises. Six sequences or cycles can be recognized, with each consisting of a basal onlapping, open marine phase which shoals upwards to shallow marine limestone or sandstone. Onlap occurs at and above a marine flooding surface (or its basinward sediment starvation equivalent) and proceeds towards the northern flexural margin of the basin. The next marine flooding surface is cut into or is in conformable contact with the top of the underlying sequence. The upper part of the sequence has a progradational to slightly aggradational seismic character, which results in an overall parallel seismic signature. The best potential Lower/Middle Jurassic clastic reservoir development in the North Celtic Sea/St George’s Channel Basins, such as the Upper Sinemurian sandstone, corresponds to the last phase of progradation at the top of a sequence. Six such sequences, with their upper boundaries at the tops of the Lower Sinemurian sandstone, Upper Sinemurian sandstone, Pliensbachian limestone, Toarcian marker, Bajocian sandstone/limestone and Bathonian limestone, respectively, can be delineated in the Lower and Middle Jurassic section in the North Celtic Sea/St George’s Channel Basins. The Lower and Middle Jurassic was largely a time of thermal subsidence in the North Celtic Sea and St George’s Channel Basins. Early thermal subsidence was interrupted by events of post-rift footwall readjustment along the northern margin of both basins. This resulted in the input of clastic sediments into both basins and deposition of Lower and Upper Sinemurian sandstones in rapidly coarsening-upward cycles and sequences. In contrast, Pliensbachian to Bathonian sequences represent deposition in a period dominated by thermal subsidence and thus coarsen upwards more gradually. With the exception of basin margin uplift and basin centre subsidence influenced by intraplate stresses, extrabasinal effects, such as eustasy, are not thought to be a factor in Upper Sinemurian sandstone deposition and Lower and Middle Jurassic sequence development in the North Celtic Sea and St. George’s Channel Basins.

A new angle on the tectonic evolution of the Ridge basin, a "strike-slip" basin in southern California

Research Article| October 01, 1993 A new angle on the tectonic evolution of the Ridge basin, a "strike-slip" basin in southern California STEVEN R. MAY; STEVEN R. MAY 1Exxon Production Research Co., Houston, Texas 77252-2189 Search for other works by this author on: GSW Google Scholar KENNETH D. EHMAN; KENNETH D. EHMAN 1Exxon Production Research Co., Houston, Texas 77252-2189 Search for other works by this author on: GSW Google Scholar GARY G. GRAY; GARY G. GRAY 1Exxon Production Research Co., Houston, Texas 77252-2189 Search for other works by this author on: GSW Google Scholar JOHN C. CROWELL JOHN C. CROWELL 2Institute for Crustal Studies, University of California, Santa Barbara, California 93106-1100 Search for other works by this author on: GSW Google Scholar Author and Article Information STEVEN R. MAY 1Exxon Production Research Co., Houston, Texas 77252-2189 KENNETH D. EHMAN 1Exxon Production Research Co., Houston, Texas 77252-2189 GARY G. GRAY 1Exxon Production Research Co., Houston, Texas 77252-2189 JOHN C. CROWELL 2Institute for Crustal Studies, University of California, Santa Barbara, California 93106-1100 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1993) 105 (10): 1357–1372. https://doi.org/10.1130/0016-7606(1993)105<1357:ANAOTT>2.3.CO;2 Article history First Online: 01 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 STEVEN R. MAY, KENNETH D. EHMAN, GARY G. GRAY, JOHN C. CROWELL; A new angle on the tectonic evolution of the Ridge basin, a "strike-slip" basin in southern California. GSA Bulletin 1993;; 105 (10): 1357–1372. doi: https://doi.org/10.1130/0016-7606(1993)105<1357:ANAOTT>2.3.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 SocietyGSA Bulletin Search Advanced Search Abstract The Ridge basin, located in southern California between the San Andreas and San Gabriel faults, contains as much as 14 km of Mio-Pliocene marine and nonmarine sedimentary fill. These strata are exposed as a northwest-dipping homoclinal sequence that becomes increasingly younger to the northwest. Pliocene to Holocene deformation, uplift, and dissection of this basin provide an opportunity to study stratal geometry and sedimentary facies in what is commonly cited as a classic "strike-slip" basin. Newly acquired seismic data from the northern Ridge basin provide new evidence for the subsurface basin geometry. These data lead us to conclude that the principal northern strand of the San Gabriel fault is a listric, east-southeast-dipping, oblique-slip fault rather than a subvertical, strike-slip fault.The principal San Gabriel fault appears to become subhorizontal at the southeastern end of the seismic line at a present-day sub-surface depth of ∼4 km. This interpretation is consistent with preliminary two-dimensional gravity models across the basin and with the homoclinal structure of basin fill. Subsidence within the Ridge basin is explained as the result of northwest- southeast extension locally accommodated along the listric, right-lateral San Gabriel and associated late Miocene strike-slip faults. As a consequence of oblique normal slip on the gently dipping San Gabriel fault, sedimentary strata were continuously tilted and moved southeastward in the hanging wall away from the depocenter. This mechanism of basin formation allowed 14 km of sediment to accumulate without deep burial. The geometry and displacement history of the San Gabriel fault controlled sediment accommodation and resultant stratal geometries within the basin. Slip along the San Gabriel fault and associated subsidence of the Ridge basin correspond temporally with regional tectonic events in southern California, reflecting both changes in the relative motion of Pacific and North American plates and the evolution of strain partitioning across this plate boundary. 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.

Variability of the sequence stratigraphic model: effects of local basin factors

The basic parameters that control stratal architecture in depositional sequences are sediment flux, rate of change of sediment accommodation (i.e., eustasy and sea-floor subsidence/uplift) and physiography. Of these parameters, only the eustatic component associated with the generation of sediment accommodation is globally significant. Consequently, local factors within a particular basin can play a relatively dominant role, vis-à-vis eustasy, in determining the internal organization of depositional sequences. In general, eustasy and sea-floor subsidence/ uplift determine the timing of sequence bounding surfaces, whereas sediment flux and physiography are most effective in determining the stratal architecture between those bounding surfaces. Basin physiography exerts an important control on the internal organization of sequences by determining, for example, whether deep-water turbidite systems will be a major part of the lowstand systems tract and whether or not fluvial incision will occur. On ramp-type basin margins with low shelf gradients, little or no fluvial incision and no deep-water turbidite deposition will occur. Lowstand deposits in this setting will consist of shoreline sands scattered at many locations within the basin. If, however, relative sea-level fall exposes a shelf/slope break, deeper fluvial incision as well as deep-water turbidite deposition will be likely. Basin physiography also plays an important role in the stratal architecture of the transgressive systems tract. The relatively deeper water setting that lies just seaward of the last clinoform of the underlying progradational wedge is the site of a depositional unit referred to herein as the “healing phase”. These early transgressive systems tract deposits commonly are relatively sand-poor and are derived primarily from eroded delta plain/coastal plain sediments. The role of sediment supply varying as an indirect response to relative sea-level change can be significant in deep water environments. Within lowstand systems tracts that form in physiographic settings characterized by discrete shelf/slope breaks, the stratigraphic expression of depositional units that accumulate in deep-water settings primarily will be a function of sand/mud ratio of sediments supplied, as well as the physiography of the slope and basin. Commonly, the highest sand/mud ratio delivered to the deep water occurs early within the lowstand systems tract. This results in stratigraphic successions that typically grade from relatively widespread tabular-bedded sand-rich turbidite deposits early within the lowstand systems tract, to confined flow leveed-channel turbidite deposits late within the lowstand systems tract when the incoming sand/mud ratio is lower.

Geohistory Analysis and Petroleum Reservoir Characteristics of Lower Cretaceous (Neocomian) Sandstones, Eastern Kopet-Dagh Basin, Northeastern Iran (1)

The eastern part of the Kopet-Dagh basin of northeastern Iran contains over 4000 m of Upper Jurassic through Tertiary strata deposited in a variety of shallow-marine and terrestrial environments. Geohistory diagrams from well and outcrop data provide a useful mechanism with which to relate the stratigraphic framework of this part of the basin to the tectonic history of the region. During some episodes of regional tectonic uplift (e.g., episodes occurring 99-95 Ma, 74-70 Ma, and 63-54 Ma), sediment accommodation space continued to be created in the basin due to sediment loading and compaction of increased amounts of fine-grained sediments, in some cases concomitant with eustatic sea level rises. Much of the post-Jurassic subsidence in this part of the Kopet-Dagh basin was aused by sediment loading rather than tectonism. The effects of basin geohistory on petroleum reservoir properties were studied using the Lower Cretaceous (Neocomian) Shurijeh Formation as an example. Detailed petrologic, sedimentologic, and geohistory analyses done on this formation show that the petroleum reservoir properties of Shurijeh sandstones were affected by their depositional settings and the subsequent subsidence of these units through meteoric and compactional hydrogeologic regimes in this part of the Kopet-Dagh basin. These rocks consist mostly of sublitharenitic red beds deposited during a regressive phase of sedimentation dominated by rapid siliciclastic sediment supply. The lower and middle parts of the interval studied were deposited in low-sinuosity braided fluvial systems, and the upper part was deposited in high- inuosity meandering systems. By relating the paragenetic sequence of the Shurijeh sandstones to the geohistory of this formation, we determined the timing of both porosity-destroying and porosity-enhancing diagenetic processes and related these processes to the timing of petroleum generation.

Loading, Subsidence, and Basin Geometry Effects on Foreland Basin Sequences, Middle Turonian through Coniacian Strata, Central Utah: ABSTRACT

Stratigraphic architecture is controlled by the interaction of eustasy, tectonic subsidence, and sediment supply. These factors determine changes in base level, which controls the space created or removed to accommodate sediment. Because tectonic subsidence defines basin geometry, it is a first-order control on the geometry of sediment accommodation space. Consequently, the stratigraphic architecture of depositional sequences should exhibit geometric variations that reflect changing basin geometries. In central Utah volcanic ash beds in middle Turouian through Coniacian strata (4 Ma) were correlated 130 km basinward from the thrust front. Stratigraphic architecture, specifically changes in a hierarchy of depositional sequences, systems tracts, facies associations, sediment volumes, and bounding surfaces were characterized. Conformable sequences along thrust margins are correlated to unconformity bounded sequences basinward of the foredeep axis because subsidence rates are higher along thrust margins. This configuration is opposite that of unconformity bounded sequences in passive margins and is attributed to geometric changes of sediment accommodation space. In central Utah the Tibbet Canyon and Ferron depositional sequences have the following attributes: (1) bounding unconformities are best developed basinward (low subsidence) and grade to conformity within the foredeep and (2) strata in the lowstand and transgressive systems tracts are a landward-thickening wedge. Themore » basal Tibbet Canyon sequence boundary is defined by a basinward shift in the coarsest lithofacies represented by a thin basinward thickening wedge of pebbly sandstone containing C. woolgari. This ammonite zone rests upon a regional unconformity present throughout the Rocky Mountains. The basal Ferron sequence boundary is also defined by a basinward shift in lithofacies.« less