[PDF] Internal Facies Architecture Of A Regressive To Transgressive Wave Dominated Delta In The Upper Cretaceous Eagle Formation South Central Montana eBook

Author : Eleanor Spangler
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Page : 125 pages
File Size : 13,76 MB
Release : 2012
Category : Electronic dissertations
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The Santonian-Campanian Eagle Formation in south-central Montana was deposited along the western margin of the Cretaceous Western Interior Seaway and is composed of a series of well preserved regressive and transgressive deposits. This study documents the depositional evolution of the informal lower member of the Eagle Formation exposed near Billings, MT. Detailed mapping and characterization of the internal stratigraphy, facies architecture, and bounding surfaces of the lower Eagle provide the basis for reconstruction of a paleodelta system that serves as a valuable reservoir analog within the Cretaceous Seaway and elsewhere. This study demonstrates that the informal lower member of the Eagle Formation in south-central Montana was deposited in a regressive to transgressive wave-dominated deltaic system. Within this deltaic succession the identification of five facies and four bounding surface types are used to establish a two-phase depositional history: 1) a regressive phase characterized by prograding pro-delta to distal delta front deposits emplaced below fair weather wave base but above storm wave base; and 2) a transgressive phase characterized by landward dipping proximal to distal shoal overwash fan deposits derived from combined-flow storm-generated turbidity currents. A maximum regressive surface (MRS) separates underlying prograding deltaic deposits from downlapping shoal overwash fan deposits above. Shoal overwash fan packages dip and stack en-echelon towards the paleoshoreline indicating landward migration of the shoal during delta transgression. A time-transgressive ravinement surface (TRS) developed on the basinward side of the transgressive shoal and migrated landward with the shoreline, truncating of shoal overwash fan deposits.

Author : Neal Auchter
Publisher :
Page : 129 pages
File Size : 30,16 MB
Release : 2012
Category : Electronic dissertations
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The Santonian-Campanian Eagle Formation in south-central Montana is composed of a series of exceptionally well preserved regressive-transgressive cycles deposited on the western margin of the Cretaceous Interior Seaway. This study focuses on the genesis of a regionally correlative basal incision surface and the subsequent fill architecture of the informal middle member of the Eagle Formation. Three stratigraphic surfaces are traced continuously for up to 15 km and include the regressive surface of marine erosion (RSE), sequence boundary (SB), and transgressive surface of tidal-fluvial erosion (TSE). Within this sequence stratigraphic framework, 4 facies association, internal lower-order architectures (i.e. channel forms, lateral accretion sets, crevasse splays) and higher-order regional surfaces (i.e. sequence boundaries) are used to establish a three-phase depositional history of valley evolution: 1) fluvial incision during decreasing accommodation concomitant with fluvial deposition and sediment storage on abandoned terraces within the valley, 2) rapid increase in accommodation significantly outpaced sediment influx concurrent with seasonal fluctuations in fluvial discharge and landward migration of the turbidity maximum, producing a flood-dominated mud-rich central valley deposit, and 3) deceleration in the rate of relative sea level rise marked by a depositional shift to tidally influenced fluvial deposition, extensive valley widening, and coal development. The resulting valley architecture is a highly diachronous composite basal incision surface. The time-transgressive multi-phase nature of valley formation and infilling produced a fill profile with a mud-rich valley center flanked by stacked, sand-rich fluvial and tidal-fluvial deposits toward the valley margins. These findings contribute to the sequence stratigraphic interpretation of incised valleys along the Late Cretaceous Western Interior Seaway, serve as an outcrop analog for potential incised valley reservoirs, and have direct application in developing reservoir models for the Eagle Formation in south-central Montana and elsewhere.

Author : Ryan Lee Harbor
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Page : 0 pages
File Size : 13,4 MB
Release : 2011
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The Eagle Ford is a well-known source rock for both sandstone (Woodbine) and carbonate (Austin and Buda) hydrocarbon reservoirs in East and South Texas. Recent discoveries have demonstrated that source rocks, such as the Eagle Ford, are capable of producing significant volumes of gas and oil. At the same time, variations in well producibility indicate that these rocks, like conventional reservoirs, display considerable geological heterogeneity. Yet, only limited research has been published on the subsurface stratigraphy and character of Eagle Ford facies. Understanding the types, controls, and distribution of these heterogeneities requires in-depth rock-based studies. In order to characterize Eagle Ford facies, 27 cores from 13 counties were investigated for rock textures, fabrics, sedimentary structures, and fossil assemblages. These studies were supported by light and electron microscopy as well as analysis of elemental chemistry and mineralogy. Regional subsurface stratigraphic correlations and facies distributions were defined using wireline logs calibrated from core studies. In South Texas, the Eagle Ford Formation was deposited during a second-order transgressive/regressive cycle on the flooded, oxygen-restricted Comanche Shelf. Nine depositional facies consisting predominately of organic-rich, fine-grained (5.0 % TOC) to coarser-grained (3.05 % TOC) fabrics were identified. Facies developed in low-energy environments episodically interrupted by higher-energy, event sedimentation (current winnowing, cohesive and non-cohesive density flows, and turbidity flows). Locally, these rocks show evidence of early diagenetic recrystallization of calcite. Concurrent water anoxia and organic matter preservation persisted locally into later Austin deposition, resulting in formation of a three-fold division of the Cenomanian-Coniacian Eagle Ford Formation. Common facies of lower and upper Eagle Ford members include (1) unlaminated, fissile, clay- and silica-rich, organic-rich mudrocks, (2) laminated, calcareous, organic-rich mudrocks, and (3) laminated, foraminifera- and peloid-rich, organic-rich packstones. The transitional Eagle Ford member consists of highly-cyclic (1) ripple-laminated, organic-rich wackestone (cycle base) and (2) burrowed, organic-lean lime wackestones (cycle top). Transitional Eagle Ford facies developed in oxygen-restricted, basinal depositional environments as distal equivalents to burrowed, foraminiferal lime wackestones of the Austin Formation. Facies complexities in the Eagle Ford stem from complicated and interrelated processes of sediment production and distribution, diagenesis, and water column chemistry. Integrated core studies shed light on both controls of facies formation and their spatial distribution. These findings provide a framework for upscaling the fine-scale, heterogeneous character of shelfal Eagle Ford mudrocks; thus allowing development of predictive models into the distribution of key reservoir properties in the subsurface.

Author : Michael Douglas Fairbanks
Publisher :
Page : 119 pages
File Size : 36,25 MB
Release : 2012
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Heightened industry focus on the Upper Cretaceous (Cenomanian-Turonian) Eagle Ford has resulted from recent discoveries of producible unconventional petroleum resource in this emerging play. However, little has been published on the facies and facies variabilities within this mixed carbonate-clastic mudrock system. This rock-based study is fundamental to understanding the controls, types, and scales of inherent facies variabilities, which have implications for enhanced comprehension of the Eagle Ford and other mixed carbonate-clastic mudrock systems worldwide. This study utilizes 8 cores and 2 outcrops with a total interval equaling 480 feet and is enhanced by synthesis of thin section, XRD, XRF, isotope, rock eval/TOC, and wireline log data. Central Texas Eagle Ford facies include 1) massive argillaceous mudrock, 2) massive argillaceous foraminiferal mudrock, 3) laminated argillaceous foraminiferal mudrock, 4) laminated foraminiferal wackestone, 5) cross-laminated foraminiferal packstone/grainstone, 6) massive bentonitic claystone, and 7) nodular foraminiferal packstone/grainstone. High degrees of facies variability are observed even at small scales (50 ft) within the Eagle Ford system and are characterized by pinching and swelling of units, lateral facies changes, truncations, and locally restricted units. Facies variability is attributed to erosional scouring, productivity blooms, bottom current reworking, and bioturbation. At the 10-mile well spacing scale and greater, the data significantly overestimates intra-formational facies continuity but is successful in defining the following four-fold stratigraphy: The basal Pepper Shale is an argillaceous, moderate TOC, high CGR and GR mudrock. The Waller Member is a newly designated name used in this study for an argillaceous and foraminiferal, high TOC, massive mudrock with a generally moderate CGR and GR profile. The Bouldin Member is a high energy, carbonate-rich (foraminiferal), low TOC, low and variable CGR but high GR zone. Finally, the South Bosque Formation is an argillaceous and foraminiferal, moderate TOC, massive and laminated mudrock with a moderate CGR and GR signature. GR logs alone are inadequate for determination of facies, TOC content, depositional environment, and sequence stratigraphic implications. Using integrated lithologic, isotopic, and wireline log data, cored wells in the study area are correlated across the San Marcos Arch. Geochemical proxies (enrichment in Mo, Mn, U, and V/Cr) indicate that maximum basin restriction occurred during deposition of the Bouldin Member. Bottom current activity influenced depositional processes and carbonate sediment input was driven by water column productivity. These primary controls on Eagle Ford stratigraphy and character are independent from eustatic fluctuation, rendering classical sequence stratigraphy unreliable.

Author : Cindy Diane Hansen
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Page : 374 pages
File Size : 25,47 MB
Release : 2007
Category : Deltas
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The Campanian basal Belly River Formation (Cycle G) of central Alberta is differentiated into two mappable facies associations (FA1 and FA2). FA1 comprises uniformly coarsening-upward successions with abundant wave- and storm-generated physical structures. FA2 forms variable and markedly heterolithic coarsening-upwards successions, dominated by current-generated structures, normal grading, convolute bedding, structureless siltstones, claystone drapes, and syneresis cracks. Both facies associations yield sporadically distributed trace fossil suites, attributable to stressed expressions of the Cruziana Ichnofacies. FA1 contains moderate-abundance and moderate-diversity ichnological suites, whereas FA2 displays low-abundance, and typically very low-diversity suites comprising predominantly facies-crossing deposit-feeding structures. Cycle G constitutes an ancient example of a prograding mixed river/wave-influenced asymmetric delta lobe. FA1 records conditions operating uplift of distributary channel discharge. FA2 corresponds to deposition downdrift of active distributaries, and displays fluvially dominated characteristics. The introduction of facies characteristics indicative of physico-chemical stresses highlights distributary channel proximity, facilitating their delineation in the subsurface.

Author : Michael Dale Sturdy
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Page : pages
File Size : 29,6 MB
Release : 2006
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The facies architecture and geometry of stratigraphic surfaces within a lignite bearing interval of the Paleocene upper Calvert Bluff Formation is mapped on a photomosaic of the 150 ft (50 m) high and 12,000 ft (4km) long "C" area highwall of Big Brown Mine, near Fairfield, Texas. Observed bedding and facies architecture are interpreted in terms of temporal changes, depositional environments and sequence stratigraphic setting. A three dimensional grid of 89 subsurface logs is correlated to this photomosaic to characterize log response patterns of facies. Six facies are observed: 1) lignite, 2) interdistributary bay mud, 3) prograding delta, 4) delta top mud, 5)distributary channels, and 6) incised valley fill. The six facies were defined by a combination of mapped photomosaic observations and subsurface log correlations. The lignite deposit formed in a low depositional energy, low sediment input, high-organic productivity interchannel basin. Overlying mud records overbank flooding followed by avulsion and progradation of delta deposits. Tidal-flat deposits overlying prograding delta deposits record fluctuating energy conditions on the emerging delta top. Channel deposits cutting into the delta top record lateral channel migration across delta top floodplains. These regressive delta deposits are capped by a local incised sequence boundary overlain by fluvial channel deposits inferred to have allowed sediment to bypass further basinward during lowstand. A sheet of channel deposits capping this highwall exposure records more recent erosion, followed by development of modern soil horizons. The Big Brown Mine highwall exposes a relatively complete high-frequency Paleocene stratigraphic sequence developed in an area landward of the shoreline positionduring maximum transgression, that progresses upsection from: 1) highstand alluvial flood basin coals, 2) a thin condensed maximum flooding interdistributary shale, 3) a thick succession of regressive deltaic strata, and 4) a high-relief, sequence-bounding erosion surface overlain by a lowstand to transgressive fill of channel deposits. Correlations with regional Wilcox Group stratigraphic studies spanning coeval shoreline and shelf strata indicate that this high-frequency sequence is within the transgressive systems tract of a 3rd order stratigraphic sequence. It appears that high-frequency sequences of sub-regional extent control the complex distribution of coal seams within central Texas.

Author : Yangyang Li
Publisher :
Page : pages
File Size : 42,13 MB
Release : 2012
Category : Sedimentology and stratigraphy
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This dissertation is focused on analysing architectural elements to understand the formative processes in linked fluvial and deltaic depositional systems in an ancient system. A compound incised valley system (IVS) and distributary channel and crevasse delta system are documented in successively more distal positions within outcrops of the Cretaceous Ferron Notom Delta in central Utah. The compound IVS is composed of three simple IVS systems, IVS3, IVS2 and IVS1 (oldest to youngest). IVS3 consists of tidally influenced deposits that form a terrace cut into lower shoreface deposits. IVS2 consists of multi-storey fluvial deposits with minor tidally influenced fluvial deposits in the upper 10%. IVS1 consists entirely of medium-grained fluvial deposits. The composite valley fill records generally increasing fluvial-dominance and decreasing tide-influence during successive cut-and-fill episodes associated with each simple valley fill. These changes are interpreted to correlate with a longer term, stepped relative fall of sea level, punctuated by stillstands, or minor rises of sea level. A lower delta-plain distributary channel system is mapped in 3-D outcrop exposures in Parasequence 5a, Sequence 2. A main channel belt about 250 m wide narrows to 200 m downstream of the branching point. The subordinate channel belt is 80 m wide. Water discharge from the main distributary channel, upstream of the branching point, is estimated to be 85-170 m3/s. Compared to paleodischarge of trunk rivers mapped in previous studies in the Notom Delta, the branching is estimated to be a 4th order split. A crevasse delta that prograded toward the west is mapped in Parasequence 6a Sequence 2, while the regional delta prograded toward the east. The crevasse delta was protected from marine influence by a wave-dominated barrier system. The proximal delta-front facies consists of planar beds which pass upward into meter-scale low-angle cross beds, which decrease in dimensions upward and finally change to decimeter-scale cross beds. Planar-stratified sandstones are interpreted to be deposited in an inertia-dominated environment and cross-stratified sandstones are interpreted to be deposits in a friction-dominated environment. The upward decrease of cross set dimensions is mainly due to the filling of accommodation and shallowing of the water.