[PDF] Evolution And Architecture Of An Incised Valley In The Upper Cretaceous Eagle Formation In South Central Montana eBook

Author : Neal Auchter
Publisher :
Page : 129 pages
File Size : 49,63 MB
Release : 2012
Category : Electronic dissertations
ISBN :

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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 : Eleanor Spangler
Publisher :
Page : 125 pages
File Size : 34,86 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 : Edward Allen Merewether
Publisher :
Page : 104 pages
File Size : 41,53 MB
Release : 1996
Category : Geology
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A multidisciplinary approach to research studies fo sedimentary rocks and their constituents and the evolution of sedimentary basins--both ancient and modern.

Author : Casey Ryan Reid
Publisher :
Page : 142 pages
File Size : 12,21 MB
Release : 2015
Category : Geology, Stratigraphic
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The Lower Cretaceous Kootenai Formation in northwestern Montana records some of the first deposition of siliciclastic sediment into the Cordilleran foreland basin system. These rocks are also of particular interest due to their viability as reservoirs for hydrocarbons. The delineation of incised valley-fill systems within in this stratigraphic interval is of specific importance to this study as these stratigraphic entities have proven to record significant changes in base level fluctuations as well as preserving productive reservoir facies. For this study a densely spaced collection of well logs, limited core, and analogous outcrop exposures were used to investigate the Cretaceous Kootenai Formation. The specific objectives of this research are three fold: (1) construct a regional stratigraphic framework of the Kootenai Formation and immediately adjacent strata in order to reconcile lithostratigraphic and chronostratigraphic units, (2) utilize the framework to delineate the stratigraphic position and architecture of local-scale incised valley-fill systems, and (3) construct a valley-fill model that incorporates environments of deposition interpreted from the observation of lithofacies in core and analogous outcrop. The stratigraphic analysis revealed a classic non-marine to marginal marine depositional sequence (Mitchum et al., 1977) within the Kootenai Formation. A sequence boundary at the base of the depositional sequence separates highstand marine strata of the Jurassic Ellis Group from lowstand incised valley-fill strata of the basal Sunburst member of the Kootenai Formation. Within the Lower Cretaceous depositional sequence, four distinct depositional environments stack to form the lowstand, transgressive, and highstand systems tract following fluvial incision into underlying Jurassic highstand strata. The first depositional environment is remnant amalgamated fluvial channel sandstone with pebble mud-clast lags. As base level began to rise a transgressive estuarine system developed. A transgressive surface is interpreted where incised valley-fill caps the valley. A lateral shift in depositional environments led to deposition of mud and fine-grained sand interpreted to represent tidal mud flats. Finally, as the rate of base level rise slowed an alluvial plain system developed, which marked the onset of the highstand systems tract.

Author : Gary J. Hampson
Publisher : SEPM Soc for Sed Geology
Page : 493 pages
File Size : 46,71 MB
Release : 2008
Category : Science
ISBN : 1565761316

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Siliciclastic shallow-marine deposits record the interface between land and sea, and its response to a variety of forcing mechanisms: physical process regime, the internal dynamics of coastal and shelfal depositional systems, relative sea level, sediment flux, tectonic setting, and climate. These deposits have long been the subject of conceptual stratigraphic models that seek to explain the interplay between these various forcing mechanisms, and their preservation in the stratigraphic record. This volume arose from an SEPM research conference on shoreline-shelf stratigraphy that was held in Grand Junction, Colorado, on August 24-28, 2004. The aim of the resulting volume is to highlight the development over the last 15 years of the stratigraphic concepts and models that are used to interpret siliciclastic marginal-marine, shallow-marine, and shelf deposits.