Tyee Basin Research Articles

Stages of sedimentary prism development on a convergent margin — Eocene Tyee Forearc Basin, Coast Range, Oregon, USA

Architecture of ancient forearc basin successions can be difficult to reconstruct because of the widespread syn-depositional and post-depositional deformations experienced by many forearc basin-fills. For this reason various techniques have been used for reconstructing forearc basin-infill geometry, including geochemical correlation. The Tyee Basin succession exposed in Coast Range of Western Oregon, USA, is an Eocene forearc-fill that includes genetically related non-marine, shallow marine and deepwater clastic deposits and is gently deformed. Reconstruction of the depositional geometry of the Tyee Basin succession from detailed outcrop and subsurface data reveals two distinct stages of development for this active basin-margin. These stages are characterized by two different basin-margin clinoform architectures and also by a pronounced change in the character of the associated deepwater deposits. During the initial stage, the basin-margin clinoforms are smaller (<250m clinoform height) and strongly progradational, with clinoform topset dominated by fluvial deposits. At this stage thick sand-rich unconfined turbidite beds accumulated on the slope segment of the clinoforms and extended out onto the basin-floor. Large scale slope conduits such as slope channels or canyons, are notably absent in this stage. The second stage is characterized by larger clinoform height (>500m), a greater degree of topset aggradation with repeated fluvio-deltaic cycles on the shelf, and well-organized, large turbidite channels on the slope. The turbidite channels supplied medium-grained sands to the extensive, stacked basin-floor fans. The first stage described above marks the early development of a shelf-slope prism on the Tyee continental margin, and has been interpreted by some earlier workers as an unique category of basin-margin architecture, termed as a ‘submarine ramp’. However, this was only the initial stage of development of the Tyee margin and it was followed by a period of basin-filling when repeated fluvial and shallow marine shelf-transit cycles fed well-organized turbidite channels on the slope as well as Tyee Basin floor fans. The large volume of sediment deposited during the initial stage, resulted from of the unique geometry of the Tyee Basin, as influenced by the presence of pre-existing topography on the accreted oceanic basement underlying the Tyee succession.

Sequence stratigraphy and hydrocarbon potential of the southern Tyee basin, Oregon Coast Range, USA

Sequence stratigraphy and hydrocarbon potential of the southern Tyee basin, Oregon Coast Range, USA

Source rock characterization and petroleum systems of Eocene Tyee basin, southern Oregon Coast Range, USA

The hydrocarbon source rock potential of the Eocene units in the southern Oregon Coast Range was evaluated using Rock-Eval pyrolysis. Most Eocene units in southern Oregon Coast Range are thermally immature and contain lean, gas prone Type III kerogen. However, some beds (coals) are sufficiently organic rich to be sources of biogenic and thermogenic methane discovered in numerous seeps. The overall hydrocarbon source rock potential of the southern Oregon Coast Range is moderately low; however, requirements for commercial accumulations of hydrocarbon probably exist locally within and adjacent areas. Two speculative petroleum systems are proposed. The first includes the southern part of the Oregon Coast Range near the border with the Mesozoic Klamath Mountains and is related to a proposed subduction zone maturation mechanism along thrust faults. The second occurs near the eastern border of the range where maturation is related to heating by sills and migration of hydrothermal fluids associated with mid-Tertiary volcanism in the western cascade arc.

Petrography, diagenesis and provenance of Eocene Tyee Basin sandstones, southern Oregon Coast Range: New view from sequence stratigraphy

Abstract Sandstone petrography considered within a sequence stratigraphic framework provides a better understanding of the characteristics of the Eocene Tyee Basin, an accretionary and forearc sequence, southern Oregon Coast Range. Detailed comparison of the relative abundance of major framework grains documents a marked difference in the sandstone composition of each depositional sequence. Such a difference is mainly due to an abrupt change in provenance, from a local Klamath Mountains metasedimentary source to a more distant extrabasinal Idaho Batholith‐Clarno volcanic arc source. Furthermore, the composition of framework grains varies systematically from the lowstand systems tract to the highstand systems tract within a depositional sequence. This suggests that relative sea level change in the depositional basin, and tectonics in the source area, can affect the patterns of sedimentation and sandstone composition. In addition, the Eocene Tyee Basin sandstones have a down‐section distribution of authigenic minerals, consisting of early formed zeolites and late‐stage quartz, as well as a change in the abundance of smectite to mixed‐layer chlorite/smectite with increasing burial depth. The down‐section distribution of authigenic minerals is also causally linked to the compositional variation of framework grains in each depositional sequence with increasing burial temperature. Much primary porosity has been filled with these authigenic minerals, which diminishes the permeability of potential reservoir rocks. Reservoir‐quality porosities and permeabilities, however, are present locally in the basin. The development of these reservoir‐quality sandstones within the Eocene Tyee Basin sequence is due to a complex burial diagenesis, which is directly related to temporal and spatial variations in original detrital mineralogy, in sedimentation pattern, and in burial temperature in the basin.

Sandstone diagenesis, reservoir potential, and sequence stratigraphy of the Eocene Tyee Basin, Oregon

ABSTRACT Sandstone petrography and diagenetic analysis within a sequence stratigraphic framework provides a better understanding of the reservoir characteristics in the Eocene Tyee basin, an accretionary and forearc sequence, southern Oregon Coast Range. Detailed comparison of relative abundance of major detrital framework grains documents a marked difference of sandstone composition in each depositional sequence. Such a difference is mainly due to an abrupt change in provenance from a local Klamath Mountains metasedimentary source to a more distant extrabasinal Idaho Batholith-Clarno volcanic arc source. Furthermore, the composition of framework grains varies systematically from the lowstand systems tract to the highstand systems tract within a depositional sequence. This suggests that the patterns of sedimentation and sandstone composition can be affected by relative changes in sea level and tectonic uplift in the source area. In addition, the Eocene Tyee basin sandstones exhibit a down-section distribution of authigenic minerals, consisting of early-formed zeolites and late-stage quartz as well as a change in the abundance of smectite to mixed-layer chlorite/smectite with increasing burial depth. The down-section distribution of authigenic minerals is also causally linked to the compositional variation of detrital framework grains in each depositional sequence with increasing burial temperature. Much primary porosity has been filled with these authigenic minerals, thus diminishing the permeability of potential reservoir rocks. Secondary porosities and permeabilities of reservoir quality (averaging 10.80%; 2.76 md), however, are present locally in some highstand delta-front sandstone facies in the southern part of the basin as well as in lowstand turbidite sandstones in the deeper part of the basin to the north. The development of these reservoir-quality sandstones within the Eocene Tyee basin sequence is due to a complex burial diagenesis, which is directly related to temporal and spatial variations in original detrital mineralogy, in sedimentation pattern, and in burial temperature in the basin.

Sandstone Diagenesis, Reservoir Potential, and Sequence Stratigraphy of the Eocene Tyee Basin, Oregon

Sandstone Diagenesis, Reservoir Potential, and Sequence Stratigraphy of the Eocene Tyee Basin, Oregon

Abstract: Sandstone Diagenesis and Reservoir Characteristics of the Eocene Tyee basin, Southern Oregon Coast Range: Viewed from Sequence Stratigraphic Framework

Abstract: Sandstone Diagenesis and Reservoir Characteristics of the Eocene Tyee basin, Southern Oregon Coast Range: Viewed from Sequence Stratigraphic Framework

Paleoecology, Biostratigraphy, and Depositional History of Paleocene to Middle Eocene Rocks of the Tyee Basin, Western Oregon: ABSTRACT

Paleoecology, Biostratigraphy, and Depositional History of Paleocene to Middle Eocene Rocks of the Tyee Basin, Western Oregon: ABSTRACT

Fission-track analysis of sandstones from Tyee Basin, Southwestern Oregon

Fission-track analysis of sandstones from Tyee Basin, Southwestern Oregon

Sequence Stratigraphy in Active Convergent Margins: Eocene Tyee Basin, Southern Oregon Coast Range

Sequence Stratigraphy in Active Convergent Margins: Eocene Tyee Basin, Southern Oregon Coast Range

Isotopic Provenance of Sandstones from the Displaced Tyee Formation, Oregon Coast Range: ABSTRACT

A significant component of the Eocene Tyee Formation of Eocene age in the Oregon Coast Range was not derived from local source areas but appears to have come from terranes that presently lie far to the east. Traditional basin analyses, including studies of paleocurrents, lithofacies, and sandstone compositions, have generally been interpreted as indicating local derivation from the Klamath Mountains which lie to the south. However, isotopic analyses of whole-rock sandstone samples and mineral separates preclude derivation solely from the Klamath region. Sandstone samples collected throughout the Tyee basin were analyzed for Sm-Nd, Rb-Sr, K-Ar, and 18O. Whole-rock negative ^egrNd values (-7.1 to -7.3) coupled with positive ^egrSr values imply a source area underlain by Precambrian continental crust. Whole-rock Rb-Sr data fall along a trend dissimilar to data from Klamath-derived sandstones. Detrital K-feldspar has 87Sr/86Sr ratios that are too high to have been derived from plutonic rocks in the Klamaths. Consistent Rb-Sr ages for white mica from samples throughout the basin indicate a Late Jurassic age, and K-Ar ages have been uniformly reset to about 68 Ma, an overprint not recognized in the Klamath terranes. ^dgr18O values of white micas cluster around 9.5 per mil, a d are similar to values for S-type granites like those in the Idaho batholith but higher than those of normal I-type granites. Also, these values are much lower than those of white micas from metamorphic rocks in the Klamath Mountains. These data preclude the Klamath Mountains as the principal source for detritus feeding the Tyee basin. The most likely source region is the Idaho batholith. Derivation of abundant sediment from this eastern source area suggests that during deposition the Oregon Coast Range basin lay much farther east and has subsequently moved westward to its present position. Such a major displacement is consistent with the inferred tectonic rotational history that has been suggested for the Oregon Coast Range since the time of deposition of the Tyee Formation. End_of_Article - Last_Page 485------------

Lithofacies and Depositional Environments of Coaledo Formation, Coos County, Oregon: ABSTRACT

The middle to upper Eocene (Narizian) Coaledo Formation, well exposed along the southwestern Oregon coast, includes seven basic lithofacies types which constitute a complex marine-deltaic sedimentary sequence. The lithofacies are defined by lithology, fossils, bedding characteristics and sedimentary structures. Petrographic examination of Coaledo sandstones indicates a dominantly andesitic volcanic source with subordinate plutonic, metamorphic, and sedimentary sources. Paleocurrent indicators suggest that these source areas were located to the southeast, from the initial calc-alkaline vents in the southern ancestral Cascades and from the northern Klamath Mountains. Regional paleocurrent analysis also suggests open-ocean conditions to the west, offshore from a wide, swampy coastal plain. The pre-Coaledo units exposed in the Cape Arago area are interpreted to be delta foreset deposits. Coarsening-upward sequences recognized within the lower Coaledo member are interpreted as delta topset deposits, including subaqueous distributary channel, interdistributary tidal flat, lagoonal, and barrier-bar facies. The lower part of the middle member is characterized by deeper marine facies. The upper part of the middle Coaledo member represents prodelta deposition during a second progradational phase. Coarsening-upward sequences are recognized in the upper Coaledo member, again representing delta topset deposits. Uppermost Coaledo sands and overlying units show a gradual return to deeper marine conditions. Coaledo sediments unconformably ovelrie gently folded fore-arc sediments of the Tyee basin. Deposition of coal-bearing deltaic sediments far to the west of the axis of the basin suggests regional tectonic uplift along the flank of the basin, or progradational filling of the continental flank of the basin. End_of_Article - Last_Page 984------------