Southern Oregon Coast Range Research Articles

Oligocene onset of uplift and inversion of the Cascadia forearc basin, southern Oregon Coast Range, USA

Abstract An extensive detrital zircon U-Pb data set (n = 6324 dates) from Eocene to Miocene sandstones and modern river sands establishes the onset of arc magmatism and forearc uplift along the Cascadia convergent margin in southwestern Oregon (United States). Middle to late Eocene marine strata in the Coos Bay area were primarily sourced from the Klamath Mountains and coeval Clarno-Challis volcanoes in central Oregon and/or Idaho. Ancestral Cascades arc magmatism initiated at 40 Ma and supplied sediment to a broad forearc basin in western Oregon during late Eocene time. Major reduction of Ancestral Cascades arc (40–12 Ma) and Clarno-Challis (52–40 Ma) zircon in the Tunnel Point Sandstone (ca. 33–30 Ma) records the isolation of the Coos Bay area from the Ancestral Cascades arc due to Oligocene onset of forearc uplift, basin inversion, and emergence of the southern Oregon Coast Range. The Tarheel formation (ca. 18–15 Ma) is characterized by disappearance of Ancestral Cascades arc zircon and a substantial increase in Clarno-Challis zircon recycled from underlying forearc strata. The ~15–20 m.y. delay between subduction initiation (ca. 49–46 Ma) and the onset of forearc uplift (ca. 33–30 Ma) supports insights from thermomechanical models that identify tectonic underplating and thermally activated lower-crustal flow as major drivers of deformation and uplift in active forearc regions.

DRAINAGE EVOLUTION AND FRESHWATER FISH ZOOGEOGRAPHY IN COASTAL OREGON AND WASHINGTON

In Oregon and Washington coastal streams, there are relatively diverse faunas on the Olympic Peninsula of Washington (Chehalis fauna), in the lower Columbia River, and on the south-central Oregon coast (Tyee fauna). Adjacent to the Tyee fauna are groups of streams with depauperate faunas (0–2 primary freshwater fishes). To the north, from the Nehalem River to the Alsea River, streams have 0–1 species (Oregon Coast Range Isolates), and to the south, from the Rogue River to the Klamath River, streams have 0–2 species (Klamath Isolates). Throughout the entire area there was no relationship between drainage area and freshwater fish diversity. Multiple processes are responsible for these patterns. Two endemic genera, Oregonichthys and Novumbra, originated by the Miocene (23–5.3 Mya) and current distributions are largely bordered by the continental flood-basalt flows of the Columbia River Basalt Group (CRBG). It is hypothesized that both genera were isolated by early Miocene Grande Ronde basalt flows, Oregonichthys to the south of the flows in an ancestral Umpqua River, and Novumbra to the north of the flows in an ancestral Chehalis River. The depauperate streams of the Oregon Coast Range Isolates are hypothesized to be the result of bisection of ancient coastal streams by uplift of the Oregon Coast Range and subsequent extinction of the ancestral fauna on west-slope streams either from changing habitats or stochastic events in smaller streams. The Klamath Isolate streams drain the southern Oregon Coast Range and Klamath Mountains, an ancient region otherwise known for its faunal and floral diversity. It is hypothesized that these streams, some of which are relatively large and would be expected to have relatively diverse faunas, have been isolated from diverse primary freshwater fish faunas to the north (Columbia) and south (Sacramento), and most taxa have simply never had access to these streams.

Correction of deposit ages for inherited ages of charcoal: implications for sediment dynamics inferred from random sampling of deposits on headwater valley floors

Inherited age is defined herein as the difference between times of carbon fixation in a material and deposition of that material within sediments from which it is eventually sampled in order to estimate deposit age via radiocarbon dating. Inheritance generally leads to over-estimation of the age by an unknown amount and therefore represents unquantified bias and uncertainty that could potentially lead to erroneous inferences. Inherited ages in charcoal are likely to be larger, and therefore detectable relative to analytic error, where forests are dominated by longer-lived trees, material is stored for longer periods upslope, and downstream post-fire delivery of that material is dominated by mass movements, such as in the near-coastal mountains of northwestern North America. Inherited age distribution functions were estimated from radiocarbon dating of 126 charcoal pieces from 14 stream-bank exposures of debris-flow deposits, fluvial fines, and fluvial gravels along a headwater stream in the southern Oregon Coast Range, USA. In the region, these 3 facies are representative of the nearly continuous coalescing fan-fill complexes blanketing valley floors of headwater streams where the dominant transport mechanism shifts from debris-flow to fluvial. Within each depositional unit, and for each charcoal piece within that unit, convolution of the calibrated age distribution with that of the youngest piece yielded an inherited age distribution for the unit. Fits to the normalized sums of inherited age distributions for units of like facies provided estimates of facies-specific inherited age distribution functions. Finally, convolution of these distribution functions with calibrated deposit age distributions yielded corrections to published valley-floor deposit ages and residence time distributions from nearby similar sites. Residence time distributions were inferred from the normalized sums of distributions of ∼30 deposit ages at each of 4 sites: 2 adjacent valley reaches ∼103 m long and within ∼102 m of 2 tributary confluences. Mean inherited ages from the observed distributions are 666, 688, and 1506 yr for debris-flow deposits, fluvial fines, and fluvial gravels, respectively. On average, correction reduced estimates of individual deposit age means by a factor of 0.71 (0.56–0.94) and increased standard deviations by a factor of 6.1 (0.97–43). Across sites, mean residence times decreased by 24.0% and standard deviations by 12.5% on average. Corrected residence time distributions have thicker tails, as indicated by gamma-distribution fits with smaller shape factors, and these changes are significant relative to the bootstrapped 95% confidence limits representing potential error in the sampling for inherited ages. The ratio of the means of sediment age and residence time ranged from 1.03 to 1.80 across sites before correction and 1.21 to 2.18 after correction, where a value of one implies that probability of evacuation from the “reservoir” comprising valley-floor deposits is independent of time since deposition. Corrected values of this ratio therefore indicate that evacuation favors younger deposits at all sites, whereas uncorrected results implied age-independent evacuation from the more downstream valley reach.

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.

Characterizing structural and lithologic controls on deep-seated landsliding: Implications for topographic relief and landscape evolution in the Oregon Coast Range, USA

In mountainous areas, landslides regulate temporal variations in sediment production and may suppress simple linkages between topographic development and tectonic forcing. Rates and mechanisms of mass wasting depend on lithology, bedrock structure, and climatic and tectonic setting. These factors tend to vary signifi cantly in active tectonic regions, thus clouding our ability to predict how landsliding modulates topographic development over human and geological time scales. Here, we use a novel DEM-based technique to document the distribution of large landslides in the Oregon Coast Range (OCR) and quantify how they affect topographic relief. We developed an automated algorithm that exploits the distinctive topographic signature (specifi cally the relationship between curvature and gradient) of large landslides to map their distribution within the gently folded Tyee Formation (Eocene deltaicsubmarine ramp sediments). In contrast to steep and highly dissected terrain frequently identifi ed as characteristic of the OCR (which exhibits steep, planar sideslopes and highly curved, low-gradient ridgetops and valleys), terrain prone to large landslides tends to have low values of both drainage density and curvature and gradient values that cluster between 0.16 and 0.44. The distribution of failure-dominated terrain in our 10,000 km2 study area is infl uenced by systematic variations in sedimentary facies and bedrock structure. The fraction of terrain altered by large landslides (>0.1 km2 ) varies from 5% in the sand-rich (delta-slope and proximal ramp facies) southern section of our study area to ~25% in the north (distal ramp facies), coincident with an increase in the thickness of siltstone beds and a decrease in the sandstone:siltstone ratio. Local relief declines progressively northward, suggesting that deep-seated landsliding is sensitive to the thickness and frequency of low-shearstrength siltstone beds and may serve to limit topographic development in the OCR. Structural controls are superimposed on facies-related variations as deep-seated landslides are frequently found on slopes whose downslope aspect corresponds to the bedrock dip direction. For 1516 strike and dip measurements in our study area, we calculated the fraction of proximal terrain (<2.5 km) altered by deep-seated landsliding. In the sand-rich southern region, the proportion of proximal slide-dominated terrain increases modestly with bedrock dip. In the silt-rich northern region, terrain altered by deep-seated landsliding is pervasive, and an increase in dip from 0° to 16° corresponds to a change in the fraction of slide-prone terrain from 10% to 28%. Our technique for mapping large landslides has utility for hazard analysis and land management. Over million-year time scales, the progradational character of the Tyee Formation suggests that continued uplift and exhumation of the OCR should result in a southward propagation of slide-prone, silt-rich distal facies. As a result, deep-seated landsliding will become increasingly prominent, and topographic relief in the central and southern OCR will progressively decline. Whereas spatial variability in climatic or tectonic forcing is often invoked to explain systematic variations in topographic development, our results emphasize the importance of structural and intraformation lithologic controls on landsliding. As such, analyses linking surface processes, climate, tectonics, and landscapes should be couched in the context of diverse geologic and topographic data.

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.

Large wood recruitment and redistribution in headwater streams in the southern Oregon Coast Range, U.S.A.

Large wood recruitment and redistribution mechanisms were investigated in a 3.9 km2 basin with an old-growth Pseudotsuga menziesii (Mirb.) Franco and Tsuga heterophylla (Raf.) Sarg. forest, located in the southern Coast Range of Oregon. Stream size and topographic setting strongly influenced processes that delivered wood to the channel network. In small colluvial channels draining steep hillslopes, processes associated with slope instability dominated large wood recruitment. In the larger alluvial channel, windthrow was the dominant recruitment process from the local riparian area. Consequently, colluvial channels received wood from further upslope than the alluvial channel. Input and redistribution processes influenced piece location relative to the direction of flow and thus, affected the functional role of wood. Wood recruited directly from local hillslopes and riparian areas was typically positioned adjacent to the channel or spanned its full width, and trapped sediment and wood in transport. In contrast, wood that had been fluvially redistributed was commonly located in mid-channel positions and was associated with scouring of the streambed and banks. Debris flows were a unique mechanism for creating large accumulations of wood in small streams that lacked the capacity for abundant fluvial transport of wood, and for transporting wood that was longer than the bank-full width of the channel.

Stochastic processes of soil production and transport: erosion rates, topographic variation and cosmogenic nuclides in the Oregon Coast Range

AbstractLandscapes in areas of active uplift and erosion can only remain soil‐mantled if the local production of soil equals or exceeds the local erosion rate. The soil production rate varies with soil depth, hence local variation in soil depth may provide clues about spatial variation in erosion rates. If uplift and the consequent erosion rates are sufficiently uniform in space and time, then there will be tendency toward equilibrium landforms shaped by the erosional processes. Soil mantle thickness would adjust such that soil production matched the erosion. Previous work in the Oregon Coast Range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield. Here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported. We quantify how soil production varies with soil thickness in the southern Oregon Coast Range and explore further the issue of landscape equilibrium. Apparent soil production is determined to be an inverse exponential function of soil depth, with a maximum inferred production rate of 268 m Ma−1 occurring under zero soil depth. This rate depends, however, on the degree of weathering of the underlying bedrock. The stochastic and large‐scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth; the spatial variation of soil depth neither supports nor rejects equilibrium morphology. Our observed catchment‐averaged erosion rate of 117 m Ma−1 is, however, similar to that estimated for the region by others, and to soil production rates under thin and intermediate soils typical for the steep ridges. We suggest that portions of the Oregon Coast Range may be eroding at roughly the same rate, but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle. Copyright © 2001 John Wiley &amp; Sons, Ltd.

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.

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

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

Erosion rates in the southern oregon coast range: Evidence for an equilibrium between hillslope erosion and sediment yield

AbstractThe relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes. In landscapes containing hillslopes crenulated by alternating topographic noses and hollows, estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows. Hollows act as local traps for a portion of the colluvium transported down hillslopes, and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area. Analysis of colluvial deposits in nine Oregon Coast Range hollows has yielded average colluvial transport rates into the hollows of about 35cm3cm−1yr−1 and average bedrock lowering rates of about 0.07 mm yr−1 for the last 4000 to 15000 yr. These rates are consistent with maximum bedrock exfoliation rates of about 0.09 mm yr−1 calculated from six of the hollows, supporting the interpretation that exfoliation rates limit erosion rates on these slopes. Sediment yield measurements from nine Coast Range streams provide similar basin‐wide denudation rates of between 0.05 and 0.08mm yr−1, suggesting an approximate steady‐state between sediment production on hillslopes and sediment yield. In addition, modern sediment yields are similar in basins varying in size from 1 to 1500 km2, suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in the landscape.

Eocene basalts from the Yakutat terrane: Evidence for the origin of an accreting terrane in southern Alaska

Research Article| November 01, 1986 Eocene basalts from the Yakutat terrane: Evidence for the origin of an accreting terrane in southern Alaska Alicé S. Davis; Alicé S. Davis 1U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar George Plafker George Plafker 1U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information Alicé S. Davis 1U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 George Plafker 1U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1986) 14 (11): 963–966. https://doi.org/10.1130/0091-7613(1986)14<963:EBFTYT>2.0.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 Alicé S. Davis, George Plafker; Eocene basalts from the Yakutat terrane: Evidence for the origin of an accreting terrane in southern Alaska. Geology 1986;; 14 (11): 963–966. doi: https://doi.org/10.1130/0091-7613(1986)14<963:EBFTYT>2.0.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 SocietyGeology Search Advanced Search Abstract Basalts from the Yakutat terrane, a composite oceanic and continental tectonostratigraphic terrane, are chemically diverse large ion lithophile element (LILE)–depleted and LILE-enriched tholeiites, interpreted as normal mid-ocean ridge and oceanic island basalt, that originated on seamounts near the Kula-Farallon spreading center during the early to middle Eocene. Coeval and geochemically similar basalts, occurring sporadically in a linear belt from southern Vancouver Island to the southern Oregon Coast Range, are correlative with the Yakutat terrane basalts. Both basaltic sequences were accreted to the continental margin during subduction of the Kula-Farallon Ridge and Kula plate about 48 Ma. The Yakutat basalts were emplaced along the coast of Washington or British Columbia. The Yakutat terrane probably originated during the Neogene as a composite terrane when it was sliced off the continental margin and started to move northward along the Queen Charlotte-Fairweather transform fault toward its present location in southern Alaska. 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.

Eocene and Oligocene planktonic foraminifera from the central and southern Oregon Coast Range

Other| October 01, 1975 Eocene and Oligocene planktonic foraminifera from the central and southern Oregon Coast Range Daniel R. McKeel; Daniel R. McKeel Univ. Calif., Dep. Geol., Davis, Calif., United States Search for other works by this author on: GSW Google Scholar Jere H. Lipps Jere H. Lipps Search for other works by this author on: GSW Google Scholar Journal of Foraminiferal Research (1975) 5 (4): 249–269. https://doi.org/10.2113/gsjfr.5.4.249 Article history first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Daniel R. McKeel, Jere H. Lipps; Eocene and Oligocene planktonic foraminifera from the central and southern Oregon Coast Range. Journal of Foraminiferal Research 1975;; 5 (4): 249–269. doi: https://doi.org/10.2113/gsjfr.5.4.249 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 SocietyJournal of Foraminiferal Research Search Advanced Search 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.