Tree-ring history of Swiss needle cast impact on Douglas-fir growth in Western Oregon: correlations with climatic variables

The fungal pathogen, Nothophaeocryptopus gaeumannii, occurs wherever Douglas-fir is found but disease damage is believed to be limited to the Coast Range and is of no concern outside the coastal fog zone (Shaw, et al., 2011). However, knowledge remains limited on the history and spatial distribution of Swiss Needle Cast (SNC) impacts in the Pacific Northwest (PNW). We reconstructed the history of SNC impacts on mature Douglas-fir trees based on tree ringwidth chronologies from the west slope of the Coast Range to the high Cascades of Oregon. Our findings show that SNC impacts on growth occur wherever Douglas-fir is found in western Oregon and is not limited to the coastal fog zone. The spatiotemporal patterns of growth impact from SNC disease were synchronous across the region, displayed periodicities of 25-30 years, strongly correlated with winter and summer temperatures and summer precipitation, and matched the patterns of enriched cellulosic stable carbon isotope indicative of physiological stress. While winter and summer temperature and summer precipitation influenced pathogen dynamics at all sites, the primary climatic factor of these three limiting factors varied spatially by location, topography, and elevation. In the 20th century, SNC impacts at low- to mid-elevations were least severe during the warm phase of the Pacific Decadal Oscillation (PDO, 1924-1945) and most severe in 1984-1986, following the cool phase of the PDO (1945-1977). At high elevations on the west slope of the Cascade Mountains, SNC impacts were the greatest in the 1990s and 2000s, a period of warmer winter temperatures associated with climate change. Warmer winters will likely continue to increase SNC severity at higher elevations, north along the coast from northern Oregon to British Columbia, and inland where low winter temperatures currently limit growth of the pathogen. Surprisingly, tree-ring records of ancient Douglas-fir logs dated ~53K radioactive years B.P. from Eddyville, OR displayed 7.5- and 20-year periodicities of low growth, similar to those found in modern day coastal Douglas-fir tree-ring records which we interpret as being due to cyclic fluctuations in SNC severity. Our findings indicate that SNC has persisted for as long as its host, and as a result of changing climate, may become a significant forest health problem in areas of the PNW beyond the coastal fog zone.

Modelling of Quaternary Glacier Extent and Climate in Tasmania, Australia

<p>The aim of this study was to improve our understanding of Quaternary glaciations in Tasmania, and to assess their climatic significance. During the Quaternary, Tasmania experienced ice cap development in the West Coast Range and Central Plateau, with smaller cirque and valley glaciers developing on surrounding mountains. Geomorphic evidence indicates at least four glacial advances occurred. A 500 m resolution, three-dimensional thermomechanical ice-sheet model was used to reconstruct and simulate these glacier fluctuations. The model, while a simplification of reality, provided a framework in which to understand the genesis of contemporary landforms and former glacial climate conditions in Tasmania. Input specifications of basal topography, temperature and precipitation were required, with the latter two interpolated from present-day datasets. Numerous experiments were carried out, involving systematic alterations to temperature and precipitation, basal sliding and atmospheric temperature lapse-rates. Modelled output was compared to empirical evidence with the aim of optimizing the parameters (temperature, precipitation) from which model mismatch was minimised. An annual temperature reduction of 6' C is required for glaciers to form in Tasmania. When temperatures cool beyond this threshold, an ice mass develops over the Central Highlands, Central Plateau, West Coast Range and other mountains. In all but the most extensive glaciations, the Central Plateau ice field consists of a relatively thin carapace of ice, and the thickest and most dynamic glaciers develop in the deep valleys of the Central Highlands. The model shows that ice readily flows down the west-facing valleys from the Central Highlands to join with West Coast Range glaciers. A temperature reduction between 7 and 9' C, with corresponding regional precipitation changes of between +/-50% and an increase in orographic precipitation is required to simulate the Last Glacial Maximum (LGM) ice cover. Earlier glacial advances require larger coolings of up to 11.25' C depending on the regional precipitation conditions prescribed. Mismatches between geomorphic evidence and modelled reconstructions probably result from model grid size issues and parameters not accommodated by the model such as wind-blown snow redistribution. This means that temperature reductions derived from the model may have been overestimated. Despite these limitations, reconstructed temperatures compare well to some multi-proxy palaeo-temperature records from Tasmania, although the cooling identified was larger than that recorded in nearby ocean sediments.</p>

Modelling of Quaternary Glacier Extent and Climate in Tasmania, Australia

<p>The aim of this study was to improve our understanding of Quaternary glaciations in Tasmania, and to assess their climatic significance. During the Quaternary, Tasmania experienced ice cap development in the West Coast Range and Central Plateau, with smaller cirque and valley glaciers developing on surrounding mountains. Geomorphic evidence indicates at least four glacial advances occurred. A 500 m resolution, three-dimensional thermomechanical ice-sheet model was used to reconstruct and simulate these glacier fluctuations. The model, while a simplification of reality, provided a framework in which to understand the genesis of contemporary landforms and former glacial climate conditions in Tasmania. Input specifications of basal topography, temperature and precipitation were required, with the latter two interpolated from present-day datasets. Numerous experiments were carried out, involving systematic alterations to temperature and precipitation, basal sliding and atmospheric temperature lapse-rates. Modelled output was compared to empirical evidence with the aim of optimizing the parameters (temperature, precipitation) from which model mismatch was minimised. An annual temperature reduction of 6' C is required for glaciers to form in Tasmania. When temperatures cool beyond this threshold, an ice mass develops over the Central Highlands, Central Plateau, West Coast Range and other mountains. In all but the most extensive glaciations, the Central Plateau ice field consists of a relatively thin carapace of ice, and the thickest and most dynamic glaciers develop in the deep valleys of the Central Highlands. The model shows that ice readily flows down the west-facing valleys from the Central Highlands to join with West Coast Range glaciers. A temperature reduction between 7 and 9' C, with corresponding regional precipitation changes of between +/-50% and an increase in orographic precipitation is required to simulate the Last Glacial Maximum (LGM) ice cover. Earlier glacial advances require larger coolings of up to 11.25' C depending on the regional precipitation conditions prescribed. Mismatches between geomorphic evidence and modelled reconstructions probably result from model grid size issues and parameters not accommodated by the model such as wind-blown snow redistribution. This means that temperature reductions derived from the model may have been overestimated. Despite these limitations, reconstructed temperatures compare well to some multi-proxy palaeo-temperature records from Tasmania, although the cooling identified was larger than that recorded in nearby ocean sediments.</p>

Tectonics and paleogeography of a post-accretionary forearc basin, Coos Bay area, SW Oregon, USA

ABSTRACT This field guide reviews 19 sites providing insight to four Cenozoic deformational phases of the Cascadia forearc basin that onlaps Siletzia, an oceanic basaltic terrane accreted onto the North American plate at 51–49 Ma. The field stops visit disrupted slope facies, prodelta-slope channel complexes, shoreface successions, and highly fossiliferous estuarine sandstones. New detrital zircon U-Pb age calibration of the Cenozoic formations in the Coos Bay area and the Tyee basin at-large, affirm most previous biostratigraphic correlations and support that some of the upper-middle Eocene to Oligocene strata of the Coos Bay stratigraphic record represents what was differentially eroded off the Coast Range crest during ca. 30–25 Ma and younger deformations. This suggests that the strata along Cape Arago are a western “remnant” of the Paleogene Tyee basin. Zircon ages and biostratigraphic data encourages the extension of the Paleogene Coos Bay and Tyee forearc basin westward beyond the Fulmar fault and offshore Pan American and Fulmar wells. Integration of outcrop paleocurrents with anisotropy of magnetic susceptibility data from the middle Eocene Coaledo Formation affirms south-southeast to north-northwest sediment transport in current geographic orientation. Preliminary detrital remanent magnetism data show antipodal directions that are rotated clockwise with respect to the expected Eocene field direction. The data suggest the Eocene paleo-shoreline was relatively north-south similar to the modern shoreline, and that middle Eocene sediment transport was to the west in the area of present-day Coos Bay. A new hypothesis is reviewed that links the geographic isolation of the Coos Bay area from rivers draining the ancestral Cascades arc to the onset of uplift of the southern Oregon Coast Range during the late Oligocene to early Miocene.

Developing landslide chronologies using landslide-dammed lakes in the Oregon Coast Range

ABSTRACT The Oregon Coast Range is a dynamic landscape that is continually shaped by shallow and deep-seated landslides that can have disastrous consequences to infrastructure and human lives. Searching for evidence of potentially coseismic mass wasting is incredibly difficult, particularly when historical observations are limited. Landslide-dammed lakes with submerged “ghost forests” in the Oregon Coast Range present the unique opportunity to establish landslide chronologies with subannual accuracy when dendrochronology is applied. This field guide will visit the unique landslide-dammed Klickitat Lake and explore a drowned ‘ghost forest’ to discuss methods used to establish a prehistoric landslide chronology in western Oregon, USA. After exploring the lake and exposing its geomorphic secrets, the guide will end with a stop on Marys Peak, a mafic volcanic intrusion composed of gabbroic dikes and pillow basalt that forms the highest point in the Oregon Coast Range. With the landscape of western Oregon laid out before us, we will discuss short- and long-term geomorphic evolution of the Oregon Coast Range and Willamette Valley.

Two new scorpion species from protected areas in Antofagasta Region, Chile (Scorpiones, Bothriuridae, Brachistosternus)

We describe two new scorpion species of genus Brachistosternus from protected areas of Antofagasta Region in northern Chile. Brachistosternus chimba n. sp. has only been collected in La Chimba National Reserve, in the Chilean Coast Range. Brachistosternus llullaillaco n. sp. is a high altitude Andean species of the Lullaillaco National Park. Both species were collected as part of the first survey of the terrestrial arthropods of the protected areas of Antofagasta Region, in the frame of the First National Biodiversity Inventory of Chile of the Integrated System for Monitoring and Evaluation of Native Forest Ecosystems (SIMEF) and Project FIC-R Recovery Plan for La Chimba National Reserve.

Field and petrographic reconnaissance of Franciscan complex rocks of Mount Diablo, California: Imbricated ocean floor stratigraphy with a roof exhumation fault system

ABSTRACT Franciscan subduction complex rocks of Mount Diablo form an 8.5 by 4.5 km tectonic window, elongated E-W and fault-bounded to the north and south by rocks of the Coast Range ophiolite and Great Valley Group, respectively, which lack the burial metamorphism and deformation displayed by the Franciscan complex. Most of the Franciscan complex consists of a stack of lawsonite-albite–facies pillow basalt overlain successively by chert and clastic sedimentary rocks, repeated by faults at hundreds of meters to &lt;1 m spacing. Widely distributed mélange zones from 0.5 to 300 m thick containing high-grade (including amphibolite and eclogite) assemblages and other exotic blocks, up to 120 m size, form a small fraction of exposures. Nearly all clastic rocks have a foliation, parallel to faults that repeat the various lithologies, whereas chert and basalt lack foliation. Lawsonite grew parallel to foliation and as later grains across foliation. The Franciscan-bounding faults, collectively called the Coast Range fault, strike ENE to WNW and dip northward at low to moderate average angles and collectively form a south-vergent overturned anticline. Splays of the Coast Range fault also cut into the Franciscan strata and Coast Range ophiolite and locally form the Coast Range ophiolite–Great Valley Group boundary. Dip discordance between the Coast Range fault and overlying Great Valley Group strata indicates that the northern and southern Coast Range fault segments were normal faults with opposite dip directions, forming a structural dome. These relationships suggest accretion and fault stacking of the Franciscan complex, followed by exhumation along the Coast Range fault and then folding of the Coast Range fault.

Upper plate deformation during blueschist exhumation, ancestral western California forearc basin, from stratigraphic and structural relationships at Mount Diablo and in the Rio Vista Basin

ABSTRACT Late Cenozoic growth of the Mount Diablo anticline in the eastern San Francisco Bay area, California, USA, has produced unique 3D exposures of stratigraphic relationships and normal faults that record Late Cretaceous uplift and early Tertiary extension in the ancestral California forearc basin. Several early Tertiary normal faults on the northeast flank of Mount Diablo have been correlated with structures that accommodated Paleogene subsidence of the now-buried Rio Vista basin north of Mount Diablo. Stepwise restoration of deformation at Mount Diablo reveals that the normal faults probably root into the “Mount Diablo fault,” a structure that juxtaposes blueschist-facies rocks of the Franciscan accretionary complex with attenuated remnants of the ophiolitic forearc basement and relatively unmetamorphosed marine forearc sediments. This structure is the local equivalent of the Coast Range fault, which is the regional contact between high-pressure Franciscan rocks and structurally overlying forearc basement in the northern Coast Ranges and Diablo Range, and it is folded about the axis of the Mount Diablo anticline. Apatite fission-track analyses indicate that the Franciscan rocks at Mount Diablo were exhumed and cooled from depths of 20+ km in the subduction zone between ca. 70−50 Ma. Angular unconformities and growth relations in the Cretaceous and Paleogene stratigraphic sections on the northeast side of Mount Diablo, and in the Rio Vista basin to the north, indicate that wholesale uplift, eastward tilting, and extension of the western forearc basin were coeval with blueschist exhumation. Previous workers have interpreted the structural relief associated with this uplift and tilting, as well as the appearance of Franciscan blueschist detritus in Late Cretaceous and early Tertiary forearc strata, as evidence for an “ancestral Mount Diablo high,” an emergent Franciscan highland bordering the forearc basin to the west. This outer-arc high is here interpreted to be the uplifted footwall of Coast Range fault. The stratigraphic and structural relations exposed at Mount Diablo support models for exposure of Franciscan blueschists primarily through syn-subduction extension and attenuation of the overlying forearc crust in the hanging wall of the Coast Range fault, accompanied by (local?) uplift and erosion of the exhumed accretionary prism in the footwall.

Aggregate mining on Mount Zion, Clayton, California

ABSTRACT Two construction aggregate companies, Cemex and Hanson Aggregates, operate respective crushed stone quarries on the east and west slopes of Mount Zion in Clayton, California. These sidehill quarries utilize a single highwall and mine Jurassic diabase of the Coast Range ophiolite that formed as a sheeted dike complex. Hydrothermal veins, some containing 20%–30% disseminated pyrite and chalcopyrite, cut the diabase. The east quarry, operated by Cemex, was started by the Harrison-Birdwell Company in 1947. The west quarry, operated by Hanson, was started by the Henry J. Kaiser Sand and Gravel Company in 1954. The Cemex quarry highwall is visible as you come into the city of Clayton on Marsh Creek Road, with a height of ~280 m (920 ft). The height of the highwall at the Hanson quarry is ~215 m (700 ft). Both operations remove weathered diabase overburden to expose fresh diabase, which is drilled, blasted, and hauled to the plant for processing. To ensure aggregate is suitable for construction, quality assurance testing is conducted in accordance with the specifications of various agencies. These quarries supply the surrounding area with aggregate for hospitals, schools, highways, dams, and other buildings. Noteworthy projects supplied by the Clayton quarries include the Concord BART Station, Interstate-680, Interstate-580, Calaveras Dam, Sherman Island Levee, Highway 4, Highway 24, and Bay Bridge epoxy asphalt. Before aggregate was mined, Mount Zion was the site of a copper rush from 1862 to 1864. Gold and silver were also reported in various assays from the Clayton district. Although prospecting created excitement around Clayton, no productive orebodies were ever discovered.

Interaction of extensional, contractional, and strike-slip elements at Mount Diablo and the surrounding eastern Coast Ranges, San Francisco Bay area, California: A model-based analysis

ABSTRACT This study presents three regional cross sections, a structural map analysis, and a schematic map restoration. The sections are constrained by surface geology and petroleum wells and were developed using model-based methods to be consistent with the regional tectonic context and balancing concepts. Together, these products depict the geometry and kinematics of the major fault systems. Insights from this research include the following. Franciscan complex blueschist-facies rocks in the Mount Diablo region were unroofed west of their current location and subsequently thrust beneath the Great Valley sequence in the mid-Eocene. East Bay structures are complicated by overprinting of Neogene compression and dextral strike-slip motion on a Paleogene graben system. Net lateral displacement between the Hayward fault and the Central Valley varies from 26 km toward 341° to 29 km toward 010° in the southern and northern East Bay Hills, respectively. Uplift above a wedge thrust generates the principal Neogene structural high, which extends from Vallejo through Mount Diablo to the Altamont Ridge. Anomalous structural relief at Mount Diablo is due to strike-parallel thrusting on the crest of a fault-propagation fold formed on the west-verging roof thrust. Uplift that exposes the Coast Range ophiolite in the East Bay Hills is formed by oblique thrusting generated by slip transfer at the northern termination of the Calaveras fault. The Paleogene extensional fault system likely extends farther west than previously documented. An east-dipping branch of that system may underlie the Walnut Creek Valley. Three-dimensional restoration should be applied to constrain geologic frameworks to be used for seismic velocity modeling.