Stratigraphy, depositional setting, and tectonic significance of the clastic cover to the Fidalgo Ophiolite, San Juan Islands, Washington

1988 ◽  
Vol 25 (3) ◽  
pp. 417-432 ◽  
Author(s):  
John Garver
Keyword(s):  
Sedimentary Cover ◽  
Hanging Wall ◽  
Upper Jurassic ◽  
San Juan ◽  
Island Formation ◽  
San Juan Islands ◽  
The North ◽  
Tectonic Significance ◽  
Tectonically Active ◽  
Depositional Setting

The San Juan Islands of northwest Washington State comprise a diverse assemblage of Paleozoic and Mesozoic terranes amalgamated during a regional Cretaceous orogenic event. Detailed tectono-stratigraphy of the sedimentary cover to the Fidalgo Complex indicates the presence of several stratigraphically distinct units, which are described and formalized in this paper. The Fidalgo Complex and its sedimentary cover are the structurally highest rocks in the San Juan thrust system.The Fidalgo Complex is a highly disrupted Middle to Upper Jurassic ophiolite with arc-related intrusives, volcanics, and sediments. The Trump unit is an informally named sequence of siliceous sediments, volcanic graywacke, and minor volcanics that occurs at the stratigraphically highest portion of the Fidalgo Complex. Complex facies, lithologies, and provenance indicate that deposition of this Oxfordian(?) to upper Tithonian unit occurred in an arc-proximal setting.The upper Tithonian and younger Lummi Group (elevated here) lies depositionally above the Fidalgo Complex; locally the contact is an angular unconformity. The James Island Formation (new) is designated as a lower unit of the Lummi Group in the Decatur Island area. The chert-rich volcaniclastic sediments of the James Island Formation, locally containing ophiolitic debris, represent submarine-fan deposition within a tectonically active basin where basement blocks were uplifted along fault scarps.Middle Cretaceous thrusting and lawsonite–prehnite–aragonite metamorphism predated deposition of the Obstruction Formation (new), which is inferred to unconformably overlie the Lummi Group – Fidalgo Complex. Metamorphism postdated the late Albian, as rocks of this age are metamorphosed. The Obstruction Formation (?Cenomanian–Turonian) does not have metamorphic lawsonite–prehnite–aragonite, which are characteristic of underlying terranes in the San Juan Islands. Instead, the Obstruction Formation contains clasts derived from underlying metamorphosed terranes in the San Juan Islands; some clasts show these high-pressure, low-temperature metamorphic minerals. The Obstruction Formation probably represents synthrusting sedimentation that occurred after the San Juan terranes were metamorphosed and rapidly brought to the surface by continued thrusting over a hanging-wall obstruction. Thrusting was most likely driven by the accretion of Wrangellia against the North American margin.

The Spieden Group: an anomalous piece of the Cordilleran paleogeographic puzzle

1981 ◽  
Vol 18 (11) ◽  
pp. 1694-1707 ◽  
Author(s):  
Samuel Y. Johnson
Keyword(s):  
Large Scale ◽  
Upper Jurassic ◽  
Alluvial Fan ◽  
San Juan ◽  
Island Formation ◽  
Shallow Marine ◽  
San Juan Islands ◽  
Structural Style ◽  
Lower Member ◽  
Volcanic Source

Spieden and Sentinel Islands, San Juan Islands, Washington, are underlain by the only known occurrence of the Spieden Group, composed of the Upper Jurassic (Oxfordian or Kimmeridgian) Spieden Bluff Formation and the Lower Cretaceous (Valanginian and Hauterivian and possibly younger) Sentinel Island Formation, separated by a disconformity.The 100 m thick Spieden Bluff Formation is subdivided into two members: (1) an 80 m thick lower member, consisting of 5 m of sandstone, siltstone, and tuff overlain by 75 m of volcanic breccia–conglomerate largely of debris flow (laharic?) origin; and (2) a 20 m thick upper member consisting of fossiliferous sandstone and siltstone deposited on a shallow marine slope. Sedimentologic, petrologic, and geochronologic data suggest that sediments of the Spieden Bluff Formation accumulated near an active volcanic source to the north contributing primarily andesite, dacite, and basaltic andesite.The 740 m thick Sentinel Island Formation is also subdivided into two members: (1) a 140 m thick lower member consisting of fossiliferous sandstone and siltstone deposited in a shallow marine environment; and (2) an unconformably overlying 600 m thick upper member consisting of volcanic conglomerate deposited as an alluvial fan. The source terrane for the Sentinel Island Formation was also primarily Upper Jurassic volcanic rocks and lay to the northeast.Rocks of equivalent age occur in the southern part of the San Juan Islands and in neighboring geologic provinces, but most of these correlative rocks differ from the Spieden in sedimentology, structural style, and metamorphism. Juxtaposition of the Spieden Group and these correlative rocks might have been accomplished by shortening and fragmentation of a regional convergent margin, by large-scale transport of allochthonous blocks, or by some combination of the two mechanisms.

Development of a Late Quaternary Marine Terraced Landscape during On-Going Tectonic Contraction, Crescent City Coastal Plain, California

1999 ◽  
Vol 52 (2) ◽  
pp. 217-228 ◽  
Author(s):  
Michael Polenz ◽  
Harvey M. Kelsey
Keyword(s):  
Coastal Plain ◽  
Late Quaternary ◽  
Hanging Wall ◽  
Thrust Fault ◽  
Cascadia Subduction Zone ◽  
Marine Terrace ◽  
Crescent City ◽  
The North ◽  
Marine Terraces ◽  
Tectonically Active

The Crescent City coastal plain is a low-lying surface of negligible relief that lies on the upper plate of the Cascadia subduction zone in northernmost California. Whereas coastal reaches to the north in southern Oregon and to the south near Cape Mendocino contain flights of deformed marine terraces from which a neotectonic history can be deduced, equivalent terraces on the Crescent City coastal plain are not as pronounced. Reexamination of the coastal plain revealed three late Pleistocene marine terraces, identified on the basis of subtle geomorphic boundaries and further delineated by differentiable degrees of soil development. The youngest marine terrace is preserved in the axial valley of a broad syncline, and the two older marine terraces face each other across the axial region. An active thrust fault, previously recognized offshore, underlies the coastal plain, and folding in the hanging wall of this thrust fault has dictated, through differential uplift, the depositional limits of each successive marine terrace unit. This study demonstrates the importance of local structures in coastal landscape evolution along tectonically active coastlines and exemplifies the utility of soil relative-age determinations to identify actively growing folds in landscapes of low relief.

Turonian (Upper Cretaceous) lithostratigraphy and biochronology, southern Gulf Islands, British Columbia, and northern San Juan Islands, Washington State

2005 ◽  
Vol 42 (11) ◽  
pp. 2001-2020 ◽  
Author(s):  
James W Haggart ◽  
Peter D Ward ◽  
William Orr
Keyword(s):  
British Columbia ◽  
Washington State ◽  
San Juan ◽  
Submarine Fan ◽  
Island Formation ◽  
Shallow Marine ◽  
San Juan Islands ◽  
Thrust System ◽  
Gulf Islands ◽  
Facies Succession

Clastic strata preserved on Sidney Island, Barnes Island, and adjacent islands of the southernmost Gulf Islands of British Columbia and the northern San Juan Islands of Washington State are assigned to new stratigraphic units: the Sidney Island Formation and the Barnes Island Formation. The Sidney Island Formation consists of basal conglomerate and sandstone that grades upward through planar-stratified sandstone into hummocky cross-stratified sandstone and siltstone, all of which are deposited in relatively shallow-marine environments. The Barnes Island Formation, in contrast, consists of deep-marine conglomerate, sandstone, and mudstone that was deposited in a submarine-fan setting. Mollusk fossils from the Sidney Island Formation are of Early to Middle Turonian age, whereas ammonites and foraminifers from the Barnes Island Formation indicate a Late Turonian age. The Sidney Island Formation thus records initial marine transgression and inundation of basement rocks, followed by basin deepening that is transitional to the deep-marine submarine-fan deposits of the Barnes Island Formation. Sidney Island Formation strata have been considered previously as derived from uplift along the nearby San Juan thrust system in mid-Cretaceous time. However, the shallow-marine strata are internally well organized, and the facies succession is persistent across the formation's outcrop area. In addition, the formation lacks the distinctive detrital metamorphic mineral assemblages that are characteristic of older rocks of the San Juan Islands. These observations suggest that strata of the Sidney Island Formation did not accumulate immediately adjacent to active thrusting but rather in a more distal setting relative to the thrust system.

Northern Cascade-Fraser River, Domain 7

2007 ◽  
Author(s):  
Earl B. Alexander ◽  
Roger G. Coleman ◽  
Todd Keeler-Wolfe ◽  
Susan P. Harrison
Keyword(s):  
British Columbia ◽  
Fault System ◽  
San Juan ◽  
Fraser River ◽  
Cascade Mountains ◽  
River Flows ◽  
San Juan Islands ◽  
The North ◽  
North American Craton ◽  
Cordilleran Ice Sheet

The Northern Cascade–Fraser River domain conforms to the Northern Cascade Mountains physiographic province in northwestern Washington and southern British Columbia, the San Juan Islands between the southern tip of Vancouver Island and the Northern Cascade Mountains, and much of the Interior Plateau province of British Columbia. The thread that connects these areas is the north–south Straight Creek–Fraser River fault system that runs through the Northern Cascade Mountains and northward along the Fraser River. The localities of domain 7 are along faults that branch off from this major fault system. The Northern Cascade Mountains are indeed mountainous, and the Interior Plateau of British Columbia is an area of dissected plateaus and scattered mountains. The Fraser River flows northwest in the Rocky Mountain Trench, which separates the North American craton on the northeast from accreted terranes on the southwest; then it turns around the northwest end of the Cariboo Mountains to the Interior Plateau. In the Interior Plateau, the Fraser River flows from Prince George south about 500 km to the Northern Cascade Mountains before turning westward toward the Pacific Coast. The northern part of domain 7 is in that part of the Fraser River basin, including tributaries northwest of Prince George, which is in the Interior Plateau province. Low, hilly terrain dominates the San Juan Islands. All of these areas in domain 7, except the Ingalls complex on southeast margin of the Northern Cascade Mountains, were covered by the Cordilleran ice sheet during the last stage of the Pleistocene glaciation, leaving <15 ka years for soil development on the current ground surfaces. Although alpine glaciers formed in the southeastern margin of the Northern Cascade Mountains, they did not cover all of the soils, allowing some of them longer time for development. Elevations in domain 7 range from sea level on San Juan Islands to mostly in the 600–1500 m range on the Interior Plateau of British Columbia, and up to 4392 m on Mt. Rainier in the Northern Cascade Mountains.

scholarly journals Miocene fan delta conglomerates in the north-western part of the Danube Basin: provenance, paleoenvironment, paleotransport and depositional mechanisms

2018 ◽  
Vol 69 (5) ◽  
pp. 467-482 ◽  
Author(s):  
Tamás Csibri ◽  
Samuel Rybár ◽  
Katarína Šarinová ◽  
Michal Jamrich ◽  
Ľubomír Sliva ◽  
...  
Keyword(s):  
Pannonian Basin ◽  
Sedimentary Cover ◽  
Hanging Wall ◽  
Fault System ◽  
Danube Basin ◽  
Oblique Collision ◽  
Accommodation Space ◽  
The North ◽  
Fan Delta ◽  
Central Western Carpathians

Abstract The Blatné Depression located in the NW part of the Danube Basin represents the northernmost sub-basins of the Pannonian Basin System. Its subsidence is associated with oblique collision of the Central Western Carpathians with the European platform, followed by the back-arc basin rifting stage in the Pannonian domain. The conglomerates recognized in the Cífer-2 well document the latest Burdigalian–early Langhian deposition in fan delta lobes situated above the footwall and hanging wall of a WSW–ENE trending fault system, the activity of which preceded the opening of the late Langhian–Serravallian accommodation space with a NE–SW direction. The provenance area of the “Cífer conglomerate” was linked to the Tatric Super-unit complexes. Similar rocks crop out in the southern part of the Malé Karpaty Mts. and are also present in the pre-Cenozoic basement of the Danube Basin. Documented extensive erosion of the crystalline basement and its sedimentary cover lasted until the early/middle Miocene boundary. The “Cífer conglomerate” has distinct clast composition. The basal part consists of poorly sorted conglomerate with sub-angular clasts of metamorphic rocks. Toward the overlying strata, the clasts consist of poorly sorted conglomerates with sub-rounded to well-rounded carbonates and granitoids. The uppermost part consists of poorly sorted conglomerates with sub-rounded to rounded clasts of carbonate, granitoid and metamorphic rock. Within the studied samples a transition from clast to matrix supported conglomerates was observed.

scholarly journals Local radon flux maxima in the quaternary sediments of Schleswig–Holstein (Germany)

2021 ◽  
Author(s):  
Johannes Albert ◽  
Maximilian Schärf ◽  
Frieder Enzmann ◽  
Martin Waltl ◽  
Frank Sirocko
Keyword(s):  
Water Content ◽  
Pore Space ◽  
Mineralogical Composition ◽  
Fault System ◽  
Near Surface ◽  
Salt Diapirism ◽  
The North ◽  
Radon Flux ◽  
Published Evidence ◽  
Tectonically Active

AbstractThis paper presents radon flux profiles from four regions in Schleswig–Holstein (Northern Germany). Three of these regions are located over deep-rooted tectonic faults or salt diapirs and one is in an area without any tectonic or halokinetic activity, but with steep topography. Contrary to recently published studies on spatial patterns of soil radon gas concentration we measured flux of radon from soil into the atmosphere. All radon devices of each profile were deployed simultaneously to avoid inconsistencies due to strong diurnal variations of radon exhalation. To compare data from different seasons, values had to be normalized. Observed radon flux patterns are apparently related to the mineralogical composition of the Quaternary strata (particularly to the abundance of reddish granite and porphyry), and its grain size (with a flux maximum in well-sorted sand/silt). Minimum radon flux occurs above non-permeable, clay-rich soil layers. Small amounts of water content in the pore space increase radon flux, whereas excessive water content lessens it. Peak flux values, however, are observed over a deep-rooted fault system on the eastern side of Lake Plön, i.e., at the boundary of the Eastholstein Platform and the Eastholstein Trough. Furthermore, high radon flux values are observed in two regions associated with salt diapirism and near-surface halokinetic faults. These regions show frequent local radon flux maxima, which indicate that the uppermost strata above salt diapirs are very inhomogeneous. Deep-rooted increased permeability (effective radon flux depth) or just the boundaries between permeable and impermeable strata appear to concentrate radon flux. In summary, our radon flux profiles are in accordance with the published evidence of low radon concentrations in the “normal” soils of Schleswig–Holstein. However, very high values of radon flux are likely to occur at distinct locations near salt diapirism at depth, boundaries between permeable and impermeable strata, and finally at the tectonically active flanks of the North German Basin.

New Meadow Mouse from the San Juan Islands, Washington

The Murrelet ◽  
1940 ◽  
Vol 21 (1) ◽  
pp. 7
Author(s):  
Walter W. Dalquest
Keyword(s):  
San Juan ◽  
San Juan Islands
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