The Brahmaputra River slices an exceptionally deep canyon through the eastern Himalaya. Fission-track and laser-ablation U-Pb ages of detrital zircon grains from the river document very rapid erosion from this region and its impact on sediment fluxes downstream in the Brahmaputra. Downstream from the canyon, 47% of the detrital zircons in the river's modern sediment load comprise a fission-track age population averaging only 0.6 Ma. Equally young cooling ages are reported from bedrock in the canyon through the Namche Barwa–Gyala Peri massif but are absent from riverbank sands of major tributaries upstream. Simple mixing models of U-Pb ages on detrital zircons from samples taken above and below this massif independently suggest that 45% of the downstream detrital zircons are derived from the basement gneisses extensively exposed in the massif. Constraints on the extent of the source area provided by bedrock cooling ages together with sediment-flux estimates at Pasighat, India, suggest exhumation rates averaging 7–21 mm yr−1 in an area of ~3300 km2 centered on the massif. This rapid exhumation, which is consistent with the very young cooling ages of the detrital zircons from this area, produces so much sediment that ~50% of the vast accumulation in the Brahmaputra system at the front of the Himalaya comes from only ~2% of its drainage. This extreme localization of rapid erosion, sediment evacuation, and bedrock cooling bear on (1) common assumptions in geodynamic and geochemical studies of the Himalaya about sources of sediment, and (2) plans for hydroelectric development and flood management in southeastern Tibet and the heavily populated areas of eastern India.
Compressional (Vp) and shear (Vs) wave velocities have been measured to 1.0 kbar for 14 cores of well-consolidated sedimentary rock from Atlantic and Pacific sites of the Deep Sea Drilling Project. The range of VP (2.05-5.38 km/sec at 0.5 kbar) shows significant overlap with the range of oceanic layer-2 seismic velocities determined by marine refraction surveys, suggesting that sedimentary rocks may, in some regions, constitute the upper portion of layer 2. Differing linear relationships between VP and Vs for basalts and sedimentary rocks, however, may provide a method of resolving layer-2 composition. This is illustra ted for a refraction survey site on the flank of the Mid-Atlantic Ridge where layer-2 velocities agree with basalt, and two sites on the Saya de Malha Bank in the Indian Ocean where layer-2 velocities appear to represent sedimentary rock.
Drilling for the exploration and extraction of oil requires the use of drilling fluids which are continuously pumped down and returned carrying the rock phase that is extracted from the well. The potential environmental impacts of contaminated fluids from drilling operations have attracted increasing community awareness and scrutiny. This review article highlights current advances in the treatment of drill cuttings and compares the technologies in terms of cost, time and space requirements. Traditionally, a range of non-biological methods have been employed for the disposal of drill cuttings including burial pits, landfills and re-injection, chemical stabilization and solidification and thermal treatments such as incineration and thermal desorption. More recently, bioremediation has been successfully applied as a treatment process for cuttings. This review provides a current comparison of bioremediation technologies and non-biological technologies for the treatment of contaminated drill cuttings providing information on a number of factors that need to be taken into account when choosing the best technology for drilling waste management including the environmental risks associated with disposal of drilling wastes.
Sediments underlying the abyssal plain in Komandorskiy basin were recovered at Deep Sea Drilling Project Site 191 in the east-central part of the basin (168.1°E). Most sedimentary fill is diatomaceous silty clay. Interbedded in the silty clay are layers of turbidite sand and volcanic ash. The sand layers range in composition from volcanic lithic sand to chert-rich sand containing as much as 40% quartzose debris. The sand probably originates on the continental shelf in the westernmost Bering Sea, and is deposited by turbidity currents crossing the abyssal plain. Chert-rich sand may originate on the shelf between Mys Olyutorskiy and Ostrov Karaginskiy, and volcanic lithic sand may originate farther south toward Mys Kamchatskiy. Below 500 m, sediments of the abyssal plain are altered extensively. The silty clay is compacted to mudstone, and sand layers are graywacke. Porosity in the sand layers is destroyed completely, and the deepest sand layer has textures that approach those of semischist. The graywacke layers contain considerable quantities of volcanic and sedimentary lithic debris, and may have originated on the continental shelf in the Komandorskiy Islands. Neogene accumulation rates in Komandorskiy basin were about 60 m/m.y.-1 in the late Miocene, increasing to 300 m/m.y.-1 in late Pliocene and early Pleistocene time. These high rates were maintained by extensive continental-shelf erosion during late Cenozoic sea-level transits, and by exceedingly high diatom productivity in the overlying waters of the Bering Sea. A slight decrease in accumulation rates in the late Pleistocene may be the result of a decline in diatom productivity. Unlithified Neogene deposits of Komandorskiy basin are distal representatives of contemporaneous deposits in continental-margin basins and have some characteristics of potential reservoir rocks. Their more proximal counterparts at shallower-water depths deserve increased attention as possible hydrocarbon sources.
Research Article| July 01, 1974 Zeolite Facies Metamorphism of Sandstone in the Western Olympic Peninsula, Washington RICHARD J. STEWART RICHARD J. STEWART 1Department of Geological Sciences, University of Washington, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar Author and Article Information RICHARD J. STEWART 1Department of Geological Sciences, University of Washington, Seattle, Washington 98195 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1974) 85 (7): 1139–1142. https://doi.org/10.1130/0016-7606(1974)85<1139:ZFMOSI>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 Email Permissions Search Site Citation RICHARD J. STEWART; Zeolite Facies Metamorphism of Sandstone in the Western Olympic Peninsula, Washington. GSA Bulletin 1974;; 85 (7): 1139–1142. doi: https://doi.org/10.1130/0016-7606(1974)85<1139:ZFMOSI>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 SocietyGSA Bulletin Search Advanced Search Abstract Authigenic laumontite is extensively developed in sandstone beds of Eocene to Miocene age exposed in the western Olympic Peninsula, Washington. In these rocks, laumontite primarily replaces calcic plagioclase, but it also forms cement and fills veins. Degree of alteration varies locally, depending primarily on the presence of calcareous cements, but also on porosity and grain size. Metamorphic grade increases eastward toward the core of the Olympic uplift and passes, apparently gradationally, into the prehnite-pumpellyite facies. Similar alteration reactions should be anticipated in other deeply buried clastic sequences in the Oregon and Washington Coast Ranges. 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.
Research Article| May 01, 1976 Turbidites of the Aleutian abyssal plain: Mineralogy, provenance, and constraints for Cenozoic motion of the Pacific plate RICHARD J. STEWART RICHARD J. STEWART 1Department of Geological Sciences, University of Washington, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1976) 87 (5): 793–808. https://doi.org/10.1130/0016-7606(1976)87<793:TOTAAP>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 RICHARD J. STEWART; Turbidites of the Aleutian abyssal plain: Mineralogy, provenance, and constraints for Cenozoic motion of the Pacific plate. GSA Bulletin 1976;; 87 (5): 793–808. doi: https://doi.org/10.1130/0016-7606(1976)87<793:TOTAAP>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 SocietyGSA Bulletin Search Advanced Search Abstract The Aleutian abyssal plain is a fossil abyssal plain of Paleogene age in the western Gulf of Alaska. The plain is a large, southward-thinning turbidite apron now cut off from sediment sources by the Aleutian Trench. Turbidite sedimentation ceased about 30 m.y. ago, and the apron is now buried under a thick blanket of pelagic deposits. Turbidites of the plain were recovered at site 183 of the Deep Sea Drilling Project on the northern edge of the apron. The heavy-mineral fraction of sand-sized samples is mostly amphibole and epidote with minor pyroxene, garnet, and sphene. The light-mineral fraction is mostly quartzose debris and feldspars. Subordinate lithic fragments consist of roughly equal amounts of metamorphic, plutonic, sedimentary, and volcanic grains. The sand compositions are arkoses in many sandstone classifications, although if fine silt is included with clay as matrix, the sand deposits are feldspathic or lithofeldspathic graywacke. The sands are apparently first-cycle products of deep dissection into a plutonic terrane, and they contrast sharply with arc-derived volcanic sandstones of similar age common on the adjacent North American continental margin. The turbidite sands are stratigraphically remarkably constant in composition, which indicates derivation from virtually the same terrane through a time span approaching 20 m.y.Comparison of Aleutian plain data with the compositions of coeval sedimentary rocks from the northeast Pacific margin shows that the Kodiak shelf area includes possible proximal equivalents of the more distal turbidites. Derivation from the volcaniclastic Mesozoic flysch of the Shumagin-Kodiak shelf is unlikely; more probably the sediments were derived from primary plutonic sources. The turbidites also resemble deposits in the Chugach Mountains and the younger turbidites of the Alaskan abyssal plain and could conceivably have been derived from the coast ranges of southeastern Alaska or western British Columbia. The Aleutian plain sediment most likely was not derived from as far south as the Oregon-Washington continental margin, where coeval sedimentary deposits are dominantly volcaniclastic.This work lends some support to earlier suggestions that the fan-shaped turbidite body originated on the continental margin in the Gulf of Alaska, and it supports models of little or modest motion of the Pacific plate relative to North America. The mineralogy alone cannot refute more ambitious motion models, but when combined with previously published evidence on size of the plain, sediment thicknesses, and nan-nofossil species diversity, the data seriously constrain models requiring large-scale northwestward motion of the Pacific plate in post-Eocene time. 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.
Diagenetic laumontite has been identified in samples of Cenozoic clastic rocks from 25 wells drilled in the southern end of the San Joaquin Valley. These occurrences, and data from 50 other wells that encountered no laumontite, define a sharp interface between zeolitized strata and overlying less altered beds. Contours on the interface have been mapped in the depth range between 2.1 and 6.1 km for an area of 2,300 sq km extending from the Bakersfield arch south to the San Emigdio Mountains. Companion maps depict generalized structure at the base of the Pliocene sedimentary section and at the basement floor. Generalizations derived from data of other regions indicate that pore-filling laumontite crystallizes from interstitial water of mineralogically immature sandstone when (1) geothermal gradients equal or exceed the range set by 59°C at 1,100 m to 180°C at 4,150 m; (2) fluid pressure gradients are near 113 bar/km (0.5 psi per ft); and (3) the solutions have exceptionally low salinities and are depleted in dissolved carbonate species. Laumontite in the map area is mostly a product of conditions prevailing during Miocene to Pleistocene time, and is thus a relic. Laumontite pore-filling in petroleum reservoir sandstones lowers porosity, drastically reduces permeability, and seriously limits the possibility of commercial production. Laumontite-bearing rocks are poor prospects for petroleum production unless there is evidence that mineralogically mature sandstone may be abundantly interbedded or that pore-fluid composition may be locally conducive to high carbonate activity. The discordant diagenetic boundary in the map area is inferred to be the product of both lateral variation in geothermal gradients during crystallization and post-diagenetic faults and folds. Entrapment of petroleum may occur where a sloping diagenetic front steeply crosses gently plunging folds. Hydrocarbon traps that are in part diagenetic have been discovered mainly by accident. Other possible diagenetic entrapment geometries that are yet to be tested and are not associated with structural closures can be delineated from our maps. End_of_Article - Last_Page 446------------
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