A comprehensive data set of more than 200 profiles across the Peru-Chile Trench between 4° and 45°S is used to describe the morphology and shallow structure of the trench axis and the downbending oceanic plate just prior to subduction. Five morphotectonic provinces (4°–12°, 12°–17°, 17°–28°, 28°–45°S) show distinct changes in trench depth, axial sediment thickness, oceanic plate fault structures, and dip of the seaward trench slope. In general, the northern and southern regions are characterized by relatively shallow axial depths, moderate to thick trench axis turbidites, and a gently dipping seaward trench slope that exhibits minor normal faults. The deeper...
Research Article| May 01, 1974 Transfer of Nazca Ridge Pelagic Sediments to the Peru Continental Margin L. D. KULM; L. D. KULM 1School of Oceanography, Oregon State University, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar JOHANNA M. RESIG; JOHANNA M. RESIG 2Hawaii Institute of Geophysics, University of Hawaii, Honolulu, Hawaii 96822 Search for other works by this author on: GSW Google Scholar TED C. MOORE, JR.; TED C. MOORE, JR. 3School of Oceanography, Oregon State University, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar VICTOR J. ROSATO VICTOR J. ROSATO 3School of Oceanography, Oregon State University, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1974) 85 (5): 769–780. https://doi.org/10.1130/0016-7606(1974)85<769:TONRPS>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation L. D. KULM, JOHANNA M. RESIG, TED C. MOORE, VICTOR J. ROSATO; Transfer of Nazca Ridge Pelagic Sediments to the Peru Continental Margin. GSA Bulletin 1974;; 85 (5): 769–780. doi: https://doi.org/10.1130/0016-7606(1974)85<769:TONRPS>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 A complex set of lithologies, including calcareous oozes, hemipelagites, and turbidites, was recovered from the landward wall of the Peru Trench at its intersection with the Nazca Ridge. The sequence occurs at a water depth of 4,900 m and overlies an acoustic basement in the lowermost continental slope. Early Pliocene calcareous ooze overlies Pliocene to Quaternary ooze; both of these deposits are sandwiched between late Pleistocene (⩽ 400,000 yr), organic-rich turbidites and hemipelagic deposits typical of the Peru Trench and margin.Planktonic and benthic foraminiferal assemblages indicate that the early Pliocene ooze originally was deposited on the Nazca Ridge above the calcium carbonate compensation depth (4,000 m) and to the west of the cool Peru-Chile Current. The Pliocene-Pleistocene ooze contains a temperate fauna associated with the Peru-Chile Current. Block faulting at the terminus of the Nazca Ridge displaced the calcareous ooze 1,900 m from the top of the ridge to the trench below. Apparently these lithologies were then folded against or thrust beneath the lower continental slope within the past 400,000 yr.The stratigraphic sequence and the physiographic setting of the Nazca Ridge–Peru Trench intersection indicate convergence of the Nazca Ridge with the South American block. A minimum convergence rate of 0.8 cm/yr is calculated for the Pleistocene based upon the past and present geographic positions of the calcareous ooze. The best estimate of the rate is 2.8 cm/yr. 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.
Cascadia Channel is the most extensive deep-sea channel known in the Pacific Ocean and extends across Cascadia Basin, through Blanco Fracture Zone, and onto Tufts Abyssal Plain. The channel is believed to be more than 2200 km in length and has a gradually decreasing gradient averaging 1:1000. Maximum channel relief reaches 300 m on the abyssal plain and 1100 m in the mountains of the fracture zone. The right (north and west) bank is consistently about 30 m higher than the left (south and east). Turbidity currents have deposited thick, olive-green silt sequences throughout upper and lower Cascadia Channel during Holocene time. The sediment is derived primarily from the Columbia River and is transported to the channel through Willapa Canyon. A cyclic alternation of the silt sequences and thin layers of hemipelagic gray clay extends at least 650 km along the channel axis. Similar Holocene sequences which are thinner and finer grained, occur on the walls and levees of the upper channel and indicate that turbidity currents have risen high above the channel floor to deposit their characteristic sediments. A thin surficial covering of Holocene sediment along the middle channel demonstrates the erosional or non-depositional nature of the turbidity currents in this area. The Holocene turbidity current deposits are graded texturally and compositionally, and contain Foraminifera from neritic, bathyal, and abyssal depths which have been size-sorted. A sequence of sedimentary structures occurs in the deposits similar to that found by Bouma in turbidites exposed on the continent. There is a sharp break in the textural and compositional properties of each graded bed. The coarser grained, basal zone of each bed represents deposition from the traction load; the finer grained, organic-rich, upper portion of each graded bed represents deposition from the suspension load. Individual turbidity current sequences are thinnest in the upper and thickest in the lower channel. Recurrence intervals between flows range from 400 years in the upper to 1500 years along portions of the lower channel. Evidently each flow recorded near shore did not extend its entire length. Turbidity currents have reached heights of at least 117 m and spread laterally 17 km from the channel axis. Calculated flow velocities range from 5.8 m/sec along the upper channel to 3.3 m/sec along the lower portion. Pleistocene turbidity currents within Cascadia Basin were much more extensive areally than the Holocene flows, and they deposited sediment which was coarser and cleaner. Pronounced levees which border the upper channel are due chiefly to Pleistocene overflow. Coarse gravels and ice-rafted pebbly clays were also deposited along Cascadia Channel during Pleistocene time.
Research Article| October 01, 1975 Late Cenozoic volcanism in the Aleutian Arc: Information from ash layers in the northeastern Gulf of Alaska K. F. SCHEIDEGGER; K. F. SCHEIDEGGER 1School of Oceanography, Oregon State University, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar L. D. KULM L. D. KULM 1School of Oceanography, Oregon State University, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar Author and Article Information K. F. SCHEIDEGGER 1School of Oceanography, Oregon State University, Corvallis, Oregon 97331 L. D. KULM 1School of Oceanography, Oregon State University, Corvallis, Oregon 97331 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1975) 86 (10): 1407–1412. https://doi.org/10.1130/0016-7606(1975)86<1407:LCVITA>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 K. F. SCHEIDEGGER, L. D. KULM; Late Cenozoic volcanism in the Aleutian Arc: Information from ash layers in the northeastern Gulf of Alaska. GSA Bulletin 1975;; 86 (10): 1407–1412. doi: https://doi.org/10.1130/0016-7606(1975)86<1407:LCVITA>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 A sequence of ash layers recovered from site 178 of the Deep Sea Drilling Project in the Gulf of Alaska was studied to determine the nature of highly explosive volcanic eruptions associated with the Aleutian Arc and Alaskan Peninsula during the last 8 m.y. The major-element chemistry of 25 distinct ash layers was determined. When the analyses are plotted on conventional major-element variation diagrams, the unusual, highly evolved, calc-alkalic characteristics of the ashes are apparent. Perhaps more significantly, there is a good correlation of certain indices of the degree of chemical evolution of each ash (SiO2 content and Larsen index) with sample age. Both parameters vary cyclically, with maximum values of both indices occurring at present, 2.5, and about 5.0 m.y. ago. The cause of the cyclic activity, as well as discontinuous volcanic activity reported for other areas by other investigators, is not precisely known. However, we suggest that variable rates of subduction provide a viable hypothesis for discontinuous volcanic activity associated with convergent plate boundaries. 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.
Records of near-bottom currents measured in Cascadia, Surveyor, and Baker deep-sea channels suggest net transport in a down-channel direction. Bottom-current velocities of up to 10 cm/sec may provide a mechanism for transporting suspended materials from the continental margin to the deep ocean basins.
The clay mineralogy and organic carbon contents of 52 surface and 53 subsurface samples were determined for Quaternary sediments of the Peru continental margin and adjacent Nazca plate. By using Q-mode factor analysis, three factors (oceanic, continental A, and continental B) can explain 99% of the variation in clay mineral composition and organic carbon content in surface sediment. Northeast Nazca plate surface sediment is characterized by an oceanic factor that is dominated by smectite with subordinate illite. Continental margin surface sediment is characterized by the following clay mineral assemblages: (1) continental factor A, which consists of smectite-chlorite mixed-layer clays and...
