HR: 1340h
AN: OS23B-1306    [Abstracts]
TI: Mass-Transport and Relative Sea Level Change in a Carboniferous Deglacial Succession: Jejenes Fm, Quebrada las Lajas, San Juan, Argentina
AU: * Dykstra, M
EM: dykstram@umail.ucsb.edu
AF: Institute for Crustal Studies, University of California at Santa Barbara, Mail Code 1100, 1140 Girvetz Hall, Santa Barbara, CA 93106-1100 United States
AU: Kneller, B
EM: ben@crustal.ucsb.edu
AF: Institute for Crustal Studies, University of California at Santa Barbara, Mail Code 1100, 1140 Girvetz Hall, Santa Barbara, CA 93106-1100 United States
AU: Milana, J P
EM: jpmilana@hotmail.com
AF: CONICET e Instituto de Geologia, Universidad Nacional de San Juan, Avda. Ignacio de la Roza 590, CUIM, Rivadavia, San Juan, 5400 Argentina
AB: Quebrada las Lajas, near San Juan, Argentina, preserves a Carboniferous deglacial/postglacial succession in a highly confined paleofjord setting. The sedimentary succession can be divided into four distinct stages. The first stage is synglacial in origin, and is characterized by two related phases; a shallow-water phase, stage 1a, and a deeper-water phase, stage 1b. Stage 1a is characterized proximally by both disorganized and stratified diamictites, fluvial and subaqueous glacial outwash fans, and distally by disorganized and stratified remobilized diamictites, and interbedded varves with rare dropstones. Stage 1b records a relative water deepening. It is characterized by siltstones interbedded with sheet sandstones and conglomerates, as well as channelized sandstones and conglomerates. Rare dropstones are present in the basal portion of this phase. Stage two records a glacioeustatic marine transgression, and a shut-off or slow-down of the clastic conduit in the paleovalley. This stage is characterized primarily by marine shales with plentiful organic matter preserved, including tree trunks and leaves, interbedded with rare, thin turbidite sandstones and conglomerates. The third stage records progressive infilling of the accommodation space created in the paleovalley due to glacial overdeepening and the glacioeustatic marine transgression. Stage three is characterized by thick-bedded turbidite sandstones and associated shales. The fourth and final stage records a fan-delta paleovalley fill and is characterized by coarse turbiditic sandstones and conglomerates. All stages exhibit mass-transport related deposits, but stage 1b exhibits the most widespread mass-transport, with a wide range of processes represented, from completely mixed debris-flow deposits to coherently slumped and rafted blocks. The scale of these mass-transport deposits (MTDs) ranges from a few meters to over 50 m thick, and up to hundreds of meters wide and long. Most of the large MTDs in this stage occurred at the transition to stage 2, implicating increased relative sea-level as a possible trigger for the slope failures. Additionally, stage three preserves several thrust faults with large offsets relative to the scale of the sedimentary succession (tens to over 100 m vertically and laterally) that are interpreted as the downdip slide-scar ramp zones of MTDs. The incredible abundance of small to large-scale mass-transport deposits at the top of stage 1b may be related to the transgression at this level, combined with post-glacial rebound-generated seismicity. The abundance and size of MTDs in stages 1b and 3 provide fundamental controls on the locus of sedimentation throughout the paleovalley.
DE: 4556 Sea level variations
DE: 3022 Marine sediments--processes and transport
DE: 1815 Erosion and sedimentation
DE: 1827 Glaciology (1863)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting