HR: 1340h
AN: T53A-1403    [Abstracts]
TI: Seismic Stratigraphy of the Mariana Forearc Sedimentary Basin
AU: * Chapp, E
EM: chapp@soest.hawaii.edu
AF: SOEST, University of Hawaii 1680 East-West Rd., Honolulu, HI 96822 United States
AU: Taylor, B
EM: taylorb@hawaii.edu
AF: SOEST, University of Hawaii 1680 East-West Rd., Honolulu, HI 96822 United States
AU: Oakley, A
EM: aoakley@hawaii.edu
AF: SOEST, University of Hawaii 1680 East-West Rd., Honolulu, HI 96822 United States
AU: Moore, G
EM: gmoore@hawaii.edu
AF: SOEST, University of Hawaii 1680 East-West Rd., Honolulu, HI 96822 United States
AB: A grid of seismic reflection profiles across the Mariana forearc between 14N-18N reveals a sedimentary basin between the Oligocene-Miocene frontal arc and the Eocene outer forearc highs. We identify and correlate several seismic stratigraphic units and use them to constrain the local and regional tectonics, which vary significantly from north to south. Four major sediment packages are distinguished in the southern forearc basin. The oldest unit, U-4, is conformable to arcward-tilted, rotated fault blocks formed during early extension, possibly associated with early Oligocene rifting prior to Parece Vela Basin spreading. Onlap relationships between the oldest sedimentary units indicate that deposition occurred before, during and after block rotation. On one profile, the U-4 sequence is deformed above a blind thrust fault in an otherwise extensional environment. Sediments that comprise the third unit, U-3, thin trenchward and onlap onto U-4. U-2 sediments onlap both sides of the basin and are characterized by nearly uniform thicknesses across the southern section. They currently dip trenchward, but are bypassed and onlapped arcward by thin recent deposits, U-1, on the three southern lines, suggesting recent relative subsidence of the outer forearc. The onset of this subsidence (during deposition of the upper strata of U-2) may have generated slope instability that triggered a large submarine slump off the frontal arc high into the forearc basin ENE of Saipan. The seismic stratigraphic units reveal both pre- and post-slump depositional boundaries including a possible post-slump debris apron around the perimeter of the toe thrust. The central region (near 16N), absent of the large rotated basement fault blocks found in the south, is characterized by high-angle normal faults that offset the seafloor by as much as 200 m. The upper section of U-4 is visible in isolated sections, but the coherency of the oldest layers is lost. Because a clear basement reflection is not resolved in this area, it is uncertain whether the absence of the oldest sediment reflections represents a lack of deposition or the limits of our imaging capabilities. The basin stratigraphy reveals a northward thickening of U-2 and U-3, indicating greater extension and increased sediment supply in the central region during deposition. U-1 is absent suggesting that the large relative subsidence of the outer forearc is restricted to the southern region. The stratigraphy of the northern forearc basin (near 18N) is interrupted by several local basement highs. U-4 and the lower sediments of U-3 are not imaged in this area. The upper strata of U-3 are resolvable in small basins formed between local highs. Above this, U-2 comprises most of the coherent basin fill. Ongoing work seeks to correlate these sequences with dated cores drilled in the area at ODP Leg 60 Sites 458 and 459.
DE: 3022 Marine sediments: processes and transport
DE: 3025 Marine seismics (0935, 7294)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 3075 Submarine tectonics and volcanism
SC: Tectonophysics [T]
MN: Fall Meeting 2005