Aleutian Trench, Shumagin Segment, Seismic Section 104
Terry R. Bruns, Roland von Huene, 1986. "Aleutian Trench, Shumagin Segment, Seismic Section 104", Seismic Images of Modern Convergent Margin Tectonic Structure, Roland von Huene, Susan Vath, Christine Sperber, Bridgett Fulop, Lee Bailey, Monique Martin
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The Shumagin segment of the eastern Aleutian convergent margin extends into the Gulf of Alaska from the Alaska Peninsula. Here the shelf is narrower and the Shumagin Islands are much smaller than islands, in the adjacent Kodiak shelf area, but many of the rocks are similar. Insular exposures are comprised of late Cretaceous sedimentary rocks metamorphosed in a low-temperature environment and once buried about 10 km deep. Paleogene rocks that crop out in the Kodiak area may continue into the Shumagin area, but they have not yet been sampled beneath the Shumagin shelf. The Paleogene rocks are cut by a major unconformity that is overlain by upper Miocene rocks in the Kodiak area. A Neogene forearc basin, Shumagin basin (Bruns and von Huene, 1977; Bruns et al., in press), contains about 2.5-km-thick strata of probable late Miocene and younger age. Landward of the basin is the Border Ranges fault (Fisher and von Huene, 1984), which probably isolates the pre-Upper Cretaceous geology of the Alaska Peninsula from that of the Shumagin shelf. The Aleutian volcanic arc forms the backbone of the Alaska Peninsula. Bristol Bay and the Bering Sea shelf constitute the backarc basin.
Structurally, the Shumagin margin has all the elements associated with a major subduction zone. However, this segment differs from the central and eastern Aleutian sections (p. 10 and 20, this volume) in having no sediment ponded in the trench axis (von Huene, 1972). Seaward of the trench axis is Zodiak fan, a Paleogene deep-sea fan complex that
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In 1980, A. W. Bally assembled and edited an innovative three-volume “picture and work” atlas of seismic reflection record sections. This compilation of more than 130 excellent seismic section reproductions provided much new data from the earth's subsurface. For petroleum geologists, academic scientists, and students, it is the field geologist's counterpart of outcrops and type sections. The smaller collection of seismic sections presented in this Studies 26 publication was inspired by Bally's atlas, and follows his general format and philosophy. The objective is to provide a reference series of sections for the earth sciences and a vehicle for continuing scientific dialogue relating to modern convergent margins. This publication's assembled sections represent a single facet of that dialogue by bringing together a series of exceptional seismic sections from the fronts of presently active convergent margins around the Pacific.