Stratigraphic architecture, magnetostratigraphy, and incised-valley systems of the Pliocene-Pleistocene collisional marine foreland basin of Taiwan

Citation
Ws. Chen et al., Stratigraphic architecture, magnetostratigraphy, and incised-valley systems of the Pliocene-Pleistocene collisional marine foreland basin of Taiwan, GEOL S AM B, 113(10), 2001, pp. 1249-1271
Citations number
78
Categorie Soggetti
Earth Sciences
Journal title
GEOLOGICAL SOCIETY OF AMERICA BULLETIN
ISSN journal
00167606 → ACNP
Volume
113
Issue
10
Year of publication
2001
Pages
1249 - 1271
Database
ISI
SICI code
0016-7606(200110)113:10<1249:SAMAIS>2.0.ZU;2-G
Abstract
Lithofacies analysis, magnetostratigraphy, and seismic profiles of Pliocene -Pleistocene foreland basin deposits of Taiwan provide a framework to evalu ate the stratigraphic development of a collisional marine foreland basin. W e have recognized several scales of stratigraphic packages and unconformiti es in deposits of the Taiwan foreland basin. Small-scale (20 to 150 m thick ) stratigraphic sequences contain upward-shallowing, marine lithofacies suc cessions that are bracketed by thin coquina sandstones. We interpret the sm all-scale stratigraphic packages as "parasequences" in the traditional sequ ence stratigraphy model, the thin coquina sandstones representing marine-fl ooding intervals. The average duration of individual small-scale packages w as in the range of 37.5 k.y., on the basis of our magnetostratigraphy. Thes e sequences are interpreted as the product of eustatic sealevel change poss ibly related to the orbital time series of obliquity. Intermediate-scale stratigraphic sequences are 150 to 1000 m thick and are bounded by unconformities that are well exposed in outcrop and can be clear ly identified in seismic sections. The unconformity surfaces have several h undred meters of relief and represent periods of major fluvial valley incis ion in the foreland basin. One of the unconformities is locally an angular one that we interpret as representing a growth structure that formed during structural uplift of the proximal margin of the foreland basin at ca. 1.25 Ma. Across this angular unconformity, there were marked increases in rates of sediment accumulation and tectonic subsidence in the foreland basin. Ot her major unconformities that bound intermediate-scale stratigraphic sequen ces are high-relief disconformities. These unconformities may be the produc t of eustatic changes, because there has been little change in rates of sed iment accumulation and tectonic subsidence across these unconformities. The duration of individual, intermediate-scale packages ranges from similar to 100 000 to 700 000 yr, on the basis of magnetostratigraphy and biostratigr aphy. We interpret the intermediate-scale sequences as "sequences" in the t raditional sequence stratigraphy model. Our analysis of the Pliocene-Pleistocene deposits of the Taiwan foreland ba sin has several implications for understanding the stratigraphic evolution of this collisional marine foreland basin. (1) Deposition in the Taiwan for eland basin appears to have been punctuated by at least five episodes of er osion and major fluvial valley incision. Large volumes of sediment were ero ded from the proximal margin of the foreland basin and transported to more distal parts of the foreland basin or to depocenters outside the foreland b asin system during all stages of basin development. (2) The presence of hig h-relief unconformities and growth structures in the Pliocene-Pleistocene f oreland basin deposits suggests a well-developed wedge-top depozone in the foreland basin system. (3) The Pliocene-Pleistocene strata of the foreland basin of Taiwan record similar to2.3 m.y. of deposition, on the basis of ou r magnetostratigraphy. Sediment accumulation rate was on the order of simil ar to 950 m/m.y. during the earlier stages of basin development. During the later stages of basin development, sediment accumulation rate increased to similar to 1900 m/m.y. Sediment accumulation rates in the collisional mari ne foreland basin of Taiwan are much higher than previously published rates from more extensively studied retroarc foreland basins and collisional non marine foreland basins.