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
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.