PROPOSED SITES
Six primary and two alternate sites are proposed for drilling (Table 2). These fall into two groups: northeastern continental slope (Fig. 9) and southern slope (Fig. 10). A summary of the water depths for each site and the expected age/penetration is given in Figure 11.
1.
Northeastern Continental Slope
Sites SCS-1 to 5 are located south of the Dongsha Islands in
the northeast SCS (Fig. 9). The sites are
designed to sample different water depths and to cover successive
time intervals since the Oligocene (SCS-1: Pleistocene; SCS-2:
middle Pliocene onward; SCS-3: Pliocene and Pleistocene; SCS-4:
middle Miocene to Pliocene; SCS-5: Oligocene to Miocene). This
suite of sites should provide the sections to identify and date
the proposed stages of monsoon evolution in East Asia.
Site
SCS-1
SCS-1 is targeted for 2050 m water depth, which is slightly
above the sill depth of the Bashi Straits (2600 m). The location
of Site SCS-1 is distinguished by extremely high
sedimentation rates. The Holocene deposits in the nearby Core
17940 (20°07ŽN, 117°23ŽE, water depth 1727 m) reach almost 7
m in thickness, and Core MD 97.2.146 extends only to the oxygen
stage 4/5 boundary at 38 m (C.Y. Huang, pers. comm., 1997). The
summer monsoon cyclicity of 102 yr in the Holocene and the
dry/humid cyclicity of 103 yr in the late Pleistocene found in
Core 17940 (Wang et al., 1995a; Sun, 1996) indicate the great
potential of this site in delivering high-resolution monsoon
records for the Pleistocene. The target penetration of 450 m is
anticipated to recover Quaternary sediments (~1 m.y.).
Site
SCS-2
Proposed Site SCS-2 is downslope of SCS-1 at a water depth of
3190 m. This location has a lower sedimentation rate and is
expected to provide a continuous record from the middle Pliocene
to Pleistocene (Holocene). Because the sill depth of the Bashi
Strait is located at ~2600 m, Sites SCS-1 and SCS-2 will also
document the Quaternary changes in water mass characteristics
across the sill, which is the only deep-water connection between
the Pacific and the SCS. SCS-2 is targeted for 400 m penetration.
Site
SCS-3C
Site SCS-3C is on the upper slope (water depth ~1265 m) near
the base of the modern oxygen minimum zone (State Oceanic
Administration, 1988; Haupt et al., 1994). This site is expected
to provide a sequence of Pliocene and Pleistocene sediments that
record changes in the intermediate water characteristics well
above the sill depth. The variables of most interest are
temperature and oxygen content, as well as surface-water
conditions. Site SCS-3C is targeted for 300 m penetration.
Site
SCS-4
Site SCS-4 is downslope of Site SCS-3C at a water depth of
2093 m. On the basis of seismic records, the proposed site should
recover a middle Miocene to Pliocene sequence, which underlies
relatively thin Pleistocene deposits. This site also lies above
the current sill depth of the Bashi Straits and, along with
SCS-5C, offers a Mio-Pliocene history of sill-related water-mass
changes. SCS-4 is targeted for 520 m penetration.
Site
SCS-5C
Site SCS-5C is located lower on the slope (3232 m) and is
expected to recover an expanded Oligocene to Miocene section. On
the basis of available seismic records and their correlation to
Chinese reflector stratigraphy, SCS-5C is targeted for 700 m
penetration. Given the expected accumulation rates and
penetration depths, SCS-5C (and the alternate SCS-5D) are the
only sites that will recover the Oligocene-Miocene history of the
SCS, including the possible onset of the East Asian monsoon.
Alternate
Sites SCS-5D and SCS-5E
Sites SCS-5D and SCS-5E are located about 65 and 20 km,
respectively, northeast of Site SCS 5C. These alternate sites
provide a somewhat expanded midsection compared to SCS-5C. They
could be cored, if SCS-5C does not meet the expectations of a
complete Oligocene-Miocene section.
2.
Southern Slope
A southern continental slope SCS site is proposed to reveal
the history of tropical East Asia and the Western Pacific Warm
Pool (Fig. 10). Although the
terrigenous deposits of the paleo-Sunda and Mekong Rivers provide
a number of attractive targets in the southern part of the SCS,
and piston cores in the region have high sedimentation rates and
display high frequency climate variations, especially since the
last glaciation. Safety considerations have entailed moving the
site farther downslope (to the north) and limiting penetration.
This southern location will be the only site within the Western
Pacific Warm Pool and will provide a thermal contrast to the
northern sites.
Site
SCS-9
Proposed Site SCS-9 is at a water depth of 2830 m.
Penetration is limited to 400 m, reaching the upper part of the
upper Miocene.