Elsevier

Marine Geology

Volume 236, Issues 3–4, 1 February 2007, Pages 165-187
Marine Geology

Sedimentary evolution of the Holocene subaqueous clinoform off the Shandong Peninsula in the Yellow Sea

https://doi.org/10.1016/j.margeo.2006.10.031Get rights and content

Abstract

A subaqueous clinoform wraps around the end of the Shandong Peninsula in the Yellow Sea. The clinoform, previously called the Shandong mud wedge, is up to 40 m thick nearshore and thins seaward. Its origin has been controversial since it was first noted in the 1980s. For our recent investigation offshore of the northeastern Shandong Peninsula, high-resolution shallow seismic profiles covering about 1700 km were obtained, and two drilling cores penetrating the clinoform were recovered. We described the lithofacies characteristics, identified benthic foraminifera and ostracoda, measured grain size, analyzed the mineral components of the cores, and obtained AMS 14C dates on 28 samples, to decipher the sedimentary evolution of the clinoform in response to postglacial sea-level changes. The shallow seismic profiles show that the clinoform comprises three units: a lowermost seismic unit (SU 3, less than 2–3 m thick) showing a retrogradational/aggradational stacking pattern with subhorizontal internal reflectors, a middle seismic unit (SU 2, up to 35 m thick) showing a prograding reflection pattern with mostly seaward-stepping reflectors separated by several erosive surfaces, and an uppermost seismic unit (SU 1, maximum thickness 18 m) exhibiting an aggradational reflection pattern with subparallel reflectors. The three seismic units are bounded on the bottom by distinct erosion surfaces. Analyses of the two cores indicate that the clinoform comprises three depositional units, DU 1, DU 2, and DU 3 in descending order, corresponding respectively to SU 1, SU 2, and SU 3. The depositional units are distinguished by lithofacies characteristics and the downcore distributions of benthic foraminiferal and ostracod assemblages. Mineral components of the cores suggest that the clinoform's provenance is predominantly Yellow River-derived sediments. AMS 14C dates suggest that DU 3 was formed from about 11.6 to 9.6 cal kyr BP, DU 2 from 9.6 to 6.5 cal kyr BP, and DU 1 after ca. 6.5 cal kyr BP. Some major meltwater pulse (MWP) events during the deglacial transgression were registered in the clinoform stratigraphy, with the basal surfaces/sediments of DU 3 and DU 2 corresponding respectively to MWP-1B (ca. 11.6–11.3 cal kyr BP) and MWP-1C (ca. 9.6–9.2 cal kyr BP) events, and with DU 2 being largely formed after the 8.4–8.2 cal kyr meltwater event. Rapid centennial- to multidecadal-scale flooding events were presumably responsible for the erosive surfaces separating the downlapping internal reflectors in SU 2. The change of depositional pattern from progradational in SU 2 to aggradational in SU 1 is attributed to a change from strong, dominantly to-and-fro tidal currents to the modern circulation in the Bohai Sea as well as to the weakening of the tidal-current field during the highstand after about 6500 cal yr BP. As a product of complex interactions among sediment supply, sea-level changes, and hydrodynamic regimes, the clinoform can be regarded as the distal part of the tidal depositional system in the eastern Bohai Sea, which was largely derived from the Yellow River.

Introduction

The Yellow Sea lies on a shallow, semi-enclosed, low-gradient shelf between the Chinese mainland and the Korean Peninsula (Fig. 1). It connects with the Bohai Sea to the northwest and the East China Sea to the south, and together the three seas form a vast marginal sea in the northwestern Pacific. A prominent subaqueous clinoform with a maximum thickness of 30 m was first noted in the 1980s to extend southward around the eastern tip of the Shandong Peninsula in the western Yellow Sea (Milliman et al., 1987), some 350 km east of the modern Yellow River mouth, which is on the western coast of the Bohai Sea. Milliman et al., 1987, Milliman et al., 1989 suggested that it is located along the escape route via which the Yellow River sediment has been transported from the Bohai Sea to the southern Yellow Sea during the last 5000 yr. Alexander et al. (1991) called the clinoform the Shandong subaqueous delta, on the basis of its similarity to the subaqueous delta system offshore of the mouth of the Amazon River, and speculated that it had formed between 6200 and 4060 yr BP, based on 14C dates of samples from a vibrocore with a total length of less than 3 m. More recent work has shown that the clinoform is also distributed along the northern side of the Shandong Peninsula (Cheng et al., 2001, Liu et al., 2002, Liu et al., 2004), and, based on high-resolution seismic profiles, Liu et al., 2002, Liu et al., 2004 identified proximal and distal phases of clinoform development in terms of the distance between the Yellow River mouth and the clinoform during the postglacial transgression. Moreover, they proposed that the underlying proximal and overlying distal sequences were formed between ∼ 11 and 9.2 cal kyr BP and after 9.2 cal kyr BP, respectively, in accordance with a presumed stepwise, postglacial sea-level rise. This debate on the origin and evolution of the subaqueous clinoform around the Shandong Peninsula arose largely because of the lack of deep boreholes through the clinoform.

During our geological survey conducted in the Yellow Sea in 2003, two boreholes up to 70 m long were drilled in the subaqueous clinoform around the Shandong Peninsula, and more than 1700 km of high-resolution seismic profiles were measured across it. In this paper, we illustrate the stratigraphic structure, lithologic characteristics, mineral compositions, and the age of the clinoform using the shallow-seismic profiles and the cores, and provide insight into its distinctive sedimentary evolution under a complex interplay of eustatic sea-level changes during the postglacial period and locally restricted processes of sediment supply affected by climate, river-mouth shifting, and depositional hydrodynamics.

Section snippets

General physiographic features and regional oceanography

The Yellow Sea is a broad, relatively shallow epicontinental sea above a flat, tectonically stable shelf (Fig. 1). It is separated from the Bohai Sea to the west by the Bohai Strait, and from the East China Sea to the south by a line connecting the north edge of the Yangtze River mouth with Cheju Island. The Shandong Peninsula separates the South from the North Yellow Sea (NYS). Water depths in the NYS are generally less than 60 m, and they deepen progressively southward and southeastward in

Materials and methods

To characterize the seafloor morphology and subsurface stratigraphic architecture as well as to ensure that cores were retrieved from suitable locations in the shallow-water area around the Shandong Peninsula, over 1700 km of high-resolution seismic profiles were acquired (Fig. 3) in May and June 2003- with a 400- to 500-J SBP/AAE sparker system fired at 1-s intervals, and records were filtered between 500 and 5000 Hz and limited to a vertical penetration of 100 ms two-way travel time. The

Seismic stratigraphy

Both the E–W and S–N seismic profiles in the study area show a sigmoidal clinoform morphology, which thins offshore to less than 1 m (Fig. 4, Fig. 5, Fig. 6). With a maximum thickness of 40 m, the clinoform wraps around the eastern end of the Shandong Peninsula and extends offshore beyond long. 123°30′E and lat. 38°30′N (Fig. 6(a)–(c); Liu et al., 2002). A close inspection of the isopach map of the clinoform (Fig. 7(a)) shows that the thickest part, demarcated by the 30-m isopachs, is 20–50 km

Depositional ages and sediment accumulation rates

Fig. 11 displays the age-depth plots (sediment accumulation curves) for the two cores, along with sea-level curves of the last 14 kyr for the East China Sea/Yellow Sea (Liu et al., 2004). The sediment accumulation curves neglect any sediment compaction effects. The postglacial sea-level rise reached its highest point around 6500 cal yr BP in the western Pacific region, and during the subsequent highstand, sea level has fallen to the present level (Nakada and Lambeck, 1989).

On the basis of the 14

Conclusions

With its thickest part decoupled from the shoreline, the sigmoidal clinoform off the eastern Shandong Peninsula has a maximum thickness of 40 m and generally thins seaward to less than 1 m. The clinoform is made up of three depositional units, DU 1, DU 2 and DU 3 in descending order, corresponding respectively to three seismic units, SU 1, SU 2 and SU 3. DU 3 consists of silt to sandy silt and shows a roughly fining-upward succession; it was deposited in a subtidal nearshore environment during

Acknowledgements

This study was funded jointly by the National Natural Science Foundation of China (Grant Nos. 40376018 and 90211022) and the National Basic Research Program (Grant Nos. 2005CB422304). We thank Dr. Zhengxin Chen, Tiehu Zhao, Xianghuai Kong, Liangyong Zhou, Yuan Liang, Shuli Wang, Yong Zhang, and Gang Hu for their help in the geological survey or in preparing this manuscript.

References (68)

  • J.D. Milliman et al.

    Modern Huanghe-derived muds on the outer shelf of the East China Sea

    Cont. Shelf Res.

    (1985)
  • C.F. Neill et al.

    Subaqueous deltaic formation on the Atchafalaya Shelf, Louisiana

    Mar. Geol.

    (2005)
  • M.E. Ren et al.

    Sediment discharge of the Yellow River (China) and its effect on the sedimentation of the Bohai and Yellow Sea

    Cont. Shelf Res.

    (1986)
  • Y. Saito et al.

    Transgressive and highstand systems tracts and post-glacial transgression, the East China Sea

    Sediment. Geol.

    (1998)
  • Y. Saito et al.

    Delta progradation and chenier formation in the Huanghe (Yellow River) delta, China

    J. Asian Earth Sci.

    (2000)
  • Y. Saito et al.

    The Huanghe (Yellow River) and Changjiang (Yangtze River) deltas: a review on their characteristics, evolution and sediment discharge during the Holocene

    Geomorphology

    (2001)
  • J.T. Teller et al.

    Freshwater outbursts to the oceans from glacial Lake Agassiz and their role in climate change during the last deglaciation

    Quat. Sci. Rev.

    (2002)
  • k. Uehara et al.

    Paleotidal regime in the Changjiang (Yangtze) Estuary, the East China Sea, and the Yellow Sea at 6 ka and 10 ka estimated from a numerical model

    Mar. Geol.

    (2002)
  • L. Wang et al.

    East Asian monsoon climate during the Late Pleistocene: high-resolution sediment records from the South China Sea

    Mar. Geol.

    (1999)
  • C. Xue et al.

    Holocene sedimentary sequence, foraminifera and ostracoda in west coastal lowland of Bohai Sea, China

    Quat. Sci. Rev.

    (1995)
  • W.W.-S. Yim et al.

    Postglacial sea-level changes in the northern South China Sea continental shelf: Evidence for a post-8200 calendar yr BP meltwater pulse

    Quat. Int.

    (2006)
  • R.B. Alley et al.

    Holocene climatic instability: a prominent, widespread event 8200 yr ago

    Geology

    (1997)
  • D.C. Barber et al.

    Forcing of the cold event of 8200 years ago by catastrophic drainage of Laurentide lakes

    Nature

    (1999)
  • E. Bard et al.

    U-Th ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years

    Nature

    (1990)
  • E. Bard et al.

    Deglacial sea-level record from Tahiti corals and the timing of global meltwater discharge

    Nature

    (1996)
  • P. Blanchon et al.

    Reef drowning during the last deglaciation: evidence for catastrophic sea-level rise and ice-sheet collapse

    Geology

    (1995)
  • G. Bond et al.

    A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates

    Science

    (1997)
  • J.C. Boothroyd

    Tidal inlets and tidal deltas

  • T.W. Cheng et al.

    Water and sediment discharges into seas from main rivers of China and their influence on coasts

    Oceanogr. Sinic.

    (1985)
  • P. Cheng et al.

    A preliminary study of the distribution of Holocene deposits in the western North Yellow Sea

    Quat. Sci.

    (2001)
  • P.U. Clark et al.

    Rapid rise of sea level 19,000 years ago and its global implications

    Science

    (2004)
  • W.L. Ding

    The characteristics of the tides and tidal currents in the Bohai and the Yellow Seas

    Stud. Mar. Sin.

    (1985)
  • L.X. Dong et al.

    Tide current in the Yellow Sea and its relationship with sediment transport

    Acta Oceanol. Sin.

    (1989)
  • R.G. Fairbanks

    A 17,000-yr glacio-eustatic sea-level record: influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation

    Nature

    (1989)
  • Cited by (178)

    View all citing articles on Scopus
    View full text