Abstract
The marginal seas of eastern Asia are supplied by some of the largest and most sediment-rich rivers on Earth (Liu et al., 2016). Many of these rivers have their sources on the Tibetan Plateau and are fed by the rains of the summer monsoon. Climate and tectonically generated topography account for the high sediment loads of the rivers that construct a number of giant deltas and some of the widest continental shelves of the world (Clift et al., 2010; Liu et al., 2009; Syvitski and Kettner, 2011). The new collection of 15 articles edited by Clift, Harff, Wu and Qiu is a timely publication presenting mainly Chinese research. It highlights recent developments in our understanding of fluvial sediment fluxes and shelf deposits with the marginal seas of eastern Asia in terms of provenance and weathering, sea-level rise and sequence stratigraphy, sediment transport, anthropogenic and environmental impacts.
Clift reviews critically the significance of provenance methods applied to the South China Sea (SCS). Thermochronology methods are best suited, with particularly apatite fission track analysis showing more diversity than other dating methods. Nonetheless, a multi-proxy approach is recommended. Shao et al. applied some of these provenance methods, including major and rare earth elements geochemistry and heavy mineral assemblages to modern sediments and Oligocene and Miocene sedimentary rocks from Pearl River Mouth Basin.
Hu et al. used major and trace elements together with clay mineral assemblages in examining the chemical weathering of fluvial-derived sediments in the SCS. In general, marine archives of fluvial sediment preserve variations in weathering linked to climate but are often influenced by reworking and erosion, especially during sea-level lowstands. Cui et al. applied geochemical proxies to investigate the intensity of weathering in the Hainan Island source regions from Holocene sediments of the Gulf of Tonkin and were able to distinguish four phases of climatic development.
Ni et al., using high-resolution seismic profiles and a sediment core spanning the past 13,000 years, identified a large shelf mud belt extending over 11,000 km2 west of Hainan Island. A homogeneous seismic unit contains the post-glacial history of this mud belt. Chen et al. reconstructed the late Pleistocene sequence stratigraphy covering the past 110,000 years using a similar approach combining seismic profiles and sediment coring east of the mud belt area in the Gulf of Tonkin.
The review paper by Zhong et al. examines the late Quaternary evolutionary history of the northern coast of the SCS. Two marine sequences, deposited during the penultimate sea-level highstand 126,000–120,000 years ago (MIS 5e) and during the Holocene, are observed in the deltaic basins of the Red, Pearl and Han rivers which are bounded by active faults.
Yang et al. consider the fate of late Quaternary sediments delivered by the Yangtze to the East China Sea (ECS). Since the Last Glacial Maximum, major sinks shifted from the outer shelf and Okinawa Trough to the present-day large delta and shelf clinoforms along the southeastern Chinese coast. Based on field observations during the 2013 monsoon season, Wu et al. focus on shelf currents in their study of trapping and escaping processes of Yangtze-derived sediments to the ECS.
Jia et al. observed dramatic morphological and hydrodynamic changes due to human activities at four river outlets in Lingdingyang Bay of the Pearl River mouth system between 2003 and 2012. Wang et al. investigated the new Diaokou lobe in the modern Yellow River delta which contains sediments of four different units deposited between 1964 and 1976, after the river changed its course by artificial diversion. The lobe system was abandoned after 1976 by a new delta-lobe switch.
Zhou et al. studied a benthic foraminiferal proxy record spanning the past 290,000 years from a sediment core on the northern slope of the SCS. Palaeo-productivity patterns in the bottom waters reflect environmental changes linked to winter-monsoon variability during glacial and interglacial stages. Zhang et al. employed diatoms for palaeo-environmental reconstructions from sediment cores across the East Asian marginal seas. Paralia sulcata varies strongly in abundance through time over the last glacial cycle. Changes in abundance are not synchronous in SCS and ECS. Gao et al. provide a synoptic study of Holocene shelf sediments comprising the Bohai, Yellow and East China seas as a single shelf environment. Holocene sediment distribution, composition and deposition rates are related to sediment transport processes induced by tides, waves, shelf currents and sediment gravity flows.
In summary, the book not only highlights several complexities of fluvial sediment transport and deposition on continental shelves but also shows the limitations of shelf deposits in the geological record. In addition to the excellent introduction, I would have liked to see a concluding chapter with a synthesis of the multi-faceted and heterogeneous collection of articles. Although the quality of the respective contributions is not consistently high, I can fully recommend this book to researchers interested in East Asian sedimentology and, more generally, in continental shelf sedimentation processes and resulting sedimentary records.