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Quaternaria Nova, VIII, (2004), 277-296
COASTAL SANDY
RIDGES AND REEFS OF SOUTHERN HAINAN ISLAND (CHINA) DEVELOPED DURING QUATERNARY
SEA-LEVEL VARIATIONS
I. Peter Martini1,
Ying Wang2, Dakui Zhu2,
Yongzhan Zhang2 and
Wenwu Tang2
1Department
of Land Resource Science, University of Guelph, Guelph, ON, Canada
2The Key
Laboratory of Coast and Island Development of Ministry of Education P. R. China
and Dept. of Geo & Ocean Sciences, Nanjing University, Nanjing, China
3Coastal
Engineering Group, Department of Civil Engineering, Osaka University, Suita,
Osaka, Japan
Hainan Island is composed of Paleozoic-Mesozoic
geological "terranes", some of Gondwana origin. It has a highly indented
coastline wi th
promontories and embayments localized and dissected by variously oriented normal
faults. To the north, basaltic eruptions have occurred, and some large deltas
have developed during
the Quaternary. During the Pleistocene glacial times, the surrounding shallow
portions of the South China Sea were exposed, and were re-inundated upon
deglaciation. Eustatic and isostatic sea-level variations that occurred are
recorded by a series of sandy coastal ridges (bars, barriers, tomboli) and
fringing reefs. Early Pleistocene sea-level highstands are indicated by a series
of raised, highly weathered, sandy coastal ridges. These older ridges cannot be
numerically dated by conventional means. The Holocene shore features (coastal
sand ridges and emerged reef platforms) can instead be readily 14C
dated. The indication is that during the last major postglacial transgression,
conditions favorable for development of siliciclastic coastal bar/barriers and
carbonate reefs started about 8000a (a= calibrated 14C years ago).
There is also indication that at about 5-6000a the relative sea level was
approximately 2-5 m higher than the present. This may be explained by the
combined effect of sea-level drop (about 2 m in the tropical to subtropical
Pacific area) and Holocene differential land uplift (about 2-3 m in southern
Hainan Island).
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