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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 with 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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