Developments of the Depositional Systems and Basin Subsidence since 50 ka of the Taipei Basin

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This study establishes the stratigraphic architecture of the Taipei Basin and its temporal and spatial paleoenvironmental development during the past 50 kyr based on analyses of 54 borehole cores and 153 age data. We calculate the rates of basin subsidence from the borehole data at depths where radiocarbon age dates are available. Our results indicate that, during the eustatic sea level falling period (50–20 ka), the basin was covered by gravelly braided river deposits in the cold but wet climate. However, during 35-20 ka, the climate changed to cold and dry, low rates of sediment supply and/or rapid basin subsidence controlled the development of sedimentary environments, leading to a change in the depositional environment from gravelly braided rivers, through sandy braided rivers, to meandering rivers with falling eustatic sea level. During the early stage of eustatic sea level rise (~20–10.2 ka), balanced rates of sediment supply and basin subsidence maintained the meandering river environment, and the meandering river deposits accumulated up to 40 m thick. On the other hand, in the relative upstream area, the far-fault area, lack of accommodation space created by the basin subsidence led to the lack of sediment preservation. Thus there is a 10-kyr gap between Sungshan Fm and Jingmei Fm. Rapid sea level rise caused by melt water pulse 1B took place during 11–8.8 ka led to the initial appearance of estuarine facies at ~10.2 ka and widened the distribution of the estuarine environment after 9.4 ka; however, the coeval phases of rapid basin subsidence ~10.6–10.2 ka, 9.4–9.0 ka and 8.9–8.5 ka promoted the first appearance and widening of the estuary, respectively. After 7 ka, when the eustatic sea level and rate of basin subsidence remained relatively stable, sufficient sediment supply gradually infilled the estuary although the eustatic sea level went stable after 6 ka. The established stratigraphy improves our understanding of the factors controlling stratigraphic development in marine-influenced inland half grabens, specifically in the Taipei Basin with high rates of sediment supply. Accommodation space in the Taipei Basin was governed by eustatic fluctuations with modulations by basin subsidence and sediment supply since the last glacial period.