Résumé
A giant piston core, MD18-3548 (20.07 m) was collected from a perched basin in the Taiwan accretionary wedge, at a water depth of 1752 m. Detailed grain-size analysis, 14C accelerator mass spectrometry (AMS) dating, and computed tomography (X-CT) scans of the core were performed. Four types of lithofacies, namely hemipelagic sediments, silty turbidite-homogenites, turbidites, and thin silty layers, are identified, along with seventeen event beds. A total of fourteen 14C AMS dating were carried out, with the depositional ages of the event beds being calculated based on the sedimentation rate of hemipelagites. The oldest event bed is ~12 cal kyrs BP, while the youngest event bed is ~64 cal yrs BP. All seven homogenite units are floored by a thin (usually <10 cm thick), coarsening-upward first and then fining-upward unit, capped by a thick structureless mud totally devoid of bioturbation. The average thickness of homogenite units is ~150 cm, while the thickest homogenite unit is ~200 cm. These homogenite units can be compared to similar deposits reported elsewhere and find particularly that these units exhibit a basal layer with gradual coarsening and fining upward trend in grain size. We therefore propose a new depositional model for the silty turbidite-homogenite units in seismically-shaken enclosed basins. This model takes into account the coarsening-then-fining upward deposition of the basal layers, reported for the first time.