Resolving allogenic forcings on shallow-marine sedimentary archives of the Taiwan Western Foreland Basin

An investigation of allogenic forcings on shallow-marine strata of the Miocene–Pliocene Kueichulin Formation, Taiwan Western Foreland Basin, reveals that shifts in palaeoenvironments were strongly controlled by: (1) orogenesis and basin subsidence, (2) precession-driven hydroclimate and (3) obliquity-driven atmospheric and ocean circulation. Shifts from a wave-dominated open shelf to a tide-dominated shallow-marine deltaic environment were controlled by basin subsidence and the uplift and erosion of Taiwan. Rapid deepening of the Western Foreland Basin (~5400 Ka) and low sedimentation rates contributed to the development of lower offshore to distal delta front environments with limited fluvial and storm influence. As the uplift and erosion of Taiwan accelerated after ~4920 Ka, sediment filled the basin, forming shallow-marine deltaic environments. The emergence of Taiwan also led to the shallowing and narrowing of the palaeo-Taiwan Strait, resulting in strengthened tidal currents. Sedimentation from Taiwan is dominantly driven by tropical cyclone precipitation with lesser monsoon contribution, which is driven by summer insolation that mainly responds to eccentricity-modulated precession. Therefore, tropical cyclone beds preserved in the strata correspond to periods of maximum precession amplitudes, with the most amalgamated expressions occurring during periods of sea-level minima. Enhanced seasonal variations in insolation during periods of high obliquity amplitude may lead to fluctuations in ocean-atmospheric circulation, resulting in increased variability in sedimentation, and by extension, shifts in depositional environments. This is preserved in the Kueichulin Formation in facies that reflect the strengthening of tidal currents during periods of high obliquity amplitudes. The findings establish high-sedimentation and high-accommodation shallow-marine basins as potential records for effectively disentangling the relative influence of allogenic forcings on sedimentary systems, which is essential for understanding the response of the Earth's surface to climate, sea-level fluctuations and tectonism in the geologic past.

Sedimentology

Sedimentology Online

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0037-0746

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