Trigger recognition of Early Cretaceous soft‐sediment deformation structures in a deep‐water slope‐failure system

Abstract

The triggers of soft‐sediment deformation structures (SSDS) that are present in the deep‐water slope‐failure system of the Early Cretaceous Lingshandao Formation on Lingshan Island have been analysed on the basis of SSDS in 5 outcrops. The sediments in these outcrops are interpreted to have been deposited on a near‐shore submarine fan. The inner and middle fans were observed in Yangjiaodong, and the outer fan outcropped in Qiancengya, Dengta, and Chuanchang. The inner and middle fans are characterized by coarse‐grained debrites, turbidites, and rare SSDS, whereas the outer fan by fine‐grained debrites, turbidites, deformed sediments, and abundant SSDS. Based on sedimentary composition, element analysis and palaeo‐geographical indication of SSDS, the source area was supposed to be uplifted Sulu Orogen in an active continental margin. Combination with sedimentary environment, tectonic setting, and the space distribution of different scaled SSDS, seismicity was proposed to be the trigger of larger scaled SSDS, and small‐scale SSDS may be triggered by gravity loading, slump‐derived shear stress, and traction effect. The seismicity may respond to active tectonism and volcanism. Besides, time consistence between the Lingshandao Formation (~131–121 Ma), cooling events, sea‐level change, stable isotope excursion, and palaeo‐seismicity events suggested a catastrophic event, which may be related to two Early‐Cretaceous Anoxic Events (Faraoni Event, ~131 Ma; OAE 1a, ~120 Ma).