Earthquake event deposits in Mesoproterozoic Kunyang Group in central Yunnan Province and its geological implications

Abstract

Earthquake and its resultant tsunami, as a kind of disaster events in geological history, may be recorded as event deposits of seismite and tsunamite. Typical characteristics of seismite and tsunamite, including seismo-fracture bed, synsedimentary microfracture, micro-corrugated lamination, molar tooth structure, hummocky bedding, occurs in Mesoproterozoic Dalongkou Formation of Kunyang Group in central Yunnan Province. Three types of sedimentary units have been recognized: seismite (unit-A, including limestone with molar tooth structure, seismic shattering rock, seismic corrugated rock, autoclastic breccia and intraclastic parabreccia), tsunamite (unit-B, intraclastic limestone with hummocky or parallel beddings) and background deposits (unit-C). Various stackings of these units construct three distinct sedimentary sequences: A-B-C, A-C and B-C. A-B-C represents an event sedimentary sequence of earthquake-tsunami-background deposits, A-C represents the sequence of earthquake and background deposits (no tsunami occurring), and B-C represents the sequence of tsunami and background deposits (far from the center of earthquake). As the central Yunnan Province was located in a tectonic setting of rift basin in Mesoproterozoic Era, the earthquake event deposits of the Dalongkou Formation are sedimentary response to tectonic activity of the rift basin.