Seismic Stratigraphic Features of the Late Miocene-Present Unconformities and Related Seismic Units, Northern Offshore Taiwan

Abstract

We investigate the seismic stratigraphic features offshore northern Taiwan by using newly collected multichannel seismic data. Two significant regional unconformities U1 and U2 have been identified, which further subdivide the sedimentary sequence into three seismic units as SU I, SU II, and SU III. The lowermost seismic unit SU I is a pre-late Miocene sequence, while the middle and upper seismic unit SU II and SU III result from the interactions between the rapid fault-controlled subsidence and the stable thermal-controlled subsidence. We consider that the present-day offshore northern Taiwan is under a post-collisional state and the unconformities U1 and U2 represent a response to the mountain collapse and to the cessation of the regional volcano-tectonic activities. It is not until 1.5 Ma that northern offshore Taiwan became a post-collisional basin and started to receive sediments, with a rapid fault-controlled subsidence. Afterward, the basin became dominated by a stable thermal-controlled subsidence at 0.2 Ma. Although the main volcano-tectonic activities in the northern offshore Taiwan are ceased, modern geophysical and geochemical investigations have suggested that the tectonism and the volcanism are still active and represent potential threatening geohazard.

Igneous Activity and Structural Development of the Mianhua Terrace, Offshore North Taiwan

“…This stratigraphic feature can be generally observed beneath the western part of the Mianhua Terrace at about 1 second in depth. Here, we followed Hsiao et al (1998) [12] and Chang et al (2017) [13] and interpreted this unconformable surface as the stratigraphic boundary that separates the Late Miocene and Pleistocene, the so-called Pleistocene regional sequence boundary (PRSB) in the work of Hsiao et al (1998) [12]. The stratigraphic sequences overlying and underlying the PRSB are post-collisional sedimentary sequences and pre-collisional Tertiary strata, respectively.…”

“…Generally, these features seem to become deeper toward the southeast. According to the drilling results and previous studies [12,13], this is an unconformity of great regional importance that separates the overlying Pleistocene strata from the underlying Late Miocene strata, and it was recognized as the cessation of collision and the beginning of the collapse of the Taiwan orogenic wedge.…”

“…In addition to the collapsed collisional mountain belt, Northern Taiwan is also characterized by the NTVZ (Figure 1) [14,15]. Three age groups are recognized ( Figure 2 , approximately coeval to the formation of the regional unconformity that represents the onset of fault-controlled subsidence [13]. The third age group (after 1 Ma) is the youngest group and is extensively distributed, mostly all over the NTVZ.…”

“…The growth of the Taiwan orogenic wedge was diachronous from north to south, and Northern Taiwan is currently at its post-collision stage (Figure 1) [9][10][11][12][13]. Regional magmatism features the Northern Taiwan Volcanic Zone (NTVZ) dominated by post-collision magmatism, including inland Tatun, Kuanyin, and Keelung volcanic groups, and offshore volcanic Mianhua, Huaping, and Pengchia Islets ( Figure 2) [14,15].…”

Post-collisional and volcanic features of the Late Miocene-Pleistocene foreland area, northern offshore Taiwan

“…The second age group is mainly composed of the volcanic edifice formed at the Pengjia Islet (2.1 Ma), the Tatun Volcanic Group (1.5 Ma) and Keelung Volcanic Group (1.4 Ma) (Figure 2). The age of second group may be similar to the onset of the deposition upon the regional unconformity that represents the onset of fault-controlled subsidence (Chang et al 2017). The third age group is mainly not younger than 0.2 Ma (Tsaolingshan: 0.3 Ma; Kobisho: 0.2 Ma), probably suggesting that 0.2 Ma may represent the age when volcanic events had ceased (Figure 2).…”