A previously overlooked, highly diverse early Pleistocene elasmobranch assemblage from southern Taiwan

The Niubu fossil locality in Chiayi County, southern Taiwan is best known for its rich early Pleistocene marine fossils that provide insights into the poorly understood past diversity in the area. The elasmobranch teeth at this locality have been collected for decades by the locals, but have not been formally described and have received little attention. Here, we describe three museum collections of elasmobranch teeth (n = 697) from the Liuchungchi Formation (1.90-1.35 Ma) sampled at the Niubu locality, with an aim of constructing a more comprehensive view of the past fish fauna in the subtropical West Pacific. The assemblage is composed of 20 taxa belonging to nine families and is dominated by Carcharhinus and Carcharodon. The occurrence of †Hemipristis serra is of particular importance because it is the first Pleistocene record in the area. We highlight high numbers of large Carcharodon carcharias teeth in our sample correlating to body lengths exceeding 4 m, along with the diverse fossil elasmobranchs, suggesting that a once rich and thriving marine ecosystem in an inshore to offshore shallow-water environment during the early Pleistocene in Taiwan.

Insolation-paced sea level and sediment flux during the early Pleistocene in Southeast Asia

Global marine archives from the early Pleistocene indicate that glacial-interglacial cycles, and their corresponding sea-level cycles, have predominantly a periodicity of ~ 41 kyrs driven by Earth’s obliquity. Here, we present a clastic shallow-marine record from the early Pleistocene in Southeast Asia (Cholan Formation, Taiwan). The studied strata comprise stacked cyclic successions deposited in offshore to nearshore environments in the paleo-Taiwan Strait. The stratigraphy was compared to both a δ¹⁸O isotope record of benthic foraminifera and orbital parameters driving insolation at the time of deposition. Analyses indicate a strong correlation between depositional cycles and Northern Hemisphere summer insolation, which is precession-dominated with an obliquity component. Our results represent geological evidence of precession-dominated sea-level fluctuations during the early Pleistocene, independent of a global ice-volume proxy. Preservation of this signal is possible due to the high-accommodation creation and high-sedimentation rate in the basin enhancing the completeness of the stratigraphic record.

Imaging active faulting in the western Taiwan Strait

Large, destructive historical earthquakes off the coast of China’s Fujian Province point to important tectonic activity in the western Taiwan Strait that, until recently, has received little attention. We present newly acquired reflection seismic data that is used to study the shallow crustal structure of the western Taiwan Strait. With these data we map the location of the Benhai fault for the first time, describe its upper crustal geometry and, in combination with seismicity and earthquake focal mechanisms, interpret its kinematics. These new data demonstrate that there is wide spread evidence of faulting that reaches the sea floor in the western Taiwan Strait, clearly indicating that the Benhai fault is active. Faults that cut up section from steep basin sidewalls to form flower structures or terraced sidewall fault zones, together with the fault and basin map pattern, are consistent with this fault zone being in the early developmental stages of a dextral strike-slip system. Earthquake focal mechanisms, although not definitive, support the model of an active dextral strike-slip fault system in the western Taiwan Strait.