Controls on the ichnology of late Miocene-Pliocene shallow-marine strata during uplift of the Taiwan Orogen: A semi-quantitative approach
Journal
Palaeogeography, Palaeoclimatology, Palaeoecology
Journal Volume
692
Start Page
113780
ISSN
0031-0182
Date Issued
2026-06
Author(s)
Abstract
Late Miocene through Pliocene shallow-marine sedimentary strata of the Kueichulin Formation are exposed along the Da'an River, Taiwan, and these strata form part of the fill of the Taiwan Western Foreland Basin (i.e., paleo-Taiwan Strait). The ichnology of these strata reflect the emergence and early evolution of Taiwan. Semi-quantitative characterization of trace fossil assemblages in the Kueichulin Formation are used to resolve the dominant controls on the preserved character of trace fossils. The described strata are divided into three phases ― pre-emergent, early emergent and emergent ― and these three phases are divided into six stages: pre-emergent-lower, pre-emergent-upper, early emergent, emergent-lower, emergent-middle, and emergent-upper. Throughout the pre-emergent-lower stage, seafloor erosion during storms that propagated across the Pacific Ocean exerted the dominant control on the preservation and character of trace-fossil assemblages resulting in a low preservation of bioturbation, especially of shallow-tier burrows. The formation and emergence of Taiwan (upper pre-emergent through emergent-upper stages) resulted in the island acting as a baffle to large storm waves and this is manifested in the increased preservation of: i) shallow-tier burrows constructed by filter feeders and interface (surface) deposit feeders, ii) bioturbated strata, and iii) diverse and abundant trace fossils. There is a noticeable decrease in the preservation of deep-tier burrows in mudstone-dominated strata deposited during the early emergence of Taiwan. Later, increased and more variable sedimentation / substrate mobility resulted in greater bed-by-bed variability in the degree of bioturbation once the Taiwan Strait began to narrow and tidal currents increased in strength (emergent-lower to emergent-upper stages). During the emergent stages, both seafloor erosion during storms and tidal reworking controlled the preservation and character of trace fossil assemblages. The ichnological analysis employed herein demonstrates the value of a semi-quantitative approach to ichnology. Systematic compilation of qualitative ichnological data can be converted into numerical values, which subsequently, can be used to resolve trends in trace fossils abundances, tiering depths, and ethologies, and these data can be used to assess variable controls on preserved character of ichnological assemblages.
Subjects
Bioturbation index
Ichnology
Process ichnology
Tidal straits
Trace fossil preservation
Publisher
Elsevier BV
Type
journal article