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Projects & Publications

Here is a list of active projects that have already produced results. Others are ongoing and will be listed as results are published.

Tropical cyclones: sedimentary and geochemical signatures

The project under discussion focuses on the characteristics of tropical cyclone (TC) deposits in the shallow waters of the Taiwan Strait. It involves analyzing sedimentological data from lower Pliocene strata to identify TC deposits based on specific criteria like basal scour surfaces, absence of bioturbation, and trough cross-stratification. The project aims to build a conceptual model for understanding deposition in the Taiwan Strait during TCs and examines the impact of TCs on sedimentation and organic material in the region. Additionally, the project explores storm-flood-dominated deltas, studying sedimentary successions along the Da'an River in Taiwan to refine depositional process interpretations for these formations, specifically focusing on the presence of tropical cyclone beds.

Tropical cyclone deposits in the Pliocene Taiwan Strait: Processes, examples, and conceptual model

The characteristics of tropical cyclone (TC) deposits are highly variable, and in the shallow waters of straits their character has not been established. Multiple coarse-grained beds in lower Pliocene strata in the Western Foreland Basin of Taiwan are interpreted as TC deposits, and the sedimentology of these beds reflects evolving TC pro- cesses and storm stages. By comparing sedimentological data from these beds with previous research on TCs, and with analysis of TCs that cross Taiwan from east to west, a conceptual model is built for understanding de- position in the Taiwan Strait during tropical cyclones.

Taiwan is impacted by more than three TCs per year, including more than two super-typhoons every 10 years. These storms can deliver immense volumes of rain over very short time periods and are associated with intense winds. During TCs, and in shallow water in the Taiwan Strait (10–35 m water depth), hyperpycnal discharge, strong bottom currents, and oscillatory wave motion all impact deposition. These processes are manifested in the resulting deposits, and we propose that the best sedimentological criteria for recognizing TC deposits, in- clude: 1) a basal scour surface; 2) an absence of within-bed bioturbation; 3) trough cross-stratification that pre- serves multi-directional, mainly shore-parallel flow with a 180° change in flow direction; 4) preservation of oscillatory structures towards the top of the bed; and, 5) organic lamina and clasts throughout the bed. Mudstone intercalated with trough cross-stratification is also a useful indicator of TC deposition as it probably reflects wave- and current-redistribution of sediment delivered to the strait through hyperpycnal and hypopycnal discharge from rivers. Contemporaneous mud deposition within TC beds is manifested as mudstone drapes on foresets and toesets, and discontinuous mudstone beds between trough cross-stratified sandstone beds. While not all TC beds exhibit all sedimentological characteristics, we hypothesize that high-probability TC beds should show three or more of them.

Dashtgard, S. E., Löwemark, L., Vaucher, R., Pan, Y.-Y., Pilarczyk, J. E., & Castelltort, S. (2020). Tropical cyclone deposits in the Pliocene Taiwan Strait: Processes, examples, and conceptual model. Sedimentary Geology, 405, 105687. 

Geochemical evidence of tropical cyclone controls on shallow-marine sedimentation (Pliocene, Taiwan)
Dashtgard etal -Figure 2.jpg

Shallow-marine sediment typically contains a mix of marine and terrestrial organic material (OM). Most terrestrial OM enters the ocean through rivers, and marine OM is incorporated into the sediment through both suspension settling of marine plankton and sediment reworking by tides and waves under fair-weather conditions. River-derived terrestrial OM is delivered year-round, although sediment and OM delivery from rivers is typically highest during extreme weather events that impact river catchments. In Taiwan, tropical cyclones (TCs) are the dominant extreme weather event, and 75% of all sediment delivered to the surrounding ocean occurs during TCs. Distinguishing between sediment deposited during TCs and that redistributed by tides and waves during fair-weather conditions can be approximated using δ13Corg values and C:N ratios of OM. Lower Pliocene shallow-marine sedimentary strata in the Western Foreland Basin of Taiwan rarely exhibit physical evidence of storm-dominated deposition. Instead they comprise completely bioturbated intervals that transition upward into strata dominated by tidally generated sedimentary structures, indicating extensive sediment reworking under fair-weather conditions. However, these strata contain OM that is effectively 100% terrestrial OM in sediment that accumulated in estimated water depths <35 m. The overwhelming contribution of terrestrially sourced OM is attributed to the dominance of TCs on sedimentation, whereby ∼600,000 TCs are estimated to have impacted Taiwan during accumulation of the succession. In contrast, the virtual absence of marine OM indicates that organic contributions from suspension settling of marine OM is negligible regardless of the preserved evidence of extensive reworking under fair-weather conditions. These data suggest that (1) even in the absence of physical expressions of storm deposition, TCs still completely dominate sedimentation in shallow-marine environments, and (2) the organic geochemical signal of preserved shallow-marine strata is not reflective of day-to-day depositional conditions in the environment.

Dashtgard, S. E., Löwemark, L., Wang, P.-L., Setiaji, R. A., & Vaucher, R. (2021). Geochemical evidence of tropical cyclone controls on shallow-marine sedimentation (Pliocene, Taiwan). Geology, 49(5), 566-570.

Storm-flood-dominated delta succession in the Pleistocene Taiwan Strait

Storm-flood-dominated deltas are sedimentary systems in which a complex interplay of hydrodynamic processes occurs during storms (e.g. tropical cyclones) due to the coeval action of continental and oceanic processes. This paper reports on a superbly exposed, 135.5 m thick stratigraphic succession of the Pleistocene Cholan Formation exposed along the Da'an River, Taiwan. The sedimentary succession comprises alternating mudstone and sandstone, is mostly fine-grained, and exhibits multiple event beds that record deposition during tropical cyclones and post-depositional deformation features produced during earthquakes. Detailed facies analyses reveal that deposition towards the base of the succession occurred in the palaeo-Taiwan Strait in storm-flood-dominated prodelta and delta-front environments passing upwards into delta-plain environments. Tropical cyclone beds are encountered throughout the subaqueous storm-flood delta successions, and are identified by (i) trough cross-stratified sandstone bedsets with erosive bases that contain both mud clasts and mudstone beds, (ii) sandstone with aggrading wave ripples and (iii) hummocky cross-stratified sandstone with rare gutter casts filled with coal fragments and shell remains. Tropical cyclone deposits are either top-down burrowed or capped by massive or laminated mudstone. Seismites are rare and are mainly recognised through soft-sediment deformation of beds; they do not show evidence of slope failure. Compared to storm-flood delta successions described elsewhere, the Cholan Formation shows significantly fewer oscillatory-generated sedimentary structures and gutter casts. This difference is attributed to the Cholan Formation being deposited in and along the margin of a strait characterised by strong shore-parallel currents and relatively small storm waves due to its position between Taiwan and mainland China. This study refines depositional process interpretations of the Cholan Formation, provides criteria for recognising storm-flood delta deposits in tectonically active straits with multiple sediment sources fed by steep drainages and short river catchments, and provides additional criteria for recognising tropical cyclone deposits in shallow-marine settings.

Vaucher, R., Dillinger, A., Hsieh, A. I., Chi, W. R., Löwemark, L., & Dashtgard, S. E. (2023). Storm‐flood‐dominated delta succession in the Pleistocene Taiwan Strait. The Depositional Record.

This project investigates sediment sources in the Taiwan Western Foreland Basin. Using various indicators such as clay mineralogy, δ13Corg, C/N ratios, and magnetic susceptibility, the study reveals that major sediment contributions from the Taiwan orogen began much earlier than previously believed, correlating closely to the uplift and emergence of the Taiwan orogen during the Miocene-Pliocene transition.

Multi-proxy evidence for rapidly shifting sediment sources to the Taiwan Western Foreland Basin at the Miocene– Pliocene transition

The Taiwan Western Foreland Basin is thought traditionally to have received sediment mainly from Eurasia until the late Pliocene–early Pleistocene, after which time, the Taiwan orogen became the dominant source. However, a combination of clay mineralogy, δ13Corg and C/N of organic matter, and mass-specific magnetic susceptibility of late Miocene to early Pliocene strata of the Kueichulin Formation indicate that onset of major sediment contributions from Taiwan occurred much earlier, and correlates closely to the uplift and initial emergence of the Taiwan orogen. Clay mineralogy shows an upsection increase in illite and illite crystallinity, and a decrease in chlorite and kaolinite after the late Miocene, and this is attributed to rapid erosion of the Taiwan orogen. Results from δ13Corg and C/N analyses show that organic material in the Kueichulin Formation changed from dominantly marine to dominantly terrestrial in the early Pliocene, and this is linked to the delivery of large quantities of terrestrial organic material from the Taiwan orogen to the adjacent Taiwan Strait. Magnetic susceptibility also decreases significantly during the early Pliocene, resulting from dilution of magnetic minerals through the influx of non-magnetic minerals delivered from the Taiwan orogenic belt. The establishment of the growing Taiwan orogen as a major sediment source to the Western Foreland Basin occurred at the Miocene–Pliocene transition, about two million years earlier than previously recognized.

Hsieh, A. I., Dashtgard, S. E., Wang, P. L., Horng, C. S., Su, C. C., Lin, A. T., Vaucher, R., & Löwemark, L. (2023). Multi‐proxy evidence for rapidly shifting sediment sources to the Taiwan Western Foreland Basin at the Miocene–Pliocene transition. Basin Research, 35(3), 932-948.

The project provides geological evidence of precession-dominated sea-level fluctuations during the early Pleistocene in Southeast Asia, utilizing clastic shallow-marine records from the Cholan Formation in Taiwan. Additionally, the project assesses hydroclimate variability in the northwest Pacific during the Pliocene-Pleistocene transition through continuous gamma-ray log analysis of shallow-marine strata in the Taiwan Western Foreland Basin, highlighting the influence of high- and low-latitude climate drivers on depositional cycles. In this project, we evaluated the impact of the rapidly uplifting Taiwan orogen on the recording of astronomical climate forcing in shallow-marine sedimentary strata, revealing how preservation of precession-driven East Asian Summer Monsoon variability is influenced by basin evolution and sedimentation rates over time.

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.

Vaucher, R., Dashtgard, S. E., Horng, C.-S., Zeeden, C., Dillinger, A., Pan, Y.-Y., Setiaji, R. A., Chi, W.-R., & Löwemark, L. (2021). Insolation-paced sea level and sediment flux during the early Pleistocene in Southeast Asia. Scientific Reports, 11(1), 16707.

Hydroclimate dynamics during the Plio-Pleistocene transition in the northwest Pacific realm

The appraisal of sedimentary archives is key for predicting sea level changes and extreme weather event behavior under varying greenhouse gas levels. Here, we assess the hydroclimate variability of the northwest Pacific realm during the Pliocene-Pleistocene transition by using a continuous record of gamma-ray log data from two boreholes comprising shallow-marine strata in the Western Foreland Basin, Taiwan. The gamma-ray records provide a high temporally resolved stratigraphic record spanning from ∼3.15 to ∼1.95 million years ago. The comparison of the astronomically tuned gamma-ray logs to global sea-level and regional sea-surface temperature reconstructions highlights the impact of high- and low-latitude climate drivers on depositional cycles during the Plio-Pleistocene transition. During the late Pliocene, the interplay between the orbitally paced East Asian Summer Monsoon and tropical cyclones dominates the fluctuation in sediment supplied from Taiwan to our study sites. With the intensification of Northern Hemisphere glaciation from the late Pliocene through the early Pleistocene, sea-level changes were ruled by increasingly pronounced glacial-interglacial cycles, and the sedimentary record during this time interval is paced initially by obliquity and later by precession. This study reveals that shallow marine strata can record a more complex history of past hydroclimate dynamics in the northwest Pacific than recorded in deep sea climate archives.

Vaucher, R., Zeeden, C., Hsieh, A. I., Kaboth-Bahr, S., Lin, A. T., Horng, C.-S., & Dashtgard, S. E. (2023). Hydroclimate dynamics during the Plio-Pleistocene transition in the northwest Pacific realm. Global and Planetary Change, 223, 104088.

Influence of a Rapidly Uplifting Orogen on the Preservation of Climate Oscillations

Climate oscillations preserved in sedimentary archives tend to decrease in resolution further back in Earth's history. High-frequency climate cycles (e.g., ∼20-Kyr precession cycles) are especially prone to poor preservation due to sediment reworking. Recent studies have shown, however, that given sufficient basin accommodation space and sedimentation rate, shallow-marine paleoclimate archives record precession-driven hydroclimate change in mid-low latitude regions. Our study evaluates how the evolution of a rapidly uplifting orogen influences the recording of astronomical climate forcing in shallow-marine sedimentary strata in the Taiwan Western Foreland Basin (WFB). Time-series analysis of gamma-ray records through the late Miocene–Pliocene Kueichulin Formation shows that during early stages of Taiwan orogenesis (before 5.4 Ma), preservation of precession-driven East Asian Summer Monsoon variability is low despite increasing monsoon intensities between 8 and 3 Ma. The Taiwan Strait had not formed, and the southeast margin of Eurasia was open to the Pacific Ocean. Consequently, depositional environments in the WFB were susceptible to reworking by large waves, resulting in the obscuration of higher-frequency precession cycles. From 5.4 to 4.92 Ma, during early stages of emergence of Taiwan, basin subsidence increased while sedimentation rates remained low, resulting in poor preservation of orbital oscillations. After 4.92 Ma and up to 3.15 Ma, Taiwan became a major sediment source to the WFB, and sheltered the WFB from erosive waves with the development of Taiwan Strait. The elevated sediment influx, increased basin accommodation as the WFB developed, and formation of a semi-sheltered strait, resulted in enhanced preservation of precession-driven East Asian Summer Monsoon variability.

Hsieh, A. I., Vaucher, R., Löwemark, L., Dashtgard, S. E., Horng, C. S., Lin, A. T., & Zeeden, C. (2023). Influence of a Rapidly Uplifting Orogen on the Preservation of Climate Oscillations. Paleoceanography and Paleoclimatology, 38(6).

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