Carbonate and organic carbon sedimentation on the continental margin off Southeastern Taiwan

Sediment and porewater data of two sediment cores from offshore southeastern Taiwan show important effects of the complex sea floor topography upon carbonate and organic carbon deposition. The variations in carbonate and organic carbon contents are attributed to the effects of carbonate compensation depths, glacial-interglacial history, and condition of anoxia. The study is of significance for environmental reconstruction and petroleum source bed evaluation of ancient analogues.     

Preface to the special issue “Tectonics and depositional infilling of western Pacific marginal sea”

Marine Geophysical Research -     

Benthic foraminiferal fauna and sediment provenance of Eocene syn-rift sequences in Taiwan: implication for onset of Asian epi-continental marginal seas off China coast

Marine Geophysical Research - Early Cenozoic rift basins developed commonly on the Mesozoic basement along the SE Asia Continent. However, Eocene–Oligocene sequences were only exposed widely...     

Evidence for the 8,200 a <Emphasis Type="SmallCaps">b</Emphasis>.<Emphasis Type="SmallCaps">p</Emphasis>. cooling event in the middle Okinawa Trough

Based on new and existing data on oxygen isotopes, alkenone-surface seawater temperature trends, planktonic foraminifers, lithology, and clay mineral composition of piston cores, a distinct cooling event has been identified around 8,200 cal a b.p. in the middle Okinawa Trough, northwest Pacific. This corresponds to the 8,200 a b.p. cooling event recorded in many places of the Northern Hemisphere. During this event, the local temperature decreased by 1°C, and the δ¹⁸O value increased by 0.6‰. A strengthened Asian winter monsoon is the most probable cause for this event, which thus adds further credibility to the contention that we are dealing here with a global phenomenon.     

南海东北部冷泉区沉积物中有机质来源的生物标志物分析与环境指示意义

Multi-biomarker indexes were analyzed for two piston cores from potential cold seep areas of the South China Sea off southwestern Taiwan. Total organic carbon(TOC) normalized terrestrial(n-alkanes) and marine(brassicasterol, dinosterol, alkenones and iso-GDGTs) biomarker contents and ratios(TMBR, 1/Pmar-aq, BIT) were used to evaluate the contributions of terrestrial and marine organic matter(TOM and MOM respectively) to the sedimentary organic matter, indicating that MOM dominated the organic sources in Core MD052911 and the sedimentary organic matter in Core ORI-_(86)0-22 was mainly derived from terrestrial inputs, and different morphologies were the likely reason for TOM percentage differences. BIT results suggested that river-transported terrestrial soil organic matter was not a major source of TOM of sedimentary organic matter around these settings.Diagnostic biomarkers for methane-oxidizing archaea(MOA) were only detected in one sample at 172 cm depth of Core ORI-_(86)0-22, with abnormally high iso-GDGTs content and Methane Index(MI) value(0.94). These results indicated high anaerobic oxidation of methane(AOM) activities at or around 172 cm in Core ORI-_(86)0-22.However in Core MD052911, MOA biomarkers were not detected and MI values were lower(0.19–0.38), indicated insignificant contributions of iso-GDGTs from methanotrophic archaea and the absence of significant AOM activities. Biomarker results thus indicated that the discontinuous upward methane seepage and insufficient methane flux could not induce high AOM activities in our sampling sites. In addition, the different patterns of TEX_(86) and U_(37)~(K′) temperature in two cores suggested that AOM activities affected TEX_(86)37 temperature estimates with lower values in Core ORI-_(86)0-22, but not significantly on TEX_(86) temperature estimates in Core MD052911.     

福建闽江和九龙江现代沉积物重矿物特征及其物源意义*

通过对闽江和九龙江沿岸沉积物中重矿物的分析,发现重矿物组合与源区岩石具有极好的相关性。两条河流流域重矿物组合为不透明铁矿类—绿帘石—锆石—电气石—角闪石,特征矿物为绿帘石,含量高达原生透明重矿物比重的70%,其成因除与高级变质岩有关外,还与中酸性岩浆岩及其与围岩接触蚀变发生的绿帘石化有关。从重矿物组合、重矿物特征指数以及与锆石年龄谱系的比对分析发现,闽江流域重矿物源自闽西北武夷山前寒武纪的变质岩、闽东广泛出露的燕山期岩浆岩和接触变质岩,而九龙江流域重矿物源自闽西南的印支—燕山期花岗岩。闽江上游沉积物重矿物以源自高级变质岩的重矿物为特征,中下游由上游来源的重矿物和下游酸性岩浆岩及接触变质岩形成的重矿物共同构成;九龙江以印支—燕山期花岗岩中的副矿物组合为特征。研究结果显示,对于中小流域面积的河流,由于搬运距离有限,重矿物组合保存的源岩信息量大,可作为研究流域内构造演化和源汇对比的重要手段。     

Sediment source and environment evolution in Taiwan Island during the Eocene–Miocene

Taiwan Island's outcropping strata can provide important insights into the sedimentary environment and source development of the southeast China margin. This research is based on the Eocene–Miocene strata of the Tsukeng area in the central Western Foothills, northeast shoreline of Taiwan Island and two sites of the East China Sea Shelf Basin(ECSSB), using petrology and detrital zircon U-Pb age for the analysis. Results show that central and northeast Taiwan Island experienced a transformation from continental to marine facies during the Eocene–Miocene, and the sandstone maturity changed with time. Source analysis shows that sediments from the Eocene–early Oligocene strata mainly originated from near-source Mesozoic rocks, whose zircon age is consistent with the igneous rock in the surrounding area and coastal Cathaysia, showing 120 Ma and 230 Ma peaks in the age spectrum diagram. Since the late Oligocene, peaks of 900 Ma and 1 800 Ma are seen, indicating that deposition of matter from the old block began. The sediments could be a mixture of the surrounding Mesozoic volcanic and fewer pre-Cambrian rocks sourced from the coastal river and sporadic old basement in the ECSSB instead of longdistance transportation.     

The Lichi Mélange in Coastal Range, eastern Taiwan: its origin, mechanism and evolution

Marine surveys show that the submarine Huatung Ridge extends northward to the Lichi Mélange in the southwestern Coastal Range, suggesting that formation of the Lichi Mélange is related to the arcward thrusting of the forearc strata in the western part of the North Luzon Trough during the active arc-continent collision off southern Taiwan. New seismic survey along 21oN transact across over the North Luzon Trough in the in-cipient arc-continent collision zone further reveals that the deformation of the Huatung Ridge occurs soon after the sedimentation in the western forearc basin, while the sedimentation is continuous in the eastern part of the remnant North Luzon Trough until the complete closure of the forearc basin approaching to SE Taiwan. This suggests that the sequence in the Huatung Ridge can just be coeval to the lower sequence of the remnant forearc basin strata. Multiple lines of new evidence, including micropaleontology, clay mineralogy and fis-sion track analyses along the Mukeng River and its tributary key sections, are used to test this thrusting forearc origin hypothesis of the Lichi Mélange.