Seismic stratigraphy of the central South China Sea basin and implications for neotectonics

Coring/logging data and physical property measurements from International Ocean Discovery Program Expedition 349 are integrated with, and correlated to, reflection seismic data to map seismic sequence boundaries and facies of the central basin and neighboring regions of the South China Sea. First-order sequence boundaries are interpreted, which are Oligocene/Miocene, middle Miocene/late Miocene, Miocene/Pliocene, and Pliocene/Pleistocene boundaries. A characteristic early Pleistocene strong reflector is also identified, which marks the top of extensive carbonate-rich deposition in the southern East and Southwest Subbasins. The fossil spreading ridge and the boundary between the East and Southwest Subbasins acted as major sedimentary barriers, across which seismic facies changes sharply and cannot be easily correlated. The sharp seismic facies change along the Miocene-Pliocene boundary indicates that a dramatic regional tectonostratigraphic event occurred at about 5 Ma, coeval with the onsets of uplift of Taiwan and accelerated subsidence and transgression in the northern margin. The depocenter or the area of the highest sedimentation rate switched from the northern East Subbasin during the Miocene to the Southwest Subbasin and the area close to the fossil ridge in the southern East Subbasin in the Pleistocene. The most active faulting and vertical uplifting now occur in the southern East Subbasin, caused most likely by the active and fastest subduction/obduction in the southern segment of the Manila Trench and the collision between the northeast Palawan and the Luzon arc. Timing of magmatic intrusions and seamounts constrained by seismic stratigraphy in the central basin varies and does not show temporal pulsing in their activities.Keywords: South China Sea, Neotectonism, Core-well-seismic integration, Seismic facies, Seismic stratigraphy, IODP Expedition 34

Total morphosynthesis of biomimetic prismatic-type CaCO₃ thin films

Biomimetic mineralization can lead to advanced crystalline composites with common chemicals under ambient conditions. An exceptional example is biomimetic nacre with its superior fracture toughness. The synthesis of the prismatic layer with stiffness and wear resistance nonetheless remains an elusive goal. Herein, we apply a biomimetic mineralization method to grow prismatic-type CaCO3 thin films, mimicking their biogenic counterparts found in mollusk shells with a three-step pathway: coating a polymer substrate, deposition of a granular transition layer, and mineralization of a prismatic overlayer. The synthetic prismatic overlayers exhibit structural similarity and comparable hardness and Young's modulus to their biogenic counterparts. Furthermore, employment of a biomacromolecular soluble additive, silk fibroin, in fabrication of the prismatic thin films leads to micro-/nano-textures with enhanced toughness and emerging under-water superoleophobicity. This study highlights the crucial role of the granular transition layer in promoting competition growth of the prismatic layer.publishe

Total morphosynthesis of biomimetic prismatic-type CaCO3 thin films

The exterior layers of mollusk shells are prismatic in nature, endowing them with stiffness and wear resistance. Inspired by these biominerals, here, Jiang and colleagues grow structurally similar prismatic-type CaCO3 thin films with comparable stiffness and hardness

Total morphosynthesis of biomimetic prismatic-type CaCO3 thin films

我校材料学院姜源副教授，与浙江大学唐睿康教授课题组、德国Konstanz大学Helmut Cölfen教授课题组合作，首次利用全合成手段获得了仿贝类棱柱层结构的碳酸钙薄膜，并实现了仿生薄膜微结构的精准调控，由此获得了优异的力学性能。本研究团队基于生物矿物的空间结构异质性，并参考了传统晶态薄膜材料合成中的液相外延方法，首次设计出了多步仿生矿化路线，在常温液相条件下成功地构筑了利用聚电解质稳定的矿物种子层，并在此基础上利用外延矿化方法构筑了碳酸钙的棱柱层结构。本研究制备的棱柱层薄膜不但与相对应的生物矿物在微结构上具有高度的相似性，同时还具有类似的硬度和杨氏模量。文中提出的基于种子层外延生长的多步矿化路线是获得棱柱层仿生结构的普适方法，也加深了人们对于生物矿化机制的认识。【Abstract】Biomimetic mineralization can lead to advanced crystalline composites with common chemicals under ambient conditions. An exceptional example is biomimetic nacre with its superior fracture toughness. The synthesis of the prismatic layer with stiffness and wear resistance nonetheless remains an elusive goal. Herein, we apply a biomimetic mineralization method to grow prismatic-type CaCO3 thin films, mimicking their biogenic counterparts found in mollusk shells with a three-step pathway: coating a polymer substrate, deposition of a granular transition layer, and mineralization of a prismatic overlayer. The synthetic prismatic overlayers exhibit structural similarity and comparable hardness and Young’s modulus to their biogenic counterparts. Furthermore, employment of a biomacromolecular soluble additive, silk fibroin, in fabrication of the prismatic thin films leads to micro-/nano-textures with enhanced toughness and emerging under-water superoleophobicity. This study highlights the crucial role of the granular transition layer in promoting competition growth of the prismatic layer.Y.J. acknowledges financial support from the National Natural Science Foundation of China (NSFC; 21303144) and Science Foundation of the Fujian Province, China (2014J01207). R.T. acknowledges financial support from NSFC (21625105). X.Y.L. thanks NSFC (U1405226), the “111” Project (B16029), Fujian Provincial Bureau of Science & Technology (2014H6022), and the 1000 Talents Program from Xiamen University

Opening of the South China Sea and its implications for southeast Asian tectonics, climates, and deep mantle processes since the late Mesozoic

The South China Sea (SCS) provides an outstanding opportunity to better understand complex patterns of continental margin breakup and basin formation. The sea is situated at the junction of the Eurasian, Pacific, and Indo-Australian plates and is a critical site linking some of the major western Pacific tectonic units. Despite extensive studies, sampling of basement rock and directly overlying basal sediment in the deep basin is lacking. This leaves a large margin of error in estimated ages of the SCS open-ing and closing, rendering various hypotheses regarding its opening mechanism and history untested. This also hampers understanding of East Asian tectonic and paleo-environmental evolution. We drilled five sites in the deep basin of the SCS. Three of these sites (U1431, U1433, and U1434) cored into oceanic basement near the fossil spreading center. The two remaining sites (U1432 and U1435) are located proximal to the northern continent/ocean boundary. We recovered a total of 1524 m of sediment/sedimentary rock and 78 m of oceanic basalt and also carried out downhole geophysical logging (triple combination and Formation MicroScanner-sonic tool strings) at the two deepest sites (U1431 and U1433). These materials and data were extensively examined and discussed during the expedition and allowed us to draw the following principal conclusions on the opening of the SCS: 1. Based on shipboard dating of microfossils in the sediment immediately above the basaltic basement and between the lava flow units, the preliminary cessation age of spreading in both the East and Southwest Subbasins is around early Miocene (16-20 Ma). Further postcruise radiometric dating of basement basalt from these sites plus additional calibration of magnetic anomaly models and paleomagnetic measurements will further refine the age range. Overall, a large difference is not apparent in the terminal ages of seafloor spreading between the two subbasins. 2. At Site U1435, we were able to drill into a structural high standing along the continent/ ocean boundary. Coring at this site recovered a sharp unconformity at ~33 Ma, above which is marine sediment and below which are poorly sorted sandstone and black mudstone, interpreted as littoral deposits. Environmental interpretation will require further shore-based studies because the sequence is almost entirely barren of marine microfossils. Nevertheless, we interpret this unconformity to be likely directly related to the continental break-up during the initial opening of the SCS. The onset of seafloor spreading is therefore estimated to be at ~33 Ma. 3. All sites contain deep marine deposits but show significant areal variations in postspreading sedimentary environment and provenance. Site U1431 records ev-idence for deep-marine turbidite deposition from terrestrial sources. The ob-served coarser silt turbidites may have a source in Taiwan or other surrounding blocks, whereas interbedded calcareous turbidites at this site could be trans-ported from local sources, such as nearby seamounts topped by carbonate plat-forms. In contrast, the source for upper Miocene clay and silt turbidites at Site U1433 could be from Borneo or mainland Southeast Asia, with the source of the interbedded carbonate turbidites likely from the Dangerous Grounds or Reed Bank area located south of the site. 4. Sites U1431 and U1434 are close to seamounts developed along the relict spread-ing center. Occurrences of basaltic clasts and mineral fragments in the volcani-clastic sandstone and breccia may reveal the magmatic history and mantle source of the seamounts and potentially their relationship with the terminal pro-cesses of spreading. The volcaniclastic breccia and sandstone at Site U1431 are dated as late middle Miocene to early late Miocene (~8-13 Ma), suggesting a 5 m.y. duration of seamount volcanism starting a few million years after the ces-sation of seafloor spreading. At Site U1434, volcaniclastic breccia and sandstone are most likely sourced from the adjacent seamount ~15 km to the north. The age of this recovered unit is late Miocene (younger than 9 Ma). Further postcruise sedimentological and geochemical studies, as well as radiometric dating of potas-sium-bearing mineral fragments, will refine the ages and timing of these sea-mount activities and reveal how magma sources at the dying spreading center evolved through time. 5. We successfully cored into ocean basement in the SCS for the first time and re-covered basalt at three sites (U1431, U1433, and U1434). The cored basalt has variable phase assemblages of plagioclase, olivine, and clinopyroxene and is con-cluded to be typical mid-ocean-ridge basalt based on petrological and geochem-ical evidence. Postcruise radiometric dating will determine the absolute ages of the basaltic basement units. Postcruise petrological and geochemical analyses on the basalts will provide information on the mantle sources, melting, and crystal-lization history of the youngest ocean crust