Effects of astronomical orbital cycle and volcanic activity on organic carbon accumulation during Late Ordovician–Early Silurian in the Upper Yangtze area, South China

Based on field outcrop data,the effects of cyclic change of astronomical orbit and volcanic activity on organic carbon accumulation during the Late Ordovician-Early Silurian in the Upper Yangtze area were studied using cyclostratigraphic and geochemical methods.d13 C and chemical index of alteration(CIA)were used to filter the astronomical orbit parameters recorded in sediments.It is found that the climate change driven by orbital cycle controls the fluctuations of sea level at different scales,obliquity forcing climate changes drive thermohaline circulation(THC)of the ocean,and THC-induced bottom currents transport nutrient-laden water from high latitude regions to the surface water of low-latitude area.Hence,THC is the main dynamic mechanism of organic-carbon supply.The marine productivity indexes of Ba/Al and Ni/Al indicate that volcanic activities had limited effect on marine productivity but had great influences on organic carbon preservation efficiency in late Hirnantian(E4).Paleo-ocean redox environmental indicators Th/U,V/Cr and V/(V+Ni)show that there is a significant correlation between volcanism and oxygen content in Paleo-ocean,so it is inferred that volcanisms controlled the organic carbon preservation efficiency by regulating oxygen content in Paleo-ocean,and the difference in volcanism intensity in different areas is an important factor for the differential preservation efficiency of organic carbon.The organic carbon input driven by orbital cycle and the preservation efficiency affected by volcanisms worked together to control the enrichment of organic carbon in the Middle–Upper Yangtze region.

Peri-Gondwanan terranes in the Romanian Carpathians:A review of their spatial distribution,origin,provenance,and evolution

The basement of the Romanian Carpathians is made of Neoproterozoic to early Paleozoic peri- Gondwanan terranes variably involved in the Variscan orogeny, similarly to other basement terrains of Europe. They were hardly dismembered during the Alpine orogeny and traditionally have their own names in the three Carpathian areas. The Danubian domain of the South Carpathians comprises the Dragsan and Lainici-Paiius peri-Amazonian terranes. The Dragsan terrane originated within the ocean surrounding Rodinia and docked with Rodinia at -800 Ma. It does not contain Cadomian magmatism and consequently it is classified as an Avalonian extra-Cadomian terrane, The Lainici-Pfiius terrane is a Ganderian fragment strongly modified by Cadomian subduction-related magmatism, It is attached to the Moesia platform. The TisoviD terrane is an ophiolite that marks the boundary between Drfagsan and Lainici-Paius terranes. The other basement terranes of the Romanian Carpathians originated close to the Ordovician North- African orogen, as a result of the eastern Rheic Ocean opening and closure. Except for the Sebes-Lotru terrane that includes a lower metamorphic unit of Cadomian age, all the other terranes （Bretila, Tulghes, Negrisoara and Rebra in the East Carpathians, Somes, Biharia and Baia de Aries in the Apuseni mountains, Fagaras, Leaota, Carat and Pades in the South Carpathians） represent late Cambrian-Ordovician rock assemblages. Their provenance, is probably within paleo-nortbeast Africa, close to the Arabian-Nubian shield. The late Cambrian-Ordovician terranes are defined here as Carpathian-type terranes. According to their lithostratigraphy and origin, some are of continental margin magmatic arc setting, whereas others formed in rift and back-arc environment and closed to passive continental margin settings. In a paleo- geographic reconstruction, the continental margin magmatic arc terranes were first that drifted out, followed by the passive continental margin terranes with the back-arc terranes in their front. They accreted to Laurussia during the Variscan orogeny. Some of them （Sebes-Lotru in South Carpathians and Baia de Aries in Apuseni mountains） underwent eclogite-grade metamorphism. The Danubian terranes, the Bretila terrane and the Somes terrane were intruded by Variscan granitoids.

Volcanism Pacing Slumping Gravity Flow Deposits during the Late Carboniferous in the Southern Margin of the Junggar Basin,China

Deep-water gravity depositional processes and evolution in arc systems have become topics of intense research focus in recent years.This study discusses the co-evolution of volcanism and deep-water gravity flow deposits at the southern margin of the Junggar Basin,based on petrology,geochronology and geochemical analyses.The results show that a massive collapse of unstable sediments from the slope was triggered by volcanism,resulting in the formation of slumping gravity flows.The occurrence of volcanic beds in the slump deposits confirm that synchronous volcanism likely affected sediment instability,triggering gravity flows.The Th/Yb,Ta/Yb and Th/Ta elemental ratios,U-Pb ages of detrital zircons and paleocurrent directions indicate that the North Tianshan(NTS)island arc represents the provenance of the Qianxia Formation.Moreover,statistical data on the pyroclastic components in the gravity flow deposits reveal an intensity index of volcanism,indicating that volcanism is strongly related to gravity flow deposits,especially in terms of the type and distribution of the deposits.A model for volcanically-triggered deep-water gravity flow deposits is established,in order to provide a more in-depth understanding of the co-evolution of volcanism and gravity flow deposits within the depositional setting of the late Paleozoic NTS oceanic subduction margin in the Junggar Basin.

Frontiers in geoscience: A tribute to Prof. Xuanxue Mo-Preface

In response to the proposal by the Earth Science community of China,we are delighted to organize this special issue of Geoscience Frontiers(GSF)in honor of the work by Xuanxue Mo,Professor of Petrology and Geochemistry of China University of Geosciences(Beijing)and Academician of the Chinese Academy of Sciences,as a tribute to him on his 80th birthday.In his over 50 years of professional career,Prof.Mo has contributed enormously to the developments of China’s Earth Sciences and it is fair to say that Prof.Mo is one of the most influential administrators,educators and researchers in China’s Earth Science community and also internationally.The research papers assembled in this special issue reflect the authors’appreciation of Prof.Mo who has benefitted them as students,collaborators and colleagues over the years.

Imaging of Hidden Structures from the North Apuseni Mts, Romania, Using Narrow-Angle Seismic Reflection Data

I present results of processing and structural interpretation of narrow-angle seismic reflection data recorded over an area of 30 × 50 km located in the southern part of the North Apuseni Mts, Romania. The investigated area is characterized by complex subsurface geology and rough topography. The seismic measurements were performed along five linear profiles, P1-P5, using an active spread of 96 geophones for each shot point;geophone spacing was 25 m. The length of each acquisition line is greater than 10 km. The signal-to-noise ratio of these data varies along the lines and its variation is considered to be an effect of rough topography, complex subsurface geology and varying surface conditions encountered during seismic data acquisition. The data processing was performed using a standard processing flow but with different processing parameters from one data set to another. I obtained five depth-converted migrated seismic sections after data processing. The accuracy of the depth values depends on that of the stacking velocities obtained from the velocity analyses performed on the filtered seismic data. Borehole information is not available, the investigated area belonging to the areas investigated for hydrocarbons. Each seismic section shows a different structural image of the subsurface and provides useful information about the tectonic and stratigraphic evolution of the investigated area. I obtained various structural images of the subsurface after the interpretation of the depth-converted migrated seismic sections, from a simple one with undeformed and inclined reflectors to a complex one with folded and faulted reflectors, especially the older ones. I interpreted intrusive bodies piercing through the overlying sediments, which are in good agreement with the results of older geophysical studies.

End-Triassic storm deposits in the lacustrine Sichuan Basin and their driving mechanisms

Storm deposits or tempestites are event sequences formed by storms,requiring at least a water temperature of 26.5℃.While inland lakes are unlikely to form storm deposits because of their limited width and water temperature.The Upper Triassic Xujiahe Formation in the Sichuan Basin is a set of coal-bearing,clastic sequences with dominant sedimentary facies varying from braided river delta to lacustrine settings,with storm deposits widely reported.In the Zilanba of Guanyuan area,in situ tree trunks on a palaeosol surface in Member Vof the Xujiahe Formation provide new evidence of a storm event.Six fallen-down directions of nine in situ tree trunks were predominant in the NW direction,contrary to the palaeocurrent direction of the underlying strata,suggesting that the southeasterlies prevailed during the end-Triassic in the northern Sichuan Basin.Massive mud clasts were frequently recorded in sandstones of the Xujiahe Formation,as well as in the Xindianzi section.These mud clasts showed a rip-up or a plastic deformation with upside-down V-shapes,were capped on an erosional surface,showed no transport traces and were therefore interpreted as a storm lag deposit.The megamonsoonal climate prevailed during the Late Triassic,although the megamonsoons themselves could not generate a storm deposition in the Xujiahe Formation due to its low maximum surface wind speed.The driving mechanism for generating storm deposits in the Xujiahe Formation is suggested to be tropical cyclones over the Tethys Ocean moving eastward,further landfalling on the western margin of the Sichuan Basin.Statistics of storm events in the circum-Tethys region show a widespread storm surge in low latitudes during the end-Triassic.The storm deposits at the top of the Xujiahe Formation represent a sedimentary response to the end-Triassic hyperthermal event.

三叠纪末期四川盆地湖泊风暴记录及其驱动机制

风暴岩是由风暴形成的事件性沉积序列.风暴的形成理论上要求水体温度26.5℃以上.由于宽度和水温的限制,使得湖泊上空不太可能形成热带气旋并出现风暴岩.四川盆地上三叠统须家河组为一套辫状河三角洲-湖泊相建造,近年来广泛报道有风暴沉积记录.广元紫兰坝剖面须五段古土壤层面的原位树木化石材料提供了风暴的新证据.9例材料中6份原位树木的倒伏方向集中呈北西向,与下伏地层中古水流数据相反,推测广元地区三叠纪末期曾盛行东南风.新店子剖面和四川盆地须家河组内砂岩内普遍发育有呈撕裂状或具塑性变形的泥砾.泥砾无搬运痕迹,显“八”字型特征,被解释为风暴滞留沉积,表明须家河组沉积时期曾普遍受到风暴作用的影响.晚三叠世期间盛行“巨型季风”气候,“巨型季风”因其表面风最大风速低,并非四川盆地须家河组风暴沉积的原因.“巨型季风”气候体制下,须家河组风暴岩的驱动机制是特提斯洋上空热带气旋东移登陆四川盆地西缘的结果.环特提斯域风暴岩对比统计数据显示,三叠纪末期特提斯低纬度地区普遍出现大规模风暴潮,四川盆地须家河组顶部广泛出现的风暴岩很可能是三叠纪末期极热事件的沉积响应.

Oxidization of the mantle caused by sediment recycling may contribute to the formation of iron-rich mantle melts

Mantle-derived primary magmas generally have FeOtot contents of about 11 wt%.However,some primary melts show extremely high FeO^tot(>13 wt%)with high MgO(>12 wt%)(ferropicrite)[1].Considering the influence of chemical and mineral compositions of the mantle source on melt compositions,it has been argued that ferropicrites may be near-primary partial melts of pyroxenite formed in the convecting mantle[2–4],whereas others favor an origin by partial melting of an iron-rich peridotitic mantle source[5,6].Melting experiments have shown that melting conditions such as pressure and temperature can strongly influence the melt compositions,such that ferropicrites may be generated by partial melting of an olivine-dominated mantle source at^5 GPa[5].Some ferropicrites seem to be more oxidized than other magmas,as suggested from the Panzhihua intrusions in the Emeishan large igneous province[7],which may imply melting of a more oxidized mantle source.Furthermore,Johnston and Stout[8]showed that oxygen fugacity exerts great control on the compositions and stabilities of Cr-Fe-rich minerals,and may therefore significantly affect mantle-derived melt compositions.Local oxygen fugacity(fO2)and solidus temperature of the mantle can be dramatically affected by recycled sedimentary carbonates.This raises the question as to whether sedimentary carbonate recycling could have indirectly contributed to the formation of iron-rich melts in the mantle.

Review of the bennettitalean genus Weltrichia

The bennettitalean male reproductive structure Weltrichia Braun 1849 emend.Harris 1969(Family Williamsoniaceae) is discussed from several points of view,including anatomy and morphology,species diversity and validity,phytogeographical and stratigraphical distribution,and reproduction strategy.A very rare fossil,genus Weltrichia includes 25 valid species distributed in both hemispheres during Triassic and Jurassic times.This contribution critically reviews the systematics of the entire genus,together with its stratigraphical and palaeophytogeographical significance.

Genus Pronephrium Presl 1851 (Thelypteridaceae) in Romania

Pronephrium stiriacum（Unger） Knobloch et Kvatek 1976（Filicales, Thelypteridaceae Holttum 1971） is reported from the Oligocene Petrosani Basin and from the Miocene Bozovici Basin in Romania. Morphological variations of this species, such as size of the leaves, venation and marginal teeth, in the Oligocene-Miocene time interval in Romania are described, discussed and illustrated. The distribution of the Thelypteridacean species Pronephrium stiriacum is also discussed regarding its European expansion during the Cenozoic. Moreover, the palaeoecology of this species is discussed based on taphonomy and occurrences, as Pronephrium stiriacum was a secondary coal generator.