Tertiary remagnetization of normal polarity in Mesozoic marly limestones from SE France

The results of our new paleomagnetic investigations on 21 sites in the Cévennes and Lure regions as well as previous studies demonstrate that all Mesozoic marly limestones of SE France exhibit similar paleomagnetic behavior with remagnetization disputed in age. The studied areas have the particularity to have been folded before (Late Eocene), the Alpine folding (Oligo–Miocene). Samples (201 marly limestones) dated from Lower Jurassic to Lower Cretaceous have been demagnetized by thermal treatment. They all present a well-defined component with a normal polarity which was mostly obtained between 200 and 350 °C. Numerous arguments lead from pretectonic to syntectonic widespread remagnetization related to orogenic fluid circulation affecting the whole basin. An Eocene age (between 35 and 40 Ma) is obtained for this remagnetization thanks both to the comparison of the average inclination of all regional paleomagnetic studies (+54.9°/−1.5°) with the expected paleomagnetic inclination and the syntectonic character of remagnetization.     

Sedimentary environments of organic matter from Middle Permian source rocks in northern Xinjiang, China

1IntroductionThe formation of the Junggar,Turpan and Ili ba-sins is ascribed to Hercynian orogeny between theJunggar and Tianshan Mountains during the MiddlePermian.The rock assemblage of thick and stable sedi-mentary dark muddy shales interbedded with th…     

Sedimentary K-Ar signatures in clay fractions from Mesozoic marine shelf environments in Israel

The K-Ar system in clay fractions from shallow marine carbonate shelf environments was investigated on silicate fractions (clay minerals, feldspar) separated from 20 Lower Jurassic to Upper Cretaceous sedimentary rocks, deposited in the southern Tethys ocean. The range of lithologies investigated included dolomite and chalk [IR (insoluble residue)<10%], marl, shale (IR= 70–85%) and sandstone (IR>90%). The results show that K-bearing clay fractions often have K-Ar ages similar to the suggested age of deposition, which means either supply of land-derived authigenic K-bearing clays or synsedimentary diagenetic authigenesis, or both. This K-Ar synsedimentary signal is recorded in clay fractions from the whole range of studied lithologies and stratigraphic units. Among the clay minerals, the synsedimentary K-Ar signature was recorded and retained in illite/smectite of the <2-um and <0.2-um fractions. A prominent synsedimentary signature is found in K-feldspars, from shaly and especially from calcareous rocks, which is substantiated by their authigenic origin based on idiomorphic crystal morphology and their limited size distribution (4–10 um). Post-depositional closure of the K-Ar system is indicated by ages up to 15 Ma younger than the stratigraphic age in different lithologies from dispersed localities. A distinct late diagenetic (20–25 Ma younger) event is recorded in the formation of authigenic K-feldspar within Upper Cretaceous chalk and shale. In the IR and >10-um fractions the K-Ar ages reflect the contribution of detrital mica and feldspar which accompanies the kaolinite-dominated samples. The overall results differ considerably from K-Ar age patterns observed in deep-sea sediments, a difference which may be connected with the occurrence of brines in these shelf deposits. The findings indicate the potential in the K-Ar dating of fine IR fractions of marine shelf sediments in terms of geochronological-stratigraphic and palaeogeographical aspects as well as in the petrology of clay minerals themselves.     

Depositional environments and iron ooid formation in condensed sections (Callovian–Oxfordian, south-eastern Paris basin, France)

Carbonate platforms across Western Europe were superseded at the Middle–Upper Jurassic (Callovian–Oxfordian) boundary either by alternating marl–limestone and widespread marl deposits or by condensed sections containing iron ooids. The characteristics of marine condensed sections in the south-eastern part of the Paris Basin (France) and their distribution pattern are examined here, and a model of iron ooid formation is developed. Iron ooids are found from the shoreface to the offshore zone. They are most abundant in the median-to-distal offshore transition zone, where they originally formed. They also occur commonly, albeit often as reworked grains, in the proximal offshore zone, to which they were transported. The contemporaneous, thick, predominantly marl sections that occur laterally are devoid of iron ooids and were deposited in deeper settings (distal offshore zone). The iron ooids are composed of goethite. Typically, they have a nucleus made up of a clump of goethite crystals and a laminated cortex. Three distinctive nanostructures are identified in the cortex laminae: (i) a nanograined crystalline structure typical of primary goethite; (ii) a secondary nanoflaked structure thought to have formed mechanically by reorientation of the goethite crystals; and (iii) a coalesced structure acquired by subsequent diagenetic recrystallization. The iron ooids formed successively (i) by lamina growth when goethite precipitated in the surface layer of the sediment (nanograined structure) and (ii) by interruption of growth when the ooids were remobilized by hydrodynamic agents, as reflected by the flaked nanostructure; (iii) these two nanostructures were sometimes transformed into a coalesced structure by recrystallization when ooids were buried.     

Characterizing the molecular structure of organic matter from natural environments: An analytical challenge

Natural organic matter (OM) is widespread in terrestrial ecosystems and it plays a major role in the global carbon cycle. Despite this high environmental importance, its characterization at the molecular level remains unsatisfactory, especially when the macromolecular OM is concerned. Such a characterization is challenging because of the diversity and heterogeneity of OM, but it is of prime importance to derive OM reactivity and, more generally, to model environmental processes in which natural OM is involved. This awareness led to a wealth of analytical developments, which are described in the present review. They include improvements of existing techniques, but also new approaches and concern spectroscopic tools along with chemical and thermal degradations.     

羌塘-三江古生代-中生代沉积盆地演化

羌塘-三江构造-地层大区的古生代-中生代沉积盆地和构造演化受特提斯洋的控制.通过综合分析前人对羌塘-三江地区大量岩石地层、生物地层、同位素年代学及构造学等研究资料,对羌塘-三江构造-地层大区各分区古生代-中生代的沉积盆地类型进行了划分,并分析了各个沉积盆地的形成和演化过程,探讨了该区的大地构造演化:早古生代该区主体属于大洋环境;晚古生代随着特提斯洋向南东、北东方向的俯冲,该区开始发育一系列活动陆缘沉积盆地,产生金沙江弧后洋、澜沧江弧后洋和甘孜-理塘弧后洋,形成多岛洋弧盆系;中生代,随着特提斯洋向北东的俯冲消减,弧后洋逐渐闭合,羌塘-三江地区发生大规模弧-弧、弧-陆碰撞增生,逐渐转化成陆.随着白垩纪特提斯洋的闭合,印度板块与中国西部碰撞、造山,羌塘-三江地区发育陆内盆地.      

Upper Jurassic Radiolaria from the Vocontian basin of SE France

Two sections of the Vocontian basin (southeast France) were explored for their radiolarian content. Preservation in calcite impeded their extraction from the Châteauneuf d’Oze section, which is well dated by ammonites. Fortunately, oligospecific assemblages of pyritized radiolaria were yielded by twelve limestone beds of the Méouge section. In general, preservation worsens towards the top of the section. The extracted fauna is dominated by Nassellaria and more particularly by Archaeodictyomitridae, Pseudodictyomitridae and Williriedellidae. It is the first time that some species are reported outside their type area or from Western Tethys. Amongst the published zonations the scheme of Baumgartner et al. (1995a) is found to be the most useful and allows correlation of the studied part of the section with the mid-late Oxfordian to late Kimmeridgian-early Tithonian time interval.     

Groundwater occurrence in cold environments: examples from Nunavik,Canada

Water availability and management issues related to the supply of drinking water in northern communities are problematic in Canada. While rivers and lakes are abundant, they are vulnerable to contamination and may become dry in winter due to freezing. Groundwater can often provide a more secure and sustainable water source, however its availability is limited in northern Canada due to the presence of permafrost. Moreover, the exploitation of northern aquifers poses a dual challenge of identifying not only permafrost-free areas, but also permeable areas which will allow groundwater recharge and exploitation. Suitable aquifers are not as common in northern Canada since the shallow subsurface is mostly composed of low-permeability crystalline rocks or unconsolidated sediments of glacial origin that are highly heterogeneous. In order to investigate groundwater occurrence and associated geological contexts in Nunavik (northern Quebec, Canada), along with exploring how these resources will evolve in response to climate change, field and compilation work were conducted in the surroundings of the four villages of Salluit, Kuujjuaq, Umiujaq and Whapmagoostui-Kuujjuarapik. These villages are located in different permafrost zones, ranging from continuous to discontinuous, as well as in different geological environments. It was found that despite the ubiquitous presence of permafrost, unfrozen aquifers could be identified, which suggests that groundwater may be available as a source of drinking water for small communities. Expected climate change, with predicted permafrost thawing and increases in temperature and precipitation, should enhance groundwater availability and may contribute to a more secure source of drinking water for northern communities.     

Sedimentary evidence of soil organic matter input to the Curuai Amazonian floodplain

A multi-proxy study has been performed on a sediment core from the Curuai floodplain, Central Amazonia. The combination of elemental, isotopic and molecular analysis of a 110 cm core (a record of ca. the last 100 yr) allowed reconstruction of the hydrological conditions of organic matter (OM) deposition. Two units could be delineated. The first (UI) was composed of three sub-units: UIa (0–15 cm), composed of highly degraded organic particles originating from the surrounding soil and indicative of restricted transport; UIb (15–48 cm), during which the region was permanently flooded and the material stored came from soil runoff, mainly from alluvial forest; and UIc (48–88 cm) composed of material from Amazon River suspended sediment, itself originating from OM degradation in forest soil. In UII (88–111 cm), the OM originated mainly from the forest soil and other plant remains in the floodplain. The data reveal that, during the four distinct depositional periods, the sedimentary OM alternated between land derived soil and alluvial vegetation due to changes in hydrodynamics.     

Quantification and characterization of condensed organic matter in sediments from the Pearl River Delta and Estuary, South China

Nonhydrolyzable carbon （NHC） and black carbon （BC） were measured upon treatments with the HCl/HF/trifluoroacetic acid method, and with the combustion method at 375 ℃, respectively in three contaminated soils from the urban area of Guangzhou and twenty-two bulk and size-fractionated sediments from the Pearl River Delta and Estuary, China. The isolated NHC and BC fractions were also characterized using elementary analysis, radiocarbon accelerated mass spectroscopy （AMS）, solid state ^13C cross-polarization and magic angle spinning unclear magnetic resonance spectroscopy （^13C-CP/MAS NMR）, Fourier transformed infrared spectroscopy （FTIR）, and Raman microspectrometry. The results showed that the NHC and BC accounted for 25.6%-84.7 % and 4.14%-17.3%, respectively, of the total organic carbon （OC） with averages of 51.9% and 11.2% in the soils and sediments. For the less contaminated, low OC fiver and estuary sediments （WR and C08）, the OC and NHC concentrations increased with decreasing particle size.     

Compositions,sources and depositional environments of organic matter from the Middle Jurassic clays of Poland

The comprehensive biomarker characteristics from previously undescribed Middle Jurassic clays of Poland are presented. The molecular composition of the organic matter (OM) derived from clays of Aalenian to Callovian age has not changed significantly through time. High relative concentrations of many biomarkers typical for terrestrial material suggest a distinct dominance of OM derived from land plants. Increasing concentrations of C₂₉-diaster-13(17)-enes towards the northern part of the basin indicate an increase in terrestrial input. This terrestrial material would have originated from the enhanced transport of organic matter from land situated at the northern bank of the basin, i.e., the Fennoscandian Shield. The organic matter was deposited in an oxic to suboxic environment, as indicated by relatively low concentrations of C₃₃–C₃₅ homohopanes, moderate to high Pr/Ph ratio values, an absence of compounds characteristic for anoxia and water column stratification, such as isorenieratane, aryl isoprenoids and gammacerane, as well as common benthic fauna and burrows. δ¹⁸O measurements from calcitic rostra of belemnites suggest that the mean value of the Middle Jurassic sea-water temperature of the Polish Basin was 13.1 °C. It is suggested that this mirrored the temperature of the lower water column because belemnites are considered here to be necto-benthic. The organic matter from the Middle Jurassic basin of Poland is immature. This is clearly indicated by a large concentration of biomarkers with the biogenic configurations, such as ββ-hopanes, hop-13(18)-enes, hop-17(21)-enes, diasterenes and sterenes. The identification of preserved, unaltered biomolecules like ferruginol, 6,7-dehydroferruginol and sugiol in Protopodocarpoxylon wood samples from these sediments present particularly strong evidence for the presence of immature OM in the Middle Jurassic sediments. Moreover, the occurrence of these polar diterpenoids is important due to the fact that they are definitely the oldest known natural products detected in geological samples.     

Asynchronizing paleo-Pacific slab rollback beneath SE China: Insights from the episodic Late Mesozoic volcanism

Extensive Late Mesozoic igneous rocks in SE China have been widely considered to be generated under the paleo-Pacific tectonic regime. Previous studies suggested a fundamental oceanward younging trend for the igneous rocks, further implying a NW-ward paleo-Pacific subduction model with gradual slab rollback. New LA–ICP–MS zircon U–Pb dating results show that early stage of the Late Mesozoic volcanic sequences (also known as the lower volcanic series) in Fujian Province was formed in three episodes: 160–148 Ma for the Changlin Formation, 145–130 Ma for the Nanyuan Formation, and 130–127 Ma for the Xiaoxi Formation, among which the second episode made the volcanism climax. Thus the entire lower volcanic series in Fujian were formed earlier than those in Zhejiang (140–118 Ma), displaying a NE-ward younging trend parallel to the potential subduction belt. Besides, in situ Hf isotope analyses on dated zircons yield an ε_Hf(t) range of − 19.2 to + 1.7 for the lower volcanic series in Fujian. The majority of the studied volcanic rocks have more radiogenic Hf than that of the metamorphic basement, requiring the involvement of juvenile components in their origin. Moreover, the zircon ε_Hf(t) value increases with time in each single area, as well as the igneous rocks elsewhere in SE China, except for the Changlin Formation which shows very opposite isotopic varying trend. Increasing zircon ε_Hf(t) values imply an increasing material contribution of contemporaneous underplated mantle-derived magmas, which was plausibly induced by gradual crustal decompression. As well as the NE-ward younging trend of the lower volcanic series, it is also identified that the juvenile material contribution in the igneous petrogenesis gradually took place in the same direction along the coastal area. Thus here we propose an asynchronizing paleo-Pacific slab rollback model during 150–120 Ma to account for the episodic magmatism and crustal extension in SE China. On the contrary, decreasing zircon ε_Hf(t) values of the Changlin Formation volcanics indicate that they were formed under enhanced crustal compression probably induced by slab advance. On the other hand, the upper volcanic series in Fujian were formed during 110–88 Ma coevally to those in Zhejiang, with more depleted zircon Hf isotopic compositions than the lower volcanic series as well, indicating that the entire coastal SE China was under the back-arc tectonic setting during that time.     

Sedimentary provenance of the Hengyang and Mayang basins,SE China,and implications for the Mesozoic topographic change in South China Craton: Evidence from detrital zircon geochronology

Detrital zircon U–Pb data from sedimentary rocks in the Hengyang and Mayang basins, SE China reveal a change in basin provenance during or after Early Cretaceous. The results imply a provenance of the sediment from the North China Craton and Dabie Orogen for the Upper Triassic to Middle Jurassic sandstones and from the Indosinian granitic plutons in the South China Craton for the Lower Cretaceous sandstones. The 90–120 Ma age group in the Upper Cretaceous sandstones in the Hengyang Basin is correlated with Cretaceous volcanism along the southeastern margin of South China, suggesting a coastal mountain belt have existed during the Late Cretaceous. The sediment provenance of the basins and topographic evolution revealed by the geochronological data in this study are consistent with a Mesozoic tectonic setting from Early Mesozoic intra-continental compression through late Mesozoic Pacific Plate subduction in SE China.     

下扬子中生代沉积盆地演化

通过对下扬子地区各地层分区中生代岩石地层序列、沉积建造详细分析以及生物地层与年代地层划分对比, 在盆地原型恢复、盆地充填序列和岩相古地理综合分析的基础上, 划分出下扬子陆块中生代不同时段的5类沉积盆地: 陆表海(T_1-2)、周缘前陆盆地(T₃-J₁)、压陷盆地(T₃-J₂)、断陷盆地(J₃-K)和拉分盆地(J₃-K), 初步建立了下扬子陆块中生代沉积盆地时空分布格架.分析了下扬子中生代盆地沉积大地构造环境演化历程: 三叠纪-早侏罗世为与特提斯海演化相关的构造阶段, 分为早三叠世-中三叠世陆表海和晚三叠世-早侏罗世前陆盆地2个亚阶段; 中侏罗世-白垩纪转化为滨太平洋构造阶段, 中侏罗世以挤压构造背景为主, 大部分地区为隆升剥蚀区, 晚侏罗世-白垩纪为强裂伸展拉张期, 发育了一系列北东向火山-沉积断陷盆地和拉分盆地, 盆-岭构造格局形成.      

Preserved organic matter in a fossil Ocean Continent Transition in the Alps: the example of Totalp,SE Switzerland

Evidence from ultraslow spreading mid-ocean ridges and both fossil and present-day Ocean–Continent Transitions (OCT) demonstrates that mantle serpentinization resulting from the interaction of mantle rock and water during tectonic exhumation is widespread. Observations at white smokers in modern ocean settings suggest that methane produced by serpentinization can support methanotrophic bio-systems, which use methane as the only source of carbon. An important question is whether such bio-systems are more generally pervasive in their association with serpentinized mantle in the subsurface. In this study, we examined whether there is evidence for such a methanotrophic system in exhumed serpentinized mantle at a magma-poor rifted continental margin, by probing for characteristic biological markers in these and associated sedimentary rocks in the Totalp unit of SE Switzerland. This unit represents a remnant of the former OCT of the southern Alpine Tethyan margin and was chosen because of its mild Alpine tectonic and low-grade metamorphic overprint during Alpine orogeny, hence giving potential for the preservation of indigenous organic matter (OM). Totalp samples are characterized by low organic carbon contents of 11–647 ppm. The majority of the samples contain hydrocarbons in the form of n-alkanes in the range C₁₇–C₃₆. Some sediments contain isoprenoids, for example pristane and phytane and a suite of steranes that are consistent with a marine origin for the OM preserved in the rocks. Traces of marine planktonic and bacterial OM are preserved in the serpentinized mantle and overlying sediments of this ancient Tethyan OCT, but there is no evidence that the OM has been generated from methanotrophic bio-systems.     

Accumulation of organic matter in Cretaceous oxygen-deficient depositional environments in the central Pacific Ocean

Complete records of organic-carbon-rich Cretaceous strata were continuouslycored on the flanks of the Mid-Pacific Mountains and southern Hess Rise in the central North Pacific Ocean during DSDP Leg 62. Organic-carbon-rich laminated silicified limestones were deposited in the western Mid-Pacific Mountains during the early Aptian, a time when that region was south of the equator and considerably shallower than at present. Organic-carbon-rich, laminated limestone on southern Hess Rise overlies volcanic basement and includes 136 m of stratigraphic section of late Albian to early Cenomanian age. This limestone unit was deposited rapidly as Hess Rise was passing under the equatorial high-productivity zone and was subsiding from shallow to intermediate depths. The association of volcanogenic components with organic-carbon-rich strata on Hess Rise in the Mid-Pacific Mountains is striking and suggests that there was a coincidence of mid-plate volcanic activity and the production and accumulation of organic matter at intermediate water depths in the tropical Pacific Ocean during the middle Cretaceous.Pyrolysis assays and analyses of extractable hydrocarbons indicate that the organic matter in the limestone on Hess Rise is composed mainly of lipid-rich kerogen derived from aquatic marine organisms and bacteria. Limestones from the Mid-Pacific Mountains generally contain low ratios of pyrolytic hydrocarbons to organic carbon and low hydrogen indices, suggesting that the organic matter may contain a significant proportion of land-derived material, possibly derived from numerous volcanic islands that must have existed before the area subsided. The organic carbon in all samples analyzed is isotopically light (δ¹³C ? 24 to ? 29 per mil) relative to most modern rine organic carbon, and the lightest carbon is also the most lipid-rich.There is a positive linear correlation between sulfur and organic carbon in samples from Hess Rise and from the Mid-Pacific Mountains. The slopes and intercepts of C-S regression lines however, are different for each site and all are different from regression lines for samples from modern anoxic marine sediments and from Black Sea cores.The organic-carbon-rich limestones on Hess Rise, the Mid-Pacific Mountains, and other plateaus and seamounts in the Pacific Ocean are not synchronous but do occur within the same general middle Cretaceous time period as organic-carbon-rich lithofacies elsewhere in the world ocean, particularly in the Atlantic Ocean. Strata of equivalent age in the deep basins of the Pacific Ocean are not rich in organic carbon, and were deposited in oxygenated environments. This observation, together with the evidence that the plateau sites were considerably shallower and closse to the equator during the middle Creataceous suggests that local tectonic and hydrographic conditions may have resulted in high surface-water productivity and the preservation of organic matter in an oxygen-deficient environment where an expanded mid-water oxygen minimum developed and impinged on elevated platforms and seamounts.     

Ozonation of triterpenoids: Implications for early diagenesis of biomarkers in oxic environments

This study examines the fate of commonly found organic natural products under exposure to ozone to simulate early oxic diagenesis. The model compounds β-amyrin, lupenone and friedelin have been investigated by ozonation in the presence of water. The transformation products were identified or proposed based on their fragmentation patterns in mass spectra. The double bonds located at the isopropenyl group of lupenone and ring C of β-amyrin are the main reaction sites in the ozonation reaction. The major products identified from the ozonation of β-amyrin are β-amyrone, 12,13-epoxyoleanan-3β-ol, 11-oxo-olean-12-en-3β-ol, 12-oxo-oleanan-3β-ol. In addition, 8,14-seco-12-oxo-olean-14-en-3β-ol, 8,14-seco-12-oxo-olean-13-en-3β-ol and 8,14-seco-oleana-3,12-dione, generated from the bond cleavage between C-8 to C-14 of 12-oxo-oleanan-3β-ol and 12-oxo-oleanan-3-one, respectively, have also been detected. 22,29,30-trisnorlup-18(19)-en-3-one, 22,29,30-trisnorlupan-3-one, 22,29,30-trisnorlupana-3,19-dione, 22,29,30-trisnorlupana-3,12-dione, lupeol, lup-22(29)-en-3-on-29-ol, 22,29-epoxylupan-3-one, lupan-3-on-29-al, lupan-3-on-29-ol and 19,22-epoxylupan-3-one are the major products from the ozonation of lupenone. No transformation product was detected for friedelin, probably due to its stability to ozonation.     

Sedimentary matter and organic compounds in the aerosols and surface waters along the Transatlantic section

Concentrations and composition of suspended particulate matter and organic compounds (OC), including Сorg, lipids, hydrocarbons (HC), and pigments, were determined in the near-water aerosol layer and in surface waters on the meridional section across the Atlantic Ocean from the port of Ushuaia to the port of Gdansk (Cruise 47^th of the R/V Akademic Ioffe, March 26–May, 7, 2015). It was established that the distribution of OC (except for pigments) in aerosols, in general, repeats the distribution of particle number and weight concentrations of aerosols, with maximums in the influence zone of fluxes from Patagonia and African deserts. The concentrations of aerosols changed within wide ranges: from 1237 to 111739 particles/L for 0.3–1 μm fraction; and from 0.02 to 19.890 μg/m³ for aerosols collected by network method (flux of 0.02–34.4 mg/m² day). The contrasting mineral composition of aeolian material reflects the diversity of its provenances. In surface waters, the studied compounds were accumulated in the frontal river–sea area (runoff of the Rio-Colorado River) and with approaching the coast, especially in the English Channel. A simultaneous change of concentrations of suspended particulate matter and OC is observed only in open oceanic waters.     

Occurrence of fossil organic matter in modern environments: Optical, geochemical and isotopic evidence

This study relates to the input and fate of fossil organic matter (FOM) in the modern environment, and focuses on two experimental watersheds overlying Jurassic marls: Le Laval and Le Brusquet (1 km² in area), located near Digne, Alpes-de-Haute-Provence, France. Considering that FOM delivery is mainly a result of different processes affecting sedimentary rocks [(bio)chemical and mechanical weathering], samples from different pools were collected: bedrocks, weathering profiles, soils and riverine particles. The samples were examined using complementary techniques: optical (palynofacies methods), geochemical (Rock-Eval 6 pyrolysis, C/N ratio), molecular (gas chromatography/mass spectrometry) and isotopic (stable C isotopic composition). As a result, FOM markers were identified and tracked through the different pools. The results highlight the contribution of FOM, which can be found in all the studied pools. Transfer of FOM between bedrocks/weathering profiles (governed mainly by chemical weathering) and bedrocks/riverine particles (governed mainly by mechanical weathering) reveals any qualitative change. Weathering profiles/soils transition [governed by (bio)chemical weathering] is characterized by alteration of the FOM, which is difficult to describe because fossil material is mixed with recent organic matter (ROM). Despite this latter point, the study provides evidence for a relative resistance of FOM to weathering processes and points to its contribution to the modern geosystem and the C cycle.     

上扬子地区中生代沉积盆地演化

以地层分区为单位对上扬子地区中生代沉积建造进行了详细分析, 对盆地原型进行了初步划分, 建立了中生代上扬子陆块沉积盆地时空分布格架.结合年代地层和生物地层划分对比、生物古地理、岩相古地理和构造演化规律的综合分析, 对上扬子地区中生代3个阶段的盆地演化过程进行生动刻画, 并以此为依据分析了盆地形成演化的大地构造环境.早三叠世上扬子陆块受印支造山运动的影响不断抬升, 海相盆地水体变浅, 形成一系列混积陆表海、台盆-台地构造相; 晚三叠世-早侏罗世上扬子西缘与其西侧的特提斯域地块或多岛弧盆增生体发生碰撞拼合, 且华南陆块与华北陆块的碰撞拼合, 使上扬子陆块西南缘、西缘和北缘发育了前陆盆地和周缘前陆盆地, 与此同时雪峰隆起进入造山过程; 中侏罗世之后, 由于受古太平洋板块向西对亚洲大陆的俯冲, 上扬子陆块进入了以陆内造山作用为主的新的构造阶段, 以雪峰山为界, 东部发育一系列断陷-坳陷盆地, 西侧则发育陆内大型压陷盆地.