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1.
The palynological assemblages from two Albian-Cenomanian boundary sections in North Bulgaria are described. The samples analyzed yielded a diverse palynological content including dinoflagellate cysts and miospores. Based on dinocyst nutrient and productivity indices a phase of enhanced nutrient availability and high primary productivity is inferred for the latest Albian interval. The pronounced predominance of peridinioid dinocysts in this interval, namely O. verrucosum, O. scabrosum and especially P. infusorioides is considered to reflect eutrophic conditions. It coincides with the increased phosphorus mass accumulation occurring at the top part of the Upper Albian Dekov Formation. OAE 1d is indicated in the Tolovitsa karst spring section, based on palynofacies dominated by high amounts of granular amorphous organic matter (AOM) related to anoxic environmental conditions. These sections serve as evidence suggesting a relationship between Cretaceous peridinioid cysts (including Palaeohystichphora infusorioides, Ovoidinium verrucosum, O. scabrosum) and anoxic/suboxic conditions and/or high primary productivity. The pollen spectrum inferred relatively stable vegetation patterns of surrounding continental areas during and after the Albian/Cenomanian boundary interval and the times of OAE 1d formation. The hinterland vegetation integrated mainly pteridophyte spores and gymnosperms. The area was part of the Southern Laurasian floral province which was characterized by warm temperate to subtropical humid climate. Angiosperms were still minor part of this vegetation.  相似文献   

2.
A qualitative and semi-quantitative study of recent dinoflagellate cysts has been undertaken in the NW part of Aegean Sea, Thermaikos Gulf (Eastern Mediteranean), before (September 2001), during (October 2001) and after 120 days (February 2002) of intensive trawling activities. This is the first survey of recent dinoflagellate cysts from Greek marine coastal environments. Sediment samples were collected with a corer and the vertical distribution of the cysts was studied at five different layers, from 0 to 10 cm. Dinoflagellate cysts were both abundant and diverse. Cysts were found over the whole sampling area and periods, with concentrations ranging between 247–3202 cysts cm−3. Thirty-six cyst types were encountered, of which 32 were identified to species level, representing 12 genera. It seems that significant local resuspension, related to the onset of the trawling period and stirring up of the sediment, contributed to mixing of the upper layers, resulting to more homogenous cyst profiles in the sediment. Viable cysts constituted 16–60% of the total cyst abundance. The abundance peaks of viable cysts within the subsurface sediment layers, observed during the undisturbed period, disappeared during October. In February, the reduction of cyst concentration was associated to a loss of viable cysts, whilst the ratio of viable/empty cysts ranged between 0.30 and 0.67. The abundance of the different dinoflagellate species, in their active form, was monitored in order to detect any relationship between the concentration of cysts in the top 10 cm of sediment and blooms of algae in the water column. Cysts of potentially toxic species, causing Paralitic Shellfish Poisoning (PSP), such as Alexandrium cf. tamarense, A. cf. affine, A. cf. minutum, as well as Gymnodinium catenatum, were detected in the cyst survey.  相似文献   

3.
The impact of sewage and stormwater effluents on phytoplankton is investigated by comparing organic-walled dinoflagellate cyst abundance and diversity from 38 surface sediment samples, flanking southern Vancouver Island. Site locations include those directly adjacent to wastewater outfall at Clover and Macaulay Points and Saanich Peninsula, as well as from a variety of near-shore environments with differing tidal flow influences. Excellently preserved dinoflagellate cyst assemblages have been recovered and 36 cyst taxa were identified. Local assemblages are characterized by a high relative proportion (average 56%) of cysts produced by heterotrophic dinoflagellates, which is typical for regions of high primary production. Relative proportional increases of cysts from heterotrophic species with particular increases of Polykrikos kofoidii/schwartzii and Dubridinium species, known to reflect areas affected by eutrophication, occur directly adjacent to all three sewage outfalls, as well as in the more stagnant waters of Esquimalt and Victoria Harbours and at the mouth of Cadboro Bay. Further effects of an anthropogenic effluent can be seen in the relatively higher concentrations of organic carbon and the diatom production proxy, biogenic opal. Results from this study clearly indicate a much larger impact zone than predicted by a sewage effluent plume model or trends found in monitored benthic biota and sediment chemistry that evidence primary outfall affects <800 m eastward of Macaulay Point and about 200 m eastward of the Clover Point. Enhanced production of cysts from potentially toxic Alexandrium species is also observed near locations of sewage outfalls.  相似文献   

4.
本文通过对郑州市大河村遗址沉积进行系统的孢粉分析,结果表明,遗址沉积时期的大部分时间,为距今5740一4410年,气候暖和润湿,气温较今稍高,其时植被面貌属森林草原类型或森林类型。遗址沉积物的地质时代属第四纪的全新世  相似文献   

5.
Permineralized osmundaceous rhizome with anatomical and phylogenetic information plays a significant role in understanding the origin,evolution,and diversity variation of the fern family Osmundaceae in geological history.The northern Hebei and western Liaoning region is one of the most important fossil localities for the Jurassic osmundaceous rhizome fossils in the Northern Hemisphere;however,the diversity character of osmundaceous rhizome fossil remains poorly known.A new structurally preserved fern rhizome species,Ashicaulis wangii sp.nov.,is described from the Middle Jurassic Tiaojishan Formation in Beipiao City,Liaoning Province,northeastern China.The rhizome is composed of heterogeneous pith,an ectophloic–dictyoxylic siphonostele,a two–layered cortex,and a mantle of adventitious roots and petiole bases.The xylem cylinder,with complete leaf gaps,consists of 15–17 xylem strands.The petiole base is characterized by a heterogeneous sclerotic ring and numerous sclerenchyma masses in the petiolar cortex.Among five known Ashicaulis species with heterogeneous sclerotic ring,four of them are documented from China.Therefore,osmundaceous rhizome fossils from China show endemic anatomical characteristics and significances for palaeobiogeography.Comparisons of anatomical features suggest that A.wangii sp.nov.bears close similarities to Osmunda pluma Miller from the Paleocene of Dakota,USA.Fossil species of A.wangii provides new evidence for further understanding the species diversity of osmundaceous rhizome fossil in China and in the Northern Hemisphere,and contributes to exploring the macroevolution process of the Mesozoic osmundaceous plants.  相似文献   

6.
To investigate the influence of towed demersal fishing gears on dinoflagellate cyst resuspension, towing trials with four gear components were carried out at three sites of differing sediment type in the Moray Firth, Scotland. Samples of sediment plumes were collected using plankton nets mounted on a towed sledge. Diversity of resuspended dinoflagellate cysts was similar at all sites and included Protoperidinium and Gonyaulax spp., Proroceratium reticulatum and unidentified ‘round brown’ cysts. Cyst concentrations per gram of resuspended sediment varied by gear component and sediment particle size distribution. Gear components with lower hydrodynamic drag generated wakes with smaller shear stresses, mobilising fewer larger sand particles, giving larger concentrations of cysts. Muddy sediments contained higher cyst concentrations which declined with increasing grain size. This study has shown that fishing gear and sediment type can influence the redistribution of dinoflagellate cysts and highlights the importance this may have in relation to dinoflagellate blooms.  相似文献   

7.
柴达木盆地沉积地层记载着青藏高原东北部的构造演化信息.对该盆地路乐河地区上中生界—新生界地层系统采样,获得千余块定向岩心样品.岩石磁学研究表明样品中的磁性矿物主要为赤铁矿和磁铁矿;磁组构研究表明为初始沉积磁组构特征.磁组构特征指示了自中侏罗统大煤沟组(J2d)至早中新统下油砂山组(N12y)7个地层单位沉积时期,古水流方向共经历了4次阶段性的变化,表明柴达木块体相应地发生了4次旋转.在中—晚侏罗世块体逆时针旋转约22°;至早白垩世,块体又顺时针旋转约65°;在65.5～32 Ma期间块体旋转方向再次改变,逆时针旋转约63°;到32～13Ma阶段块体又发生约50°的顺时针旋转.柴达木块体的旋转及其方向的转换,可能与其南的羌塘块体、拉萨块体和印度板块阶段性北向碰撞挤压紧密相关.拉张环境与挤压环境的多次转换可能与中特提斯的关闭、新特提斯的张开和闭合、高原快速隆升后其边部松弛相联系.  相似文献   

8.
The distribution and abundance of dinoflagellate cysts in recent sediments from Visakhapatnam harbour, east coast of India was investigated and compared with sediment characteristics and physico-chemical variables of the overlying water column. The cyst abundance varied from 11 to 1218 cysts g–1 dry sediment. Changes in the cyst assemblages from phototrophic to heterotrophic forms were observed from inner to outer harbour stations, and related to changes in environmental characteristics. Enhanced cyst production of potentially harmful dinoflagellate Protoceratium reticulatum was recorded in the inner harbour stations with higher nutrient concentrations. Protoperidinium cysts were the most diversified group, and were dominant in the outer harbour stations having improved water conditions and circulation. This study points out the potential use of dinoflagellate cyst populations in providing information on environmental conditions.  相似文献   

9.
Dinoflagellate cysts acquired from sediment cores were analyzed in order to reconstruct historical nutrient levels in Gamak Bay, Korea and Ariake Bay, Japan. Dinoflagellate cyst assemblages in Gamak Bay were characterized by high proportions of heterotrophic cysts such as Brigantedinium spp., Protoperidinium americanum and Polykrikos cysts, which suggested that nutrients levels may have already been high before 1970s, and then increased further to the hypertrophic conditions of the 1990s. In contrast, dinoflagellate cyst assemblages in Ariake Bay were characterized by high relative abundances of Lingulodinium machaerophorum and Spiniferites spp., which suggested that nutrient levels in Ariake Bay had increased gradually since the mid 1960s, and may have been significantly enhanced by the mid 1980s. Dinoflagellate cyst assemblages reflecting environmental changes in the two bays are contrasting, perhaps due to different nutrient enrichment mechanisms. This suggests that the indicators of nutrient levels encoded in dinoflagellate cyst assemblages may exhibit site-specific information.  相似文献   

10.
Masayuki  Ehiro  Satoru  Kojima  Tadashi  Sato  Talat  Ahmad  Tomoyuki  Ohtani 《Island Arc》2007,16(1):124-132
Abstract   Callovian (late Middle Jurassic) ammonoids Macrocephalites and Jeanneticeras were recovered from the Shyok suture zone, northeast of Chang La Pass, Ladakh, northwest India. They are the first reliable Jurassic fossils and the oldest chronologic data from the Shyok suture zone. The ammonoid-bearing Jurassic strata, newly defined as the Tsoltak Formation, consist largely of terrigenous mudstone with thin sandstone beds and were probably a part of the continental basement to the Cretaceous Ladakh Arc.  相似文献   

11.
The timing of the "Yanshanian Movement" and the tectonic setting that controlled the Yanshan fold-and-thrust belt during Jurassic time in China are still matters of controversy. Sediments that filled the intramontane basins in the Yanshan belt perfectly record the history of "Yanshanian Movement" and the tectonic background of these basins. Recognizing syn-tectonic sedimentation, clarifying its relationship with structures, and accurately defining strata ages to build up a correct chronostratigraphic framework are the key points to further reveal the timing and kinematics of tectonic deformation in the Yanshan belt from the Jurassic to the Early Cretaceous. This paper applies both tectonic and sedimentary methods on the fold-and-thrust belt and intramontane basins in the Zhangjiakou area, which is located at the intersection between the western Yanshan and northern Taihangshan. Our work suggests that the pre-defined "Jurassic strata" should be re-dated and sub-divided into three strata units: a Late Triassic to Early Jurassic unit, a Middle Jurassic unit, and a Late Jurassic to early Early Cretaceous unit. Under the control of growth fold-and-thrust structures, five types of growth strata developed in different growth structures: fold-belt foredeep type,thrust-belt foredeep type, fault-propagation fold-thrust structure type, fault-bend fold-thrust structure type, and fault-bend foldthrust plus fault-propagation fold composite type. The reconstructed "source-to-sink" systems of Late Triassic to Early Jurassic,Middle Jurassic and Late Jurassic to early Early Cretaceous times, which are composed of a fold-and-thrust belt and flexure basins, imply that the "Yanshanian Movement" in our study area started in the Middle Jurassic. During Middle Jurassic to early Early Cretaceous times, there have been at least three stages of fold-thrust events that developed "Laramide-type" basementinvolved fold-thrust structures and small-scale intramontane broken "axial basins". The westward migration of a "pair" of basement-involved fold-thrust belt and flexure basins might have been controlled by flat subduction of the western Paleo-Pacific slab from the Jurassic to the Early Cretaceous.  相似文献   

12.
We report a large cyst bed of the potentially toxic and bloom-forming dinoflagellate Alexandrium tamarense species complex in bottom sediments from the port of Halifax, Nova Scotia, Canada. The average cyst concentrations of that species ranged from 4033 ± 2647 to 220 872 ± 148 086 cysts g?1 of dry sediments and the highest concentrations were found near ship terminals in Bedford Basin. Although this species is endemic to this region, our work strongly suggests that some of the cysts of A. tamarense species complex found in the port of Halifax were introduced through discharged ballast water and sediments.  相似文献   

13.
New progresses on geothermal history of Turpan-Hami Basin, Xinjiang, China   总被引：2，自引：0，他引：2  
A comprehensive study on geothermal history of the Turpan-Hami Basin by vitrinite reflectance, fluid inclusion geothermometry, apatite fission track and40Ar-39Ar dating displays that the main effects influencing geotemperature distribution are burial depth of the basement, heat flow, magmatic activities, as well as tectonic movement, having a rugulation to be higher in the east and north, lower in the west and south, as well as higher in the past and lower at the present. The heat of the mantle source and the Indo-China tectonic thermal event have extremely influenced maturation of source rocks of the upper Lower Permian and the Middle and Upper Triassic in the lndo-China epoch. While, the geothermal gradient and the weak tectonic geothermal event of the Early Yanshan Movement provided necessary heat for the maturation of source rock in coal-bearing strata of the Middle and Lower Jurassic.  相似文献   

14.
We investigated the influences of temperature, salinity and pH on the calcium isotope as well as trace and minor element (uranium, strontium, magnesium) to Ca ratios on calcium carbonate cysts of the calcareous dinoflagellate species Thoracosphaera heimii grown in laboratory cultures. The natural habitat of this species is the photic zone (preferentially at the chlorophyll maximum depth) of temperate to tropical oceans, and it is abundant in deep-sea sediments over the entire Cenozoic. In our experiments, temperatures ranged from 12 to 30 °C, salinity from 36.5 to 38.8 and pH from 7.9 to 8.4. The δ44/40Ca of T. heimii cysts resembles that of other marine calcifiers, including coccolithophores, foraminifers and corals. However, its temperature sensitivity is considerably smaller and statistically insignificant, and T. heimii might serve as a recorder of changes in seawater δ44/40Ca over geologic time. The Sr/Ca ratios of T. heimii cysts show a pronounced temperature sensitivity (0.016 mmol/mol °C? 1) and have the potential to serve as a palaeo-sea surface temperature proxy. No clear temperature- and pH-dependences were observed for Mg/Ca. U/Ca seems to be influenced by temperature and pH, but the correlations change sign at 23 °C and pH 8.2, respectively.  相似文献   

15.
From Middle-Upper Jurassic volcanics at the western margin of the Maranha?o Basin (6.4°S, 47.4°W) 15 sites (121 samples) have a mean magnetization directionD = 3.9°,I = ?17.9° withα95 = 9.3°,k = 17.9 after AF cleaning (all sites have normal polarity). This yields a pole (named SAJ2) at 85.3°N, 82.5°E (A95 = 6.9°) which is near to the other known Middle Jurassic South American pole. For 21 sites (190 samples) from Lower Cretaceous basalt intrusions from the eastern part of the Maranha?o Basin (6.5°S, 42°W) the mean direction isD = 174.7°,I = +6.0° withα95 = 2.8°,k = 122 (all sites have reversed polarity) yielding a pole (SAK9) at 83.6°N, 261°E (A95 = 1.9°) in agreement with other Lower Cretaceous pole positions for South America. Comparing Mesozoic pole positions for South America and Africa in the pre-drift configuration after Bullard et al. [13] one finds a significant difference (with more than 95% probability) for the Lower Cretaceous and Middle Jurassic poles and also a probable difference for the mean Triassic poles indicating a small but probably stationary separation of the two continents from the predrift position in the Mesozoic until Lower Cretaceous time which may be due to an early rifting event.  相似文献   

16.
Calcareous nannoplankton experienced rapid diversification at the Jurassic/Cretaceous boundary, including the appearance of several highly successful and long-ranging Cretaceous genera. This study examines, at high-resolution, calcareous nannofossil assemblages and bulk-rock oxygen and carbon isotopes of lower Tithonian to lower Berriasian (∼ 151 to 142 Ma) sediments recovered in Deep Sea Drilling Project Hole 534A, central Atlantic Ocean. The results show major changes in assemblage composition and abundance of three genera (Conusphaera, Nannoconus, and Polycostella). Conusphaera dominates the nannolith assemblage in the late middle Tithonian (“Conusphaera world”), while the nannoconid dominance (“Nannoconus world”) began in the Berriasian. The acme peak of the genus Polycostella in the late Tithonian partially superimposes that of Conusphaera. Although these genera are indicators of warm, oligotrophic surface waters, stable isotope data suggest that the individual taxa may flourish in slightly different ecological regimes. Nannoconus flourished under warmer and possibly more nutrient-depleted surface waters than Polycostella, a genus that thrived in relatively cooler waters. These findings imply paleoceanographic changes across the J/K boundary interval with a cooling in the late Tithonian, followed by a temperature increase in the Berriasian. Because the transfer of these heavily calcified nannolith taxa to the seafloor is more efficient than that of average coccolithophorids, the J/K evolutionary event changed carbonate cycling and burial in the oceans.  相似文献   

17.
The palynological assemblages from two Albian-Cenomanian boundary sections in North Bulgaria are described.The samples analyzed yielded a diverse palynological content including dinoflagellate cysts and miospores.Based on dinocyst nutrient and productivity indices a phase of enhanced nutrient availability and high primary productivity is inferred for the latest Albian interval.The pronounced predominance of peridinioid dinocysts in this interval,namely O.verrucosum,O.scabrosum and especially P.infusorioides is considered to reflect eutrophic conditions.It coincides with the increased phosphorus mass accumulation occurring at the top part of the Upper Albian Dekov Formation.OAE 1d is indicated in the Tolovitsa karst spring section,based on palynofacies dominated by high amounts of granular amorphous organic matter(AOM)related to anoxic environmental conditions.These sections serve as evidence suggesting a relationship between Cretaceous peridinioid cysts(including Palaeohystichphora infusorioides,Ovoidinium verrucosum,O.scabrosum)and anoxic/suboxic conditions and/or high primary productivity.The pollen spectrum inferred relatively stable vegetation patterns of surrounding continental areas during and after the Albian/Cenomanian boundary interval and the times of OAE 1d formation.The hinterland vegetation integrated mainly pteridophyte spores and gymnosperms.The area was part of the Southern Laurasian floral province which was characterized by warm temperate to subtropical humid climate.Angiosperms were still minor part of this vegetation.  相似文献   

18.
The Jurassic is an important period of global coal formation, including the development of several large coalfields in central Asia and northern China. Individual seams within these peatlands represent sustained periods of terrestrial carbon accumulation and a key environmental indicator attributed to this record is the rate of carbon accumulation. Determining the rate of carbon accumulation requires a measure of time contained within the coal and this study aimed at determining the rate via the identification of Milankovitch orbital cycles using spectral analysis. Spectral analyses of geophysical data from two thick coal seams, No. 43(35.9 m) and No. 3(13.2 m), of the Middle Jurassic of the southern Junggar coalfield were conducted to identify significant signals of variations in ash content. The results showed that the variations in ash content of the coal showed spatial cycles at 0.2, 0.7 and 1.1 m~(-1), which were interpreted to represent 123 ka(eccentricity), 37.1 ka(obliquity), and 21.2 ka(precession) orbital periodicities, respectively. Using this timeframe, the depositional time of the No. 43 and No. 3 coal seams were calculated to be 876–970 and 322–357 ka, respectively. In combination with an understanding of carbon loss during coalification, the carbon accumulation rates of these Middle Jurassic peatlands were calculated to be 58.6–64.9 and60.3–66.8 g C m~(-2) a~(-1) for the No. 43 and No. 3 coal seams, respectively. Given that the net primary productivity(NPP) was 4.3 times the value of the carbon accumulation in a mid-latitude region of 40°–45°N, an NPP of 251.8–279.1 and259.1–287.1 g C m~(-2) a~(-1) was calculated for the No. 43 and No. 3 coal seams, respectively. In the context of the same paleolatitude(40°–45°N) and peat type, the NPP values of the Middle Jurassic strata in the study area were higher than those of the peatlands of the Holocene and Permian, and were similar to the NPP values of Early Cretaceous peatlands. Considering the NPP of a peatland is predominantly controlled by atmospheric CO_2 and O_2 levels and temperature, the lower content of CO_2 and an excessive O_2 level in the temporal atmosphere would lead to a decrease in peatland NPP. Therefore, it is inferred that the CO_2 level during the Middle Jurassic was higher than that of the icehouse Permian and Holocene periods, and it was similar to the CO_2 level of the greenhouse Cretaceous period. The results are consistent with the global CO_2 variation curve of Berner. In conclusion, Milankovitch orbital cycles calculated from geophysical logs can be used to infer the NPP of temporal peatlands during different geological periods, based on which the deep-time paleoclimates can be analyzed.  相似文献   

19.
Cretaceous climate was warmer than today.The Songliao Basin contains one of the most important Late Cretaceous non-marine deposits in China for the research of the paleoenvironment and paleoclimate.This research is based on core samples from the SK1(S)borehole.The strata sampled are the upper part of the Quantou Formation to member 2 of the Nenjiang Formation,where spores,pollen,dinoflagellates,and other microfossils are abundantly preserved.Based on analysis of the spores and pollen fossils from the core samples,the following six fossil assemblage zones have been recognized in ascending order:The Cicatricosisporites-Cyathidites-Pinuspollenites,Schizaeoisporites-Cyathidites-Classopollis,Cyathidites-Schizaeoisporites,Schizaeoisporites-Cyathidites-Proteacidites,Proteacidites-Cyathidites-Dictyotriletes,and the Lythraites-Callistipollenites-Schizaeoisporites zones.The six fossil zones range from the late Cenomanian to early Campanian.The Late Cretaceous dinoflagellate cysts in the Songliao Basin are of high abundance and low diversity.Specific phytoplankton types reflect salinity changes of the Songliao Lake.Paleoecology of the dinoflagellates suggests that sediments of members 2 and 3 of the Yaojia Formation(K2y2+3)were deposited in a freshwater environment,whereas members 2 and 3 of the Qingshankou Formation(K2q2+3)and members 1 and 2 of the Nenjiang Formation(K2n1+2)were deposited in freshwater to brackish water environments.Combined with the paleoecology of dinoflagellates and the palynomorph biozones,valuable information of the paleoclimate was provided.The quantitative analyses of spores and pollen fossils,such as vegetation type,climate type,and humidity type,diversity and dominance,indicate a relatively sub-humid,mid-subtropical paleoclimate,with slight climatic fluctuation and/or temporal change.  相似文献   

20.
The Jurassic stratigraphy in China is dominated by continental sediments. Marine facies and marine-terrigenous facies sediment have developed locally in the Qinghai-Tibet area, southern South China, and northeast China. The division of terrestrial Jurassic strata has been argued, and the conclusions of biostratigraphy and isotope chronology have been inconsistent.During the Jurassic period, the North China Plate, South China Plate, and Tarim Plate were spliced and formed the prototype of ancient China. The Yanshan Movement has had a profound influence on the eastern and northern regions of China and has formed an important regional unconformity. The Triassic-Jurassic boundary(201.3 Ma) is located roughly between the Haojiagou Formation and the Badaowan Formation in the Junggar Basin, and between the Xujiahe Formation and the Ziliujing Formation in the Sichuan Basin. The early Early Jurassic sediments generally were lacking in the eastern and central regions north of the ancient Dabie Mountains, suggesting that a clear uplift occurred in the eastern part of China during the Late Triassic period when it formed vast mountains and plateaus. A series of molasse-volcanic rock-coal strata developed in the northern margin of North China Craton in the Early Jurassic and are found in the Xingshikou Formation, Nandailing Formation, and Yaopo Formation in the West Beijing Basin. The geological age and markers of the boundary between the Yongfeng Stage and Liuhuanggou Stage are unclear. About 170 Ma ago, the Yanshan Movement began to affect China. The structural system of China changed from the near east-west Tethys or the Ancient Asia Ocean tectonic domain to the north-north-east Pacific tectonic domain since 170–135 Ma. A set of syngenetic conglomerate at the bottom of the Haifanggou or Longmen Fms. represented another set of molasse-volcanic rock-coal strata formed in the Yanliao region during the Middle Jurassic Yanshan Movement(Curtain A1). The bottom of the conglomerate is approximately equivalent to the boundary of the Shihezi Stage and Liuhuanggou Stage. The bottom of the Manas Stage creates a regional unconformity in northern China(about 161 Ma, Volcanic Curtain of the Yanshan Movement, Curtain A2). The Jurassic Yanshan Movement is likely related to the southward subduction of the Siberian Plate to the closure of the Mongolia-Okhotsk Ocean. A large-scale volcanic activity occurred in the Tiaojishan period around 161–153 Ma. Note that 153 Ma is the age of the bottom Tuchengzi Formation, and the bottom boundary of the Fifth Stage of the Jurassic terrestrial stage in China should have occurred earlier than this. This activity was marked by a warming event at the top of the Toutunhe Formation, and the change in the biological assembly is estimated to be 155 Ma. The terrestrial Jurassic-Cretaceous boundary(ca. 145.0 Ma) in the Yanliao region should be located in the upper part of Member 1 of the Tuchengzi Formation, the Ordos Basin in the upper part of the Anding Formation, the Junggar Basin in the upper part of the Qigu Formation, and the Sichuan Basin in the upper part of the Suining Formation The general characteristics of terrestrial Jurassic of China changed from the warm and humid coal-forming environment of the Early-Middle Jurassic to the hot, dry, red layers in the Late Jurassic. With the origin and development of the Coniopteris-Phoenicopsis flora, the Yanliao biota was developed and spread widely in the area north of the ancient Kunlun Mountains, ancient Qinling Mountains, and ancient Dabie Mountain ranges in the Middle Jurassic, and reached its great prosperity in the Early Late Jurassic and gradually declined and disappeared and moved southward with the arrival of a dry and hot climate.  相似文献   

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