• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Morphology and features of Cambrian oncoids and responses to palaeogeography of the North China Platform

    2020-06-23 02:35:32EnZhaoXiaoMingXiangMeiShuJiangandTehseenZafar
    Journal of Palaeogeography 2020年2期

    En-Zhao Xiao ,Ming-Xiang Mei,Shu Jiang and Tehseen Zafar

    Abstract

    Keywords: Morphological classification, Microbial mat, Girvanella, Carbon and oxygen isotopes,Miaolingian series,North China

    1 Introduction

    As a significant type of carbonate grain, oncoids have attracted extensive attention from geologists for decades.Oncoids in the geological record are characterized as unattached, rounded, and mm- to cm-sized and commonly exhibit a micritic cortex consisting of more or less concentric and partially overlapping laminae around a bio- or lithoclastic nucleus (Jones and Renaut 1997;Shapiro et al. 2009; Flügel and Munnecke 2010; Han et al. 2015; Wang and Xiao 2018). Studies of oncoids have revealed that clear understanding of the formation mechanism, classification and microbial metabolism recorded by exquisite internal structures (Zhang et al.2013; Han et al. 2015; Wilmeth et al. 2015) can guide the reconstruction of palaeogeography and palaeoenvironments (Dahanayake 1977; Peryt 1983; Jones 1992,2011; Jones and Renaut 1997, 2010; Gradziński et al.2004; Védrine et al. 2007; Védrine 2008; Yang et al.2009, 2011; Flügel and Munnecke 2010; Zhang et al.2014a, 2014b, 2015; Wang and Xiao 2018). Previous studies usually noted that the oncoid nucleus is composed of biodetritus or carbonate debris (Peryt 1983;Tucker and Wright 1990; Riding 1991), which was captured and surrounded by calcareous particles during the growth processes of microorganisms or algal communities (Flügel and Munnecke 2010). In recent years,through further studies of potential biosignatures from geological records and microbial-mediated organomineralization, the discussion of oncoids, including definition,genesis, type characteristics, classification and positions within microbialites (Wang and Xiao 2018), has again become a major topic in sedimentology.

    Cambrian oncoids have been reported in the southern and eastern margins of the North China Platform(Zhang et al. 2014a, 2014b), including western Henan Province (Zhang et al. 2015; Qi et al. 2016) and western Shandong Province of China. However, very few studies have examined the oncoids in the Cambrian Miaolingian Series that are exposed in the northern margin of the North China Platform in detail. Therefore, this study was conducted to provide an extensive range of reference materials for the latter. In total, 240 representative oncolitic limestone samples were collected from Wuhai,Diaoquan, Xiaweidian, Sandaogou, Fuzhou Bay, and Jinzhou Bay sections (Figs. 1, 2). The standard carbonate microfacies analysis shows morphological differentiation of oncoids in the study area. The study aims to demonstrate the origin of these oncoids and analyze possible factors that led to their morphological differentiation through comparative studies in a large region using sedimentological and geochemical methods.

    2 Materials and methods

    Field observations were conducted, involving measuring and sampling the Cambrian Miaolingian Series exposed in six sections in the North China Platform (Fig. 1).Stratigraphic successions were reconstructed based on field and laboratory studies. Two hundred fouty fresh,representative oncolitic limestone samples were collected from the Xuzhuang and Zhangxia formations, i.e.,40 from each section. Microfacies observations of polished samples and thin sections (under crosspolarized light (XPL) and plane-polarized light (PPL))were performed to identify the main lithological and biological components.

    Fig. 1 Cambrian outcrops in the North China Platform and the locations of studied sections (red stars). A-Wuhai section: Gandel Mountain,Wuhai City, Inner Mongolia Autonomous Region, China; B-Diaoquan section: Diaoquan village, Lingqiu county, Datong City, Shanxi Province,China; C-Xiaweidian section: Xiaweidian village, Mentougou district, Beijing, China; D-Sandaogou section: Sandaogou village, Suizhong county,Huludao City, Liaoning Province, China; E-Fuzhou Bay section: Fuzhou Bay town, Jinzhou district, Dalian City, Liaoning Province, China; F-Jinzhou Bay section: Dalian City, Liaoning Province, China. Topographically, the western margin of Yimeng landmass was steeper than the eastern during the Cambrian, which means that the Cambrian successions in the Wuhai section is related to a deeper water environment than those of the other five sections(Feng 2004)

    Fig. 2 Lithology and sedimentary facies of the Cambrian Miaolingian Series in the six studied sections (Peng et al. 2012; Xiao et al. 2017a, 2017b).Among these sections, Wuhai section has the thinnest succession, with a small thickness of limestone, and a large thickness of mudstone and dark-green organic muddy-sandy shale, which indicates deep-water deposition. The other five sections in the east reveal similar lithological variations and comparable boundaries. The Xuzhuang Formation shows a transition from red shale associated with tidal flats to oolitic limestone associated with grain banks (Ma et al. 2017; Xiao et al. 2017a, 2017b; Xiao et al. 2019a). Sedimentary facies of the Zhangxia Formation display cyclic changes from nongrain bank to grain bank and from deep-water to shallow-water, demonstrating shallowing-upward trends (Xiao et al.2017a, 2017b).The oncoids mainly developed in the Xuzhuang and Zhangxia formations

    Among these samples, 10 from each section, i.e., a total of 60 samples were selected, and were prepared into 60 small cubes with fresh broken surfaces as well as 60 polished thin sections, which were observed under a FEI Quanta 200F scanning electron microscope (SEM). Meantime, the 60 polished thin sections were gold-coated for secondary electron imaging.Semiquantitative elemental analyses of submicronsized spots during SEM observations were attained through energy dispersive X-ray spectroscopy (EDX).The voltage of the EDX element analysis was 10.0 kV,and the current pulse ranged from 19.83 kcps to 42.58 kcps.

    Another 30 samples, i.e., 5 from each section, were microdrilled on their fresh surface to prepare microsamples for carbon and oxygen isotope analyses. The micro-sampling process was taken under a microscope to avoid calcite veins and neomorphic processes. Isotopic compositions (δ13C and δ18O) were measured by a Thermo Scientific Delta V Advantage continuous-flow isotope ratio mass spectrometer. The results are presented in delta (δ) notation relative to the Vienna Pee Dee Belemnite (VPDB) standard. In addition, the precision of the carbon and oxygen isotopic ratios for duplicate analyses was better than 0.1%. The bulk mineral compositions of the samples were determined by XRD analyses, which were performed on prepared powder samples using the Bruker D2 PHASER instrument. All geochemical analyses of oncolitic limestone samples were performed in the State Key Laboratory of Oil and Gas Geology and Exploitation, Chengdu University of Technology, China.

    A total of 200 oncoids from each section were randomly selected and observed under a microscope to identify oncoid types as well as their proportions in different sections.

    3 Results

    3.1 Macroscopic characteristics of oncoids

    The studied oncoids mainly developed in shallow-water environments. They occur within oolitic limestones(Fig. 2), which range in thickness from approximately 0.3 m to 5 m, and are composed of layered limestone interbedded with thin micritic limestone layers. The oncoids are ellipsoidal or elongated in shape, with the long axis approximately 0.3-2.3 cm long (Table 1;Fig. 3).

    These oncoid-bearing beds are relatively thin, i.e., 0.3 m thick in the Wuhai section and 2.2 m thick in the Diaoquan section, respectively. In contrast, they are much thicker in the other four sections, i.e., 3.75 m thick in the Xiaweidian section, 4.5 m thick in the Sandaogou section, 5.2 m thick in the Fuzhou Bay section, and 4.9 m thick in the Jinzhou Bay section, respectively(Table 1).

    3.2 Microscopic characteristics of oncoids

    Microscopic observation shows that the oncoids grow together with ooids in the studied sections. The individual oncoids are circular to subcircular in shape and vary in size. Most oncoids contain a nucleus, which is typically composed of dark micrite, trilobite debris or echinoderm debris. In addition, most oncoids are characterized by alternating light and dark laminae and can be thought of as spherical stromatolites (Logan et al. 1964). Petrographically, the light laminae are composed of microspar, while the dark laminae are composed of dark micrite. In addition, filamentous cyanobacterial fossils,particularly Girvanella, are observed in the cortex and inside the interior laminae of oncoids.

    Based on the oncoid morphology, including the internal structure revealed by petrography, development of nucleus and laminae, location of nucleus, and other morphological features, the oncoids are divided into six varieties as follows: type 1, concentric fine-laminar oncoids; type 2, concentric rough-laminar oncoids;type 3, lateral-growth oncoids; type 4, multicore oncoids; type 5, flaggy oncoids; and type 6, thincortex oncoids.

    3.2.1 Type 1, concentric fine-laminar oncoids

    Concentricfine-laminar oncoids are the most common type of oncoids documented in geological records (Li et al.2000;Schaefer et al. 2001;Shi and Chen 2006;Reolid and Nieto 2010; Yang et al. 2011; Wang and Xiao 2018). Based on microscopic observations, this type is circular or elliptical in shape, with obvious nuclei and relatively smooth edges (Fig. 4a), and contains a large number of 50-μm-thick concentric laminae, which are highly-distinct and in light-and-dark color. Additionally,filamentous microbial fossils are observed inside the dark laminae and between the light and dark laminae at a high magnification. They show typical features of Girvanella, i.e., a dark-micrite sheath and microspar interior (Fig. 4b) (Riding 2011; Xiao et al. 2018),which are intertwined with each other inside the oncoid laminae (Fig. 4b).

    Except in the Wuhai and Diaoquan sections, type 1 oncoids are observed with a relatively large spatial distribution and make up a large proportion among all oncoid types in the Jinzhou Bay (73%, 146 in 200), Fuzhou Bay(79%, 158 in 200), Sandaogou (72%,144 in 200) and Xiaweidian (56.5%, 113 in 200) sections.

    Table 1 Field observation characteristics of various oncoids in the Cambrian Miaolingian Series, North China Platform

    3.2.2 Type 2, concentric rough-laminar oncoids

    Concentric rough-laminar oncoids have characteristics similar to those of type 1 oncoids containing concentric laminae (Han et al. 2015). However, the present study classifies them as two independent categories for the following reasons: (1) individual type 2 oncoids are noticeably smaller, and their concentric laminae are very sparse (Fig. 4c); (2) the concentric laminae of type 2 oncoids display light-dark differentiation, with their single lamina being much thicker than that in type 1 oncoids (Fig. 4d); (3) the nucleus volume of type 2 oncoids occupies a larger proportion of the oncoid than does that of type 1 oncoids (Fig. 4c); and (4) Girvanella is absent in the light laminae but present and intertwined in the dark laminae in type 2 oncoids (Fig. 4d).Among the six measured sections, type 2 oncoids are most abundant in the Diaoquan (14%, 28 of 200) and Xiaweidian (33%, 66 in 200) sections, and accounts for 5% (10 of 200) in the Wuhai section. However, the proportions drop to 1% (2 in 200) in the Sandaogou,Fuzhou Bay and Jinzhou Bay sections.

    3.2.3 Type 3, lateral-growth oncoids

    Lateral-growth oncoids show thick alternating light and dark laminae, smooth edges, a high degree of regularity in individuals, and nuclei usually composed of trilobite debris, making these oncoids analogous to type 1 oncoids microscopically.

    The differences are that the majority of lateral-growth oncoids are larger than type 1 oncoids, with the nucleus not located in the center (Fig. 5a). The laminae on one side of the nucleus are thick and well-developed,whereas they are thin and poorly-developed on the other side (Fig. 5b). Some dispersed sparry calcite microcrystals are observed inside the laminae, mostly on the well-developed side (Fig. 5c). Girvanella filaments are observed inside the dark micrite with an intertwined arrangement (Fig. 5b) or aligned parallel to the laminae with an ideal orientation (Fig. 5c). Type 3 oncoids are observed in the Jinzhou Bay(23%,46 in 200),Fuzhou Bay(19%,38 in 200)and Sandaogou(19%,38 in 200)sections respectively.

    3.2.4 Type 4, multicore oncoids

    Each multicore oncoid typically contains more than two nuclei. They are irregular in shape, mainly long and narrow but occasionally round to subround, and can reach large sizes. The nucleus is often made up of trilobite debris or ooids. The inner laminae near the nucleus are usually concentric (Fig. 6a, b). The relatively outer laminae are composed of light microspar and dark micrite. Typical Girvanella filaments are observed inside the dark micritic bands(Fig. 6c, d).

    Fig. 3 Macroscopic characteristics of oncoids in the Cambrian Miaolingian Series, North China Platform. a Oncoids from the Xuzhuang Formation,Wuhai section; b Oncoids from the Zhangxia Formation, Diaoquan section; c Oncoids from the Xuzhuang Formation, Xiaweidian section; d Oncoids from the Zhangxia Formation, Sandaogou section; e Oncoids from the Zhangxia Formation, Fuzhou Bay section; f Oncoids from the Zhangxia Formation,Jinzhou Bay section

    Notably, multicore oncoids are recognized and exhibit similar morphological characteristics in the Diaoquan and Sandaogou sections. However, in the Sandaogou section, they contain light and dark laminae and are analogous to type 1 oncoids (Figs. 6a,4a), while in the Diaoquan section, the light and dark laminae are poorly developed in the multicore oncoids and are comparable to those of type 2 oncoids (Figs. 6b, 4c).

    3.2.5 Type 5, flaggy oncoids

    Fig. 4 Microscopic characteristics of types 1 and 2 oncoids. a A type 1 oncoid from the Sandaogou section, characterized by concentric finelaminar structure and clear nucleus (made up with trilobite debris and dark micrite); b Local magnification of a, showing the interlaced and intertwined calcified filamentous fossils of Girvanella; c A type 2 oncoid from the Diaoquan section, characterized by a concentric rough-laminar structure with lower frequency alternation than that in type 1; d Local magnification of c, showing the micrite conglomeration and rough edges of the oncoid.Girvanella fossils can be observed inside the dark micrite laminae with a disordered winding occurrence

    Flaggy oncoids differ greatly from other oncoid varieties in shape (Fig. 7a). Their composition is fairly simple and predominantly composed of a nucleus and surrounding dark micrite layer. The nucleus is made up of slender trilobite debris (Fig. 7a). Only a small number of flaggy oncoids show laminar structures. Most flaggy oncoids are irregular in shape and are much smaller in size than other oncoids. Girvanella filaments are observed inside the dark micritic cortex(Fig. 7b).

    Flaggy oncoids are only observed in the Wuhai, Diaoquan and Xiaweidian sections. Importantly, the numbers of flaggy oncoids in these sections differ greatly. The proportion in the Xiaweidian section is only 5.5% (11 in 200) but reaches 26% (52 in 200) in the Diaoquan section and 42% (84 in 200) in the Wuhai section.

    3.2.6 Type 6, thin-cortex oncoids

    This type of oncoid is typically determined as thincortex oncoids (Han et al. 2015). They are irregularly shaped and sized (Fig. 7c), with a long axis of 4-6 mm long, while the short axis is around 800 μm long.The nuclei are made up of ooids, trilobite debris and dark micrite grains and are surrounded by a uniform thin dark micritic cortex. Further observations via high-power microscopy reveal the presence of Girvanella (Fig. 7c) inside the dark micrite in these oncoids.

    Thin-cortex oncoids are widely distributed in the Wuhai, Diaoquan, Xiaweidian and Jinzhou Bay sections,with different proportions and sizes. The Jinzhou Bay and Xiaweidian sections have minute proportions (3%, 6 in 200, and 5%, 10 in 200, respectively) of the total number of oncoids, with measured sizes of approximately 800 μm long. However, the proportion reaches 45% (90 in 200) in the Diaoquan section and 53% (106 in 200) in the Wuhai section, with sizes of 4-6 mm long in both sections.

    Fig. 5 a A type 3 oncoid, characterized by concentric laminae, an off-center nucleus and lateral growth; b Local magnification of a, showing the disordered Girvanella fossils with intertwined arrangement; c Local magnification of a,showing the directional arrangement of Girvanella fossils

    3.3 Ultramicroscopic characteristics of oncoids and the mineral composition of lamina

    According to SEM observations, the dark and light laminae of oncoids exhibit different ultrastructures(Fig. 8a, b). The light laminae are composed of CaCO3microspars (Fig. 8a-c, g), showing welldeveloped cleavage and relatively smooth surfaces.The dark laminae are composed of micrite, whose main component is also CaCO3, showing a distinct morphological structure (Fig. 8a, d, f). The micrite is similar to microbially-derived carbonate mud, which is consistent with the findings of previous studies(Perry 1999; Flügel and Munnecke 2010; Guido et al.2012; Edgcomb et al. 2013; Ka?mierczak et al. 2015;Gischler et al. 2017; Yu et al. 2019). Moreover, two kinds of pyrite particles are observed in the micrite(Fig. 8e): ordinary massive pyrite and framboidal pyrite. The framboidal pyrite is associated with sulfatereducing bacteria and stimulates the microbial metabolism of carbonate precipitation, which therefore indicates a microbial origin of the studied oncoids(Baumgartner et al. 2006; Xiao et al. 2017c, 2018,2019b).

    3.4 Geochemical analysis

    In this study, the oncolitic limestones are similar in lithology and strata position; however, the microscopic analysis reveals that oncoids from different sections differ obviously in terms of variety and abundance. To examine whether these differences are linked to the Cambrian palaeogeographic settings of the North China Platform,XRD and carbon and oxygen isotopic analyses were conducted on the samples of oncolitic limestone collected from the six sections.

    3.4.1 XRD

    Fig. 6 Microscopic characteristics of type 4 oncoids. a A type 4 oncoid from the Sandaogou section, characterized by a concentric laminar structure and two nuclei (made up of trilobite debris and dark micrite); b A type 4 oncoid from the Diaoquan section, characterized by a concentric rough-laminar structure, unsmooth edges and two nuclei; c Local magnification of a, showing typical Girvanella fossils inside the dark micritic laminae with an intertwined arrangement;d Local magnification of b, showing typical Girvanella fossils inside the dark micritic laminae

    Five samples of oncolitic limestone were taken from each section of the Cambrian Miaolingian Series, specifically, from the Xuzhuang and Zhangxia formations,and XRD analysis was performed to determine the basic mineral components (Table 2). The results show that the main mineral component of the oncolitic limestone in the six sections is calcite; however, there are several differences in other mineral components,as follows. (1) In the Jinzhou Bay, Fuzhou Bay, Sandaogou and Xiaweidian sections, the content of quartz in the oncolitic limestone samples is 1%-2%, while in the Wuhai and Diaoquan sections, this value is markedly higher, reaching 9%. (2) Feldspar is not observed in the samples from the Jinzhou Bay and Fuzhou Bay sections, and its content in the Sandaogou and Xiaweidian sections is extremely low. Conversely, it has relatively higher content in the Wuhai and Diaoquan sections, reaching 4%. (3) Although dolomite occurs in all six sections, its content is much higher in the Wuhai and Diaoquan sections than in the other sections. (4) Additionally, the contents of pyrite and clay minerals are low and exhibit no obvious regularity.

    3.4.2 Carbon and oxygen isotopes

    Carbon and oxygen isotopic compositions of marine limestone can reflect the sedimentary environment (Li et al. 2013, 2017). Therefore, carbon and oxygen isotopic analysis was applied to 30 oncolitic limestone samples to further interpret the depositional environments of oncoids. The results show that the mean δ13C values in the Xuzhuang and Zhangxia formations decrease from west to east (Table 3). The mean δ13C value of the Xuzhuang Formation in the Wuhai section is ?0.302‰VPDB, which is higher than those of the Xuzhuang Formation in the Xiaweidian section (?0.788‰ VPDB),Fuzhou Bay section (?0.890‰ VPDB) and Jinzhou Bay section (?0.716‰ VPDB) (Table 3). In addition, the mean δ13C values of the samples from the Zhangxia Formation also exhibit the same pattern, i.e., the mean value of ?0.626‰ VPDB in the Diaoquan section (west) is higher than that of ?0.796‰ VPDB in the Sandaogou section (east) (Table 3; Fig. 9).

    The δ18O values in the six sections also exhibit apparent variations. The mean δ18O values in the western sections are higher than those in the eastern sections. (1)The value of the Xuzhuang Formation decreases from?6.664‰VPDB in the Wuhai section to ?8.758‰VPDB in the Xiaweidian section, to ?9.712‰ VPDB in the Fuzhou Bay section, and to ?10.404‰ VPDB in the Jinzhou Bay section (Table 3; Fig. 9). (2) The value of the Zhangxia Formation in the Diaoquan section is?6.65‰ VPDB, which is higher than that of ?7.854‰VPDB in the Sandaogou section (Table 3).

    Fig. 7 a A type 5 oncoid, marked by an irregular shape with a clearly external enveloping micritic cortex and the nucleus; b Local magnification of a, showing the typical Girvanella fossils inside the dark micritic cortex. Some spherical cross-sections can be observed; c A type 6 oncoid,marked by a larger individual size, irregular shape and thin cortex. The local magnifications show the two arrangements of Girvanella fossils,which are parallel and intertwined

    4 Discussion

    The study of ancient oncoids can indicate changes in depositional conditions and the controlling effects of microbial activities on their formation; therefore, the results are important for reconstructing palaeoclimate,palaeoenvironments, sea-level fluctuations and chemical conditions in sedimentary environments (Peryt 1983;Védrine et al. 2007; Védrine 2008; Yang et al. 2011;Zhang et al. 2014a,2014b; Zhou et al. 2017).

    4.1 Classification and biogenicity of oncoids

    The classification of oncoids has not been comprehensively interpreted and is considered as an important direction of oncoids study (Dahanayake 1977; Peryt 1983).The macro- and microcharacteristics and the mineral compositions of oncoids are influenced by the physical,chemical and biological conditions of the aquatic environment and microbial activity. The current classifications include: (1) morphological classification (Yang et al. 2011); (2) mineral component classification (Flügel and Munnecke 2010); and (3) formational environment classification (Védrine et al. 2007; Védrine 2008). In this study, the classification of oncoids on the basis of morphological characteristics is applied.

    The morphological similarities of the oncoids reported in this study compared to those of previous works on oncoids in similar or different environments suggest that the oncoids in the Cambrian Miaolingian Series, North China Platform, are microbial in origin (Table 4) (Krumbein and Cohen, 1977; Zeng et al, 1983; Gerdes et al,1994;Davaud and Girardclos,2001;Flügel and Munnecke,2010;Jones,2011;Han et al,2015;Wang and Xiao,2018).Typical filamentous cyanobacterial fossils, including Girvanella (Riding 2011; Xiao et al. 2018), are abundant among the oncoids in this study (Figs. 4-7), which is clearly related to microorganisms and indicates that the origin of these oncoids is associated with the calcification of cyanobacteria-dominated microbial communities and the biodegradation of heterotrophic bacteria. The framboidal pyrite particles were produced by the sulfate reduction reaction dominated by sulfate-reducing bacteria (Fig.8e)(Xiao et al.2017c,2019b).

    Fig. 8 SEM and EDX analyses of the light and dark laminae. a Various mineral structures of oncoids, with the two points of EDX analysis marked;b A cortex showing a bimineralic structure; c Local magnification of b, showing calcite crystals in the light laminae; d Local magnification of b,showing amorphous calcium carbonate mud in the dark laminae; e Two kinds of pyrite particles observed inside the oncoids: framboidal pyrite(pink arrows)and ordinary massive pyrite(yellow arrows);f, g EDX results of the two analyzed points in a

    As concluded in the above discussion, the oncoids in this study are predominantly composed of calcite. The alternation of light and dark laminae is associated with different microstructures of the calcium carbonate minerals (Fig. 8a, b). The light laminae are composed of calcite microspar, whereas the dark laminae are mainly composed of amorphous calcium carbonate (ACC),which is inferred to be the product of Girvanella calcification (Pratt 2001) and can be comparable to previously documented examples of ACC (Jones and Peng 2012;Diaz et al., 2017). Similarly, the discovery of Girvanella inside oncoids and the ultrastructure of the dark micrite laminae, including the presence of framboidal pyrite, are likely related to cyanobacteria-dominated calcification and the involvement of heterotrophic bacteria in the promotion of calcium carbonate precipitation (Dupraz et al. 2009).

    4.2 Response to palaeogeography and palaeoenvironment

    The formation process of an oncoid can be inferred from its structure and form, including the nucleus development, concentric laminae, and cortex morphological characteristics. It is controlled by palaeogeographic and palaeoenvironmental factors, such as the water and atmospheric chemical conditions, as well as sea-level changes (Védrine et al. 2007; Védrine 2008).Therefore, the study of the morphology and origin of oncoids may provide remarkable insights for reconstructing palaeogeography and palaeoenvironments(Peryt 1983; Yang et al. 2011; Zhang et al. 2013, 2015;Zhou et al. 2017).

    The oncoids from the six sections developed during approximately the same period.This study based on sedimentology and stratigraphy, in combination with previous reports on the Cambrian palaeogeography of the North China Platform (Feng 2004; Ma et al. 2017),clarifies that the thicknesses of the oncolitic limestone in the two sections of nearshore environment (0.3 m thick in the Wuhai section and 2.2 m thick in the Diaoquan section) are obviously thinner than those in the other four sections of offshore setting (Table 1). Additionally,macroscopic observations in the field show that the Xuzhuang Formation in the Diaoquan section and Wuhai section has more crossbeds and scouring surfaces. These characteristics can be explained by the fact that sea-level change on a steeper slope resulted in more rapid environmental changes over time, which caused the smaller thicknesses of the oncolitic limestone in the Wuhai and Diaoquan sections.

    Table 2 XRD analysis results showing the mineral compositions and contents of the oncolitic limestone from the Cambrian Miaolingian Series, North China Platform

    In addition, there are obvious differences in the types and proportions of each type of oncoids in each section(Fig. 10). In total, 200 oncoid individuals were randomly selected from each section for microscopic observation.Based on their morphology, six types of oncoids were classified, and their proportions in each section were determined. The results demonstrate that the types andproportions of different types of oncoids have the following patterns. (1) Oncoids with well-developed laminae (type 1, concentric fine-laminar oncoids, and type 3,lateral-growth oncoids)mostly develop in sections of offshore environment (Fig. 10a). (2) Oncoids with poorlydeveloped laminae (type 2, concentric rough-laminar oncoids) and irregular oncoids (type 5, flaggy oncoids,and type 6, thin-cortex oncoids) predominantly occur in the two sections of nearshore setting (Wuhai and Diaoquan sections) (Fig. 10a). The proportions of the most abundant oncoid varieties (types 5 and 6) are 95% and 71% in the Wuhai and Diaoquan sections, respectively.In contrast, in the Jinzhou Bay section, type 6 oncoids account for only 3% (Fig. 10a). (3) Type 4 oncoids only occur in the Zhangxia Formation in the study area and comprise only a small proportion (14% in the Diaoquan section and 8% in the Sandaogou section).

    Table 3 Carbon and oxygen isotopes of the oncolitic limestone samples from the Cambrian Miaolingian Series, North China Platform

    Fig. 9 C-O isotopic data for the oncolitic limestone from the Cambrian Miaolingian Series, North China Platform. The progressive decreasing trend of carbon and oxygen isotopic data from west to east can be obviously observed

    These clear patterns can be summarized as follows.Oncoids with fine laminae, clear cores and regular shapes exist in almost all offshore sections, and in contrast, oncoids with poorly-developed laminae and irregular shapes occur in nearshore sections (Fig. 10a). These patterns are also perceptibly associated with the main mineral compositions (Table 2; Fig. 10b, c) and the carbon and oxygen isotopic compositions (Table 3; Figs. 9,10d, e) of the oncoids in different sections. The XRD results confirm that the proportions of quartz and feldspar in the two nearshore sections (i.e., the Wuhai and Diaoquan sections) are significantly higher than those of the offshore sections (Table 2; Fig. 10b, c), which suggests that the carbonate sediments contain more terrigenous clasts. The presence of dolomite indicates the occurrence of dolomitization (burial, evaporation, etc.) caused by the shallowing depositional environment during the process of relative sea-level fall (Fig. 2) (Kendall and Schlager 1981; Hardie 1987; Xiao et al. 2017c). The occurrence of detrital quartz and feldspar signifies the input of terrigenous clasts during the deposition of the limestone and indicates that the depositional environment of the oncolitic limestone was characterized by shallow water and offshore conditions.

    The results of the isotopic study show that the carbon and oxygen isotope values exhibit a decreasing trend from west to east (Table 3; Fig. 10d, e). The δ18O and δ13C trends can be further explained as signifying the depositional environment changing from west to east during the same period in the North China Platform.This observation also confirms the macroscopic sedimentology and stratigraphic inference that the depositional environment of Wuhai and Diaoquan sections differed from that of Xiaweidian, Sandaogou, Fuzhou Bay and Jinzhou Bay sections (Table 1; Figs. 1, 2). The results are consistent with the palaeogeographic conditions of the sections and signify that the nearshore sections are dominated by higher carbon and oxygen isotopic values and that the offshore sections are dominated by lower isotopic values. This isotopic trend reflects geochemical changes related to differences in the depositional environments of the six sections, which may have been controlled by terrigenous inputs. Furthermore, the variations in the palaeoenvironmental conditions had a noticeable impact on the occurrence of oncoids in different sections. For example, types 2, 5 and 6 oncoids are the main oncoid varieties produced in the nearshore sections, whereas types 1 and 3 oncoids are the main types produced in the offshore sections(Fig. 10a-c).

    These features are evident in the morphological characteristics of two groups of oncoids from the Zhangxia Formation in the Diaoquan and Sandaogou sections.Multicore oncoids (type 4) only occur in these two sections (Fig. 10a). In the Sandaogou section, the laminae of multicore oncoids are distinct, and the oncoid morphology is irregular due to the multiple nuclei and theinner and outer laminae in the cortex of these oncoids,whereas in the Diaoquan section, the inner laminae are relatively rough, with an extremely irregular cortex (Fig.6a, b). Additionally, the closer location of these oncoids related to the ancient Yimeng landmass resulted in a greater influence of terrigenous debris, greater salinity and higher overall topography. These factors resulted in a shorter time required for the development of cyanobacteria (Girvanella)-dominated microbial mats and caused the formation of oncoids with less-exquisite laminae and less-regular shapes (Fig. 10a). In contrast, the offshore sections are featured by a more favorable environment with less interference from terrigenous debris and a gentler terrain, which provided a stable environment for cyanobacteria (Girvanella)-dominated microbial mats and promoted oncoids with well-developed laminae and regular shapes.

    Table 4 Morphological classification of oncoids from the Cambrian Miaolingian Series in the study area

    5 Conclusions

    1) Six Cambrian sections in the North China Platform contain exquisitely preserved oncoids with different shapes in the Xuzhuang and Zhangxia formations of the Miaolingian Series. Based on the morphologies and internal structures revealed by microscopy, the oncoids can be divided into six types: type 1, concentric finelaminar oncoids; type 2, concentric rough-laminar oncoids; type 3, lateral-growth oncoids; type 4, multicore oncoids; type 5, flaggy oncoids; and type 6, thin-cortex oncoids.

    2) The morphological and ultrastructural characteristics and XRD results of the oncoid samples reveal the presence of carbonate minerals, predominantly calcite.SEM observations of the oncoid microstructure indicate that the light laminae are composed of calcite microspar and that the dark laminae are composed of ACC. Girvanella fossils and framboidal pyrite can be found inside oncoids. These observations suggest a biogenic origin of the Cambrian oncoids exposed in the North China Platform. These oncoids are inferred to have formed through the interaction between cyanobacteria and heterotrophic bacteria (sulfate-reducing bacteria) inside microbial mats.

    Fig. 10 a Types and proportions of oncoids in different sections, with a total of 200 oncoids from each section randomly selected and observed under a microscope; b and c Approximate positions of different sections relative to the Yimeng landmass during different periods (Meng et al.1997; Feng 2004); d and e Variation trend of C-O isotopic values from west to east. MMC: Main mineral component; Q: Quartz; Pl: Potassium feldspar;C:Calcite;D:Dolomite;P:Pyrite;Cm:Clay minerals

    3) The occurrence of detrital quartz and feldspar in the oncolitic limestone in the Cambrian Xuzhuang and Zhangxia formations signifies the input of terrigenous clasts. The presence of small amounts of dolomite suggests a shallowing depositional environment during relative sea-level fall. The carbon and oxygen isotopes further imply that the formational environments of the oncolitic limestone varied spatially in the study area.The oncoids in nearshore environments were significantly influenced by the terrigenous input, and the steeper terrain resulted in relatively rapid changes in accommodation space during sea-level changes, resulting in rougher oncoid growth (rough and indelicate laminae,uneven cortex, and irregular shape). In contrast, the oncoids that developed in offshore sections were less affected by terrigenous factors, resulting in an environment favorable for the production of exquisite oncoids in cyanobacteria (Girvanella)-dominated microbial mats in a stable carbonate platform that was comparatively flat in the east.

    Abbreviations

    ACC: Amorphous calcium carbonate; EDX: Energy dispersive X-ray spectroscopy; MMC: Main Mineral Component; PPL: Plane-polarized light;SEM: Scanning electron microscopy/microscope; VPDB: Vienna pee dee belemnite; XPL: Cross-polarized light; XRD: X-ray diffraction

    Acknowledgements

    We gratefully acknowledge Prof. Zeng-Zhao Feng for the critical review of the earlier version of the manuscript. We are also thankful for the help from Dr. Muhammad Riaz and Dr. Khalid Latif in the field work.

    Authors’ contributions

    EZX proposed the viewpoint, carried out the analysis, and wrote the manuscript. MXM instructed the field work. SJ instructed the manuscript writing. TZ improved the language. All authors read and approved the final manuscript.

    Funding

    National Natural Science Foundation of China (Nos. 41472090 and 40472065).

    Availability of data and materials

    The data used to support the findings of this study are available from the corresponding author upon request.

    Competing interests

    The authors declare that they have no competing interests.

    Author details

    1School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China.2Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education and Faculty of Earth Resources, China University of Geosciences (Wuhan), Wuhan 430074, China.3Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.4Institute of Geology, University of the Punjab, Lahore 54590, Pakistan.

    Received: 15 May 2019 Accepted: 16 January 2020

    国产淫语在线视频| 久久久精品区二区三区| 一区二区三区四区激情视频| xxxhd国产人妻xxx| 天堂8中文在线网| 青青草视频在线视频观看| 淫妇啪啪啪对白视频 | av免费在线观看网站| 亚洲欧美激情在线| 午夜免费观看性视频| 少妇裸体淫交视频免费看高清 | 午夜两性在线视频| 蜜桃在线观看..| 久久免费观看电影| 男女高潮啪啪啪动态图| 欧美精品亚洲一区二区| 久久久欧美国产精品| 99国产精品一区二区蜜桃av | 久久久精品国产亚洲av高清涩受| 午夜福利视频精品| 老司机靠b影院| 亚洲第一青青草原| 国产一区二区三区av在线| 亚洲欧洲精品一区二区精品久久久| 曰老女人黄片| 蜜桃在线观看..| 免费看十八禁软件| 黄片播放在线免费| 欧美 日韩 精品 国产| 在线永久观看黄色视频| 男女边摸边吃奶| 2018国产大陆天天弄谢| 久热爱精品视频在线9| 精品一品国产午夜福利视频| 18在线观看网站| √禁漫天堂资源中文www| 女性被躁到高潮视频| 丝袜喷水一区| 91av网站免费观看| 夫妻午夜视频| 亚洲中文字幕日韩| 欧美日本中文国产一区发布| 欧美日韩成人在线一区二区| 亚洲国产av影院在线观看| 国产片内射在线| 自拍欧美九色日韩亚洲蝌蚪91| netflix在线观看网站| 亚洲专区中文字幕在线| 精品乱码久久久久久99久播| 国产精品自产拍在线观看55亚洲 | 12—13女人毛片做爰片一| 两个人免费观看高清视频| 亚洲精品中文字幕一二三四区 | 国产精品一区二区免费欧美 | 日本撒尿小便嘘嘘汇集6| 精品第一国产精品| 老汉色∧v一级毛片| 亚洲av美国av| 国产欧美日韩综合在线一区二区| 一本大道久久a久久精品| 日本91视频免费播放| 国产有黄有色有爽视频| 国产男女内射视频| 亚洲三区欧美一区| 99精品欧美一区二区三区四区| 国产黄频视频在线观看| 91精品国产国语对白视频| 成人国产一区最新在线观看| 国产精品二区激情视频| 国产av又大| 久久99热这里只频精品6学生| 91九色精品人成在线观看| 午夜免费成人在线视频| 国产一区二区激情短视频 | 亚洲一区中文字幕在线| 日韩视频在线欧美| 最近中文字幕2019免费版| 成年人黄色毛片网站| 天堂8中文在线网| 国产精品一区二区精品视频观看| 一个人免费看片子| 日韩欧美一区视频在线观看| 两性夫妻黄色片| 欧美另类亚洲清纯唯美| 国产亚洲精品一区二区www | 国产一区二区三区av在线| 国产男人的电影天堂91| 老司机深夜福利视频在线观看 | 一区二区三区精品91| 亚洲精品乱久久久久久| a 毛片基地| 午夜福利视频在线观看免费| av超薄肉色丝袜交足视频| 菩萨蛮人人尽说江南好唐韦庄| 男女国产视频网站| 黄色 视频免费看| 国产淫语在线视频| 99国产精品一区二区蜜桃av | 日韩视频一区二区在线观看| 免费在线观看黄色视频的| 亚洲精品国产色婷婷电影| 午夜福利影视在线免费观看| 精品国产一区二区三区四区第35| 亚洲欧美精品自产自拍| 99久久精品国产亚洲精品| 淫妇啪啪啪对白视频 | 亚洲第一欧美日韩一区二区三区 | 少妇被粗大的猛进出69影院| 丝袜喷水一区| tocl精华| 国产精品 国内视频| 母亲3免费完整高清在线观看| 视频在线观看一区二区三区| 久久性视频一级片| 亚洲天堂av无毛| 亚洲欧美成人综合另类久久久| 中文字幕人妻熟女乱码| 国产高清国产精品国产三级| 亚洲精品成人av观看孕妇| 99国产精品一区二区三区| 国产野战对白在线观看| 日韩视频一区二区在线观看| 日韩有码中文字幕| 熟女少妇亚洲综合色aaa.| 亚洲欧美精品自产自拍| 午夜免费成人在线视频| 男女午夜视频在线观看| 丁香六月天网| 免费少妇av软件| 一个人免费在线观看的高清视频 | 国产精品成人在线| 国产一区二区 视频在线| 狂野欧美激情性bbbbbb| 另类亚洲欧美激情| 欧美精品人与动牲交sv欧美| 国产一区二区 视频在线| 国产精品99久久99久久久不卡| 午夜福利视频在线观看免费| 久久国产精品大桥未久av| 国产精品成人在线| av天堂久久9| 9热在线视频观看99| 91成人精品电影| 亚洲av电影在线进入| 成人黄色视频免费在线看| 久久久久精品国产欧美久久久 | 久久av网站| 亚洲欧美精品自产自拍| 亚洲免费av在线视频| 国产人伦9x9x在线观看| 狠狠精品人妻久久久久久综合| 少妇被粗大的猛进出69影院| 欧美在线一区亚洲| 亚洲美女黄色视频免费看| 丰满人妻熟妇乱又伦精品不卡| 又黄又粗又硬又大视频| av线在线观看网站| 国产一区二区激情短视频 | 日韩免费高清中文字幕av| 亚洲伊人色综图| 欧美日本中文国产一区发布| 久久香蕉激情| 中文字幕av电影在线播放| 曰老女人黄片| 成年动漫av网址| 大香蕉久久成人网| 一级毛片女人18水好多| 老司机靠b影院| 美女高潮喷水抽搐中文字幕| 亚洲色图 男人天堂 中文字幕| 国产一区二区 视频在线| 国产精品一二三区在线看| 欧美变态另类bdsm刘玥| 99久久精品国产亚洲精品| 91九色精品人成在线观看| 国产在线一区二区三区精| 女人久久www免费人成看片| 一区在线观看完整版| 亚洲av电影在线观看一区二区三区| 国产精品一区二区精品视频观看| 日韩欧美一区视频在线观看| 亚洲人成电影观看| av一本久久久久| 亚洲欧美精品综合一区二区三区| 欧美老熟妇乱子伦牲交| 亚洲天堂av无毛| 窝窝影院91人妻| 久久久久久免费高清国产稀缺| av有码第一页| 两人在一起打扑克的视频| 欧美日韩国产mv在线观看视频| 美女视频免费永久观看网站| 亚洲人成77777在线视频| 午夜老司机福利片| 亚洲欧美一区二区三区久久| 另类精品久久| tube8黄色片| 日韩免费高清中文字幕av| 9191精品国产免费久久| 国产精品久久久久成人av| 黄网站色视频无遮挡免费观看| 99国产精品一区二区三区| 久久99热这里只频精品6学生| 无限看片的www在线观看| 建设人人有责人人尽责人人享有的| 亚洲国产欧美日韩在线播放| 国产日韩欧美在线精品| 欧美黑人精品巨大| 亚洲av日韩精品久久久久久密| 久久99一区二区三区| 国产黄频视频在线观看| 午夜精品久久久久久毛片777| 最新在线观看一区二区三区| 国产精品欧美亚洲77777| 亚洲 欧美一区二区三区| 高清欧美精品videossex| 精品少妇一区二区三区视频日本电影| 亚洲精品中文字幕在线视频| 极品少妇高潮喷水抽搐| 国产淫语在线视频| 岛国毛片在线播放| 91av网站免费观看| 国产精品 国内视频| 法律面前人人平等表现在哪些方面 | 国产免费现黄频在线看| 国产精品久久久久久人妻精品电影 | 无遮挡黄片免费观看| 国产精品香港三级国产av潘金莲| 亚洲中文av在线| 永久免费av网站大全| 国产亚洲欧美精品永久| 亚洲精品久久午夜乱码| 高清欧美精品videossex| 天堂俺去俺来也www色官网| 999久久久国产精品视频| 女性生殖器流出的白浆| 久久免费观看电影| 国产精品秋霞免费鲁丝片| 多毛熟女@视频| 日韩中文字幕欧美一区二区| 日本精品一区二区三区蜜桃| 欧美精品一区二区免费开放| 天堂8中文在线网| 在线亚洲精品国产二区图片欧美| 国产精品九九99| 三级毛片av免费| 窝窝影院91人妻| 999久久久国产精品视频| 亚洲精品一二三| 男女边摸边吃奶| 亚洲伊人久久精品综合| 久久国产精品人妻蜜桃| 十分钟在线观看高清视频www| 亚洲一卡2卡3卡4卡5卡精品中文| 最黄视频免费看| 精品欧美一区二区三区在线| 日日摸夜夜添夜夜添小说| 国产精品99久久99久久久不卡| 天天躁夜夜躁狠狠躁躁| 一区福利在线观看| 在线 av 中文字幕| 久久人人爽人人片av| 亚洲欧美色中文字幕在线| 免费高清在线观看视频在线观看| 爱豆传媒免费全集在线观看| 久久久久久久久免费视频了| 我要看黄色一级片免费的| 精品国产国语对白av| 777久久人妻少妇嫩草av网站| 午夜视频精品福利| 久久国产精品男人的天堂亚洲| 亚洲久久久国产精品| 精品福利永久在线观看| 一进一出抽搐动态| 日韩中文字幕视频在线看片| 啦啦啦视频在线资源免费观看| 亚洲午夜精品一区,二区,三区| 999久久久国产精品视频| 欧美黑人精品巨大| 午夜免费观看性视频| 五月开心婷婷网| 精品久久久久久电影网| 中国国产av一级| av不卡在线播放| 亚洲全国av大片| 国产精品国产av在线观看| 亚洲av日韩在线播放| 大码成人一级视频| a 毛片基地| 国产深夜福利视频在线观看| 免费在线观看完整版高清| 国产免费现黄频在线看| 十八禁人妻一区二区| 黄色片一级片一级黄色片| 国产激情久久老熟女| 黄色a级毛片大全视频| 亚洲国产精品成人久久小说| 天天躁夜夜躁狠狠躁躁| 两个人免费观看高清视频| www.av在线官网国产| 又大又爽又粗| 夜夜夜夜夜久久久久| 亚洲欧美日韩高清在线视频 | 久久ye,这里只有精品| 在线观看免费高清a一片| 在线 av 中文字幕| av在线app专区| 国产精品自产拍在线观看55亚洲 | 欧美大码av| 91九色精品人成在线观看| 每晚都被弄得嗷嗷叫到高潮| 日韩精品免费视频一区二区三区| 久久人妻福利社区极品人妻图片| 青草久久国产| 亚洲综合色网址| 99九九在线精品视频| 老熟妇仑乱视频hdxx| 国产不卡av网站在线观看| 国产av又大| av天堂久久9| 手机成人av网站| 国产亚洲av片在线观看秒播厂| 亚洲中文av在线| 久久香蕉激情| netflix在线观看网站| 久久久久久免费高清国产稀缺| 91成年电影在线观看| tocl精华| 欧美少妇被猛烈插入视频| 亚洲自偷自拍图片 自拍| 天天躁夜夜躁狠狠躁躁| 国产欧美日韩精品亚洲av| 免费看十八禁软件| 亚洲五月婷婷丁香| 亚洲国产中文字幕在线视频| 免费在线观看视频国产中文字幕亚洲 | 精品福利观看| 色老头精品视频在线观看| 国产精品麻豆人妻色哟哟久久| 大香蕉久久网| 在线av久久热| 亚洲av片天天在线观看| 一区二区三区激情视频| 1024香蕉在线观看| 叶爱在线成人免费视频播放| 99热国产这里只有精品6| 欧美性长视频在线观看| 黄色 视频免费看| 人妻一区二区av| a级毛片在线看网站| 精品一区二区三区av网在线观看 | 色94色欧美一区二区| 亚洲国产欧美一区二区综合| 高清av免费在线| 搡老熟女国产l中国老女人| 色老头精品视频在线观看| 成年av动漫网址| 亚洲国产精品999| 成年人免费黄色播放视频| 黄片大片在线免费观看| 久久久久国产一级毛片高清牌| 久久 成人 亚洲| 蜜桃国产av成人99| 人妻 亚洲 视频| 最近中文字幕2019免费版| 亚洲伊人久久精品综合| 丁香六月欧美| 亚洲精品中文字幕在线视频| 考比视频在线观看| 午夜精品久久久久久毛片777| 日本av手机在线免费观看| 色老头精品视频在线观看| 日本欧美视频一区| 亚洲九九香蕉| 国产免费一区二区三区四区乱码| 美女午夜性视频免费| 日本av免费视频播放| 91大片在线观看| 悠悠久久av| 欧美日韩中文字幕国产精品一区二区三区 | 热99国产精品久久久久久7| 国产精品影院久久| 国产一区二区三区综合在线观看| 一二三四社区在线视频社区8| 如日韩欧美国产精品一区二区三区| 亚洲国产中文字幕在线视频| 亚洲专区字幕在线| 欧美+亚洲+日韩+国产| 欧美老熟妇乱子伦牲交| 纵有疾风起免费观看全集完整版| 成人三级做爰电影| 不卡av一区二区三区| 亚洲av成人不卡在线观看播放网 | 亚洲av欧美aⅴ国产| 欧美日韩亚洲国产一区二区在线观看 | 十分钟在线观看高清视频www| 在线观看免费高清a一片| 国产成人系列免费观看| 欧美黑人精品巨大| 老鸭窝网址在线观看| 99热国产这里只有精品6| 精品一区二区三区av网在线观看 | 久热这里只有精品99| 亚洲七黄色美女视频| 人人妻人人澡人人看| 色播在线永久视频| 亚洲 国产 在线| 女人久久www免费人成看片| 国产极品粉嫩免费观看在线| 中文字幕av电影在线播放| 中文字幕制服av| 精品乱码久久久久久99久播| 亚洲国产精品一区二区三区在线| 91麻豆av在线| 无限看片的www在线观看| www.自偷自拍.com| 日韩欧美免费精品| 最新在线观看一区二区三区| 超碰成人久久| 午夜影院在线不卡| 久久人妻福利社区极品人妻图片| 各种免费的搞黄视频| 超碰成人久久| 国产成人系列免费观看| 成年人免费黄色播放视频| 嫁个100分男人电影在线观看| 久久青草综合色| 91字幕亚洲| 久久精品国产亚洲av高清一级| 亚洲国产中文字幕在线视频| 精品福利观看| 国产一区二区激情短视频 | 国产av国产精品国产| 丰满饥渴人妻一区二区三| 精品人妻熟女毛片av久久网站| 91av网站免费观看| 久久久久视频综合| 麻豆乱淫一区二区| 国产91精品成人一区二区三区 | 日韩欧美国产一区二区入口| 久久av网站| 如日韩欧美国产精品一区二区三区| 日韩有码中文字幕| 一级片'在线观看视频| 色老头精品视频在线观看| 两个人免费观看高清视频| 麻豆av在线久日| 青春草亚洲视频在线观看| 少妇粗大呻吟视频| 黄色视频不卡| 制服诱惑二区| 精品少妇内射三级| 日本欧美视频一区| av超薄肉色丝袜交足视频| 极品人妻少妇av视频| 午夜福利影视在线免费观看| 18禁观看日本| 国内毛片毛片毛片毛片毛片| 成人国语在线视频| 热99国产精品久久久久久7| 国产精品久久久人人做人人爽| 又大又爽又粗| 啦啦啦视频在线资源免费观看| 一个人免费看片子| 天天添夜夜摸| 少妇人妻久久综合中文| 欧美人与性动交α欧美软件| 国产精品香港三级国产av潘金莲| 久久精品国产亚洲av高清一级| 99久久99久久久精品蜜桃| 午夜影院在线不卡| 国产黄色免费在线视频| 久久久久久久久免费视频了| 妹子高潮喷水视频| 亚洲精华国产精华精| 丝袜美足系列| 国产又爽黄色视频| 嫁个100分男人电影在线观看| 一级毛片精品| 午夜免费成人在线视频| 男女免费视频国产| 精品久久久精品久久久| 国产免费av片在线观看野外av| 人人妻人人澡人人看| 成人av一区二区三区在线看 | 99香蕉大伊视频| 精品少妇一区二区三区视频日本电影| 成人免费观看视频高清| 欧美日韩亚洲国产一区二区在线观看 | 91国产中文字幕| 一区二区三区乱码不卡18| 国产一卡二卡三卡精品| 18禁黄网站禁片午夜丰满| 999久久久国产精品视频| 天堂中文最新版在线下载| 国产一区二区 视频在线| 国产精品一二三区在线看| av网站免费在线观看视频| 久久久久久久精品精品| 精品亚洲成国产av| 又大又爽又粗| 久久99热这里只频精品6学生| 中文字幕制服av| 啦啦啦 在线观看视频| 久久久久国内视频| 亚洲欧洲日产国产| xxxhd国产人妻xxx| 亚洲va日本ⅴa欧美va伊人久久 | 亚洲五月婷婷丁香| 国产av又大| 午夜激情久久久久久久| 狂野欧美激情性bbbbbb| 国产精品一区二区在线观看99| 国产成人啪精品午夜网站| 国产日韩欧美视频二区| 国产男女超爽视频在线观看| 国产亚洲午夜精品一区二区久久| 亚洲国产欧美日韩在线播放| 精品久久久久久久毛片微露脸 | 久久免费观看电影| 老司机福利观看| 亚洲成人免费av在线播放| 久久性视频一级片| 亚洲国产欧美网| 国产野战对白在线观看| 亚洲一区二区三区欧美精品| 久久99热这里只频精品6学生| 午夜影院在线不卡| 欧美日韩视频精品一区| 亚洲专区字幕在线| 国产不卡av网站在线观看| 99热国产这里只有精品6| 热99国产精品久久久久久7| 99re6热这里在线精品视频| 黄色片一级片一级黄色片| 丰满迷人的少妇在线观看| 久久天堂一区二区三区四区| 老司机午夜十八禁免费视频| 又紧又爽又黄一区二区| 久久国产精品大桥未久av| 欧美大码av| 午夜福利,免费看| 桃花免费在线播放| 亚洲精品在线美女| 91av网站免费观看| 欧美另类一区| 自线自在国产av| cao死你这个sao货| 女性被躁到高潮视频| 日韩熟女老妇一区二区性免费视频| 精品欧美一区二区三区在线| 免费黄频网站在线观看国产| 一级片'在线观看视频| 国产主播在线观看一区二区| 午夜成年电影在线免费观看| 久热这里只有精品99| 国产高清videossex| 两个人免费观看高清视频| 久久久久精品国产欧美久久久 | 亚洲欧美精品自产自拍| 老司机影院成人| 在线看a的网站| 色老头精品视频在线观看| 男女免费视频国产| 手机成人av网站| 国产精品久久久久久人妻精品电影 | 亚洲国产欧美在线一区| 国产日韩欧美在线精品| 精品欧美一区二区三区在线| 美女中出高潮动态图| 国产激情久久老熟女| 久久天堂一区二区三区四区| 一级毛片女人18水好多| 成人免费观看视频高清| 色播在线永久视频| 国产精品av久久久久免费| 国产老妇伦熟女老妇高清| 久久天堂一区二区三区四区| 亚洲成国产人片在线观看| 久久久久久人人人人人| 高清黄色对白视频在线免费看| 91老司机精品| 精品国产一区二区三区四区第35| 18禁黄网站禁片午夜丰满| 午夜激情av网站| 免费观看人在逋| 国产成人av教育| 国产精品1区2区在线观看. | 成年av动漫网址| 欧美在线一区亚洲| 午夜福利影视在线免费观看| 1024香蕉在线观看| 黄色a级毛片大全视频| 成年动漫av网址| 各种免费的搞黄视频| 日韩欧美国产一区二区入口| 成人国语在线视频| 一边摸一边做爽爽视频免费| 亚洲色图 男人天堂 中文字幕| 在线 av 中文字幕| 国产精品av久久久久免费| 青春草亚洲视频在线观看| 他把我摸到了高潮在线观看 | 成人亚洲精品一区在线观看| 男女国产视频网站| 欧美在线黄色| 国产成人免费观看mmmm| 9191精品国产免费久久| 国产一区二区激情短视频 | 精品第一国产精品| 国产在线免费精品| 午夜免费鲁丝| 另类亚洲欧美激情| 黑人猛操日本美女一级片| 国产一区二区三区综合在线观看|