Geochemistry of lower Jurassic shales of the Shemshak Formation, Kerman Province, Central Iran: Provenance, source weathering and tectonic setting

Lower Jurassic shales of the Shemshak Formation of Kerman Province, Central Iran, were analyzed for major and selected trace elements to infer their provenance, intensity of palaeoweathering of the source rocks and tectonic setting. Plots of shales on Al₂O₃ wt.% versus TiO₂ wt.% diagram and Cr (ppm) versus Ni (ppm) diagram indicate that acidic (granitic) rocks constitute the source rocks in the provenance. Average CIA, PIA and CIW values (84%, 92%, 93%, respectively) imply intense weathering of the source material. Plots of shales on bivariate discriminant function diagram reveal an active continental margin setting for the provenance. The inferred tectonic setting for the Lower Jurassic shales of the Shemshak Formation of Kerman Province is in agreement with the tectonic evolutionary history of the Central Iran during the Jurassic period.     

Provenance and Paleoclimate of the Triassic to Middle Jurassic Adigrat Sandstone, Blue Nile Basin, Central Ethiopia

Mineralogical and geochemical studies have been undertaken on the Triassic to Lower Jurassic Adigrat Sandstone of the Blue Nile Basin of central Ethiopia to infer its source rock type, paleoweathering, and paleoclimatic history. The Adigrat Sandstone occurs at the basal section of the Mesozoic sedimentary formation and unconformably overlays the Neoproterozoic–Paleozoic crystalline rocks, or locally, the Karroo sediments in the northern Blue Nile Basin. A mineralogical study reveals that quartz (Q), feldspars (F), and lithic fragments (L) are the framework grains of the sandstone. On the QFL diagram, the plot of the modal composition of the sandstone mainly falls within the feldspathic arenite and quartzose arenite fields. The geochemical data of the lower section of the sandstone mainly falls within the arkose and subarkose fields, whereas the upper section data falls within the quartzose and sublithic arenite fields. Mineralogical and geochemical weathering indices indicate that the provenances of the Adigrat Sandstone were exposed to pronounced weathering intensity, where the lower part of the sandstone was controlled by arid to semi-arid conditions, whereas the upper section was linked to humid to semi-humid (tropical to subtropical) climatic conditions. Mineralogical and geochemical data also indicate that mafic to intermediate basement rocks were the primary source rocks of the sediment. Perhaps the sediment was assumed to have been reworked by multi-cyclic sedimentary processes. The discriminant function diagram, the REE pattern, La/Th vs. La/Yb, and the Th–Hf–Co plot are consistent. A comparison of provenance studies for the Adigrat Sandstone in the Blue Nile Basin and the Mekele outlier of northern Ethiopia indicates that the sediment of the former is highly sorted, experienced higher weathering intensity, and compositionally derived from mafic to intermediate crystalline rocks. On the other hand, the sediment of the latter is essentially a weathering product of felsic rocks.     

Provenance, diagenesis, tectonic setting and geochemistry of Tawil Sandstone (Lower Devonian) in Central Saudi Arabia

The Tawil Sandstone (Lower Devonian) in Central Saudi Arabia overlies the Sharwara Member of the Tayyarat Formation (Silurian) and succeeded conformly by the Shaiba Member of the Jauf Formation. Petrographical data reveal that the Tawil Sandstone comprises 96% quartz, 3% feldspar, and 1% rock fragments and all samples are classified as quartz arenites. The presence of well sorted, altered to fresh feldspar, and discriminate function analysis suggests that the sediments have been subjected to substartial reworking resulting in a high level of maturity. Modal analysis data (Q–F–L) suggest a stable cratonic provenance for the sediments and accumulation in a passive margin basin is indicated (binary plot of SiO₂ vs K₂O/Na₂O). Diagenetic features include dissolution of feldspar and rock fragments, compaction, reduction of the existing pore space through rearrangements, and rotation and fragmentation of grains resulting in dissolution of quartz grains and cementation.     

Geochemistry of the Jurassic and Upper Cretaceous shales from the Molango Region,Hidalgo, eastern Mexico: Implications for source-area weathering,provenance, and tectonic setting

This study focuses on the Jurassic (Huayacocotla and Pimienta Formations) and Upper Cretaceous (Méndez Formation) shales from the Molango Region, Hidalgo, Mexico. In this article, we discuss the mineralogy, major, and trace element geochemistry of the Mesozoic shales of Mexico. The goal of this study is to constrain the provenance of the shales, which belong to two different periods of the Mesozoic Era and to understand the weathering conditions and tectonic environments of the source region.     

Provenance, Tectonic Setting and Geochemistry of Ahwaz Sandstone Member (Asmari Formation, Oligo-Miocene), Marun Oilfield, Zagros Basin, SW Iran

The Asmari Formation deposited in the Zagros foreland basin during the OligoceneMiocene. Lithologically, the Asmari Formation consists of limestone, dolomitic limestone, dolomite, argillaceous limestone, some anhydrite(Kalhur Member) and sandstones(Ahwaz Member). This study is based on the analysis of core samples from four subsurface sections(wells Mn-68, Mn-281, Mn-292 and Mn-312) in the Marun Oilfield in the Dezful embayment subzone in order to infer their provenance and tectonic setting of the Ahwaz Sandstone Member. Petrographical data reveal that the Ahwaz Sandstone comprises 97.5% quartz, 1.6% feldspar, and 0.9% rock fragments and all samples are classified as quartz arenites. The provenance and tectonic setting of the Ahwaz Sandstone have been assessed using integrated petrographic and geochemical studies. Petrographic analysis reveals that mono- and poly-crystalline quartz grains from metamorphic and igneous rocks of a craton interior setting were the dominant sources. Chemically, major and trace element concentrations in the rocks of the Ahwaz Sandstone indicate deposition in a passive continental margin setting. As indicated by the CIW′ index(chemical index of weathering) of the Ahwaz Sandstone(average value of 82) their source area underwent "intense" recycling but "moderate to high" degree of chemical weathering. The petrography and geochemistry results are consistent with a tropical, humid climate and low-relief highlands.     

西藏羌塘盆地古近纪康托组沉积物源及构造背景分析

沉积岩中的主微量元素和稀土元素特征可以指示其物源、构造背景和沉积环境等。康托组地层沉积时代为古近纪,是青藏高原早期隆升后首先沉积的陆相碎屑岩,对该地层的物源信息及构造背景分析对于研究羌塘盆地新生代演化和高原隆升过程具有积极意义。本文对羌塘盆地半岛湖地区康托组地层进行了地层学、岩石学、元素地球化学和黏土含量分析,研究了其物源特征及构造背景。研究区康托组主要为岩屑砂岩、岩屑石英砂岩,分选性和磨圆度较差,发育平行层理。对17件样品进行元素地球化学分析测试,结果显示中等的化学蚀变指数CIA值（69.57~80.81）,较高的化学风化指数CIW值（81.07~95.02）和斜长石风化指数PIA值（77.32~93.96）,表明物源区整体经历了较强的化学风化作用。Th/U、Sc/Th、Rb/Sr等微量元素比值接近大陆上地壳值,结合稀土元素的配分模式,表明近源快速堆积的特点。根据TiO2/Zr、Co/Th、La/Sc、Th/Sc、Cr/Zr值和δEu、δCe的负异常,结合相关判别图解说明康托组物源主要来自于长英质岩石。La—Th—Sc、Th—Sc—Zr/10、TiO2—Fe2O3T+MgO、Al2O3/SiO2—Fe2O3T+MgO和主量元素双因素构造判别图解表明物源区主要为被动大陆边缘。结合构造演化分析,指示了半岛湖地区康托组形成于陆内沉积环境。     

西藏羌塘盆地古近纪康托组沉积物源及构造背景分析

沉积岩中的主微量元素和稀土元素特征可以指示其物源、构造背景和沉积环境等.康托组地层沉积时代为古近纪,是青藏高原早期隆升后首先沉积的陆相碎屑岩,对该地层的物源信息及构造背景分析对于研究羌塘盆地新生代演化和高原隆升过程具有积极意义.本文对羌塘盆地半岛湖地区康托组地层进行了地层学、岩石学、元素地球化学和黏土含量分析,研究了其...     

川东南地区志留系小河坝组砂岩特征及物源分析

通过对川东南地区小河坝组砂岩的碎屑组分、岩屑类型、重矿物组合、地球化学（稀土元素、微量元素）及古流向的研究,分析了小河坝组砂岩的物源方向、母岩类型及源区的构造背景。结果显示：源区为盆地东边江南－雪峰山隆起西侧上元古界板板溪群及其侵入板溪群中的基性岩体、中基性喷出岩体。具有活动大陆边缘、大陆岛弧及被动大陆边缘的构造背景。地球化学研究进一步证明,母岩主要为更老的沉积岩再旋回沉积物及少量岩浆岩。在早志留世小河坝期以华南板块缓慢向扬子板块蠕动方式相拼接,致使扬子板块整体缓慢抬升,同时沉积中心不断向西北方向迁移,造成研究区具有明显沉积旋回性的物源供给特征。     

苏北盆地古近系阜三段物源特征及其形成的构造背景分析

综合碎屑组分、砾石成分、稀土元素、砂岩含量分布和砂砾岩分布特征的分析,并借鉴前人的研究成果,可以得出,苏北盆地古近系阜三段的物源区主要有6个.(Ⅰ,Ⅱ)建湖隆起分别向南北两侧供源:向南为金湖东部凹陷、高邮北部凹陷和海安凹陷供源,母岩成分主要为中酸性火成岩、石英岩和花岗岩;向北为盐城凹陷供源,母岩成分主要为中酸性火成岩、...     

徐州地区山西组砂岩岩石学特征及物源分析

徐州地区山西组砂岩中碎屑组分鉴定统计的结果显示,长石的含量为29%~52%,平均40%,明显高于周边地区。研究区岩石类型以长石砂岩为主,分选差-中等,磨圆次棱角状-次圆状,说明碎屑为短距离搬运;砂岩中斜长石的牌号显示源区主要为酸性岩;砂岩组分的Dickinson三角图解表明,物源总体来自大陆物源区的隆起基底,经分析确定物源区为丰-沛隆起。     

Provenance analysis and tectonic setting of the Ordovician clastic deposits in the southern Puna Basin, NW Argentina

Provenance studies on Early to Middle Ordovician clastic formations of the southern Puna basin in north-western Argentina indicate that the sedimentary detritus is generally composed of reworked crustal material. Tremadoc quartz-rich turbidites (Tolar Chico Formation, mean composition Q_t89 F7 L4) are followed by volcaniclastic rocks and greywackes (Tolillar Formation, mean Q_t33 F42 L25). These are in turn overlain by volcaniclastic deposits (mean Q_t24 F30 L46) of the Diablo Formation (late Arenig–early Llanvirn) that are intercalated by lava flows. All units were deformed in the Oclóyic Orogeny during the Middle and Late Ordovician. Sandstones of the Tolar Chico Formation are characterized by Th/Sc ratios > 1, La/Sc ratios ≈ 10, whereas associated fine-grained wackes show slightly lower values for both ratios. LREE (light rare earth elements) enrichment of the arenites is ≈ 50× chondrite, Eu/Eu* values are between 0·72 and 0·92, and flat HREE (heavy rare earth elements) patterns indicate a derivation from mostly felsic rocks of typical upper crustal composition. The ε_{Nd(t = sed)} values scatter around −11 to −9. The calculated Nd-T_DM residence ages vary between 1·8 and 2·0 Ga indicating contribution by a Palaeoproterozoic crustal component. The Th/Sc and La/Sc ratios of the Tolillar Formation are lower than those of the Tolar Chico Formation. Normalized REE (rare earth elements) patterns display a similar shape to PAAS (post-Archaean average Australian shale) but with higher abundances of HREEs. Eu/Eu* values range between 0·44 and 1·17, where the higher values reflect the abundance of plagioclase and feldspar-bearing volcanic lithoclasts. Average ε_{Nd(t = sed)} values are less negative at −5·1, and Nd-T_DM are lower at 1·6 Ga. This is consistent with characteristics of regional rocks of upper continental crust composition, which most probably represent the sources of the studied detritus. The rocks of the Diablo Formation have the lowest Th/Sc and La/Sc ratios, lower LREE abundances than the average continental crust and are slightly enriched in HREEs. Eu/Eu* values are between 0·63 and 1·17. The Nd isotopes (ε_{Nd(t = sed)} = −3 to −1; T_DM = 1·2 Ga) indicate that one source component was less fractionated than both the underlying Early Ordovician and the overlying Middle Ordovician units. Synsedimentary vulcanites in the Diablo Formation show the same isotopic composition. Our data indicate that the sedimentary detritus is generally composed of reworked crustal material, but that the Diablo Formation appears to contain ≈ 80% of a less fractionated component, derived from a contemporaneous continental volcanic arc. There are no data indicating an exotic detrital source or the accretion of an exotic block at this part of the Gondwana margin during the Ordovician.     

Provenance of Conglomerate and Sandstone from Early Permian Shoushangou Formation in Xi Ujimqin, Inner Mongolia: Implications for Understanding Paleo-Asian Ocean Subduction

During the Late Carboniferous to Early Permian, a rift was formed by post-collisional extension after ocean closure or an island arc-related basin formed by Paleo-Asian Ocean (PAO) subduction in the Xi Ujimqin area. Nevertheless, the closure time of the PAO is still under debate. Thus, to identify the origin of the PAO, the geochemistry and U-Pb age of zircons were analyzed for the extra-large deep marine, polymict clastic boulders and sandstones in the Shoushangou Formation within the basin. The analyses revealed magmatic activity and tectonic evolution. The conglomerates include megaclasts of granite (298.8 ± 9.1?Ma) and granodiorite porphyry (297.1 ± 3.1?Ma), which were deposited by muddy debris flow. Results of this study demonstrated that the boulders of granitoids have the geochemistry of typical I-type granite, characterized by low Zr + Nb + Ce + Y and low Ga/Al values. The granitoid boulders were formed in island arc setting, indicating the presence of arc magmatism in the area that is composed of the Late Carboniferous to Early Permian subduction-related granitoid in southern Xi Ujimqin. Multiple diagrams for determining sedimentary provenance using major and trace elements indicate that Shoushangou sediments originated from continental island arc-related felsic rocks. Detrital zircon U-Pb age cluster of 330–280?Ma was obtained, indicating input from granite, ophiolite, Xilin Gol complex, and Carboniferous sources to the south. The basin was geographically developed behind the arc during the Early Permian period because the outcropped intrusive rocks in the Late Carboniferous to Early Permian form a volcanic arc. The comprehensive analyses of source areas suggest that Shoushangou sediments developed in a backarc basin in response to the northward subduction of the PAO. The backarc basin and intrusive rocks, in addition to previously published Late Carboniferous to Early Permian magmatic rocks of arc unit in Xilin Gol, confirm the presence of an Early Permian trench-arc-basin system in the region, represented by the Baolidao arc and Xi Ujimqin backarc basin. This study highlights the importance and potential of combined geochemical and geochronological studies of conglomerates and sandstone for reconstructing the geodynamic setting of a basin.     

柴达木盆地鱼卡地区中侏罗统石门沟组砂岩碎屑组分特征及其物源构造环境分析

利用砂岩碎屑骨架成分统计和碎屑颗粒结构特征分析,研究柴达木盆地北缘鱼卡地区中侏罗统石门沟组碎屑岩的源岩类型及其构造环境。石门沟组砂岩成分成熟度中等、结构成熟度较低,具有近源物源的特点。砂岩碎屑骨架成分统计结果表明石门沟组的物源区构造背景属于再旋回造山带。结合柴达木盆地北缘中侏罗统古地理特征,确认鱼卡地区石门沟组物源区为祁连山造山带。砂岩碎屑组分可能来自于南祁连山上石炭世宗务隆山群火山岩和达肯达坂山群变质岩。     

四川盆地南部须家河组砂岩组分特征及物源分析

上三叠统须家河组是四川盆地南部地区重要的油气勘探层位。通过对碎屑组分和重矿物分析,表明川南地区须家河组存在龙门山、康滇古陆、雪峰古隆起和黔中古隆起等多个物源区。其中,龙门山物源主要影响研究区西北部,以提供岩浆岩和变质岩岩屑为典型特征,北西-南东向展布的（短轴）三角洲沉积体系较发育;研究区东北部和东南部所含泥岩、粉砂岩和变质岩岩屑则主要来自雪峰古隆起,该区发育南东-北西向展布的远源（长轴）三角洲沉积体系;康滇古陆、黔中古隆起控制着研究区西南部和南部,重矿物分析也支持上述观点。     

安徽东南部二叠系龙潭组砂岩碎屑组分及物源分析

       砂岩碎屑组分分析是研究盆地沉积物源及其构造演化的重要途径。龙潭组是我国南方重要的含煤层位之一,进一步确定其沉积物来源和源区构造背景具有重要意义。安徽东南部二叠系龙潭组砂岩碎屑组分特征为：单晶石英含量为25%~40%,多晶石英含量为30%~65%,而且细砂岩中,石英多具有溶蚀的边缘;长石含量变化较大,在细砂岩中含量在5%~15%之间,在中粗粒砂岩中含量仅为1%左右;岩屑在细砂岩中的含量为15%~25%,在中粗粒砂岩中含量为10%~20%。砂岩物源分析结果显示,龙潭组砂岩来源于再旋回造山带与消减杂岩带的混合蚀源区,结合含近源砾石特征及区域大地构造背景,可推测研究区龙潭组物源区很可能来自华夏板块与扬子板块碰撞的接壤地带--江南造山带。     

Geochemistry of Lower Jurassic sandstones of Shemshak Formation,Kerman basin,Central Iran: Provenance,source weathering and tectonic setting

Lower Jurassic sandstones of Shemshak Formation of Kerman basin, central Iran were analyzed for major and select trace elements to infer their provenance, palaeoweathering of source rocks and tectonic setting. Average modal framework components (Qt: F: L= 67.25: 2.41: 30.48) and chemical composition of the sandstones classify them as litharenites. The sandstones are quartz-rich (～ 67% quartz; 75.34 wt.% SiO₂) and derived from a recycled orogen composed of quartzose sedimentary rocks. Average CIA, PIA and CIW values (69%, 76% and 80%, respectively) indicate moderate to intense chemical weathering of the source material. The inferred index of weathering/alteration is the sum total of intensities of weathering witnessed by the lithocomponents during atleast two cycles of sedimentation involving (1) chemical weathering of the source rocks («ultimate» granodiorite source and «proximal» quartzose sedimentary source), (2) chemical weathering during fluvial transport of the detritus, (3) chemical weathering of the detritus in depocenters, and (4) chemical weathering during diagenesis. Sandstones exhibit moderate maturity and were deposited under humid climatic conditions. Plots of the chemical analyses data on tectonic setting discrimination diagrams indicate active continental margin setting, which is in agreement with the tectonic evolutionary history of the Central Iran during Jurassic period.     

粤东盆地早侏罗世金鸡组物源分析及其对华南构造背景的约束

华南早中生代构造背景一直存在争议。粤东盆地位于华南东南缘,记录了华南早中生代构造背景的地质信息。文章 以粤东盆地早侏罗世金鸡组碎屑沉积岩为研究对象,采用锆石U-Pb定年方法,结合岩相学、地球化学和古水流数据,探讨 盆地物源及构造背景。测年结果显示早侏罗世金鸡组样品存在八个峰值：196 Ma、247 Ma、320 Ma、432 Ma、770 Ma、 1060 Ma、1820 Ma和2430 Ma。物源分析表明粤东盆地金鸡组物源主要来自盆地的东北侧和北侧两个方向。粤东盆地碎屑 锆石与位于盆地东北侧的永安盆地和北侧的东坑盆地的物源特征相似,反映出早侏罗世中国东南部盆地尽管还是以稳定的 克拉通边缘盆地为特征,但古太平洋板块向华南板块更东侧的俯冲已经开始为中国东南缘盆地提供物源。     

柴达木盆地北缘牦牛山组物源分析及其构造意义

柴达木盆地北缘牦牛山组为一套由砂砾岩组成的陆相紫红色粗碎屑沉积岩,其时代一直存在争议。本文对两个剖面牦牛山组的沉积特征、古水流、砾石成分进行了研究,并对砂质充填物中锆石进行了LA-ICP-MS测年分析。结果表明,牦牛山组发育冲击扇沉积,古流向主要为自北西至南东和自南东至北西两个方向。两个剖面砾石成分差异显著,城墙沟剖面砾石成分以碳酸盐岩为主,而旺尕秀剖面砾石成分则较为复杂。砂质充填物中碎屑锆石U-Pb年龄可分为3个组:360～560Ma、890～1050Ma和2200～2500Ma。它们代表本区3次构造事件,包括早古生代柴达木盆地北缘由洋-陆至陆-陆的碰撞过程,新元古代Grenville造山事件及新太古代陆壳的增长。其中最小的碎屑锆石U-Pb年龄为365±3Ma,结合区域地质背景与古生物等资料,表明牦牛山组的时代为晚泥盆世。本区早古生代第三期和第四期花岗岩类的锆石U-Pb年龄与本文最年轻的一组锆石U-Pb年龄在误差范围内一致,表明这两期岩体发生了快速抬升剥蚀。结合前人研究,柴达木盆地北缘在牦牛山组沉积期处于后碰撞阶段。     

库车坳陷侏罗系砂岩碎屑组分及物源分析

库车坳陷位于塔里木盆地的北部,其侏罗系发育良好,为一套陆相含煤沉积,可分为中、下部的煤系地层和上部的杂色碎屑沉积两部分。侏罗系包括阿合组、阳霞组、克孜勒努尔组、恰克马克组、齐古组和喀拉扎组。该区砂岩碎屑成分以石英为主,其次是长石及各种岩屑,有时含少量云母及绿泥石等碎屑矿物。砂岩结构不一,粗砂、中砂和细砂状结构均有,很少一部分为含砾结构。砂岩分选性以中等为主,少量分选好或分选差。砂粒的磨圆度各层位有所差异。本文对库车坳陷侏罗纪地层的砂岩进行了骨架矿物统计分析,通过碎屑岩矿物成分与结构的变化研究了库车坳陷侏罗系沉积岩石学特征,并应用Dickinson的分析理论及结果,对库车坳陷的碎屑岩进行物源与板块构造关系的分析与探讨,重点对库车河剖面的砂岩作了系统采样和测定,显微镜下观察了砂岩的碎屑组分,并对各组分采用点记法进行整个全视域薄片的砂岩的骨架矿物成分统计工作,根据碎屑组分特征与重矿物组合特征,结合区域构造、沉积古地貌及盆地演化史,对库车坳陷的物源进行了探讨。认为侏罗系下部的碎屑岩物源区以再旋回造山带为主,已经过一段时间的风化开始隆升,遭受强烈剥蚀,反映了前陆盆地形成时的早期旋回阶段的特征,来自三叠纪古前隆的物源较少,母岩以沉积岩为主;侏罗系中上部碎屑物源仍以盆地边缘再旋回造山带为主,但三叠纪古前缘隆起提供物源已比较明显。除此之外,在盆地边缘形成的早期沉积物经水流机械破碎、改造作用的泥砾沉积物增多,受双物源区的控制,母岩为沉积岩。     

Provenance of the Early–Middle Devonian Shugouzi Formation in the Quruqtagh, Northeastern Xinjiang: Constraints from Sandstone Geochemistry and Heavy Mineral Analysis

The Early-Middle Devonian Shugouzi Formation in the Quruqtagh block consists mainly of clastic rocks.However,their provenance has been scarcely studied since it was named.Geochemistry of clastic rocks was commonly used to interpret the provenance.Detrital heavy mineral analyses help frame the U-Pb age from zircon grains,integrated with geochemical data from detrital tourmaline and spinels.These techniques were used to characterize components of the sediment flux and define erosion areas in the Qurugtagh block,further providing evidence about the tectonic evolution of the South Tianshan and Tarim plate.The maximum depositional age constrained by detrital zircon dating was Early-Middle Devonian.Multiple diagrams for sedimentary provenance using major and trace elements indicate that continental island arc-related felsic rocks were the major source rocks for the Shugouzi Formation.Detrital tourmalines are dravite and schorl.The results of detrital tourmaline electron probe microanalysis(EPMA)show that the source rocks are mainly metasedimentary rocks and granitoids.The detrital chromian spinels within the sediments are characterized by high chroumium(Cr^#)and varying magnesium(Mg^#).The discrimination plots reveal that these spinels were sourced from island arc magmatic rocks.The laser ablation inductively-coupled plasma mass spectrometry(LA-ICP-MS)U-Pb chronology of detrital zircons suggests that the sediments were derived mainly from 414-491 Ma and 744-996 Ma magmatic rocks.Paleocurrent restoration,sandstone geochemistry,EPMA,and detrital zircon geochronology indicate that the source rocks were predominantly derived from Late Ordovician and Devonian magmatic rocks and subordinately from recycled Neoproterozoic magmatic rocks.Comprehensive analyses of the source areas suggest that a remnant arc still existed in the Early Devonian and the Shugouzi Formation was deposited in a passive continental margin.