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1.
岩相学研究表明阿尔金南缘淡水泉一带出露的花岗质片麻岩的峰期矿物组合为Grt+Kfs+Ky+Rt+Qz,为典型的高压麻粒岩相矿物组合。利用Thermocalc3.33程序计算的P-T视剖面图和矿物温压计,确定其峰期变质温压条件为T=875~925℃,P=14.5~15.9kbar,该岩石后期还经历了以矿物组合Grt+Kfs+Bt+Pl+Sill+Ilm+Qz为代表的麻粒岩相和以Sill+Bt+Pl+Mu+Qz±Ilm为代表的角闪岩相的退变质作用,具有一个早期快速等温降压,后期近等压降温的顺时针型的退变质P-T演化轨迹。锆石的U-Pb同位素定年结果显示其原岩的时代为866±5Ma,峰期变质时代为505±5Ma。其中该岩石原岩的形成时代与阿尔金及其周缘地区广泛发育的由Rodinia超大陆裂解事件导致的岩浆活动时代一致,而峰期变质时代则与南阿尔金高压/超高压变质岩的峰期变质时代(486~509Ma)一致,说明花岗片麻岩原岩的形成与罗迪尼亚超大陆裂解有关,并在早古生代卷入了陆壳深俯冲事件,构成了南阿尔金高压/超高压变质带的一部分。 相似文献
2.
阿尔金淡水泉早古生代泥质高压麻粒岩及其P-T演化轨迹 总被引：8，自引：7，他引：1
南阿尔金构造带淡水泉一带出露的含石榴石蓝晶石黑云母片麻岩是一套典型的泥质高压麻粒岩,其峰期特征矿物组合为石榴子石+蓝晶石+钾长石+金红石+石英.根据矿物内部一致性热力学数据和Thermocalc 3.23程序计算,确定其峰期变质温压条件为T>850℃和P>11kbar.结合岩相学研究和P-T视剖面图计算,可识别出该岩石经历了4个阶段的变质演化,构成了一个早期快速等温降压,后期近等压降温的顺时针型的退变质P-T演化轨迹,为与陆壳俯冲碰撞有关的高压变质事件的产物.该岩石锆石阴极发光图像显示其内部具有明显的核.边结构,核部为残留的原岩碎屑锆石,边部则表现为面状或扇状生长的变质锆石的特征.微区原位LA-ICP-MS微量元素分析表明,核部测点的重稀土含量较高,对应Th/U接近于0.4,具有岩浆锆石的特征;边部测点的重稀土相对亏损,重稀土配分曲线平坦,对应Th/U比值均小于0.1,显示与石榴子石平衡共生的变质锆石特征.LA-ICP-MS微区定年获得其变质年龄为486±5Ma,该年龄值与阿尔金江尕勒萨依和英格利萨依两地超高压变质岩石的变质年龄相近,进一步证明沿阿尔金构造带南缘断续存在一条早古生代的高压-超高压变质岩带.另外,本次研究在获得该泥质高压麻粒岩峰期变质时代的同时,还获得该岩石原岩的形成时代上限值约为719Ma,从而限定阿尔金构造带南缘阿尔金群的形成时代可能不属古元古代,而应属新元古代. 相似文献
3.
南阿尔金尤努斯萨依花岗质高压麻粒岩的发现及其地质意义 总被引：1，自引：1，他引：0
南阿尔金尤努斯萨依地区首次发现一套高压麻粒岩相特征矿物组合的含蓝晶石石榴子石的花岗质片麻岩,其矿物组合为Grt+Ky+Per(+Ksp)+Ru+Q。依据矿物内部一致性热力学数据,基于THERMOCALC 3. 40程序平台,计算出P-T视剖面图,并结合矿物等值线、矿物组合稳定域及三元长石温度计等,确定其早期变质温压条件为T=970～1010℃,P=23. 2～25. 3kbar,达到了榴辉岩相变质条件。同时,根据岩相学观察获得的矿物共生组合与矿物变质显微结构以及P-T视剖面图,可识别出该岩石在早期变质之后还经历了以矿物组合Grt+Ky+Per(+Ksp)+Pl+Ru+Q为代表的麻粒岩相、以及Grt+Ky+Ksp+Pl+Bi+Ru+Ilm+Q为代表的麻粒岩-高角闪岩相和以Ky+Ksp+Pl+Q+Bi+Mu+Ru+Ilm为代表的角闪岩相三期退变质作用,它们共同构成了一个顺时针型降温降压的退变质P-T演化轨迹,指示出与大陆俯冲-深俯冲相关的高压变质事件和俯冲碰撞后的折返事件。利用LA-ICP-MS进行的锆石原位微区U-Pb定年和微量元素分析表明,该高压岩石峰期变质年龄497. 8±2. 7Ma,与南阿尔金地区已发现的高压-超高压岩石的峰期变质时代完全一致,表明它们应属同一变质岩带;其原岩形成时代为900. 2±4. 1Ma,与南阿尔金已报道的正变质的高压-超高压岩石原岩的形成时代基本一致,指示它们可能具有相同的原岩属性。这套花岗质高压麻粒岩的确定为进一步约束南阿尔金早古生代高压-超高压变质岩带的时空分布规律提供了新的限定。 相似文献
4.
南阿尔金造山带是目前报道的具有最深俯冲记录的大陆超高压变质带，其内出露有高压-超高温麻粒岩，它们对深入理解大陆地壳岩石超深俯冲与折返过程具有重要意义.介绍了对南阿尔金巴什瓦克地区长英质麻粒岩和基性麻粒岩的岩相学、矿物化学、相平衡模拟及锆石U-Pb年代学研究成果.其中基性麻粒岩主要记录了深俯冲大陆地壳折返过程的变质演化:包括高压榴辉岩相、高压-超高温麻粒岩相、低压-超高温麻粒岩相及随后的近等压降温演化阶段；长英质麻粒岩除了记录与基性麻粒岩相似的折返过程外，还记录了从角闪岩相到超高压榴辉岩相的进变质演化过程.结合已有研究资料，确定超高压榴辉岩阶段峰期条件> 7~9 GPa和>1 000℃，可达到斯石英稳定域.锆石年代学显示两种岩石类型的原岩和变质年龄均分别在900 Ma和500 Ma左右.变质作用与年代学研究表明，南阿尔金大陆地壳岩石在早古生代发生超深俯冲至200~300 km后，折返至加厚地壳底部发生高压-超高温变质作用，随后被快速抬升至地壳浅部发生低压-超高温变质作用并经历迅速冷却. 相似文献
5.
北秦岭高压-超高压岩石的多期变质时代及其地质意义 总被引：14，自引：12，他引：2
在岩相学观察和锆石CL图像研究的基础上,利用LA-ICP-MS原位微区定年分析方法,本文确定北秦岭清油河退变榴辉岩的峰期变质时代为490±6Ma,退变质时代为453±9Ma,原岩形成时代为655±9Ma;松树沟超高压长英质片麻岩的峰期变质时代为497±8Ma,两期退变质时代分别为448±4Ma和421±2Ma,原岩形成时代上限832±25Ma;寨根石榴石辉石岩的峰期变质时代为498±2Ma,中压麻粒岩相退变质时代为450±3Ma,角闪岩相退变质时代为426±1Ma,原岩形成时代为573±40Ma;西峡北榴闪岩的角闪岩相变质时代为423±3Ma,原岩形成时代为843±7Ma。新确定的这些岩石的峰期变质时代与前人已报导的区内高压-超高压岩石的峰期变质时代在误差范围内基本一致,结合区内高压-超高压岩石不仅分布在秦岭岩群北缘的官坡-双槐树一带,而且断续出露在秦岭岩群中部或偏南侧的清油河北-松树沟-寨根北甚至西峡北东西一线,进一步表明它们应是同一期构造地质事件的产物。北秦岭已发现的全部正变质的高压-超高压岩石均呈透镜体状分布在围岩片麻岩中,松树沟超高压长英质片麻岩的原岩为典型的陆壳沉积物,因此,这些高压-超高压岩石的形成可能都是陆壳俯冲-深俯冲作用的产物。结合岩相学观察、锆石CL图像和锆石U-Pb定年表明,这些高压-超高压岩石在～500Ma经历了峰期变质作用后,又分别在～450Ma和～420Ma遭受了中压麻粒岩相和或角闪岩相退变质作用的叠加,充分说明这些高压-超高压岩石经历了一个完整的由陆壳俯冲-深俯冲、之后连续两次抬升的构造演化过程。另外,本次研究新获得的这些岩石的原岩形成时代介于843±7Ma～573±40Ma之间,结合官坡榴辉岩的原岩形成时代为791～814Ma以及松树沟榴闪岩原岩时代为787±16Ma的研究,共同表明北秦岭高压-超高压岩石的原岩形成时代均为新元古代,因此,限定俯冲-深俯冲的陆壳物质应来自形成时代为新元古代的大陆地壳或地质体。结合区域地质背景和前人研究成果综合分析,本文初步认为,北秦岭高压-超高压变质岩带的形成是商丹洋向北俯冲拖曳南秦岭新元古代陆壳物质在～500Ma发生陆壳俯冲-深俯冲作用的产物,之后在～450Ma与～420Ma经历了两期抬升。 相似文献
6.
南阿尔金木纳布拉克地区长城系巴什库尔干岩群LA-ICP-MS锆石U-Pb定年及其地质意义 总被引：3，自引：0，他引：3
采用LA-ICP-MS微区原位锆石U-Pb同位素测定技术,测得木纳布拉克地区原划长城系巴什库尔干岩群红柳泉组的二云二长片麻岩和扎斯勘赛河组二云石英片岩的原岩形成年龄分别介于498~840Ma和500~647Ma之间,表明这2种岩石原岩的形成时代均为新元古代,而不是之前认为的中元古代。另外,红柳泉组二云二长片麻岩边部锆石表现为重稀土元素相对富集型稀土配分模式,其Th/U值大部分小于0.1,为变质锆石,测得其变质时代为498±4Ma,与该地区高压麻粒岩的峰期变质时代(486±5Ma)一致,且与南阿尔金阿尔金岩群中的高压-超高压岩石的峰期变质时代一致,推断其为阿尔金俯冲碰撞引发的高压-超高压变质作用的产物,属于南阿尔金高压-超高压变质带的一部分。通过原岩残留碎屑锆石的年代学对比,发现研究区内这2种岩石及已发现的高压麻粒岩均具有与阿尔金岩群相似的锆石年龄信息,表明本区红柳泉组和扎斯勘赛河组的这3种岩石不应再划归为中元古代的长城系巴什库尔干岩群,将其归属为阿尔金岩群更为合适。 相似文献
7.
在中阿尔金南缘西段尤努斯萨依北部原划长城系巴什库尔干岩群中首次发现一套高压泥质片麻岩。根据岩相学观察和矿物化学成分可识别出其四期矿物共生组合:早期为石榴子石+多硅白云母+单斜辉石(?)+斜长石+黑云母+石英+金红石+钛铁矿;第二期为石榴子石+蓝晶石+钾长石+斜长石+黑云母+石英+金红石+钛铁矿;第三期为石榴子石+夕线石+钾长石+斜长石+黑云母+石英+金红石+钛铁矿;晚期为石榴子石+夕线石+斜长石+黑云母+石英+钛铁矿。依据矿物内部一致性热力学数据,基于THERMOCALC 3. 40程序平台,计算出P-T视剖面图,并结合矿物等值线、矿物对温压计等计算,依次确定四期变质温压条件为15. 8～18. 3kbar/646～729℃、10. 30～12. 30kbar/781～821℃、8. 50～9. 60kbar/812～838℃和4. 65～5. 70kbar/698～725℃。上述四期变质阶段共同构成一个早期降压升温后降压降温的顺时针型演化的P-T轨迹,指示出与陆壳俯冲-折返相关的变质地质事件。利用LA-ICP-MS进行的锆石原位微区U-Pb定年和微量元素分析结果表明,该岩石记录了432. 0±2. 7Ma、401. 4±2. 5Ma和381. 1±2. 4Ma三期变质年龄,可能分别代表了该岩石早期高压、中期高压麻粒岩相-麻粒岩相和后期角闪岩相变质阶段的时代。该高压岩石出露于中阿尔金地块西段南缘长城系巴什库尔干岩群之中,与南侧以断裂带分隔的赋存于阿尔金岩群之中的南阿尔金高压-超高压岩石出露的构造位置明显不同,其峰期变质时代(～432Ma)亦明显不同于南阿尔金高压-超高压岩石的峰期变质时代(～500Ma)。因此,该高压岩石与南阿尔金高压-超高压岩石显然不能构成同一条变质岩带。结合区域地质背景和前人关于柴北缘陆壳属性高压-超高压岩石峰期变质时代(～430Ma)的研究成果综合分析,本文初步认为该高压岩石可能是柴北缘高压-超高压变质岩带的西延或是被中新生代以来阿尔金复杂多期次走滑断裂系迁移而就位于中阿尔金南缘的部分柴北缘高压-超高压变质岩片/岩块。 相似文献
8.
《吉林大学学报(地球科学版)》2015,(Z1)
南阿尔金俯冲碰撞杂岩带早古生代存在517、501~496、462~451和426~385 Ma 4个期次的花岗质岩浆岩。第一期岩浆岩早于区内蛇绿岩型镁铁质岩石的形成时间,第一期岩浆岩侵位于区内蛇绿岩型镁铁质岩石之中(≥500 Ma),后三期分别对应于该构造带高压—超高压岩石~500 Ma的峰期变质、及其~450 Ma和~420 Ma的两期退变质时间。结合区域地质背景、镁铁—超美铁质岩和高压—超高压变质作用研究成果综合分析,这四期花岗质岩浆作用的发生分别是南阿尔金早古生代板块俯冲碰撞过程中,先期俯冲洋壳在517 Ma部分熔融、之后陆壳深俯冲导致地壳加厚引发下地壳在~500 Ma部分熔融,以及深俯冲板片断离导致中上地壳在~450 Ma部分熔融和造山后伸展减薄阶段在~420 Ma的部分熔融作用的产物。其中,洋壳型埃达克岩的形成时代(517 Ma)为南阿尔金洋壳俯冲作用时限提供了直接约束,陆壳深俯冲引发的高压-超高压峰期变质时代(~500 Ma)作用滞后这一事件约10 myr,表明南阿尔金早古生代时期由洋壳俯冲转换为陆壳俯冲可能是一个连续的构造演化过程。这四期花岗质岩石与区内蛇绿岩型镁铁—超镁铁质岩石以及高压—超高压变质岩石的形成,共同记录了南阿尔金早古生代时期从大洋俯冲、之后的大陆深俯冲碰撞再到后来深俯冲陆壳折返抬升的完整构造演化过程。 相似文献
9.
造山带中成对出现的高压麻粒岩与榴辉岩及其地球动力学意义 总被引：18，自引：13，他引：5
在一些典型碰撞造山带中,高压麻粒岩与榴辉岩在空间和时间上密切相关,它们之间的关系对揭示碰撞造山带的造山过程和造山机制具有重要意义.本文以中国西部的南阿尔金、柴北缘及中部的北秦岭造山带为例,详细陈述了这3个地区榴辉岩和相关的高压麻粒岩的野外关系、变质演化和形成时代,目的是要建立大陆碰撞造山带中榴辉岩和相关高压麻粒岩形成的地球动力学背景模式.南阿尔金榴辉岩呈近东西向分布在江尕勒萨依,玉石矿沟一带,与含夕线石副片麻岩、花岗质片麻岩和少量大理岩构成榴辉岩一片麻岩单元,榴辉岩中含有柯石英假象,其峰期变质条件为P=2.8～3.0GPa,T=730～850℃,并在抬升过程中经历了角闪岩-麻粒岩相的叠加;大量年代学研究显示其峰期变质时代为485～500Ma.南阿尔金高压麻粒岩分布在巴什瓦克地区,包括高压基性麻粒岩和高压长英质麻粒岩,它们与超基性岩构成了一个大约5km宽的构造岩石单元,与周围角闪岩相的片麻岩为韧性剪切带接触.长英质麻粒岩和基性麻粒岩的峰期组合均具有蓝晶石和三元长石(已变成条纹长石),形成的温压条件为T=930～1020℃,P=1.8～2.5GPa,并在退变质过程中经历了中压麻粒岩相变质作用叠加.锆石SHRIMP测定显示巴什瓦克高压麻粒岩的峰期变质时代为493～497Ma.都兰地区的榴辉岩分布柴北缘HP-UHP变质带的东端,在榴辉岩和围岩副片麻岩中均发现有柯石英保存,形成的峰期温压条件为T=670～730℃和P=2.7～3.25GPa,退变质阶段经过了角闪岩相的叠加;榴辉岩相变质时代为420～450Mao都兰地区的高压麻粒岩分布在阿尔茨托山西部,高压麻粒岩包括基性麻粒岩长英质麻粒岩,基性麻粒岩的峰期矿物组合为Grt+Cpx+Pl±Ky±Zo+Rt±Qtz,长英质麻粒岩的峰期矿物组合为：Grt+Kf+Ky+Pl+Qtz.峰期变质条件为T=800～925℃,P=1.4～1.85GPa,退变质阶段经历了角闪岩-绿片岩的改造,高压麻粒岩的变质时代为420～450Ma.北秦岭榴辉岩分布在官坡-双槐树一带,榴辉岩的峰期变质组合为Grt+Omp±Phe+Qtz+Rt,所计算的峰期温压条件为T=680～770℃和P=2.25～2.65GPa,年代学数据显示榴辉岩的变质时代为500Ma左右.北秦岭高压麻粒岩分布在含榴辉岩单元的南侧松树沟一带,包括高压基性麻粒岩和高压长英质麻粒岩,与超基性岩在空间上密切伴生,高压麻粒岩的峰期温压条件为T=850～925℃,P=1.45～1.80GPa,锆石U-Pb年代学研究显示其峰期变质时代为485～507Ma.以上三个实例显示,出现在同一造山带、在空间上伴生的高压麻粒岩和榴辉岩有各自不同的变质演化历史,但榴辉岩中的榴辉岩相变质时代和相邻的高压麻粒岩中的高压麻粒岩相变质作用时代相同或相近,这种成对出现的榴辉岩和高压麻粒岩代表了它们同时形成在造山带中不同的构造环境中,即榴辉岩的形成于大陆俯冲带中,而高压麻粒岩可能形成在俯冲带之上增厚的大陆地壳根部. 相似文献
10.
苏鲁高压—超高压变质地体的陆—陆碰撞深俯冲剥蚀模式 总被引：17，自引：4，他引：17
中国苏鲁高压-超高压变质地体由2个不同时代的变质基底组成.南苏鲁(临沭-连云港地区)中不同类型高压-超高压变质岩石的原岩形成于由大陆玄武质岩石、辉长岩、表壳岩和花岗岩组成的被动大陆边缘拉伸构造环境.研究表明南苏鲁高压-超高压变质岩石的原岩所代表的花岗岩浆和基性岩浆作用为罗迪尼亚超大陆形成后的新元古代(780-700Ma)裂解事件的响应.北苏鲁(青岛-威海)超高压变质地区的花岗质片麻岩锆石SHRIMPU-Pb定年表明,变质基底的年龄是2400Ma(或>2400Ma),并经历了1800-1700Ma和-200Ma的变质事件,研究表明苏鲁高压-超高压变质地体由2个不同时代变质基底组成,北苏鲁的变质基底属于北中国板块胶辽朝地块的一部分,形成时代比南苏鲁基底老得多,其与南苏鲁地块之间的界限位于五莲以北到海阳所以南一线.由于在北苏鲁含柯石英的透辉石石英岩锆石SHRIMPU-Pb定年获得精确超高压峰期变质年龄为(234.1±4.2)Ma,退变质年龄为(218.2±1.5)Ma,表明南、北苏鲁2个不同时代基底地块同时经历了超高压变质作用.根据上述事实,提出苏鲁高压-超高压变质地体的陆-陆碰撞俯冲剥蚀新模式,即扬子板片在240-220Ma的深俯冲作用中拽动上部胶辽朝板片的-部分老变质基底岩石向下俯冲至大于100km的深度,并形成楔形俯冲剥蚀体,之后又与南苏鲁俯冲板片一起快速折返上来,使胶辽朝地块的楔形俯冲剥蚀体经历了高压-超高压变质和折返退变质作用 相似文献
11.
Fabien Knoll Gilles Cuny Pierre-Olivier Mojon Raquel López-Antoñanzas 《Proceedings of the Geologists' Association. Geologists' Association》2014
The palaeontological content (charophytes and vertebrates) of organic-rich layers from the Middle Jurassic (Bathonian) of the Grands Causses at Mostuéjouls (Aveyron, France) has been examined. It is rich in gyrogonites of Porochara douzensis. The vertebrates of the lower layer include a single hybodontiform tooth, “semionotiform” teeth and scales, and one pycnodontiform tooth whereas the upper layer has yielded one hybodontiform tooth, a variety of actinopterygian remains (mostly Caturus sp. and indeterminate pycnodontiforms) and a few possible reptile remains. The variation in fauna between the two layers is ascribed to a different degree of marine influence. 相似文献
12.
Stephen K. Donovan James Isted 《Proceedings of the Geologists' Association. Geologists' Association》2014
Nineteenth-century references to clavate borings in woody substrates in the Lower Greensand of the Isle of Wight used a variety of names, but Teredo (a wood-boring bivalve, not a boring), Teredolithes (a junior synonym of Teredolites) and Gastrochaena (a bivalve borer of rock and shelly substrates, not a boring in wood) are all nomenclatorially incorrect. Borings in a beach clast derived from the Lower Greensand Group and recently collected from Sandown Bay, Isle of Wight, are referred to Teredolites isp. cf. T. longissimus Kelly and Bromley. This specimen confirms the presence of Teredolites in the Lower Greensand Group and demonstrates a common ichnological problem of beach clasts; borings, either fossil or modern, are incompletely preserved, making confident classification below the level of ichnogenus problematic. 相似文献
13.
Kyanite-rich and quartz-rich eclogites occur as lenses within amphibolite-facies quartzo-feldspathic gneisses in the Pohorje Mountains, Northern Slovenia, that form the easternmost Austroalpine basement. Major and trace elements indicate that the kyanite-rich eclogites were derived from plagioclase-rich gabbroic cumulates, whereas the quartz-rich eclogites represent more fractionated basaltic compositions. Both varieties are characterized by a LREE-depleted N-MORB type REE signature. Geothermobarometry and P-T pseudosections indicate that eclogites equilibrated at 1.8-2.5 GPa and 630-700 °C, consistently with the lack of coesite and with equilibration conditions of the chemically similar eclogites from the adjacent basement units at Koralpe and Saualpe type localities. Decompression reaction textures include (i) clinopyroxene-plagioclase intergrowths after omphacite, (ii) replacement of kyanite by corundum-plagioclase-spinel±sapphirine symplectites, (iii) breakdown of phengite to biotite-plagioclase sapphirine symplectites. The results of this study indicate that Koralpe, Saualpe and Pohorje high-pressure rocks represent former MORB-type oceanic crust that was subducted in the course of the late Cretaceous (approximately 100 Ma ago) collision between the European and the Apulian plates. 相似文献
14.
缅甸硬玉岩地区的热液型钠长石岩 总被引：2，自引：0，他引：2
产于俯冲带内的低温高压带的由单矿物构成的硬玉岩通常伴有钠长石岩,目前对于硬玉岩研究的关注度较高,而对于钠长石岩则相对较低,很少有相关论文报导.产于缅甸翡翠矿区的钠长石岩,经常与硬玉岩相伴而生,是良好的研究样品.钠长石岩的主要矿物成分是低温钠长石,其次含有硬玉、绿辉石、透辉石等辉石类矿物和钠透闪石、蓝透闪石、镁钠闪石等闪石类矿物,此外还有钠沸石等.钠长石沿着解理和裂隙交代硬玉,说明钠长石形成晚于硬玉岩.钠长岩中的主要组成矿物钠长石的形成温度小于300℃,且其形成压力小于0.5kb,推测是在硬玉岩抬升程中通过交代与沉淀作用形成.其内的透辉石有两种类型,一类可能是被交代的硬玉中的透辉石组分会渐进增加,最终形成透辉石.另一类是被绿辉石包裹的透辉石残留,其很有可能是早期来自地幔楔或者俯冲带岩石中的矿物残留,即异剥钙榴岩或辉石岩类,可以视作硬玉化绿辉石岩和硬玉化异剥钙榴岩的矿物学证据.热液型钠长石岩的存在进一步说明缅甸翡翠矿区钠化热液存在现象的普遍性与穿越性. 相似文献
15.
The origin of the genus Bos is a debated issue. From ∼ 0.5 Ma until historic times, the genus is well known in the Eurasian large mammal assemblages, where it is represented by Bos primigenius. This species has a highly derived cranial anatomy that shows important morphological differences from other Plio-Pleistocene Eurasian genera of the tribe Bovini such as Leptobos, Bison, Proamphibos-Hemibos, and Bubalus. The oldest clear evidence of Bos is the skull fragment ASB-198-1 from the middle Pleistocene (∼ 0.6-0.8 Ma) site of Asbole (Lower Awash Valley, Ethiopia). The first appearance of Bos in Europe is at the site of Venosa-Notarchirico, Italy (∼ 0.5-0.6 Ma). Although the origin of Bos has traditionally been connected with Leptobos and Bison, after a detailed anatomical and morphometric study we propose here a different origin, connecting the middle Pleistocene Eurasian forms of B. primigenius with the African Late Pliocene and early Pleistocene large size member of the tribe Bovini Pelorovis sensu stricto. The dispersal of the Bos lineage in Western Europe during middle Pleistocene times seems to coincide with the arrival of the Acheulean tool technology in this continent. 相似文献
16.
Vegetation and climate change on the Bolivian Altiplano between 108,000 and 18,000 yr ago 总被引：1，自引：0，他引：1
Alex Chepstow-Lusty Mark B. Bush Paul A. Baker Sherilyn C. Fritz James Aronson 《Quaternary Research》2005,63(1):90-98
A 90,000-yr record of environmental change before 18,000 cal yr B.P. has been constructed using pollen analyses from a sediment core obtained from Salar de Uyuni (3653 m above sea level) on the Bolivian Altiplano. The sequence consists of alternating mud and salt, which reflect shifts between wet and dry periods. Low abundances of aquatic species between 108,000 and 50,000 yr ago (such as Myriophyllum and Isoëtes) and marked fluctuations in Pediastrum suggest generally dry conditions dominated by saltpans. Between 50,000 yr ago and 36,000 cal yr B.P., lacustrine sediments become increasingly dominant. The transition to the formation of paleolake “Minchin” begins with marked rises in Isoëtes and Myriophyllum, suggesting a lake of moderate depth. Similarly, between 36,000 and 26,000 cal yr B.P., the transition to paleolake Tauca is also initiated by rises in Isoëtes and Myriophyllum; the sustained presence of Isoëtes indicates the development of flooded littoral communities associated with a lake maintained at a higher water level. Polylepis tarapacana-dominated communities were probably an important component of the Altiplano terrestrial vegetation during much of the Last Glacial Maximum (LGM) and previous wet phases. 相似文献
17.
18.
The hatchling sizes of the Cretaceous nautiloids (Hercoglossa forbesianus and Cimomia angustus; Hercoglossidae) are reported here for the first time as ranging between 20.4-22.2 mm in diameter. These new data for Hercoglossidae and the previously reported data for Nautilidae and Cymatoceratidae suggest that all Cretaceous nautiloids had large hatchlings irrespective of their taxonomy relative to those in ammonoids. Based on the relationship between hatching events and the nepionic constriction in modern nautili, the hatchling size of nautiloids can be recognized by the constriction on the shell surface of the innermost whorl. The range of hatchling diameter in all Cretaceous nautiloids (9-35 mm) is comparable to those of modern nautili (20-32 mm), although the Cretaceous nautiloids are characterized by a wider range with the smaller minimum diameter. The large hatchling size in Cretaceous nautiloids stands in marked contrast to those in ammonoids, which had much smaller hatchling size (mostly <2 mm in diameter) and became extinct at the end of the Cretaceous. Such distinct differences in reproductive strategy (i.e., hatchling and egg sizes) suggest that these differences may have played a significant role in the fate of ammonoids and nautiloids through the K/T mass extinction, as previously hypothesized by several paleontologists. 相似文献
19.
William T. Blows Kerri Honeysett 《Proceedings of the Geologists' Association. Geologists' Association》2014
A new partial skeleton of the armoured ornithischian dinosaur Polacanthus found in the Wadhurst Clay Formation (Valanginian stage) of Bexhill, Sussex is the oldest recorded occurrence of this taxon. Previous discoveries suggested that at least two armoured ornithischians occur in the Wealden succession: Polacanthus, which was mostly restricted to the Barremian, and Hylaeosaurus, which was recorded as present only in the Valanginian. The new discovery extends the stratigraphic range of Polacanthus into the Valanginian. Although these two taxa appear to be closely similar anatomically, their osteology now suggests they are not synonymous. The new specimen includes the first known jugal as well as a comparatively rare polacanthid plate/spine (splate) which probably comes from the shoulder (pectoral) area of these animals. 相似文献
20.
Paulo C. Boggiani Claudio Gaucher Alcides N. Sial Marly Babinski Cynthia M. Simon Claudio Riccomini Valderez P. Ferreira Thomas R. Fairchild 《Precambrian Research》2010
The Corumbá Group, cropping out in the southern Paraguay Belt in Brazil, is one of the most complete Ediacaran sedimentary archives of palaeogeographic, climatic, biogeochemical and biotic evolution in southwestern Gondwana. The unit hosts a rich fossil record, including acritarchs, vendotaenids (Vendotaenia, Eoholynia), soft-bodied metazoans (Corumbella) and skeletal fossils (Cloudina, Titanotheca). The Tamengo Formation, made up mainly of limestones and marls, provides a rich bio- and chemostratigraphic record. Several outcrops, formerly assigned to the Cuiabá Group, are here included in the Tamengo Formation on the basis of lithological and chemostratigraphical criteria. High-resolution carbon isotopic analyses are reported for the Tamengo Formation, showing (from base to top): (1) a positive δ13C excursion to +4‰ PDB above post-glacial negative values, (2) a negative excursion to −3.5‰ associated with a marked regression and subsequent transgression, (3) a positive excursion to +5.5‰, and (4) a plateau characterized by δ13C around +3‰. A U-Pb SHRIMP zircon age of an ash bed interbedded in the upper part of the δ13C positive plateau yielded 543 ± 3 Ma, which is considered as the depositional age ( Babinski et al., 2008a). The positive plateau in the upper Tamengo Formation and the preceding positive excursion are ubiquitous features in several successions worldwide, including the Nama Group (Namibia), the Dengying Formation (South China) and the Nafun and Ara groups (Oman). This plateau is constrained between 542 and 551 Ma, thus consistent with the age of the upper Tamengo Formation. The negative excursion of the lower Tamengo Formation may be correlated to the Shuram–Wonoka negative anomaly, although δ13C values do not fall beyond −3.5‰ in the Brazilian sections. Sedimentary breccias occur just beneath this negative excursion in the lower Tamengo Formation. One possible interpretation of the origin of these breccias is a glacioeustatic sea-level fall, but a tectonic interpretation cannot be completely ruled out. 相似文献