北京十三陵——西山髫髻山组火山岩年龄及其地质意义

北京西北部地区分布着大量的火山岩,对北京西山大台和十三陵地区的髫髻山组火山岩分别进行了SHRIMP锆石U-Pb和LA-ICP-MS定年,并对十三陵地区的髫髻山组火山岩进行了地球化学研究。结果表明,十三陵地区的髫髻山组火山岩地球化学特征和北京西山髫髻山组火山岩具有相似性。火山岩地球化学特征表现为高Al_2O_3、Ca O、Na_2O,低Ti O_2和Mg O,在TAS图中落入粗安岩和英安岩区域,REE分馏明显,LREE富集,HREE亏损,Eu异常不明显,富集大离子亲石元素K、Sr、Ba,亏损高场强元素Nb、Ta、Ti,高的Sr/Y比值,同时Yb和Y的含量较低。在大台地区,分别获得了髫髻山组火山岩底部角砾岩和中部安山岩的SHRIMP锆石U-Pb年龄为152.1±1.9Ma、149±2Ma,侵入到髫髻山组下覆九龙山组地层中一闪长岩岩床年龄为149±3.2Ma;在十三陵地区,分别获得了髫髻山组底部凝灰岩、中部火山角砾岩和上部安山岩的LA-ICP-MS锆石U-Pb年龄分别为157.2±1.2Ma、155.2±1.7Ma、153.1±2.2Ma。结合前人研究,十三陵地区髫髻山组火山时代为157~153Ma,大台地区髫髻山组火山活动时间为152~137Ma,十三陵地区的火山活动时间要稍早于北京西山大台地区。大台地区和十三陵地区地球化学、地质年代学及区域地质特征表明,北京西山和十三陵地区喷发时间的差异是由于燕山运动所形成不整合面的穿时性导致的,位于髫髻山组之下的不整合是一个主不整合面。     

An integrated study of upper Campanian-lower Maastrichtian carbon isotopes and calcareous plankton biostratigraphy of the Kurdistan Region,northeastern Iraq

New carbon (δ¹³C) isotope records calibrated by planktonic bioevents provide general support for a late Campanian age assignment of the Shiranish Formation (Fm.) and its boundaries in the Dokan section (NE Iraq). The Shiranish Fm. is characterised at the base by a mid-Campanian unconformity as can be interpreted by absences of nannofossil zones CC20-21. The Shiranish Fm. then spans nannofossil biozones CC22-CC23a (UC15d-e^TP to UC16a^TP). Results obtained on carbon isotopes suggest that diagenesis affected and compromised a few carbonate samples in the uppermost 50 m of the section. However, once these samples are discarded, pristine trends suggest that the top of the section records a negative carbon isotope excursion that is interpreted as CMBa-c events that straddle the Campanian–Maastrichtian boundary. This interpretation is supported by the lowermost occurrence of planktic foraminifers Rugoglobigerina scotti and Contusotruncana contusa some 30 m above the base of the negative excursion and 10 m below a positive excursion identified as the Maastrichtian M1+ event. Discrepancies in the stratigraphic range of several planktic foraminifer bioevents are highlighted and advocate for the need of many more integrated records of planktic foraminifer and nannofossil biostratigraphy alongside carbon isotope stratigraphy in the eastern Tethys in order to improve regional and global schemes.     

关于吉林黄榆、吉昌地区石炭系磨盘山组穿时性的讨论

本文主要就吉林省永吉县至磐石市一带石炭系磨盘山组地层穿时的讨论,从沉积的石灰岩特征和所含生物化石特征阐述这套巨厚的石灰岩具有穿时特征,根据不同位置测量剖面及化石对比进一步验证了对这一问题的看法。     

山东九龙群炒米店组概念新议

山东地区寒武系-奥陶系界线以往是以三叶虫和角石生物带为依据来确定,由于在界线上下几十米难以获得这类可供鉴定的大化石,这一重要年代地层界线实际上就划在三山子组b段之底。在长清区崮山镇范庄剖面上该界线确定在炒米店组之顶界,因而山东炒米店组被定义为"上寒武统最上部的一个岩石地层单位"。近年来,在长清张夏—崮山地区、青州尧王山地区和莱芜黄羊山地区,根据牙形石"Cordylodus lindstromi"准确确定的寒武系-奥陶系界线均位于炒米店组内部,分别距炒米店组顶9.05m、58.10m和4.00m。根据上述成果和岩石地层单位命名原则,炒米店组应定义为跨寒武纪与奥陶纪的岩石地层单位。