广西来宾瓜达鲁普统—乐平统界线地层的牙形类化石——一个独立验证报告

王成源（Wang,2000）和金玉Gan（Jin，2000）提出了关于乐平统底界定义的不同论点。为了对此进行独立的验证，卡尔加里大学微体古生物实验室对采自华南广西来宾地区瓜达鲁普统－乐平统界线地层的牙形类化石大块样品进行了处理。结果如下：1.Jinogondolella和Clarkina在样品中没有共生；2.由Jinogondolella granti演化为Clarkina postbitteri的变化发生在层115－6i；3.C.postbitteri的首次出现层位（FAD）在蓬莱滩剖面位于层115－6i上部；4.这个变化标志着一个才的生物信号和一个重要的点断演化事件。Jinogondolella granti演化为Clarkina postbitteri的事件很可能是受瓜达鲁普统与乐平统之交的海平面降至最低水位所触发和控制。层115－6i下部为较浅水相颗粒灰岩，代表瓜达鲁普统末期层序高位域之顶或上覆层序低位域之底部。作为Clarkina属的第一个代表，Clarkina postbitteri是界线地层中最易识别的种之一，而Clarkina postbitterigkp带的识别较容易和稳定一致。Clarkina postbitteri和Clarkina dukouensis可以通过基于锯齿型式，居群和个体发育的分类体系来加以稳定地区分。Clarkina postbitteri和Clarkina dukouensis之间的过渡是渐变的，其间的分界点只能人为地确定，如果采用这样一个人为确定的点来定义全球界线层型（GSSP），将难以稳定一致地对其加以识别。来自层114.6-6k的被Wang(2000)鉴定为Clarkina dukouensis的标本应当是C. postbitteri，或精确地可能是C. postbitteri的一个新亚种，没有争议的Clarkina dukouensis在蓬莱滩剖面最早出现于层114－7e。从生物演化和层序地层的角度看，C. postbitteri的首次出现层位（FAD）是瓜达鱼普统和乐平统界线在最清楚的侯选位置。

CONODONTS AROUND THE GUADALUPIAN-LOPINGIAN BOUNDARY IN LAIBIN AREA, SOUTH CHINA: A REPORT OF INDEPENDENT TEST

Wang (2000) and Jin (2000) presented very different arguments regarding the definition for the base of the Lopingian Series. Large samples have been collected from the Guadalupian Lopingian boundary interval in Laibin area, Guangxi, South China and processed at the micropaleontology laboratory at the University of Calgary as an independent test for the boundary position. The results are as follows: 1. no overlap between Jinogondolella and Clarkina species has been found from the samples; 2. the change from Jinogondolella granti to Clarkina postbitteri occurs in Bed 115 6i; 3. the FAD of C. postbitteri occurs in the upper part of Bed 115 6i at the Penglaitan section, and 4. this change marks a distinct biotic signature and a major punctuated evolutionary event. It is very likely that this Jinogondolella to Clarkina evolutionary event is triggered or controlled by the lowstand of sea level that marks the Guadalupian Lopingian boundary interval. The lower part of Bed 115 6i is the top of the late Guadalupian sequence where very shallow grainstone carbonate forms the top of the HST or the early LST of the overlying sequence. As the first representative of Clarkina, Clarkina postbitteri is one of the most easily recognized species within the boundary interval, and the Clarkina postbitteri Zone is well established and can be easily and consistently recognized. Clarkina postbitteri and Clarkina dukouensis can be differentiated consistently with a taxonomic system that emphasizes denticulation of the carina, the need to view the entire population and the recognition of ontogenetic changes. The transition between Clarkina postbitteri and Clarkina dukouensis is gradual and the point that Clarkina postbitteri becomes Clarkina dukouensis can only be picked arbitrarily. Such an arbitrary point, if used as the definition for the GSSP, would be very difficult to recognize consistently. Specimens illustrated from Bed 114.6 6k by Wang (2000) as Clarkina dukouensis are here regarded as C. postbitteri , but it is possible that they could be referred to as a new subspecies of C. postbitteri. The first undisputed Clarkina dukouensis occurs in Bed 114 7e at the Penglaitan Section. The FAD of Clarkina postbitteri is the clearest possible boundary position for the Guadalupian Lopingian boundary in terms of biologic evolution and from a sequence stratigraphic perspective.