Late Devonian-Early Carboniferous Radiolarian Evolution And Response To The Global Bio-crisis Events In Bancheng, Guangxi

It is an important scientific problem to divide in detail the biostratigraphic zones and to establish the global comparable radiolarian zones in the Middle Devonian to Lower Carboniferous pelagic chert sequences with the thick in thickness and longer in duration at Bancheng near Qinzhong city of Guangxi, South China. During the decade geologists have much studied on the radiolarian stratigraphy, and a Helenifore laticlavium fauna for Frasnian Stage, a Holoecisicus foremanae fauna for Famennian Stage was determined by Wang et al. (Wang et al., 2000, 2003). Wu et al. (1994) have reported radiolarians from the Lower Carboniferous (Wu et al., 1994). However, how to correlate the radiolarian zones from pelagic chert sequence with the conodont zones from limestone sequence, as well as to identify the stratotype points of the Givetian-Frasnian, Frasnian-Famennian and Devonian-Carboniferous boundaries that is necessary to understand.When author recovered the radiolarians using the 5% solution of HF acid, some conodont elements ware found together with radiolarians from the chert samples in Bancheng section, therefore an idea to trance the G-F, F-F and D-C boundary in the pelagic chert sequence by both conodont and radiolarian zonations. Introduced under the professor Xia Wenchen, I measured in detail this section again in 2000. Two hundreds and twenty eight chert beds were distinguished according to variation of color, lithology and thickness, each bed was marked using paint, and 567 samples were took for recovering radiolarians and conodonts. For two years, I treated all off samples and traced these three boundaries again and again, Finally, three global comparable conodont and radiolarian sections are established respectively near the G-F, F-F and D-C boundaries by high-resolution stratigraphy. These results have exactly indicated the points of the G-F, F-F and D-C boundaries in the Bancheng chert section, and identified three radiolarian first appearance data for identifying respectively the G-F, F-F and D-C boundaries. Also seventeen radiolarian phylozones are established in range from the upper Givetian Stage to Visean Stage.The GSSP of the Mid-Upper Devonian (G-F) boundary was defined by the FAD of the conodont Ancyrodella rotundiloba (Bryant) at the GSSP in Col du Puech de la Suqus section of southeastern St. Nazaire-de-Ladarez, Montagne Noir, South France in 1986 (Klarpper et al., 1987; Ogg, 2003). This boundary was determined at the 1.80 meter level above the base of Gubi Formation in Liujing section, Guangxi, South China by the first appearance of Ancyrodella rotundiloba (Bryant) early form (Yu, et al., 2000; Jiang et al., 2000). Author has recovered conodonts Mesotaxis falsiovalis Sandberg, Ziegler & Bultynck 和 M. ovalis (Ziegler & Klarpper) from the chert bed of SE23-19 in the Bancheng section, and Mesodaxis asymmetricus (Bisehoff & Zieg!er) M ovalis (Ziegler & Klarpper) and Anryrodella rotundiloba Bryant from the chert bed of SE24-35 that is 1.40 m above the bed of SE23-19. Never conodont was found from the beds underlain the SE23-19, except the radiolarian Stigmosphearostylus hystricuosa (Aitchoson) and Tr. vetusta Hinde were recovered only from the chert bed of SE 23-34 in the Bancheng section. Therefore, I propose that the conodont falsiovalis Zone could begin with thefirst appearance of Mesotaxis falsiovalis, that is determined at the base of bed SE 23-19 in the Bacheng section. The G-F boundary is defined nat the base of the bed SE 23-35 by the first appearance of Ancyrodella rotundiloba Bryant. By this result, the ages of radiolarian zones above the G-F boundary should be exactly identified.The Frasnian-Famennian boundary is located at the top of a massive extinction horizon (upper Kellwasser horizon) that punctuated the conodont Ancyrodella and Ozarkdina genus, as we as the Geniatites genus of Gephuroceratidae and Beloceratidae of Ammonoidea. The GSSP of F-F boundary was defined at the base of bed 32a in the upper Coniatites section, Cessenon, Montagne Noir, South Frabce by the first appearance of Palma...