南极乔治王岛菲尔德斯半岛几个地层划分命名问题之商榷

本文对菲尔德斯半岛群的划分提出了一个新的方案 ,时代从晚白垩世一直延续到中新世早期 ;新建立的半三角组系湖相沉积 ,孢粉及同位素年龄数据 (71 .3 +0 .3 Ma)均指示属晚白垩世后期 ,是目前所知菲尔德斯半岛出露最早的岩层 ,也是南极仅知的晚白垩世陆相沉积地层 ;据岩层区域分布、岩相及含古生物组分的差别 ,始新统化石山组可进而划分为上、下两部分 ,层型剖面仅代表该组下部地层 ,上部在别林斯高晋站油库附近出露较好 ;文中命名“苏菲尔角火山岩”以表示菲尔德斯半岛更新时代的火山活动 ,但尚需深入研究。

DISCUSSION ON STRATIGRAPHIC SUBDIVISION AND NOMENCLATURE IN FILDES PENINSULA, KING GEORGE ISLAND,ANTARCTICA

Fildes Peninsula contains subalkaline volcanic rocks and rich flora-bearing pyroclastic-sedimentary sequence which was named as Fildes Peninsula Group(FPG)(Hawkes,1961;Barton ,1965; Birkenmajer,1982; Li et al.,1989).FPG is divided into five formations and an abnormal lithostratigraphic unit based on differences in lithologic, biotic and volcanic characteristics in the present paper(table 1). 1.Upper Cretaceous Half Three Point Formation(HTPF) This formation is defined as a new lithostratigraphic unit on an inlet near Half Three Point of Fildes Peninsula of King George Island(Figs.1-3)(Shen,1991). The sedimentaty rocks cropping out consist of well-consolidated and finely laminated dark-greyish tuffites,tuffaceous siltstones and mudstones which was attributed to Eocene Fossil Hill Formation by Li and Liu (1987). The palynomorph assemblage found in the formation is of Late Cretaceous in age(probably Campanian-Maastrichtian)(Cao,1990).The isochron age of the tuffites by Rb-Sr wholerock is 71.3±0.3 Ma (Wang and Shen, in press).Therefore,HTPF probably represents the oldest beds in the Fildes Peninsula, King George Island. 2.Paleocene strata Paleocene volcanic rocks are subdivided into two formations based on volcanic charateristics and radiometric date in Fildes Peninsula (Li and Liu,1987;Liet al., 1989).The Jasper Hill Formation which is only exposed in the south western part of the peninsula consists of massive basalts and volcanic breccias, about 107m thick.So far no fossils have been found.The Agate Beach Formation is widely distributed in the peninsula.It consists largely of amygdaloidal basalts,volcanic breccias and agglomerates. The thickness of this formation ranges from 30m to 140m.Several woods have been found from pyroclasts at Northwest Platform near Collins Glacier, and at Rip Point of Nelson Island (Shen,1990).The isochron age of both formations is 64.60±1～53±1Ma (Li et al.,1989). 3.Eocene strata Eocene volcanic-sedimentary sequence consists of two formations (Fossil Hill Formation and Block Hill Formation). Fossil Hill is a famous locality with the occurrence of flora and bird footprints. Fossil Hill Formation (FHF) can be further subdivided into lower and upper parts based on lithology,depositional environment and biotas in the present paper.The strata outcropped in the type area only represent the lower part of formation which is composed of a suit of volcano-clastic sediments, basically from coarse to fine in ascending order, interbedded with coal seams, about 12.5m in thickness. The rock outcropping near the Rocky Cove with a visible thickness over 36m possible represent the upper part of the FHF, where a good section is exposed during the austral summer. They are largely composed of tuff containing fossil flora, coarse volcaniclastic and interbedded lavas. With the exception of the spore pollen and flora, no other fossils were found from this locality. Both Rocky Cove and Fossil Hill have a similar Eocene floral assemblage, but the former being slightly younger than the latter based on the stratigraphical sequence and floral differentiation, although relationships between both strata are not directly shown.The plant-bearing tuffs in Rocky Cove extend northeastward to the Artigas Station(Uruguay) near Suffied Point and to the margin of Collins Glacier. The volcaniclastic rocks in the west side of Ardley Island are probably related to those of Rocky Cove and Suffied Point. The clastic lavas of the Block Hill Formation, only 35m thick,are a product of autoclasis of top, bottom and tongue parts of the lavas(Li et al.,1989). 4.Miocene volcanic rocks An isotopic age(22.06Ma) obtained from the lavas in the Suffied Point (Zheng et al.,1991) provides leads for further study on the Oligocene or Miocene volcanic rocks in Fildes Peninsula. In this paper,the rocks was provisionally named as "Suffied Point Volcanics",reflecting Late Oligocene or Early Miocene volcanism of the peninsula.