南极乔治王岛始新统化石山组沉积火山碎屑岩特征

南极乔治王岛化石山剖面的化石山组主要由沉积火山碎屑岩（包括沉火山角砾岩和沉凝灰岩）组成，上部夹正常沉积岩和两层薄煤层，形成从粗到细的两个沉积旋回。第１旋回的沉火山角砾岩和沉凝灰岩由不同粒级的火山岩岩屑、斜长石晶屑和细火山尘基质组成，火山碎屑物质含量在９０％以上，沉积特征显示从火山碎屑流（？）到低密度流的快速堆积性质。其中第１、２层沉凝灰岩受强烈的沸石化（浊沸石和方沸石）作用，而泥级沉凝灰岩夹层的细火山尘物质多已变成绿泥石－蒙脱石规则混层矿物；因为这种混层矿物也常常被沸石化，故其形成应在沸石化作用之前。Ｘ－衍射分析显示较多钠长石的存在。钠长石和方沸石的钠可能来自中长石被浊沸石化后释放出的Ｎａ＋。第２旋回由沉火山角砾岩、沉凝灰岩夹岩屑长石杂砂岩和薄煤层组成，显示正常沉积物经常被携入沉积盆地。第３、４层的泥级沉凝灰岩以显著的蒙皂石化为特征，沸石化作用不发育；其中的斜长石主要是中长石和（或）拉长石。化石山组泥级沉凝灰岩的微量元素组分及含量与下伏玛瑙滩组顶部安山岩的相当，但第２～３层间有某些元素迁移和富集，这可能与层间热水溶液的活动有关。Ｂ含量特别低（＜１×１０－６），不仅指示背景值低，而且也说明沉积环境与海水没有关

PETROLOGICAL CHARACTERISTICS OF THE SEDIMENTARY VOLCANICLASTIC ROCKS OF THE FOSSIL HILL FORMATION(EOCENE) IN KING GEORGE ISLAND,WEST ANTARCTICA

The typical section of the Fossil Hill Formation is at Fossil Hill between the Great Wall Station and President Frei Station in Fildes Peninsula, King George Island.The formation chiefly consists of sedimentary volcanic breccia and tuffites,intercalated with normal sedimentary rocks and two thin beds of inferior coal at the upper part.It can be divided into two cycles of sedimentation.The sedimentary volcanic breccia and tuffites in cycle Ⅰ are composed of volcanic detritus, plagioclase crystallinoclats and matrix of fine volcanic ash which reach to more than 90%.The sedimentary characteristics reflect a rapid deposition from volcaniclastic debris flow to low density flow.The coarse tuffites of Beds 1 and 2 were obviously zeolitized by laumontite and analcite. The fine volcanic ash of the mudstone like tuffite intercalations had been changed into the regularly mixed layer mineral of chlorite and montmorillonite before the zeolitization,because the mixed layer mineral was also often replaced by zeolite.In the fine tuffites of Bed 2 there are a number of albite by X ray diffraction analysis. It is inferred that Na + of albite and analcite might take its source at laumontitization of andesine. Cycle Ⅱ consists of sedimentary volcanic breccia and tufittes intercalated with greywacke as well as thin coal Beds. It reflects that normal sedimentary materials entered the basin.The mudstone like tuffites of Beds 3 and 4 are characterized by strong smectitization and poor zeolitization. Plagioclase of these rocks mostly is andesine and (or) labradorite. The composition and content of trace elements of the tuffites correspond with underlying andesite of the Agate Beach Formation. The movement and concentration of some elements in the Beds 2 and 3 are referred to the process of thermal fluid. Low content of B(<1×10 -6 ) in the section indicates that the sedimentary environment is not related to sea water. Excepting graded rhythmite, various structures are developed in Bed 2 of cycle I, such as small zeolitized “concretions” on the Bedding surface and the “window lattice like” fractures resulted from tectonic pressed stress after diagenesis which were described respectively as “rain print” and “mud crack” in the previous literature. The remain mottled structure produced by zeolitization is commonly visible in Bed 2. On the basis of petrologic and palaeontologic characteristics,the Fossil Hill formation of the Fossil Hill section probably represents a fluvio lacustrine depositional environment. It was in near shore or bay and under the warm and moist climate condition. The sedimentation was affected by both volcanic action and seasonal flood.