南极乔治王岛菲尔德斯半岛晚白垩世火山岩地层的古生物证据

南极乔治王岛菲尔德斯半岛半三角附近的火山沉积岩,首次发现孢粉、叶化石,显示出晚白垩世的组合面貌。它们表明菲尔德斯半岛存在两个时代不同的植物层,即晚白垩世半三角植物层及始新世化石山植物层;菲尔德斯半岛火山活动始自中生代后期,而不是以前认为的侏罗纪,也非第三纪早期。这也是南设得兰群岛首次发现的晚白垩世陆相古生物证据。

PALAEONTOLOGICAL EVIDENCE FOR UPPER CRETACEOUS VOLCANO-SEDIMENTARY ROCKS IN FILDES PENINSULA OF KING GEORGE ISLAND, ANTARCTICA

During the austral summer of 1987-1988, the author carried out palaeontological investigation on Fildes Peninsula of King George Island and the Northern Nelson Island. At Half Three Points located on the southeast edge of Fildes Peninsula, there two islets, on one of which the sedimentary rocks crop out with a thickness of about 5m, They mainly consist of dark-greyish tuffaceous siltstones and sandstones intercalated with carbonaceous sediments, containing pyrite and siderite, and showing fine lamellar strueture, which may belong to marsh-lacustrine deposits under a low energy and reducing condition.Many spore pollens and some leaf fossils were firstly discovered from the sedimentary intercalation of volcanic rocks at Half Three Points. The leaves comprise the following genera: Dryopteris sp., Acmopyle sp., Nothofagus sp., Dictylophyllum spp. The palynomorphs preliminarily determined includes fern (over 90%) , Deltoidospora hallii, D.Microleoides, D. regularis, D. sp., Cyathidites minor, C. sp., Osmundacidites sp., Ornatisporites sp., Asterisporites sp., Gleichiniidites senonicus, G. sp., Polypodisporites favus, P. sp.; gymnosperm ( 1-2%) , Araucariacitessp.; angiosperm ( 5%) , Nothofagidites senectus, N.nonus, N.sp., Tricolporopollenites sp. The palynomorph assemblage is characterized by abundant Gleicheniidites which was flourishing in Cretaceous. Asterisporites plays an important role in the determination of stratigraphic age. The genus is mainly distributed in Cretaceous or earlier strata. Nothofagidites firstly occurred in late Cretaceous and ranged in Tertiary and Quaternary. Therefore, the fossil-bearing beds should be of late Cretaceous age. It differs from those on Fossil Hill and near Rocky Cove on Fildes Peninsula, as the two latters belong to Eocene age.Thus, the volcanic activities seem to be set in late Mesozoic, instead of Jurassic or Paleogene in Fildes Peninsula of King George Island, The finding of flora-bearing deposits at Half Three Points fills in the gaps of late Cretaceous palynomorphs of South Shetland Islands, and is of importance for studying of geological and paleoclimatic evolutions and plate tectonics of West Antarctica.