Cretaceous (Late Albian) coniferales of Alexander Island, Antarctica. 1: Wood taxonomy: a quantitative approach

Silicified conifer woods are very common in the mid-Cretaceous (Late Albian , 100 Ma) Triton Point Member of the Neptune Glacier Formation (Fossil Bluf f Group), SE Alexander Island, Antarctica. These occur as up to 7 m high ii ? situ tree trunks and stumps rooted in carbonaceous palaeosols and as allo chthonous logs and wood fragments in fluvial channel and sheet sandstone fa cies. Sixty-eight wood samples were examined in this study and were classif ied in terms of five form taxa using a quantitative approach. Araucarioxylo n (1.5% of specimens) is characterised by dominantly multiseriate, alternat ely arranged bordered pitting on radial tracheid walls and by 1-4 araucario id cross-field pitting. Araucariopitys (11.8% of specimens) is characterise d by dominantly uniseriate tracheid pitting with subordinate biseriate, alt ernate tracheid pitting and by 1-4 araucarioid cross-field pitting. Podocar poxylon sp. 1 (63.1% of specimens) is characterised by contiguous, uniseria te tracheid pitting and 1-2 podocarpoid cross-field pits. Podocarpoxylon sp . 2 (22.1% of specimens) is similar to P. sp. 1, differing only in that ray height is lower, tracheid pits are dominantly spaced more than one pit dia meter apart and abundant axial parenchyma is present. These first four taxa all possess growth rings with subtle boundaries. Taxodioxylon (1.5% of spe cimens) is characterised by 1-2 seriate, oppositely arranged, bordered trac heid pitting, 1-2 taxodioid cross-field pitting and very marked ring bounda ries. These woods were derived from large trees with basal stump diameters of up to 0.5 m and probable heights of up to 29 m. Data from leaf traces su ggest that Araucariopitys and Podocarpoxylon sp. 1 and sp. 2 (97% of specim ens) were evergreen with leaf retention times of > 5 years. These predomina ntly evergreen conifer forests grew in a mild, high latitude (75 degrees S) environment during the mid-Cretaceous greenhouse climate phase. (C) 2000 E lsevier Science B.V. All rights reserved.