Gymnosperm woods from the Cretaceous (mid-Aptian) Cerro Negro Formation, Byers Peninsula, Livingston Island, Antarctica: the arborescent vegetation of a volcanic arc

Silicified gymnosperm trunks usually more than 30 cm in diameter and several metres in length occur abundantly in the lower part of the mid-AptianCerroNegroFormation, which crops out on ByersPeninsula, LivingstonIsland, northern Antarctic Peninsula. These fossil woods are found within silicic ignimbrites, tuffs and lapilli-tuffs interpreted as the product of hot pyroclastic flows, and in silicic and andesitic conglomerates interpreted as fluvially-reworked volcanic sediments. A detailed quantitative study of the wood taxonomy has revealed the presence of three form genera, Araucarioxylon,Podocarpoxylon , and Sahnioxylon. The former two genera represent the conifer families Araucariaceae and Podocarpaceae respectively and the latter probably belongs to the extinct gymnosperm order Bennettitales. These wood genera represent the remains of the arborescentvegetation, which grew on the margins of an active pyroclastic volcanic cone near the edge of the mid-Cretaceous Antarctic Circle (palaeolatitude 62°S)

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

Silicified conifer woods are very common in the mid-Cretaceous (LateAlbian, 100 Ma) Triton Point Member of the Neptune Glacier Formation (Fossil Bluff Group), SE AlexanderIsland, Antarctica. These occur as up to 7 m high in situ tree trunks and stumps rooted in carbonaceous palaeosols and as allochthonous logs and wood fragments in fluvial channel and sheet sandstone facies. Sixty-eight wood samples were examined in this study and were classified in terms of five form taxa using aquantitativeapproach. Araucarioxylon (1.5% of specimens) is characterised by dominantly multiseriate, alternately arranged bordered pitting on radial tracheid walls and by 1–4 araucarioid cross-field pitting. Araucariopitys (11.8% of specimens) is characterised by dominantly uniseriate tracheid pitting with subordinate biseriate, alternate tracheid pitting and by 1–4 araucarioid cross-field pitting. Podocarpoxylon sp. 1 (63.1% of specimens) is characterised by contiguous, uniseriate 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 diameter apart and abundant axial parenchyma is present. These first four taxa all possess growth rings with subtle boundaries. Taxodioxylon (1.5% of specimens) is characterised by 1–2 seriate, oppositely arranged, bordered tracheid pitting, 1–2 taxodioid cross-field pitting and very marked ring boundaries. 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 suggest that Araucariopitys and Podocarpoxylon sp. 1 and sp. 2 (97% of specimens) were evergreen with leaf retention times of >5 years. These predominantly evergreen conifer forests grew in a mild, high latitude (75°S) environment during the mid-Cretaceous greenhouse climate phase

Leaf phenology of some mid-Cretaceous polar forests, Alexander Island, Antarctica

The leaf longevity and seasonal timing of leaf abscission within a plant community is closely related to climate, a phenomenon referred to as leaf phenology. In this paper the leaf phenology of some mid-Cretaceous (late Albian) forests which grew at latitude of 75° S on Alexander Island, Antarctica, is analysed. Five independent techniques for determining leaf longevity are applied to the fossil remains of each of the canopy-forming trees. These techniques utilize: (1) the anatomical character of growth rings in trunk woods, (2) leaf trace persistence in juvenile branch and stem woods, (3) leaf physiognomy, (4) comparison with nearest living relatives, and (5) leaf taphonomy. The application of techniques 1–5 suggests that the araucarian and podocarp conifers, which comprised more than 90 % of the canopy-forming vegetation, were evergreen with leaf retention times in excess of 5–13 years. The application of techniques 3–5 to rare taxodioid conifers indicates the existence of both evergreen and deciduous habits in this group, whilst both ginkgos and taeniopterids, which are locally abundant, are interpreted as possessing a deciduous habit. The polar forests of Alexander Island were therefore dominantly evergreen. Preliminary analysis of five other mid-Cretaceous polar forests suggests the presence of dominantly evergreen vegetation in Australia and Antarctica, and mixed evergreen– deciduous vegetation in Alaska, northern Russia and New Zealand. Cold month mean temperature probably exerted the largest influence on the leaf phenology at each of these forest sites

Fire-prone plant communities and palaeoclimate of a Late Cretaceous fluvial to estuarine environment, Pecinov quarry, Czech Republic

The botanical identity and facies distribution of fossil charcoal is described from Middle to Late Cenomanian (90–94 Ma) fluvial to estuarine units at Pecínov quarry, near Prague, Czech Republic. Braided alluvial facies associations contain charred conifer woods (family Pinaceae) possibly derived from upland forest fires, and abundant charred angiosperm woods, flowers and inflorescences (families Lauraceae and ?Platanaceae) derived from riparian gallery forest fires (Unit 2). Retrogradational coastal salt marsh facies associations contain abundant charred conifer wood (families Cheirolepidiaceae and Cupressaceae/Taxodiaceae) derived from fires in halophytic backswamp forest, and rare pinaceous charred cones and lauraceous angiosperm wood washed downstream from fires further inland (Units 3–4). Progradational coastal facies associations within an estuary mouth setting contain abundant charred conifer wood (family Cupressaceae/Taxodiaceae), common taxodiaceous conifer and angiosperm leaves, fern rachises, and lycopsid stems derived from fires in mesic backswamp taxodiaceous forests and supra-tidal fern-lycopsid thickets (Unit 5). Growth rings in angiosperm and conifer woods, leaf physiognomy and computer models indicate that climate was equable, warm and humid, but that there was a short annual dry season; most fires probably occurred during these annual drought periods. The abundance of charcoal and the diversity of taxa preserved in this state indicate that nearly all plant communities were fire-prone. Physiognomically, the Pecínov flora resembles present-day seasonally-dry subtropical forests where fires are a common occurrence

Biodiversity and terrestrial ecology of a mid-Cretaceous, high-latitude floodplain, Alexander Island, Antarctica

The biodiversity and terrestrial ecology of the Late Albian Triton Point Formation (Fossil Bluff Group), Alexander Island, Antarctica is analysed to improve our understanding of polar biomes during the mid-Cretaceous thermal optimum. This formation was deposited on a high-latitude (75°S) floodplain and consists of two facies associations, a lower braided alluvial plain unit and an upper coastal meander-belt unit. Analysis of fossil plants in well exposed palaeosols reveals the existence of spatially complex plant communities. Braidplains supported patchy, low-density (91 trees/ha) stands of podocarp and taxodioid conifers on floodbasin substrates, and conifer–cycadophyte–fern–angiosperm thickets in riparian settings. Coastal meander-belts supported medium density (568 trees/ha) podocarp–araucarian conifer forests on mature floodbasin soils, and fern–angiosperm–ginkgo thickets in riparian settings. Growth-ring analysis indicates plants experienced stressful growing conditions on the braidplain characterized by high-frequency flood events, but more favourable growing conditions on the coastal plain. Additional vegetation disturbances were caused by arthropod–fungal attack, frost and wildfire. In terms of structure, composition, ecology and productivity these predominantly evergreen, broad-leafed conifer forests bear similarities to the extant temperate rainforests of New Zealand