Special Papers in Palaeontology No. 72 Lower
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S P E C I A L P A P E R S I N P A L A E O N T O L O G Y N O . 7 2 L O W E R J U R A S S I C F L O R A S F R O M H O P E B A Y A N D B O T A N Y B A Y , A N T A R C T I C A B Y P . M . R E E S a n d C . J . C L E A L with 22 plates, 2 tables and 7 text-®gures T H E P A L A E O N T O L O G I C A L A S S O C I A T I O N L O N D O N October 2004 C O N T E N T S Page ABSTRACT 5 MATERIAL AND METHODS 5 SYSTEMATIC PALAEONTOLOGY 8 AGE OF THE HOPE BAY AND BOTANY BAY FLORAS 72 PALAEOENVIRONMENT AND PALAEOCLIMATE 78 CONCLUSIONS 82 REFERENCES 83 ABSTRACT. Hope Bay and Botany Bay, Graham Land, Antarctica have yielded two of the most diverse ¯oras known from the Jurassic. Because of its high diversity, as well as its early discovery and description Cby T. G. Halle in 1913), the Hope Bay ¯ora has served as a taxonomic standard for studies of other Mesozoic ¯oras from Gondwana. This paper presents a major revision of the Hope Bay ¯ora, based on extensive subsequent collections. A nearby ¯ora from Botany Bay is described for the ®rst time. Thirty-seven species are now recognised in the Hope Bay ¯ora and 32 from Botany Bay. The ¯oras are closely similar; 80 per cent of the Botany Bay species also occur at Hope Bay. They are shown here to be Early Jurassic, which contradicts the results of previous studies that suggested a Late Jurassic or earliest Cretaceous age. The revision of their age has special signi®cance for our understanding of the Mesozoic geological history of the Antarctic Peninsula. It also highlights the need for reappraisal of a number of other Mesozoic Gondwanan ¯oras that had been dated mainly on their close similarity to the Hope Bay ¯ora. The taxonomic work has resulted in establishment of a new combination, Taeniopteris taeniopteroides, and emendation of the diagnoses of Coniopteris oblonga, Sphenopteris nordenskjoeldii, Sphenopteris pecten and Komlopteris indica. KEY WORDS: Jurassic, palaeobotany, leaf impressions, Antarctica. H O P E Bay, northern Graham Land, Antarctica CPl. 1 ®g. 2) has yielded one of the most diverse ¯oras known from the Mesozoic. Its great diversity, as well as its early discovery and description, has made it a standard for ¯oristic and biostratigraphical studies on Mesozoic Gondwanan ¯oras. It is also important for understanding volcanic arc evolution and palaeogeography of the northern Antarctic Peninsula. The only complete descriptions published to date are by Halle C1913) and Gee C1989), based on 220 rock samples collected during the Swedish 1901±1903 expedition. Halle C1913) described 59 species, with two forms of unknown af®nity, which Gee C1989) revised to 43 species. Subsequent larger collections from Hope Bay were made by British expeditions in 1945 during Operation Tabarin and in 1946 by W. N. Croft as part of the Falkland Islands Dependencies Survey CFIDS), but these were not described. Material was also collected but not described from the nearby Botany Bay locality CPl. 1, ®g. 1), by W. N. Croft CFIDS, 1946), and by G. W. Farquharson as part of the 1979/1980 British Antarctic Survey CBAS) ®eld programme. Further material was collected by one of us CPMR) as part of the 1986/1987 BAS ®eld programme. The British collections have enabled a comprehensive account of these important ¯oras. The results formed part of a doctoral thesis CRees 1990), and some aspects have been published previously CRees 1993a±d; Rees and Cleal 1993). Dipteridaceaen ferns from Hope Bay and Botany Bay were described by Rees C1993a), and Morel et al. C1994) subsequently documented other Botany Bay specimens. However, what follows is the ®rst description of the entire Botany Bay ¯ora as currently known and the ®rst complete revision of the Hope Bay ¯ora, using new material, since Halle's C1913) monograph. M A T E R I A L A N D M E T H O D S This study is based on over 2000 rock samples from Hope Bay and Botany Bay CPl. 1; Text-®g. 1) collected between 1945 and 1987 mainly by FIDS and BAS expeditions. Some are still stored in the BAS collections at Cambridge, but the majority are now housed in The Natural History Museum, London. Nevertheless, except for some previously ®gured plant specimens, they are all still stored under their original BAS registration numbers, with a D. pre®x. Where specimens are listed in the Systematic Palaeontology section, they are only those that are ®gured and used in the descriptions. The suf®xes A and B refer to the upper and lower surface of each rock sample. To ensure complete documentation, one of us CPMR) has also examined the Halle Collection in The Natural History Museum, Stockholm. The leaf ¯oras are preserved as impressions and coali®ed compressions. Attempts to recover identi®able palynomorphs from the plant beds at Hope Bay and Botany Bay have been unsuccessful CT. H. Jefferson in Farquharson 1984; D. Guy-Ohlson in Gee 1989; Rees 1990). In addition to diagenetic processes, the Hope Bay plant beds have been affected by contact metamorphism Cto biotite grade; Farquharson 1984), so no microscopic characters Ce.g. epidermal cell structures) are preserved. Only one specimen from Botany Bay showed epidermal detail CPachypteris indica; Pl. 10). Latex and acetate replication of impression surfaces, transfer preparation and scanning electron microscopy were used on other specimens, but did not contribute any signi®cant information. [Special Papers in Palaeontology, 72, 2004, pp. 5±90, 22 pls] q The Palaeontological Association Palaeontology SP72 PALA 110841 DISK SR 12/7/4 15:02 ALDEN 6 S P E C I A L P A P E R S I N P A L A E O N T O L O G Y , 7 2 TEXT-FIG. 1. Map of Hope Bay and Botany Bay. Inset shows an Early Jurassic palaeogeographical reconstruction Cafter Rees et al. 2000) showing the location of these Antarctic sites. Also shown, for broad comparative purposes, is the location of the Middle Jurassic Stones®eld ¯ora CCleal and Rees 2003). The specimens were studied and photographed using standard binocular microscopy, ®bre optics unidirectional lighting Cto enhance venation details), cross-polarised light or immersion in industrial alcohol Cto enhance contrast between the fossil and its surrounding matrix). Specimens that proved dif®cult to photograph using these more straightforward techniques were coated with a thin layer of ammonium chloride. Specimen frequencies were measured in the Botany Bay sequence using a 0´5-m quadrat. This, combined with sedimentological observations, has enabled lithological controls on the distribution of each plant species and changes in species associations to be determined Csee Text-®g. 7). E X P L A N A T I O N O F P L A T E 1 Fig. 1. View of Botany Bay, northern Graham Land, looking west. The plant beds of the Botany Bay Group are in the foreground. Church Point, the mountain to the left of the picture, is 337 m high. Fig. 2. View of Mount Flora, Hope Bay, northern Graham Land. The man CPaul Wood) is standing on the contact between the plant-bearing beds of the Botany Bay Group Cbelow) and the volcanic rocks of the Antarctic Peninsula Volcanic Group Cabove). Palaeontology SP72 PALA 110841 DISK SR 12/7/4 15:03 ALDEN P L A T E 1 REES and CLEAL, Botany Bay and Mount Flora, Hope Bay Palaeontology SP72 PALA 110841 DISK SR 12/7/4 15:03 ALDEN 8 S P E C I A L P A P E R S I N P A L A E O N T O L O G Y , 7 2 Systematic descriptions follow standard format. Synonymy lists have been annotated using the same scheme as in Cleal and Rees C2003): *, publication of the protologue of the basionym; T, any published illustrations of the type; and }, any published records of specimens from Botany Bay or Hope Bay. Otherwise, only references that are critical for understanding the taxonomy of the species, especially as it relates to the Botany Bay and Hope Bay material, are included. The taxonomic hierarchy used is based mainly on that given in Cleal and Thomas C1999). S Y S T E M A T I C P A L A E O N T O L O G Y Division EQUISETOPHYTA Class EQUISETOPSIDA Order EQUISETALES Family EQUISETACEAE Richard ex Michaux, 1803 Genus EQUISETUM Linnaeus, 1753 Type. Equisetum ¯uviatile Linnaeus, 1753. Remarks. Watson and Batten C1990) have argued that equisetalean fossils that cannot be con®dently assigned to Equisetum should be placed in Equisetites Sternberg. However, we can see no obvious reason why our material is not cogeneric with the living plants and have therefore followed Harris C1961) and referred them to Equisetum. Equisetum laterale Phillips emend. Gould, 1968 Plate 2, ®gures 1±4 *1829 Equisetum laterale Phillips, p. 153, pl. 10, ®g. 13. }1913 Equisetites approximatus Halle, pl. 1, ®gs 6±14; text-®g. 1. 1961 Equisetum laterale Phillips; Harris, p. 20. 1965 Equisetites patagonica Herbst, pl. 1, ®gs 1, 3; pl. 2, ®gs 9±10. 1968 Equisetum laterale Phillips; Gould, p.