32


Journal of Paleontology 90(1):31–42


mainland than any other factors. The Late Cretaceous and early Paleogene molluscan faunas of the Chatham Islands are essen- tially tectonically controlled facies faunas relating to the separation of Zealandia from Marie Byrd Land, West Antarc- tica, with their origins reflecting the divergent plate motions and the resultant deposition of volcaniclastic, transgressive sedi- ments along the Chatham Peninsula/Chatham Rise during this interval (Stilwell, 1997; Consoli and Stilwell, 2011). Links with the early Paleocene ‘Wangaloan’ assemblages are relatively weak, except for bivalves such as Nemocardium (Pratulum) and gastropods, such as ‘Pyropsis,’ Taieria, Polinices (Polinella), Amaea, Volutomitra, and Zemacies. Most of the Red Bluff Tuff assemblages comprise a dominance of suspension-feeding bivalves at approximately 96% and carnivorous (39%) and browsing-grazing gastropods (34%), including the carnivorous volute described in this paper, Teremelon onoua n. sp. In the next section, the new volutes in this paper are placed in their appropriate tectono-stratigraphic context, and also following, their significance in terms of early Paleogene, post K-Pg molluscan composition in the Austral Realm.


Tectono-stratigraphic setting of Zealandia in the Paleogene


Figure 1. The ‘Zealandia’ region and location of the mostly submerged Chatham Rise (CR) and Chatham Islands, New Zealand. LHR, Lord Howe Rise; NR, Norfolk Ridge; ChP, Challenger Plateau; NI, North Island (New Zealand); SI, South Island (New Zealand); CP, Campbell Plateau. Adapted from Stilwell and Consoli (2012).


the greenhouse phase during the early Paleogene, there was still a warm-water element to the molluscan composition of 28% for bivalves and 25% for gastropods during this time, and subse- quently, lower levels of global distributions of clams and snails, and thus a 23% and 6.5% cosmopolitan component, respec- tively (Stilwell, 2003). At species level, nearly every recorded invertebrate from the Paleocene of New Zealand is endemic, including the crinoid Metacrinus sp. (Stilwell et al., 1994) and the decapod Glyphea stilwelli Feldmann, 1993, the latter of which being the only record of this group in the Cenozoic, having survived the K-Pg boundary event. Possible exceptions include the cucullaeid bivalve, Cucullaea (Cucullaea) inarata Finlay and Marwick, 1937, which may be conspecific with the slightly younger Australian species from the Pebble Point Formation, C.(C.) psephea Singleton, 1943, with only minor characters differentiating the two; there is a definite, close rela- tionship. Taieria allani Finlay and Marwick, 1937, a rare, early cassid gastropod, is closely allied with a congeneric species in the Chatham Islands from the late Paleocene-early Eocene, but these taxa are probably distinct, given that the ‘Wangaloan’ species has many more tubercles on the periphery relative to the species from the Red Bluff Tuff. As stated by Maxwell in Campbell et al. (1993), the


differences between the coeval latest Paleocene-early eocene Mollusca of the Chatham Islands relate more to distinct litho- facies between eastern Zealandia and the New Zealand


The Late Cretaceous intervalmarked the end of the New Zealand and Chatham Rise region as a Gondwanan margin entity, due to the fragmentation of western and eastern ‘Zealandia’ (ca. 1.7 million km²; see Fig. 1) from what is now West Antarctica. Zealandia comprised collectively what is known asNewZealand, Campbell Plateau, Lord Howe Rise, Norfolk Ridge, New Caledonia, and the ChathamRise, including the ChathamIslands (Luyendyk, 1995). In terms of comparable size, Zealandia as a continental crust entity covered an area approximately half the size of Australia, comprising today 700+ islands and islets. The divergence and opening of the Tasman Sea separating Zealandia from Antarctica occurred 85–80Ma, and more refined timing recently indicates a separation time of 83.0–82.5Ma (R. Sutherland in Stilwell et al., 2006; Campbell and Hutching, 2007). This major event in the southern high latitudes created widespread block faulting and uplift, forming a series of mostly east-west trending, half-grabens (20–50km wide), which exten- ded to the Canterbury region, South Island; the uplifted basement rock and volcanic provinces served as sources for sediment fill many kilometers thick, concurrently with subsidence (see review in Stilwell and Consoli, 2012). During the Campanian to Maastrichtian stages in Zealandia, there was a dominance of a gradual transgression, as reflected in the widespread, fossilifer- ous, marine deposits of this age, relating to crustal thinning and thermal subsidence of the region and the subsequent erosion of the basement ranges, forming broad floodplains. In the Chathams’ region, there is evidence of a significant deepening event, represented by deposition of a widespread limestone (‘Unnamed Haumurian Limestone’ of Campbell et al. 1993)— a probable response to localized tectonism at a time of global eustatic sea-level fall (see Herzer and Wood, 1988; Wood et al., 1989). At the Cretaceous-Paleogene (K-Pg) boundary 66.03 Ma, Zealandia had drifted north (Chatham Islands region originally


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