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ISJS 5.07.Qrk ISJS Newsletter 34 (1), 2007, pp.21-33 21 The Triassic-Jurassic transition at Kunga Island, Queen Charlotte Islands, British Columbia, Canada Louise M. Longridge1, Elizabeth S. Carter2, James W. Haggart3, Paul L. Smith1 1Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia,V6T 1Z4, Canada; [email protected], [email protected] 2Department of Geology, Portland State University, Portland, Oregon, 97207-0751, USA; [email protected] 3Geological Survey of Canada, Vancouver, British Columbia, V6B 5J3; [email protected] 1. Introduction If radiolarian sequences are not selected as the pri- Several stratigraphic sections in the Queen Charlotte mary standard, then we propose that they should be con- Islands of British Columbia, Canada contain exceptional- sidered as a secondary standard and that the Kunga Island ly well-preserved radiolarian faunas that cross the section be designated as a parastratotype in order to better Triassic-Jurassic boundary (TJB). In particular, a section characterize the Triassic-Jurassic transition. In some cir- at Kunga Island shows a dramatic turnover of radiolarians cles, parastratotypes are also known as auxiliary reference that could be used to define and constrain the TJB to with- sections. In addition to radiolarians, the Kunga Island in one metre, a precision that is greater than any other fos- sequence permits the calibration of time scales based on sil group. The Kunga section was originally proposed as a ammonites, radiometric ages and, indirectly, with the car- GSSP candidate for the base of the Jurassic by Carter & bon isotope curve. The aim of designating any stratotype Tipper (1999) and again by Haggart et al. (2002). These is, of course, to provide the international community with proposals are updated here. We propose that, if radiolari- the widest spectrum of stratigraphic information that an sequences are selected as the primary standard (sensu helps both to define the boundary and to characterize it as Callomon, 1984) for defining the TJB, then the section at thoroughly as possible. This maximizes the potential for Kunga Island should be selected as GSSP. regional and global correlation. No single section is per- fect in this regard and, consequently, the International Stratigraphic Guide of the IUGS Commission on Stratigraphy (Salvador, 1994) has recognized the benefit of designating a parastrato- type. The holostratotype is the GSSP and, of course, always has precedence in defining the bound- ary. The parastratotype provides critical information not present in the holostratotype. The designation of parastratotypes is a well-estab- lished procedure and there are sev- eral examples in stratigraphic stud- ies of the Jurassic. These include the definition of the Bajocian, where the Murtinheira section at Cabo Mondego, Portugal, is the GSSP and the Bearreraig Bay section on the Isle of Skye, Scotland, is desig- nated an auxiliary stratotype (Pavia & Enay, 1997) and the establish- ment of the Lower Jurassic ammonite zonation of North America (Smith et al., 1988; Jakobs et al., 1994; Taylor et al., 2001; Longridge et al., 2006a). Below, we summarize the details of the Kunga Island section Figure 1: Localities of sections bearing latest Triassic and early Hettangian ammonite and radio- as currently understood. larian faunas in the Queen Charlotte Islands 22 faunas (Monger, 1984; Belasky, 1994; Belasky et al., 2002), Sinemurian and Pliensbachian bivalve faunas (Aberhan, 1999 and references therein), and Pliensbachian ammonite faunas (Smith & Tipper, 1986; Smith et al., 2001; Smith, 2006) tie the terrane to the Northern Hemisphere and the eastern Pacific. The distri- bution of the ammonites Sunrisites and Badouxia are additional evidence that Wrangellia was located in the eastern Pacific during the Hettangian (Taylor et al., 1984; Smith, 2006; Longridge et al., in press). 4. Tectonic history and structural setting The Kunga Island section was deposited in the Mesozoic Hecate Basin (Haggart, 1993). The basin was affected by southwest directed folding and contractional faulting in the Middle Jurassic, block faulting in the Late Jurassic, northeast-directed folding in the Late Cretaceous, and extensional block faulting and reverse faulting in the Paleogene (Thompson et al., 1991). Despite this regional deformation, the section at Kunga Island is, for the most part, structurally intact. 5. Lithostratigraphy and depositional paleoenvironment The Kunga Island section is part of the Sandilands Figure 2: Proposed stratotype section on Kunga Island. View to NE. Adopted from Smith (1998, p.188, fig.4.32). Photo E. Carter. Inserted arrow indicates the boundary level, but not exactly the stratotype point 2. Location and access The proposed section is located in the supratidal region on the southeast shore of Kunga Island (NTS 103 B/13, Zone 9; 52˚45.573’, 131˚33.638’) (Figure 1, section 1, Figure 2). Kunga Island is a small island on the southeastern edge of the Queen Charlotte Islands (QCI), British Columbia (Figure 1) and is part of Gwaii Haanas National Park Reserve. Although this means a permit is necessary prior to collecting, it also provides protection and conser- vation of the site (Haggart, in press). Access to Kunga Island involves flying into Sandspit, on Moresby Island, QCI, approximately 55km from the Kunga Island site. The section is then accessed by vehicle over about 60km of logging road and then by boat. 3. Paleogeographical context Kunga Island is part of the Wrangellia terrane, considered to be allochthonous to North America. During Triassic/Jurassic time, Wrangellia was more southerly and further outboard of its current position, relative to the cra- ton, but it was eventually accreted to North America at some time during the Middle Jurassic (van der Heyden, 1992; Thompson et al., 1991; Haggart et al., 1995), Cretaceous (Monger, 1998) or Paleogene (Ward et al., Figure 3: Proposed Kunga Island section showing upper Rhaetian and 1997). The constraints on its location at the end of the lower Hettangian radiolarian, upper Rhaetian conodont, and lower Triassic and beginning of the Jurassic are reasonably well Hettangian ammonite localities. R = radiolarians, C = conodonts, A = documented. Permian coral, brachiopod, and fusulinid ammonites. Modified after Haggart et al. (2002) and Longridge et al. (2007) 23 Radiolarian species R R R R R R R R R R R R R R R R 1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 0 1 2 3 4 5 6 Betraccium inornatum Blome X Betraccium sp. C sensu Carter 1993 X Canoptum sp. A sensu Carter 1993 X Plafkerium fidicularium Carter X Plafkerium sp. A sensu Carter 1993 X Praecitriduma apexensis Carter X Nabolella aff. desrochersi (Carter) X Entactinosphaera? amphilapes Carter X X Nabolella causia (Carter) X X Nabolella aff. causia (Carter) X X Nabolella desrochersi (Carter) X X Betraccium aff. inornatum Blome X X Ferresium sp. C sensu Carter 1993 X X Plafkerium sp. B sensu Carter 1993 < X Citriduma sp. C sensu Carter 1993 X X X Triassocrucella aff. triassicum Kozur & Mostler < X Globolaxtorum cristatum Carter X X X Amuria sp. A sensu (Carter 1993) < X X Haeckelicyrtium karcharos Carter < X X Citriduma asteroides Carter X X X X X Plafkerium keloense Carter X X XXX Spumellaria gen. et sp. indet. C sensu Carter 1993 < X Veghicyclia austriaca Kozur & Mostler X X X X Amuria sp. B sensu (Carter 1993) X X X X X Betraccium kennecottense Carter X X XXXXX Betraccium nodulum Carter X X XXXXX Betraccium sp. E sensu Carter 1993 X X X X X X X Bipedis acrostylus Bragin < X X X Bistarkum cylindratum Carter X X XXXXXXX Canoptum aff. dixoni Pessagno & Whalen X X X X X X Canoptum triassicum Yao X X X XXXX Canoptum aff. unicum Pessagno & Whalen < X X X X X X Canoptum sp. B sensu Carter 1993 X X X X X X X Cantalum gratum Carter X X X X XXX Cantalum sp. A sensu Carter 1993 < X X X Canutus? beehivensis Carter X X X X X XX Crucella? sp. A sensu Carter 1993 X X X X X X X X Deflandrecyrtium nobense Carter X X XXXXXX Deflandrecyrtium ithacanthum (Sugiyama) < XXX Entactinosphaera? aff. simoni Kozur & Mostler X X X X X X Entactinosphaera? spinulata Carter < X X X X X X Eucyrtid gen. et sp. indet sensu Carter 1993 < X X X X X X X Ferresium teekwoonense Carter X X X X X XX Fontinella clara Carter X X X XXX Fontinella louisensis Carter X X X Globolaxtorum tozeri Carter X X XXXXXXX Haliomma swellensis Carter X X XXXX Icrioma? sp. A sensu Carter 1993 X X X X X X X Figure 4: Latest Rhaetian and early Hettangian radiolarians from the proposed section at Kunga Island, Queen Charlotte Islands. < indicates range extends lower, > indicates range extends higher Formation of the Kunga Group. The Sandilands age from early Rhaetian to mostly the latest Sinemurian, Formation is several hundred metres thick and ranges in although its upper contact is diachronous and locally 24 Radiolarian species R R R R R R R R R R R R R R R R 1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 0 1 2 3 4 5 6 Pseudoheliodiscus aff. sandspitensis (Blome) < X X X X Laxtorum capitaneum Carter X X X X X XX Laxtorum perfectum Carter X X X X X XX Laxtorum porterheadense Carter X X X X X XX Liassosaturnalis aff. parvis Kozur & Mostler X X XXX Livarella densiporata Kozur & Mostler X X X X X Loupanus thompsoni Carter X X X XXXXX Orbiculiformella multibrachiata (Carter) X X X X XXX Pantanellium newkluense Carter X X X XXX Paronaella beatricia Carter < XXXXXXX Paratriassoastrum crassum Carter X X X XXX Paratriassoastrum omegaense Carter < XXXXXXXX Paratriassoastrum sp. A sensu Carter 1993 X X X X X X X X Paratriassoastrum sp.
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