New dates for Permian palynostratigraphic biozones in the Sydney, Bowen, Gunnedah, Galilee and Canning basins, Australia  

Authors / CoAuthors

Laurie, J.R. | Bodorkos, S. | Nicoll, R.S. | Crowley, J. | Mantle, D.J. | Mory, A.J. | Wood, G. | Holmes, E. | McKellar, J. | Phillips, L. | Smith, T.E. | Stephenson, M.

Abstract

Australia has some of the best documented Permian basins in Gondwana, but much of the succession is nonmarine. Calibration of the local palynostratigraphic scheme (Price, 1997) to the global timescale was indirect and very difficult, having traditionally relied on correlations from relatively sparse, high-latitude, marine strata, within which ammonoids and conodonts are rare, fusulinids are unknown, and much of the other fauna (brachiopods, bivalves) is endemic. Tie points are rare and often tenuous (Mantle et al., 2010): one example is the record of a single specimen of the ammonoid Cyclolobus persulcatus from the Cherrabun Member of the Hardman Formation, in the Canning Basin, Western Australia (Foster and Archbold, 2001), dated as ¿post-Guadalupian¿ by Glenister et al. (1990) and ¿Capitanian¿Dzhulfian¿ by Leonova (1998). In eastern Australia, the Permian succession is replete with felsic ash beds, many of which contain zircons. Ash beds are rare in Western Australia, but some have been found in the Canning Basin. Sampling of ash beds has been coupled with sampling of adjacent clastics for palynomorphs, mostly from drillcore and coalmines in the Sydney, Gunnedah, Bowen and Galilee basins in eastern Australia, and drillcore in the Canning Basin in Western Australia. The zircons have been subjected to the Chemical Abrasion-Isotope Dilution Thermal Ionisation Mass Spectrometry (CA-IDTIMS) technique for U-Pb dating (Mattinson, 2005). The resultant radioisotopic dates, with associated palynostratigraphic determinations, permit the direct calibration of the Price (1997) scheme to the numerical timescale. Some of the data has been cited previously (Smith & Mantle, 2013; Nicoll et al., 2015, 2016; Metcalfe et al., 2015; Phillips et al., 2016). A more detailed synthesis of the Guadalupian and Lopingian will be published soon (Laurie et al., in press) and a study of the Cisuralian is in progress. The results of Laurie et al. (in press) indicate that the palynozones in the Guadalupian and Lopingian of Australia are significantly younger than currently calibrated (Figure 1). The recalibrations indicate: 1. the top of the Praecolpatites sinuosus (APP3.2) Zone lies in the early Roadian; 2. the top of the Microbaculispora villosa (APP3.3) Zone lies in the middle Roadian; 3. the top of the Dulhuntyispora granulata (APP4.1) Zone lies in the Wordian; 4. the top of the Didecitriletes ericianus (APP4.2) Zone lies in the first half of the Wuchiapingian; 5. the entire Dulhuntyispora dulhuntyi (APP4.3) Zone lies within the Wuchiapingian; and 6. the top of the Dulhuntyispora parvithola (APP5) Zone lies at or near the Permian¿Triassic boundary. These new calibrations involve some major changes, the most significant being the base of the Dulhuntyispora parvithola (APP5) Zone, which is about 6 million years younger than previously calibrated. A preliminary assessment of the Cisuralian, in eastern Australia, suggests that the Pseudoreticulatispora pseudoreticulata (APP2.1) Zone and the Microbaculispora trisina (APP2.2) Zone (APP2.2) are both of greater duration than previously thought. Contrastingly, the Pseudoreticulatispora confluens (APP1.2.2) Zone is older and of shorter duration than previously suggested (Mantle et al., 2010). However, at this stage this interpretation is based on relatively few dated ash beds (Figure 1). Preliminary data indicates that similar miscorrelations are also a feature of the current Mesozoic palynomorph zonation, and future work will attempt to remedy this.

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document

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101683

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Keywords

• Biostratigraphy

• Geochronology

• Permian

• CA-IDTIMS

• Published_Internal

Publication Date

2017-12-04T23:52:51

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2016-08-25T10:00:00

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Australian Government Security ClassificationSystem    

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External publication updating Permian work in Timescales CA-IDTIMS project

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geoscientificInformation

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Short publication in Timescales CA-IDTIMS project

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[-44, -9, 112, 154]

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