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Volume 32 Issue 3
Jun.  2021
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Andrew Simpson, David Mathieson, Jiri Fryda, Barbora Frydová. Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek. Journal of Earth Science, 2021, 32(3): 512-523. doi: 10.1007/s12583-021-1310-9
Citation: Andrew Simpson, David Mathieson, Jiri Fryda, Barbora Frydová. Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek. Journal of Earth Science, 2021, 32(3): 512-523. doi: 10.1007/s12583-021-1310-9

Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek

doi: 10.1007/s12583-021-1310-9
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  • The Ireviken Event was the first Middle Paleozoic event consisting of synchronised faunal, isotopic and facies change to be recognised. An analysis of the conodont faunas throughout the Boree Creek/Borenore Limestone succession in the central western region of the Tasman fold belt of New South Wales (Australia) revealing all five conodont zones that comprise the event is presented. While some zonal boundaries are precise, allowing direct comparison of stratigraphic intervals on other paleo-continents, some can only be approximated. Conodont data from pre-Ireviken Event strata, in contrast, only permit the identification of a broad Telychian chronology. The identification of Wenlock post-Ireviken Event conodont zones is incomplete due to lithological variability, namely the presence of tuffaceous beds near the top of the formation and an unconformity between the Boree Creek and overlying Borenore Limestone. The Boree Creek Formation contains the only example of the Ireviken Event discovered to date from the Tasman fold belt of eastern Gondwanaland.
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  • Adrian, J., 1971. Stratigraphic Units of the Molong District, New South Wales. Geological Survey of New South Wales, Records, 13(4): 179-198
    Armstrong, H. A., 1990. Conodonts from the Upper Ordovician-Lower Silurian Carbonate Platform of North Greenland. Bulletin, Grønlands Geologiske Undersøgelse, 159: 1-151 doi:  10.34194/bullggu.v159.6709
    Barrick, J. E., Klapper, G., 1976. Multielement Silurian (Late Llandoverian-Wenlockian) Conodonts of the Clarita Formation, Arbuckle Mountains, Oklahoma, and Phylogeny of Kockelella. Geologica et Palaeontologica, 10: 59-100 http://www.researchgate.net/publication/284762363_Multielement_Silurian_late_Llandoverian-Wenlockian_conodonts_of_the_Clarita_Formation_Arbuckle_Mountains_Oklahoma_and_phylogeny_of_Kockelella
    Bischoff, G. C. O., 1997. Amelia mischa n. sp. (Conodonta) from Late Llandoverian and Early Wenlockian Strata of Midwestern New South Wales. Neues Jahrbuch für Geologie und Paläontologie-Monatshefte, 1997(8): 477-488. https://doi.org/10.1127/njgpm/1997/1997/477 http://www.researchgate.net/publication/293077966_Amelia_mischa_n_sp_Conodonta_from_late_Llandoverian_and_early_Wenlockian_strata_of_midwestern_New_South_Wales
    Bischoff, G. C. O., 1998. New Species of Panderodus (Conodonta) from Late Llandoverian and Early Wenlockian Strata of Midwestern New South Wales. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, 210(2): 267-288. https://doi.org/10.1127/njgpa/210/1998/267 doi:  10.1127/njgpa/210/1998/267
    Bischoff, G. C. O., 1986. Early and Middle Silurian Conodonts from Midwestern New South Wales. Courier Forschungsinstitut Senckenberg, 89: 1-337 http://www.researchgate.net/publication/308340881_Early_and_Middle_Silurian_conodonts_from_midwestern_New_South_Wales
    Brand, U., Azmy, K., Veizer, J., 2006. Evaluation of the Salinic I Tectonic, Cancañiri Glacial and Ireviken Biotic Events: Biochemostratigraphy of the Lower Silurian Succession in the Niagara Gorge Area, Canada and USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 241(2): 192-213. https://doi.org/10.1016/j.palaeo.2006.03.004 doi:  10.1016/j.palaeo.2006.03.004
    Branson, E. B., Mehl, M. G., 1933. Conodont Studies No. 1: Conodonts from the Bainbridge (Silurian) of Missouri. University of Missouri Studies, 8(1): 39-52
    Cockle, P., 1999. Conodont Data in Relation to Time Space and Environmental Relationships in the Siluran (Late Llandovery-Ludlow) Succession at Boree Creek (New South Wales, Australia). Abhandlungen der Geologischen Bundesanstalt, 54: 107-133
    Cramer, B. D., Saltzman, M. R., 2005. Sequestration of 12C in the Deep Ocean during the Early Wenlock (Silurian) Positive Carbon Isotope Excursion. Palaeogeography, Palaeoclimatology, Palaeoecology, 219(3/4): 333-349. https://doi.org/10.1016/j.palaeo.2005.01.009
    Downes, P. M., Colquhoun, G. P., Blevin, P. L., et al., 2013. Bathurst 1: 250 000 Metallogenic Map (2nd Edition), Geological Survey of New South Wales, Sydney
    Drygant, D. M., 1974. Simple Conodonts from the Silurian and Lowermost Devonian of the Volyno-Podolia. Paleontologicheskii Sbornik, 10(2): 64-70
    Frýda, J., Lehnert, O., Joachimski, M., 2015. First Record of the Early Sheinwoodian Carbon Isotope Excursion (ESCIE) from the Barrandian Area of Northwestern Peri-Gondwana. Estonian Journal of Earth Sciences, 64(1): 42-46. https://doi.org/10.3176/earth.2015.08 doi:  10.3176/earth.2015.08
    Frýda, J., Simpson, A. J., Frýdová, B., 2019. First Complete Record of the Early Sheinwoodian Carbon Isotope Anomaly from Australia. In: Petti, F. M., Innamorati, G., Carmina, B., eds., 3rd International Congress on Stratigraphy-Strati 2019: Abstract Book. Societa Geologica Italiana, Milan
    Glen, R. A., Meffre, S., Scott, R. J., 2007. Benambran Orogeny in the Eastern Lachlan Orogen, Australia. Australian Journal of Earth Sciences, 54(2/3): 385-415. https://doi.org/10.1080/08120090601147019
    Helfrich, C. T., 1975. Silurian Conodonts from the Wills Mountain Anticline, Virginia, West Virginia, and Maryland. Geological Society of America, Special Paper, 161: 1-82 http://ci.nii.ac.jp/ncid/BA55077019
    Holloway, D. J., Lane, P. D., 1998. Effaced Styginid Trilobites from the Silurian of New South Wales. Palaeontology, 41(5): 853-896
    Igo, H., Koike, T., 1967. Ordovician and Silurian Conodonts from the Langkawi Islands, Malaya, Part 1. Geology and Palaeontology of Southeast Asia. In: Kobayashi, T., Toriyama, R., eds., Geology and Palaeontology of Southeast Asia 3. University of Tokyo Press, Tokyo. 3: 1-35
    Jell, J. S., Talent, J. A., 1989. Australia: The Most Instructive Sections. In: Holland, C. H., Bassett, M. G., eds., A Global Standard for the Silurian System. National Museum of Wales, Geological Series, 9: 183-200
    Jenkins, C. J., 1978. Llandovery and Wenlock Stratigraphy of the Panuara Area, Central New South Wales. Proceedings of the Linnean Society of New South Wales, 102(3): 109-130
    Jeppsson, L., 1990. An Oceanic Model for Lithological and Faunal Changes Tested on the Silurian Record. Journal of the Geological Society, 147(4): 663-674. https://doi.org/10.1144/gsjgs.147.4.0663 doi:  10.1144/gsjgs.147.4.0663
    Jeppsson, L., 1997a. The Anatomy of the Mid-Early Silurian Ireviken Event and a Scenario for P-S Events. In: Brett, C. E., Baird, G. C., eds., Paleontologic Events-Stratigraphic, Ecological and Evolutionary Implications. Columbia University Press, New York. 451-492
    Jeppsson, L., 1997b. A New Latest Telychian, Sheinwoodian and Early Homerian (Early Silurian) Standard Conodont Zonation. Transactions of the Royal Society of Edinburgh: Earth Sciences, 88(2): 91-114. https://doi.org/10.1017/s02635933000068544 doi:  10.1017/S0263593300006854
    Jeppsson, L., 1998. Silurian Oceanic Events, Summary of General Characteristics. In: Landing, E., Johnson, M. E., eds., Silurian Cycles. New York State Museum Bulletin, 491: 239-257
    Jeppsson, L., 1984. Sudden Appearances of Silurian Conodont Lineages: Provincialism or Special Biofacies?. Geological Society of America, 196: 103-112. https://doi.org/10.1130/spe196-p103
    Jeppsson, L., Männik, P., 1993. High-Resolution Correlations between Gotland and Estonia near the Base of the Wenlock. Terra Nova, 5(4): 348-358. https://doi.org/10.1111/j.1365-3121.1993.tb00268.x doi:  10.1111/j.1365-3121.1993.tb00268.x
    Kaljo, D., Grytsenko, V., Martma, T., et al., 2007. Three Global Carbon Isotope Shifts in the Silurian of Podolia (Ukraine): Stratigraphical Implications. Estonian Journal of Earth Sciences, 56(4): 205-220. https://doi.org/10.3176/earth.2007.02 doi:  10.3176/earth.2007.02
    Kaljo, D., Kiipli, T., Martma, T., 1997. Carbon Isotope Event Markers through the Wenlock-Pridoli Sequence at Ohesaare (Estonia) and Priekule (Latvia). Palaeogeography, Palaeoclimatology, Palaeoecology, 132(1/2/3/4): 211-223. https://doi.org/10.1016/S0031-0182(97)00065-5
    Loydell, D. K., 1998. Early Silurian Sea-Level Changes. Geological Magazine, 135(4): 447-471. https://doi.org/10.1017/s0016756898008917 doi:  10.1017/S0016756898008917
    Loydell, D. K., Frýda, J., 2007. Carbon Isotope Stratigraphy of the Upper Telychian and Lower Sheinwoodian (Llandovery-Wenlock, Silurian) of the Banwy River Section, Wales. Geological Magazine, 144(6): 1015-1019. https://doi.org/10.1017/s0016756807003895 doi:  10.1017/S0016756807003895
    Männik, P., 2007. An Updated Telychian (Late Llandovery, Silurian) Conodont Zonation Based on Baltic Faunas. Lethaia, 40(1): 45-60. https://doi.org/10.1111/j.1502-3931.2006.00005.x doi:  10.1111/j.1502-3931.2006.00005.x
    Männik, P., 1998. Evolution and Taxonomy of the Silurian Conodont Pterospathodus. Palaeontology, 41(5): 1001-1050
    Männik, P., Aldridge, R. J., 1989. Evolution, Taxonomy and Relationships of the Silurian Conodont Pterospathodus. Palaeontology, 32(4): 893-906
    Molloy, P. D., 2006. Ananlysis of the Ireviken Extinction Event in the Boree Creek Formation, New South Wales, Australia based on Late Llandovery-Early Wenlock Conodonts: [Dissertation]. Macquarie University, Sydney
    Molloy, P. D., Simpson, A., 2012. An Analysis of the Ireviken Event in the Boree Creek Formation, New South Wales, Australia. Earth and Life. Springer Netherlands, Dordrecht. 615-630
    Munnecke, A., Samtleben, C., Bickert, T., 2003. The Ireviken Event in the Lower Silurian of Gotland, Sweden-Relation to Similar Palaeozoic and Proterozoic Events. Palaeogeography, Palaeoclimatology, Palaeoecology, 195(1/2): 99-124. https://doi.org/10.1016/s0031-0182(03)00304-3
    Percival, I. G., Glen, R. A., 2007. Ordovician to Earliest Silurian History of the Macquarie Arc, Lachlan Orogen, New South Wales. Australian Journal of Earth Sciences, 54(2/3): 143-165. https://doi.org/10.1080/08120090601146789
    Percival, I. G., Webby, B. D., Pickett, J. W., 2001. Ordovician (Bendigonian, Darriwilian to Gisbornian) Faunas from the Northern Molong Volcanic Belt of Central New South Wales. Alcheringa: An Australasian Journal of Palaeontology, 25(2): 211-250. https://doi.org/10.1080/03115510108619105 doi:  10.1080/03115510108619105
    Pickett, J., 1982. The Silurian System in New South Wales. Geological Survey of New South Wales, Bulletin, 29: 1-264 http://www.researchgate.net/publication/259297653_Pickett_JW_editor_1982a_The_Silurian_System_in_New_South_Wales_Bulletin_of_the_Geological_Survey_of_NSW_29_1-264
    Pogson, D. J., Watkins, J. J., 1998. Bathurst 1: 250 000 Geological Sheet. SI/55-8: Explanatory Notes. Australian Geological Survey Organisation and Geological Survey of New South Wales, SI/55-8
    Racki, G., Baliński, A., Wrona, R., et al., 2012. Faunal Dynamics across the Silurian-Devonian Positive Isotope Excursions (δ13C, δ18O) in Podolia, Ukraine: Comparative Analysis of the Ireviken and Klonk Events. Acta Palaeontologica Polonica, 57(4): 795-832. https://doi.org/10.4202/app.2011.0206 doi:  10.4202/app.2011.0206
    Saltzman, M. R., 2001. Silurian δ13C Stratigraphy: A View from North America. Geology, 29(8): 671-674. https://doi.org/10.1130/0091-7613(2001)0290671:scsavf>2.0.co;2 doi:  10.1130/0091-7613(2001)029<0671:SCSAVF>2.0.CO;2
    Savage, N. M., 1985. Silurian (Llandovery-Wenlock) Conodonts from the Base of the Heceta Limestone, Southeastern Alaska. Canadian Journal of Earth Sciences, 22: 711-727 doi:  10.1139/e85-077
    Serpagli, E., Corradini, C., 1999. Taxonomy and Evolution of Kokellela (Conodonta) from the Silurian of Sardinia (Italy). Bollettino delle Societẚ Paleontologica Italiana, 37 (2/3): 275-289
    Sherwin, L., 1971. Stratigraphy of the Cheesemans Creek District, New South Wales. Geological Survey of New South Wales, Records, 13(4): 199-237
    Sherwin, L., Rickards, B., 2002. Late Silurian (Pridoli) Graptolites from the Wallace Shale, New South Wales. Alcheringa: An Australasian Journal of Palaeontology, 26(1): 87-101. https://doi.org/10.1080/03115510208619245 doi:  10.1080/03115510208619245
    Simpson, A., 1995. Silurian Conodont Biostratigraphy in Australia: A Review and Critique. Courier Forschungsinstitut Senckenberg, 182: 325-345
    Simpson, A., 1999. Early Silurian Conodonts from the Quinton Formation, Northeastern Australia. Abhandlungen der Geologisches Bundesanstalt, 54: 181-199
    Simpson, A., Talent, J. A., 1996. Middle Palaeozoic Orogenic Events in the Southern Lachlan Fold Belt: Age Constraints from Conodont Data. Geological Society of Australia, Abstracts, 41: 396
    Simpson, A., Talent, J. A., 1995. Silurian Conodonts from the Headwaters of the Indi (Upper Murray) and Buchan Rivers, Southeastern Australia, and Their Implications. Courier Forschungsinstitut Senckenberg, 182: 79-215
    Sloan, T., Talent, J. A., Mawson, R., et al., 1995. Conodont Data from Silurian-Middle Devonian Carbonate Fans, Debris Flows, Allochthonous Blocks and Adjacent Autochthonous Platform Margins: Broken River and Camel Creek Areas, North Queensland, Australia. Courier Forschungsinstitut Senckenberg, 182: 1-78
    Talent, J. A., Berry, W. B. N., Boucot, A. J., et al., 1975. Correlation of the Silurian Rocks of Australia, New Zealand, and New Guinea. Geological Society of America Special Papers. Geological Society of America. 1-115. https://doi.org/10.1130/spe150-p1
    Talent, J. A., Mawson, R., Simpson, A., 2003a. Silurian of Australia and New Guinea. In: Landing, E., Johnson, M. E., eds., Silurian Lands and Seas-Paleogeography outside Laurentia. New York State Museum Bulletin, 493: 181-200
    Talent, J. A., Mawson, R., Simpson, A., 2003b. The "Lost" Early Ordovician-Devonian Georgetown Carbonate Platform of Northeastern Australia. Courier Forschungsinstitut Senckenberg, 242: 71-79
    Talent, J. A., Mawson, R., Andrew, A. S., et al., 1993. Middle Palaeozoic Extinction Events: Faunal and Isotopic Data. Palaeogeography, Palaeoclimatology, Palaeoecology, 104(1/2/3/4): 139-152. https://doi.org/10.1016/0031-0182(93)90126-4 http://www.sciencedirect.com/science/article/pii/0031018293901264
    Talent, J. A., Mawson, R., Simpson, A. J., et al., 2002. Palaeozoics of North East Queensland: Broken River Region. Post-5 Field Excursion Guidebook, IPC2002, July 11-17, 2002. Macquarie University Centre for Ecostratigraphy and Palaeobiology, Special Publication, 1: 1-82 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12829
    Talent, J. A., Mawson, R., 1999. North-Eastern Molong Arch and Adjacent Hill End Trough (Eastern Australia): Mid-Palaeozoic Conodont Data and Implications. Abhandlungen der Geologischen Bundesanstalt, 54: 49-105
    Trotter, J. A., Williams, I. S., Barnes, C. R., et al., 2016. New Conodont δ18O Records of Silurian Climate Change: Implications for Environmental and Biological Events. Palaeogeography, Palaeoclimatology, Palaeoecology, 443: 34-48. https://doi.org/10.1016/j.palaeo.2015.11.011 doi:  10.1016/j.palaeo.2015.11.011
    Valentine, J. L., Brock, G. A., Molloy, P. D., 2003. Linguliformean Brachiopod Faunal Turnover across the Ireviken Event (Silurian) at Boree Creek, Central-Western New South Wales, Australia. Courier Forschungsinstitut Senckenberg, 242: 301-328
    Vandenberg, A. H. M., 1998. The Benambran Deformation, Eastern Lachlan Fold Belt: Some Observations on a Complex Event. Geological Society of Australia, Abstracts, 49: 449
    Vecoli, M., Riboulleau, A., Versteegh, G. J. M., 2009. Palynology, Organic Geochemistry and Carbon Isotope Analysis of a Latest Ordovician through Silurian Clastic Succession from Borehole Tt1, Ghadamis Basin, Southern Tunisia, North Africa: Palaeoenvironmental Interpretation. Palaeogeography, Palaeoclimatology, Palaeoecology, 273(3/4): 378-394. https://doi.org/10.1016/j.palaeo.2008.05.015
    Walker, W. B., 1959. Palaeozoic Stratigraphy of the Area to the West of Borenore, NSW. Journal and Proceedings of the Royal Society of New South Wales, 93(1-4): 39-46
    Walliser, O., 1964. Conodonten des Silurs. Abhandlungen der Hessischen Landesamtes für Bodenforschung, 41: 1-106
    Wenzel, B., 1997. Isotopenstratigraphische Untersuchungen an Silurischen Abfolgen Und Deren Paläozeanographische Interpretation. Erlanger Geologische Abhandlungen, 129: 1-117
    Wenzel, B., Joachimski, M. M., 1996. Carbon and Oxygen Isotopic Composition of Silurian Brachiopods (Gotland/Sweden): Palaeoceanographic Implications. Palaeogeography, Palaeoclimatology, Palaeoecology, 122(1/2/3/4): 143-166. https://doi.org/10.1016/0031-0182(95)00094-1
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Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek

doi: 10.1007/s12583-021-1310-9

Abstract: The Ireviken Event was the first Middle Paleozoic event consisting of synchronised faunal, isotopic and facies change to be recognised. An analysis of the conodont faunas throughout the Boree Creek/Borenore Limestone succession in the central western region of the Tasman fold belt of New South Wales (Australia) revealing all five conodont zones that comprise the event is presented. While some zonal boundaries are precise, allowing direct comparison of stratigraphic intervals on other paleo-continents, some can only be approximated. Conodont data from pre-Ireviken Event strata, in contrast, only permit the identification of a broad Telychian chronology. The identification of Wenlock post-Ireviken Event conodont zones is incomplete due to lithological variability, namely the presence of tuffaceous beds near the top of the formation and an unconformity between the Boree Creek and overlying Borenore Limestone. The Boree Creek Formation contains the only example of the Ireviken Event discovered to date from the Tasman fold belt of eastern Gondwanaland.

Andrew Simpson, David Mathieson, Jiri Fryda, Barbora Frydová. Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek. Journal of Earth Science, 2021, 32(3): 512-523. doi: 10.1007/s12583-021-1310-9
Citation: Andrew Simpson, David Mathieson, Jiri Fryda, Barbora Frydová. Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek. Journal of Earth Science, 2021, 32(3): 512-523. doi: 10.1007/s12583-021-1310-9
  • The Early Silurian Ireviken Event is one of the most profound intervals of species turnover during the Paleozoic that has been identified to date. Jeppsson(1990, 1984) first developed an oceanic model for the Silurian based on observed patterns of change in conodont faunas through time. He proposed two types of stable and four types of unstable oceanic states, the former referred to as an "episode" and the latter, an "event". He (Jeppsson, 1998) postulated strong causal links between the characteristics of an event and the preceding and subsequent episodes. Events exhibited an internal architecture of datum planes and step-wise sequential extinction of conodont taxa. Although the model was derived to explain the patterns of chronology of conodont taxa in the intensely sampled Gotland succession, geographic terms were applied to event nomenclature so as not to limit the effectiveness of these terms with non-specialists (Jeppsson, 1998, p. 240).

    The Ireviken Event is associated with a prominent early Sheinwoodian carbonate carbon isotope anomaly that reaches up to +5 δ13C (Munnecke et al., 2003). This perturbation of carbon cycle has been reported from different parts of Laurussia, including its Laurentian part (e.g., Brand et al., 2006; Saltzman, 2001), the Baltoscandian Basin (e.g., Racki et al., 2012; Kaljo et al., 2007; Munnecke et al., 2003) and the Avalonian part of Laurussia (e.g., Loydell and Frýda, 2007). There is one study from tropical Gondwana (New South Wales; Talent et al., 1993) and only two records from higher latitudes of peri-Gondwana (Frýda et al., 2015) and Gondwana (Vecoli et al., 2009; Wenzel, 1997). The only available geochemical measurements from eastern Gondwana are 5 elevated δ13Ccarb values reported by Talent et al. (1993) from the Boree Creek Formation, a unit of limestones and volcaniclastic sediments from the Middle Paleozoic Waugoola Group, in the Lachlan fold belt of central western New South Wales, Australia. The only closely sampled conodont data from eastern Gondwana through this time interval also comes from the Boree Creek Limestone (Molloy, 2006; Cockle, 1999; Bischoff, 1986).

  • The stratigraphy of the Boree Creek Formation has been considered in several papers, principally by Walker (1959), Sherwin (1971), Talent et al. (2003a, 1993, 1975), Pickett (1982), Bischoff (1986), Holloway and Lane (1998), Jell and Talent (1989), Cockle (1999), and Valentine et al. (2003). Talent et al. (1975) and Pickett (1982) have covered discussion on the relationship of the Boree Creek Formation to other units.

    The Boree Creek Formation (Sherwin, 1971) is a Silurian unit of limestones and volcaniclastic sediments forming part of the Middle Paleozoic Waugoola Group (Pogson and Watkins, 1998; Jenkins, 1978) in the Lachlan fold belt of central western New South Wales, Australia. This suite of rocks is interpreted as representing a marginal platform to deep water sequence (Downes et al., 2013) formed through the deposition of strata from the accretion of the intra-oceanic Macquarie arc to the Gondwana Plate (Glenn et al., 2007).

    The Boree Creek Formation (Figs. 1 and 2) unconformably overlies volcanics and volcaniclastics of the Cheesemans Creek Formation (Sherwin, 1971) dated as Late Ordovician on graptolite evidence (Percival and Glen, 2007; Percival et al., 2001). The formation is unconformably overlain by the Borenore Limestone, a bedded to massive and brecciated unit of carbonates with a thickness of up to 600 m (Pickett, 1982) that is believed to be the lateral equivalent of the Mirrabooka Formation and the Molong Limestone (Pickett, 1982; Talent et al., 1975).

    Figure 1.  Regional geological map of the Boree Creek area (after Cockle, 1999 and Molloy and Simpson, 2012) showing the location of Kalinga Gully and the stratigraphic sequence sampled (Fig. 3).

    Three informal units have previously been identified within the Boree Creek Formation (Sherwin, 1971) in ascending order: (1) the lowest, limestone unit A, essentially equivalent to the Rosyth Limestone of Walker (1959), consists of thinly bedded nodular limestones rich in fossils including small brachiopods and corals topped by a reddish coarse grained limestone (Cockle, 1999); (2) tuffaceous trilobite bed; (3) limestone unit B, a thin to moderately thickly bedded, partially dolomotised interval of limestones (Bischoff, 1986).

    This three-fold subdivision (Sherwin, 1971) was largely adopted by subsequent authors such as Pickett (1982), Bischoff (1986), Holloway and Lane (1998) and Cockle (1999). These three units are easy to discriminate in the designated type section at Cheesemans Creek, however, it has been noted by a number of authors that lateral facies variation and interfingering lithologies can make the identification of unit boundaries problematic (Valentine et al., 2003; Pickett, 1982).

    The section studied in this investigation is the easternmost exposure of the Boree Creek Formation outcropping on both sides of Kalinga Gully, approximately 1 km from Borenore Caves (Fig. 2). This is the same section studied by Bischoff (1986, Section B) and also the subject of a study of linguliformean brachiopods through the Ireviken Event (Valentine et al., 2003: BM Section). The section was resampled by Molloy (2006: BM Section) in a quest for better chronologic resolution through the event using conodonts, and for partial correlation of these results with intervals on other continental blocks (e.g., Molloy and Simpson, 2012). As part of an earlier investigation of a range of Mid Paleozoic extinction events, Talent et al. (1993: BOC Section) undertook whole rock analyses for carbon and oxygen isotopes in Kalinga Gully in essentially the same position as Bischoff's (1986) B Section. This work identified a major isotopic excursion corresponding to Jeppsson's(1998, 1997a, b, 1990) Datum 2 of the Ireviken Event.

    Figure 2.  Detailed geological map of the Kalinga Gully area studied (after Molloy and Simpson, 2012).

    In Kalinga Gully, six separate lithological units of the Boree Creek Formation can be discriminated (Fig. 3). The lowermost unit is a thinly bedded argillaceous limestone. The contact with the underlying Cheesemans Creek volcanics is obscured by soil cover, but the unit was estimated to be approximately 40 m thick (Cockle, 1999), it is highly fossiliferous with pyritised foraminifers, gastropods, ostracods and brachiopods (Valentine et al., 2003). Algae, stromatoporoid fragments and silicified corals have also been reported from this interval (Valentine et al., 2003). Overlying this is a massive coarse grained red 5 m thick limestone unit. Molloy and Simpson (2012) reported subtle differences in lithology within the red limestone unit. Valentine et al. (2003) indicated that the red colour is the result of fine grained haematite iron particles and stylolites. These two units combined comprise the equivalent of Sherwin's (1971) limestone unit A (Fig. 3). Overlying the red limestone is a 5 m thick unit of fine-grained lensoidal grey limestone considered to be the basal portion of Sherwin's tuffaceous trilobite bed (Fig. 3), this unit is not present in the type section of the Boree Creek Formation. Valentine et al. (2003) reported that this unit is topped with a thin coarse-grained red limestone bed with abundant brachiopods and trilobites. This unit is overlain by a succession of poorly bedded tuffaceous calcareous sandstones representing the upper part of Sherwin's (1971) tuffaceous trilobite unit. The sandstone is composed of sub-rounded, diagenetically altered components from a reworked tuff that is set with a calcitic cement (Cockle, 1999). The tuffaceous beds are overlain by a 7 m interval of dolomitic carbonates equivalent to Sherwin's (1971) limestone unit B (Figs. 2 and 3). It is more massive and sparsely fossiliferous in comparison with underlying carbonates and, unlike other units in the formation, appears to thicken towards the west (Valentine et al., 2003). These five units were identified by Valentine et al. (2003) who concluded that limestone unit B was unconformably overlain by the marly carbonates of the Borenore Formation. However, in resampling to pursue additional conodont data, Molloy (2006) identified another smaller tuffaceous sandstone bed overlying limestone unit B and underlying the Borenore Formation in Kalinga Gully.

    Figure 3.  Stratigraphic section through Boree Creek Formation and overlying Borenore Limestone showing distribution of main conodont taxa and highest resolution biostratigraphic intervals through pre-Ireviken, Ireviken and post-Ireviken strata. BM0 is located at the top of the lowermost grey limestone. The meterage of samples taken above that in the section is expressed with positive numbers, samples from within the lowermost limestone, below BM0 are expressed with negative meterage measurements.

    As noted above, the Borenore Formation unconformably overlies the Boree Creek Formation in Kalinga Gully. It has a thickness of up to 900 m and is laterally equivalent to the primarily clastic Mirrabooka Formation (Pogson and Watkins, 1998). In the area to the west of Kalinga Gully the Borenore Formation interfingers with the latter. The Borenore Formation consists of two principle outcrop types. One is a well bedded, poorly outcropping, low relief limestone, the other is a massive, high relief and often brecciated limestone (Pickett, 1982) considered by some to possibly be the result of debris flow emplacement (e.g., Cockle, 1999). The Borenore Formation is also considered to be the lateral equivalent of the Molong Limestone (Adrian, 1971). The Mirrabooka Formation and the Borenore Formation are both overlain by the Wallace Shale (Fig. 4).

    Figure 4.  Schematic diagram showing broad relationships over time between stratigraphic units in central western New South Wales discussed in the text (after Pickett, 1982).

  • Silurian conodont zonation schemes were originally based on the presence of zonal index species. The late Llandovery to early Wenlock interval was originally based on what was interpreted as the presence of two consecutive species of the genus Pterospathodus (Walliser, 1964). While this allowed broad global correlations, much higher level biostratigraphic precision emerged with the recognition of periods of high species turnover involving a stepwise succession of faunal changes through relatively short chronological intervals (Jeppsson, 1997b; Jeppsson and Männik, 1993).

    The late Llandovery early Wenlock interval has one of the most profound Middle Paleozoic extinction events because of the impact on conodont faunas. Also known as the Ireviken Event, the stepwise faunal changes, originally identified as eight datum points (Jeppsson, 1997a) in the Gotland interval, has become the basis for a new biostratigraphic scheme offering higher level precision. The broad zones have been divided into new schema involving a hierarchy of biostratigraphic concepts encompassing superzones, zones and subzones (Männik, 2007), and also the concept of zonal groups (Jeppsson, 1997b).

    Jeppsson (1997b) identified 5 zones in a biostratigraphic scheme based on the datum points of the Ireviken Event and correlated these with other successions around the world, including Boree Creek. This was based on his examination of published and unpublished faunas of Bischoff (1986). Further developments in our understanding of the evolution of Pterospathodus (Männik, 1998; Männik and Aldridge, 1989) have allowed the subdivision of the Telychian pre-Ireviken interval, based on Baltic successions, into six zones and six subzones (Männik, 2007).

    The biostratigraphic interpretations of the Boree Creek Section given here are primarily based on the conodont faunas of Molloy (2006) augmented by faunas from earlier work (Cockle, 1999; Bischoff, 1986) from the same interval supplemented with additional collecting by us. It is clear that the Boree Creek/Borenore Limestone Section in Kalinga Gully contains pre-Ireviken, Ireviken and post-Ireviken Event strata, these are discussed separately below. However, it is worth noting that more substantial faunas are required to accurately delineate some of the high resolution biostratigraphic boundaries within the section.

    This analysis indicates that, although it is clear that conodont faunas and extinction patterns for the Ireviken Event are broadly similar to the better documented and understood equivalents, particularly from Baltica, there are still some significant differences, possibly paleogeographic in aspect, that require resolution before a more nuanced and advanced biostratigraphic understanding can emerge. Apart from some apparent differences in the range of some taxa (e.g., Pseudooneotodus bicornis, Panderodus n. sp. N), of particular relevance are the Pterospathodus faunas, specifically the absence in Australia of Pt. amorphognathoides.

    Two similar species of Pterospathodus are identified in this study, Pt. n. sp. A and Pt. rhodesi. Männik (1998, p. 1041) synonymised taxa from Boree Creek described by Bischoff (1986) as Pt. amorphognathoides with Pt. rhodesi. While the respective Pa elements show some morphological similarities, their stratigraphic ranges vary and the two forms co-occur in one interval withPt. n. sp. A as a distinct, but minor, constituent of the fauna. For this reason they are treated as a separate species with the lesser known taxon kept in open nomenclature until larger faunas provide more insights on phylogeny. Selected conodont taxa are illustrated in Fig. 5.

    Figure 5.  Boree Creek Plate explanation. A. Apsidognathus tuberculatus (Walliser, 1964), upper view of Pa element, AMF131096 from BM 9.9; B. Apsidognathus tuberculatus lobatus Bischoff, 1986, upper view of Pa element with extended anterior lobe, AMF131108 from BM 9.9; C. Aulacognathus chapini Savage, 1985, upper view of (?gerontic) Pa element, AMF131153 from BM 11.9; D. Distomodus staurognathoides (Walliser, 1964), upper view of Pa element (gamma morphotype), AMF131182 from BM 12.06; E. Kockelella ranuliformis (Walliser, 1964), upper view of Pa element, AMF131202 from BM 12.5; F. Kockelella walliseri (Helfrich, 1975), upper view of Pa element, AMF131212 from BM 60; G. Ozarkodina cadiaensis Bischoff, 1986, oblique lateral view of Pa element, AMF131218 from BM 5.05; H. Ozarkodina waugoolaensis Bischoff, 1986, inner lateral view of Pa element, AMF131246 from BM 21.4; I. Ozarkodina excavata excavata (Branson and Mehl, 1933), lateral view of Pa element, AMF131214 from BM 60.3; J. Pseudooneotodus tricornis Drygant, 1974, upper view of dextral element, AMF131251 from BM 11.09; K. Pseudooneotodus panuarensis Bischoff, 1986, upper view, AMF131257 from BM 12.5; L. Pseudooneotodus bicornis Drygant, 1974, upper view of dextral element, AMF131252 from BM 16.8; M. Pterospathodus n. sp. A, upper view of Pa element, AMF131261 from BM 4.4; N. Pterospathodus pennatus procerus (Walliser, 1964), upper view of Pa element, AMF131271 from BM 12.5; O. Pterospathodus rhodesi Savage, 1985, upper view of Pa element, AMF131316 from BM 3.65; P. Pterospathodus rhodesi Savage, 1985, upper view of Pa element, AMF131265 from BM 6.1; Q. Ansella mischa Bischoff, 1997, outer lateral view of geniculate element, AMF130973 from BM 10.9; R. Panderodus greenlandensis Armstrong, 1990, inner lateral view of aq element, AMF131020 from BM 63.5; S. Panderodus langkawiensis (Igo and Koike, 1967), lateral view of Sa element, AMF131027 from BM 11.09; T. Pseudooneontodus boreensis Bischoff, 1986, posterior view of slender element, AMF131259 from BM 11.09; U. Pseudobelodella silurica Armstrong, 1990, outer lateral view of ap element, AMF131054 from BM 3.65; all scale bars=100 μm.

  • In regards to the pre-Ireviken Event stratigraphy of the Boree Creek Formation, Simpson (1995) speculated that the grey limestone at the base of the Boree Creek Section (Fig. 2) could be celloni Zone in age. Bischoff (1986, table 8) collated Pterospathodus Pa elements with platform ledges as Pterospathodus amorphognathoides Walliser from the grey basal limestone of the formation. However, both illustrated Pa elements (Bischoff, 1986, pl. 30, fig. 19; pl. 31, fig. 22) were recovered from the overlying red limestone unit. Männik's (1998) revision of Pterospathodus reconceptualised Pt. amorphognathoides Walliser as a succession of populations including early forms with Pa elements lacking developed platforms (Männik, 1998: p. 1015). This included a number of new zonal-specific subspecies that are recognised in European successions but not, to date, outside of Europe.

    Männik (1998) synonymised Bischoff's (1986) examples of Pterospathodus celloni and Pterospathodus pennatus into the new taxon, Pterospathodus eopennatus. This species formed the basis of the oldest Telychian Superzone. None of these forms were reported by Bischoff (1986) from the Boree Creek Formation, either as illustrations or tabulations. Bischoff's (1986) 'celloni-form' Pa elements (Bischoff, 1986, pl. 29, figs. 1–8) were from Quarry Creek localities and his 'pennati- form' Pa elements (Bischoff, 1986, pl. 30, figs. 12–14, 23–30) were from Cobblers Creek localities. These are separate carbonate units of the Waugoola Group (Pogson and Watkins, 1998) cropping out to the southwest and south of the Boree Creek Formation, respectively.

    Molloy (2006) recovered two Pterospathodus Pa elements from 12.5 and 6.8 m below the top of the basal grey limestone unit interpreted as Pterospathodus?celloni. These elements are insufficient, in isolation, to allow any specific chronostratigraphic insights for the basal unit of the Boree Creek Formation other than tentatively ascribing a broad Pt. celloni Superzone age. Bischoff (1986) recovered an associated conodont fauna from the basal grey unit including Pseudolonchodina borenorensis (Bischoff), Apsidognathus tuberculatus tuberculatus Walliser, Distomodus staurognathoides (Walliser), Ozarkodina waugoolensis Bischoff, Ozarkodina cadiaensis Bischoff and Oulodus rectangularis Bischoff. Molloy (2006) recovered a similar fauna but also reported the presence of long-ranging coniform taxa of Panderodus and Walliserodus. Panderodus n. sp. A is restricted to the basal grey limestone unit (Fig. 4). Männik (2007: Fig. 1) reports three subspecies ofApsidognathus tuberculatus that range through the Pt. eopennatus Superzone and into the lower parts of the overlying Pt. celloni Superzone. Larger populations of specimens from Boree Creek are required for comparison with the Baltic material before any conclusions can be drawn.

    Unlike the basal grey unit of the Boree Creek Formation, the overlying red unit has abundant conodont faunas. Bischoff (1986) documented Apsidognathus tuberculatus ssp., Aulacognathus borenorensis Bischoff, Distomodus staurognathoides (Walliser), Pseudolonchodina borenorensis (Bishoff), Pterospathodus amorphognathoides Walliser (=Pterospathodus n. sp. A herein), Pterospathodus rhodesi Savage (=Pterospathodus latus Bischoff). Kockelella ranuliformis (Walliser) and Ozarkodina excavata excavata (Branson and Mehl) appear high in the red limestone unit.

    Molloy (2006) recorded a similar fauna from the red limestone unit (Fig. 3) including Pterospathodus pennatus procerus (Walliser), and the long-ranging coniform taxa Dapsilodus praecipuus Barrick, Dapsilodus obliquicostatus Branson and Mehl, Decoriconus fragilis Branson and Mehl, Walliserodus ssp., Panderodus recurvatus Rhodes, Panderodus unicostatus Branson and Mehl, and Panderodus langkawiensis Igo and Koike. Ansella mischa Bischoff and Panderodus dueteroconus Bischoff were restricted to the red limestone unit as was Pseudobelodella silurica Armstrong, with the exception of a single element recovered from the underlying grey limestone. Molloy (2006) noted Pterospathodus rhodesi Savage from the red limestone unit with a range just extending into the overlying limestone (i.e., Ireviken Event strata). Pterospathodus rhodesi Savage has not been recovered from the intensely sampled Baltic sections and its phylogenetic and ecological relationship with other Pterospathodus taxa is unknown.

    Based on the Pterospathodus elements from Boree Creek, Bischoff (1986) argued that the celloni and amorphognathoides zones of Walliser (1964) should be replaced by an amended definition for the former (Bischoff, 1986p. 51) and a Pterospathodus amorphognathoides-Pterospathodus latus Assemblage Zone for the latter (Bischoff, 1986, p. 54). Bischoff (1986) concluded that his stratigraphically lowest 31 samples (Bischoff's B00 to B29) and 10 samples from the overlying red limestone (his samples B29 to B38) spanned the amorphognathoides-latus Zone. Simpson (1995, p. 335) argued this redefinition was unnecessary because of the revision of Pterospathodus by Männik and Aldridge (1989) that demonstrated that not all Pa elements of Pterospathodus without platform ledges were Pt. celloni.

    It is also worth noting that Molloy and Simpson (2012) identified a datum point (Datum Point 0) not recognised in the Gotland succession within the red limestone preceding the Ireviken Event. It was at sample BM 7.65 which marks a temporary drop in the diversity of mostly coniform conodont taxa and the introduction of Aulacognathus chapini Savage and Kockelella ranuliformis Walliser (Molloy and Simpson, 2012: 624) with the latter recovered by Bischoff (1986) but not reproduced in the follow-up study of Molloy (2006).

    It has subsequently been shown that the evolution of Kockelella is more complex than previously understood. Faunas recovered to date from the Boree Creek Formation are inadequate to determine precise ages within the Llandovery for the pre-Ireviken strata represented by the thinly-bedded, basal, argillaceous grey limestone and the majority of the overlying coarse-grained red limestone. The latter unit obviously represents a late Llandovery time period due to its proximity to the Ireviken Event and most probably represents at least in part the Pterospathodus amorphognathoides amorphognathoides Zone (sensu Männik, 2007), whereas the basal grey limestone unit may represent strata of the Pterospathodus celloni Superzone and/or, towards the base of the unit, even earlier Telychian aged strata. It is anticipated that a higher resolution biostratigraphy will emerge for the pre-Ireviken Event interval with further sampling.

  • Datum 1 of the Ireviken Event is located in the red limestone between BM 9.9 and BM 10.5 (Molloy and Simpson, 2012). This coincides with the upper boundary of the Pt. amorphognathoides Zone (Männik, 2007; Jeppsson, 1997b) and represents the commencement of the Ireviken Event. The results from Molloy (2006) show a marked decline in the abundance of conodont specimens at this level. Jeppsson (1997b) identified sample B35 of Bischoff (1986) as representing the close of the pre-Ireviken interval in Boree Creek, however the decline in the diversity of taxa is evident in both samples B34 and B35.

    Datum 2, marking the upper boundary of the overlying Lower Ps. bicornis Zone, and the most dramatic reduction of conodont taxa during the event, is located between BM 11.09 and BM 11.18 (Molloy and Simpson, 2012) at the top of the red limestone (Fig. 3). This is the approximate position of the Llandovery Wenlock boundary. It coincides with the disappearance of Pterospathodus n. sp. A, Apsidognathus tuberculatus tuberculatus, Apsidognathus tuberculatus lobatus, Pseudolonchodina borenorensis, Aulacognathus chapini, Oulodus rectangularis n. ssp., and Decoriconis fragilis (which reappears higher in the section). Datum 2 is also the equivalent level of the upper boundary of Bischoff's (1986) Pterospathodus amorphognathoides-Pterospathodus latus Assemblage Zone. There is a dramatic drop in conodont diversity at this level (Molloy, 2006) impacting coniform taxa including the extinction of Ansella mischa (Bischoff, 1997) and Panderodus deuteroconus (Bischoff, 1998) and reductions in the abundance of other Panderodus species such as P. langkawiensis Igo and Koike, P. n. sp. N Jeppsson and Männik and P. recurvatus (Rhodes). Two taxa Pterospathodus rhodesi and Apsidognathus cf. A. ruginosus are found in very small numbers in strata directly above Datum 2. While this datum is known elsewhere for the extinction of Apsidognathus taxa, this Apsidognathus taxon is aberrant. Datum 2 representing the upper boundary of the Lower Ps. bicornis Zone is best interpreted, in the absence of the nominate species, as at this level, with the largest extinction impact.

    Datum 3 represents the upper boundary of the Upper Ps. bicornis Zone, and the Ps. bicornis Superzone, the oldest Wenlock conodont superzone, it is located between BM 12.00 and BM 12.06 in the light grey limestone (Molloy and Simpson, 2012). This is tentatively established between 12.00 and 12.06 where there is a decrease in abundance of most species and the last occurrence of Apsidognathus cf. A. ruginosus. This datum is only established tentatively due to the relatively few specimens of Apsidognathus cf. A. ruginosus found, however, the marked decrease in abundance is down to approximately 17% yields in comparison with the underlying sample for both coniform and non-coniform taxa (Molloy and Simpson, 2012). Jeppsson (1998, fig. 3) equates this level with extinction of Pt. amorphognathoides, whereas Pt. rhodesi is indicated as having a questionably extended range slightly above this.

    This gives a total section interval of stratigraphic exposure for the Ps. bicornis Zone at Boree Creek of around 2 m (equal to 1.6 m true thickness), finer sampling would be needed to improve the accuracy of this figure. Jeppsson (1997b) correlates Bischoff's (1986) samples B36–B38 with the Lower Ps. bicornis Zone and his samples B39, B40 with the Upper Ps. bicornis Zone.

    The UpperPs. bicornis Zone is followed sequentially by the Lower Pt. procerus Zone, then the Upper Pt. procerus Zone. Jeppsson (1997b) noted that it is often difficult to distinguish between the two, this is the case with data from the Boree Creek Section. The boundary between the Upper and Lower P. procerus zones is Datum 4 of the Ireviken Event, this can't be identified in the Boree Creek Formation on currently available data (Molloy and Simpson, 2012). The top of the Upper P. procerus Zone, the equivalent of datum 6 of the Ireviken Event is marked by the extinction of Pterospathodus and other taxa, it occurs at BM 17.2 in Boree Creek. Molloy and Simpson (2012) recognized Datum 5 (not associated with a zonal boundary) as occurring between BM 15 and BM 15.4. We can therefore infer, that with more extensive sampling, the boundary between the Upper Pt. procerus Zone and the Lower Pt. procerus zones in the Boree Creek Formation will be located somewhere between BM 12.06 and BM 15. Indirect support for the interpretation of these datum planes as boundary locations at Boree Creek is given by the extinction pf Panderodus langkawienses at BM 12.8. This is associated with Datum 3.3 (Jeppsson, 1998, fig. 3) within the Lower Pt. p. procerus Zone.

    The faunas of the Pt. procerus Superzone at Boree Creek are dominated by Pt. procerus (Walliser), various morphotypes of Distomodus staurognathoides (Walliser), Kockellela ranuliformis (Walliser) and Oulodus rectangularis (Bischoff). This superzone also marks the first appearance ofOzarkodina excavata excavata (Branson and Mehl). Unlike Ireviken Event faunas elsewhere, Ps. bicornis does not appear in the faunas until BM 16.17 high in the Pt. p. procerus Zone and Panderodus n. sp. N does not become extinct at Datum 3, the close of the Ps. bicornis Superzone, but persists to the lower parts of the Upper Pt. p. procerus Zone, i.e., up to Datum 5, as a very minor constituent of the fauna. Jeppsson (1997b) noted the presence of the Lower Pt. p. procerus Zone in Bischoff's (1986) samples B41 and B42 and the Upper Pt. procerus Zone in sample B45.

    Before the recognition of the internal architecture of the Ireviken Event and its utility in high resolution biostratigraphy, Bischoff (1986) recognised the K. ranuliformis Zone as the oldest Wenlock Zone in the Boree Creek Section. He (Bischoff, 1986, p. 58) adapted and modified the definition of Barrick and Klapper (1976) by redefining the base of the zone with the closure of the previous zone. The lower part of this zone is now recognised as part of the final (youngest) strata of the Ireviken Event.

  • The upper boundary of the Ireviken Event is marked by Datum 8 and equates with the upper boundary of the Lower K. ranuliformis Zone. Molloy and Simpson (2012) argued that on available data this boundary can't be identified with any certainty in the Boree Creek Section and speculated that the boundary representing the closure of the event might have occurred during the deposition of the tuffaceous sandstone unit. Above this level the post-Ireviken faunas of both Bischoff (1986) and Molloy (2006) are sparse, it is difficult to identify the zonal scheme of Jeppsson (1997b). However, Jeppsson (1997b) suggested that the uppermost carbonates in the Boree Creek Formation have faunas equivalent to the Upper K. ranuliformis Zone noting that the Lower K. ranuliformis Zone can be seen in Bischoff's (1986) B46 sample and the Upper K. ranuliformis Zone is probably represented in samples B63 to B77.

    Bischoff (1986) identified two distinct sequential faunas in his K. ranuliformis Zone, but did not separate them into formal subzones. The main difference between the two faunas is the single taxon of Kockelella (i.e., K. ranuliformis) in the lowermost parts of the range, and multiple taxa of this genus in the higher parts of the zone. Evolutionary developments in the genus Kockelella were the basis for subdividing much of the Wenlock and early Ludlow of North America (Barrick and Klapper, 1976). For most of the Boree Creek Formation above the Ireviken Event, only the single taxon of Kockelella has been recovered. However Bischoff (1986, table 9) recovered a single element of Kockelella latidentata Bischoff from the uppermost sample of the formation and a small number of Kockelella n. sp. A, near the top of the unit. Molloy (2006) however, only recovered K. latidentata Bischoff from the basal sample of the overlying Borenore Formation, but did record the presence of K. walliseri (Helfrich) from limestone unit B in the upper reaches of the Boree Creek Formation. Much larger faunas are required to test the more recent evolutionary scheme for this genus (Serpagli and Corradini, 1999) for this taxa to be biostratigraphically useful in the Boree Creek Section.

    Immediately above the unconformity, the limestones of the Borenore Formation have faunal elements from the uppermost K. patula Zone (Jeppsson, 1997b) and higher still, faunal elements similar to the uppermost K. walliseri range are present (Jeppsson, 1997b). Bischoff (1986, p. 61) indicated the presence of the Sheinwoodian K. amsdeni Zone within the Borenore Formation (samples B121–B129). Higher still (samples B152 and B164), Bischoff (1986, p. 62) records elements of the Ludlow taxon Kokelella variabilis Walliser. Jeppsson (1997b , p. 103) however noted this identification could be problematic. Jeppsson (1997b) concluded that the highest of Bischoff's (1986) samples (sample 175) may be close to the boundary of the Homerian O. s. sagitta Zone.

    Away from the Kalinga Gully Section Cockle (1999) also studied the Borenore Limestone and retrieved some conodont data. The DSC Section (Cockle, 1999, p. 115–116) was considered to extend throughout the entire Borenore Formation, yields were poor but both Kokelella ranuliformis and K. amsdeni were reported. Kockelella ranuliformis was also reported from a short section within the Borenore Formation that crossed from the well-bedded low relief limestone to the massive brecciated limestone (Cockle, 1999, BOR1 Section). Cockle (1999) reported the occurrence of K. ranuliformis and K. variabilis fragments from the stratigraphically highest occurrence of the Borenore Formation investigated (BN28 Section). Simpson (1995) had previously indicated the presence of a morphotype of K. ranuliformis in the mid Ludlow of Australia that largely retains the same morphology, so the co-occurrence with K. variabilis is possible.

    Elsewhere in the Borenore Formation equivalent, the Mirrabooka Formation, Cockle (1999, BUN Section) reported the occurrence of two faunas, an amorphognathoides Zone fauna and a younger fauna with long-ranging Silurian conodont taxa. The Mirrabooka shales enclosing this carbonate 'pod' have yielded mid-Ludlow, scanicus to leintwardinensis Zone, graptolites (Sherwin, 1971). The carbonates from the BUN Section (Cockle, 1999) can therefore be interpreted as cannibalised equivalents of the Boree Creek Formation (Fig. 1).

    The conodonts, from the top of the Borenore Formation (Cockle, 1999, BN28 Section) include Kockelella variabilis giving a maximum Ludlow age for the unit. Graptolites from the Wallace Shale, conformably overlying the Mirrabooka Formation east of 'Mirrabooka' homestead, were considered to be of late Přídolí age by Sherwin and Rickards (2002) specifically representing the Monograptus perneri/M. transgrediens biozones in the lower half of the formation. Pogson and Watkins (1998, p. 131) stated that the upper part of the Wallace Shale probably extends into the Early Devonian. Cockle (1999) reported a spot sample from a carbonate within the Wallace Shale, some 100 m above the base of the unit, where it conformably overlies the Mirrabooka Formation. This sample yielded Belodella anomalis Cooper, Belodella coarctata and Coryssognathus dubius. This fauna can be interpreted as either late Ludlow or Přídolí. It is the youngest Silurian conodont fauna recovered from the region to date. But, like the underlying Mirrabooka Formation, the Wallace Shale also contains carbonates that are clearly allochthonous blocks derived from pre-existing carbonate platform successions (Fig. 1). Talent and Mawson (1999, TEZ Section) documented an Early Silurian conodont fauna similar to the Boree Creek Formation with Distomodus staurognathoides, K. ranuliformis, Panderodus greenlandensis, Panderodus n. sp. A and Ozarkodina excavata excavata. Talent and Mawson (1999, Text Fig. 2) argued that the Barnby Hills Shale is a junior synonym for the Wallace Shale and this carbonate block (TEZ Section) was derived from the Nandillyan Limestone. The Wallace Shale can be considered as representing the terminal flooding facies of a Silurian transgression over much of the northern Molong Rise (Pickett, 1982).

  • As is seen in many other parts of the world, the sequential conodont extinctions through the Ireviken Event in the Boree Creek Limestone are marked by high δ13C values particularly from the Upper Ps. bicornis Zone through to the end of the Ireviken Event (Frýda et al., 2019; Frýda et al., in preparation). The linked and synchronous changes in geochemistry, biostratigraphy and facies have been well documented for the Ireviken Event in many parts of the world. Geochemical data has been known from Baltica (e.g., Munnecke et al., 2003; Loydell, 1998; Kaljo et al., 1997; Wenzel and Joachimski, 1996), Avalonia (e.g., Loydell and Frýda, 2007), Laurentia (e.g., Cramer and Saltzman, 2005) but the only geochemical results to date for east Gondwanaland are those documented by Talent et al. (1993). The Boree Creek Formation is the most prospective section discovered to date in the Tasman fold belt for understanding changes in conodont faunas during the Ireviken interval.

    In other areas of the Tasman fold belt of eastern Australia, autochthonous successions of carbonates of an appropriate age are poorly known. In the northern parts of the fold belt, late Llandovery to early Wenlock conodonts are documented mostly from allochthonous sources (Talent et al., 2003b; Simpson, 1999; Sloan et al., 1995) although one poorly constrained succession at the base of the Jack Group in the Broken River Province is known (Talent et al., 2002). In the southern region of the fold belt, Simpson and Talent (1995) speculated that the McCarty Member of the Towanga Formation could transgress the Llandovery-Wenlock boundary and provided evidence that the lower carbonate unit of the Claire Creek Limestone could extend into "post-amorphognathoides" Zone strata. Vandenberg (1998) suggested that all the carbonates in this area could be allochthonous, but Talent et al. (2003a) and Simpson and Talent (1996) argued the succession is stratigraphically and chronologically coherent.

    The relationship between these Silurian extinction events, such as the Ireviken at Boree Creek, with glaciations, sea-level change, oceanic turnover and euxinia remains unclear in terms of causality. Trotter et al. (2016) provided a discussion about the limitations of different data sets but concluded that global climate change played an important role in producing these phenomena.

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