Abstract
A profound transformation of the marine biosphere took place during the Great Ordovician Biodiversification Event (GOBE), recognized as the longest interval of sustained biodiversification in the history of life. Successions through the Middle Ordovician Stairway Sandstone of the Amadeus Basin in central Australia and the approximately coeval to slightly younger Cashions Creek Limestone in south central Tasmania have been sampled with the aim of investigating the local expression of GOBE in different facies.
Two stratigraphic sections measured through the Stairway Sandstone were logged and systematically sampled for macrofossils. Additionally, conodont samples were collected in order to facilitate regional and international correlation. This study represents the first systematic palaeontological analysis of the Stairway Sandstone and provides new data on faunal assemblages and correlation. The study of the Cashions Creek Limestone from south central Tasmania investigates the brachiopod biodiversity in stromatoporoid mounds in the upper part of the formation and compares it with the coeval fauna entombed in the surrounding sediment.
The faunal assemblages comprise many different faunal groups, but the diversity is generally relatively low. The bivalves are the most dominant and diverse group in the central Australian fauna, whereas the brachiopods are the most dominant and diverse group in the Tasmanian fauna. Thirteen trilobite, five brachiopod, four conodont and 22 mollusc taxa have been documented from the Stairway Sandstone, whereas nine brachiopod and five mollusc taxa have been documented from the Cashions Creek Limestone. The new trilobite species Basilicus (Parabasilicus) brumbyensis sp. nov. is described along with the new brachiopod species Amadeuphyla joanae gen. et sp. nov. and Paralenorthis luritjaorum sp. nov. As well as the new bivalve species Modiolopsis pojetai sp. nov. and Sthenodonta paenesymmetrica sp. nov. All new species derive from the Stairway Sandstone. Several other trilobites, brachiopods and bivalves, described in open nomenclature, probably represent new species, but the preservation and low number of specimens prevent formal definition of additional new taxa.
Although highly endemic at species level, the investigated brachiopod, trilobite and mollusc faunas display a high degree of overall similarity at generic level with Middle Ordovician faunas from North China. Other palaeocontinents with similar generic signatures include Laurentia, South China, Kazakhstan and southern Gondwanan margins.
The studied Australian faunas do not exhibit a particular high marine biodiversity during this part of GOBE. It may be related to local palaeoenvironmental conditions, but as the investigated environments are rather dissimilar the study indicates that GOBE is not particularly well-expressed in the Middle Ordovician in Australia - at least not at a local scale.
Two stratigraphic sections measured through the Stairway Sandstone were logged and systematically sampled for macrofossils. Additionally, conodont samples were collected in order to facilitate regional and international correlation. This study represents the first systematic palaeontological analysis of the Stairway Sandstone and provides new data on faunal assemblages and correlation. The study of the Cashions Creek Limestone from south central Tasmania investigates the brachiopod biodiversity in stromatoporoid mounds in the upper part of the formation and compares it with the coeval fauna entombed in the surrounding sediment.
The faunal assemblages comprise many different faunal groups, but the diversity is generally relatively low. The bivalves are the most dominant and diverse group in the central Australian fauna, whereas the brachiopods are the most dominant and diverse group in the Tasmanian fauna. Thirteen trilobite, five brachiopod, four conodont and 22 mollusc taxa have been documented from the Stairway Sandstone, whereas nine brachiopod and five mollusc taxa have been documented from the Cashions Creek Limestone. The new trilobite species Basilicus (Parabasilicus) brumbyensis sp. nov. is described along with the new brachiopod species Amadeuphyla joanae gen. et sp. nov. and Paralenorthis luritjaorum sp. nov. As well as the new bivalve species Modiolopsis pojetai sp. nov. and Sthenodonta paenesymmetrica sp. nov. All new species derive from the Stairway Sandstone. Several other trilobites, brachiopods and bivalves, described in open nomenclature, probably represent new species, but the preservation and low number of specimens prevent formal definition of additional new taxa.
Although highly endemic at species level, the investigated brachiopod, trilobite and mollusc faunas display a high degree of overall similarity at generic level with Middle Ordovician faunas from North China. Other palaeocontinents with similar generic signatures include Laurentia, South China, Kazakhstan and southern Gondwanan margins.
The studied Australian faunas do not exhibit a particular high marine biodiversity during this part of GOBE. It may be related to local palaeoenvironmental conditions, but as the investigated environments are rather dissimilar the study indicates that GOBE is not particularly well-expressed in the Middle Ordovician in Australia - at least not at a local scale.
| Original language | English |
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| Publisher | Natural History Museum of Denmark, Faculty of Science, University of Copenhagen |
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| Number of pages | 209 |
| Publication status | Published - 2013 |