Calcareous nannofossil biostratigraphy: an assessment of foraminiferal and sedimentation events in the Eocene of the Otway Basin, southeastern Australia

From a study of middle to late Eocene calcareous nannofossil assemblages in four sections in the Otway Basin of southeastern Australia, a sequence of biostratigraphic events has been deduced, spanning the interval from the lowest appearance of Cyclicargolithus reticulatus (middle Eocene) to the disappearance of Discoaster saipanensis (latest Eocene). The sequence is compared with its coumerpart in New Zealand, and is placed against the planktic foraminiferal P. zones of the tropics. The previously determined foraminiferal biostratigraphy of the sections studied has been compared with the nannofossil biostratigraphy, and, as a result, the local highest appearance of the foraminiferid Acarinina primitiva is now placed in zone P. l3 of the tropics , and not P.12 or P.14, as previously. The disappearance up the section of the foraminiferid Acarinina collactea is found to be locally inconsistent with other evidence. During the middle Eocene, marine ingressions, represented by isolated nannofossil assemblages, occurred in the Gambier Embayment of the western Otway Basin, but did not reach the Browns Creek area, eastern Otway Basin, attesting to the diachroneity of Eocene marine sedimentation in the basin . The diachroneity is also indicated by transgressive rock units in the Gambier Embayment. The ingressions seem to coincide with a major change in the sea-floor spreading rate south of Australia. During the latest middle to early late Eocene, a major transgression began synchronously in widely separated areas across the basin. The upper Eocene section in the Gambier Embayment represents condensed sedimentation and ends in a sharp disconformity, indicated by the simultaneous disappearance of Cyclicargolithus reticulatus and Discoaster saipanensis. At Browns Creek, that part of the section between the highest appearances of C. reticulatus and D. saipanensis is thick, suggesting relatively rapid rates of sedimentation. However, in the expanded part of the section at Browns Creek and also at Castle Cove, there is evidence that extreme shoal conditions existed as a result of imbalance between sedimentation and subsidence. During the middle and late Eocene, conditions along the Australian southern margin were generally temperate, with surface-water temperature decreasing eastward, and the depositional environment was essentially shallow marine - nearshore or shelf.

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Date (Publication)
1983-01-01T00:00:00
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Geoscience Australia Persistent Identifier/https://pid.geoscience.gov.au/dataset/ga/81130

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Bureau of Mineral Resources, Geology and Geophysics

 Canberra
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Shafik, S.

 1
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BMR Journal of Australian Geology and Geophysics

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8:1:1-17

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Commonwealth of Australia (Geoscience Australia)
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Commonwealth of Australia (Geoscience Australia)

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  • Earth Sciences

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4.0

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2018-11-01T00:00:00
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English
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Australian Government Security ClassificationSystem

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2018-11-01T00:00:00
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https://www.protectivesecurity.gov.au/Pages/default.aspx

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Unclassified

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urn:uuid/fae9173a-7047-71e4-e044-00144fdd4fa6

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English
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UTF8
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Commonwealth of Australia (Geoscience Australia)

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AGSO BMR Journal

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eCatId/81130

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https://ecat.ga.gov.au/geonetwork/srv/eng/catalog.search#/metadata/fae9173a-7047-71e4-e044-00144fdd4fa6

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2018-04-20T06:10:04
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2014-06-03T00:00:00

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AU/NZS ISO 19115-1:2014

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ISO 19115-1:2014

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ISO 19115-3

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Geoscience Australia Community Metadata Profile of ISO 19115-1:2014

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Version 2.0, September 2018

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https://pid.geoscience.gov.au/dataset/ga/122551

 
 

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