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Nannofossil and planktic foraminiferal biostratigraphy around the Oligocene-Miocene boundary in parts of the Indo-Pacific region

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Created 20/01/2025

Updated 20/01/2025

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Nannofossil evidence suggests that the up-sequence appearance of Globigerinoides quadrilobatus primordius is depth-related, and first occurs at a lower stratigraphic level in shallow marginal-marine than in deep oceanic sediments. The species is recorded associated with several late Oligocene nannofossil species, such as Sphenolithus ciperoensis, in three marginal-marine sections within the Indo-Pacific region; a study of the literature has revealed similar coeval occurrences elsewhere. However, evidence in deep oceanic sediments indicates that the lowest occurrence of G. quadrilobatus primordius is early Miocene in age. Globorotalia opima opima occurs with G. quadrilobatus primordius in one section; published data indicate that this overlap is repeated elsewhere. This suggests that the planktic foraminiferal Zones N.3 and N.4 should be combined into Zone N3/4, the base of which is defined by the lowest occurrence of Globigerinoides quadrilobatus primordius. To account for the difference in the timing of the lowest occurrence of G. quadrilobatus primordius in hemipelagic and oceanic sediments, changes in the thickness of the zone between the lysocline and carbonate compensation depth during the latest Oligocene, and bathymetric shifts of this zone during the earliest Miocene, are invoked. Evidence for precisely delineating the Oligocene-Miocene boundary is tenuous; the Globigerinoides datum is late Oligocene in age, contrary to the unratified recommendation of the Neogene Committee at Bologna in 1967, and at present no general agreement has been reached on nannofossil evidence to mark the boundary. For these reasons, a buffer zone representing the Oligocene-Miocene transition is suggested for the interval between the definite late Oligocene Sphenolithus ciperoensis (extinction) datum and the definite early Miocene Sphenolithus belemnos (base of range) datum. In hemipelagic sediments, this buffer zone may include several biostratigraphic events, such as the disappearance of the solution-prone Zygrhablithus bijugatus.

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Title Nannofossil and planktic foraminiferal biostratigraphy around the Oligocene-Miocene boundary in parts of the Indo-Pacific region
Language eng
Licence Not Specified
Landing Page https://devweb.dga.links.com.au/data/dataset/6ee35af9-5645-4109-ac8b-f1dd37524b26
Contact Point
Geoscience Australia
clientservices@ga.gov.au
Reference Period 20/04/2018
Geospatial Coverage
Map data © OpenStreetMap contributors
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Data Portal Data.gov.au