Palaeoenvironmental and climatic changes in Australia during the early Cretaceous

Oosting, Antje Margriet (2004) Palaeoenvironmental and climatic changes in Australia during the early Cretaceous. PhD thesis, James Cook University.

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Abstract

Scope and outline of the thesis: With the aim set for this study, the European sequence chosen as reference for global correlation is the Barremian type section at Angles, SE France (Birkelund et al., 1984). Various studies on this section, which contains a Barremian-Aptian transition interval, have already described its ammonite stratigraphy (Delanoy, 1995), δ13C isotope stratigraphy (Wissler et al., 2002), and dinocyst content (e.g. De Renéville and Raynaud, 1981; Srivastava, 1984; Wilpshaar, 1995). A corresponding stratigraphic interval was sampled at Deep Sea Drilling Project (DSDP) site 263 located on the NW Australian continental margin. To test the established bio-stratigraphic framework for Australia, further drillholes were chosen from two other depositional basins, i.e., from the Carpentaria Basin the Bureau of Mineral Resources (BMR) Mossman-1 core, and from the Eromanga Basin: Geological Survey of Queensland (GSQ) Hughenden-7, GSQ Manuka-1, and GSQ Eromanga-1, drillcores. In Chapter 2 the direct correlation between an Australian Barremian-Aptian marine section with European ammonite controlled standard successions, based on corresponding stratigraphic events in the compositional development of the dinoflagellate assemblages is presented. It outlines the correlation between the Barremian-Aptian part of DSDP site 263 in NW Australia, and the equivalent interval in the Barremian stratotype section at Angles, SE France. The correlation provides a suit of nine dinoflagellate cyst (dinocyst) index events, which are useful for cross-

hemisphere comparisons. These dinocyst events further enable age-assessment for the Australian dinocyst zonation scheme traditionally used for Austral biostratigraphic correlation. Palaeoenvironmental evaluation of the dinoflagellate cyst assemblages in DSDP site 263 indicates that the NW Australian margin was affected by cool water-currents during the Barremian-Aptian.

In Chapter 3 the established timeframe from chapter 2 is applied to BMR Mossman-1 located in northeastern Australia. Comparison of the palynostratigraphic framework, elaborated with δ13Corg data, with time equivalent Tethyan and Atlantic records shows identical bio- and geochemical stratigraphic changes and reveals an interval in BMR Mossman-1, which most likely corresponds to oceanic anoxic event (OAE) 1a. Palaeoenvironmental reconstructions are based on groups distinguished within the dinocyst and spore/pollen assemblages. These groups indicate warmer and wetter conditions prior to OAE

1a changing to cooler and drier conditions starting at the onset of OAE 1a. The δ13Corg results add new detail to global stratigraphic changes in Barremian-Aptian carbon isotope records and confirm the assumption that OAE 1a was of global extent. In comparison with the global sea-level chart of Hardenbol et al. (1998), the changes in palynology, carbon isotope stratigraphy, and lithology allow identification of variations within a third order cycle. In Chapter 4 the dinoflagellate cyst zonation as presented in chapter 2 and 3 is further tested by applying it to three cores from the Eromanga Basin in eastern Australia; GSQ Hughenden-7, GSQ Manuka-1, and GSQ Eromanga-1, respectively. The dinocyst events combined with the δ13Corg records inferred an Early Aptian to Albian age for the studied sections. The changes in palynology, isotope stratigraphy and lithology are deduced to reflect third order sea-level fluctuations. Comparison of the data with the BMR Mossman-1 core from the Carpentaria Basin reveals that the start of the mid-Cretaceous marine incursion into the Eromanga Basin is related with the earliest Aptian sea-level rise. Further comparison with time-equivalent Tethyan records shows that the Toolebuc Formation relates to OAE 1c and correlates with the inflexion point of a relative maximum sea-level fall in the earliest Late Albian. The same palaeoenvironmental groups as in the previous chapter have been used, they indicate cooler and drier conditions at the onset, changing to warmer and more humid conditions within the upper part of the Toolebuc Formation. In Chapter 5 comparison of Barremian to Albian sequences from the three Early Cretaceous depositional basins in Australia show similar variations within the δ13Corg stratigraphy as in timeequivalent Atlantic and Pacific sequences. The observed excursions in the isotope records from the European and Australian sequences can be correlated by biostratigraphic events. For the Barremian-Albian time interval eleven successive dinocyst events proof to be useful for global comparisons. Correlation of the selected results reveals similar patterns and responses in the δ13Corg records for the Tethyan, Boreal and Austral realms, and that two periods of oceanic anoxic events, representing OAE 1a and 1c, can be recognized in Australia as well. Furthermore, it enabled recognition of mid-Cretaceous stage and substage boundaries in Australia, and as such provides age assessment for the Australian dinocyst zonation scheme. The similar patterns in the carbon isotope records, and the response of the palynological assemblages from Australia and other areas to palaeoenvironmental and climatic changes during the mid-Cretaceous indicate that OAE 1a and 1c were of global extent. The first anoxic event lies within the transgressive systems tract of cycle T13, and the latter correlates to the inflexion point of the regressive R14 and following transgressive systems tract of cycle T15, indicating that the underlying driving forces for the various OAEs differ.

Item ID: 1803
Item Type: Thesis (PhD)
Keywords: global correlation, cross-hemisphere comparisons, biostratigraphy, Angles, France, Barremian-Aptian transition interval, Albian, Australia, continental margin, Carpentaria Basin, Mossman, Eromanga Basin, dinoflagellate assemblages, dinocyst events, index events, palaeoenvironmental changes, climatic changes, Oceanic Anoxic Event, palynology, carbon isotope stratigraphy, lithology, Tethyan, Boreal, Austral, realms, mid-Cretaceous
Date Deposited: 08 Jan 2008
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040311 Stratigraphy (incl Biostratigraphy and Sequence Stratigraphy) @ 0%
04 EARTH SCIENCES @ 0%
04 EARTH SCIENCES > 0403 Geology > 040308 Palaeontology (incl Palynology) @ 0%
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