Adkins, Rhonda Michelle (2003) Mid-Permian cyclothem development in the onshore Canning Basin, Western Australia. PhD thesis, James Cook University.

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Abstract

Earth's climate during the latter part of the Permian has long been the subject of speculation and debate. Some studies suggest that Permo-Carboniferous glaciation persisted on parts of Gondwana up to at least the Permo-Triassic boundary. Other studies argue that deglaciation occurred as early as the late Sakmarian (lower Early Permian). Many such investigations have been based upon the sometimes ambiguous occurrence of direct glacial deposits (e.g. striated clasts, tillites). In contrast, this study evaluates the likelihood of post-Sakmarian glaciation by testing high-frequency, sedimentary cycles for a glacio-eustatic driving mechanism.

The focus of this thesis is the Artinskian (upper Early Permian) Tuckfield Member of the Poole Sandstone. The Tuckfield Member is exposed around the periphery of the St George, Poole, and Grant Ranges of the Fitzroy Trough (onshore Canning Basin, Western Australia). In the St George and Poole Ranges, the Tuckfield Member outcrops as a 50 to 100 m thick package of vertically stacked, laterally continuous, coarsening- and thickening-upward cycles. In contrast, the Tuckfield Member outcrops in the Grant Range as a less than 50 m thick package of vertically stacked, laterally discontinuous, fining- and thinning-upward cycles. Primary sedimentary structures, trace fossils, and the vertical succession of facies suggest that the Tuckfield Member records shallow-marine, shorezone deposition in the St. George and Poole Ranges and non-marine, coastal plain deposition in the Grant Range.

Gamma-ray and grainsize data, collected from 17 measured outcrops (11 in the St George Ranges; 4 in the Poole Range; 2 in the Grant Range), were analyzed for cyclicity. Spectral analyses identified several orders of meter- to decameter-scale cycles in both the shallow-marine and non-marine facies. The average periodicities of the identified cycles occur in the ratio of ~36:10:4:2 m. This ratio correlates strongly with the known mid-Permian orbital periodicities of elongated eccentricity, eccentricity, obliquity, and precession (~410:100:40:20 thousand years).

Additionally, the Tuckfield Member is herein traced throughout the northern Fitzroy Trough and onto the adjacent Lennard Shelf via sub-surface data. Similar to outcrop, subsurface gamma-ray logs display several orders of meter- to decameter-scale cycles that correlate strongly with the orbital periodicities. This cyclicity is manifested by the systematic bundling of smaller-scale cycles into larger-scale cycles that can be traced laterally for more than 200 km.

For comparison, correlative shallow-marine cycles from the Artinskian to Ufimian Pebbley Beach Formation (Sydney Basin, New South Wales) were also studied. Four outcrop sections were measured and correlated, giving a total stratigraphic column of approximately 45 m. Spectral analysis of gamma-ray data identified several orders of meter- to decameter-scale cycles. These cycles correlate strongly with the mid-Permian orbital periodicities and the identified Tuckfield Member cycles.

The favorable comparison between the Tuckfield Member cycles and the orbital parameters indicates that Milankovitch-forcing of climate influenced the formation of depositional cyclicity. Furthermore, it is highly probable that these cycles are glacioeustatic in origin due to their laterally extensive nature and positive correlation with identified cyclicity in New South Wales. This suggests that Permo-Carboniferous glaciation must have persisted into at least the Ufimian stage of the Late Permian.

Item ID:	1345
Item Type:	Thesis (PhD)
Keywords:	Artinskian; Canning Basin; cyclicity; cyclothems; Fitzroy Trough; glacioeustacy; glacio-eustacy; Grant Ranges; Permian; Poole Ranges; Poole Sandstone; sedimentary cycles; St George Ranges; stratigraphy; Sydney Basin; Tuckfield Member; Western Australia
Date Deposited:	19 Jan 2007
FoR Codes:	04 EARTH SCIENCES > 0403 Geology > 040310 Sedimentology @ 33% 04 EARTH SCIENCES > 0403 Geology > 040301 Basin Analysis @ 33% 04 EARTH SCIENCES > 0403 Geology > 040311 Stratigraphy (incl Biostratigraphy and Sequence Stratigraphy) @ 34%
SEO Codes:	97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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