High frequency sea‐level fluctuations in the Pillara Limestone, Guppy Hills, Lennard Shelf, Northwestern Australia

Abstract

The Frasnian back‐reef Pillara Limestone from Guppy Hills, Lennard Shelf, northwestern Australia consists of 267 m of biostromal limestone. Seven facies are described and these form seventy‐six interpreted shallowing‐upward cycles, with an average thickness of 3.47 metres. These cycles differ only slightly from cycles described from Menyous Gap, but more markedly from those described from Windjana Gorge. The duration of the Guppy Hills cycles is estimated to be between 26 and 33 ka. This estimate is not well constrained, but falls in the band for estimated Milankovitch frequencies, and is probably influenced by precession. The Menyous Gap and Windjana Gorge cycle durations also fall into Milankovitch frequencies, but are thought to be influenced by obliquity. A Fischer plot for the Guppy Hills cycles, shows a negative shift, suggesting an overall shallowing trend. However, there is evidence of a rapid deepening implying contemporaneous tectonic activity. Correlation between this plot and one of a similar age from the Frasnian of Canada suggests part of the plot may be recording a third‐order eustatic fluctuation.

Key words:

• Devonian
• Frasnian
• shallowing‐upward cycles
• Milankovitch
• Fischer plots
• spectral analysis

Notes

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