Milankovitch Cyclicity in Late Cretaceous Sediments from Exmouth Plateau off Northwest Australia
- P. L. de Boer4 and
- D. G. Smith5
Published Online: 29 APR 2009
Copyright © 1994 The International Association of Sedimentologists
Orbital Forcing and Cyclic Sequences
How to Cite
Boyd, R., Huang, Z. and O'Connell, S. (1994) Milankovitch Cyclicity in Late Cretaceous Sediments from Exmouth Plateau off Northwest Australia, in Orbital Forcing and Cyclic Sequences (eds P. L. de Boer and D. G. Smith), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304039.ch13
Utrecht, The Netherlands
- Published Online: 29 APR 2009
- Published Print: 28 JAN 1994
Print ISBN: 9780632037360
Online ISBN: 9781444304039
- Milankovitch cyclicity in Late Cretaceous sediments of Exmouth Plateau;
- Santonion-campanion boundary;
- Carbon content of dark and light beds;
- Diagenetic overprint
Well-developed early Campanian to early Maastrichtian pelagic cyclic sediments were recovered from Hole 762C on the Exmouth Plateau, off northwest Australia during Ocean Drilling Program (ODP) Leg 122. The cycles consist of nannofossil chalk (light beds) and clayey nannofossil chalk (dark beds), which are strongly to moderately bioturbated, alternating on a decimetre scale, and exhibit gradual boundaries. Trace fossils, which introduced material from a bed of one colour into an underlying bed of another colour, and differences in composition between the light and dark beds indicate that the cycles in these sediments are a depositional feature rather than a diagenetic outcome.
Walsh spectral analysis was applied to the upper Campanian–lower Maastrichtian cyclic sediments to examine the regularity of the cycles. With an average sedimentation rate of 1.82 cm/ka in this interval, the most predominant wavelengths of the colour cycles yield periods of around 21 ka and 41 ka, respectively, comparable to the precession and obliquity cycles, strongly suggesting an orbital origin for the cycles.
On the basis of sedimentological evidence and plate tectonic reconstructions, we propose the following mechanism for the formation of the cyclic sediments during the Late Cretaceous in this region. The cyclic variations in insolation in response to periodic orbital changes controlled the alternation of two prevailing climates in the area. During the wetter, equable and warmer climatic phases under high insolation, more clay minerals and other terrestrial materials were produced on land and supplied by higher runoff to an ocean with low bioproductivity, and the dark clayey beds were deposited. During the drier and colder climatic phases under low insolation, fewer clay minerals were produced and supplied to the ocean, bioproductivity was increased, and the light beds were deposited.