Milankovitch Cyclicity in Late Cretaceous Sediments from Exmouth Plateau off Northwest Australia

  1. P. L. de Boer4 and
  2. D. G. Smith5
  1. R. Boyd1,
  2. Z. Huang2 and
  3. S. O'Connell3

Published Online: 29 APR 2009

DOI: 10.1002/9781444304039.ch13

Orbital Forcing and Cyclic Sequences

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

Editor Information

  1. 4

    Utrecht, The Netherlands

  2. 5

    London, UK

Author Information

  1. 1

    Centre for Marine Geology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3J5

  2. 2

    Atlantic Geoscience Centre, Geological Survey of Canada, Bedford Institute of Oceanography, Box 1006, Dartmouth, Nova Scotia, Canada B2Y 4A2

  3. 3

    Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06457, USA

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 28 JAN 1994

ISBN Information

Print ISBN: 9780632037360

Online ISBN: 9781444304039



  • Milankovitch cyclicity in Late Cretaceous sediments of Exmouth Plateau;
  • Santonion-campanion boundary;
  • Bioturbation;
  • 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.