A review of the Sarawak Cycles: History and modern application

Abstract

This review examines the history of the Sarawak “Cycles” and their application in subdividing offshore Cenozoic stratigraphy. The Cycles are widely but inconsistently used, at least in part because important reports and data collections were never published (e.g. Geiger, 1964; Hageman et al., 1987; Hageman maps, 1985, eventually reproduced in Madon, 1999 and Hutchison, 2005; and Taylor et al., 1997) or were published in highly abridged summaries only (Ho Kiam Fui, 1978; Hageman, 1987; Mansor et al., 1999). The lack of a data-audit trail left open possibilities for ambiguity and confusion, as has been commented on by several workers (e.g. Snedden et al., 1995; Ismail & Tucker, 1999). This account reviews the major contributions, published and unpublished, and the concepts of the Cycles, especially over times of geological change. The data behind the model is cited in order to give confidence when integrating Sarawak stratigraphic data into a regional geological model. The Cycles began with an assumption that transgressions over regressive surfaces were distinct and approximately synchronous events for correlation. By including biostratigraphic data these transgressive events could be traced into clay-dominated areas, where lithological and seismic contrast was weak. This integrated approach was carried out through the 1970’s and 80’s, during which time the data pushed the model towards a three dimensional view of sedimentation, with the basin shape evolving and changing through time. However, development of a full tectono-stratigraphic model paused during the period of accelerated seismic capabilities of the 1990’s and early 21st Century. While geophysical data coverage increased, application of geological analyses decreased, and the integrated approach lost momentum. This review aims to re-establish the role of the Cycles as a part of a large scale geological model. An initial integration with regional geological events is attempted, linking some of the Cycle boundaries with times of known tectonic change.