Orbital Forcing on Continental Depositional System–Lacustrine and Fluvial Cyclicity in the Devonian of East Greenland
- P. L. de Boer2 and
- D. G. Smith3
Published Online: 29 APR 2009
Copyright © 1994 The International Association of Sedimentologists
Orbital Forcing and Cyclic Sequences
How to Cite
Olsen, H. (1994) Orbital Forcing on Continental Depositional System–Lacustrine and Fluvial Cyclicity in the Devonian of East Greenland, in Orbital Forcing and Cyclic Sequences (eds P. L. de Boer and D. G. Smith), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304039.ch26
Utrecht, The Netherlands
- Published Online: 29 APR 2009
- Published Print: 28 JAN 1994
Print ISBN: 9780632037360
Online ISBN: 9781444304039
- Orbital forcing on continental depositional systems - lacustrine and fluvial cyclicity, East Greenland;
- Andersson land formation;
- Wimans Bjerg formation;
- laminated siltstones and brecciated to massive mudstones;
- contractions of ephemeral lakes;
- precession and eccentricity cycles
Remarkable cyclicity in a lacustrine succession, the Wimans Bjerg Formation in the Devonian basin in East Greenland, has previously been pointed out by Nicholson & Friend. The present study of the Wimans Bjerg Formation has been carried out to outline the processes leading to the cyclicity.
The Wimans Bjerg Formation is composed of two facies, laminated siltstones and brecciated to massive mudstones, and exhibits a pronounced cyclicity. Individual cycles average 3.6 m in thickness and consist of a unit dominated by laminated siltstones and a unit exclusively composed of brecciated/massive mudstones. A higher order cyclicity is also observed in the variation in thickness of the laminated siltstone units. These mega-cycles are 18.7 m thick on average.
The Wimans Bjerg Formation is interpreted in terms of a playa environment. The brecciated/massive mudstones indicate periods of exposed playa mudflat conditions. The laminated siltstone beds reflect the existence of ephemeral lakes on the playa mudflat.
The cyclicity indicates regular variations in environmental conditions between periods with frequent ephemeral lake expansions and contractions and periods exclusively characterized by playa mudflats. The higher order of cyclicity indicates long-term variations in the periods of punctuated ephemeral lake conditions.
In this paper a comparison is made between the playa lake cyclicity of the Wimans Bjerg Formation, and the cyclicity of the slightly older fluvial Andersson Land Formation in the East Greenland basin. Both units indicate a ratio of mega-cycle thickness to cycle thickness in the order of 5.1–5.2. The cyclic variations may in both cases be explained by cyclic variations in precipitation and could reflect orbital forcing of climate, i.e. astronomical periods of 17.0–20.1 ka and 94.9 ka, controlled by precession and eccentricity cycles.