--> Abstract: Non-Eustatic Mechanisms for the Origin of Unconformities, by M. J. Saurborn; #90925 (1999)

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SAURBORN, MELISSA J., Columbia University, Dept. of Earth and Environmental Sciences, New York, NY

Abstract: Non-Eustatic Mechanisms for the Origin of Unconformities

One of the most fundamental, as well as controversial, issues in sedimentary geology is the origin of unconformities. Since the emergence of seismic and sequence stratigraphy in the late 1970s, these surfaces have been predominantly interpreted in terms of eustatic fluctuations. This interpretation relies on the apparently abrupt basinward shifts in onlap (implying rapid falls of sea level), as well as on the purported global synchroneity of unconformities. Furthermore, it has been generally assumed that tectonic processes operate on longer timescales (greater than 106 years), leaving eustasy as the only known plausible mechanism for the origin of higher frequency cyclicity (104 to 105 years).

Studies of sedimentation during glacial times indicates that glacial-eustasy plays an important role for these periods, but it remains questionable whether eustasy is the driving force behind unconformity generation in non-glacial (e.g. Cretaceous) times, especially in tectonically active basins. Alternative (non-eustatic) mechanisms, specifically focusing on the role of in-plane force variations, will be quantitatively assessed using the well-known stratigraphy of a tectonically active region: the Cretaceous Cardium and Dunvegan formations of the Alberta foreland basin.

The proposed research is important for understanding the way in which sediments accumulate at geological timescales, and for determining with greater precision the effect of tectonic phenomena on sedimentation patterns. To the extent that unconformities are due not only to eustatic fluctuations, the research bears on our perception of the geological record of sealevel change and earth’s climatic history. 

AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid