Paul L. Heller¹, Merren A. Jones²

(1) University of Wyoming, Laramie, WY
(2) University of Leeds, Leeds, England

ABSTRACT: (Keynote): Time Lag of Syntectonic Indicators in Foreland Basin Deposits

Types of syntectonic markers used by various authors to interpret fault timing include: (1) compositional indicators of unroofing; (2) increasing vertical sedimentation rates due to increased sediment flux and/or subsidence rates; and (3) increase in gravel fraction of the derived sediment, reflecting an increase in production rate in the source area. Tectonic timing is simplest to interpret in the case where the first occurrence of all three types of indicators are found in the same stratigraphic interval. However, across most basins first occurrences are not synchronous because each is influenced by different processes of transport and storage. As a result, the time lag between the first arrival of each of these indicators in any single stratigraphic section can be geologically significant and increases with distance across a basin.

We demonstrate this signal attenuation in the thrust-belt-derived Horta-Gandesa alluvial system (late Eocene-Oligocene) - exposed along the southeast margin of the Ebro Basin, Spain. A 945 m alluvial sequence can be broken into 5 tectonostratigraphic sequences based on composition, paleoflow, and mean grain size. In sections that are close (~1 km) to the palinspastically restored thrust front, gravel progradation coincides with the onset of new clast compositions. However, in more distal sections (~10 km) abrupt compositional changes coincide with retraction of the gravel front. After about 1 m.y. the gravel front once again progrades basinward. Thus the greater the distance from the source, the greater the lag time between different syntectonic signals.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado