FACTORS AFFECTING THE WORLDWIDE DEVELOPMENT OF LONG-TIMESCALE FLUVIAL TERRACE STAIRCASES

摘要

A comparison of fluvial terrace sequences from around the world based on data collected as part of International Geoscience Programme (IGCP) Project No. 449, has revealed significant patterns. River terraces provide important records of uplift, which is essential for their formation, and of landscape evolution. Their cyclic formation, however, almost invariably seems to have been a response to climatic fluctuation. Sequences in the European core area of IGCP 449, which has the longest and most extensive research history, have been used as templates for worldwide comparison. There is evidence for a global acceleration Of uplift at the time of, and perhaps in response to, the Mid-Pleistocene Revolution, when climatic fluctuation switched to 100 ky Milankovitch cycles. Terraces formed prior to this generally consist of wide aggradational sheets that probably each represent formation over several 41 ky cycles. Subsequently, river valleys became more steeply entrenched. and terraces formed in response to the stronger 100 ky climatic forcing, in many cases at approximately one per cycle. This paper uses the new data resource to explore differences between records in different climate zones and crustal provinces, between sequences with variable numbers of Middle-Late Pleistocene terraces and between systems in which the all-important incision event has occurred in different parts of climatic cycles.