Drainage Responses to Oblique and Lateral Thrust Ramps: A Review
- Gary Nichols,
- Ed Williams and
- Chris Paola
Published Online: 30 MAR 2009
Copyright © 2007 International Association of Sedimentologists
Sedimentary Processes, Environments and Basins: A Tribute to Peter Friend
How to Cite
Vergés, J. (2007) Drainage Responses to Oblique and Lateral Thrust Ramps: A Review, in Sedimentary Processes, Environments and Basins: A Tribute to Peter Friend (eds G. Nichols, E. Williams and C. Paola), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304411.ch3
- Published Online: 30 MAR 2009
- Published Print: 7 DEC 2007
Book Series Editors:
- Ian Jarvis
Series Editor Information
School of Earth Sciences & Geography, Centre for Earth & Environmental Science Research, Kingston University, Penrhyn Road, Kingston upon Thames KT1 2EE, UK
Print ISBN: 9781405179225
Online ISBN: 9781444304411
- drainage responses to oblique and lateral thrust ramps;
- interplay between fluvial deposits and basins transported on thrusts;
- ancient examples from southern Pyrenees;
- Ripoll basin - middle Eocene example on footwall of major oblique ramp;
- change from tectonic reentrant to uplifted block during thrusting;
- two-step evolution maps of Pedraforca reentrant in southern Pyrenees;
- contribution of Group of Dynamics of Lithosphere (GDL)
The relationships between oblique or lateral ramps in fold-and-thrust belts and their impact on syntectonic fluvial drainage are analysed in this review. Both ancient and recent cases from Cenozoic belts are examined. The southern flank of the Pyrenees provides good examples to decipher the long-term effects of oblique ramps on fluvial arrangement. Recent examples from the Indus River across the front of the Himalayas in northwest Pakistan, the frontal domains of the Andes in Bolivia and the northwest Zagros Mountain Belt provide examples of the short-term interaction between oblique or lateral thrust ramps and foreland drainage systems. The interpretation of these case studies, some of them developed on top of blind thrust ramps, can facilitate the analysis of drainage distortions in active complex tectonic regions.
Oblique ramps are present either permanently or episodically at different scales in all fold-and-thrust belts. The simplest scenario is related to piggyback basins, which display an oblique ramp linked to each frontal thrust termination. This oblique ramp forms the natural outlet for confined longitudinal systems along the piggyback basin. The change in topography across the ramp constrains the position of deltaic deposits between a subaerial fluvial system deposited in its hangingwall and an open marine system deposited in its footwall. Fluvial systems can also develop either in the hangingwall or in the footwall of larger oblique ramps that grow by the tectonic inversion of earlier structures. The growth of a large oblique ramp beneath a fluvial system operates in the same way as oblique ramps related to piggyback basins. However, its larger scale causes a larger differential topographic elevation across it, accommodating fluvial deposits in its hangingwall and deep marine turbidites in its footwall. In opposition, large oblique ramps growing in front of river systems create a topographic barrier that deflects the drainage.
A complication of the interaction of oblique ramps and drainage occurs where two opposed oblique ramps form a tectonic reentrant. These tectonic reentrants form at different scales and are characterized by lower topography. The confined domains concentrate rivers flowing out from surrounding higher topographic deformed regions. Further development of deeper thrusts can uplift these reentrants, modifying the previous concentrated drainage and diverting the river courses towards regions with lower topography.
As an example, the late Miocene longitudinal fluvial system flowing along the foreland basin of the Zagros during the deposition of the lower Agha Jari Formation was shifted to the southwest in the earliest Pliocene by the uplift of the Pusht-e Kuh Arc. The present river configuration is incising through the Pusht-e Kuh Arc anticlines and flows towards the lowlands of the Dezful Embayment (tectonic reentrant), limited by two major oblique ramps along the Mountain Front Flexure. The large-scale Mountain Front Flexure confines the Tigris River towards the southwest of the front of the Pusht-e Kuh Arc.