loading page

Asynchronous strath terrace formation in a collisional mountain belt
  • +8
  • Jesse Zondervan,
  • Martin Stokes,
  • Sarah Boulton,
  • Anne Mather,
  • Matt Telfer,
  • Jan-Pieter Buylaert,
  • Mayank Jain,
  • Andrew Murray,
  • Alaeddine Belfoul,
  • Madeleine Hann,
  • Nawfal Taleb
Jesse Zondervan
University of Plymouth

Corresponding Author:jesse.zondervan@protonmail.com

Author Profile
Martin Stokes
University of Plymouth
Author Profile
Sarah Boulton
University of Plymouth
Author Profile
Anne Mather
University of Plymouth
Author Profile
Matt Telfer
University of Plymouth
Author Profile
Jan-Pieter Buylaert
Nordic Laboratory for Luminescence Dating, Department of Geoscience, Aarhus University, Risø Campus
Author Profile
Mayank Jain
Technical University of Denmark
Author Profile
Andrew Murray
Nordic Laboratory for Luminescence Dating
Author Profile
Alaeddine Belfoul
Ibn Zohr University
Author Profile
Madeleine Hann
The University of Manchester
Author Profile
Nawfal Taleb
Ibn Zohr University
Author Profile

Abstract

Structural and lithological controls in mountain valleys have been shown to affect the erosional connectivity of hillslopes, tributaries and alluvial fans, as well as the formation and preservation of strath terraces. In this study we explore the synchronicity of fluvial bedload aggradation and bedrock incision in valleys of one river draining a collisional mountain belt through geomorphological, sedimentological and chronological datasets of strath terraces. Along the M’Goun River on the southern flank of the central High Atlas Mountains strath surfaces and bedload sediments are preserved in valleys with differing structure and lithology throughout the thrust front and wedge-top basin. We (1) extract terrace surface and river channel elevations from a digital elevation model and field mapping to reconstruct river long profiles; (2) collect grain size and lithology data from terraces to derive information on sediment source and transport; (3) constrain the timing of bedload aggradation within the two latest strath levels using a new approach to OSL dose rate correction of gravels. Strath terraces form in weak sedimentary bedrock in valleys confined by limestone and conglomerate units, and are capped by up to 3 to 10 m of gravel bedload and overbank sands. The record of strath burial and incision extends to 180 ka, but only includes one synchronous bedload aggradation event during the last interglacial maximum MIS 5a (~130-110 ka). Reconstructed paleo-river long profiles and chronology demonstrate time-transgressive bedrock incision through the thrust front and wedge-top basin on the order of 10^4 – 10^5 yrs, representing strath incision of 12 to 40 m. A lack of a downstream bedload grain-size trend and presence of locally derived clast lithologies indicate lateral input of gravel from valleys in addition to downstream transport. These results allow for the development of a conceptual model of asynchronous strath terrace formation in a collisional mountain belt.