Construction and evolution of submerged deltaic bodies on the high energy SE African coastline: The interplay between relative sea level and antecedent controls

Luke Engelbrecht, Andrew Green, Andrew Cooper, Annette Hahn, Matthias Zabel, CF McKay

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

This paper investigates the interplay between allocyclic controls and antecedent topography in the evolution of submerged coastal landforms, including a back-stepped delta. Using high-resolution tools, we examine the wave-dominated Thukela shelf, and define the major seismic units. Key features identified comprise incised valleys scoured into bedrock, that have overspilled to form lagoons at depths of 50 m. These are in turn overlain by two prograding and backstepped sandy delta systems at 40 m and 32 m depth respectively. The deltas interfinger with muddy prodelta deposits and are truncated by the Holocene ravinement, overlain by the contemporary prodelta of the Thukela River system. A bedrock high separates two physically separate strato-morphological zones; landward a sediment stripped, steep and shallow nearshore zone, and seaward a gentle zone downdip
where the deltaic accumulations are sited. Delta development was favoured during sea-level stillstands at−40 m and −32 m respectively. The step-back of the deltas corresponds to sharp increases in the rate of sea-level rise associated with meltwater pulses. The overall gentle palaeo-bathymetric gradient has moderated erosion associated with rising sea level, preserving a sandy back-stepping delta and a draping mud clinoform.

Submerged delta positioning relates to underlying incised valleys, suggesting a synchronous transgressive evolution of the drainage and the delta. Incised valley network positioning is further governed by Late Pliocene aged growth faults in the basement rocks. The geological framework has acted as a recurring primary control to the geomorphic evolution of the area, partitioning accommodation for sediment accumulation and moderating the efficiency of ravinement.
Original languageEnglish
Article number106170
JournalMarine Geology
Volume424
Early online date14 Mar 2020
DOIs
Publication statusPublished - 1 Jun 2020

Bibliographical note

Funding Information:
We acknowledge the captain and crew of the RV Meteor, cruise M123. We further acknowledge our colleagues on the cruise, Marc Humphries, Lauren Pretorius, Errol Wiles, Talicia Pillay, Hayley Cawthra, Nadia Du Plessis, Sergio Andò, and Peter Frenzel. Rev. Doug Slogrove is thanked for his assistance in a second seismic survey campaign. This project has been supported by the Bundesministerium für Bildung und Forschung (BMBF; projects RAiN2 and MA-RAIN; Grant No. 03G0862A and 03F0731A ). LE acknowledges a scholarship from the National Research Foundation/African Coelacanth Ecosystem Programme (Grant No 97968 ). Finally, we thank the two anonymous reviewers and the editor, Prof. E. Anthony, for their valuable inputs to the paper.

Publisher Copyright:
© 2020 Elsevier B.V.

Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.

Keywords

  • Coastal
  • Geomorphology
  • Sea level changes
  • Sedimentology - marine cores
  • Thukela

Fingerprint

Dive into the research topics of 'Construction and evolution of submerged deltaic bodies on the high energy SE African coastline: The interplay between relative sea level and antecedent controls'. Together they form a unique fingerprint.

Cite this