Coastal conglomerates around the Hadjer el Khamis inselbergs (western Chad, central Africa): new evidence for Lake Mega-Chad episodes
This paper reports on a study dealing with the rhyolitic inselbergs of Hadjer el Khamis that formed palaeoislands during Lake Mega‐Chad events. Field observations have shown that: (1) conglomeratic patches of immature to mature clasts are preserved at the feet of the Hadjer el Khamis inselbergs; (2)...
Saved in:
Published in | Earth surface processes and landforms Vol. 28; no. 10; pp. 1059 - 1069 |
---|---|
Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Chichester, UK
John Wiley & Sons, Ltd
15.09.2003
Wiley |
Subjects | |
Online Access | Get full text |
Cover
Loading…
Summary: | This paper reports on a study dealing with the rhyolitic inselbergs of Hadjer el Khamis that formed palaeoislands during Lake Mega‐Chad events. Field observations have shown that: (1) conglomeratic patches of immature to mature clasts are preserved at the feet of the Hadjer el Khamis inselbergs; (2) in cross‐section, their profile reveals a well defined cliff–platform junction at a constant elevation (325 m). The monolithological clasts show all degrees of roundness, from angular cobbles to well rounded pebbles. This wide range of maturity suggests a coastal origin for these cobbles. The system was permanently fed with angular clasts, which were progressively worn by waves. Cobbles that were wave‐worked for the longest time are the best rounded. The cliff–platform junction is the result of erosion by waves, which attacked and undercut the inselberg cliffs during Lake Mega‐Chad events. Asymmetrical erosion profiles moreover suggest a wind regime dominated by SW to NE oriented winds. These interpretations have two implications. The elevation of the cliff–platform junction is an indication of the highest water level of Lake Mega‐Chad at 320–325 m, which is in agreement with other observations elsewhere in the basin. The SW to NE oriented winds show that monsoon‐related winds were prevalent during Lake Mega‐Chad events, suggesting the Inter‐Tropical Convergence Zone was located higher in latitude than today. Copyright © 2003 John Wiley & Sons, Ltd. |
---|---|
Bibliography: | Ministère Tchadien de l'Enseignement Supérieur et de la Recherche ark:/67375/WNG-92GFD294-0 Centre National de la Recherche Scientifique (CNRS) istex:CB4C2A93EA13DFA259A07B3C2189E46DF576151F Centre National d'Appui de la Recherche (CNAR) ArticleID:ESP502 French Ministère des Affaires Etrangères ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0197-9337 1096-9837 |
DOI: | 10.1002/esp.502 |