From the strand plain to the reef: A sedimentological–geomorphological study of a Holocene coast affected by mud diapirism (Archipélago Rosario- Barú, Colombia)

Abstract

The Archipélago Rosario-Barú evolved off-shore of the Caribbean Coast in N Colombia during the Holocene. From the geodynamic point of view its host rocks belong to the rather stable foreland of the modern Andean fold belt, from the sedimentological point of view the environment has, however, to be ranked among the highly mobile zones. The swiftly rising orogen in the hinderland triggered a huge amount of sediment load that is very rapidly dumped at the end of the river run in wave-induced deltas which subsequently were reworked into large barrier sands along the Caribbean Coast. The modern terrigenous sedimentation in context with a pervasive neotectonic faulting along deep-seated lineaments contributed to the instability of the clastic substrate and sparked mud diapirism which is accountable for the built-up and destruction of the cays and reefs of the Archipélago Rosario-Barú. Mineralogical, chemical, paleontological, and sedimentological studies were combined with radio‑carbon dating to decipher the stepwise evolution of the archipelago and applied in a catena-like approach covering the entire sequence from the onshore strand plain to the offshore reef. The impact of the mud diapirism is indicated by marker minerals such as smectite and chlorite, and displays a set of typical chemical features in the base metal contents and the stable carbon and oxygen isotopes straddling around zero. All of these characteristics point to a deep-seated basic source of the fluids vented as a slurry along lineamentary zones. The actuogeological study of these sites rife with mud volcanoes can be taken on one hand as a modern equivalent to ancient limestone-hosted Cu deposits and on the other hand use as a replica of ancient salt deposit undergoing halokinetic processes as far as the petrophysical processes are concerned.