Recent Stratigraphic Sequences Affected by Neotectonics Movements in a Reef Key, Morrocoy National Park, Falcon State, Venezuela

By

Harald W. Stockhausen¹, Franck A. Audemard², Gonzalo Fernandez-Viejo³

(1) Universidad de Vigo/Union Fenosa, Vigo, Pontevedra, Spain (2) Funvisis, Caracas, Venezuela (3) Union Fenosa, Cairo, Egypt

 At the northwestern coast of Venezuela, an Holocene coastal reef is developed as a continuous chain of keys. One of them, Cayo Sal (Salt Key) is the biggest key of the entire park, with a carbonate stratigraphic record for the last 10,000 years.

The key was tilted toward south by an earthquake, which caused anomalous geomorphological features, such as an embayment at the northeastern corner, and a strait coastline along the northern edge of the key, being an excellent case study for stratigraphic sequences affected by tectonic movements.

Reefs surround this key, with an inner shallow hypersaline lagoon protected by sandbars, suggesting that it is the oldest and most evolved key, according to Maxwell (1968) classification.

In the hypersaline lagoon, cores (no deeper than 4 m) were taken in nine locations. Five samples from four locations were selected (2 Acropora cervicornis fragments embedded in deepest sequence, and 3 mangrove peat layer samples, at the lower upper section) for 14C radiocarbon dates.

An evolution model was proposed, based on the cores' stratigraphic sequences and above 14C dates, reflecting a distinctive carbonate Highstand System Tract, starting approximately 7700 years BP.

The earthquake, not reported before to our knowledge in this area, took place between 2750 ± 350 years BP and 540 ± 75 years BP. This is support by the fact that the mangrove peat layer is found in a tilt angle and the presence of angular unconformity, caused by a sea transgression in the lagoon from the south.