FORAMINIFERAL AND SEDIMENTOLOGICAL EVIDENCE OF ENVIRONMENTAL CHANGE IN AN INCISED INLET, BOKA ASCENSION, CURAÇAO, LESSER ANTILLES

Investigating past environmental conditions by collection of sediment cores helps to characterize the changes that have occurred throughout time and provides insight into how conditions may continue to change in the future. A ~1-meter sediment core was taken at Boka Ascension, Curaçao, Lesser Antilles. Boka Ascension is a long, narrow inlet incised through an uplifted Pleistocene marine terrace, with decreasing wave energy moving further inland. The core was taken at the water’s edge at the very back of the boka. One sediment sample was taken from each lithologic change within the core. Ten samples were analyzed for sedimentological characteristics and foraminiferal content. Grain size increases from fine-grained sand in the oldest sample to coarse-grained sand in the youngest. A ternary plot of percentage rotaliid/miliolid/agglutinated tests indicate all samples are more similar to lagoon rather than marsh environments. Cluster analysis of these data resolved four biofacies that were combined with grain size and shell content data to identify three depositional facies (DF): higher-energy normal marine conditions (DF I), reworked back-reef sediments (DF II), and oscillating energy conditions (DF III). The distribution of depositional facies within the core suggest at least two different sediment regimes that are interrupted by a thin, high-diversity, poorly-sorted layer, potentially representing a storm event (DF II). Below this layer DF III represents cyclical deposition recorded as thinly-interbedded mud and sand. Such deposition could be the result of tidal changes, seasonal fluctuations in rainfall causing variations in fluvial deposition at the head of the boka, or, on a larger time scale, sea-level fluctuations. A greater sense of depositional rate is necessary to discriminate the cause of the layers. After this influx, the top facies observed in the core (DF I) consists of coarser-grained sediment that could be the result of erosion further seaward, increasing the site’s exposure to the ocean and resulting in higher energy conditions than previously seen in this record. Additional cores from Boka Ascension will be analyzed to further characterize the depositional history of the northeast shore of Curaçao.