FACIES DISTRIBUTION ANALYSIS IN A RIVER-DOMINATED DELTA, LAKE IZABAL, GUATEMALA: EXPLORING A UNIQUE EXAMPLE WITH SEDIMENT CORE DATA

End-member river-dominated deltas display unique sedimentation and facies distribution patterns. However, few modern deltas are ideal end-members. Rather, most deltas reflect the combined impact of fluvial, wave, and tidal processes. Many models have been proposed to understand the sedimentary processes, the facies characteristics, and facies distribution of deltas. However, a true end-member delta system is rare, owing in part to the difficulty in finding a modern analogue that is only dominated by river processes.

We conducted a preliminary sedimentological study of a short core from the prodeltaic environment of the Polochic delta system in Lake Izabal, Guatemala. Detailed sedimentological analyses using textural, compositional, structural and paleontological description of the core allowed the identification of grain-sized trends, sedimentary structures, clast composition, and bioturbation patterns.

These data were used to identify lithofacies and interpret the processes that drive this highly-progradational system. This core, combined with other two short cores collected around the shelf and interdistributary bay setting of the Polochic delta, provide a better understanding of the mechanisms that control facies, facies distribution, and staking pattern of lithofacies in a river-dominated setting. This study reveals that the Polochic delta system is a sandy river-dominated delta that is highly progradational with common hyperpycnal flow deposits along the gentle slopes of the delta front.

Preliminary results indicate that this is an end-member model with minimal wave and no tidal reworking. This study opens an opportunity to investigate a modern system and provide a better understanding of a sandy river-dominated delta system with a “birdfoot” geometry and the mechanisms and processes that drive delta growth and progradation.