MULTIPLE EXAMPLES OF PLANT-SEDIMENT INTERACTIONS IN TERRESTRIAL AND SHALLOW MARINE ENVIRONMENTS OF THE BAHAMAS

Rhizoliths represent various modes of plant root preservation and are the most common evidence of past plant-sediment interactions in the Bahamas. One well-known modern example of such interaction includes the role of red mangrove (Rhizophora mangle) root systems in trapping sediment and preventing coastal erosion. Although not as well documented, other examples of substrate modification by terrestrial and marine plants constitute important evidence of past vegetation and can be used as paleoclimate indicators of temperature and precipitation regimes. Modification of sediment by plants can also produce significant amounts of post-lithification porosity and permeability, which can increase reservoir quality of the host rocks.

The following examples of plant interactions with carbonate sediment from coastal and shallow subtidal settings in the Bahamas demonstrate their highly variable nature and products: 1) eolian deposits with impressions of silver thatch palm fronds (Coccothrinax argentata); 2) impressions of terrestrial plant roots (sea grape = Coccoloba uvifera), prostrate stems (bay geranium = Ambrosia hispida), runners (railroad vine = Ipomoea pes-caprae), and blades (sea oats = Uniola paniculata) in eolian and back-beach deposits; 3) large vertical pipes present in Holocene eolianite and possibly representing buried palm tree trunks and/or roots, although roots can exploit pre-existing paths created by dissolution or other mechanisms; 4) highly porous “spongiform” texture of Holocene eolianite, which likely forms by sand trapping and lithification around dense roots, stems and organic litter of grass and shrub vegetation, including various microbial, fungal and insect communities, as well as accumulation and burial of marine algae (e.g., Sargassum) and seagrasses in beach sediment; and 5) extensive modern seagrass (Thalassia testudinum) root systems that trap sediment in shallow marine subtidal settings and have potential to leave traces in the geological record, but have not commonly been documented from ancient strata. Similarly, large and extensive palm tree roots do not seem to be easily preserved and recognized in carbonate grainstone, but they may be partially responsible for producing the commonly observed spongiform texture of Holocene non-marine deposits in the Bahamas.