Spatial patterns of sediment accumulation on a Holocene carbonate tidal flat, northwest Andros Island, Bahamas

To characterize spatial patterns of sedimentation and analyze the morphology of part of the modern tidal flats of northwest Andros Island in the Bahamas, this study integrated remote sensing, geographic information systems (GIS), and carbonate sedimentology. The fundamental data are a Landsat TM image that has been classified to create a thematic map of eight subfacies, interpreted to represent a distinct tidal-flat subenvironment such as adjacent marine, exposed levee-beach ridge, pond, and algal marsh. Spatial statistics of the thematic map characterize the patterns of sediment accumulation. Quantitative analysis highlights several interesting results concerning subfacies character and distribution: (1) of the eight mapped subfacies, low algal marsh is most widespread, representing 27.5% of the total area, whereas exposed levee-beach ridge is the least widespread, accounting for 10% of the area; (2) the patches of different subfacies have different shape complexities, with low algal marsh, high algal marsh, and mangrove ponds being the least complex and exposed levee-beach ridge being the most complex; (3) Markov chain analysis suggests that lateral transitions between different subfacies are highly ordered; and (4) frequency distribution of subfacies patch area and lacunarity (gap size distribution) data exhibit power law relationships over several orders of magnitude, consistent with fractal characteristics. The fractal nature of patch size and gaps between facies illustrate that on this tidal flat neither the size nor the spatial distribution of subfacies has a characteristic scale. This statistical behavior is consistent with the presence of self-organization, or emergence of pattern in the absence of a template or external forcing. The statistical self-organization on the tidal flat is the cumulative expression of local processes, but it becomes apparent only through analysis of the whole system. These results are inconsistent with models suggesting that tidal flats include a migrating complex of randomly distributed, randomly sized subenvironments. Ancient successions that include random patterns may reflect the more pronounced influence of forces external to the sedimentary system, instead of an absence of those forces.