Abstract

The sulfur (S) content of coal is often used to infer aspects of paleoclimate, trophic state, and proximity to marine influence, of the mire in which it was deposited. In this study, the S content of peat in a large back-barrier mire complex on the Caribbean coast of Panama is related to climatic, biological, and tectonic factors of the depositional environment. Earthquake-generated subsidence is greatest to the southeast, leading to drowning of the deposit beneath Almirante Bay, and 40% of the peat is now below sea level. Coastal mangrove peats with moderately high S content (1-5 wt % S) and high salinity (> 1.0 wt %) dominate the eastern margin and extend beneath the salt water and shallow marine sediments of the adjoining bay. Marine influence extends only a short distance onshore, except in the vicinity of brackish blackwater creeks that drain the swamp. Peats associated with these tidal channels are low in salinity (< 1.0 wt %) and very high in S (5 to nearly equal 14 wt % S), apparently the result of a biogeochemical chain of S reactions leading to the concentration of C-S sulfides. The western part of the deposit is domed, and the vegetation and the peat are concentrically zoned. Stunted, sawgrass-dominated vegetation that produces fibric, very low S (< 0.25 wt % S) peat occupies the central bog plain. Around the bog plain, mixed-forest and palm-forest swamps produce dense hemic and fine heroic peat with higher S content (0.250.5 wt % S). The S content is in proportion to the degree of humification of the peat, and both are independent of the pH of the groundwater. The distribution of forms of organic and inorganic sulfur in the tropical peats are found to be comparable to published values for temperate and subtropical peats, despite differences in vegetation and climate. The distribution of high-sulfur peats in the eastern part of the deposit and low-sulfur peats in the western part, and the SE-NW transgression parallel to the trend of the coastline, reflects the regional structural trend of coseismic subsidence greatest to the southeast.

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