SEDIMENTARY CIS RELATIONSHIPS IN A LARGE TROPICAL ESTUARY - EVIDENCE FOR REFRACTORY CARBON INPUTS FROM MANGROVES

Mud islands in the Fly River estuary were deposited under dominantly b rackish conditions. Changes in C/S ratio with depth in sediment cores reflect geomorphic development of islands and/or changes in location o f river channels. An unusual feature of the C/S relationships is posit ive carbon-axis intercepts, indicating the presence of an organic phas e that is resistant to decomposition. Nonzero intercepts mean that the slope of the C/S plot, and not individual C/S values, must be used to determine paleoenvironments. Moreover, a nonzero intercept may be use ful for indicating proximity to a source of refractory carbon, such as mangroves.