THE MORPHODYNAMICS AND SEDIMENTOLOGY OF A SEASONALLY CONTROLLED MICROTIDAL TIDAL INLET: THE NARIVA RIVER TIDAL INLET, COCOS BAY, TRINIDAD

Abstract

The geomorphology and sedimentology of the Nariva River tidal-inlet complex, a microtidal fluvially influenced tidal-inlet complex, was analyzed. The complex comprises a recurved spit, an ebb-tidal channel, and an ebb-tidal delta. Morphological trends in the spatio-temporal evolution of the inlet complex were observed and recorded from Google Earth™ timelapse satellite images taken from 2003 to 2019. The two-dimensional internal architecture of the inlet complex and the sedimentary succession of the recurved spit, an ebb spit, the swash platform (of the ebb-tidal delta), a mouth bar (associated with the wet-season river-dominated inlet complex erosion), the ebb-tidal channel, and the adjacent foreshore were observed and documented from six shallow sedimentary cores.The Nariva River inlet width ranges from 17 to 40 m through its seasonal evolution, has a tidal prism of ∼ 2.17 × 105 m3, a cross-sectional area of 29.52 m2, and a depth ∼ 1.4 m (calculated at peak dry season near the inlet throat). The inlet complex undergoes an annual geomorphological evolution linked to the seasonally induced migration of the fluvial-to-marine transition zone (FMTZ). Increased fluvial discharge during the wet and hurricane seasons results in the basinward migration of the FMTZ rendering the inlet river dominated and resulting in the erosion of the inlet complex. During the dry season, low fluvial discharge, tidal dominance, and fair-weather conditions promote sedimentation in the inlet and the redevelopment of the inlet complex. The inlet has a complex (CX) internal architecture (fill pattern) defined by the laterally migrating recurved spit and ebb spit on their updrift margin, and conformable, mounded elements on their downdrift (e.g., mouth bar, swash platform, and foreshore). Two sedimentary successions were developed for ebb-tidal-delta deposits: off-axis of the ebb-tidal channel and on-axis. The off-axis succession is considerably similar to the adjacent foreshore-to-shoreface succession which can pose a challenge when attempting to identify these deposits in the rock record. The on-axis succession, however, despite thickness variability, showed a positive correlation to studied mesotidal tide-dominated inlet successions.