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AAPG ACE 2018

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Amazon Fluid Mud Impact on Previous HitWaveNext Hit- and Tide-Dominated Pliocene Orinoco Delta (Trinidad) Shoreline

Abstract

The modern Orinoco delta is the terminus of the world’s largest alongshore mud dispersal system, and it receives significant amount of mud (108 tons/yr) from the Amazon via the coastal Guyana Current. The influence of these huge volumes of Amazon mud on the paleo-Orinoco Delta succession has never been investigated.

New research is showing that abundant fluid-mud deposits were preserved with different styles in the paleo-Orinoco delta in storm Previous HitwaveNext Hit-dominated, tide-dominated and Previous HitwaveNext Hit-influenced, and tide-dominated delta lobes from the Pliocene Mayaro, Manzanilla and Lower Morne L’Enfer formations, respectively. The Mayaro Formation parasequences are characterized by alternating fluid-mud intervals (5-30 cm thick) and hummocky cross-stratified sandstones (HCS) passing upwards into amalgamated swaley cross-stratified (SCS) sandstones. The fluid-mud intervals have flat or irregular tops occasionally overlain by amalgamated SCS sandstones with mud clasts. In places, very thick (1-1.5 m) fluid-mud intervals containing small HCS are overlain by amalgamated SCS sandstones. The Manzanilla Formation parasequences exhibit majority of fluid-mud layers (2-3 cm thick) associated with bi-directional current rippled-sandstones in the uppermost part overlying interbedded fluid-mud layers (0.5-1.5 cm thick) and erosion-based sandstones with symmetrical ripples and small SCS. The Lower Morne L’Enfer Formation displays three Previous HittypesNext Hit of fluid-mud deposits: (A) very thin (1-5 mm) layers that amalgamate to form mud bedsets or drape along ripple laminae; (B) thick (0.5-1.5 cm) layers interbedded with structureless to rippled-sandstone beds; (C) very thick (1-10 cm) deformed layers with load structures at their top and laterally variable thickness. The Previous HittypesNext Hit A and B occur mainly in the lower parts of parasequences, and they change upwards to type C.

The fluid mud deposited in Previous HitwaveNext Hit- or tide-dominated environments with over 1 m thick units suggest large muddy bedforms similar to mudbanks that migrate along the modern Amazon-Orinoco coast. However, there are differences between fluid-mud architectures in the Previous HitwaveNext Hit- and tide-dominated settings. Storm waves tend to erode and re-suspend sediments in shallow water, and re-deposit fine-grained sediment into deeper water below the storm Previous HitwaveTop base (15-50 m water depth). Tide-dominated deltaic shorelines, in contrast, more likely to trap fine-grained sediments in water depth less than 10 m with less escaping offshore.