Significant Techno-stratigraphic development of the Caroni Basin, recorded in outcrops of the late Neogene Manzanilla and Springvale Formations, NE Trinidad

摘要

The Manzanilla and Springvale Formations outcrop along a 1.9 km stretch on the eastern coast of Trinidad, and provide vital information about the development of the Caroni Basin and north-central Trinidad. The Manzanilla Formation contains deposits that range from deepwater to delta plain facies. Sandstone turbidites are the oldest deposits and these transition upward into muddy slope deposits then shelf mudstones, siltstones and sandstones. The occurrence of sporadic conglomerate beds suggests debris flows or other coarse-grained sediment gravity flows additionally entering the basin at this time. The upper parts of the Manzanilla succession reflect marginal marine environments with delta front (including mouth-bar), crevasse splay, bay fill and marsh deposits. Most of these deposits originated as the northernmost part of the east to northeast flowing paleo-Orinoco Delta. The anomalous interfingering of coarse-grained lithic-rich debris flow deposits with the delta-derived deposits, strongly suggests a derivation directly from the steep-sloped alluvial-fan and fan-delta deposits eroding off of the Northern Range orogenic belt, some 10 km to the north. The facies associations of the Springvale Formation reflect channelized estuarine environments strongly influenced by tidal processes. Subtidal channels associate with and are succeeded by wave and tidal influenced intertidal facies and their overlying supratidal mudstones, paleo-sols and lignite beds.Examination of these two formations reveals that the Neogene Caroni Basin developed quite differently from the coeval Southern and Columbus basins to the south. The Southern and Columbus Basins are true foreland basins with growing accommodation space and expanded shelf section due to the movement of huge listric faults. When compared to similar aged formations in the Southern Basin, the Caroni Basin succession is relatively thin, starved of sediment, contains internal discontinuities and tectonically derived coarse-grained conglomerates. This contrast is due to the fact that the Caroni Basin is sited immediately adjacent to the northern Trinidad zone of Caribbean and South American plate-margin convergence. The compressional forces acting on the basin produced alternating periods of uplift/erosion and subsidence which inhibited continuous deposition. The outcrops examined herein present new detail of the tectonic impact on the evolving Caroni foreland basin within northern Trinidad, where compression-driven base level changes left their signals in the foreland succession.