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Hologene evolution of the changuinola peat deposit, Panama: sedimentology of a marine-influenced tropical peat deposit on a tectonically active coat

University of British Columbia

The evolution and structure of a large peat deposit on the Caribbean coast of western Panama, Central America is evaluated as a possible analogue for the deposition of low-ash, low sulphur coals. Effects of earthquake-driven subsidence events on the peat and the peat-forming vegetation are investigated, and implications of tectonic subsidence on the evolution of this deposit and on the currently developing model of coastal tropical coal deposition are described. The deposit is approximately 80 km² in extent, averages 6.5 m in thickness, and occupies the width of the narrow coastal plain between the Talamanca Cordillera and barrier beach on a seismically active part of the Caribbean coast. Based on vegetation zonation, topography and hydrology, the modern Changuinola mire complex can be divided into a raised, concentrically zoned, ombrotrophic western section, and a dissected and partially rheotrophic eastern section. Differing hydrological regimes of these two sections are reflected in the physical and chemical stratigraphy of the peat. In the western section, a vertical succession of peat types, highly humified at the base and margins, and more fibric in the upper central part, is the result of internal hydrological boundaries, created by density and permeability variations in the peat. The mire is insulated from marine and fluvial influences by topography and hydrology, and displays no evidence of fluctuating sea level. Coal formed in such an environment would be low in sulphur and ash, dull and massive at the base and margins, and finely banded in the upper central part. The eastern section of the mire is in part rheotrophic, with a complex mosaic of vegetation types, and is segmented into distinct drainage areas by tidal blackwater creek channels. Effects of this marine influence are localized to the bay and channel margins. Coals formed in this environment would have large variations in sulphur over distances of a few metres laterally, and a few centimetres vertically. Earthquake-driven coastal subsidence is greatest in the southeast, and has lead to drowning of the deposit. Subsidence events raise the level in the blackwater creeks, moving the front of marine influence to the northwest (inland), and leading to the replacement of freshwater vegetation with mangroves. The degree of penetration of marine waters remains restricted, however, to marginal peats. An increase in the scale of subsidence events may overcome the response capability of the mangroves and lead to disruption of internal hydrological boundaries and ultimate deflation and drowning of the mire.

Thesis/Dissertation

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2009-06-04

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http://hdl.handle.net/2429/8729

Geological Sciences

University of British Columbia

UBCV

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