Geochemical origins of trvertines limestones in the Edward Basin, Albertine Riff DRC - Uganda
Citation:
MANGONI, SYLVAIN KEZIR, Geochemical origins of trvertines limestones in the Edward Basin, Albertine Riff DRC - Uganda, Trinity College Dublin.School of Natural Sciences, 2020Download Item:
FINAL MSC SUBMITED 1402020.pdf (PDF) 36.31Mb
Abstract:
From 2007 to 2014, geological field surveys have been undertaken within the East African Rift System where hot spring Travertine and limestones have been discovered, precipitated at active, or palaeo-spring sites around the margins of the Lake Edward, Lake George and Lake Albert basins. These Travertines are often outcroping over deep-seated rift-bounding faults, linking their origin to meso- and hydro-thermal groundwater flux along fault planes. For this groundwater to attain the necessary high concentration of bicarbonate to potentially precipitate the calcite found in spring pools at the surface, the requirement is that this ground water must have percolated through a substantial carbonate bedrock unit at depth, typically a regional sedimentary limestone. However, the Lake Albert and Lake Edward - Lake George rift basins are infilled by fluvial, deltaic and lacustrine siliciclastic sediments, such as sandstones, claystones and conglomerates. No limestone beds have been documented so far in Albertine rift-fill sediments, either at the surface in outcrop, or at subsurface level in well penetration. Thin caliche paleosols are probably present in rift-fill sediments exposed around the margins of the lake, but these are only poorly developed carbonate concretionary horizons and have not developed into full, laterally continuous calcretes. Thus the presence of these Travertine outcrops, and more specifically, the origin of their bicarbonate, remains enigmatic. Considering the groundwater carbonate chemistry required to precipitate these Travertines, and the complete absence of any fluvial or lacustrine limestone beds in the Lake Albert and Lakes Edward – George rift-fill stratigraphy, the big question remains about how and why these unexpected Travertine limestones have been formed? The present Master of Science degree by research titled 'Geochemical Origins of Travertines in the Lake Edward Basin, Albertine Graben, DRC/ Uganda', succed to understand through the reversible reaction Ca2+ + 2HCO3-- = CaCO3 + CO2 + H2O, the source of the Bicarbonate by which carbonates, and therefore Travertine, are precipitated respectively in cold and hot springs very localized in lines along many Eastern Africa rifts bounding faults. This geochemical origin inquiry has actually found evident answers by running from 2013 to 2018 three series of ICP-MS analyses on Rare Earth Element (& Yttrium) concentrations in a suite of 50 Travertines samples collected within the EARS. Carbon δ13/Oxygen δ18 stables isotopes analyses on selected Travertine samples revealed the surface fractionation processes within the hot spring pools at the surface, because they are mostly affected from CO2 outgassing as the water bubbles to the surface. Strontium isotope ratios low values (~0.703) suggested hydrothermal carbonatite origin while the marine sediment and the continental weathering origin has been easily recorded by their intermediate and high values (~0.708 and ~0.711).(Wierzbowski, 2013) The Travertine respective REE concentrations MUQ normalized values gave the evidence to have derived their bicarbonate from one of three carbonate sources at depth: – Igneous Carbonatites, either present at depth as buried carbonatite lavas, or as intrusives – Marine Limestone, which suggests that it is part of a pre-Tertiary rift unit; likely to be either a failed Karoo-Mesozoic rift package, or part of the 'basement' Proterozoic (possibly Neoproterozoic 'Schisto-Calcaire') – 'half-way house' mixture between these two end-members.
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Ministry of Hydrocarbons DR Congo
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https://tcdlocalportal.tcd.ie/pls/EnterApex/f?p=800:71:0::::P71_USERNAME:SMANGONIDescription:
APPROVED
Author: MANGONI, SYLVAIN KEZIR
Advisor:
Nicholas, ChristopherPublisher:
Trinity College Dublin. School of Natural Sciences. Discipline of GeologyType of material:
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petroleum geology East African RiftLicences: