PhDENV (Geology) / Department of Mining and Environmental Geology / The Cretaceous period marked the breaking up of Gondwana, giving rise to the
separation of the African and South American continents with the subsequent emergence
of the South Atlantic Ocean. Most correlation studies between the two continents with
respect to paleoenvironmental conditions and tectonic settings during the Cretaceous-
Tertiary periods have been concentrated more on the use of flora and fauna as indicators
with less application of kaolinite as paleoenviromental proxies, hence, this study.
The research involved the evaluation of paleoenvironmental conditions and tectonic
settings of four (4) selected Cretaceous-Tertiary kaolin deposits with two (2) each from
the Eastern Dahomey (Eruku and Lakiri) and Niger Delta (Awo-Omama and Ubulu-Uku)
Basins in Nigeria. Representative kaolin samples collected from the selected deposits
were analysed for physico-chemical, mineralogical, geochemical, isotopic, and
geochronological data. The geochemical data obtained by x-ray fluorescence (XRF)
spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LAICPMS)
were used in unraveling the provenance and tectonic settings of the kaolins. The
kaolinite stable isotopic data for oxygen and hydrogen determined using a Finnigan Delta
XP Mass Spectrometer were used to assess the paleoenvironmental and paleoclimatic
conditions under which the kaolins were formed. The detrital zircon geochronological data
acquired by laser ablation – single collector – magnetic sectorfield – inductively coupled
plasma – mass spectrometry (LA-SFICP-MS) as well as kaolinite stable isotopic data
were employed in constraining the probable timing of kaolinisation. The industrial
applications of the kaolins were assessed based on the physico-chemical (Colour, particle
size distribution (PSD), pH, electrical conductivity, and Atterberg limits), mineralogical,
and geochemical data. The mineralogical data were obtained through x-ray diffractometry
(XRD), Fourier transform infrared (FTIR) spectroscopy, Thermogravimetric analysis and
differential scanning calorimetry, and scanning electron microscopy (SEM). Correlative
studies between selected Cretaceous African and South American kaolins were
conducted.
The results showed that the dominant colour in the studied kaolins was pale red (39 %)
followed by pinkish and light grey (35 %) as well as reddish yellow, light pink, light brown,
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reddish brown, and pinkish white. The pH and EC values generally ranged from 4.27 to
5.29 and 0.2 to 13.1 μS/cm, respectively. The kaolins predominantly have clay to sandy
clay textures with plasticity indices between 10 and 22 wt %.
Bulk mineralogical quantitative results indicated that the Cretaceous kaolins have
kaolinite, quartz, and muscovite present in that decreasing order with anatase, goethite,
and hematite in traces whereas Tertiary kaolins have kaolinite and quartz present in that
decreasing order with anatase and goethite in traces. In the silt fractions, kaolinite and
quartz were the dominant mineral constituents, whereas in the clay fractions, the
dominant clay mineral was kaolinite accounting for 69 to 99 wt % with the non-clay
minerals like quartz, anatase, hematite and goethite accounting for percentages between
1 to 28 wt % in the Cretaceous – Tertiary kaolins. Morphologically, the studied kaolins
were characterised by pseudohexagonal stacks to books and thin platy kaolinite particles
with moderate structural order.
The chemical compositions of the Cretaceous-Tertiary kaolin deposits were identical to
hydrated alumino-silicates based on the dominance of SiO2, Al2O3 and LOI. The chemical
index of alteration (CIA) and chemical index of weathering (CIW) values varied between
96.98 to 99.39 % and 98.95 to 99.89 %, respectively. The clay fractions were enriched in
Cr, Nb, Sc, Th, U, V, Zr, and LREE and depleted in Ba, Co, Rb, Sr, and HREE,
respectively, relative to the average Upper Continental Crust (UCC). The Th/Sc, La/Sc,
Th/Cr, and Eu/Eu* ratios were within the range of sediments derived from felsic rocks.
The TiO2 versus Al2O3 and La-Th-Sc plots indicated source rocks with granitic –
granodioritic - gabbroic compositions. Geochemical discrimination plots showed that the
Cretaceous and Tertiary kaolins were deposited in passive margin tectonic settings.
The stable isotopic results indicated that the values of the Cretaceous kaolins ranged
from – 47 to – 57 ‰ and 19.1 to 19.8 ‰, respectively, with paleotemperatures between
29.0 and 32.2 ˚C, whereas the δD and δ18O corresponding values for the Tertiary kaolins
ranged from – 54 to – 66 ‰ and 20 to 21.5 ‰, respectively, with paleotemperatures
between 17.0 and 23.9 ˚C.
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The U-Pb dating of the detrital zircons showed that the Cretaceous - Tertiary kaolins have
inputs from rocks of Eburnean (2500 – 2000 Ma) and Pan African (750 – 450 Ma) ages.
The age of maximum deposition determined from the least to statistically robust approach
corresponds to the Ediacaran Period (645 – 541 Ma) of the Neoproterozoic Era (1000 –
541 Ma).
The Cretaceous – Tertiary kaolins were formed under intense anoxic chemical
paleoweathering conditions of predominantly felsic rocks in addition to contributions from
intermediate and mafic rocks in passive margin tectonic settings. The Cretaceous kaolins
were formed under warmer conditions relative to the Tertiary kaolins. The West African
Massif rocks were the main sediment sources for the Cretaceous kaolins, whereas both
the West African and Northern Nigerian Massif rocks were the major sediment sources
for the Tertiary kaolins. The most probable timing of kaolinisation for the Cretaceous –
Tertiary kaolins occurred between the Ediacaran (645 – 541 Ma) and Early Cretaceous
Periods for the Cretaceous kaolins and between the Ediacaran Period (645 – 541 Ma)
and Oligo – Miocene age for the Tertiary kaolins. The Nigerian and Brazilian Cretaceous
kaolins formed under similar warm tropical paleoclimate. The study corroborated the
occurrence of the Eburnean (Transamazonian) and Pan African (Brasiliano) orogenic
events across the African and South American continents. Beneficiation of the
Cretaceous – Tertiary kaolins will allow large scale industrial applications in paper
coating, ceramics, pharmaceutical, and cosmetics industries.
The major contributions from this study have been: the better understanding of the past
environmental conditions and tectonic settings, the dating of the possible timing of
kaolinisation, and improvement on the potential industrial applications of the Cretaceous
– Tertiary kaolins. / NRF
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:univen/oai:univendspace.univen.ac.za:11602/1104 |
| Date | 18 May 2018 |
| Creators | Oyebanjo, Olaonipekun Moses |
| Contributors | Ekosse, G. E., Odiyo, J. O. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 1 online resource (xliv, 289 leaves : chiefly color illustrations, color maps) |
| Rights | University of Venda |
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