Publication: Mapping geological stages of climate-dependent iron and clay
weathering alteration on lithologically uniform sedimentary units using
Thematic Mapper imagery (Tertiary Duero Basin, Spain)
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Publication Date
2000
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Taylor & Francis
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Abstract
Weathering processes are responsible for slight surface mineralogical
differences allowing the distinction between lithologically similar geological units
using Thematic Mapper (TM) data. Two different stages throughout time of
overlying iron alteration are notoriously distinctive on the imagery and laboratory
spectra. Their diverse spectral behaviour follows the dominant iron hydroxide
with kaolinite and carbonate crusts on the Pliocene Ochre Alteration typical of
a humid warm climate, compared with the dominant nonhydratated iron oxides
with smectite on the Miocene Red Alteration developed under a mediterranean
dry climate. Iron materials with carbonate hinder appearance of the typical iron
absorption features in the visible wavebands. Therefore, the iron weathering
alteration coatings will be obscured on the imagery when it is developed on
carbonate sediments or detritic sediments with carbonate cement or matrix. The
presence of carbonate within the sediment as cement or alteration product
decreases the overall reflectance of laboratory nonconsolidated rocks and the clay
size fraction from rocks, apart from smoothing the 2200 nm absorption typical of
OH-bearing minerals. The presence of carbonate cement and carbonate crusts
favours the differentiation of some units. Digital mapping through image processing
of different series of digital data leads to a sequential masking of classes
to produce a final map. The sequence of masking produces different maps which
can be used as a tool to model aspects of the sedimentary basin and geological
processes throughout time.