A mineralogic approach to estimating the volume of dissolution,
alteration, and unaltered residue from weathering of different
provenance lithotypes
Abstract
Evaluation of the approximate magnitude of the gross discrepancy between
the volume of sediment produced on the hinterland and the volume
deposited in the basin, over long time and length scales, is required to
make source-to-sink sediment mass-balance calculations more accurate so
that multiple sources for a single widespread stratigraphic unit, or
bypass of the unit, might be more easily detected.
This paper outlines a method to characterize the sources of sediments,
or provenance lithotypes, according to their relative ability to produce
dissolved ions, clay minerals, and unaltered residue at different levels
of weathering. Estimating the relative proportion of the hinterland that
is dissolved supports mass-balance analysis comparing hinterland
denudation with basinal deposition, whereas estimating the relative
proportion of clay (both original clay, eroded from mudstone, for
example, as well as newly created clay produced by weathering of
feldspar) supports potential identification of multiple sediment
sources. The method is illustrated with a practical example from the
Bohemian Massif and documented with an Excel workbook.
This is a mineralogical approach based on mineral inventories of
weathering profiles. Even if the prediction is necessarily uncertain
because the mineralogical representation of the PLs are gross
abstractions, the modelled transformation processes are crude cartoons,
and the extent of transformation under different environmental
conditions is wild speculation based on sparse examples, quantitative
provenance analysis will be more accurate and more precise than it would
be if dissolution and alteration were not explicitly accounted. There is
ample opportunity for the community to improve the procedure!