Publication: Diagenetic paths in the margin of a Triassic Basin:
NW zone of the Iberian Chain, Spain
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Publication Date
2005
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Springer Science Business Media
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Abstract
Buntsandstein deposits generated in a slowly
subsiding basin on the western margin of the Iberian
Chain are represented by a stratigraphic succession of
fluvial deposits less than 100 m thick (conglomerates,
sandstones, and shales). Diagenetic processes in sandstones
can be grouped as eodiagenetic, mesodiagenetic,
and telodiagenetic. Eodiagenesis can be associated
with Muschelkalk, Keuper, and probably early Jurassic
times. Mesodiagenesis is probably related to
Jurassic times. Diagenetic chemical reactions suggest a
maximum burial less than 1.5 km and low temperatures
(<120ºC). Patterns of porosity reduction by
compaction and cementation suggest four diagenetic
stages: (1) Loss of primary porosity by early
mechanical compaction; (2) early cementation (Kfeldspar
and dolomite); (3) dissolution of cements; and
(4) framework collapse by re-compaction. These stages
are manifested by the presence of two types of sandstone.
Type I sandstones present high intergranular
volume (mean, 30%). Type II sandstones are characterized
by high compactional porosity loss and exhibit
low values of intergranular volume (mean, 16.9%).
Type II sandstones are associated with the dissolution
of cement and later re-compaction of type I sandstones.
An intermediate telodiagenetic phase is deduced
and related to the sharp unconformity between
Lower Cretaceous sediments and the underlying sediments.
This suggests that a mechanically unstable
framework collapsed during the Cretaceous, generating
type II sandstones. The analyzed diagenetic paths have
a wide applicability on similar marginal areas of rift
basins.