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Keywords:

  • Siliciclastic rocks;
  • distribution pattern;
  • sequence stratigraphy

Summary

The spatial and temporal distribution of diagenetic alterations in siliciclastic sequences is controlled by a complex array of interrelated parameters that prevail during eodiagenesis, mesodiagenesis and telodiagenesis. The spatial distribution of near-surface eogenetic alteration is controlled by depositional facies, climate, detrital composition and relative changes in sea-level. The most important eogenetic alterations in continental sediments include silicate dissolution and the formation of kaolinite, smectite, calcrete and dolocrete. In marine and transitional sediments, eogenetic alterations include the precipitation of carbonate, opal, microquartz, Fe-silicates (glaucony, berthierine and nontronite), sulphides and zeolite. The eogenetic evolution of marine and transitional sediments can probably be developed within a predictable sequence stratigraphic context. Mesodiagenesis is strongly influenced by the induced eogenetic alterations, as well as by temperature, pressure and the composition of basinal brines. The residence time of sedimentary sequences under certain burial conditions is of key importance in determining the timing, extent and patterns of diagenetic modifications induced. The most important mesogenetic alterations include feldspar albitization, illitization and chloritization of smectite and kaolinite, dickitization of kaolinite, chemical compaction as well as quartz and carbonate cementation. Various aspects of deep-burial mesodiagenesis are still poorly understood, such as: (i) whether reactions are accomplished by active fluid flow or by diffusion; (ii) the pattern and extent of mass transfer between mudrocks and sandstones; (iii) the role of hydrocarbon emplacement on sandstone diagenesis; and (iv) the importance and origin of fluids involved in the formation of secondary inter- and intragranular porosity during mesodiagenesis. Uplift and incursion of meteoric waters induce telogenetic alterations that include kaolinitization and carbonate-cement dissolution down to depths of tens to a few hundred metres below the surface.