Predictive diagenetic clay-mineral distribution in siliciclastic rocks as a tool for identifying sequence boundaries in non-marine successions: the Coalspur Formation, west-central Alberta

Abstract

The study of upper Cretaceous -lower Tertiary fluvial deposits of the Coalspur Formation in the Foothills region of west-central Alberta reveals that the distribution of early authigenic kaolinite has a well-defined relation to the sequence stratigraphic framework. In this context, it has been observed that the kaolin mineral content increases in sandstones lying below subaerial unconformities, which mark the most significant stratigraphic hiatuses and hence the sequence boundaries in fully fluvial successions. The increased abundance of authigenic kaolinite immediately below sequence boundaries may have been caused by the infiltration of meteoric water during times of subaerial erosion, resulting in the dissolution of unstable minerals (e.g., micas and feldspar) and the formation of kaolinite and secondary porosity. It is therefore suggested that the change in clay mineral assemblages in the stratigraphic section depends in part on the position of the analyzed sandstone samples relative to the sequence boundaries. In a larger context, the method of using authigenic clays to delineate depositional sequences in non-marine successions needs to be evaluated on a caseby-case basis, as the diagnostic early diagenetic minerals underlying the sequence boundary may change as a function of palaeoclimate and also as a function of late diagenetic processes.

Basin‐axial progradation of a sediment supply driven distributive fluvial system in the Late Cretaceous southern Utah foreland

“…Meteoric water flow causes an alteration zone that moves downward at a rate on the order of 10s m∙Myr −1 (Bjørkum et al ., ). As such, similarly high concentrations of authigenic kaolinite within sandstones have been previously tied to unconformities (Emery et al ., ; Macaulay et al ., ; McCarthy & Plint, ; Ketzer et al ., ; Khidir & Catuneanu, ).…”

Origin and Distribution of Carbonate Cement in Tight Sandstones: The Upper Triassic Yanchang Formation Chang 8 Oil Layer in West Ordos Basin, China

“…Besides the dissolution of Ca-feldspars, clay mineral transformations such as illitization of smectite are also accompanied by a release of Ca 2+ and Mg 2+ into solution [12,53]. Carbonate cement (mainly Type II) would precipitate with enrichment of Ca 2+ and Mg 2+ ions and a decrease in CO 2 concentration under Fe-and Mn-reducing, suboxic to sulfate-reduction geochemical conditions [57][58][59][60]. With increasing burial depth and temperature, the decomposition of organic acid decarboxylation would be enhanced, and more clay mineral transformation would occur [12].…”