Friday, May 22, 2015

Highlights—Why is the Holder tight? The impact of early diagenesis

Diagenesis represents the progressive alteration of sediment and rock; it is never simple. To examine diagenesis, many studies of carbonate successions focus on detailed petrographic study and bulk geochemical analyses. To test the hypothesis that multiple episodes of early diagenesis (subaerial exposure) are recorded as multi-phase calcite cements, Wasson and Lohmann examine petrographic and geochemical character of the Holder Formation (Pennsylvanian, New Mexico, USA). This study integrates field observations of the phylloid-algal and microbial mounds with microsampled geochemical data from some of the key features, and clarifies the detailed diagenetic and developmental history of the unit. The results illustrate that most primary and secondary porosity of the units was occluded within the first 500 m of burial, by Early Permian time, and highlight how early diagenesis can markedly impact carbonate strata. [Ed. Note: the Osmonds knew this in 1972.)

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