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Basic: Detrital Indicators

The detrital log suite is useful for distinguishing sediment packages with similar mineralogy but a different source or digenetic history.  Quartz and Zr tend to accumulate together from detrital sediments because they have similar physical and chemical weathering properties.  Generally deposition of sediments from the same source have a similar ratio of quartz to Zr.  A change in that ratio indicates either a change in source or the addition of quartz cement into the system. Illite and K-Spar incorporate Rb into their structure in different trace amounts because it substitutes for K.  Changes in the Rb/K2O ratio can help distinguishing between illite and K-spar in the mineralogy calculations.  Similar analyses can be done for other clays.  Dolomite and calcite are present in the formation as detrital material and/or cements.  A similar relationship exists with Sr, where by it replaces Ca in the carbonate structure such that dolomite tends to be lower in Sr while calcite is significantly higher.  Sr also tends to accumulate in very high concentrations in hydrothermal anhydrite or barite.


Figure A.  Detrital Log Suites from Core Analysis in the Duvernay Formation.



Figure B.  Detrital Log Suites from Drill Cuttings Analysis in the Duvernay Formation.