Diagenetic regimes and the foraminiferal record in the Beaufort-Mackenzie Basin and adjacent cratonic areas

David H. McNeil


Wpływ procesów diagenetycznych na zachowanie skorupek otwornic w osadach Basenu Beauforta-Mackenzie i przyległych basenach obszarów kratonicznych

Terrigenous clastic, deltaic-dominated, sedimentary basins, such as the Beaufort-Mackenzie Basin of Arctic Canada, are thick, areally extensive bodies of sediment that undergo a wide variety of diagenetic processes in a wide variety of physical and chemical environments. Diagenetic processes and effects are unique to various parts of the basin, but four diagenetic regimes can be isolated to encompass many of the diagenetic processes affecting sedimentary basins. These are the early, burial, overpressured, and meteoric diagenetic regimes. Foraminiferal preservation may be affected by chemical, physical, and biological activities in the diagenetic regimes.

Early diagenetic conditions are generally favourable for the preservation of foraminifers, but bacterial production of CO2 could lead to the dissolution of calcareous foraminifers and early diagenetic pyrite often infills foraminiferal tests.

The burial diagenetic regime is dominated by increasing temperature, pressure, and compaction. Increased temperature is reflected by thermal, colour alteration of organic cement in the test of agglutinated foraminifers. Thermally controlled mineralogical changes are also evident in the burial diagenetic regime and include silicification of the agglutinated test, chloritization of calcareous foraminifers, and precipitation o f secondary clay minerals such as kaolinite, smectite, illite, and chlorite within the foraminiferal test. Thermal maturity can be assessed by application o f the Foraminiferal Colouration Index (FCI). Mineralogical changes in foraminifers allow for the establishment o f four broad burial diagenetic zones (A to D).

The overpressured regime may be responsible for a retardation in thermal alteration of agglutinated foraminifers and silicification of agglutinated foraminifers may be a precursor as well as an effect o f overpressured fluids in sedimentary basins.

The meteoric regime is significant during periods of extensive erosion. Interactions between organic and inorganic detritus and meteoric waters may lead to dissolution of calcareous foraminifers and precipitation of secondary minerals such as kaolinite and minor amounts of quartz.

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