COLOUR ALTERATION INDEX STUDIES IN WESTERN AND ARCTIC CANADA; A DEDICATION TO ANITA HARRIS

As evident from this session, preserved conodont elements have been utilized in a wide variety of ways including as relative time capsules in biostratigraphic studies from Upper Cambrian to Upper Triassic rocks or as geochemically diagnostic crystals for stratigraphic correlation using strontium isotopes or ocean temperature determination using oxygen isotopes. However, perhaps the most routine analysis conducted by ‘conodontologists’ is a comparison of the conodont colour as a thermal maturity indicator or index. This process or CAI analysis was ‘invented’ by the ground-breaking study by Anita Harris (Epstein) published in USGS Professional Paper 995 in 1977. Anita passed away recently this year and so I offer the following in dedication to the brilliant and inspirational career she enjoyed. My CAI analyses are performed by using one of the standard sets provided to me by Anita many years ago – all of my subsequent students have been instructed to “handle with care”. Variation of CAI values of reworked conodonts can help determine provenance and reconstruct burial histories as described earlier in this session. My MSc and PhD in the Sverdrup Basin of the Canadian Arctic provided part of the data set for a thermal maturity study published in GSC Paper 89-19 in 1989. This paper shows a relatively symmetrical basin in terms of thermal maturity and correlates known oil and gas discoveries. It also highlights prospective areas in this frontier hydrocarbon region. In northeastern British Columbia, CAI values are locally higher than expected in Pennsylvanian compared to immediately overlying Permian strata. These anomalies may be attributed to a heating event possibly associated with tectonic events prior to deposition of the Permian, thereby contributing to the geologic history of terrane collision in this region. Alternatively, hydrothermal fluids may have later altered certain units preferentially. In the same region, the Lower Triassic is prospective for a major fairway of unconventional gas. Other thermal maturity indicators like T-max values suggest that the region is overmature and yet conodont CAI points to dry to wet gas conditions; it seems the conodonts have it right. Thanks Anita!