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J.A. Cooper

Publications and source records attributed to J.A. Cooper.

5 recordsLinked to original sources

Identification guide to skates (Family Rajidae) of the Canadian Atlantic and adjacent regions

Ecosystem-based management requires sound information on the distribution and abundance of species both common and rare. Therefore, the accurate identification for all marine species has assumed a much greater importance. The identification of many skate species is difficult as several are easily confused and has been found to be problematic in both survey data and fisheries data collection. Identification guides, in combination with training and periodic validation of taxonomic information, improve our accuracy in monitoring data required for ecosystem-based management and monitoring of populations. This guide offers a comparative synthesis of skate species known to occur in Atlantic Canada and adjacent regions. The taxonomic nomenclature and descriptions of key morphological features are based on the most up-to-date understanding of diversity among these species. Although this information will aid the user in accurate identification, some features vary geographically (such as colour) and others with life stage (most notably the proportion of tail length to body length; the presence of spines either sharper in juveniles or in some cases not yet present; and also increases in the number of tooth rows as species grow into maturity). Additional information on juvenile features are needed to facilitate problematic identifications (e.g. L. erinacea vs. L. ocellata). Information on size at maturity is still required for many of these species throughout their geographic distribution.

Report↗

Geochronology of Precambrian granites and associated U-Ti-Th mineralization, northern Olary province, South Australia

Proterozoic granitoids and metamorphic rocks in the Olary province of the Willyama block of South Australia host ore-grade amounts of U-Th-Ti and U-Fe-Ti-Th minerals. U-Pb-Th isotope analyses on zircons from all granitoids associated with the Crocker Well brannerite deposit indicate that these granitoids were intruded within a short time span, close to the 1579.2??1.5 m.y. age of the brannerite-bearing host-rock. Though the early Paleozoic Delamerian orogeny was intense in this region, the zircon isotopic systems remained unaffected; rather, the best-defined zircon chords on concordia plots show a welldefined lower intercept of 43.8??6.5 Ma, which can only be associated with early Tertiary block faulting. Pb-U-Th isotope analyses on brannerite from the Crocker Well deposit and davidite from the Mt. Victoria deposit and the Radium Hill deposit yield badly scattered and discordant apparent ages that suggest a primary age at least as old as the age of the Crocker Well granitoids, followed by a severe disturbance in the early Paleozoic. ?? 1984 Springer-Verlag.

Contributions to Mineralogy and Petrology↗

An evaluation of the zircon method of isotopic dating in the Southern Arabian Craton

A zircon study has been made on eleven samples of igneous rocks from the Saudi Arabian Craton. Ages of sized and magnetic fractions of zircon concentrates show variable degrees of discordance which seem to result from a very young disturbance that produces linear arrays in the Concordia plot. Model age calculations based on a statistically and geologically reasonable lower intercept produce very consistent internal relationships. The Pan African Orogeny, considered to be responsible for loss of radiogenic argon and strontium from minerals of many rocks, does not appear to have affected the zircon data, even though uplift had exposed the rocks of the Arabian Shield at that time. Tonalite, granodiorite, and crosscutting leucoadamellite bodies in the southern part of the An Nimas Bathylith yield ages in the time range 820-760 Ma. A narrow time range of 660 to 665 million years was indicated for ages of widely separated and compositionally different intrusive bodies all to the east of the An Nimas Bathylith. This work suggests that the younger end of the age spectrum established from regional K-Ar and Rb-Sr measurements may be underestimated, and that magmatic activity could be more episodic than previously assumed.

Contributions to Mineralogy and Petrology↗

An evaluation of the zircon method of isotopic dating in the southern Arabian Craton, Kingdom of Saudi Arabia

A zircon study has been made on 11 samples of igneous rocks from the Saudi Arabian craton. Ages of sized and magnetic fractions of zircon concentrates show variable degrees of discordance, which seem to result from a very young disturbance that produces linear arrays in the Concordia plot. Model age calculations based on a statistically and geologically reasonable lower intercept produce very consistent internal relationships. The Pan African Orogeny, considered to be responsible for loss of radiogenic argon and strontium from minerals of many rocks, does not appear to have affected the zircon data, even though uplift had exposed the rocks of the Arabian Shield at that time. Tonalite, granodiorite, and crosscutting leuco-adamellite bodies in the southern part of the An Nimas batholith yield ages in the time range 820-760 m.y. A narrow time range of 660 to 665 million years was indicated for ages of widely separated and compositionally different intrusive bodies all to the east of the An Nimas batholith. This work suggests that the younger end of the age spectrum established from regional K-Ar and Rb-Sr measurements may be underestimated, and that magmatic activity could have been more episodic than previously assumed.

Open-File Report↗