Conodonts recovered from the carbonate xenoliths in the kimberlites confirm the Paleozoic cover on the Hall Peninsula, Nunavut

Abstract

Hall Peninsula, located on southeastern Baffin Island, Nunavut, hosts the newly discovered Chidliak kimberlite province. Presently, this area lacks Phanerozoic sedimentary cover, except for the unconsolidated glacial deposits; however, Late Ordovician and Early Silurian microfossil conodonts have been recovered from carbonate xenoliths preserved in the Late Jurassic -Early Cretaceous kimberlites. Over 1300 conodont specimens were recovered, among which 32 species representing 23 genera are recognized, with four elements indeterminate. The well-preserved conodont faunas provide reliable evidence on the Hall Peninsula for (i) reconstructing the Lower Paleozoic stratigraphic units, including the Upper Ordovician Frobisher Bay, Amadjuak, Akpatok, and Foster Bay formations, and the Lower Silurian Severn River Formation, (ii) estimating a total of 270-305 m in thickness of Lower Paleozoic sedimentary cover prior to the emplacement of the kimberlites, (iii) tracing the erosion history after the emplacement of the kimberlites, and (iv) calculating a minimum erosion rate of 2 m/Ma. The conodonts have a wide range of conodont Color Alteration Index (CAI) values between 1.5 and 8, which is the largest range recorded in any known suite of xenoliths entrained in kimberlites.Résumé : La péninsule de Hall, située dans le sud-est de l'île de Baffin (Nunavut), renferme la province kimberlitique de Chidliak, découverte récemment. Si la région ne présente actuellement aucune couverture sédimentaire d'âge phanérozoïque, à l'exception de dépôts glaciaires non consolidés, des microfossiles de conodontes d'âge ordovicien à silurien précoce ont toutefois été récupérés de xénolites carbonatés préservés dans des kimberlites d'âge jurassique tardif à crétacé précoce. Plus de 1300 spécimens de conodontes ont été récupérés, parmi lesquels 32 espèces représentant 23 genres ont été reconnues, en plus de quatre éléments indéterminés. Les faunes de conodontes bien conservées fournissent des données fiables pour la péninsule de Hall permettant (i) de reconstituer les unités stratigraphiques du Paléozoïque inférieur, y compris les Formations de la baie de Frobisher, d'Amadjuak, d'Akpatok et de la baie de Foster de l'Ordovicien supérieur, et la Formation de la rivière Severn du Silurien inférieur, (ii) d'estimer à un total de 270-305 m l'épaisseur de la couverture sédimentaire du Paléozoïque inférieur avant l'intrusion des kimberlites, (iii) d'établir l'historique d'érosion après la mise en place des kimberlites et (iv) de calculer un taux d'érosion minimum de 2 m/Ma. Les conodontes définissent une grande fourchette de valeurs de l'indice d'altération de la couleur (IAC) allant de 1,5 à 8, soit la plus grande fourchette observée pour une suite de xénolites entraînés dans des kimberlites. [Traduit par la Rédaction]

Reconstructing deep‐time histories from integrated thermochronology: An example from southern Baffin Island, Canada

“…Our integrated model suggests southern Baffin fully exhumed by the latest Neoproterozoic to early Palaeozoic and regional apatite fission‐track data generally suggest that burial of < 3–4 km occurred in the late Palaeozoic to early Mesozoic, followed by renewed unroofing in the Carboniferous to Triassic–Jurassic. Further work is required to evaluate regional burial, but minor Cretaceous burial on the order of ~1‐2.5 km was probably isolated to southernmost Cumberland and Hall peninsulas based on kimberlite constraints (Zhang & Pell, ), our much younger < 150 Ma Cumberland AFT ages, and the consistently older AFT age trends to the northwest (McGregor et al., ).…”

“…We do not impose any constraints on the Proterozoic t–T history other than requiring cooling through closure for the apatite U–Pb system. The independent geological constraints on the Phanerozoic t–T history are as follows: (a) Preserved Foxe Basin and Baffin Island sediments imply crystalline bedrock was near surface in the Late Ordovician (Zhang & Riva, ); (b) Early Palaeozoic xenoliths from the c. 156–138 Ma Chidliak kimberlites on Hall Peninsula (Heaman, Pell, Grütter, & Creaser, ; Zhang & Pell, ) demonstrate Palaeozoic strata were fully eroded to within ~200–300 m by the Late Jurassic; and (c) preserved sediment remnants near Cape Dyer (Figure ) locally suggest minor late Cretaceous–Palaeocene burial (Burden & Langille, ). We assume that the constraints are regional (at least for Cumberland and Hall Peninsula) because the oldest known sediments encountered in the offshore Baffin Island shelf (i.e.…”

The stromatoporoidHabrostromain the upper Silurian (uppermost Pridoli)–Lower Devonian (Lochkovian) of North America, and the paleobiogeographic significance ofH.centrotum(Girty, 1895)

“…Even more impactful are the discoveries of Devonian-age xenoliths composed of normal-marine sedimentary rocks in kimberlites in the Canadian Shield of Northwest Territories (Cookenboo et al, 1998), the Ontario-Quebec boundary area (McCracken et al, 2000), and southern Baffin Island, Nunavut (Zhang and Pell, 2014) (Fig. 11.2).…”

Rare stromatoporoids from the Lower Devonian (Emsian) of Nevada, and their biostratigraphic and paleobiogeographic significance

“…He saw this basin as isolated from basins to the west during the Devonian, and noted that it received sediments intermittently at that time (i.e., there are several unconformities in the Devonian sequence). Even more exciting is the discovery of Devonian-age xenoliths composed of normal-marine sedimentary rocks in Jurassic kimberlites in the Canadian Shield of Northwest Territories (Cookenboo et al, 1998), the Ontario-Quebec boundary area (McCracken et al, 2000), and southern Baffin Island, Nunavut (Zhang and Pell, 2014; Fig. 4).…”