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New data and interpretations on geological relationships of igneous rocks at Mokka Fiord, Axel Heiberg Island, Nunavut, provide insight into the timing and nature of magmatism associated with the Sverdrup Basin and High Arctic Large Igneous Province (HALIP). Field relationships indicate that the igneous rocks, previously interpreted to be volcanic flows, are most likely an intrusive unit discordant to regional bedding. An intrusive origin helps resolve chronostratigraphic inconsistencies in previous work. The host rocks are palynologically constrained to be late Barremian to late Aptian in age and are interpreted to be Paterson Island or Walker Island member of the Isachsen Formation. If the igneous body is intrusive, it's previously reported Ar--Ar age (102.5 [+ or -] 2.6 Ma) is no longer in conflict with accepted stratigraphic interpretations and probably reflects the emplacement age of the intrusion. Lingering uncertainties in interpreting the normal and reverse magnetic polarities determined in the previous work remain, and both are considered viable. Although this uncertainty precludes definitive conclusions on the significance of paleomagnetic data at Mokka Fiord, examination of the stratigraphic, paleomagnetic, and geochronologic relationships there highlight potential for the study of excursions, or reversed magnetic polarity subchrons, in the Cretaceous Normal Superchron elsewhere in the HALIP.De nouvelles donnees et interpretations sur les relations geologiques de roches ignees dans le fjord Mokka (ile Axel Heiberg, Nunavut) fournissent de nouveaux renseignements sur la chronologie et la nature du magmatisme associe au bassin de Sverdrup et a la grande province ignee de l'Extreme Arctique (HALIP). Les relations de terrain indiquent que les roches ignees, interpretees precedemment comme etant des coulees volcaniques, constituent tres probablement une unite intrusive discordante par rapport au litage regional. Une origine intrusive aide a resoudre des incoherences chronostratigraphiques dans des travaux anterieurs. Il est determine, du point de vue palynologique, que les roches hotes sont d'age barremien tardif a aptien tardif et sont interpretees comme etant le membre de l'ile Paterson ou de l'ile Walker de la Formation d'Isachsen. Si le corps igne s'avere intrusif, son age Ar--Ar (102,5 [+ or -] 2,6 Ma) deja publie n'entre plus en conflit avec les interpretations stratigraphiques acceptees et reflete probablement l'age de mise en place de l'intrusion. Des incertitudes demeurent concernant l'interpretation des polarites magnetiques normales et inverses determinees dans les etudes anterieures, et les deux sont jugees viables. Si ces incertitudes empechent de tirer des conclusions definitives sur la signification de donnees paleomagnetiques au fjord Mokka, l'examen des relations stratigraphiques, paleomagnetiques et geochronologiques font ressortir un potentiel pour l'etude d'excursions, ou de sous-chrons de polarite magnetique inversee, dans le superchron normal du Cretace ailleurs dans l'HALIP. [Traduit par la Redaction], IntroductionCretaceous siliciclastic and igneous rocks of the Sverdrup Basin near the mouth of Mokka Fiord, Axel Heiberg Island (Fig. 1), were examined to clarify conflicting and apparently irreconcilable published data [...]

Although the Jurassic was a period of high diversity in ichthyosaurs, only a small number of specimens have been recorded from Canada to date. We describe here a new occurrence of an ophthalmosaurid ichthyosaur from a shallow marine depositional environment within the Bowser Basin of northern British Columbia. Based on vertebral diameters and the size of the humerus, the ichthyosaur was relatively large compared to other contemporaneous forms, yet possessed teeth that were small for its body size. As well, the height to length ratio of the preserved vertebrae suggests it may have had a more elongate, less regionalized body shape. Although indeterminate at a generic level, the presence of Late Jurassic ichthyosaurs in nearshore waters of northwestern North America further demonstrates their cosmopolitan distribution. Si le Jurassique fut une periode de forte diversite chez les ichthyosaures, seul un petit nombre de specimens a ete enregistre au Canada a ce jour. Nous decrivons une nouvelle occurrence d'ichthyosaure ophthalmosauride d'un milieu de sedimentation marin peu profond dans le bassin de Bowser du nord de la Colombie-Britannique. A la lumiere du diametre des vertebres et de la taille des humerus, l'ichthyosaure etait relativement grand par rapport a d'autres formes contemporaines, mais possedait de petites dents pour la taille de son corps. Le rapport entre la hauteur et la longueur des vertebres preservees semble en outre indiquer une forme du corps plus allongee et moins regionalisee. Bien que le genre ne soit pas determine, la presence d'ichthyosaures au Jurassique tardif dans les eaux littorales du nord-ouest de l'Amerique du Nord constitue une nouvelle demonstration de leur repartition cosmopolite. [Traduit par la Redaction], Introduction Ichthyosaurs were a diverse and cosmopolitan group of highly aquatic marine reptiles that first appeared in the Early Triassic and survived until the Late Cretaceous (Sander 2000; McGowan and [...]

The Cordillera in northern Canada is underlain by westward tapering layers that can be followed from outcrops of Proterozoic strata in the Foreland belt to the lowermost crust of the orogenic interior, a distance of as much as 500 km across strike. They are interpreted as stratified Proterozoic rocks, including ~1.8-0.7 Ga supracrustal rocks and their basement. The layering was discovered on two new deep seismic reflection profiles in the Yukon (Line 3; ~650 km) and northern British Columbia (Line 2; ~1245 km in two segments) that were acquired as part of the Lithoprobe Slave-Northern Cordillera Lithospheric Evolution (SNORCLE) transect. In the Mackenzie Mountains of the eastern Yukon, the layering in Line 3 is visible between 5.0 and 12.0 s (~15 to 36 km depth). It is followed southwestward for nearly 650 km (~500 km across strike) and thins to less than 1.0 s (~3.0-3.5 km thickness) near the Moho at the Yukon-Alaska international boundary. In the northern Rocky Mountains of British Columbia, the upper part of the layering on Line 2 correlates with outcrops of Proterozoic (1.76-1.0 Ga) strata in the Muskwa anticlinorium. At this location, the layering is at least 15 km thick and is followed westward then southward into the middle and lower crust for ~700 km (~300 km across strike). It disappears as a thin taper at the base of the crust ~150 km east of the coast of the Alaskan panhandle. The only significant disruption in the layering occurs at the Tintina fault zone, a late to postorogenic strike-slip fault with up to 800 km of displacement, which appears as a vertical zone of little reflectivity that disrupts the continuity of the deep layering on both profiles (~300 km apart). The base of the layered reflection zone coincides with the Moho, which exhibits variable character and undulates in a series of broad arches with widths of ~150 kin. In general, the mantle appears to have few reflections. However, at the southwest end of Line 3 near the Alaska-British Columbia border, a reflection dips eastward from ~14.0 s to ~21.0 s (~45 to 73 km depth) beneath exposed Eocene magmatic rocks. It is interpreted as a relict subduction surface of the Kula plate. Our interpretation of Proterozoic layered rocks beneath most of the northern Cordillera suggests a much different crustal structure than previously considered: (1) Ancient North American crust comprising up to 25 km of metamorphosed Proterozoic to Paleozoic sediments plus 5-10 km of pre-1.8 Ga crystalline basement projects westward beneath most of the northern Canadian Cordillera. (2) The lateral (500 km by at least 1000 km) and vertical (up to 25 km) extent of the Proterozoic layers and their internal deformation are consistent with a long-lived margin for northwestern North America with alternating episodes of extension and contraction. (3) The detachments that carry deformed rocks of the Mackenzie Mountains and northern Rocky Mountains are largely confined to the upper crustal region above the layering. (4) Accreted terranes include thin klippen that were thrust over North American pericratonic strata (e.g., Yukon-Tanana), and terranes such as Nisling and Stikinia that thicken westward as the underlying Proterozoic layers taper and disappear. (5) The ages of exposed rocks are not necessarily indicative of the ages of underlying crust, a frequent observation in Lithoprobe interpretations, so that estimates of crustal growth based on surface geology may not be representative. INDEX TERMS: 7205 Seismology: Continental crust (1242); 8102 Tectonophysics: Continental contractional orogenic belts; 8110 Tectonophysics: Continental tectonics--general (0905); KEYWORDS: crustal structure, seismic reflection, northern Cordillera.

Clastic strata composing the northern Bowser basin record the accretion of Stikinia to the composite western edge of the North American plate (Cache Creek-Quesnellia-Slide Mountain-Kootenay-North America) in early Middle Jurassic time and the concomitant demise of the intervening Cache Creek ocean. Initial flexural subsidence of the northern Bowser basin, resulting from thrust loading of Cache Creek terrane on Stikinia, is represented by an organic-rich shale of Aalenian age (the Abou Formation of the Spatsizi Group). Coarse-grained sediment first appeared in early Bajocian time following uplift and subaerial exposure of Cache Creek rocks in the upper plate. Thus, the inception of the Bowser basin was Aalenian, rather than Bajocian, as believed by earlier workers. Aalenian southwest-vergent thrusting at the composite western edge of North America is also known from southern British Columbia, a coincidence that implicates collision with Stikinia in the south as a cause of that deformation.