Sir,
Reference HudsonHudson (1983) reported evidence for glacial activity on Hans Island, but discussed two directions of ice movement over the island. In 1988, while studying the Palaeozoic strata in the vicinity of Nares Straight, I observed well-preserved rock sculpturing which indicated a clear direction for glacial movement across the island. The implications of this evidence to the glacial history of the High Arctic are discussed briefly in the following correspondence.
Scours, grooves, and crescent fractures are present near the summit of the island, on dolomitic limestones essentially void of till; yet, erratics are ubiquitous. Striae and plucked bedrock record movement from south-south-west to north-north-east, essentially parallel to the nearby coasts of Nares Strait. Striae occur on relatively smooth dolomitic limestone approximately 160m a.s.l. (Figs 1 and 2). The highest point on the island, recorded very close to the observed glacial sculpturing, is 168 m as measured by the Geodetic Survey of Canada. Channel bottom, within a 10 km radius of the island centre is between 473 and 264 m below sea-level. The island is cross-cut by numerous normal faults, probably related to early Tertiary tectonism, but strati-graphic offset is less than 10 m. Thick-bedded dolomitic limestone of the island dips 10–15° towards the north-west, following the attitude of contiguous Palaeozoic strata of north Greenland. These strata are in marked contrast to those of northern Ellesmere Island, a tightly folded and faulted carbonate and clastic sequence.
Two ideas pertinent to the present observations are that Nares Strait was a conduit for extensive Innutian and Greenland ice flux (Reference WeidickWeidick, 1978; Reference BlakeBlake, 1987) until the latest deglaciation which commenced 8–9 ka B P., or that it was subject to three episodes of glaciation, occurring approximately at 8, 80, and 500 ka to 1 Ma B.P. However, the two latest, areally restricted glacial episodes produced glaciers which probably did not occupy Nares Strait, implying that the strait was glacier-free from perhaps 500 ka to 1 Ma (Reference EnglandEngland, 1987). It is possible that the oldest (500 ka to 1 Ma B.P.) glacial advance of Greenland ice on to Ellesmere Island may have produced the Hans Island glacial features, but this would require that striae be preserved in relatively good condition on carbonates since ice retreat about 500 ka to 1 Ma B.P.
Fig. 1. View of glacial striae observed at 160m a.s.l. on Hans Island. Note plucking on north-north-east side of outcrop (Geological Survey of Canada (GSC) photograph 204814).
Fig. 2. Detail of striae and well-developed crescent fractures on limestone. Arrow indicates articulate megalo-dont bivalve, a typical fossil component of Hans Island strata. The notebook at the top of the photograph is 21 cm long (GSC photograph 204815A).
The relationship between striae-preservation potential and weathering is unclear but, if the weathering characteristic of the Hans Island glaciated carbonates is generally comparable to glaciated rocks of Baffin Island (Reference DykeDyke, 1979), it would indicate that Hans Island striae were inscribed considerably more recently than during a glacial episode about 500 ka to 1 Ma B.P. A similar case was made for glacial striae on Pim Island (Reference BlakeBlake, 1978). There, the age of organic sediments in lakes, the occurrence of striae at a high elevation, and the precariously positioned erratics constrain glaciation to within a similar time frame to that hypothesized for Hans Island. Thus, the relative lack of glacial drift at this locality, the occurrence of striae higher than the recorded position of sea-level during the latest “full glacial sea” (120 m according to Reference EnglandEngland (1987)), and the vulnerability of the carbonates to weathering support a relatively recent time of formation. If, indeed, these structures were the result of an earlier glacial event (e.g. >500 ka B.P.), one would expect erosion of the evidence but, until a quantitative study of weathering of these strata is done, the relationship of time and striae preservation is a moot point.
The implication of the observed glacial structure is that Nares Strait was a conduit for a large glacier which moved from the south. Additional evidence for contiguous (?) glacial movement is recorded from east-central Ellesmere Island, on Pim Island, and vicinity. There, abundant sculpturing and scouring of granites indicates a southward ice movement. The present data support the theory of a large grounded glacier in Nares Strait. Ice flowing from two source areas, Ellesmere Island and Greenland, perhaps coalesced in Kane Basin and moved north and south between Greenland and Ellesmere Island (the hypothesis of BIake (1978)). The good preservation of striae may indicate a more recent time for Nares Strait glaciation than that previously hypothesized, for example, occurring up to 10 ka B.P., thereby agreeing with similar episodes of Nares Strait glaciation proposed by Reference BlakeBlake (1978) and Reference WeidickWeidick (1978); but, clearly, more definitive glacial chrono-stratigraphy and additional field data would facilitate a more accurate interpretation.
I am grateful to W. Blake of the Geological Survey of Canada (GSC) for drawing my attention to the significance of these observations and for proof-reading a draft of this letter.
