Geological structure of Charity Shoal crater, Lake Ontario, revealed by multibeam bathymetry

作者：Holcombe Troy L^*; Youngblut Scott; Slowey Niall

来源：Geo-Marine Letters, 2013, 33(4): 245-252.

DOI：10.1007/s00367-013-0322-6

Acoustic images of Charity Shoal in Lake Ontario, derived from a 1 x 1 m grid model of bathymetry assembled by the Canadian Hydrographic Service in 2010-2011, confirm the existence of a crater, as revealed by its surface morphology. With these higher quality data, it is possible to describe the crater in much greater detail, and arrive at a better interpretation of the geology than was possible using the earlier bathymetry of Lake Ontario. This new bathymetry of Charity Shoal reveals a continuous rim encircling an ovoid-shaped crater floor 1,200-1,500 m in diameter, with the crater floor being largely devoid of relief. Extending 3-4 km southwest of the crater is a ridge capped by a linear zone of unstratified debris that resembles a medial moraine. NE-SW erosional valleys cut across the crater rim in its southwestern sector. Apparently, glacial erosion has stripped the soil zone off stratified bedrock beneath the crater rim, exposing an intricate pattern of micro-ridges and grooves that bear the record of differential resistance to erosion of successive beds within the sequence of rock strata. Mapping of the shallow structure of the bedrock reveals a continuous ring anticline coinciding with the crater rim, with rock strata dipping gently in both directions away from the rim axis. In combination with existing evidence on the regional stratigraphy, these observations and interpretations are consistent with the Charity Shoal crater having formed in a shallow marine environment by an extraterrestrial impact event in the Middle Ordovician, followed by post-impact sedimentation, and much later, erosion during Pleistocene glaciations. Apparently, post-impact sediments infilled the crater and eventually covered the crater rim, leaving only a diminished structural expression of a crater having no more than 20 m of surface relief. Further details of crater history and origin, and a test of the hypothesis of impact, will likely come from acoustic reflection profiling and direct sampling.

• 出版日期2013-8