Identification of the Bloody Creek structure, a possible impact crater in southwestern Nova Scotia, Canada

Abstract

Abstract--An approximately 0.4 km diameter elliptical structure formed in Devonian granite in southwestern Nova Scotia, herein named the Bloody Creek structure (BCS), is identified as a possible impact crater. Evidence for an impact origin is based on integrated geomorphic, geophysical, and petrographic data. A near-continuous geomorphic rim and a 10 m deep crater that is infilled with lacustrine sediments and peat define the BCS. Ground penetrating radar shows that the crater has a depressed inner floor that is sharply ringed by a 1 m high buried scarp. Heterogeneous material under the floor, interpreted as deposits from collapse of the transient cavity walls, is overlain by stratified and faulted lacustrine and wetland sediments. Alteration features found only in rim rocks include common grain comminution, polymict lithic microbreccias, kink-banded feldspar and biotite, single and multiple sets of closely spaced planar microstructures (PMs) in quartz and feldspar, and quartz mosaicism, rare reduced mineral birefringence, and chlorite showing plastic deformation and flow microtextures. Based on their form and crystallographic orientations, the quartz PMs consist of planar deformation features that document shock-metamorphic pressures ≤25 GPa.The age of the BCS is not determined. The low depth to diameter ratio of the crater, coupled with anomalously high shock-metamorphic pressures recorded at its exposed rim, may be a result of significant post-impact erosion. Alternatively, impact onto glacier ice during the waning stages of Wisconsinian deglaciation (about 12 ka BP) may have resulted in dissipation of much impact energy into the ice, resulting in the present morphology of the BCS.

Origin and provenance of spherules and magnetic grains at the Younger Dryas boundary

“…† Two other features, one (Charity Shoal) submerged in Lake Ontario (21) and the other (Bloody Creek) in Nova Scotia (22), may represent additional or alternate impact craters associated with the YDB event. They have not been accurately dated, but their proposed range of dates spans the YD onset.…”

The North structure: evidence for a second possible impact event at the Bloody Creek site, Nova Scotia, Canada

“…It is possible that post-glacial landscape evolution, in particular lateral erosion by Bloody Creek during the early and Mid-Holocene, may have reworked any large erratics and produced the coarse gravel that was noted above the diamicton in the percussion cores. It is also possible that the structure postdates active, erosive glaciation (Spooner et al 2009). …”

“…BP (Stea and Mott 1998). The till in the study area is generally thin (<5 m thick) and is characterized by a sandy matrix with angular stones and boulders derived from local bedrock (Spooner et al 2009). Bedrock exposure is poor due to till, lake, wetland and forest cover, but, where present, is glacially sculpted.…”

“…The interpretation of a possible impact origin for the Bloody Creek structure in Nova Scotia was based on an integrated analysis of geomorphic, geophysical, and petrographic data (Stevens 1995;Spooner et al 2009). Aerial photographs taken before the Bloody Creek structure site was flooded reveal a prominent elliptical rim (0.42 km × 0.35 km), and geophysical surveys confirmed a 5 m-deep depression in-filled with post-glacial lacustrine and wet-The North structure: evidence for a possible second impact near the Bloody Creek site, Nova Scotia, Canada…”

“…The study land sediments. Petrographic analysis revealed planar deformation features broadly supportive of shock metamorphism (Spooner et al 2009). Here we present evidence for an additional elliptical impact feature in Nova Scotia, located 1 km north of the Bloody Creek structure and hence termed the North structure.…”