THE LATE DEVONIAN APOLLO-ATEN ASTEROID MAXIMUM: APPALACHIAN BASIN LITHOLOGIC AND BIOTIC RESPONSE

The Late Devonian of the Appalachian Basin preserves two stage boundaries: (1) Givetian/Frasnian (G/F) at ~370Ma, and (2) Frasnian/Famennian (F/F) ~364Ma. The G/F boundary separates the calcareous shales and argillaceous limestones of the Hamilton Group-Tully Formation from the black shales of the Geneseo Formation with an associated mass extinction event. The Panther Mountain structure of eastern New York State may have formed at this time. The F/F boundary lies within the Hanover Formation and is associated with high organic carbon content and a prolonged (~3My) mass extinction (~80% of marine biota). The 120 km Woodleigh impact structure of Western Australia may be associated with this mass extinction and related global Iridium anomalies and microtektites at the F/F boundary.

The greatest concentration of well-dated Paleozoic impact structures occurs in the Late Devonian: Alamo (367±2Ma), Charlevoix (~357±15Ma), Flynn Creek (369±1Ma), Ilyinets (395±5Ma), Kaluga (380±10Ma), Lac la Moinerie (395±15Ma), Panther Mountain (~370Ma), Siljan (361.9±1.1Ma), Woodleigh (359±4Ma), and possibly the ~370Ma Amonau Event. Associated elevated PGE levels suggest that chondritic impactors formed most of these structures. A significant increase in asteroid belt gap delivery of apollo-aten Earth-crossing asteroids 350-390 Ma would explain this intense cratering record and provide a forcing mechanism for the major lithologic and biotic changes preserved in the Late Devonian Appalachian Basin.