T76 Trace Fossils, Mass Extinctions, and Event Boundaries: Endobenthic and Fossorial Responses to Terrestrial and Extraterrestrial Perturbations

Monday, 29 October 2007
8:00 AM - 12:00 PM

ICHNOLOGY OF THE LOWER TRIASSIC BLIND FIORD & BJORNE FORMATIONS, SVERDRUP BASIN, ARCTIC CANADA

Paper number: T76-4
Program: Technical Sessions
Time: 8:50 AM – 9:10 AM

Authors

Abstract

Lower Triassic strata in the Sverdrup Basin are represented by basin-center shale, & minor sandstone of the Blind Fiord Formation & basin-margin sand-dominated successions of the Bjorne Formation. Both units are dominantly siliciclastic successions that interfinger extensively reflecting a series of three major marine transgressions & regressions. The Bjorne-Blind Fiord succession rests upon chert, shale & siliceous siltstone of the Van Hauen & Lindstrom Formations. This contact is conformable in the basin center & erosional on the basin margins. Trace fossil assemblages within these strata provide unique insight into the health of infaunal communities during the Permian-Triassic biotic crisis & the Early Triassic recovery interval on the northern margin of Pangaea.

Latest Permian successions in the Sverdrup basin are dominated by proximal offshore through lower shoreface successions containing a moderately diverse suite of traces including Asterosoma, Phycosiphon, Scalarituba, Skolithos, Thalassinoides & exceptionally large Zoophycos.

Early Triassic proximal offshore & offshore transition successions, preserved in basin center settings, contain few trace fossils. Those that do occur are small, horizontal feeding traces (Planolites & Helminthopsis). Exceptions occur within event beds transported from shallower settings including (Asteriacites & Kouphichnium). Early Triassic lower shoreface successions contain moderately diverse assemblages that include Arenicolites, Cruziana, Cylindrichnus, Diplocraterion, Lockeia, Palaeophycus, Siphonichnus, Thalassinoides & Spongeliomorpha. Although trace fossils were not observed in upper shoreface successions, intertidal flats contain a variety of trace fossils, particularly those constructed by molluscs (Beaconichnus, Gyrochorte, Lockeia, Neonerites & Protovirgularia).

Early Triassic fluvially-dominated successions include Cochlichnus, Fuersichnus, Lockeia, Skolithos, rare tetrapod footprints & a wide range of insect brooding traces. Comparison of these trace fossil assemblages with those from similar environmental settings in coeval western & northern Canadian successions suggests that environmental constraints limited infaunal diversity primarily distal of the lower shoreface.