Sequence stratigraphy, biotic change, Sr-87/Sr-86 record, paleoclimatic history, and sedimentation rate change across a regional late Cenozoic unconformity in Arctic Canada

Eustasy, tectonics, and climate contributed to a remarkable Miocene-Pliocen e regional unconformity in the Beaufort-Mackenzie area of Arctic Canada. Th e unconformity extends from beneath deep basin turbidites on the continenta l rise, upslope across an erosional paleocontinental shelf, onto the craton ic margin as a regional paleosurface (peneplain) in the Mackenzie Delta are a, and into pediment surfaces cut into the orogenic highlands of the Richar dson Mountains. The unconformity was initiated by shelf exposure during lat est Messinian or earliest Pliocene eustatic lowstand and was accentuated by tectonic uplift from the culmination of a major Late Miocene compressional pulse on the basin margin. Palynomorph, benthic foraminiferal, strontium i sotopic, paleomagnetic, and radiometric data document the climatic and chro nological events surrounding the unconformity. A widespread hardground (K-5 9 limestone) occurs at the unconformity and caps the Late Miocene Akpak Seq uence. The hardground yields the benthic foraminifera Cibicides grossus, a regional marker in the Arctic Pliocene, and the bryozoan Adeonella sp. aff. A. polystomella, previously known from temperate North Atlantic environmen ts. The Sr-87/Sr-86 data and new biostrati gra phic data indicate that the C. grossus Zone in the Beaufort-Mackenzie area may be younger than previous ly estimated, ranging into the earliest Pleistocene. Late Miocene regional uplift across the cratonic margin, coupled with eustatic lowstand followed by Early Pliocene tectonic quiescence and dry cool climatic conditions, com bined to produce widespread erosion (pediments and peneplanation). Rapid er osion contributed to the >4 km-thick, Pliocene-Pleistocene Iperk Sequence a nd a 23-fold increase in sedimentation rates relative to the Early and Midd le Miocene.