The Late Albian (Joli Fou) Continental Flooding Event: Not a Simple Story

Abstract

In north-central Alberta, Middle Albian time is recorded by the transgressive-regressive couplet comprising the muddy Harmon and sandy Cadotte alloformations, deposited in the southern, closed end of an Arctic embayment. The overlying Paddy alloformation is an easterly-thinning clastic wedge, that unconformably onlaps the Cadotte and represents a distinct tectono-sedimentary episode. The Paddy consists of marine rocks in the north, and lagoonal and alluvial facies to the South. Lagoonal deposits pass eastward, first into sandy estuarine facies and then into marine mudstone assigned to the Joli Fou alloformation. The Paddy and Joli-Fou alloformations have been considered time-equivalent rock units, but the nature of the transition has never been established. In parts of Alberta, the lateral transition between sandy Paddy and muddy Joli Fou rocks seems to correspond to a region of marked stratal thinning, possibly indicative of localized tectonic control. Estuarine Paddy strata exposed on the Peace River comprise distinct, disconformity-bounded units of interstratified quartz arenites, probably of eastern or southern provenance, and cherty litharenites derived from the western Cordillera. The implications of this bimodal petrographic signature in the Paddy has not been previously recognized. It suggests interaction of two major river systems across more than 300 km of the basin, to produce the observed interstratification of chert-rich and quartzose sandstones. The Joli Fou mudstone marks flooding of the continental interior by the Arctic Ocean and Gulf of Mexico in the early Late Albian. The detailed paleogeographic evolution from an Arctic embayment, typical of Middle Albian time, to a through-going continental-scale seaway in Late Albian time has not been established. For example, was it a single transgressive event, or did it progress in pulses? New observations of the Joli Fou on the Athabasca River reveal numerous internal disconformities and lag-strewn surfaces suggestive of repeated sea-level changes. This presentation will show how sandy nearshore deposits of the Paddy alloformation in the west relate, in time and space, to offshore marine deposits of the Joli Fou and Viking alloformations in the east, during a time when the basin switched from an Arctic Ocean embayment, to a through-going seaway linked to the Gulf of Mexico. This change was accompanied by reorganization of river systems in response to tectonic tilting and sea-level fluctuations.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016