Jp. Zonneveld et al., LITHOFACIES ASSOCIATIONS AND DEPOSITIONAL-ENVIRONMENTS IN A MIXED SILICICLASTIC-CARBONATE COASTAL DEPOSITIONAL SYSTEM, UPPER LIARD FORMATION, TRIASSIC, NORTHEASTERN BRITISH-COLUMBIA, Bulletin of Canadian petroleum geology, 45(4), 1997, pp. 553-575
Tile upper Liard Formation (Middle Triassic, Upper Ladinian) in the Pe
ace River Foothills of northeastern British Columbia comprises a progr
adational succession of at least eleven parasequences deposited within
a mixed siliciclastic-carbonate depositional system on the western ma
rgin of the North American craton. Sediments accumulated along a low g
radient shoreface-continental ramp within an embayed/restricted portio
n of the northwestern Pangean continental margin, Thirteen sedimentary
facies are recognized within the following three lithofacies successi
ons: A) progradational elastic offshore/shoreface, B) progradational m
ixed-siliclastic carbonate shoreface and C) mixed siliciclastic-carbon
ate marginal marine. Lithofacies association A is a coarsening-upwards
offshore/lower shoreface succession, locally incised by tidal channel
s. Lithofacies association B consists of a coarsening-upwards, mixed s
iliciclastic-carbonate shoreface. Thick bioclastic accumulations withi
n this unit are interpreted as terebratulid brachiopod-echinoid domina
ted reef mounds. Lithofacies association C consists of a mixed silicic
lastic-carbonate intertidal-supratidal succession of mud flats, algal
mats, evaporites and minor tidal channels, The terebratulid-echinoid r
eef mounds were initiated by allogenic taphonomic feedback, Storm-gene
rated skeletal concentrations provided ''islands'' of comparably stabl
e substrate, These islands provided a locus for colonization by rocky
substrate-preferring organisms such as terebratulid brachiopods, cidar
oid echinoids and articulate crinoids, The Liard reef mounds accumulat
ed during periods of comparably low siliciclastic input to the shorefa
ce, likely during the later stages of a highstand systems tract.