Stratigraphy of the devonian Miette Reef Complex and associated strata, eastern Jasper National Park, Alberta
Authors: Mountjoy E 
Published: December 2015

The Miette reef complex, which is 1,400 feet thick and has a present area of about 30 square miles, is surrounded by a slightly thinner succession of shales and argillaceous carbonates and is exposed in three thrust sheets. It occurs on a central part of the
pre-Devonian arch that parallels the trend of the Front Ranges of eastern Jasper National Park. The initial Upper Devonian transgression over a relatively flat erosion surface of Cambrian rocks was followed by deposition of calcarenites and stromatoporoilal carbonites with local biostromes (Flume).
In areas favourable to organic growth slightly thicker accumulations of stromatoporoidal carbonates were deposited and probably formed path reefs or mounds above the level of the surrounding carbonate platform. Increasing depth of water drowned much of the stromatoporoid platform and restricted
organic growth to the higher areas where from 300 to 500 feet of carbonates (upper Cairn) accumulated. Fine-grained, argillaceous calcarenites (Maligne), which occur above the platform carbonates and adjacent to the hoistroom, probably represent eroded detritus from the reef. As the water deepened
small bioherms grew locally along the margin of the reef complex and were later dolomitized to massive structure less dolomite containing coarse breccia's. Black, pyritic terrigenous muds ( Perdrix) deposited in the '&amp;gt;Urrotmding hasin during reef development is indicative of stagnant
condition&amp;gt;. Change of environment above the reef complex to shallow-water hank conditions is reflected by a progressive change from organic to lime sand carbonates (lower Southesk. Peechee) and mark5 the time when there was a change from a riing sea-level to one of general stability. The
thick sequence of tlJC sL' sediments indicates that bank conditions pretested for a long time. A short temporary return In somewhat deeper water conditions closed deposit ion of a thin ;Jmf'hif'nra and coral c~1rbonate (Grotto). Basin relief was gradually decreased dming the last two stages by
inllu of terrigenous muds and fine carbonate mud and detriment Hawk) derived from the bank. Small coral hoistrooms developed locally on the bank margins and in the adjacent shale basin. Continued basin filling caused further shallowing and permitted lateral extemions of the banks and widespread
deposition of lime sands (upper Southesk. Ares). Quartz silts were intr11duccd and mixed with lime' sands during the final regression (Ronde). Eustatic changes in sea-level or epeirogenic movements have exerted the dominant control on reef development together with differential subsidence within the
positive pre-Devonian arch. Remnants of the stromatoporoidal biostromes of the Flume platform carbonates that survived the gradually increasing depth of water formed the sites of later, more prolific reef growth. The stratigraphic relationships of the Miette reef that appear to be useful in locating
similar reds in the adjacent subsurface are (I) thickening and greater organic content of the platform (Flume) and overlying argillaceous calcarenites (Maligne) towards the reef; (2) a gradual increase in carbonate content of the basin shales (Perdrix and particularly the Mount Hawk) in a
2-to-..J-mile zone around the reef; and ( 3) presence of a lime sand carbonate I upper Southesk) above the basin shales (Mount Hawk).