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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 52 (1968)

Issue: 3. (March)

First Page: 545

Last Page: 546

Title: Allochthonous Carbonate Debris Flows at Devonian Bank ("Reef") Margins, Alberta: ABSTRACT

Author(s): L. C. Pray, H. E. Cook, E. W. Mountjoy, P. N. McDaniel

Article Type: Meeting abstract

Abstract:

Field work suggests that allochthonous carbonate-debris flow deposits containing large blocks occur locally in the upper Perdrix and Mt. Hawk basinal strata adjacent to three Devonian bank complexes--Ancient Wall, Miette, and Southesk (Mt. MacKenzie). The deposits are mostly pebble to boulder carbonate mudstone conglomerate and breccia with pervasive, dark, interstitial micrite.

The largest of the deposits interpreted as debris flows occur southeast of Mt. Haultain (Ancient Wall). Here, disoriented blocks (as large as 20 by 50 m in cross section) of shoal-water limestone occur in two sheet-like deposits of irregular thickness (up to 25 m); these deposits are exposed for 1 km from the bank edge. Similar, possibly correlative, deposits up to 12 m thick and containing disoriented blocks 10 m across occur 3 km from the bank edge. The allochthonous clasts mostly are limestone and range from nonfossiliferous mudstone to grainstone rich in normal marine fossils. Some clasts are coral-growth frameworks several meters across. Smaller debris lenses commonly rich in basinal clasts fill channels adjacent to bank edges at all localities. Most debris deposits of both sheet and channel form have graded calcarenite-to-calcilutite tops a few inches thick.

The writers believe that these allochthonous materials were transported largely by submarine-debris flows from upslope basinal and bank environments. Many flows were followed by density currents. The larger debris deposits probably formed when the relief and slope at the bank margin were higher than normal, perhaps involving 50 m or more of relief and slopes of 5°-10°; some may be related to bank-margin unconformities.

Allochthonous-debris deposits containing large

End_Page 545------------------------------

blocks may occur at other Devonian bank margins in both the surface and subsurface. Recognition of such deposits can assist in determining bank proximity; in better interpretation of bank and bank-margin genesis; in determining time of diagenesis, particularly cementation and dolomitization; and in correlation.

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