ABSTRACT

History of the Franklin miogeosyncline and adjacent Central Stable Region between Proterozoic and Late Devonian is well displayed on Ellesmere Island. Three long persistent sedimentary regimes displayed in these rocks are broadly similar to rocks in eastern and western belts of North America. The mildly positive Bache Peninsula arch projects westward from the Shield, across the Central Stable Region and miogeosyncline; it was active at least from Early Cambrian through Late Silurian time. Formational names shown as (new) will be proposed in forthcoming Geological Survey of Canada publications.

Proterozoic rocks include fine-grained clastics of the Kennedy Channel Formation (new) and unconformable younger dolomites of the Ella Bay Formation (new). They are confined to the geosyncline and total 6,000 feet. Lower Lower Cambrian rocks of the geosyncline include the Ellesmere Group (new) and its four contained new formations. This group reaches 3,500 feet of fine-grained clastic rocks of mainly cratonic source, that are mainly quartz sandstone grading upward and basinward to dark grey shale. It encroached onto the Central Stable Region, where its equivalent is the thin Rensselaer Bay Formation. In the geosyncline, the upper Lower Cambrian Scoresby Bay Formation (new) is up to 2,825 feet of dolomite, and in the northwest is locally unconformable. Its shelf equivalent is about 300 feet of predominantly dolomite that includes the Cape Leiper, Cape Ingersoll, Police Post and Cape Kent Formations. Middle Cambrian rocks are mainly limestones, represented in the geosyncline by the Parrish Glacier Formation (maximum thickness, 2,000 feet) and on the shelf by the Cape Wood Formation (thickness about 140 feet). Middle Cambrian and Lower Ordovician formations on Ellesmere Island are separated by a regional disconformity that may coincide with a widespread Late Cambrian hiatus in the Arctic.

Lower and Middle Ordovician formations, whose total thickness reaches 10,500 feet, are predominantly carbonate and/or evaporite. Most units have maximum thicknesses in the central miogeosyncline, and thin toward both the Central Stable Region, and eugeosyncline. The lower Lower Ordovician Copes Bay Formation is thin-bedded limestones and minor gypsum, everywhere resting with regional disconformity on older strata. The Lower Ordovician Baumann Fiord Formation (new) is gypsum-anhydrite, lens-shaped and ranging from 0 to 2,560 feet thick. The Eleanor River Formation is upper Lower to lower Middle Ordovician limestone, 500 to 3,000 feet thick. The Lower and Middle Ordovician Cornwallis

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Group (new) has been elevated from a formation, and includes the Bay Fiord (new), Thumb Mountain (new), and Irene Bay (new) Formations. In ascending order these correspond to three units recognized in the type section of the Cornwallis Formation of Cornwallis Island.

A marked change in the sedimentary pattern occurred in Late Ordovician (Ashgillian) time and persisted through Late Devonian time; during this period sedimentation was typified by extreme and rapid facies changes. Late Ordovician through Silurian is represented on the east and south by the thick Allen Bay and Read Bay carbonate Formations, which grade westward into considerably thinner black, graptolitic shales and siltstones of the Cape Phillips Formation. The facies boundary is sinuous and carbonates project westward on the Bache Peninsula arch. An Early Devonian emergence of the Central Stable Region and the Bache Peninsula arch resulted in the local westward spread of varicoloured quartz sandstones of the Verdom Fiord Formation (new). In Middle Devonian, biostromal reef development on the eastern edge of the miogeosyncline occurred within the Blue Fiord Formation, which is mainly thin-bedded limestones and some dolomite. The lower Blue Fiord grades basinward into shaly limestones of the Eids Formation. The upper part grades into, and is progressively overlapped by, northwesterly-derived varicoloured quartz sandstones of the Okse Bay Formation. All Upper Ordovician (Ashgillian) through Upper Devonian formations finally grade westward and northwestward into the Cape Rawson Group. This group is an enormous wedge of fine-grained clastic rocks of northwesterly provenance, reaching 15,000 feet in thickness, that spread progressively farther and farther southward and eastward.

Southeasterly-directed folds of Late Devonian to Middle Pennsylvanian age transformed the Franklin miogeosyncline of Ellesmere Island into the Central Ellesmere fold belt, and were deformed again in Tertiary time.

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