Abstract: Submarine-Fan Complex, Cap Enrage Formation (Middle Cambrian to Lower Ordovician), Quebec

F. J. Hein

The Cap Enrage Formation is approximately 250 m thick and consists of conglomerates, graded pebbly sandstones, and massive medium-grained sandstones in association with classical turbidites. The formation is divided into three members which can be assigned to a submarine fan-base-of-slope complex.

Member 1 is dominantly a massive medium-grained sandstone with an average bed thickness of 1.6 m. Longitudinal scours (0.2 to 2.5 m depth) are common. Locally, fluid-escape features predominate. These features seem to be syndepositional or early postdepositional. Syndepositional fluid-escape features are shown by truncation of dishes by "B-division" parallel lamination, and by alternation of dish structures or fluid-escape tubes with massive subunits within a single bed. Early postdepositional origins of fluid-escape features are suggested by disruption of overlying cross-laminated beds due to water escaping from the fluid-escape bed and by convolution of dish structures due to loading from overlying beds.

Member 2 has a loaded/scoured basal contact with member 1 and is mainly conglomeratic. The lower part of this member is characterized by shallow multiple-channel complexes which grade into very coarse-grained conglomerates. These coarse-grained conglomerates become finer, thinner, and develop stratification upsection. Overlying pebbly sandstones display load/scour contacts and shallow multiple-channel complexes. Fluid-escape features are less common than in member 1.

Member 3 gradationally overlies member 2 and is dominantly massive pebbly sandstone. Thin conglomerate beds and large-scale pebbly-trough cross-stratification are common. Fluid-escape structures are usually few and poorly defined. The top of member 3 consists of classic turbidites with interbedded massive pebbly sandstones. The Ladriere Formation conformably overlies member 3 and also consists of classic turbidites.

Members 1 and 2 possibly can be assigned to the inner fan and/or braided region of the suprafan, but both members display features that make simple application of the present submarine-fan model inappropriate. The pebbly sandstones and classic turbidites of member 3 suggest deposition in a less proximal area of the submarine-fan model.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA