Abstract: Late Devonian Sequence Stratigraphy of the Canning Basin, Western Australia: New Results from McWhae Ridge

Ann E. Holmes, Nicholas Christie-Blick

Seismic and sequence stratigraphic studies in the Canning basin, Western Australia, have led to a re-evaluation of existing interpretations of the well-known Late Devonian carbonate platforms. New high-resolution work in outcrop at McWhae Ridge updates our previously published interpretation of the physical stratigraphy, and permits refinement of ages for several sequence boundaries with reference to the recently developed goniatite zonation scheme of R.T. Becker and colleagues. On the basis of measured sections and 1:5,000 scale mapping of physical surfaces on aerial photographs, we infer the presence of six sequence boundaries in the interval between the latest Givetian/early Frasnian and early Famennian, a span of about 12-15 m.y. Where these boundaries are observed as correlative onformities, they can he dated to better than single-zone resolution (less than ~1 m.y.). The two lowest sequence boundaries (early to middle Frasnian) are characterized in platform to marginal-slope settings by an abrupt upward-coarsening from stromatoporoid-bearing boundstone/wackestone to crinoid grainstone/rudstone. The ages of these boundaries are constrained only as older than the Probeloceras (E₂) goniatite zone. The next sequence boundary in the succession corresponds to a middle Frasnian hiatus between the Probeloceras (E₂) and Mesobeloceras (G₂) zones, and on this basis is dated approximately as within the Prochorites (F) Zone. This boundary is located at a sharp contact in marginal slope to basin deposits between deep-water sponge- and stromata tis-bearing wackestone and ooid grainstone. Three late Frasnian and early Famennian surfaces are interpreted tentatively as sequence boundaries on the basis of well-developed baselap. The lowest surface, near the base of the Playfordites (I) Zone, is underlain by microbial boundstone containing lenses of ooids and bioclastic material, and is overlain by lime mudstone. The second surface, near the base of the Archoceras (K) Zone, is underlain by bioclastic-rich microbial boundstone, and overlain also by lime mudstone. At McWhae Ridge, the Frasnian-Famennian boundary lies within an interval of prograding marginal slope deposits (highstand systems tract). The uppermost sequence boundary is located within the Palmatolepis triangularis conodont zone of the early Famennian between microbial bo ndstone and generally fine-grained basinal carbonate rocks. Correlation of these interpreted sequence boundaries with those previously recognized in the subsurface and in the Van Emmerick Range suggests that the lower boundaries of the Frasnian 4 and Frasnian-Famennian sequences of J. M. Kennard correspond to the boundaries interpreted here as at or near the base of the I and K goniatite zones.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994