Controls on Carbonate Platform Geometries and Facies Stacking Patterns: Influence of Second-Order Sea-Level Fluctuations and Sediment Supply, Upper Devonian, Rocky Mountains, Alberta

M. T. Whalen, G. P. Eberli, F. S. P. Van Buchem, E. W. Mountjoy, P. Homewood

Variations in platform margin geometries and facies stacking patterns within the isolated Miette and Ancient Wall buildups and surrounding basinal sediments reveal the effects of carbonate sediment production and clastic sediment supply within a hierarchy of relative sea-level change.

Six third order depositional sequences were deposited during a second order transgressive-regressive cycle. Sequences (1-3) deposited during the second order transgressive phase thicken upward (3-25 m). Parasequences are subtidally dominated and capped initially by relatively thin but laterally extensive bulbous stromatoporoid framestones and later by thick tabular to massive stromatoporoid framestones. Subaerial exposure is recorded only at the top of such sequences. Parasequences of sequences (4-6) deposited during the second order regressive phase generally thin upward (20-3 m). They are initially capped by relatively thick but laterally restricted tabular-massive stromatoporoid framestones but become more peritidal dominated upwards and record repeated periods of subaerial exposur . The above patterns indicate that the Frasnian second order sea-level rise accentuated short term rises and suppressed short term falls of sea-level, whereas the second order sea-level fall suppressed higher frequency rises and accentuated higher frequency falls.

Sequence geometries vary systematically within the second order transgressive-regressive cycle. The transgressive phase sequences record ramp, low-angle prograding, and backstepping to aggrading styles of platform development, whereas the regressive phase is initially aggradational and then progrades across late stage mixed carbonate-siliciclastic basin infill in a forced regression. Progradational geometries occur during early second order transgression and late regression. Aggradational geometries are found during late second order transgression and early regression. The second order transgressive phase effectively sequestered siliciclastic sediments to the eastern portion of the basin. High rates of carbonate productivity fostered the development of a prograding platform across the underlying homoclinal ramp during early second order transgression followed by an aggrading, bypass platform margin during late transgression and early regression. Basin filling due to increased siliciclastic input during the second order regressive phase reduced the paleotopography permitting late regressive platform progradation. Thus, platform margin geometries are affected by second order relative sea-level but are also influenced by the interplay between carbonate productivity and clastic sediment supply.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995