Abstract The Middle Jurassic succession in the Sunrise and Troubadour gas-condensate fields (Bonaparte Basin, Timor Sea, Australia, and Timor Leste) is represented by marginal marine strata that were deposited in either fluvial-dominated or wave-dominated, but pervasively tide-influenced coastal environments. The core, biostratigraphic, and wireline log data allow the 225-m-thick succession to be broken down into 9 facies associations that are arranged into 6 third-order sequences, 12 systems tracts, and 24 parasequences. Vertical changes in depositional style are recognized within the sequence stratigraphic framework and are related to fluctuations in relative sea level, variations in the effectiveness of fluvial and wave energy, accommodation to sediment supply ratio (A/S), and basin morphology. The study indicates that there are direct relationships between the A/S ratio, basin morphology, and the dominant character of the preserved depositional systems. When A/S ratios were high, typical in transgressive and early highstand systems tracts (steeply rising shoreline trajectories), sedimentation rates were too low to fill all the space that was created and the underlying basin morphology became the overriding factor in determining coastline geometry and hence the dominant sedimentation style. The coastline became more embayed and protected from wave energy, such that the depositional systems that evolved were fluvial-dominated. During periods of lower A/S ratios, typical in late highstand or lowstand systems tracts (slightly rising or flat shoreline trajectories), or during periods of accommodation reduction typical in falling-stage systems tracts (falling shoreline trajectories), the sedimentation rate kept pace with or exceeded the rate of accommodation development. Hence, the underlying basin geometry became less important as the basin was rapidly infilled and the coastlines became less embayed and more open to the direct influence of wave energy. These shorelines were therefore wave-dominated. The depositional trend of switching from fluvial-dominated, tide-influenced deposits to wave-dominated, tide-influenced deposits in response to decreasing A/S ratios on a deposystem scale is repeated at a larger, sequence-set scale and appears to be related to a lower- order (second-order) decrease in A/S ratios and its consequent impact on paleomorphology. The persistent tidal influence throughout the succession is attributed to the embayed nature of the Bonaparte Basin during the Middle Jurassic. A model to predict dominant and subordinate coastal depositional processes related to variability in fluvial and wave effectiveness, and a range of basin morphologies in low-A/S and high-A/S regimes is presented. The relationships between these parameters are broadly scale invariant, hence the models can be used to predict alongshore variations in coastal depositional style and vertical-deposystem-scale and sequence-set-scale changes in process dominance.

Abstract The transition from the Bearpaw to Horseshoe Canyon Formation (Campanian-Maastrichtian) is about 60 m thick and is exposed in three-dimensions along the Red Deer Valley near Drumheller, Alberta. These elastic marine to marginal-marine deposits are divided into seven allomembers (A to G) defined by marine to brackish flooding surfaces. The deposits of allomember B fill an incised valley over 50 km long, up to 12 km wide, and about 20 m deep. The incision was cut either during a fall in relative sea level or by avulsion of a deltaic distributary channel. The estuarine fill of the incision appears to be transgressive. In outcrop, two main facies associations are recognised; they are interpreted to represent (1) the estuarine-marine zone and (2) the paleoseaward end of the turbidity maximum zone. Within the estuary, there was lateral shifting of individual channels along with lateral accretion of inclined heterolithic stratification (IHS). The IHS includes centimeter and meter-scale alternating sandy and muddy strata. These probably reflect daily tidal cycles and the seasonal migration of the turbidity maximum zone up and down the estuary, respectively. Tidal bundle sequences in Facies Association I suggest a semi-diurnal tidal cyclicity. The lateral juxtaposition of estuarine-marine filled channels with turbidity maximum zone filled channels indicates that the overall transgression was probably punctuated by higher frequency sea-level fluctuations. This makes it difficult to distinguish the products of allocyclic and autocyclic processes within the valley. The base of the incised valley is a candidate for a sequence boundary and the estuarine fill is assigned to a transgressive systems tract.