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The type section of the late Ediacaran (ca565 Ma) Bonney Sandstone in South Australia provides an opportunity to interpret a succession of Precambrian clastic sediments using physical sedimentary structures, lithologies and stacking patterns. Facies models, sequence stratigraphic analysis, and process-based architectural classification of depositional elements were used to interpret depositional environments for a series of disconformity-bounded intervals. This study is the first detailed published work on the Bonney Sandstone, and provides additional context for other Wilpena Group sediments, including the overlying Rawnsley Quartzite and its early metazoan fossils. Results show that the ∼300 m-thick section studied here shows a progressive change from shallow marine to fluvially dominated sediments, having been deposited in storm-dominated shelf and lower shoreface environments, lower in the section, and consisting primarily of stacked channel sands, in a proximal deltaic environment near the top. Based on the degree of influence of wave, tidal or fluvial depositional processes, shallow marine sediments can be classified into beach, mouth bar, delta lobe and channel depositional elements, which can be used to assist in predicting sandbody geometries when only limited information is available. Sediments are contained within a hierarchical series of regressive, coarsening-upward sequences, which are in turn part of a larger basin-scale sequence that likely reflects normal regression and filling of accommodation throughout a highstand systems tract. Paleogeographic reconstructions suggest the area was part of a fluvially dominated clastic shoreline; this is consistent with previous reconstructions that indicate the area was on the western edge of the basin adjacent to the landward Gawler Craton. This research fills in a knowledge gap in the depositional history of a prominent unit in the Adelaide Rift Complex and is a case study in the interpretation of ancient deposits that are limited in extent or lacking diagnostic features. [ABSTRACT FROM AUTHOR]

Shelf-edge deltas (SEDs) forming during periods of relative sea level fall and lowstand are generally efficient in transferring sediments to the slope and basins, and their identification in subsurface data is often considered a good indication of coeval development of slope and basin-floor turbidite reservoirs. This study investigates the seismic stratigraphic evolution of a forced-regressive and normal regressive shelf-edge delta (Bonaparte SED) that accumulated on the edge of the NW Australian margin during the late Quaternary. High resolution 2D and 3D reflection seismic data allow reconstruction of the main episodes of delta progradation and understanding of the extrinsic and intrinsic controls on their deposition. The lack of a significant turbidite system forming off the shelf-edge delta throughout the Quaternary is a striking feature of the Bonaparte SED. Instead, slope sedimentation is dominated by the accumulation of plume-derived mud belts and their reworking through mass-transport processes. Seismic geomorphology permits interpretation of the process regime of the youngest shelf-edge depocentre by applying a new process-based shallow-marine classification scheme to the 3D seismic attribute data. Results suggest either a tide or wave dominated delta with fluvial processes being of tertiary significance. A tide or wave-dominated, fluvial-affected shelf-edge delta classification is consistent with the paleogeographical reconstruction of the margin during the last glacial maximum (ca. 25 ka BP). The comparison of this mixed-process shelf-edge delta and starved slope system with a fluvial-dominated counterpart with significant sandy slope deposits emphasizes the potential of assessing the process regime of shelf-edge deltas as a rapid, first approach for predicting the presence or absence of coeval slope and basin-floor reservoirs. [ABSTRACT FROM AUTHOR]

Studies of modern sediments from tide-dominated marine coastal environments in the 1970s and 1980s led to the recognition of what were suggested to be unique sedimentary features formed by tidal currents. These features could be directly related to astronomical forcing by the Sun and Moon. Sedimentary structures formed by marine tidal processes are now frequently described in modern and ancient deposits. Here, we detail similar sedimentary features from shoreline deposits of Lake Eyre, Australia, a present-day, intracratonic playa lake setting, thus challenging the current paradigm that these structures are indicative of marine tidal influence. We attribute the formation of these features in Lake Eyre to meteorological tides generated by daily changes in wind direction and velocity, along with weekly to monthly discharge variations in the feeder river system. This is the first time such sedimentary features have been documented together in a continental setting. A key implication of this is that the classic "tidal" sedimentary structures recognized in ancient rock successions should not automatically be attributed to astronomical or marine tidal currents, since similar structures can be generated by meteorological processes in continental environments. Some interpretations of ancient marine tidal deposits without other lines of evidence supporting a marine depositional environment may therefore require reevaluation. Playa lakes and shallow perennial lacustrine settings should also be considered in the interpretation of strata containing what have formerly been considered classic marine tidal indicators. [ABSTRACT FROM AUTHOR]

A major challenge in sequence stratigraphy is objectively identifying stratigraphic surfaces and sequences across multiple scales of observation. Identification is commonly dependent on the resolution of the data used (i.e., seismic vs. well data), its dimension (i.e., 1D vs. 2D vs. 3D) or the criteria chosen to select sequence boundaries. Through shelf-edge trajectory analysis, the clinothem (i.e., highest order seismic sequence identified on seismic data) can constitute the elementary building block of an observation-based and data-driven quantitative workflow to develop sequence stratigraphic frameworks across different orders and ranks of hierarchy. Here, we use high-quality 3D seismic data to interpret a Late Tithonian–Early Cretaceous shelf margin, the Lower Barrow Group (LBG), developed in the Northern Carnarvon Basin on the North West Shelf of Australia. Based on full-volume seismic interpretation techniques that integrate the 3D variability of the data when identifying seismic unconformities, a high-resolution seismic stratigraphic framework was built (73 interpreted clinothems with an average time duration of ~63,000 yrs). The computation of high-frequency shelf-edge trajectory angle (T se) curves on selected seismic cross-sections is used to objectively pick sequence stratigraphic surfaces based on the accommodation succession method, thereby highlighting small changes in trajectory and proposing a method reproducible by interpreters based on the same quantitative data. Within the D. lobispinosum interval (142.3–140.9 Ma), the definition of stratigraphic sequences and composite stratigraphic sequences through this workflow is used to discriminate the controls at high and low temporal frequency on the vertical and lateral variability (which is here quantified) of this shelf-slope-basin system. The results show that the high-frequency interplay between short-term glacio-eustasy (i.e., Milankovitch eccentricity cycles of ~100,000 yrs) and sediment supply (locus of fluvial input along the margin) impacted the three-dimensional stratigraphic architecture of the LBG. In contrast, tectonic subsidence had a significant impact on the stratigraphic architecture of the LBG within the main depocentre at lower temporal frequency by overprinting the eustatic signal and accelerating/decelerating the rates of accommodation creation. However, identification of long-term glacio-eustatic Milankovitch cycles (~400,000 yrs) outside the main depocentre, where the rates of accommodation creation due to rift-related subsidence are moderate, also suggests low-frequency eustatic control. Therefore, the vertical and lateral variability of the LBG results from variations in sediment supply and subsidence regime under local (i.e., process regime, currents), regional (i.e., tectonics) and global (i.e., eustasy, climate) forcing parameters interplaying across timescales. In contrast to standard sequence stratigraphic workflows that are based on model-dependent choices to select sequence boundaries, quantitative 3D seismic stratigraphy constitutes an improved method to interpret 3D seismic data in shelf-margin depositional systems within a sequence stratigraphic framework, which provides an observation-based and model-independent tool allowing the definition of stratigraphic sequences with results that are reproducible across multiple stratigraphers. This work highlights the need for developing new sequence stratigraphic tools and methods that integrate the 4D variability of depositional systems and moves beyond the two-dimensionality inherent to current sequence stratigraphic methods. Quantitative 3D seismic stratigraphy represents a first step towards the creation of 3D sequence stratigraphic workflows that could improve the prediction of stratigraphic patterns and facies relationships (source, reservoir, seal distribution) across shelf margins. • A high-resolution seismic stratigraphic framework was built using 3D seismic data. • Shelf-edge trajectory angle curves are used to pick sequence stratigraphic surfaces. • Lateral and vertical variability of the clinothems is quantified. • Controls are identified at high and low temporal frequency. • Quantitative 3D seismic stratigraphy represents a first step towards 3D sequence stratigraphy. [ABSTRACT FROM AUTHOR]

The Barrow Group was deposited in the Northern Carnarvon Basin from the latest Tithonian to the Late Valanginian. This moderately deep-water shelf-margin is composed of ~ 100–500 m high clinoforms that prograded during a syn-rift to post-rift transition. Integration of well data with extensive 2D and 3D seismic data was used to constrain the stratigraphic evolution of the Barrow Group in seven 3 rd order seismic sequences (calibrated to dinocyst zones) across four main depocentres. Five shelf-margin categories were recognized based on stratal stacking patterns, the trajectory styles and angles ( T se ), and the progradation/aggradation ratios ( P se / A se ) that were interpreted in terms of rates of accommodation creation and sediment supply ( A / S ratio). Following the uplift of the Southern Carnarvon Basin (sediment source), the stratigraphic evolution of the Barrow Group developed in three stages. During the first stage (late syn-rift I; 148–143.5 Ma), the shelf-margin prograded in a period of tectonic quiescence with relatively limited subsidence. During the second stage (late syn-rift II; 143.5–138.2 Ma), the shelf-margin was affected by increasing rates of accommodation and high sediment supply, which reflects an active period of rifting triggering both tectonic subsidence in the basin, and active uplift in the hinterland. During the third stage (early post-rift I; 138.2–135.4 Ma), the uplift of the continental shelf, following continental break-up, provided a new local source of sediment supply to the Barrow Group that then developed as a passive margin. The Lower Barrow Group (late syn-rift I and II) mainly developed under supply-dominated conditions. However, lateral variations in subsidence regime and shifts in sediment supply led to significant variations in shelf-margin architecture along-strike, directly impacting sediment partitioning between the shelf and the deep-water areas. Flat shelf-edge trajectories were associated with sediment bypass and increase in bottomset thicknesses, whereas rising shelf-edge trajectories were linked with sediment storage on the shelf. In contrast, the Upper Barrow Group (early post-rift I) developed in low-supply conditions with slow thermal subsidence, reflecting the passive context of the margin at this time. The Barrow Group provides a unique example of how rift tectonics can control the stratigraphic architecture of a regressive margin and reciprocally, how studying shelf-margin architecture can help constraining the dynamics and timing of rifting around the break-up stage. [ABSTRACT FROM AUTHOR]