Ephemeral sandy fluvial-lacustrine deltas and terminal splays associated with dryland depositional environments are important reservoirs in many basins around the world, in both pericratonic and intracratonic settings (Triassic of Algeria; Triassic of the North Sea; and Pliocene of the Caspian Sea). Research on modern depositional analogues from dryland basins offers insights into these types of reservoirs. Australia’s modern Lake Eyre Basin, an arid to hyper-arid, low-accommodation intracratonic basin in central Australia, provides an ideal natural laboratory.This paper highlights field observations of modern, sand-prone, reservoir analogues from the Neales River and Umbum Creek, on the western fringe of Lake Eyre, including unique aerial observations of sedimentation from a rare flood event in an ephemeral fluvial system. These rivers flow irregularly in a dryland setting, but are prone to flash flooding and highly variable discharge that moves large volumes of sediment over a few hours or days. Although there are variations in sediment type and discharge, similarities exist with the key reservoir elements common to most modern and ancient dryland fluvial-lacustrine systems.Distinctive elements include fluvial point bar and associated overbank deposits, distributive avulsion channels and down-dip terminal splays, either on the floodplain or onto the playa lake fringe. The terminal splays are formed, where there is not a pre-existing standing body of water, during rapidly decelerating flows with high-flow regime, transitional to low-flow regime conditions. Typical structures include parallel lamination, convex-upward parallel lamination, climbing ripples and small-scale 2D and 3D dunes. Flow interference with in-channel and floodplain vegetation is an important sediment-trapping mechanism with reservoir quality implications. Aeolian deflation is also significant as it causes the removal of fine-grained sediments during dry periods. The main controls on sediment preservation include the overall low-accommodation setting and rare major lake-filling events controlled by flooding out-of-phase with flows down the western rivers. Depositional products are either high-net-to gross fluvial- terminal splay sheet sands or lower net-to-gross fluvial- terminal splay-lacustrine delta sand sheets or stringers.

Ichnofossils and paleosols are powerful tools for reconstructing paleoenvironments and depositional histories of sediments in the coastal transition zone, where physicochemical factors of the continental and marine realms meet. Distinguishing alluvial, coastal-plain, deltaic, and estuarine environments in this zone is a major issue in outcrop and core. Alluvial environments contain terrestrial and freshwater ichnofossils and paleosols, although deposits in paralic settings may record tidal influence as evidenced by mud drapes, reactivation surfaces, and bidirectional crossbeds. Deltaic, estuarine, and coastal-plain environments contain a variety of marine, terrestrial, and freshwater ichnofossils and paleosols, depending on the salinity, sedimentation rate, groundwater profile, water oxygenation, and depositional-energy flux from fluvial, wave, and/or storm action. Delta-plain environments commonly contain weakly to moderately developed, poorly aerated, and waterlogged paleosols formed in proximal-to-distal settings. Ichnofossils and palynomorphs in the lower delta plain, including the distributary-channel, interdistributary-floodbasin, and associated lacustrine deposits, may reflect fluctuating salinity from freshwater to brackish water. Interdistributary-bay deposits commonly resemble deposits of estuarine settings, recording freshwater through brackish to open-marine water salinities. More marine conditions favor an increase in marine ichnofossil diversity and abundance. Environmental stress resulting from the input of freshwater, fine-grained sediments, and/or terrigenous organic material are recorded by lower ichnofossil diversity and/or greater abundance; freshwater deposits record few and simple ichnofossils not indicative of a particular animal or environment. Subsequent subaerial exposure of these settings by sea-level fall or strandline progradation produce a vertical sequence containing marine ichnofossils overlain by traces of terrestrial plants and animals commonly associated with paleosols. In many cases, continental ichnofossils and other pedogenic features overprint marine ichnofossils and facies. The juxtaposition, tiering, and crosscutting relations among ichnofossils and paleosols in the coastal transition zone, therefore, differentiate sediments deposited in alluvial, coastal-plain, estuarine, and deltaic environments. Introduction The purpose of this paper is to provide a brief overview and synopsis of the use of ichnofossils (i.e., trace fossils) and paleosols for reconstructing the depositional history of sedimentary successions in core and outcrop. In particular, we focus on sedimentary successions formed in alluvial, coastal-plain, and deltaic settings—the transition zone where continental and marine depositional systems and physicochemical controls meet. Here, fluvial, lacustrine, eolian, and palustrine (paludal) systems grade into and interfinger with the marine realm to create beaches, deltas, bays and estuaries, and barrier shorelines and islands (e.g., Reineck and Singh, 1980). Identification of trace fossils and paleosols, when used in conjunction with lithofacies and the understanding of their formation, help identify environments of deposition, subdivide lithofacies and depositional environments, interpret changes in salinity between freshwater and marine aquatic settings, and delineate relative changes in sea level (e.g., Hasiotis, 2002; MacEachern et al., 2007a).

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The Donkey Bore Syncline in the Northern Flinders Ranges of South Australia contains a generally finegrained deepwater succession of Early Cambrian age (Bunkers Sandstone) that outcrops on three sides of a syncline and flanks an active salt diapir to the east (Wirrealpa Diapir). Within the succession lies a basal sand-prone interval interpreted as a basin floor fan (BFF) ponded within a mini-basin on a topographically complex slope.The BFF comprises over 30 m of section with deposits that are dominantly massive clean sandstone beds (0.1– 3 m thick) that are stacked or interbedded with siltstones and pinch out along strike.Eight stratigraphic sections and accompanying spectral gamma ray logs (using a hand held scintillometer) were measured through the BFF. Using spectral gamma ray log analysis combined with stratigraphic logs, four alternative correlation panels were constructed.Quantitative analysis of sand-prone intervals interpreted in each of the panels provided data on the vertical and horizontal connectivity within the BFF as different correlation methods were explored and the geological model improved. Quantitative analysis of vertical and horizontal connectivity values indicates a high degree of heterogeneity within the BFF, with poor–moderate vertical connectivity, with individual beds rarely correlating >500 m along strike. This heterogeneity is poorly resolved using conventional wireline log suites, but is greatly improved if spectral gamma ray logs are used (especially Thorium).The data set provides a high-resolution analogue for understanding the internal architecture of deepwater hydrocarbon reservoirs.

A new sequence stratigraphic framework (SSF) for the Early–Late Jurassic Surat Basin, eastern Australia, is evolving. A second and third order framework based upon an integrated methodology of well-to-well correlations supported by well tied seismic data is being developed. The integration of an additional dataset (palynology) to test for regionally consistent sequence stratigraphic well correlations offers an improvement in defining sequence boundaries related to the geological timescale. The palynological data from 33 wells covering the north-east Surat Basin were extracted from the Queensland Digital Exploration (QDEX) open-file reports, some of which date back to the 1960s. These data were correlated and superposed on the SSF for age comparison. The dataset used in this study represents only a subset of all existing palynology information, as not all data are captured in QDEX. However, the palynology data in this exploratory study generally fits and supports the new SSF with only one exception, the reason for which is not understood at this stage. We recommend expanding this study to include more data because palynology can support stratigraphic interpretation, especially in wells that do not intercept, or have log data across, regional datums.