Subglacial meltwater drainage can enhance localized melting along grounding zones and beneath the ice shelves of marine-terminating glaciers. Efforts to constrain the evolution of subglacial hydrology and the resulting influence on ice stability in space and on decadal to millennial timescales are lacking. Here, we apply sedimentological, geochemical, and statistical methods to analyze sediment cores recovered offshore Thwaites Glacier, West Antarctica to reconstruct meltwater drainage activity through the pre-satellite era. We find evidence for a long-lived subglacial hydrologic system beneath Thwaites Glacier and indications that meltwater plumes are the primary mechanism of sedimentation seaward of the glacier today. Detailed core stratigraphy revealed through computed tomography scanning captures variability in drainage styles and suggests greater magnitudes of sediment-laden meltwater have been delivered to the ocean in recent centuries compared to the past several thousand years. Fundamental similarities between meltwater plume deposits offshore Thwaites Glacier and those described in association with other Antarctic glacial systems imply widespread and similar subglacial hydrologic processes that occur independently of subglacial geology. In the context of Holocene changes to the Thwaites Glacier margin, it is likely that subglacial drainage enhanced submarine melt along the grounding zone and amplified ice-shelf melt driven by oceanic processes, consistent with observations of other West Antarctic glaciers today. This study highlights the necessity of accounting for the influence of subglacial hydrology on grounding-zone and ice-shelf melt in projections of future behavior of the Thwaites Glacier ice margin and marine-based glaciers around the Antarctic continent.

The upper Cambrian Wilberns Formation in central Texas records deposition on a low-gradient shelf within a mixed carbonate-siliciclastic tidal-flat system that changes offshore to subtidal shelf and open-marine oolitic skeletal shoals with large microbial mounds. Siliciclastic sediment is interpreted to have been delivered to the tidal flat by aeolian processes because of the narrow range in grain size and paucity of clay. Tidal influence is dominant as evidenced by reversing currents and desiccation on the tidal flat, and megaripples with reversing current indicators in offshore shoals. Intraclastic conglomerates were deposited in broad channels on the tidal flats during storm surges. Microbialite deposition is interpreted to be controlled by accommodation favouring amalgamated thin biostromes developed in the tidal flat vs. larger mounds with greater synoptic relief in the offshore, and current energy resulting in preferential elongation of offshore mounds in a NE-SW orientation. Intertidal mounds and biostromes grew in the presence of significant siliciclastic flux and trapped it within their structure, whereas offshore large buildups incorporated little siliciclastic component. Oolite and skeletal grainstone formed in tide agitated shoals associated with large subtidal microbial mounds. Storms extensively recycled and redistributed skeletal and oolitic sands from the offshore shoals across the shelf as thin sand sheets. Spatial mixing of siliciclastic and carbonate sediment occurred across the tidal flat and shelf. Low-frequency and intermediate-frequency stratigraphic cycles were driven by shifts in the shoreline and changes in rate of siliciclastic flux in response to relative sea-level fluctuation. Random facies stacking and the lack of metre-scale cyclicity are interpreted to reflect stratigraphic incompleteness and an episodic signal introduced by storms.K E Y W O R D S Cambrian, carbonate, Laurentia, microbialite, oolite, siliciclastic 278 | LEHRMANN Et AL.microbialites, oolites and other deposits such as flat-pebble conglomerates, and the controls on cyclicity, in the Wilberns Formation through evaluation of the environmental constraints provided by sedimentary structures and sediment composition in detailed stratigraphic sections of a mixed carbonate-siliciclastic system.

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Patawarta Diapir, located in the Central Flinders Ranges, South Australia, has been interpreted as a single allochthonous salt sheet containing Tonian-aged igneous and layered evaporite sedimentary intrasalt inclusions derived from the Callanna Group. Using detailed field mapping, petrographic analysis, and lithostratigraphic correlation within Patawarta Diapir, five primarily silty limestone inclusions are re-interpreted as Ediacaran-aged Wonoka Formation and Patsy Hill member of the Bonney Sandstone (Wilpena Group). The Ediacaran-aged inclusions are concentrated on the diapir's south side where they are juxtaposed against 300-million-year older Tonian-aged Curdimurka Subgroup (Callanna Group) inclusion. The Ediacaran-aged silty carbonate inclusions in the Patawarta Diapir are interpreted to represent a suprasalt condensed section forming a carapace composed of Wonoka Formation and lower beds of the Patsy Hill member (Bonney Sandstone). Based on this geometric configuration, the Patawarta Diapir is composed of two separate evaporite bodies that encase the suprasalt carapace at an allosuture zone. The encasement process was likely driven by a combination of factors including regional shortening during the Delamerian Orogeny, high sedimentation rates forming local depocenters, and down-dip gravity sliding on the low-angle regional shelf. By using modern concepts in salt tectonics, this study represents the first documented example of a diagenetically altered Ediacaran Shuram Excursion due to the stratigraphy being encased in a diapir in the Flinders Ranges, South Australia.