Tectonic , eustatic and climate controls on facies architecture during the 1 transition to the Neoproterozoic icehouse in the Adelaide Superbasin , 2 Australia 3

12 The Tonian to Cryogenian (ca. 1000–635 Ma) marks a crucial turning point in Earth’s history, where 13 tectonic reorganisation and fluctuating oceanic and atmospheric geochemistry plunged the globe into 14 icehouse conditions. This was followed by a postglacial warming period that delivered large volumes 15 of nutrients to the oceans and stimulated eukaryotic evolution. The Adelaide Superbasin in South 16 Australia hosts a thick repository of Neoproterozoic and lower Cambrian sedimentary successions that 17 preserve the depositional conditions during this unique time. In this study, detailed sedimentological 18 data was collected from over 8,350 m of measured section at seven locations across the northern 19 Flinders Ranges. Tonian deposits reveal a carbonate platform setting, where deposition was controlled 20 by basin geometry and proximity to uplifted source areas. In the early Cryogenian, sedimentary 21 successions were affected by the Sturtian glaciation, characterised by two glacial advance-retreat 22 phases that coincide with climatically driven regression. The end of the Sturtian glaciation was 23 marked by basin subsidence and widespread transgression into a more distal subaqueous environment. 24 Despite the lithostratigraphic and sequence stratigraphic similarity between Tonian–Cryogenian 25 Virgo et al – Accepted version – https://doi.org/10.57035/journals/sdk.2023.e11.1083 2 successions globally, their correlation remains contentious. The influence of local tectonic regimes 26 during the Tonian created a potential oceanic restriction between developing basins, which challenges 27 the chemostratigraphic correlation between these deposits. Further, limited geochronological ages and 28 opposing interpretations of glacial cyclicity put into question the timing and extent of the Sturtian 29 glaciation. Conversely, the post glacial transgression appears to be the most globally consistent as it 30 results from climatically controlled sea level rise that was driven by melting ice sheets. 31

phases that coincide with climatically driven regression. The end of the Sturtian glaciation was 23 marked by basin subsidence and widespread transgression into a more distal subaqueous environment. 24 Despite the lithostratigraphic and sequence stratigraphic similarity between Tonian-Cryogenian successions globally, their correlation remains contentious. The influence of local tectonic regimes 26 during the Tonian created a potential oceanic restriction between developing basins, which challenges 27 the chemostratigraphic correlation between these deposits. Further, limited geochronological ages and 28 opposing interpretations of glacial cyclicity put into question the timing and extent of the Sturtian 29 glaciation. Conversely, the post glacial transgression appears to be the most globally consistent as it 30 results from climatically controlled sea level rise that was driven by melting ice sheets. regimes. Although many of these changes are local, global climatic fluctuations and tectonic 98 reorganisation could also be responsible for the major temporal and spatial variability in stratigraphy, 99 potentially providing a platform from which these sections may be correlated globally. 100 In this study, we use detailed sedimentological data collected from multiple sites across the northern 102 Flinders Ranges to construct a sequence stratigraphic framework and correlate facies across the width 103 of the Adelaide Superbasin during the Neoproterozoic. This is achieved through extensive analyses of 104 grain sizes, sedimentary structures, bedding thicknesses, and palaeocurrent directions, followed by 105 lithostratigraphic correlations and the interpretation of sequence stratigraphic boundaries and 106 palaeoenvironmental settings. The temporal and spatial distributions of depositional environments can 107 subsequently be correlated to other basins across the globe in order to better differentiate local vs.

172
This study encompasses several field sites located across the northern Flinders Ranges (Figure 1). Site 173 selection was based on previous geological mapping (Coats, 1973), access to site location, geographic 174 spread, and stratigraphic thickness. Coordinates for each section were recorded with a handheld GPS 175 and the stratigraphy was measured bed by bed at approximately one metre-resolution using a tape 176 measure. Detailed descriptions of grain size, sedimentary structures, bedding thicknesses and 177 palaeocurrent direction were recorded ( Supplementary Figures 1-7). 178

179
Sedimentary logs produced in the field were digitised using EasyCore software and palaeocurrent data 180 were analysed with the software Stereonet. Lithofacies were classified based on grain size and represents the Tindelpina Shale Member of the Tapley Hill Formation. The measured sections only  236   capture the base of Tapley Hill Formation (between 30m and 400 m thick), while the entirety of this  237 formation can reach stratigraphic thicknesses over 2000 m in the northern Flinders Ranges (Preiss, 238 1987). 239

Environmental Interpretations 393
The deposition of both low-energy fine-grained lithofacies, and higher-energy, inverse-graded 394 carbonate lithofacies are consistent with a setting that experiences both quiescent, subtidal conditions (B2) likely corresponds to a high-relief carbonate platform geometry (Grotzinger, 1988;, 2012;

Environmental Interpretations 413
The prevalence of fine-grained lithofacies, storm reworking, soft sediment deformation and debrite 414 breccias are consistent with a slope to basinal (C) setting ( Upper plane beds and ripple cross-stratification are likely deposited from a similar process to that 444 outlined in the inner platform setting (Ashley, 1990;Reading, 2009;Boggs, 2014). However, the 445 unimodal current orientation of flows could indicate deposition from low-density turbidity currents 446 rather than a tidal source (Lowe, 1982;Kneller, 1995;Shanmugam, 1997

Environmental Interpretations 458
The mix of structured and massive lithofacies was likely deposited in a subaqueous environment from 459 turbidity and debris flows, respectively (Lowe, 1982;Kneller, 1995;Shanmugam, 1997;; structures reflect liquefaction in response to differential sediment densities or lateral loading (Owen, 475 2003). Dropstones that deform underlying beds provide evidence for ice-rafted debris that were likely

Environmental Interpretations 483
The repeated emplacement of fine-grained turbidite successions, transitioning from massive 484 sandstone, rippled, cross-stratified and convolute sandstone and siltstone, to laminated mudstone, 485 along with ice-rafted dropstones, have been interpreted as distal proglacial deposits (F), (Figure 9; More specifically, a subaqueous fan (F1) could have provided the large sediment supply and 488 facilitated the slope instability necessary for the development of these turbidity currents (Figure 9; 489 e.g., Bouma, 1964;Middleton & Hampton, 1976;Lowe, 1982;Shanmugam, 1997 been mapped at this location (Coats, 1973). Sequence 2 can also be correlated to the Vulkathunha- Yankaninna. However, the correlation is uncertain as it cannot be constrained from the previous 548 mapping. Sequence 3.1 appears to pinch out towards the east in the Vulkathunha-Gammon Ranges 549 section, where Sequence 2 is directly overlain by the Sturtian glaciogenic deposits. 550

Sequence 3.2 551
The top of Sequence 3 is marked by a microbial-dominated unit that is prevalent in the west and  Sequence 2 is not present in the north central portion of the basin. The first is that these locations were too proximal and topographically high to be affected by the rise in base level. The second possibility 698 is that they were restricted from the fluvial sources of sediment input. Thirdly, sediments in these 699 locations may have been subaerially exposed and eroded during the subsequent drop in base level. The widespread siltstone and dolostone unit (Sequence 3.1) that succeeds Sequence 2 is consistent 703 with a low energy, lagoonal outer platform setting deposited during a transgression (Figure 11). This 704 rise in base level creates a backstepping geometry as the mixed clastic and carbonate material 705 retrograde over the underlying sandstone unit. The increase in accommodation was largely 706 tectonically controlled (Preiss, 1987), but could also be in part eustatic due to the prevalent deposition 707 of fine-grained sediment across the basin (Figure 11). 708

Sequence 3.2 709
The inner platform microbial succession at the top of Sequence 3 represents deposition during a 710 highstand systems tract (Figure 11), where the accumulated sediment outpaced base-level rise and the 711 carbonate platform aggraded and prograded basinward (Catuneanu, 2006). Like the rest of the pre- The basal diamictite in the bottom of Sequence 4 unconformably overlies the pre-glacial successions, 721 which is represented by a sequence boundary (SB; Figure 11). Sequence 4 could have been deposited 722 during a lowstand systems tract and would be capped by an MRS (Figure 11). This was likely driven by climatic fluctuations and glacio-eustatic fall and marked by widespread deposition across the basin 724 during a glacial maximum. Although sediment is typically eroded during drops in eustacy, the 725 predominance of climatic control on deposition during the glaciation prompted a decrease in fluvial 726 discharge and resulted in glacio-fluvial aggradation (e.g., Blum, 1994;Catuneanu, 2006). Le

Sequence 5.1 751
The overlying fine-grained unit (Sequence 5.1) is consistent with deposition during a transgression 752 (Figure 11), which would similarly have been driven by eustacy and climate. The implication of this 753 sequence is that the Sturtian glaciation likely reflects more of a "slushball" than a hard "snowball" shedding material related to diapiric movements (Young & Gostin, 1990). Areas that were previously 763 dominated by glacial scour, particularly those in the east, received significant amounts of sediment 764 and resulted in thick deposition (Figure 11; Young & Gostin, 1991). Sequence 5.1 is exposed at the 765 Vulkathunha-Gammon Ranges section and is lithologically dissimilar to other sections in the basin, 766 likely due to its proximal proglacial location where coarse material continued to deposit despite the 767 glacial recession. 768

Sequence 5.2 769
The ice proximal till of Sequence 5.2 represents deposition during a second basinward prograding 770 package that represents either a highstand and/or lowstand systems tract, capped by an MRS (Figure  771 11). Like the lower diamictite (Sequence 4), this coincides with a glacial advance and an eustatic sea-772 level fall. However, this represents slightly more distal, subaqueous deposition relative to the first 773 glacial advance (Young & Gostin, 1988;. This unit does not appear in the Mt Lyndhurst 774 and North Yankaninna sections ( Figure 11). As these sections correlate with a central high (horst) in 775 the basin, Sequence 5.2 may not have been deposited or was potentially eroded. 5.8.6. Sequence 6 777 5.8.6.1. Sequence 6.1 778 Like the lower heterogenous unit (Sequence 5.1), Sequence 6.1 is characterised by transgressive, fine-779 grained lithofacies (Figure 11), although deposited during widespread deglaciation rather than an ice 780 retreat. This was probably driven by climatic warming following the glacial maximum and eustatic 781 sea level rise, where fine-grained subaqueous sediment backstepped and retrograded landward. 782 Sequence 6.1 is only recorded along the western margin (Figure 11), which could correspond to the 783 tabular geometry here and subsequent susceptibility to flooding. 784

Sequence 6.2 785
The slope to basinal succession of Sequence 6.2 is consistent with deposition during a widespread 786 transgression (Figure 11), where postglacial sediments backstepped over the continental margin. 787 Consequently, this succession is recorded on the adjacent Stuart Shelf in the west and right over the 788 Curnamona province to the Barrier Ranges in New South Wales to the east (Preiss, 1987). The 789 predominance of fine-grained material (Figure 11), and depositional spread and synchronicity across 790 the basin have been used to suggest that post-rift thermal subsidence likely assisted the eustatic rise 791 (Preiss, 1987;Powell, 1994). Deglaciation delivered large amounts of detritus into the marine 792 environment, which resulted in considerable stratigraphic thicknesses of this postglacial succession in 793 the Adelaide Superbasin (Lloyd et al., 2020). This has been hypothesised to have stimulated eukaryote 794 evolution through the flux of detrital bio-essential nutrients (Brocks et al., 2017). 795 796 Carbonate rocks ("cap carbonates") at the base of Sequence 6.2 are recorded in the northern most 797 sections of this study (Figure 11), which could be due to their more restricted setting relative to other 798 locations in the basin. These more restricted settings provide an optimal environment for cap 799 carbonate precipitation due to the increased effect of ocean stratification, low salinity, and greater 800 alkalinity production (Yu et al., 2020). This was likely due to their relative proximity to continental 801 weathering sources.  With that said, the development of basins during the Tonian largely resulted from active tectonism 927 associated with the breakup of supercontinent Rodinia (Merdith et al., 2021), and corresponds to a 928 suite of local tectonic conditions (e.g., rifting, subsidence and slab rollback) that would have 929 influenced the production of accommodation space. These local tectonic controls may modify the 930 lithostratigraphic trends recorded in Tonian successions, and by extension, the chemostratigraphic 931 record. 932

Syn-glacial 933
The Sturtian glaciation is recognised in the stratigraphic record through the deposition of distinct 934 diamictite intervals capped by carbonate rocks, which, accompanied by palaeomagnetic and 935 geochemical data, facilitated the correlation of these deposits globally (Hoffman & Schrag, 2002). However, the stratigraphic thicknesses of these units and the presence or absence of finer-grained 937 interbeds have resulted in contention surrounding the extent and cyclicity of the icehouse. 938

939
Although the glacial successions in North America appear to record a very similar two-fold glacial 940 advance-retreat cycle to that in South Australia (Eisbacher, 1985;Link et al., 1994), Le Heron et al. 941 (2020) suggested that these instead represent regional, diachronous glacial cycles. In fact, Le Heron et For these reasons, although age constraints and detailed paleoenvironmental interpretations are 964 improving, it is still uncertain whether the Sturtian glacial cycle advances were global (eustatically 965 driven) or happening at different times and at more local scales (tectonically driven). 966