The Kingston Peak Formation is a diamictite-bearing succession that crops out in the Death Valley region, California, USA. An exceptionally thick (>1.5 km) outcrop belt in its type area (the Kingston Range), provides clear insights into the dynamics of mid-Cryogenian ('Sturtian') ice sheets in Laurentia. Seven detailed logs allow the lateral and vertical distribution of facies associations to be assessed. We recognise (1) diamictite facies association (ice-proximal glacigenic debris flows), (2) lonestone-bearing facies association (ice-marginal hemipelagic deposits and low-density gravity flows with iceberg rafting), (3) pebble to boulder conglomerate facies association (ice-proximal co-genetic glacigenic debris flows and high-density turbidites), (4) megaclast facies association (olistostrome and hemipelagic sediments subject to ice-rafting), and (5) interbedded heterolithics facies association (low-density turbidites and hemipelagic deposits). The stratigraphic motif allows three glacial cycles to be inferred across the range. Ice-minimum conditions interrupting the Kingston Peak are associated with the development of an olistostrome complex, succeeded by a thick accumulation of boulder conglomerates deposited during ice re-advance. The data testify to a strong glacial influence on sedimentation within this ancient subaqueous succession, and to highly dynamic ice sheet behaviour with clear glacial cycles during the Sturtian glaciation.

This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1111/sed.12210The Kingston Peak Formation is an archetypal Cryogenian succession that crops out across the Death Valley region of eastern California. Above pre-glacial strata (KP1), two distinct glacial phases have been recognized and are interpreted to be allied to the panglacial Sturtian (KP2 and KP3) and Marinoan (KP4) icehouse events. The thickest and most extensive unit, KP3, forms the entire exposed section at Sperry Wash. At this locality, ice-distal turbidites are succeeded in turn by ice-medial and ice-proximal facies, comprising a spectrum of ice-rafted debris-bearing turbidites, debrites and shales. These are overlain by ice-marginal grounding-line fan deposits interbedded with glacitectonically deformed heterolithics, supporting local advance to an ice-contact position. The succession records accumulation within a glacier-fed subaqueous shelf, wherein the clear progradational signature is driven by ice advance towards the south-east. Evolution of the subaqueous complex is five-fold, comprising: (i) ice-distal outwash; (ii) build-out of ice-medial depositional lobes; (iii) ice-proximal deposition and increased calving; (iv) resumed ice-margin advance; and (v) growth of ice-contact grounding-line fan. This sequence is unique in the Death Valley region for recording the first evidence of advance to ice-marginal and ice-contact settings, thereby enabling the location of the glacier terminus to be documented for the first time.authorsversionPeer reviewe

The Chuos Formation is a diamictite-dominated succession of Cryogenian age, variously interpreted as the product of glaciomarine deposition, glacially-related mass movement, or rift-related sediment remobilisation in a non-glacial environment. These interpretations have wide ranging implications for the extent of ice cover during the supposedly pan-global Neoproterozoic icehouse. In the Otavi Mountainland, northern Namibia, detailed analysis of soft sediment deformation structures on the macro-and micro-scale support glacitectonic derivation in response to overriding ice from the south/south-east. Overall, the upward increase in strain intensity, predominance of ductile deformation features (e.g. asymmetric folds, rotational turbates and necking structures, clast boudinage, unistrial plasmic fabrics) and pervasive glacitectonic lamination support subglacial deformation under high and sustained porewater pressures. In contrast, soft sediment structures indicative of mass movements, including flow noses, tile structures, and basal shear zones, are not present. The close association of subglacial deformation, abundant ice-rafted debris and ice-contact fan deposits indicate subaqueous deposition in an ice-proximal setting, subject to secondary subglacial deformation during oscillation of the ice margin. These structures thus reveal evidence of dynamic grounded ice sheets in the Neoproterozoic, demonstrating their key palaeoclimatic significance within ancient sedimentary successions.

The Cryogenian record of South Australia houses the type region of the Sturtian glaciation, the oldest of three pan-global icehouse intervals during the Neoproterozoic. Data are presented from previously little described sections at Holowilena Creek, Oladdie Creek and Hillpara Creek in the central and southern Flinders Ranges, where five facies associations are recognized. These are (i) diamictite and conglomerate, (ii) interbedded heterolithics, (iii) hummocky cross-stratified sandstone, (iv) lonestone-bearing siltstone, and (v) ferruginous siltstone and sandstone. The succession reveals significant lateral and vertical facies variation, which is linked to a complex inherited palaeotopography and distance from the sediment source. Repeated stratigraphic occurrences of striated clasts and abundant ice-rafted debris strongly support recurrent glacial influence on sedimentation. The intercalation of gravitationally re-worked diamictites, dropstonebearing siltstone and dropstone-free siltstone testifies to dynamic sedimentation within a periodically glacially-influenced subaqueous environment. Sequence stratigraphic analysis identifies four glacial advance systems tracts (GAST), separated by three glacial retreat systems tracts (GRST), wherein hummocky cross-stratified sandstones attest to open water conditions. These findings support dynamic ice sheet behaviour in South Australia, and provide clear evidence for repeated intra-Sturtian ice sheet recession.

One of the major issues in Neoproterozoic geology is the extent to which glaciations in the Cryogenian and Ediacaran periods were global in extent and synchronous or regional in extent and diachronous. A similarly outstanding concern is determining whether deposits are truly glacial, as opposed to gravitationally initiated mass flow deposits in the context of a rifting Rodinia supercontinent. In this paper, we present 115 publically available, quality-filtered chronostratigraphic constraints on the age and duration of Neoproterozoic glacial successions, and compare their palaeocontinental distribution. Depositional ages from North America (Laurentia) clearly support the idea of a substantial glacial epoch between about 720-660 Ma on this palaeocontinent but paradoxically, the majority of Australian glacial strata plot outside the previously proposed global time band for the eponymous Sturtian glaciation, with new dates from China also plotting in a time window previously thought to be an interglacial. For the early Cryogenian, the data permit either a short, sharp 2.4 Ma long global glaciation, or diachronous shifting of ice centres across the Rodinia palaeocontinent, implying regional rather than global ice covers and asynchronous glacial cycles. Thus, based on careful consideration of age constraints, we suggest that strata deposited in the ca. 720-660 Ma window in North America are better described as belonging to a Laurentian Neoproterozoic Glacial Interval (LNGI), given that use of the term Sturtian for a major Neoproterozoic glacial epoch can clearly no longer be justified. This finding is of fundamental importance for reconstructing the Neoproterozoic climate system because chronological constraints do not support the concept of a synchronous panglacial Snowball Earth. Diachroneity of the glacial record reflects underlying palaeotectonic and palaeogeographic controls on the timing of glaciation resulting from the progressive breakup of the Rodinian supercontinent.

The Sturtian is the oldest (ca 716Ma) of three pan-global glaciations in the Cryogenian. At Omutirapo, in northern Namibia, a 2km wide, 400m deep palaeovalley is filled by glaciogenic strata of the Chuos Formation, which represents the Sturtian glacial record. Sedimentary logging of an exceptionally high-quality exposure permits detailed stratigraphic descriptions and interpretations, allowing two glacial cycles to be identified. At the base of the exposed succession, strong evidence supporting glaciation includes diamictites, ice-rafted dropstones and intensely sheared zones of interpreted subglacial origin. These facies collectively represent ice-proximal to ice-rafted deposits. Upsection, dropstone-free mudstones in the middle of the succession, and the absence of diamictites, imply sedimentation free from glacial influence. However, the reappearance of glacial deposits above indicates a phase of Sturtian glacial re-advance. Comparison with age-equivalent strata in South Australia, where evidence for sea-ice free sedimentation has been established previously, suggests that a Sturtian interglacial may have been extensive, implying global-scale waxing and waning of ice sheets during a Cryogenian glacial event.Peer reviewe

The Bolla Bollana Formation is an exceptionally thick (ca 1500 m), riftrelated sedimentary succession cropping out in the northern Flinders Ranges, South Australia, which was deposited during the Sturtian (mid Cryogenian) glaciation. Lithofacies analysis reveals three distinct facies associations which chart changing depositional styles on an ice-sourced subaqueous fan system. The diamictite facies association is dominant, and comprises both massive and stratified varieties with a range of clast compositions and textures, arranged into thick beds (1 to 20 m), representing stacked, ice-proximal glaciogenic debris-flow deposits. A channel belt facies association, most commonly consisting of normally graded conglomerates and sandstones, displays scour and fill structure of ca 10 m width and 1 to 3 m depth: these strata are interpreted as channelized turbidites. Rare mud-filled channels in this facies association bear glacially striated lonestones. Finally, a sheet heterolithics facies association contains a range of conglomerates through sandstones to silty shales arranged into clear, normally graded cycles from the lamina to bed scale. These record a variety of non-channelized turbidites, probably occupying distal and/or inter-channel locations on the subaqueous fan. Coarsening and thickening-up cycles, capped by dolomicrites or mudstones, are indicative of lobe build out and abandonment, potentially as a result of ice lobe advance and stagnation. Dropstones, recognized by downwarped and punctured laminae beneath pebbles to boulders in shale, or in delicate climbing ripple cross-laminated siltstones, are clearly indicative of ice rafting. The co-occurrence of ice-rafted debris and striated lonestones strongly supports a glaciogenic sediment source for the diamictites. Comparison to Pleistocene analogues enables an interpretation as a trough mouth fan, most probably deposited leeward of a palaeo-ice stream. Beyond emphasizing the highly dynamic nature of Sturtian ice sheets, these interpretations testify to the oldest trough mouth fan recorded to date.

The Kingston Peak Formation is a Cryogenian sedimentary succession that crops out in the Death Valley area, California, USA. It is widely accepted to record pre‐glacial conditions (KP1), followed by two glaciations of pan‐global extent, the older Sturtian (KP2 to KP3) and younger Marinoan glaciation (KP4). In the type area (the Kingston Range), detailed facies analysis of the Sturtian succession reveals that a basal diamictite unit and an upper boulder conglomerate were deposited by proglacial subaqueous sediment gravity flows. An olistostrome unit punctuating the succession is interpreted to result from tectonically induced downslope mobilization during isostatic rebound, triggered by significant ice‐meltback. Focussing on strata onlapping the olistostrome, this article provides insight into the processes of glacial re‐advance following an intra‐Sturtian glacial minimum. The first 50 m of strata above the olistostrome are thinly bedded turbidites that are devoid of lonestones. A trend towards thicker graded beds upsection, in concert with the gradual appearance and then abundance of lonestones, testifies to the influence of ice rafting and to the resumption of a direct ice sheet influence upon sedimentation. Stratigraphic organization into thickening and coarsening upward bedsets over a multi‐metre scale reveals a subaqueous gravity flow‐dominated succession composed of a spectrum of high to low density turbidites, with thick graded boulder‐conglomerates at intervals. The finer‐grained facies assemblage is heterolithic: current ripple cross‐laminated sandstones intercalated with shales that bear delicate granule to pebble‐sized dropstones in abundance. Intervals of dropstone‐bearing and dropstone‐free strata are attributable to dynamic oscillation of the ice margin in the hinterland. Integrating palaeocurrent data with observations from neighbouring outcrop belts allows a detailed palaeogeographic map of the eastern Death Valley area to be compiled for the first time.