Pulsed iceberg delivery driven by Sturtian ice sheet dynamics: An example from Death Valley, California

Abstract

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.

Sedimentological perspectives on climatic, atmospheric and environmental change in the Neoproterozoic Era

“…In the Death Valley area, Busfield & Le Heron () identify a grounding‐line fan with evidence for subglacial shear modification but, distally, these deposits pass into proglacial turbidites with no evidence for ice grounding in the marine environment (Le Heron & Busfield, , this issue). The existence of two palaeo‐ice masses was proposed, namely an ice sheet pinned on the Nopah uplands in the north, and a Mojave ice sheet in the south: an area of open water was posited between them (Fig.…”

“…Basinward of ice‐grounding zones and marine shelves, the deep‐water glaciomarine realm is well‐represented, particularly in Sturtian‐age rift basins, and notably in the Death Valley area (Miller, ; Prave, ; MacDonald et al ., 2013b; Le Heron et al ., 2014a; Busfield & Le Heron, , this issue; Le Heron & Busfield, , this issue). Comparable age strata in the northern Flinders Ranges, South Australia, bear some comparison with a similar range of facies (Young & Gostin, ).…”

“…The duration of early Cryogenian glaciation (often referred to as Sturtian after the South Australian Adelaide Basin succession) is interpreted to be ca 55 Myr (717 to 662 Ma) in a recent compilation (Rooney et al ., ), but its internal architecture is complex, and below the still‐viable proposition of Allen & Etienne () that this is not a single synchronous glaciation is discussed. Palaeogeographic reconstructions of Sturtian glacial events in California and Siberia are made respectively by Le Heron & Busfield (, this issue) and Sovetov & Le Heron (, this issue) while Busfield & Le Heron (, this issue) provide a detailed reconstruction of processes close to a grounding line in Death Valley, California. The between‐glacial time period is referred to as the late Cryogenian Warm Interval by Shields‐Zhou et al .…”

The Cryogenian record in the southern Kingston Range, California: The thickest Death Valley succession in the hunt for a GSSP

“…Le Heron et al (2014) and Le Heron and Busfield, 2016) proposed that the supraolistostrome succession accumulated in a basin that was dominated by turbidite and debrite delivery. The occurrence of dropstones both in fine-grained facies toward the base of the supra-olistostrome succession and in diamictites at its top, testifies to a strong glacial influence (and possibly control upon) stratigraphic architecture.…”

“…belts of the KPF byLe Heron et al (2014),Le Heron and Busfield (2016) andBusfield and Le Heron (2016). These studies emphasise the co-genetic development of turbidites and icecontact diamictites(Busfield and Le Heron, 2016).…”