A diamictite dichotomy: Glacial conveyor belts and olistostromes in the Neoproterozoic of Death Valley, California, USA

D.P. Le Heron,D.O. Ali,S. Tofaif,T. Vandyk

doi:10.1130/g38460.1

Abstract

Multiple intercalations of glacially derived and slope-derived diamictites testify to the drawbacks of correlating Neoproterozoic diamictites more widely, but shed new light on the close interrelationship of these processes in the Cryogenian world. In the Neoproterozoic of Death Valley, California (USA), rifting of Rodinia occurred concomitantly with a major glacial event that deposited the Kingston Peak Formation. A new sedimentologic investigation of this formation in the Silurian Hills demonstrates, for the first time, that some diamictites are ultimately of glacial origin. Abundant dropstone textures occur in interstratified heterolithic deposits, with clasts of identical composition (gneiss, schist, granite, metabasite, quartzite) to those of boulder-bearing diamictites suggesting a common source (the glacial conveyor belt). In stark contrast, megaclast-bearing diamictites, yielding clasts of carbonate and siliciclastic preglacial strata as much as 100 m across, are interpreted as olistostromes. The occurrence of syn-sedimentary faults within the succession allows glacial versus slope-derived material to be distinguished for the first time.

Highlights

The distinction between diamictites of glacial origin and those of mass flows derived from slope collapse is of fundamental paleoclimatic importance and has remained a prominent part of the research agenda in Neoproterozoic studies for over 50 yr (e.g., Schermerhorn, 1974; Eyles and Januszczak, 2004; Domack and Hoffman, 2011; Nascimento et al, 2016)
IMPLICATIONS AND CONCLUSIONS Based on the data it is proposed that at least four principal pulses of boulder-bearing diamictite—which we interpret as glaciogenic debris-flow deposits (GDFs)—represent multiple phases of sediment release from the paleo–ice margin
Dovetailed with observations in the southern Kingston Range some 30 km to the east (Le Heron et al, 2014), this suggests that the glacial record is much more complicated, with potentially many more glacial phases recognized, than the popular two-phase model for Death Valley which seeks to incorporate putative Sturtian and Marinoan panglacials (Macdonald et al, 2013; Smith et al, 2016)

Summary

Introduction

The distinction between diamictites of glacial origin and those of mass flows derived from slope collapse is of fundamental paleoclimatic importance and has remained a prominent part of the research agenda in Neoproterozoic studies for over 50 yr (e.g., Schermerhorn, 1974; Eyles and Januszczak, 2004; Domack and Hoffman, 2011; Nascimento et al, 2016). Misinterpreting slope deposits as glacial, or vice versa, means that the number of glacial cycles in Earth’s history could be either under- or overemphasized (Arnaud and Etienne, 2011). Such an understanding is of profound importance in the Cryogenian, with putative panglacial (sensu Hoffman, 2009) episodes in the Neoproterozoic ~720–635 m.y. ago (Spence et al, 2016). In Death Valley (California, USA), the Kingston Peak Formation (KPF) was deposited in a regional sediment trap that received sediment from multiple directions (Mahon et al, 2014). The Silurian Hills (SH) are one of the Death Valley outcrop belts that have received

Methods

Conclusion