How to Determine the Origin of Potential Cryogenian Neoproterozoic Dropstones From Death Valley

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

Authors:

Le Heron et al

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.

Erk: Devil's Hole Pupfish Might be "Man Made"

Evaluating an icon of population persistence: the Devil's Hole pupfish

Authors:

Reed et al

Abstract:

The Devil's Hole pupfish Cyprinodon diabolis has iconic status among conservation biologists because it is one of the World's most vulnerable species. Furthermore, C. diabolis is the most widely cited example of a persistent, small, isolated vertebrate population; a chronic exception to the rule that small populations do not persist long in isolation. It is widely asserted that this species has persisted in small numbers (less than 400 adults) for 10 000–20 000 years, but this assertion has never been evaluated. Here, we analyse the time series of count data for this species, and we estimate time to coalescence from microsatellite data to evaluate this hypothesis. We conclude that mean time to extinction is approximately 360–2900 years (median 410–1800), with less than a 2.1% probability of persisting 10 000 years. Median times to coalescence varied from 217 to 2530 years, but all five approximations had wide credible intervals. Our analyses suggest that Devil's Hole pupfish colonized this pool well after the Pleistocene Lakes receded, probably within the last few hundred to few thousand years; this could have occurred through human intervention.

Death Valley's 'Sailing Stones' Mystery Solved

The Racetrack Playa — a barren lakebed in Death Valley National Park — is home to one of the world’s natural wonders: “sailing stones” that mysteriously meander across the dried mud, leaving tracks in their wake. Since the 1940s, these rocks have fueled wonder and speculation because no one had seen them in action — until now.

A team of U.S. scientists recorded the first observation of these boulders in motion, using GPS monitors and time-lapse photography. By meticulously tracking weather data, scientists also explained how these rocks slog across the playa. What was one of the world’s natural wonders now appears to be the perfect combination of rain, wind, ice and sun.

link.

Geological Record of Death Valley From the Stenian Mesoproterozoic to the Ediacaran NeoProterozoic

Detrital zircon provenance and paleogeography of the Pahrump Group and overlying strata, Death Valley, California

Authors:

Mahon et al

Abstract:

The Mesoproterozoic and Neoproterozoic Pahrump Group of Death Valley, California spans ca. 1300 to 635 Ma and provides a greater than 500 million-year record of geologic events in southwestern Laurentia. The strata analyzed include preserved sequences separated by unconformities recording syn-Rodinia basin development (Crystal Spring Formation); Rodinia stability; regional extension culminating in Neoproterozoic rifting of the Laurentian margin of Rodinia (Horse Thief Springs through Johnnie Formations); and multiple phases of glacial sedimentation and subsequent cap carbonate deposition (Kingston Peak Formation and Noonday Dolomite). U-Pb detrital zircon analyses were conducted on samples from the entire Pahrump Group and the Noonday Dolomite in the southeastern Death Valley region (20 samples, 1,945 grains) to further constrain hypotheses for regional basin development during the development of the southwestern Laurentian margin.

Our interpretation of provenance data expands upon and clarifies previous models defining a series of tectonostratigraphic units including: A) the less than 1400 Ma basal conglomerate of the Crystal Spring Formation, comprised of metasedimentary quartzite clasts, and exhibiting a unimodal detrital zircon sample distribution at 1690 Ma with northerly source; B) the ca. 1320-1080 Ma Crystal Spring Formation exhibiting unimodal zircon distributions derived from southerly, local Paleoproterozoic basement sources punctuated by a ca. 300 Ma duration unconformity; C) the ca. 780-740 Ma sequence of the Horse Thief Springs Formation, Beck Spring Dolomite, and KP1 unit of Kingston Peak Formation deposited in a marine basin with mixed southwestern Laurentian provenance; D) a ca. 710-635 Ma glaciogenic sequence (KP2-KP4 members of Kingston Peak Formation), recording the onset of Rodinia rifting, and Sturtian and Marinoan “Snowball Earth” intervals. Provenance data suggest derivation from erosion and recycling of older Pahrump Group strata; E) the ca. 635 Ma cap dolostone of the Sentinel Peak Member of the Noonday Dolomite, representing post-glacial drainage reorganization with more regional provenance; and followed by F) the <635 500="" a="" addition="" age="" analysis="" and="" basement="" bimodal="" blockquote="" ca.="" complement="" data="" derivation="" distributions="" dolomite="" for="" from="" in="" indicating="" laurentian="" local="" ma="" margin.="" marked="" member="" new="" noonday="" of="" overlying="" previous="" provenance="" radcliff="" result="" shift="" showing="" sources.="" southwestern="" strata="" studies="" synthesize="" the="" these="" to="" units="">