Downhill from Austin and Ely to Las Vegas: U-Pb detrital zircon suites from the Eocene–Oligocene Titus Canyon Formation and associated strata, Death Valley, California

ABSTRACT In a reconnaissance investigation aimed at interrogating the changing topography and paleogeography of the western United States prior to Basin and Range faulting, a preliminary study made use of U-Pb ages of detrital zircon suites from 16 samples from the Eocene–Oligocene Titus Canyon Formation, its overlying units, and correlatives near Death Valley. The Titus Canyon Formation unconformably overlies Neoproterozoic to Devonian strata in the Funeral and Grapevine Mountains of California and Nevada. Samples were collected from (1) the type area in Titus Canyon, (2) the headwaters of Monarch Canyon, and (3) unnamed Cenozoic strata exposed in a klippe of the Boundary Canyon fault in the central Funeral Mountains. Red beds and conglomerates at the base of the Titus Canyon Formation at locations 1 and 2, which contain previously reported 38–37 Ma fossils, yielded mostly Sierran batholith–age detrital zircons (defined by Triassic, Jurassic, and Cretaceous peaks). Overlying channelized fluvial sandstones, conglomerates, and minor lacustrine shale, marl, and limestone record an abrupt change in source region around 38–36 Ma or slightly later, from more local, Sierran arc–derived sediment to extraregional sources to the north. Clasts of red radiolarian-bearing chert, dark radiolarian chert, and quartzite indicate sources in the region of the Golconda and Roberts Mountains allochthons of northern Nevada. Sandstones intercalated with conglomerate contain increasing proportions of Cenozoic zircon sourced from south-migrating, caldera-forming eruptions at the latitude of Austin and Ely in Nevada with maximum depositional ages (MDAs) ranging from 36 to 24 Ma at the top of the Titus Canyon Formation. Carbonate clasts and ash-rich horizons become more prevalent in the overlying conglomeratic Panuga Formation (which contains a previously dated 15.7 Ma ash-flow tuff). The base of the higher, ash-dominated Wahguyhe Formation yielded a MDA of 14.4 Ma. The central Funeral Mountains section exposes a different sequence of units that, based on new data, are correlative to the Titus Canyon, Panuga, and Wahguyhe Formations at locations 1 and 2. An ash-flow tuff above its (unexposed) base provided a MDA of 34 Ma, and the youngest sample yielded a MDA of 12.7 Ma. The striking differences between age-correlative sections, together with map-based evidence for channelization, indicate that the Titus Canyon Formation and overlying units likely represent fluvial channel, floodplain, and lacustrine deposits as sediments mostly bypassed the region, moving south toward the Paleogene shoreline in the Mojave Desert. The profound changes in source regions and sedimentary facies documented in the Titus Canyon Formation took place during ignimbrite flareup magmatism and a proposed eastward shift of the continental divide from the axis of the Cretaceous arc to a new divide in central Nevada in response to thermal uplift and addition of magma to the crust. This uplift initiated south-flowing fluvial systems that supplied sediments to the Titus Canyon Formation and higher units.

Supplemental Material: Stratigraphy of the Eocene–Oligocene Titus Canyon Formation, Death Valley, California, and Eocene extensional tectonism in the Basin and Range

<div>Text: Additional explanation of the methods used to recalculate the Ar/Ar ages of Gutenkunst (2006), Saylor and Hodges (1994), and Saylor (1991). Figure S1: Analytical plots recalculated from ⁴⁰Ar/³⁹Ar data originally produced by Gutenkunst (2006). Figure S2: Scans of a large scale map and seven isochron plots for five samples provided by B. Saylor (personal commun., 2015). Table S1: Detrital zircon U-Pb analytical data. Table S2: Zircon (U‐Th)/He analytical data. Table S3: Analytical data for ⁴⁰Ar/³⁹Ar ages of Gutenkunst (2006).<br></div>

„Jakaś groza wieje od tych pól ponurych” – świadkowie i dziedzictwo masowych, drugowojennych zbrodni w Dolinie Śmierci w Chojnicach

This paper discusses the results of the research carried out in a project entitled An archaeology of the Death Valley. First, the historical context related to mass killings on the outskirts of Chojnice during the Second World War is sketched. Then, the results of the archaeological field research are presented. The last part is about ethnographic research which allowed to document various memories related to mass killings in the Death Valley as well as human and non-human witnesses of these events. The idea behind this paper is to show that archaeology and ethnography are crucial in discovering and documenting sites of mass killings and their heritage.

Fracture Spacing Variability and the Distribution of Fracture Patterns in Granitic Geothermal Reservoir: A Case Study in the Noble Hills Range (Death Valley, CA, USA)

Scanlines constitute a robust method to better understand in 3D the fracture network variability in naturally fractured geothermal reservoirs. This study aims to characterize the spacing variability and the distribution of fracture patterns in a fracture granitic reservoir, and the impact of the major faults on fracture distribution and fluid circulation. The analogue target named the Noble Hills (NH) range is located in Death Valley (DV, USA). It is considered as an analogue of the geothermal reservoir presently exploited in the Upper Rhine Graben (Soultz-sous-Forêts, eastern of France). The methodology undertaken is based on the analyze of 10 scanlines located in the central part of the NH from fieldwork and virtual (photogrammetric models) data. Our main results reveal: (1) NE/SW, E/W, and NW/SE fracture sets are the most recorded orientations along the virtual scanlines; (2) spacing distribution within NH shows that the clustering depends on fracture orientation; and (3) a strong clustering of the fracture system was highlighted in the highly deformed zones and close to the Southern Death Valley fault zone (SDVFZ) and thrust faults. Furthermore, the fracture patterns were controlled by the structural heritage. Two major components should be considered in reservoir modeling: the deformation gradient and the proximity to the regional major faults.

Whole-lithosphere shear during oblique rifting

Processes controlling the formation of continental whole-lithosphere shear zones are debated, but their existence requires that the lithosphere is mechanically coupled from base to top. We document the formation of a dextral, whole-lithosphere shear zone in the Death Valley region (DVR), southwest United States. Dextral deflections of depth gradients in the lithosphere-asthenosphere boundary and Moho are stacked vertically, defining a 20–50-km-wide, lower lithospheric shear zone with ~60 km of shear. These deflections underlie an upper-crustal fault zone that accrued ~60 km of dextral slip since ca. 8–7 Ma, when we infer that whole-lithosphere shear began. This dextral offset is less than net dextral offset on the upper-crustal fault zone (~90 km, ca. 13–0 Ma) and total upper-crustal extension (~250 km, ca. 16–0 Ma). We show that, before ca. 8–7 Ma, weak middle crust decoupled upper-crustal deformation from deformation in the lower crust and mantle lithosphere. Between 16 and 7 Ma, detachment slip thinned, uplifted, cooled, and thus strengthened the middle crust, which is exposed in metamorphic core complexes collocated with the whole-lithosphere shear zone. Midcrustal strengthening coupled the layered lithosphere vertically and therefore enabled whole-lithosphere dextral shear. Where thick crust exists (as in pre–16 Ma DVR), midcrustal strengthening is probably a necessary condition for whole-lithosphere shear.

Population genomic analysis of the speckled dace species complex (Rhinichthys osculus) identifies three species-level lineages in California

The speckled dace ( Rhinichthys osculus ) is small cyprinid fish that is widespread in the Western USA. Currently treated as a single species, speckled dace consists of multiple evolutionary lineages that can be recognized as species and subspecies throughout its range. Recognition of taxonomic distinctiveness of speckled dace populations is important for developing conservation strategies. In this study, we collected samples of speckled dace from 38 locations in the American West, with a focus on California. We used RAD sequencing to extract thousands of SNPs across the genome from samples to identify genetic differences among seven California populations informally recognized as speckled dace subspecies: Amargosa, Owens, Long Valley, Lahontan, Klamath, Sacramento, and Santa Ana speckled dace. We performed principal component analysis, admixture analysis, estimated pairwise Fst, and constructed a phylogeny to explore taxonomic relationships among these groups and test if these subspecies warrant formal recognition. Our analyses show that the seven subspecies fit into three major lineages equivalent to species: western (Sacramento-Klamath), Santa Ana, and Lahontan speckled dace. Death Valley speckled dace were determined to be two lineages (Amargosa and Long Valley) within Lahontan speckled dace. Western and Lahontan speckled dace lineages had branches that can be designated as subspecies. These designations fit well with the geologic history of the region which has promoted long isolation of populations. This study highlights the importance of genetic analysis for conservation and management of freshwater fishes.

List of Analogues for Highly Productive Rocks Around Salt Domes

In the Dnipro-Donets depression, the Devonian salt during Carboniferous time became movable and created salt domes in the Permian, moving to the sea bottom and flowing therewith, forming bodies visible today as salt canopies and overhangs. These features are clear pieces of evidence of salt exposure on the surface, especially considering belts of reservoirs around salt domes. These reservoirs can be extremely prolific in some wells. Previous exploration targeting such deposits was driven mainly by drilling wells within the areas of known deep fields such as Medvedivske, Zakhidno-Khrestyschenske and others in the central part of the DDB. These reservoirs are composed of poorly sorted coarse material of wide variety of rocks including sandstones, carbonates, dolomites, igneous rocks of deep (granites), and shallow (diabases) formations. Currently, with the availability of 3D seismic surveys, these deposits become visible as bright spots and flat spots. Although it is not a 100% indicator due to fact that shallow salt canopies and lithology changes of rocks around salt domes may also interpret seismic reflections. It is good to mention that the Permian is an aridic environment with gradually losing water influx to the basin from base to top within the thickness of more than 1-2 kilometers. It could be utilized as boundary analogues to cover most of the possible intermediate scenarios in three areas. The first analogue is the outcropped salt dome in Solotvyno village in Carpathian mountains in western Ukraine close to the Romania border. This salt dome is an important example of showing the current deposition of transported coarse material from depth around salt domes. The second one is salt domes exposed as mountains of the Oman desert where it is possible to follow the material path approaching the salt uplift. And the third example is the Death Valley in Arizona, USA. The valley is an example of fans mostly deposited by gravity rather than permanent water flows. It good to mention that there are more examples that could be treated as direct analogues (the Zagros mountains in Iran) but they are not easily accessible for field trips if needed. For recognizing real targets vs artifacts, applying the knowledge of current deposition examples around the world would help dramatically (Western Ukraine, Oman, Death Valley in Arizona).

Stratigraphy of the Eocene–Oligocene Titus Canyon Formation, Death Valley, California, and Eocene extensional tectonism in the Basin and Range

Geologic mapping, measured sections, and geochronologic data elucidate the tectono-stratigraphic development of the Titus Canyon extensional basin in Death Valley, California, and provide new constraints on the age of the Titus Canyon Formation, one of the earliest syn-extensional deposits in the central Basin and Range. Detrital zircon maximum depositional ages (MDAs) and compiled 40Ar/39Ar ages indicate that the Titus Canyon Formation spans 40(?)–30 Ma, consistent with an inferred Duchesnean age for a unique assemblage of mammalian fossils in the lower part of the formation. The Titus Canyon Formation preserves a shift in depositional environment from fluvial to lacustrine at ca. 35 Ma, which along with a change in detrital zircon provenance may reflect both the onset of local extensional tectonism and climatic changes at the Eocene–Oligocene boundary. Our data establish the Titus Canyon basin as the southernmost basin in a system of late Eocene extensional basins that formed along the axis of the Sevier orogenic belt. The distribution of lacustrine deposits in these Eocene basins defines the extent of a low-relief orogenic plateau (Nevadaplano) that occupied eastern Nevada at least through Eocene time. As such, the age and character of Titus Canyon Formation implies that the Nevadaplano extended into the central Basin and Range, ~200 km farther south than previously recognized. Development of the Titus Canyon extensional basin precedes local Farallon slab removal by ca. 20 Ma, implying that other mechanisms, such as plate boundary stress changes due to decreased convergence rates in Eocene time, are a more likely trigger for early extension in the central Basin and Range.

Supplemental Material: Stratigraphy of the Eocene–Oligocene Titus Canyon Formation, Death Valley, California, and Eocene extensional tectonism in the Basin and Range

<div>Text: Additional explanation of the methods used to recalculate the Ar/Ar ages of Gutenkunst (2006), Saylor and Hodges (1994), and Saylor (1991). Figure S1: Analytical plots recalculated from ⁴⁰Ar/³⁹Ar data originally produced by Gutenkunst (2006). Figure S2: Scans of a large scale map and seven isochron plots for five samples provided by B. Saylor (personal commun., 2015). Table S1: Detrital zircon U-Pb analytical data. Table S2: Zircon (U‐Th)/He analytical data. Table S3: Analytical data for ⁴⁰Ar/³⁹Ar ages of Gutenkunst (2006).<br></div>

Supplemental Material: Stratigraphy of the Eocene–Oligocene Titus Canyon Formation, Death Valley, California, and Eocene extensional tectonism in the Basin and Range

<div>Text: Additional explanation of the methods used to recalculate the Ar/Ar ages of Gutenkunst (2006), Saylor and Hodges (1994), and Saylor (1991). Figure S1: Analytical plots recalculated from ⁴⁰Ar/³⁹Ar data originally produced by Gutenkunst (2006). Figure S2: Scans of a large scale map and seven isochron plots for five samples provided by B. Saylor (personal commun., 2015). Table S1: Detrital zircon U-Pb analytical data. Table S2: Zircon (U‐Th)/He analytical data. Table S3: Analytical data for ⁴⁰Ar/³⁹Ar ages of Gutenkunst (2006).<br></div>