Testing the Synchronicity of Splay-Fault Ruptures in Carson Valley, Nevada, United States

ABSTRACT The Carson City and Indian Hills faults in Carson City, Nevada, splay northeastward from the major range-bounding Genoa fault. Each splay is part of the Carson range fault system that extends nearly 100 km northward from near Markleeville, California, to Reno, Nevada. Stratigraphic and structural relationships exposed in paleoseismic excavations across the two faults yield a record of ground-rupturing earthquakes. The most recent on the Carson City fault occurred around 473–311 B.P., with the two penultimate events between 17.9 and 8.1 ka. Two trench exposures across the Indian Hills fault record the most recent earthquake displacement after ∼900 yr, preceded by a penultimate surface rupture ≥∼10,000, based on radiocarbon and infrared-stimulated luminescence dating of exposed sediments. The age estimates allow that the Carson City and Indian Hills faults ruptured simultaneously with a previously reported large earthquake on the Genoa fault ∼514–448 B.P. Similar synchronicity of rupture is not observed in the record of penultimate events. Penultimate ages of ruptures on the Carson City and Indian Hills faults are several thousand years older than that of the Genoa fault from which they splay. Together, these observations imply a variability in rupture moment through time, demonstrating the importance of considering multi-fault rupture models for seismic hazard analyses.

Spatiotemporal Rates of Tectonic Deformation and Landscape Evolution above a Laterally Propagating Thrust Fault: Wheeler Ridge Anticline, California, USA

The Wheeler Ridge anticline, located in the southern San Joaquin Valley of California, USA, is a well-studied and classic example of a laterally growing fault propagation fold. New high-resolution lidar elevation data combined with nine infrared stimulated luminescence (IRSL) ages of discrete geomorphic surfaces that are bounded by prominent transverse wind and river gaps allow for investigation of tectonic topography through time. Luminescence ages from four of the six surfaces yield depositional ages that range from 32 ka to 153 ka, which are broadly consistent with a previously published soil chronosequence. Our graphical modeling indicates an average surface uplift rate of ~2.1 mm/yr and an average along-strike fold propagation rate of ~20 mm/yr. However, our probabilistic modelling and topographic analysis suggest a rate decrease of both uplift and lateral propagation toward the fault tip from ~2.4 to 0.7 mm/yr and from ~49 to 14 mm/yr, respectively. Rate decreases are not progressive but rather occur in punctuated deformational intervals across previously documented structural barriers (tear faults) resulting in a fold that is characterized by discrete segments that exhibit a systematic deformational decrease toward the east. The punctuated tectonic growth of Wheeler Ridge has also locally controlled the topographic evolution of the anticline by effecting the formational timing and position of at least seven wind and river gaps that result from multiple north-flowing antecedent streams that traverse the growing structure. We quantify the timing of wind and river gap formation, based on IRSL results and inferred incision rates, and present a model for the spatiotemporal evolution of transverse drainages and the topographic development of Wheeler Ridge. Our chronology of gap formation broadly correlates with regional Late Pleistocene dry climate intervals suggesting that both tectonics and climate were integral to the geomorphic development of the Wheeler Ridge anticline.

A multimethod dating study of ancient permafrost, Batagay megaslump, east Siberia

Dating of ancient permafrost is essential for understanding long-term permafrost stability and interpreting palaeoenvironmental conditions but presents substantial challenges to geochronology. Here, we apply four methods to permafrost from the megaslump at Batagay, east Siberia: (1) optically stimulated luminescence (OSL) dating of quartz, (2) post-infrared infrared-stimulated luminescence (pIRIR) dating of K-feldspar, (3) radiocarbon dating of organic material, and (4) 36Cl/Cl dating of ice wedges. All four chronometers produce stratigraphically consistent and comparable ages. However, OSL appears to date Marine Isotope Stage (MIS) 3 to MIS 2 deposits more reliably than pIRIR, whereas the latter is more consistent with 36Cl/Cl ages for older deposits. The lower ice complex developed at least 650 ka, potentially during MIS 16, and represents the oldest dated permafrost in western Beringia and the second-oldest known ice in the Northern Hemisphere. It has survived multiple interglaciations, including the super-interglaciation MIS 11c, though a thaw unconformity and erosional surface indicate at least one episode of permafrost thaw and erosion occurred sometime between MIS 16 and 6. The upper ice complex formed from at least 60 to 30 ka during late MIS 4 to 3. The sand unit above the upper ice complex is dated to MIS 3–2, whereas the sand unit below formed at some time between MIS 4 and 16.

Luminescence dating of Youfangbei early late Pleistocene site, Nihewan Basin, North China

Sites dated to the early late Pleistocene are still limited in North China, which has hindered the detailed analysis of the development of Paleolithic industries in the late Pleistocene in this area. The Youfangbei (YFB) site is a newly excavated small-flake-tool Paleolithic site near the Youfang (YF) microblade site in the Nihewan Basin, North China. Because the small-flake-tool industry still existed in the late part of the late Pleistocene and might be related to the emergence of microlithic industries, the relationship between the two sites needs to be determined through a chronological study. Two profiles were excavated, and most of the artifact assemblages were unearthed in the lower profile (T1) from a depth of 0.9 m from the bottom. In this study, the feldspar post-infrared infrared stimulated luminescence method was applied to determine the age of the YFB site. Results showed that the upper profile was deposited from 86–0.5 ka, and the cultural layer in T1 yielded age of 124–82 ka, corresponding to Marine Isotope Stage (MIS) 5, with an irregular but generally mild climate. The age of the YFB site is too old to be directly related to that of the YF site, but it partly bridges a chronological gap of human occupation in the Nihewan Basin.

Chronology of the Huxushan Paleolithic site in south China: Inferred from multiple luminescence dating techniques

The Huxushan archaeological site in northern Hunan Province, China, was recently excavated, from which stone tools including handaxes were unearthed. The deposits of the site are chemically weathered, which makes it difficult to date the site using numerical dating techniques except for optically stimulated luminescence (OSL) method. Here, we used various luminescence procedures including single-aliquot regenerative-dose (SAR), sensitivity-corrected multiple-aliquot regenerative-dose (SMAR) and thermally transferred optically stimulated luminescence (TT-OSL) SAR procedures on fine-grained quartz, and two-step post-infrared infrared stimulated luminescence (pIRIR) and multi-elevated-temperature pIRIR (MET-pIRIR) procedures on fine polymineral fractions. The results show that the fine quartz grains have excellent luminescence properties and the quartz SAR-, SMAR- and TT-OSL ages for the samples agree with each other and in stratigraphical order except for one sample. The fine polymineral fractions exhibited relatively weak pIRIR and MET-pIRIR signals, resulting in difficulty in constructing the dose-response curve for MET-pIRIR signals and the stratigraphically inconsistent pIRIR(100, 275) ages. The seven samples yielded their quartz OSL ages ranging from about 62 ka to 133 ka. The two samples from the cultural layer was dated to 78 to 92 ka using different procedures on fine quartz . However, given the systematically older pIRIR ages obtained with the fine polymineral grains for the two samples, their quartz OSL ages are considered to represent the minimal ages of this layer, and their pIRIR(100, 275) ages of 118 and 110 ka represent the upper age limit, indicating that the site was occupied by hominins during Marine Isotope Stage 5.

Residual dose of K-feldspar post-IR IRSL of beach-shoreface sands at Kujukuri, eastern Japan

We assessed the residual dose of K-feldspar grains from modern and Holocene beach– shoreface sands at Kujukuri, eastern Japan. Samples from the modern foreshore and shoreface (to 34 m depth) show residual doses <0.2 Gy for infrared-stimulated luminescence (IR)50 measured during post-IR infrared-stimulated luminescence (pIRIR)50/150, equivalent to potential burial age overestimation of only several decades for given dose rates. Residual doses of 1–3 Gy are retained by pIRIR50/150, equivalent to 400–1,300 years; pIRIR50/290 residual doses are up to 30 Gy, suggesting possible overestimation by >10,000 years. Residual doses of Holocene sands were also assessed by comparison with radiocarbon ages, revealing consistent results with modern sands. The pIRIR50/290 results show no pronounced correlation of residual dose with water depth, except for a few samples from <5 m depth with residual doses several tens of per cent lower than those of deeper sands, suggesting that most samples were not fully bleached and that sustained subaerial sunlight bleaching diminishes the difficult-to-bleach component. Compared to the uncertainties associated with other factors, such as the fading correction, the residual doses of IR50 and pIRIR50/150 are negligible for samples older than late and early Holocene, respectively. In contrast, the residual dose of pIRIR50/290 may lead to critical age overestimation of Late Pleistocene deposits if the residual dose is not properly corrected.

Supplemental Material: Late Pleistocene–Holocene flood history, flood-sediment provenance and human imprints from the upper Indus River catchment, Ladakh Himalaya

Figure S1: (A) Infrared Stimulated Luminescence (IRSL) of LD-1818 exhibiting feldspar contamination. (B) IRSL counts of all samples after complete etching including LD-1818 after re-etching. (C) Optical Stimulated Luminescence (OSL) decay curves of all samples; Figure S2: (A) Pre heat test (dotted line represents 220 °C plateau) and (B) Dose recovery test of LD-3170; Figure S3: OSL characteristics of LD-2011. (A) Probably distribution of ED all discs and (B) Sensitivity corrected luminescence growth curve; Figure S4: Radial plot of all OSL samples with ages; Table S1: Elemental, isotopic and age details of detrital zircon U-Pb geochronology of paleoflood deposits.

Supplemental Material: Late Pleistocene–Holocene flood history, flood-sediment provenance and human imprints from the upper Indus River catchment, Ladakh Himalaya

Figure S1: (A) Infrared Stimulated Luminescence (IRSL) of LD-1818 exhibiting feldspar contamination. (B) IRSL counts of all samples after complete etching including LD-1818 after re-etching. (C) Optical Stimulated Luminescence (OSL) decay curves of all samples; Figure S2: (A) Pre heat test (dotted line represents 220 °C plateau) and (B) Dose recovery test of LD-3170; Figure S3: OSL characteristics of LD-2011. (A) Probably distribution of ED all discs and (B) Sensitivity corrected luminescence growth curve; Figure S4: Radial plot of all OSL samples with ages; Table S1: Elemental, isotopic and age details of detrital zircon U-Pb geochronology of paleoflood deposits.

Insight into the sediment dynamics of a high-impact low-frequency mass movement event using single-grain feldspar luminescence in the Pokhara valley, Nepal

&lt;p&gt;Mass movements play an important role in landscape evolution of high mountain areas such as the Himalayas. Yet, establishing numerical age control and reconstructing transport dynamics of past events is challenging. To fill this research gap, we investigated the potential of Optically Stimulated Luminescence (OSL) dating and tracing methods. OSL dating analyses of Himalayan sediments is extremely challenging due to two main reasons: i) the OSL sensitivity of quartz, typically the mineral of choice for dating sediments younger than 100 ka, is poor, and ii) highly turbid conditions during mass movement transport hamper sufficient OSL signal resetting prior to deposition which eventually results in age overestimation. In this study, we aim to bring OSL dating to the test in an extremely challenging environment. First, we assess the applicability of single-grain feldspar dating of mass movement deposits in the Pokhara valley, Nepal. Second, we exploit the poor bleaching mechanisms to get insight into the sediment dynamics of this paleo-mass movement through bleaching proxies. The Pokhara valley is a unique setting for our case-study, considering the availability of an extensive independent radiocarbon dataset (Schwanghart et al., 2016) as a geochronological benchmark.&lt;/p&gt;&lt;p&gt;Single-grain infrared stimulated luminescence signals were measured at 50&amp;#176;C (IRSL50) and post-infrared infrared stimulated luminescence signals at 150&amp;#176;C (pIRIR-150). As expected, results show that the IRSL50 signal is better bleached than the pIRIR150 signal. A bootstrapped Minimum Age Model (bMAM) is applied to retrieve the youngest subpopulation to estimate the palaeodose. However, burial ages calculated based on this palaeodose overestimate the radiocarbon ages by an average factor of ~8 (IRSL50) and ~35 (pIRIR150). This shows that dating of the Pokhara Formation with our single-grain approach was not successful. Large inheritances in combination with the scatter in the single-grain dose distributions show that the sediments have been transported prior to deposition under extreme limited light exposure which corresponds well with the highly turbid nature of the sediment laden flood and debris flows that emplaced the Pokhara Formation.&lt;/p&gt;&lt;p&gt;To investigate the sediment transport dynamics in more detail we studied three bleaching proxies: the percentage of grains in saturation (2D0 criteria), percentage of well-bleached grains (2&amp;#963; range of bMAM-De) and the overdispersion (OD). Neither of the three bleaching proxies indicate a spatial relationship with run-out distances of the mass movement deposits. We interpret this as virtual absence of bleaching during transport, which reflects the catastrophic nature of the event. While single-grain feldspar dating did not provide reliable burial ages of the Pokhara mass movement deposits, our approach has great potential to provide insight in sediment transport dynamics of high-impact low-frequency mass movement events in mountainous region.&lt;/p&gt;&lt;p&gt;&lt;em&gt;References&lt;/em&gt;&lt;/p&gt;&lt;p&gt;Schwanghart, W., Bernhardt, A., Stolle, A., Hoelzmann, P., Adhikari, B. R., Andermann, C., ... &amp; Korup, O. (2016). Repeated catastrophic valley infill following medieval earthquakes in the Nepal Himalaya.&amp;#160;Science,&amp;#160;351(6269), 147-150.&lt;/p&gt;

Flood and desiccation events reconstructed based on luminescence profiles and palaeobotanical proxies from the High Arctic lake Tenndammen, Svalbard

&lt;p&gt;We present a 700-year reconstruction of the environmental changes in the Colesdalen, Svalbard, inferred from a sediment core retrieved from lake Tenndammen (N 78&amp;#176;06.118; E 15&amp;#176;02.024). A comparison of modern and old maps revealed that the lake was artificially connected to its western tribute that now inputs additional water and sediment into the lake, but earlier lake Tenndammen was mainly fed by discharge and groundwater from the main valley. A multi-proxy approach was applied involving sedimentary ancient DNA (sedaDNA), pollen, spores, plant macrofossils, sedimentology and biogeochemistry. Establishing a chronology for this core was problematic as nine of the fourteen AMS dates were revered. However, core imaging as well as X-ray fluorescence (XRF) demonstrated clear stratification and undisturbed sediment layers. This is supported by the clear and coherent data obtained from the plant palaeo-proxies in terms of vegetation and environmental changes indicated by all proxies at the same core depths. From these observations, we inferred that lake Tenndammen experienced a number of floods which brought older sediments into the lake and produced a high proportion of the reversed dates. In order to test this hypothesis, portable optically stimulated luminescence (pOSL) and infrared stimulated luminescence (pIRSL) was employed. The pIRSL, pOSL and pIRSL/pOSL profiles suggested a series of 15 flooding and 8 drying events occurring at the depths associated with the reversed dates. However, relatively high amount of spheroidal carbonaceous particles (SCP, up to 1300 per gram of dried sediment mass) helped to improve the core chronology through a comparison with the calendar dates of the history of the coal mining and power production in Svalbard. SCP record allowed to find three tie points for the age-depth model at (1) the construction time of the power plant in 1911-1913 in Colesdalen, (2) the abrupt decrease in SCPs associated with the Second World War in 1941-1946, and (3) the highest output of the power plant in Colesdalen in the middle of the 1950s. When combined with the earlier non-reversed dates this provides an age-depth model with the basal age of the core at c. 730 cal. yr. BP and with the upper sediments deposited at c. 1950-1980s. Using this revised age-depth model, four chrono-stratigraphic units were described and, according to the data on luminescence profiling, the most intensive floods were associated with the second unit, which corresponded with the most intensive ice melting in the study area (c. 1670 - 1420 BP). The strongest drying events took place at the end of the second unit and in the first part of the third unit (c.&amp;#160; 1655 BP). This was supported by the plant proxies with an abundance of the aquatic and swamp bryophyta &lt;em&gt;Warnstorfia exannulata/Warnstorfia fluitans&lt;/em&gt;, algae (i.e. &lt;em&gt;Closterium littorale, Cosmarium botrytis&lt;/em&gt; and &lt;em&gt;Staurastrum punctulatum&lt;/em&gt;) both in the non-pollen microfossils record and the sedaDNA. &amp;#160;This study shows that a combination of biological proxies, sedimentology and pOSL can detect flood and desiccation events, and that lake Tenndammen was a highly sensitive fluvio-lacustrine systems during the late Holocene/Anthropocene.&lt;/p&gt;