Infrared Stimulated Luminescence Research Articles

Multi-Method Luminescence Dating of Old Fluvial Sediments from Northern Tian Shan, China

At the eastern tip of Anjihai anticline on the northern piedmont of Tian Shan (northwest China), deformed fluvial deposits have recorded active folding since the Pleistocene, but the absence of accurate ages makes it difficult to evaluate the anticline's shortening rate. Geological studies ascribed the fluvial strata to the early Pleistocene, which poses potential challenges for luminescence dating. In this study, multi-methods luminescence dating was applied to a fluvial sand sample taken from the sandy bed of the deformed basal strata. Single grain post-Infrared Infrared Stimulated Luminescence (pIRIR) and multiple-aliquot-regenerative (MAR) dose along with multiple-elevated-temperature pIRIR (MET-pIRIR) procedures were applied to determine the paleodose of the sample. The methodological uncertainties, such as thermal transfer and initial sensitivity change, were treated by increasing the test dose and performing dose recovery test. With consideration of the potential partial bleaching and anomalous fading, various statistical metrics were applied to the D<sub>e</sub> values determined by using the single grain pIRIR<sub>225</sub>, single grain pIRIR<sub>290</sub> and MAR-MET-pIRIR<sub>290</sub> signals. The minimum age model (MAM) D<sub>e</sub> values are 11% – 17% lower than the central age model (CAM) D<sub>e</sub> values in general, and the MAM D<sub>e</sub> values determined by the single grain pIRIR procedures are underestimated by more than 40% when compared with those determined by MAR-MET-pIRIR<sub>290</sub> procedure. The MAM MAR-MET-pIRIR<sub>290</sub> D<sub>e</sub> of 811 ± 44 Gy results in a burial age of 284 ka for the basal deformed fluvial strata, which is much younger than the proposed early Pleistocene age.

Applicability of OSL Dating to Fine-Grained Fluvial Deposits in the Mekong River Floodplain, Cambodia

Abstract Optically stimulated luminescence (OSL) dating of fine-grained (4–11 μm) fluvial sediments is rarely attempted but is crucial for constraining the evolution of mud-dominated floodplains. This study investigated the applicability of OSL dating to fine-grained deposits in the Mekong River, Cambodia based on a very young (<600 yr) point-bar to riverbank succession and modern flood deposits. In succession, fine-grained quartz OSL provided the youngest ages, whereas age estimates by multi-grain sand-sized quartz OSL, and feldspar and polymineral infrared-stimulated luminescence are >200 years older than the fine-grained quartz OSL age estimates. Ages of fine-grained quartz OSL are concordant with the minimum ages obtained from the single-grain quartz OSL. These results are supported by the generally small residual doses (<0.1 Gy) measured in modern fine-grained flood-plain deposits. This indicates that fine-grained sediments in the Mekong River (Cambodia) are sufficiently bleached at deposition and can yield reliable quartz OSL ages for establishing the chronology of the floodplain. The sufficient bleaching of fine-grained quartz partly results from the long transport distance and may also occur in other large river systems.

Evaluation of TL and OSL responses of CaF2:Tm for electron beam processing dosimetry

The thermoluminescence (TL) and infrared stimulated luminescence (IRSL) responses of in-house produced CaF2:Tm dosimeters are investigated in this work, envisaging their application in electron beam (EB) radiation processing. The irradiations were performed at an industrial EB accelerator (1.5 MeV) covering a dose rate range of 2–8 kGy/s and dose up to 10 kGy. In general, the TL glow curves display four peaks, termed as peaks 2, 3, 4, and 5, corresponding to temperatures at ~150, 200, 240, and 300 °C, respectively. The intensity of the low-temperature peaks (2 and 3) grows with the dose, while the others remain constant (saturated). Nevertheless, an evident dose effect on the glow curves manifests in decreased peak3/peak2 ratio with increasing doses.The CW-IRSL curves exhibit similar patterns with an initial signal increase, followed by an exponential decay. Instead of the normal monotonic decays, these peak-shaped curves might be due to the charge capture competition between empty shallow traps and recombination centers. Both TL and IRSL intensities increase linearly with doses up to 6 kGy, and for higher doses, they become sub-linear with a saturation trend around 10 kGy. Another common feature of TL/IRSL response is its dose rate dependence, being more sensitive at higher dose rates. Despite being dose-rate dependent, the CaF2:Tm dosimeters might be suitable for EB processing dosimetry. However, for their use as routine dosimeters, relevant dosimetric characteristics, such as fading and response reproducibility, have to be investigated. Work in this direction is underway.

Synthesized luminescence ages of palaeo-beach ridges in Krishna–Godavari twin delta plain, east coast of India

Abstract Luminescence ages of eight sandy beach-ridge samples from the Krishna–Godavari delta region on the east coast of India were obtained by synthesizing ages based on three luminescence signals, i.e., optically stimulated luminescence (OSL) from quartz, infrared stimulated luminescence (IRSL), and post-infrared (pIR) IRSL290°C from feldspar. Standard statistical procedures and hierarchical Bayesian modeling (ChronoModel) were used to synthesize the ages that are consistent within an uncertainty of ±10% and conforming to most of the published radiocarbon (AMS 14C) ages from this region. This approach, therefore, provides for the conjunctive use of luminescence signals of quartz and feldspar for a single and possibly more accurate age. Additionally, our study showed the potential that the reworked sediment could be identified, and pristine beach ridge sand grains could be isolated using single grain quartz luminescence measurements using appropriate statistical models. Further methodological development may improve the precision of these ages, if not the accuracy.

Luminescence properties and dating of glacial to periglacial sediments from northern Switzerland

Abstract. Luminescence dating has become a pillar of the understanding of Pleistocene glacial advances in the northern foreland of the Swiss Alps. However, both quartz and feldspar from the region are equally challenging as dosimeters with anomalous fading and partial bleaching being some of the obstacles to overcome for the establishment of decisive chronologies. In this study, luminescence properties of coarse- and fine-grained quartz, feldspar, and polymineral fractions of eight samples from a palaeovalley, Rinikerfeld in northern Switzerland, are systematically assessed. Standard performance tests are conducted on all four fractions. Deconvolution of luminescence signals of the quartz fractions is implemented and shows the dominance of stable fast components. Reader-specific low preheat temperatures are investigated on the infrared stimulated luminescence (IRSL) signal of feldspar. Thermal stability of this signal is found for low preheats, and thermal quenching could be excluded for higher preheats. However, anomalous fading is observed in the feldspar and polymineral IRSL signals and two correction approaches are applied. For one approach, fading corrected coarse-grained feldspar ages are consistent with those derived from quartz. In general, coarse-grained quartz and feldspar, as well as the fine-grained polymineral fraction of one sample, are in chrono-stratigraphic agreement and present negligible evidence for partial bleaching. However, ages derived from fine-grained quartz are found to underestimate those of the coarse-grained quartz fractions. Hence, the impact of alpha efficiency and water content on the dose rate and thus the ages are assessed. A finite explanation for the observed discrepancies remains lacking, but this systematic investigation of different luminescence signals allows for the establishment of a chronology for the palaeovalley fill dating back to at least Marine Isotope Stage 6 (MIS 6).

First reliable chronology for the Early Khvalynian Caspian Sea transgression in the Lower Volga River valley

During the late Quaternary, dramatic changes in relative sea level (~170 m) are known to have occurred in the Caspian Sea. However, all previous attempts at resolving the uncertainty associated with the timing of these transgressive/regressive events, primarily using radiocarbon, have produced inconclusive or controversial results. Here we present the first reliable chronology for the largest known transgression (Early Khvalynian). This was derived using optically stimulated luminescence (OSL) analysis of sand‐sized quartz, with support from infrared stimulated luminescence (IRSL) from K‐rich feldspar grains, all extracted from 16 sediment samples collected along the Lower Volga River. These samples were taken from loessic sediments, marine clays (known as Chocolate Clays) and the overlying modern soils exposed at three sections (Srednyaya Akhtuba, Raygorod, Leninsk) ~200 km upstream of the present‐day estuary. The differential bleaching rates of the quartz OSL and feldspar IRSL signals were used to evaluate the degree of resetting of quartz (and feldspar) signals; it was possible to conclude that all signals, and particularly quartz OSL, were sufficiently reset at deposition to allow accurate age estimation. Our results show unambiguously that the Early Khvalynian marine Chocolate Clays present at all three sections were deposited post‐LGM, between ~17 and ~13.1 ka ago. These age estimates are further constrained by those from the overlying Kastanozem soils (9.6–0.7 ka) and underlying loess‐soil series (32–19 ka), confirming a young (17–13 ka) age of the transgressive stage of the Early Khvalynian. Relative sea level during this period must have been well above the sampling altitudes of 11.7 m a.s.l. (Srednyaya Akhtuba), 11.3 m a.s.l. (Raygorod) and 4.7 m a.s.l. (Leninsk) to explain the absence of significant alluvial sand and to allow the deposition of the fine Chocolate Clays marker horizon.

Chronology of the marine terraces of the Crotone Peninsula (Calabria, southern Italy) by means of infrared-stimulated luminescence (IRSL)

The Crotone Peninsula (southern Italy) preserves a well developed flight of marine terraces generated by the interplay of uplift of the Calabrian arc and late Quaternary eustatic oscillations. Good chronologic control on the formation of these raised geomorphic features would help constrain regional tectonic and stratigraphic models. However, precise age assignment and correlation of the individual terraces is hampered by lack of material suitable for radiometric dating.With the goal of improving the resolution of the chronology of the terraces, nine samples were collected from four stratigraphically distinct terraced units and dated with the infrared-stimulated luminescence (IRSL) technique applied on feldspar grains. The obtained ages are consistent with the stratigraphic arrangement of the terraces, with samples from higher terraces older or overlapping in age with those from lower terraces. Three samples from the highest (Cutro) terrace indicated a minimum age ≥ MIS (Marine Isotope Stage) 7. Two samples from the second of the four examined terraces, which is generally correlated with MIS 5.3, gave ages that correlate instead with MIS 5.5 and 5.1, revealing more internal complexity and tectonic disruption than previously inferred from this terrace. Luminescence dating was applied for the first time to the deposits of the Capo Colonna terrace, with results indicating a MIS 5.1 age. Finally, one sample from the lowermost (Le Castella) terrace confirmed the preservation of raised marine deposits from MIS 3, a relatively uncommon finding for the Mediterranean region.These results highlight how IRSL dating can contribute to the development and refinement of a chronostratigraphic context for a flight of marine terraces and, ultimately, to a clearer understanding of the combined tectonic and eustatic controls affecting the morphodynamic evolution of a marine coastal sector. More specifically, they confirm the persistence of relatively high average uplift rates (on the order of 1 mm/yr) over the last two glacial cycles in the Crotone Peninsula and the important role of a local component of tectonic and deformative displacement superimposed on the regional uplift.

Fluvial terraces as quantitative markers of late Quaternary detachment folding and creeping thrust faulting in the Peruvian Huallaga basin

In the western Huallaga basin, located in the Peruvian Subandes, a series of nine fluvial terraces with elevations of up to 160 m above current floodplain level (+FP) were formed against the Biabo anticline. The terraces are progressively more folded with age and terrace elevation and present growth strata, suggesting ongoing folding of the anticline. Optically and InfraRed Stimulated Luminescence (OSL and IRSL) dating of fluvial terrace sediments yielded ages of 10.8 ± 0.7 ka for the T2, 24.2 ± 2 ka for the T4 and 46 ± 9 ka for the T7 terrace. Uniform uplift rates of 2 mm a−1 for the past 46 ka were calculated. Terrace profiles and two new seismic profiles that cross the Biabo anticline longitudinally and transversally were used to calculate shortening rates of 2.6 mm a−1 for the anticline over the past 46 ka. Our calculations took into account potential contributions of detachment thrusting parallel to the Biabo fold and reverse tear faulting perpendicular to the fold tip as visible on the seismic sections. A maximum uplift rate of 0.62 mm a−1 due to reverse thrusting of the Bellavista tear fault for the past 46 ka could have contributed to the overall uplift of the Bellavista terraces. Based on trigonometric relationships, a reverse fault slip rate of 0.86 mm a−1 and an age of 137 ka were calculated for this fault.In the eastern part of the Huallaga basin, a series of two fluvial terraces were formed with elevations of 13–15 m and 30 m + FP and with OSL ages of 6.9 ± 0.7 ka for T1 and 30.2 ± 3.1 ka for T2. The interpretation of a third new seismic profile crossing the study area in combination with field observations and trigonometric relationships shows that the terraces were formed by a complex system of oblique ramp and strike-slip faulting resulting in uplift and shortening rates of 1 mm a−1 and 1.96 mm a−1 between 30.2 ka and 6.9 ka respectively; and uplift and shortening rates of 2 mm a−1 and 3.70 mm a−1 from 6.9 ka until the present. Reverse slip of the Shapaja oblique ramp, that was responsible for uplift of the terraces, was calculated at 2.19 mm a−1 for the period 30.2 to 6.9 ka and 4.15 mm a−1 from 6.9 ka until the present. Measured total slip in combination with the calculated slip rates allowed an age calculation of 181 ka for the Shapaja thrust ramp. Our inferences showed that the studied tectonic structures absorb most of the present-day deformation in the Huallaga basin. The calculated uplift and shortening rates are compatible with published, present-day crustal movement velocities, and Miocene to present shortening rates for various, studied sites of the tropical Subandes and suggest that it is deforming at a relatively uniform rate.The timing of sedimentation of the terrace sediments may have corresponded to periods of increased precipitation which occurred coeval with the Heinrich events of the Northern Hemisphere. Terrace records similar as ours have been described for other, tectonically highly active areas in the tropical Subandes, but not in the tectonically less active Amazonian lowlands. It is suggested that uplift rates of at least 1 mm a−1 are needed to preserve suborbital climate cycles as individual terraces. The tropical Subandes could therefore be a new key area to investigate the interactions between tectonics, suborbital climate forcing and fluvial response during the late Quaternary.

Refined chronostratigraphy of a late Quaternary Sedimentary sequence from the Yangtze River delta based on K-feldspar luminescence dating

Dating of sediments in the tidal-dominated Yangtze River delta remains a challenge because of extremely complicated processes during sediment transport and deposition in such a fluvial-marine transition zone. To better understand the late Quaternary sedimentary history of the Yangtze River delta, we explore the applicability of K-feldspar luminescence dating techniques to deposits through a case study on a 60-m-long borehole core (YZ07) in the delta and then establish a spanning ~50,000-year-long chronological sequence. A series of luminescence pre-tests, including dose recovery tests and determination of residual dose and fading rates, were implemented using the modified single-aliquot-regenerative dose (SAR) protocol for post-infrared (IR) IR stimulated luminescence (IRSL) measured at 150 °C after prior IRSL at 50 °C (pIRIR150), respectively. Luminescence characteristics of the prior IRSL (IR50) and pIRIR150 were then analyzed to check their validity. Two fading-correction models were utilized to correct apparent ages obtained from IR50 and pIRIR150 signals. The newly obtained K-feldspar luminescence ages were compared with quartz OSL ages and 14C ages. Our results indicate that most of ages derived from pIRIR150 signals were overestimated due to incomplete bleaching; in contrast, the fading-corrected ages from IR50 measured in pIRIR150 protocol are robust as they are consistent with quartz OSL ages and 14C ages as well as the stratigraphy. Additionally, IR50 ages are characterized by negligible residual dose, and thus used for defining chronology of the investigated sequence over the past 50 ka. In combination with sedimentological and paleontological analyses of core YZ07, we find that fluvial to tide-influenced fluvial deposits were emplaced during the period 30–50 ka, which were then overlain by post-glacial tidal-river (13–11.5 ka), and Holocene estuarine-shelf, delta system, and tidal flat deposits in the Yangtze River delta. Together with other chronostratigraphy from the selected cores, we confirm the existence of Marine Isotope Stage (MIS) 3 depositional units along the marginal coast of the Yangtze River delta in relation to the interstadial sea-level highstand. Our stratigraphic correlation based on the refined chronology reveals offshore transition of the MIS 3 unit into facies deposited in deeper and offshore marine environments.

Exploring the use of a low temperature preheat in IRSL dating of feldspar in Beringian archaeological contexts

A new luminescence dating protocol was developed to circumvent the problem of thermal transfer and poor thermal stability of Infrared Stimulated Luminescence (IRSL) of samples from late glacial loess sediments in Central Alaska, USA. This new protocol is proposed as an alternative to routine procedures for which scattered and erratic results were obtained using standard IRSL and post-IR IRSL protocols on loess samples from the McDonald Creek archaeological site.The difficulty to date Alaskan loess has been acknowledged in the past, but the reasons for this phenomenon have not been clearly identified. This difficulty is even greater for young samples, as shown in this study. It is suggested here that the particular mineralogical composition of the Central Alaskan loess can be related to problematic luminescence behaviour.To overcome problematic results, we developed a Low Preheat IRSL (LPH-IRSL) protocol. This protocol is minimally affected by the presence of other minerals than K-feldspars in the samples, such as albite, muscovite and clinochlorite, which can be very difficult to eliminate during the preparation steps prior to IRSL measurements. Dose recovery experiments and multiple other tests indicate that a protocol with low preheat temperature yields the best results in this specific context. Thermally transferred luminescence induced during the measurement is kept at a minimal level. Consequently, considering independent age controls available from radiocarbon, equivalent doses are successfully determined, their distribution is narrow, and the g-value has low scatter. This protocol has great potential for dating polymineral samples, whether it is silt-sized sediments like loess, fine-grained like clay and micro-samples like art pieces, common in archaeological contexts.The chronological results obtained for this project suggest a human occupation of the area during the Late Pleistocene to mid-Holocene period, which is in excellent agreement with preliminary radiocarbon chronology obtained during site testing and also with the regional archaeological framework.

A comparison of multiple luminescence chronometers at Voordrag, South Africa

Abstract A suite of 10 samples collected from an 11 m thick colluvial sequence at Voordrag, KwaZulu-Natal, South Africa, have been used to undertake a comparison of different luminescence methods. Good agreement is found between single grain quartz optically stimulated luminescence (OSL) and single grain K-feldspar post-infrared infrared-stimulated luminescence (post-IR IRSL) ages, with the exception of the basal samples where the quartz OSL signal is saturated. Multiple grain quartz OSL consistently yields ages older than single grain OSL methods. Multiple grain feldspar ages derived from the IRSL50 signal are underestimated due to anomalous fading. A previously published radiocarbon chronology yields ages that are younger than those from single grain quartz OSL and post-IR IRSL, and this is most likely due to contamination with younger carbon. Identifying the effect of saturation on the quartz OSL signal remains challenging when quartz is dated in isolation. However, using a paired quartz/feldspar dating approach is an effective way of identifying the impact of saturation on the OSL signal.

Review of the Post-IR IRSL Dating Protocols of K-Feldspar.

Compared to quartz, the infrared stimulated luminescence (IRSL) of K-feldspar saturates at higher dose, which has great potential for extending the dating limit. However, dating applications with K-feldspar has been hampered due to anomalous fading of the IRSL signal. The post-IR IRSL (pIRIR) signal of K-feldspar stimulated at a higher temperature after a prior low-temperature IR stimulation has significantly lower fading rate. Different dating protocols have been proposed with the pIRIR signals and successful dating applications have been made. In this study, we review the development of various pIRIR dating protocols, and compare their performance in estimating the equivalent dose (De). Standard growth curves (SGCs) of the pIRIR signals of K-feldspar are introduced. Single-grain K-feldspar pIRIR dating is presented and the existing problems are discussed.

Deep-penetrating geochemistry for concealed sandstone-type uranium deposits: A case study of Hadatu uranium deposit in the Erenhot Basin, North China

Traditional geochemical exploration methods are not effective for locating concealed sandstone-type uranium deposits occurring at depths of hundreds of meters in sedimentary basins. In order to identify and trace the geochemical anomalous sources from the deposits in overburden regions, systematical luminescence intensity analyses have been carried out on mineral particles from both near-surface late Quaternary sediments and drill-core samples from the Hadatu sandstone-type uranium deposit in the Erenhot Basin. Luminescence intensity analyses yielded much older optically stimulated luminescence (OSL) ages for quartz minerals in late Quaternary sediments than their true depositional ages. In the same sedimentary layer, the apparent quartz OSL ages around the medium-grade borehole are particularly higher than those of the low-grade borehole. Therefore, the anomalies and the variations of these quartz OSL ages in late Quaternary sediments were ultimately controlled by concealed sandstone-type uranium deposits beneath. In contrast, the feldspar infrared stimulated luminescence (IRSL) signals of drill-core samples show no co-variations with deposits grade and sampling depth. Given the oversaturated luminescence signals on minerals from drill-core samples, they have no potential to unravel concealed sandstone-type uranium deposits. The strongly positive correlation between quartz OSL ages and previously published near-surface Rn anomalies in sediments confirms that the combination of OSL and areal Rn measurements is a cost-effective prospection approach for concealed sandstone-type uranium deposits.

Identification of humid periods in the Atacama Desert through hillslope activity established by infrared stimulated luminescence (IRSL) dating

Geological records indicate that the hyper-aridity in the Atacama Desert has prevailed since at least the mid-Miocene, with shorter periods of increased humidity punctuating long-term aridity. The 7-m-high accumulation of colluvial sediments at the Salar Grande (21°S/70°W) studied here provides a key palaeoclimate record to understand hillslope dynamics and its relation to humid periods. While 10Be surface exposure ages point to long-term surface stability of the flat upslope surface, a combination of humidity-driven soil creep, overland flow and soil creep related to seismic shaking, caused denudation of the hillslope and accumulation of several metres of colluvium over much shorter timescales during the last 130 ka. A robust chronology for the hillslope sediments has been established by using Infrared Stimulated luminescence (pIR-IR225 protocol) on K-feldspar extracts from nine samples collected within the accumulation. A series of tests has been carried out to confirm the suitability of the method. The estimated ages indicate accelerated sedimentation at 35–80 ka, and 100–130 ka, which are interpreted as periods with more humid climate conditions than present. These findings agree with climate variations in the hyper-arid Atacama indicated by the activity of coastal alluvial fans and river catchments.

The Chronostratigraphy of the Aurignacian in the Northern Carpathian Basin Based on New Chronometric/Archeological Data from Se\u0148a I (Eastern Slovakia)

The northern Carpathian Basin has important geological, paleoenvironmental, and archeological records that are key to our understanding of the first modern human occupation of Europe. However, the nature and timing of hominin settlements in the region during the Late Pleistocene remain poorly understood. New fieldwork at Seňa I, Slovakia, has identified the only known stratified open-air Aurignacian site in the region and assigned the assemblage to at least 33.5 ± 2.4 ka ago through infrared-stimulated luminescence dating. Additionally, new archeological and geoscientific data are presented. This paper discusses the Seňa I findings in the context of the regional archeological record and shows how they contribute to the establishment of clear time constraints for the Aurignacian in eastern central Europe.

Pleistocene lakes and paleohydrologic environments of the Tecopa basin, California: Constraints on the drainage integration of the Amargosa River

Abstract The Tecopa basin in eastern California was a terminal basin that episodically held lakes during most of the Quaternary until the basin and its modern stream, the Amargosa River, became tributary to Death Valley. Although long studied for its sedimentology, diagenesis, and paleomagnetism, the basin’s lacustrine and paleoclimate history has not been well understood, and conflicting interpretations exist concerning the relations of Tecopa basin to the Amargosa River and to pluvial Lake Manly in Death Valley. Previous studies also did not recognize basinwide tectonic effects on lake-level history. In this study, we focused on: (1) establishing a chronology of shoreline deposits, as the primary indicator of lake-level history, utilizing well-known ash beds and new uranium-series and luminescence dating; (2) using ostracodes as indicators of water chemistry and water source(s); and (3) correlating lake transgressions to well-preserved fluvial-deltaic sequences. During the early Pleistocene, the Tecopa basin hosted small shallow lakes primarily fed by low-alkalinity water sourced mainly from runoff and (or) a groundwater source chemically unlike the modern springs. The first lake that filled the basin occurred just prior and up to the eruption of the 765 ka Bishop ash during marine isotope stage (MIS) 19; this lake heralded the arrival of the Amargosa River, delivering high-alkalinity water. Two subsequent lake cycles, coeval with MIS 16 (leading up to eruption of 631 ka Lava Creek B ash) and MIS 14 and (or) MIS 12, are marked by prominent accumulations of nearshore and beach deposits. The timing of the youngest of these three lakes, the High lake, is constrained by a uranium-series age of ca. 580 ± 120 ka on tufa-cemented beach gravel and by estimates from sedimentation rates. Highstand deposits of the Lava Creek and High lakes at the north end of the basin are stratigraphically tied to distinct sequences of fluvial-deltaic deposits fed by alkaline waters of the Amargosa River. The High lake reached the highest level achieved in the Tecopa basin, and it may have briefly discharged southward but did not significantly erode its threshold. The High lake was followed by a long hiatus of as much as 300 k.y., during which there is evidence for alluvial, eolian, and groundwater-discharge deposition, but no lakes. We attribute this hiatus, as have others, to blockage of the Amargosa River by an alluvial fan upstream near Eagle Mountain. A final lake, the Terminal lake, formed when the river once again flowed south into Tecopa basin, but it was likely short-lived due to rapid incision of the former threshold south of Tecopa. Deposits of the Terminal lake are inset below, and are locally unconformable on, deposits of the High lake and the nonlacustrine deposits of the hiatus. The Terminal lake reached its highstand at ca. 185 ± 21 ka, as dated by infrared-stimulated luminescence on feldspar in beach sand, a time coincident with perennial lake mud and alkaline-tolerant ostracodes in the Badwater core of Lake Manly during MIS 6. A period of stillstand occurred as the Terminal lake drained when the incising river encountered resistant Stirling Quartzite near the head of present-day Amargosa Canyon. Our studies significantly revise the lacustrine and drainage history of the Tecopa basin, show that the MIS 6 highstand was not the largest lake in the basin as previously published (with implications for potential nuclear waste storage at Yucca Mountain, Nevada), and provide evidence from shoreline elevations for ∼20 m of tectonic uplift in the northern part of the basin across an ENE-trending monoclinal flexure.

Victoria Cabrera Site: A Middle Stone Age site at Olduvai Gorge, Tanzania

Olduvai Gorge (Tanzania) is a key site for the study and comprehension of human evolution in East Africa. However, the origin of Homo sapiens and the Middle Stone Age have been poorly understood in the Gorge thus far. In this study, we present the dating, taphonomic, technological and typological analyses of the lithic industry and faunal remains excavated at the Victoria Cabrera Site (VCS) during the 2017 fieldwork season. The stratigraphic sequence of the site contains several levels of fluvial origin, some of them with lithic and faunal remains. Most remains (lithics and bones) are affected by rounding processes. Infrared stimulated luminescence (IRSL) dating has provided ages between 90 and 70 ka BP for these layers that can be related to the Marine Isotope Stage 5a. Lithics are scarce and the dominant raw materials are Naibor Soit quarzite and basalt, followed by phonolite, chert and quartz as the most common raw materials. The lithic technology is based on the production of flakes obtained from prepared cores, with the discoid method and, to a lesser extent the Levallois method being the most frequently used. The retouched blanks are described as “substratum” or “domestic” tools (sidescrapers, notches or denticulates). There is just one heavy duty piece and points are absent. The faunal assemblage includes Alcelaphinae, Antilopinae and Equidae. The major parts of the unidentified faunal remains are size 3 ungulates, followed by carcasses of size 2 and size 4 species. We cannot relate lithic and bones because no cut marks or percussion marks have been identified and carnivore action is scarce. In sum, VCS represents the first accurately dated Middle Stone Age site, with lithic and faunal remains in Olduvai Gorge.

New Chronology and Stratigraphy for Kathu Pan 6, South Africa

Kathu Pan 6 (Northern Cape Province) is an open-air site exposed by sinkhole activity that includes a Middle Stone Age Howiesons Poort (HP) component in a stratigraphic sequence that also includes Later Stone Age, early Middle Stone Age, and Earlier Stone Age (Fauresmith) assemblages. Here, we present the dating of the Kathu Pan 6 sequence using multiple luminescence signals: optically stimulated luminescence (blue OSL) and thermally transferred OSL (TT-OSL) on quartz; and the infrared stimulated luminescence (IRSL) post IR-IR290 signal on potassium feldspar. The results obtained from analyses of different minerals and signals for the archaeological deposits do not always conform but the quartz OSL provides the most accurate set of ages for the HP at KP6 (between 100 ± 6 and 74 ± 5 ka). This age range places the KP6 HP earlier than any of the scenarios considered plausible by Jacobs and Roberts (Journal of Human Evolution, 107, 1–13 2017) but fits well with the extended duration for the HP at Diepkloof proposed by Tribolo et al. (Journal of Archaeological Science, 36(3) 730–39 2009) and promoted by Feathers (Journal of Archaeological Science, 63, 164–174 2017). Two OSL ages bracket the Later Stone Age Wilton industry at KP6, placing it between 5.7 ± 0.3 ka and 2.3 ± 0.1 ka. These fit with known ages for the Wilton and place the KP6 occupation contemporary with Strata 4c–3b at Wonderwerk Cave.

Correlation between isothermal Tl and Irsl in K-Feldspars of various types

Feldspars are used as natural dosimeters to date geological and archaeological materials. These minerals are widely used in dosimetric methods of dating using luminescence signals, such as Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Infrared Stimulated Luminescence (IRSL). The present work is an effort to compare the Isothermal decay Thermoluminescence signals (ITL) to the IRSL signals from four K-feldspar samples which belong to two different species, namely microcline, and sanidine. The experimental data were fitted by analytical expressions coming from a tunneling recombination model. The results prove that all ITL and IRSL signals can be fitted very accurately with the analytical equations and that only two tunneling components are needed to obtain a high-quality fit. These tunneling components consist of a very fast and intense component, which is followed by an extended slowly decaying component. Significant differences were found between the best-fit parameters of the ITL and IRSL signals, indicating that thermal excitation processes may reach different traps from optical excitation processes in these samples.

A multi-dating approach to age-modelling long continental records: The 135 ka El Cañizar de Villarquemado sequence (NE Spain)

Abstract We present a multidisciplinary dating approach - including radiocarbon, Uranium/Thorium series (U/Th), paleomagnetism, single-grain optically stimulated luminescence (OSL), polymineral fine-grain infrared stimulated luminescence (IRSL) and tephrochronology - used for the development of an age model for the Canizar de Villarquemado sequence (VIL) for the last ca. 135 ka. We describe the protocols used for each technique and discuss the positive and negative results, as well as their implications for interpreting the VIL sequence and for dating similar terrestrial records. In spite of the negative results of some techniques, particularly due to the absence of adequate sample material or insufficient analytical precision, the multi-technique strategy employed here is essential to maximize the chances of obtaining robust age models in terrestrial sequences. The final Bayesian age model for VIL sequence includes 16 AMS 14C ages, 9 single-grain quartz OSL ages and 5 previously published polymineral fine-grain IRSL ages, and the accuracy and resolution of the model are improved by incorporating information related to changes in accumulation rate, as revealed by detailed sedimentological analyses. The main paleohydrological and vegetation changes in the sequence are coherent with global Marine Isotope Stage (MIS) 6 to 1 transitions since the penultimate Termination, although some regional idiosyncrasies are evident, such as higher moisture variability than expected, an abrupt inception of the last glacial cycle and a resilient response of vegetation in Mediterranean continental Iberia in both Terminations.