Infrared Stimulation Research Articles

A 300 kyr record of past hydroclimate change from alluvial fans in the southern Central Andes

AbstractAlluvial fans are hypothesised to record signals of past hydroclimate changes in their depositional chronologies and slopes. However, direct tests of this hypothesis have been limited due to challenges in precisely dating the responses of alluvial fans to past climate forcing. Here, we present a new chronology of alluvial‐fan deposition at the Sierra de Aconquija in the southern Central Andes (27°S) spanning ~300 kyr and based on 35 cosmogenic 10Be‐derived exposure ages and eight infrared‐stimulated (IRSL) and optically stimulated luminescence (OSL) ages. The ages reveal that fan deposition was phased with past climate changes. Orbitally‐forced weakening and strengthening of the South American Summer Monsoon coincided with fan aggradation during dry episodes and incision during wetter episodes, consistent with predictions from alluvial‐channel models. These results are in precise agreement with independent palaeoclimate constraints spanning timescales of 103 to 105 years. Fan aggradation‐incision cycles record a predominant influence of precession‐induced variations in precipitation, although climate shifts as rapid as 1 kyr also triggered incision, and fan architecture appears to be further modulated by orbital eccentricity cycles. Incision events on the fans coincide with the ages of moraines in the headwater catchments, including those formed during the Younger Dryas and Last Glacial Maximum. Furthermore, the fan chronology indicates dry conditions in the southern Central Andes during Heinrich Stadial 1, suggesting that enhanced precipitation during this episode was limited to more northerly latitudes. Our results demonstrate that climate change exerts a primary control on simple, source‐to‐sink sedimentary systems and show that alluvial fans can, in some cases, be utilised as terrestrial palaeoclimate archives with which the spatio‐temporal variability of past climate changes can be constrained.

High density laminar recordings reveal cell type and layer specific responses to infrared neural stimulation in the rat neocortex

Infrared neural stimulation has consistently shown that temperature is a critical neuronal state variable. However, a comprehensive understanding of the biophysical background is essential. In this study, using high-density laminar electrode recordings, we investigated the impact of pulsed and continuous-wave infrared illumination on cortical neurons in anesthetized rats (). By analyzing the infrared (IR) stimulation-related responses of more than 7500 single units, we found that elevating tissue temperature with IR stimulation resulted in a significant increase in the number of cells affected, including a substantial rise in the number of inhibited cells. Pulsed stimulation affected an average of of units, resulting primarily in increased activity. In contrast, continuous stimulation significantly increased the percentage of affected cells to , with single units tending to be suppressed. Furthermore, when analyzing cell types, a higher percentage of principal cells displayed increased firing rates () compared to suppressed activity (). Meanwhile, more interneurons were suppressed () than showed increased activity (). On average, the firing rate of neurons reached 90% of the maximal activation within approximately 36 seconds after the onset of infrared stimulation. The proportion of neurons with suppressed activity decreased with cortical depth, while the proportion of neurons with elevated activity increased in deeper layers. These results provide valuable data to understand the mechanism of infrared neural stimulation in the living brain.

An Injectable Magnesium-Based Cement Stimulated with NIR for Drug-Controlled Release and Osteogenic Potential.

Magnesium phosphate bone cement (MPC) has gained widespread usage in orthopedic implantation due to its fast-setting and high initial strength benefits. However, the simultaneous attainment of drug-controlled release and osteogenic potential in MPC remains a significant challenge. Herein, a strategy to create a smart injectable cement system using nanocontainers and chondroitin sulfate is proposed. It employs nanocontainers containing alendronate-loaded mesoporous silica nanoparticles, which are surface-modified with polypyrrole to control drug release in response to near-infrared (NIR) stimulation. The alendronate-incorporated cement (ACMPC) exhibits improved compressive strength (70.6 ± 5.9 MPa), prolonged setting time (913 s), and exceptional injectability (96.5% of injection rate and 242 s of injection time). It also shows the capability to prevent degradation, thus preserving mechanical properties. Under NIR irradiation, the cement shows good antibacterial properties due to the combined impact of hyperthermia, reactive oxygen species, and alendronate. Furthermore, the ACMPC (NIR) group displays good biocompatibility and osteogenesis capabilities, which also lead to an increase in alkaline phosphatase activity, extracellular matrix mineralization, and the upregulation of osteogenic genes. This research has significant implications for developing multifunctional biomaterials and clinical applications.

Resonating with Cellular Pathways: Transcriptome Insights into Nonthermal Bioeffects of Middle Infrared Light Stimulation and Vibrational Strong Coupling on Cell Proliferation and Migration.

Middle infrared stimulation (MIRS) and vibrational strong coupling (VSC) have been separately applied to physically regulate biological systems but scarcely compared with each other, especially at identical vibrational frequencies, though they both involve resonant mechanism. Taking cell proliferation and migration as typical cell-level models, herein, we comparatively studied the nonthermal bioeffects of MIRS and VSC with selecting the identical frequency (53.5 THz) of the carbonyl vibration. We found that both MIRS and VSC can notably increase the proliferation rate and migration capacity of fibroblasts. Transcriptome sequencing results reflected the differential expression of genes related to the corresponding cellular pathways. This work not only sheds light on the synergistic nonthermal bioeffects from the molecular level to the cell level but also provides new evidence and insights for modifying bioreactions, further applying MIRS and VSC to the future medicine of frequencies.

The sensitisation of quartz extracted from andesite

Low quartz sensitivities have been reported in several studies in Iran, and in part this is presumed to be a result of the volcanic provenance of many of the sediments in the study areas. In this study we test experimentally whether a quartz sample, extracted from an andesitic rock and showing an insensitive fast component in the Optically Stimulated Luminescence (OSL) signal, can be sensitised using optical and thermal methods.The luminescence characteristics of quartz extracted from a rock sample from a landslide in Iran (Rudbar-Manjil) are compared to those of a well-characterised quartz sample. We find that very few of aliquots prepared from extracted quartz grains show any sensitivity of the most easily stimulated part of the OSL signal, but that ∼23% of aliquots give detectable initial signals after repeated dosing and bleaching. Surprisingly, a large fraction of the most easily stimulated quartz OSL is removed by infra-red stimulation, even though there is no significant IRSL signal in the UV. However thermal annealing at 700 °C gives rise to a test-dose response that is unaffected by IR. This annealing sensitises all aliquots to some degree and induces a signal which is stable up to 260 °C, in contrast to that following optical sensitisation, which begins to decrease when heated to 140 °C. The implications of these observations are discussed, both in terms of luminescence process and potential for dating.

Heat accumulation during infrared stimulation impacts the response of ex vivo rat sciatic nerve.

Infrared neural stimulation (INS) is a neuromodulation technique that involves short optical pulses delivered to the neural tissue, resulting in the initiation of action potentials. In this work, we studied the compound neural action potentials (CNAP) generated by INS in five ex vivo sciatic nerves. A 1470 nm laser emitting a sequence of 0.4 ms light pulses with a peak power of 10 W was used. A single 4 mJ stimulus is not capable of eliciting a nerve response. However, repetition of the optical stimuli resulted in the induction of CNAPs. Heat accumulation induced by repetition rates as high as 10 Hz may be involved in the increase in CNAP amplitude. This sensitization effect may help to reduce the pulse energy required to evoke CNAP. In addition, these results highlight the importance of investigating the role of the slow nerve temperature dynamics in INS.

Development of a hyper-avulsive river course during the Holocene on the Himalayan frontal plains

The rivers flowing over the Quaternary foreland plains of the Himalayas embody a history of hyper-avulsiveness. The present study is an attempt to identify a major flow trajectory of the Torsa River and the dynamics of the major flow path during the Holocene. This study is focused on identifying the major distributive system of the Torsa River, active during the Holocene and preceding known historical palaeochannels, using geomorphic and sedimentary archives of the floodplain on the foreland part of the eastern Himalayas. Satellite image processing, sediment analysis from trenches and cores, geochemical and paleocurrent analysis along with the determination of the age of deposits using the Infrared Stimulated Luminescence (IRSL) dating technique were used to identify paleochannels and validate the findings. Moreover, the sequence of channel succession and major avulsion events was also identified from the facies reconstruction and stratigraphy of fluvial depositions. The oscillatory nature of the river is well preserved within the floodplain stratigraphy in the form of lenses of channel deposits intercalated with proximal floodplain depositions. A total of three avulsion events were found between 1.6 ± 0.1 ka and 0.9 ± 0.1 ka where the latest significant channel switching occurred between 1.14 ± 0.1 ka and 0.9 ± 0.1 ka within the distributive system identified in this study and an eastern branch of the fluvial system. The newly identified palaeo-flow trajectory of the system can be utilised for water resource management and the avulsion regime may be useful for understanding future flow oscillations within the river basin.

Infrared Stimulated Luminescence of Ce3+ Doped YAG Crystals.

In this study, the infrared optically stimulated luminescence (IRSL) of single crystals of Ce3+ doped yttrium aluminum garnet (YAG) was investigated for the first time. It was found that infrared stimulation of these crystals, following previous exposure to beta radiation, produces a strong luminescence signal. The highest luminescence efficiency was exhibited by the YAG crystal with 0.1% of Ce. With this crystal, it was possible to measure as low doses as 0.1 mGy. Moreover, IRSL is mainly related to the TL peak at a relatively high temperature of c.a. 175 °C, which leads to quite good stability of the signal in time. These properties create good prospects for potential applications of YAG:Ce in dosimetric radiation measurements.

A flexible luminescence film with temperature and infrared response based on Eu2+/Dy3+ co-doped Sr2Si5N8 phosphors for optical information storage applications

Deep-trap luminescent materials have attracted great attention for optical information storage applications. However, the flexible luminescence films based on red luminescence materials with temperature and infrared response are scarce. In this study, we have successfully developed various novel flexible red emitting films based on Eu2+/Dy3+ co-doped Sr2Si5N8 phosphors through screen-printing and spin-coating technologies, respectively. Interestingly, the fabricated flexible luminescence films exhibit unique temperature and infrared responsive properties for optical information storage by releasing photons in response to thermal or infrared stimulation. Notably, deep-trap red emitting Eu2+/Dy3+ co-doped Sr2Si5N8 phosphors are crucial for the optical information storage properties of the films. Two emission peaks of Sr2Si5N8:Dy3+ phosphors at 476 nm and 577 nm are observed under excitation at 345 nm, corresponding to the radiative transition occurs from the 4F9/2 level to the 6H13/2 and 6H15/2 levels of Dy3+. When Dy3+ and Eu2+ ions are co-doped in Sr2Si5N8, the energy transfer from Dy3+ to Eu2+ in Sr2Si5N8 matrix is found and the decay time confirms that Dy3+ ions can be acted as deep trap centers to storage photons. For Sr2Si5N8:Eu2+,Dy3+ phosphors and the corresponding flexible luminescence films, the specific patterns (for example apple and note patterns) are firstly recorded under NUV or blue light excitation and then reappear through thermal stimulation or near-infrared photo-stimulation (980 nm laser). This work not only validates the feasibility of Sr2Si5N8:Eu2+,Dy3+ phosphors as deep-trap red emitting luminescence materials, but also suggests the applications of flexible luminescence films for optical information storage.

Luminescence chronology of the Sankosh river terraces in the Assam- Bhutan foothills of the Himalayas: Implications to climate and tectonics

Himalaya is an active fold and thrust belt formed due to continent-continent collision between the Eurasian and Indian plates. It comprises a 3000 km long chain of mountains that span ∼1000 km across, with major boundary thrusts viz., Main Central Thrust (MCT), Main Boundary Thrust (MBT) and the Main Frontal Thrust (MFT). MFT is marked as mountain front and is the most active thrust; however, evidence of tectonic activity along MCT and MBT also exists. Tectonic activity along MFT created uplifted terraces which now serve as geomorphic archives of past tectonic events. The present study focussed on a glacial-fed river Sankosh that originates in northern Bhutan, and crosses MCT, MBT and MFT before joining the Brahmaputra River in Assam. Due to tectonic uplift, the river shows a deflection at MFT, incising and thus forming four levels of strath terraces. Luminescence chronology, geomorphic studies and analysis of satellite images suggest four levels of terraces T4 (highest level, 195 m asl), T3, T2 and T1 (lowest level, 120 m asl). The quartz was found insensitive for luminescence dating, and thus fading corrected Infra-Red Stimulated Luminescence (IRSL) ages on feldspar minerals were measured that provided ages of 143-77 ka (T4), 65-36 ka (T2) and 35-14 ka (T1), respectively. The T3 terrace was present only on the right bank of the river and could not be accessed. These ages accord with other studies at the Chalsa and Malbazar, North Bengal (west of the study area) and this regional disposition of similar ages suggest that these formed during glacial-interglacial periods. The strath terraces indicate a time-averaged tectonic uplift with a 0.5 mm/year rate over the past 150 ka.

OSL Dating of the Sukor Earthquake-induced Rockslide in Gorny Altai: Paleoseismological and Paleogeographic Implications

Abstract —Lacustrine sediments, related subaerial aeolian sands, as well as fluvioglacial sands enclosed in ablation moraines in the Chuya River valley between the Chuya and Kurai basins in Gorny Altai, have been dated by optically stimulated (OSL) and infrared stimulated (IRSL) luminescence. The OSL and IRSL ages indicate that the formation of the lake, which spread into the Chuya Basin, was caused by the Sukor rockslide that dammed the Chuya Valley. The rockslide was triggered by a large earthquake (shaking intensity at least IX-X) generated by an active fault in the Kurai Fault Zone about 16 ka, which is the oldest known date for its activity. Thus, large landslides or rockslides can remain geomorphically expressed for at least 16 ka in the climate and landscape conditions as in the Chuya and Kurai basins. The lake existed till ~10 ka BP and then was gradually drained. The Kuyuktanar glacier reached its greatest extent in the early marine isotope stage (MIS) 2, and its ablation moraines formed about 25 ka. Judging by the age and good preservation of moraines left by the glacier, the hilly terrain in the area of the Sukor rockslide, and the presence of lacustrine sands in the vicinity of the lake dam, no catastrophic flooding events in the Chuya and Katun valleys have occurred since the Last Glacial Maximum (LGM; ~20 kyr BP). The water table of the glacier-dammed lake that occupied the Kurai Basin around the LGM could not have exceeded 1750 m above sea level (a.s.l.). Higher lake terraces traceable till elevations of 2100–2200 m a.s.l. should be attributed to more ancient lake stages. Archaeological sites in the area of the junction between the Chuya and Kurai basins were formed in the post-lake period, the oldest dating back to the latest Late Paleolithic time.

Graphene Oxide/Nanofiber-Based Actuation Films with Moisture and Photothermal Stimulation Response for Remote Intelligent Control Applications.

The rapid development of intelligent technology and industry has induced higher requirements for multifunctional materials, especially intelligent materials with stimulus-responsive self-actuation behavior. In this study, a Cu@PVA-co-PE/GO composite actuation film, with an asymmetric sandwich structure, was prepared by attaching graphene oxide (GO) to the surface of a polyvinyl alcohol ethylene copolymer (PVA-co-PE) nanofiber composite film containing copper nanoparticles (Cu) through layer-on-layer adsorption. This unique structural design endowed the composite film with not only excellent structural stability but also different bending directions (in response to moisture and infrared light). The actuation performance shows that when the adsorption time was 4 h, the maximum bending angle of the Cu@PVA-co-PE/GO composite film was up to 90° within 5.99 s. Furthermore, the actuation behavior was stable after 100 cycles of reversible moisture stimulation. Additionally, the maximum actuation strain of the composite film was up to 1.35 MPa during the illumination time of 6.8 s and maintained an excellent stability for 400 s under continuous infrared stimulation of 0.53 W/cm2. The rapid and sensitive stimulus response of the Cu@PVA-co-PE/GO composite film exhibited self-actuation behavior under the remote control of moisture and infrared light. This, in turn, suggests prospects for wide applications in emerging technologies, such as intelligent switches, artificial muscles, intelligent medical treatment, and flexible robots.

New efficient OSL detectors based on the crystals of Ce3+ doped Gd3Al5−xGaxO12 mixed garnet

In this study, the infrared optically-stimulated luminescence (IR-OSL) of single crystals of Ce3+ doped Gd3(GaxAl5−x)O12 mixed garnet with Ga content x = 2.5, 2.7, 3 was investigated for the first time. It was demonstrated that infrared stimulation of these crystals previously exposed to beta radiation produces a strong luminescence signal comparable with conventional OSL phosphors. The intensity of the IR-OSL highly depends on Ga content, reaching maximum for x = 2.5. The IR-OSL decay curves are multicomponent, with predominant fast components with the decay time around 1 s. The relation between IR-OSL and thermoluminescence was also studied. It was found that the most intense fast components of IR-OSL decay are related to the low-temperature peaks in thermoluminescence glow curves occurring at the temperature range 78–96 °C. The observed high intensity of the IR-OSL signal creates perspectives for possible applications of Gd3(GaxAl5−x)O12 mixed garnet crystals for passive radiation measurements and dosimetry.

PL2. Noninvasive brain stimulation – The past, the present and the future

Non-invasive brain stimulation started in the antiquity by treating headache with electric fishes (∼ 1 A, ∼ 700 V). Transcranial direct current stimulation dominated research in the 19 th century after the invention of the voltaic pile (∼ 1 mA, ∼10 V). At present the main applications involve either weak electric stimulation of many different types (transcranial direct, alternating, random noise or combinations) of currents or high energy pulsed stimulations (∼8 kA, ∼ 10 µs) mediated by transcranial magnetic energy transfer (transcranial magnetic stimulation: TMS). Inhibitory or excitatory after-effects are guided by stimulus intensity, duration and intervals (cf. theta burst, quadripulse and others). In general, lower intensities lead to inhibition and higher intensities to excitation. There is no linear correlation between the duration of stimulation and the size of the after-effects, prolongation of stimulus duration may lead to an oscillating pattern of inhibition or excitation. Missing the right windows in time or in amplitude may lead to no or opposite results explaining the variability and conflicting data in the field. Intracellular calcium increase may be a key leader for deciding between LTD- or LTP-like after-effects. Uncontrolled consumption of nicotine and caffeine increase variability further. Co-application of drugs may guide after-effects in terms of selectivity and duration of after-effects. Current developments encompass new physical techniques such as varying TMS pulse widths, multi-electrode stimulation, interference fields, ultrasound or near infrared stimulation, hypothesis driven protocols based on neurophysiological features of cortical neurons, optimized techniques on realistic individual head models for targeting current flow to predefined areas and others. Clinical applications targeting cortical excitability increases (e.g. depression, pain) or decreases (e.g. epilepsy, migraine) seem to be more rewarding than those requiring structural repair (e.g. stroke).

Possible new evidence for Mid-Pleistocene glaciation in the Vale of Pickering, North Yorkshire, UK

Whilst the Late Devensian glaciation (MIS2) of the Vale of Pickering is well-documented, earlier glaciations within it are not. A proposed limited glaciation in the Mid-Pleistocene, thought to be of Marine Isotope Stage 8 (MIS) age is not well constrained. This paper aims to obtain preliminary ages for two of the most prominent geomorphic features in the Vale of Pickering to see if they related to pre-Devensian glaciations. New luminescence dating by infra-red stimulation of feldspars from sand accumulations near the summit of Gallows Hill, part of the Wykeham Moraine, and from a section through poorly sorted fluvial sand and gravel on the flanks of the Hutton Buscel Terrace in Yedman Dale gave ages of 176 ± 14 ka and 156 ± 12 ka, respectively. Evidence suggests they represent a glacial incursion (MIS 6) into the Vale of Pickering blocking its eastern end and forming a pre-Devensian Glacial Lake Pickering. Whilst they could be older, this style of glaciation is very different to the limited plateau ice-field proposed for MIS 8 at the western end of the Vale of Pickering. Taken at face value, these preliminary ages suggest that the Vale of Pickering was partially glaciated in MIS 6 as part of a wider ice sheet and contemporary with the Saalian glaciation in Europe.

Characterization of TL and CW-OSL signals of natural brazilian topaz with different colours

Topaz [Al2SiO4(OH,F)2] is usually found in nature and can presents different colours. The aim of this paper is to evaluate the thermoluminescence (TL) and the optically stimulated luminescence (OSL) response of five types of topaz collected from three different Brazilian states. The topaz samples studied have a yellow, blue and colourless coloration. The TL results showed that colourless samples from the state of Rio Grande do Norte present a TL glow curve with a main peak at ~260ºC. The others colourless topaz from Teofilo Otoni e Mato Grosso do Sul, besides the peak of ~260ºC, the present another peak at 160 ºC. The highest TL intensity was observed with the colourless topaz from RN. A linear TL dose curve response was also observed with these samples from the gamma radiation of 60Co in the range of 0.01 Gy to 3.5 Gy. The blue light stimulation (BSL) showed almost the same intensity response for the three colourless topaz samples. None topaz sample showed response to optical infrared stimulation (IRSL).

Near-infrared stimulation of the auditory nerve: A decade of progress toward an optical cochlear implant.

ObjectivesWe provide an appraisal of recent research on stimulation of the auditory system with light. In particular, we discuss direct infrared stimulation and ongoing controversies regarding the feasibility of this modality. We also discuss advancements and barriers to the development of an optical cochlear implant.MethodsThis is a review article that covers relevant animal studies.ResultsThe auditory system has been stimulated with infrared light, and in a much more spatially selective manner than with electrical stimulation. However, there are experiments from other labs that have not been able to reproduce these results. This has resulted in an ongoing controversy regarding the feasibility of infrared stimulation, and the reasons for these experimental differences still require explanation. The neural response characteristics also appear to be much different than with electrical stimulation. The electrical stimulation paradigms used for modern cochlear implants do not apply well to optical stimulation and new coding strategies are under development. Stimulation with infrared light brings the risk of heat accumulation in the tissue at high pulse repetition rates, so optimal pulse shapes and combined optical/electrical stimulation are being investigated to mitigate this. Optogenetics is another promising technique, which makes neurons more sensitive to light stimulation by inserting light sensitive ion channels via viral vectors. Challenges of optogenetics include the expression of light sensitive channels in sufficient density in the target neurons, and the risk of damaging neurons by the expression of a foreign protein.ConclusionOptical stimulation of the nervous system is a promising new field, and there has been progress toward the development of a cochlear implant that takes advantage of the benefits of optical stimulation. There are barriers, and controversies, but so far none that seem intractable.Level of evidenceNA (animal studies and basic research).

Optical dating of cobble surfaces determines the chronology of Holocene beach ridges in Greenland

We constrain the age of a cobble beach ridge system in Greenland using Optically Stimulated Luminescence (OSL) dating of buried cobble surfaces. Luminescence signals from six cobbles are measured using infrared (IR) stimulation at 50 °C (IR50) and 180 °C (pIRIR180); these cobbles represent four progressively younger beach ridges lying between ~35 and ~6 m above present sea level. Luminescence–depth profiles show that the IR50 signals in all the samples and pIRIR180 signals in four out of six samples are well bleached to depths >1.2 mm into the cobble surfaces. Equivalent doses in well‐bleached cobble surface slices (i.e. <1.2 mm) are measured and divided by the effective environmental dose rate to the cobble surfaces in order to derive burial ages. Both IR signals are corrected for anomalous fading using the sample‐specific ratio of the field to the laboratory saturation levels. Our results are consistent with a depositional model predicting that the investigated portion of the beach ridge system built out continuously during relative sea level fall between ~5.3 and ~1.9 ka ago. The optical ages suggest that the rate of construction varied considerably, with the highest rates ~3.4 ka ago. Additionally, the lowest‐elevation beach ridge investigated here provides the first evidence for a higher‐than‐present relative sea level, between 1.5 and 2 ka ago, in the Disko coastal region.

Comparison of Equivalent Doses Obtained with Various post-IR IRSL Dating Protocols of K-Feldspar

Five dating protocols with post-infrared infrared (IR) stimulated luminescence signals (<i>i.e.</i> pIRIR) were performed on the K-feldspar of loess samples. Two of them were the single-aliquot regenerative-dose protocol (SAR) with two-step pIRIR stimulation, with the first IR stimulation at 50°C or 200°C and the second at 290°C (pIR<sub>50</sub>IR<sub>290</sub>, pIR<sub>200</sub>IR<sub>290</sub>). Two of them were the SAR protocols with five-step or six-step IR stimulation at multiple elevated temperatures to 250°C or 300°C (MET-pIRIR<sub>250</sub>, MET-pIRIR<sub>300</sub>). The final one was the multiple-aliquot regenerative-dose (MAR) protocol with the MET-pIRIR<sub>300</sub> signal, together with a 500°C heat treatment administered before the test dose (‘MAR with heat’). The results show that when the equivalent dose (<i>D</i><sub>e</sub>) of the sample was less than 500 Gy, all of the protocols gave consistent results; however, when <i>D</i><sub>e</sub> exceeded 750 Gy, all of the SAR protocols underestimated <i>De</i>. The pIR<sub>50</sub>IR<sub>290</sub> signal had the highest degree of underestimation, while the pIR<sub>200</sub>IR<sub>290</sub>, MET-pIRIR<sub>250</sub> and MET-pIRIR<sub>300</sub> signals had similar <i>De</i> values and similar degrees of underestimation. Possible reasons for the SAR <i>D</i><sub>e</sub> underestimation are discussed. We suggest that only the ‘MAR with heat’ protocol is suitable for samples with <i>D</i><sub>e</sub> exceeding 750 Gy.

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.