Reliable Chronology Research Articles

Morphometric analysis of monogenetic volcanoes in the Garrotxa Volcanic Field, Iberian Peninsula

The Garrotxa Volcanic Field is situated in the northeast region of the Iberian Peninsula. It represents the most recent volcanic area within the Catalan Volcanic Zone, which is one of the volcanic provinces of the European Rift System, featuring over 50 dispersed eruptive vents.This study presents a comprehensive morphometric analysis of volcanic edifices, aiming to enhance our understanding of both volcanostratigraphy and the geomorphology of landforms within the Garrotxa Volcanic Field. Our methodology involved extensive fieldwork and detailed analysis of Digital Elevation Models (DEMs) to precisely determine the spatial distribution and morphometric parameters of the best-preserved volcanic structures in the area. The Garrotxa Volcanic Field exhibits an uneven spatial distribution of various volcanic landforms, with approximately 50 % comprising magmatic cones, primarily formed through Strombolian eruptions. The remaining 50 % is evenly divided between magmatic-phreatomagmatic volcanoes and phreatomagmatic tuff rings-maars. The morphometric characteristics of the three genetic types overlap significantly, showing no clear differences, although a few distinctions can sometimes be identified.The Garrotxa Volcanic Field displays a variety of eruption styles: 46 % of the identified eruptive sequences begin with phreatomagmatic activity, while 54 % start with predominantly magmatic explosive activity. Most eruptions show a transition through different phases.Data also indicate that the morphometric variability at the Garrotxa Volcanic Field stems from differences in the properties of pyroclastic sequences, resulting from their diverse eruption styles, as well as pre- and post-eruptive factors. Consequently, the results of the morphometric analysis are deemed insufficient for establishing a reliable chronology for the Garrotxa Volcanic Field.

Periodisasi Sejarah Sastra Masa Andalusia

The periodization of Arabic literature in Andalusia as shown by historians differs from one another. This is interesting to research, especially examining the differences in periodization. This research aims to find a reliable chronology of the periodization of the history of Arabic literature in Andalusia. To find the correct chronology of the periodization of Arabic literary history, researchers use historical methods. Researchers found the following periodization: chronologically, the historical periods of Arabic literature in Andalusia are divided into six. First, 711-755 AD, no literary manuscripts have been found. Second, 755-912 AD, literary texts were found under Ad-Dakhil's reign but were still oriented towards Masyriq literature. Third, 912-1013 AD, namely the period when the group of kings called "Mulukut Tawaif" was formed and literary critics began to appear. Fourth, 1013-1086 AD, literature at this time was still oriented towards Masyriq literature but the difference lay in the ability of Andalusian writers to use more real and imaginative wording. Fifth, 1086-1248 AD, during this time poets and philosophers emerged, among the famous ones being Ibnu Thufail and Ibnu Rushd. Sixth, 1248-1492 AD, during this period lament literature began to be introduced and continued to develop rapidly.

Post-glacial small delta process uncovered by luminescence and radiocarbon chronology of core sediments from coastal South China Sea

Reliable chronology is crucial for reconstructing delta processes. The past decades witnessed a boost of dating works on the most economically influential large deltas (i.e., subaerial area >1000 km2), but chronology remains lacking on many small deltas (i.e., subaerial area <1000 km2) that are also densely populated and economically active. Luohe River Delta (LRD) in the coastal South China Sea is such a small delta, whose evolution concerns hundreds of thousands of people, and literally no reliable dating results have been reported to support research of its processes. Herein, dating work combining radiocarbon (14C) on mollusk shells and quartz Optically Stimulated Luminescence (OSL) methods were performed on core LFZK06 from LRD, to test applicability of both methods by age comparison and to establish a chronological framework, using Bayesian age-depth models, of LRD for the first time. 14C ages are systematically c. 0.5–1 ka younger than OSL ages from the same depths. Such young bias of 14C ages in LRD contrasts with previously observed overestimated 14C results in the nearby Pearl River Delta (PRD), likely due to the distinction in bedrock types between Luohe River (granites and sandstones only) and Pearl River (limestone prevalence causing hardwater effect) drainages. Ages of core LFZK06 span from 57 ± 7 ka to 3.42 ± 0.05 cal ka BP and contain a hiatus between 57±7–11.9 ± 1.7 ka. Holocene deltaic sequence of the core shows three-stage sedimentary processes: (1) rapid deposition of prodelta/delta front sediments at 10.2‐0.4+0.5 ka–7.7‐0.3+0.4 ka related to rapid sea level rise, (2) hiatus during 7.7‐0.3+0.4 ka–5.7‐0.8+0.5 ka likely due to reduced sediments input or river channel migration, (3) rapid accumulation of delta plain sediments during 5.7‐0.8+0.5 ka–3.42‐0.85+0.42 ka reflecting depocenter shift toward core location. Moreover, changes of quartz OSL sensitivity were detected, indicative of sediment provenance transition. A change in sediment source from nearby granite weathering towards fluvial long-transported materials occurred at a depth of 24.7 m, with low quartz OSL sensitivity in the gravelly layer below (11.9 ± 1.7 ka) and one magnitude higher quartz OSL sensitivity in prodelta deposits above (10.2‐0.4+0.5 ka).

Middle to late Holocene climate change in the monsoon-dominated southeastern Tibetan Plateau and its relationship with human activity

Aeolian deposits on the southeastern Tibetan Plateau (SETP) can provide evidence of how prehistoric humans were influenced by climatic and environmental changes in high-altitude regions. We present the results of multi-proxy analyses of a middle–late Holocene aeolian section in the SETP, together with the probability density of the ages of various cultural sites within and around the study area. Quartz optically stimulated luminescence dating provides a reliable chronology for this section, and analyses of geochemical elements, color and grain size are used to reconstruct the pattern of climate change during the middle–late Holocene. The results suggest a trend of gradually decreasing moisture from the middle Holocene (∼6 ka) onwards, followed by a slight increase at ∼2 ka, which is supported by TraCE-21 ka simulation results. These changes were closely related to variation in the Indian summer monsoon (ISM) caused by decreasing Northern Hemisphere summer insolation and an increase in the Atlantic Meridional Overturning Circulation. The variations in dust activity are inversely related with moisture and there was a significant decrease in dust activity after ∼2 ka. The drought conditions during the 4.2 ka event recorded within the section appear to be a continuation of the trend of middle–late Holocene climatic deterioration, which is superimposed on a weakening trend of the ISM. The permanent human occupation of the study area after ∼2 ka corresponded to an interval of mild and wet climate when dust activity was relatively weak. An observed correlation between the intensity of human activity and dust storms suggests that the enhancement of human activities played a significant role in increasing the occurrence of dust storms. Overall, our results provide new insights into human-environmental interactions in the SETP.

Chronology and paleoclimatic context of hominin occupations in the Fenhe River Basin of northern China during the middle to Late Pleistocene

The relationship between climate change and hominin evolution over the Pleistocene in East Asia is still poorly understood, in particular due to the limited number of archaeological finds and fossils with reliable chronologies. Paleolithic sites preserved in loess-paleosol sequences in eastern Chinese Loess Plateau provide prospective evidence for understanding hominin evolution and dispersion across the Middle to Late Pleistocene in northern China. The Fenhe River Basin has been known as a key area for paleolithic sites and fossil hominins. Here, quartz Optically stimulated luminescence (OSL) and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) dating was employed on 61 samples from 13 paleolithic sites in the Fenhe River Basin. The reliability of the ages are checked by analysis of luminescence characteristics and comparison between quartz OSL and K-feldspar pIRIR ages. Paleoclimatic records were established using alternating loess-paleosol sequences, and multi-proxy indices of grain size, magnetic susceptibility, CaCO3 and color from the dated sites. These results provide the reliable chronology for hominin presence in the Fenhe River Basin spanning the past three glacial-interglacial cycles. Our results show that this region experienced predominantly dusty, dry and cold conditions during glacials and comparatively moist and warm interglacial conditions, that are sensitive to variations in East Asian Summer and Winter Monsoon (EASM and EAWM respectively) intensities over glacial-interglacial timescales. The Fenhe River Basin is a key geographic refuge for hominins during glacial-interglacial climatic changes in northern China. It was occupied over glacial and interglacial periods spanning at least the last 370 ky, and the evidence for hominin presence is especially clear from ∼250 to 60 ka and since ∼35 ka. The frequency of hominin activity, as indicated by the number of archaeological sites and density of stone artifacts, increased during warm and humid periods of MIS 7 and MIS 5, in contrast to the cold, windy, and dry period of MIS 6. Site numbers increased in MIS 3 and the Last Glacial Maximum, in association with microblade technology. The dating results indicate that hominins with ‘modern’ features may have occurred in the Fenhe River Basin ∼140 ka ago, however, the exact timing of modern human occupation in the region needs a more combined approach consisting of morphological, ancient DNA and geochronological studies.

An integrated study of constraining the initial 230Th of a stalagmite and its implications

High-precision U–Th age is the key to promoting speleothem as an important archive for paleoclimate study. Notably, obtaining reliable U–Th age primarily relies on the accurate initial 230Th correction. However, correcting the U–Th age of stalagmite with the average 232Th/238U value in the crust is sometimes not enough to eliminate the effect of the initial 230Th, using other dating methods (e.g., 14C) and referring to the characteristics of speleothem δ18O values are useful to guide its age correction and establish the chronology. This paper presents a comprehensive study of the chronology and isotopic record of a stalagmite XBL-5 from Xiaobailong Cave, Yunnan, China, using a combination of stalagmite U–Th dating, 14C dating, and δ18O wiggle match dating. The low uranium content of this stalagmite and the apparent inversion of U–Th dating prevent us from establishing the proxy profiles with reliable chronology. We determined the actual age range based on 14C ages assuming various dead carbon proportion (DCP) and uncorrected U–Th ages, along with the characteristic of stalagmite δ18O variations, and then established a credible chronology of this stalagmite through wiggle match of δ18O records. Taking the tuned ages as a reference, the initial 230Th/232Th values were reciprocally calculated. The initial 230Th/232Th atomic ratio of the studied samples was back-calculated to be 75.7 ± 11.4 × 10−6, an order of magnitude higher than the commonly used correction value. The reconstructed XBL-5 δ18O record spans the Younger Dryas (YD) period, indicating that the precipitation δ18O generally increased within the YD chronozone with significant centennial scale oscillations in regions affected by the Indian summer monsoon, in contrast to the speleothem records from East Asian summer monsoon domains which show no or even weakly decreased long-term trend in precipitation δ18O. This study highlights the importance of initial thorium correction in stalagmite chronology study and provides a paradigm for sequence reconstruction of similar samples.

A Bayesian luminescence chronology for the Bawa Yawan Rock Shelter at the Central Zagros Mountains (Western Iran)

Bawa Yawan Rock Shelter is one of the critical Palaeolithic sites discovered recently in the Central Zagros in Western Iran. The site exhibits a rich assemblage from the Middle Palaeolithic (Zagros Mousterian) to the Epipalaeolithic, and it discloses one Neanderthal canine tooth. The site stands out as one of the handfuls of Palaeolithic sites in the Central Zagros that contain human remains. Therefore, establishing a reliable chronology revealing the temporal period in which Neanderthals inhabited the region plays a significant role in our understanding of the human past in the region. We employed luminescence dating in combination with Bayesian modelling to improve the precision of the estimated ages. Our results indicate that the Middle Palaeolithic assemblages unearthed from geological layers GH3 to GH5 in the site fall in the [58–80] ka time frame (68% credible interval). More importantly, the Bayesian age for the layer containing the Neanderthal remains exhibited [65–71] ka (68%). This age contradicts the previous 14C-based chronology. We argue that it is likely that the 14C dates underestimate the timing of the Middle Palaeolithic industries at Bawa Yawan.Furthermore, our study reveals the first luminescence age for the Epipalaeolithic in the Central Zagros, which is dated to [13–15] ka (68%).

The marine reservoir age of Greenland coastal waters

Abstract. Knowledge of the marine reservoir age is fundamental for creating reliable chronologies of marine sediment archives based on radiocarbon dating. This age difference between the 14C age of a marine sample and that of its contemporaneous atmosphere is dependent on several factors (among others, ocean circulation, water mass distribution, terrestrial runoff, upwelling, and sea-ice cover) and is therefore spatially heterogeneous. Anthropogenic influence on the global isotopic carbon system, mostly through atmospheric nuclear tests, has complicated the determination of the regional reservoir age correction ΔR, which therefore can only be measured in historic samples of known age. In this study we expand on the few existing measurements of ΔR for the coastal waters around Greenland, by adding 92 new radiocarbon dates on mollusks from museum collections. All studied mollusk samples were collected during historic expeditions of the late 19th and early 20th centuries, and besides coastal sites around Greenland, the new measurements also include localities from the western Labrador Sea, Baffin Bay, and the Iceland Sea. Together with existing measurements, the new results are used to calculate average ΔR values for different regions around Greenland, all in relation to Marine20, the most recent marine radiocarbon calibration curve. To support further discussions and comparison with previous datasets, we use the term ΔR13, where the suffix 13 refers to the previous calibration curve Marine13. Our study explores the links between the marine reservoir age and oceanography, sea-ice cover, water depth, mollusk feeding habits, and the presence of carbonate bedrock. Although we provide regional averages, we encourage people to consult the full catalogue of measurements and determine a suitable ΔR for each case individually, based on the exact location including water depth. Despite this significant expansion of the regional reservoir age database around Greenland, data from the northern coast, directly bordering the Arctic Ocean, remain missing.

Zeroing of IRSL signals in cobbles surfaces from a modern river floodplain in the Manas river, Tian Shan

A newly developing method, rock surface luminescence dating, provides a novel means of constraining the burial age of fluvial gravel and unveiling the transport and exposure-burial process of fluvial bed-load. A crucial requirement for successful age determination in luminescence dating of buried rock surfaces is that a sufficiently thick surficial layer was reset to a near-zero level of signal prior to deposition and burial. However, little such effort has been made on modern fluvial gravels from various depositional environments to provide a sound justification for the use of luminescence dating in such settings. In this study, we reported an investigation of daylight bleaching in modern cobbles with different sizes and shapes at a modern river floodplain from the Manas River, Tian Shan, to test the reliability and applicability of fluvial cobble optical dating. Four multi-elevated-temperature post-infrared infrared (MET-pIRIR) stimulated luminescence signals of rock slices were measured using a modified MET-pIRIR protocol to establish residual luminescence-depth profiles. The residual does of pIRIR and MET-pIRIR signals of sub-surface rock slices were also estimated using different modified SAR protocols. The results showed that the high temperature IRSL signal could be reset to ∼2–3 mm depth into cobbles surface and flat cobbles seem easier to bleach than spherical cobbles. The residual doses of sub-surface rock slices of cobbles from modern river floodplain was ∼0.4 Gy and ∼1.1 Gy for the IR50 and the pIRIR170 signal respectively, suggesting a residual age of ∼0.1 ka and ∼0.2 ka. The residual ages of MET-pIRIR signals of sub-surface rock slices of cobble MNS2-5 were ∼0.5–1 ka at higher stimulation temperature. Our results show that the fluvial cobble optical dating techniques have great potential for providing reliable chronologies for river floodplain gravel and other fluvial depositional events.

210Pb-dating of sediments with models assuming a constant flux: CFCS, CRS, PLUM, and the novel χ-mapping. Review, performance tests, and guidelines

The 210Pb-based method has been widely used for five decades to determine absolute ages in recent sediments on the centennial scale. Decoding a chronology from the empirical data set requires a series of assumptions that define a mathematical model of the sedimentary conditions. This work aims to provide a comprehensive review of the fundamentals of the existing family of models assuming a constant flux of excess 210Pb at the sediment surface, namely the CFCS, CRS, and PLUM models, and to present the novel χ-mapping versions of the CFCS and CF models. Their performance is assessed with a selected group of five cores from literature data, with varve chronologies or independent time marks. The PLUM model did not produce reliable chronologies in any of the cores studied. The CRS model is too sensitive to an accurate estimation of the total inventory. A weighted-fit and the χ-mapping versions of the CFCS model are prone to over-represent the younger regions of the core. The CFCS model with least squares fitting and the χ-CF models performed best under the most common sedimentary conditions, which involve temporal variability in the fluxes randomly distributed in the time line. A practical strategy is suggested to identify the occurrence of such sedimentary conditions through the combined use of a set of models, providing this way further strength to the 210Pb-dating.

210Pb-based dating of recent sediments with the χ-mapping version of the Constant Sediment Accumulation Rate (CSAR) model

The 210Pb-based method aims at determining the absolute age of recent sediments on the centennial scale. A family of models assumes that at the sediment-water interface the flux of unsupported 210Pb (210Pbexc), F, relates to its initial activity concentration, Ao, and the mass sedimentation rate, w, as: F=Aow. Additional specific assumptions that allow for analytical formulations of the models are: i) constant Ao (CIC), constant F (CF), and constant F with constant w (CFCS). A model with constant w (CSAR) was suggested for completeness but never used because of the lack of a suitable analytical formulation. The TERESA model assumes random and independent variability for Ao and w, described by normal distributions. It systematically generates a large number (∼105) of potential solutions, whose performance for fitting the empirical 210Pbexc profile is quantified through the χ-function. This work aims to adapt the above methodology to formulate the χ-mapping version of the CSAR model. The performance of the model is evaluated with a set of synthetic and real cores for which an independent chronology is available. CSAR is able to capture the mean sedimentation rate from the 210Pbexc data and provides reliable chronologies and paleorecords of Ao, useful for tracking past changes in sedimentary conditions. CSAR provides an interesting different perspective for researchers working with 210Pb-based dating of recent sediments.

Aeolian process and climatic changes in loess records from the eastern Tibetan Plateau: Implications for paleoenvironmental dynamics since MIS 3

The Tibetan Plateau (TP) is extremely sensitive to climate change. However, climate variability during the last glaciation in the TP is not well-understood. The widely distributed loess deposits on the eastern TP serve as a significant archive for retrieving past climate changes and aeolian dust dynamics. Through detailed quartz optically stimulated luminescence and radiocarbon dating and the analysis of environmental proxies, we have established a reliable chronology of the Maerkang loess sequence in the eastern TP and reconstructed well-constrained histories of dust activities and environmental variation. Our results demonstrate that the accumulation of aeolian loess in this region occurred at least 60 thousand years ago. The dust mass accumulation rate (MAR) varied highly in the last glacial period, with high MARs in the Last Glacial Maximum and relatively low MARs in marine isotope stage (MIS) 3. Humid conditions occurred in MIS 3 (approximately 50–32 ka) due to the intensified Indian summer monsoon. The rapid climate variations of the Maerkang loess might be correlated to the Dansgaard–Oeschger cycles and the Heinrich events, which implies the significant impact of the North Atlantic climatic system on the TP. Our findings provide new evidence for a better understanding of the history of environmental variations since MIS 3 in the eastern TP.

Holocene occupation of the Andean highlands: A new radiocarbon chronology for the Telarmachay rockshelter (Central Andes, Peru)

The Andean highlands challenged but did not prevent human exploration and occupation starting in the Late Pleistocene. The timing and nature of these events is an ongoing area of research and debate for which reliable chronologies are required. Our goal is to revise the chronological framework of the Telarmachay rockshelter, a key site from the Andean highlands. To achieve this objective, we have conducted a new AMS dating programme utilizing 33 camelid bone samples from 6 archaeological layers and used a Bayesian modelling approach to determine the chrono-stratigraphy. Our chronology spans a greater than 5000 year sequence dated between 9.0–8.0 and 3.7–3.1 kyr BP, permitting reassessment of the antiquity and duration of the Telarmachay occupation, facilitating comparison with other sites, and allowing examination of domestic and symbolic practices in relation to Holocene climatic variation in the Central Andes. This study highlights the importance of the Junín area in the Andean highland occupation sequence. It also underlines the need for new radiocarbon dates to reassess previous data and directly date artifacts.

High-resolution ∼55 ka paleomagnetic record of Biển Hồ maar lake sediment from Vietnam in relation to detailed 14C and 137Cs geochronologies

Vietnam's Central Highlands in Pleiku feature numerous volcanic craters (i.e. maars) formed over 0.2 Ma ago that contain continuous high-resolution lacustrine sediment records extending from the Late Pleistocene through the Holocene. Their evolution and sedimentary proxies are potentially powerful archives for interpretation of East-Asian monsoon variability across Vietnam, as well as for local to regional changes in landcover. The focus of this study is to develop a reliable chronology for the Biển Hồ 25-m-long lake sediment sequence in Vietnam's Central Highlands. We present a combined sediment chronology extending back to 55 ka cal BP that is based on 137Cs surface sediment chronology, paleomagnetic dating, and 47 14C dates distributed evenly throughout the sequence. Based on sedimentary facies analysis and a smooth age-depth model based on 137Cs and 14C data, we infer a long-term stable rate of sedimentation in Biển Hồ lake without unconformities or erosional hiatuses, except for the uppermost section (ca. 100 years) where human activities increase the rate of sedimentation significantly. The Biển Hồ sequence thus provides a complete and uninterrupted record of the lake's depositional history. The present contribution is a geochronologic opening salvo for future contributions from Biển Hồ lake featuring multi-disciplinary evidence for longer-term paleoclimate and environmental changes.

High-resolution record of stable isotopes in soil carbonates reveals environmental dynamics in an arid region (central Iran) during the last 32 ka

Although central Iran is pivotal for palaeoclimatic correlations, palaeoenvironmental data for this region is very sparse and a reliable chronology for pedogenic features is lacking. We therefore tried to answer the question how the environmental conditions and, in particular, the climate developed over time by using the isotopic signatures of pedogenic carbonates. We present a chronology of pedogenic carbonates in association with stable carbon and oxygen isotopes in both the matrix and coating carbonates of a relict palаeosol (Baharan palaeosol) in central Iran to understand the dynamics of environmental changes in this region during the late Quaternary. The palаeosol experienced several episodes of leaching during pedogenesis as reflected in its morphology (carbonate coatings under the rock fractions) and geochemical characteristics (Ba/Sr ratios). The δ18O values of both the matrix and coating carbonates in the upper 60 cm (especially in the upper 20 cm) of the pedon are enriched (∼4‰) compared to the subsoil and are mainly related to the impact of evaporation. Moreover, the δ13C values of the carbonates are in isotopic disequilibrium with the modern vegetation cover (desert shrubs) of the study area and are enriched in different degrees. The carbonates in the top 60 cm are formed by the input of atmospheric CO2 and calcareous dust while deeper carbonates formed in an environment exhibiting a higher contribution of C4 plants. Based on the radiocarbon chronology of carbonate coatings, it seems that three main stages of palaeoenvironmental changes occurred in the region during the last 32 ka. The first stage lasted ca. 5,000 years (between 31.6 and 26.0 ka) and was accompanied by deep leaching under sub-humid climatic conditions and the expansion of C4 plants. Under the dominance of semi-arid conditions during the second stage until the late Holocene, a gradual increase in the δ18O values and aridity occurred in the region. The last phase in the late Holocene was characterised by the establishment of an arid and evaporative environment with a sparse vegetation cover. A climatic correlation using the oxygen isotopic composition of secondary carbonates from the Baharan palaeosol, Soreq Cave (the Levant) and Hoti Cave (Oman; both having speleothems records) suggested a climatic connection between central Iran and the eastern Mediterranean during the late Pleistocene and between central Iran and northern Oman during the late Holocene.

Rock surface luminescence dating of gravel determines the age of a glacial outburst megaflood, Glacial Lake Missoula, Montana, USA

AbstractGiant gravel bars are important archives of megafloods; however, determining their depositional ages requires reliable geochronometric methods. Five gravel bars, reaching heights of 150–170 m, formed in the bedrock-lined Alberton Gorge along the Clark Fork River, Montana (USA), during draining of Glacial Lake Missoula (GLM). We report the first numerical ages for megaflood deposits in the GLM basin by successfully applying the novel optically stimulated luminescence (OSL) rock surface dating technique to date cobbles collected from three locations along one bar’s transport direction. Depth-dependent infrared stimulated luminescence and post-infrared pulsed OSL signals showed that exteriors of only 3 out of the 38 collected cobble samples were well bleached by exposure to daylight before burial, and hence suitable for dating. The cobbles provided ages of 16.5 ± 0.9, 18.5 ± 1.4, and 21.7 ± 1.1 ka, all of which are indistinguishable from the average cosmogenic nuclide age of 18.2 ± 1.5 ka (n = 4) for a large megaflood in the Channeled Scabland, eastern Washington State. The average of the two younger ages, 17.5 ± 1.0 ka, is our best estimate of the deposit age. We interpret the older age to be from a cobble that was reworked by the flood. Our results show that these techniques have great potential for providing reliable chronologies for paleofloods and other high-energy depositional events.

North Atlantic Drift Sediments Constrain Eocene Tidal Dissipation and the Evolution of the Earth‐Moon System

AbstractCyclostratigraphy and astrochronology are now at the forefront of geologic timekeeping. While this technique heavily relies on the accuracy of astronomical calculations, solar system chaos limits how far back astronomical calculations can be performed with confidence. High‐resolution paleoclimate records with Milankovitch imprints now allow reversing the traditional cyclostratigraphic approach: Middle Eocene drift sediments from Newfoundland Ridge are well‐suited for this purpose, due to high sedimentation rates and distinct lithological cycles. Per contra, the stratigraphies of Integrated Ocean Drilling Program Sites U1408–U1410 are highly complex with several hiatuses. Here, we built a two‐site composite and constructed a conservative age‐depth model to provide a reliable chronology for this rhythmic, highly resolved (&lt;1 kyr) sedimentary archive. Astronomical components (g‐terms and precession constant) are extracted from proxy time‐series using two different techniques, producing consistent results. We find astronomical frequencies up to 4% lower than reported in astronomical solution La04. This solution, however, was smoothed over 20‐Myr intervals, and our results therefore provide constraints on g‐term variability on shorter, million‐year timescales. We also report first evidence that the g4–g3 “grand eccentricity cycle” may have had a 1.2‐Myr period around 41 Ma, contrary to its 2.4‐Myr periodicity today. Our median precession constant estimate (51.28 ± 0.56″/year) confirms earlier indicators of a relatively low rate of tidal dissipation in the Paleogene. Newfoundland Ridge drift sediments thus enable a reliable reconstruction of astronomical components at the limit of validity of current astronomical calculations, extracted from geologic data, providing a new target for the next generation of astronomical calculations.

Late Pleistocene to Holocene sedimentary history in the Pearl River Delta revealed by OSL and radiocarbon dating

A reliable chronology is essential to understand deltaic sedimentation processes in response to sea-level fluctuations and climatic changes. In the Pearl River Delta (PRD), high-resolution chronostratigraphy is still limited which hinders the detailed interpretation of sedimentary history. In this study, optically stimulated luminescence (OSL) dating and radiocarbon (14C) dating were applied to establish a chronological framework of core P5-4 (30 m depth) in the southern PRD. Fifteen OSL and four 14C samples produced ages ranging from c. 8 ka to 0.5 ka, and two older OSL samples produced minimum ages of 75 and 62 ka. 14C ages are generally older (up to c. 1 ka) than the corresponding OSL ages and the discrepancy increases with depth. The ages and sedimentary data of sixteen published cores have been compiled to correlate the regional stratigraphy and reconstruct the late Pleistocene to Holocene deltaic process. It is concluded that: (1) The bottom subaerially-exposed deposits of core P5-4 were dated to marine isotope stage (MIS) 5, which is consistent with similar OSL-based records in the PRD. The laterally correlation shows that a depositional hiatus during c. 70–8 ka prevailed in the PRD and may attribute to strong erosion due to weathering and fluvial scouring. (2) Due to the relatively high altitude of bedrock, the post-glacial marine deposition of the PRD started at c. 8 ka, postdating other megadeltas by at least 2–4 ka. During 8–0.5 ka, a three-stage sedimentary process that is common in the PRD occurred in P5-4, i.e., early-Holocene (8–6 ka) rapid accumulation rate (5.44 m/ka) associated with rapid sea level rise, followed by mid-Holocene (6–3 ka) decelerated sedimentation rate (1.17 m/ka) in response to reduced sediment supply and strong tidal forces and late-Holocene (3–0.5 ka) accelerated sedimentation rate (2.28 m/ka) due to enhanced human activity.

A cosmogenic nuclide-derived chronology of pre-Last Glacial Cycle glaciations during MIS 8 and MIS 6 in northern Patagonia

Abstract. The precise environmental mechanisms controlling Quaternary glacial cycles remain ambiguous. To address this problem, it is critical to better comprehend the drivers of spatio-temporal variability in ice-sheet evolution by establishing reliable chronologies of former outlet-glacier advances. When spanning multiple glacial cycles, such chronologies have the capacity to contribute to knowledge on the topic of interhemispheric phasing of glaciations and climate events. In southern Argentina, reconstructions of this kind are achievable, as Quaternary expansions of the Patagonian Ice Sheet have emplaced a well-preserved geomorphological record covering several glacial cycles. Moreover, robust ice-sheet reconstructions from Patagonia are powerful barometers of former climate change, as Patagonian glaciers are influenced by the Southern Westerly Winds and the Antarctic Circumpolar Current coupled to them. It is essential to better constrain former shifts in these circulation mechanisms as they may have played a critical role in pacing regional and possibly global Quaternary climate change. Here, we present a new set of cosmogenic 10Be and 26Al exposure ages from pre-Last Glacial Cycle moraine boulder, glaciofluvial outwash cobble, and bedrock samples. This dataset constitutes the first direct chronology dating pre-Last Glacial Maximum (LGM) glacier advances in northern Patagonia and completes our effort to date the entire preserved moraine record of the Río Corcovado valley system (43∘ S, 71∘ W). We find that the outermost margins of the study site depict at least three distinct pre-Last Glacial Cycle stadials occurring around 290–270, 270–245, and 130–150 ka. Combined with the local LGM chronology, we discover that a minimum of four distinct Pleistocene stadials occurred during Marine Isotope Stages 8, 6, and 2 in northern Patagonia. Evidence for Marine Isotope Stage 4 and 3 deposits were not found at the study site. This may illustrate former longitudinal and latitudinal asynchronies in the Patagonian Ice Sheet mass balance during these Marine Isotope Stages. We find that the most extensive middle-to-late Pleistocene expansions of the Patagonian Ice Sheet appear to be out of phase with local summer insolation intensity but synchronous with orbitally controlled periods of longer and colder winters. Our findings thus enable the exploration of the potential roles of seasonality and seasonal duration in driving the southern mid-latitude ice-sheet mass balance, and they facilitate novel glacio-geomorphological interpretations for the study region. They also provide empirical constraints on former ice-sheet extent and dynamics that are essential for calibrating numerical ice-sheet and glacial isostatic adjustment models.

Inconsistent patterns of Holocene rainfall changes at the East Asian monsoon margin compared to the core monsoon region

Documenting spatiotemporal patterns of the Holocene Optimum (HO) at the climatically sensitive East Asian monsoon (EAM) margin are essential for understanding monsoon climate dynamics. However, the timing of the onset of the HO at the EAM margin is still debated and progress has been partly hindered by age uncertainties in different proxy records. To avoid the bias of these chronological uncertainties, we compared moisture variations from the marginal EAM region reconstructed from dust and aluminum (Al) flux records with tree pollen percentages in a dated lake sediment core that tracked moisture changes in the region around the lake. We show a delay (∼1500 years) of HO initiation in the core EAM region in northeastern China compared to the monsoon margin. Synthesizing pollen records with reliable chronologies show a synchronous HO occurrence at ∼8000-7000 cal yr BP at the monsoon margin, which is likely attributed to the shrinkage of the Northern Hemisphere ice sheet. Therefore, although the monsoon margin has always been considered a climate-sensitive area, it might be sensitive to different forcing factors from the core monsoon region.