Deciphering non-steady landscape evolution by in-situ cosmogenic nuclide depth profile

In-situ cosmogenic nuclide s are receiving growing attention in surface Earth system science in which the steady-state denudation is an important assumption for estimating the surface denudation of long-lived(103-106 years)surfaces.However,distinguishing steady-state denudation and deciphering a reliable denudation rate from non-steady state denudation region are difficult.Recent depth profile models for investigating the denudation rate,exposure age and inheritance are widely used for sediment and regolith of steady-state denudation region.Here we present in-situ co smogenic nuclides^(10)Be and^(26)Al from two typical granite regolithes from Jixian in Tianjin and Tengchong in Yunnan to model non-steady landscape evolution process by using steady state(Model 1)and non-steady state(Model 2,continuous exposure;Model 3 a,changed denudation rate;Model 3 b,abrupt denudation event)models.The results of steady state model show that both regolithes are in non-steady state.^(10)Be non-steady state models of Jixian regolith reveal that the surface has likely experienced a denudation rate change or an abrupt denudation event during the past several millennia,resulting in a non-steady state.The similar Model 3 a and 3 b denudation rates of 14.6-12.9^(+9.4)and 14.7-14.7^(+9.0)mmkyr^(-1),respectively,might demonstrate the long-term denudation rate rather than the exaggerated rate s of 39.0-2.3^(+2.6)and 39.0-2.4+^(2.5)mm kyr^(-1)calculated by assuming steady-state denudation and ignoring inheritance.The non-steady state model results of Tengchong regolith suggest that the surface has likely experienced a strong denudation about 157 ka(^(10)Be)or 127 ka(^(26)Al)ago.This timing is basically consistent with the termination of the MIS 6(TII:130 ka)and the climate change events in the Tibetan Plateau,suggesting a strong surface landscape denudation during the transition from glacial to interglacial.The compiling of basin-wide denudation rates in the Tibetan Plateau shows a good positive correlation with the regional tectonic activity,indicating that the denudation rate derived from non-steady state region with strong tectonic activity is likely to be overestimated by assuming steady state.We suggest that a combination of steady state and non-steady state depth profile models should be used to quantify denudation rate and exposure age more accurately and effectively in strong tectonic activity or climate change regions.

Cosmogenic ^(10)Be and ^(26)Al Chronology of the Last Glaciation of the Palaeo-Daocheng Ice Cap,Southeastern Qinghai-Tibetan Plateau

The glacial landforms of the Qinghai-Tibetan Plateau （QTP） provide a unique opportunity to research hemispheric and global environmental changes. In this study, we focus on the glacial history of the palaeo-Daocheng Ice Cap （p-DIC） in the southeastern QTP during the last glacial cycle. Based on field investigations, morphostratigraphy, and surface exposure dating of roche moutonnée, polished surface and moraine debris through the terrestrial cosmogenic nuclides （TCN） ^10Be and ^26Al. We identify glacial deposits of the last deglaciation, with minimum ages of 14.9±1.3-18.7±1.7 ka, the Last Glacial Maximum （LGM） of 24.7±2.2 ka, and the early part of the last glacial period （marine oxygen isotope stage （MIS） 3） of 37.1±3.4-45.2±3.9 ka. Our results show that in this region, the extent of the glacial advance during MIS 3 was larger than that during the traditional LGM （MIS 2）. These ages are consistent with prior chronologies, and the ^10Be age is consistent with the ^26Al age for the same sample. Thus, these data provide reliable constraints on climate change in the QTP, during the last glaciation.

10Be Exposure Ages Obtained From Quaternary Glacial Landforms on the Tibetan Plateau and in the Surrounding Area

In situ terrestrial cosmogenic nuclide （TCN） exposure dating using 10Be is one of the most successful techniques used to determine the ages of Quaternary deposits and yields data that enable the reconstruction of the Quaternary glacial history of the Tibetan Plateau and the surrounding mountain ranges. Statistical analysis of TCN 10Be exposure ages, helps to reconstruct the history of glacial fluctuations and past climate changes on the Tibetan Plateau, differences in the timing of glacier advances among different regions. However, different versions of the Cosmic-Ray-prOduced NUclide Systematics on Earth （CRONUS-Earth） online calculator, which calculates and corrects the TCN ages of Quaternary glacial landforms, yield different results. For convenience in establishing contrasts among regions, in this paper, we recalculate 1848 10Be exposure ages from the Tibetan Plateau that were published from 1999 to 2017 using version 2.3 of the CRONUS-Earth calculator. We also compare the results obtained for 1594 10Be exposure ages using different versions （2.2, 2.3 and 3.0） of the CRONUS- Earth calculator. The results are as follows. （1） Approximately 97% of the exposure ages are less than 200 ka. A probability density curve of the exposure ages suggests that greater numbers of oscillations emerge during the Holocene, and the peaks correspond to the Little Ice Age, the 8.2 ka and 9.3 ka cold events; the main peak covers the period between 12 and 18 ka. （2） In most areas, the newer versions of the calculator produce older 10Be exposure ages. When different versions of the CRONUS-Earth calculator are used, approximately 29% of the 10Be exposure ages display maximum differences greater than 10 ka, and the maximum age difference for a single sample is 181.1 ka.

Initiation and Development of the Late Cenozoic Uplift of Daluo Mountains,Northeastern Margin of the Tibetan Plateau

Daluo Mountains lie at front of the arcuate tectonic belt at the northeastern margin of the Tibetan Plateau,and are the landform boundary zone between the active Tibetan Plateau and the stable North China Craton.Studying of the late Cenozoic uplift evolution of Daluo Mountains is important for understanding the expansion mechanism of the northeastern margin of the Tibetan Plateau and its influence on the western North China Craton.In this study,the late Cenozoic uplift of Daluo Mountains is constructed from the development of the late Cenozoic alluvial fan around Daluo Mountains.The entire sedimentary sequence and framework of the fan was revealed by the newly obtained drilling core data.The cosmogenic nuclide,optically stimulated luminescence,and detrital zircon U-Pb dating results provide new evidences for discussion about the initial timing of the late Cenozoic uplift of Daluo Mountains and the key stages of uplift during the Pleistocene.The late Cenozoic alluvial fan at front of Daluo Mountains overlies a set of fluvial-facies strata;therefore,development of the alluvial-fan marks the start of late Cenozoic uplift of Daluo Mountains.The timing of this event can be constrained to~4.64 Ma.Two extensive gravel layers(dated to ca.0.76–0.6 Ma and~0.05 Ma)developed during the Pleistocene,indicating two episodes of considerable uplift.This study provides a new time scale for the uplift and expansion of the arcuate tectonic belt at the northeastern margin of the Tibetan Plateau.

Last Deglaciation Climatic Fluctuation Record by the Palaeo-Daocheng Ice Cap, Southeastern Qinghai-Tibetan Plateau

The last deglaciation, a key period for understanding present and future climate changes, has long been the hot topic for palaeoclimatological study. The Qinghai-Tibetan Plateau（QTP） is often a target study area for understanding hemispheric, or even global environment changes. The glacial landforms on the QTP provide a unique perspective for its climate change. In order to investigate the onset of the last deglaciation at the QTP and its regional correlation, the terrestrial cosmogenic nuclides（TCN） 10 Be and 26 Al surface exposure dating was chosen to date the roche moutonnée, the polished surface and the moraine debris located at the palaeo-Daocheng Ice Cap（pDIC）, southeastern QTP. Our results show that the onset of the last deglaciation is at about 19 ka, followed by another warming event occurring around 15 ka in the p-DIC area. These timings agree well with other records, e.g. equivalent with a rapid sea level rise at 19 ka and the onset of B？lling warming event at about 15 ka. Thus, our new data can provide good reveal constraint on the climate evolution at the QTP.

Reconstructing the post-LGM deglacial history of Hollingsworth Glacier on Ricker Hills,Transantarctic Mountains,Antarctica

The Transantarctic Mountains are an important corridor between the East Antarctic Ice Sheet and the Western Ross Sea,where most current ice streams and outlet glaciers arise.We investigated Ricker Hills,the largest exposed mountainous region between Southern Victoria Land and Terra Nova Bay,and dated the glacial landforms using in-situ cosmogenic-nuclide 10 Be surface exposure dating to reconstruct the paleo-glacial dynamics.The surface of the Hollingsworth glacier lowered since the middle of Marine Isotope Stage(MIS)2(22.1 ka);therefore,the Last Glacial Maximum(LGM)occurred before that period.Cosmogenic,geomorphic,and climatic records constrained the glacial surface slope to be between 5.4°and 6.8°.The ice was 270-320 m thicker at the LGM(MIS 2)than presently but did not override the top surface of the Benson Knob.Moreover,previous glacial periods such as the local LGM(MIS 4)or Penultimate Glacial Maximum(MIS 6)maintained thicker ice than the LGM(MIS 2).The Ross Ice Shelf opening during the mid-Holocene(~6 ka)caused the rapid collapse of the terminal outlet glaciers and supplied notable snow accumulation upstream,which stagnated lowering.The greatest lowering and retreat occurred during the late Holocene(2.3~0.8 ka),when elephant seal colonies thrived in the Ross Embayment.

10Be exposure ages of Quaternary Glaciers in Antarctica

In situ terrestrial cosmogenic nuclide(TCN)has been widely applied to date the ages of Quaternary glacial deposits in Antarctica and plays an important role in reconstructing the glacial evolution and climate change.It helps to under‐stand the Antarctic ice sheet's evolution process in Quaternary and shed light on the application of Cosmogenic Nu‐clide exposure dating technique in Glacial Geomorphology.In this paper,we retrieved 49510Be age samples in Ant‐arctica from literature published between 2004 and 2020 and recalculated the TCN ages using version 3.0 online cal‐culator of Cosmic-Ray Produced Nuclide Systematics on Earth(CRONUS-Earth).Several conclusions can be drawn from the results:(1)75%of the exposure ages are younger than 400 ka,and 91%younger than 1,100 ka.Northern Antarctic Peninsula exposure result is visibly younger than the main glaciers in East Antarctica due to climate change and geological evaluation since the LGM(Last Glacial Maximum).(2)TCN ages are relevant to the samples'relative positions in the Antarctic continent,but a relationship between their ages and elevations is yet to be determined based on the collected data.

Exposure ages and radiogenic ages of ureilite(GRV 024516) and ordinary chondrite(GRV 024517) from Antarctica

The GRV 024516 and GRV 024517 meteorite samples collected from Grove Montains,Antactica are ureilite and H5 ordinary chondrite,respectively.Based on the study of mineralogy-petrology,the cosmic-ray exposure ages and gas retention ages of these two meteorites were determinated and calculated.Their cosmic-ray exposure ages are 33.3 Ma,51.7 Ma,and gas retention ages are 1936.8 Ma and 3720 Ma,respectively.The ureilite contains diamond,graphite and amorphous C,which are mainly carrier of noble gases indicating obviously shock metamorphism effects,which induced 40Ar partial loss.The H5 chondrite indicates thermal metamorphism of parent body,its gas retention age fall the range between 3220 Ma and 4510 Ma of the least shocked H5 chondrites.

COSMOGENIC^(10)Be,NOBLE GASES AND IRRADIATION HISTORY OF CHONDRITES ZHAODONG,NAN YANG PAO,LUNAN AND ZAOYANG

10Be is mainly produced in meteorite by spallation reactions of cosmic ray particles with oxygen, magnesium, silicon or nitrogen in it. The threshold energy is above 500 MeV. The half lifetime of 10Be in between 26Al and 53Mn is 1.6 Ma. Thus the possibility of routine determination of 10Be in a large number of meteorites constitutes an improvement in studying the exposure conditions of