SSP3.2 | Limnogeology - reading the geological record of lakes
EDI

Sedimentary systems are excellent archives of past environmental change across the globe and have contributed significantly to our understanding of the planetary system. The increasing number of available short and long (ICDP) sediment cores, along with seismic and bathymetric data, continues to be pivotal for assessing climate and environmental change, human activities as well as tectonic and volcanic activity, amongst others.

We invite contributions that use sedimentological, geochemical, biological, and chronological tools in lakes and their sedimentary archives to deduce quantitative and spatial rates of change, causes and consequences of long- and short-term climate variability, impact, magnitude, and frequency of tectonic and volcanic activity. We particularly encourage submissions about novel analytical approaches (destructive and non-destructive) and data analysis (statistics, machine learning, AI) that guide future research directions in limnogeology.

Public information:

Join our virtual limnogeology networking event after the oral session (Monday, April 24 at 12:30 Vienna time:

Search for the event here ("Virtual Beer & Networking SSP3.2 Limnogeology - reading the geological record of lakes"): https://webforms.copernicus.org/EGU23/pop-up-networking-events - you will see the zoom link when you're logged in to the EGU system.

Co-sponsored by IAS
Convener: Marina MorlockECSECS | Co-conveners: Marta Marchegiano, Stefano C. FabbriECSECS, Yin Lu
Orals
| Mon, 24 Apr, 10:45–12:25 (CEST)
 
Room -2.31
Posters on site
| Attendance Mon, 24 Apr, 16:15–18:00 (CEST)
 
Hall X3
Posters virtual
| Attendance Mon, 24 Apr, 16:15–18:00 (CEST)
 
vHall SSP/GM
Orals |
Mon, 10:45
Mon, 16:15
Mon, 16:15

Join our virtual limnogeology networking event after the oral session (Monday, April 24 at 12:30 Vienna time:

Search for the event here ("Virtual Beer & Networking SSP3.2 Limnogeology - reading the geological record of lakes"): https://webforms.copernicus.org/EGU23/pop-up-networking-events - you will see the zoom link when you're logged in to the EGU system.

Orals: Mon, 24 Apr | Room -2.31

Chairpersons: Marta Marchegiano, Marina Morlock
Paleohazards
10:45–10:55
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EGU23-16228
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SSP3.2
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ECS
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solicited
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On-site presentation
William Rapuc, Bruno Wilhelm, Benjamin Amann, Flavio S. Anselmetti, Fabien Arnaud, Juliette Blanchet, Achim Brauer, Markus Czymzik, Charline Giguet-Covex, Adrian Gilli, Lukas Glur, Martin Grosjean, Ralf Irmler, Marie Nicolle, Pierre Sabatier, Tina Swierczynski, and Stefanie B. Wirth

Flooding is a ubiquitous natural hazard, and climate change is likely to exacerbate the risks worldwide. Mountainous areas, such as the densely populated Alps, are of particular concern because topography and atmospheric conditions can lead to large, flash floods, and because they are experiencing a high rate of warming, which will likely result in more intense precipitation events.

In his latest publication, Bruno Wilhelm and his colleagues have compiled 33 paleoflood records to test the impact that these climate trends might have on the frequency and magnitude of floods in the Alps. The paleoflood records are derived from lake sediments, the only archive that guarantees continuity of records over long periods of time. The dataset passed a selection procedure of hydrological, sedimentary and geochronological controls, resulting in a final selection of 27 records that continuously cover the last 150 to 10,000 years, documenting a total of 7,792 floods. We perform three analyses with this dataset:

(i) analogous to modern projections that assess changes in climate variables between current and warmer future conditions, we determine changes in the occurrence of large (≥10 year) floods between cooler and warmer past subperiods.

(ii) following trend analysis techniques using modern streamflow data, we analyze trends in the occurrence of large (≥10-year) floods during warmer or cooler periods.

(iii) we replicate the first analysis by considering the occurrence of extreme floods (≥100 years) between colder and warmer past subperiods.

From these analyses, we show that a warming of +0.5-1.2°C led to a 25-50% decrease in the frequency of large floods (return period ≥10 years). This downward trend is not observed in records spanning less than 200 years (i.e., the maximum period of the instrumental series), but it is persistent in those ranging from 200 to 9000 years. In contrast, extreme floods (return period > 100 years) may increase with a similar degree of warming in some small Alpine catchments. This may result from a local intensification of extreme precipitation with higher temperature. The latest results of Bruno and his colleagues show how long and continuous paleoflood records can be used to unravel the complex relationships between climate and flooding.

How to cite: Rapuc, W., Wilhelm, B., Amann, B., Anselmetti, F. S., Arnaud, F., Blanchet, J., Brauer, A., Czymzik, M., Giguet-Covex, C., Gilli, A., Glur, L., Grosjean, M., Irmler, R., Nicolle, M., Sabatier, P., Swierczynski, T., and Wirth, S. B.: In Memory of Bruno Wilhelm: Impact of warmer climate periods on flood hazard in the European Alps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16228, https://doi.org/10.5194/egusphere-egu23-16228, 2023.

10:55–11:05
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EGU23-16653
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SSP3.2
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On-site presentation
Fabien Arnaud, Pierre Sabatier, Jérôme Poulenard, Charline Giguet-Covex, Jean-Philippe Jenny, Erwan Messager, Jean-Jacques Delannoy, Emmanuel Malet, Cécile Pignol, Françoise Allignol, and Bruno Wilhelm

On April 7th 2022 we learnt the devastating news: our friend and colleague, Bruno Wilhelm, had passed in the mountain while ascending a steep slope in the aim of skiing it. One year after, our group, within which he came and grow to science up to the defence of his PhD thesis in 2012, is still graving. In that context, we are grateful to the organisers of this session for offering us the opportunity of reminding our scientific community the multiple advancements it owes to Bruno.

Bruno Wilhelm indeed did a hard and innovative work in the aim of reading the geological record of lakes. He focused himself on the recording of extreme events in lake sediments. In this keynote, we will emphasize how Bruno proposed original ways of characterising what we call “instant deposits”, mostly in the early stages of his too short career. He then particularly worked the question of distinguishing among triggering factors of those “alien” layers that often interbed within lake sediment calm sedimentation. Bruno also proposed a detailed reflexion aiming at quantifying or, at least, ranking the intensity of those triggering events. He hence proposed several ways of assessing past floods intensity. In the same spirit, he explicitly proposed a procedure to assess the “recordability” of past earthquake events within a given lake system, based on historical chronicles. He also led a common reflexion about the ability of lake sediment to record a regional flood signal. After his PhD he committed himself in the scientific animation of the PAGES’ “Floods” working group which led him to coordinate the establishment of a comprehensive database and to participate in the redefinition of a collaborative work to better understand past flood patterns in the iam of anticipating future changes due to global warming.

It is undeniable that Bruno Wilhelm had a brilliant and far too short career. However, with this speech we hope that the community will be even more aware about the important legacy he left us.

How to cite: Arnaud, F., Sabatier, P., Poulenard, J., Giguet-Covex, C., Jenny, J.-P., Messager, E., Delannoy, J.-J., Malet, E., Pignol, C., Allignol, F., and Wilhelm, B.: A tribute to Bruno Wilhelm’s legacy in reading the geological record of lakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16653, https://doi.org/10.5194/egusphere-egu23-16653, 2023.

11:05–11:15
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EGU23-6005
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SSP3.2
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On-site presentation
Stéphanie Girardclos, Renaldo Gastineau, Katrina Kremer, and Flavio S. Anselmetti

Mass transport deposits (MTDs) are common features in lakes that impose a significant natural hazard as they can be tsunamigenic (e.g., in Lake Geneva; Kremer et al., 2012). MTDs can be assigned to different categories, such as lateral-slope landslides, margin collapses, delta collapses and rockfalls (Sammartini et al., 2019). In 1996 AD, a MTD occurred in Lake Brienz, a 260 m deep Alpine lake at the frontal range of the Bernese Swiss Alps. The 1996 MTD extends over ∼8.5 km2 and has a total volume of 2.7 106 m3, which amounts to ∼8.7 years of the lake’s annual sediment input. The 1996 MTD had no specific trigger and occurred as a spontaneous failure due to sediment accumulation on the Aare Delta (Girardclos et al., 2007).

However, the 1996 delta collapse was not a unique event: a dense grid of 240 km of seismic lines reveals at least four older massive MTDs in the lake basin with similar dimensions. Our study aims to identify the ages and the processes behind these large deposits. For this purpose, we focus on long sediment cores with a cumulative length of about 40 m from four coring locations. A combined analysis of seismic profiles and sediment cores, coupled with an age model combining radionuclides, radiocarbon, coal and steamboat slag, and historical flood events, allows us to explore the feedback between climate and anthropogenic impact acting upon these MTDs. The MTDs are analysed regarding their source areas, either the Aare or the Lütschine deltas, both occurring at the opposite ends of the elongated lake basin. Moreover, we investigate whether earthquakes, spontaneous failures or a shift of the Lütschine River could act as potential triggers, as well as the role of sediment loading in the deltas related to climate changes or anthropogenic impacts in the watershed. Altogether, these factors have likely affected the recurrence rates of these significant sedimentological events.

 

References:

Girardclos, S., Schmidt, O.T., Sturm, M., Ariztegui, D., Pugin, A., Anselmetti, F.S., 2007. The 1996 AD delta collapse and large turbidite in Lake Brienz. Mar. Geol. 241, 137–154. https://doi.org/10.1016/j.margeo.2007.03.011

Kremer, K., Simpson, G., Girardclos, S., 2012. Giant Lake Geneva tsunami in AD 563. Nat. Geosci. 5, 756–757. https://doi.org/10.1038/ngeo1618

Sammartini, M., Moernaut, J., Anselmetti, F.S., Hilbe, M., Lindhorst, K., Praet, N., Strasser, M., 2019. An atlas of mass-transport deposits in lakes. Submar. Landslides Subaqueous Mass Transp. Depos. Outcrops Seism. Profiles 201–226. https://doi.org/10.1002/9781119500513.ch13 

How to cite: Girardclos, S., Gastineau, R., Kremer, K., and Anselmetti, F. S.: What are the causes of repeated mass-transport deposits in perialpine Lake Brienz (Switzerland)?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6005, https://doi.org/10.5194/egusphere-egu23-6005, 2023.

11:15–11:25
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EGU23-3825
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SSP3.2
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ECS
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Highlight
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Virtual presentation
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Zhicong Huang, Xingqi Liu, and Yin Lu

The 1500-km-long Kunlun strike-slip fault is one of the largest and most active faults in the Tibetan Plateau. The eastward extrusion of Tibet has generated the 2001 Mw 7.8 Kunlunshan earthquake along the eastern Kunlun fault (elevation ≥ 4500 m) that produced the longest surface rupture yet recorded on land, ~400 km. The knowledge of past earthquake history and long-term fault behavior along the eastern Kunlun fault is still limited by short seismological records. Moreover, suitable sites for paleoseismological trenching are rarely available due to the active freeze-thaw action in such an extreme environment. Lacustrine paleoseismology, exploits lacustrine sediments to retrieve a much longer record of paleoseismic shaking, may shed light on earthquake occurrence and fault behavior along the eastern Kunlun fault.

Lake Kusai is bounded by the eastern Kunlun fault in the north, and its north end was once ruptured by the 2001 Mw 7.8 Kunlunshan earthquake. Sedimentary sequence from the lake is characterized by layered sediments, thus an ideal site for lacustrine paleoseismology investigation. A 8.2 m-long core has been drilled from the lake in 2006. 210Pb/137Cs and AMS14C dating, and detailed varve counting confirm that the upper 165 cm of the drilled sedimentary sequence is varved and spans the last 2000 years. This sedimentary sequence is therefore ideal for event deposits recognition and high-resolution seismic record reconstruction. We identify sedimentary imprint of the 2001 Mw 7.8 earthquake and another 13 deeper horizons of in situ soft sediment deformations and micro-faults from the sedimentary sequence. The primary data reveals a clustered earthquake recurrence pattern with a mean recurrence interval of ~150 years on the central part of the eastern Kunlun fault.

 

Keywords: Eastern Kunlun fault; Northern Tibetan Plateau; Lake Kusai; Varved lake sediment; Soft sediment deformation structure; Paleoseismic events.

How to cite: Huang, Z., Liu, X., and Lu, Y.: Paleoseismic events inferred from soft sediment deformation structure of varved lake sediment in Lake Kusai of northern Tibetan Plateau during the past 2000 years, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3825, https://doi.org/10.5194/egusphere-egu23-3825, 2023.

Quaternary limnogeology
11:25–11:35
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EGU23-17373
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SSP3.2
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ECS
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Virtual presentation
Yongtao Zhao, Yunfa Miao, Xin Jia, Yuan Li, Haiming Li, Weimiao Dong, Jiaju Zhao, Xuelian Wang, Xianyong Cao, and Chengbang An

To distinguish how climatic and human factors influence Holocene fire dynamics in arid, westerlies-dominated areas of Central Asia, we examined micro-charcoal and pollen records in well-dated sediment cores from Balikun lake, eastern Tianshan region, Central Asia. Our results show that vegetation biomass primarily controlled the suborbital-time-scale fire dynamics, with an increasing trend of fire intensity from the early to late Holocene. Evidence for substantial anthropogenic influence on fires is mainly related to the expansion of prehistoric agriculture during ~3.6-2.2 cal kyr BP in our study area. These human activities caused a departure from “natural” background fire levels that vary with climate change.

In contrast, the human-linked fire peak in the nearby Hexi Corridor, which lies in Asian summer monsoon dominated regions of eastern China, occurred before ~3.6 cal kyr BP. This may reflect differences in the timing and sequence of cultural development under regions dominated by different circulation patterns. The weakening of the Asian summer monsoon after ~3.6 cal kyr BP likely promoted the Hexi Corridor population to migrate to eastern Tianshan, as evidenced by the similar pottery from eastern Tianshan to those of the Siba culture (4.0-3.5 cal kyr BP) that originated from the Hexi Corridor. This migration facilitated the formation of the westward cultural exchange route known as the “Painted Pottery Road”, enhancing regional human activity and causing an increase of fires in eastern Tianshan.

How to cite: Zhao, Y., Miao, Y., Jia, X., Li, Y., Li, H., Dong, W., Zhao, J., Wang, X., Cao, X., and An, C.: Holocene fire-vegetation history and its relationship with climate and human activity revealed by lake sediments from eastern Tianshan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17373, https://doi.org/10.5194/egusphere-egu23-17373, 2023.

11:35–11:45
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EGU23-1756
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SSP3.2
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Highlight
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On-site presentation
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Reinhard Pienitz and Olivier Jacques

The impacts of asbestos mining activities and wastes on aquatic ecosystems are generally assumed to be minimal, yet have been poorly studied. To evaluate their importance, we analyzed several sediment cores collected in the Bécancour River Basin, notably in 4 fluvial lakes located downstream from Thetford Mines (Quebec, Canada): Stater Pond, Trout Lake, Lake William, and Lake Joseph. This region has been the center of more than a century of asbestos mining activities (1877–2011 CE), which resulted in the accumulation of huge piles of wastes (tailings and waste rock) on riverbanks. Age-depth models, primarily derived from radiometric dating (137Cs, 210Pb, 14C), revealed extreme increases in sediment accumulation rates in Stater Pond and lakes Trout and William, corresponding with the 1955–1959 CE drainage and excavation of an upstream lake for mining purposes. This event also corresponded with their strong eutrophication, as revealed by sudden changes in diatom assemblage composition (e.g., proliferation of Cyclostephanos invisitatus/makarovae, Cyclotella meneghiniana). ICP-MS/ICP-AES analyses revealed that post-1960 sediments at Stater Pond and lakes Trout and William, which maintained very high accumulation rates, were distinctively enriched in magnesium, chromium, and nickel. This provided evidence that they are contaminated by asbestos mining wastes, hence that the piles on the riverbanks are exposed to heavy erosion. Analyses by transmission electron microscopy demonstrated that post-1960 sediments contain important asbestos fiber concentrations (up to 6.9 wt%). Evidence of asbestos mining contamination has also been found in Lake Joseph, which showed that it spreads over ≥ 25 km in the Bécancour River system. We conclude that asbestos mining activities and wastes are susceptible to cause high sediment loads, as well as metal and fiber contamination in aquatic ecosystems (among other undesirable effects). Therefore, more efforts should be invested in the restoration of such mining sites and in controlling pollution they cause.

How to cite: Pienitz, R. and Jacques, O.: Impacts of asbestos mining activities on lake ecosystems: insights from a multi-proxy paleolimnological investigation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1756, https://doi.org/10.5194/egusphere-egu23-1756, 2023.

11:45–11:55
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EGU23-10214
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SSP3.2
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ECS
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On-site presentation
Léo Chassiot, Patrick Lajeunesse, François-Xavier L'Heureux-Houde, Ariane Frigon, Kai-Frederik Lenz, Catalina Gebhardt, and Pierre Francus

Manicouagan, the ‘Eye of Québec’, is an annular-shaped impact structure located in northeastern Canada (51˚N). The completion of a large hydroelectric dam in 1970 CE flooded two 60-km long lakes that were located on east and west sides of the inner ring. The drowning of the lakes under 135 m of water marked the final stage of the Late Quaternary history of Manicouagan. The morpho-sedimentary record combining sismo-acoustic imagery, swath bathymetry, and sediment cores aims to (1) reconstruct the Late Quaternary history of Manicouagan; and (2) assess the impacts of damming, in this case the drowning of a large boreal lake that used to be an indigenous cultural habitat. At the eastern end, the flooded Lake Manicouagan, has a fjord-like setting characterized by a shelf representing the lowest lake-level, steep walls > 45˚, and deep environments. The glacial-postglacial evolution, linked to the northward retreat of the Laurentian Ice Sheet, is preserved in overdeepened basins reaching 455 m deep, that is 105 m below modern sea-level. To the north, these basins are buried under a postglacial drape resulting from strong river inputs. Downstream, sedimentary units build channel-and-levee systems along a deep canyon. At mid-lake, a sill connects to southern basins displaying a hummocky topography. Postglacial conditions are characterized by a lake-wide record of gravity events originating from the shelf and above. Core-scanning techniques along with dating information (14C, 210Pb, 137Cs) on a transect of short-cores highlight the role of natural and human-induced water-level fluctuations on the generation of slope hazards. Ongoing analyses expect to (1) precise the nature, timing, extent and impacts of natural and man-made hazards; (2) reconstruct environment-climate evolution from a remote boreal region where limnogeological records are scarce.

How to cite: Chassiot, L., Lajeunesse, P., L'Heureux-Houde, F.-X., Frigon, A., Lenz, K.-F., Gebhardt, C., and Francus, P.: The morpho-sedimentary record of impact crater Lake Manicouagan in northeastern Canada, from an overdeepened valley to a large hydroelectric reservoir, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10214, https://doi.org/10.5194/egusphere-egu23-10214, 2023.

Beyond the Quaternary
11:55–12:05
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EGU23-17424
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SSP3.2
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solicited
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Highlight
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Virtual presentation
Yunfa Miao, Xiaomin Fang, Jimin Sun, Wenjiao Xiao, Yongheng Yang, Xuelian Wang, Alex Farnsworth, Kangyou Huang, Yulong Ren, Fuli Wu, Qingqing Qiao, Weilin Zhang, Qingquan Meng, Xiaoli Yan, Zhuo Zheng, Chunhui Song, and Torsten Utescher

The Tibet Plateau is the world’s highest inhabited terrain, with an area >2.5×106 km2 and an average elevation >4000 m asl. Its uplift has been regarded as the main factor driving the evolution of the Asian monsoon regime and alpine biodiversity. The Miocene epoch is now deemed critical for understanding the timing of the attainment of the highest paleoelevation of the Tibet Plateau, the development of the modern Asia monsoon regime, and the acceleration of the evolution of alpine biodiversity. However, the northern Tibet Plateau remains poorly investigated.

Tsuga, Podocarpus, Abies, and Picea are four typical montane conifer genera. Although influenced by factors such as precipitation, geographical location, and soil properties, these taxa have elevation-specific habitats in Asia: Tsuga and Podocarpus usually grow at middle elevations (300 to 3500 and 600 to 2000 m asl, respectively) whereas Abies and Picea grow at higher elevations (500 to 4700 and 300 to 4700 m asl, respectively). Therefore, the representation of these genera in pollen assemblages can be used to reconstruct paleoelevation.

We tested new pollen analysis from Miocene sedimentary sequences of Huaitoutala section, and compiled them with other three sites (Core Sino-German-1, Core KC-1, and Yahu section in the Qaidam Basin (paleo-Qaidam Lake), northern Tibet Plateau. We selected these pollen records of Tsuga, Podocarpus, Abies, and Picea to build a new paleoaltimetry to construct two parallel midrange paleoelevation sequences in the northern Tibet Plateau at 1332 ± 189 m and 433 ± 189 m, respectively, during the Middle Miocene (~15 Ma). They increased rapidly to 3685±87 m in the Late Miocene (~11 Ma) in the east, and to 3589±62 m at ~7 Ma in the west. Our estimated rises in the east and west parts of the northern Tibet Plateau during 15-7 Ma, together with data from other Tibet Plateau regions, indicate that during the Late Miocene the entire plateau may have reached a high elevation close to that of today, with consequent impacts on atmospheric precipitation and alpine biodiversity.

How to cite: Miao, Y., Fang, X., Sun, J., Xiao, W., Yang, Y., Wang, X., Farnsworth, A., Huang, K., Ren, Y., Wu, F., Qiao, Q., Zhang, W., Meng, Q., Yan, X., Zheng, Z., Song, C., and Utescher, T.: A new biologic paleoaltimetry applied to the paleo-Qaidam Lake sedimentary sequences indicating Late Miocene rapid uplift of northern Tibet Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17424, https://doi.org/10.5194/egusphere-egu23-17424, 2023.

12:05–12:15
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EGU23-17355
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SSP3.2
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ECS
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Virtual presentation
Yudong Liu, Yibo Yang, Xiaomin Fang, and Bowen Song

Drainage evolution and source-to-sink history across the Tibetan plateau and the surroundings as the consequence of changes in landscape and climate, provide a window to understand the growth of the Tibetan Plateau and its environmental impacts. Previous studies focus mostly on the reconstruction of siliciclastic sediment, but less on the dissolved load that displays distinct transport dynamics. Here we provide a solute perspective for deciphering source-to-sink history in NE Tibet through the carbonate 87Sr/86Sr ratio. The modern observations around NE Tibet exhibit a remarkable contrast of the solute Sr isotopic regime. That is, the Qilian Shan supplies high 87Sr/86Sr ratios caused by the exhumation of high-grade metamorphic rocks, while the East Kunlun Shan and West Qinling provide low 87Sr/86Sr ratios.

Here, we reconstruct solute Sr evolution of basin paleowater using bulk carbonate from parallel lacustrine and fluvial sections in the Qaidam, Lanzhou, and Xining Basins, NE Tibet. In the Qaidam Basin, solute 87Sr/86Sr ratios of the paleo-Qaidam Lake and fluvial sediments remain constant at ~0.713 in most Cenozoic periods, indicating that the solute Sr sourced solely from the Qilian Shan. But two low 87Sr/86Sr ratio periods at ~44.5 - ~32 Ma and after ~16 Ma might be caused by hydrological connections between the northern source (Qilian Shan) and the southern source (dominantly from East Kunlun Shan) in the Paleogene western basin and Neogene eastern basin, respectively. The two time periods correspond to two stages of the paleo-Qaidam Lake that developed following a south-eastward migration of basin depocenter due to the tectonic evolution of the surrounding mountains.

In the Lanzhou and Xining Basins, 87Sr/86Sr ratios of the paleo-Longzhong Lake and fluvial sediments maintained similarly low values and turned into an increase after ~32 Ma, reflecting an elevated proportion of solute supply from high 87Sr/86Sr source area, i.e., Qilian material input. A diverse evolution of solute 87Sr/86Sr ratio in the Lanzhou and Xining Basins after ca. 25-23 Ma, suggests that there was a drainage reorganization in response to the growth of NE Tibet. Our study implies that radiogenic Sr is a useful proxy for tracing drainage adjustment in response to large-scale tectonics.

How to cite: Liu, Y., Yang, Y., Fang, X., and Song, B.: Deciphering drainage reorganization in the NE Tibet: Insights from 50 Ma-long solute Sr isotopic records of Cenozoic lacustrine-fluvial sequences, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17355, https://doi.org/10.5194/egusphere-egu23-17355, 2023.

12:15–12:25
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EGU23-17427
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SSP3.2
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ECS
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Virtual presentation
Chengcheng Ye, yibo Yang, Xiaomin Fang, Weilin Zhang, Zengguang Guo, and Yudong Liu

The thick and continuous lacustrine-fluvial sediments in the Qaidam Basin (paleo-Qaidam Lake), NE Tibetan Plateau, serve as excellent archives to reconstruct the Asian inland climate evolution history and explore the driven factors involving Tibetan Plateau uplift, Paratethys retreat, and global climate change. However, the debated elevation history of the Tibetan Plateau and the overlapping climate effects of the Tibetan Plateau uplift and Paratethys retreat makes it difficult to assess the driving mechanism on regional climate change in a particular period. Fortunately, some recent progress suggests that precisely dated Paratethys transgression/regression cycles appear to have fluctuated over broad regions with low relief in the northern Tibetan Plateau before 26 Ma, when the global climate was characterized by generally continuous cooling, thus offering an opportunity to distinguish between the climatic effects of the Paratethys retreat and those of global cooling.

Here, we present detailed mineralogical and geochemical investigations of clay minerals collected from the Hongliugou section, northern Qaidam Basin, to reconstruct paleolake salinity variation and basin weathering history in the Paleogene (~54-26 Ma), aiming to obtain a complete regional climate change record and its controlling factors. The paleolake salinity, indicated by two clay-fraction paleosalimeters, equivalent boron and Couch’s salinity, collectively present a long-term lake salinization, from slightly mesohalobic environment (averaging ~4.4‰) in middle Eocene (42-~34 Ma) to mesohalobic/polysaline environment (averaging ~8.3‰) in late Eocene-early Oligocene (~34-~29 Ma). Regarding regional weathering history, the clay mineral assemblage, the clay-fraction geochemistry index (e.g., CIA and Mg/Al ratios) and monomineral indices involving illite chemistry index, beidellite content and chlorite chemistry index and Mg/Al ratios collectively suggest a long-term decreasing trend in 54-26 Ma. The history of both paleolake hydrological evolution (salinity) and basin weathering matches well with the global climate change as indicated by benthic oxygen isotope. We thus reasonably speculate that the secular trend of regional climate change is primarily controlled by global cooling, which regulates regional climate change by influencing the evaporation capacity in the moisture source of Qaidam Basin and the westerly wind strength. Superimposed on this trend, the Paratethys transgression/regression cycles served as an important factor regulating wet/dry fluctuations in the Asian interior.

How to cite: Ye, C., Yang, Y., Fang, X., Zhang, W., Guo, Z., and Liu, Y.: Global cooling controls Paleogene (54-26 Ma) paleolake hydrological evolution and regional chemical weathering processes in the Qaidam Basin, NE Tibet, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17427, https://doi.org/10.5194/egusphere-egu23-17427, 2023.

Posters on site: Mon, 24 Apr, 16:15–18:00 | Hall X3

Chairpersons: Marta Marchegiano, Marina Morlock
X3.68
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EGU23-4959
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SSP3.2
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Kuan-Yi Hsu and Ludvig Löwemark

    Monsoon rainfall in East Asia is a subsystem of the global monsoon system and affects nearly one-quarter of the world's population. Taiwan, an island in the subtropical East Asian monsoon system, provides the unique opportunity to study monsoon and typhoon variability over the western subtropical Pacific on both historical and geological time scales. However, the Holocene paleoclimate records retrieved from various lakes in Taiwan have shown discrepancies in their recorded climate variability. This could partly be caused by the lack of modern sedimentological observations, limiting our understanding of the mechanisms controlling lake sedimentation and thus introducing uncertainty in the interpretation of lake records. To understand the paleoclimate records archived in lacustrine sediments, a robust age model is essential. The aim of this study is to understand the complex processes that led to the formation of a small wetland (24°30' N, 121°35' E, 2095 meters above sea level), which is located in the Taiping Mountains, Yilan County, NE Taiwan.

    In this study, we use several cores from different parts of the wetland, including wooded swamps, fens, and the open pond, to construct a robust model for lake formation and succession. However, cores from different parts of the wetland display puzzling differences in both maximum ages and sedimentation rates. Moreover, one core displays a major age reversal. Multiple radiocarbon dates corroborate that this reversal is not a sampling or analytical artifact but actually reflects an inversion of the sediment sequence. Possible hypotheses explaining this age reversal include typhoons, landslides, and overturned floating fens. Examples from other mountain lakes in Taiwan demonstrate that floating islands consisting of a mixture of aquatic plants, bryophytes, helophytes, and sediment can move hundreds of meters during typhoons. If a floating island is blown by typhoon winds, it may become turned upside down, resulting in an inverse age sequence.

How to cite: Hsu, K.-Y. and Löwemark, L.: Radiocarbon constraints on lake succession and sedimentation processes in a small mountainous lake in NE Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4959, https://doi.org/10.5194/egusphere-egu23-4959, 2023.

X3.69
|
EGU23-14489
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SSP3.2
|
ECS
Kamill Lisson, Maarten Van Daele, Laurenz Schröer, and Veerle Cnudde

X-ray computed microtomography (μCT) is a non-destructive 3D imaging and analysis technique that is increasingly used in geosciences, including the analysis of grains, pores, structures, fluid flow and morphological features. In Quaternary sedimentology, particularly in disciplines that study unconsolidated sediment cores from (glacio)lacustrine environments, μCT scanning of smaller subsamples is proving to be a valuable integration tool to the traditional thin section micromorphology, as it allows visualisation of internal 3D sediment composition, texture and structure at high resolution. We created an integrated methodology of μCT and thin section analysis by developing a 3D-printed subsampler that can effectively (1) extract areas of interest from soft sediment cores, (2) stabilise the unconsolidated “wet” sediment during μCT scanning and (3) allow dehydration and impregnation to be carried out while the sample is in the subsampler, which ensures an undisturbed sample for thin section preparation.

Here we apply our new methodological approach on sediment cores from Alaskan, Chilean and Swiss lakes. Medical X-ray CT scans of sediment cores from these lakes have proven to be valuable for studying seismically, volcanically and climatically induced event deposits. However, higher resolution μCT data with a voxel size of 5 μm is required to isolate individual grains larger than medium silt to determine their grain size, shape and orientation. Subsamples (8.0 x 1.5 x 1.5 cm) of different types of event deposits (turbidites, lahars and avalanches) were extracted from the sediment cores, scanned at the Centre for X-ray Tomography (UGCT, Ghent University) and thin sections were prepared. μCT scanning of the “wet” sediment subsamples allowed 3D characterisation of grains and structures of the original sediment microstructure and radiodensity contrast at high resolution, while the thin sections provided additional mineralogical and high resolution structural 2D information. This detailed analysis of the orientations of mud clasts, silt/sand grains and dropstones (in deposits from historical events) will lead to a better understanding of the relationships between paleoflow direction and grain deposition, and thus improve the reconstructions of past natural hazard events in the study areas.

How to cite: Lisson, K., Van Daele, M., Schröer, L., and Cnudde, V.: An integrated methodology of micro-CT and thin-section analysis for paleoflow reconstructions in lacustrine event deposits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14489, https://doi.org/10.5194/egusphere-egu23-14489, 2023.

X3.70
|
EGU23-12096
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SSP3.2
|
ECS
|
Alexandrine N'nanga and Flavio S. Anselmetti

Central Africa experiences desertification hazards mostly due to deforestation in context with climate change and human activities like iron melting and agricultural practices. However, one of the most severe obstacles for sustainable development in Central Africa is the Sahel desertification whose speed of progress is underexplored. Among multiple lines of evidence recorded in geological archives, which suggest its southward progress in Central Cameroon over the Anthropocene epoch, the southward shift of the Intertropical Convergence Zone since 3.6 kyr BP is the most warning signal followed by forest disruption in favor of savannah expansion. This project aims at estimating the speed of the Sahel desertification progress in Central Africa, by quantifying its progress rate in Central Cameroon located between the sahelian zone, to the north, and the equatorial zone, to the south. For this purpose, four lake-sediment cores were collected in four shallow lakes on the Adamawa Plateau. They are investigated for sedimentology, geochemistry, mineralogy, and radiocarbon chronology. The goal of this study is to characterize the sedimentary sequences, pinpoint related environmental change in sediment supply and source area and differentiate relevant paleoclimate indicators of intensification of dry conditions over time. The importance of these centennial to decadal natural trends and variations as well as possible effects of human activities will contribute to a better understanding of the Sahel desertification progress in Central Africa.

How to cite: N'nanga, A. and Anselmetti, F. S.: The southward expansion rate of the desertification in the Adamawa Plateau (Central Cameroon): implication for the speed of the Sahel desertification progress in Central Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12096, https://doi.org/10.5194/egusphere-egu23-12096, 2023.

X3.71
|
EGU23-17339
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SSP3.2
|
ECS
Rebecca Doyle, Marta Marchegiano, Marion Peral, Steven Goderis, Antonio García-Alix, Gonzalo Jiménez-Moreno2, Jon Camuera, Alejandro López-Avilés, and Philippe Claeys

The Eemian (~130 to 115 ka yr BP), also called Marine Isotope Stage (MIS) 5 or the Last Interglacial, was the most recent interglacial period prior to the Holocene. Since temperatures during the Eemian were, on average, ~2 °C warmer than today, studies of this period offer insights into how variables like effective moisture may change under near-future warming scenarios. Such information could improve climate projections for drought-prone regions like the Mediterranean that are particularly vulnerable to future warming. Therefore, a study was initiated to investigate carbonate-rich, Eemian-aged sediments from Padul Wetland (southern Iberia), a site which contains one of the oldest (>200 ka yr) continuous sediment records in the Mediterranean. The resulting proxy record includes stable isotope (δ13C and δ18O) and clumped isotope (Δ47) compositions of aquatic gastropods (e.g., Radix balthica, Anisus spirorbis) and bivalves (e.g., Pisidium sp.). An age-depth model for the entire 200 000-year record was previously established using a mixture of 43 Accelerator Mass Spectrometry (AMS) radiocarbon dates, 10 Amino Acid Racemization (AAR) dates from gastropods (hydrobiid Milesiana schuelei), and two different sediment accumulation rates (SAR) for peat and carbonate/marl lithologies. Variations in δ18O and δ13C closely correspond with the Pollen Climate Index (PCI) for Padul, which is used to discriminate between cold/arid and warm/humid conditions. The close resemblance of these records suggests that variations in δ18O and δ13C at Padul are also sensitive to moisture changes. Variations in δ18O and δ13C of shelly fauna at Padul also resemble shifts in δ18O from the NGRIP ice core(Greenland) and alkenone-based marine sea surface temperature (SST) records of the western Mediterranean region. Similarities among these records underscore the sensitivity of Padul Wetland to regional- and global-scale climatic changes as well as more local moisture variations. One measurement of Δ47 in the aquatic gastropod Radix balthica suggests that average temperatures at Padul during the Eemian were 19.7 ± 2.6 °C, which is consistent with marine records from the Iberian margin. The interpretation of Δ47 in Pisidium sp. is more complicated, perhaps due to vital effects or because Pisidium sp. have highly variable lifespans and individuals that lived only a few months may not reflect average annual conditions. In summary, the stable and clumped isotope records generated in this ongoing study build on previous Eemian-aged reconstructions from southern Iberia by providing higher resolution proxy data constrained by quantitative temperature reconstructions. This research deepens our understanding of how effective moisture in southern Iberia may change in the near future.

How to cite: Doyle, R., Marchegiano, M., Peral, M., Goderis, S., García-Alix, A., Jiménez-Moreno2, G., Camuera, J., López-Avilés, A., and Claeys, P.: A continuous, centennial-scale lake record from southern Iberia captures fluctuations in effective moisture and temperature throughout the EemianMarta, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17339, https://doi.org/10.5194/egusphere-egu23-17339, 2023.

X3.72
|
EGU23-17346
|
SSP3.2
A 7,500-year-long record of extreme wave events from tidal Lake Hamana, south-central Japan
(withdrawn)
Marc De Batist, Evelien Boes, Osamu Fujiwara, Yusuke Yokoyama, Yosuke Miyairi, Masanobu Shishikura, Philipp Kempf, Sabine Schmidt, Atsunori Nakamura, Svenja Riedesel, Helmut Brückner, and Vanessa M.A. Heyvaert and the the QuakeRecNankai team
X3.73
|
EGU23-7196
|
SSP3.2
Jens Kallmeyer, Sulung Nomosatryo, Cynthia Henny, Daniel Lipus, Anja Schleicher, and Rik Tjallingii

Lake Sentani consists of  four interconnected sub-basins with different water depths and water column characteristics, ranging from fully mixed to permanently stratified. Its catchment is comprised of highly diverse lithologies, ranging from mafic and ultramafic rocks to clastic sediment and carbonates, so each sub-basin receives a distinct sediment input. Lake Sentani is also influenced by anthropogenic activity due to the growing population around the lake, potentially leading to local eutrophication. Due to its unique characteristics, we investigated the effects of catchment lithology and water column structure on sediment composition. We also investigated microbial community composition and diversity in surface sediments across Lake Sentani as well as in the partially ephemeral tributary rivers and the river mouths, which form the connection between riverine and the lacustrine habitats.

Using multivariate statistical analyses of mineralogical and major element compositions obtained by X-ray diffraction (XRD) and X-ray Fluorescence (XRF) analyses we could identify three main types of sediment based on distinct compositional differences between rivers, shallow/proximal and deep/distal lake sediments. There is large spatial heterogeneity within the lake’s sub-basins that is mainly caused by catchment geology and topography, river runoff as well as bathymetry and the depth of the oxycline.The different sediment types are mainly characterized by the amounts of organic carbon (TOC) and sulfur as well as elements associated with siliciclastic rocks (Ti, Al, Si, K). Depending on the sedimentary environment, the redox-sensitive elements Fe and Mn change from a positive correlation with siliciclastic elements in river samples to a negative correlation in the lake.

Using 16S rRNA based analyses to investigate microbial community structure and diversity, we detected highly diverse microbial communities across the different lake basins and catchment river sediments, suggesting a wide variety of biogeochemical processes taking place. The molecular biological data broadly agree with the sedimentological differentiation of the sediment into three major groups, but they also provide a different perspective on the biogeochemical processes in the lake. However, our study also suggested increased anthropogenic stressors impacting the microbial community, most probably caused by population growth and urbanization, especially along the northern and northeastern parts. River and river mouth sediments, particularly from these more urbanized areas, were enriched in microbial taxa frequently associated with eutrophication and affiliated with human waste and industrial pollution.Our study highlights the value of multi-disciplinary datasets for a holistic lake management under increasing anthropogenic stress.

How to cite: Kallmeyer, J., Nomosatryo, S., Henny, C., Lipus, D., Schleicher, A., and Tjallingii, R.: Sedimentology and microbiology of Lake Sentani, Papua Province, Indonesia – A multidisciplinary study of a tropical lake system under increasing anthropogenic stress, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7196, https://doi.org/10.5194/egusphere-egu23-7196, 2023.

X3.74
|
EGU23-4848
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SSP3.2
|
ECS
Xinping Liang

There are different mechanisms of reduction water column for the formation and preservation of organic matter during the depositional period of the continental lake basin. Therefore, determining the nature of the water column and its influencing factors is the key factor for differential enrichment of organic matter. In this study, by analyzing the TOC, mineral types, iron speciation, elements and isotopes characteristics of typical freshwater and saline lake organic-rich shales, the water column of synsedimentary environment of different lake shale deposits was compared. Our results show that the organic-rich shale of the Chang 7 Member (Ch7) of Yanchang Formation in the Ordos Basin and the Lucaogou Formation (P2l) in the Jimsar Sag of Junggar Basin in freshwater-saline environments have an intensity of sulfate reduction (BSR) (SRI < 1.375), the shales of Fengcheng Formation (P2f) in saline lake of the Mahu Sag in Junggar Basin have strong BSR (SRI > 1.375). This indicates that in ferruginous conditions the organic matter consumed by BSR is lower than the preserved organic matter, resulting a higher TOC content; in euxinic conditions caused by excessive volcanic activity or the input of hydrothermal fluids, a large amount of organic matter was degraded and consumed, causing more iron oxides (and other iron-containing minerals) dissolve gradually to form pyrite, reducing the TOC content. This study not only enabled to understand the shale oil enrichment, but also proposed a better theoretical and practical model for hydrocarbon accumulation in shale formations, to guide future shale oil exploration efforts.

How to cite: Liang, X.: Differential enrichment mechanism of organic matter under reduction conditions in freshwater and saline lakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4848, https://doi.org/10.5194/egusphere-egu23-4848, 2023.

Posters virtual: Mon, 24 Apr, 16:15–18:00 | vHall SSP/GM

Chairpersons: Yin Lu, Stefano C. Fabbri
vSG.5
|
EGU23-246
|
SSP3.2
|
Nuannuan Ji

The thick-bedded fine-grained sedimentary rock2) of the second member of the Kongdian Formation is a typical lacustrine source rock, and has been considered as the main target of shale oil exploration in recent years. Fine-grained sedimentary rocks have strong heterogeneity and poor plane continuity, which is the basis of shale oil and gas accumulation. Therefore, it is of great significance to strengthen the research on lithology, lithofacies and lithofacies combination of fine-grained sedimentary rocks.

Based on the observation and description of cores from Well G108-8, Well GD12, and Well GD14, combined with analysis of thin sections and X-ray diffraction data, lithofacies of the Ek2 fine-grained sedimentary rocks can be divided into six types, including laminated felsic fine-grained sedimentary facies according to mineral compositions and sedimentary structures, massive felsic fine-grained sedimentary rocks, laminated mixed fine-grained sedimentary rocks, massive mixed fine-grained sedimentary rocks, laminated carbonate fine-grained rocks, and massive carbonate fine-grained sedimentary rocks. Due to the vertical frequent alternation of lithofacies, lithofacies assemblages are proposed to describe the distribution law of the Ek2 fine-grained sedimentary rocks, which can be named felsic lithofacies assemblages, felsic bedded with carbonate lithofacies assemblages, mixed lithofacies assemblages, carbonate bedded with felsic lithofacies assemblages, and carbonate lithofacies assemblages. The mineral compositions, sedimentary structures, and containing lithofacies types show significant differential among these lithofacies assemblages, which can be consisted with the evolution of sedimentary environment.

The method of combining the acoustic travel time (AC) log and density log is established to identify lithofacies assemblages in the study area, which can be used to study the distribution law. Lithofacies assemblages transformed from mixed to felsic bedded with carbonate in the lower part of the Ek21, while from felsic to carbonate in the upper part of the Ek21. From the margin to center of the lacustrine basin, lithofacies assemblages have two trends during the sedimentary period of Ek21. Lithofacies assemblages present felsic, felsic bedded with carbonate, and mixed from the margin to center with the humid climate and strong detrital input. Furthermore, lithofacies assemblages present mixed, carbonate bedded with felsic, and carbonate from the margin to center with the arid climate and weak detrital input.

How to cite: Ji, N.: Lithofacies Combination Characteristics and Distribution Law of Fine-grained Sedimentary Rocks in the Ek2 Member of Cangdong Sag, Bohai Bay Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-246, https://doi.org/10.5194/egusphere-egu23-246, 2023.

vSG.6
|
EGU23-2502
|
SSP3.2
|
ECS
Ge Taoyuan

Jianghan Basin is the largest terrestrial saline lake basin in China, with the largest salinization area in the Paleogene. Research on salt rhythmite formations is crucial for petroleum exploration in salt lake basins. With alternating dry and wet climates, the difference in the organic matter (OM) provenance and enrichment remain controversial. In this study, petrology, element geochemistry, and molecular geochemical analyses were performed for the Qianjiang Formation to determine the depositional environment and provenance of its OM. The response of OM enrichment in the saline lake to the alternating dry and wet climates was reassessed. Three lithofacies associations (LAs) were designated: (1) LA1 was rich in argillaceous dolomite and argillaceous limestone with high total organic carbon (TOC); (2) LA3 was interbedded argillaceous glauberite and argillaceous dolomite with low TOC; (3) LA2 was a mixture of the above minerals with moderate TOC values. LA1 was deposited during desalination with a reducing environment and water stratification. The ∑C21-/∑C22+, C29/C30 hopane and maceral indicate the OM of LA1 derive from algae. Compared with LA1, LA2 was deposited with higher salinity and less algae. LA3 was deposited during intense evaporation, high salinity, and a disturbed environment. The OM sources of LA3 include higher plants and low aquatic organisms. Dry and wet climates control changes in organic enrichment. Hypersalinity is unfavorable to algae but beneficial to preservation. The stratified deep water is conducive to the accumulation of OM. The desalination is a crucial period for organic matter enrichment in the saline lake.

How to cite: Taoyuan, G.: Salt rhythmite formation and organic matter enrichment in the Qianjiang Formation, Jianghan Basin, China: Constraints from alternating dry and wet climates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2502, https://doi.org/10.5194/egusphere-egu23-2502, 2023.

vSG.7
|
EGU23-17150
|
SSP3.2
|
Yibo Yang, Albert Galy, and Xiaomin Fang

Chemical weathering of the continental rocks exerts a dominant force on atmospheric CO2 levels and global climate. How continental weathering works during the Quaternary cooling on glacial-interglacial scales is still poorly understood. Here we reconstructed continental weathering history over the past 800 kyr in a High-Mountain Asia catchment impacted by glaciers. The 87Sr/86Sr ratio of lake water, a proxy of catchment weathering, was lower during interglacials while it was higher during glacials and cold stages of interglacials. This higher level in 87Sr/86Sr ratio is assumed to be caused by a glacier-forced release of radiogenic strontium from reactive minerals.

Conversely, 87Sr/86Sr ratio of weathering solution in the Chinese Loess Plateau, a non-glaciated region, displayed lower values during glacials (loess formation) and higher values during interglacials (paleosol formation), which is modulated by temperature dominance of mineral weathering rate. Such contrasting weathering dynamics in glaciated and non-glaciated regions suggest that 87Sr/86Sr ratios of river water delivered into the ocean would be greatly buffered by the contrasting Sr release regimes within continents. This process may limit seawater 87Sr/86Sr variation within a narrow range on glacial-interglacial time scales and provide a novel indicator for tracing the onset of glacial development during the deep past.

How to cite: Yang, Y., Galy, A., and Fang, X.: Contrasting weathering dynamics within continents during the past glacial cycles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17150, https://doi.org/10.5194/egusphere-egu23-17150, 2023.