SSP2.3

The Anthropocene as a concept originated in 2000, suggested by Paul Crutzen in an Earth System science context. Only later was it considered as a putative geological series, including in GTS2012 (Zalasiewicz et al. 2012). This was barely three years after the establishment of the Anthropocene Working Group (AWG), tasked by the Subcommission on Quaternary Stratigraphy to examine the Anthropocene for potential inclusion in the GTS and to formulate a definition. In GTS2012 a likely generalised stratigraphic signature was postulated to comprise: a) lithostratigraphic signals, both direct modification of the landscape and indirect influences on sedimentary facies through rapidly modifying drivers; b) sequence stratigraphic signals due to modern sea-level rises, envisaging a near-future marine transgression; c) biostratigraphic signals through increased extinction rates, range changes especially through unprecedented rates of species invasions; and d) chemostratigraphic signals including inorganic and organic contaminants, isotopic shifts of carbon and nitrogen and fallout from nuclear bomb testing. By the time of GTS2020 (Zalasiewicz et al. 2020), not only could specific examples of temporal variations in many of these proxies be demonstrated, but also numerous new proxies, such as inorganic crystalline mineral-like compounds, microplastics, fuel ash and black carbon had been demonstrated and more information was available on the scale of human terraforming of landscape and anthropogenic modification of river systems. Further, the intervening eight years had seen a strengthening of the evidence of climate warming, sea-level rise and ocean acidification.

In GTS2012, three levels for the beginning of the Anthropocene were considered: the Early Holocene; the onset of the Industrial Revolution; and the mid-20^th century, and only the first option was definitively excluded. GTS 2020 was able to report the findings of the AWG that the Anthropocene represented “geological reality”, was best considered at epoch level, should be linked with the plethora of proxies that initiate or show marked perturbations at around the 1950s and is best defined using a GSSP. In GTS2020, the ongoing task of researching potential GSSP candidate sections for the Anthropocene Series was also outlined and this work is anticipated to be completed by 2022. The eleven current sites encompass diverse environments that will best preserve the extensive range of proxies suitable for characterising the prospective Holocene–Anthropocene transition. All sections will be in borehole/drill cores, most showing annually resolved laminations that can be independently dated radiometrically to confirm a complete succession extending back to pre-Industrial times. The strengths and weaknesses of distinct environments are discussed in GTS2020 for lake deposits, marine anoxic basins, estuaries and deltas, speleothems, glacial ice, coral reefs, trees and peat. The evidence collected already suggests that the Anthropocene may be widely recognised and delineated as a sharply distinctive chronostratigraphic unit reflecting major Earth System change that will have geologically lasting consequences.

Zalasiewicz, J., Crutzen, P.J. & Steffen, W. 2012. Chapter 32: The Anthropocene. The Geologic Time Scale 2012. https://doi.org/10.1016/B978-0-444-59425-9.00032-9 

Zalasiewicz, J., Waters, C. & Williams, M. 2020. Chapter 31: The Anthropocene. The Geologic Time Scale 2020. https://doi.org/10.1016/B978-0-12-824360-2.00031-0

How to cite: Waters, C. N., Zalasiewicz, J., and Williams, M.: Progress in assessment of the Anthropocene Series in the Geological Time Scale (GTS), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9491, https://doi.org/10.5194/egusphere-egu21-9491, 2021.

The Holocene and Pleistocene series/epochs have each long been divided into Early, Middle and Late subseries/subepochs, although their formalization had been complicated by the hitherto absence of this rank from the International Chronostratigraphic Chart.  On 14th June 2018, the Holocene was formally subdivided into the Greenlandian, Northgrippian and Meghalayan stages/ages and their corresponding Lower/Early, Middle, Upper/Late subseries/subepochs, each defined by a Global Boundary Stratotype Section and Point (GSSP). The GSSP for the lowermost stage, the Greenlandian, is that of the Holocene as previously defined in the NGRIP2 Greenland ice core, and dated at 11,700 yr b2k (before 2000 CE). The GSSP for the Northgrippian is in the NGRIP1 Greenland ice core, and dated at 8236 yr b2k, whereas that for the Meghalayan is located in a speleothem from Mawmluh Cave, Meghalaya, northeast India with a date of 4250 yr b2k (Walker et al., 2018).  The Pleistocene Series/Epoch of the Quaternary System/Period has been divided unofficially into three subseries/subepochs since at least the 1870s.  On 30th January 2020, two proposals were ratified: 1) the Lower Pleistocene Subseries, comprising the Gelasian Stage and the superjacent Calabrian Stage, with a base defined by the GSSP for the Gelasian Stage, the Pleistocene Series, and the Quaternary System, and currently dated at 2.58 Ma; and 2) the term Upper Pleistocene, at the rank of subseries, with a base currently undefined but provisionally dated at ~129 ka.  The Middle Pleistocene and its corresponding Chibanian Stage/Age had meanwhile been formalized on January 17, 2020 with a GSSP in the Chiba section, Japan.  The GSSP is placed 1.1 m below the directional midpoint of the Matuyama–Brunhes Chron boundary, at the base of a regional lithostratigraphic marker, the Ontake-Byakubi-E tephra bed, in the Chiba section. The GSSP has an astronomical age of 774.1 ka and is placed just below the top of Marine Isotope Substage 19c.  These ratifications nominally complete the official division of the Quaternary into subseries/subepochs, although the Upper Pleistocene and its corresponding stage remain to be defined by GSSP.  The Anthropocene is currently an unofficial unit, while analysis of potential candidate GSSP locations is progressing in preparation for a formalization proposal.  If approved, it would terminate the Holocene at around the year 1952, assuming it is defined at series/epoch rank.

Head, M.J., Pillans, B., and Zalasiewicz, J.A., in press. Formal ratification of subseries/subepochs for the Pleistocene Series/Epoch of the Quaternary System/Period. Episodes

Suganuma, Y., Okada, M., Head, M.J., et al., in press. Formal ratification of the Global Boundary Stratotype Section and Point (GSSP) for the Chibanian Stage and Middle Pleistocene Subseries of the Quaternary System: the Chiba Section, Japan.  Episodes

Walker, M., Head, M.J., Berkelhammer, M. et al., 2018.  Formal ratification of the subdivision of the Holocene Series/Epoch (Quaternary System/Period): two new Global Boundary Stratotype Sections and Points (GSSPs) and three new stages/subseries. Episodes 41(4): 213–223. 

How to cite: Head, M. J., Gibbard, P. L., and Zalasiewicz, J.: Subdivision of the Quaternary System: formal subseries and new corresponding stages for the Pleistocene and Holocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6919, https://doi.org/10.5194/egusphere-egu21-6919, 2021.

The palaeoanthropological record of Western Romania is a prime archive of the early modern human presence in Southeastern Europe. Regional stratified early Upper Palaeolithic open-air and karstic sites enable us to infer temporal and spatial patterns of early modern human behaviour in various geomorphological settings. However, open-air sites are often prone to reworking processes caused by local landscape instabilities. The pristine archaeological and palaeoenvironmental stratigraphic evidence is often overprinted by fluvial and slope processes. Therefore, heavily reworked sites are often neglected by researchers. Nevertheless, reworked archaeological and sediment sequences are crucial archives of landscape evolution because they record fluctuations in subsequent erosional and depositional phases. Here, we present the results of a multi-proxy geoarchaeological investigation of the Upper Palaeolithic site of Temereşti Dealu Vinii. This site is located in the Bega Valley, a well-known area for early Upper Palaeolithic open-air localities. Despite the identification of various Upper Palaeolithic cultural units, the artefacts show no discernible horizontal or vertical distribution patterns and stratigraphic inconsistencies. Geochemical and granulometric data aided by luminescence and radiocarbon dating as well as stratigraphic evidence suggest a sub-continuous hydrological sorting over short transport distances during the Holocene. Consistent luminescence ages and characteristics suggest that erosion and deposition occurred sub-continuously during this period. This record of landscape dynamics is consistent with other archives from the area that show evidence for anthropogenically induced phases of soil erosion during the Holocene. This study highlights the importance of reworked archaeological sites such as Temereşti Dealu Vinii not only as viable archives of human presence during the Late Pleistocene – but also as valuable records of subsequent landscape evolution. Detailed analyses of post-depositional disturbances of archaeological sites enable us to improve the accuracy of early modern human behavioural interpretations, and to better contextualise sites such as Temereşti Dealu Vinii within the assemblage of both “in-situ” and reworked loessic Upper Palaeolithic localities in the Danube Basin to evaluate the importance of palaeogeography for human occupation

How to cite: Pötter, S., Chu, W., Nett, J. J., and Schulte, P.: Holocene landscape instability in the context of a loessic early Upper Palaeolithic open-air site in the Middle Danube Basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8634, https://doi.org/10.5194/egusphere-egu21-8634, 2021.

Paleoclimate and vegetation reconstruction of Abric Romani (Capellades, Spain) during MIS-3, 4, and MIS-5 (a-d)

Demet Biltekin^1,2, Francesc Burjachs^1,3,4, Josep Vallverdú^1,4, Warren D. Sharp⁵, Regina Mertz-Kraus⁶, M. Gema Chacón^1,4,  Palmira Saladié^1,4, James L. Bischoff⁵, Eudald Carbonell^1,4

¹Institut Català de Paleoecologia Humana i Evolucio Social (IPHES), Zona Educacional 4, Campus Sescelades URV, edifici W3, 43007 Tarragona, Spain.

²Istanbul Technical University, Eurasia Institute of Earth Sciences, Ayazağa Campus, Maslak, Sarıyer, 34469, Istanbul/Turkey

³ICREA, Barcelona, Catalonia, Spain.

⁴URV, Universitat Rovira i Virgili, Facultat de Lletres, Avinguda Catalunya, 35, 43002 Tarragona, Catalonia, Spain.

⁵Berkeley Geochronology Center, Berkeley, CA 94709, United States.

⁶Institute for Geosciences, Johannes Gutenberg University, Mainz, Germany.

This new pollen data provides the vegetation and climate history during ca. 110 ka-55 ka BP from Abric Romaní archaeological site using pollen analysis of a 30 m-long sedimentary sequence. The beginning of the MIS 3 starts an abundance in steppes and herbs, indicating cold and dry climate in the region. However, this was replaced by a slight increase in deciduous Quercus and Mediterranean trees. During the MIS 4, the pollen records reflect a predominance of Artemisia steppes and herbaceous communities (Poaceae and Asteraceae families), indicating dry and cold conditions in Abric Romaní. The MIS 5 was well recorded with its substages, including 5a, 5b, 5c and 5d. The MIS 5d is characterized by Pinus and Artemisia steppes with herbaceous assemblages. The higher abundance of Artemisia during the second part of the MIS 5b, reflecting cold and dry climate, while temperate forest and Mediterranean trees decline. Mélisey II stadial was marked by an increase in Artemisia and herbs. This suggests that cold climatic conditions existed during this time period. The abundance of oaks during the MIS 5c indicate warmer and humid climate in the region. Other deciduous and broadleaved forest developed as well, including Ulmus, Viburnum, Juglans and Castanea. A short cooling Montaigu event was also recorded within this interstadial, which is dominated by a high percentage of Ericaceae with Artemisia. The first part of the MIS 5a is characterized by Corylus, Carpinus, Hedera, Ulmus, Betula, pointing to warmer climatic conditions. In contrast, the high amount of Artemisia steppes may indicate an enhanced degree of continentality during the second half of the MIS 5a in the north-eastern Iberian Peninsula.

Keywords: paleovegetation, climate, pollen analysis, Late Pleistocene, Spain

How to cite: Biltekin, D., Burjachs, F., Vallverdú, J., Sharp, W. D., Mertz-Kraus, R., Chacón, M. G., Saladié, P., Bischoff, J. L., and Carbonell, E.: Paleoclimate and vegetation reconstruction of Abric Romani (Capellades, Spain) during MIS-3, 4, and MIS-5 (a-d), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3008, https://doi.org/10.5194/egusphere-egu21-3008, 2021.

Isotopic fluctuation of certain stable isotopes, notably Oxygen, provide important information on paleoenvironmental change along geological times. However, interpreting isotopic change along continental series depends on our ability to understand its recording, for instance in soils or in mammal teeth. In the case of continental series yielding most of available information on hominid diversification and expansion within and beyond Africa, isotopic information even seems to show discrepancies depending on the archive. In our study, we use isotopic composition in crocodilian tooth enamel. We assume that, for these ectotherms that regulate their temperature, isotopic composition recorded in their teeth mainly depends on drinking water, itself depending on precipitation. Moreover, crocodilian fossil teeth are abundant and widely distributed within continental series, thus constituting an interesting archive. We sampled crocodilian teeth from the Shungura Formation (Lower Omo Valley, Ethiopia), which spans major steps of human evolution between 3.6 Ma and ~1.0 Ma, tentatively correlated with major environmental changes in eastern Africa (intensification of seasonal contrasts, increasing aridity and landscape opening). The analyses of δ¹⁸O of hundreds of crocodilian teeth have identified environmental changes. Whereas the isotopic composition of paedogenic carbonates displays a different trend over time, that of crocodilian teeth relates changes already observed in mammal teeth, notably a major shift between 2.6 Ma and 2.3 Ma toward more arid conditions. Our study indicates that crocodilian teeth are a relevant archive of environmental change in continental contexts, and calls for further study to strengthen interpretations of isotopic composition in fossil archives. 

How to cite: Gardin, A., Pucéat, E., Garcia, G., Boisserie, J.-R., and Otero, O.: Stable isotope composition of crocodilian teeth provides new information on climatic change in the East-African Rift along the Plio-Pleistocene period (Shungura Formation, Lower Omo Valley Ethiopia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5203, https://doi.org/10.5194/egusphere-egu21-5203, 2021.

It’s nearly forty years ago that ‘A Geologic Time Scale 1982’ appeared (Harland et al. 1982); it was succeeded by major updates in 1989 (Harland et al. 1990), 2004 and 2012 (Gradstein et al. 2004, 2012 – known as GTS2004 and GTS2012, respectively). The primary rationale was “to show as clearly as we can how such a scale has been constructed” (Harland et al. 1982). Each update was about twice the length of the previous version. Consistently aiming to achieve a common language with respect to chronostratigraphic units and geological time, these books have served as state-of-the-art summaries for the entire geological community, both in academia and industry. The last two time scale books contained a discrete and extensive chapter devoted entirely to the stratigraphy of the Paleogene, summarizing information on all stages, established GSSPs, various biozonations and the creation of the time scale  (Luterbacher et al. 2004; Vandenberghe et al. 2012). After a three-year-long preparation GTS2020 was published in November 2020.

All Paleocene and Oligocene stages (Danian, Selandian, Thanetian, resp. Rupelian, and Chattian) have formally ratified definitions and so have the Ypresian, Lutetian, and Priabonian stages of the Eocene. We anticipate that the Global Boundary Stratotype Section and Point (GSSP) for the Bartonian Stage still requires more research before all stages of the Paleogene (66-23 Ma) are formally defined. Paleogene marine microfossil groups (planktonic and larger benthic foraminifera, calcareous nannofossils, radiolarians, organic-walled dinoflagellate cysts) provide robust zonation schemes for regional to global correlation and are integrated within the magneto-biochronological framework. Since land mammal faunas are also increasingly being studied with an integrated magnetostratigraphic and/or chemostratigraphic and geochronologic approach, their age calibrations have considerably been improved since GTS2012. Stable isotope analysis and XRF (X-ray fluorescence) scanning have become key tools in Paleogene high-resolution stratigraphy, correlation, and time scale construction. Stable oxygen and carbon isotope records also provide insight into trends in paleoclimate and carbon cycling, such as the warming trend starting in the middle Paleocene and culminating during the Early Eocene Climatic Optimum, and the subsequent cooling leading to a change from greenhouse to icehouse conditions at the onset of the Oligocene. Numerous short-term isotope excursions mark high climatic variability, expressed in hyperthermal (transient global warming) events (62-40 Ma) and cooling/glaciation events (38-23 Ma). At the same time, these stable isotope excursions provide accurate stratigraphic constraints and enable land-sea correlations, such as for the Paleocene-Eocene Thermal Maximum, the “Mother of all hyperthermals.” Orbital tuning of sedimentary cycles, calibrated to the geomagnetic polarity and biostratigraphic scales, has greatly improved the resolution of the Paleogene time scale over the last two decades. We now have astronomical age control for almost all geomagnetic polarity reversals, but differences between published age models still persist through the “Eocene astronomical time scale gap” spanning Chrons C20r through C22n (43.5-49.5 Ma).

How to cite: Speijer, R. P., Pälike, H., Hollis, C. J., Hooker, J. J., and Ogg, J. G.: GTS2020: The Paleogene Period, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13175, https://doi.org/10.5194/egusphere-egu21-13175, 2021.

The Cretaceous period was punctuated by several episodes of widespread deoxygenation of the sea floor referred to as Oceanic Anoxic Events. The OAE1b around the Aptian - Albian boundary is characterized by a series of black shales deposits, namely Jacob, Kilian, Paquier and Leenhardt levels. They are well documented in the Vocontian Basin, and their equivalent have been observed in different basins across the globe. Disagreement of more than a million of years exist about the timing of these events, leaving vast uncertainties about the causes of these recurring environmental changes. In order to better understand the relation between the climate perturbation and anoxic events during the Aptian-Albian period, we have focused on high-resolution investigations of magnetic susceptibility of Col de Pré-Guittard section, Drôme, France (GSSP of the Albian Stage; Kennedy et al., 2017). This section in the Blue Marls Formation consists of monotonous dark-grey marlstones interrupted by limestone beds and organic-rich layers. Spectral analyses were conducted on a magnetic susceptibility signal sampled every 5 cm. From this, we detected the record of the eccentricity, obliquity and precession cycles. We used the 100-kyr eccentricity cycles to construct an orbital time scale and shows that the interval starting above the Jacob level and ending above the Leenhardt level contains 21 repetitions of the 100-kyr eccentricity in the magnetic susceptibility data, leading to a duration of ca. 2.1 Myr. This duration is significantly shorter than the duration of 4 Myr provided by the current geologic time scale (Gale et al., 2020) but agrees with the U-Pb ages anchored to a δ¹³C_org curve from the High Arctic (Herrle et al., 2015).

References:

Gale, A.S., Mutterlose, J., Batenburg, S., 2020. Chapter 27: The Cretaceous Period, in: Gradstein, F.M., Ogg, J.G., Schmitz, M.D., Ogg, G.M. (Eds.) Geologic Time Scale 2020. Elsevier BV, Amsterdam, The Netherlands, pp. 1023–1086.

Herrle, J., Schröder-Adams, C.J., Davis, W., Pugh, A.T., Galloway, J.M., Fath, J., 2015. Mid-Cretaceous High Arctic stratigraphy, climate, and Oceanic Anoxic Events. Geology 43, 403–406.

Kennedy, J.W., Gale, A.S., Huber, B.T., Petrizzo, M.R., Bown, P., Jenkyns, H.C., 2017. The Global Boundary Stratotype Section and Point (GSSP) for the base of the Albian Stage, of the Cretaceous, the Col de Pré-Guittard section, Arnayon, Drôme, France. Episodes 40, 177–188.

How to cite: Ait-Itto, F.-Z., Martinez, M., Deconinck, J. F., Boué, D., and Bodin, S.: Astronomical calibration of the OAE1b, Col de Pré Guittard, Vocontian Basin, France, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12170, https://doi.org/10.5194/egusphere-egu21-12170, 2021.

Several carbon isotope curves were recently published for the Early and Middle Triassic in Tethys. Recent work has also been done on the Early Triassic of Svalbard, but not yet for the Middle Triassic. This work is the first to measure δ¹³C for different Middle Triassic localities on Svalbard, which was then part of the Boreal Ocean on northern Pangea. Our aim is to understand the controls on the Svalbard carbon isotope curve and to place them in a global setting.

Correlating Triassic rocks around the world is interesting for several reasons. The Triassic Period was a tumultuous time for life, and the Arctic archipelago of Svalbard has shown to be an important locality to understand the early radiation of marine vertebrates in the Triassic. Much effort is also made to understand the development of the Barents Sea through Svalbard’s geology.

Carbon isotope curves are controlled by depositional environment and global fluctuations. Global factors such as the carbon cycle control the long-term carbon isotopic compositions, while short-term fluctuations may reflect the origin of organic materials in the sediment (e.g. algal or terrestrial matter), stratification of the water column, and/or surface water productivity. Carbon isotopes can therefore be useful to understand the depositional environment and to correlate time-equivalent rocks globally.

The dataset was collected through three seasons of fieldwork in Svalbard with localities from the islands Spitsbergen, Edgeøya and Bjørnøya. Detailed stratigraphic sampling has resulted in high-resolution δ¹³C curves. These show three strong transitions; 1) on the boundary between the Early and Middle Triassic, 2) in the middle of the formation and 3) at the Middle and Late Triassic boundary. Several Tethyan localities show a possibly similar Early-Middle Triassic signal. Current work in progress is sedimentological analysis by thin sections and X-ray fluorescence spectroscopy (XRF) to further understand the sedimentary environment.

How to cite: Engelschiøn, V. S., Hammer, Ø., Wesenlund, F., Hurum, J. H., and Mørk, A.: Global carbon isotope signal in the Middle Triassic on Svalbard, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15701, https://doi.org/10.5194/egusphere-egu21-15701, 2021.

There's no doubt that nowadays detrital zircon U-Pb geochronology is actually required method of sedimentary basins analysis. Furthermore, this approach may have a lot of applications, such as a stratigraphic correlation. Here we present the first results of U–Pb LA–ICP–MS dating of detrital zircon from the Permian-Triassic red beds located within the Moscow Basin of the East European platform. Two outcrops have been studied: the Zhukov Ravine P/T boundary reference section and the Nedubrovo strata with uncertain stratigraphic position (uppermost Permian or lower Triassic?).

U–Pb ages of detrital zircon grains have been obtained for two samples – the Upper Permian and Lower Triassic age, which were taken in the proximity to the Permian–Triassic boundary in the Zhukov Ravine. Corresponding age distributions show contrasting provenance of the studied sedimentary rocks, pointing out that principal change in source of clastic material occurred on the Paleozoic-Mesozoic boundary. It means that detrital zircon U–Pb geochronology can be used as an additional independent tool for stratigraphic correlation of the Permian-Triassic red beds, at least within the Moscow Basin. We demonstrate this in the case of the Nedubrovo section with debated (Permian or Triassic?) stratigraphic position: the obtained data on detrital zircons persuasively suggests Early Triassic age of the Nedubrovo strata.

This study is supported by the Russian Foundation for Basic Research (project no. 18-05-00593).

How to cite: Chistyakova, A. and Veselovskiy, R.: Stratigraphic correlation of the Permian-Triassic red beds constrained by detrital zircon geochronology: Moscow basin, East European platform, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10294, https://doi.org/10.5194/egusphere-egu21-10294, 2021.

The Cambrian Explosion is characterised by a large diversification of life. The precise nature of this major evolutionary event is heavily debated, featuring anomalously fast versus more gradual evolutionary scenarios. Our ability to distinguish between such scenarios hinges on the quality of global correlations and corresponding timescales. With Cambrian temporal uncertainties often in the order of millions of years, establishing such correlations and timelines is a challenging task. Here, we present a novel approach to this problem based on a probabilistic Bayesian conceptual framework. Major advantages of the Bayesian approach include the consideration of multiple information sources in a single analysis and explicit uncertainty formulations.

In the absence of good index fossils, early Cambrian correlations rely heavily on carbon isotope chemostratigraphy and ‘expert-based’ correlations. Inspired by approaches in the radiocarbon community, we have been exploring representations of stable carbon isotope variations using random walk and spline fitting models. Implementation is undertaken using Markov-chain Monte-Carlo (MCMC) approaches. Temporal calibration is mainly dependent on published state-of-the-art U-Pb zircon dating. Our model also allows for the use of different sedimentary facies. Simultaneous analysis of several sections and multiple stratigraphic variables will allow each section to inform the correlation of every other, leading to a single, objectively derived and quantitative reference curve. Ultimately, the aim is to have a coupled Bayesian model setup of both stratigraphy and morphological evolution of the fossil record. These models will better inform us on the origins of diverse animal-dominated ecosystems and their impact on Earth processes.

How to cite: Sinnesael, M., Millard, A. R., and Smith, M. R.: An integrated Bayesian stratigraphic correlation approach for the Cambrian Explosion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9588, https://doi.org/10.5194/egusphere-egu21-9588, 2021.

Profound environmental and biological changes took place during the Cambrian, yet, compared to other Phanerozoic intervals, the Cambrian time framework remains poorly constrained, which severely hinders a detailed understanding of the timing and progression of these major geological events. In this study, we report a radiometrically anchored astrochronologic framework across the late Cambrian interval, using high-resolution aluminum (Al) series (1 mm resolution) through the Alum Shale Formation in Scania, southernmost Sweden, based on the fully cored Albjära-1 well. Significant cycles with periods of 405 kyr (long eccentricity), 108 kyr (short eccentricity), 30.4 kyr (obliquity) and 18.8 kyr (precession), associated with long-term amplitude modulation of obliquity and precession, confirmed the orbital imprint on late Cambrian climate. Using the U-Pb dating at 486.78±0.53Ma for the Cambro-Ordovician boundary as anchor point, our timescale spans from ~483.9 to ~500.0 Ma, covering 7 trilobite superzones and 3 graptolite zones. The calibration indicates ages of 491.2±0.54 Ma, 493.9±0.67 Ma, 497.3±0.67 Ma and 500.4±0.67 Ma for the lower boundaries of provisional Stage10, Jiangshanian, Paibian and Guzhangian stages, respectively. This radiometrically anchored astrochronology also provides precise age constrains on regional superzones or even biozones within Scandinavia, and hopefully pave the way for better understanding the late Cambrian major geological events globally.

How to cite: Zhao, Z., Thibault, N., Dahl, T. W., Schovsbo, N. H., Sørensen, A. L., Rasmussen, C. M. Ø., and Nielsen, A. T.: Synchronizing Rock Clocks in the Cambrian, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5082, https://doi.org/10.5194/egusphere-egu21-5082, 2021.

The Ediacaran records a transition from a planet largely dominated by microscopic organisms to macroscopic multicellular organisms during the Phanerozoic. Temporal calibration of the record of changing climates and coevally diversifying biota is crucial to understand how metazoan life gained an early foothold on Earth.

A causal link between climate-driven environmental perturbations and biotic changes is generally accepted. However, a chronological relationship is needed to prove which event acted as a trigger for the biological turnover, i.e. extinction or the development of new organizational levels. A connection between environmental perturbations associated with the appearance and disappearance of the Ediacaran biota is profoundly complicated because of the scarcity of available geochronological and chemostratigraphical records. Therefore, it is crucial to expand existing datasets for this period, particularly through additional chronology.

The Nama Group in southern Namibia serves as a unique archive for major geobiological changes across the Ediacaran–Cambrian transition exemplified by a near complete section through the terminal Ediacaran. The region exposes the full stratigraphic range of the Nama assemblage and records several environmental perturbations. Establishing a precise timeframe of the terminal Ediacaran environmental and biological changes in Nama group enables a much-enhanced understanding of the nature and rates of the evolutionary changes.

Following pioneering research by Grotzinger et al. (1995), the Ediacaran–Cambrian boundary in Namibia has recently been dated ca. 2 Ma younger than previously assumed [1]. Additional high-precision U-Pb CA-ID-TIMS zircon ages from silicified tuffs of the Nama Group allow additional insights for the timeframe of the entire terminal Nama. Our results indicate that (i) the oldest ash bed in the Zaris subbasin is 547.3 Ma old, which makes it more than 0.5 Ma younger than the previously dated tuff in the same subbasin; (ii) a newly explored section at the base of the terminal Ediacaran Spitskop Member near the MTC tower (Witpütz Nord farm) revealed a slightly younger age of 539 Ma, which permits a precise correlation of this section with the Swartpunt section and indicates the position of the Ediacaran-Cambrian boundary.

[1] Linnemann, U. et al., (2019) Terra Nova 31(1) 49-58.

How to cite: Messori, F., Linnemann, U., Hofmann, M., Zieger, J., Geyer, G., Vickers-Rich, P., and Ovtcharova, M.: New high precision U-Pb CA-ID-TIMS zircon ages from the Ediacaran in Namibia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15112, https://doi.org/10.5194/egusphere-egu21-15112, 2021.

Reconstructing the high-resolution astrochronology framework for the Ediacaran is critical to fully understand the evolution of the sedimentary environment and the carbon cycle in South China. The Ediacaran was perhaps one of the most important intervals in the Earth's sedimentary environment and biological evolution history, which witnessed the carbon isotope perturbation frequently, the emergence and evolution of metazoans, and the extreme climate change. There are many controversies for the characteristics and origin of these geological, biological and extreme climate events due to the lack of continuous and high-resolution astronomical time scale in the Ediacaran. We here propose to study the systematic cyclostratigraphic analysis of the Doushantuo Formation based on the Jiulongwan section in South China, and then use the long-eccentricity (405-kyr) for astronomical tuning to establish continuous and high-resolution astrochronologic framework, which would provide chronological constraints on carbon isotope negative  excursions, biological evolution and the extreme climate change for the Ediacaran. In order to reveal the inner correlation of the onset age, sequence of these major geological events as well as biological evolution in the Doushantuo Formation on the Ediacaran. Moreover, we also try to discuss the astronomical orbits-forcing factor that may lead to the occurrence and evolution of these major geological events, which would provide scientific evidence for studying the global climate change in the future.

How to cite: Sui, Y., Wang, Z., and Huang, C.: Astronomical time scale for the  Doushantuo Formation ofEdiacaran in South China: Implications for the duration of the negative δ13C excursion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6880, https://doi.org/10.5194/egusphere-egu21-6880, 2021.