Seasonal to sub-seasonal palaeoenvironmental changes in Lake Sihetun (Lower Cretaceous Yixian Formation, NE China)

Hethke, Manja; Fürsich, Franz T.; Jiang, Baoyu; Pan, Yanhong

doi:10.1007/s00531-012-0799-7

Cited by 28 publications

(43 citation statements)

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“…Carbonized soft tissues have not been observed from the accompanying, aquatic Jehol fossils in this study ( Supplementary Fig. 18) or in previous reports 14,37 . Thus, the carbonized soft tissues of the terrestrial vertebrates cannot be explained as the degraded remains of original tissues.…”

Section: Resultssupporting

confidence: 52%

“…In the former case, the carcasses would have been covered by deposits of the water's suspended load, so that the resulting laminae would have been laterally continuous as commonly observed in lacustrine deposits of suspended sediments 10,14 . This mode of deposition is not consistent with the features of the tuff laminae that we observed.…”

Section: Resultsmentioning

confidence: 99%

“…1) 7,8 . The laminae have been interpreted as the result of suspension loads and turbidity currents in thermally stratified lacustrine environments 10,14 .…”

Section: Resultsmentioning

confidence: 99%

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New evidence suggests pyroclastic flows are responsible for the remarkable preservation of the Jehol biota

et al. 2014

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The lower Cretaceous Yixian and Jiufotang formations contain numerous exceptionally wellpreserved invertebrate, vertebrate and plant fossils that comprise the Jehol Biota. Freshwater and terrestrial fossils of the biota usually occur together within some horizons and have been interpreted as deposits of mass mortality events. The nature of the events and the mechanisms behind the exceptional preservation of the fossils, however, are poorly understood. Here, after examining and analysing sediments and residual fossils from several key horizons, we postulate that the causal events were mainly phreatomagmatic eruptions. Pyroclastic density currents were probably responsible for the major causalities and for transporting the bulk of the terrestrial vertebrates from different habitats, such as lizards, birds, non-avian dinosaurs and mammals, into lacustrine environments for burial. Terrestrial vertebrate carcasses transported by and sealed within the pyroclastic flows were clearly preserved as exceptional fossils through this process.

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confidence: 52%

Section: Resultsmentioning

confidence: 99%

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New evidence suggests pyroclastic flows are responsible for the remarkable preservation of the Jehol biota

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“…Sedimentological evidence was put forward by Jiang et al (2012), who recognized four phases of lake evolution. Hethke et al (2013) added a high-resolution microfacies analysis by focusing on two of these phases (2 and 3), which yield most of the excellently preserved fossils mentioned above.…”

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confidence: 99%

“…Fürsich et al (2007) proposed seasonal dysoxia during summer owing to the consumption of oxygen by respiration processes coupled with winter mixing and reoxygenation. Jiang et al (2012) and Hethke et al (2013) refined this model by proposing a mainly stratified water column during Phase 2 with convective mixing seldom reaching the lake floor and leading to short-lived oxygenation events.…”

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confidence: 99%

Oxygen deficiency in Lake Sihetun; formation of the Lower Cretaceous Liaoning Fossillagerstätte (China)

Hethke

Fürsich

Jiang

et al. 2013

JGS

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The redox state of Lake Sihetun, represented by the Lower Cretaceous Yixian Formation (western Liaoning, China), is evaluated to understand the formation of this Konservat-Lagerstätte. Lake evolution is subdivided into four phases, of which Phases 2 and 3 exhibit excellent fossil preservation. Exceptional preservation and mass mortality events within Phase 2 were previously attributed to synsedimentary volcanism and oxygen deficiency. However, the volcanic trigger for mass mortality events remains enigmatic and distinction between anoxia and dysoxia has not been put forward so far. To resolve the redox state of the lake during Phase 2, 5394 diameters of pyrite framboid pseudomorphs in 29 thin sections from three localities have been measured. Framboid size distributions reveal that Lake Sihetun was governed by dysoxic bottom waters with spells of anoxia, recording pronounced environmental stress. Hence, holomictic, eutrophic conditions were episodically replaced by meromictic interludes. Spatial variations in redox state were common and oxic conditions were detected in two of the three studied localities. Concentrated iron sulphide layers resulted from biofilms at the lake floor or the development of microenvironments around organic remains, which preserved highly reactive organic compounds. In contrast, sediments of Phase 3 record oxic conditions and an entirely holomictic lake. research-articleResearch ArticleXXX10.1144/jgs2012-102M. Hethke et al.Oxygen Deficiency in Lake Sihetun 2013 at University of Birmingham on August 24, 2015 http://jgs.lyellcollection.org/ Downloaded from M. HETHKE Et AL. 818 Fig. 3. Lithologs of excavations zJG, LXBE, and JSG. Framboid-yielding horizons analysed in this study are marked. Beds 2 and 3 of the Jianshangou Unit are separated by a dotted line. at University of Birmingham on August 24, 2015 http://jgs.lyellcollection.org/ Downloaded from OXYGEN DEFICIENCY IN LAKE SIHETUN 821 Fig. 4. Phase 2 sediments of allochthonous clay-silt couplets (Mf 1) and intercalated tuff layers (Mf 5). (a) Plane-polarized light. (b-f) BSE images. (a) Framboids appear red (arrowed) to dark under plane-polarized light. (b , c) Original framboid structures are retained in thin section LXBE L1 and single microcrystallites exhibit reaction rims made up of iron oxide-hydroxides. This thin section was used for a case study (see Fig. 7) that aimed at discriminating between concentrated and matrix framboids. (d) Overview of the profoundly altered sediment of thin section LXBE E and (e) close-up of a concentrated iron sulphide horizon made up of framboids as well as single microcrystals. Smaller framboids (arrowed) have probably been overlooked during size measurements, as concentrated layers often merge to one dark red layer under plane-polarized light. (f) Progressive alteration is expressed by the formation of hollow, lobate (EDS spectrum) or meniscus-like structures (arrowed) that surround framboid remnants. An almost completely disintegrated structure is traced (13.9 µm).at University of Birmingham on Aug...

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Varves in the Yixian Formation, western Liaoning: Constraining the palaeoclimate in the Early Cretaceous

et al. 2021

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The study of the palaeoenvironment of the Early Cretaceous has been a significant research topic, largely due to the “Jehol Biota” in western Liaoning and the important prospect of fossils in Dakangpu Layer. Based on the sedimentology of Dakangpu Layer, it is helpful to get a deeper understanding of the living environment of the “Jehol Biota.” Varves are highly developed in the Dakangpu Bed of lower Cretaceous Yixian Basin in western Liaoning, China, supplying reliable and high‐quality proxies to explore the palaeoclimate. This paper reconstructs the palaeo‐lake environment and palaeoclimate, using petrography, facies associations, varves components, and geochemistry. Detailed petrographic studies helped to recognize 11 lithofacies which were grouped into two facies associations: Shallow lake and deep to semi‐deep lake sequences. The delicate structure of varves in the Dakangpu Bed were divided into two categories: Clastic and endogenic. Additionally, two sub‐types of clastic varves have been discovered, with distinct components, thickness, and distribution in vertical sequence. Nineteen representative samples of varves reveal that rare earth and trace elements have a similar change trend. The composition, formation, and preservation of the varves in the Dakangpu Bed depicted a deep lake, with stratified water and oxygen‐depleted bottom layer environment. The U/Th ratios and V/Cr ratios are in the ranges of 0.37–1.55 and 0.97–10.47 respectively, supporting the redox environment's minor fluctuation. The varve thickness, flood frequency, sporopollenin collections, and geochemical data indicated that precipitation and humidity decreased gradually in the sedimentary period, and the climate changed to warmer and drier, with fluctuations in the middle to later periods.

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Seasonal to sub-seasonal palaeoenvironmental changes in Lake Sihetun (Lower Cretaceous Yixian Formation, NE China)

Cited by 28 publications

References 36 publications

New evidence suggests pyroclastic flows are responsible for the remarkable preservation of the Jehol biota

New evidence suggests pyroclastic flows are responsible for the remarkable preservation of the Jehol biota

Oxygen deficiency in Lake Sihetun; formation of the Lower Cretaceous Liaoning Fossillagerstätte (China)

Varves in the Yixian Formation, western Liaoning: Constraining the palaeoclimate in the Early Cretaceous

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