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Exceptional Preservation Within Pleistocene Lacustrine Sediments of Shiobara, Japan

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A new conservation Lagerstätte is described from the middle Pleis-tocene Shiobara Group of central Japan. The biota includes mam-mals, birds, amphibians, fish, insects, arachnids, flowers, abundant leaves, fungi, and bacteria preserved within laminites that were de-posited in a lacustrine environment. Comminuted plant material in medium-grained, massive sandstones was deposited from high-density flows. This fragmentation of plant material probably indi-cates that it had decayed prior to transport. Plant and animal re-mains are largely nonfragmented and were thus transported prior to decay. The laminites are composed of rhythmic, millimeter-scale al-ternations of clay-to-silt-grade clastics with siliceous, diatom-rich lay-ers. In the western part of the basin the diatoms are preserved as opal-A, but in the eastern part, where soft-part preservation is most common, they have been altered to opal-CT and form thin, white, porcelaneous layers with a lepispheric texture. Soft parts are pre-served as carbon residues and microbial films, and although siliceous laminae enclose the fossils, permineralization of tissues is infrequent. Soft-part preservation was promoted by the self-sedimentation of ag-gregated mats of diatoms that shrouded the biota on the lakebed. This stabilized the carcasses and prevented them from being dis-turbed. It also prevented the diffusion of both the incoming nutrients and outgoing metabolic by-products between carcasses and sur-rounding water and may thus have promoted soft-part preservation. Silica cementation also inhibited the destruction of fossils by the in-tense weathering in the humid Japanese climate.
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... Although the conclusion that microbial biofilms contribute to the mineral coating of fossils is consistent with experiments and fossil analyses of other soft-bodied organisms (Briggs 2003), many fossil leaves confirmed to be preserved in biofilms show no evidence of associated iron oxides (e.g., Harding and Chant 2000;Allison et al. 2008;O'Brien et al. 2008), indicating that iron oxide enhancement of fossil leaf preservation is not universal, and probably depends on iron availability. An alternative and complementary taphonomic explanation for the preservation of leaf impression fossils is suggested by studies of the taphonomy of some Ediacaran soft-bodied organisms, which are preserved in close association with microbially mediated clay minerals, either as impressions in sandstones (e.g., Aspidella, Laflamme et al. 2011) or compressions in shales (e.g., Shaanxilithes, Meyer et al. 2012). ...
... Our results are consistent with previous studies demonstrating the importance of microbial biofilms in leaf preservation (e.g., Dunn et al. 1997;Harding and Chant 2000;Allison et al. 2008), but show a heretofore unrecognized, widespread association of clays with LAFs. Although few in number, the leaf fossils included in this study represent diverse depositional environments, ages, lithologies, and modes of adpression preservation, and all of them are encased in fine-grained aluminosilicates distinct in appearance and composition from the surrounding matrix. ...
... The thickness, microbe-to-clay ratio, density, and exact elemental composition of the biofilm-clay template varies depending on the nature of the biofilm (both its organic composition and microbial community: Michalopoulos and Aller 2004;Pacton et al. 2007), availability of metals, burial rate, sediment permeability, and oxygen concentrations (Konhauser 2011;Mikutta et al. 2011). For example, a biofilm-clay template forming under oxidizing iron-rich, silica depleted tropical soils may be composed of a mixture of aluminosilicates and iron oxides (Locatelli 2013), whereas leaves encased in a diatomaceous biofilm within a lake will have more aluminum, potassium, and silicon (Michalopoulos and Aller 2004;Allison et al. 2008). Microbial decay, particularly via anaerobic iron-reducing respiration, may affect the elemental composition of the clay precipitates, as living cells actively scavenge certain metals (e.g., K, Mg, Na) required for metabolism and remove reactive iron (III) from the available metal pool, resulting in the concentration of aluminum within the EPS matrix of the biofilm (Konhauser et al. 1993). ...
Article
Leaf adpression fossils vary in their organic content, relief, and quality of preservation. Some of the most enigmatic adpressions, known as leaf molds, retain fine morphological and anatomical details despite being found in coarse sandstones - a widespread phenomenon attributed to the presence of fine-grained minerals on the fossil surface. Previous taphonomic studies have demonstrated the importance of microbial biofilms in promoting mineralization and argued that authigenic iron oxides can serve as the preserving medium. Here, we propose that this role is played more commonly by biologically precipitated aluminosilicate phases (clays). To test this hypothesis, we conducted energy dispersive X-ray spectroscopy (EDS) analysis of thin sections through fossil leaves from five localities differing in age and depositional environment. Point spectra taken directly from the leaf-sediment interface revealed that cation-rich clays separate the leaf fossils from the matrix. Additional EDS analyses of biofilms on a fossil leaf and on modern oak leaves decaying in freshwater also revealed aluminosilicates, for which we infer a biofilm-mediated, authigenic origin. These results are the basis of a novel 'Biofilm-Clay Template' taphonomic model, whereby microbially mediated clay authigenesis is commonly the first step in leaf adpression preservation.
... Although observing the external part of the main body is not possible, the mat probably covers the entire tadpole and acted as a protective sarcophagus. Rapid burial and anoxia in diatomaceous beds also facilitates preservation (Allison et al. 2008). The preservation of the soft parts of the tadpole could have been further promoted by the self-sedimentation of aggregated mats of diatoms that shrouded the corpse on the lake bottom, as described by Allison et al. (2008) in lacustrine diatomaceous deposits of Japan. ...
... Rapid burial and anoxia in diatomaceous beds also facilitates preservation (Allison et al. 2008). The preservation of the soft parts of the tadpole could have been further promoted by the self-sedimentation of aggregated mats of diatoms that shrouded the corpse on the lake bottom, as described by Allison et al. (2008) in lacustrine diatomaceous deposits of Japan. These diatoms would have held the carcass together physically, preventing its dismemberment. ...
... Such diatomaceous sediments have associated bacterial communities that arrest decay and facilitate the preservation of dead tissues (Harding and Chant 2000). These sediments also restrict chemical and metabolic by-product diffusion between the carcass and the surrounding water (Allison et al. 2008), promoting isolated in situ putrefaction and fossilization. ...
Article
An anuran tadpole recovered from a late Miocene (Turolian, MN13) lacustrine diatomaceous Konservat-Lagerstätte deposit near Tresjuncos (Spain) was studied. X-ray diffraction, micro-Raman spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy analyses were completed with the aim of determining the sequence of diagenetic events that led to its preservation and fossilization. These analyses performed on the fossil, host rock and contact between them indicate that varied and successive diagenetic processes conditioned by microbial activity intervened in its fossilization. The tadpole was buried in the lake during a massive planktonic diatom sedimentation event. A layered microcrystalline calcite coating was found and likely originated from a microbial mat that acted as a protective general sarcophagus. A differentiated environment was generated in the carcass, explaining the presence of authigenic minerals that are absent in the surrounding diatomites. The fossil is mainly formed by spar calcite mosaics, showing unusual spherical pits interpreted as external moulds of coccoid bacteria; however, some may also be derived from dissolved melanosomes. Sulphate reduction, possibly coupled with the anaerobic oxidation of methane, may have promoted the formation of spar calcite within the organic network of the carcass. The occurrence of sulphate minerals in different zones of the fossil reveals that saline water was present during the anaerobic organic decomposition and the fossilization process. The genesis of fibrous Mg-rich clay minerals that cover the pitted calcite crystals could have been bioinduced or inorganic.
... Shikama, 1955;Hasegawa and Aoshima, 1988) have been discovered. Because of the remarkable preservation, the locality has recently been described as a conservation Lagerstätten (Allison et al., 2008), and new specimens are being obtained from the quarry in the museum. The fossil bearing rock comprises whitish liminite, which consist of rhythmic alternations of gray and white thin parallel laminae. ...
... The fossil bearing rock comprises whitish liminite, which consist of rhythmic alternations of gray and white thin parallel laminae. Allison et al. (2008) observed that the former gray laminae is clastic layer and the latter is white cemented laminae of porcelaneous opaline silica. These liminae may be regarded as annual rhythmites (Akutsu, 1964;Aiba, 2015). ...
... The fact that the two flies of our specimen remained is in a mating posture with little disturbance confirms that the specimen was rapidly buried. Fossil animals are mostly limited in laminite in Shiobara lacustrine deposits and rapid burying and anoxia probably protected them from scavenging (Allison et al., 2008;TuZino et al., 2009). Soft tissue preservation requires fast diagenesis (Briggs, 2003). ...
Article
Full-text available
Preservations illustrating insect reproductive behaviors are much rarer in compression fossils than in amber. We discovered a copulating compression fossil of the sciarid flies from the Pleistocene Shiobara Group, Tochigi Prefecture, Japan, which is briefly described herein. The specimen represents one of the rare examples of a compression fossil showing mating dipteran insects. This finding implies that the small bodies of sciarid flies which readily fall onto the water surface may have contributed to the preservation of our copulating fossil. Moreover, the depositional environment of the paleo-Shiobara Lake was the main factor that served to preserve this specimen.
... Although the conclusion that microbial biofilms contribute to the mineral coating of fossils is consistent with experiments and fossil analyses of other soft-bodied organisms (Briggs 2003), many fossil leaves confirmed to be preserved in biofilms show no evidence of associated iron oxides (e.g., Harding and Chant 2000;Allison et al. 2008;O'Brien et al. 2008), indicating that iron oxide enhancement of fossil leaf preservation is not universal, and probably depends on iron availability. An alternative and complementary taphonomic explanation for the preservation of leaf impression fossils is suggested by studies of the taphonomy of some Ediacaran soft-bodied organisms, which are preserved in close association with microbially mediated clay minerals, either as impressions in sandstones (e.g., Aspidella, Laflamme et al. 2011) or compressions in shales (e.g., Shaanxilithes, Meyer et al. 2012). ...
... Our results are consistent with previous studies demonstrating the importance of microbial biofilms in leaf preservation (e.g., Dunn et al. 1997;Harding and Chant 2000;Allison et al. 2008), but show a heretofore unrecognized, widespread association of clays with LAFs. Although few in number, the leaf fossils included in this study represent diverse depositional environments, ages, lithologies, and modes of adpression preservation, and all of them are encased in fine-grained aluminosilicates distinct in appearance and composition from the surrounding matrix. ...
... The thickness, microbe-to-clay ratio, density, and exact elemental composition of the biofilm-clay template varies depending on the nature of the biofilm (both its organic composition and microbial community: Michalopoulos and Aller 2004;Pacton et al. 2007), availability of metals, burial rate, sediment permeability, and oxygen concentrations (Konhauser 2011;Mikutta et al. 2011). For example, a biofilm-clay template forming under oxidizing iron-rich, silica depleted tropical soils may be composed of a mixture of aluminosilicates and iron oxides (Locatelli 2013), whereas leaves encased in a diatomaceous biofilm within a lake will have more aluminum, potassium, and silicon (Michalopoulos and Aller 2004;Allison et al. 2008). Microbial decay, particularly via anaerobic iron-reducing respiration, may affect the elemental composition of the clay precipitates, as living cells actively scavenge certain metals (e.g., K, Mg, Na) required for metabolism and remove reactive iron (III) from the available metal pool, resulting in the concentration of aluminum within the EPS matrix of the biofilm (Konhauser et al. 1993). ...
Conference Paper
Most fossil leaves are preserved as adpressions, a form of preservation spanning a continuum from organic-poor impressions to well-preserved organic compressions. Some of the most enigmatic adpressions are known as leaf molds, which retain fine morphological details (e.g. veins, stomata impressions) despite being preserved in coarse sandstones – a widespread phenomenon attributed to a fine-grained mineral coating on the fossil surface. Previous taphonomic studies have demonstrated the importance of microbial biofilms in promoting mineral precipitation in this and other contexts, and some authors have hypothesized that authigenic iron-oxides are responsible for the preservation of leaf morphology in coarse sediments. However, the iron-oxide hypothesis is not sufficient to explain the variation of quality observed in leaf adpression fossils more broadly. Here, we test an alternative hypothesis — that authigenic aluminosilicate clays are the minerals responsible for leaf mold preservation. Using energy dispersive X-ray spectroscopy (EDS), we analyzed thin sections through fossil leaves from five localities that differ in age (Cretaceous through Oligocene) and depositional environments (fluvial, lacustrine, and floodplain). Elemental point spectra taken directly from the leaf–sediment interface reveal that cation-enriched aluminosilicate clays separate the leaf fossils from the host matrix. Additional EDS spectra taken from biofilms from both the surface of a fossil leaf and from modern oak leaves decaying experimentally in freshwater demonstrate an aluminosilicate composition, consistent with the results of the thin section analyses, and establish a biofilm-mediated, authigenic origin. Informed by results, we present a novel taphonomic model of leaf adpression formation, the ‘Biofilm-Clay Template’ model’ in which microbially mediated authigenic clay authigenesis is the first step in leaf adpression preservation.
... Its caldera lake deposits are formed after Quaternary volcanic activities, and the laminae developed in the lacustrine siltstone include abundant leaf fossils of a variety of broadleaf species (Aiba, 2015). Certain beds produce fossil animals such as mammals, freshwater fish, frogs, spiders, and insects (Allison et al. 2008). Among the insect fossils, 82 species of six orders have been reported (Aiba, 2015(Aiba, , 2020Horiguchi et al., 2019;Suzuki et al., 2019). ...
... These specimens represent rare fossil records of extant species in Psephenidae. The fossils do not conclusively indicate the presence of a river that flows into the lake, but the well-preserved fragile small bodies indicate that they were deposited in still waters where diatoms are deposited at a high density, resulting in exceptional preservation (Allison et al., 2008). Although there is not enough geological and paleontological evidence of the presence of inflowing rivers, some Psephenidae larvae are known to be lotic and inhabit lakes. ...
Article
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The Middle Pleistocene lake deposits in Shiobara yield abundant animal and plant fossils. Three specimens of Psephenidae larvae were newly discovered, and identified as Ectopria opaca (Kiesenwetter, 1874) and an indeterminate genus of the Psepheninae. The former is the first fossil record of the species. The latter is probably Malacopsephenoides japonicus (Masuda, 1935) whose fossilized pupa was reported from the same site previously. These larvae are lotic species, suggesting the existence of rivers. However, as lotic species inhabit modern lakes (e.g., Lake Biwa in Honshu), Psephenidae larvae were also presumed to have inhabited lakes and the remains were preserved in the deposits.
... The concept of Lagerstätte was firstly defined by Seilacher (1970) and describes sedimentary deposits where the unusual amount and quality of biological remains are optimal for palaeoenvironmental reconstructions (e.g., Allison 1988;Allison et al. 2008;Bodzioch and Kowal-Linka 2012;Bauersachs et al. 2014;Kaulfuss et al. 2018;Métais and Sen 2018;Beardmore and Furrer 2019;Bustillo et al. 2019;Jauvion et al. 2020;Uhl et al. 2020). They form in different sedimentary environments that promote an exceptional fossil preservation, which in some cases includes soft tissue remains (Seilacher et al. 1985;Allison 1988). ...
... silicic volcanic glass, which is highly active (Hay, 1966;Jones et al., 1969;Sheppard and Gude, 1969). Paleolakes influenced by volcanic activity make available a high abundance of sulfur compounds (Allison et al., 2008), which oxidize into sulfates in aquatic environments. Furthermore, reactive iron minerals are frequently abundant in sedimentary volcanic deposits (Pan et al., 2014). ...
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Spinicaudatans (‘clam shrimps’) are small branchiopod crustaceans enclosed in a chitinous bivalved carapace that is often the only preserved element in the fossil record. However, few studies have analyzed the preservation of these carapaces, which have been found in continental facies from the Devonian to the present. The aim of this study was to contribute to a better understanding of the chemical preservation of fossil spinicaudatan carapaces, and it focused on spinicaudatan carapaces of the Cañadón Asfalto Formation from the Jurassic of Argentina. Semiquantitative energy-dispersive X-ray spectrometry (EDS) analysis provided elemental composition data that were interpreted using principal component analysis (PCA). The results showed a complex chemical mode of preservation for spinicaudatan carapaces. In some parts, EDS spectra of the specimens exhibit peaks of calcium, phosphorous, aluminum, and fluorine, representing the retention of original carapace material with some diagenetic recrystallization. Certain zones of the carapace show low-intensity peaks of the elements mentioned, while silicon and oxygen peaks (from the rock matrix) become the dominant spectral signals. These modes of preservation modify the interpretations and observations of the ornamentation of the carapace, which are used as taxonomic features. Our results suggest that specific diagenetic processes play a fundamental role in the preservation of spinicaudatans.
... was such a pioneer plant, it may well have colonized such empty spaces, flourishing for some time in Lake Enspel and subsequently declining at times of environmental stability and growing competition from other plants. Self-sedimentation of aggregated mats of diatoms (algal blooms) following the introduction of nutrients by the (re) sedimentation of tuffites (like S15) may have contributed to the preservation of the biota by shrouding it on the lakebed (Allison et al. 2008). ...
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The new species Groenlandia pescheri D. Uhl & Poschmann sp. nov., belonging to the family Potamogetonaceae, is described from the Late Oligocene Fossil-Lagerstätte Enspel (Westerwald, Germany). The species is characterized by sub-oppositely arranged leaves without observable stipule-like appendages at the leaf bases and a very thin exocarp (both characteristics of the aquatic genus Groenlandia J. Gay) with a spiked crest (which differs from the only other species included in this genus, the modern Groenlandia densa (L.) Four.). The taxon represents the first pre-Quaternary record of the genus Groenlandia , which is usually regarded as a basal sister group of all other Potamogetonaceae.
... Ichnofaunas from fully lacustrine deposits have been recorded nearly worldwide in Cenozoic deposits. They have been documented from the Paleogene of the western United States (Moussa 1968(Moussa , 1970Melchior and Erickson 1979 ;Loewen and de Gibert 1999 ;Bohacs et al. 2007 ;Martin et al. 2010 ;Scott and Smith 2015 ), Antarctica (Yang and Shen 1999 ;Perea et al. 2001 ), the Neogene of the eastern (O'Brien and Pietraskek-Mattner 1998 ;Benner et al. 2009 ;Knecht et al. 2009 ) and western (Smith et al. 1982 ) United States, eastern Canada (Gibbard and Dreimanis 1978 ), Hungary (Babinszski et al. 2003 ;Magyar et al. 2006 ;Cziczer et al. 2009 ), Slovakia (Starek et al. 2010 ;Hyžný et al. 2015 ), England (Gibbard and Stuart 1974 ), Lithuania (Uchman et al. 2008(Uchman et al. , 2009, Finland (Gibbard 1977 ), Sweden (Uchman and Kumpulainen 2011 ), Germany (Walter 1985 ;Walter and Suhr 1998 ), Greece (Owen et al. 2011 ), Turkey (Price and McCann 1990 ;Uchman et al. 2007 ), China (Yang 1996 ), Indonesia (Whateley and Jordan 1989 ), Thailand (Gibling et al. 1985 ;Flint et al. 1989 ), Japan (Allison et al. 2008), Kenya (Feibel 1987 and New Zealand (Lindqvist 1994 ). ...
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