Fossil Assemblages Research Articles

The Lower Cambrian deposits of the Le Rozel Formation (Normandy, NW France): Insight into a newly described ichnofossil assemblage

The rise of morphological complexity and taxonomic diversity of trace fossils during the Cambrian Period has been a prominent focus to track the evolution and diversification of early animals. Here, we present a newly described trace fossil assemblage from the lower Cambrian Le Rozel Formation in Normandy (Northwestern France) composed of the following ichnogenera: Archaeonassa, Bergaueria, Helminthoidichnites, Helminthopsis, Nereites, Psammichnites, and Treptichnus. Trace fossils are exquisitely preserved on top of strata (i.e., epirelief), and are distributed through the entire thickness of the siliciclastic succession of about 200 m. This thick sedimentary succession shows sedimentary environments with ripples generated by unidirectional current processes or by oscillatory processes, such as hummocky cross-stratification (HCS) storm facies, tidal facies with flaser stratification, and unidirectional current ripples. In addition, syneresis cracks and microbially induced sedimentary structures (MISS) suggest that the Le Rozel Formation was deposited in a shallow marine shelf environment. New U-Pb dating of detrital zircon grains suggests a late Ediacaran maximum deposition age of 549 ± 3 Ma. This dating is supplemented by the substantial preservation of the three-dimensional burrow systems (Treptichnus pedum) and the large sediment bulldozers (Nereites, Psammichnites). Collectively, our findings suggest that the trace fossils assemblage was deposited during the Terreneuvian Epoch, beneath the first archaeocyaths and the first trilobite-bearing facies from both other lower Cambrian Carteret and Saint-Jean-de-la-Rivière Formation. The ichnofauna described from the Le Rozel Formation complements the worldwide trace fossil record around this critical time of life history.

SUBRECENT POLLEN ASSEMBLAGES IN ALLUVIAL DEPOSITS OF THE DON AND KUBAN RIVERS AND THEIR SIGNIFICANCE FOR PALAEOGEOGRAPHIC RECONSTRUCTIONS

The paper presents the results of studying modern alluvial deposits of the Don and Kuban rivers by the pollen analysis method. The study was carried out to clarify methodological issue, including the movement of pollen and spores by flowing waters. The obtained data show that pollen assemblages of river sediments formed in the process of pollen mixing by water and air characterize the composition of the regional vegetation cover rather than local nearriver plant groups. According to the results for the subrecent sediments of the Don River the transfer of pollen grains and spores by water was insignificant, which can be clearly seen at the border of the forest-steppe and steppe zones. Pollen assemblages of the forest-steppe zone contain 50% of tree species pollen, while in the steppe zone, including its northern part, tree species make up less than 30-35%. Sporadic forest elements such as Picea pollen, Lycopodium species spores and Sphagnum mosses in alluvial deposits of the steppe section of the Don River, as well as in the subrecent sediments of the Sea of Azov, could be neglected in the palaeoreconstructions. The composition of subrecent pollen assemblages of the Kuban River sediments is less variable from the middle course to the mouth with rather stable ratio of components. Pollen of the Caucasian flora elements (Fagus orientalis, Carpinus caucasica) is poorly dispersed by water from high and midmountain landscapes of the upper reaches of the river. The comparison of pollen assemblages from alluvial and marine (the Sea of Azov) sediments have shown that the distortion of fossil assemblages’ composition due to material input by water is minimal

Rich specialized insect damage on Pliocene leaves from the Mahuadanr Valley (India) growing under a warm climate with weak seasonality.

Plant-insect interactions play a crucial role in shaping terrestrial ecosystems, influencing abundance and distribution of plant species. In the present study, we investigated leaf-mining patterns on fossil leaves from Pliocene strata of the Mahuadanr Valley, Jharkhand, eastern India, deposited under a seasonal tropical climate, and reported complex interactions between plants and insects. We identified 11 distinct mining morphotypes. These morphotypes were mainly found on Dipterocarpaceae, Fabaceae, Lauraceae, and Moraceae; similar mining traces were also observed in the contemporary vegetation surrounding the fossil site. Although mining richness was relatively high, only 2.6% of all leaves in the fossil assemblage were mined. We compared mining richness and abundance values with previously reported values for galling. While richness was slightly lower for galling, almost 50% of all fossil leaves were galled. A literature survey on mining and galling patterns in modern vegetation suggests that there is no global explanation for richness of mining or gall-inducing insects. Thus, low nutrient availability in the ancient forest, dominance of semideciduous leaves with hard texture, and different habitats in the same forest ecosystem, such as well-drained forests and riparian stands, may all have favored different types of specialized plant-insect interactions.

The Occurrence of Suids in the Post-Olduvai to Pre-Jaramillo Pleistocene of Europe and Implications for Late Villafranchian Biochronology and Faunal Dynamics

It has been proposed that suids were absent from Europe during the post-Olduvai to pre-Jaramillo Early Pleistocene (from less than 1.8 to more than 1.2 Ma) and that their “re-appearance” in the late Early Pleistocene would mark the end of the late Villafranchian and the beginning of the Epivillafranchian. Arguments enumerated in favor of this “suid gap” are the lack of suid remains from extensively sampled fossil localities of this age and the high reproductive potential (r-strategy) of suids, which would translate in a high commonness of their remains in the fossil record. However, here it shown that while suids’ reproductive potential is certainly exceptional within artiodactyls, there is no direct relationship between the reproductive strategy and preservation rate of a taxon in the fossil record. In Early Pleistocene localities of Europe and adjoining areas, where suids are present in a fossil assemblage, they are always rare. In terms of number of occurrences (frequency), suids range from being moderately common (~2.0–1.8 Ma) to moderately rare (~1.1–1.0 Ma). Suid material is also described herein from Peyrolles (Issoire, France; reference locality for MNQ 19), a site dated at 1.47 Ma, providing direct evidence for the presence of suids within the purported “suid gap”. The case of suids underlines an important source of caveat in inferring faunal dynamics of the late Early Pleistocene of western Europe—including the dispersal of hominins—i.e., the unequal geographical distribution of the paleontological sites of post-Olduvai to pre-Jaramillo age. Indeed, Peyrolles is the only large mammal site in western Europe located outside the Iberian and Italian Peninsulas reliably dated around 1.5 Ma. In the post-Olduvai to pre-Jaramillo period, there is a paucity of radiometric estimates (or they have too coarse a resolution) and of paleomagnetic excursions detectable in continental deposits. Basically, for this time span, there is a high dependence on biochronological correlations, although, at the same time, these correlations are less reliable—because these are based on a few sites not covering the entire spectrum of environments present in Europe and the sites are not independently dated with methods that outperform biochronology—than those for other periods.

Small mammal records from Limay river basin (Northwestern Patagonia) in the Anthropocene from a taphonomical and paleoecological perspective

The studies of the small mammal fossil and recent assemblages from the Limay river basin (Northwestern Patagonia) have strongly increased during the last decade. Taxonomic, taphonomic, and paleoecological information about small rodents and marsupials recovered from fossil sites offers the opportunity to discuss the periods of change and stability in the conformation of their communities through the Anthropocene. Here, we used two large data matrix of fossil and recent small mammal samples. As starting point, we considered the small mammal record of Epullán Grande cave (LL thereafter), which covers the Early Holocene/Post-hispanic Period, in order to assess the impact of anthropic activities on the small mammal communities during the Anthropocene. The taphonomic analysis performed on the newest samples from LL confirms the predatory activity of Tyto furcata on sigmodontines and human consumption on caviomorphs (mostly for the last ca. 1000 years). The analysis of manganese oxide staining suggested higher levels of moisture during the earliest formation of the LL sequence. The taxonomic results indicate a major diversity in the small mammal fossil assemblages to the later periods of LL and other fossil sequences of the Limay basin of the Anthropocene. Conversely, opportunistic sigmodontines ( Abrothrix olivacea, Calomys musculinus, Eligmodontia spp. and Oligoryzomys longicaudatus) experienced a growth in the recent samples. Some stenoic and specialist species ( Euneomys spp., Lestodelphys halli, Loxodontomys micropus and Reithrodon auritus) were abundant in the temporal units associated with the Anthropocene, but now are in retraction. Additionally, the drop in the diversity of recent assemblages supports a restructuration of small mammal communities from Limay river basin occurred in the 20th century.

Interpreted depositional conditions of balanced-fill lake basin strata incorporating vertebrate and invertebrate trace fossils, Triassic Santa Clara sub-basin, Cuyana rift basin, Argentina

ABSTRACT The Santa Clara Abajo and Santa Clara Arriba formations host a diverse assemblage of trace fossils that record a wide range of behaviors and a broad array of ecological niches during the Middle Triassic—a critical period in the evolution of continental fauna with the diversification of both synapsids (cynodont and dicynodont) and archosauromorphs (dinosaurs, pterosaurs, and crocodilians) that represent post-Permian faunal recovery. The Santa Clara formations are part of the continental infill of the Cuyana rift basin in Argentina and represent a lacustrine system with fluvial input and delta development. Sedimentological characteristics of these units as well as their stacking patterns characterize a “fluctuating profundal” facies association typical of a balanced-fill lake basin. The lacustrine and associated terrestrial environments preserve a rich record of invertebrate traces with 26 ichnogenera from ethological classes of fodichnia, domichnia, repichnia, pascichnia, and cubichnia occupying all continental tiers (subaerial and subaqueous, surficial, and/or very shallow, shallow, mid, and deeper) and ecological niches (epiterraphilic, terraphilic, hygrophilic, and hydrophilic). In association with invertebrate traces, two taphonomic modes of tetrapod footprints have been found: a moderate-fidelity mode and a high-fidelity mode. Physical sedimentary features, burrows, trails, and tracks, and their stratigraphic positions are integrated to interpret the main factors involved in footprint preservation in these subsettings. The most significant and variable preservational factor found is water-table fluctuation controlled by the paleohydrology of a balanced-fill lake system. These data show that in balanced-fill lake systems, diverse trace assemblages occur in the lake and associated subsettings such as delta plains and lake-margin settings, whereas trace fossils can be totally absent in coeval lake-center strata, particularly if anoxic lake-bottom conditions occur, as probably occurred in the meromictic Santa Clara lake system.

Characterization of dental calculus in the South American Quaternary proboscidean Notiomastodon platensis (Ameghino, 1888)

ABSTRACTDental calculus, or tartar, is a mineralized biofilm that develops on the teeth, and is often observed on the teeth of the South American proboscidean Notiomastodon platensis. This structure can provide details on paleoecological, paleoenvironmental and paleopathological aspects of a species. However, characterization of tartar in N. platensis is lacking. The aim of this study was to provide a macromorphological characterization of tartar on N. platensis molars, and evaluate its prevalence, distribution patterns and severity. A total of 117 molariforms from Brazilian Quaternary fossiliferous assemblages were analyzed. Thirty‐five (29.9%) molars presented tartar. The majority displayed moderate severity. Calculus was present at least on one inteloph(id) of each molar, and prevailed on the posterior region. It predominated on lower and third molars. Adult individuals showed a predominance compared to juveniles. These patterns in N. platensis are probably due to the susceptible oral environment, molar morphology, mature age and tooth replacement. These results suggest that N. platensis and probably other proboscideans were relatively susceptible to tartar development.

Body fossil assemblages from the Lower Idzików Beds (Coniacian) in the Upper Nysa Kłodzka Graben, south-west Poland: Preliminary taphonomic, palaeoecological and palaeogeographical data

From mudstones and sandstones referred to as the Lower Idzików Beds, as exposed at Stary Waliszów (Upper Nysa Kłodzka Graben, south-west Poland), a rich assemblage of body fossils has been recovered. This comprises rare ammonites (Baculites incurvatus, Forresteria cf. petrocoriensis, ?Scalarites sp.), nautiloids (Anglonautilus sinuatoplicatus), numerous bivalves, inclusive of inoceramids such as Inoceramus frechi and Volviceramus involutus, oysters (Ceratostreon, Vultogryphaea and Hyotissa) and other common genera such as Scabrotrigonia, Protocardia, Cucullaea, Neithea, Pinna, Liopistha, Panopea and Goniomya. Gastropods include mainly aporrhaids, turritellids, naticids and ampullinids. Echinoids are rare and comparatively poorly preserved, comprising only irregular forms (cardiasterids, micrasterids and hemiasterids), some of them being recorded from the Upper Cretaceous of Poland for the first time. Decapod crustaceans are fairly abundant in the Lower Idzików Beds, with axiideans predominating. A taphonomic analysis shows that this assemblage is well preserved, suggesting rapid burial as a result of storm events, while a palaeoecological assessment of taxonomic composition and trophic modes implies that deposition took place in a shallow-marine, well-oxygenated environment with a soft-bottom substrate, rich in nutrients and close to the fair-weather wave base. The presence of stenohaline taxa such as ammonites and echinoderms provides evidence of normal salinity.

Estuaries House Earth’s oldest known non-marine eukaryotes

Some of the oldest postulated non-marine eukaryotic microfossils occur in the 1.1–1.0 Ga Poll a’Mhuillt, Loch na Dal, and Diabaig formations in NW Scotland. These sedimentary strata have traditionally been interpreted as lacustrine. Here we report new trace element, sulfur isotope and metal abundance data and sedimentological observations for the latter two units. The geochemical data imply low salinity, oxic conditions whereas sedimentological features indicate marine tide and storm processes. Interpreting their depositional settings as estuaries, rather than lakes, with seawater-freshwater mixing fronts reconciles the contrasting datasets. Thus, whist these microbial habitats likely experienced frequent seawater input, they appear to have experienced the lowest salinity conditions of all known in situ fossil assemblages in the Precambrian. The Torridonian may in fact be representative of the low-salinity habitats predicted for ancestral eukaryotes based on phylogenetic reconstructions. Estuarine settings with gradients in water chemistry over space and time may have facilitated the transition of eukaryotic life from land to sea.

Humid and cold forest connections in South America between the eastern Andes and the southern Atlantic coast during the LGM

The presence of Andean plant genera in moist forests of the Brazilian Atlantic Coast has been historically hypothesized as the result of cross-continental migrations starting at the eastern Andean flanks. Here we test hypotheses of former connections between the Atlantic and Andean forests by examining distribution patterns of selected cool and moist-adapted plant arboreal taxa present in 54 South American pollen records of the Last Glacial Maximum (LGM), ca. 19–23 cal ka, known to occur in both plant domains. Pollen taxa studied include Araucaria, Drimys, Hedyosmum, Ilex, Myrsine, Podocarpus, Symplocos, Weinmannia, Myrtaceae, Ericaceae and Arecaceae. Past connectivity patterns between these two neotropical regions as well as individual ecological niches during the LGM were explored by cluster analysis of fossil assemblages and modern plant distributions. Additionally, we examined the ecological niche of 137 plant species with shared distributions between the Andes and coastal Brazil. Our results revealed five complex connectivity patterns for South American vegetation linking Andean, Amazonian and Atlantic Forests and one disjunction distribution in southern Chile. This study also provides a better understanding of vegetation cover on the large and shallow South American continental shelf that was exposed due to a global sea level drop.

Depositional history of Devonian to lower Carboniferous (Tournaisian) strata, northern Wyoming and southern Montana, USA

The lower Frasnian (Upper Devonian) Maywood Formation records incision of valleys into lower Paleozoic bedrock in fluvial to estuarine settings in northern Wyoming and deposition in estuarine to marine environments in southern Montana (USA). A distinctive fossil assemblage of microconchids, plant compression fossils, fish fossils, and microspores represent fauna and flora that lived in, and adjacent to, salinity-stressed ecological niches in the upper reaches of the Maywood valleys. A similar fossil assemblage is recorded in older Devonian valley-fill deposits of the Lower Devonian Beartooth Butte Formation, indicating that valley incision and subsequent transgression, occurred repeatedly over a span of nearly 30 million years with organisms tracking the marine incursions into the valleys. The fossil charcoal in the Maywood Formation captures a record of fire in adjacent terrestrial ecosystems. The amount of dioxygen (O2) was thus above the fire window level (16% by volume) and might have been near modern levels in the earliest Late Devonian atmosphere. The nearshore deposits of the Maywood Formation are overlain by extensive shallow carbonate shelf strata of the Jefferson Formation, likely resulting from a global transgression in the earliest Frasnian. A paired positive and negative δ13Ccarbonate [carb] isotopic excursion in the Jefferson with a range of >6‰ is a signal of the globally recognized “punctata” Event. The unconformably overlying Madison Limestone is lower Carboniferous, except for a thin basal Upper Devonian unit with marine palynomorphs. The Madison regionally records eastward transgression and establishment of widespread marine deposition. It also contains two positive δ13Ccarb excursions (up to ∼7.5‰) that make up the mid-Tournaisian (= Kinderhookian−Osagean boundary) carbon isotope excursion (TICE/KOBE). These isotope data provide a framework for regional and global correlation of northern Rocky Mountain strata and an archive of environmental and evolutionary change during the middle−late Paleozoic transition.

Plant-insect interactions across the Triassic–Jurassic boundary in the Sichuan Basin, South China

Plants and insects are the most diverse and ecologically important organisms in the terrestrial biosphere. Their interactions are also among the richest biotic relationships, and offer significant insights into the evolution of terrestrial ecosystem complexity through the geological record. This investigation of the late Rhaetian Xujiahe and the earliest Jurassic Zhenzhuchong floral assemblages provides the first data on foliar herbivory generated by terrestrial arthropods across the Triassic–Jurassic transition in the eastern Tethys (East Asia) region. The damage types from two fossil assemblages are collectively attributed to seven functional feeding and egg-laying categories (i.e., hole feeding, margin feeding, surface feeding, skeletonization, piercing and sucking, oviposition, and galling). Most feeding strategies are spread across the major plant groups and persist through the Triassic–Jurassic boundary, with the exception of skeletonization (a category of external foliage feeding), which was restricted to the latest Triassic within dipteridacean ferns. The survey reveals that the respective frequency and diversity of interactions between plants and insects prior to and following the end-Triassic mass extinction event are almost the same, despite a substantial turnover of floral components. This suggest that insect herbivores were largely able to transfer to alternative (but commonly related) plant groups during the dramatic floristic turnover and environmental changes at the end of the Triassic. Sporadic occurrences of foliar modifications, such as marginal cusps on pinnules of Pterophyllum and prominent ridges on the rachises of some ferns and bennettites are interpreted as adaptations for defense against insect herbivores. A few differences in taxonomic composition and herbivory representation between the latest Triassic Xujiahe flora and the earliest Jurassic Zhenzhuchong flora are more likely to be related to collection and preservational biases rather than reflecting palaeoecological changes. We encourage further investigations exploring the distribution of insect damage in fossil floras from other palaeolatitudinal zones and spanning other major extinction events to develop a better understanding of terrestrial ecosystem responses to major crises in Earth’s history.

Integrated biostratigraphy of Upper Cretaceous deposits from an exceptional continental vertebrate-bearing marine section (Transylvanian Basin, Romania) provides new constraints on the advent of ‘dwarf dinosaur’ faunas in Eastern Europe

The present paper outlines the results of a detailed study of calcareous nannofossils and small foraminifera made on Campanian marine deposits from the southwestern part of the Transylvanian Basin, Romania, part of the marine-to-continental transitional Petrești succession that yielded the oldest temporally well-constrained continental vertebrate remains in this area. These results are integrated with new and previously published palynostratigraphic information as well as with novel detrital zircon geochronometry data. All three groups of fossils (calcareous nannofossils, small foraminifera, and palynomorphs) convergently indicate an early to middle Late Campanian age for the marine part of the Petrești section. Based on detrital zircon analyses, the most likely maximum depositional age of the studied deposits is 76 ± 1.7 Ma, thus confirming the age supported by microfossil assemblages. Palaeoenvironmental interpretation of the fossil assemblages recovered from the marine part of the Petrești section suggests that despite their flysch-like facies, these beds were deposited in a continental shelf setting, under suboxic conditions and frequent fluctuations in nutrient supply to the seafloor, but quite stable environmental conditions within the water column. The synthesis of all currently available biostratigraphic and geochronologic data from the Petrești succession suggests a middle-late Late Campanian start for the expansion of the emergent land areas that made up the latest Cretaceous Hațeg Island, earlier than previously accepted dates (Maastrichtian) for this event. Furthermore, it documents the establishment of a diversified continental vertebrate faunal assemblage by the second half of the Late Campanian on these emergent lands while also providing further evidence for a later, post-Campanian arrival of certain iconic Hațeg Island dinosaur groups such as titanosaurs and hadrosauroids. Finally, our data show that kogaionid multituberculate mammals were already members of the earliest known Hațeg Island faunas, extending the fossil record of this group from the Maastrichtian into the later part of the middle Late Campanian.

New taxa of the Rhaphoneidaceae Forti (Bacillariophyta) from the middle Eocene

Rhaphoneis amphiceros (Ehrenberg) Ehrenberg is one of the commonest extant rhaphoneid diatoms and has been reported from multiple fossil deposits, but our work suggests this taxon may not be as common in the fossil assemblages as indicated by the literature. Indeed, the original description of the species, made by Ehrenberg, is not as detailed as modern descriptions, which can lead to confusion when identifying taxa. Recent studies show that diatom species previously reported to occur over time intervals of tens of millions of years may actually represent groups of taxa lumped together due to inaccurate identifications. In this article, we present two new species that, without careful SEM examination, can be confused with R. amphiceros. These new species, interpreted to represent two new genera in the Rhaphoneidaceae, were found in middle Eocene sediments from Ocean Drilling Program (ODP) Hole 1050A (30°06’N, 76°14.1’W), drilled on Blake Nose, western North Atlantic. Rhomboneis shtapovii Figus & Witkowski and Rosaforma paillesiae Figus & Witkowski show unique morphological characteristics that lead us to create new genera. Rhomboneis shtapovii has two rimoportulae per valve and an unusual type of velum occluding the areolae. Rosaforma paillesiae has a peculiar asymmetric apical pore field occupying half the valve pole, the other half contains a rimoportula with two apical pores.

Fossils from the Upper Miocene (Pannonian) sands of the Pécsvárad sand pit (Eastern Mecsek Mts., SW Hungary)

The Mecsek Mountains in SW Hungary represent an uplifted basement block of the Pannonian Basin. Their Neogene cover includes deposits both from the Middle Miocene Central Paratethys and from its Late Miocene (Pannonian) brackish?water descendant, Lake Pannon. Along the mountain front, the Pannonian sands of the P?csv?rad sand pit contain a mixed vertebrate fossil assemblage, which gives insight into terrestrial and aquatic biota during various time intervals of the Miocene. The fossil?bearing sands accumulated between 7.6?6.8 Ma, in a high?energy littoral setting of Lake Pannon, as indicated by the mollusc remains. The verte brate fossil assemblage is relatively diverse compared to the number of finds. The most abundant group, aquatic mammals, encompasses a minimum of four odontocete species and a few mysticete taxa, which originally lived in the Para tethys during the Badenian and the Sarmatian. Rhinocerotid remains are reworked from sediments aged somewhere between the Karpatian and earliest Pannonian. The single shark tooth must be Badenian, and the scombrid fishes probably also date back to that age. Fossils of other fishes (sparids, latids and acipenserids), giant salamanders, turtles, crocodilians and cervids might originate from older Miocene deposits but can be coeval with the host sands as well. Tapirs and giraffids must have lived on the lakeshores of Lake Pannon, probably contemporaneously with sand deposition or not much earlier. The erosion, enrichment and mixing of the fauna is a result of the uplift and denudation of the Mecsek Mountains during Lake Pannon sedimentation, caused by neotectonic basin inversion. This example shows that in spite of the uncertainties in the dating of some fossils, mixed faunas can provide important data on the evolution history of an area.

Paleontological Reassessment of Bukit Bucu, Batu Rakit, Terengganu, Malaysia

Bukit Bucu is situated close to Terengganu’s northern coast. The entire sequence comprises of minor slate, sandstones, and shales that have been gently folded to produce an anticline that plunges towards the NNW. These interbedded sandstones and shales are dipping ENE or WSW and striking NNW. There is evidence of slaty cleavage and well-preserved sedimentary formations in the rocks of Bukit Bucu, which are subjected to very low metamorphism grade. Fossils assemblages that have been identified in Bukit Bucu include brachiopods, trilobites, bryozoans, crinoids and bivalves, indicating a shallow marine depositional environment. This sedimentary rock also produced several plant fossils from our most recent visit. Some of the fossils that have been recognized were Avonia sp. and Dictyoclustus sp. (brachiopods), Posidonia sp. and Euomphalus sp (mollusks), Fenestella pahangensis (bryozoan), Phillipsia sp. (trilobite) and Calamites sp (plants). Bukit Bucu’s most recent age has been determined to be Carbo-Permian, which is consistent with low-grade metamorphism sequences that extend from Terengganu’s north to Johor’s south. The purpose of this study is to bring Bukit Bucu’s fossil record up to date since it was last kept in 1986.

The Pliocene succession of Lyon Metropolis (SE France): an overfill of a Messinian incised-valley

The Pliocene ria, a narrow seaway running up the Rhône Valley, has been mapped for a while by field geologists. Only much later, after the DSDP Leg 13 in 1970, a consensus was reached that this unique geological feature of the Rhône Valley was created by the major Mediterranean sea-level drop associated with the Messinian Salinity Crisis, followed by a sudden sea-level rise caused by the breach of the Strait of Gibraltar and the invasion of the Mediterranean Basin by the Atlantic waters. At the regional level of the Lyon Metropolis in the upper Rhône Valley, main issues were however remaining about the course and depth of the Messinian valley, and about the valley fill, namely where and how do the Pliocene marine strata of the Rhône Valley pass to the continental deposits of the Bresse Basin to the north? These are key-questions in that the Plio-Pleistocene makes up a large fraction of the basement that holds up a large city, not free from potential geological hazards and subject to problems of groundwater management, high-cost tunneling projects, etc. Our survey reviews first the historical researches − descriptions of the outcrops and fossil assemblages. It is followed by an unprecedented analysis and correlation of a thousand boreholes, which makes it possible to physically link and reconcile ancient local observations. Sections across the Messinian valley reveal a proper canyon morphology for the segments that cut the crystalline basement. The magnitude of the incision has been calculated as 335 m to a minimum, three hundred kilometers away from the river mouth. Three major depositional systems are distinguished for the Pliocene − Lower Pleistocene succession. The valley that initially ran much farther north of Lyon was occupied in the Zanclean by a series of pounded lakes, dammed by transverse local alluvial fans, filled by minor Gilbert-type deltas, and repeatedly flooded by marine ingressions. The valley wings were then encroached during the Piacenzian by a major, Alps-rooted alluvial sheet. At the level of Lyon, the fluvial deposits were deflected to the north (Sables de Trévoux) and to the south (Alluvions jaunes) as a dichotomy. The succession was then capped by a gravel-dominated fluvio-glacial fan (Alluvions jaunes sommitales) at the Plio-Pleistocene transition. It spread out from the north-east to the south, and intersected the previous valley overfill due to the shift to the north, i.e., South Jura, of the feeder stream. The depositional and current elevations of the marine-influenced episodes, i.e. marker bands that punctuate the regional Neogene succession, are used to bring out successive uplift and subsidence phases of the region. Finally, we tentatively link the major shifts in the depositional patterns of the Late Neogene succession in the Lyon area to major changes in the thrust belt activity, exhumation story, and outset of glaciers in the western Alps.

U–Pb zircon–rutile dating of the Llangynog Inlier, Wales: constraints on an Ediacaran shallow-marine fossil assemblage from East Avalonia

The Llangynog Inlier of south Wales contains an assemblage of Ediacaran macrofossils from a shallow-marine environment, including discoidal morphs of Aspidella and rare examples of Hiemalora , Palaeopascichnus and Yelovichnus . These are taxa found at other sites in the Avalonian microcontinent (e.g. Charnwood Forest and eastern Newfoundland) and in the younger White Sea Ediacaran assemblages. As the Charnwood fossils reflect a deep-water environment, and no macrofossils have been found in the Ediacaran rocks of the Long Mynd, the fossils of the Llangynog Inlier represent a unique glimpse of shallow-marine life in southern Britain (East Avalonia). However, the lack of absolute age constraints has hampered direct comparison with other assemblages. Here, we report in situ zircon and rutile U–Pb dates from a rhyolitic ash-flow layer of the Coed Cochion Volcaniclastic Member, Llangynog Inlier, which constrains the age of the fossiliferous strata. A weighted mean single grain zircon isotope dilution thermal ionization mass spectrometry U–Pb age of 564.09 ± 0.70 Ma is interpreted as the rhyolite's crystallization age. This age is consistent with in situ laser ablation inductively coupled plasma mass spectrometry zircon and rutile U–Pb dating. The Llangynog age temporally correlates these fossils to dated horizons within East Avalonia at the Beacon Hill Formation, Charnwood (565.22 ± 0.89 Ma) and the Stretton Shale Formation, Long Mynd (566.6 ± 2.9 Ma). Correlations to West Avalonia include the time-equivalent Fermeuse Formation, St John's Group, eastern Newfoundland (564.13 ± 0.65 Ma). The data presented here establish the biota of the Llangynog Inlier as a lateral equivalent to the similarly shallow-marine, tidally influenced ecosystem of the upper Fermeuse Formation. Intra-terrane depositional environmental variability also affects what is preserved in Avalonian fossil sites. Further, time-constrained geochemical data reinforce the Llangynog Inlier's classification within the Wrekin Terrane. Supplementary material : U–Pb data, reference material and figures showing sedimentary structures are available at https://doi.org/10.6084/m9.figshare.c.6965642

Diverse Lophoctenium burrows from the Upper Devonian (Famennian V and VI) of Algeria

Three ichnospecies of Lophoctenium (L. comosum, L. richteri and L. cf. haudimmineri) are reported from the Upper Devonian Argiles de Marhouma Formation (southwestern Algeria) for the first time. This formation contains a diverse assemblage of trace fossils belonging to the Nereites ichnofacies. We describe three ichnospecies of Lophoctenium that correspond to three different feeding strategies among the diverse ichnofauna of the Argiles de Marhouma Formation. The strategy of L. comosum evidences food-rich sediments as it maximises the amount of collected food per foraged distance. The strategy of L. richteri is probably most efficient for feeding in slightly less nutrient rich sediment, but gives the opportunity to discover more prolific feeding sites by moving on longer distances. The strategy with a straight central burrow and probes on both sides of the main burrow with long interspaces (L. cf. haudimmineri) was presumably used in the least food rich sediment. It seems that the Lophoctenium was widespread in the Devonian, but restricted to seas surrounding Gondwana.

Facies architecture and sequence stratigraphy of Kungurian Amb Formation, western Salt Range, Pakistan

The Amb Formation of the Permian age is exposed in the Salt Range in the upper Indus basin of Pakistan. This rock unit is mainly composed of sandstone and shale in which three facies (named AF1, AF2, AF3) and five microfacies were distinguished based on field and petrographic study, respectively. Porosity and permeability have changed and exhibit various diagenetic processes. Sequence stratigraphy identifies the zones of all upward concaving cycles and HST. The petrophysical study indicates good reservoir characteristics for the Amb Formation and this can act as reservoir rock in the petroleum system. Fossil assemblages, including Fusulina spp., identified during petrographic analysis indicate an Early Permian age of the Amb Formation in the study area. The multidisciplinary study carried out in the study area allowed us to reconstruct the depositional model for the Amb Formation which occurred in the middle to inner shelf and in a shallow marine environment. Interpretation of well logs of the Dhermund well show good reservoir properties of the Amb Formation including total porosity (13%), effective porosity (9.04%), volume of shale (14.54%), water saturation (34%), hydrocarbon saturation (65%), permeability (121.92 mD), total thickness of the formation (107 m) and net reservoir thickness (13.12m). This research approach of combined field and laboratory stratigraphy and biostratigraphy would be applied in other areas of exposure of the Amb Formation to unravel the age and depositional environment of this formation.