Nouvelles données paléontologiques,paléoécologiques et sédimentologiques sur le Berriasien de la région de Lamoricière (ouled Mimoun et E1 Rhoraf,Monts de Tlemcen,Algérie)

In the Western Algerian area, the Ouled Mimoun and El Rhoraf sections are particularly appropriate for the study concerning the berriasian formations.From tha lithostratigraphical point of view, the upper section of the carbonated platform corresponds to the lower Berriasian and a part of the middle Berriasian. The «Argiles de Lamoricière which dominate it belong to the middle and upper Berriasian. The subjacent detritic formation known as «Grès de Berthelot probably begins with the lower Valanginian. The stratigraphical results are based on an abundant fauna (ammonites, ostracods) collected in situ, the main species of which have been the subject of a paleontological review and abondantly illustrated.The studied series offer a good example of the evolution of sedimentary conditions which accompany the temporary opening of a carbonated platform towards the open sea.The variations in fauna composition are closely related to changes in environment. In particular, the presence of ammonites in the Boissieri zone can be connected to the highest point of marine advance, although the depth remained relatively shallow (an upper infratidal zone being likely). It is to note that during this period the low level of sedimentary activity favored the settling of some remarkable epilithic fauna.Above the «Argiles de Lamoricière, the massive detritic sedimentation (grès de Berthelot) could indicate an important paleogeographical change in the interior. In the area studied, the ostracods encountered in the basal section of the last formation still mean a shallow marine environment.     

Bryozoans as taphonomic engineers,with examples from the Upper Ordovician (Katian) of Midwestern North America

A combination of encrusting calcitic bryozoans and early seafloor dissolution of aragonitic shells recorded in the Cincinnatian Series of the upper Midwest of North America allowed the preservation of abundant moulds of mollusc fossils bioimmured beneath the attachment surfaces of the bryozoans. We here call this preservational process ‘bryoimmuration’, defined as a bryozoan‐mediated subset of bioimmuration. The bryozoans moulded very fine details of the mollusc shells, usually with more accuracy than inorganic sediment moulds. Most of the bryozoans are heterotrypid trepostomes with robust low‐Mg calcite skeletons. The molluscs are primarily bivalves, gastropods, nautiloids and monoplacophorans with their originally aragonitic shells now dissolved. Many of the encrusting bryozoans are so thin and broad that they give the illusion of calcitic mollusc shells clinging to the moulds. Some molluscs in the Cincinnatian, especially monoplacophorans and epifaunal bivalves, would be poorly known if they had not been bryoimmured. Unlike internal and external moulds in sediment, bryoimmured fossils could be transported and thus record aragonitic faunas in taphonomic assemblages (e.g. storm beds) in which they would otherwise be rare or absent. In addition, bryoimmurations of aragonitic shells often reveal the ecological succession of encrustation on the shells by exposing the earliest encrusters and borings that were later overgrown. Bryoimmuration was common during the Late Ordovician because the calcite sea at the time quickly dissolved aragonitic shells on the seafloor before final burial, and large calcitic bryozoans very commonly used molluscs as substrates. Bryoimmuration is an important taphonomic process for preserving aragonitic faunas, and it reveals critical information about sclerobiont palaeoecology. Several Cincinnatian mollusc holotypes are bryoimmured specimens. Bryozoans involved in bryoimmuration enhance the preservation of aragonitic fauna and thus act as taphonomic engineers.     

Evolution of pelagic swells from hardground analysis (Bathonian–Oxfordian, Eastern External Subbetic, southern Spain)

The Middle Bathonian to Middle Oxfordian interval in the Eastern External Subbetic (Betic Cordillera, SE Spain) is characterized by Ammonitico Rosso facies including various stratigraphic breaks. Five hardground-bounded units are recognized in relation to hiatuses in the ammonite record at the following stratigraphic boundaries: Hg1 (Lower–Middle Bathonian), Hg2 (Middle–Upper Bathonian), Hg3 (Lower–Middle Callovian), Hg4 (Middle–Upper Callovian), and Hg5 (Callovian–Oxfordian). Interesting features of these hardgrounds include their microfacies, ferruginous crusts and macro-oncoids, taphonomy of macroinvertebrates, trace fossils, neptunian dykes, and the hiatuses associated with each of them. The main hardgrounds (Hg1, Hg2, and Hg5) contain trace fossils of the Cruziana and Trypanites ichnofacies as well as abundant fossil macroinvertebrates with taphonomic features evidencing corrasion, early diagenesis, and reworking, indicating substrate evolution from softground to hardground. Neptunian dykes affected the trace fossils and ammonoid moulds, and their walls and the hardground surfaces were colonized by ferruginous microbial crusts. These features are characteristic of the External Subbetic pelagic swells, where the absence of sedimentation, sediment bypassing and erosion, and early diagenesis during relative sea-level falls produced hardgrounds. The neptunian dykes are indicative of tectonic activity in the areas of pelagic swells. Ferruginous crusts and macro-oncoids developed only on hardground surfaces and neptunian dykes walls prior to deposition of condensed bioclastic beds, which are interpreted as the first deposits after hardground development and are related to the onset of transgression. The varying ranges of the gaps as well as lateral facies changes are related to different local paleobathymetry controlled by the activity of listric faults.     

Structural and taphonomic analysis of a columnar coralline algal build-up from SE Sicily

Unusual “coralligenous” build-ups were found at the infra–circalittoral boundary from SE Sicily. They are columnar, rising up perpendicularly from the bottom, and consist of an inter-growth of encrusting algae and invertebrates. A selected build-up and its longitudinal section, together with some thin sections of selected parts, were studied to detail the growth structures, composition and fabric of the trapped sediments. The coralline algae show a succession of “concentric”, “fruticulose” and “foliaceous” structures. The framework delineates cavities bounded by algal thalli, sometimes filled by sediments. The organisms constituting the framework were grouped into functional guilds (Fagerström, 1991): “primary frame builders” (mainly coralline algae); “secondary frame builders” (vermetids, serpulids and some bryozoans); “bafflers” (erect, flexible bryozoans, some sponges and soft algae); “binders” (encrusting bryozoans, some crustose coralline algae and serpulids); “destroyers” (a few endolithic algae, rare sponges and bivalves); “dwellers” (brachiopods, foraminifers, bivalves, small bryozoans and some motile organisms). The distribution pattern of taphonomic features (composition, grain size and distribution of sediments filling cavities; presence of cement and its location; mineralogical composition and crystal size), together with interactions between growth structures and functional guilds, allowed one to distinguish three taphofacies, each recording different environmental conditions. They have been tentatively related with cyclic sequences testifying to local hydrodynamic regimes, with subsequent slighter and stronger intensity phases, during the last 2200 years.     

Microtaphonomy of bioclasts and paleoecology of microencrusters from Upper Jurassic spongiolithic limestones (External Prebetic,Southern Spain)

Microencrusters and microtaphonomic features of the Oxfordian spongiolithic limestones of the External Prebetic were studied using thin-section analysis. The spongiolithic limestone is a bioclastic-rich packstone with common echinoderm, mollusc and brachiopod remains. The bioclasts show a high fragmentation index and frequent microborings. The encrustation index (E _i) is higher for fragments of serpulids, ammonoids and bivalves, and increases with the initial grain-size of bioclasts. The main microencrusters consist of benthic microbial communities (BMC) and nubeculariids, as well as subordinate calcareous and siliceous agglutinated foraminifera, serpulids and bryozoans. BMC are usually the first colonizers, and encrusting foraminifera mainly appear on bioclasts larger than 2 mm. BMC dominate in well-developed encrustations on upward facing surfaces of larger bioclasts that are also colonized by foraminifera (nubeculariids and Subdelloidina). Bullopora, serpulids and bryozoans are more common on lower surfaces. The fact that the values of encrustation index, encrustation thickness and diversity of the microencrusters increase with the size of bioclasts is related to a higher stability and exposure time of the available bioclastic substrate. The microencruster distribution on upper and lower surfaces of large bioclasts may be related to photic control, space competition and/or predation avoidance.     

Ammonoid taphonomy, palaeoenvironments and sequence stratigraphy at the Bajocian/Bathonian boundary on the Bas Auran area (Subalpine Basin, south-eastern France)

Bas Auran, in south‐eastern France, is the candidate area for Global Boundary Stratotype Section and Point (GSSP) of the base of the Bathonian Stage (Middle Jurassic). In the Bas Auran area, upper Bajocian and lower Bathonian deposits are made up of limestone beds alternating with marls that correspond to the ‘Marno‐calcaires àCancellophycus’, below the ‘Terres Noires’ Formation. Taphonomic analyses of the successive ammonoid fossil assemblages provide new and complementary data for biostratigraphic completeness, palaeoenvironmental setting and sequence stratigraphy. Lithologic differentiation between limestone and marl intervals resulted from alternating episodes of carbonate input and starvation. Both lithologic phases may contain evidence for sedimentary and taphonomic reworking, associated with scours, that reflects low rates of sedimentation and stratigraphic condensation. Three successive types of elementary cycles resulted from increasing rates of stratigraphic condensation, sedimentary condensation and substrate stabilization during early Bathonian. The occurrence of reelaborated ammonoids (i.e. exhumed and displaced before their final burial) implies that tractive current flows or winnowing affected the burial of concretionary internal moulds. In the lower Bathonian strata, the dominance of homogeneous concretionary internal moulds of phragmocones, completely filled with sediment, is indicative of low rates of sedimentation and sediment accumulation, respectively associated with low degrees of stratigraphic and sedimentary condensation. However, at the Bajocian/Bathonian transition, hemipelagic, bed‐scale limestone–marl alternations show a maximum value of biostratigraphic completeness and there is no evidence for taphonomic condensation in the ammonoid fossil assemblages. Taphonomic analyses of the successive ammonoid fossil assemblages and taphofacies confirm the development of a deepening phase associated with sedimentary starvation, which characterizes the last episode within the deepening half‐cycle of third and second order cycles, in the Bas Auran area of French Subalpine Basin during early Bathonian.     

An integrative ichnological and taphonomic approach in a transgressive–regressive cycle: a case study from Devonian of Paraná Basin,Brazil

The palaeoenvironmental context of a section of the Devonian Ponta Grossa Formation (Paraná Basin) was examined using an integrated ichnological and taphonomic approach. Three taphofacies (T‐A, T‐B and T‐C) and six ichnofabrics are recognized. T‐A is mainly composed of disarticulated organisms and is associated with Chondrites, Planolites‐Palaeophycus, Asterosoma‐Zoophycos and Asterosoma‐Chondrites ichnofabrics, representing the Cruziana ichnofacies. The upward increase in diversity and abundance of body fossils for Taphofacies A can be explained by changes in sedimentation rates during aggradational to progradational phases. T‐B beds, represented by articulated brachiopods, occur in distal tempestites associated with the Skolithos ichnofabric (Skolithos ichnofacies) and represent higher hydrodynamic energy and oxygenation than in T‐A. Taphofacies C, characterized by a mix of articulated and disarticulated organisms, generally lacks bioturbation except for Chondrites ichnofabrics occurring only at the bed tops, suggesting low substrate oxygenation and low‐energy conditions. T‐C indicates the maximum transgression in the T‐R cycle, characterizing it as a good indicator of maximum flooding surfaces. The composite Asterosoma‐Teichichnus ichnofabric (bioturbation degree 5) occurs in layers without body fossils and represents suites of the Cruziana ichnofacies. This likely reflects intense intrastratal activity at all substrate levels, which facilitated the oxygenation of the substrate disallowing the preservation of organism remains. This observation indicates that the bioturbation is an important factor controlling the loss of taphonomic information within the TAZ, mainly when associated with detritus‐feeding trace fossils.     

The encrustation of fossil and recent sea-urchin tests: ecological and taphonomic significance

A comparison of fossil ( Echitwlampas sp. from the Lower Miocene Zogelsdorf Formation, Austria) and Recent ( Schizaster canaliferus from the northern Adriatic Sea) irregular sea-urchin tests shows that, upon their death, burrowing echinoids can serve as a substrate for a dense epigrowth. Size, shape, stable orientation, and surface residence-time were identified as key factors governing encrustation. The encrusters on fossil Echinolampas were bryozoans, serpulid polychaetes, barnacles, and coralline algae, while the recent material was initially encrusted by serpulids and hydrozoan colonies, and ultimately covered by the full range of sessile, hemi-sessile, and vagile species characterizing the benthic community in the Adriatic. In Echinolampas , epigrowth was more abundant on the lower (oral) surface; this specific distribution was echoed in S. canaliferus , where epigrowth started on the bottom side and grew upward. This indicates that the tests have a stable orientation and a surface residence-time long enough to allow intense encrustation. A taphonomic model is developed, and the role of encrustation on such special substrates for overall community structure is discussed. The Recent/fossil comparison provides new insights for both fields of study: the recent material indicates the role of soft-bodied faunas as well as the complexity of small-scaled ecological processes; the fossil material reflects many of the above phenomena and adds important taphonomic details on the fate of encrusted biogenic structures and on encruster growth patterns and distributions.     

The infaunal echinoid Micraster: Taphonomic pathways indicated by sclerozoan trace and body fossils from the Upper Cretaceous of northern Spain

Micraster echinoid fossils are common in the Upper Cretaceous Olazagutía Formation of northern Spain. Tests frequently record sclerobiont signatures (including bioerosion and encrustation), left by reaction and/or coaction phenomena. Among bioerosion structures, Oichnus simplex, O. paraboloides, O. ichnosp. A, Trypanites solitarius, Rogerella ichnosp. indet., Centrichnus cf. eccentricus, Maeandropolydora ichnosp. indet. and fungal microborings are found, as well as pits and fractures. As for sclerozoan body fossils, bivalves (Dimyidae, Anomiidae, Plicatulidae and other Pectinacea), polychaete annelids (serpulids and spirorbids), lituolid foraminiferans (Haddoniidae and Coscinophragmatidae) and bryozoans (cheilostomate ones and others undetermined), as well as other less common groups, have been identified. Taphonomic paths followed by Micraster tests are analysed, based on conservation state and degree of colonisation and sedimentary filling. This allows to distinguish between accumulated fossils and non accumulated ones (including resedimented and reelaborated ones).     

Taphonomy of dense concentrations of juvenile ammonoids in the Upper Cretaceous Mancos Shale,east-central Utah,USA

Dense concentrations of juvenile ammonoids were recently discovered in the Upper Cretaceous Mancos Shale of east-central Utah. In this paper, we describe this remarkable fossil occurrence and propose a taphonomic model to explain it. Large accumulations of cephalopods are not uncommon in the stratigraphic record, though concentrations of juveniles are relatively rare. Lithologic, geochemical, and stratigraphic evidence suggest that the unusual fossil occurrence we document here resulted from a combination of factors. We think the cause of these dense concentrations of juvenile ammonoids involves the hypothesized semelparous reproductive strategy of ammonoids, environmentally driven mass mortality, and a peculiar taphonomic phenomenon. In our model, an important role is played by the adverse oceanographic conditions common during the extreme greenhouse global climate regime of the Cretaceous, manifested by the well-known Ocean Anoxic Events around the time when these deposits were formed. The proposed mechanisms responsible for the mass accumulations we report here have operated at other times in Earth history, and may help explain similar occurrences elsewhere in the fossil record.     

Vertical displacement and taphonomic filtering of nannofossils by bioturbation in the Cretaceous–Palaeogene boundary section at Caravaca,SE Spain

K?dzierski, M., Rodríguez‐Tovar, F.J. & Uchman, A. 2011: Vertical displacement and taphonomic filtering of nannofossils by bioturbation in the Cretaceous–Palaeogene boundary section at Caravaca, SE Spain. Lethaia, Vol. 44, pp. 321–328. At the Caravaca section, SE Spain, the position of the Cretaceous–Palaeogene (K–Pg) boundary is well‐defined, with multidisciplinary datasets from a thin rusty layer at the base of the 10 cm dark boundary layer. Nannoplankton assemblages containing the Danian taxon Neochiastozygus sp. and enriched in Thoracosphaera spp. are displaced below the K–Pg boundary into the trace fossils Zoophycos, Thalassinoides and Chondrites. These trace fossils are filled with dark‐coloured sediments of the dark boundary layer. The nannofossil assemblage from the 1‐cm thick interval below the boundary, enriched in Thoracosphaera spp. and Braarudosphaera spp., may have been displaced by Chondrites tracemakers, the traces of which are abundant in this interval. The downward transport of the Danian nannofossils into the Maastrichtian by the tracemakers seems to be one of the common mechanisms responsible for their apparent appearance below the K–Pg boundary. The dark boundary layer contains very rare Danian specimens and abundant Maastrichtian nannofossils. The Maastrichtian taxa were most likely conveyed up on to the seafloor by tracemakers during the Danian. The redistribution of nannoplankton down and up across the rusty layer (K–Pg), challenges the usefulness of nannofossils for high‐resolution stratigraphy of the K–Pg boundary. □Nannoplankton, Cretaceous–Palaeogene boundary event, biogenic mixing, trace fossils.     

寒武纪早期宽川铺生物群中圆管螺化石显微结构及显微谱学分析

陕南寒武系底部宽川铺组不仅保存了大量的小壳化石,还以磷酸盐化的方式立体保存了多种软躯体动物的胚胎和成体化石,为研究早期动物矿化模式、个体发育方式以及动物躯体构型的早期辐射过程提供了非常关键的信息。然而宽川铺生物群的研究大多聚焦于化石系统分类及亲缘关系探索,对生物群的沉积背景、埋藏过程和保存模式的分析甚少。本文以宽川铺生物群的核心产出层位——陕西省西乡县大河镇宽川铺组下部磷质碎屑灰岩为研究对象,对其中的一类管状化石圆管螺及其围岩进行了显微结构学和显微谱学综合分析,获得了化石显微结构和关键结构对应的元素、矿物成分等信息,讨论了管状化石圆管螺的埋藏过程和保存模式,并在此基础上对其生物学特征进行了初步探讨。该研究对理解宽川铺生物群的埋藏机制提供了新的线索。     

Famennian (Late Devonian) ammonoids from the Ouarourout section (Saoura Valley,Algeria)

In North Africa, the ammonoids constitute an important part of the Devonian marine macro-invertebrates. New material has been recently collected in the ‘Argiles de Marhouma’ Formation from several sections located near Béni-Abbès in the Saoura Valley (Ougarta Mountains, Algerian Sahara). Red nodular limestones (i.e., ‘griotte’ facies) characterize this formation rich in ammonoids. The assemblages from the Ouarourout section are composed of Goniatitida and Clymeniida constituting 30 species and 19 genera belonging to 11 families, with Cyrtoclymenia, Erfoudites, Kosmoclymenia, Planitornoceras, Platyclymenia, and Prionoceras, as the most abundant genera. The taxonomic comparison and the biostratigraphic correlations are made by considering the assemblages recorded in the Anti-Atlas of Morocco, which are very close to those observed in Algeria. In the Ouarourout area, the ‘Argiles de Marhouma’ Formation contains middle and late Famennian ammonoid assemblages and three biostratigraphic intervals can be identified: Planitornoceras, Platyclymenia and Medioclymenia.     

Influence of microbial biofilms on the preservation of primary soft tissue in fossil and extant archosaurs

Background

Mineralized and permineralized bone is the most common form of fossilization in the vertebrate record. Preservation of gross soft tissues is extremely rare, but recent studies have suggested that primary soft tissues and biomolecules are more commonly preserved within preserved bones than had been presumed. Some of these claims have been challenged, with presentation of evidence suggesting that some of the structures are microbial artifacts, not primary soft tissues. The identification of biomolecules in fossil vertebrate extracts from a specimen of Brachylophosaurus canadensis has shown the interpretation of preserved organic remains as microbial biofilm to be highly unlikely. These discussions also propose a variety of potential mechanisms that would permit the preservation of soft-tissues in vertebrate fossils over geologic time.

Methodology/Principal Findings

This study experimentally examines the role of microbial biofilms in soft-tissue preservation in vertebrate fossils by quantitatively establishing the growth and morphology of biofilms on extant archosaur bone. These results are microscopically and morphologically compared with soft-tissue extracts from vertebrate fossils from the Hell Creek Formation of southeastern Montana (Latest Maastrichtian) in order to investigate the potential role of microbial biofilms on the preservation of fossil bone and bound organic matter in a variety of taphonomic settings. Based on these analyses, we highlight a mechanism whereby this bound organic matter may be preserved.

Conclusions/Significance

Results of the study indicate that the crystallization of microbial biofilms on decomposing organic matter within vertebrate bone in early taphonomic stages may contribute to the preservation of primary soft tissues deeper in the bone structure.     

Upper Pliocene bivalve shell concentrations from the Lower Chelif basin (NW Algeria): Systematics,sedimentologic and taphonomic framework

Sedimentologic and palaeontological investigation of the Upper Pliocene Slama Formation in the Lower Chelif Basin (NW Algeria) led us to collect important bivalve assemblages for taxonomic and taphonomic purposes. A rather comprehensive inventory list of Upper Pliocene bivalves from northwestern Algeria is now available and consists of 30 species, 17 of which are extinct ones. Four principal taphonomic attributes were analysed: bioerosion, encrustation, fragmentation, and abrasion. Physical and biogenic sedimentary structures are used for palaeoenvironmental interpretations. The taphonomic, sedimentologic and ichnological characteristics of most of the deposits suggests they originated from discontinuous processes of winnowing and bypassing of sediments, probably due to the action of storms in shallow waters, mainly in the shoreface depositional environment. The bivalve assemblage is dominated by disarticulated valves and displays significant taphonomic alteration in the shells. Sclerobionts traces in shells particulary affect the oyster shells. Bioerosion traces are predominately those of clionid sponges (Entobia isp.), polychaetes (Maeandropolydora isp. and Caulostrepsis isp.), bivalves (Gastrochaenolites isp.), and of predatory gastropods (Oichnus isp.). Among the sclerobionts, the identified encrusters were juvenile oyster recruits, barnacles, polychaetes (serpulid tubeworms), bryozoans (Microporella sp. and Acanthodesia sp.), and vermetid gastropods (Petaloconchus intortus).     

贵州寒武纪杷榔组古蠕虫类埋藏特征及意义*

贵州剑河寒武纪杷榔组辣子寨剖面含有丰度较高的古蠕虫类化石。化石鉴定为Wronascolex geyiensis, 主要保存在三个层位。在对三个层位的岩石、沉积特征、化石成因及埋藏特征探讨分析后, 证实W. geyiensis化石保存于快速的沉积事件导致的浊流沉积层内, 而化石埋藏的完美程度受到成岩过程中埋藏位置、沉积物中矿物结晶和充填方式的影响, 这些后期的成岩、成矿作用对先期形成的化石精细结构产生了直接和间接的破坏作用。本文通过对W. geyiensis化石体上黏土矿物、草莓状黄铁矿、自形–半自形黄铁矿的成因分析后, 获得最适合保存软躯体化石的环境应该为缺氧且生物体与孔隙水中的硫酸盐无接触的原地和近原地埋藏条件。     

Serpulids and other calcareous tube-dwelling encrusting polychaetes from the Early Cretaceous Agrio Formation (Neuquén Basin,Argentina)

Serpulids and other related tube-dwelling polychaetes are often ignored when found as fossil remains. They are, however, a widespread and important group today, and abundant literature has been published on them. Knowledge of fossil serpulids is centered on European material, and little has already been done on South American fossil calcareous tubes. In this paper, seven serpulid and sabellid morphotypes are described from the Early Cretaceous marine Agrio Formation of Argentina, revealing a diversity of worms recorded as encrusters on bivalves, ammonites and corals. Sabellids are represented by Glomerula cf. serpentina. Serpulids are represented by two subfamilies: “Serpulinae” includes Mucroserpula mucroserpula, Parsimonia antiquata, Placostegus cf. conchophilus, Propomatoceros semicostatus and P. sulcicarinatus; Spirorbinae is represented by heavily worn tiny coiled tubes assigned to ?Neomicrorbis. Serpulids and sabellids are one of the main components of the mollusk-encrusting fauna recorded in the Agrio Formation, along with small oysters but much more diverse. They are most commonly found as post-mortem encrusters, but some cases of unquestionable living interaction are also found, such as serpulid tubes embedded on coral branches. They are often overgrown by bryozoans, and sometimes by oysters; they frequently occur aggregated.     

Paleoecology of Sphenothallus on an Upper Ordovician hardground

A hardground from the Upper Ordovician Dillsboro Formation near Dillsboro, Indiana, U.S.A., preserves an assemblage of encrusting and boring fossils on both top and bottom surfaces. The slab is inferred to have been an undercut ledge, and the dominant fossils of the assemblage, holdfasts of the tube-building worm Sphenothallus and trepostome bryozoans, are prevalent on both sides. The clumping of Sphenothallus holdfasts has been statistically demonstrated using a nearest-neighbor technique. Sphenothallus has also been shown to withstand overgrowth in interactions with bryozoans.     

The Ediacaran Aspidella‐type impressions in the Jinxian successions of Liaoning Province,northeastern China

Macroscopic impression fossils from the Xingmincun Formation of the Jinxian Group, Liaoning Province of northeastern China, are identified as members of the Aspidella plexus of Ediacaran age. This is the first recognition of the taxon in the Liaoning Province, although such fossils have been previously recorded in the succession, but were referred to as new species and relegated to an earlier Neoproterozoic age. A revision of the taxonomic interpretation and relative age estimation of the previous record is provided, as well as an evaluation of abiotic vs. biotic processes that could produce similar structures to studied impressions. The mode of preservation of the fossils is considered from a biochemical point of view and along with the properties of organic matter in the integument of soft‐bodied metazoans. The selective preservation of the Ediacaran organisms, including metazoans, as impressions (moulds and casts) against the organically preserved contemporaneous cyanobacterial and algal microfossils, and an exceptionally small number of terminal Ediacaran metazoan fossils (Sabellidites, Conotubus and Shaanxilithes), demonstrates the non‐resistant characteristics and the very different biochemical constitution of the Ediacaran metazoans compared with those that evolved in the Cambrian and after. The refractory biomacromolecules in cell walls of photosynthesizing microbiota (bacterans, cutans, algaenan and sporopollenin groups) and in the chitinous body walls of Sabellidites contrast sharply with the labile biopolymers in Ediacaran metazoans known only from impressions. The newly emerging biosynthesis of resistant biopolymers in metazoans (chitin and collagen groups) initiated by the annelids at the end of Ediacaran and fully evolved in Cambrian metazoans, considered with the ability to biomineralize, made their body preservation possible. The Chengjiang and Burgess Shale metazoans show evidence of this new biochemistry in body walls and cuticles, and not only because of the specific taphonomic window that enhanced their preservation.