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Integrated microfacies, macrobenthos and trace-fossil analysis of the lower‒middle Miocene succession of Gebel Gharra, Cairo-Suez District, Egypt

Mandor Mona, El Hedeny Magdy, El-Sabbagh Ahmed, Nagm Emad, Abdelaal Abdelaal, Rashwan Mohamed, Mansour Heba

Annales Societatis Geologorum Poloniae

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2023

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Vol. 93, No. 4

381--409

EN

The palaeoecology and palaeoenvironments of the lower–middle Miocene succession in Gebel Gharra, NW of Suez, Egypt, are interpreted, on the basis of a detailed study of microfacies, trace fossils, and macrofaunal benthic assemblages. This succession consists of a lower siliciclastic part (the Gharra Formation) and a carbonate-dominated upper part (the Geniefa Formation), corresponding to a general transgression-regression cycle. Facies characteristics indicate depositional palaeoenvironments, ranging from supratidal, lagoonal, to shoal settings on an inner ramp that was influenced proximally by clastic input. At least seven ichnotaxa were recorded in the lower Miocene Gharra Formation, representing suites of the Skolithos ichnofacies. Among them, the ichnogenus Polykladichnus is recorded for the first time in Egypt. The macrobenthic taxa identified in 13 statistical samples are grouped into five assemblages (A–E) that are described and interpreted as the remains of communities. The faunal distribution and trophic structure of most of these assemblages confirm the existence of relatively stable and low-stress conditions. However, the trophic structure of the assemblages reflects the influence of particular environmental parameters, the dissolution of aragonitic shells and/or sample-size effects. Environmental parameters, controlling the distribution of trace and/or body fossils, include substrate consistency, bathymetry, water energy, productivity level, rate of sedimentation, salinity, and oxygen availability. The results of integrated lithoand biofacies analysis confirm that the succession studied was deposited in different environmental settings, providing perfect conditions for the occurrence and preservation of trace-fossil and macrobenthos assemblages.

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Aszulcicrinus, a new genus of the Triassic crinoid family Dadocrinidae (Articulata; Encrinida) from Poland

Hagdorn Hans

Annales Societatis Geologorum Poloniae

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2020

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Vol. 90, No. 4

381--390

EN

The new genus and species Aszulcicrinus pentebrachiatus of the family Dadocrinidae from the ear-ly Middle Triassic Lower Gogolin Formation of Upper Silesia Upland is described. In contrast to Dadocrinus, the second primibrachial of Aszulcicrinus is not axillary for articulation with two arms but articulates with a third primibrachial and the first pinnule. This character results in five unbranched arms, which is unique in the order Encrinida. The significance of this character is discussed and paedomorphic or ecophenotypic explanations are excluded. The presence of only five unbranched arms predominates through the ontogeneny of Aszulcicrinus from early postlarval to adult stage. Within the family Dadocrinidae (Aszulcicrinus - Dadocrinus - Carnallicrinus), a phylogenetic trend towards size increase coincident with increasing arm number and denser pinnulation is inter-preted as an improvement in filter-feeding efficiency. The sedimentological and taphonomic setting of the obru-tional conservation lagerstätte of the type locality is described.

3

Large cruzianid trace fossils in the Ordovician of the peri-Baltic area : the case of the Bukówka Formation (Holy Cross Mountains, Poland)

Stachacz M., Łaska W., Uchman A.

Geological Quarterly

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2018

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Vol. 62, No. 2

400--414

EN

The Middle Ordovician Bukówka Formation, composed of fine-grained quartz sandstones with siltstone intercalations, belongs to the Kielce Region of the Holy Cross Mountains (peri-Baltic palaeogeographic position). It contains trace fossils of low diversity and poor preservation. Particularly noteworthy are the large Cruziana and Rusophycus, that are typical of peri-Gondwanan areas. They consist of casts of bilobate furrows showing diverse preservation. Other trace fossils include mostly horizontal pascichnia, cubichnia, and fodinichnia, but also vertical domichnia. The trace fossil assemblage is typical of the archetypal Cruziana and partly of the Skolithos ichnofacies. Some beds contain abundant orthid brachiopods. The trace fossils and sedimentary structures (horizontal, low-angle and wave ripple cross-laminations, hummocky cross-stratification) suggest deposition on the middle and lower shoreface with storm influence. The poor preservation and low diversity of the trace fossils are related to the homogeneous lithology, low accumulation rate, shallow burial of organic matter and strong bioturbation. Therefore, animals burrowed strongly but mostly in shallow tiers. Thus, the preservation potential of their traces was much lower than in many peri-Gondwanan sections but still higher than in Baltica sedimentary rocks. This explains the provincial differences in ichnofauna during the Ordovician, which at least partly were influenced by the preservation potential.

4

Scrutinizing Barremian coprolite inclusions to record digestive strategies

Barrios-de Pedro S., Buscalioni Á. D.

Annales Societatis Geologorum Poloniae

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2018

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Vol. 88, No. 2

203--221

EN

The exceptional preservation of the Las Hoyas coprolites allows the taphonomic study of inclusions on twelve morphotypes and twenty-three specimens. Non-destructive techniques were applied to study the digestion features (pitting, corrosion lines, shape of the fractures at the ends) and the arrangement, number, and size of inelusions. An analysis based on non-metric, multidimensional scaling ordination identified the similarities among the inclusion features and morphotypes. The morphotypes are clustered on the basis of the way of ingestion and the digestive process. The authors recognize three digestive strategies for the Las Hoyas coprolites: (1) ingestion of prey with limited processing in the mouth, scarce to less effective acid secretions, and/or defecation in a short period of time; (2) ingestion of the prey with mastication prior to deglutition, and defecation over a longer period of time; (3) mastication and long retention time of food in the digestive system with more effective acid secretions. This study is a first step in the understanding of the feeding ecology of the Las Hoyas Barremian lentic ecosystem, based on coprolites.

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Benefits and weaknesses of radiocarbon dating of plant material as reflected by Neolithic archaeological sites from Poland, Slovakia and Hungary

Nowak M., Moskal-Del Hoyo M., Mueller-Bieniek A., Lityńska-Zając M., Kotynia K.

Geochronometria

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2017

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Vol. 44, no. 1

188--201

EN

Radiocarbon dating of the plant material is important for chronology of archaeological sites. Therefore, a selection of suitable plant samples is an important task. The contribution emphasizes the necessity of taxonomical identification prior to radiocarbon dating as a crucial element of such selection. The benefits and weaknesses of dating of taxonomically undetermined and identified samples will be analysed based on several case studies referring to Neolithic sites from Hungary, Slovakia and Poland. These examples better illustrate the significance of the taxonomical identification since plant materials of the Neolithic age include only a limited number of cultivated species (e.g. hulled wheats) and typically do not contain remains of late arrived plants (e.g. Carpinus betulus and Fagus sylvatica). For more accurate dating results cereal grains, fruits and seeds, which reflect a single vegetative season, are preferred. Among charred wood, fragments of twigs, branches and external rings should mainly be taken into account, while those of trunks belonging to long-lived trees should be avoided. Besides the absolute chronology of archaeological features and artefacts, radiocarbon dating of identified plant remains might significantly contribute to the history of local vegetation and food production systems.

6

Serpukhovian (Early Carboniferous) Rugosa (Anthozoa) from the Lublin Basin, eastern PolandSerpukhovian (Early Carboniferous) Rugosa (Anthozoa) from the Lublin Basin, eastern Poland

Fedorowski J.

Annales Societatis Geologorum Poloniae

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2015

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Vol. 85, No. 1

221--270

EN

Sixteen rugose coral species, two known previously, nine new, three left in open nomenclature, and two identified as affinis, are described from the early Serpukhovian strata of the Lublin area, eastern Poland. Rugose corals of that age here are described for the first time from Poland. New genera include Birkenmajerites, Chelmia and Occulogermen. New species include: Axisvacuus tenerus, Birkenmajerites primus, Chelmia radiata, Nervophyllum lukoviensis, Occulogermen luciae, Rotiphyllum plumeum, Sochkineophyllum symmetricum, Zaphrentites rotiphylloides and, Zaphrufimia anceps. A brief analysis of the taphonomy, possible relationships and geographical connections of the corals described here to rugose coral faunas from adjacent areas also is included.

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How many Upper Triassic bone–bearing levels are there in Upper Silesia (southern Poland)? A critical overview of stratigraphy and facies

Szulc J., Racki G., Jewuła K., Środoń J.

Annales Societatis Geologorum Poloniae

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2015

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Vol. 85, No. 4

587--626

EN

At least three widely separated bone-bearing intervals in the Upper Triassic succession of Upper Silesia, ranging in age from the Carnian to Rhaetian (i.e., in the interval of 25 Ma), are presented in papers by the Warsaw research group, led mainly by Jerzy Dzik and/or Grzegorz Niedźwiedzki. The stratigraphic arguments are reviewed for the vertebrate localities studied so far, in particular for the well-known middle Keuper sites at Krasiejów and Lipie Śląskie, to show that the previously proposed age assignments are still inadequately documented and questionable. This unreliability is exemplified by the evolving stratigraphic correlation of the fragmentary Silesian sections (8–18 m thick) with informal subsurface units from central-western Poland and with the German standard succession, ultimately not corroborated by comparison with the composite reference succession of the Upper Silesian Keuper, including new profiles (ca. 260 m thick) from the Woźniki K1 and Patoka 1 wells. Based on a multidisciplinary stratigraphic study covering consistent litho-, bio-, climato- and chemostratigraphic premises, focused on the regional reference section, two bone-bed levels only are recognized in the Patoka Marly Mudstone-Sandstone Member (= Steinmergelkeuper) of the Grabowa Formation, not very different in age (Classopollis meyeriana Palynozone; probably IVb Subzone): (1) the localized Krasiejów bone breccia level (early Norian in age) in the Opole region, and (2) the far more widely distributed Lisowice bone-bearing level (middle Norian) in a vast alluvial plain (braided to anastomosing river system) during the Eo-Cimmerian tectonic-pluvial episode. As a consequence of the principal uncertainties and controversies in Upper Triassic terrestrial stratigraphy, this is still a somewhat preliminary inference. Typical skeletal concentra- tions of a combined hydraulic/sedimentologic type, related to fluvial processes, are common in the Upper Silesian Fossil-Lagerstätten, although factors governing preservation are probably important, as well.

8

Evidence of wildfires during deposition of the Upper Silesian Keuper succession, southern Poland

Kubik R., Uhl D., Marynowski L.

Annales Societatis Geologorum Poloniae

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2015

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Vol. 85, No. 4

685--696

EN

Charcoals from the Upper Triassic vertebrate-bearing clays of the Zawiercie area (Upper Silesia, S-Poland) were analyzed using petrographic methods, to reconstruct burning temperatures as well as taphonomic processes. SEM and reflected light microscopy show excellent preservation of charcoals most probable connected with early diagenetic permineralization by calcite. The charcoal was assigned to three morphotypes, probably corresponding to three different fossil taxa. Fusinite reflectance data suggest, that the highest temperature reached above 600 °C (fusinite reflectance of 3.59%), what counterparts to the lower limit crown fire temperature. The values for most of the samples are lower (ca. 1% to 2.5%) what is typical for surface fires. In many cases fusinite reflectance values depends on the measured zone within the sample. Such zonation formed due to charring tem- perature differences. In zones remote from the potential fire source, reflectance values gradually decreases. It implies that calculation of fire temperatures based on average fusinite reflectance values might be too far-reaching simplification. Occurrence of fungal hyphae within the charcoal supports the interpretation of a predomination of surface fire, consuming dead twigs and stems. The low content of micro-charcoals in charcoal-bearing rocks as well as rounded to sub-rounded shapes of large specimens indicates that they were transported after burning, deposited away from the burning area, and finally early diagenetic mineralization.

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Taxonomy and taphonomy of Cenomanian (Upper Cretaceous) nautilids from Annopol, Poland

Machalski M., Wilmsen M.

Acta Geologica Polonica

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2015

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Vol. 65, no. 4

495--506

EN

A nautilid faunule of seven specimens, comprising Eutrephoceras bouchardianum (d’Orbigny, 1840), Cymatoceras deslongchampsianum (d’Orbigny, 1840), and Cymatoceras tourtiae (Schlüter, 1876) is described from a condensed middle Cenomanian interval at Annopol, Poland. C. tourtiae is recorded for the first time in Poland. The studied material consists of reworked phosphatised internal moulds of phragmocones, which may be of early or middle Cenomanian age, given the stratigraphic range of the associated ammonites. The nautilid moulds vary in inferred mode of infilling, and in intensity of abrasion, bioerosion and mineralisation. The sediment entered the phragmocones in two ways: 1) through punctures in the shell, the result of bioerosion or mechanical damage; 2) through siphonal openings by intracameral currents. In contrast to the fossil moulds from the Albian phosphorites of Annopol, which originated via direct precipitation of apatite around and/or inside fossils, the present nautilid moulds seem to have originated through secondary phosphatisation of the initially calcareous moulds. Diversity of taphonomic signatures in nautilid material from the middle Cenomanian interval at Annopol is compatible with the complex, multievent depositional scenario proposed for this level.

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Geology and taphonomy of the base of the Taquaral Member, Irati Formation (Permian, Paraná Basin), Brazil

Chahud A., Petri S.

Acta Geologica Polonica

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2015

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Vol. 65, no. 3

379--387

EN

The taphonomy of Early Permian vertebrates from a sandy facies at the base of the Taquaral Member, Irati Formation, was surveyed in order to acquire data for the interpretation of the sedimentary processes and paleoenvironment of deposition. Six outcrops from the Rio Claro municipality and surrounding areas, from the Brazilian State of São Paulo, were investigated. The vertebrate groups are Chondrichthyes (Xenacanthiformes, Ctenacanthiformes and Petalodontiformes), Osteichthyes (Actinopterygii and Sarcopterygii) and Tetrapodomorpha. They occur as loose teeth, scales, spines and bone remains. The sandy facies is characterized by fining upward deposition. The coarser sandstone immediately above the underlying Tatuí Formation is rich in Chondrichthyes. However, the fine sandstone above, immediately beneath the silty shale facies, is devoid of Chondrichthyes, though Osteichthyes scales, teeth and bones were present. The taphonomy is important for inferring sedimentary processes and then the paleoenvironments. The poor sorting of the sandstone and the presence of fossils that are mostly abraded or worn are indicative of a high energy environment. In contrast, the presence of fossils in a good state of preservation, some without abrasion and breakages are indicative of only limited transport. Differences of fossil spatial density, numbers of specimens and taxa may be explained by the dynamics of deposition, from details of the palaeoenvironment can be obtained.

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The results of palaeontological excavations in the Sadowa Góra quarry (2012-14)

Surmik D., Skreczko S., Wolny M.

Contemporary Trends in Geoscience

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2014

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Vol. 3, iss. 1

90--99

EN

Palaeontological fieldwork (2012‒14) in the Sadowa Góra quarry carried out under the auspices of the University of Silesia, within the framework of a research project supported by the National Science Centre, helped to document the taxonomic diversity of Middle Triassic marine vertebrates from the Cracow-Silesia region. Accumulations of fossil bones are correlated with storm deposition and are time-averaged.

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Coprolite of a durophagous carnivore from the Upper Cretaceous Godula Beds, Outer Western Carpathians, Poland

Bajdek P.

Geological Quarterly

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2013

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Vol. 57, No. 2

361–-364

EN

The Upper Cretaceous turbidite sandstones of the Godula Beds at Międzybrodzie Bialskie, Outer Western Carpathians, Poland, yielded a specimen here interpreted as a coprolite due to its elongated morphology and a high content of fragmented inoceramid shells. The coprolite was produced by a durophagous carnivore, which was most likely a teleost fish, or possibly a reptile. Coprolites are therefore confirmed to have a potential utility as aggregations of body fossils in macrofossil-poor sedimentary rocks, exemplified by the Godula Beds.

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Polskie Solnhofen

Kin A., Błażejowski B.

Przegląd Geologiczny

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2012

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Vol. 60, nr 7

375-379

EN

We briefly report on recent discovery of a new Fossil-Lagerstätte at Owadów-Brzezinki quarry (central Poland), where Upper Jurassic (Upper Tithonian = Middle Volgian) shallow water carbonates are exposed. Th section includes a richly fossiliferous horizon of lithographic-type limestones, formed in a lagoonal depositional environment. Numerous organic and phosphatic remains of wide range of both marine and terrestrial creatures, including horseshoe crabs and decapods, disarticulated fish skeletons, remains of marine reptiles, ammonites, dragonflies, beetles, and rare isolated pterosaur bones and teeth, were found in association with an extremely abundant small bivalves Corbulomima obscura. The richly fossiliferous horizon at Owadów-Brzezinki is stratigraphically closely related to one of the world's most famous Fossil-Lagerstätte sites – Solnhofen (Bavaria, south-central Germany).

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Wstępne dane o tropach stawonogów z furongu (górnego kambru) Wiśniówki Wielkiej (Góry Świętokrzyskie) i ich tafonomii

Sadlok G.

Przegląd Geologiczny

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2011

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Vol. 59, nr 1

82-90

EN

Previous works on arthropod trace fossils from the Furongian (Upper Cambrian) section exposed at theWioeniówkaWielka quarry (Holy Cross Mountains, Poland) focused on trilobite-made structures referred to as Rusophycus polonicus and Cruziana semiplicata. Arthropod trackways did not receive much attention. The present paper contains preliminary data on new records of arthropod trackways from the Furongian of the Wioeniówka Wielka section and on their taphonomy. The material studied comprises undetermined arthropod tracks and specimens belonging to three ichnogenera: ?Asaphoidichnus, Diplichnites and Petalichnus.

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The usefulness of a taphonomic approach for studies of Pleistocene mammals

Pawłowska Kamilla

Geologos

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2010

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Vol. 16, No. 3

183--189

EN

The potential usefulness of taphonomical research for studies of Pleistocene mammal remains is detailed. The required taphonomical research involves two stages. The first one is the biostratinomical stage, which concerns the time between the death of the organism and its burial; for this time-span, the spatial distribution of the remnants is analysed, as well as the weathering marks, the activity of predators (i.e. gnawing and digestion), the influence of temperature, intentional human activity, rodent marks (i.e. gnawing), and trampling. in the second one is the diagenetic stage, which deals with the time-span from the burial of the remnants to their discovery; for this time-span, the influence of physical and chemical processes (including diagenetic alterations of the deposit, the influence of water, and plant-root marks) are considered. The application of taphonomical analysis provides the possibility of reconstructing the environmental conditions under which the skeleton or bone complex was preserved, as well as the depositional history of the bones (postconsumption remnants, flood remains, accumulation of bones by predators). This opens new possibilities for the study of Pleistocene bones in Poland.

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Unusual preservation of Ophiomorpha in middle Miocene rocks of Wadi Zablah, east Matruh area, northwestern Egypt

Gameil M., Sadek S.

Acta Geologica Polonica

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2010

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Vol. 60, no. 1

39-44

EN

Unusual biogenic structures in the form of hollow burrows are preserved in middle Miocene sandy limestones (calcarenites) exposed in Wadi Zablah, east of the town of Mersa Matruh along the Egyptian Mediterranean coast. This calcarenite unit is about 30 m thick and lies in the middle part of the Marmarica Formation. The burrows commonly are up to 2.5 m long and can reach a length of 3 m in some outcrops. The internal diameter ranges from 1 to 5 cm. In most cases there is a hard cemented zone surrounding the hollow burrows that ranges in thickness from 0.2 to 0.4 cm. In several burrows where the hard cemented zone is preserved, a knobby sculpture is visible on the internal surfaces of the burrows. This is considered to be a negative mold of the pelleted wall of Ophiomorpha. This inverted knobby sculpture is formed by the cemented zone, which permitted the trace fossils. preservation, the original Ophiomorpha wall having been dissolved away during or subsequent to lithification by subsequent weathering processes. The presence of these burrows in association with marine fossils suggests a littoral to very shallow shelf environment.

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Indirect biostratigraphy in condensed successions: a case history from the Bajocian of Normandy (NW France)

Pavia G., Martire L.

Volumina Jurassica

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2009

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Vol. 7, no. 1

67-76

EN

The fossil assemblages of the Bajocian of Normandy are affected by taphonomic condensation, and the use of these assemblages for biostratigraphy must be carried out with great care because of the taphonomic reworking (reelaboration) of most of them. Nevertheless such beautiful fossils, ammonites in particular, retain their value at least as taxonomic references if their relative stratigraphic position is recognized. Such a goal has been achieved in the Bretteville section, where the "Oolithe Ferrugineuse de Bayeux" Formation (OFB), consisting of 14 beds contained within 170 cm of strata, is exposed. Each bed contains a condensed ammonite assemblage in which the overall chronologic interval represented by fossils is longer than the time of sedimentation of the bed, and no ammonites can be defined as contemporaneous with the enclosing matrix, except for the topmost two beds. The timing of biologic and sedimentary events in this Fe-oolitic succession must thus be established in an indirect way, through a stratigraphy of fossils based on their taphonomically delayed first occurrence. In particular, we can only define the maximum age of each layer, constrained by the youngest recorded fossil. On the basis of this approach, the lower part of the OFB is shown to fall within the middle to upper part of the Bajocian Stage (Humphriesianum to Parkinsoni chrons), whereas the uppermost OFB can be referred to as the uppermost Bajocian (latest Parkinsoni Chron). We conclude that, at Bretteville and in general for the Fe-oolites of Normandy, fossiliferous horizons with condensed assemblages have no value for definition of the biostratigraphic standard scale, and that indirect biostratigraphy is useful to assign minimal chronologic values to taxa when (1) their stratigraphical range has not yet been established in expanded successions, (2) they are new taxa, and (3) they are present only in a condensed succession that suffered from the same taphonomic constraints as the Bajocian of Normandy.

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Kopalne zygospory glonów Zygnemataceae (Chlorophyta) z osadów górnego miocenu KWB Bełchatów

Worobiec E., Worobiec G.

Przegląd Geologiczny

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2008

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Vol. 56, nr 11

1000-1004

EN

The Zygnemataceae are an extant family of freshwater filamentous green algae which produce acid-resistant zygospores. Palynomorphs of probable zygnematacean affinity occur in sediments of the Carboniferous to Holocene age (van Geel & Grenfell, 1996). These algae reproduce using four types of spores, but only zygospores and probably aplanospores are acid-resistant and can be preserved in the fossil record. The majority of recent species have zygospores of constant form of three types: elliptical (occurring in genera Debarya and Spirogyra), square (occurring in Mougeotia) or circular (occurring in Zygnema). The zygospores normally have a three-layered wall (exospore, mesospore and endospore), but only mesospore contains a decay and acid-resistant substance (most probably algaenans), so usually only this layer is preserved in fossil state, and is of interest to palynologists. The mesospore layer is smooth or ornamented with various sculptures (Kadłubowska, 1972; Grenfell, 1995). The shape and sculpture are very important features for determination of both the recent and fossil species. Two samples from the Bełchatów Lignite Mine were palynologically examined and two types of probable fossil zygnematacean zygospores, differing in shape, were encountered. The following species have been distinguished: Tetraporina sp., Spintetrapidites quadriformis Krutzsch & Pacltová as well as Ovoidites elongatus (Hunger) Krutzsch, and O. ligneolus Potonié ex Krutzsch. The fossil genus Tetraporina is usually related to the recent zygnematacean algae zygospores of Mougeotia genus, fossil Ovoidites is the nearest the recent zygospores of Spirogyra and Sirogonium, while Spintetrapidites is similar to both zygospores of Zygnemataceae and Tetraedron green algae. Species of recent genera Mougeotia and Spirogyra are usually found in shallow, freshwater, oxygen-rich environments such as ponds, lake margins (paludal or low gradient fluvial), ditches and very slowly moving streams (Kadłubowska, 1972). Occurrence of Tetraporina and Ovoidites zygnematacean zygospores in the material studied from Bełchatów points out at presence of water basin(s) during sedimentation time. That confirms the previous geological results that formation of examined sediments took place in the environment of a meandering river (including ox-bow lakes).

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Updated Middle Oxfordian biostratigraphy in the Central Iberian Chain (Spain) and state of progress of perisphinctid systematics

Bello J., Melendez G., Page K., Ramajo J.

Volumina Jurassica

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2006

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Vol. 4, no. 1

230-230

EN

Middle Oxfordian deposits in the Central Iberian Range (E Spain) are generally developed in biohermal to biostromal sponge limestones (Yatova Fm.). A major stratigraphic gap at the Callovian/Oxfordian boundary typically omits most of the Lower Oxfordian - excepting a few ephemeral sedimentary episodes - and the basal Middle Oxfordian Plicatilis Biozone. Despite being locally incomplete, however, the Transversarium and Bifurcatus biozones are well developed throughout the basin and display a remarkably complete ammonite succession. Perisphinctids are the key-group for biostratigraphic purposes and research carried out over the last 25 years has significantly contributed to refining the zonal scale for this interval. New information on this sequence indicates the following key points: 1. Recent progress includes the widespread recognition and correlation, including outside of Iberia, of the Rotoides Subbiozone at the top of the Transversarium Biozone and its further subdivision into two well-defined biohorizons: a lower, Universalis Biohorizon (Index: Per. universalis Bello, sp. nov. =Per. jelskii Siemiradzki, 1899, non 1891) and an upper Wartae Biohorizon. The latter is important as the direct forerunner of true representatives of Per. (Dichotomoceras) of the stenocycloidesbifurcatoides group. In addition, the identification of a Malinowskae Biohorizon with Per. malinowskae Br-Lewifski at the top of Bifurcatus Biozone (=Upper Grossouvrei Subbiozone) provides a valid name and level for specimens long misinterpreted as Per. bifurcatus (Quenstedt). 2. Taphonomic analysis of ammonite associations has provided an important tool for interpreting the sedimentary processes and the palaeogeographic evolution of the basin, including establishing the duration and reconstructing the processes associated with stratigraphic gaps. Similarly, taphonomic features shown by ammonite internal moulds across the Middle-Upper Oxfordian boundary (Bifurcatus-Hypselum chronozones) has facilitated the interpretation of this interval as a deepening stage on the platform, and therefore highly relevant for sequence and palaeogeographic analysis. 3. Finally, substantial progress achieved on the Perisphinctinae indicates the benefits of "re-shapeing" the systematics of the group in terms of modern, biological nomenclature. An open proposal is made considering the possibility of a unified taxonomy combining dimorphic pairs and a classification of the subfamily at the genus level, either a succession of genera as evolutionary links or perhaps a succession of species under a unique genus Perisphinctes (M & m).

20

Relative biostratigraphy in condensed succession: a case history from the Bajocian of Normandy

Pavia G., Martire L.

Volumina Jurassica

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2006

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Vol. 4, no. 1

201-202

EN

The classic dm-thick sections of the Bajocian of Normandy, NW France, such as those of St. Honorinedes- Pertes (formerly d’Orbigny’s stratotype), Sully and St. Vigor in the surroundings of Bayeux are affected by taphonomic and stratigraphic condensations (Pavia 1994). The use of their fossils for biostratigraphic purpose to date the embedding sediments must be avoided because of the taphonomically reworked state of most of them. Such beautiful fossils, ammonites in particular, would become useful again as taxonomic reference if their relative position is recognized. This goal is what Gauthier et al. (1996) tried to achieve in the more than 2 m thick section of Feuguerolles, south of Caen; but the fossil preservation is poor and the Quaternary weathering altered the Fe-oolitic limestone so that beds are not clearly discernible and taphonomic analysis is difficult. A succession similar to that of Feuguerolles was exposed more than ten years ago during a highway construction at Bretteville, SW Caen (Martire & Torta 2000). The succession of the Oolite Ferrugineuse de Bayeux Formation consists of evenly bedded limestones which total the thickness of 140 cm. Even more important beds are lenticular so that, correlating two separated sections, 20 metres far one to the other, we numbered 13 interfingered layers each one with a distinct fossil assemblage. Beds are rich in fossils and a large collection of them is stored in the Museo di Scienze Naturali di Torino. Most ammonites, if not all, are reelaborated and the taphonomic reworking could have been repeated many times; consequently beds contain fossils belonging to different taphorecords, each one characterized by a definite state of fossil preservation discernible from that of other mixed fossils. The taphonomic condensation (sensu Gomez & Fernandez-Lopez 1994) does not allow any reliable biostratigraphy. Nevertheless, the detection of bed interfingering and the careful collection of fossils, bed by bed, led us to consider the 13 successive fossil assemblages as the product of spatially restricted sedimentary events whose age could be outlined by the biochronologic relationships of ammonites contained in superposed beds. Each bed gets in this way a minimal relative age. This provided a relative biostratigraphic succession even if all fossils are reelaborated, which helps in using fossils at least for taxonomic purposes. It is worth noting that such a practice does not constitute any reference either for standardizing biozonation nor for correlation purpose except at regional extent. An example from the Bretteville section could put into practice this procedure. Bed 9 delivered more than 35 identified ammonites; all specimens are reelaborated and biochronologically span the Humpriesianum and Niortense zones; no taxa of the above Garantiana Zone are present. The overlying bed 10 is equally rich in reelaborated ammonites with taxa again referable to the Humpriesianum and Niortense Zones, but also taxa such as Pseudogarantiana and Prorsisphinctes stompus which point to the Garantiana Zone. In conclusion, we are confident to assign the bed 9 to the passage between Niortense and Garantiana zones.