Sedimentary environment of Devonian pelagic limestones in the Southern Alps

Primary sedimentary structures combined with the geometry of Devonian and Lower Palaeozoic lithosomes in the Southern Alps (Austria and Italy) suggest many doubts about the published environmental and bathymetric interpretation of some Lower to Middle Devonian pelagic nodular limestones as 'deep-water' abyssal deposits. Every graded bed is not necessarily aturbidite; a single or some turbiditic beds are not necessarily deep-water or abyssal deposits; carbonate dissolution does not necessarily take place only below the carbonate compensation depth (CCD). Data show that graded allodapic beds, like those of the Lower to Middle Devonian of the Alps, may have been deposited as storm layers at a depth not exceeding some hundreds of metres. Accordingly the margins between Lower Devonian shallow-water platform and basins were characterized by low gradient and transitional sedimentary conditions. They became very steep only at the Devonian–Carboniferous transition because of synsedimentary block faulting.     

Stratigraphy, geometry, and facies of a Middle Devonian ramp-to-basin transect (Eastern Anti-Atlas, SE Morocco)

Summary In the castern Anti-Atlas (SE Morocco), a small sedimentary basin (Mader Basin) evolved during the late Palacozoic. The Middle Devonian deposits consist of shales and limestones with a thickness up to 700 m in the depocentre. Sedimentary structures and sole marks of Middle Devonian limestones indicate transport from the northwest and the south towards the basin centre, located in the central Mader area. Lithostratigraphic, biostratigraphic, and dynamic stratigraphic approaches were applied to correlate stratigraphic sections. Five correlatable large-scale base-level hemicycles were recognized in the Middle Devonian succession. Thickness trends of Middle Devonian deposits, regional correlations, and facies-trends reveal the geometry of a carbonate ramp. The carbonate ramp was slightly inclined (<1°) to the NE. A sedimentary wedge, consisting of limestones and limestone/marl alternations, was deposited during the Eifelian and marks the transition from the ramp to the adjacent basin. Middle Devonian water depths are estimated as close to and within the storm wave-base at the southern area of the ramp and far below storm wave-base in the northeastern part of the ramp. Shallowest conditions (inner-ramp environment), close or within the fairweather wave-base, existed during the early Givetian as documented by the abundance of recfal fauna (stromatoporoids, corals) and calcimicrobes (lumps, micritic envelopes) in the eastern and southeastern area of the ramp.     

Onset and demise of the Wetterstein Carbonate Platform in the mélange areas of the Zlatibor Mountain (Sirogojno,SW Serbia)

A kilometer-sized block in the Sirogojno carbonate-clastic mélange provides a complete succession of the Wetterstein Carbonate Platform evolution. The platform starts its progradation in Early Carnian times over hemipelagic Late Ladinian cherty limestones with fine-grained allodapic limestone intercalations. Shallow-water reef-slope, reefal to back-reef/lagoonal limestones evolved in the Early Carnian. The top of the platform is recrystallized and partly slightly dolomitized, and in parts karstification is visible. After a period of omission caused by uplift, new subsidence started in the early Late Carnian. This is documented by a flooding respectively drowning sequence of the same age, starting with reefal carbonates and rapidly followed by hemipelagic-influenced limestones. The evolution of the onset and the drowning of the Wetterstein Carbonate Platform prove a paleogeographic derivation of this block from the outer shelf-area facing the Neotethys Ocean, but still in a shallow-water carbonate platform position transitional to the Hallstatt facies zone. This paleogeographic position is especially confirmed by the new pulse of subsidence in the Late Carnian after a long lasting phase of omission. The evolution of the Wetterstein Carbonate Platform in the Inner Dinarides corresponds to successions known from the Northern Calcareous Alps or the southern Western Carpathians. In the Late Triassic both regions belong to the same northeast–southwest striking shelf area facing the Neotethys Ocean to the east and southeast, respectively.     

Facies analysis and sequence stratigraphy of an Upper Jurassic carbonate ramp in the Eastern Alborz range and Binalud Mountains, NE Iran

Upper Jurassic (Oxfordian-Kimmeridgian-Tithonian?) strata of NE Iran (Lar Formation) are composed of medium- to thick-bedded, mostly grainy limestones with various skeletal (bivalves, foraminifera, algae, corals, echinoderms, brachiopods, and radiolaria) and nonskeletal (peloids, ooids, intraclasts, and oncoids) components. Facies analysis documents low- to high-energy environments, including tidal-flat, lagoonal, barrier, and open-marine facies. Because of the wide lateral distribution of facies and the apparent absence of distinct paleobathymetric changes, the depositional system likely represents a westward-deepening homoclinal ramp. Four third-order depositional sequences can be distinguished in each of five stratigraphic measured sections. Transgressive system tracts (TST) show deepening-upward trends, in which shallow-water (tidal flat and lagoonal) facies are overlain by deeper-water (barrier and open-marine) facies. Highstand systems tracts (HST) show shallowing-upward trends in which deep-water facies are overlain by shallow-water facies. All sequence boundaries in the study area (except at the top of the stratigraphic column) are of the nonerosional (SB2) type. Correlation of depositional sequences in the studied sections show that relatively shallow marine (tidal-flat, lagoonal, barrier, and shallow open-marine) conditions dominated in the area. These alternated with deep-water open-marine wackestone and mudstones representing zones of maximum flooding (MFZ).     

Fossil-Lagerstätten,palaeoecology and preservation of invertebrates and vertebrates from the Devonian in the eastern Anti-Atlas,Morocco

In some Devonian strata in the eastern Anti-Atlas, fossil invertebrates are abundant, display a high taxonomic diversity and indicate many shifts in palaeoecology. This is reflected in changes in faunal composition of invertebrates and vertebrates. Fossils of jawed vertebrates of late Lochkovian and younger age have been recorded and are relatively common with their abundance and diversity increasing towards the Late Devonian. Environmental changes in the Devonian also left their mark in the preservation of vertebrates and invertebrates from the Anti-Atlas, which varies strongly through time and regionally. This variation partially reflects environmental changes linked with the evolution of small marine basins during the disintegration of the continental shelf of Gondwana in this region, fluctuations of the regional sea level and other environmental changes. To improve our understanding of these ecological changes, of shifts in preservation through the succession and of the formation of Fossil-Lagerstätten, we analysed the mineral composition of some invertebrate and vertebrate samples of Devonian and Early Carboniferous age by Raman spectroscopy and X-ray diffraction. Additionally, we characterized some of these Fossil-Lagerstätten using palaeontological and sedimentological parameters. We examined eight Devonian Konzentrat-Lagerstätten and two Konservat-Lagerstätten with soft-tissue preservation (the Famennian Thylacocephalan Layer and the Hangenberg Black Shale of the southern Maïder). The last two are the first Konservat-Lagerstätten described from the Devonian of North Africa. The taphonomic and oceanic settings suggest that these Konservat-Lagerstätten are formed because of stagnation (related to vertical restriction of water exchange and water depth rather than limited spatial water exchange and a lateral restriction) in the relatively small Maïder Basin with limited water exchange with the neighbouring Tafilalt Basin. The temporally low oxygen levels in the Maïder Basin are a possible reason for the reduced chondrichthyan diversity (missing demersal and shallow water species) compared to the Tafilalt Platform.     

Transitional reef-to-basin facies of Lower Frasnian limestones determined by microfacies analysis (Wietrznia,Holy Cross Mts,Poland)

Wietrznia section is situated between the shallow-water carbonate platform in the Kielce region and the Łysogóry basin. The transitional facies of the Wietrznia Frasnian includes two overlapping types of deposits: (1) thin-bedded dark-coloured limestone-marl alternations similar to the basin facies and (2) coarse-grained detrital limestones. Three lithotypes of limestones were identified: laminated or graded micritic, nodular, and detrital. The petrographic study makes it possible for the recognition of six major microfacies (MF 1 to MF 6). These lithotypes were formed by redeposition in a low- to high-energy environment. Their source material was the stromatoporoid-coral Dyminy reef in the central part of the Kielce region. Storms are considered to be the main agent, which causes in erosion and transport; micritic limestones and distal tempestites occur together, whereas detrital limestones are associated with proximal tempestites. Most probably, part of the detrital beds was formed as a result of grain-flow initiated under storm conditions.     

Palaeozoic oolitic ironstones on the North American Craton

More than 40 mostly minor Palaeozoic oolitic ironstones (OI) accumulated on low-latitude cratonic North America, almost entirely in USA. A few Middle Cambrian OI, among the oldest anywhere, were deposited on the western cratonic shelf of USA. Widely scattered Late Cambrian ones developed on the southwestern, southeastern and northeastern flanks of the Transcontinental Arch. Middle Ordovician OI were deposited on the cratonic interior and on the southern and southeastern cratonic margins. In latest Ordovician time Neda OI spread across north-central USA east of the Arch and south of the Laurentian upland. Minor ones developed in the southern part of the Taconian foreland basin after major orogeny. Early and Middle Silurian Clinton OI flourished throughout the foreland basin in eastern USA, producing the largest OI deposit on the North American craton. Minor early Late Silurian OI accumulated in the central part of the basin. Middle and Late Devonian OI in the Acadian foreland basin in northeastern cratonic USA developed progressively westward of the encroaching Catskill delta. An isolated Middle Devonian one accumulated in southwestern cratonic USA, and latest Devonian ones in north-central USA east of the Arch.

During this Palaeozoic episode sites of OI deposition shifted eastward across the craton. Most of the OI were deposited during a hiatus in normal sedimentation, accumulating in the upper part of shoaling-upward sequences. Some early Palaeozoic ones occur in glauconitic siliciclastic-carbonate facies and contain mostly spherical hematitic ooids. These suggest derivation from iron-rich soils developed on glauconitic deposits. OI in wholly siliciclastic facies, containing distorted chamositic ooids with cores of mud peloids, were common in later Palaeozoic time. These OI, like many other Phanerozoic ones, suggest a synsedimentary to early diagenetic origin.     

Favositidae (Tabulata) from Emsian to Middle Devonian limestones of the Tamworth Group (N.S.W., Australia)

Several different species and species groups of the familiy Favositidae from the Emsian and Middle Devonian limestones of the Tamworth Group (N.S.W., Australia) are described. The Emsian Sulcor Limestone Member yieldedFavosites sp. aff.F. basalticus (Goldfuss, 1826),Favosites sp. aff.F. salebrosus Etheridge, 1899,Favosites stellaris Chernyshev, 1937,Squameofavosites nitidus (Chapman, 1914),Sq. bryani (Jones, 1937),Pachyfavosites rariporosus Dubatolov, 1963, andP. tumulosus Yanet, 1965. The Middle Devonian Moore Creek Limestone Member yieldedFavosites ex gr.goldfussi D’Orbigny, 1850, exclusively. In the Emsian limestones occur favositids in a wide array of different facies, with most being found in stratified biostromes and in bedded nodular limestones. In the Middle Devonian most favositids are found in nodular and lumpy limestones which occur at the base and at the top of some successions      

A new skull of early cetacean Remingtonocetus harudiensis from the Eocene of Kutch Basin,India

A nearly complete skull of Remingtonocetus harudiensis was discovered from the Harudi Formation of the Kutch Basin, western India. Though several specimens have been collected over the last two decades by earlier workers, this skull shows variations in morphology within the species that were not known earlier. Hence, this finding is significant because it helps in expanding our knowledge of the skull morphology with the addition of characters such as the larger size of the skull, the difference in dental morphology, and the two-ridged external nasal feature and our understanding of how the molar morphology can vary within the same species. The newly excavated skull is the largest Remingtonocetus skull so far discovered and is similar to the size of Dalanistes ahmedi from Kutch, India and from Baluchistan, Pakistan. Thus, the range of the overall body size of the species will change considerably towards the higher side nullifying a major distinction between Dalanistes and Remingtonocetus. The new skull was excavated from the chocolate brown shales of the clastic facies of the Harudi Formation, in the inner ramp of a lagoonal phase. It is approximately 4 m above the nodular limestones from which the other Remingtonocetus materials were previously described. The limestone represents the carbonate facies of the Formation formed in a middle to outer ramp setting. An emended diagnosis of R. harudiensis is provided in this study. The Bartonian Harudi Formation of the Kutch Basin, thus, becomes unique in having Remingtonocetus specimens discovered from two different lithological facies from both the inner and outer ramp settings.     

Bioerosional structures and pseudoborings from Late Jurassic and Late Cretaceous-Paleocene shallow-water carbonates (Northern Calcareous Alps, Austria and SE France) with special reference to cryptobiotic foraminifera

Examples of bioerosional processes (boring patterns) are described from shallow-water limestones of the Late Jurassic Plassen Carbonate Platform (PCP) and the Late Cretaceous to Paleocene Gosau Group of the Northern Calcareous Alps, Austria. Some micro-/macro-borings can be related to distinct ichnotaxa, others are classified in open nomenclature. In the Alpine Late Jurassic, bioerosional structures recorded from clasts in mass-flows allow palaeogeographical conclusions concerning the source areas. In particular, these are borings of the Trypanites-ichnofacies detected from clasts (Barmstein limestones) of the PCP or special type of bored ooids of unknown source areas or restricted autochthonous occurrences. In the Lower Gosau Subgroup, Gastrochaenolites macroborings occur in mobile carbonate clast substrates of shore zone deposits (“Untersberg Marmor”). Different types of borings are recorded from rudist shells and coral skeleton, some of which are referable to the ichnotaxon Entobia produced by endolithic sponges. In the present study, special attention is paid to the occurrences of the cryptobiotic foraminifera Troglotella incrustans Wernli and Fookes in the Late Jurassic and Tauchella endolithica Cherchi and Schroeder in the Late Cretaceous. The latter is so far only known to be from the Early Cenomanian of France and is reported here for the first time from the Late Turonian-Early Coniacian stratigraphic interval where it was found in turbulent carbonate deposits within borings penetrating bivalve shells or coralline algae. The records of cryptobiotic foraminifera from the Northern Calcareous Alps are supplemented by a single finding from the Middle Cenomanian of SE France. A palaeoenvironmental interpretation of the occurrences of the cryptobiotic foraminifera is provided.     

The western edge of the Mediterranean Pelagian Platform: A Messinian mixed siliciclastic–carbonate ramp in northern Tunisia

The marine Messinian deposits of Tunisia cover a narrow littoral strip some 300 km long between the northern Bizerte and Cap Bon areas and the central–eastern Sahel region. Litho- and biofacies analysis of six stratigraphic sections reveals the distinctive features of these deposits.The lower Messinian deposits are characterized by ubiquitous siliciclastics and abundant oolitic/bioclastic limestones organized in an eastward facing ramp. Westward (landward), this ramp changes into coastal lagoons, sometimes containing evaporites. Eastward, the ramp passes to the reefal Pelagian Platform extending as far as Lampedusa.Two main sedimentary cycles are distinguished: 1) an early Messinian siliciclastic retrogradational then oolitic/bioclastic progradational cycle (Beni Khiar Formation and lower Oued bel Khedim Formation); 2) a late Messinian brackish to continental cycle that probably accumulated in rapidly subsiding lagoons (Oued el Bir Formation and upper Oued bel Khedim Formation). The Tunisian early Messinian cycle is partly eustatically controlled, but the late Messinian cycle cannot be confidently correlated to other well-known Messinian series because of tectonic movements.The lower Messinian deposits of Tunisia are also characterized by abundant suspension-feeding organisms (molluscs and bryozoans) and rare corals, calcareous algae, echinoids, and larger benthic foraminifers. The proposed palaeoenvironmental model shows that the lower Messinian ramp of Tunisia was located on a current-protected margin and subjected to continent-derived sediment and nutrient supply. Eastward, nutrient influx diminished and a shallow-water isolated carbonate platform with coralgal facies developed between the western and the eastern Mediterranean basins. The main hydrological connection between these two basins occurred through a narrow seaway situated to the northeast of the Pelagian Platform, south of Sicily and Malta.     

High-frequency cycles in Upper-Miocene ramp-temperate carbonates (Sorbas Basin,SE Spain)

Uppermost-Tortonian temperate carbonates occur at the southern margin of the Sorbas Basin (Almería, SE Spain). These carbonates, included in the Azagador Member, formed in a gentle, shallow-water ramp. Six facies cycles in ramp deposits comprise alternating bivalve-shell concentrations and coralline algal beds. The basic cycle reflects the landward advance, as relative sea level rose, of coralline algal deposits, which were the facies of the outer ramp, over bivalve biostromes, which grew in the shallower areas of the mid-ramp. Biostromes were mainly built by oysters and locally by Isognomon. In many cases, however, the removal of smaller shells by storms left only thin, discontinuous patches of large bivalves as residual remains of the oyster biostromes. Some original cycles might be missing due to complete removal of bivalve shells from the biostromes. The six cycles recognised, therefore, should be considered as the minimum number of original cycles in the Azagador carbonates. The available age constraints suggest these cycles were forced by orbital precession or some higher-frequency process. Lithological cycles forced by precession are characteristic of the basinal deposits laterally equivalent to the Azagador carbonates.     

Platform-basin transect of a middle to late Jurassic large-scale carbonate platform system (Shotori mountains,Tabas area,east-central Iran)

Summary Following a phase of predominantly siliciclastic sedimentation in the Early and Middle Jurassic, a large-scale, low-latitude carbonate depositional system was established in the northern part of the Tabas Block, part of the central-east Iranian microplate, during the Callovian and persisted until the latest Oxfordian/Early Kimmeridgian. Running parallel to the present eastern block margin, a NNW/SSE-trending carbonate platform developed in an area characterized by reduced subsidence rates (Shotori Swell). The growth of this rimmed, flat-topped barrier platform strongly influenced the Upper Jurassic facies pattern and sedimentary history of the Tabas Block. The platform sediments, represented by the predominantly fine-grained carbonates of the Esfandiar Limestone Formation, pass eastward into slope to basin sediments of the Qal'eh Dokhtar Limestone Formation (platform-derived allochthonites, microbialites, and peri-platform muds). Towards the west, they interfinger with bedded limestones and marlstones (Kamar-e-Mehdi Formation), which were deposited in an extensive shelf lagoon. In a N−S direction, the Esfandiar Platform can be traced for about 170 km, in an E-W direction, the platform extended for at least 35–40 km. The width of the eastern slope of the platform is estimated at 10–15 km, the width of the western shelf lagoon varied considerably (>20–80 km). During the Late Callovian to Middle Oxfordian, the Esfandiar Platform flourished under arid climatic conditions and supplied the slope and basinal areas with large amounts of carbonates (suspended peri-platform muds and gravitational sediments). Export pulses of platform material, e.g. ooids and aggregate grains, into the slope and basinal system are interpreted as highstand shedding related to relative sealevel variations. The high-productivity phase was terminated in the Late Oxfordian when the eastern platform areas drowned and homogeneous deep water marls of the Upper Oxfordian to Kimmeridgian Korond Formation onlapped both the Qal'eh Dokhtar Limestone Formation and the drowned Esfandiar Limestone Formation. Tectonic instability, probably caused by faulting at the margins of the Tabas Block in connection with rotational movements of the east-central Iranian block assemblage, was responsible for the partial drowning of the eastern platform areas. In some areas, relicts of the platform persisted to produce shallow-water sediments into the Kimmeridgian.     

Upper Eocene larger foraminiferal–coralline algal facies from the Klokova Mountain (southern continental Greece)

Within the Gavrovo–Tripolitza area (southern continental Greece), marine carbonate platforms existed from the Late Triassic to the Late Eocene. The Middle–Upper Eocene marine shallow-water carbonates of the Klokova Mountain represent remnants of the large volumes of sediment that were produced on a middle ramp sedimentary system which culminated in the Lower Oligocene terrigenous deposits. Facies analysis of Bartonian–Priabonian shallow-water carbonate successions and the integration with palaeoecological analysis are used to produce a detailed palaeoenvironmental model. In the proximal middle ramp, porcelaneous foraminiferal packstone facies is characterised by larger foraminifera such as Praturlonella and Spirolina. These forms thrived in a shallow-water setting with low turbidity, high-light intensity and low-substrate stability. The foraminiferal packstone facies, the thin coralline wacke–packstone facies and the rhodolith packstone facies deposited approximately in the same depth range adjacent to one another in the middle-ramp. Nummulitids (Nummulites, Assilina, Pellatispira, Heterostegina and Spiroclypeus) increase in abundance in the middle to distal mid-ramp together with the orthophragminids. Coralline algae, represented by six genera, are present in all facies. Rhodoliths occur in all facies but they show different shapes and growth forms. They develop laminar sub-ellipsoidal shapes in higher turbulence conditions on mobile sand substrates (foraminiferal packstones and rhodolith rudstones), whilst sub-discoidal shapes often bound by thin encrusting coralline plants in lower hydrodynamic settings. The distinctive characteristics of the palaeoecological middle-ramp gradient are an increase in dominance of melobesioids, a thinning of the encrusting coralline plants and a flattening of the larger benthic foraminiferal shells.     

Signatures of hydrocarbon venting in a Middle Devonian Carbonate Mound (Hollard Mound) at the Hamar Laghdad (Antiatlas, Morocco)

Summary The Middle Devonian Hollard Mud Mound is situated in the eastern Hamar Laghdad, which is a small mountain range in the Tafilalt in SE Morocco. In contrast to the well known Lower Devonian Kess-Kess mounds, the Hollard Mound is of Middle Devonian age. The facies in the core of this mud mound differs from that of the other parts of the mound, and exhibits signatures of ancient hydrocarbon venting. The carbonate phases of the core facies are derived from the oxidation of vent fluids and consist of clotted micrite, a cryptocrystalline carbonate associated with spheres of uncertain origin, and a calcitic rim cement (rim cement B). These vent carbonates show δ¹³C values in the range of −11 to −20% PDB indicating that some of their carbon is derived from isotopically light hydrocarbons. Fossiliferous micrite has been affected by hydrocarbon venting in the proximity of the vent site, which is indicated by intermediate δ¹³C values between vent carbonates and not affected sediments. Bivalves occur in dense populations within the core facies. They form autochthonous shell accumulations and are almost exclusively articulated. it is likely that these bivalves were dependent on chemosynthesis similar to their counterparts at modern vents. The vent deposits also exhibit an unusual prasinophyte assemblage, which might have been linked to the specific nutrient availability at the vent site. The ancient vent site is characterized by an enhanced carbonate precipitation and rapid lithification. The latter is corroborated by the three-dimensional preservation of phytoplankton (prasinophytes and acritarchs) and the occurrence of stromatactoid pores. An early phase of carbonate corrosion predating the formation of vent carbonates affected the fossiliferous micrite of the core facies and is thought to be related to a phase of H₂S-rich venting.     

Relationships between foraminiferal assemblages and depositional sequences in Jahrum Formation,Ardal area (Zagros Basin,SW Iran)

The Jahrum Formation was deposited in the foreland basin in southwest Iran (Zagros Basin). The Zagros mountain belt of Iran, a part of the Alpine–Himalayan system, extends from the NW Iranian border through to SW Iran, up to the strait of Hormuz. The various facies of the Jahrum Formation were deposited in four main genetically related depositional environments, including: tidal flat, lagoon, shoal and open marine. These are represented by 14 microfacies. The Jahrum Formation represents sedimentation on a carbonate ramp. Tidal flat facies are represented by fenestral fabric, stromatolitic boundstone and thin-bedded planes. Carbonate deposition in a shallow marine lagoon was characterised by wacke–packstone, dominated by various taxa of imperforate foraminifer. The shoals are made up of medium- to coarse-grained skeletal and peloidal grainstone. This facies was deposited predominantly in an active high energy wave and current regime, and grades basinward into middle ramps facies are represented by wackestones–packstones with a diverse assemblage of echinoderm and large benthic foraminifers with perforate wall. Outer ramp facies consist of alternating marl and limestones rich in pelagic foraminifera. There is no evidence for resedimentation processes in this facies belt. The sequence stratigraphy study has led to recognition of three third-order depositional sequences.     

Ludlovian,Pridolian and Lochkovianin la Meignanne (Massif Armoricain): Biostratigraphy and correlations based on Bivalvia and Chitinozoa

Black carbonate rocks («ampelitic limestones)exposed in la Meignanne, NW of Angers, Massif Armoricain, as tectonic lenses within a complex tectonic structure of grey Pragian limestones are assigned from Bivalvia and Chitinozoa to the Upper Silurian and Lowermost Devonian. Biostratigraphical and paleoecological analyses show that the Silurian-Devonian boundary in this area is developed in offshore facies and that it may be correlated directly with the international stratotype of the Prague Basin (Barrandian, Bohemia). Paleogeographical communication between the two areas is indicated by 28 species of bivalves in common from two Pridolian assemblages (with Cheiopteria bridgei and with Snoopyia insolita) and one Lochkovian (with Antipleura bohemica). Stratigraphical correlation with the Prague Basin is also based on the chitinozoan zonal index species for the Uppermost Pridolian (Urnochitina urna) and Lowermost Lochkovian (Eisenackitina bohemica). A Lochkovian age is further supported by the discovery of Monograptus uniformis uniformis in the assemblage with Antipleura bohemica. A Ludlovian age is indicated by the occurence of «Hemicadium elevatum and an abundance of the ostracode Entomozoe (Richteria) migrans, which is an index species for the Middle Ludlovian in Bohemia.