Middle Givetian Research Articles

Middle Devonian brachiopods from Qujing of eastern Yunnan, China and their biostratigraphical and palaeoecological implications

The Middle Devonian Qujing Formation at its type locality in eastern Qujing City, Yunnan was investigated for the first time. At the Wutaishan section, the formation is characterized by fossiliferous limestone and marls with massive terrigenous inputs. About 1292 individual specimens and several fragmented stringocephalid brachiopods were collected and systematically identified in this study. They are assigned into 18 species of 13 genera from 9 families in 6 orders. Undispiriferoides species and their detailed internal structures are for the first time illustrated, with a new species Undispiriferoides qujingensis being established. We recognize the assemblages of Stringocephalus and Ambothyris-Spinatrypa. The former is characterized by Stringocephalus burtini and accompanied with plenty of Meristella kütsingensis, M. flayelli, and Desquamatia sp. that are commonly present in the middle Givetian in South China. Whereas the latter is identified in the late Givetian and mainly contains small-sized, smooth spiriferides (e.g., Emanuella takwanensis, Ambothyris panxiensis) and atrypides Spinatrypa. The brachiopod assemblages in the section were largely correlated with environmental parameters and ecological factors in the near-shoal belt, where alternating clastic and marine carbonate depositions were disrupted by sea-level fluctuations. The Stringocephalus fauna favorably diversified in reefal and carbonate-dominated substrates and was replaced by the soft-bottom dwelling habitants of the Ambothyris-Spinatrypa assemblage, coinciding with multiple and progressive sea-level fluctuations in the Givetian.

New Givetian Conodonts of the Genus <i>Icriodus</i> from the Kolyvan-Tom Folded Area (South of West Siberia)

New species Icriodus alchedatensis sp. nov., I. kuzbassiensis sp. nov. I. lebedyankensis sp. nov. and Latericriodus sp. E are described from stratotype sections of the Mazalovy Kitatian regional Substage of the Middle Givetian from the Kolyvan-Tom folded area. The taxa of the genus Icriodus belong to two phylolines of the genus Icriodus: the I. struvei phylolines and the I. regularicrescens phylolines according to the concept of Weddige (1977).

Lithology, Geochemistry of the Middle Devonian Sediments and the Influence of Volcanism on Sedimentation in the Southeast of West Siberia

Abstract —Dataset on the Middle Devonian volcanic-carbonate–terrigenous sediments of Salair and the Kuznetsk trough, submerged northward under the Mesozoic–Cenozoic West Siberian geosyneclise (WSG) cover, have been presented. Mainly deep water sediments composed of thin- and fine-grained clastic material (with predominance of tephroids) and thin-, fine-clastic biodetrital limestones with slope slide breccia, as well as turbidites and peculiar “conglomerate-like” limestones (paleoseismites) were found. Sedimentary and geodynamic environments have been reconstructed for the Middle Devonian strata. Predominantly andesitic composition of pyroclastic ashes with fewer values of felsic and basic volcanic components have been determined. The structures related to the continental margin environments of the Siberian continent, the continental slope and its basement have been found. According to sedimentary and geochemical data, the paleogeodynamic environment within the studied region was relatively stable and generally corresponded to the island arc conditions. The paleoclimate of the source area changed from semi-humid in the late Emsian–early Eifelian (Malaya Salairka age) to aridic in the middle Givetian (Kerlegesh age). Basin sediments formed in the deep water oxic environments with good water aeration, excepting euxinic environments found in the lowermost part of studied succession.

Non-tetrapod sarcopterygians from the Valentia Slate Formation (Givetian, Devonian) of the Iveragh Peninsula, south-western Ireland: systematic reappraisal and palaeobiogeographic implications

The Middle Devonian (Givetian) Valentia Slate Formation in the Iveragh Peninsula, southwest Ireland, is more renowned for the second oldest record of tetrapod trackways in the world than for its heavily metamorphosed bone remains. The present study focuses on new discoveries of non-tetrapod sarcopterygian fish fossils from the Valentia Slate Formation. Micro-CT scanning technology allows a re-interpretation of a previously published acanthodian fin spine as a fanged coronoid of a probable Rhizodontida and the identification of a Dipnoi tooth plate and bone. In addition, a scale of Holoptychius is described. The presence the rhizodont suggests Gondwanan ties and a first northward dispersal wave of these vertebrates into Euramerica as early as middle Givetian. This hypothesis is supported by the common occurrence of the placoderm Bothriolepis in the Valentia Slate Formation.

Biostratigraphy of Yazdanshahr No.2 section in Kerman area, Central Iran, based on conodont communities

Yazdanshahr No.2 section, which consists mostly of Bahram and Sibzar formations is located in the Zarand city, northern Kerman province (Central Iran). Five biozones have been identified based on the conodont community. The first biozone, which includes Padehat (15 meter) and Sibzar formations (75 meter), was distinguished based on genera Bipennatus and Icriodus and the probable corresponding age was considered to span Emsian to Eifelian. The second biozone is recognized by the first appearance of index taxon Polygnathus varcus (varcus Zone: early to middle Givetian). The third biozone starts with the firth appearance of the index genus Icriodus expansus (expansus zone: middle Givetian). The base of the Fourth biozone is recognized by the first appearance of the genus I. subterminus (subterminus Zone: middle to late Givetian) and the last biozone was distinguished with the first appearance of genera Ancyrodella and Polygnathus incompletes in the Givetain-Frasnian boundary (falsiovalis to crepida Zone?: Frasnian to Famenian?). Bahram Formation (94 meter) consists of Fossiliferous limestone (varcus to subterminus Zone) at the lower part, and alternation of dolomite and sandstone (falsiovalis to crepida Zone?) at the upper part. Sibzar Formation consists of Middle Devonian dolomite and limy dolomite containing intercalation of sandstone and limestone layers.

The Bothriolepis (Placodermi, Antiarcha) material from the Valentia Slate Formation of the Iveragh Peninsula (middle Givetian, Ireland): Morphology, evolutionary and systematic considerations, phylogenetic and palaeogeographic implications.

Material of the antiarch placoderm Bothriolepis from the middle Givetian of the Valentia Slate Formation in Iveragh Peninsula, Ireland, is described and attributed to a new species, B. dairbhrensis sp. nov. A revision of the genus Bothriolepis is proposed, and its taxonomic content and previous phylogenetic analyses are reviewed, as well as the validity of morphologic characteristics considered important for the establishment of the genus, such as the shape of the preorbital recess of the neurocranium. A series of computerised phylogenetic analyses was performed, which reveals that our new species is the sister taxon to the Frasnian Scottish form B. gigantea. New phylogenetic and biogeographic analyses of the genus Bothriolepis together with comparisons between faunal assemblages reveal a first northward dispersal wave from Gondwana to Euramerica at the latest in the mid Givetian. Other Euramerican species of Bothriolepis seem to belong to later dispersal waves from Gondwana, non-excluding southward waves from Euramerica. Questions remain open such as the taxonomic validity and stratigraphic constraints for the most ancient forms of Bothriolepis in China, and around the highly speciose nature of the genus.

Pre-Taghanic (Lower to lower Middle Givetian) brachiopods from Miłoszów in the Holy Cross Mountains (Poland)

Pre-Taghanic (Lower to lower Middle Givetian) brachiopods from Miłoszów in the Holy Cross Mountains (Poland)

Biostromal unit from the Middle Devonian Jinbaoshi Formation, Sichuan, Southwest China: Implications for ecological structure of coeval reef communities

This study provides a comprehensive palaeontological and palaeoecological analysis of a middle Givetian (Middle Devonian) coral-stromatoporoid biostromal unit from the upper member of the Jinbaoshi Formation, northern Sichuan Province, Southwest China. The biostromal unit is 17.7 m of medium- to thick-bedded limestones, and lacks observable morphological relief in the field. Diverse shallow marine benthic fossils are common elements of the biostromal unit encompassing stromatoporoids (7 genera), tabulate corals (4 genera), brachiopods (2 genera), plus unidentified rugose corals, chaetetids, bryozoans, tubeworms, ostracods, gastropods, crinoids and calcimicrobes. In terms of the biotic composition and biostrome-building contributors, three ecological units are recognized: Alveolites–Clathrocoilona community (EU 1), Salairella–Pseudotrupetostroma community (EU 2) and Scoliopora–Idiostroma community (EU 3). High fragmentation of bioclasts partially with micritic envelopes in wackestone, packstone to grainstone matrix and the dominance of low-profile stromatoporoids indicate deposition in shallow water conditions with episodic high sedimentation rate and frequent turbulent periods. Muddy silt- to sandstone facies overlie the biostromal unit, and are interpreted to represent a shallowing-up sequence, together with terrigenous input, thus triggering termination of the biostromal unit. This biostromal unit is similar to the other early to middle Givetian reefs of South China, East Australia, West Europe, East Europe and North Africa in relation to their fossil composition and reef-building characteristics. The stability of the reef communities (i.e. no conspicuous extinction) and common occurrence of unusual reef structures (e.g. coverstone) are thus interpreted as significant biotic factors for the expansion of large-scale ecosystems during the Phanerozoic reef-building acme.

Discovery of Upper Devonian conodonts and event stratigraphy from the Eastern Jebilet, Morocco

The Abichat section in the Eastern Jebilet, including allochthonous siltstones and sandy limestones rocks, revealed the presence of a Givetian and Early Frasnian conodont fauna. The Upper Devonian is discovered for the first time in Eastern Jebilet. A continuous biostratigraphic record could not be established, because of the gap that occurs in the Upper Givetian. However, six conodont Zones are recognized: rhenanus/varcus and ansatus to semialternans of Middle Givetian, Lower-Middle falsiovalis (MN1-2), Upper falsiovalis (MN3) and transitans (MN4) of Lower Frasnian. Notably, the conodont fauna contains particularly several species of Ancyrodella, Mesotaxis and Icriodus. Givetian conodonts show a polygnathid biofacies and Lower Frasnian conodonts reveal a mixed conodont biofacies with the Ancyrodella as dominating genus. Two anoxic global events are recognized for the first time in the Massif of Jebilet, the Upper Frasnes Event and the Timan Event. The Eastern Jebilet Devonian nappes have close links with the nappes of Azrou and Mrirt-Ziyar whose the sediments, characterized by stratigraphic gaps, were deposited along the disintegrated northern continental margin of Gondwana.

Rare earth element geochemistry of Middle Devonian reefal limestones of the Dianqiangui Basin, South China: implications for nutrient sources and expansion of the reef ecosystem.

The Givetian Age witnessed the greatest expansion of stromatoporoid-coral reefs from low to higher latitudes of the Phanerozoic. Multi-proxy seawater surface temperature reconstruction suggests the establishment of a super-greenhouse climate as a major reason for reef expansion, yet many questions remain. This article presents the results of a rare earth element and yttrium (herein referred to as REY, derived from REE + Y) geochemical study as well as mineralogy and oxygen isotope values of two well-documented Middle Givetian reefal carbonate sections (Jiwozhai and Buzhai) of the Jiwozhai Formation of South China. The nearshore Jiwozhai patch reef succession displays greater biodiversity and more abundant coral than the marginal platform Upper Buzhai reef. Reefal and micritic carbonates of the Jiwozhai section are characterized by shale-like post-Archean Australian Shale (PAAS)-normalized REY patterns, by very weak negative Ce anomaly values (Ce/Ce* 0.80–0.96; average = 0.89), slightly elevated Y/Ho values (28.9–39.1; average = 34.1), and near-unity values of (Pr/Yb)N (average = 0.87), (Pr/Tb)N (average = 0.80), and (Tb/Yb)N (average = 1.09). Moreover, REY patterns of deposits of the Jiwozhai section differ markedly from those of modern seawater. The described geochemical aspects of the Jiwozhai section and the positive correlation of REY and Th contents displayed by the section point to a terrestrial siliciclastic contribution contemporaneous with reef-building. In contrast, REY patterns of the Upper Buzhai reef section samples are similar to those of modern seawater characterized by light rare earth element (LREE) depletion (average (Pr/Yb)N = 0.76), negative Ce anomalies (average Ce/Ce* = 0.88), and average super-chondritic Y/Ho ratios (average = 45.4)). Slightly positive Eu anomalies (Eu/Eu* = 0.93–1.94; average = 1.36) of the Upper Buzhai reef section samples are attributed to the negligible effect of hydrothermal fluids. Middle REE (MREE) enrichment (average (Tb/Yb)N = 1.48) of Buzhai section carbonate samples and positive correlation of REY and Th suggest a riverine input. Combined with siliciclastic mineralogy, oxygen isotope values, and reef-building biota morphology of the studied two sections, we suggest that terrestrial nutrients delivered by rivers far outweighed upwelling as a source of nutrients supplied to the Givetian reef ecosystem of South China. Coral and stromatoporoid in tropic oceans thrived in turbid water containing abundant terrestrial sediment and the nutrient-laden water helped expand reef-builder habitats during the Givetian time.

Revision of Middle Devonian conodont biostratigraphy in the Negheleh section, Central Iran

Fifteen conodont species and subspecies from the Negheleh section, Soh area, north of Esfahan represent early Eifelian to middle Givetian time interval. Five biozones: costatus to australis, kockelianus, ensensis to hemiansatus, timorensis and rhenanus to ansatusare recognized. The present study suggests the Eifelian age for the base of Bahram Formation in the Sanandaj-Sirjan and the western part of Central Iran Microplate. The oldest known occurrence of thelodont turiinid species, Neoturinia hutkensis is reported from the early Eifelian strata of the Negheleh section. New age range from the late Eifelian to late Frasnian is proposed for Icriodus excavatus Weddige.Keywords: Middle Devonian, Eifelian, Givetian, conodonts, biostratigraphy.

Habitats in the Pre-Taghanic (Givetian, Middle Devonian) muddy carbonate ramp at Miłoszów (Holy Cross Mountains, Poland): geochemical and microfacies evidence

The well-known fossiliferous and lithologically variable Middle Devonian Shaly-Calcareous Skały Formation in the Łysogóry Region (northern part of the Holy Cross Mountains, central Poland) was studied for the first time in terms of elemental geochemistry, carbon isotope stratigraphy and limestone microfacies. Three Lower to Middle Givetian marly-limestone successions, exposed at Miłoszów, represent middle to outer facies belts of the vast carbonate ramp, characterized by very rich epifaunal and infaunal benthic life in muddy, oxic, eutrophic, and photic zone habitats. Brachiopods and occasionally corals (in mesophotic association), erect branching bryozoans, and tiny crinoids played a leading role among flourishing sessile suspension-feeders. High-energy storm events, possibly even a tsunami, during the brief Early Givetian time strengthened a prolific carbonate ooze delivery system from shallow ramp areas, including restricted back-ramp lagoons and a variety of organic buildups, populated by corals and stromatoporoids. The ecologically mixed skeletal grain association is characterized by the rich occurrence of a typical lagoonal biota, calcispheres and amphiporoids. The effective carbonate factory declined stepwise regionally during the Middle Givetian because of an intermittent progradation of the deltaic system of the Świętomarz Beds, linked with climate cooling and the activation of block movements. The regional carbonate crisis resulted in the demise of diverse benthic life, including the prolific calcified microbiota. The higher Skały Formation succession, deposited between the important Kačák and Taghanic bioevents, is noticeable for a background carbon-isotope pattern in carbonate and organic matter signatures, with the baseline δ 13 C carb values between 1‰ and 2‰. The microfacies and chemostratigraphic data confirm that at least the lower pumilio bioevent was not recorded in the Łysogóry Region.

The pre-Taghanic (Givetian, Middle Devonian) ecosystems of Miłoszów (Holy Cross Mts, Poland)

The middle and upper parts of the Skały Fm, Early to Middle Givetian in age, were investigated in four sections at Miłoszów Wood in the Łysogóry Region (northern region of the Holy Cross Mountains, central Poland). The dating is based on conodonts ( Polygnathus timorensis Zone to the later part of the Polygnathus varcus / Polygnathus rhenanus Zone; early Polygnathus ansatus Zone cannot be excluded) and spores (Ex1–2 subzones) and, coupled with cartographic analysis and geophysical investigation, allows correlation within the strongly faulted succession. Significant lateral facies variations within the carbonate ramp depositional system in comparison with the better studied Grzegorzowice–Skały section, about 3 km distant, are documented, thanks to conodont-based correlation of both successions. Foraminifers, fungi, sponges, rugose and tabulate corals, medusozoans, microconchids and cornulitids, polychaetes (scolecodonts), molluscs (bivalves, rostroconchs, and gastropods), arthropods (trilobites and ostracods), bryozoans, hederelloids, ascodictyids, brachiopods, echinoderms (mostly crinoids, rare echinoids, holuthurians, and ophiocistoids), conodonts, fish, plants (prasinophytes, chlorophycophytes, and land plant spores), and acritarchs are present. Brachiopods are the most diverse phylum present (68 species), other richly represented groups are bryozoans and echinoderms; in contrast, cephalopods and trilobites are low in diversity and abundance. The muddy, middle to outer ramp biota (200 marine taxa, including 170 species of marine animals, 22 photoautotrophs, 6 forams) represents a mixture of allochthonous shallower-water communities (upper BA3), including storm- and possibly tsunami-affected coral mounds, and autochthonous deep-water soft-bottom brachiopod (e.g., Bifida–Echinocoelia ) communities (BA 4–5). The richness and diversity of the Miłoszów biota is relatively high, comparable with other approximately coeval pre-Taghanic ecosystems during the Devonian climatic deterioration (cooling). Preliminary data indicate that in the Holy Cross Mountains, no large-scale replacement of brachiopod (and probably many other benthic ones, like crinoids) communities took place between the Early–Middle Givetian and the Early Frasnian, in contrast to the demise of the Hamilton/Upper Tully fauna in the Appalachian Basin. Such a similarity of pre- and post-Taghanic faunas does not exclude the occurrence of environmental perturbations and transient community turnovers, caused by immigrations during the Taghanic Biocrisis, but evidences the successful recovery of the indigenous biota.

Middle Devonian Skały Formation in the Holy Cross Mountains (Poland) – formal description and subdivision based on new field data

The well-known fossiliferous and lithologically variable clay-carbonate series in the Łysogóry Region (northern part of the Holy Cross Mts, central Poland), enclosed between the Middle Devonian Amphipora dolomites and limestones (Kowala Formation) and siliciclastics (Świętomarz Beds), is defined formally as the Shaly-Calcareous Skały Formation. This Upper Eifelian to Middle Givetian, ca. 250–280 m thick unit, consists of marly and clay shales, interbedded many times with various limestone types (including encrinite and biohermal varieties), as well as with marls and siltstones. Its diagnostic feature is the presence of variable skeletal accumulations, formed by exceptionally numerous, well-preserved and diverse macrofauna (including brachiopods, corals, crinoids, bryozoans), described since the 19th century. The stratotype is located in the eastern slope of the Dobruchna stream near the Skały village and belongs to the Silurian to Upper Devonian Grzegorzowice-Skały section. Compared to the previously used term, Skały Beds sensu Pajchlowa (1957), the lower boundary is redefined, owing to a new exposure in the active Skała Quarry, and placed higher, at the base of the famous brachiopod shales (set XIV of Pajchlowa), instead of the formerly accepted lower boundary at the base of set XIII. Set XIV is formally distinguished as the Dobruchna Brachiopod Shale Member. The higher part of the Skały Fm (sets XV–XXVA) is not subdivided further, as the poorly exposed succession, including in particular the type area, precludes a more accurate recognition of lithological variability. The upper boundary of the Skały Fm is placed at the top of set XXV sensu Pajchlowa (1957), corresponding to the boundary between subsets XXVA and XXVB sensu Malec and Turnau (1997). A hypostratotype of the upper boundary is selected in the outcrop M0 at Miłoszów, 2.5 km westwards from the type section, allowing recognition of the diachroneity of lithological change defining the transition from the Skały Fm to Świętomarz Beds. A borehole situated in a key location would be an obvious next step in the further elucidation of the stratigraphic sequence of the Łysogóry Region.

Middle Devonian Foraminifera from the Holy Cross Mountains

The Middle Devonian was an exceptional time for foraminiferal evolution because of the emergence of the first true calcareous multilocular taxa. Despite being key forms for an understanding of the origin of foraminiferal multilocularity, which is one of the most intriguing events in the evolutionary history of the group, they are largely unstudied. These unique foraminifera, including representatives of the genera Cremsia , Moravammina , Pseudopalmula , Semitextularia, and Vasicekia, are presented herein as well as foraminifer-like microfossils of uncertain biological position. The studied material comes from the Middle Givetian strata of the Miłoszów section and the Eifelian part of the Grzegorzowice-Skały section (Holy Cross Mountains, Poland). Described isolated specimens are in an exceptionally good state of preservation on a worldwide scale, which enabled the detailed analysis of test morphologies, complementing previous papers based on less well-preserved material. The suggested systematics of the foraminifera collected attempts to revise scarce taxonomic data that is still under debate, especially the classification of Moravammina , Cremsia, and Vasicekia . The Devonian foraminifers presented were prominent endobenthic and epibenthic inhabitants of common organic coral-stromatoporoid buildups. Palaeobiogeographical records show that during the Middle Devonian, the studied forms extended their exclusive European distribution into further Laurussian shelves and shallow seas, located in the northern and southeastern parts of the Rheic basin. This assumes that such assemblages may be used as palaeoenvironmental indicators. However, at present, their correlative potential is unknown.

Upper Eifelian and Givetian (Middle Devonian) conodont sequence at Renanué (Aragonian Pyrenees, Spain): a relevant section for Givetian Chronostratigraphy

ABSTRACT The study of 111 conodont samples has provided the first detailed biostratigraphical subdivision of the Renanué section ranging from the upper Eifelian ensensis Zone into the uppermost Givetian norrisi Zone. The conodont record supports the global threefold subdivision of the Givetian. The lower boundary of the Lower Givetian coincides with the lower boundary of the Givetian and is recognised in the uppermost 5 cm of Bed −8 with the entry of Polygnathus hemiansatus. The lower boundary of the Middle Givetian is identified in Bed 5 with the joint entry of P. varcus and P. rhenanus. Lack of Schmidtognathus precludes identification of the Upper Givetian lower boundary, but the conodont assemblage suggests its position around the lower part of Bed 55. Absence of Ancyrodella and other key taxa impeded precise identification of the Frasnian lower boundary and its earliest zones. Our lowest record of P. webbi seconds its global downwards range extension into the Upper Givetian. The uppermost local record of P. rhenanus might sustain the upward extension of its range into the latifossatus Zone.

Teleostomata rackii gen. et sp. nov.: an acritarch from the Devonian (Givetian) of south-central Poland

The acritarch Teleostomata rackii gen. et sp. nov. is described and illustrated from the Middle Devonian Skały Beds that outcrop at Miłoszów, Holy Cross Mountains, Poland. At the type locality, its stratigraphical range is within the ‘Geminospora’ extensa (Ex) Miospore Zone (= hemiansatus–varcus Conodont Zones), which correspond to the early and middle Givetian. The same acritarch has been illustrated from the Eifelian strata of the Gondwanan shelf in Tunisia, but it was unnamed at the time. This acritarch from Miłoszów can be distinguished from other phytoplankton genera of tetrahedral shape because of its broad processes with distal pore-like openings.

A New Addition to the Devonian Elasmobranch Fauna of Michigan, U.S.A.

A tooth of Phoebodus cf. P. sophiae (Chondrichthyes, Elasmobranchii) was recovered from the Middle Devonian, Early Givetian, Rockport Quarry Limestone Formation in Alpena, Michigan. It is the first known record of the taxon in Michigan and the third known locality from North America. It is the oldest known record in North America, and possibly worldwide, and may extend the known temporal range of the genus. Previous known records for P. sophiae have been confined to the middle Givetian Polygnathus varcus conodont zone, and the taxon was thought to be a possible index fossil for the middle Givetian. The present record extends the taxon to the early Givetian P. hemiansatus conodont zone and, thus, complicates the use of P. sophiae as a proxy index fossil for the P. varcus zone.

Palynology and organic geochemistry of an early to Middle Devonian succession from TCB X-1001– tacobo borehole, sub-Andean basin, southern Bolivia

Palynological and organic geochemical analyses have been performed on an Early to Middle Devonian clastic marine sedimentary succession of the TCB X-1001 – Tacobo borehole, in the Foothills of the southern sub-Andean ranges of Bolivia. The studied subsurface section encompasses shallow marine deposits of the Icla, Huamampampa and Los Monos formations. Eighteen from the twenty-three cutting samples available were productive, yielding variable abundance, diversity and preservation of organic-walled phytoplankton and miospores, with an increasing trend of terrestrial palynomorphs transpiring towards the younger beds. The palynological assemblage of the Icla Formation contains Bimerga nuda, Cordobesia cf. C. uruguayensis, Duvernaysphaera angelae, and Dibolisporites echinaceus. The Huamampampa Formation includes Polyedryxium sp. cf. P. condensum, Umbellasphaeridium deflandrei and Acinosporites eumammillatus. Arkonites bilixus, Maranhites mosesii, Polyedryxium “talus”, Stellinium comptun, Archaeozonotriletes variabilis, Chelinospora timanica, Convolutispora subtilis, Cymbosporites cyathus, Dibolisporites farraginis, Geminospora lemurata, Grandispora permulta, Samarisporites eximius and Verrucosisporites premnus are among the most relevant taxa of the Los Monos Formation. Based on the organic-walled phytoplankton and the miospores of the studied section, the Icla, Huamampampa and Los Monos formations are assigned to the late Pragian - Emsian, Emsian and Eifelian?- middle Givetian, respectively. The palynomorph distribution, relative abundance and preservation throughout the studied samples support the palaeoenvironment interpretation based on sedimentology and sequence stratigraphy. RockEval pyrolysis, TOC, HI and Tmax data were analysed to determine type and quality of the kerogen and hydrocarbon potential of the stratigraphic units.

Middle Givetian to late Famennian (Middle to Late Devonian) conodonts from the northern margin of Gondwana (Kerman region, Central Iran)

ABSTRACT The Givetian to Famennian (Middle-Upper Devonian) Bahram Formation deposits (Bondar and Shahzadeh Mohammad sections) in the Kerman region, Central Iran were sampled for conodonts. The conodonts were described, their distribution investigated, and the studied sections were correlated. In the previous conodont-based papers, the age of the Bahram Formation in the Kerman region was from the upper Givetian hermanni Zone to the middle Famennian Uppermost marginifera Zone (Middle to Late Devonian). However, the new results of this study show that the Bondar section spans from the middle Givetian ansatus Zone to the upper Famennian (middle part of the Middle expansa Zone = Bispathodus aculeatus aculeatus Zone) and the Shahzadeh Mohammad section spans from the middle Givetian ansatus Zone to the lower Famennian (Uppermost crepida = Palmatolepis glabra pectinata) Zone. In both of the studied sections, the Givetian/Frasnian boundary has been identified by the first occurrence of Ancyrodella rotundiloba pristina, but there is no obvious (sedimentological or biostratigraphic) evidence to define the Frasnian/Famennian boundary.