Refining the late Silurian sea-level history of the Prague Syncline—a case study based on the Přídolí GSSP (Czech Republic)

A 50-m-thick section in the Po?áry quarry, Prague Syncline (Czech Republic) spanning the upper Silurian (uppermost Ludlow and P?ídolí) to the lowermost Devonian (Lochkovian) has been studied using sedimentological and physical stratigraphical (gamma-ray spectrometry) methods combined with conodont biostratigraphy. Conodont data demonstrate the presence of local conodont biozones: “Ozarkodina” crispa (uppermost Ludlow)—Zieglerodina zellmeri (base of P?ídolí)—Zieglerodina ivochlupaci—Delotaxis detorta—“Ozarkodina” eosteinhornensis s.s.—Zieglerodina klonkensis—Icriodus hesperius-optima (lowermost Lochkovian). The studied section represents a transgressive–regressive facies succession characterized by a transition from distal calciturbidites deposited in a distally steepened carbonate platform during transgression and sea-level highstand (crispa to lower ivochlupaci zones) to mixed calciturbidites/coarse-grained bioclastic limestones (falling-stage systems tract, upper ivochlupaci to lower klonkensis zones). The upper part of the succession consists of bioclastic limestones corresponding to a subtidal setting between storm-wave and fair-weather wave base (lowstand systems tract in upper klonkensis and hesperius-optima zones). This interpretation corresponds to the late Silurian global sea-level pattern as recorded in other regions. Thus the depositional system is interpreted as mostly driven by eustasy with short-lived periods of influence from local tectonics.     

Katian (Upper Ordovician) conodonts from Wales

Middle and upper Katian conodonts were previously known in the British Isles from relatively small collections obtained from a few localities. The present study is mainly based on 17 samples containing more than 17 000 conodont elements from an approximately 14‐m‐thick succession of the Sholeshook Limestone Formation in a road cut near Whitland, South Wales, that yielded a diverse fauna of more than 40 taxa. It is dominated by representatives of Amorphognathus, Aphelognathus/Plectodina and Eocarniodus along with several coniform taxa. Representatives of Decoriconus, Istorinus and Sagittodontina are reported from the Ordovician of UK for the first time. The fauna is a typical representative of the British Province of the Atlantic Realm and includes a mixture of taxa of North American, Baltoscandic and Mediterranean affinities along with pandemic species. Based on the presence of many elements of Amorphognathus ordovicicus and some morphologically advanced specimens of Amorphognathus superbus, the Sholeshook Limestone Formation is referred to the lower A. ordovicicus Zone. Most of the unit is also coeval with Zone 2 of the Cautleyan Stage in the British regional stage classification, and stage slice Ka3 of the middle Katian Stage in the global stratigraphical classification, an age assignment consistent with data from trilobites, graptolites and chitinozoans. The unusually large collection of M elements of Amorphognathus provides insight into the complex morphological variation in this element of some Katian species of this genus. The Sholeshook conodont fauna is similar to those of the Crûg and Birdshill limestones, but differs in several respects from the slightly older ones from the Caradocian type area in the Welsh Borderland. Although having some species in common, the Sholeshook conodont fauna clearly differs from coeval Baltoscandic faunas and is even more different in composition compared with equivalent North American Midcontinent faunas.     

Palaeoecology and palaeogeography of Late Ordovician (Katian–Hirnantian) cephalopods of the Boda Limestone,Siljan district,Sweden

The carbonates associated with the Late Ordovician (Katian–Hirnantian) Boda mounds of the Siljan district, Sweden, contain a rich cephalopod fauna. Cephalopods are rare in the micritic stromatactis facies of the Katian Boda Core Member, but are concentrated together with other molluscs and trilobites in synsedimentary fillings of caves and crevices of the lithified mound limestone. More than 60 cephalopod species are known from these fillings. The assemblage is dominated in richness and abundance by small orthoconic proteoceratids of the genus Isorthoceras and by curved barrandeocerids, and is considerably less endemic than the benthic fauna of the Boda mounds. Similarities are remarkable at the species level with assemblages from elsewhere in Baltica, with Avalonia and south‐western Kazakhstan. A genus‐level comparison reveals affinities with Laurentia. However, the genus‐level similarities are interpreted as reflecting mainly similarities of the depositional environment and of physicochemical conditions. The presence of calcareous algae in the Boda Limestone and maximum hydrostatic septal strength of cephalopods indicate a depositional depth of <100 m, well within the euphotic zone. The dominance and diversity of cephalopods with vertical migrant lifestyle and the absence of actinocerids indicate a cool, nutrient‐rich deeper neritic environment. The post‐Katian sediments contain a drastically reduced diversity, dominated by orthocerids. The maximum hydrostatic septal strength of the Hirnantian cephalopods and sedimentological features indicate a shallowing during the Hirnantian, but a continuation of high food availability for cephalopods in the water column.     

The oldest bryozoans of Baltoscandia from the lowermost Floian (Ordovician) of north-western Russia: two new rare,small and simple species of Revalotrypidae

We describe two new species of esthonioporate bryozoans, Revalotrypa inopinata sp. nov. and R. yugaensis sp. nov., from the Lower Ordovician, south-east of Lake Ladoga, north-western Russia. The colonies of the two species are very small and were extracted from limestone nodules found in the lower part of glauconitic sandstone in the Joa Member (lowermost Floian). Revalotrypa inopinata sp. nov. and R. yugaensis sp. nov. are the oldest known bryozoans from Baltoscandia. Study of the two species includes scanning electron microscopy (SEM) imaging and X-ray microtomography (micro-CT). The palaeogeographic distribution of the oldest known bryozoans from the Lower Ordovician and the advantages and disadvantages of micro-CT for the study of Palaeozoic bryozoans are discussed. The authorship of Revalotrypidae, which has been inconsistently allocated in the literature, is discussed.     

Termite mound building

Termite mounds present a convenient record of the behaviour of their builders which can be studied at leisure. More usually, insect behaviour has results of a transitory nature, difficult to record and subject in their interpretation to the personal idiosyncrasies of the observer. A behaviour pattern which is specific to a particular termite may, however, result in mounds which appear superficially different under different environments, while two different species may produce mounds which appear to be similar in the same environment. It follows that the use of termite mounds as indications of species behaviour must be considered with care if there are wide differences in environmental factors in the areas being dealt with. The following remarks arise mainly from observations made in Eastern Africa on the large mounds constructed by three species of the genusMacrotermes. Of these,Macrotermes bellicosus (Smeath) is the most widely distributed, occuring from Eritrea (and Aden) in the north to the borders of the Union of South Africa in the south, from sea-level to 1 800 metres, under most conditions other than tropical rain forest and desert sand.Macrotermes natalensis (Hav.) andMacrotermes goliath (Sjost.) have more restricted distributions within the range ofbellicosus.     

New Middle Devonian conodont data from the Dong Van area,NE Vietnam (South China Terrane)

Middle Devonian conodonts from the Si Phai section in NE Vietnam are described. The section ranges from the Middle Devonian ensensis to timorensis conodont zones to the Late Devonian rhomboidea conodont Zone. A rich overall assemblage is described, including 27 taxa of species or subspecies rank and 11 taxa described in an open nomenclature. Among the dominant Polygnathus forms, four new taxa are described: Polygnathus linguiformis saharicus subsp. nov., Polygnathus linguiformis vietnamicus subsp. nov., Polygnathus rhenanus siphai subsp. nov., and Polygnathus xylus bacbo subsp. nov. Conodont assemblages are attributed to polygnathid, polygnathid-klapperinid, and klapperinid conodont biofacies representing hemipelagic to pelagic environments. The klapperinid biofacies, unreported in the previous literature, are here attributed to offshore areas of the external shelf. The taxonomic compositions of the studied conodont assemblages, as well as their CAI characteristics (CAI 4–5), suggest a palaeogeographic affinity of the studied strata to the Chinese Devonian Guangxi Basin, and the South China Terrane in general. Furthermore, the conodont biofacies and the palaeogeographic distribution of the fauna are discussed.     

Carbonate breccias in the lower-middle Ordovician Maggol Limestone (Taebacksan Basin,South Korea): Implications for regional tectonism

Summary Carbonate breccias occur sporadically in the Lower-Middle Ordovician Maggol Limestone exposed in the Taebacksan Basin, South Korea. These carbonate breccias have been previously interpreted as intraformational or fault breccias. Thus, little attention has been focused on tectonic and stratigraphic significance of these breccias. This study, however, indicates that the majority of these breccias are solution-collapse breccias, which are causally linked to paleokarstification. Carbonate facies analysis in conjunction with conodont biostratigraphy suggests that an overall regression toward the top of the Maggol Limestone probably culminated in subaerial exposure of platform carbonates during the early Middle Ordovician. Extensive subaerial exposure of platform carbonates resulted in paleokarst-related solution-collapse breccias in the upper maggol Limestone. This subaerial exposure event is manifested as a major paleokarst unconformity elsewhere beneath the Middle Ordovician sequence, most notably North America and North China. Due to its global extent, the early Middle ordovician paleokarst unconformity (‘the Sauk-Tippecanoe sequence boundary’) has been viewed as a product of second-order eustatic sea level drop during the early Middle Ordovician. Although we recognizes a paleokarst breccia zone in the upper Maggol Limestone beneath the Middle Ordovician sequence, the early Middle Ordovician sequence boundary appears to be a conformable transgressive surface or a drowning unconformity, rather than a major paleokarst unconformity. The paleokarst breccia zone in the upper Maggol Limestone is represented by a thinning-upward stack of exposure-capped tidal flat-dominated cycles that are closely associated with multiple occurrences of paleokarst-related solution-collapse breccias. The paleokarst breccia zone in the upper Maggol Limestone was a likely consequence of repeated high-frequency sea level fluctuations of fourth- and fifth-order superimposed on a second-and third-order eustatic fall in sea level that was less than the rate of tectonic subsidence across the platform. It suggests that second- and thirdorder eustatic sea level drop may have been significantly tempered by substantial tectonic subsidence near the end of maggol deposition. The tectonic subsidence in the basin is also evidenced by the occurrence of coeval off-platform lowstand siliciclastic quarzite lenses as well as debris flow carbonate breccias. With the continued tectonic subsidence, subsequent rise in the eustatic cycle caused drowning and deep flooding of carbonate platform, forming a conformable transgressive surface or a drowning unconformity on the top of the paleokarst breccia zone. This tectonic implication contrasts notably with the slowly subsiding carbonate platform model for the Taebacksan Basin as previously intepreted. Here we propose that the Taebacksan Basin evolved from a slowly subsiding carbonate platform to a rapidly subsiding intracontinental rift basin during the early Middle Ordovician. This study also provides a good example that the falling part of the eustatic sea-level cycle may not produce a significant event at all in a rapidly subsiding basin where the rate of eustatic fall always remained lower than the rate of subsidence.     

Lower Ordovician microfacies and microfossils from Cerro San Pedro (San Pedro de la Cueva,Sonora, Mexico), as a westernmost outcrop of the newly defined <Emphasis Type="Italic">Nuia</Emphasis> Province

The lowermost carbonate beds of the Cerro San Pedro (San Pedro de la Cueva, Sonora State, Mexico) previously assigned to the Mississippian, belong in fact to the lower Ordovician. The limestone of this succession is often dolomitized and chertified, and displays gastropods, pelmatozoans, sponges, and trilobites as major bioclastic components. The different microfacies show that high-energy grainstones, proximal tempestites, and distal tempestites dominated the sedimentation. The paleoenvironments of deposition correspond to an inner ramp, a mid-ramp, and perhaps the upper part of an outer ramp. The strata are characterized by the incertae sedis cyanobacteria Nuia sibirica. A taxonomic revision and discussion of these cyanobacteria, often confused with ooidic grains, is emphasized. Some data are presented on other microfossils, such as primitive, monothalamous foraminifers: Rauserina sp., Vicinesphaera sp., and Neoarchaesphaera sp., leperditicopida and their endolithic microperforations, and primitive chaetetids. Compared to the contemporaneous deposits of the USA, some paleobiological components, e.g., the lithistid siliceous sponges Archaeoscyphia, stromatoporoids? Pulchrilamina, and receptaculacean algae Calathium, are quite rare in the studied section of Sonora, but the predominance of tempestites in the carbonate succession shows that boundstones formed before were systematically eroded and resedimented. The paleogeographic implications are the following: (1) a lower Ordovician intertropical Nuia Province is newly defined in the western part of the lower Ordovician intertropical belt; (2) San Pedro de la Cueva constitutes one of the westernmost outcrops of this new Nuia Province; (3) from Sonora, Nuia extends eastward as far as South China; (4) due to its westernmost paleoposition, San Pedro de la Cueva was frequently affected by tropical storms; and (5) northern lower Ordovician terranes of Mexico (Sonora, Chihuahua, and Baja California) are entirely distinct from the southern ones (Oaxaca). The paleopositions and paleogeographic connections of these northern Mexican terranes with Laurentia, Avalonia, and peri-Gondwanan parts of South America, through the Iapetus and Rheic oceans, still remain disputable or unknown.     

Morphogenesis,phylogenetic relationships,and distribution of the bryozoans of the genus <Emphasis Type="Italic">Orbipora</Emphasis> Eichwald, 1856 (order Trepostomida)

Five species of the genus Orbipora, including two new species, O. lynnensis sp. nov. and O. ukhakuensis sp. nov., are described from the Middle Ordovician of the Leningrad Region and Estonia. The colonies of the species O. acanthophora Bassler, 1911 and O. solida Bassler, 1911 are measured and figured for the first time. The stratigraphic range and geographic distribution of O. acanthophora are refined. A scheme of possible phylogenetic relationships and distribution maps of the species of the genus are presented.     

Sedimentary and biofacies records in calciturbidites at the Devonian-Carboniferous boundary in Moravia (Moravian-Silesian Zone, Middle Europe)

Summary At the Devonian/Carboniferous boundary, major climatic and oceanographic changes influenced sedimentation on carbonate platforms and in peri-platfrom asreas. Three deep-water carbonate successions in Moravia, which were selected to represent different paleotectonic settings, have been studied with the aim of testing the influence of eustatic, climatic and tectonic controls on sedimentation and conodont paleoecology and taphonomy. On the slopes of the wide carbonate platforms of the Moravian Karst Development (Lesní lom and Grygov sections), an exemplary highstand shedding systems developed in the upper Famennian (expansa Zone), marked by a pronounced thickness of their respective calciturbidite successions and an abundance of shallow-water skeletal grains.Palamatolepis— andBispathodus-dominated conodont assemblages contain an admixture ofPolygnathus representing a transported, near-shore component. The eustatic sea-level fall in the praesulcata Zone and the lowstand conditions at the D/C boundary resulted in a decline of carbonate platform production and condensed deposition or nondeposition. In the Lesní lom section, a condensed sequence of turrbiditic calcarenites and shales (Middle praesulcata—lowermost sulcata Zone) was followed by lime mud calciturbidites (sulcata and duplicata Zones). In the conodont assemblages, the first event in the Lower praesulcata Zone was associated with the reduction of ‘mesopelagic’Palmatopic and a bloom of epipelagicPolygnathus communis. The second event in the Middle praesulcata Zone corresponds to the onset of polygnathidprotogranthodid biofacies, indicating a carbonate slope environment. In the Grygov section, a pronounced thickening and upward-coarsening succession of tubiditic calcilutites through calcarenites and intraclast breccias, with poor palmatolepid-bispathodid connodont assemblages (expansa Zone), indicates a progradation of the calciturbidite system associated with sea-level highstand. After a break in sedimentation, covering the interval from the Lower praseulcata to the base of Lower crenulata Zone, thick-bedded, fine-grained calciturbidites were deposited in the Lower crenulata Zone, and are associated with poor, mixed assemblages where siphonodellids and polygnathids predominate. At the isosticha-Upper crenulata/Lower typicus boundary, coasre grained, turbiditic calcarenites and breccias rich in clastic quartz grains and mixed conodont assemblages with reworked Frasnian and Famennian conodonts indicate a deep erosion of the source area, presumably due totectonic uplift (relative lowstand). In the Jesenec section, on the flanks of the volcanic seamount (the Drahany Development), a deep-water Upper Famennian condensed succession of calciturbidites and presumably winnowed pelagic limestones is marked by conodont assemblages of palmatolepid-bispathodid biofacies. More proximal calciturbidites with mixed deep-water and shallowwater conodonts prograde at the top of the Upper Famennian succession (Middle to Upper expansa Zone). A striking hiatus, covering the interval from the Early preaesulcata to the base of Lower crenulata Zone, resulted from extreme condensation and submarine bottom current erosion due to sea-level lowstand in the late Famennian and early Tournaisian. The renewed middle Tournaisian calciturbidite sedimentation with strong evidence of erosion at the source area indicates global eustatic rise and tectonic uplift of the Drahany Development seamounts (relative lowstand). The earlier occurrence of the uplift in the Jesenec area, relative to the Grygov section, shows the advance of tectonic processes over time in the Moravian-Silesian basin (orogenic polarity) as a consequence of Variscan orogenic movements.     

Effect of host species,host nest density and nest size on the occurrence of the shining guest ant <Emphasis Type="Italic">Formicoxenus nitidulus</Emphasis> (Hymenoptera: Formicidae)

Understanding habitat requirements of species is important in conservation. As an obligate ant nest associate, the survival of the globally vulnerable shining guest ant, Formicoxenus nitidulus, is strictly tied to that of its hosts (mound building Formica ants). We investigated how host species, nest density, inter-nest distance and nest mound size relate to the occurrence of F. nitidulus. In total, 166 red wood ant nests were surveyed in SW Finland (120 Formica polyctena, 25 F. rufa, 14 F. aquilonia, 5 F. pratensis, and 2 F. lugubris). Overall, F. nitidulus was found in 60% of the nests. For the actual analysis, only F. polyctena and F. rufa nests were included due to the small number of other nests. F. nitidulus was more likely to be found among F. polyctena than F. rufa. Also, while inter-nest distance was not important, a high nest density, commonly found in polydomous (multi-nest) wood ant colonies, was beneficial for F. nitidulus. The guest ant was also more likely to be found in large host nests than small nests. Thus, our results show that the best habitat for the guest ant is a dense population of host nest mounds with a high proportion of large mounds. Conservation efforts should be directed at keeping the quality of the red wood ant habitats high to preserve their current populations and to increase colonization. This will not only benefit the guest ant, but also a plethora of other species, and help in maintaining the biodiversity of forests.     

Reefal and mud mound facies development in the Lower Devonian La Vid Group at the Colle outcrops (León province, Cantabrian Zone, NW Spain)

In the locality of Colle (Cantabrian Zone, NW Spain), the upper part of the Valporquero Shale Formation (Emsian, La Vid Group) contains an interval of shales and marlstones (barren, greenish-grey shales and fossiliferous, greenish-grey or reddish shales/marlstones) with beds and packages of homogeneous and cross-bedded skeletal limestones. Metre-scale mud mounds and coral biostromes occur encased in the fossiliferous reddish and greenish-grey shale/marlstones, respectively, with the coral biostromes overlying conspicuous skeletal limestone bodies. These rocks were deposited on a carbonate ramp, ranging from above storm wave base for the cross-bedded skeletal limestones to below the storm wave base for the remaining deposits, organic buildups included. The vertical stacking of these facies and the occurrence of the two types of buildups are interpreted to reflect the interplay among several (possibly 4th and 5th) orders of relative sea-level variations, during a 3rd-order highstand. Coral biostromes occur in early 5th-order transgressive system tracts developed within late 4th-order highstand, and are interpreted to have thrived on a stable granular substrate (skeletal limestones) in non-turbid waters, being later aborted by the onset of muddy sedimentation. Biostrome features suggest that they developed under environmental conditions essentially different from those related to the sedimentation of their granular substrate. Mud mounds occur in 5th-order transgressive and early highstand system tracts tied to early 4th-order sea-level rise. Field relationships suggest that mud mounds grew coevally with muddy sedimentation, with high-frequency variations in carbonate vs. terrigenous mud sedimentation influencing their development.An erratum to this article can be found at     

Crustacean metamorphosis: an omics perspective

We quantified the independent impacts of flooding salinity, flooding depth, and flooding frequency on the native species, Phragmites australis and Scirpus mariqueter, and on the invasive species Spartina alterniflora in the Yangtze River Estuary, China. Total biomass of all three species decreased significantly with increasing salinity, but S. alterniflora was less severely affected than P. australis and S. mariqueter. Elevated flooding depth significantly decreased their live aboveground biomass of P. australis and S. mariqueter, while S. alterniflora still had high live aboveground biomass and total biomass even at the highest flooding depth. These findings indicated that S. alterniflora was more tolerant to experimental conditions than the two native species, and an unavoidable suggestion is the expansion of this non-native species in relation to the native counterparts in future scenarios of increased sea-level and saltwater intrusion. Even so, environmental stresses might lead to significant decreases in total biomass and live aboveground biomass of all three species, which would potentially weaken their ability to trap sediments and accumulate organic matter. However, the relatively high belowground-to-aboveground biomass ratio indicated phenotypic plasticity in response to stressful environmental conditions, which suggest that marsh species can adapt to sea-level rise and maintain marsh elevation.     

On Frasnian ammonoids of the New Siberian Islands

Ammonoids from the basal beds of the Nerpalakh Formation (Lower Frasnian) of Belkovsky Island (New Siberian Archipelago) are systematically studied. Taxonomically, the assemblage studied (Manticoceras insulare sp. nov., Tornoceras typum (Sandberger, 1851), and T. contractum Glenister, 1958) is similar to the Early Frasnian ammonoid assemblage of South Timan, from which its is distinguished by the absence of the genera Timanites and Komioceras. The same beds contain conodonts of the Palmatolepis transitans Zone (= MN 4 Zone of the Montagne Noire standard succession), which allow the correlation of the beds studied with the Timanites keyserlingi and Komioceras stuckenbergi ammonoid zones of South Timan. The Early Frasnian ammonoids could supposedly have entered the region of the New Siberian Archipelago from the southwest at the time of a major transgression, which facilitated the distribution of the genera Manticoceras and Tornoceras. A new species of the genus Manticoceras is described.     

下扬子区奥陶纪牙形刺多样性演变初探

根据前人和作者现有资料,对下扬子地区,特别是宁镇地区奥陶纪已经报道的牙形刺属种进行厘定,并按牙形刺带逐带进行多样性统计分析,初步编制出该地区奥陶纪牙形刺属种的地层延限表.研究表明;下扬子区牙形刺在奥陶纪的宏演化经历了3次较明显的辐射事件,分别发生在特马豆克期晚期-弗洛期早期(Serratognathus diversua带)、大坪期早期(Baltoniodus triangularis带)、达瑞威尔期晚期(Eoplacognathus suecicus带);此外,还经历了2次快速增长期,分别发生在达瑞威尔期早期(Lenodus antivariabilis带)、桑比期晚期至凯迪期早期(Hamarodus europaeus带),后者可能与局部环境变化有关.研究表明:华南海平面升降对下扬子区牙形刺宏演化趋势有重要影响.     

Siluro-devonian Conodonts from the Camelford Limestone, Wellington, New South Wales, Australia

Conodont data have been utilized to identify the Silurian/Devonian boundary within the Camelford Limestone near Wellington, NSW. Conodont faunas are documented from the eosteinhornensis Zone to early delta Zone with one new species of Walliserodus ( W. multistriatus ) and two new species of Ozarkodina ( O. brocki and O. camelfordensis ) described. An apparatus reconstruction of Belodella anomalis is also presented.     

<Emphasis Type="Italic">Perturbatacrusta</Emphasis><Emphasis Type="Italic">leini</Emphasis> n. gen., n. sp. a new microencruster incertae sedis (? sponge) from Late Jurassic to earliest Cretaceous platform margin carbonates of the Northern Calcareous Alps of Austria

A new microencruster of unknown systematic position is described as Perturbatacrusta leini n. gen., n. sp. from the Late Jurassic Plassen Carbonate Platform of the Northern Calcareous Alps and its resediments (p.p. Barmstein Limestone). The labyrinthic interior canal system and marginal openings reveal a possible sponge origin. Differences and affinities to allied taxa such as Radiomura cautica Senowbari-Daryan and Schäfer are discussed. The biostratigraphic range of Perturbatacrusta leini n. gen., n. sp. known so far is Kimmeridgian to Tithonian (?Early Berriasian) so far reported from Austria, Bulgaria, Romania, and Greece. Perturbatacrusta leini was detected in boundstones with a diverse association of microencrusters and mainly encrusting sponges occurring together with microbial crusts. Together with the other encrusting organisms and reef builders, Perturbatacrusta leini played an important role for the carbonate production and stabilization of the reefal and slope carbonates in the Late Jurassic to earliest Cretaceous of the western Neotethys realm.     

Paleoecologic and stratigraphic significance of the freshwater algae <Emphasis Type="Italic">Pediastrum</Emphasis> in the Upper Cretaceous (Turonian) marine deposits,north Western Desert,Egypt

Palynological investigations of samples collected from the Abu Roash Formation, Faghur Hj5-1 well, north Western Desert, Egypt show a low diversity in palynomorph assemblage. This assemblage is mainly dominated by a clear proliferation of Pediastrum (and other allied algal forms, e.g., Scenedesmus and Botryococcus) which today lives exclusively in freshwater. Such a prominent record within the current marine deposits could be considered a good biostratigraphic datum in the Upper Cretaceous (Turonian) period rather than an ecologic event in the north Western Desert, Egypt. The influence of freshwater input on the studied deposits is proven by the presence of heavy minerals including kyanite, zircon, staurolite, and amphiboles encountered in siliciclastic sediments. Most of these minerals are sub-rounded to rounded so they were derived probably from sedimentary rocks. In the studied succession, the presence of Pediastrum reflects sea level fall (i.e., lowstand systems tracts). The occurrence of Pediastrum and other algae in such marine deposits reflects the predominant deposition of fluviatile sediments related to the discharge of rivers into shelf seas.