Pristiograptus Dubius Research Articles

Lithostratigraphy, graptolites and brachiopods communities of the Ludlow (Silurian) of the Eastern slope of the Baltic Syneclise

Milaiciai-103 well is located on the East slope of the Baltic Sineclise. Dubysa, Mituva and Ventspils formations of the Ludlow Stage were defined within the slope. The Sesupė and Nova beds are distinguished in the Dubysa Formation. The Sesupė Bed is composed of ten sedimentation cycles of limestone and marl rhythmical interbedding. The lower boundary of the Sesupė Bed is unclear in the Milaiciai-103 well because the borehole was drilled without core sampling starting from the depth of 1 301.0 m. The Nova Bed is composed of two cycles composed of limestone in the lower part and marlstone in the upper part. The Mituva Formation is composed of four cycles of limestone and marlstone rhythmical interbedding. The Ventspils Formation is composed of three limestone layers showing different features. The Ludlovian biostratigraphy is based on graptolite fauna. There are distinguished progenitor-scanicus, incipiens graptolite biozones of the Gorstian and praecornutus, cornutus, bohemicus tenuis, balticus and valleculosus biozones of the Ludfordian. The description of zonal species Monograptus valleculosus Tsegelnuk is given like Pristiograptus dubius cf. frequens Jaekel. There are distinguished Lissatrypa obovata–Jonsea grayi, Isorthis amplificata–Lissatrypa obovata, Gypidula–Atrypoidea, Atrypa reticularis–Shaleria ornatella and Isorthis parvulus – Atrypoidea brachiopod communities in the Ludlow section of the well Milaiciai-103. According to the lithological composition and described graptolites and brachiopods the Milaiciai-103 well contains different ecostratigraphic levels.

Phyletic Evolution and Iterative Speciation in the PersistentPristiograptus dubiusLineage

Urbanek, A., Radzevicius, S., Kozlowska, A., and Teller, L. 2012. Phyletic evolution and iterative speciation in the per− sistent Pristiograptus dubius lineage. Acta Palaeontologica Polonica 57 (3): 589–611. The paper focuses on patterns of the evolution of the simplest and longest−ranging (approximately 18 Ma) Silurian graptolite Pristiograptus dubius. The Pristiograptus dubius species group consists of the P. dubius stem lineage repre− sented by a sequence of a number of subspecies displaying only small morphological changes as well as derivative species produced from the stem lineage by means of iterative speciation. This long raging graptolite lineage is the only one, apart of one retiolitid, which survived the most severe environmental event for graptolites, the Cyrtograptus lundgreni Event. Based on three−dimensional, isolated material two P. dubius groups taxa are distinguished. One group has an obtuse angle between the thecal lip and the succeeding thecal wall, the second group has a right or acute angle. Other characters differ− entiating P. dubius forms are: the shape of the apertural lips, differences in rhabdosome shape and size, and a different number of sicular rings. Sixteen species and subspecies of Pristiograptus from the East European Platform, Poland and Lithuania are discussed. Five new subspecies P. dubius magnus, P. dubius paezerensis, P. dubius praelodenicensis, P. dubius postfrequens, and P. dubius postmagnus are proposed.

Mid-Ludfordian coeval carbon isotope, natural gamma ray and magnetic susceptibility excursions in the Mielnik IG-1 borehole (Eastern Poland)—Dustiness as a possible link between global climate and the Silurian carbon isotope record

The graptolite-bearing upper Silurian succession of the Mielnik IG-1 borehole (eastern Poland) represents a periplatform setting on a neritic carbonate platform located on the palaeocontinent of Baltica and records widely recorded positive mid-Ludfordian Carbon Isotope Excursion (CIE). The initial increase of δ13C values occurs in the uppermost part of the Neocucullograptus kozlowskii Zone whereas pronounced increase and maximal values (+6.74‰) are noted in the N. kozlowskii–Pseudomonoclimacis latilobus interzone (Pristiograptus dubius bloom interval). The thickness–time relation in the section indicates that the main, initial shift in carbon isotope ratio (of 2.7‰) occurred over a very short time, estimated to be around 4000years, and is coeval with a rapid initiation of deposition of rock-forming, silt-sized detrital dolomite and quartz. The CIE decline is interpreted as steeper than in inner shelf sections, and is coincident with a flooding event in the Ps. latilobus–Slovinograptus balticus Zone; whereas the end of the excursion is coeval with the next flooding surface marked by the Ps. Latilobus–Uncinatograptus acer graptolite assemblage. Combined SGR (Spectral Gamma Ray), facies, and faunal records during the CIE suggest prolonged sea-level lowstand conditions. The abundant detrital material (‘dolomite siltstone facies’), occurring exclusively in the CIE interval, is noted in microfacies as well as in the geophysics record—as pronounced negative excursions in total natural gamma ray and magnetic susceptibility, both resulting from dilution by diamagnetic and low-radioactivity minerals. The perfectly sorted, vertically equally-sized silt material contains unique, constant and low diversified grain assemblage (euhedral dolomite, quartz, minute ooids)—suggesting its provenance exclusively from the shallower and/or emerged parts of the carbonate platform interior. The spot findings of graptolites and nautiloids along with delicate parallel lamination of sediments indicates relatively deep environment, with absence of traction processes. These features, along with the lack of dolomite detritus in accompanying redeposited carbonates, suggest its derivation by wind. With regard to the earlier noted presence of aeolian detritus in the middle Ludfordian, we suggest dustiness as a plausible driving force of the CIE. In the hypothesis proposed, bioavailable Fe-bearing dust inflow in concert with antiestuarine circulation on shelfs, caused nutrient (N:P ratio) disturbances, resulting in methanogenesis in surface layer of the seas. The surface layer methanogenesis should resulting in bathymetric gradient of isotope fractionation, what is consistent with the CIE record. Coincidence of sea-level lowstand, low-latitude aridity, and gustiness of the global climate, are in accordance with the hypothetical short-lived glaciation in mid-Ludfordian time.

Palaeocope ostracods from the Silurian Wenlock Series of Arctic Canada

Silurian Wenlock Series deposits of the Cape Phillips Formation on Baillie-Hamilton Island and Cornwallis Island, Arctic Canada, have yielded a silicified ostracod assemblage that spans the late Sheinwoodian and Homerian stages. Sixteen palaeocope ostracod species are recorded, including the new species Beyrichia ( Beyrichia ) marssae , Gabrielsella ? copelandi , and Platybolbina ( Abruptobolbina ) adraini . The ostracod faunas can be linked into local trilobite, microvertebrate, and graptolite zonal schemes, and a few of the ostracod species offer potential for local and perhaps wider biostratigraphical correlation. The ostracods are mostly known only from the Cape Phillips Formation, but also include two taxa found in the Wenlock Series of the Avalanche Lake area, Northwest Territories, Canada. Other ostracod species suggest links with Silurian successions in northern Canada and the Baltic. Low-diversity ostracod faunas characterize the level of a marked positive carbon isotope excursion and coeval mid-Homerian regression at the level of the regional Pristiograptus dubius – Gothograptus nassa graptolite Biozone. Comparison with the pattern of distribution of coeval ostracod faunas elsewhere in Canada suggests that diversity changes in the Cape Phillips Formation ostracod faunas are controlled by local palaeoenvironmental factors perhaps linked to global sea-level change.

The lundgreni event in the Silurian of the East European Platform, Poland

The lundgreni event (late Wenlock, Silurian) is here interpreted in terms of palaeontologic (graptolites, microphytoplankton, benthos), biostratigraphic and geochemical evidence derived from Homerian deposits drilled in the Bartoszyce well (East European Platform in Poland). The lundgreni event in the graptolite record of Bartoszyce comprises extinction, survival and recovery phases. The graptolite extinction proceeded in three steps: lundgreni, testis and flemingii-dubius. The testis extinction eliminated the largest number of species. Only the long-lasting Pristiograptus dubius survived the combined extinctions and was joined during the survival phase by the opportunistic Gothograptus nassa and Pristiograptus parvus. The graptolite recovery is expressed by the diachronous arrival of new species in association with P. dubius. All documented phytoplankton taxa survived the lundgreni event. Phytoplankton frequency and diversity patterns, together with total organic carbon (TOC) fluctuations, indicate that oligotrophy/productivity regime was unsteady during the testis and flemingii-dubius extinctions and stable during the early graptolite survival. There is no evidence for extinction within benthic fauna assemblages. Diversified benthos appeared in a great abundance during the early survival phase. This records a redox-related event of substrate colonization that took place simultaneously with local decline in primary productivity. The last two phases of graptolite extinction and the onset of the survival correlate with strong, positive anomalies of δ 18O, δ 13C org and δ 13C carb. The anomalies coincide with the fall in local primary productivity and the enhanced storage of organic carbon in peri-Gondwanan upwelling zones (Sudeten, Thuringia). The stepped graptolite extinction in Bartoszyce occurred in an environment that was situated within the low-latitude Baltica shelf and was markedly stable in terms of bathymetry, distance from land and oxic regime. This local extinction was most likely caused by catastrophic fluctuations in nutrient supply, breaking primary productivity. The trophic perturbations on the Baltica shelf were coeval with and related to eutrophication of the high-latitude upwelling zones of the Rheic Ocean. The postulated spatial fluctuations in the trophic resource continuum may reflect palaeooceanographic changes that accompanied the global, late sea-level highstand of that time.

The Pristiograptus dubius (Suess, 1851) species group and iterative evolution in the Mid- and Late Silurian

Synopsis Pristiograptus dubius (Suess, 1851), one of the longest-known graptolites, is also one of the simplest and longest ranging (about 20 Ma). As well as giving rise to new genera, such as Colonograptus Přibyl (1943 c ) and Saetograptus Přibyl (1943 c ) amongst others, it also repeatedly gave rise to both broad and narrow short-lived pristiograptids, cases of iterative development. These closely resemble P. d. dubius and are often difficult to distinguish from it, especially in cases of indifferent preservation or tectonic deformation: a stratigraphy known on independent criteria is a great facilitator to identification! There is no difference in the overall range of broad versus narrow species, but the latter are more numerous. The parent species P. d. dubius survives them all and extends almost to the top of the Přídolí. The origin of the P. dubius lineages is probably through P. initialis Kirste (1919) and P. pergratus in the latest Llandovery, and P. praedubius (Bouček, 1931) in the earliest Wenlock. Pristiograptus d. dubius is a stem lineage in the sense of Urbanek (1998).

Pristiograptus (Graptoloidea) from the perneri - lundgreni biozones (Silurian) of Lithuania

Two new forms of Pristiograptus dubius, here designated as varieties A and B, are described and figured. Both were found in core samples representing the perneri through lundgreni biozones of the Wenlock epoch. The cores are from boreholes Šiupyliai-69, Parovėja-9, Likėnai-396, Paežeriai-222 and Sutkai-87 in central and northern Lithuania. The associated graptolites Cyrtograptus perneri Boucek, C. radians Tornquist, C. lundgreni Tullberg, Monograptus flemingii flemingii (Salter), M. testis testis (Barrande), Monoclimacis flumendosae (Gortani) and Pristiograptus pseudodubius (Boucek) (= P. parvus) are all indicative of the perneri, radians and lundgreni biozones of the Wenlock. Two species of Pristiograptus occur in this time-stratigraphic interval: P. dubius and P. lodenicensis. In P. dubius the degree and manner of extension of the thecal apertural lip (thecal hood) onto the succeeding theca distinguish it from otherwise very similar taxa. The thecal morphology of P. lodenicensis differs from that of a typical Pristiograptus in that the apertural lip has a central depression and is rounded into small lobes laterally.

Systematics, biostratigraphy and evolution of the Late Ludlow and Pridoli (Late Silurian) graptolites of the Yass district, New South Wales, Australia

Graptolites from the Yass district of New South Wales include important material from: low in the Black Bog Shale; from the Yarwood Siltstone Member; 2 levels high in the Black Bog Shale; 2 levels low in the Rosebank Shale; low in the Cowridge Siltstone; and in the lower part of the Elmside Formation. The faunas from the lower 4 levels are late Ludlow (early Late Silurian), and the higher 4 levels are P^ ridoli (late Late Silurian). Twenty-seven graptolite taxa, a considerable increase on previous records from Yass, have been identified in the late Ludlow and P^ ridoli of the district. These taxa enable the Ludlow-P ^boundary to be identified some 20 m above the base of the Rosebank Shale (Booroo Ponds Group); our stratigraphically highest collection from the Elmside Formation is latest P ^ supporting the previous placement of the base of the Devonian approximately midway through the Elmside Formation (Barambogie Group). The following graptolite Biozones have been identified: praecornutus, cornutus, parultimus, bouceki and transgrediens. Twenty Yass taxa are described, including the new species Bohemograptus paracornutus, Pristiograptus shearsbyi, Neocucullograptus? yassensis and N.? mitchelli and the new subspecies Monograptus perneri elmsidensis and M. formosus jenkinsi. The following are recorded from Australia for the first time: Bohemograptus praecornutus Urbanek, 1970; Crinitograptus operculatus Munch, 1938; and Pristiograptus kolednikensis P^ 1940. Dictyonema sp. cf. D. sherrardae Rickards et al., 1995 and D. elegans Bulman, 1928 are considered late evolutionary derivatives of long-ranging dendroid species. Linograptus posthumus introversus Rickards & Wright, 1997 is interpreted as a short-lived, late Ludlow offshoot of the long-ranging L. p. posthumus Richter, 1875. Bohemograptus praecornutus is regarded as the ancestor of B. paracornutus, the B. cornutus evolutionary plexus being recognised for the first time in Australia. Late forms of Pristiograptus dubius (Suess, 1851) probably gave rise to P. shearsbyi n.sp. and Pristiograptus kolednikensis probably arose in the basal P^ ridoli from the late Ludlow P. fragmentalis (Boucek, 1936). Some material described and discussed by Brown & Sherrard (1952) is reinterpreted. Bohemograptus paratenuis n.sp. is proposed for material assigned by Urbanek (1970) to B. bohemicus aff. tenuis (Boucek, 1936); this species is known only from Poland.

Prídolí graptolites from the Iberian Peninsula: a review of previous data and new records

Prídolí graptolites are relatively rare in Iberia and, in fact, in much of southwestern Europe, because Prídolí to Early Devonian rocks are largely represented by shallow-water sandstones or siltstone-sandstone alternations. The first unambiguous find of Prídolí graptolites was the 1979 recovery of Colonograptus? transgrediens from limestone nodules occurring within the lower part of the "Upper Graptolite Shales'' in the Ossa Morena Zone of the Hesperian Massif, Spain. Recent detailed studies of the immediately underlying "Scyphocrinites Limestone'' unit reveal two levels of graptolites: a lower marly shale band with poorly preserved but large numbers of Pristiograptus dubius (s.l.), Colonograptus? cf. parultimus, and Linograptus sp., and a limestone band near the top of the unit yielding specimens of C.? transgrediens preserved in relief. In the Barrancos area of the Ossa Morena Zone of Portugal, a recently sampled 8 m thick section of shales and shales and sandstones has yielded six bands of graptolites, the lowest containing lower or middle Ludlow graptolites, and the three stratigraphically higher collections yielding the lower to middle Prídolí species Linograptus posthumus, Colonograptus? parultimus, C.? parultimus?, Monograptus formosus, and Monograptus bouceki, the last-named species occurring only in the highest collection and suggesting a mid-Prídolí age. The occurrence of Prídolí graptolites (Colonograptus? ultimus) is confirmed in the Sil syncline of the northernmost part of the Central Iberian Zone (northwestern Spain). Outside Iberia, but still within the southwestern European part of the North Gondwanan realm, Prídolí graptolites are known in the Armorican Massif of western France (Normandy and probably central Brittany), in Montagne Noire (southern France), and in southwestern Sardinia (Italy).

Wenlock–Ludlow graptolite biostratigraphy and extinction: a reassessment from the southwestern Iberian Peninsula (Spain and Portugal)

A detailed reexamination of a key Wenlock–Ludlow transition section in the Valle syncline region, Spain, and the incorportation of data from a coeval section in the Barrancos area, Portugal, both within the Ossa Morena Zone, reveal seven biostratigraphic units. These are Monograptus belophorus? and Cyrtograptus lundgreni−Monograptus testis biozones, representing the upper Sheinwoodian and the preextinction, lower Homerian faunas, respectively; the Pristiograptus dubius "parvus" – Gothograptus "nassa" Concurrent Range Biozone, Colonograptus? praedeubeli – Colonograptus? deubeli Biozone, and Colonograptus? ludensis Biozone, representing the upper Homerian postextinction faunas; and the Ludlow Neodiversograptus nilssoni and Saetograptus fritschi linearis biozones. The extinction beds between the lower Homerian lundgreni−testis Biozone and the lowest upper Homerian dubius "parvus"−"nassa" Interval Biozone make up a several centimetre thick, soft, orange-weathered, almost barren, volcanic? bed.

Upper Homerian (Wenlock, Silurian) graptolites and graptolite biostratigraphy, Arctic Archipelago, Canada

Integration of graptolite data obtained from isolated and flattened material from Arctic Canada permits the recognition of three upper Homerian biostratigraphic zones. These, from oldest to youngest, are the Pristiograptus dubius – Gothograptus "nassa" interval Biozone, Colonograptus? praedeubeli – Colonograptus? deubeli Biozone, and Colonograptus? ludensis Biozone. Species of flattened graptolites described in this study include C.? deubeli, C.? ludensis, C.? praedeubeli, Colonograptus? schedidoneus,Lobograptus ? angustus n.sp., Lobograptus? claudiae, Lobograptus? sherrardae, Plectograptus macilentus, Agastograptus clathrospinosus, and Gothograptus "nassa." With only a few exceptions, the zone-by-zone diversity of monograptid and plectograptine graptolites of the Canadian Arctic is remarkably similar to that elsewhere.

The graptolites "Pristiograptus" praedeubeli (Jaeger) and "Pristiograptus" ludensis (Murchison) (uppermost Wenlock, Silurian) from Arctic Canada: taxonomy and evolution

Isolated, uncompressed specimens of Pristiograptus dubius, "Pristiograptus" praedeubeli, and "Pristiograptus" ludensis are described from Arctic Canada. Pristiograptus dubius and early forms of "P." praedeubeli are very similar, suggesting a respective, ancestor-descendant relationship. The study shows that "P." praedeubeli and "P." ludensis are generally readily distinguishable, but that the sicular region of the latter shows a much greater variation than previously recognized. End member morphs of "P." ludensis are remarkably similar to "P." deubeli, further confirming a close evolutionary link between them. To facilitate refined biostratigraphic division of the uppermost Wenlock, therefore, large collections of specimens are required to separate those two species when co-occurring.

Atavograptus primitivus (Li) from the earliest Silurian of Arctic Canada: implications for monograptid evolution

It has long been considered that all monograptids have theca 1 originating from a primary porus in the sicula (i.e., sinus and lacuna stages; Bulman, 1970). The major basis for this assumption has been studies of Late Silurian monograptid species such as Saetograptus chimaera (Barrande), Pristiograptus bohemicus (Barrande), and Pristiograptus dubius (Suess) (e.g., Eisenack, 1942; Walker, 1953; Urbanek, 1958). That all monograptids possessed this type of development was not questioned due to the lack of well-preserved, early monograptid specimens clearly showing the sicula–theca 1 relationship. Hutt et al. (1970) described Monograptus gregarius Lapworth, from the gregarius Zone, as having theca 1 originating through a primary porus (Hutt et al., 1970; Rickards and Hutt, 1970, referred to this as a “primary notch” although, according to Bulman, 1970, p. V11, the notch corresponds only to the sinus stage). Their figures of these specimens, however, do not unequivocally confirm its presence (Hutt et al., 1970, p. 14, Pl. 3, figs. 65, 67). Rickards and Hutt (1970) alluded to the possible presence of a primary porus in Atavograptus ceryx (Rickards and Hutt) from the persculptus Zone, but could not determine its existence with certainty. Mitchell (1987) was the first to question the presence of this mode of development of theca 1 in relation to the origin of the monograptids. He proposed, however, that the development of the fully uniserial rhabdosome was coincident with a change in both the sicular structure (the sinus and lacuna stages) and the early ontogeny of theca 1. He suggested that the sinus and lacuna stages represented a homologue of the hooded foramen seen in the th 11 protheca of some Pattern H species, from which th 12 emerges and that, in the uniserial monograptids, this feature is accelerated in the astogenetic sequence, appearing in the metasicular ontogeny rather than that of the first theca. He pointed out that this hypothesis could only be tested once suitable, isolated specimens of earliest monograptids could be studied to see if the sinus and lacuna stages were, indeed, coincident with the achievement of a fully uniserial rhabdosome. New evidence from isolated, early monograptid material allows us to test Mitchell's theory on monograptid origin.

Extinction and opportunistic evolution among late Wenlock graptolites

The late Homerian was a time of profound importance to graptolites. Following the complete extinction of Cyrtograptus and the near extinction ofMonograptus(s.s.)at the end of thelundgrenitestis Zone(lower Homerian, upper Wenlock), the morphologically simple and long-ranging Pristiograptus dubius lineage underwent rapid (opportunistic) cladogenesis during the succeeding upper Homerian. Two clades, each with novel and sometimes complex sicular and thecal structures, appeared. One clade, the ‘Pristiograptus’ praedeubeli group, gave rise to similar but more complex species, such as ‘P.‘ ludensis and ‘P.‘deubeli, which in turn gave rise to Ludlow taxa, including Saetograptus (s.l.) and Pseudomonclimacis. The other clade, the Lobograptusgroup, gave rise to Ludlow taxa Lobograptus, Neolobograptus, Bohemograptus, and Neocucullograptus some with very complex thecal structures. Ludlow and younger monograptid faunas therefore comprise at least three separate lineages: Monograptus (s.s.), the Lobograptus group (clade), and the ‘Pristiograptus’ praedeubeli group (clade).Cladogenesis, evolution, extinction, Homerian, PRISTIOGRAPTUS, LOBOGRAPTUS

Late Wenlock-Ludlow graptolite extinction and evolution: perspectives from Arctic Canada

An abrupt change in the composition of graptolite faunas just below, and at, the Wenlock-Ludlow boundary has recently been demonstrated in southeastern Germany and Kirgizistan. JAEGER (1991) terms that changeover the “Big Crisis”.On a global scale, throughout all but the uppermost Wenlock, Monograptus (s.s.), Cyrtograptus, and plectograptine retiolitids are moderately diverse and very abundant. This fauna is abruptly replaced in the uppermost Wenlock by an acme of simply thecate Pristiograptus dubius types and “pristiograptids”, and a marked increase in the diversity of the plectograptines. The succeeding earliest Ludlow fauna, which too appears abruptly, is marked by a mostly new fauna of plectograptines and new forms of monograptids the earliest of which include Lobograptus, Neodiversograptus and Bohemograptus. Two “crises” are therefore manifest, the earlier one being more profound.The Cape Phillips Formation of the Arctic Islands, Canada, yields a superb late Wenlock and early Ludlow graptolite, fauna. The late Wenlock lundgreni-testis Biozone has yielded isolated specimens of about 15 species of monograptids (including Monograptus (s.s.); especially M. testis), Cyrtograptus (several species), and at least seven species of plectograptines. About half of the fauna continues from the underlying zone. The overlying uppermost Wenlock ludensis Biozone is markedly different. Pristiograptus (of the P. dubius type) and “Pristiograptus” (Pseudomonoclimacis?) with novel thecal and sicular development (four or five species) are very abundant, and ten species plectograptines, only two of which continue from the underlying zone, appear abruptly. Cyrtograptus and Monograptus (s.s.) are totally absent.The succeeding earliest Ludlow is also characterized by rather abrupt appearances, again of several or more species of plectograptines, most very small, as well as monograptids with new thecal/rhabdosomal styles; these include Lobograptus. Neodiversograptus, Bohemograptus and Colonograptus, and slightly later, Saetograptus and the reappearance of Monograptus (s.s.). Plectograptines apparently become totally extinct by about mid Ludlow.

Late Wenlock (Middle Silurian) global Bioevent: Possible chemical cause for mass graptolite mortalities

Graptolites nearly became extinct in the latest Wenlock in all preserved stratigraphic sequences of this age. Graptolite mortalities occurred along the western coast of Laurentia and at sites that surrounded the Proto‐Tethys. Graptolite mass mortalities took place among deep‐water, open ocean dwelling organisms. After the mass mortalities, only the Pristiograptus dubius group and retiolids surface or near‐surface dwellers, survived. For a period of time, little speciation or diversification occurred. The base of the Ludlow is marked by diversification, with appearances of S. colonus, M. nilssoni and other groups which occur in near surface waters. None of the extensive plate movements postulated for the Silurian readily explain the mass extinctions that occurred. During the Silurian, global temperatures were warmer than present and atmospheric oxygen concentrations were lower, creating extensive oceanic anoxia. Below the oxygenated surface layers of the ocean, was an anoxic, non‐sulfidic zone (i.e. nitrat...

Late Wenlock graptolite-bearing tuffaceous sandstone from Bomholm, Denmark

Late Wenlock (Silurian) graptoliferous dark grey mudstone and tuffaceous sandstone lithofacies occur, mainly as loose boulders, at the southeast coast of Bomholm. The mudstone may be estimated to repre­sent a 25 m thick sequence, and contains a graptolite fauna indicating the Cyrtograptus lundgreni Zone. The fauna is correlated with sequences of similar age from other areas, specially from Scania. Monograp-tus flemingi and Pristiograptus dubius pseudodubius are virtually the only species in the tuffaceous sandstone, some of which were deposited by turbidity currents. There is evidence from the taphonomy and diversity of the sandstone graptolites to suggest that the two species lived at a lower level in the water column than other, coexisting species. Size-frequency analyses are inconclusive as to whether or not the fauna in the tuffaceous sandstone represents a rapidly buried life-assemblage. The tuffaceous sandstone samples represent at least 3 airfall water deposited tuff beds and one bed deposited by turbidity current action. Mineral composition and grain-size of the tuffaceous sandstone indicate an origin from plinian eruptions at an estimated distance of about 300 km from Bomholm, and deposition at a depth of 1000 m ± 300 m, on the outer rim of the Fennoscandian platform. The volcanoes were probably situated on a continent south of Bomholm. The eruption centre later may either have disappeared within the Caledo­nian foldbelt or have been displaced by early Palaeozoic large-scale strike-slip faults towards the SE, along the SW border of the East-European craton.

The lithology, fauna and stratigraphy of two drill cores from the Upper Wenlock in western Skåne, southern Sweden

Abstract Two cores drilled through late Wenlockian rocks in the Ostra Odarslov area of Skane are described. They consist of grey shale intercalated with yellowishgrey laminae and thin beds of dark, dense, silicified limestone. There are also thin beds of dense, non-stratified, silicified shale. The shale contains a meagre fauna, consisting mainly of poorly preserved graptolites. Core No. 1 is characterized by Pristiograptus dubius (Suess) and Gothograptus nassa (Holm). No other determinable graptolites have been found. The fauna is considered to be an equivalent to the nassa/dubius Interregnum of Jaeger (1959), belonging to the uppermost Wenlock. In core No. 2, P. dubius predominates. Monograptus cf. flemingii (Salter) and M. testis cf. inornatus Elles occur sparsely. Cyrtograptus lundgreni Tullberg is relatively common, and a fragmentary specimen of C. radians Tornquist has been found. Some species of inarticulate brachiopods, Cardiola interrupta (Sowerby), two specimens of hyolithids and some flattened ...