Basis Of Brachiopods Research Articles

Dasycladacean alga Palaeodasycladus in the northern Tethys (West Carpathians, Poland) and its new palaeogeographic range during the Early Jurassic

The green alga Palaeodasycladus was recognized in Lower Jurassic shallow-marine high-energy calcarenites of the Choc Nappe (Hronicum Domain) in the Tatra Mts in Poland. This occurrence indicates the most Northern record of Palaeodasycladus as it is known mostly from the southern part of the Western Tethys. The stratigraphic range of Palaeodasycladus (Norian, Sinemurian–Pliensbachian) and the upper Pliensbachian age of the overlying calcarenites (previous data on the basis of brachiopods) suggest that the studied part of the section was deposited during the Sinemurian–early Pliensbachian. The previous and current reports on occurrences of Palaeodasycladus allowed determination of a new northern palaeogeographic range of the shallow-marine Mediterranean biota during the Early Jurassic time.

Brachiopod faunas, facies and biostratigraphy of the Pridolian to lower Eifelian succession in the Rhenish Massif (Rheinisches Schiefergebirge, Germany)

Abstract The succession of Pridolian to lower Eifelian (uppermost Silurian to lowermost Middle Devonian) rhynchonelliformean brachiopod faunas from the Rhenish Massif (Germany) is described and interpreted against the background of sedimentary sequences and facies development. The predominant rhenotypic (‘Rhenish’) facies is redefined as a neritic-siliciclastic facies type of the Devonian. It is subdivided into eurhenotypic, pararhenotypic and allorhenotypic subfacies, based on sedimentary features and specific brachiopod assemblages reflecting different shallow-marine palaeoenvironments under more or less terrigenous influence. The studied sedimentary successions are subdivided biostratigraphically on the basis of brachiopods, correlated on a supraregional scale, and calibrated in terms of the global chronostratigraphy. Stratigraphic intervals with characteristic brachiopod faunas are distinguished. Faunal turnovers between these are attributed to regional events in the context of short or more extended phases of palaeoenvironmental change presumably caused mainly by sea-level fluctuations in combination with varying crustal subsidence and sedimentation rates. These changes resulted in shelf-wide or more regional extinction or emigration of substantial parts of a brachiopod fauna and subsequent replacement by a largely new one. Finally, new taxa of brachiopods are introduced: Sartenaerirhynchus gen. nov., Paraspirifer ( Mosellospirifer ) subgen. nov., Paraspirifer ( Laurentispirifer ) subgen. nov., Iridistrophia ( Flabellistrophia ) subgen. nov. and Iridistrophia ( Flabellistrophia ) musculosa sp. nov.

Devonian ecological-evolutionary subunits in the Appalachian Basin: a revision and a test of persistence and discreteness

Abstract New data compilations for successive formation scale intervals, approximately third-order sequences, permit a statistical characterization of the ecological–evolutionary subunits (EESUs) or faunas of the Latest Silurian to mid-Late Devonian interval in the Appalachian Basin. Cluster analysis using the Jaccard coefficient of similarity show that certain formations cluster tightly together on the basis of faunal composition while in other cases units are sharply set off from superseding units. This result indicates both the coherence of faunal composition within EESUs and the discreteness of their boundaries. The results also require minor revision of EESUs previously delineated, including the addition of three new units. The Esopus Formation is designated as a distinct unit separate from the Schoharie on the basis of brachiopods from shallow water facies of the Skunnemunk outlier in New York; in addition, a short-lived Stony Hollow fauna is recognized in shallow shelf facies of the Union Springs Formation and coeval units (formerly referred to as the lower Marcellus Formation) and the lower transgressive beds of the overlying Oatka Creek Formation. This fauna, consisting of subtropical Old World Realm (OWR) emigrants, is distinctive from both the underlying Onondaga fauna and that of the overlying Hamilton Group. Moreover, the Tully Formation presents another case of a short-lived incursion of tropical OWR taxa followed by the extermination of this fauna and reappearance of a suite of typically Hamilton taxa. This case illustrates that EESUs may persist globally despite their local extermination or emigration from a large region, such as the Appalachian Basin. Review of the broader context of EESU turnover suggests that these crises are geologically rapid and synchronous. Moreover, most of the Devonian EESU boundaries coincide with recognized global bioevents, within the limits of combined biostratigraphic and sequence stratigraphic resolution. Hence, these crises, although perhaps locally accentuated in the Appalachian Basin, are allied to global causes. They appear mostly to be associated with rapid rises in sea level, periods of widespread climatic change and hypoxic events in basinal areas.

Jurassic evolution of the Arabian carbonate platform edge in the central Oman Mountains

The Jurassic Sahtan Group exposed in northern Oman was deposited in shallow marine environments at the edge of the Arabian Platform facing the Neo-Tethys (Hamrat Duru Basin). The upper Sahtan Group is made up of a mixed siliciclastic–carbonate unit overlain by pure carbonate deposits, assigned to a Bathonian and Early Callovian age on the basis of brachiopods and foraminifers. These carbonate depositional systems were composed of outer oolitic shoals that underwent subaerial exposure, and a deeper, somewhat restricted, gently dipping shelf interior. Oolitic material was shed off the platform edge into the deep-sea depositional complex of the Guweyza Formation. The Sahtan Group is affected by an important thickness reduction towards northeastern Jabal Akhdar. The angular unconformity (0.2%) at the top of the Sahtan Group is shown to result from tilting and top truncation of genetic sequences. This unconformity is overlain by the Rayda Formation, a veneer that shows an onlap pattern including a gradual deepening upwards facies evolution. The minimal time span of the stratigraphic hiatus is Mid-Callovian–Kimmeridgian. Oxfordian and Kimmeridgian sequences were probably never deposited in this area because of lack of accommodation space and/or because of subaerial exposure. It is proposed herein that the unconformity was shaped by subaerial carbonate dissolution during a steady, tectonically driven exhumation of the platform edge. During the Tithonian, a major eustatic sea-level rise caused transgression of the Rayda Formation upon the platform edge and normal shelf marine conditions resumed in the eastern Arabian Peninsula.

The northern most Emsian crinoids known, a Devonian fauna from the Chuluun Formation, Shine Jinst area, Southern Mongolia

The most northerly known Emsian crinoids were located at approximately 45° to 50° N latitude. They are the first Devonian crinoid cups discovered in Mongolia. Specimens are reported from excellent exposures of the informally designated crinoidal beds in the upper part of the stratotype section of the Chuluun Formation, between N44° 22.119', E99° 27.130' and N44° 22.201', E99° 26.906', near the Tsakhir Well, in the foothills south of Tsagaan Khaalga Mountain, Shine Jinst area, southern Mongolia. All specimens are crushed, altered by low-grade metamorphism, and ossicles flake as they weather. Five genera are present including a new genus of the Periechocrinidae, two indeterminant camerates, an undesignated new species of Cyathocrinites, and one indeterminant crinoid. These genera agree with a middle Emsian age previously assigned to the upper part of the Chuluun Formation on the basis of brachiopods and conodonts. They show affinity to European and North American Emsian faunas.

Middle Devonian lycopsids from high southern palaeolatitudes of Gondwana (Argentina)

Fossil plants are described from the upper part of the Devonian Lolén Formation, Sierra de la Ventana, Buenos Aires Province, Argentina, in the area of Estancia Las Acacias. The sequence is composed mainly of dark grey shales, and fossils were found in a single horizon where thin interlayered beds of fine reddish-brown micaceous sandstones appear where the environment of marine deposition became more shallow. The age of the Lolén Formation is presently established on the basis of brachiopods, these being characteristic elements of the Malvinokaffric realm from the Gondwana Lower Devonian (Emsian). The fossil plants are remarkably preserved given that they are in rocks that have undergone intense deformation. The plants are identified as Haplostigma sp. and Haskinsia cf. H. colophylla, and suggest a Middle Devonian age (Givetian) for the fossil-bearing levels. Haskinsia, identified on the basis of leaf morphology, is the first well-delimited Middle Devonian lycopsid genus described from Argentina, and the record from the most southerly palaeolatitude. During the Middle Devonian, Haskinsia was distributed in tropical, warm temperate and high southern latitude, ?cool temperate zones.

Middle Permian brachiopods from central Peninsular Malaysia — faunal affinities between Malaysia and west Cambodia

A moderately diverse Permian brachiopod fauna is described from a new rock unit, the Bera Formation, in the Bera District, central Pahang, Peninsular Malaysia. The fauna consists of 19 taxa, including 14 genera and 17 (both identified and unidentified) typically Tethyan species. The fauna appears to be correlative on the basis of brachiopods with the Neoschwagerina-Yabeina fusulinid Zones in Indochina and South China. In particular, it has strong linkage to Member C ( Yabeina beds) of the Sisophon Limestone, west Cambodia. This is indicated by three of the Bera species — Urushtenoidea chaoi (Ching), Spyridiophora gubleri Termier and Termier, and Transennatia termierorum sp. nov., being shared with the Cambodian fauna. A possible early Capitanian (Middle Permian) age is proposed for the Bera brachiopod fauna.

Thanatocoenoses and biotopes of Lower Jurassic brachiopods in central and western Bulgaria

Brachiopod biotopes are recognized in the Early Jurassic rocks of Bulgaria. The geographical distribution of these is plotted for each of the stratigraphical zones determined earlier on the basis of brachiopods. The biotopes are related in turn to bathymetry, energy level and bottom type.

Die Stratigraphie des Maastricht von Dänemark und Norddeutschland aufgrund von Brachiopoden

Die Stratigraphie des Maastricht von Dänemark und Norddeutschland aufgrund von Brachiopoden

Stratigraphic Scheme of Ordovician of Northeastern USSR and Its Correlation: ABSTRACT

Ordovician deposits occur in marginal uplifts of the Kolyma medial massif (different facies zones of the Omulevka Mountains, Selennyakh Ridge, Tas-Khayakhtakh Ridge), middle part of the Kolyma River, in the Verkhoyansk fold-mountains region (Sette-Daban Ridge), in the Chukotsk Peninsula. Recent data indicate the presence of Ordovician in the Omolon and Okhotsk medial massifs. A correlation chart was prepared, and it shows the correlation of Ordovician deposits of all principal regions of the northeastern part of USSR by ostracod, brachiopod, trilobite, and graptolite associations. The biostratigraphic zones corresponding to the Upper Ordovician of the international stratigraphic standard are accepted as principal units of regional stratigraphic importance. However, the st atigraphic positions of some biostratigraphic suites have been revised. This resulted in the revision of the contents and names of some zones. The oldest Ordovician deposits (Inaya horizon) are correlated conditionally with the Tremadocian of England, the Gasconadian Stage of North America, and the Ust'kut Stage of the Siberian platform. The correlation is based on brachiopod and trilobite associations and stratigraphic position. The Khita horizon is compared with Beekmantown Stage of North America and the Chunya Stage of the Siberian platform on the basis End_Page 2489------------------------------ of trilobite and brachiopod associations. The Elgenchak horizon is comparable with the Llanvirnian on the basis of graptolite associations, and is comparable with the Whiterock Stage and probably a part of the Marmor Stage of North America on the basis of the brachiopods. The Lachug horizon corresponds to the Llandeilian; it definitely is comparable with the Krivoluk Stage of the Siberian platform and is conditionally compared with Ashby Stage of North America. The Lachug horizon is characterized by rich graptolite, brachiopod, ostracod, and trilobite associations. The Kharkindzha horizon unites heterofacies deposits and corresponds to the lower and middle Caradocian of England, the Mangaseya Stage of the Siberian platform, and conditionally to the Porterfield Stage of North America. he base of this zone is the most distinctive faunal boundary in the Ordovician of northeastern Asia and is characterized by the appearance of rich graptolite faunas of the Nemagraptus gracilis zone and by numerous ostracod, brachiopod, and trilobite associations. The Omuka horizon correlates with the deposits corresponding to upper Caradocian and Ashgillian. The upper part of the Omuka horizon definitely is comparable with the Ashgillian on the basis of graptolite associations, and with horizon 5b of Norway on the basis of corals and brachiopods. End_of_Article - Last_Page 2490------------

Age and Position of Lower Devonian Graptolite Zones Relative to the Appalachian Standard Succession

The monograptid fauna extends almost to the top of the Lower Devonian in the Old World, but monograptids do not occur in the Lower Devonian succession of New York or elsewhere in the central or southern Appalachians. Monograptid occurrences in the northern Appalachians are too sparse to demonstrate equivalence of any Old World graptolite zone with a definite level in the New York succession. Three Lower Devonian graptolite zones occur in sequence interbedded with shelly and conodont-bearing carbonate rocks in central Nevada. The Nevada succession, coupled with an auxiliary succession at Royal Creek, Yukon Territory, Canada, can be correlated with the Appalachian Lower Devonian standard according to New York terminology, principally on the basis of brachiopods and conodonts. Allowing for relatively small, eventually correctable errors of inexactness, the Monograptus uniformis Zone correlates with the Coeymans Limestone, the M. praehercynicus Zone with the New Scotland Formation, and the M. hercynicus Zone with the Becraft Limestone. The position of the Monograptus yukonensis Zone corresponds to the Oriskany-Esopus interval. These correlations will provide the basis for a continent-wide evaluation of paleogeography and tectonism in terms of chronostratigraphic units smaller than series for the first time.

Societies and Academies

LONDON. Geological Society, November 3.—Sydney S. Buck-man: Jurassic chronology (iii.): Some faunal horizons in Cornbrash. Faunal dissimilarity within strata of a supposedly synchronous time-unit, the Cornbrash, were observed about seventy years ago, but were not understood. Series of faunal analyses of the brachiopod species south of the Humber disclose a series of syn-clines, anticlines, and various non-sequences in the strata of the South Humbrian Cornbrash. The divisions of Cornbrash time on the basis of brachiopods and of ammonoids are compared and also the Cornbrash and the inferior oolite. If the time-value of brachiopod species be the same in the Cornbrash as in the inferior oolite—and there is every reason that it should be—then the Cornbrash must have taken in deposition a time far in excess of that of the middle and upper inferior oolite, with all its numerous ammonoid hemera.