Middle Triassic Ammonoid Research Articles

SIDELINED SEASHELLS: REAPPRAISAL OF THE MIDDLE TRIASSIC AMMONOIDS OF SAMOBOR AND ŽUMBERAK MTS. (NORTH-WESTERN CROATIA) AND THEIR SYSTEMATICS AND BIOSTRATIGRAPHIC IMPLICATIONS

Basinal Middle Triassic successions of the Samobor and Žumberak Mts. (north-western Croatia) have historically produced fossils of ammonoids. These finds have, however, largely been neglected in the later literature. This paper describes and redescribes a large collection of ammonoids, most of which were collected by previous researchers throughout the 20th century. Aside from the detailed taxonomic descriptions and revisions, several taxa previously unknown from these localities were identified. Of the species whose holotypes were designated at the Gregruć Breg locality, some are found to be dubious, with validity of other remaining inconclusive and a single taxon, Eoprotrachyceras dorae comb. nov., being treated as valid. Certain Middle Triassic ammonoid genera may also require future comprehensive revisions. A preliminary, modified ammonoid zonal/sub-zonal scheme for the Ladinian of the Tethyan province is proposed, to be inclusive of most of the data from the literature. The need for improvement of the subdivision of this stage is recognized. Based on ammonoids, condensed red nodular limestones of the Gregurić Breg locality (Samobor Mts.) most likely span the Avisianum subzone (upper Illyrian) – Longobardicum subzone (“middle” Longobardian), indicating that subsidence began in the earlier part of the Illyrian. At Mt. Žumberak, scant ammonoid remains indicate that the upper, limestone-rich portion of this succession spans at least the Avisianum subzone (upper Illyrian) – Longobardicum subzone (“middle” Longobardian), but additional data is needed for drawing more robust conclusions. Overall, the timing of basinal deposition is well correlated between Gregurić Breg and Žumberak localities (lower Illyrian – upper Longobardian).

Toward an understanding of cosmopolitanism in deep time: a case study of ammonoids from the middle Permian to the Middle Triassic

AbstractCosmopolitanism occurred recurrently during the geologic past, especially after mass extinctions, but the underlying mechanisms remain poorly known. Three theoretical models, not mutually exclusive, can lead to cosmopolitanism: (1) selective extinction in endemic taxa, (2) endemic taxa becoming cosmopolitan after the extinction and (3) an increase in the number of newly originated cosmopolitan taxa after extinction. We analyzed an updated occurrence dataset including 831 middle Permian to Middle Triassic ammonoid genera and used two network methods to distinguish major episodes of ammonoid cosmopolitanism during this time interval. Then, we tested the three proposed models in these case studies. Our results confirm that at least two remarkable cosmopolitanism events occurred after the Permian–Triassic and late Smithian (Early Triassic) extinctions, respectively. Partitioned analyses of survivors and newcomers revealed that the immediate cosmopolitanism event (Griesbachian) after the Permian–Triassic event can be attributed to endemic genera becoming cosmopolitan (model 2) and an increase in the number of newly originated cosmopolitan genera after the extinction (model 3). Late Smithian cosmopolitanism is caused by selective extinction in endemic taxa (model 1) and an increase in the number of newly originated cosmopolitan genera (model 3). We found that the survivors of the Permian–Triassic mass extinction did not show a wider geographic range, suggesting that this mass extinction is nonselective among the biogeographic ranges, while late Smithian survivors exhibit a wide geographic range, indicating selective survivorship among cosmopolitan genera. These successive cosmopolitanism events during severe extinctions are associated with marked environmental upheavals such as rapid climate changes and oceanic anoxic events, suggesting that environmental fluctuations play a significant role in cosmopolitanism.

Nitrogen and Carbon Isotope Data of Olenekian to Anisian Deposits from Kamenushka/South Primorye, Far-Eastern Russia and Their Palaeoenvironmental Significance

The Kamenushka Formation, exposed in the northern part of South Primorye (Kamenushka-1 and Kamenushka-2 sections), is one of the few localities in the world with richly fossiliferous Lower–Upper Olenekian sedimentary successions. Lower to Middle Triassic ammonoid-, brachiopod- and conodont-bearing silty-clayey deposits of the Kamenushka-1 and Kamenushka-2 sections have been isotope-geochemically investigated in detail. As a result, these sections, together with the previously investigated Abrek Section, exposed in the southern part of South Primorye, provide almost complete 15Norg- and 13Corg- records for the Lower Triassic of this region. Nine N-isotope intervals and the five negative C-isotope excursions, reflecting, apparently, unstable climatic and hydrological conditions, have been distinguished in the Lower Triassic of South Primorye. On the basis of the new C-isotope data the Mesohedenstroemia bosphorensis Zone (upper part), Shimanskyites shimanskyi and Neocolumbites insignis zones of South Primorye are correlated now with the Lower Smithian part of the Yinkeng Formation, the Upper Smithian part of the Helongshan Formation and the Middle Spathian part of the Nanlinghu Formation in South China, respectively, as has been observed in the Abrek, Kamenushka-2, West Pingdingshan and Majiashan sections.

Using abundance data to assess the relative role of sampling biases and evolutionary 2 radiations in Upper Muschelkalk ammonoids

The Middle Triassic ammonoid genus Ceratites diversified spectacularly within the Germanic Muschelkalk Basin during the Anisian/Ladian (244–232 Mya). Previous studies have interpreted this diversification as a sequence of rapid, endemic radiations from a few immigrant taxa. Here we investigate the possibility that geological and sampling biases, rather than ecological and evolutionary processes, are responsible for this pattern. A new specimen-based dataset of Ceratites species-richness and abundance was assembled. This dataset was combined with 1:200 000 geological maps in a geodatabase to facilitate geospatial analyses. One set of analyses compared species richness per geological map with the number of occurrences and localities per map. Per-map change in the amount of rock available to sample for fossils was also included as a variable. Of these three variables, number of occurrences is the most strongly correlated with richness. Variation in the amount of rock is not a strong determinant of species-ri...

Middle Triassic ammonoid fossils from Aring, Kelantan, Malaysia

Middle Triassic ammonoid fossils from Aring, Kelantan, Malaysia

Triassic ammonoid biostratigraphy: an overview

Abstract The Triassic chronostratigraphic scale was built on two centuries of research on ammonoid biostratigraphy and biochronology. Two Triassic stage bases and all of the Triassic substages are currently defined by ammonoid bioevents. The study of Triassic ammonoids began during the late 1700s, and in 1895, Edmund von Mojsisovics, Wilhelm Waagen and Carl Diener published an essentially complete Triassic chronostratigraphic scale based on ammonoid biostratigraphy. This scale introduced many of the Triassic stage and substage names still used today, and all terminology of stages and substages subsequently introduced has been based on ammonoid biostratigraphy. Early Triassic ammonoids show a trend from cosmopolitanism (Induan) to latitudinal differentiation (Olenekian), and the four Lower Triassic substage (Griesbachian, Dinerian, Smithian and Spathian) boundaries are globally correlated by widespread ammonoid biotic events. Middle Triassic ammonoids have provinciality similar to that of the Olenekian and provide a basis for recognizing six Middle Triassic substages. Late Triassic ammonoids provide a basis for recognizing three stages divided into five substages. The main uncertainty for the future of Triassic ammonoid biostratigraphy is not the decline of the ammonoids as a tool for dating and correlation of Triassic strata but, rather, the dramatic decrease in the number of specialists, due to the lack of replacement of experienced palaeontologists who started their activity in the 1950s and 1960s.

Morphological fluctuations of ammonoid assemblages from the Muschelkalk (Middle Triassic) of the Germanic Basin—indicators of their ecology, extinctions, and immigrations

For a stratophenetic analysis of Middle Triassic ammonoids from the German Muschelkalk (Anisian, Ladinian), whorl expansion rates, whorl width indexes, umbilical width indexes, maximal conch sizes, body chamber lengths, the orientations of the aperture, and a number of sculpture parameters of approximately 500 specimens were identified. 274 of these data sets, sorted according to their stratigraphic age, were evaluated in scatter plots as well as canonical discriminant function analyses. Several of the diagrams that were produced in these analyses reflect more or less steady changes in conch morphology through geological time, except for some intervals with abrupt and rather drastic transformations. These morphological discontinuities are synchronous with immigrations into the Germanic Basin of crinoid and brachiopod taxa. This discovery indicates disturbances in the endemic evolution of the ammonoids caused by such immigrations. At a small scale, this case study demonstrates that a rising sea level may have boosted the faunal exchange between an open marine and a restricted epicontinental basin, causing a minor regional increase in biodiversity. It also demonstrates that the evolution of ‘Germanic’ ceratites happened mainly within the Germanic Basin but partially probably also within the Tethyan Sea. The ecology of the ceratites from this Basin is discussed. Accordingly, they were stenohaline, good backward swimmers with a good manoeuvrability, and able to achieve neutral buoyancy.

The early and middle Triassic ammonoid succession of the Himalayas in western and central Nepal Part. 7.Late Anisian ammonoids from west Nepal, and world wide correlations for early and early middle Triassic ammonoid faunules

The early and middle Triassic ammonoid succession of the Himalayas in western and central Nepal Part. 7.Late Anisian ammonoids from west Nepal, and world wide correlations for early and early middle Triassic ammonoid faunules

The early and middle Triassic ammonoid succession of the Himalayas in western and central Nepal Part 6. Systematic studies of the Mukut (mostly Anisian) ammonoids from Manang

The early and middle Triassic ammonoid succession of the Himalayas in western and central Nepal Part 6. Systematic studies of the Mukut (mostly Anisian) ammonoids from Manang

Magnetostratigraphy and biostratigraphy of the Middle Triassic Margon section (Southern Alps, Italy)

A magnetostratigraphic study has been performed on the paleontologically well constrained pelagic Middle Triassic (Lower/Upper Ladinian boundary) section at Margon (Trento, Southern Alps, Italy). Rock magnetic investigations indicate the presence of both, high and low coercivity minerals. Specimens subjected to progressive thermal demagnetization procedures show that nearly all of them exhibit a low temperature magnetization component, parallel to the present-day field before bedding correction, and a high temperature one, characterized by either positive or negative and opposite polarity, considered as the characteristic Triassic magnetization. The comparison of the Margon magnetic polarity zonation with those of two coeval sections poses some problems when ammonoid- and conodont-based stratigraphies have to be correlated. However, good correlation has been obtained for the recognized Middle Triassic ammonoid biozones in the Tethyan realm. Valuable data to the construction of a standard magnetostratigraphic and paleontological scale are contributed by the results from the Margon section.

The early and middle Triassic ammonoid succession of the Himalayas in western and central Nepal Part 5. Systematic studies of the early Ansian

The early and middle Triassic ammonoid succession of the Himalayas in western and central Nepal Part 5. Systematic studies of the early Ansian

The early and middle Triassic ammonoid succession of the Himalayas in western and central Nepal

The early and middle Triassic ammonoid succession of the Himalayas in western and central Nepal

The Early and Middle Triassic ammonoid succession of the Himalayas in Western and Central Nepal Part 3. Late Middle Scythian ammonoids

The Early and Middle Triassic ammonoid succession of the Himalayas in Western and Central Nepal Part 3. Late Middle Scythian ammonoids

The Early and Middle Triassic ammonoid succession of the Himalayas in Western and Central Nepal Part 2. Systematic Studies of the Early Middle Scythian

The Early and Middle Triassic ammonoid succession of the Himalayas in Western and Central Nepal Part 2. Systematic Studies of the Early Middle Scythian

A high resolution Middle Triassic ammonoid standard scale in the Tethys realm; a preliminary report

A high resolution Middle Triassic ammonoid standard scale in the Tethys realm; a preliminary report

The Early and Middle Triassic ammonoid succession of the Himalayas in western and central Nepal Part 1. Stratigraphy, classification and Early Scythian ammonoid systematics

The Early and Middle Triassic ammonoid succession of the Himalayas in western and central Nepal Part 1. Stratigraphy, classification and Early Scythian ammonoid systematics

Triassic ammonoids from Jabal Safra and Wadi Alwa, Oman, and their significance

Abstract Triassic ammonoids are recorded from Jabal Safra and Wadi Alwa, Oman. Most or all are from olistoliths. The ammonoids from Jabal Safra are of Early Triassic (Smithian and Spathian) age and are from metre-sized blocks in the Jurassic Guwayza Formation. Those from Wadi Alwa are from blocks ranging from metre- to more than decimetre-size and are Early Triassic (Smithian and Spathian), Middle Triassic (Anisian) and Late Triassic (Norian). The Early and Middle Triassic ammonoids from both localities are in dense, highly fossiliferous, commonly red limestone where they occur to the exclusion of all other macrofossils. The facies is that of the Hallstatt Limestone which is known from many localities, all in the Tethys. The Late Triassic ammonoids are in a red argillaceous limestone like the Ammonitico Rosso, another characteristic facies in Tethys. The occurrences at Jabal Safra are in the Hawasina allochthon. The olistoliths evidently came from the east, not from the platform to the west. Seamounts east of the main Hawasina depocentre seem the most likely source for all the Triassic blocks.

Lower and Middle Triassic ammonoids and bivalves from Nordaustlandet (Spitsbergen) collected by Dr Oskar Kulling in 1931

Abstract Posidonia aranea Tozer (Bivalvia), of the latest Lower Triassic (Spathian) age, and representatives of the Middle Triassic (Anisian) ammonoid genera (Stenopopanoceras, Hollandites, Anagymnotoceras, Japonites, Intornites, Isculites, Leiophyllites and Ussurites) are recorded from the Torellneset area, Nordaustlandet, Spitsbergen, from a collection made by O. Kulling in 1931. Hollandites and Anagymnotoceras indicate that beds of Middle Anisian age are represented.