Rhaetian Research Articles

Strontium isotope stratigraphy of the Gabbs Formation (Nevada): implications for global Norian–Rhaetian correlations and faunal turnover

The Luning and Gabbs formations in west-central Nevada, USA represent a Late Triassic shallow marine sedimentary succession with global significance (the Gabbs Formation was a candidate for the basal Jurassic GSSP). Typically, the Norian–Rhaetian stage boundary is placed at the contact between the formations, and the Rhaetian–Hettangian boundary (the Triassic–Jurassic boundary) is within the Muller Canyon Member of the Gabbs Formation. However, the use of different biostratigraphical index-species schemes in Norian–Rhaetian successions between Tethys and Panthalassa, the two largest ocean basins at the time, makes precise correlation problematic. Here, we compare 87Sr/86Sr measurements of well-preserved carbonate shell material from Nevada to the well-known and biostratigraphically constrained 87Sr/86Sr record from Tethys, where a negative excursion in 87Sr/86Sr is noted across the Norian–Rhaetian boundary. Our new 87Sr/86Sr data from the Luning and Gabbs formations reveal a comparable trend, with a sharp drop in 87Sr/86Sr within the Nun Mine Member of the Gabbs Formation, suggesting the position of the Norian–Rhaetian boundary is higher in the succession, and not between the Luning and Gabbs formations as previously defined. Relating the stage boundary using global isotopic signals is a useful tool for biostratigraphical correlation of successions between Tethys and Panthalassa, and for estimating the rate of faunal turnover at the Norian–Rhaetian stage boundary in comparison with the succeeding Late Triassic mass extinction. If correct, this biostratigraphical–chemostratigraphical correlation suggests that the current index groups for the Panthalassic stage boundary should be changed.

Latest Triassic climate humidification and kaolinite formation (Western Carpathians, Tatric Unit of the Tatra Mts)

The Tomanová Formation, of Rhaetian age, overlying the Norian Carpathian Keuper in the Tatra Mts. is built of cyclic parasequences of mudstones and sandstones. Quartz (15 to 70 wt.%), kaolinite (13 to 46 wt.%) and 2:1 Al dioctahedral phyllosilicates (dioct 2:1: muscovite, illite, illite/smectite: 5 to 39 wt.%) represent the major mineral phase. The kaolinite/dioct 2:1 ratio decreases upwards in the section (from 4.3 to 0.5) and signals variability in weathering/erosion intensity and changing water salinity. Major and trace elements (LILE, HSFS, REE) indicate a uniform source – felsic rocks located probably in the Vindelician Highlands. The sedimentation rate (83 mm/ky) was controlled by climate. Alternation of dry and humid periods is refered by sedimentary textures and by maturity of quartz (aeolian vs. fluvial grains), and organic matter content and composition (Corg and d13Corg). Authigenic siderite or bethierine documents wet and reduced conditions in the upper part of the Tomanová Formation. The sedimention rate of the marine Dudzinec Formation attained 25 mm/ka and the character of cycles preserved in the sequence is similar as that of the Tomanová Formation (fining upwards parasequences). However, the different clay mineralogy, the recycled character of the silicates, the different d13Corg and elevated imput of carbonate detritus with specific C and O isotopic patterns document a discontinuity in the section. The transgressive character of the Dudzinec Fm. was deduced from the stratigraphic distribution and environmental characteristics of the benthic foraminifera present. Involutinids and spirillinids dominate in the lower part, endothyrinids govern the middle part, and in the upper part nodosariids and Ammodiscus-type microfauna occur. These age-diagnostic microfossils indicate a late Rhaetian age. Sea level rise in the Tatric Zone triggered by thermal expansion of the Central Atlantic Rift was gradual, being affected by input of terrestrial clastic sediment both by freshwater and by wind. The Tatric Triassic sequence in the Western Carpathians helps understanding of the development of sedimentation, palaeoclimate (kaolinite weathering), and palaeogeography of the northernmost Tethyan Domain.

Norian to Rhaetian scleractinian corals in the Ferdows Patch Reef (Nayband Formation, east central Iran)

The Nayband Formation is one of the best known sedimentary units in central Iran. The type section consists of a thick succession of shale, siltstone, reef limestone and sandstone that is subdivided into five distinct members: Gelkan, Bidestan, Hoz-e-Sheykh, Howz-e- Khan and Qadir. Abundant and well-preserved framework-building scleractinian corals are included among the macrofossils of the Nayband Formation; these corals characterize the formation and are the subject of this study. The Hassan-Abad section, located in northeast Iran in Lute Block (northwest of Ferdows city), was chosen for detailed study and sampling. Analysis of sedimentary lithofacies and faunal assemblages in the Bidestan and the Howz-e-khan members indicate both biostromal and biohermal characters for the former shallow-water patch reefs and support a Norian to Rhaetian age. The useful biostratigraphic hydrozoanHeterastridium conglobatumwas studied along with 14 taxa of scleractinian corals:Stylophyllopsis rudis, Distichophyllia norica, Paradistichophyllum dichotomum, Retiophyllia frechi, Retiophyllia norica, Retiophyllia robusta, Chondrocoenia schafhaeutli, Chondrocoenia ohmanni, Astraeomorpha crassisepta, Astraeomorpha confusa, Astraeomorpha minor, Procyclolites triadicus, Pamiroseris rectilamellosa,andEocomoseris ramosa. These fossils clarify the stratigraphy of the Nayband Formation, as well as provide new information on the patch reefs and the framework constructors of these reefs.

Where and when the earliest coccolithophores?

Gardin, S., Krystyn, L., Richoz, S., Bartolini, A. & Galbrun, B. 2012: Where and when the earliest coccolithophores? Lethaia, Vol. 45, pp. 507–523. New calcareous nannofossil analyses from the Northern Calcareous Alps of Austria are herein used to update and improve the state of knowledge about the oldest occurrence of coccolithophores reported in the literature. Previously reported Norian occurrences of coccoliths were based on an obsolete Triassic chronostratigraphy, in which the Rhaetian stage was subsumed into the Norian (‘Sevatian 2’). The oldest stratigraphical record of coccoliths spp. lies just below the Norian-Rhaetian boundary and the first coccolith species, Crucirhabdus minutus, is recorded from the base of Rhaetian stage. The latter bio-event is located just above the First Occurrence of the conodont Misikella posthersteni and the first occurrence of the ammonoid Paracochloceras suessi in the Steinbergkogel section (Austria), Global Stratotype Section and Point (GSSP) candidate for the Norian–Rhaetian boundary. The appearance of the coccolith Crucirhabdus minutus is seen as a robust biochronological datum that will provide useful constraints for Triassic biostratigraphy, palaeoclimatic modelling and phylogenetic reconstructions. The new calcareous nannofossil biochronology of Steinbergkogel that we present herein completes the existing biostratigraphic characterization of the Norian-Rhaetian transition based on conodonts and ammonoids and strengthens the position of Steinbergkogel as the best GSSP proposed section for the base of the Rhaetian. The record of coccolithophores across the Norian–Rhaetian boundary at Steinbergkogel takes place along with a discernible increase in abundance of Prinsiosphaera triassica, as well as the appearance of Euconusphaera zlambachensis, which are the two most important Rhaetian pelagic carbonate producers. This succession of bio-events is interpreted as the initiation of the pelagic carbonate production driven by the successful spreading of calcareous nannofossils in the Western Tethys during the Rhaetian. □Austria, Calcareous Alps, coccolithophores, Triassic.

Major environmental change and bonebed genesis prior to the Triassic–Jurassic mass extinction

We present new geochemical and sedimentological data from marginal marine strata of Penarth Bay, south Wales (UK) to elucidate the origin of widespread but enigmatic concentrations of vertebrate hard parts (bonebeds) in marine successions of Rhaetian age (Late Triassic). Sedimentological evidence shows that the phosphatic constituents of the bonebeds were subjected to intense phosphatization in shallow current-dominated settings and subsequently reworked and transported basinward by storms. Interbedded organic-rich strata deposited under quiescent and poorly oxygenated conditions record enhanced phosphorus regeneration from sedimentary organic matter into the water column and probably provided the main source of phosphate required for heavy bonebed clast phosphatization. The stratigraphically limited interval showing evidence for oxygen depletion and accelerated P-cycling coincides with a negative 4‰ organic carbon isotope excursion, which possibly reflects supra-regional changes in carbon cycling and clearly predates the ‘initial isotope excursion’ characterizing many Triassic–Jurassic boundary strata. Our data indicate that Rhaetian bonebeds are the lithological signature of profound, climatically driven changes in carbon cycling and redox conditions and support the idea of a multi-pulsed environmental crisis at the end of the Triassic, possibly linked to successive episodes of igneous activity in the Central Atlantic Magmatic Province. Supplementary material: Sample positions, data table and a detailed stratigraphic log from the upper Triassic of Penarth Bay, south Wales, UK are available at http://www.geolsoc.org.uk/SUP18510 .

Latest Triassic marine Sr isotopic variations, possible causes and implications

Terra Nova, 24, 130–135, 2012AbstractLarge igneous provinces have been suggested to trigger global environmental perturbations and, in turn, major biotic crises. The high resolution of marine biostratigraphy is here applied to constrain the detailed timing of the Central Atlantic Magmatic Province onset. Analyses of biogenic apatite from stratigraphically well‐constrained Tethyan realm conodont samples indicate two significant shifts of the oceanic 87Sr/86Sr composition during the latest Triassic: a rapid drop of 87Sr/86Sr during the lower Rhaetian, followed by an increase during the upper Rhaetian. These shifts are positively correlated with synchronous variations of oceanic 187Os/188Os and they may be attributed to a rapid emplacement and erosion of the Central Atlantic Magmatic Province, followed by a rapid increase in continental weathering. These interpretations require a short duration for the Rhaetian stage (<2 Ma) and are consistent with volcanogenic triggering of end‐Triassic climatic perturbations and biotic crisis starting from the Norian–Rhaetian and culminating at the Triassic–Jurassic boundary.

DUOSTOMINIDAE (FORAMINIFEREA, ROBERTINIDA) FROM THE UPPER TRIASSIC BEDS OF THE SLOVENIAN BASIN (SOUTHERN ALPS, SLOVENIA)

Twelve species of genera Diplotremina Kristan-Tollmann, 1960, Duostomina Kristan-Tollmann, 1960, and Variostoma Kristan-Tollmann, 1960 have been described from the Norian and Rhaetian strata of the Slovenian Basin (eastern Southern Alps). A lamellar wall structure has been confirmed for Duostomina and observed for the first time in Variostoma. The multi-layered nature of the lamellae of Diplotremina and Duostomina may be a result of a diagenetic alteration of the single-layered lamellae. The position of Variostoma in the family Duostominidae remains doubtful due to the alveolar nature of its wall.

The Rhaetian flora of Rögla, northern Scania, Sweden

Abstract: Rögla is the northernmost locality yielding Mesozoic plant fossils in Scania, southern Sweden, and is one of the northernmost Rhaetian assemblages in Europe. The assemblage consists of over 500 specimens collected 50–60 years ago, of which 139 yielded identifiable plant remains referable to 15 plant species; another 19 specimens are tentatively assigned to four species because of their fragmentary preservation. The flora includes sphenophytes, ferns, cycads, bennettitaleans, seed ferns of uncertain alliance, conifers and some leaf remains that are tentatively assigned to ginkgophytes based on their epidermal anatomy. The species‐level composition of the assemblage is consistent with a Rhaetian age and is similar to well‐known floras from nearby Höganäs and Bjuv, except for the absence of cycads belonging to Nilssonia, which are very common in most other Scanian floras. The fossil assemblage is interpreted to derive from multi‐storey vegetation occupying moist habitats on a coastal plain. Strong affinities are evident with the coeval floras of Jameson Land, Greenland, reinforcing the concept of a distinctive North Atlantic floristic sub‐province at the close of the Triassic.

GEOCHEMICAL AND PETROLOGICAL CHARACTERISTICS OF LATE TRIASSIC BASIC VOLCANIC ROCKS FROM THE KOCALI COMPLEX; SE TURKEY: IMPLICATIONS FOR THE TRIASSIC EVOLUTION OF SOUTHERN TETHYS

The Kocali Complex in SE Anatolia is mainly composed of tectonically imbricated slices of pelagic rock suits (pelagic limestones; cherts; etc); platform carbonates; clastics; serpentinites and basic volcanics. It can be subdivided into four main parts as the Tarasa Unit; the Konak Unit; the Cilo Limestones and the Kale Ophiolite. In this paper; geochemical characteristics of basic volcanic rocks associated with pelagic sediments (radiolarian cherts; pelagic limestones; etc) have been studied along four stratigraphical sections (the Tarasa; the Bulam-2; the Korun-1 and the Korun-2) in the Konak and the Tarasa Units. The age of the volcanic sequences have been assigned to Late Triassic (middle Carnian to Rhaetian) based on the radiolarian data from the associated pelagic rock units. Geochemical data indicates the presence of two different types of Late Triassic volcanic rock groups characterized by E-MORB-type (Group-1 volcanites from the Tarasa Unit formed by mixing of OIB and MORB-type melts) and OIB-type (Group-2 volcanites from the Konak Unit) mantle sources. None of the samples from the Kocali Complex has characteristics of N-MORB type mantle source and was affected by crustal contamination. Based on these data; it can be suggested that all these volcanic rocks formed in a marginal oceanic basin away from the ocean ridge. The presence of Radiolaria and Bivalvia-bearing pelagic limestones and cherts associated to the basic volcanic rocks in the Kocali Complex also emphasize that they all formed in deep marine basin. Geochemical characteristics of Late Triassic volcanics in the Kocali Complex have great similarities and well-correlative to the coeval volcanics previously studied in the Southern Tethyan Belt (e.g. the Baer-Bassit region in NW Syria; the Mamonia Complex in SW Cyprus and the Antalya Nappes in SW Turkey). Taking into the consideration of the geochemical data obtained from Late Triassic basic volcanics in the Kocali Complex and geochemical characteristics of the coeval volcanics in the adjacent units in the Southern Tethyan Belt; it can be suggested that rifting age of the Southern Tethyan Oceanic Basin in SE Anatolia is probably earlier than early Late Triassic (middle Carnian time).

Magnetostratigraphic dating of the proposed Rhaetian GSSP at Steinbergkogel (Upper Triassic, Austria): Implications for the Late Triassic time scale

The Global Stratotype Section and Point (GSSP) for the Rhaetian Stage has recently been proposed at Steinbergkogel in Austria. We re-sampled the Steinbergkogel sections (STK-A and STK-B+C) in high-resolution to establish a robust magnetostratigraphy that allows global correlation. The palaeomagnetic signal at Steinbergkogel is composed of three components, which can be separated by thermal demagnetization. The highest temperature component, revealed between 280/300 and maximum 600°C is of dual polarity and is interpreted as primary. Rock magnetic experiments showed that the signal is carried by magnetite. Our results allow correlation between the two individual Steinbergkogel outcrops. Subsequently, we correlate the two key biostratigraphic horizons for the base of the Rhaetian, the FO of M. hernsteini and the FAD of M. post-hernsteini to other sections of the Tethys domain. The correlation to the astronomically dated continental successions of the Newark basin indicates that these positions for the base of the Rhaetian are most likely determined in chrons E16n and E16r, respectively. This correlation is confirmed by cyclostratigraphic control on the marine Pizzo Mondello (Italy) section, where a combination of long period Milankovitch cycles (~175-Myr) and short-eccentricity cycles (~100-kyr) provide additional correlation constraints, respectively supporting a long duration of the Rhaetian. Our study implies that the Norian and Rhaetian Stages have durations of ~17 and ~9Myr.

New biostratigraphical constraints for the Norian/Rhaetian boundary: data from Lagonegro Basin, Southern Apennines, Italy

Giordano, N., Rigo, M., Ciarapica G. & Bertinelli A. 2010: New biostratigraphical constraints for the Norian/Rhaetian boundary: data from Lagonegro Basin, Southern Apennines, Italy. Lethaia. 10.1111/j.1502-3931.2010.00218.x. Four stratigraphic sections belonging to Lagonegro succession (Southern Apennines) at Mt S. Enoc, Pignola-Abriola, Sasso di Castalda and Mt Volturino have been studied in detail under to provide a new micro-palaeontological data set based on conodonts and radiolarians for the characterization of the Norian/Rhaetian interval. The studied sections represent the different settings of the Lagonegro Basin (from proximal to distal facies) and permit a detailed, integrated, biostratigraphy of the Calcari con Selce (cherty limestones) and Scisti Silicei formations (bedded cherts with radiolarians) to be drawn up. The upper portion of the Calcari con Selce Formation, exhibits intermediate characteristics between the Calcari con Selce and Scisti Silicei Formation, in particular the progressive decrease in carbonate content against an increase in shales and cherts. Within the four sections studied, the Norian/Rhaetian interval has been documented both with conodonts and radiolarians. Because of the continuity and the absence of condensed facies, it has been possible to recognize the morphocline between species Misikella hernsteini and Misikella posthernsteini, here represented by all the transitional forms characterized by common features between the two species, gathered in three evolutionary steps. Moreover, the morphocline between M. hernsteini and M. posthernsteini has been involved in the definition of the Norian/Rhaetian Boundary, recognizing thus the FAD of M. posthernsteini, one of the possible biomarkers proposed for the boundary. The rich, well-preserved, radiolarian associations of Pignola-Abriola, Sasso di Castalda and Mt Volturino permit the correlation of Tethyan and American conodont successions, highlighting the importance of the mostly coincident occurrences of M. posthernsteini and Epigondolella mosheri morphotype A, which correspond to the base of Proparvicingula moniliformis A. Z. and the disappearance of bivalve Monotis. These coincident bioevents are used here to define the base of the Rhaetian stage. □Biostratigraphy, conodonts, Lagonegro Basin, Late Triassic, Norian/Rhaetian boundary, radiolarians.

The Triassic Marine Biota of Eastern Indonesia and its Interregional and Global Correlation: A Review

DOI: 10.17014/ijog.v5i1.91The interregional and global correlation of the Triassic biota of Indonesia was based on the review of previous workers and the author himself. Scythian Epoch (Early Triassic) in Timor is subdivided into Early Scythian with Ophiceras demisso, Meekoceras sp., Pseudomonotis subaurita, Gervillia subpannonica, and Myophoria sp., whilst Late Scythian is indicated by the presence of Owenites egrediens and Sibirites sp. The presence of Anisian Stage (Middle Triassic) in Misool is indicated by ammonite Beyrichites and bivalve Daonella lilintana. In Timor, this stage is pointed out by the presence of Joannites cymbiformis, Monophyllites wengensis, Protrachyceras archaelus, Daonella indica, Tracyceras cf. aon, Brochidium timorense, and Lima subpunctatoides. Terebellina mackayi found above Beyrichites-bearing bed in Misool has an age range from Anisian to Ladinian. It is concluded that the boundary between Anisian and Ladinian lies between beds with Beyrichites and Terebellina mackayi. Early Carnian Stage (Late Triassic) in Timor is indicated by the presence of Joanites cymbiformis, Waldhausenites sp., Miltites sp., and Halogyra cipitiensis; whereas Late Carnian is indicated by the presence of Cladicites crassestriatus and Tropites subbulatus. The presence of Halobia verbeeki, Pinacoceras parma, Neobetites sp., Parabetites sp., Malayites sp., Amarassites sp., and Halorites sp., indicates the Early Norian Stage, whilst the presence of Cladiscites tornatus, Cyrtopleurits malayicus, and Trachypleuraspidites sp. implies the Late Norian. The Rhaetian Stage in Timor contains Choristoceras indoaustralicum, whereas in Misool it contains Choristoceras sp. and Cochloceras sp.

Microfacies and depositional setting of the Upper Triassic mid-oceanic atoll-type carbonates of the Sambosan Accretionary Complex (southern Kyushu, Japan)

The Upper Triassic shallow-water limestones of the Sambosan Accretionary Complex are reconstructed as a remnant of a mid-oceanic atoll-type build-up upon a seamount in the Panthalassan Ocean. The Sambosan atoll-type carbonates and its pedestal were accreted along with deep-water ribbon-chert and related siliceous rocks to the eastern margin of Asia during the Late Jurassic to Early Cretaceous. Studied limestones crop out in southern Kyushu Island, southwest Japan. Although the prevailing and intense deformation during the accretionary process prevents measurement of sections in stratigraphic successions, and sedimentary structures are poorly preserved, microfacies description and foraminifers analysis allow us to speculate the depositional setting of the Sambosan limestones. Seventeen microfacies are distinguished and several foraminifers of Tethyan affinity are identified. Foraminifers indicate a Late Carnian to Rhaetian age. The Tethyan affinity of the macro- and microfaunas suggests that the Sambosan seamount was located presumably in a low- to middle-latitudinal zone of the southern hemisphere during the Late Triassic.

Late Triassic palynoflora from the Pranhita–Godavari Valley, India: evidence from vertebrate coprolites

Vijaya, Prasad, G.V.R. & Singh, K., June, 2009. Late Triassic palynoflora from the Pranhita–Godavari Valley, India: evidence from vertebrate coprolites. Alcheringa 33, 91–111. ISSN 0311-5518. The Upper Triassic Maleri Formation, represented by red clays and sandstones, has to date not produced any plant macrofossils or palynomorphs. Many spiral and non-spiral coprolites collected during this study from the Maleri Formation of the Pranhita-Godavari Valley were analysed for palynomorphs. Based on shape, nature of coiling and size, the Maleri coprolites are classified into seven groups. Of these, only Group-I, Type 5 (non-spiral) and amphipolar (spiral) types yielded diverse gymnospermous and pteridophytic spores, pollen, other plant debris and sparse fungal spores and algal remains. Occurrences of Antulsporites varigranulatus, Aratrisporites spp., Cadargasporites baculatus, Dubrajisporites isolatus, Enzonalasporites vigens, Foraminisporis coelatus, Grandispora spinosa, Kraeuselisporites saeptatus, Polycingulatisporites reduncus, Staurosaccites spp., Tethysispora unica and Tikisporites balmei confirm a Late Triassic age for the coprolite-bearing red clays. Records of Classopollis classoides and Callialasporites turbatus/dampieri in these assemblages more precisely suggest a Norian to Rhaetian age. The non-spiral coprolites were possibly produced by aquatic piscivorous animals whereas the spiral coprolites may have been produced by an as yet unidentified fish taxon. The coprolite-producing animals (spiral and non-spiral groups) possibly ingested gymnospermous and pteridophytic plant remains passively along with water or their herbivorous prey.

Stage boundaries of the Triassic in Northeast Asia

The International Union of Geological Science approved the stage boundaries suggested by the international working groups for the Tethyan Triassic. In this work we estimate the possibility of their establishment and correlation in the Boreal sections of Northeast Asia, based on the analyzed distribution of ammonoids and conodonts. As the conodonts of the Induan Stage have not been identified for sure in the region under study, the lower boundary of the Triassic System is defined here at the base of the Otoceras concavum Zone of the ammonoid scale. In addition to the ammonoids Hedenstroemia hedenstroemi (Keyserling), the first occurrence of the conodonts Pseudogondolella nepalensis (Kozur et Mostler) is suggested to be the biomarker of the Olenekian Stage base. The lower boundaries of the Anisian and Ladinian stages, defined respectively at the basal levels of the Paracrochordiceras-Japonites Beds in Northern Dobrogea and the Eoprotrachyceras curionii Zone in the Brescian Prealps are recognizable, though with some reservations, at the base of the Grambergia taimyrensis and Eonathorstites oleshkoi zones in Northeast Asia. According to the priority principle and similarity between the ammonoid faunas of the Daxatina cf. canadensis Subzone and Frankites regoledanus Zone, the lower boundary of the Carnian Stage is defined at the base of the Alpine Trachyceras aon Zone. In Northeast Asia, this boundary is established at the base of the “Protrachyceras” omkutchanicum Zone, as we take into account the fact that the Daxatina and Stolleyites ammonoid genera occur in sections of British Columbia below the stratigraphic level of the Trachyceras forms. The lower boundary of the Norian Stage is concurrent with the base of the Guembelites jandianus Zone in the Alps and equivalent Stikinoceras kerri Zone in North America and Striatosirenites kinasovi Zone in Northeast Asia. The conodont species Norigondolella navicula (Huckriede) that is most important for the Boreal-Tethyan correlation cannot be used as a biomarker of the Norian lower boundary because of its problematic diagnosis and rare occurrence in the Boreal sections. The Rhaetian Stage base is defined at the appearance level of the Misikella conodont genus in the Hallstatt region, Austria, that is simultaneously the disappearance level of the characteristic Norian bivalves (Monotis) and ammonoids (Metasibirites). In Northeast Asia, this boundary is established at the top of the Monotis ochotica Zone. The correlation between the biostratigraphic units of the Middle-Upper Triassic conodont scale established in Northeast Asia and standard ammonoid zonation is verified.

Late Triassic Phaeodarian Radiolaria from the Northern Chichibu Belt, Shikoku, Japan

A new genus (Triassiphaeodina gen. nov.) and two new species (Medusetta japonica sp. nov. and Triassiphaeodina niyodoensis sp. nov.) of Late Triassic (Rhaetian) phaeodarian Radiolaria are described from a phosphatic nodule found in mélange rocks of the Northern Chichibu Belt, Shikoku, Japan. The Rhaetian age of the nodule and of the phaeodarian new taxa is based on co-occurring Polycystina Radiolaria, including Bipedis acrostylus Bragin, Livarella densiporata Kozur and Mostler, Fontinella primitiva Carter, and Ferresium sp. A of Carter (1993). This finding shows that phaeodarian Radiolaria were already represented in Late Triassic oceans, with morphologies similar to those known in the Late Cretaceous and Cenozoic, from which they have previously been reported. The new taxa described herein represent the oldest known phaeodarian fossils.

Late Triassic and Early Cretaceous sedimentary sequences of the northern Isfahan Province (Central Iran): stratigraphy and paleoenvironments

This research gives a general outline of the Upper Triassic and Lower Cretaceous sequences cropping out north of Isfahan, Central Iran. Upper Triassic Nayband Formation subdivided into the Gelkan, Bidestan, Howz-e-Sheikh, Howz-e Khan and Qadir members. Two biostromal levels are documented in the Bidestan and Howz-e-Khan members. Due to a suitable condition in Late Triassic time including light, oxygen and nutrient, fauna such as: corals, sponges, hydrozoas, bivalves, gastropods, brachiopods, echinoderms and Dicroidium were flourished in water and flora on land. The first appearance of Heterastridium spp. in level of the Bidestan Member is apparently the first occurrence of this taxon in Central Iran. Qadir Member has several key beds, one key bed with land flora Clathropteris spp., and three key beds with bivalve Indopecten glabra, dating as Rhaetian Stage. An angular unconformity can be traced between Rhaetian sediments and red conglomerates and sandstones of Lower Cretaceous Sequences in Isfahan area which encompasses all Jurassic rocks. This gap can be related to Cimmerian tectonic phase.

A Dicynodont-Theropod Association in the Latest Triassic of Poland

It is generally accepted that during the Triassic the composi− tion of tetrapod faunas underwent a series of fundamental transformations, mainly as a result of diversification of archosaurs and decline of therapsids (Benton 1994, 2004, 2006). The last herbivorous basal synapsids, dicynodonts, disappeared from the record in the early Norian of the Americas, about 220 Ma (Langer et al. 2007), being un− known from the Late Triassic of Europe. Here, we report a partially articulated skeleton and isolated bones of a giant rhino−size dicynodont in the Upper Triassic fluvial sedi− ments at Lisowice (Lipie Śląskie clay−pit) in southern Po− land. Paleobotanical data indicate an early Rhaetian age for the fauna (Dzik et al. 2008; Niedźwiedzki and Sulej 2008). The dicynodont bones are associated with bones of carnivo− rous dinosaurs, pterosaurs, as well as capitosaur and plagio− saur amphibians. Dicynodonts were represented in the Ger− manic Basin throughout the Late Triassic, as proven by findings of smaller dicynodonts in older deposits in the same area, associated there with temnospondyl amphibians. It ap− pears, thus, that the fossil record of tetrapod succession in the Late Triassic was strongly controlled by ecological fac− tors and biased by uneven representation of particular envi− ronments. The Lisowice assemblage proves that faunas dominated by dicynodonts did not entirely disappear at least until the end of the Triassic.

RHAETIAN (LATE TRIASSIC) MONOTIS (BIVALVIA: PECTINOIDA) FROM THE EASTERN NORTHERN CALCAREOUS ALPS (AUSTRIA) AND THE END‐NORIAN CRISIS IN PELAGIC FAUNAS

Abstract: Species of marine bivalves of the pectinoid genus Monotis provide useful biochronologic indices for the Late Triassic (middle Norian–earliest Rhaetian). We report the succession of Monotis at Hernstein in Lower Austria where typical late Norian Monotis salinaria (Schlotheim) are overlain by strata with apparently the youngest Monotis known of demonstrable Rhaetian age: Monotis hoernesi Kittl and Monotis rhaetica sp. nov., a species closely related to M. rudis Gemmellaro. A Rhaetian (Sevatian 2) age is confirmed by the co‐occurrence of Monotis with the platform conodont Misikella posthernsteini and close association with the ammonoid Paracochloceras. A review of late Norian monotid species indicates that a profound extinction event occurred in the pelagic realm at or close to the Norian/Rhaetian boundary where c. 15 monotids (Monotis s.l. and Maorimonotis) became extinct. The surviving Monotis are dwarfed when compared to their Norian predecessors and may represent an ecological/phylogenetic response to the crisis.

UPPER TRIASSIC TO CRETACEOUS RADIOLARIA FROM NICARAGUA AND NORTHERN COSTA RICA - THE MESQUITO COMPOSITE OCEANIC TERRANE

We propose a new terrane subdivision of Nicaragua and Northern Costa Rica, based on Upper Triassic to Upper Cretaceous radiolarian biochronology of ribbon radiolarites, the newly studied Siuna Serpentinite Melange, and published 40Ar/39Ar dating and geochemistry of mafic and ultramafic igneous rock units of the area. The new Mesquito Composite Oceanic Terrane (MCOT) comprises the southern half of the Chortis Block, that was assumed to be a continental fragment of N-America. The MCOT is defined by 4 corner localities characterized by ultramafic and mafic oceanic rocks and radiolarites of Late Triassic, Jurassic and Early Cretaceous age: 1. The Siuna Serpentinite Melange (NE-Nicaragua), 2. The El Castillo Melange (Nicaragua/Costa Rica border), 3.The Santa Elena Ultramafics (N-Costa Rica) and, 4. DSDP Legs 67/84. 1. The Siuna Serpentinite Melange contains, high pressure metamorphic mafics and Middle Jurassic (Bajocian-Bathonian) radiolarites in original, sedimentary contact with arc-metandesites. The Siuna Melange also contains Upper Jurassic black detrital chert formed in a marginal (fore-arc?) basin shortly before subduction. A phengite 40Ar/39Ar -cooling age dates the exhumation of the high pressure rocks as 139 Ma (earliest Cretaceous). 2. The El Castillo Melange comprises a radiolarite block tectonically embedded in serpentinite that yielded a diverse Rhaetian (latest Triassic) radiolarian assemblage, the oldest fossils recovered so far from S-Central America. 3. The Santa Elena Ultramafics of N-Costa Rica together with the serpentinite outcrops near El Castillo (2) in Southern Nicaragua, are the southernmost outcrops of the MCOT. The Santa Elena Unit (3) itself is still undated, but it is thrust onto the middle Cretaceous Santa Rosa Accretionary Complex (SRAC), that contains Lower to Upper Jurassic, highly deformed radiolarite blocks, probably reworked from the MCOT, which was the upper plate with respect to the SRAC. 4. Serpentinites, metagabbros and basalts have long been known from DSDP Leg 67/84 (3), drilled off Guatemala in the Nicaragua-Guatemala forearc basement. They have been restudied and reveal 40Ar/39Ar dated Upper Triassic to middle Cretaceous enriched Ocean Island Basalts and Jurassic to Lower Cretaceous depleted Island arc rocks of probable Pacific origin. The area between localities 1-4 is largely covered by Tertiary to Recent arcs, but we suspect that its basement is made of oceanic/accreted terranes. Earthquake seismic studies indicate an ill-defined, shallow Moho in this area. The MCOT covers most of Nicaragua and could extend to Guatemala to the W and form the Lower (southern) Nicaragua Rise to the NE. Some basement complexes of Jamaica, Hispaniola and Puerto Rico may also belong to the MCOT. The Nicoya Complex s. str. has been regarded as an example of Caribbean crust and the Caribbean Large Igneous Province (CLIP). However, 40Ar/39Ar - dates on basalts and intrusives indicate ages as old as Early Cretaceous. Highly deformed Jurassic and Lower Cretaceous radiolarites occur as blocks within younger intrusives and basalts. Our interpretation is that radiolarites became first accreted to the MCOT, then became reworked into the Nicoya Plateau in Late Cretaceous times. This implies that the Nicoya Plateau formed along the Pacific edge of the MCOT, independent form the CLIP and most probably unrelated with he Galapagos hotspot. No Jurassic radiolarite, no older sediment age than Coniacian-Santonian, and no older 40Ar/39Ar age than 95 Ma is known from S-Central America between SE of Nicoya and Colombia. For us this area represents the trailing edge of the CLIP s. str.