Lower Carnian Research Articles

Foraminiferal fauna recovered after the Late Permian extinctions in Iberia and the westernmost Tethys area

The mass extinction at the end of the Permian has long been recognized as the greatest in the history of life. Foraminifers were common throughout the Permian–Triassic (P–T) interval and provide one of the best, and certainly the most informative, fossil records of the P–T crisis. This study addresses the recovery of foraminiferal faunas during the Triassic after the Late Permian extinction in the western Tethys, and particularly in Iberia, through the analysis of evolution rates both at the species and genus level. For the Tethys area in general, a rapid recovery of these faunas during the Olenekian is reflected by high rates of appearance of new taxa along with the reappearance of many “Lazarus” taxa. These taxa became stabilized throughout the Anisian and Ladinian, with a reduction in the rates of origination of new taxa and the presence of associations that were highly diversified, comprising large numbers of species. The first foraminifers in the Triassic of Iberia can be observed at two different levels. The first of these is in the Upper Anisian, while the second level corresponds to the Upper Ladinian (Longobardian)–Lower Carnian. The Triassic associations of the basins of Iberia show paleobiogeographic characteristics that are generally “Tethyan”, most of these associations being well known for the “alpine” Triassic. For the Ladinian, some associations from NE Iberia (NE Iberian basin, Catalonian basin, and Pyrenean basin) also show “Germanic” affinities. Finally, also for the Ladinian, there is some evidence of the possible southward movement of faunas from the Sephardic domain to the Betic basin. This point, however, requires further investigation. With the exception of faunas associated with the reefs of the Ladinian Catalonian basin, communities are usually of low diversity and typical of unstable, shallow marine facies.

Problems of the “Cordevolian” Limestone and Dolomite” in the Slovenian part of the Southern Alps

Stratigraphic position and age of the so called Cordevolian limestone and dolomite in the Slovenian part of the Southern Alps is a long lasting problem. Its name originates from the (somewhere abandoned) Cordevolian substage (Lower Carnian). Limestone and dolomite both correspond to the Cassian dolomite from the Italian Southern Alps. Platform type of limestone and dolomite, which could be genetic and time equivalent with the Ladinian Schlem (Scilliar) dolomite, is unknown in Slovenia. In the NE part of the Kamnik-Savinja Alps, the Korošica formation (Upper Ladinian) overlies platform limestone and dolomite of the Ojstrica Formation (Ladinian). Diplopora annulata is also present in the Ojstrica formation. Various Ladinian rocks in the Julian Alps and Southern Karavanke are mainly of the Lover Ladinian age, whereas the overlying massive limestone and dolomite (“Cordevolian limestone and dolomite”) are partially of the Ladinian and partially of the Carnian age. There are no Upper Ladinian “Wengen” beds in the carbonate massive, so it is impossible to draw a time line between the Ladinian and the Carnian stages. We can therefore conclude, that litological boundaries do not coincide with the chronostratigraphic ones.

Cephalopods of the “Falang Formation” (Triassic) from Guanling and Zhenfeng Counties, Guizhou Province, China

Abstract The “Falang Formation” of western Guizhou was previously called the “Halobia Bed” and considered to be Ladinian in age. It was subdivided upward into the Zhuganpo, Laishike and Longchang members based on ammonites and the Trachyceras multitubertulatum Zone of the Longchang Member was put in the Lower Carnian. Here in the present paper, 4 genera and 9 species of ammonites and 1 nautiloid genus and species collected from the upper part of the “Falang Formation” (i.e. the Wayao Formation used in this paper, equivalent to the Laishike Member from Guanling and Zhenfeng counties are described. The geological and geographical distribution of these cephalopods, as well as the co‐existing conodonts, put the Wayao Formation to the late early Carnian.

UPPER TRIASSIC AMBER FROM THE DOLOMITES (NORTHERN ITALY).A PALEOCLIMATIC INDICATOR?

Amber in Triassic deposits in the Dolomites is demonstrated for the first time. The amber-bearing deposits belong to the middle part of the Durrenstein Formation, referred to uppermost Julian (Lower Carnian, about 225 My). Chemico-physical features of amber, which occurs as small yellow to reddish droplets, have been determined. Infrared (IR) spectroscopy shows typical bands of fossil resins; the fingerprint region of the spectrum presents a unique pattern that cannot be referred to any other known fossil resin. Palynological investigation of amber-bearing layers shows a large prevalence of bisaccates and circumpolles. Particularly, the taeniate bisaccates are frequent (41%) and suggest a correlation with the amber-producing species. Amber production and preservation is possibly related to a humid climatic event.

Upper Anisian to Lower Carnian magnetostratigraphy from the Northern Calcareous Alps (Austria)

We present a magnetostratigraphic study of three pelagic limestone sections (Gamsstein, Mendlingbach and Mayerling) from the eastern part of the Northern Calcareous Alps. Together these sections, which contain a rich conodont fauna, yield a sedimentary record encompassing the uppermost Anisian, the Ladinian and the Lower Carnian. Thermal demagnetization and isothermal rémanent magnetization experiments indicate that the magnetization is essentially carried by a mineral of the magnetite family. The high unblocking temperature components isolated from the three sections provide clear magnetic polarity zonations. Correlations between these results, based on the biostratigraphic data and tephrochronology, allow the construction of a composite magnetic polarity sequence from the Illyrian substage (Upper Anisian) to the Julian 2 zone (Lower Carnian). This sequence contains 17 well‐defined polarity reversals, and eight more poorly defined intervals. Correlations can be suggested between the new data and other magnetostratigraphic results previously obtained from marine sections. We estimate that the magnetic reversal frequency was 2.5 to 3.6 reversals per million years during the Ladinian.

First biostratigraphic evidence for the presense of Triassic at Me lia (Western Thrace, Greece)

All previous studies on the Drimos – Melia Formation ("series") suggest a Cretaceous or Cretaceous - Palaeocene? age. Along a short section close to the north-western entrance of the village of Melia (Alexandropoulos District), we found in a bed of dark-gray silty shales of this formation prints of two thin-shell bivalve specimens identified as Halobia superba Mojs. This is a typical Triassic species known from the Upper Ladinian and Lower Carnian. Thus, several important conclusions are drawn, and namely, that for the first time the presence of non-metamorphic Triassic (Upper Ladinian – Lower Carnian) terrigenous rocks is proven in the area, and that such is the age of at least a part of the Drimos – Melia Formation.

THE MIDDLE-UPPER TRIASSIC OF THE SAN DONATO UNIT AUCT. (NORTHERN CALABRIA): STRATIGRAPHY, PALEOGEOGRAPHY AND TECTONIC IMPLICATIONS

In this paper are presented stratigraphic and sedimentological data on the carbonate successions occurring in the Cozzo del Pellegrino massif (Cosenza), generally considered as pertaining to the metamorphic San Donato Unit. The successions start with thick phyllites and intercalated carbonate lenses containing Anisian-lower Ladinian algae. To the phyllites follows the informally defined calcari formation, locally occurring also as its lateral equivalent. The calcari formation consists of two members, the first of which (Piano del Minatore Mbr.)consists of black, often marly limestones, showing nodular and bioturbated textures, with a scarce and banal fauna represented by ostracods, gastropods and bivalves. Algal mounds, with porostromata and crinoids are locally intercalated in these facies. In the upper part of the formation the black limestones pass laterally to a reef complex (Monte Caramolo Mbr.) of Ladino-Carnian age, consisting mainly of boundstones with sponges and biogenic crusts, as well as of fore-reef breccias. These lithotypes have been interpreted as deposited on a carbonate ramp evolving to a restricted, poorly oxygenated lagoonal area, bordered by bioconstructed margins. In the lower Carnian a carbonate-marly horizon, containing traces of evaporites, whose thickness is decreasing toward the east, allows a lithostratigraphic correlation betweenmost of the studied successions. The calcari formation is followed by the Scifarello formation, mainly outcropping in the eastern parts of the studied area. It consists generally of tidal dolomites with some tempestites deposited on an shallow open shelf, followed by dolomites and laminated, often marly, dolomitic limestones, deposited in a subtidal, restricted environment. On the basis of foraminifers and bivalves data, the upper part of the Scifarello formation has been ascribed to the upper Carnian-Norian. Moreover, a strong tectonic activity of Lower Norian age is evidenced by the presence of mass-flows and sedimentary dikes in the more easterly areas of the massif. The general paleoenvironmental evolution, in the period spanning between Anisian and Early Norian, can be envisaged firstly in a carbonate sedimentation on a wide shelf, grading toward the east to deeper, possibly basinal areas, whose location was controlled by the Ladinian and/or Norian synsedimentary tectonics. This shelf was bordered on the west by a peri-continental area, with silicoclastic to evaporitic deposits, better represented in the Cetraro area. Finally, the Norian dolomites pertaining to the Verbicaro Unit, usually considered as have been thrusted onto rhe Triassic carbonates of the San Donato Unit, have been often observed to occur in normal stratigraphical superposition over the latter. Therefore, also considering the ambiguous evidence presented in the literature on the Jurassic-Miocenic evolution of the San Donato Unit AUCT, we interpret the Norian Verbicaro dolomites as being the most natural evolution of the Anisian-Lower Norian San Donato lithotypes. It follows that for a really valid paleogeographic reconstruction a complete redefinition of the tectonic units in the whole area is needed.

Origin and Evolution of Turkish blocks during the Late Triassic from magnetostratigraphic data

A palaeomagnetic and magnetostratigraphic study has been carried out on lower Carnian and Norian rocks (Late Triassic) from four different sections of two different units of the Upper Antalya Nappes in the Taurus region of southwestern Turkey, the Bakirli Dag unit and the Kaymaz Dag unit. The origin of these nappes is uncertain and under debate. This study provides well defined directions of probable primary origin and good magnetostratigraphic correlations between the different sections, which allows us to propose a palaeogeographic interpretation. The Bakirli Dag unit of the Upper Antalya Nappes were located at a palaeolatitude of 6.9°N ± 1.5° during the early Carnian and at 10.2°N ± 1.0° during the latest Carnian-middle Norian. This slight northward movement is accompanied by a large clockwise rotation (29.5° ± 6.7°) which may correspond to an important breakup-phase of the north African margin during middle-late Carnian time. The palaeo­magnetic results from the Kavur Tepe section of the Kaymaz Dag unit, previously considered to belong also to the Upper Antalya Nappes, show a palaeolatitude of 17.4°S ± 1.1° during Norian time. This result surprisingly indicates that this unit was located in the vicinity of the northern Indian margin during the Late Triassic.

Magnetostratigraphy of the Late Triassic Bolücektası Tepe section (southwestern Turkey): implications for changes in magnetic reversal frequency

A magnetostratigraphic study of light-pink to white pelagic limestones from the Bolücektası Tepe section (southwestern Turkey) provides a magnetic polarity sequence well calibrated with the conodont zonation for the Lower Carnian and uppermost Carnian-Middle Norian (Late Triassic). Thermal (between 400 and 550°C) and alternating field (30–60 mT) demagnetizations isolate the characteristic remanent components. Rock magnetic experiments suggest that magnetite is the dominant magnetic carrier, but a small hematite fraction also exists in the Lower Carnian light-pink limestones. A major sedimentary gap (Middle-Upper Carnian) divides the section in two submembers which reveal two statistically different mean directions, differing in declination by about 30°. A sequence of 39 polarity intervals is obtained, 18 in the Carnian (ten in the Lower Carnian and eight in the uppermost Carnian) and 21 in the Lower-Middle Norian. The magnetic reversal frequencies which can be derived from these results, together with the available magnetostratigraphic data for the Middle-Early Jurassic, Triassic and Late Permian, show a pattern which is in rough agreement with the suggested 150–200 million year time constant in the reversal process since the Kiaman superchron. However, significant short-period fluctuations in reversal frequency cannot be excluded.

Triassic conodont biostratigraphy in the Malay Peninsula

Conodonts representative of the Lower, Middle and Upper Triassic are now known in the Malay Peninsula and all the Triassic Stages except the Rhaetian are represented. The best known sequence of Triassic conodonts occurs in the Kodiang Limestone ofKedah but there are still significant gaps in the known conodont succession. In particular, Griesbachian and Dienerian conodonts are poorly known and conodonts representative of the Upper Spathian, Lower Ladinian, Middle and Upper Norian and Rhaetian are unknown. New data from the Kodiang Limestone ofBukit Mulong and Bukit Kepelu help to fill some of these gaps in the Carnian and Norian conodont succession. The Chuping Limestone of Per lis has also recently yielded some Lower Norian conodonts which implies a correlation with the Kodiang Limestone to the south. Other recent discoveries include early Late Triassic (Lower Carnian) conodonts from the Chert Member of the Semanggol Formation, Kedah, Early Triassic (Spathian) conodonts from north-west Pahang and Early Triassic (upper Dienerian) and Middle Triassic (upper Anisian) conodonts from the Jerus Limestone, Cheroh, west Pahang.

A new calcitic sphinctozoan sponge belonging to theDemospongiae from the Cassian Formation (Lower Carnian; Dolomites, Northern Italy) and its phylogenetic relationship

A new species of a coralline sponge, Cassianothalamiazardinii n. gen. n.sp., from the Lower Carian Cassian Beds (northern Italy) is described. The new species possesses a secondary thalamid basal skeleton with a spongocoel and the internal structure is constructed of horizontal elements (trabecula) and vesiculae. The microstructure of the basal skeleton is composed of an irregular high Mg-calcite. From the spicular skeleton aster-microscleres can be preserved. In rare cases, monaxonid megascleres can also be found. Therefore the new sponge is probably a representative of the demospongid order Hadromerida.

On the structural development of the salt dome province in NW Jutland, Denmark, based on seismic studies

As a result of the renewed interest in Danish salt structures the Geological Survey of Denmark (DGU) engaged the author to outline the structural development of the salt dome province in NW Jutland, which is a part of the Norwegian Danish Basin. The work comprised the interpretation of 79 seismic sections and construction and analysis of 9 two-way time maps, 13 isopach maps and 11 cross-sections (Boldreel 1983, and in preparation). In this article only three two-way time maps, four isopach maps and two cross-sections are diseussed to iIIustrate some of the most important results. Within the area investigated there are seven salt diapirs and one salt pillow. There is a marked correlation between the positions of the stationary salt diapirs and faults in the base of Zechstein, and also between the temporal development of the diapirs and the isopachs of post-Zechstein sediments. The growth of salt pillows started in the Lower Carnian (Upper Triassic). Development of salt diapirs with associated second order peripheral sinks took place asymmetrically without lateral movement of the salt structures. In contrast the one remaining salt pillow, which has not developed diapirically, has moved from its original position in the northern part of the area towards the north-west. The movement of Zechstein deposits is minimal at present thicknesses of 300-600 m and has ceased at present thicknesses of less than 300 m. This leads to the conclusion that the Zechstein sequence does not consist of pure halite.

The Cassian patch reefs (lower Carnian, southern Alps)

The fauna of the upper Cassian Formation is composed mainly of reef-building and reef-dwelling organisms which occur as reeeposited material in basinal sediments, but have not been found as original reef bodies. Such bodies have now been discovered in the uppermost Cassian Formation of the central Dolomites from the Sella Group in the west to the Monti Cadini in the east. Generally they are small-scale patch reefs, not exceeding a few metres in thickness and lateral extent, which are intercalated in well-bedded detrital and micritic limestones. locally, larger biostromes spread out from the margins of the Cassian Dolomite buildups. Four types of faunal communities have been encountered in these reefs: 1. The thrombolite-calcareous algae community, composed of small patchy cryptalgal structures binding poorly sorted debris and associated with other Cyanophyta, sessile formainifera and scattered calcareous sponges and corals. This type is the most common within the calcareous and marly-tuffaceous facies of the Cassian Formation. 2. The calcareous sponge-coral community, composed mostly of calcareous sponges (stromatoporoids, some pharetronids) and, to a lesser extent, colonial corals and thrombolites. This community corre-sponds well to the Cassian reef fauna, best known from erratic blocks at Alpe di Specie, but has been found in situ only at one locality. 3. The Spongiomorpha-Solenopora community, associated with scattered calcareous sponges and colonial corals, forming a thin biostrome at one locality. 4. Coral communities, composed predominantly of colonial Scleractinia; found only in small or stratigraphically illdefined outcrops and in erratic blocks.

Mesozoic Dasycladaceae from Romania: Distribution and biostratigraphical importance

Dasycladaceae are important indexfossils in Mesozoic shallow-water limestones of Romania. A critical survey of the dasycladacean associations known from the Romanian Middle and Upper Triassic and from the Upper Jurassic-Lower Cretaceous is given. Triassic Dasycladaceae are known from the Apuseni Mountains (Padurea Craiului Mountains and Vascau Plateau). Eastern Carpathians (Rarau, Persani and Brasov), Southern Carpathians (Resita-Moldova Noua Zone), and Northern Dobrogea (Tulcea Zone). A biostratigraphical zonation is possible in the Upper Pelsonian and Lower Illyrian, as well as in the Upper Illyrian and Ladinian and Lower Carnian. No algae are known from the Middle Illyrian. The best information on the sequence of the coenozones can be taken from the sections in the Padurea Craiului Mountains (Fig. 2). A facies model of the Triassic Bihor carbonate platform (Fig. 4) shows a shifting of the facies zones during the Lower and Middle Triassic from continental and supratidal to intertidal and subtidal environments, which are characterized by shallow lagoons with various dasycladacean assemblages and small patch reefs built by sphinctozoan sponges on the inner slope of the lagoons. Upper Jurassic and Lower Cretaceous Dasycladaceae are known from the Eastern and Southern Carpathians, from the Apuseni Mountains, the Moesian Platform, and from the Southern Dobrogea. Several assemblage zones, defined by dasycladacean algae and foraminifera, characterize the Tithonian to Lower Aptian time intervall in the Eastern Carpathians (see Fig. 8). In the Southern Carpathians Dasycladaceae are known from the Tithonian to the Upper Aptian except from the Hauterivian. In the Apuseni Mountains Valanginian and Hauterivian dasyclads are lacking because of the discordant superposition of Tithonian reef limestones by Barremian and Aptian limestones. The Tithonian, Necomian and the Barremian to Lower Aptian is known from wells in the eastern part of the Moesian platform. Berriasian to Lower Aptian algal zones have been recognized in Southern Dobrogea.

Aragonite in Permian Reefs

PRESERVATION of aragonite in fossils decreases the further we go back in the geologic record. In the Palaeozoic, aragonitic remains have been found only in clayey–bituminous deposits which have largely inhibited diagenetic alterations of unstable mineral phases (for example, Buck-horn Asphalt and Kendrick Shale, both Upper Carboniferous of USA1, and Upper Oil Shale Group, Lower Carboniferous of Scotland2). Palaeontological information preserved in these facies is restricted, however, to those organic remains which lived in the equivalent basinal environments or were transported into them. Original mineralogy and microstructures of ancient reef organisms can generally only be deduced from analogies with equivalent younger counterparts. The oldest known reef-organisms with preserved aragonitic microstructures were found in the Upper Triassic (Lower Carnian) of the Southern Alps3. Here, early burial of patch reefs and reef detritus by clayey–tuffaceous sediments and porosity diminution of the carbonates by subsequent cementation have probably inhibited transformation of aragonitic micro-structures into calcite4. In this report we describe investigations of micrestructures and diagenesis in calcareous sponges which have revealed aragonitic primary structures and cements in material from the Upper Permian of Djebel Tebaga, Southern Tunisia.

Hokonui Stratigraphy of the Awakino-Mahoenui area, South West Auckland

Summary Trias-Jura rocks of the Awakino-Mahoenui area constitute part of the western limb of the Kawhia Syncline in its southern-most exposure. The syncline is approximately meridional in alignment and pitches northwards at a low angle. Strata have dips varying from nearly vertical in the west of the area to about 15° east at the top of the succession in the east. The strata form the Herangi Range which originated as a north-south fold or the peneplained surface resulting from the post-Hokonui orogeny. This fold is believed to be faulted on its western edge, but while this is also the case on the eastern limb farther north, in the Awakino-Mahoenui area faulting seems not to have occurred at the surface. The oldest beds exposed are 7,000 ft of Oretian (lower Carnian) which are believed to be the equivalent of 2,100 ft of strata above the Moeatoa conglomerate at Marakopa. These are followed conformably by 2,200 ft of Otamitan strata (Carnian), 1,800 ft to 2,300 ft of Warepan (Norian), 2,800 ft of Otapirian (Rhaetian), 2,500 ft of Aratauran (Hettangian-Sinemurian), about 2,000 it of Ururoan (Pliensbachian-Toarcian), about 4,000 ft of Temaikan (Bajocian-Oxfordian), and 4,300 ft of Heterian (Kimeridgian), giving a total of 14,000 ft of Triassic and 12,000 it of Jurassic strata. Beds of. Heterian age make up a greater thickness than in other North Island localities. On the south shore of Kawhia Harbour there are some 500 ft of beds, including Temaikan, between the type Temaikan and the black, gritty sandstone of Totara Peninsula, whereas below the Palmer Creek Shellbed (the same horizon as the black sandstone) there are 3,500 ft of Heterian strata. The sediments are mainly bedded sandstones and siltstones, with scattered and widespread tuffaceous material. True conglomerates are rare and thin, but grits are more common. Carbonaceous beds occur in the Otapirian and Heterian and accompany thin coals in the Oretian, but no non-marine beds typical of the type Temaikan sequence were observed in strata of Temaikan age. Calcareous beds are found at various levels in the Jurassic sequence but only Aratauran strata were found to contain microfossils. Marine fossils are widespread and allow closer subdivision of some stages. Warepan beds contain numerous forms of Monotis whose stratigraphic distribution enables four subdivisions to be recognized in the area. M. richmondiana is found in the older beds; M. calvata. is confined to the upper Warepan; while middle Warepan strata contain a very varied fauna including forms recognized by Trechmann (1918) and others recorded from New Caledonia (Avias, 1953). The Otapirian Stage is divided after Campbell (1956) although his basal fauna was not recognized in the area. Ururoan beds are divided into those containing Pseudaucella (Pliensbachian) and those with Dactylioceras (Toarcian). This ammonite was not found, but the fauna enables ready correlation wi'th the beds containing it at Ururoa Point.