196,033 research outputs found
In the search for a “golden” event to define the GSSP of the Norian Stage (Upper Triassic): bivalve events and their ammonoid calibration
No full textCarnian-Norian halobiids from the Pizzo Mondello section (Sicani Mountains, Sicily, Italy).
No full textAnatomy of carbonate mounds from the Middle Anisian of Nakhlak (Central Iran): architecture and age of a subtidal microbial-bioclastic carbonate factory
No full textThe Anisian succession of Nakhlak (in Central Iran) is characterized by a siliciclastic succession with minor carbonate units, with massive carbonate mounds up to 50 m thick in its upper part. The mounds, constrained in age to the late Bithynian (Ismidicus Zone) by ammonoids and conodonts, are characterized by a flat top and a lateral pinch-out marked by clinostratified slopes (about 15A degrees in dip). Stratigraphic and microfacies analyses document an inner part of the mound characterized by massive microbial carbonates with open-space structures (stromatactis) filled with fine-grained internal sediments and marine cements. Isolated sponges (up to 5 cm), serpulids and bryozoans are present, which grew on the calcimicrobial limestone. A narrow bioclastic margin (mainly with crinoids and brachiopods) produces most of the slope facies (consisting of bioclastic grainstone and packstone, with intraclasts from the inner part of the mounds) which interfinger basinward with volcaniclastic sandstones. The demise of carbonate productivity is marked on the top of the carbonate mounds by a condensed surface, rich in ammonoids, glaucony grains, and articulated crinoids, documenting a rapid drowning. Paleolatitude data support deposition in a tropical setting, and sedimentological constraints indicate deposition close to the fair-weather wave base, within the photic zone. The late Bithynian Nakhlak carbonate mounds developed before the appearance (documented since the Pelsonian in different parts of the world) of scleractinians which, despite the favorable environmental conditions, are absent at Nakhlak. The Nakhlak mounds thus represent one of the last occurrences of the microbial factories (which developed after the Permo-Triassic extinction event and persisted for most of the Middle Triassic, but with a gradually increasing role played by scleractinians) before the first appearance of the Mesozoic corals
LATE CARNIAN-EARLY NORIAN AMMONOIDS FROM THE GSSP CANDIDATE SECTION PIZZO MONDELLO (SICANI MOUNTAINS, SICILY)
No full textA small collection of ammonoids from the Upper Triassic Scillato Formation at Pizzo Mondello (Agrigento, Sicily) is studied. The specimens were collected in a framework of a project aimed at providing an integrated high-resolution bio-chronostratigraphic support to the Upper Carnian-Norian magnetostratigraphic scale defined at this site, that is located in an historical area from which G.G. Gemmellaro collected the Upper Triassic of ammonoids monographed at the beginning of the XX century. The specimens from Pizzo Mondello were bed-by-bed sampled and represent the first collection of Upper Triassic ammonoids described from Sicily since Gemmellaro time. Quite several levels of the Pizzo Mondello section yielded ammonoids, but very few levels have provided more than one specimen. Due to the scarcity of specimens the taxonomic analysis has been complex because Gemmellaro, who described 166 new species, did not explain the variability of many of his taxa. Sixsteen taxa belonging to eleven genera are described. They include Placites sp. ind., Discotropites plinii (Mojsisovics), Anatropites sp., Microtropites cf. paronai, Metathisbites cf. affinis, Hyattites aff. praefloridus, Projuvavites boehmi (Gemmellaro), Projuvavites inflatus (Gemmellaro), Gonionotites cf. italicus, Gonionotites aff. recuperoi, Dimorphites noricus n. sp., Dimorphites selectus Mojsisovics, Dimorphites sp., Pregriesbachites n. gen. , P. bukowskii (Gemmellaro), Discophyllites insignis. Among the new taxa, Dimorphites noricus n. sp. formalizes the nomen nudum “Dimorphites n. sp. 1” quoted in literature for several years, that is index of the lowest subzone of the Norian stage.
The small collection document the Discotropites plinii and Gonionotites italicus subzones of the uppermost Carnian Spinosus Zone and the Dimorphites noricus and D. selectus subzones of the Jandianus Zone, the first zone of the Lower Norian. This chronostratigraphic classification firmly tie the Pizzo Mondello succession to the Tethyan chronostratigraphic scale, and is crucial for the calibration of the Halobia and conodont bioevents identified in the section. The chronostratigraphic correlations based on ammonoids of the Pizzo Mondello section with Feuerkogel (Austria), Jomsom (Nepal), West Union Canyon (Nevada, USA) and Black Bear Ridge (British Columbia, Canada) is discussed. These are the most complete ammonoid-bearing sections in the world spanning the Carnian/Norian boundary, but all of them show a discrete distribution of ammonoid-bearing beds across the boundary. Ammonoid will not provide the primary marker event for the definition of the GSSP of the Norian, but they are crucial for the selection of the most significant events
Anatomy of microbial–bioclastic carbonate mounds from the Middle Anisian of Nakhlak (Central Iran): A genetic model for a shallow subtidal carbonate factory.
No full textLate Carnian-Early Norian ammonoids from the GSSP candidate section Pizzo Mondello (Sicani mountain, Sicily).
No full textThe new Carnian (Norian section of “Pizzo Lupo” (Castronovo di Sicilia, Sicily) and its bearing to the definition of the GSSP of the Norian stage.
No full textThe Triassic pre-Cimmerian stratigraphic evolution of Central Iran. MEBE report of the 2004 activity
No full text
Bio-chronostratigraphic calibration of the Upper Carnian-Lower Norian magnetostratigraphic scale at Pizzo Mondello (Sicani Mountains, Sicily)
No full textPizzo Mondello section is known since 15 years because
of the continuous Late Triassic pelagic record of great
significance for the establishment of an integrated chronostratigraphy
of the Late Triassic (Gullo et al. 1996;
Muttoni et al. 2001, 2004).
During the last 4 years, Pizzo Mondello section has been
studied in detail to provide a new and high resolution integrated
bio-chronostratigraphy for the calibration of the
magnetostratigraphy and chemostratigraphy proposed by
Muttoni et al. (2001, 2004), and now it is one of the GSSP
candidates for the definition of the base of the Norian.
The lowest 143 m of the Cherty Limestone, straddling the
C/N boundary have been studied in detail. The preliminary
data of the ongoing research have been presented in all the
meetings of the STS from Albuquerque 2007 and here we
summarize the final results.
The key correlation to the standard marine Triassic Scale
is provided by the ammonoids. They are relatively rare,
however the available collections document the Upper
Carnian Discotropites plinii and Gonionotites italicus
Subzones, from meter 15 to meter 80 from the base of the
section. The following 15 meters are poor in ammonoids,
while higher up the lower part of the Lower Norian Guembelites
jandianus Zone is documented by Dimorphites cf.
n. sp.1 of Krystyn, 1980.
Conodonts are very abundant and have a great potential
as practical tool for global correlations. The abundance
of specimens at Pizzo Mondello gave the opportunity to
point out clear relationships among the five most widespread
Upper Camian/Lower Norian conodont genera
(Paragondolella, Carnepigondolella, Metapolygnathus,
Epigondolella and Norigondolella) and to identify trends
of the generic turnovers (Mazza et al. 2010). The two biomarkers
so far proposed as possible marker events for the
GSSP were the FAD of E. quadrata (sample FNP88A) and
the FAD of M. communisti (sample NA35). However, the
FAD of E. quadrata occurs within the Gonionotites italicus
Subzone, while the FAD of M. communisti is on its top.
Halobiids are extremely common in the Cherty Limestone
and they have also a great potential for large scale correlations.
Nine species of Halobia have been recognized:
Halobia carnica, H. lenticularis, H. simplex, H. superba,
H. cf. rugosa, H. radiata, H. austriaca, H. styriaca and H.
mediterranea. The best possible marker for the base of the
Norian is the first occurrence of Halobia austriaca, that is
recorded in the middle of the interval between the record
of the Gonionotites italicus Subzone and the Guembelites
jandianus Zone.
Radiolarians were found in few samples but with high
diversity assemblages. In the upper Gonionotites italicus
Subzone to the Guembelites jandianus Zone there is an
overlap of species previously considered Late Carnian
with species usually regarded as Early Norian. About 4 m
above the FAD of E. quadrata, in the Gonionotites italicus
Subzone, the first assemblage with Capnuchosphaera
deweveri Kozur & Mostler, Capnuchosphaera tricornis
De Wever, Kahlerosphaera norica Kozur & Mock and
Xiphothecaella longa Kozur & Mock, usually referred to
Early Norian, occurs.
These integrated bio-chronostratigraphic studies lead to
identify some possible GSSP marker events especially on
conodonts and halobiids, which occur in the upper part of
magnetozone PM 4n, within PM 4r and in the lower part
of PM 5n.
Possibly the most suitable magnetostratigraphic event to
recognize the basal Norian is the base of magnetozone
PM 5n, as already suggested by Krystyn et al. 2002 and
Muttoni et al. 2004
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