1,720,984 research outputs found
Latest Ordovician (Hirnantian) miospores from NL-2 well, Algeria, North Africa, and their evolutionary significance
No full textMicrofloristic assemblages have been recovered from the Hirnantian-aged Hassi el Hadjar (‘Argiles
Microconglomratiques’) and M’Kratta formations in borehole Nl-2, northeast Algerian Sahara. These formations
are genetically related to glacial sedimentary dynamics, and represent, according to previous analysis, glacial
diamictites resulting from the melting of the Saharan ice cap, and post-glacial shelf conditions, respectively. Previous studies have analyzed in detail the microplankton (acritarchs and chitinozoans) content of the Nl-2 section, providing precise biostratigraphic control. This contribution presents for the first time a diverse Hirnantian
miospore microflora from Algeria, comprising cryptospores and trilete spores, and compares it with previously
reported coeval spore assemblages from worldwide localities at different palaeolatitudes. The palynological
microfloristic association is mainly characterized by cryptospores in permanent tetrad and dyad configurations,
along with minor occurrences of laevigate monads and rare trilete spores. The present results, in conformity with
previous suggestions, show apparent planet-scale homogeneity of the bryophyte-like earliest terrestrial flora during Hirnantian times. The diversity and abundance of early land plants was not affected by the Hirnantian glaciation
Mid- to late Permian microfloristic evidence in the metamorphic successions of the Northern Apennines: insights for age-constraining and palaeogeographical correlations
No full textRecent studies on the stratigraphy of Paleozoic successions belonging to key sectors of the inner Northern Apennines
provide data that can be used to propose new hypotheses about the palaeogeography of the western Mediterranean domain
during post-Hercynian times.We report here the first evidence of mid- to late Permian (Guadalupian–Lopingian) palynomorphs
in the chronostratigraphically highly debated metamorphic units of the Northern Apennines (the Rio Marina Formation, the Mt
Calamita Formation and the Le Cetine Formation) and consider the stratigraphic implications for the Tuscan ‘basement’ to
which the study rocks belong and their palaeogeographical attribution considering their Gondwana affinity. These results agree
with the interpretation that the Alpine Tethyan sedimentary cycle was already active during the mid- to late Permian
Implicazioni stratigrafico-paleoclimatiche ed evoluzione paleogeografica della successione Retico-Hettangiano del M. Albenza (Prealpi Bergamasche)
No full textThe affinities of Chordecystia chalasta Foster, and its questionable use as a global chronostratigraphic marker for the Permian-Triassic boundary
No full textPalynology of the Permian and Triassic of the Tesero and Bulla sections (Western Dolomites, Italy) and consideration about the enigmatic species Reduviasporonites chalastus.
Full text linkA palynological study of two Permian-–Triassic sections of the Southern Alps (Tesero and Bulla sections) was carried out in order to correlate the palynological data with the available conodont zones. Both the sections crop out in the Western Dolomites, the Tesero section in Fiemme Valley and the Bulla section in Badia valley.
The two sections include the uppermost Bellerophon Formation and the overlying Werfen Formation. In the latter the Permian/Triassic boundary (Farabegoli et al., 2007) has been defined by conodonts. The palynological assemblages collected in both sections throughout the Bellerophon up to the Werfen formations show compositional variation marked by: a) a dominance of taeniate and non -taeniate bisaccates in the Bellerophon Formation dated as Late Permian; b) a bloom of the organic microfossil incertae sedis Reduviasporonites chalastus in the lower Tesero Member (Werfen Formation), found only in the Tesero section. This interval should stratigraphically lie below the Permian/Triassic boundary, as defined by conodonts recorded in the Bulla section; c) poorly preserved acavate and bisaccate taxa in the upper Tesero Member, above the Permian/Triassic boundary, and in the overlying Mazzin Member of the Tesero section. The origin and the ecological preferences of Reduviasporonites chalastus and the implications of its worldwide distribution across the Permian/Triassic boundary are also discussed
Cryptospore assemblages from Upper Ordovician (Katian–Hirnantian) strata of Anticosti Island, Québec, Canada, and Estonia: Palaeophytogeographic and palaeoclimatic implications
No full textThe palynostratigraphy of the Lower Carboniferous (middle Tournaisian–upper Viséan) Shishtu Formation from the Howz-e-Dorah section, southeast Tabas, central Iranian Basin
No full textPalynological analysis from the Shishtu 2 Member of the Shishtu Formation located in the Howz-e-Dorah area (Southeast Tabas, Central Iran Basin) suggests a middle Tournaisian-late Viséan age for this rock unit. The Shishtu 2 Member consists of shale, sandstone, dolostone and limestone. Three palynological assemblages are recognized and mainly correlated with the miospore biozones of Northern Gondwana. A microfloristic comparison with other sections in Western Gondwana (South America) is also proposed. We identify a sedimentary hiatus between Shishtu 1 and Shishtu 2 members. Our findings suggest that the Mush horizon is the basal part of the Shishtu 2 Member, unlike the Iranian literature where it is considered as the uppermost part of the Shishtu 1 Member
Stratigraphy and depositional environment of the Mt. Argentario sandstone Fm. (Southern Tuscany, Italy)
No full textStructural architecture, tectonic stacking and extensional reactivation of nappe contacts in the southern Middle Tuscan Ridge, Inner Northern Apennines orogenic belt (Italy)
No full textInterpreting tectonic stacking patterns and the nature of contacts between tectonic units is a major challenge in orogenic belts, particularly when mafic rock slices are embedded within the tectonic stack. These occurrences raise fundamental questions about their origin and the tectonic processes responsible for their emplacement. Such complexities, which characterize several orogenic belts worldwide, are especially prominent in the inner Northern Apennines orogenic belt (Italy). This belt is characterized by abrupt metamorphic discontinuities, local omissions of portions of the tectonic stack, significant stratigraphic gaps within individual tectonic units and contains discontinuous mafic bodies within the nappe pile. These features point to a polyphase tectonic evolution, which over the last decades has led to a range of hypotheses concerning the Neogene evolution of the inner Northern Apennines. Testing these models requires integrated structural, petrological, and stratigraphic investigations. This study presents structural, kinematic and stratigraphic data on detailed field mapping in the southern Middle Tuscan Ridge (southern Tuscany), a key area within the inner Northern Apennines. Our results document a polyphase extensional evolution characterised by the sequential development of normal faults during post-orogenic deformation (∼19–20 Ma). Based on this evidence, we propose an updated tectonic model that integrates the geometry, timing, and evolution of extensional structures in this part of the chain. The model refines the regional tectonic framework and provides a basis for further investigation into the metamorphic evolution, the chronology of tectonic events, and the origin of mafic bodies within continental units. On a broader scale, it offers a reference for interpreting post-collisional extensional settings in other orogenic belts worldwide
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