The initiation of the Mesoproterozoic Bylot basins (Nunavut, Arctic Canada) as recorded in the Nyeboe Formation, Fury and Hecla Group

ABSTRACT Reconstructing Precambrian sedimentary environments over broad cratonic regions often relies on a combination of facies, structural, and provenance analyses. The Mesoproterozoic (ca. 1270–1090 Ma) Fury and Hecla Group, exposed on the Melville Peninsula and northern Baffin Island (Nunavut, Canada), is considered broadly correlative with strata of the Borden, Hunting–Aston, and Thule basins (together referred to as the Bylot basins). We present the results of updated mapping and the first high-resolution sedimentologic and stratigraphic analysis of the lowermost unit in the Fury and Hecla Group, the Nyeboe Formation. The Nyeboe Formation comprises five distinct facies associations: alluvial to fluvial, eolian-backshore, marine-intertidal, marine foreshore to shoreface, and marine-offshore. Thin mafic units are interbedded within the marine shoreface facies and are interpreted to represent volcanic flows. Lateral relationships between facies associations are complex, but generally, facies associations transition from a terrestrial environment at the base to a nearshore marine environment at the top, indicating a transgression. Considering both the along-strike and -dip thickness trends, the presence of mafic volcanic rock units, and possible syndepositional fault orientations crosscutting the deposits, we infer that the Fury and Hecla Group was deposited in a regime of crustal thinning in a half-graben setting. Our results from the Nyeboe Formation suggest a lithostratigraphic correlation to the Nauyat and Adams Sound formations of the Borden Basin. Therefore, this study establishes a geodynamic link between the opening of the Fury and Hecla Basin to the other Bylot basins and contributes to the understanding of a large late Mesoproterozoic intracontinental-basin system.

Permian sporomorphs from upper Palaeozoic succession of Southern Tuscany (Italy): new constraints for the stratigraphy and palaeogeographic setting of the Tuscan Domain

<p>Recent biostratigraphic and sedimentological studies in the inner Northern Apennines (Italy) permit to refine the upper Palaeozoic successions of southern Tuscany, allowing new hypothesis to frame these formations in the palaeogeographic scenario inherited by the Variscan orogenesis. The Tuscan pre-Triassic successions, now exposed in the Monticiano-Roccastrada Unit, are generally barren or scarce in term of biomineralized fossiliferous content. They were mostly affected by HP-LT to LP-HT metamorphism that, together with their limited exposures, made difficult the stratigraphic correlations. This presentation is focused on three units (i.e. Falsacqua, Torrente Mersino and Carpineta formations) which age attribution and correlation were strongly debated. The Falsacqua Formation is mainly characterized by black to dark-grey phyllite, metasiltstone and metasandstone with dark metacarbonate intercalation. Due to the lack of biomineralized fossil content, by lithostratigraphic correlation with other Tuscan successions, this formation was referred to late Carboniferous-early Permian or Devonian. The Torrente Mersino Formation mainly consists of black to dark-grey quartz-phyllite, quartz metaconglomerate, light-grey quartzite, green phyllite and quartzite and light-grey phyllite. This formation is barren of fossil content and has been alternately assigned to Ordovician-Silurian, Silurian-Devonian, late Carboniferous-Permian and Triassic by lithostratigraphic correlation with other Tuscan and Sardinian successions. The Carpineta Formation is characterized by graphite-rich mudstones with carbonate-siltitic nodules. This unit was referred to the upper Visean-Serpukhovian based on its palaeontological content within the carbonate nodules. The first finding of a well-preserved microflora of middle Permian age in the Falsacqua and Torrente Mersino formations and of middle-late Permian age in the Carpineta Formation adds more constrains to the age attribution. This new age assignment permits to correlate the investigated Falsacqua and Torrente Mersino formations with the coeval ones belonging to southern Tuscany (i.e. Farma and Poggio al Carpino formations) and Elba Island (Rio Marina Formation) characterized by a similar microfloral content and to support a younger deposition of the Carpineta Formation than the Farma Formation one. Moreover, the occurrence of Gondwana-related sporomorphs in all the considered formations proposes a new palaeogeographic scenario for the northern Gondwana margin. Specifically, the present integrated study suggests that the northern margin of Gondwana fragmented through a series of transtensional phases. In this framework, the investigated upper Palaeozoic formations recorded marine siliciclastic sedimentation within either coeval pull-apart basins or laterally related facies of the same basin.</p><p><strong> </strong></p>

The Serbian Lake Pannon formations - their significance and interregional correlation

The problem of correlating Lake Pannon sediments across its basin has been the occupation of many geologists. At first, it was hampered by the prevalence of biostratigraphic, rather than lithostratigraphic correlation. The task became accomplishable when, thanks to seismic survey data, the strongly progradational character of Lake Pannon sedimentation had been understood. Thus, this paper aims to describe the formations from all parts of Lake Pannon and compare them to the ones described in Serbia. Material used includes published and unpublished data from all countries w ith Pannonian Basin System upper Miocene and lower Pliocene deposits, in the form of seismic, borehole and outcrop data. Even though the system is strongly asymmetric, both spatially and temporally, the formation synthesis framework should help better understanding among geologists operating w ithin the basin. For the first t ime the informal formations are proposed for all Lake Pannon sediments in Serbia. The formations are linked to a progradational deltaic system w ithin the following succession: basinal plain-turbidite-slope-delta front-delta plain-lacustrine and alluvial environments. The lithostratigraphic correlation has a huge potential in the context of industry. The main potential surely lies in petroleum geology, but it could be also very useful for exploration of geothermal energy, hydrogeology and construction materials.

Permian sporomorphs from upper Palaeozoic succession of Southern Tuscany (Italy): new constraints for the stratigraphy and palaeogeographic setting of the Tuscan Domain

<p>Recent biostratigraphic, sedimentological and petrological studies in the inner Northern Apennines (Italy) permit to refine the upper Palaeozoic successions of southern Tuscany, allowing new hypothesis to frame these formations in the Permian palaeogeographical scenario of the western Mediterranean domain. The Tuscan pre-Triassic deposits, belonging to the Monticiano-Roccastrada Unit, are generally barren or scarce in term of biomineralized fossiliferous content. They were mostly affected by HP-LT to LP-HT metamorphism that, together with the limited distribution of deposits, made difficult their stratigraphic correlation.</p><p>The present study is focused on two metamorphic units (i.e. Filladi e metacalcari di Fosso della Falsacqua Formation and Filladi e quarziti del Torrente Mersino Formation) which age attribution and correlation was strongly debated in the literature.</p><p>The Filladi e metacalcari di Fosso della Falsacqua Formation (minimum estimated thickness of about 150 m), cropping out in Monte Leoni area, is mainly characterized by black to dark-grey phyllite, metasiltstones and metasandstones with dark limestone intercalations. Due to the lack of biomineralized fossil content, by lithostratigraphic correlation with other formations cropping out in Tuscany, this formation was differently assigned to late Carboniferous-early Permian or Devonian.</p><p>The Filladi e quarziti del Torrente Mersino Formation (minimum estimated thickness of about 200 m) crops out in the Boccheggiano mining area and mainly consists of black to dark-grey quartz-phyllite, quartz metaconglomerates, light-grey quartzites, green phyllites and quartzites and light-grey phyllites. This formation resulted barren of fossil content and has been differently assigned to Ordovician-Silurian, Silurian-Devonian, late Carboniferous-Permian and Triassic by lithostratigraphic correlation with other Tuscan-Sardinian successions.</p><p>In the present study, the first finding of a middle Permian well-preserved microflora adds more constrains to the age attribution of these studied formations. This new age assignment permits to correlate the investigated formations with the coheval ones belonging to southern Tuscany (i.e. Farma Formation) and Elba Island (Rio Marina Formation) characterized by a similar microfloral content. Moreover, the occurrence of Gondwana-related sporomorphs, in all the studied formations, points to a new palaeogeographic scenario of the upper Palaeozoic successions from the northern Gondwana margin. The results of this integrated study inclines to consider the fragmentation of the northern margin of Gondwana as a result of several transtensional (pull-apart) basins where different laterally-related depositional environments leaded the sedimentation of these Tuscan middle Permian formations.</p>

Regional correlation of the Sonsela Member (Upper Triassic Chinle Formation) and detrital U-Pb zircon data from the Sonsela Sandstone bed near the Sonsela Buttes, northeastern Arizona, USA, support the presence of a distributive fluvial system

The Sonsela Sandstone bed was first named as an informal unit in the lower part of the Chinle Formation in northern Arizona, USA, and it was later assigned a type section near the Sonsela Buttes, where it is composed of two prominent sandstone units separated by a predominately siltstone unit. The Sonsela Sandstone bed has been correlated to a number of specific sandstones within the thicker, formal Sonsela Member at Petrified Forest National Park in northern Arizona. Here, we present the first detrital U-Pb zircon data for the Sonsela Sandstone bed at the Sonsela Buttes to hypothesize the maximum deposition age of that unit (216.6 ± 0.3 Ma) that are consistent with the proposed lithostratigraphic correlation with the fossiliferous Jasper Forest bed of the lower part of the Sonsela Member at the Park. These results are corroborated by previous high-resolution U-Pb dates and detrital zircon provenance studies from Petrified Forest National Park and similar sections in northern Arizona and western New Mexico, USA. The hypothesized chronostratigraphic correlation of these sandstones throughout northern Arizona permits the recognition of diachronous facies distributions in the lower part of the Chinle Formation as these coarse sediments prograded from the southwest into a continental basin already receiving finer-grained fluvial sediments from the southeast. The new age data corroborate the Norian age designation for the Sonsela Member (and the Sonsela Sandstone bed) and suggest that the Sonsela Sandstone bed at the Sonsela Buttes is within the Adamanian land vertebrate estimated holochronozone.