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Carnets Geol., Article, vol. 24, no. 05

Bruno R.C. Granier & Philippe Lapointe.- The Kalkowski Project - Chapter VI. A panorama of synsedimentary broken ooids.- Broken ooids are known to occur in both aragonitic and calcitic ooids with radial fabrics. In the literature, it has been suggested that synsedimentary breakage could be related to attrition/mechanical impacts, hypersalinity, or desiccation. However, this paper demonstrates that none of the aforementioned phenomena provides a valid explanation. Although the exact process remains unknown (potentially involving some synsedimentary recrystallization), it is shown that: 1) the breakage is genetically linked to the radial fabrics; 2) the ratio of ooid breakages increases with the relative thickness of the radial cortical layers; 3) fracture growth in broken ooids proceeds centripetally.
Thu, 29 Feb 2024 17:53:56 GMT

Carnets Geol., Article, vol. 24, no. 04

Artur Artur, Gabriella da C. Pereira, Paulo R. de O. Costa & Mercedes Okumura.- A new record of ground sloth in the Ribeira de Iguape valley, southeastern Brazil.- In the early 1980s, an assemblage of extinct and extant vertebrates was collected from the Abismo Ponta de Flecha, a vertical cave in southern São Paulo, Brazil, for archaeological, geological, and paleontological analyses. While materials identified as ground sloths have been referenced in earlier publications, they have never been thoroughly described. In this study, we provide the first detailed description of a large, previously unidentified taxon found in Brazil, interpreted herein as belonging to the family Nothrotheriidae. Although direct dating of the specimen was not possible, other dated occurrences from the Ribeira de Iguape Valley suggest that it may have inhabited the region during the Late Pleistocene, coinciding with the local presence of a dense forest cover.
Wed, 31 Jan 2024 17:53:18 GMT

Carnets Geol., Article, vol. 24, no. 03

Bruno R.C. Granier & Philippe Lapointe.- The Kalkowsky Project - Chapter V. Asymmetric ooids from the Yacoraite Formation (Argentina).- Asymmetric ooids are documented in a brackish Maastrichtian to Danian paleolake in NW Argentina. Their distinctive asymmetric growth pattern is likely related to an uneven distribution of the Extracellular Polymeric Substances (EPS) around the coated allochem, within which calcite fibers (i.e., the 'fibrite') have grown. This pattern is unlikely to be mistaken for that of other 'eccentric' ooids, such as wobbly ooids, spiny ooids, hiatus ooids, half-moon ooids, 'broken' ooids sensu lato, or collapsed oomolds (referred to as 'distorted' ooids).
Sat, 20 Jan 2024 18:19:36 GMT

Carnets Geol., Article, vol. 24, no. 02

Ricardo L.M. Azevedo, Rogério L. Antunes, Mauro D.R. Bruno, Thomas R. Fairchild & Dimas Dias-Brito.- The Central South Atlantic: The origin of its waters, its evolution and effects beyond.- The primitive sea that occupied the Central South Atlantic (CSA), part of the intra-Gondwana rift during the Early Cretaceous, allowed precipitation of an extensive and thick layer of evaporites, the Ibura Salt, followed by the deposition of a prominent Albian carbonate package. Although the shallow platform facies do not contain classical benthic Tethys markers, the pelagic open sea carbonates are essentially dominated by planktonic elements coming from the Tethys Realm. This condition led some researchers to think that Tethys waters also contributed to salt formation, an idea that clashes with the geotectonic model of northward separation of Africa and South America and ingression of predominantly Austral marine waters. Now, a new controversy arises as to the age of this salt layer when trying to position bio-events and lithological and chemostratigraphic markers from these rocks with respect to established data for the Global Boundary Stratotype Section and Point for the Aptian/Albian boundary (GSSP-Alb). Biochronostratigraphic information on planktonic foraminifera points to an Aptian age as opposed to the earliest Albian traditionally accepted for the carbonate section that overlies the giant salt layer. On the other hand, stratigraphic and geochronological data suggest an age of 113 Ma for the base of the salt, very near to the 113.2 ± 0.1 Ma arbitrated for the GSSP-Alb. In this study, we adopt the base of the evaporite bed as the Aptian/Albian boundary in the CSA, Equatorial South Atlantic (ESA), and northeastern Brazilian interior basins (BNE) as well. Based on these criteria, a broad review and the integration of available information have led to new interpretations regarding the earliest phase of these segments of the South Atlantic and adjacent areas. Initially, during the Aptian-Albian transition, an ephemeral interior sea within Brazil, drawing its waters from the north, would have contributed to salt deposition in the intra-Gondwana rift (evaporitic stage of the CSA). Afterward, but still within the earliest Albian, the evaporitic system evolved into a carbonate gulf when the northern barrier, the Exception Zone (EZ), disappeared. The lagoonal circulation pattern that then formed in the CSA created a hypersaline and warm outflow plume that swept across the marine bottom of the ESA and part of the Tethys Sea. Paleoceanographic events registered at Site 545, Mazagan Plateau, support this new hypothesis and illustrate the potential complexity of correlation of organic-rich deposits in which local influences have been greater than global ones. This long, narrow, and continuous carbonate gulf disappeared at the end of the Albian with the arrival of southern waters from the Meridional South Atlantic (MSA), and the South Atlantic became consolidated as a proto-ocean.
Sat, 20 Jan 2024 18:17:18 GMT

Carnets Geol., Article, vol. 24, no. 01

Hanane Bahaj, Nadia Barhoun, Naima Bachiri Taoufiq, Jihad Rahmouna, Soukaina Targhi, Naima Berry, Jean-Pierre Suc & Speranta-Maria Popescu.- Paleoenvironmental changes preceding the onset of the Messinian salinity crisis in the western Mediterranean Sea (pre-evaporitic Messinian of the Melilla-Nador Basin, NE Morocco).- In order to contribute to the understanding of the evolution of marine and continental environments, preceding the onset of the Messinian salinity crisis in the western Mediterranean, we conducted an integrated study of the pre-evaporitic Messinian sedimentary series in the Melilla-Nador basin. Three sections have been carried out in the marl-diatomite series and were the subject of a detailed biostratigraphic and palynological study. The study of planktonic foraminifera, pollen, dinocysts, and palynofacies allowed us to characterize the evolution of these environments. From 6.83 to 6.52 Ma, the marine environment was relatively open, calm, probably subject to the action of upwellings and received periodic continental inputs. Starting 6.52 Ma, the abundance and diversity of planktonic foraminifera decreased. Continental inputs gradually dominate, alternating with marine ones, and reflecting a succession between proximal and distal neritic environments. The surface water conditions were warm. After 6.35 Ma, began the degradation of marine conditions. The continental environment shows an open vegetal landscape dominated by herbaceous plants, reflecting a tropical to arid subtropical climate, slightly less dry than that of the South Rifian Corridor. This study confirms the existence of several parameters that contributed to the deposition of the cyclical marl-diatomite series: on the one hand, the hot and dry climate favored the reduction of the plant landscape and therefore erosion (continental inputs); on the other, the tectonics (volcanism and uplift).
Wed, 17 Jan 2024 18:13:15 GMT

Carnets Geol., Article, vol. 23, no. 09

Bruno Granier, Seyedeh Saeideh Mortazavi, Morteza Taherpour-Khalil-Abad & Farokh Ghaemi.- Chapter 1 - Preliminary investigations on the Zard Formation at its type locality (North Khorasan Province, Iran).- This chapter presents a revision of the Zard Formation in its type area, i.e., in the North Khorasan Province (Iran), including at its type locality. It comprises a description of the sedimentological and micropaleontological criteria that permit it to be distinguished from the Mozduran Formation (below) and the Tirgan Formation (above). At its type locality, its lower boundary is a heavily bored surface. Actually, both contacts with the framing formations correspond to transgressive surfaces, which imply that this lithostratigraphic unit is an Unconformity-Bounded Unit. With respect to biostratigraphy, this formation contains a few second-order markers: Holosporella sugdeni, Kopetdagaria sphaerica, and Torinosuella peneropliformis, which are also found in the unit above, i.e., in the Tirgan Formation. Because the latter contains markers that first appear in the Barremian: Bakalovaella elitzae, Pseudoactinoporella iranica, and Balkhania balkhanica, but also Montseciella arabica, the total range of which spans the Upper Barremian, the Zard Formation (i.e., the Zardian regional stage) should partly covers the Hauterivian to Barremian interval. Finally, although it cannot be definitely excluded that the lowermost part of the Zard Formation could be Valanginian in age, this option still requires proper documentation.- DOI:
Sun, 10 Sep 2023 01:22:59 GMT

Carnets Geol., Article, vol. 23, no. 08

Simon F. Mitchell.- A new pseudolepidinid foraminifer, Hanovolepidina browni gen. nov. sp. nov., from the middle Eocene (mid-Lutetian) of Jamaica and its significance.- The new larger benthic foraminifer, Hanovolepidina browni gen. nov. sp. nov., is described from the Chapelton Formation (mid-Lutetian, middle Eocene, ABZ7) of Jamaica. The genus shows the characteristic transition from a single to double equatorial layer about mid-way across the radius as seen in axial sections that characterises the family Pseudolepidinidae. Equatorial sections show the embryo followed by 4 or 5 spiral rotaliid chambers with the last chamber giving rise to a primary spiral and secondary (counter-) spiral of equatorial chambers. The presence of a long rotaliid stage suggests a more primitive form that Pseudolepidina, and Hanovolepidina gen. nov. differs also from the latter in lacking the extra principal accessory chamber seen in axial section. Hanovolepidina gen. nov. is provisionally suggested as an ancestor of the late Eocene Triplalepidina. The new discovery demonstrates a greater diversity of the family Pseudolpeidinidae in the Caribbean that previously recorded, although occurrences of this family are very restricted stratigraphically suggesting that it may appear in the region due to migration events.- DOI:
Sun, 27 Aug 2023 01:19:09 GMT

Carnets Geol., Article, vol. 23, no. 07

Bruno R.C. Granier, Serge Ferry & Mohamed Benzaggagh.- Hiatuses and redeposits in the Tithonian-Berriasian transition at Le Chouet (Les Près, La Drôme, SE France): Sedimentological and biostratigraphical implications.- Our new study of the Tithonian and lower Berriasian succession of Le Chouet (Les Près, La Drôme, France) better characterizes the lithological succession, the macro- and microfacies, and the stratigraphic ranges of some microfossils mostly calibrated on the calpionellid biozonation. On the lithological side, the Tithonian strata are dominantly characterized by thick-bedded breccias representing debris flows and related calciturbidites whereas the Berriasian strata are typically white limestones that also comprises scattered intercalations of thin-bedded breccias and calciturbitides (including cryptic mud calciturbidites). In thin sections, these white limestones display mud- to wackestone textures and their allochems are mostly tiny bioclasts (e.g., radiolarians, calpionellids, saccocomids). Breccias are lithoclastic rudstones and/or floatstones with a matrix similar to the calciturbidites. Their lithoclasts are either extraclasts sensu stricto (i.e., material derived from updip shallow-water areas) or pseudointraclasts, representing reworked subautochthonous material (i.e., mud- and wackestone lithoclasts with radiolarians, saccocomids and/or calpionellids). In addition to the erosional features observed at the bases of the gravity flows, these pseudointraclasts document the intensity of submarine erosion. Locally they help to estimate the depths of erosion updip of the deposit. A number of bioclasts are reworked from updip shallow-water areas; among them, it is worth mentioning the foraminifer Protopeneroplis ultragranulata (Gorbatchik), the first occurrence of which is dated to late early Tithonian. Saccocomids are part of the dominating pelagic biota reported from the lower and lower upper Tithonian interval whereas calpionellids replace them in the uppermost Tithonian to lower Berriasian interval. Intervals with saccocomids characteristic of zones 4-5 and zones 6-7 are respectively ascribed here to the lower Tithonian (4-5) and pro parte to the upper Tithonian (6-7). The biozonation of the calpionellid group sensu lato allows identification of the Boneti Subzone of the chitinoidellids, the Crassicollaria Zone with its four subzones (A0-A3), and the Alpina Zone with its first subzone (B1). On the basis of biostratigraphical and sedimentological data (including the rates of sedimentation), most zonal boundaries are located at the erosional bases of breccia or turbidite layers and thus coincide with hiatuses.- DOI:
Tue, 27 Jun 2023 01:15:38 GMT

Carnets Geol., Article, vol. 23, no. 06

Hamed Yarahmadzahi & Daniel Vachard.- Gzhelian (latest Carboniferous) Pseudoacutella partoazari foraminiferal assemblage from the Tabas Block (Central Iran).- A foraminiferal assemblage is reported from the Zaladou Formation in the Tabas Block (Shishtu Section), Central Iran. This assemblage comprises 16 species belonging to 14 genera, and encompasses the fusulinids Pseudoacutella partoazari, Grovesella tabasensis, Gr. aff. australis, Gr. sphaerica, Gr. sphaerica var. quadrata, Gr. cf. staffelloides, Schubertina sp., Schubertella sp., and the smaller foraminifers Eotuberitina sp., Lasiodiscus tenuis, Raphconilia cf. minor, R. multihelicis, R. modificata, Tetrataxis cf. parviconica, Globivalvulina ex gr. bulloides, Gl. graeca, Calcivertella heathi, Tansillites sp., Palaeonubecularia? sp., Hemigordiellina sp., Nodosinelloides longa, and N. longissima. The age of this assemblage is considered to be Gzhelian. The assemblage is dominated by the fusulinid Pseudoacutella partoazari with a low total diversity of smaller foraminifers. This assemblage is compared to similar assemblages in other parts of Iran and well as the USA. An evolutionary lineage of Pseudoacutella partoazari is also proposed. It is confirmed that Pseudonovella differs from Pseudoacutella by the periphery rounded-carinate (carinate in Pseudoacutella), pseudochomata less developed, and the type of coiling (Pseudoacutella is truly planispiral involute). Pseudonovella is suggested here as the ancestor of Pseudoacutella. This assemblage bears one unusual attribute, the overwhelming dominance of the fusulinid Pseudoacutella and the relatively low total diversity, compared with similar foraminifera from Alborz, Sanandaj-Sirjan, Sabzevar and central Iran, which present warm and humid conditions during the Late Carboniferous.- DOI:
Fri, 30 Jun 2023 01:12:44 GMT

Carnets Geol., Article, vol. 23, no. 05

Olev Vinn & İzzet Hoşgör.- The first record of Middle Jurassic serpulids from SE Turkey, equatorial Tethys.- The Jurassic platform margin succession in the Hezan area, called the "Hezan Unit" (Diyarbakır), on the north of the Arabian platform in southeastern Turkey includes five formations of carbonate-dominated rocks. The most interesting is the upper part of the Hezan unit (the Kuran Formation) that contains unique layers of oolitic and clayey limestone. A first record of the calcareous polychaete tubeworm Propomatoceros lumbricalis is described from the Middle Jurassic lower part of the Kuran Formation of the Hezan area. Most knowledge of fossil serpulids is centered on European material, and little has been done on Middle East fossil calcareous tubes. The taxonomic information recorded as a result of this study will add to our understanding of the biogeographic history of the Middle Jurassic calcareous polychaete associations and help to interpret the structure and paleoecology of its marine communities.- DOI:
Fri, 30 Jun 2023 01:10:55 GMT

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