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Palaeobiogeography, palaeoecology, and sequence stratigraphy of the Upper Jurassic carbonate succession of the Lar Formation, central Alborz Zone, Iran

Saleh Zahra, Reháková Daniela

Geological Quarterly

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2023

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Vol. 67, No. 2

art. no. 15

EN

Foraminifera, ammonites, and calcareous dinoflagellates were used for stratigraphy and, together with microfacies, for the assessment of the palaeoenvironmental conditions of the Upper Jurassic deposits in the central Alborz Zone of northern Iran. The Lar Formation (Lar Fm.) in the Polur section is of latest Oxfordian to early Kimmeridgian age. The ammonite Subnebrodites planula and the calcareous dinoflagellate Colomisphaera nagyi have been introduced as new biomarkers of the lower Kimmeridgian in the central Neo-Tethys. The distribution of calcareous dinoflagellates reflects possible dispersal routes along a narrow seaway between the western Neo-Tethys and the Alborz Zone in the central Neo-Tethys. The Terebella-Crescentiella associations of the Lar Fm. represent a low-energy setting under dysoxic conditions in the Central Neo-Tethys Ocean. The benthic foraminiferal assemblages in this formation show a high dominance of infaunal taxa and r-selected strategists. This assemblage is reminiscent of eutrophic conditions and low oxygen levels in the lower part of the Lar Fm. Good preservation of the hexactinellid sponges in the upper part of the Lar Fm. also indicates an oxygen-minimum zone. Three third-order depositional sequences can be distinguished in the study area based on six microfacies. Depositional sequence 1 (DS1) is composed mainly of argillaceous limestone and medium- to thick-bedded limestone, corresponding to an outer ramp-to-middle ramp environment. Depositional sequence 2 (DS2) comprises breccia limestone and thick-bedded limestone facies in its lower part and thin-bedded limestone to massive limestone in its upper part. The breccia limestone facies may be associated with subaerial exposure and reworking of previously deposited sediment during a relative sea level fall. The thin-bedded limestone to massive limestone of DS2 consists mainly of bioclastic mudstone to wackestone (outer ramp). These represent an deep-water outer homoclinal ramp facies. Depositional sequence 3 (DS3) consists mainly of massive limestone to thick-bedded limestone with a bioclastic peloidal microbial Crescentiella packstone (middle ramp). The relative stratigraphic positions of DSs1–3 and sequence boundaries in the uppermost Oxfordian to lower Kimmeridgian of the Polur area show a fair match to the upper Oxfordian to lower Kimmeridgian sequences (JOx7, JOx8, JKi1 and JKi2) on the global sea level curve.

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The proposal of a GSSP for the Berriasian Stage (Cretaceous System): Part 1

Wimbledon William A.P., Reháková Daniela, Svobodová Andrea, Elbra Tiiu, Schnabl Petr, Pruner Petr, Šifnerová Krýstina, Kdýr Šimon, Dzyuba Oksana, Schnyder Johann, Galbrun Bruno, Košťák Martin, Vaňková Lucie, Copestake Philip, Hunt Christopher O., Riccardi Alberto, Poulton Terry P., Bulot Luc G., Frau Camille, De Lena Luis

Volumina Jurassica

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2020

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Vol. 18, no. 1

53--106

EN

Here in the first part of this publication we discuss the possibilities for the selection of a GSSP for the Berriasian Stage of the Cretaceous System, based on the established methods for correlation in the Tithonian/Berriasian interval. This will be followed, in the second part, by an account of the stratigraphic evidence that justifies the locality of Tré Maroua (Hautes-Alpes, SE France) as the proposed GSSP. Here we discuss the possibilities for correlation in the historical J/K boundary interval, and the evolution of thinking on the positioning of the boundary over recent generations, and in relation to research in the last ten years. The Tithonian/Berriasian boundary level is accepted as occurring within magnetosubzone M19n.2n. The detailed distribution of calpionellids has been recorded at numerous sites, tied to magnetostratigraphy, and the base of the calpionellid Alpina Zone is taken to define the base of the Berriasian Stage. This is at a level just below the distinctive reversed magnetic subzone M19n.1r (the so-called Brodno reversal). We discuss a wide range of magnetostratigraphic and biostratigraphic data from key localities globally, in the type Berriasian areas of France and wider regions (Le Chouet, Saint Bertrand, Puerto Escaño, Rio Argos, Bosso, Brodno, Kurovice, Theodosia etc.). The characteristic datums that typify the J/K boundary interval in Tethys and its extensions are detailed, and the correlative viability of various fossil groups is discussed. The boundary level is correlated to well-known J/K sections globally, and a series of secondary markers and proxies are indicated which assist wider correlation. Particularly significant are the primary basal Berriasian marker, the base of the Alpina Subzone (marked by dominance of small Calpionella alpina, Crassicollaria parvula and Tintinopsella carpathica) and secondary markers bracketing the base of the Calpionella Zone, notably the FOs of the calcareous nannofossil species Nannoconus wintereri (just below the boundary) and the FO of Nannoconus steinmannii minor (just above). Notable proxies for the boundary are: 1) the base of the A rctoteuthis tehamaensis Zone in boreal and subboreal regions, 2) the dated base of the Alpina Subzone at 140.22 ±0.14 Ma, which also gives a precise age estimate for the system boundary; and 3) the base of radiolarian “unitary zone” 14, which is situated just above the base of the Alpina Subzone.

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The proposal of a GSSP for the Berriasian Stage (Cretaceous System): Part 2

Wimbledon William A.P., Reháková Daniela, Svobodová Andrea, Elbra Tiiu, Schnabl Petr, Pruner Petr, Šifnerová Krýstina, Kdýr Šimon, Frau Camille, Schnyder Johann, Galbrun Bruno, Vaňková Lucie, Dzyuba Oksana, Copestake Philip, Hunt Christopher O., Riccardi Alberto, Poulton Terry P., Bulot Luc G., De Lena Luis

Volumina Jurassica

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2020

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Vol. 18, no. 2

121-160

EN

In part 1 of this work we discussed the possibilities for the selection of a GSSP for the Berriasian Stage of the Cretaceous System, based on prevailing practical methods for correlation in that J/K interval, traditional usage and the consensus over the best boundary markers that had developed in the last forty years. This consensus has developed further, based on the results of multidisciplinary studies on numerous sites over the last decade. Here in Part 2 we give an account of the application of those results by the Berriasian Working Group (ISCS), and present the stratigraphic evidence that justifies the selection of the locality of Tré Maroua (Hautes-Alpes, SE France) as the proposed GSSP. We describe a 45 m-thick section in the Calcaires Blancs vocontiens – that part of the formation covering the calpionellid Chitinoidella, Remanei. Intermedia, Colomi, Alpina, Ferasini, Elliptica and Simplex biozones. The stratigraphic data collected here has been compiled as part of a wider comparative study of complementary Vocontian Basin sites (with localities at Charens, St Bertrand, Belvedere and Le Chouet). Evidence from Tré Maroua thus sits in this substantial regional biostratigraphic and magnetostratigraphic context. For the purposes of the GSSP definition, here we particularly concentrate on the unbroken sequence and biotic markers in the interval immediately below the boundary, the Colomi Subzone (covering circa 675,000 years), and immediately above, the Alpina Subzone (covering circa 725,000 years). Particularly significant fossil datums identified in the Tré Maroua profile are the primary basal Berriasian marker, the base of the Alpina Subzone (a widespread event marked by dominance of small Calpionella alpina, with rare Crassicollaria parvula and Tintinopsella carpathica): the base of the Berriasian Stage is placed at the base of bed 14, which coincides with the base of the Alpina Subzone. Secondary markers bracketing the base of the Calpionella Zone are the FOs of the calcareous nannofossil species Nannoconus wintereri, close below the boundary, and the FO of Nannoconus steinmannii minor, close above. The Tithonian/Berriasian boundary level occurs within M19n.2n, in common with many documented sites, and is just below the distinctive reversed magnetic subzone M19n.1r (the so-called Brodno reversal). We present data which is congruent with magnetostratigraphic and biostratigraphic data from other key localities in France and in wider regions (Le Chouet, Saint Bertrand, Puerto Escaño, Rio Argos, Bosso, Brodno, Kurovice, Theodosia…), and thus the characteristics and datums identified at Tré Maroua are key for correlation and, in general, they typify the J/K boundary interval in Tethys and connected seas

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Middle to Late Jurassic carbonate-biosiliceous sedimentation and palaeoenvironment in the Tethyan Fatricum Domain, Krížna Nappe, Tatra Mts, Western Carpathians

Jach Renata, Reháková Daniela

Annales Societatis Geologorum Poloniae

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2019

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Vol. 89, No. 1

1--46

EN

The Jurassic of the Alpine-Mediterranean Tethys was characterized by the formation of several interconnected basins, which underwent gradual deepening and oceanization. Sedimentation in each basin was influenced by a specific set of interrelated factors, such as tectonic activity, seawater circulation, climate, chemistry and trophic state of seawater as well as evolutionary changes of the marine biota. This paper deals with the Fatricum Domain (Central Carpathians, Poland and Slovakia), which in the Jurassic was a pull-apart basin on a thinned continental crust. The sedimentation history of this domain during the Bajocian-Tithonian and its governing factors have been revealed. Facies analysis of the Bajocian-Oxfordian deposits evidences considerable relief of the basin-floor topography. Deposits in the Western Tatra Mts represent sedimentation on a submarine intrabasinal high, whereas the coeval deposits of the eastern part of the Tatra Mts accumulated in a deeper basin. The basin succession began with Bajocian bioturbated “spotted” limestones and siliciclastic mudstones (Fleckenmergel facies). These were succeeded by uppermost Bajocian - middle Bathonian grey nodular limestones, affected by synsedimentary gravitational bulk creep. The coeval deposits of the intrabasinal high are represented by well-washed Bositra-crinoidal limestones with condensed horizons. Uniform radiolarite sedimentation commenced in the late Bathonian and persisted until the early late Kimmeridgian. The basal ribbon radiolarites (upper Bathonian - lower Oxfordian), which consist of alternating chert beds and shale partings, are a record of seawater eutrophication, a related crisis in carbonate production and the rise of the CCD, which collectively resulted in biosiliceous sedimentation. The overlying calcareous radiolarites (middle Oxfordian - lowermost upper Kimmeridgian) marked a gradual return to carbonate sedimentation. The return of conditions that were favourable for carbonate sedimentation took place in the late Kimmeridgian, when the red nodular limestones were deposited. They are partly replaced by basinal platy limestones (uppermost Kimmeridgian - Tithonian) in the Western Tatra Mts. This lateral variation in facies reflects a change in the sedimentary conditions governed by a bathymetric reversal of the seafloor configuration, attributed to a further stage in the pull-apart transcurrent tectonics of the Fatricum Domain.