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Fluvial architecture element analysis of the Brushy Basin Member, Morrison Formation, western Colorado, USA

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Galli K.

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tom Vol. 12, no. 2

69--106

EN

The 85-m Brushy Basin Member of the Morrison Formation in western Colorado, USA, comprises dinosaur-bearing sandstones (architectural element CHR and CH), crevasse-splay deposits and minor levee deposits (architectural element CS), mudstones, marlstones, altered ash beds and minor limestones as well as caliche paleosols and noncalcareous paleosols (architectural element FF). Channel sandstones occur at five stratigraphic levels at Trail Through Time (TT), eleven levels at Fruita Paleontological Research Area (FP), and at five levels at Echo Canyon (EC). River-channel sandstones hosted by floodplain mudstones tend to have cut down to resistant caliche paleosols. Depositional facies and architectural element analysis show that the rivers were low gradient, mainly anastomosing, with perennial flow, but seasonal with “flashy” peaks in discharge. Dinosaur bone accumulations are found in some floodplain ponds. Isolated bones are present in anastomosing channel sandstones at TT and in channel sandstone 2 at EC. At FP, major accumulations of bones were rapidly buried in the deep pools at three bends in the meandering river resulting in the formation of channel sandstone 2. There is no evidence for a large lacustrine or playa system at the three localities.

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Lower Kimmeridgian facies and sedimentary succession of a shallow-water coated-grain-dominated carbonate ramp of the northern peri-Tethyan shelf : an example from the Radomsko Folds (central Poland)

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Olchowy P. , Krajewski M.

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tom Vol. 64, No. 4

969--987

EN

An Upper Jurassic succession is exposed in the active Rogaszyn Quarry (Kodrąb area) located in the Radomsko Folds structure (central Poland). Six facies types were distinguished, comprising oolitic, oncolitic, biodetrital and pelitic limestones as well as marls and marly clays. Typical lithologies are limestones with coated grains deposited in shallow-water, fore-shoal, shoal and lagoonal parts of a carbonate ramp. Three types of ooid and three types of oncoid were identified, which display several shapes and sizes, and a complex structure of cortices. The ooid types show micritic, radial-fibrous and mixed, micritic/radial-fibrous cortices. Type 1 oncoids comprise micritic or bioclastic nuclei enveloped by non-laminated or laminated micritic cortices. Type 2 oncoids are composed of micritic or bioclastic nuclei and laminated, fossil-bearing cortices covered by microbial envelopes. Type 3 oncoids are the largest of the oncoids observed, attaining cm-scale dimensions. These oncoids are formed of a Bacinella-dominated meshwork incorporating smaller ooids and oncoids, or they have bioclastic or micritic nuclei covered by complex cortices with micritic, laminated, fossil-bearing, Bacinella-dominated fabric and microbial envelopes. Boundaries between the specific types of cortical envelopes are usually sharp and accentuated by organic encrustations, elongated bioclasts or borings. Commonly found are chambers of the ichnogenus Entobia representing the boring traces of carbonate-excavating sponges and the cryptoendolithic foraminifer Troglotella incrustants. The complex cortices indicate different growth stages of oncoids at different conditions of currents and microbial activity. Carbonate deposition was accompanied by mixed siliciclastic-carbonate sedimentation resulting in multiple intercalated layers of marls and pelitic limestones as well as marly clays. The deposits exposed in the Rogaszyn Quarry as well as in the Kodrąb area are compared with the neighbouring Upper Jurassic deposits of the Szczerców area and the Sw margin of the Holy Cross Mts. (both central Poland). The successions from the Kodrąb area are generally similar to the Lower Kimmeridgian sequences known from adjacent areas, but with locally observed facies variability.

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High-resolution cyclostratigraphic analysis of magnetic susceptibility record from a Kimmeridgian alternating marl-limestone succession (La Méouge, Vocontian Basin, France)

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Boulila S. , Galbrun B. , Collin P.-Y. , Collin P.-Y. , Schnyder J.

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tom Vol. 4, no. 1

149-150

EN

The Kimmeridgian deep-water sediments of La Méouge section (South East Basin of France) show alternating marl-limestone successions. The limestone beds are mudstones or wackstones with benthic foraminifera, radiolarians and filaments which are characteristic of the pelagic realm (Colombié & Strasser 2003). We studied a 43 m thick well exposed interval of mainly Early Kimmeridgian (De Rafélis 2000). Cyclostratigraphic studies of marl-limestone alternations are commonly based on measuring the thickness of beds and bundles and counting their number to extract sedimentary cyclicities. By using high resolutions magnetic susceptibility (MS) measurements, we developed a methodology for detecting and quantifing sedimentary cyclicities recorded in this kind of facies. To perform high-resolution MS measurements, the sampling interval was fixed at nearly 7 cm. All the samples were measured with a Kappabridge KLY-2 susceptometer. The MS variations follow a net cyclic pattern (high and low frequencies). Spectral analysis of MS data show evidence of about all range of Milankovitch cyclicities (precession, obliquity, 100 ky and 400 ky-eccentricity) as demonstrated by the frequencies” ratios methodology and tuning technique. For this latter, we tuned MS data to 405 ky-eccentricity of astronomical solutions (Laskar et al. 2004). Moreover, we found highly significant periods of climatic precession not only in the original MS record but also in the tuned MS. Evolutive harmonic analysis (Maurer et al. 2004) was performed to examine the persistence of the Milankovitch properties throughout the whole section and the possible variations of sedimentation rate. Specifically, the two high peaks, seen in power spectra domain representing the short and the long precession, are characterized in amplitude spectrogram domain by obvious continuous lines, particularly the latter. This means that the precession cycles have much larger amplitudes than the other recognized cycles and are persistent too throughout the entire section. Furthermore, we noted that the long precession cycles show a sudden change in sedimentation rate occurring in the lower part of Lothari ammonite Subzone where the sedimentation rate shifted roughly from 2 to 3 cm/ky. This study proved that MS is a very useful tool for cyclostratigraphic analysis of Mesozoic sections, particularly in alternating marl-limestone successions, and it is also a powerful proxy to detect and estimate possible variations in sedimentation rate.

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New stratigraphic and isotope data on the Kimmeridgian-Volgian boundarybeds of the Subpolar Urals, Western Siberia

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Rogov M. A. , Price G. D.

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tom Vol. 54, No 1

33-40

EN

A review and new data regarding the ammonite faunas and biostratigraphy of the uppermost Kimmeridgian-lowermost Volgian of theSubpolar Urals are presented. The combined ranges of almost all ammonite genera in the lowermost Volgian of the Subpolar Urals supports the traditional point of view regarding the equivalence of the Magnum Zone with the two lowermost Bolonian Zones and with thebulk of the Klimovi Zone. This stratigraphic interpretation permits the stable isotope data (carbon and oxygen) derived from associatedbelemnites to be presented in context. The isotopic records from the belemnites suggest that the lower Volgian sediments of the YatriaRiver, Subpolar Ural Mountains were deposited in a warm marine environment consistent with a warm high latitude scenario. If reducedsalinites are invoked apparent temperatures are lowered by ~5°C, but still remain well above freezing and are relatively warm comparedto some recent modelled estimates of Late Jurassic ocean temperatures.

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Comments on the identification of Ammonites planula Hehl in Zieten, 1830 (Upper Jurassic, SW Germany)

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Schweigert G. , Kuschel H.

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tom Vol. 15, no 1

1--16

EN

Ammonites planula Hehl in Zieten, 1830 is the type species of the Late Jurassic ammonite genus Subnebrodites Spath, 1925 and the index species of the well-established Planula Zone of the Submediterranean Province. Recently, Enay and Howarth (2017) classified this stratigraphically important ammonite species as a ʻnomen dubiumʼ and considered it to be the possible macroconch counterpart of Idoceras balderum (Oppel, 1863). These authors claimed “Subnebrodites planula Spath, 1925” instead of Ammonites planula (Hehl in Zieten, 1830) to be the type species of Subnebrodites. However, their nomenclatorial acts are based on erroneous assumptions. For future taxonomic stability we here propose a neotype for Ammonites planula (Hehl in Zieten, 1830) and a lectotype for Ammonites planula gigas Quenstedt, 1888. In addition, dimorphism within the stratigraphically much younger Idoceras balderum (Oppel) is demonstrated showing that there is no morphological resemblance and no closer relationship with Ammonites planula (Hehl in Zieten, 1830).

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Development and chronology of the Late Jurassic shallow-water carbonate deposits of the Holy Cross Mountains area, central Poland

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Wierzbowski A.

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2023

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tom Vol. 21

39--82

EN

The Late Jurassic shallow-water carbonates with intervening clayey-marly deeper-water deposits in the Holy Cross Mts. area formed over large bank of the elevated part of the Northern Tethyan Shelf during about 12 myr. They comprise three main successions (I, II and III) deposited partly in different environmental conditions, controlled by tectonic and climatic factors, and still preserved in the north-eastern margin, the north-western margin and the south-western margin of the Holy Cross Mountains. The history of sedimentation is presented according to the concept of the large tectono-stratigraphic units COK, LUK and KVB, which owe their origin to variable rates of tectonic subsidence, as introduced by Kutek (1994) for the area of central Poland. The studied deposits of the COK megasequence cor- responding to the Upper Oxfordian and the Lower Kimmeridgian up to the Hypselocyclum Zone consist of coral limestones, various grained (including oolitic) limestones, and micritic limestones formed over the gradually enlarging shallow-water carbonate platform of the Holy Cross Mts. This platform was subsequently subdivided into two elevated areas, separated by a depressed zone in the middle, bounded by the Nowe Miasto–Iłża–Bałtów Fault Zone in the north-east and the Holy Cross Fault System in the south. The younger mega- sequence LUK with it strongly transgressive character marks the successive stages of the marine transgression which entered the central, lowered part of the area of the Holy Cross Mts. from the west, where it appeared already in the early Hypselocyclum Chron. It succes- sively spread across the Holy Cross Mts. area towards the north-east and south bringing everywhere the deposition of various oyster lu- machelles and marls with ammonites at the end of the Hypselocyclum Chron and during the Divisum Chron of the Early Kimmeridgian to the Acanthicum/Mutabilis Chron of the earliest Late Kimmeridgian. The following megasequence KVB is represented by the detrital lu- machelles and chalky limestones with nereineids of the Eudoxus Chron of the Late Kimmeridgian marking the development of still younger shallow-water carbonate platform in the uplifted areas in the north-eastern and possibly the south-western margins of the moun- tains, allegedly subdivided by a deeper area of sedimentation of marly deposits. The youngest Late Jurassic deposits of the Holy Cross Mts., are very fragmentarily preserved, mostly because of Early Cretaceous uplift and erosion. They suggest an initial episode of complete drowning of the carbonate platform which became covered by marly deposits during the Early Tithonian, and the subsequent restoration of shallow-water carbonate sedimentation at the end of the Early Tithonian.

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The succession of ammonites of the genus Amoeboceras in the Upper Oxfordian – Kimmeridgian of the Nordvik section in northern Siberia

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Rogov M. , Wierzbowski A.

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tom Vol. 7, no. 1

147-156

EN

A collection of ammonites of the genus Amoeboceras located carefully in the section of Nordvik Peninsula in northern Siberia has enabled recognition of the standard Boreal ammonite zones of the Upper Oxfordian and Kimmeridgian. The recognition of the standard Amoeboceras zones, well known in NW Europe and the Barents Sea area, in northern Siberia indicates the uniform character of the Late Oxfordian and Kimmeridgian ammonite faunas across the whole Boreal Province. Some comments on the occurrence of Boreal oppeliids of the genus Suboxydiscites in the studied section are also given.