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The bivalve Cuneamya from the Late Ordovician of Bohemia

Abstract

The bivalve species Cuneamya catilloides from the Late Ordovician of Bohemia, previously assigned to the genus Grammysia, is revised. Cuneamya catilloides is an important element of the Modiolopsis Community Group in the Letná Formation. The genus Grammysia very probably does not occur in the Ordovician of Bohemia and is restricted to the Silurian and Devonian strata. Cuneamya catilloides with strong commarginal costae was probably an infaunal filter feeder. Cuneamya is a cosmopolitan genus, occurring on Avalonia, Baltica, Laurentia, Perunica and West Gondwana.

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The calcareous nannofossils and magnetostratigraphic results from the Upper Tithonian–Berriasian of Feodosiya region (Eastern Crimea)

Abstract

This article is concerned with nannofossil study of Tithonian–Berriasian sediments of Eastern Crimea. The NJT 16, NJT 17a, NJT 17b, NKT, and NK 1 nannofossil zones were determined. The occurrence of Nannoconus kamptneri minor, one of the potential marker-types of the Tithonian–Berriasian boundary (the base of the NKT Zone) of the Tethyan sequence in the Feodosiyan section is assigned here to the Pseudosubplanites grandis ammonite Subzone and the magnetic Chron M18n. The base of the NKT Zone is closer to the Grandis Subzone base than to the base of the Jacobi Subzone. Contradictions in the interpretation of magnetic chrons obtained by the present authors (Arkadiev et al. 2018) and by Bakhmutov et al. (2018) might be caused by mistakes admitted in the latter work on the compiled section.

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Cambrian hyoliths of the Příbram-Jince Basin (Barrandian area, the Czech Republic): A review of recorded taxa

Abstract

Hyoliths recorded from the middle Cambrian Jince Formation of the Barrandian area in the Czech Republic are reviewed and listed, based on various published papers printed since 1854. Up to now, only five species of hyolithids and three species of orthothecids have been reported, classified within seven genera. The reported material was collected from more than twenty small occasional outcrops and/or sections measuring up to several tens of meters in thickness, all situated exclusively in the area between the villages Felbabka and Čenkov in the Litavka River Valley. From the Paseky Shale member of the Holšiny-Hořice Formation at the Medalův mlýn locality, the first hyolith classified as “Hyolith genus and species indeterminate” is described. The new study of two specimens described and figured by Barrande in 1867 as Hyolithes primus made it possible to classify them as Jincelites vogeli and Jincelites sp. respectively.

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Cenoceras islands’ in the Blue Lias Formation (Lower Jurassic) of West Somerset, UK: nautilid dominance and influence on benthic faunas

Abstract

Substantial numbers of the nautilid Cenoceras occur in a stratigraphically limited horizon within the upper part of the Lower Jurassic (Sinemurian Stage) Blue Lias Formation at Watchet on the West Somerset Coast (United Kingdom). Individual nautilid conchs are associated with clusters of encrusting organisms (sclerobionts) forming ‘islands’ that may have been raised slightly above the surrounding substrate. Despite the relatively large numbers of nautilid conchs involved, detailed investigation of their preservation suggests that their accumulation reflects a reduction in sedimentation rates rather than an influx of empty conches or moribund animals. Throughout those horizons in which nautilids are present in relative abundance, the remains of ammonites are subordinate or rare. The reason for this unclear, and preferential dissolution of ammonite conchs during their burial does seem to provide a satisfactory solution to the problem.

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Conch structures, soft-tissue imprints and taphonomy of the Middle Ordovician cephalopod Tragoceras falcatum from Estonia

Abstract

Tragoceras falcatum (Schlotheim, 1820) is a common, loosely coiled estonioceratid (Tarphycerida, Cephalopoda) occurring in the Kunda Regional Stage (early Darriwilian, Middle Ordovician) of Estonia. Although the species is quite well-known, we document some features for the first time. For example, one specimen from the Harku quarry (Estonia) with a phosphatized replacement shell exhibits growth halts (megastriae) on the body chamber. As they are not preserved in smaller specimens, we suggest that these megastriae formed at the approach of maturity, possibly also reflecting sexual dimorphism and cycles of reproduction (iteroparity?). Additionally, the specimen shows minute soft-tissue imprints (drag bands and pseudosutures). These imprints are comparable to patterns in other cephalopods such as ammonoids, bactritids and other nautiloids, but have not yet been reported from Palaeozoic nautiloids. However, they might have been misinterpreted as oncomyarian muscle attachment scars previously. Lastly, we discuss the taphonomy of the specimen, which was encrusted by multiple bryozoan colonies post-mortem. Furthermore, it shows questionable traces of bioerosion.

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Empty cephalopod conchs as substrates for gastropod eggs from the Hangenberg Black Shale (Late Devonian) of the Maïder Basin (Morocco)

Abstract

In the latest Famennian, black shale deposition occurred in many regions, some suggested a marine transgression as the explanation while others saw a link with higher organic input from the land. In either case, the Hangenberg Black Shale was most likely deposited under low oxygen conditions, which enabled exceptional fossil preservation in some regions such as the southern Maïder Basin of Morocco. Here, we provide the first account of small circular structures, in some cases with thin carbon films, which remained on ammonoid and bactritoid conchs. Due to similarities in their morphology and size with other occurrences documented from Europe, we propose that these structures may represent gastropod eggs. We also discuss whether egg-deposition occurred in the water column or on the sediment surface.

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The First International Conference on ‘Processes and Palaeo-Environmental Changes in the Arctic: From Past to Present’ (PalaeoArc)
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Integrated bio- and cyclostratigraphy of Middle Triassic (Anisian) ramp deposits, NW Bulgaria

Abstract

A cyclostratigraphic interpretation of peritidal to shallow-marine ramp deposits of the early Middle Triassic (Anisian) Opletnya Member exposed in outcrops along the Iskar River gorge, NW Bulgaria, is presented. Based on facies trends and bounding surfaces, depositional sequences of several orders can be identified. New biostratigraphic data provide a time frame of the studied succession with placement of the boundaries of the Anisian substages and show that the Aegean (early Anisian) substage lasted about 1.6 Myr. In the corresponding interval in the two studied sections, 80 elementary sequences are counted. Five elementary sequences compose a small-scale sequence. The prominent cyclic pattern of the Opletnya Member can thus be interpreted in terms of Milankovitch cyclicity: elementary sequences represent the precession (20-kyr) cycle and small-scale sequences the short eccentricity (100-kyr) cycle in the Milankovitch frequency band. Medium-scale sequences are defined based on lithology but only in two cases can be attributed to the long eccentricity cycle of 405 kyr. The transgressive-regressive facies trends within the sequences of all scales imply that they were controlled by sea-level changes, and that these were in tune with the climate changes induced by the orbital cycles. However, the complexity of facies and sedimentary structures seen in the Opletnya Member also implies that additional factors such as lateral migration of sediment bodies across the ramp were active. In addition, three major sequence boundaries have been identified in the studied sections, which can be correlated with the boundaries Ol4, An1, and An2 of the Tethyan realm.

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