Dmitry A. Ruban

The challenge of reconstructing the Phanerozoic sea level and the Pacific Basin tectonics

The challenge of reconstructing the Phanerozoic sea level and the Pacific Basin tectonics The relationships between the interior dynamics of our planet and global sea level can be unravelled when plate-tectonic reconstructions are available for the entire Earth. A review of global tectonics reveals significant deficiencies in our understanding of the geodynamic evolution of the Pacific (Panthalassa or Proto-Pacific) during the Cambrian-Jurassic time-span. This particular, but major, shortcoming presents a true challenge for modern geoscientists, who are encouraged to produce a detailed plate-tectonic reconstruction of the Pacific for the pre-Cretaceous in order to advance our understanding of Phanerozoic sea-level change. A set of approaches, including geological/geophysical modelling, investigation of accretionary prisms, palaeobiogeographical studies, and careful examination of eustatic sea-level changes, are proposed that will help geoscientists tackle the challenge of understanding how Pacific geodynamics affected global sea level during the Phanerozoic.

Diversity Dynamics of Callovian-Albian Brachiopods in the Northern Caucasus (Northern Neo-Tethys) and a Jurassic/Cretaceous Mass Extinction

Abstract. The fossil records of the Northern Caucasus (southwestern Russia) provide an exceptional opportunity to reveal the evolution of brachiopods during the Callovian-Albian time interval and to evaluate the regional evidence for a Jurassic/Cretaceous mass extinction. Stratigraphic ranges of 119 species, 52 genera, 25 families, 13 superfamilies, and 2 orders of brachiopods are considered to document the main patterns of their diversity dynamics. The total number of taxa was high in the Callovian-Oxfordian, then dropped in the Kimmeridgian, increased again in the Tithonian, decreased significantly in the Berriasian, and remained relatively low until the end of the Early Cretaceous except for a minor peak in the Barremian. Species, genera, families, and superfamilies of brachiopods declined remarkably in the Northern Caucasus in the Berriasian, which is regional evidence for a Jurassic/Cretaceous mass extinction. Both an acceleration in disappearance rate and a drop in appearance rate contributed to this collapse. Recovery began in the Valanginian-Hauterivian, but it was not completed at the level of species. Transgressions/regressions, growth of the carbonate platform, a salinity crisis, and oxygen depletion were important controls on the brachiopod diversity dynamics in the Northern Caucasus. A regressive episode around the Jurassic-Cretaceous transition seems to be a plausible cause of the relevant brachiopod decline. A comparison of changes in the total number of brachiopod taxa between the Neo-Tethys Ocean and the Alpine Tethys Ocean shows some difference, but both domains provide evidence for a Jurassic/Cretaceous mass extinction, which was less severe in the Swiss Alps and the Jura Mountains (Alpine Tethys) than in the Northern Caucasus (Neo-Tethys).

Do partly outdated palaeontological data produce just a noise? An assessment of the Middle Devonian-Mississippian biodiversity dynamics in central Asia on the basis of Soviet-time compilations

Do partly outdated palaeontological data produce just a noise? An assessment of the Middle Devonian-Mississippian biodiversity dynamics in central Asia on the basis of Soviet-time compilations Interregional tracing of trends and events in the biotic evolution is an important task of modern palaeobiology. In Soviet times (1917-1991), numerous palaeontological data have collected for the territory of Russia and neighbouring U. S. S. R. countries. Later, these data were compiled and published in a series of reference volumes. Although this information cannot be updated in a conventional way, it remains valuable for quantitative analyses, particularly because of its comprehensive and unique character. Assessment of the previously collected data on the stratigraphic distribution of Middle Devonian-Mississippian marine invertebrates in three regions of central Asia (central Kazakhstan, Uzbekistan and Tajikistan) reveals some general patterns of biodiversity dynamics. The total number of genera generally declined during the Givetian-Famennian, whereas a remarkable diversity peak occurred in the Visean. This is consistent with the global pattern and, thus, permits to hypothesize a regional signature of the global trends. Changes in the extinction rate differ, however, between central Asia and the Earth in its entirety, which may be explained particularly by biases in either the regional or the global records. Evidence of the Givetian and Frasnian/Famennian mass extinctions is found in the three regions under study. Results of this tentative study indicate important directions for further research and suggest that central Asia is a highly important domain for studies of mid-Palaeozoic biodiversity dynamics.

Megaclasts in geoconservation: sedimentological questions, anthropogenic influence, and geotourism potential

Abstract Megaclasts are sedimentary particles larger than boulders. Their huge size and scattered occurrence make them objects that deserve geological heritage, requiring conservation. Investigation of megaclasts for the purpose faces difficulties because of the distinction between boulders and megaclasts. Local study of Quaternary large stones in Mountainous Adygeja (W Caucasus, SW Russia) suggests ~ 2 m as a suitable size criterion, although only locally. Shape, occurrence, and origin of megaclasts require additional attention. Geoconservation may result in anthropogenic disturbances of the natural landscape through removal of vegetation, access constructions, and restoration. The geotourism potential of megaclasts is partly determined by their huge size and their rare and scattered occurrence. Aesthetic qualities, local legends, and co-occurrence with prehistoric megalithic constructions increase this potential. The Maiden’s Stone in Mountainous Adygeja, which is ~ 35 m long, has been a tourist attraction already for decades. It is an impressive example of geoconconservation and geotourism connected with megaclasts. Generally, megaclasts increase the value (including the scientific importance) of the geological heritage of Mountainous Adygeja, where a geopark might be established.

Mesozoic mass extinctions and angiosperm radiation: does the molecular clock tell something new?

Mesozoic mass extinctions and angiosperm radiation: does the molecular clock tell something new? Angiosperms evolved rapidly in the late Mesozoic. Data from the genetic-based approach called ‘molecular clock’ permit an evaluation of the radiation of flowering plants through geological time and of the possible influences of Mesozoic mass extinctions. A total of 261 divergence ages of angiosperm families are considered. The radiation of flowering plants peaked in the Albian, early Campanian, and Maastrichtian. From the three late Mesozoic mass extinctions (Jurassic/Cretaceous, Cenomanian/Turonian, and Cretaceous/Palaeogene), only the Cretaceous/Palaeogene event coincided with a significant, abrupt, and long-term decline in angiosperm radiation. If their link will be further proven, this means that global-scale environmental perturbation precluded from many innovations in the development of plants. This decline was, however, not unprecedented in the history of the angiosperms. The implication of data from the molecular clock for evolutionary reconstructions is limited, primarily because this approach deals with only extant lineages.

Dynamics of the middle-rank taxonomic diversity structure of brachiopods: a quantitative assessment of the Phanerozoic fossil record

Ruban, D.A., September 2012. Dynamics of the middle-rank taxonomic diversity structure of brachiopods: a quantitative assessment of the Phanerozoic fossil record. Alcheringa 36, 413–426. ISSN 0311-5518. Taxonomic diversity structure indicates how higher-rank taxa influence the diversity of lower-rank taxa. Brachiopods experienced significant changes in the superfamily–family, superfamily–genus and family–genus components of diversity structure during the Phanerozoic. The most intense changes occurred at the Cambrian–Ordovician, Devonian–Carboniferous and Permian–Triassic transitions, when new higher-rank taxa began to determine the diversity at lower taxonomic levels. In contrast, the similarity of successive brachiopod assemblages was relatively high during the Ordovician–Devonian, Carboniferous–Permian, Triassic–Cretaceous and Paleogene–Quaternary intervals indicating a form of evolutionary stagnation. High dissimilarity between older and younger assemblages was established at the Cambrian–Ordovician and Permian–Triassic transitions, which mark the distinctions between the Cambrian, Palaeozoic and Modern evolutionary faunas within the target fossil group, i.e., brachiopods. Changes in superfamily–family, superfamily–genus and family–genus components of diversity structure were similar. All ‘Big Five’ mass extinctions left a more or less significant imprint in the dynamics of the diversity structure of brachiopods, but the Late Devonian and end-Permian catastrophes were especially important. Results of the present study may be refined with future improvements to brachiopod suprageneric systematics.

Notable Glaciokarsts of the World

In this chapter, notable glaciokarsts of the world are presented. Geographical location, geologic and tectonic settings, climatic conditions, glaciation phases as well as surface and underground karst landforms are presented about each selected region. Obviously, the areal extent, the degree of exploration and the amount of publicly available information are different in each case. Historically, the first glaciokarst studies were based on the Alps, the Pyrenees, the Dinaric Alps and the British Isles, and they have remained in the focus since then. Hence, these regions are presented here in more detail, but even these presentations can be considered only short overviews. Some other glaciokarst terrains, such as Scandinavia or the Rocky Mountains, have also been thoroughly studied but later in history; nevertheless, there are abundant internationally available publications about them. Certain parts of the Balkan Peninsula, the Apennines or even Anatolia received high attention more recently and novel methods have been used to investigate their glaciokarst terrains. The Carpathians and the Appalachians, which are also discussed in this chapter, are extensively studied mountains in general, but glaciokarsts occupy a relatively small proportion in them. On the other hand, there are still regions, which are difficult to access, where glaciokarsts are poorly explored, and/or the available literature is limited (or the publications are only in Russian, for instance). Some of them, namely, the Altai Mountains, the Greater Caucasus, the Tian Shan, the Pamir and the Patagonian archipelago, are also briefly presented here. Finally, it is noted that our selection does not contain all glaciokarsts of the world because it is beyond the scope of this chapter.

New data on Callovian (Middle Jurassic) belemnites and palynomorphs from the Northern Caucasus, southwest Russia

Abstract Palaeontological data on the Caucasus are highly important for large-scale stratigraphical and palaeobiogeographical assessment of the northern Tethyan margin, but this information is often scarce and not available in English. Field studies in the Northern Caucasus have now permitted to amass some new data. Two belemnite species are described from the stratotype section of the Kamennomostskaja Formation (Callovian, Middle Jurassic) near the town of Kamennomostskij in Adygeja (Northern Caucasus). These are Belemnopsis subhastata (von Zieten, 1831) and Rhopaloteuthis ominosa Gustomesov, 1968. The latter is a rare species, and the present find allows new insights into its taxonomy. A palyno-logical analysis of the belemnite-bearing sample was carried out, and a diverse assemblage of dinocysts, acritarchs and prasinophytes, plus pollen and spores recognised. The most abundant palynomorphs are Micrhystridium and Classopollis. Data on belemnites coupled with those on palynomorphs indicate the early Callovian age of the sample level. This interpretation differs slightly from previous conclusions based on ammonites and dinocysts. If this age is correct, the degree of condensation of Callovian deposits in the section studied was lesser than previously assumed.