Zdzislaw Belka

Frasnian plants from the Dra Valley, southern Anti-Atlas, Morocco

Anatomically preserved plant fragments are reported from Devonian marine deposits exposed in the Dra Valley of southern Anti-Atlas, Morocco. Associated conodont and tentaculite faunas indicate that the sediments yielding plants, which consist of black shales with intercalated calcareous concretions, are early Frasnian in age and most probably represent Zone 2 of the conodont zonation. This is the first record of Frasnian plants in North Africa. The specimens found all correspond to decorticated portions of axes. Six are referable to Callixylon , the organ genus corresponding to anatomically preserved axes of the progymnosperm tree Archaeopteris . Based on wood characters, especially ray structure, they are assigned to the species C. henkei , formerly described from the Famennian of Europe. One single specimen is compared to Xenocladia , a cladoxylopsid genus previously known from the Middle Devonian of Europe, USA and Kazakhstan. Interestingly, Archaeopteridales and Cladoxylopsida are two groups that dominate the younger plant assemblages of Famennian age recently described from the eastern Anti-Atlas. Callixylon henkei -type axes occur both in the Frasnian and in the Famennian deposits of the Anti-Atlas and they are all devoid of growth rings. These results are in accordance with a close position of Gondwana and Euramerica during Late Devonian times.

Cryptic coral-crinoid “hanging gardens” from the Middle Devonian of southern Morocco

An unusual and exceptionally well preserved cryptic community of cnidarians, crinoids, sponges, and microbes developed in a submarine cavity of Middle Devonian age in the Hamar Laghdad area (Morocco). The biota encrusted the cavity roof and grew predominantly in an upside-down position, forming spectacular “hanging gardens.” The investigated assemblage differs strikingly from both its Paleozoic and modern analogues; it constitutes one of a very few known examples of fossil cryptic assemblages developed in relatively deep water settings, and is the first report of a cryptic paleoecosystem dominated by rugose corals. The results support the view that during the middle Paleozoic there was no distinct polarization between open-surface and cryptic faunas in deep-water environments, but keen competition for space already existed in Devonian cryptic assemblages. The regional species pool seems to have been the main determinant of the ecological succession and structure of this cryptic community.

Stable Isotope Signatures of Middle Palaeozoic Ahermatypic Rugose Corals – Deciphering Secondary Alteration, Vital Fractionation Effects, and Palaeoecological Implications

This study investigates stable isotope signatures of five species of Silurian and Devonian deep-water, ahermatypic rugose corals, providing new insights into isotopic fractionation effects exhibited by Palaeozoic rugosans, and possible role of diagenetic processes in modifying their original isotopic signals. To minimize the influence of intraskeletal cements on the observed signatures, the analysed specimens included unusual species either devoid of large intraskeletal open spaces (button corals: Microcyclus, Palaeocyclus), or typified by particularly thick corallite walls (Calceola). The corals were collected at four localities in the Holy Cross Mountains (Poland), Mader Basin (Morocco) and on Gotland (Sweden), representing distinct diagenetic histories and different styles of diagenetic alteration. To evaluate the resistance of the corallites to diagenesis, we applied various microscopic and trace element preservation tests. Distinct differences between isotopic compositions of the least-altered and most-altered skeleton portions emphasise a critical role of material selection for geochemical studies of Palaeozoic corals. The least-altered parts of the specimens show marine or near-marine stable isotope signals and lack positive correlation between δ13C and δ18O. In terms of isotopic fractionation mechanisms, Palaeozoic rugosans must have differed considerably from modern deep-water scleractinians, typified by significant depletion in both 18O and 13C, and pronounced δ13C-δ18O co-variance. The fractionation effects exhibited by rugosans seem similar rather to the minor isotopic effects typical of modern non-scleractinian corals (octocorals and hydrocorals). The results of the present study add to growing evidence for significant differences between Scleractinia and Rugosa, and agree with recent studies indicating that calcification mechanisms developed independently in these two groups of cnidarians. Consequently, particular caution is needed in using scleractinians as analogues in isotopic studies of extinct coral lineages. Answering some of the pertinent palaeoecological questions, such as that of the possibility of photosymbiosis in Palaeozoic corals, may not be possible based on stable isotope data.

Frutexites encrustations on rugose corals (Middle Devonian, southern Morocco): complex growth of microbial microstromatolites

Microbially induced Frutexites microstromatolites developed on corallites of the Givetian rugose coral “Amplexus” in the sedimentary cover of a submarine volcanic intrusion in the eastern Anti-Atlas of southern Morocco. The corals lived in proximity to submarine hydrothermal fluid emissions. Frutexites form irregular shrubs encrusting external walls of corallites. The shrubs, consisting of alternations of calcitic and hematitic laminae, grew predominantly on abandoned corallites. Some Frutexites grew within the sediment, whereas others developed entirely above the seafloor, or started their accretion in water and continued to grow during burial. Three types of Frutexites encrustations have been distinguished. They look similar macroscopically, but differ significantly in their microstructure and mineralogical characteristics, resulting primarily from spatial and temporal variations in redox conditions. Both hematitic and calcitic laminae are primary features of Frutexites. The shrubs accreted as a result of mineralization of microbial biofilms under fluctuating environmental conditions, caused by changes in pH, Fe2+-supply and/or oxygenation, presumably related to discharges of reducing hydrothermal fluids. The calcitic laminae are interpreted to have formed due to activity of heterotrophic (mainly sulphate-reducing) microbes, whereas the hematitic laminae developed as a result of enhanced activity of nitrate-reducers or due to periodical passive mineralization of biofilms with iron. Cathodoluminescence data provide evidence that the nitrate and sulphate reduction preceded the Mn(IV) and Fe(III) reduction, presumably due to increased accumulation of organic matter and a high stability of the iron oxides present.

New bivalves from a Middle Devonian methane seep in Morocco: the oldest record of repetitive shell morphologies among some seep bivalve molluscs

A fauna of bivalve molluscs is described from methane seep carbonates of the Middle Devonian (c. 390 Ma) Hollard Mound in the eastern Anti-Atlas, Morocco. We describe a new modiomorphid genus Ataviaconcha gen. nov. with the type species Ataviaconcha wendti sp. nov. This is a very large, semi-infaunal species occurring in large colonies similar to those formed by Recent chemosymbiotic cold-seep and hydrothermal vent bivalves. It is the second modiomorphid bivalve known from Palaeozoic chemosynthesis-based ecosystems, after the roughly coeval Sibaya ivanovi Little, Maslennikov, Morris & Gubanov, 1999, from the Sibay hydrothermal vent deposit in the Ural Mountains, Russia. The second and much less numerous bivalve species described in this paper is the solemyid Dystactella? eisenmanni sp. nov., belonging to a genus known also from Ordovician to Devonian marine environments distinct from cold seeps and hydrothermal vents. As with other fossil and Recent solemyids, it was an infaunal burrower, most likely living in symbiosis with chemoautotrophic bacteria. These new findings show that bivalves are ancient in chemosynthesis-based ecosystems, thriving there for at least 390 Myr, and that the bivalve-dominated faunas predated the first occurrence of dimerelloid brachiopods at seeps. The early evolutionary adaptation of some bivalves to chemosynthesis-based ecosystems is probably related to a symbiosis-based metabolism allowing efficient exploitation of chemosynthetic food resources. Ataviaconcha wendti sp. nov. represents a morphology which recurred several times throughout the following 390 Myr in different bivalve groups that flourished at hydrocarbon seeps. This strongly suggests environmental control on the evolution of adaptations in seep biotas. http://zoobank.org/urn:lsid:zoobank.org:pub:A83D5CB1-67D2-4D05-8EBC-BFCA6E6845D8

Sr isotope tracing of multiple water sources in a complex river system, Noteć River, central Poland.

Anthropogenic impact on surface waters and other elements in the environment was investigated in the Noteć River basin in central Poland. The approach was to trace changes in the Sr isotope composition ((87)Sr/(86)Sr) and concentration in space and time. Systematic sampling of the river water shows a very wide range of (87)Sr/(86)Sr ratios, from 0.7089 to 0.7127. This strong variation, however, is restricted to the upper course of the river, whereas the water in the lower course typically shows (87)Sr/(86)Sr values around 0.7104-0.7105. Variations in (87)Sr/(86)Sr are associated with a wide range of Sr concentrations, from 0.14 to 1.32mg/L. We find that strong variations in (87)Sr/(86)Sr and Sr concentrations can be accounted for by mixing of two end-members: 1) atmospheric waters charged with Sr from the near-surface weathering and wash-out of Quaternary glaciogenic deposits, and 2) waters introduced into the river from an open pit lignite mine. The first reservoir is characterized by a low Sr content and high (87)Sr/(86)Sr ratios, whereas mine waters display opposite characteristics. Anthropogenic pollution is also induced by extensive use of fertilizers which constitute the third source of Sr in the environment. The study has an important implication for future archeological studies in the region. It shows that the present-day Sr isotope signatures of river water, flora and fauna cannot be used unambiguously to determine the baseline for bioavailable (87)Sr/(86)Sr in the past.

Mass occurrence of seep-specific bivalves in the oldest-known cold seep metazoan community

One of the most striking features of modern chemosynthesis-based ecosystems surrounding methane seeps is the presence of abundant chemosymbiotic bivalves. However, such accumulations have rarely been reported from Palaeozoic to mid-Mesozoic seeps, and it is widely thought that general trends in the evolution of chemosynthetic communities paralleled those typifying most marine environments, with the bivalve prevalence starting in the Mesozoic and with Palaeozoic seeps being dominated by brachiopods. Here, we report a discovery of bivalve clusters in the oldest-known methane seep that hosted metazoan fauna, dated to the late Silurian. We identify the bivalves, externally very similar to modern chemosymbiotic forms, as members of the extinct family Modiomorphidae, known previously from a younger, Devonian seep. The bivalves inhabited the seep at a stage of increased fluid flow, when they co-occurred with atrypid brachiopods, and display a set of morphological characteristics suggesting a seep-obligate lifestyle. We conclude that bivalves colonised chemosynthesis-based ecosystems at least as early as brachiopods and apparently first developed specialized lineages able to thrive in seep-related habitats for a prolonged period of time. Rather than being simple ecological successors of brachiopods, rich bivalve communities represent an ancient and recurring theme in the evolution of chemosynthetic assemblages.

Strontium isotope identification of water mixing and recharge sources in a river system (Oder River, central Europe): A quantitative approach

1 Institute of Geoecology and Geoinformation, Adam Mickiewicz University, Poznań, Poland Poznań Science and Technology Park, Adam Mickiewicz University Foundation, Poznań, Poland 3 Isotope Laboratory, Adam Mickiewicz University, Poznań, Poland 4 Institute of Geology, Adam Mickiewicz University, Poznań, Poland Correspondence Mateusz Zieliński, Isotope Laboratory, Adam Mickiewicz University, 61‐680 Poznań, Poland. Email: mateusz.zielinski@amu.edu.pl Funding information Polish National Science Center (NCN), Grant/ Award Number: 2012/07/B/ST10/03885