Ichnology, sedimentology, and orbital cycles in the hemipelagic Early Jurassic Laurasian Seaway (Pliensbachian, Cardigan Bay Basin, UK)

This is the final version. Available on open access from Elsevier via the DOI in this recordAn uncommonly continuous Lower Jurassic (uppermost Sinemurian and Pliensbachian) section (Llanbedr (Mochras Farm) Borehole, Cardigan Bay Basin, UK) comprises hemipelagic calcareous mudstone, wackestone/siltstone and subordinate packstone/sandstone. Some beds show bigradational grading, and their sedimentary structures are typical of contourite drift facies. On the basis of the long-term persistence and stability of the currents that formed these deposits, sedimentation was likely controlled by thermohaline-driven geostrophic contour currents circulating between the Boreal ocean and Peri-Tethys through the narrow and relatively deep Cardigan Bay Basin (Cardigan Bay Strait). Trace fossils are strongly dominated by Phycosiphon incertum, which was produced by opportunistic colonizers. Thalassinoides, Schaubcylindrichnus and Teichichnus are common, accompanied by less common Zoophycos, Planolites, Palaeophycus, Trichichnus and dwelling structures such as cf. Polykladichnus, Siphonichnus and Skolithos. The ichnofabrics are usually simple, which results from generally high rates of deposition, unstable, water-saturated soft-ground substrate, and the domination of well-adapted Phycosiphon, but there are also cyclic appearances of more complex ichnofabrics with dwelling structures, reflecting more stable bottom conditions. A new detailed analysis of the core has allowed cycles to be distinguished based on combination of ichnological and sedimentological features, pointing to distinct cyclicity of oceanographic mechanisms influenced by orbital forcing and driving the inferred fluctuations in benthic life conditions, controlled mainly by variation in contour current intensity and oxygenation of bottom water reflected by trace fossils. The ichnological cycles show four-order hierarchy, which can be attributed to the orbital cycles: precession and obliquity (4th order), short eccentricity (3rd order), and long eccentricity (2nd order). The longest (~ 2.5 Myr) 1st order cyclicity is attributable to the longer ‟grand orbital cycles” (period related to the Earth–Mars secular resonance), with long-term impacts on palaeoclimatic and oceanic circulation dynamics, and is recorded in large-scale changes in ichnodiversity, correlating with long-term changes of clay minerals and carbonate content. Possibly, there is also ~ 9 Myr cyclicity, expressed in observed modulation of frequency of precession cycles by eccentricity. Harmonic analysis of the cyclicity gives high confidence of orbital signals and allows refined estimation of duration of the Pliensbachian (~8.4 Myr) and the jamesoni (~2.8 Myr), ibex (~ 2.0 Myr), davoei (~ 0.47 Myr), margaritatus (~ 2.33 Myr) and spinatum zones (~ 0.8 Myr) with an overall stable sedimentation rate of 4.5–5.1 cm/kyr. Obtained durations show improved fit between 2nd–4th and 1st order cycle and removes the problem of an anomalously long duration and resulting much lower sedimentation rate for the spinatum Zone, previously obtained by other methods. A higher diversity of trace fossils is noticed in intervals enriched in smectite; most likely, this clay mineral occluded pore spaces and limited the competition from the opportunist Phycosiphon makers, allowing development of other, more specialized forms. The continuous, expanded ichnological record of deep-water hemipelagic/contour drift sediments is sensitive to climatic and oceanographic changes controlled by orbital cycles. The Cardigan Bay Strait played an important role in the Early Jurassic (at least Pliensbachian) oceanic circulation, providing a major link between the northern and southern part of the Laurasian Seaway (and in general between the Boreal and Peri-Tethys domains), funneling currents flowing from the north to the south.National Science Centre, PolandInternal Polish Geological InstituteNatural Environment Research Council (NERC

Early Jurassic extrinsic solar system dynamics versus intrinsic Earth processes: Toarcian sedimentation and benthic life in deep-sea contourite drift facies, Cardigan Bay Basin, UK

This is the final version. Available on open access from Springer via the DOI in this recordAvailability of data and materials: All data generated during this study are included in the paper and its Additional files. Downhole log data from Mochras are available via the UK Onshore Geophysical Library (UKOGL) website https://ukogl.org.uk/The Cardigan Bay Basin (UK) may have functioned as a deep and narrow strait, and thereby influenced Early Jurassic oceanic circulation through the northern and southern Laurasian Seaway, and between Boreal and Peri-Tethys domains. Toarcian hemipelagic deposits of the basin in the Mochras borehole show strongly bioturbated contourite facies. Trace fossils are strongly dominated by Phycosiphon incertum (represented by four morphotypes), which was produced by opportunistic colonizers. Thalassinoides, Schaubcylindrichnus and Trichichnus are common (the latter is a deep-tier trace fossil produced by filamentous sulfide-oxidizing bacteria with a high tolerance for dysoxia), accompanied by less common Zoophycos, Planolites, Palaeophycus, Teichichnus, Rhizocorallium, Chondrites, and dwelling and resting structures, such as cf. Polykladichnus, Siphonichnus, Skolithos, Arenicolites, Monocraterion and Lockeia. Ichnological and lithological signals suggest repetitive fluctuations in benthic conditions attributed to a hierarchy of orbital cycles (precession and obliquity [4th order], short eccentricity [3rd order], long eccentricity [2nd order] and Earth–Mars secular resonance [1st order]). The Pliensbachian–Toarcian transition appears to be a significant palaeoceanographic turning point in the Cardigan Bay Basin, starting a CaCO3 decline, and with the most severe oxygen crisis of the Tenuicostatum Zone (here dysoxic but not anoxic) ending at the onset, in the early Serpentinum Zone (Exaratum Subzone), of the Toarcian negative carbon isotope excursion (To-CIE—linked with the Toarcian Oceanic Anoxic Event occurring in the lower part in the Serpentinum Zone). This trend contrasts with the prevalence of anoxia synchronous with the To-CIE in many other settings. Minor dysoxia returned to the Mochras setting in the latest Thouarsense to Dispansum zone interval. Extreme climate warming during the To-CIE may have enhanced and caused a reversal in the direction of deep marine circulation, improving oxygenation of the sea floor. Spectral analysis of binary data on ichnotaxa appearances gives high confidence in orbital signals and allows refined estimation of ammonite zones and the duration of the Toarcian (minimum ~ 9.4 Myr).National Science Centre, PolandPolish Geological InstituteNatural Environment Research Council (NERC

Glaciotectonic structures of Trzebnica Hills

Wzgórza Trzebnickie wraz z innymi mezoregionami Wału Śląskiego stanowią morenę spiętrzoną, która charakteryzuje się budową glacitektoniczną. Procesami glacitektonicznymi objęte są zarówno utwory neogenu, jak i plejstocenu, do głębokości co najmniej 200 m. Główny etap rozwoju struktur glacitektonicznych odbył się w czasie recesji lądolodu zlodowacenia Sanu II. Wielkoskalowe struktury seryjne wykazują, zgodną z glacitektoniczną koncepcją statyczno-kinetyczną, strefowość imbrykacji łusek w obszarze proksymalnym i rozwój fałdów w obszarze dystalnym. Ważnym elementem budowy geologicznej Wzgórz Trzebnickich są też różnowiekowe, znacznie mniejsze struktury glacitektoniczne. W odsłonięciu koło Cerekwicy stwierdziłem m.in. melanż glacitektoniczny i fałd z dobrze wykształconym kliważem. Z kolei, w dolinie potoku Włóknica nie wykluczam obecności łuski glacitektonicznej. Wzgórza Trzebnickie odróżniają się od pozostałych mezoregionów Wału Trzebnickiego odmienną orientacją struktur glacitektonicznych (przeważnie o kierunku równoleżnikowym, natomiast na Wzgórzach Wińskich – o kierunku południkowym) i wergencją struktur glacitektonicznych (przeważnie ku S, a na Wzgórzach Wińskich – ku W). Budowa Wzgórz Trzebnickich odróżnia się od budowy Wzgórz Dalkowskich także większą głębokością, do jakiej doszło do zaburzeń glacitektonicznych utworów kenozoiku. Rozwój domen deformacji glacitektonicznych jest związany przede wszystkim z morfologią podłoża podkenozoicznego, ruchami pionowymi w jego obrębie oraz znaczną ilością wody roztopowej obecną podczas recesji lądolodu. Cechą glacitektonicznej budowy Wzgórz Trzebnickich w rzeźbie terenu jest regularny układ domen geomorfologicznych.Along with other mesoregions of Silesian Rampart, Trzebnica Hills constitute the push moraine of glaciotectonic origin. Glaciotectonic structures are present in Neogene and Pleistocene rocks to depths greater than 200 m. The main stage of multi-phase development of glaciotectonic structures took place during deglaciation of Elsterian ice sheet. Zonal arrangement of large-scale multiple-occuring structures seems to correspond with “static-kinematic conception” of glaciotectonics. Imbricate thrust stacks are present in proximal zone, while folds are in distal zone. Smaller-scale structures of various age are also an important component of Trzebnica Hills’ geology. In an outcrop near Cerekwica glaciotectonic mélange and fold with well-developed cleavage has been described. Presumed glaciotectonic thrust scale has been detected in the vicinity of Włóknica stream’s valley. Orientation (mostly latitudinal, meridional on Wińsko Hills) and vergence (mostly S, W on Wińsko Hills) of glaciotectonic structures are factors that distinguish Trzebnica Hills from other mesoregions of Silesian Rampart. Vertical extent of glaciotectonic structures is larger on Trzebnica Hills than on Dalków Hills. The development of glaciotectonic deformation domains may be associated both with morphology of pre-cainozoic basement and with vertical movements within it. Also an abundant amount of meltwater constituted an important factor. Regular pattern of geomorphological domains is considered to be reflecting the features of glaciotectonism

Glaciotectonics of the Leszno Lakeland during the Vistulian glaciation

Pojezierze Leszczyńskie jest położone na obszarze strefy glacimarginalnej zlodowacenia Wisły. Struktury glacitektoniczne o różnych typach i wielkości udokumentowano w dziewiętnastu odsłonięciach na obszarze tego pojezierza. Struktury te występują poniżej najmłodszej gliny morenowej, zdeponowanej przez lądolód vistuliański. W czterech odsłonięciach obserwowano występowanie warciańskich lub odrzańskich glin morenowych w obrębie zdeformowanych serii osadów glacjalnych i fluwioglacjalnych. Orientacja struktur glacitektonicznych wskazuje na ich rozwój pod naciskiem lądolodu transgredującego z NE/NNE. Procesy glacitektoniczne dotknęły utwory plejstoceńskie i neogeńskiego podłoża, do głębokości co najmniej 20 m. Rozwój domen ze strukturami glacitektonicznymi odbywał się w strefie proglacjalnej, zgodnie z przyjętą glacitektoniczną koncepcją dynamiki frontalnej. W dwóch odsłonięciach glacitektonitów, powstałych w obrębie subglacjalnej warstwy o intensywnej deformacji, stwierdzono zatarcie struktur sedymentacyjnych, pokruszenie ziaren i rozwój nowej więźby glacigenicznej. Zaproponowano model rozwoju małoskalowych glacitektonitów w warunkach progresywnego procesu ścinania prostego i czasowego wzrostu ciśnienia porowego wody w podłożu lądolodu. Rozwojowi glacitektoniki na obszarze Pojezierza Leszczyńskiego sprzyjały: wyjątkowo szybka transgresja lądolodu, płytkie zaleganie iłów poznańskich i urozmaicona morfologia podłoża lądolodu. Dodatkowo, wykonano testy statystyczne na zróżnicowanie pomiędzy średnimi orientacjami i zróżnicowanie koncentracji orientacji powierzchni strukturalnych. Zaproponowano sposoby interpretacji wyników tych testów w świetle badań glacitektoniki na terenie Pojezierza Leszczyńskiego.The Leszno Lakeland is situated in the zone of maximum extent of the Vistulian Ice Sheet. Glaciotectonic structures, representing varied types and extents, have been documented in nineteen outcrops located in the region. The structures are present below the youngest till deposited during the Vistulian glaciation. Older (Wartanian or Odranian) tills also have been observed in some outcrops of deformed sedimentary series. The orientation of glaciotectonic structures suggests, that the ice sheet was advancing from NE/NNE. Both Pleistocene deposits and Neogene substratum were affected by glaciotectonic processes at least to depths greater than 20 m. The arrangement of glaciotectonic structures seems to correspond with the “frontal dynamics conception” of glaciotectonism. Glaciotectonites, that orginated within sub-glacial deformable bed, have been observed in two outcrops. Symptoms of the development of new glaciogenic fabric, including blurring of sedimentary structures and crushing the grains, have been documented in these outcrops. Model of the development of such glaciotectonites, under the conditions of progressive simple shearing and phased increase of pore water pressure, have been proposed. The development of glaciotectonic deformation domains may be associated both with pre-glacial topographic relief and with occurrence of the Poznań Clays shallow under the ground surface. However, exceptionally fast transgression of an ice sheet constituted the most important factor. Statistical differences between mean orientations of structural planes and the difference between structural planes’ vectorial concentrations have been tested. Interpretations of the glaciotectonic results of these statistical tests on the Leszno Lakeland have been proposed