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An endemic ichnoassemblage from a late Miocene paleolake in SE Iceland
Abstract and Figures
In Þórisdalur valley, a small relict of a sedimentary body was identified in southeastern Iceland. It probably represents a remnant of the deep, tectonically arranged paleolake (Late Miocene, 8–9 Ma), and filled by volcaniclastic material from nearby, active volcanic centers. In the profile of tuffitic sandstone, siltstone and claystone, the ripple-bedding layers, molds and flute casts indicate periodic mass flow episodes. In the sedimentary profile, the characteristic arrangement of sediments is evident, showing features of the Bouma sequences. In the claystone layers, deposited during episodes of lowest kinetic energy, a specific ichnoassemblage was found, represented by Thorichnus ramosus igen. et isp. nov., T. corniculatus igen. et isp. nov., Mammillichnis jakubi isp. nov., Helminthoidichnites multilaqueatus comb. nov., Vatnaspor jachymi igen. et isp. nov. and five preliminarily identified trace fossils. The assemblage belongs to Mermia ichnofacies, the nonmarine representative of an ichnofacies, developed in a turbiditic environment; most of identified trace fossils are so far endemic.
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... In the Carboniferous of Great Britain, Mammillichnis have been found in deltaic sediments [Eagar et al. 1985]; they also have been found in the Cretaceous and Paleogene deep-water fan sediments of Switzerland [Crimes et al. 1981]. Pokorný et al. [2017] reported Mammillichnis jakubi Pokorný et al., 2017 from lacustrine turbidite sediments. All of the trace fossils Mammillichnis monstrum examined in this study also come from turbidite rocks. ...
... In the Carboniferous of Great Britain, Mammillichnis have been found in deltaic sediments [Eagar et al. 1985]; they also have been found in the Cretaceous and Paleogene deep-water fan sediments of Switzerland [Crimes et al. 1981]. Pokorný et al. [2017] reported Mammillichnis jakubi Pokorný et al., 2017 from lacustrine turbidite sediments. All of the trace fossils Mammillichnis monstrum examined in this study also come from turbidite rocks. ...
... nov. is described from the Donets Basin, Ukraine. Mammillichnis monstrum morphologically differs from Mammillichnis jakubi Pokorný et al., 2017. Apparently, Mammillichnis are burrows of large sedentary coelenterates, such as Actiniaria. ...
A new ichnospecies Mammillichnis monstrum isp. nov. (Domi-
chnia) is described from turbidite sandstone in the upper part of
the Mospyne Formation (late Bashkirian, Early Pennsylvanian)
of southern Luhansk Oblast, eastern Ukraine. Mammillichnis
monstrum isp. nov. is represented by hypichnial, hemispherical,
slightly 扯attened passive 捯llings of a large burrow; the apex of bur-
row casts has concentric depression or a small rounded tubercle.
Mammillichnis monstrum isp. nov. di੦ers from Mammillichnis ag-
geris Chamberlain, 1971 (Vendian–Oligocene) and Mammillichnis
jakubi Pokorny et al., 2017 (late Miocene, Neogene) by its much
larger size. 㰠e depth of burrows varies greatly, which seems to
be related to the di੦erent preservation of burrow casts, as well as,
apparently, di੦erent maturity of burrow producers. In addition,
such an important diagnostic feature as a rounded tubercle at the
apex of the burrow casts is not observed in all specimens, which is
probably also due to the di੦erent types of preservation of the trace
fossils. Perhaps, the di੦erences in the morphology of the apex of
some examined specimens are due to the activity of organisms
that lived in the burrows a呰er the death of the trace fossil produc-
er. 㰠e producers of the trace fossils Mammillichnis are apparently
sea anemones (Actiniaria). 㰠e fossil record of Actiniaria has sig-
ni捯cant gaps because these animals lack a mineral skeleton that
can be preserved as a fossil. 㰠e oldest sea anemones are known
from the Vendian; there is no data on post-Carboniferous fossil
Actiniaria. It seems that the only way to study the evolution of
this group of animals is studying of their trace fossils, such as bur-
rows (e.g. ichnogenera Astropolichnus, Bergaueria, Conostichus,
and Kulindrichnus), which demonstrate some details of the body
morphology of their producers. 㰠e trace fossils Mammillichnis
monstrum apparently marks insigni捯cant pauses in sedimentation
preceding the accumulation of turbidite sandstones. In the coarse
sandy sediments are preserved mainly large depressions le呰 by
sessile coelenterates. Trace fossils are well preserved in some sand-
stone lenses and poorly preserved in others. 㰠is circumstance is
apparently related to the di੦erent intensity of erosive activity of
turbidity currents.
... Bergaueria is a plug-shaped burrow, considered as a cubichnion (Arai and Arai and McGugan, 1968;Fürsich et al., 2018) or a domichnion (Pickerill, 1989;Pokorný et al., 2017) of suspension feeding actinarians (e.g., Seilacher, 1956;Alpert, 1973), showing a wide range of deposition environments from shallow to deeper marine setting (e.g., Crimes and Anderson, 1985;Fillion and Pickerill, 1990;Uchman, 1995Uchman, , 1998Cherif et al., 2015;Shitole et al., 2019;Belaid et al., 2020). Bergaueria is reported from the Precambrian (e.g., Pokorný et al., 2017) to the Recent (Baucon and Felletti, 2013 ...
... Bergaueria is a plug-shaped burrow, considered as a cubichnion (Arai and Arai and McGugan, 1968;Fürsich et al., 2018) or a domichnion (Pickerill, 1989;Pokorný et al., 2017) of suspension feeding actinarians (e.g., Seilacher, 1956;Alpert, 1973), showing a wide range of deposition environments from shallow to deeper marine setting (e.g., Crimes and Anderson, 1985;Fillion and Pickerill, 1990;Uchman, 1995Uchman, , 1998Cherif et al., 2015;Shitole et al., 2019;Belaid et al., 2020). Bergaueria is reported from the Precambrian (e.g., Pokorný et al., 2017) to the Recent (Baucon and Felletti, 2013 ...
... The different forms of Bergaueria of the upper Jurassic Argiles de Saïda Formation are preserved on the sole of fine-grained sandstone beds, and filled with the same material as the host sandstone rock. Bergaueria occurs from shallow-water deposits (Narbonne, 1984;Crimes and Anderson, 1985;Cherif et al., 2015;Belaid et al., 2020) to deep-sea deposits (Prantl, 1945;Książkiewicz, 1977;Crimes and Crosseley, 1991;Uchman, 1995Uchman, , 1998 from the late Precambrian (e.g., Crimes and Anderson, 1985;Pokorný et al., 2017) to Recent (Baucon and Felletti, 2013). This trace is abundant in siliciclastic deposits with softground substrate (e.g., Chamberlain, 1971;Knaust, 2017), but also it can occur in carbonate facies (Knaust, 2007). ...
Plug-shaped trace fossils B. perata, B. hemispherica, Bergaueria isp., Calycraterion samsonowiczi, Conostichus ornatus and Conostichus isp. are found in the middle-upper Oxfordian fine-grained sandstone of the Argiles de Saïda Formation (northwestern Algeria). Except for the trace Calycraterion which is interpreted as an annelid trace, these traces correspond to distinct behaviours of sea anemones, and their occurrence within tempestite deposits is influenced by a stress factors in a storm-dominated environment. The abundance of these plug-shaped trace fossils suggests that the upper Jurassic siliciclastic shelves with fine-grained soft clastic substrate were colonised by actinarian sessile benthos.
... Some of the research lines on continental invertebrate ichnology include characterization of additional ichnofacies (Buatois and Mángano, 1995;Genise et al., 2000Genise et al., , 2010; application of the ichnofabric approach to the study of continental deposits (Genise et al., 2004), trends in colonization of continental environments through geologic time Gibling, 2010, 2013;Buatois et al., 2016;Minter et al., 2017), ichnology of paleosols (Genise, 2017), and refined approaches to experimental neoichnology (Hembree, 2016). A combination of sedimentologic and ichnologic datasets has been increasingly used in the study of lacustrine basins (e.g., Metz, 2000;Melchor, 2004;Uchman et al., 2007;Buatois and Mángano, 2009;Scott et al., 2012;Pokorný et al., 2017). Arguably, fine tuning of these two datasets has not been performed to the same degree in fluvial successions, although the number of studies documenting trace-fossil distributions in alluvial successions is growing (e.g., Eberth et al., 2000;Uchman et al., 2004;Buatois et al., 2007;Ronchi, 2008;Melchor et al., 2006Melchor et al., , 2012Krapovickas et al., 2009;Menezes et al., 2019). ...
... Helminthoidichnites is distinguished from Helminthopsis by having straight, curved to circular courses rather than a tendency to meander (Hofmann and Patel, 1989;Hofmann, 1990;Buatois et al., 1997). Helminthoidichnites tenuis differs from H. multilaqueatus by the circular course of the latter (Pokorný et al., 2017). Helminthoidichnites is a grazing trail (pascichnion) produced by nematomorphs or insect larvae (Buatois et al., 1997). ...
... Helminthoidichnites is a facies-crossing ichnotaxon. It has been recorded from a broad range of depositional environments, but is particularly common in freshwater settings (e.g., Buatois et al., 1997;Gaigalas and Uchman, 2004;de Gibert and Sáez, 2009;Pokorný et al., 2017). ...
The Oligocene Lower Freshwater Molasse of Switzerland is host to spectacular outcrops of fluvial deposits. In distal areas of the Swiss Molasse Basin, deposits of a north-eastward draining meandering system are exposed. Combined sedimentologic and ichnologic observations in the Chli Sunnhalde and Roggwil quarries allow an improved understanding of animal-substrate interactions in deposits of meandering fluvial systems. Strata include meander-belt sandstone, levee sandstone and mudstone, crevasse-channel and splay sandstone, floodplain mudstone and sandstone, and paleosols. While the meander belt and the more proximal crevasse-channel deposits are typically unbioturbated, the more distal deposits show a clear biogenic overprint, with distal crevasse-channel, crevasse-splay, and floodplain deposits being intensely bioturbated.
Simple grazing and locomotion trails (included in the Cochlichnus anguineus-Helminthoidichnites tenuis suite) were formed subaqueously in ponded areas of the floodplain. Meniscate burrows (Taenidium isp. suite) and root trace fossils occur along the margin of these floodplain water-bodies and at the top of crevasse-splay deposits. Some of the floodplain, crevasse-splay, and crevasse-channel deposits are pervasively bioturbated by crayfish burrows (Camborygma litonomos suite). Crevasse-splay deposits locally host escape trace fossils.
Where cross-cutting relationships are apparent, a colonization sequence can be established as follows: the Cochlichnus anguineus-Helminthoidichnites tenuis suite is cross-cut by the Taenidium isp. suite, which in turn is cross-cut by the Camborygma litonomos suite and root trace fossils. Composite ichnofabrics are common in these meandering river deposits, recording progressive lowering of the water table in overbank subenvironments. Frequency of depositional events was a first-order control on degree of bioturbation. Position of the water table and degree of substrate consolidation exerted considerable influence over the types of trace fossils produced. Distinct bioturbation phases may result in the formation of different trace-fossil suites - representative of disparate ichnofacies - preserved on a single bedding plane. This study further supports the notion that meandering fluvial systems are characterized by trace-fossil suites belonging to the Scoyenia, Camborygma and/or Mermia ichnofacies.
... The trace fossil Bergaueria is a plug-shaped burrows, regarded as cubichnion (Arai and McGugan 1968;Fürsich et al. 2018) or domichnion (Pickerill 1989;Pokorny et al. 2017), of suspension feeding actinarian sea anemones (Seilacher 1956;Alpert 1973;Shitole et al. 2019). It is reported from shallow marine, deep-marine and wave-dominated prograding deltaic deposits (Crimes and Anderson 1985;Uchman 1998;Cherif et al. 2015;Shitole et al. 2019;Belaid et al. 2020), ranging from the Precambrian to the Miocene (e.g., Pokorny et al. 2017). ...
... The trace fossil Bergaueria is a plug-shaped burrows, regarded as cubichnion (Arai and McGugan 1968;Fürsich et al. 2018) or domichnion (Pickerill 1989;Pokorny et al. 2017), of suspension feeding actinarian sea anemones (Seilacher 1956;Alpert 1973;Shitole et al. 2019). It is reported from shallow marine, deep-marine and wave-dominated prograding deltaic deposits (Crimes and Anderson 1985;Uchman 1998;Cherif et al. 2015;Shitole et al. 2019;Belaid et al. 2020), ranging from the Precambrian to the Miocene (e.g., Pokorny et al. 2017). Chondrites isp. Figure 5E Description Chondrites isp. is preserved in hypichnion small tree-like burrow systems filled with yellow fine-graind material from the Kechab section. ...
Forty-three ichnospecies belonging to 30 ichnogenera are described from the Upper Jurassic Argiles de Saïda Formation (north-western Algeria), which consists of mixed shallow marine siliciclastic-carbonate sediments. The ichnological analysis reveals that the majority of the ichnoassemblages are represented by non-graphoglyptid traces dominated by Bergaueria isp., Ophiomorpha isp., O. rudis, Neonereites biserialis, N. triserialis. Furthermore, Chondrites isp., Palaeophycus isp., Phycosiphon isp., Planolites isp., Protovirgularia isp., Scolicia isp. and Thalassinoides isp. are common ichnotaxa. Ancorichnus isp., Archaeonassa isp., Gordia isp., Helminthoidichnites isp., Helminthopsis isp., Nereites isp., Ophiomorpha annulta, Oravaichnium isp., Oravaichnium hrabei, Protovirgularia dichotoma, Rutichnus rutis, Thalassinoides suevicus are rare, whereas, Chondrites targionii, Nereites irregularis, Neonereites uniserialis, Ptychoplasma excelsum, Spongeliomorpha isp., Taenidium isp., Taenidium serpentinum, ?Tubulichnium isp. and Zoophycos isp. are rare to scarce ichnotaxa. The graphoglyptid assemblage has very low diversity with only three ichnotaxa which are Megagrapton isp., Megagrapton submontanum and Scolicia strozzii. The described ichnoassemblages are assigned to the Cruziana to Cruziana-Nereites ichnofacies transition.
... The ichnogenus Bergaueria Prantl, 1945 shows a wide geological range. It is reported from the Precambrian (Crimes and Germs, 1982;Hofmann and Aitken, 1979;Kumar et al., 1984) to Miocene (Pokorný et al., 2017;Solórzano et al., 2017) sediments deposited in the marine environment. Bergaueria is interpreted as being a cubichnion (Arai and McGugan, 1968;Bayet-Goll and De Carvalho, 2017;Bhatt and Patel;Fürsich, 1974;Fürsich et al., 2018;Hakes, 1976;Häntzschel, 1965Häntzschel, , 1975Narbonne, 1984) or a domichnia (Alpert, 1973;Pickerill, 1989;Pokorný et al., 2017). ...
... It is reported from the Precambrian (Crimes and Germs, 1982;Hofmann and Aitken, 1979;Kumar et al., 1984) to Miocene (Pokorný et al., 2017;Solórzano et al., 2017) sediments deposited in the marine environment. Bergaueria is interpreted as being a cubichnion (Arai and McGugan, 1968;Bayet-Goll and De Carvalho, 2017;Bhatt and Patel;Fürsich, 1974;Fürsich et al., 2018;Hakes, 1976;Häntzschel, 1965Häntzschel, , 1975Narbonne, 1984) or a domichnia (Alpert, 1973;Pickerill, 1989;Pokorný et al., 2017). ...
The probable trace maker of B. hemispherica is the fact that one encounters different agegroups of sea anemone burrows extended at variable depths in soft, unconsolidated, non-fluidized mud to get stability. It occurs as densely packed, vertical to subvertical, usually unornamented, occasionally showing faint, thin, ring-like structures, allochemic sandstone-filled cylinders with hemispherical base extending to variable depths in the shale. The diameter-to-height ratio calculated for 44 burrow specimens shows that the diameters of most of the specimen are smaller than their height. The probable trace maker of B. hemispherica is the fact that one encounters different age groups of sea anemones, which extended their column at variable depth in soft, unconsolidated, non-fluidized mud to get stability. The inclined nature of paired burrows towards each other suggests social aggression while unpaired inclined burrows suggest swaying in search of food. The monodominant occurrence of B. hemispherica as pre-storm colonization of r-selected organisms(sea anemones) suggest stressed environment and simultaneous vacation of the burrower reflects rapid sedimentation due to high-energy storm events. Further, storm and inter-storm events deposited sandy allochemic limestone and shale series, respectively, but did not form an identical condition for the colonization of the sea anemone. The species B. hemispherica of the Bagh Group revealed physicochemical parameters (energy conditions, turbidity, sedimentation rate, bathymetry, suspended organic matter, substrate consistency, oxygen, and salinity) of the Late Cretaceous transgressive sea.
Full text available at: https://authors.elsevier.com/a/1Yz~7_b5X4nnAJ
... To demonstrate this benefit, let us name, for example, the first indirect evidence of the presence of animals in the fossil record of the Faroe Islands (Helminthoidichnites isp. and Palaeophycus isp.; Pokorný et al., 2015), or a similar description of the endemic assemblage composed exclusively of soft-bodied invertebrates (Pokorný et al., 2017). ...
The fossil record of the Azores still lacks evidence of terrestrial invertebrates. Based on a study of the collections of Quaternary fossil plant imprints from the Azores, located in the depositories of public collections and also newly conducted field research, several samples of fossil leaves with traces of plant–animal interactions were found. These are evidence of marginal feeding (Phagophytichnus ekowskii) and anophionome mine (Cuniculonomus isp.). One specimen with traces of boring in fossil wood (Xylonichnus trypetus), previously only briefly mentioned in the literature, was also described in detail. In addition to a detailed description of the found traces, the present study also discusses the possible trace‐makers, using a comparison with the recent phytophagous fauna in relation to the original vegetation of the Azores (that includes laurisilva forest). It is thus possible to consider butterfly caterpillars (group Macrolepidoptera) or locust larvae (Orthoptera/Caelifera) as possible originators of marginal feeding. The ophionome mine could have been caused by the larvae of leaf‐miner flies (Agromyzidae) or moths from the group Microlepidoptera (Gracillariidae). Wood‐destroying beetles could be the cause of the boring in fossil wood.
... Lockeia siliquaria represents resting traces (cubichnia) produced by bivalves (Osgood Jr., 1970;Seilacher and Seilacher, 1994), whilst small crustaceans (e.g., Conchostracans) may have also made such traces in freshwater settings (Bromley and Asgaard, 1979). Lockeia in nonmarine environments is found in fluvial environments (Gluszek, 1995;Goldring et al., 2005;Lawfield and Pickerill, 2006) and has been reported from the Late Permian to Middle Triassic fluvial-lacustrine system in North China (Guo et al., 2019); from Triassic marginal lacustrine and fluvial deposits, in Argana Basin, Western High Atlas, Morocco (Zouheir et al., 2022); from Upper Triassic lacustrine systems of marginal lacustrine settings in Germany (Schlirf et al., 2001); from the Lower Cretaceous marginal lacustrine settings in southern England (Goldring et al., 2005;Radley et al., 1998); and from the Late Miocene lacustrine setting of south-eastern Iceland (Pokorný et al., 2017). ...
The lateral and vertical distribution of sedimentary facies and ichnofacies in lacustrine systems records sensitive climatic variations and rates of subsidence. The Upper Jurassic–Lower Cretaceous lacustrine system of the Pastos Bons Formation in the Parnaíba Basin, northeastern Brazil, is an excellent opportunity to evaluate the depositional history of the post-CAMP thermal subsidence. This subsidence event succeeded the voluminous emplacement of mafic magma linked to the Central Atlantic magmatic province (CAMP), ~201 Ma, forming a large subsiding area in West Gondwana. In this sense, this paper developed outcrop-based facies and ichnofacies analysis, allowing the interpretation of two depositional phases and four facies associations (FA): 1) The lower depositional phase comprises lacustrine deposits showing an aggradational stacking pattern. FA1 - central lake record fibrous gypsum interbedded with fossiliferous shale beds, forming shallowing-upward cycles. 2) The upper depositional phase reveals a fluvio-lacustrine succession, forming a progradational stacking pattern. Central lake (FA1) central lake comprises laminated mudstone and sandstone beds hosting a suite representative of Mermia ichnofacies, forming coarsening-upward cycles. Lakeshore (FA2) comprising mudstone beds, limestone lenses, and sandstone beds hosting a suite representative of Scoyenia ichnofacies, forming shallowing-upward cycles; and conglomerate lenses overlaid by sandstone beds hosting a suite representative of Skolithos ichnofacies, forming fining-upward cycles. Braided fluvial (FA3) comprising conglomerates and sandstone beds, forming fining-upward cycles. Delta front (FA4) comprises mudstone lenses and sandstone beds hosting a suite representative of Skolithos ichnofacies, organized in coarsening-upward cycles. The fluvial discharge and wave activity oxygenated the water lake in the progradational phase, creating chemical and biological conditions that allowed the establishment of the epifaunal and infaunal benthic communities, represented by the well-preserved ichnological record. The rates of the post-CAMP thermal subsidence (accommodation) balanced with the increase of the wet periods to the top of the succession (sedimentary supply) indicate a depositional evolution from underfilled to overfilled lake basin, during Upper Jurassic-Lower Cretaceous, in West Gondwana.
... Helminthopsis comprises meandering, unbranched, horizontal trails that typically do not touch or crosscut each other, and which lack selfovercrossing (Han and Pickerill, 1995;Wetzel and Bromley, 1996;Buatois et al., 1998;Uchman et al., 2005;Hanken et al., 2016). This is distinct from Helminthoidichnites, which consists of slightly winding (rather than meandering) horizontal trails locally showing scribbling patterns and commonly displaying overlap among specimens (Buatois et al., 1998;Pokorný et al., 2017). Both ichnotaxa are typically preserved as negative epirelief or positive hyporelief. ...
The Ediacaran–Cambrian transition marks one of the most important geobiological revolutions in Earth History, including multiple waves of evolutionary radiation and successive episodes of apparent mass extinction. Among the proposed drivers of these events (in particular the extinction of the latest Neoproterozoic ‘Ediacara biota’) is the emergence of complex metazoans and their associated behaviors. Many metazoans are thought to have crucial geobiological impacts on both resource availability and the character of the physical environment – ‘ecosystem engineering’ – biological processes best preserved in the geological record as trace fossils. Here, we review this model using the trace fossil record of the Ediacaran to Cambrian Nama Group of southern Namibia, combining previous published accounts with the results of our own field investigations. We produce a revised ichnostratigraphy for the Nama Group that catalogues new forms, eliminates others, and brings the trace fossil record of the Nama into much closer alignment with what is known from other Ediacaran sections worldwide. We provide evidence for a link between sequence stratigraphy, oxygen, and the emergence of more complex bilaterian behaviors. Lastly, we show that observed patterns of extinction and survival over pulses of Ediacaran extinction are hard to ally with any one specific source of ecological stress associated with bioturbation, and thus a biologically-driven extinction of the Ediacara biota, if it occurred, was more likely to have been driven by some combination of these factors, rather than any single one.
... Bergaueria is regarded as a cubichnion or domichnion structure produced by suspension feeding actinarians (Prantl, 1945;McGugan, 1968, 1969;Alpert, 1973;. The ichnogenus Bergaueria is known from the earliest Cambrian to the Pleistocene sequences (Crimes and Germs, 1982;Crimes, 1987;Pemberton and Jones, 1988;Pemberton and Magwood, 1990;Jensen and Grant, 1998;Pokorny et al., 2017;Solórzano et al., 2017;Hoşgör and Yilmaz, 2018). Bergaueria perata ranges mostly from the early Cambrian to the late Silurian (Ludlow) (Orlowski and Radwanski, 1996;Jensen and Grant, 1998;Seilacher, 2007;Pacześna, 2010;Stachacz, 2016;Hoşgör and Yilmaz, 2018). ...
Trace fossils Arthrophycus cf. A. brongniartti, Asterosoma ludwigae, Bergaueria perata, Cruziana semiplicata, Cruziana furcifera, Curvolithus simplex, Diplichnites gouldi, Monomorphichnus lineatus, Phycodes circinatum, Phycodes palmatum, Phycodes rarus, Palaeophycus striatus, Planolites isp., Rusophycus leifeirikssoni, Rusophycus petraeus, Rusophycus latus, Rusophycus isp.-A , Rusophycus isp.-B, Rusophycus isp.-C, ?Rhabdoglyphus isp, and Treptichnus pedum are reported from the Arkosic Sandstone Member (Koti Dhaman Formation, Tal Group), Nigalidhar syncline, Lesser Himalaya. Cruziana semiplicata ranges from Furongian to early Ordovician and the trace fossils of the Cruziana rugosa group are considered as typical Ordovician in age; their
presence suggests an Ordovician transgression in the Indian Lesser Himalaya and an extension of the sea from Gondwana on to the Indian plate. It implies a hiatus between the Arkosic Sandstone Member and the underlying lower Cambrian Shale Member. The contact between the two shows angular and erosional discordance. The angular discordance is related to the Cambro-Ordovician Kurgiakh orogeny event. The Ordovician trace fossil bearing Arkosic Sandstone together with overlying sequence is being separated from the Tal Group is now designated as the Deona Formation. This contribution introduces a significant facet to the evolution of the Himalaya in general and the Lesser Himalaya in particular.
Upper Cretaceous to lower Palaeogene carbonate and siliciclastic deposits that crop out widely in the Haymana and Polatlı districts (Ankara Province) of the Haymana Basin (Central Anatolia) are rich in larger benthic foraminifera, various macrofossils and ichnofossils. The ichnofossils of the Haymana and Yeşilyurt formations were studied at five localities. The Upper Cretaceous siliciclastics of the Haymana Formation contain moderately diverse trace fossils, belonging to the deep-sea Nereites ichnofacies. The Paleocene siliciclastic and
carbonate deposits of the Yeşilyurt Formation comprise similar trace fossils, which do not show significant changes in comparison to the Haymana Formation. This indicates that the K-Pg boundary extinction event did not affect the ichnofauna with any longer consequences.
The Upper Cretaceous coarser, siliciclastic deposits of the Haymana and Beyobası formations are rich in shallow-marine, larger benthic foraminifera, including species of Orbitoides, Omphalocyclus, Siderolites, Hellenocyclina, and Loftusia, whereas fine siliciclastic deposits contain abundant planktonic, open-marine foraminifera,
such as Globotruncana and Heterohelix. Palaeogene siliciclastic to carbonate deposits of the Kartal, Yeşilyurt and Çaldağ formations are rich in the larger, benthic foraminifera Nummulites, Discocyclina, Assilina and Alveolina. The larger foraminifers have been redeposited from nearby, shallow-marine parts of the basin.
Key words : Trace fossils, benthic foraminifera, Campanian, Paleocene, Turkey.
Iceland and Faroe Islands represent a classical example of an area fully formed by volcanic activity. Their geological history goes back to the Lower Palaeogene when the northern part of Mid-Atlantic Ridge was active in the area of hotspot expression. Thick effusions and sheet intrusions of tholeiitic plateau basalts of Palaeogene age are characteristic for the Faroe Islands. Undersea volcanism which continuously cropped up and extruded the surface began in the Middle Miocene. The sequence of volcano-stratigraphic units with numerous volcaniclastic sedimentary layers is typical for both regions. However, there is one significant difference – in Iceland the marine and coastal deposits dominate but in the Faroe Islands mostly freshwater sediments are concerned.
Marine fauna is often preserved in the Icelandic sediments, for example Bivalvia, Gastropoda, Scaphopoda, Cirripedia, Annelida etc. In non-marine ecosystems, fossil plants, which locally form coal layers, dominate. Freshwater and terrestrial animals are much rarer. Fossil records of animal activities have not been studied there yet; however, their information potential has a great potential. Before the research presented in here, only three ichnologic papers were published and in several others the traces are only marginally mentioned.
No animal fossils from the Palaeogene age have been discovered in the Faroe archipelago yet, the same goes for the trace fossils. The only knowledge relates to the fossil plants. From the period after the end of the volcanic activity the finds of fossils are mostly limited to the Holocene age, except the Eemian wood fragments from the unique locality on the Borðoy Island.
In 2012–2018, a detailed paleontological research was carried out in the above mentioned European part of Arctic and Subarctic. Various bioerosion traces of Weichselian age were identified in the glaciomarine sediments, which remained after mechanic damages on shells of mollusc or barnacle, caused by the activity of predators; or after attachment of epibiotic organisms (e.g. Anellusichnus, Caulostrepsis, Centrichnus, Clionolithes, Finichnus and Oichnus), a lot of traces of locomotion were also found on the surface or inside sediment (will be published in the coming years). Resting traces and escape traces were also found here in the marine and also freshwater environments (Miocene).
It is not surprising that the marine ichnoassemblages show the worldwide geographic range; on the other hand, the lacustrine trace fossils are mostly endemic (Helminthoidichnites, Mammillichnis, Thorichnus igen. nov. and Vatnaspor igen. nov.).
In the Faroe Islands, the character of the Palaeogene landscape and ecosystems was quite well known based on the knowledge about the fossil plants and lithology of the volcaniclastic sediments. However, the proof of the animal presence was still missing. Although expected, the finding of Helminthoidichnites isp. and ?Palaeophycus isp. on the Eysturoy Island was important. Another but significantly younger trace fossils (Teredolites) were identified in the wood fragments comes from gyttja coastal cliffs of Eemian age. Terminal deposit place of driftwood in the lake basin connected with sea allows a big discussion about principal directions of sea currents in the last interglacial, despite their origin in high seas. The youngest confirmed traces come from the late Holocene soil profile. These are rhizoliths that testify the change of the landscape in the age of first human settlement of Faroe Islands. At present, the trace fossils mentioned above represent the first and only occurrence of trace fossils on the Faroe Islands.
Iceland is the only known terrestrial place in the subarctic North Atlantic providing a fairly continuous sedimentary and plant fossil record over the past 15millionyears. While the basic palaeobotanical framework of this pattern has been well established during the last decade, less attention has been paid to the abundant insect traces on fossil leaves/leaflets. Here, we assess the diversity and frequency of insect herbivory on 4349 fossil angiosperm leaves/leaflets from six plant-bearing sedimentary formations exposed at 18 localities. By combining analyses of environmental factors, species interactions, ecology, biogeography, and the geological history, our results demonstrate how patterns of herbivory have changed over time in relation to temperature fluctuations that profoundly influenced levels of insect-mediated damage diversity and frequency. In addition, higher structural complexity, particularly the establishment of species-rich herb layer communities seems to have positively influenced the structure of insect communities in early late Miocene palaeoforests of Iceland.
Tidal rhythmites of the Tonganoxie Sandstone Member (Stranger Formation, Douglas Group) at Buildex Quarry, eastern Kansas, contain a relatively diverse ichnofauna. The assemblage includes arthropod locomotion ( Dendroidichnites irregulare, Diplichnites gouldi types A and B, Diplopodichnus biformis, Kouphichnium isp., Mirandaichnium famatinense , and Stiaria intermedia ), resting ( Tonganoxichnus buildexensis ) and feeding traces ( Stiallia pilosa, Tonganoxichnus ottawensis ); grazing traces ( Gordia indianaensis, Helminthoidichnites tenuis, Helminthopsis hieroglyphica ); feeding structures ( Circulichnis montanus, Treptichnus bifurcus, Treptichnus pollardi , irregular networks), fish traces ( Undichna britannica, Undichna simplicitas ), tetrapod trackways, and root traces. The taxonomy of some of these ichnotaxa is briefly reviewed and emended diagnoses for Gordia indianaensis and Helminthoidichnites tenuis are proposed. Additionally, the combined name Dendroidichnites irregulare is proposed for nested chevron trackways. Traces previously regarded as produced by isopods are reinterpreted as myriapod trackways ( D. gouldi type B). Trackways formerly interpreted as limulid crawling and swimming traces are assigned herein to Kouphichnium isp and Dendroidichnites irregulare , respectively.
Taphonomic analysis suggests that most grazing and feeding traces were formed before the arthropod trackways and resting traces. Grazing/feeding traces were formed in a soft, probably submerged substrate. Conversely, the majority of trackways and resting traces probably were produced subaerially in a firmer, dewatered and desiccated sediment.
The Buildex Quarry ichnofauna records the activity of a terrestrial and freshwater biota. The presence of this assemblage in tidal rhythmites is consistent with deposition on tidal flats in the most proximal zone of the inner estuary, between the maximum landward limit of tidal currents and the salinity limit further towards the sea.
The Tertiary igneous rocks of Greenland, Iceland, the Faeroes and Britain have been the subject of study and debate for more than a hundred years. Iceland is of particular significance because the coincidence of a mantle plume with the Mid-Atlantic Ridge combines the two fundamental forces that promote magmatism, namely the elevated mantle potential temperature induced by the Iceland plume and adiabatic decompression in response to spreading at the ridge. Furthermore, the exposed Iceland crust contains evidence of major ridge-jumps over the last 16 million years and this relocation of the magmatic focus has been a prominent process in the evolution of the island. The control oil ridge-jumping is clearly related to the interaction of the mantle plume with the overlying lithospheric plate. This process has had a significant impact on the investigation of magmatic, tectonic and sedimentary processes. The bulk of the Tertiary region is made of subaerial tholeiitic flood basalts separated by minor clastic interbeds, usually of volcanic origin. The relatively monotonous Tertiary lithology is interrupted where central volcanoes occur with their buried palaeotopography, evolved rocks, hydrothermal alteration and stratigraphic complexities. It has become clear that the range of chemical composition of Tertiary basalt is much more, limited than that seen among Pleistocene and Holocene basalt, and depleted basalt appears, surprisingly, to be absent from the Tertiary succession. These observations call be explained by processes of crustal accretion operating today in the active rift zones of Iceland. It is a widely held assumption that V-shaped ridges observed in the gravity field around the Reykjanes Ridge imply variation in plume temperature and plume activity. Temporal variations in some isotope ratios in the Tertiary lava flows seem to coincide with the formation of the V-shaped features, and this could be consistent with a pulsating plume model.
On the western side of the Tjornes Peninsula in North Iceland a long sequence of fossiliferous marine sediments, basalts, and diamicitites records the climatic history of the North Atlantic during the Pliocene and Lower Pleistocene. The Pliocene Tjornes beds are divided in three biozones; the Tapes Zone (oldest), the Mactra Zone, and the Serripes Zone (youngest). The Tjornes beds consist mainly of marine silt- and sandstones but there art, also several fossiliferous terrestrial beds in the lower part. The marine faunas in the Tapes and Mactra Zones are mainly boreal, but during the deposition of the Serripes Zone the fauna greatly diversified with immigration of Pacific molluscan species with more arctic elements. They reached the North Atlantic at 3.6 Ma after migration through the Bering Strait coeval with closing of the Central American Seaway. Marine molluscs of Pacific ancestry it? the Tapes and Mactra Zones post-date also the first opening of the Bering Strait. In the Breioavik Group, diamictite beds alternate with volcaniclastic mudrocks and sandstones, and basaltic lava flows. Fourteen lithological cycles are identified in the Breidavik Group each one starting with a diamictite interpreted as lodgement tillite and ending with terrestrial sediments and lava flows. Interbedded marine fossiliferous mudrocks and sandstones contain arctic to boreal faunal assemblages. The oldest cycle in the Breioavik group was probably deposited about 2.5 Ma, just after the Gauss/Matuyama polarity reversal.
During the last few decades, many new ethological categories for trace fossils have been proposed in addition to the original five given by Seilacher. In this article, we review these new groups and present a version of the scheme of fossil animal behaviour originally published by Bromley updated with regard to modern ethological concepts, especially those of Tinbergen. Because some behaviours are more common in certain environments than others, they are useful in palaeoecological reconstructions, forming the original basis of the ichnofacies concept. To simplify, we summarise some ethological categories as previously done by others. However, the tracemaker’s behaviour in some cases is so distinctive that subcategories should be employed, especially in ecological interpretations of certain environments where a special behaviour may be dominant.
Palaeontological research on the Miocene and Pliocene oras and faunas of Iceland date back to the 1770's. At that time, plant fossils from Iceland were considered belonging to a single ora, and in the early 20th century scientist considered this ora of Eocene age. During the past few decades systematic palaeontology, palaeoclimatology, stratigraphy, and palaeogeography have been linked to results from isotopic (K/Ar and Ar/Ar) absolute age determinations and palaeomagnetic measurements of Cainozoic lavas in Iceland. As a result, numerous fossil oras and a few faunas identied from terrestrial sediments in Iceland are now known to give a contiguous record dating back 15 Ma. The oldest oras are therefore Middle Miocene in age. Younger oras are quite different from the older ones and their composition changed as the Miocene came to an end. Gradual cooling that occurred on Iceland since 12 Ma, when the climate was mild with no dry season and warm summers, and continuous isolation of Iceland, in the northern North Atlantic, had its affect on the Icelandic ora. Thermophilous plants soon became extinct and more cold tolerant species became prominent.
Extreme environments are characterised by the presence of physicochemical stressors and provide unique study systems to address problems in evolutionary ecology research. Sulphide springs provide an example of extreme freshwater environments; because hydrogen sulphide’s adverse physiological effects induce mortality in metazoans even at micromolar concentrations. Sulphide springs occur worldwide, but while microbial communities in sulphide springs have received broad attention, little is known about macroinvertebrates and fish inhabiting these toxic environments. We reviewed qualitative occurrence records of sulphide spring faunas on a global scale and present a quantitative case study comparing diversity patterns in sulphidic and adjacent non-sulphidic habitats across replicated river drainages in Southern Mexico. While detailed studies in most regions of the world remain scarce, available data suggests that sulphide spring faunas are characterised by low species richness. Dipterans (among macroinvertebrates) and cyprinodontiforms (among fishes) appear to dominate the communities in these habitats. At least in fish, there is evidence for the presence of highly endemic species and populations exclusively inhabiting sulphide springs. We provide a detailed discussion of traits that might predispose certain taxonomic groups to colonize sulphide springs, how colonizers subsequently adapt to cope with sulphide toxicity, and how adaptation may be linked to speciation processes.
On five occasions from 2000 to 2002, we sampled the macroinvertebrate fauna of the Sunbeam Hot Springs in central Idaho, USA. Spring surface water temperatures ranged from 52 to 58°C, and a relatively depauperate community was found, which comprised Coleoptera, Diptera, Hydracarina, and Ostracoda. The community varied little among the sampling dates, with total animal density of 86–168 ind./m and total richness of seven taxa. The fauna of the Sunbeam Hot Springs resembles the fauna reported from hot springs in Washington, Alberta, and British Columbia more that the fauna from hot springs of Yellowstone National Park. The aquatic beetle Hydroscapha natans, a southern species not common to either the Pacific Northwest or Yellowstone, was collected in this Idaho hot spring.
Mud volcanism and diapirism have puzzled geoscientists for ~2 centuries. They have been described onshore and offshore in many places on Earth, and although they occur in various tectonic settings, the majority of the features known to date are located in compressional tectonic scenarios. This paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described. Mud volcanoes show variable geometry (up to tens of kilometers in diameter and several hundred meters in height) and a great diversity regarding the origin of the fluid and solid phases. Gas (predominantly methane), water, and mud may be mobilized at subbottom depth of only a few meters but, in places, can originate from several kilometers depth (with minor crustal or mantle input). The possible contribution of mud extrusion to global budgets, both from quiescent fluid emission and from the extrusive processes themselves, is important. In regions where mud volcanoes are abundant, such as the collision zones between Africa and Eurasia, fluid flux through mud extrusion exceeds the compaction-driven pore fluid expulsion of the accretionary wedge. Also, quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and, hence, to greenhouse climate.
Surging outlet glaciers are important in draining large ice caps, but the mechanisms controlling surge periodicities are poorly known. We investigated a sediment sequence from the glacier-fed Lake Lögurinn in eastern Iceland, and our unique annually resolved data, based on sedimentary varves, imply that Eyjabakkajökull, an outlet glacier of Vatnajökull, began surging about 2200 cal a BP (before 1950 AD). Approximately 1700 cal a BP, the glacier started to surge at a uniform 34- to 38-year periodicity that prevailed until the coldest part of the Little Ice Age when the periodicity almost halved to 21–23 years. Since the late 1800 s the surge periodicity of Eyjabakkajökull has returned to a longer period of 35–40 years. We suggest that surge periodicities of Eyjabakkajökull are forced by climatically driven mass balance changes, which may be a common forcing factor for similar surge-type outlet glaciers. Copyright © 2011 John Wiley & Sons, Ltd.
Volcanic strata in the Skaftafell region, southeast Iceland, record a sequence of at least 16 glacial and interglacial intervals since 5 Ma. Two composite sections of 2 to 2.8 km thickness have been constructed from multiple, overlapping, cliff profiles. The timing of alternating sequences of subaerial lava flows, pillow basalts, and hyaloclastite deposits is provided by magnetostratigraphic mapping and K-Ar radiometric dating. We find that the frequency and intensity of glaciations increased significantly at ca. 2.6 Ma, and particularly since 0.8 Ma, amplifying topographic relief in this area from
Detailed low-level aeromagnetic data between Iceland and 70oN are combined with published bathymetric, seismic reflection, and other data to yield a new tectonic synthesis of this region of anomalously shallow sea floor. On Kolbeinsey Ridge short transform faults have repeatedly formed and disappeared over the last 7-8 Ma. Spreading from Kolbeinsey Ridge began about anomaly 6C time (24 Ma) ; total opening rates increased from 1.5 cm/a to 2 cm/a about 12-13 Ma ago. The Intermediate-Iceland-Plateau extinct axis thus does not exist, and oceanic crust must underlie much of the Greenland margin, perhaps up to the coast itself. This in turn implies locally over 100 km prograding, much of which probably occurred during Plio-Pleistocene glacial periods. The Iceland shelf has been prograded locally 25 km or more. -Authors
Various trace fossils from the Hassberge Formation and the Löwenstein Formation (Middle Keuper, Upper Triassic) of the Haßberge
region are described. Twenty-three different forms have been identified, 17 of which are named, includingCruziana pascens n. isp.,Lockeia cunctator n. isp., andRusophycus versans n. isp.Lockeia siliquaria
James, 1879,L. amygdaloides (Seilacher, 1953),L. triangulichnus
Kim, 1994, andL. elongata (Yang, 1984) are revised and synonymized under the oldest available name,L. siliquaria
James, 1879.Rusophycus eutendorfensis (Linck, 1942) andR. carbonarius
Dawson, 1864 are revised. The diagnosis ofPolykladichnus
Fürsich, 1981 is emended, and a diagnosis forHelminthoidichnites
Fitch, 1850 is given for the first time. Among the described ichnotaxa,Skolithos ispp.,Rusophycus carbonarius, andTaenidium barretti are the most common forms. The trace fossil association is typical of theScoyenia ichnofacies, which indicates non-marine, periodically or completely inundated environments, such as floodplains and lake
margins. Two palaeoichnocoenoses are identified. One ichnocoenosis, dominated byCruziana problematica, cf.Polykladichnus isp., andSkolithos isp. B characterizes margins of trough cross-bedded sandstones. Another ichnocoenosis, dominated byRusophycus versans n. isp.,Taenidium barretti,Scoyenia gracilis andSkolithos isp. A is related to ephemeral lake deposits. Taxonomic recommendations for the use of hitherto described and figured invertebrate
Keuper trace fossils from Germany are given.
We use a model of plate motions relative to major hotspots underneath the African, Indian, North American, South American, and Australian plates to compute the track of the Iceland hotspot after 130 Ma. The present-day hotspot is located under eastern Iceland offset about 240 km east of the Reykjanes and Kolbeinsey ridges. At 40 Ma, the Kangerlussuaq region of East Greenland would have been directly above the hotspot. The anomalous postdrift uplift of the East Greenland margin can also be explained by passage of the rifted margin over a hotspot. At 60 Ma, the Umanak Fjord region of the west coast of Greenland was above the hotspot, where picrites and hyaloclastites of nearby Disko Island are dated at approximately 64 to 59 Ma. Our reconstruction shows Ellesmere Island above the hotspot between 130 and 100 Ma. Latest Albian to early Cenomanian volcanic rocks on Axel Heiberg Island and northern Ellesmere Island indicate a nearby hotspot at that time. At 130 Ma, our model locates the hotspot near the northern margin of Ellesmere Island, close to the intersection of the Alpha Ridge with the coast. The hotspot would have been located beneath the Arctic Alaska-Chukotka plate when it formed the Mendeleyev Ridge, and as the spreading center migrated over the hotspot, it transferred to the North American plate, where it formed the Alpha Ridge. Our model suggests that the initiation of the Iceland hotspot predates the opening of the North Atlantic by at least 70 m.y. and that the massive early Tertiary volcanism along the North Atlantic plate margins reflects the effect of rifting in the vicinity of existing thinned crust, rather than the arrival of a plume head. [References: 41] 41
16. 1997. The North Atlantic Igneous Province. In: (eds) , . 100, .
Here we describe fossil Bibionidae (Diptera) insects from the late Miocene Hrútagil locality (part of the 9–8 Ma Skarðsströnd–Mókollsdalur formation) in Iceland. This material offers a rare chance to study a fossil insect fauna from a North Atlantic oceanic island. The material includes three species, one from each genera of Bibio, Dilophus and Penthetria, but only the former is sufficiently well preserved to warrant description as a new taxon, Bibio edda sp. nov., most superficially similar to B. brevis Heer, 1849 but differs in wing and tibial characters, among others. Finally, we compare the species to other fossil Bibionidae known from the Miocene of continental Europe.
Ichnology is the study of traces created in the substrate by living organisms. This is the first book to systematically cover basic concepts and applications in both paleobiology and sedimentology, bridging the gap between the two main facets of the field. It emphasizes the importance of understanding ecologic controls on benthic fauna distribution and the role of burrowing organisms in changing their environments. A detailed analysis of the ichnology of a range of depositional environments is presented using examples from the Precambrian to the recent, and the use of trace fossils in facies analysis and sequence stratigraphy is discussed. The potential for biogenic structures to provide valuable information and solve problems in a wide range of fields is also highlighted. An invaluable resource for researchers and graduate students in paleontology, sedimentology and sequence stratigraphy, this book will also be of interest to industry professionals working in petroleum geoscience.
Ichnodisparity has been recently introduced as a concept to assess the variability of morphologic plans in biogenic structures, revealing major innovations in body plan, locomotory system and/or behavioral program. Whereas ichnodiversity is measured in terms of the number of ichnotaxa (i.e. ichnogenera or ichnospecies), ichnodisparity is evaluated based on the identification of categories of architectural design. Seventy-nine categories of architectural designs (58 for bioturbation structures and 21 for bioerosion structures), encompassing 523 ichnogenera (417 for bioturbation structures and 106 for bioerosion structures), are defined. They are restricted to invertebrate ichnotaxa, whereas vertebrate trace fossils were not included. Although the scheme is designed to be comprehensive, the proposed categories are necessarily works in progress because of the state of flux in ichnotaxonomy and the need to adjust the definitions of categories according to the scope and scale of the analysis. Although it may be said that the establishment of categories of architectural design is to a certain degree a subjective enterprise, this is not different from ichnotaxonomy because classifying trace fossils from a taxonomic perspective implies observing the morphology of the trace and interpreting it in terms of behavior. The concept of ichnodisparity is free of some of the vagaries involved in ichnotaxonomy. The fact that ichnodiversity and ichnodisparity exhibit different trajectories during the Phanerozoic underscores the importance of adding the latter to the ichnologic toolkit.
This review is based on compilations of dips, the distribution of amygdale minerals, and the intensity of the dyke swarms. These compilations enable the position of the original top of the crust to be deduced. The top lies generally well above the present summit levels, but is highest in the belt of country within which the highest summits occur. There is also a general rise southwards along the length of the belt to a maximum in the Quaternary volcanic district along the edge of the Vatnajokull. The non-parallelism of lava isochrons and dyke isochrons implies that there was a progressive southward shift in the zone of maximum spreading and probably a progressive intensification of activity as well.
This chapter discusses the extent and chronology of glaciations in Iceland. The distribution of glacial deposits and the correlation between rock sequences in Iceland show a distinct trend during the Pliocene–Pleistocene transition indicating a gradually growing ice sheet from the southeast toward the west and north. The oldest glacial deposit identified based on detailed sedimentological analyses is found imbedded within c. 3.8 to 4.0 My old lava flows in Fljótsdalur, eastern Iceland. Another glacial bed found higher up in the sequence at the same site has an estimated age of 3.4 My. As it has not been possible to trace these two glacial beds over a larger area, they are thought to represent only local glacier activity. Recent palaeomagnetic study and K–Ar radiometric dating on the stratigraphy of Skaftafell, southeast Iceland, also suggests an increased glaciation at c. 2.6 Ma. More extensive glaciation is indicated by glacial deposits in all parts of the country dating from 2.4 to 2.5 My ago. From the period between 2.9 and 1.6 My, at least 6 glaciations and possibly 8 glaciations are indicated, but the geological record implies a decrease in glacial activity in the period between 1.6 to 1.2 My.
Four marine molluscan species that migrated to Iceland during the deposition of sedimentary sequences on the north side of Snaefellsnes, western Iceland, at about 1.1 Ma, are not living in Iceland today. Three of these species are arctic and reached the area during an Early Pleistocene deglaciation. The fourth is thermophilic and arrived during the following interglacial, together with several littoral species now living in Iceland. The arctic species probably migrated to Iceland from the west or northwest due to a southward shift of the cold and euhaline East Greenland Current to the Icelandic west coast. At that time the Polar Front was lying considerably south of Iceland, but then followed a periodic northward shift of the front. The fact that the arctic species did not reach northern Iceland at this time may indicate a rapid shift of the Polar Front across the north coast of Iceland that minimized the influence of the East Icelandic Current during the deglaciation. Several thermophilic littoral species that migrated to western Iceland during the following interglacial did not reach northern Iceland. They came from the south or southeast during strengthening of the warm Irminger Current. However, the current's influence on the Icelandic north and northeast coasts was probably limited because of mixing with colder water masses with reduced salinity from the East Icelandic Current.
Well-preserved arthropods are reported from Miocene sedimentary rocks of the Skarðsströnd-Mókollsdalur (9–8 Ma) and Hreðavatn-Stafholt (7–6 Ma) Formations in Iceland. Fossil remains of terrestrial and/or freshwater animals have rarely been reported from the island before. Here we provide the first overview of the surprisingly rich Tortonian fauna from the Hrútagil locality and additional Messinian-aged trichopteran larval cases from the Stafholt locality. The Hrútagil fauna includes representatives of Cladocera (Crustacea: Branchiopoda) and seven insect orders, including several morphotypes of the orders Plecoptera, Dermaptera, Hemiptera (Cercopoidea, Aphididae), Coleoptera, Hymenoptera, Trichoptera (Drusinae), and Diptera (Bibionidae). Previous studies on the Miocene of Iceland have been based principally on pollen analysis and the macrobotanical record with little attention paid to other aspects of the island’s palaeontology. This study provides the first comprehensive systematic description of Miocene arthropods from the northern North Atlantic region and offers the opportunity for a rare glimpse into the late Cenozoic arthropod fauna of Iceland in the context of transatlantic migration and palaeobiogeography and the onset of major global cooling events.
Continental flood basalts, volcanic passive margins, and oceanic
plateaus represent the largest known volcanic episodes on our planet,
yet they are not easily explained by plate tectonics. Indeed, some are
likely to record periods when the outward transfer of material and
energy from the Earth's interior operated in a significantly different
mode than at present. In recent years, interest in large-scale mafic
magmatism has surged as high-precision geochronological, detailed
geochemical, and increasingly sophisticated geophysical data have become
available for many provinces. However, the sheer amount of recent
material, often in the form of detailed collaborative research projects,
can overwhelm newcomers to the field and experts alike as the literature
continues to grow dramatically. The need for an up-to-date review volume
on a sizable subset of the major continental and oceanic flood basalt
provinces, termed large igneous provinces, was recognized by the
Commission on Large-Volume Basaltic Provinces (International Association
of Volcanology and Chemistry of the Earth's Interior), and the
co-editors were charged with organizing and implementing such a volume.
We hope that this volume will be valuable to researchers and graduate
students worldwide, particularly to petrologists, geochemists,
geochronologists, geodynamicists, and plate-tectonics specialists; it
may also interest planetologists, oceanographers, and atmospheric
scientists.
Deep-sea paleoclimatic records show that the Quaternary climate around Iceland was, and probably still is, very sensitive to rapid shifts in North Atlantic oceanic circulation. Studies of several key sections in Iceland indicate that similar oscillations are reflected in the late Pliocene and early Pleistocene terrestrial stratigraphy. Correlations between six rock sequences in western, northern, eastern, and southern Iceland show a fairly distinct trend during the Pliocene-Pleistocene transition indicating the progressive growth of an ice sheet from southeast toward the north and west. The correlations are based on K/Ar dates and paleomagnetic studies. A total of 11 glacial horizons are recorded in a stratigraphic column from eastern Iceland extending back 6.5 myr. In western Iceland, 7 glacial horizons are preserved in a rock section dated from 7.0 to 1.8 myr, and in northern Iceland 14 glacial horizons are identified in a section that extends back to 9.0 myr. Well over 20 glacial horizons have been identified in the stratigraphic column in Iceland. Full-scale glacial-interglacial cyclicity with regional ice cover is indicated at approximately 2.6 myr. A further amplification leading to islandwide glaciations is identified at 2.2-2.1 myr. These results show that changes in the ice cover in Iceland correlate with the deep-sea oxygen isotope records from benthic and planktonic foraminifera as well as IRD studies from the North Atlantic.
Sheet intrusions (inclined sheets and dykes) in the deeply eroded volcanoes of Geitafell and Dyrfjöll, eastern Iceland, were studied at the surface to identify the location, depth, and size of their magmatic source(s). For this purpose, the measured orientations of inclined sheets were projected in three dimensions to produce models of sheet swarm geometries. For the Geitafell Volcano, the majority of sheets converge toward a common focal area with a diameter of at least 4 to 7 km, the location of which coincides with several gabbro bodies exposed at the surface. Assuming that these gabbros represent part of the magma chamber feeding the inclined sheets, a source depth of 2 to 4 km below the paleoland surface is derived. A second, younger swarm of steeply dipping sheets crosscuts this gabbro and members of the first swarm. The source of this second swarm is estimated to be located to the SE of the source of Swarm 1, below the present-day level of exposure and deeper than the source of the first swarm. For the Dyrfjöll Volcano, we show that the sheets can be divided into seven different subsets, three of which can be interpreted as swarms. The most prominent swarm, the Njardvik Sheet Swarm, converges toward a several kilometers wide area in the Njardvik Valley at a depth of 1.5 to 4 km below the paleoland surface. Two additional magmatic sources are postulated to be located to the northeast and southwest of the main source. Crosscutting relationships indicate contemporaneous, as well as successive activity of different magma chambers, but without a resolvable spatial trend. The Dyrfjöll Volcano is thus part of a complex volcanic cluster that extends far beyond the study area and can serve as fossil analog for nested volcanoes such as Askja, whereas in Geitafell, the sheet swarms seem to have originated from a single focus at one time, thus defining a single central volcanic complex, such as Krafla Volcano.
Unusually high volcanic productivity caused by mid-ocean ridge magmatism has resulted in unique preservation of the Tertiary and Quaternary depositional record in Iceland, where sediment horizons are covered and protected from erosion by basaltic lava flow sequences. Lava flows are deposited in ice-free regions representing interglacials, interstadials, or ice-free periods, whereas hyaloclastites (subglacially formed volcanics) and till represent glaciations. Mapping and dating of remnants of glacial deposits found imbedded within the basaltic lava flows of Iceland have revealed at least 22 glacial–interglacial cycles during the last ca. 3 Ma indicating an intermittent record of glaciation since the late Pliocene. Three phases of ice growth in Iceland are indicated: (1) an initial build-up phase, between >4 and 3Ma, (2) a transitional growth phase (3.0–2.5Ma), and (3) finally, development of an Iceland Ice Sheet that left glacial deposits in all studied section across the country by 2.5Ma. The number of identified ancient glacial deposits in Iceland and comparison with the deep-sea proxy record and studies of glacier cyclicity imply that the late Tertiary and Pleistocene terrestrial record in Iceland does capture the large-scale palaeoclimatic processes in the North Atlantic region from before the onset of the last Ice Age.
The glauconitic facies is widespread on present-day continental shelves from 50° S to 65° N and at water depths between 50 and 500 m, and is in particularly great abundance on the upper slope and outer shelf between 200 and 300 m. It is also common in many ancient rocks of post-late Precambrian age.
It occurs as sand- to pebble-sized, essentially green particles (granular facies) but also as a surface coating on particles and hardgrounds and as a diffuse impregnation (film and diffuse facies). We suggest the replacement of the term ‘glauconite’, which has been interchangeably used to designate a morphological form and a specific mineral, by glaucony (facies) and glauconitic smectite and glauconitic mica as end members of the glauconitic mineral family.
The widely accepted model of Burst and Hower for glauconitization requires a degraded, micaceous (2: 1 layer lattice structure) parent clay mineral. However, detailed analysis of numerous samples of Recent glaucony reveals that such a parent substrate is exceptional. The model therefore requires modification. Generally the parent material is carbonate particles, argillaceous (kaolinitic) faecal pellets, infillings of foraminiferal tests, various mineral grains and rock fragments, that pass gradually into the commonly occurring green grains.
We show that the process of glauconitization is achieved by de novo authigenic growth of automorphous crystallites in the pores of the substrate, accompanied by progressive alteration and replacement of the substrate. It is this two-fold evolution that causes the ‘verdissement’of granular substrates, macrofossils and hardgrounds. The authigenic mineral is an iron-rich and potassium-poor glauconitic smectite. While new smectites are growing into the remaining pore space the earlier smectites are modified by incorporation of potassium, producing decreasingly expandable minerals with a non-expandable glauconitic mica as the end member. This mineralogical diversity of the glauconitic mineral family explains the highly variable physical and chemical properties of glaucony. Four categories, nascent, little-evolved, evolved and highly-evolved glaucony are distinguished.
Glauconitization appears to be controlled by a delicate balance between degree of physical confinement of a particle and the amount of ionic exchange between the micro-environment and ambient open marine sea water. The optimum conditions for glauconitization are those of semi-confinement. As a result the interior of a grain is more glauconitized than its less confined periphery. Similarly, for identical substrate types, large grains (500μm) provide more favourable substrates for glauconitization than lesser confined small grains.
On a larger scale the formation of glaucony is governed by the availability of iron and potassium and the balance between detrital influx and winnowing. Low accumulation rates expose grains to the open marine environment for sufficiently long times (105-106 years for highly-evolved glaucony).
Aquifer fluid compositions and aqueous species distribution have been calculated for 22 samples collected from producing wells in the Krafla and Námafjall geothermal areas, Iceland. Overall mineral–solution equilibrium is rather closely approached in the aquifer beyond the depressurization zone around wells for all major components entering hydrothermal minerals. The minerals involved are in alphabetical order: albite, calcite, chlorite, epidote, K-feldspar (adularia), prehnite, pyrite, pyrrhotite, quartz and wairakite. Calculated saturation indices for OH-bearing Al–silicates show more scatter than for minerals of simpler composition. A large scatter is also observed for pyrite and pyrrhotite. The main uncertainty involved in calculating mineral saturation indices, particularly in the case of “excess” enthalpy well discharges, lies in the model adopted to calculate the aquifer water composition and its aqueous species distribution and not in the quality of the thermodynamic data on the aqueous species and the minerals with the possible exception of epidote and Fe2+.
Two ichnofacies are typical of lacustrine depositional systems. The Scoyenia ichnofacies characterizes transitional terrestrial/nonmarine aquatic substrates, periodically inundated or desiccated, and therefore is commonly present in lake margin facies. The Mermia ichnofacies is associated with well oxygenated, permanent subaqueous, fine-grained substrates of hydrologically open, perennial lakes. Bathymetric zonations within the Mermia ichnofacies are complicated by the wide variability of lacustrine systems. Detected proximal–distal trends are useful within particular lake basins, but commonly difficult to extrapolate to other lakes. Other potential ichnofacies include the typically marine Skolithos ichnofacies for high-energy zones of lakes and substrate-controlled, still unnamed ichnofacies, associated to lake margin deposits. Trace fossils are useful for sedimentologic analysis of event beds. Lacustrine turbidites are characterized by low-diversity suites, reflecting colonization by opportunistic organisms after the turbidite event. Underflow current beds record animal activity contemporaneous with nearly continuous sedimentation. Ichnologic studies may also help to distinguish between marine and lacustrine turbidites. Deep-marine turbidites host the Nereites ichnofacies that consists of high diversity of ornate grazing traces and graphoglyptids, recording highly specialized feeding strategies developed to solve the problem of the scarcity of food in the deep sea. Deep lacustrine environments contain the Mermia ichnofacies, which is dominated by unspecialized grazing and feeding traces probably related to the abundance and accessibility of food in lacustrine systems. The lower diversity of lacustrine ichnofaunas in comparison with deep-sea assemblages more likely reflects lower species diversity as a consequence of less stable conditions. Increase of depth and extent of bioturbation through geologic time produced a clear signature in the ichnofabric record of lacustrine facies. Paleozoic lacustrine ichnofaunas are typically dominated by surface trails with little associated bioturbation. During the Mesozoic, bioturbation depth was higher in lake margin facies than in fully lacustrine deposits. While significant degrees of bioturbation were attained in lake margin facies during the Triassic, major biogenic disruption of primary bedding in subaqueous lacustrine deposits did not occur until the Cretaceous.
The Tertiary central volcano of Breiddalur, the first to be described of several--perhaps many --such volcanoes in Iceland, has a volume of about IOO cubic miles of basic, intermediate, and acid lavas and pyroclastic rocks, with a maximum thickness of 5000 to 6000 ft. The basic lavas are unusually thin owing to the fact that they were erupted on a sloping surface. The central volcanicity contrasts with the flood-basalt fissure-eruptions of the surrounding country; at times the volcano stood up as a co ne above the flood-basalt plains, but flood-basalts were all the time being erupted; they were interdigitated with the products of the volcano (so strikingly that the term 'cedar-tree volcano' seems appropriate), and later completely buried it. The core of the volcano is marked by a profusion of acid lavas, pyroclastic rocks, and minor intrusions; in it the rocks are drastically altered and show variable and sometimes abnormally high dips indicative of cauldron-subsidence. A swarm of dykes locally constituting as much as 20 per cent of the country passes through the core. The rocks above the core probably in part occupy a crater or caldera; they include agglomerate containing blocks of granophyre, granite, and gabbro from inferred syngenetic intrusions below the volcano; a palagonite-tuff and breccia with basalt pillows, probably formed in a crater lake; two welded acid tufts; and a thick rhyolite flow joined to its plug-feeder. Acid rocks are mostly concentrated in or near the core, except for a spectacular group of parasitic rhyolites in which all stages in uncovering of the plug-feeders by erosion are seen. Simultaneous eruption of basic and acid magma from the same orifice is evidenced by one rock, which represents an emulsion of the two magmas, and also by a composite lava, with basic and acid components, which was erupted from a composite dyke.
The proximity of a hotspot to a spreading center may result in the channeling of asthenosphere to the section of rise crest closest to the hotspot. This produces more basalt and thicker crust at these locations, thus forming a plateau over time. The geometric constraints of such a model predict a unique orientation, location, and age progression for a plateau formed by this mechanism. The hotspot will channel material to the closest part of the rise; therefore the orientation of the plateau will differ from that of a hotspot track by the component of absolute motion perpendicular to the rise axis. The plateau will be symmetric with respect to the location of the rise axis at the time of formation. Also, the age progression of the plateau will be contemporaneous with the age of formation of the seafloor on either side because the plateau is seafloor, just with thicker crust. A set of reconstructions based upon magnetic isochrons and a fixed hotspot reference frame is presented for the Norwegian-Greenland Sea as a means of evaluating the model's predictions. By locating the Iceland hotspot, reconstructing the relative positions of the Greenland and European plates, and then assuming material would be channeled from the hotspot to the closest section of the rise crest, we can trace the tectonic evolution of the Greenland-Faeroe and Voring plateaus. The model is able to locate the plateaus, explain their orientations, and predict an age progression that satisfies observed age determinations. The analysis demonstrates that both plateaus could have been formed by the Iceland hotspot with the Greenland-Faeroe Plateau being in effect a continuation of the Voring Plateau, which was cut off due to transform motion between the northern and southern spreading centers.
The geothermal surface alteration of basalts and associated water chemistry at Krýsuvík, SW Iceland were studied. The geothermal area was characterised with zones of intensive surface alteration, steam vents, mud pots and hot springs. The steam-heated geothermal surface waters had pH values between 1.69 and 7.67 and total dissolved solid (TDS) concentrations between 154 and 6660ppm, with Cl and SO4 concentration decreasing and increasing with decreasing pH, respectively. Alteration mineral assemblages observed were strongly associated with the surface intensity. In areas of most intensive activity the basaltic rocks were altered to amorphous silica, anatase and pyrite with a crust of native sulphur at the surface. With decreased activity, kaolinite became important, as well as iron oxyhydroxides and oxides. On the flanks of the area montmorillonite was the predominant alteration product. Based on these observations the surface geothermal activity was divided into three groups: (1) high activity areas with active steam vents and mud pots and intensive acid leaching, (2) medium activity areas where the ground is hot, steam vents and mud pots are uncommon and the surface alteration is less intensive and (3) low activity areas on the margins of the surface geothermal activity. The primary factors influencing the steam-heated acid sulphate alteration of basalts included the redox state (oxidation front), supply of acids and pH, and the extent of reaction. The formation of iron- and sulphur-containing minerals and the respective elemental mobility depended on the redox conditions with pyrite formation under reduced conditions and goethite and/or hematite under oxidised conditions. At low pH, Ca, Mg, K and Na were mobile and leached out, whereas Fe, Ti and Al and to a large degree Si were retained in the alteration product. At higher pH values >5 the mobility of Ca, Mg, K and Na was reduced due to the formation of clays.
There are abundant and highly varied trace fossils in the Sinian—Cambrian boundary beds in eastern Yunnan. Collections from 27 sections and their study give altogether 45 ichnogenera and 87 ichnospecies. Among them, 2 ichnogenera and 7 ichnospecies are new, and 31 known ichnogenera and 38 known ichnospecies first found in the region. According to their order of appearance in the boundary beds and their assemblage features, the trace fossils in the Sinian—Cambrian boundary beds in the region may fall into 4 trace fossil assemblage zones in ascending order. In the paper they are correlated with those in the equivalent horizons abroad and their geological significance is discussed preliminarily.
The large-scale volcanic lineaments in Iceland are an axial zone, which is delineated by the Reykjanes, West and North Volcanic Zones (RVZ, WVZ, NVZ) and the East Volcanic Zone (EVZ), which is growing in length by propagation to the southwest through pre-existing crust. These zones are connected across central Iceland by the Mid-Iceland Belt (MIB). Other volcanically active areas are the two intraplate belts of Öræfajökull (ÖVB) and Snæfellsnes (SVB). The principal structure of the volcanic zones are the 30 volcanic systems, where 12 are comprised of a fissure swarm and a central volcano, 7 of a central volcano, 9 of a fissure swarm and a central domain, and 2 are typified by a central domain alone.
Physical observations on features such as temperature, pressure, and formation permeability are integrated with alteration intensity, fluid and secondary mineral compositions, and textures to show the most important thermal, chemical, hydrodynamic, and kinetics factors that control the evolution of two Icelandic geothermal systems, the Reykjanes and Svartsengi systems. There is an increase in alteration intensity and the abundance of fracture and vesicle fillings, a decrease in the abundance of primary minerals, and more extensive compositional heterogeneity near many aquifers, which are defined by circulation losses and temperature and pressure profiles. Features such as resorption and overgrowth textures, absence of systematic element partitioning, metastability, and undersaturation/supersaturation are widespread and are indicative of mineral-mineral and mineral-fluid disequilibrium. The composition of chlorite is more sensitive to changes in the physico-chemical conditions of the fluid compared to other secondary minerals. Chlorite geothermometry is used to map out the temperature patterns and extract information on permeability variations. In many chlorite-filled vesicles, chlorite grains show a systematic rim-to-core increase in temperatures derived from chlorite compositions and grain size and a decrease in smectite content due to heating of cooler waters or late pulses of hot, reduced fluids. Both systems are cooling due to heat source decay, cooler water incursions, or both. The results of this study will be useful in testing experimental studies and computer models of seawater-basalt reaction and recognizing the thermal, chemical, kinetics, and hydrodynamic factors that control secondary alteration in submarine hydrothermal systems. 118 refs., 20 figs., 8 tabs.
The systematics of the single-entrance, plug-shaped, soft-substrate trace fossils have long been in need of revision. At least 15 ichnogenera, comprising 32 ichnospecies, have been used, but an examination of the type material that is available suggests that this is excessive. A review of ichnotaxa indicates that the valid ichnospecies can be encompassed within five ichnogenera as follows: Conostichus (five ichnospecies), Bergaueria (including Kulindrichnus, three), Conichnus (including Amphorichnus, two), Dolopichnus (one), and Astropolichnus (one). In addition, several minor ichnogenera for related structures are considered. These are Calycraterion, Margaritichnus, and Mammillichnis.The majority of plug-shaped structures are interpreted as cubichnia or domichnia, dominantly of actinarian sea anemones. The occurrence of these trace fossils is predominantly in Paleozoic rocks.