Guido Meinhold

Geochemical constraints on the provenance and depositional setting of sedimentary rocks from the islands of Chios, Inousses and Psara, Aegean Sea, Greece: implications for the evolution of Palaeotethys

The provenance and depositional setting of Late Palaeozoic and Early Mesozoic clastic sediments from the eastern Aegean archipelago are examined here for the first time using whole-rock geochemistry and composition of detrital chrome spinel. Major- and trace-element data for Late Palaeozoic and Permo-Triassic clastic sediments from the Lower and Upper Units of Chios are compatible with an acidic to intermediate source, minor input of (ultra)mafic detritus and recycling of older sedimentary components. Chondrite-normalized REE profiles are uniform with light REE enrichments (LaN/YbN c. 7.7), negative Eu anomalies (Eu/Eu* c. 0.67) and flat heavy REE patterns (GdN/YbN c. 1.5), indicating an upper continental crustal source and/or young differentiated arc material. Detrital chrome spinel from the clastic sediments of Chios has Cr-number (Cr/(Cr + Al)) values between 0.29 and 0.89 and Mg-number (Mg/(Mg + Fe2+)) values between 0.24 and 0.70, suggesting a probably mixed (ultra)mafic source involving ridge peridotites (mid-ocean ridge type), fore-arc peridotites and island-arc basalts. The metasediments from the islands of Inousses and Psara have similar whole-rock chemical signatures to those of Chios, although no evidence was found for an (ultra)mafic source. We conclude that both the Late Palaeozoic sediments from the Lower and Upper Units of Chios and the metasediments from Inousses and Psara were deposited in a continental island-arc setting until at least Late Permian times, probably at a single Palaeotethyan margin. They are interpreted to be allochthonous, tectonically transported to their present position by Late Mesozoic to Cenozoic orogenic processes.

New Ordovician-Silurian drill cores from the Siljan impact structure in central Sweden: an integral part of the Swedish Deep Drilling Program

New drill cores from the largest known impact structure in Europe, the relict of the Siljan meteorite crater, provide new possibilities to reconstruct Early Palaeozoic marine environments and ecosystems, and to document changes in sedimentary facies, sea level and palaeoclimate in Baltoscandia. The impact crater is an important target of the project “Concentric Impact Structures in the Palaeozoic” within the framework of the “Swedish Deep Drilling Program”. Two core sections, Mora 001 and Solberga 1, have been analysed. The sedimentary successions of these core sections include strata of late Tremadocian through late Wenlock ages. Our preliminary studies show not only that several of the classical Palaeozoic units of Sweden are represented in the area, but also that other significantly different facies are preserved in the Siljan district. An erosional unconformity representing a substantial hiatus occurs between Middle Ordovician limestone and a Llandovery-Wenlock (Silurian) shale succession in the western part of the Siljan structure and suggests an extended period of uplift and erosion. This may be related to forebulge migration due to flexural loading by the Caledonian thrust sheet to the west. Thus, this part of Sweden, previously regarded as a stable cratonic area, presumably was affected by the Caledonian collision between Baltica and Laurentia.

Detrital zircon ages from the islands of Inousses and Psara, Aegean Sea, Greece: constraints on depositional age and provenance

U–Pb LA–SF–ICP–MS analyses of detrital zircons from a metalitharenite on Inousses Island, Greece, gave major age groups of 310–350, 450–500, 550–700, 900–1050 and 1880–2040 Ma and minor peaks between 2600 and 2800 Ma. The youngest concordant zircon grains of 310–330 Ma indicate the maximum age of deposition to be Late Carboniferous, rather than Ordovician, as had been earlier assumed. The lack of zircon ages between 1.1 and 1.8 Ga, coupled with the occurrence of c. 2-Ga-old zircons, imply a northern Gondwana-derived source. Detrital zircons from a garnet–mica schist on Psara Island yielded a major age group of c. 295–325 Ma and only minor Early Palaeozoic and Late Neoproterozoic ages. The youngest grains around 270 Ma indicate the maximum age of deposition to be Late Permian. The Early Palaeozoic ages support a source from terranes at the southern margin of Laurussia during the Late Palaeozoic and hence clarify the palaeotectonic position of units from the eastern Aegean Sea within the Palaeotethyan realm.

Did lingering ice sheets moderate anoxia in the Early Palaeozoic of Libya

The Hirnantian glaciation of West Gondwana produced a glacially sculpted topography, which is draped by organic-rich latest Ordovician and early Silurian ‘hot shales’. Although these are the most important Early Palaeozoic source rock in North Africa, organic enrichment is distributed unevenly. For example, in Al Kufrah Basin, Libya, ‘hot shales’ are elusive, but outcrop analysis at the western basin demonstrates why this is the case. The topmost Mamuniyat Formation, of Hirnantian age, comprises glaciogenic sandstones, passing upward into mixed facies of the Tanezzuft Formation, which has a latest Ordovician–early Silurian age. The basal Tanezzuft Formation contains a shelly carbonate (cool-water deposits accumulated under oxygenating conditions) and bioturbated sandstone succession. Above, hummocky cross-bedded and graded sandstone intervals are intercalated with shale and siltstone (storm influx onto a muddy shelf). These are interrupted by several lonestone-bearing intervals (ice-rafted debris), a striated pavement (of subglacial origin), and manganese oxide crusts and concretions. The concretions and bioturbation imply oxygenation of the sea floor during transgression. These putative glacial deposits were deposited following the main phase of the Hirnantian glaciation, at the same stratigraphic level as ‘hot shales’ elsewhere in northern Gondwana. Lingering ice caps may have produced well-oxygenated marine waters precluding ‘hot shale’ deposition.

U-Pb SHRIMP ages of detrital granulite-facies rutiles: further constraints on provenance of Jurassic sandstones on the Norwegian margin

Electron microprobe analyses of 128 detrital rutile grains from two Jurassic sandstone samples (Hettangian and Bajocian–Bathonian in age) from hydrocarbon exploration wells on the Norwegian margin confirm that more than 85 % of the rutiles were derived from metapelitic rocks. Zr-in-rutile geothermometry confirms that about 83 % of the rutile was formed under high-grade metamorphism (>750 °C). Sixty-two rutile grains, including 60 of the identified high-temperature rutile population, were also analysed for U–Pb geochronology using SHRIMP. The 206 Pb– 238 U rutile ages range from approximately 485–292 Ma, with a major cluster between 450 and 380 Ma. These data suggest that the detrital rutile was predominantly derived from a felsic source that experienced granulite-facies metamorphism about 450–380 Ma ago. This conclusion is consistent with derivation from high-grade Caledonian metasedimentary rocks, probably the Krummedal sequence in central East Greenland, as previously suggested by an earlier provenance study using conventional heavy mineral analysis, garnet geochemistry and detrital zircon age dating. The present study underscores the importance of rutile geochemistry and geochronology in quantitative single-mineral provenance analysis of clastic sedimentary rocks.

The Rhodope Zone as a primary sediment source of the southern Thrace basin (NE Greece and NW Turkey): evidence from detrital heavy minerals and implications for central-eastern Mediterranean palaeogeography

Detrital heavy mineral analysis coupled with a regional geological review provide key elements to re-evaluate the distribution of the Rhodope metamorphic zone (SE Europe) in the region and its role in determining the evolution of the Thrace basin. We focus on the Eocene–Oligocene sedimentary successions exposed in the southern Thrace basin margin to determine the dispersal pathways of eroded crustal elements, of both oceanic and continental origins, as well as their different contributions through time. Lithological aspects and tectonic data coupled with geochemistry and geochronology of metamorphic terranes exposed in the area point to a common origin of tectonic units exposed in NW Turkey (Biga Peninsula) with those of NE Greece and SE Bulgaria (Rhodope region). The entire region displays (1) common extensional signatures, consisting of comparable granitoid intrusion ages, and a NE-SW sense of shear (2) matching zircon age populations between the metapelitic and metamafic rocks of the Circum-Rhodope Belt (NE Greece) and those of the Çamlica–Kemer complex and Çetmi mélange exposed in NW Turkey. Detrital heavy mineral abundances from Eocene–Oligocene sandstones of the southern Thrace basin demonstrate the influence of two main sediment sources mostly of ultramafic/ophiolitic and low- to medium-grade metamorphic lithologies, plus a third, volcanic source limited to the late Eocene–Oligocene. Detrital Cr-spinel chemistry is used to understand the origin of the ultramafic material and to discriminate the numerous ultramafic sources exposed in the region. Compositional and stratigraphic data indicate a major influence of the metapelitic source in the eastern part (Gallipoli Peninsula) during the initial stages of sedimentation with increasing contributions from metamafic sources through time. On the other hand, the western and more external part of the southern Thrace margin (Gökçeada, Samothraki and Limnos) displays compositional signatures according to a mixed provenance from the metapelitic and metamafic sources of the Circum-Rhodope Belt (Çamlıca–Kemer complex and Çetmi mélange). Tectonic restoration and compositional signatures provide constraints on the Palaeogene palaeogeography of this sector of the central-eastern Mediterranean region.

Geochemistry and biostratigraphy of Eocene sediments from Samothraki Island, NE Greece

Elevated whole-rock concentrations in Cr, Ni and V as well as the occurrence of detrital chrome spinel suggest an input of (ultra)mafic detritus into the Eocene elastic sediments of Samothraki Island. Detrital chrome spinel chemistry indicates a mixed source of MOR-type peridotites and supra-subduction zone (SSZ) peridotites, and minor volcanic rocks, supposedly island-arc basalts and MORB-type rocks, most likely derived from Vardarian ophiolites. Wackestones from the southwest of Samothraki contain a moderately well-preserved calcareous microfossil assemblage, comprising Nummulites fabianii (PREVER), Nummulites striatus (BRUGUIERE), Pellatispim sp., and Operculina sp., indicating an early Priabonian age (Late Eocene). The sedimentation of the Eocene succession was influenced by regional tectonic and volcanic activity. The rocks have been deposited contemporaneous with the extensional exhumation of the eastern Rhodope Massif.

Insights into crust formation and recycling in North Africa from combined U–Pb, Lu–Hf and O isotope data of detrital zircons from Devonian sandstone of southern Libya

Abstract Combined U–Pb, Lu–Hf and O isotope data of detrital zircons from the Devonian sandstone of southern Libya provide important new boundary parameters for reconstruction of palaeosource areas and sediment transport and may lead to novel approaches to test current plate tectonic models, with important implications for our understanding of the evolution of northern Gondwana (in present-day coordinates) during the Palaeozoic. Detrital zircon U–Pb ages from Devonian sandstone of the eastern margin of the Murzuq Basin show four main age populations: 2.7–2.5 Ga (13%), 2.1–1.9 Ga (10%), 1.1–0.9 Ga (25%) and 0.7–0.5 Ga (46%). The ubiquitous occurrence of c. 1.0 Ga detrital zircons is characteristic of the Saharan Metacraton sedimentary cover sequence and provides new insights into palaeogeographic reconstructions of Gondwana-derived terranes in the Eastern Mediterranean and SW Europe. The Lu–Hf isotope data suggest that zircons crystallized within a narrow time interval from magmas with heterogeneous Hf isotope compositions. These magmas were derived by melting of pre-existing rocks, rather than being juvenile. The calculated Hf model ages range from 3.7 Ga to 1.3 Ga, with a major population between 2.8 Ga and 1.9 Ga, indicating prominent recycling of Archaean and Palaeoproterozoic crust.

Ordovician stratigraphy of the Stumsnäs 1 drill core from the southern part of the Siljan Ring, central Sweden

The Stumsnäs 1 core, drilled in 2011 in the southern part of the Siljan Ring, provides new insights into the stratigraphy of the Ordovician succession in central Sweden. The core section shows evidence of the structural complications caused by the late Devonian meteorite impact in the area. In the core, about 90 m of Tremadocian to Darriwilian strata are sandwiched between Proterozoic igneous basement rocks. At the lower contact, the sedimentary succession starts with glauconitic, fine-grained siliciclastics and carbonates directly resting on the weathered basement. The basal siliciclastic unit is overlain by a ca. 19-m-thick limestone succession, well-known from this part of the Baltoscandian Basin, includes strata corresponding to the Latorp Limestone through the upper Holen Formation. This succession is covered by a limestone–marl alternating sequence, representing some yet unknown deeper water facies, presumably coeval to the topmost Holen Formation through upper Dalby Limestone. The upper third of the sedimentary succession in the core includes numerous slices of partly overturned strata, including relatively thick successions of the Slandrom Formation, Fjäcka Shale and Jonstorp Formation, as well as carbonate and siliciclastic units of yet unknown stratigraphic origin.

Petrography and geochemistry of Palaeozoic quartz-rich sandstones from Saudi Arabia: implications for provenance and chemostratigraphy

The Arabian Peninsula hosts a thick Palaeozoic succession, ranging from the Cambrian through the Permian. It not only contains deposits of the two major Palaeozoic glaciations but also holds both the major Palaeozoic hydrocarbon source and reservoir rocks. In addition, Palaeozoic sandstones serve as important aquifers. The succession is dominated by highly mature quartz arenites, as seen in thin sections. It is starved of fossils and very uniform in lithology. In order to better understand provenance, tectonic setting and stratigraphic relationships, the petrography as well as major and trace element geochemistry of sandstones were studied. Samples were taken from two study areas in southern (Wajid area) as well as central and northern (Tabuk area) Saudi Arabia. The dataset we present here is the first comprehensive study to cover the entire Palaeozoic succession in both the southern and northern part of the Arabian Peninsula. The collisional signal from some samples is a relic from the last stages of the amalgamation of Gondwana, carried into the basin by glaciogenic sediments. Major and trace element geochemistry indicate the Neoproterozoic basement of the nearby Arabian Shield as the most likely source for the detritus. Tectonic discrimination diagrams suggest that deposition of sandstones took place in an intracratonic setting, which is in accordance with the established model for the evolution of the Arabian Plate. An influx of fresh material, probably sourced from the Shield, did occur in the late Palaeozoic units of the Wajid area but did not reach the Tabuk area. Geochemical methods have shown some success in characterising the provenance of both study areas but were unable to reliably assess sedimentary recycling. A (meta-)sedimentary source for the Palaeozoic sandstones could therefore neither be proven nor refuted. Multivariate cluster and principal component analysis of geochemical data revealed significant differences between the two study areas.