Middle Eocene calcareous algae from Southwestern Kachchh,Gujarat

The Fulra limestone (middle Eocene) exposed in the areas around Jhadwa and Harudi villages, southwestern, Kachchh reveals presence of a rich assemblage of calcareous algae belonging to the Chlorophyceae and Rhodophyceae along with abundant foraminifera. In the present paper, eight species belonging to eight genera of calcareous algae are described. These include Dissocladella longijangensis, Sporolithon keenani, Corallina crossmanni, Arthrocardia sp. Misra et al. 2001, Lithothamnion ishigakiensis, Melobesioideae gen. et spec. indet. 1, Melobesioideae gen. et spec. indet. 2 and Lithoporella melobesioides. Out of these, one taxon belongs to the family Dasycladaceae. Among the remaining taxa, one taxon to the family Sporolithaceae, three taxa to the family Corallinaceae and three to the family Hapalidiaceae. Two coralline species, Corallina crossmanni and Lithothamnion ishigakiensis, are recorded for the first time from India. Another species (Dissocladella longijangensis), though known from other areas of India, is new to the study area.     

Middle Eocene diatoms from the Pervoocherednaya hole,eastern Sea of Okhotsk

The results of the study on diatoms revealed in Eocene deposits of the Cenozoic sequence of the Pervoocherednaya hole, which was drilled near the Southwestern Kamchatka coast, are presented. The taxonomic composition of the studied diatom assemblage including marine diatom plankton is characterized. These are the first findings of Middle Eocene planktonic diatoms having a stratigraphic value in sequences of the eastern Sea of Okhotsk region.     

Middle Eocene ostracoda from the Tadkeshwar lignite mine, Cambay Basin, Gujarat

Previous work on the fauna and flora of the Cambay shale underlying as well as inter-bedded within the lignite seams of Vastan lignite mine, Gujarat allows the shale to be assigned a Lower Eocene age. However, there is no record of occurrence of any fossil from the sedimentary beds succeeding the shale-lignite sequence that might fix upper age limit of the Cambay shale. We record a characteristic Middle Eocene ostracod assemblage from the Nummulitic marl/limestone, immediately overlying the shale-lignite sequence from the Tadkeshwar lignite mine close to the Vastan lignite mine. The assemblage comprises 22 species, many of which widely occur in the Middle Eocene beds of Kachchh, Rajasthan and adjacent areas of Pakistan.     

Eocene continental dyke swarm from Central Iran (Khur area)

The Eocene dyke swarm with east-west general trend intrudes the Cretaceous sedimentary rocks in ～25 km north of the Khur city (Central Iran). Some of the studied dykes can be followed for over 7 km, but the majority of exposures in the area are less than 5 km long. The dykes commonly exhibit a chilled contact with the wall rocks. These dykes are trachybasalt and basalt in composition. The trachybasalt dykes are much more abundant. The basaltic dykes cross cut the trachybasalt dykes in some locations, indicating that trachybasalt dykes are older than the basaltic ones. Primary igneous minerals of the basaltic dykes are olivine (chrysolite), clinopyroxene (diopside, augite), plagioclase (labradorite), sanidine, magnetite, orthopyroxene (enstatite), spinel and phlogopite, and secondary minerals are zeolite (natrolite and mesolite), chlorite (diabantite), calcite and serpentine. The trachybasalt dykes are composed of clinopyroxene (diopside), plagioclase (labradorite), sanidine, mica (biotite and phlogopite), amphibole (magnesio-hastingsite) and magnetite as primary minerals, and chlorite and calcite as secondary ones. Whole rocks geochemical data of the studied dykes indicate their basic and calc-alkaline nature and suggest that these two set of dykes were derived from the same parental magma. The chondrite-normalized REE patterns and the primitive mantle-normalized multi-elemental diagram of the Khur dykes show enrichment of light rare earth elements (LREE) relative to heavy rare earth elements (HREE), and negative anomalies of high field strength elements (HFSE) (e.g. Ti, Nb and Ta). These rocks show enrichment of the large ion lithophile elements (LILE) (e.g. Cs, Ba, Th and U) and depletion of the HREE and Y relative to MREE, Zr and Hf. In the chondrite-normalized REE diagram, the basalts show elevated REE abundances relative to the trachybasalt samples. Geochemical analyses of the studied samples suggest a spinel lherzolite from the mantle as the source rock and confirm the role of subduction in their generation. The chemical characteristics of the Khur dykes resemble those of continental arc rocks, and they were possibly formed by subduction of the Central-East Iranian microcontinent (CEIM) confining oceanic crust and decompression melting of a lithospheric subcontinental mantle spinel lherzolite enriched by subduction.     

Spore-pollen complexes from Upper Aptian of South Turkmenia

Spores and pollen have been obtained from four Upper Aptian ammonite- and pelecypod-bearing clays of the Badkhyz Highlands and Kopet-Dag. Species of Gleichenia and Classopollis are invariably present in large quantities, along with smaller numbers of pollen of Cupressaceae, Podozamitaceae, and Schizaeaceae. These spores and pollen can now be used as standards to identify deposits of the upper part of the Aptian stage.—D.C. McGregor     

Coupling of oceanic and continental crust during Eocene eclogite-facies metamorphism: evidence from the Monte Rosa nappe,western Alps

High precision U–Pb geochronology of rutile from quartz–carbonate–white mica–rutile veins that are hosted within eclogite and schist of the Monte Rosa nappe, western Alps, Italy, indicate that the Monte Rosa nappe was at eclogite-facies metamorphic conditions at 42.6 ± 0.6 Ma. The sample area [Indren glacier, Furgg zone; Dal Piaz (2001) Geology of the Monte Rosa massif: historical review and personal comments. SMPM] consists of eclogite boudins that are exposed inside a south-plunging overturned synform within micaceous schist. Associated with the eclogite and schist are quartz–carbonate–white mica–rutile veins that formed in tension cracks in the eclogite and along the contact between eclogite and surrounding schist. Intrusion of the veins at about 42.6 Ma occurred at eclogite-facies metamorphic conditions (480–570°C, >1.3–1.4 GPa) based on textural relations, oxygen isotope thermometry, and geothermobarometry. The timing of eclogite-facies metamorphism in the Monte Rosa nappe determined in this study is identical to that of the Gran Paradiso nappe [Meffan-Main et al. (2004) J Metamorphic Geol 22:261–281], confirming that these two units have shared the same Alpine metamorphic history. Furthermore, the Gran Paradiso and Monte Rosa nappes underwent eclogite-facies metamorphism within the same time interval as the structurally overlying Zermatt-Saas ophiolite [∼50–40 Ma; e.g., Amato et al. (1999) Earth Planet Sci Lett 171:425–438; Mayer et al. (1999) Eur Union Geosci 10:809 (abstract); Lapen et al. (2003) Earth Planet Sci Lett 215:57–72]. The nearly identical P–T–t histories of the Gran Paradiso, Monte Rosa, and Zermatt-Saas units suggest that these units shared a common Alpine tectonic and metamorphic history. The close spatial and temporal associations between high pressure (HP) ophiolite and continental crust during Alpine orogeny indicates that the HP internal basement nappes in the western Alps may have played a key role in exhumation and preservation of the ophiolitic rocks through buoyancy-driven uplift. Coupling of oceanic and continental crust may therefore be critical in preventing permanent loss of oceanic crust to the mantle.     

Middle Eocene vertebrates from the sabkha of Gueran,Atlantic coastal basin,Saharan Morocco,and their peri-African correlations

The sabkha of Gueran in the Southwest Moroccan Sahara has yielded a rich and diverse fauna of late middle Eocene vertebrates that include the world's richest Bartonian age archaeocete assemblage. Archeocete remains were described previously and here we report on the rest of the vertebrate fauna. The Gueran fauna includes abundant chondrichthyan species belonging to Lamniformes, Carcharhiniformes and Rhinopristiformes, and actinopterygian assemblage consisting of Cylindracanthus, of a siluriform, and of Perciformes. Turtles are represented by at least two marine taxa referred to as Cheloniidae and Dermochelyidae. Crocodylian remains belong to at least two longirostrine species, including gavialoid remains. Snakes are represented by Pterosphenus cf. schweinfurthi (Palaeophiidae). Seabirds are represented by a pseudo-toothed bird (Pelagornithidae). The avian fossil belonged to a gigantic soaring bird and constitutes the earliest occurrence of the genus Pelagornis. The presence of proboscideans is attested by dental fragments. This fossil assemblage from Gueran shows affinities with those of the Eocene beds of Egypt and Libya. The numerous shared taxa support a close biogeographical connection between faunas from southeastern and southwestern coasts of the Mediterranean Sea.     

Clasts of high-grade Sanbagawa schist in Middle Eocene conglomerates from the Kuma Group, central Shikoku, south-west Japan

Middle Eocene conglomerates which overlie the Sanbagawa metamorphic rocks contain clasts of metamorphic rock with isotope ages of 120-85 Ma, which fall within the age range reported from the Sanbagawa metamorphic rocks. They were derived from the chlorite to oligoclase zones of the Sanbagawa metamorphic belt. Clasts of garnet amphibolite and oligoclase-biotite schist show a mineral assemblage similar to the highest grade Sanbagawa schists. However, the metamorphic temperatures estimated by various mineralogical thermometers show that some of the clasts were formed at higher temperatures than the in situ Sanbagawa metamorphic rocks. Such higher grade rocks were at the surface by the Middle Eocene and for the most part they have been eroded away. Cretaceous and post-Cretaceous sediments overlie, or are in fault contact with, the Sanbagawa metamorphic rocks which suggests that rocks in the belt were uplifted and eroded from the latest Cretaceous to Middle Eocene time after strike-slip movement along the Median Tectonic Line. Since the Middle Eocene, the belt has experienced relatively slow uplift which was locally around 2 km in central Shikoku.     

Ushia - a new genus from Kamyshin Paleocene flora

Ushia kamyschinensis (Goeppert) n. gen. and n. comb. is established as a monotypic genus for leaves peculiar to the Paleocene of the U. S. S. R. The specimen designated as the holotype is that described by Goeppert in 1845 as Phyllites kamyschinensis from the Paleocene (Saratov Stage) found at Mt. Ushi near Kamyshin. The leaf, although very polymorphous, is ovate-oval to ovateprolate in outline with a broadly rounded to rounded cuneate base, generally somewhat asymmetrical. The leaf margin is entire below the basal secondary veins, crenate to crenulate above. The veins are coarse and prominent. Secondary veins alternate, 8-12 (14) in number, straight or slightly arcuate. Tertiary veins are almost perpendicular to secondary veins, mostly unbranched. Lowest pair of secondary veins branch unilaterally outward, the branchlets forming loops along the base of the leaf. This latter character differentiates the leaf from other members of the Fagaceae, the family to which Ushia most probably should be assigned. -- F. M. Hueber.     

Garnet crystal plasticity in the continental crust,new example from south Madagascar

Garnet (10 vol.%; pyrope contents 34–44 mol.%) hosted in quartzofeldspathic rocks within a large vertical shear zone of south Madagascar shows a strong grain‐size reduction (from a few cm to ～300 μm). Electron back‐scattered diffraction, transmission electron microscopy and scanning electron microscope imaging coupled with quantitative analysis of digitized images (PolyLX software) have been used in order to understand the deformation mechanisms associated with this grain‐size evolution. The garnet grain‐size reduction trend has been summarized in a typological evolution (from Type I to Type IV). Type I, the original porphyroblasts, form cm‐sized elongated grains that crystallized upon multiple nucleation and coalescence following biotite breakdown: biotite + sillimanite + quartz = garnet + alkali feldspar + rutile + melt. These large garnet grains contain quartz ribbons and sillimanite inclusions. Type I garnet is sheared along preferential planes (sillimanite layers, quartz ribbons and/or suitably oriented garnet crystallographic planes) producing highly elongated Type II garnet grains marked by a single crystallographic orientation. Further deformation leads to the development of a crystallographic misorientation, subgrains and new grains resulting in Type III garnet. Associated grain‐size reduction occurs via subgrain rotation recrystallization accompanied by fast diffusion‐assisted dislocation glide. This plastic deformation of garnet is associated with efficient recovery as shown by the very low dislocation densities (10¹⁰ m^?3 or lower). The rounded Type III garnet experiences rigid body rotation in fine‐grained matrix. In the highly deformed samples, the deformation mechanisms in garnet are grain‐size‐ and shape‐dependent: dislocation creep is dominant for the few large grains left (>1 mm; Type II garnet), rigid body rotation is typical for the smaller rounded grains (300 μm or less; Type III garnet) whereas diffusion creep may affect more elliptic garnet (Type IV garnet). The P–T conditions of garnet plasticity in the continental crust (≥950 °C; 11 kbar) have been identified using two‐feldspar thermometry and GASP conventional barometry. The garnet microstructural and deformation mechanisms evolution, coupled with grain‐size decrease in a fine‐grained steady‐state microstructure of quartz, alkali feldspar and plagioclase, suggests a separate mechanical evolution of garnet with respect to felsic minerals within the shear zone.     

Strenulagus (Mammalia: Lagomorpha) from the Middle Eocene Irdin Manha Formation of the Erlian Basin, Nei Mongol, China

New material of Strenulagus solaris, a stem lagomorph, from the lower part of the Middle Eocene Irdin Manha Formation at the Irdin Manha and Huheboerhe localities, Erlian Basin, Nei Mongol, China includes remains of isolated cheek teeth, fragmentary upper incisors(d I2) and postcranial elements, reported from the species for the first time. The tarsal bones display advanced features, such as a wide calcaneofibular articulation surface and, along with an increase in hypsodonty, the new data document the early stage of lagomorph evolution in the Middle Eocene of the Erlian Basin. This finding is stratigraphically well constrained and probably predates that of the type material of S. solaris from the Khaychin Formation, Bugin-Tsav Basin, Mongolia.     

Cyclicity in the Middle Eocene Yamak turbidite complex of the Haymana basin,Central Anatolia,Turkey

The Haymana basin in central Anatolia (Turkey) formed on a Late Cretaceous to Middle Eocene fore-arc accretionary wedge. A sequential model is proposed for the 1-km-thick Lutetian Yamak turbidite complex (YTC) which is the youngest paleotectonic unit of the basin. The YTC represents a prograding submarine fan subdivided into three depositional sequences (DS), each several hundred meters thick. Each depositional sequence consists of a turbidite system (TS), with sandstone and conglomeratic sandstone beds alternating with mudstones, overlain by basin plain mudstones. In each turbidite system, the sandstone and mudstone sequential organization allows the distinction of smaller subdivisions, namely, basic sequences (BS) and basic units (BU), with each basic sequence being composed of several basic units. This subdivision, associated with a two-dimensional geometric reconstruction of the YTC, leads to a better understanding of the evolution in time and space of the submarine fan system. Lower to middle fan depositional lobes, and upper fan and slope channels, are represented. As a whole, the YTC progressed from a sand-poor to a sand-rich system. Depositional sequences (DS) of the YTC may correspond to third-order sea-level cycles of tectonic origin. Accordingly, fourth- and fifth-order cycles might be proposed for the BS and BU, respectively. However, partly because of the limited extent of exposures, the allocyclic origin of these finer subdivisions remains problematic.     

Adakitic rocks derived from the partial melting of subducted continental crust: Evidence from the Eocene volcanic rocks in the northern Qiangtang block

Eocene is a critical time for the elevation of Tibetan Plateau and global climate change, and previous studies suggested that the Eocene elevation was caused by intra-continental subduction of the Songpan–Garze block beneath the Qiangtang block. This paper reports zircon U–Pb age and geochemistry of the Eocene volcanic rocks from the Zuerkenwula mountain area in the northern part of Qiangtang block, and proposes that both slab break-off of the Neo-Tethys oceanic slab along the Bangong–Nujiang suture and intra-continental subduction of the Songpan–Garze block beneath the Qiangtang block caused the extensive partial melting of lithospheric mantle and subducted Songpan–Garze continental crust, which resulted in the significant elevation of the Tibetan Plateau. The volcanic rocks have LA-ICP MS U–Pb zircon age of 40.25 ± 0.15 Ma (MSWD = 2.1, 2σ), which is contemporaneous with the Eocene eclogites in the Great Himalayan and K-rich lavas in the southeastern Tibet. They display some adakitic characteristics with SiO₂ = 57.44 to 68.72%, TiO₂ = 0.38 to 0.81%, Na₂O = 2.89 to 4.35%, K₂O = 2.77 to 4.48%, Al₂O₃ = 13.92 to 18.22%, A/CNK = 0.69 to 1.03, MgO = 0.27 to 5.86% with Mg# ranging from 13.2 to 72.0, strongly depleted in heavy rare earth elements (HREEs) (Yb = 0.92 to 1.51 ppm and Y = 10.1 to 24.1 ppm), in combination with their positive Sr anomalies, high Sr/Y ratios and no significant Eu anomalies, which suggest a garnet-in and plagioclase-free source residue. These volcanic rocks can be divided into high-Mg# (> 45) and low-Mg# (< 45) groups. Both of the two groups share evolved Sr–Nd–Pb isotopic compositions with ⁸⁷Sr/⁸⁶Sr = 0.707412–0.708284; ε_Nd(t) = ? 4.0 to ? 5.7; ²⁰⁶Pb/²⁰⁴Pb = 18.7499–18.8189, ²⁰⁷Pb/²⁰⁴Pb = 15.7189–15.7384; ²⁰⁸Pb/²⁰⁴Pb = 39.166–39.262. The geophysical data and regional geological setting suggest that the low-Mg# adakitic rocks were derived from the decompression melting of a subducted lower continental crust, when low-Mg# adakitic melts in the overlying peridotite mantle wedge captured some olivine crystals, resulting in their elevated Mg# and MgO values.     

Shark and ray faunas in the Middle and Late Eocene of the Fayum Area, Egypt

The Eocene rocks exposed in the Fayum Area, Egypt, are well known for their fossil vertebrates but in recent times the sharks and rays have been largely neglected. Extensive surface collecting, supplemented with bulk samples, has produced large collections from the Midawara, Gehannam, Birket Qarun and Qasr el-Sagha formations, spanning the Bartonian and Priabonian stages and from palaeoenvironments varying from open muddy shelf to very shallow estuarine systems. In total about 90 species of sharks and rays are recorded, many of them previously unrecognised, resulting in some of the most diverse fossil chondrichthyan assemblages known from the Tertiary. Teeth of these species suggest that they occupied a wide range of ecological niches from top predator to tiny benthic invertebrate feeder to planktivore. Many of the species are limited in their stratigraphical range and show potential to be used, at least locally, as biostratigraphical indicators for stratigraphically poorly constrained vertebrate sites elsewhere in North Africa. Distinctly different faunas from different sedimentary environments indicate a strong environmental control on the distribution of many species.