Early Miocene Age Research Articles

Biostratigraphy of Oligocene and Lower Miocene deposits, Anneh Anticline, Folded Zagros, SW of Iran

One stratigraphic section was selected to study the biostratigraphy of the Oligocene and Lower Miocene deposits in Folded Zagros. The sediments include Asmari Formation (345 m) and the upper parts of Pabdeh Formation (180 m). Lithostratigraphy studies show that the Pabdeh Formation is composed of marls and medium-bedded argillaceous limestone alternation. The Asmari Formation is generally composed of medium- to thick-bedded limestone. Biostratigraphy studies for Pabdeh Formation indicate the four genera and six species of planktonic foraminifers. Based on assessment of foraminifera, one assemblage zone has been proposed for the Pabdeh Formation. The Asmari Formation biostratigraphy studies led to identify 27 genera and 35 species of benthic foraminifers. Based on the distribution of foraminifera, three assemblage zones and one indeterminate zone for Asmari Formation are suggested. Micropaleontology studies are offered Early Oligocene for Upper Pabdeh Formation and Late Oligocene to Early Miocene age for Asmari Formation.

Thermal and exhumation history of Sakhalin Island (Russia) constrained by apatite U-Pb and fission track thermochronology

Sakhalin Island represents a key locality to study the tectonic evolution of the western Pacific. The island is located at the Amur-Okhotsk plate margin and records a complex thermotectonic history. Apatite double dating (U-Pb and fission track) and thermal history modelling were applied to three late Eocene granitoid massifs within central and southern Sakhalin: the Aniva, Okhotsk and Langeri complexes. Apatite U-Pb results yield consistent late Eocene (∼40–37Ma) ages, suggesting rapid post-magmatic cooling. Apatite fission track results reveal bimodal age distributions with late Eocene – early Oligocene (∼38–33Ma) and early Miocene (∼20–17Ma) age populations that can be correlated with variations in Uranium and Chlorine concentrations. Thermal history modelling translates the AFT age bimodality into two-phase cooling histories. The timing of the early cooling phase (∼38–33Ma) corresponds with the apatite U-Pb ages, indicating rapid cooling to at least ∼100°C during the late Oligocene. The second cooling phase at ∼20–17Ma cooled the samples to near-surface temperatures. Both cooling phases correspond with regional unconformities and subsequent accelerations in sedimentation rate, suggesting that cooling was a response to rapid exhumation. In addition, our data suggests that the studied terranes record differential exhumation with respect to the structural architecture. The Miocene exhumation pulse is coeval with the timing of transpressional fault displacement and the subsequent opening of the Kuril Basin.

Discovery of the oldest Gobius (Teleostei, Gobiiformes) from a marine ecosystem of Early Miocene age

Gobiidae (Gobiiformes, Teleostei) is among the largest families of vertebrates. These fishes are distributed worldwide and contribute significantly to species diversity in marine habitats and reefs. However, their fossil record is sparse prior to the Miocene and little is known about the course of diversification of the clade. Here we report exceptionally well-preserved skeletal remains of the oldest known Gobius from an Early Miocene (Burdigalian) marine ecosystem of Central Europe (Czech Republic). Gobius jarosi Přikryl & Reichenbacher sp. nov. is dated to 19.1–20.4 Ma by biostratigraphical analysis of calcareous nannoplankton from small fragments of the holotype matrix. Gobius jarosi sp. nov. is characterized by a pterygiophore formula of 3-22110 and a premaxilla with a distinctive postmaxillary process, has 11 abdominal and 16–17 caudal vertebrae, six thin spines in the first dorsal fin and one spine and 12 soft rays in the second dorsal fin, one spine and 11 rays in the anal fin, and two anal fin pterygiophores preceding the first haemal spine. Large ctenoid scales cover the body except for its anterior portion and the head. A comparative analysis of meristic and osteological data suggests close affinities between G. jarosi sp. nov. and the extant species G. niger, G. roulei and G. vittatus. Accompanying fish fossils and nannoplankton assemblages indicate that G. jarosi sp. nov., like G. roulei and G. vittatus, lived in an inshore to offshore marine ecosystem. The discovery of such an early member of the lineage leading to the present-day species of Gobius has important implications for the origin and evolution of the Gobiidae, and indicates that diversification of the European Gobiidae began in, but not before, the Early Miocene.http://zoobank.org/urn:lsid:zoobank.org:pub:3229739B-3428-4DFB-9588-4CE875D732D8

Rich shallow-water benthic ecosystem in Late Miocene East Antarctica (Fisher Bench Fm, Prince Charles Mountains)

Abstract A single shell of a pectenoid bivalve was found in the lower part of the Fisher Bench Formation (Fisher Massif, Prince Charles Mountains). In contrast to glacigenic sediments that form extensive outcrops in this area and are almost barren of foraminifera, small pieces of muddy sand attached to this shell contained a rich assemblage of calcareous and siliceous microfossils. The diatom assemblage associated with this shell was dominated by marine benthic forms with abundant Saeptifera, associated with subordinate marine neritic taxa, and Chaetoceros resting spores. Benthic foraminifera are very abundant but of low diversity, strongly dominated by Rosalina globularis with uniform chambers. It is the first Miocene foraminiferal assemblage reported from East Antarctica excluding the Ross Sea area. These new results confirm the early Late Miocene age of the shell that was dated by Sr isotope values in an earlier study, and suggest an initial phase of deposition in a shallow-water (possibly no > 10 m) marine, cold, and possibly oligotrophic environment. After initial burial in microfossil-bearing sediment that was weakly lithified, the shell was eroded and transported to be incorporated in fossil-poor glacigenic sediments. Since transport from a nearby location could have been facilitated by glacial and/or down-slope movements in this fjordal setting, the shell is considered para-autochthonous. Based on the Antarctic foraminiferal fossil records, it appears that through most of the Cenozoic, those parts of the Antarctic continental shelf that were deeper than a few tens of meters, with the exception of the Ross Sea area, were mostly unfavorable for development and/or preservation of calcareous microfossils.

Evidence from paleosols for low to moderate elevation of the India-Asia suture zone during mid-Cenozoic time

The post-collisional uplift history of the India-Asia suture zone in southern Tibet is important for understanding the geodynamic conditions of the India-Asia collision and how it may have modified regional and global climate. Here we use stable isotope and major element analyses of paleosols preserved in the Liuqu Conglomerate to reconstruct India-Asia suture zone paleoclimate and paleoelevation. Paleosol carbonate δ13C (Vienna Peedee belemnite) average values of −9.4‰ ± 1.1‰ indicate that Liuqu paleosols were well vegetated by C3 plants, unlike thinly vegetated and arid modern Tibet. Major element weathering indices show that these soils experienced significant collapse and loss of cations due to weathering of similar intensity to that in the wet, low elevations of the Neogene Himalayan foreland. Age estimates for the Liuqu vary, but current evidence points to an early Miocene age. Our evidence requires that the India-Asia suture zone experienced wet, well-vegetated conditions during Liuqu Conglomerate deposition. Geodynamically this implies that the suture zone was at relatively low elevation and was topographically open to monsoon moisture as late as 40 m.y. after the start of the India-Asian collision. This challenges the idea that uplift of the India-Asia suture zone was monotonic and tied directly to crustal thickening.

Origin of an extensive network of non-tectonic synclines in Eocene limestones of the Western Desert, Egypt

Satellite images of the Western Desert of Egypt display conspicuous sinuous color patterning that previous workers have interpreted as erosional flutes formed by catastrophic flooding. Our work with high resolution satellite imagery shows that the patterning is not erosional but, rather, the result of a network of thousands of narrow synclines in the Eocene bedrock capping the Limestone Plateau. Synclines form as isolated, 200-400 meter-wide downwarps in otherwise flat-lying strata. Limb dips are shallow, and doubly plunging hinges form multiple basin closures along syncline lengths. Anticlines form “accidentally” in inter-syncline areas where two adjacent synclines lie close together. Synclines have two dominant orientations, WNW-ESE and NNW-SSE, parallel to two prominent joint and fault sets, and synclines branch, merge, and change orientation along their lengths. Synclines are all at the same scale with neither larger structures nor parasitic structures and are best described as non-tectonic sag synclines. An Egypt-wide inventory reveals that these synclines are both confined to Eocene limestones and developed, albeit it sporadically, over nearly 100,000 km2. The syncline network predates plateau gravels of the Katkut Formation, which have been interpreted as Oligocene or early Miocene in age, and the network is cut by faults related to Western Desert extension associated with Red Sea rifting. The mechanism that caused sag of overlying layers is not clear. Modern karst collapse, subsurface dissolution of evaporites, and collapse of paleokarst are all unlikely mechanisms given the timing of formation and the underlying stratigraphy. Silica diagenesis and downslope mobilization of underlying shales are possibilities, although uncertainty about the origin of silica in the limestones, plus the consistency of syncline orientations over large areas, make these models problematic. Hypogene karst, perhaps related to aggressive fluids associated with basaltic intrusions, may be the model most consistent with the admittedly limited data we currently have for the network.

Palaeoenvironments during a terminal Oligocene or early Miocene transgression in a fluvial system at the southwestern tip of Africa

A multi-proxy study of an offshore core in Saldanha Bay (South Africa) provides new insights into fluvial deposition, ecosystems, phytogeography and sea-level history during the late Paleogene-early Neogene. Offshore seismic data reveal bedrock topography, and provide evidence of relative sea levels as low as −100m during the Oligocene. 3D landscape reconstruction reveals hills, plains and an anastomosing river system. A Chattian or early Miocene age for the sediments is inferred from dinoflagellate taxa Distatodinium craterum, Chiropteridium lobospinosum, Homotryblium plectilum and Impagidinium paradoxum. The subtropical forest revealed by palynology includes lianas and vines, evergreen trees, palms and ferns, implying higher water availability than today, probably reduced seasonal drought and stronger summer rainfall. From topography, sedimentology and palynology we reconstruct Podocarpaceae-dominated forests, Proto-Fynbos, and swamp/riparian forests with palms and other angiosperms. Rhizophoraceae present the first South African evidence of Palaeogene/Neogene mangroves. Subtropical woodland-thicket with Combretaceae and Brachystegia (Peregrinipollis nigericus) probably developed on coastal plains. Some of the last remaining Gondwana elements on the sub-continent, e.g., Araucariaceae, are recorded. Charred particles signal fires prior to the onset of summer dry climate at the Cape. Marine and terrestrial palynomorphs, together with organic and inorganic geochemical proxy data, suggest a gradual glacio-eustatic transgression. The data shed light on Southern Hemisphere biogeography and regional climatic conditions at the Palaeogene-Neogene transition. The proliferation of the vegetation is partly ascribed to changes in South Atlantic oceanographic circulation, linked to the closure of the Central American Seaway and the onset of the Benguela Current ~14Ma.

An Integrated Wireline-Log and Biostratigraphic Appraisal of Olure-1 and Abigboro-1 Wells, Onshore Niger Delta

Studies of two wells within the coastal swamp onshore Niger Delta were carried out in order to determine the chronology, biozonation, and establishment of sequence stratigraphic framework for the representative wells. A total of twenty-eight (28) cutting samples were recovered and analysed from Abigboro-1 and Olure-1 exploratory wells for their foraminifera, calcareous nannofossils and palynomorphs’ compositions. The results indicated the presence of diverse species within the wells, which include Lenticulina grandis, Florilus ex. gr. costiferum, Hanzawaia concentrica, Hopkinsina bononiensis, Marginulina costata and pseudonodosaria sp., Bolivina mandoroveensis, Eponides eshira, Lenticulina grandis, Lenticulina grandis, Cibicorbis inflata, Heterolepa floridana, Florilus ex. gr scaphum, Poroeponides lateralis, Uvigerina sparsicostata, Uvigerina subperegrina, Bolivina ex. gr. scalptrata, Valvulineria sp. and Epistominella pacifica. An inner neritic (1694 m - 2161 m), coastal deltaic (1557 m - 1640 m) and shallow inner neritic (1347 m - 1554 m) palaeoenvironment was suggested for Olure-1 well while a broad grouping of the intervals as inner to middle neritic was suggested for Abigboro-1 well. The ratio of species abundance/diversity and integration of log suite data predicted two Maximum Flooding Surfaces (MFS) and one Sequence Boundary (SB) for Olure-1 well. The MFS were encountered at depths 2728 m (MFS 1) and 1797 m (MFS 2), while the SB was predicted at depth 2602 m (SB1). Diverse systems’ tracts were identified and delineated from wireline logs of Olure-1 well and the implication for petroleum exploration was discussed. Late Oligocene - early Miocene age has been assigned for the wells based on the recovered diagnostic species.

Age and conditions of formation of sedimentary cover of the Ulleung Plateau of the Sea of Japan according to micropaleontological data

The paper reports on the micropaleontologcal (diatoms, silicoflagellates, radiolarians, and pollen flora) data substantiating the age and conditions of sedimentary cover formation of the submarine Ulleung Plateau (Krishtofovich Rise) in the Sea of Japan. Five rock complexes with different age and origin were distinguished on the basis of micropaleontological and petrographic data. Complex 1 (tuffites, tuffogenous siltstones) with numerous freshwater diatoms and pollen flora that prove the lacustrine genesis and the Early Miocene age occurs at the base of the sedimentary cover. Complexes 2–5 are composed of marine tuffogenous sedimentary deposits of end of Early Miocene–Pleistocene age. Stratigraphic unconformity between continental and marine deposits involves a short-time interval in the end of the Early Miocene and points to rather fast tectonic submersion of the Ulleung Plateau. Marine sedimentation in bathyal conditions dominated from the end of the Early Miocene. In the Late Miocene, in the northern part of the plateau, the region of the large rise was characterized by shallow-water conditions, indicating supposed existence of an island territory in this place.

A study on tectonic and sedimentary development in the rifted northern continental margin of the South China Sea near Taiwan

A series of Cenozoic rifted basins developed in the northern margin of the South China Sea (SCS). Tainan Basin is one of these rifted basins near Taiwan, lying in the outer margin. We have used reflection seismic data in the deepwater areas and boreholes drilled in the shelf of the Tainan Basin to understand the tectonic and sedimentary development in the northern SCS margin near Taiwan. Four key stratal surfaces (i.e., the base of the Pleistocene Series, the base of the Pliocene Series, the 17 Ma maximum flooding surface [MFS], and a breakup unconformity of approximately 30 Ma in age) and seven seismic facies (i.e., continuous- and parallel-layer seismic facies, wavy seismic facies, chaotic seismic facies, U-shaped canyon-cut seismic facies, imbricated-layer seismic facies, high-amplitude reflector package seismic facies, and extrusive volcanism seismic facies) are recognized from seismic data with ages constrained by borehole stratigraphy drilled in the shelf. We have established a model for Cenozoic tectonic and sedimentary development in the rifted northern margin of the SCS near Taiwan. The occurrence of Paleogene fault-bounded grabens/half-grabens topped by a breakup unconformity and draped by postrift sediments indicates that these deepwater rifted basins developed on the continental crust, attesting that a thinned continental crust underlies the deepwater study area, rather than oceanic crust as reported in some literature. Postbreakup extrusive volcanic bodies, of early Miocene age, were buried by thick deepwater sediments. Fairly continuous stratal surfaces of 17 Ma MFS reveal that volcanic activities ceased to be active since middle Miocene. A series of channel cut-and-fills is observed in late Miocene, Pliocene, and Pleistocene strata beneath and to the south of the modern Formosa Canyon. Two distinct fields of deepwater sediment waves developed since middle Pleistocene are found lying to the west of modern deformation front/Manila Trench and to the north and south of the Formosa Canyon, respectively.

Modeling of Two-Phase Relative Permeability in Cambrian and Early Miocene Sandstone Reservoirs: A Case Study, Egypt

The relative permeability is the ratio of the effective permeability to the absolute permeability. Due to the importance of relative permeability in reservoir simulation, there is a dominant need to upscale it. So, several models were introduced to modeling the relative permeability. Some correlation models were dependent on capillary pressure measurements, while other models did not require such measurements. In this study, four relative permeability correlation models were chosen to apply them on two sandstone reservoir (labeled A and B) data sets. The two reservoirs belong to different ages and depositional environments. Both reservoirs are located in the Southern Gulf of Suez, Egypt. Reservoir A is the Nubian sandstone of Cambrian age. Reservoir B is the Nukhul clastic of Early Miocene age. The data sets include laboratory measurements of unsteady-state gas–oil relative permeability and steady-state water–oil relative permeability tests. The results indicate that the practical and modified Corey models were the most applicable model for the studied reservoirs. Additionally, prediction of relative permeability at saturation end points was carried out based on using routine core porosity and permeability by introducing new empirical equations. The relative permeability was used to identify rock wettability, water cut, water cutoffs and the areal and vertical sweep efficiencies.

HYDROTHERMAL NATIVE COPPER IN OCEAN ISLAND ALKALI BASALT FROM THE MINEOKA BELT, BOSO PENINSULA, CENTRAL JAPAN

Native copper grains are found in aphyric amygdaloidal basalt of early Miocene age (ca. 20 Ma) in the southern Mineoka belt of Boso Peninsula, central Japan. The native copper was precipitated in the amygdules or veins along with calcite and analcime. The temperature of precipitation and salinity of the fluids related to the native copper are approximately 133° to 183°C and 0.9 to 3.9 wt % as estimated by fluid inclusions trapped in the calcite containing grains of the native copper. The native copper is interpreted as related to low-temperature, reducing, alkaline hydrothermal fluids. A sulfur-poor environment is inferred by the lack of sulfur-bearing minerals. The host rock of the Mineoka native copper is alkali basalt of oceanic island affinity. Native copper is well known to occur in mid-ocean ridge, island arc, oceanic island tholeiitic basalts, and continental tholeiitic basalt, but this is the first detailed description of an occurrence in ocean island alkali basalt.

Subsidence and conversion of the Dead Sea basin to an inland erosion base level in the early middle Miocene as inferred from geomorphological analysis of its ancient western fluvial outlet

The first major subsidence of the Dead Sea pull-apart basin (DSB) is evidenced by the thick Hufeira Member of the terrestrial Hazeva Formation. The age of the Hufeira Member and the conversion of the DSB to an inland erosion base level are not well constrained. For this purpose we studied the effect of the evolving basin on its ancient fluvial outlet to the Arad-Be'er Sheva Valley (ABSV), which served as a Miocene corridor between the embryonic DSB region in the east and the Mediterranean Sea in the west. We mapped and analyzed the morphostratigraphy of four series of rock-cut erosion surfaces (from top to bottom: the Barir, Kuseifa, Ar'ara, and Shemen surfaces). They are manifested in the east as fluvial erosion surfaces, capped by conglomerates, passing laterally westward to marine wave-cut surfaces, capped by a shallow marine limestone of the early middle Miocene Ziqlag Formation. The age of these surfaces is constrained to the early middle Miocene (Langhian) based on morphostratigraphy correlation with the Ziqlag Formation. Paleogeographic reconstruction of the two higher and older surfaces reveals transverse valleys, which drained the DSB region and crossed the present route of the regional water divide. These transverse valleys were presumably the western outlets to the Mediterranean Sea of the newly subsiding basin. Precambrian components in the assemblage of the clasts that cover the Kuseifa surface were not found in the Hufeira Member and thus reflect an ongoing post-Hufeira exumation of the DSB drainage basin. Hence, this early middle Miocene surface postdates the Hufeira Member, assigning an age of late early Miocene to the first major subsidence of the DSB. The two lower and younger surfaces represent local drainage systems confined to the ABSV. This transition from regional to local drainage system marks the establishment of the present regional water divide and the conversion of the DSB to an inland erosion base level during the early middle Miocene.

Geochemical and isotopic composition of volcanic rocks of the heterogeneous Miocene (~ 23–19 Ma) Tepoztlán Formation, early Transmexican Volcanic Belt, Mexico

We present the first geochemical data (major and trace elements, as well as Sr, Nd, and Pb isotopes) on volcanic rocks from the Tepoztlán Formation in the central Transmexican Volcanic Belt. The Tepoztlán Formation is up to 800m thick and comprises a wide range of primary volcanic rocks (lavas, pyroclastic density current deposits, pyroclastic fall deposits), and their secondary reworked products due to mass flow (lahars) and fluvial processes. Magnetostratigraphy combined with K/Ar and Ar/Ar geochronology suggests an age of Early Miocene (23–19Ma) for this Formation. Lava flows, pyroclastic rocks, dykes and volcanic clasts range from basaltic andesite to rhyolite, with a clear dominance of andesites and dacites. All samples are subalkaline and hy-normative. These rocks show homogeneous REE patterns with LREE enrichment and higher LILE concentrations with respect to HFSE, notably the typical negative anomaly of Nb, Ta, and Ti, suggesting a subduction-related magma genesis. Major and trace element concentrations show that either assimilation of heterogeneous continental crust or crustal recycling by subduction erosion and fractional crystallization are important processes in the evolution of the Tepoztlán Formation magmas. Isotopic compositions of the Tepoztlán Formation samples range from (87Sr/86Sr)t=0.703693 to 0.704355 and (143Nd/144Nd)t=0.512751 to 0.512882, falling within the mantle array. All geochemical characteristics indicate that these rocks originated from a heterogeneous mantle, modified and evolved through assimilation of country rock and fractional crystallization in the upper crust.

Early Miocene age of the Stare Bystre Formation based on calcareous nannofossils (Magura Nappe, Outer Carpathians, Poland)

The area of investigation is situated close to the contact zone between the Pieniny Klippen Belt, Krynica Subunit of the Magura Nappe and the Neogene strata of the Orava–Nowy Targ Intramontane Basin (southern Poland). In the area studied, marine deposits of the Stare Bystre Formation outcrop at the surface where they emerge from beneath freshwater and terrestrial Neogene and Quaternary deposits. Nannofossil assemblages from all samples are strongly dominated by reworked species. The Early Miocene age (NN2) of the Stare Bystre Formation has been determined on the base of the first occurrence of Sphenolithus disbelemnos after Shackleton et al. (2000). During the Late Oligocene (NP25/NN1), the frontal part of Magura Nappe was thrust northwards on to the terminal Krosno flysch basin. The northwards thrusting of the Magura Nappe was accompanied by the formation of the piggy-back basin on the Magura Nappe, filled with the synrorogenic turbidites belonging to the Zawada, Kremna and Stare Bystre formations (NN2).

Paleoclimate of Antarctica reconstructed from clast weathering rind analysis

Previous analysis of extractable Fe/Al in paleosols near New Mountain, Antarctica, suggests a pre-Middle Miocene, possibly Late Oligocene–Early Miocene age for paleosol 831 emplaced during the alpine event prior to the growth of the Inland Ice Sheet. Recent analysis of weathering zones in clasts with encrusted Fe/salts from the pebble pavement overlying the 831 paleosol reveals a succession of three weathering zones in a sandstone clast that record a paleoclimate transitioning from warm/wet (temperate) to cold/dry (polar). The first zone corresponds to an association of quartz cemented with berthierine (smectite–serpentine) and illite clay minerals. The second zone transitional from weathered clast to Na-encrusted rind contains smaller amounts of berthierine and illite formed in grains of partially dissolved quartz with minor salt content. Zone three corresponds to an ~3mm (3×106nm) thick mass of porous nitrate and gypsum. The contact between zones 2 and 3 appears to be correlative with the transition from temperate to polar ice which is considered to have occurred prior to or coincident with the Middle Miocene Climatic Optimum.

Geochemical characterization and palynological studies of some Agbada Formation deposits of the Niger Delta basin: implications for paleodepositional environments

Forty-two ditch cutting samples of the KR-1 offshore well from depths of 9660 ft to 10,920 ft composited at 90-ft intervals were subjected to sedimentological, micropaleontological, and geochemical analyses using standard procedures and the laser ablation-induced coupled plasma mass spectrometry technique, respectively. Sedimentological analysis revealed the presence of glauconites and the rare occurrence of framboidal pyrites, indicative of deposition in a slightly anoxic marine environment. Palynomorph percentage distribution shows that there are more terrestrially derived miospores (dominated by Zonocostites ramonae (Rhizophora spp.), Psilatricolporites crassus (Tabernaemontana crassa), Acrotichum aureum, and Laevigatosporites sp.) than marine phytoplanktons. Rare occurrence of Globoquadrina venezuelana, Globigerinoides promordius, and Globigerina sp. denotes an Early Miocene age and proximal shelf. These indicate that the main environment of deposition in the KR-1 well is coastal to marginal marine consisting of coastal deltaic-inner neritic, made up of tidal channel and shoreface deposits. Geochemical results show that the average concentrations of considered rare earth elements are less than their concentrations in world average shale. Trace metal ratios (such as Th/Cr, Cr/Th, Th/Co, and Cr/Ni) suggest that the investigated sediments were derived from felsic source rocks. Rare earth element patterns (such as La/Yb, Gd/Yb, La/Sm, and Eu/Eu) and Th data established the felsic composition of the source rocks. Ratios of U/Th, Ni/Co, Cu/Zn, and V/Sc suggest a well-oxygenated bottom water condition. Estimated europium and cerium anomalies of the studied samples suggest an oxidizing environment of deposition. Nonetheless, the ratios of V/Cr suggest a range of environmental conditions. Moreover, ratios of V/(V+Ni) suggest the rare occurrence of suboxic to anoxic environments of deposition.

New record of anchithere (Anchitherium aurelianense) in the Miocene of Eastern Siberia, Russia

New material on anchithere is described from Miocene of Eastern Siberia (Tagay locality, Olkhon Island, Lake Baikal). Based on the structure of teeth and postcranial bones, the Baikalian record is referred to the widespread Eurasian species Anchitherium aurelianense. This form shows low crowned lophodont type teeth without cement. Metaloph is mostly connected with ectoloph, protoloph does not connect with ectoloph; secondary structures of the anterior wall of metaloph (crochet) are not developed or incipient. The Early Miocene age of the Siberian anchithere is inferred from the archaic skeletal morphology and comparison with European and Asian records.

The earliest record (early Miocene) of a bony-toothed bird from South America and a reexamination of Venezuelan pelagornithids

ABSTRACTPelagornithids or bony-toothed birds were an enigmatic group of very large marine birds that existed throughout most of the Tertiary, with remains recovered in all continents. The currently recognized record of pelagornithids in South America extends from the middle Miocene to the Pliocene. Here, a fragment of a ramus mandibulae recently discovered in the Cerro La Cruz site (Castillo Formation, Lara State, northwestern Venezuela), is assigned to Pelagornis. With an early Miocene age (18.27–18.85 Ma), the fossil constitutes the earliest unequivocal record of the group in South America. The reexamination of another pelagornithid specimen recovered from Capadare Formation (middle Miocene), which was previously assigned to Pelagornithidae indeterminate, allows us to recognize the presence during the Miocene of Venezuela of a second pelagornithid morphotype, here tentatively referred to Pelagornis chilensis Mayr and Rubilar-Rogers, 2010. Originally recorded from the middle Miocene-early Pliocene of Chile, the possible presence of P. cf. P. chilensis during the middle Miocene of Venezuela might represent the first record of this bony-toothed species outside Chile and expands its distribution area by 3500 km, to the tropical waters of northern South America. Citation for this article: Solorzano, A., and A. D. Rincon. 2015. The earliest record (early Miocene) of a bony-toothed bird from South America and a reexamination of Venezuelan pelagornithids. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2014.995188.

Paleogene Xenarthra and the evolution of South American mammals

Recent studies show Xenarthra to be even more isolated systematically from other placental mammals than traditionally thought. The group not only represents 1 of 4 primary placental clades, but proposed links to other fossorial mammal taxa (e.g., Pholidota, Palaeanodonta) have been contradicted. No unambiguous Paleocene fossil xenarthran remains are known, and Eocene remains consist almost exclusively of isolated cingulate osteoderms and isolated postcrania of uncertain systematic provenance. Cingulate skulls are unknown until the late middle Eocene, and the oldest sloth and anteater skulls are early Oligocene and early Miocene age, respectively; there are no nearly complete xenarthran skeletons until the early Miocene. Ecological reconstructions of early xenarthrans based on extant species and the paleobiology of extinct Neogene taxa suggest the group's progenitors were myrmecophagous with digging and perhaps some climbing adaptations. The earliest cingulates were terrestrial diggers and likely myrmecoph...