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Data on finds of silicoflagellates in the marine Cenozoic section of West Kamchatka in the Kvachina Bay are presented. Based on analysis of the stratigraphic occurrence of taxa in the section, biostratigraphic units are identified at the rank of beds with flora. The discovery of stratigraphically important taxa in the studied assemblages allowed their correlation with associations of Oligocene zones based on silicoflagellates in nontropical regions. The conclusion that the host sediments are dated within the Early–Late Oligocene is supported by data on diatoms. [ABSTRACT FROM AUTHOR]

Megalolamna is an extinct lamniform shark genus that is known from Miocene marine deposits. In this study, three new specimens of Megalolamna collected from the eastern USA are newly described, and the diagnosis of the genus is emended to include a previously undocumented dental characteristic. The new specimens are represented by one tooth from the upper Oligocene Chandler Bridge Formation in South Carolina and two isolated teeth from the lower Miocene Calvert Formation in Maryland. The specimens from the Calvert Formation represent the northern-most occurrence of Megalolamna. Although the taxonomic identification of the specimen from the Chandler Bridge Formation is somewhat tentative, it is considered to represent geologically the oldest record of Megalolamna, suggesting the likelihood that the enigmatic genus has its origin in the Palaeogene no later than 23.5 Ma. [ABSTRACT FROM AUTHOR]

A new species Theronia qaidamensis sp. nov. (Ichneumonidae, Pimplinae) is described from the Oligocene Shangganchaigou Formation of the northwestern Qaidam Basin (Huatugou area), northeast of the Tibetan Plateau (TP). The new species represents the first report of the Ichneumonidae from the Qaidam Basin, which reveals an insect linkage between the Qaidam Basin and Europe. In addition, the study of associated fossils from the Shangganchaigou Formation shows that the palaeoenvironment of the northwestern Qaidam Basin during the Oligocene was warm and moist, which provided suitable living conditions for the current fossil. [ABSTRACT FROM AUTHOR]

Chiton (Class Polyplacophora) fossils are rare globally, mostly because they are restricted to hard habitats such as rocky shores that are taphonomically under-represented in the geological record. New Zealand is rich in Cenozoic marine molluscan fossils, but chitons are very uncommon. The earliest New Zealand records of fossil chiton species are all from the Late Oligocene (Duntroonian) Chatton Formation in Southland. They include Callochiton chattonensis Ashby 1929 [New Zealand fossil Polyplacophora (Chitons). Transactions and Proceedings of the Royal Society of New Zealand. 60:366–369], Acanthochitona (Notoplax) ashbyi (Laws 1932 [New Tertiary Mollusca from New Zealand. No. 2. Transactions and Proceedings of the New Zealand Institute. 62:183–199]) and Rhyssoplax allanthomsoni Mestayer 1929 [Notes on New Zealand Mollusca. Transactions and Proceedings of the Royal Society of New Zealand. 60(4):247–150]. At Cosy Dell farm, Waimumu, New Zealand, the Chatton Formation contains a diverse chiton fauna representing seven families and seven genera, including Callochiton cf. chattonensis, Acanthochitona cf. ashbyi, Ischnochiton sp., Leptochiton cf. inquinatus, Lorica sp., Plaxiphora sp., and Rhyssoplax sp., the highest recorded fossil chiton diversity in New Zealand. All genera described in the fossil assemblage are associated with extant taxa around modern New Zealand rocky intertidal and shallow near shore environments. The study extends the New Zealand stratigraphic range of four genera (Ischnochiton, Plaxiphora, Lorica and Leptochiton) back to the Duntroonian (Late Oligocene), provides the first taxonomic descriptions of each chiton taxon from the site and discusses the paleoecological and biostratigraphic significance of these rarely preserved components of a rocky shore ecosystem. [ABSTRACT FROM AUTHOR]

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The palynological analysis of the Paleogene and Neogene sequences of the southern part of West Siberia (borehole 2, Novosibirsk oblast) showed that the conifer bisaccate pollen in the spore–pollen spectra exhibits a series of morphological features allowing its comparison with the modern pollen of Cathaya argyrophylla Chun et Kuang. These palynomorphs belong to relict vegetation, which currently occurs in the wet subtropical climate of South China, and are important climate indicators. The palynomorphs are ascribed to the ancestral forms of the species Cathaya as Abietineaepollenites sellowiiformis (Zaklinskaja) Doweld 2018. The pollen is described, and its distribution along the section is shown. The maximum amount of the A. sellowiiformis pollen (up to 23.7%) is confined to the upper part of the Oligocene and the Lower Miocene and its last appearance is recognized in the Middle–Upper Miocene. These data expand our knowledge on the geographic range of the Cathaya ancestral form and its role in plant communities of Central Asia in the Cenozoic. [ABSTRACT FROM AUTHOR]

Eomysticetidae are a clade of early diverging functionally toothless, longirostrine and likely baleen-bearing stem mysticete whales. Eomysticetid fossils are rare but known worldwide from Oligocene strata. The richest assemblage of eomysticetids has been uncovered in New Zealand from the Kokoamu Greensand and Otekaike Limestone (North Otago and South Canterbury regions, South Island). This includes some of the largest known eomysticetids, Tokarahia kauaeroa and Tokarahia lophocephalus, some older and more archaic forms such as Matapanui waihao, the fragmentary Tohoraata raekohao and Tohoraata waitakiensis, and the well-known Waharoa ruwhenua represented by several well-preserved skulls and mandibles of adults and juveniles. Studies of these New Zealand fossils strongly indicates monophyly of Eomysticetidae and suggest possible skim feeding behaviour, possession of non-functional teeth and baleen, extreme rostral lengthening during growth and peramorphic evolution, rostral kinesis, use of Zealandia as a calving ground, and probable extinction at or near the Oligo-Miocene boundary. [ABSTRACT FROM AUTHOR]

Studies involving anatomical description and taxonomy of fossil odontocetes offer insights into their evolutionary history and diversity. This study analyses tusk-like teeth in odontocetes including the description of a new species, Nihoroa reimaea, from the Waitaki valley, North Otago, New Zealand. Dental features of Nihoroa reimaea, a gracile, longirostrine odontocete with procumbent tusk-like anterior teeth and slightly denticulate cheek teeth, are described in detail. A comparative analysis of tusk-like teeth from New Zealand specimens and from elsewhere in the world was performed allowing a classification of tusk-like teeth in odontocetes and highlighting the differences between true tusks and rooted procumbent teeth. Correlation analyses revealed significant associations between rostrum proportions and tooth crown morphology. This study contributes to the understanding of tusk-like teeth and illuminates their significance in odontocete evolution. Nihoroa reimaea expands our knowledge of fossil cetaceans and highlights the importance of New Zealand's exceptional fossil record of odontocetes with tusk-like teeth. [ABSTRACT FROM AUTHOR]

Recent research on mysticete fossils from the Late Eocene and Oligocene has revolutionised our understanding of the diversity and evolutionary scenarios for early baleen whales. For example, aetiocetids are a possible, though controversial, lineage that bridges the gap between the toothed and baleen-bearing mysticetes, and eomysticetids show a further transitional step towards the baleen-bearing status, with the presence of non-functional dentition in adults. However, information about the origin of crown mysticetes, including the most recent common ancestor of all extant lineages and its descendants, is critical to further understanding the evolution of baleen whales. The phylogenetic positions of the Oligocene Toipahautea, Whakakai, Horopeta, and Mauicetus from New Zealand remain unresolved and problematic, but all four genera show a close relationship with crown mysticetes. The original and subsequent cladistic analyses have consistently revealed a sister relationship between the Toipahautea-to-Mauicetus grade and crown mysticetes, and Horopeta has been placed close to the cetotheriids within the crown group. This review aims to stimulate more research on this topic by elucidating the origin of crown mysticetes, which likely experienced a poorly known radiation event during the Oligocene that established the modern lineages. [ABSTRACT FROM AUTHOR]

Background and aimsCAM photosynthesis is hypothesized to have evolved in atmospheres of low CO2 concentration in recent geological time because of its ability to concentrate CO2 around Rubisco and boost water use efficiency relative to C3 photosynthesis. We assess this hypothesis by compiling estimates of when CAM clades arose using phylogenetic chronograms for 73 CAM clades. We further consider evidence of how atmospheric CO2 affects CAM relative to C3 photosynthesis.ResultsWhere CAM origins can be inferred, strong CAM is estimated to have appeared in the past 30 million years in 46 of 48 examined clades, after atmospheric CO2 had declined from high (near 800 ppm) to lower (

We report the discovery of an ancient forest bed near Stanley, on the Falkland Islands, the second such ancient deposit identified on the South Atlantic island archipelago that is today marked by the absence of native tree species. Fossil pollen, spores and wood fragments preserved in this buried deposit at Tussac House show that the source vegetation was characterized by a floristically diverse rainforest dominated by Nothofagus -Podocarpaceae communities, similar to cool temperate Nothofagus forests/woodlands and Magellanic evergreen Nothofagus rainforests. The age limit of the deposit is inferred from the stratigraphic distribution of fossil pollen species transported by wind, birds or ocean currents from southern Patagonia, as well as similar vegetation types observed across the broader region. The deposit is suggested to be between Late Oligocene and Early Miocene, making it slightly older than the previously analysed Neogene West Point Island forest bed (200 km west of Tussac House). The combined evidence adds to our current knowledge of the role of climate change and transoceanic dispersal of plant propagules in shaping high-latitude ecosystems in the Southern Hemisphere during the late Palaeogene and Neogene. [ABSTRACT FROM AUTHOR]

Anomaluroid rodents (i.e. Anomaluridae + Zenkerellidae) have a long evolutionary history in Africa dating back to at least the middle Eocene, but Palaeogene fossil members of the anomaluroid crown group have never been found south of the Sahara. Here, we describe the oldest crown anomaluroid from sub-Saharan Africa, Eliwourus topernawiensis (new genus and species) from the early Oligocene Topernawi Formation of northern Kenya. Bayesian phylogenetic tip-dating analysis of a combined molecular-morphological dataset places ~29.5 Ma Eliwourus as an advanced stem anomalurid, and suggests that crown Anomaluridae originated ~28.2 Ma. The gliding behaviour seen in all crown anomalurids had, therefore, likely evolved before the close of the early Oligocene. Bayesian geocoordinates analysis places the origin of crown Anomaluroidea (~47.2 Ma) in northern Africa, and identifies a stem anomalurid dispersal into equatorial eastern Africa in the latest Eocene or earliest Oligocene. We present the first quantitative analysis of the pace of anomaluroid dental evolution and confirm a remarkably slow or bradytelic rate of phenotypic change, despite significant transformations in postcranial morphology related to the evolution of gliding behaviour during the same interval. The Topernawi area was evidently sufficiently forested during the early Oligocene to support both arboreal rodents and primates. [ABSTRACT FROM AUTHOR]

The Jiaozigou Formation, the lowest fossiliferous stratum in the Linxia Basin, produces the most abundant mammalian fossils in East Asia. Although the Jiaozigou Fauna is renowned for the ‘giant rhino’ (Paraceratheriidae), evidence of relatively small rhinocerotoids is scant, consisting only of fragments. The newly identified species, Megacanodon dongxiangense gen. et sp. nov. is characterised by its small-sized body, the presence of a large canine, nearly completely molarised upper premolars, retracted nasal notch, and not-elevated occipital part. It remains unclear whether the new genus is phylogenetically close to Hyracodontidae, Eggysodontidae, or Rhinocerotidae. We tentatively designate it as a basal genus within Rhinocerotoidea, with the uncertain family affiliation. [ABSTRACT FROM AUTHOR]

X-ray diffraction analyses (XRD) were performed on marine Palaeogene (Upper Eocene--Lower Oligocene) clay minerals from Central Germany (Schneidlingen 1/2018 research well). Geochemical and grain size analyses gave supporting information on eustatic controlled system tracts, transgressions, sediment supply and flow conditions during the time of sedimentation and served to structure the research well in the formations. Except for three transgressions, long-lasting steady flow conditions occurred in the forefield of the Central German Estuary ("Mitteldeutsches Ästuar" -- MdÄ). The clay mineral kaolinite could be identified as a delivery area indicator for the Central Saxon Hills ("Mittelsächsisches Hügelland"). The other studied clay minerals smectite, illite and chlorite indicate three cooling trends between or within the formations and the transition from a chemical to a physical weathering regime with the beginning of the Rupelsilt/-clay Subformation. Although there are hints for authigenic or early diagenetic influences, distinct changes within the clay mineral distribution describe prominent trends that correlate well with other insights from the sedimentation area. It has been shown be evidenced, that clay mineralogical studies of marine sediments from Central Germany can be used to determine source areas and climatic trends. [ABSTRACT FROM AUTHOR]

Although the evolutionary history of anthropoid primates (monkeys, apes, and humans) appears relatively well‐documented, there is limited data available regarding their origins and early evolution. We review and discuss here the earliest records of anthropoid primates from Asia, Africa, and South America. New fossils provide strong support for the Asian origin of anthropoid primates. However, the earliest recorded anthropoids from Africa and South America are still subject to debate, and the early evolution and dispersal of platyrhines to South America remain unclear. Because of the rarity and incomplete nature of many stem anthropoid taxa, establishing the phylogenetic relationships among the earliest anthropoids remains challenging. Nonetheless, by examining evidence from anthropoids and other mammalian groups, we demonstrate that several dispersal events occurred between South Asia and Afro‐Arabia during the middle Eocene to the early Oligocene. It is possible that a microplate situated in the middle of the Neotethys Ocean significantly reduced the distance of overseas dispersal. [ABSTRACT FROM AUTHOR]

Summary: A petrified wood resembling the modern wood of Mammea africana Sabine is described from the Oligocene Gebel Ahmer Formation from Egypt. The fossil wood is attributed to Mammeoxylon lanneoides Lemoigne according to the xylotomical homologies with the species recorded previously from Ethiopia. The wood anatomy observed in the fossil specimen, along with the climatic information available from the Nearest Living Relative comparison, suggests a tropical humid climate at the site of growth. This is the oldest record of Mammeoxylon Lemoigne in Africa, which contributes towards the understanding of the origin and paleo-dispersal pathways of the genus. A list of 46 Egyptian Oligocene wood species attributed to 11 families is also given. [ABSTRACT FROM AUTHOR]

In order to address the challenges related to exploration target search and sustainable development of oilfields in the Weixinan Sag of Beibuwan Basin, this study focused on fault-lithologic composite traps within the structural trap development section of the third member of Oligocene Weizhou Formation in the No.2 fracture zone of Weixinan Sag. By examining the relationship between the evolution of depression-controlling faults and the sedimentary characteristics of the third member of Weizhou Formation, it was observed that the No.2 fault zone exhibited weak activity during the sedimentary period of the third member, facilitating the continuous transportation of underwater distributary channels of the braided river delta along the long axis direction of the sag towards the depression. Conversely, the regional tectonic activities were intense during the sedimentary periods of the second and first members of Weizhou Formation, leading to the formation of a series of en-echelon faults. The interaction between relatively isolated underwater distributary channels of the braided river delta front and en-echelon faults resulted in angled staggered formations and intersecting channels, ultimately creating a distinctive channel-type structural-lithologic trap group characterized by NE-SW trending fault sealing and NW-SE trending sand body pinching. The research findings indicate the development of a three-factor coupling fault-lithologic trap model in the third member of the Weizhou Formation. This model includes the depression faulted uplift background of the No.2 fracture zone, low-frequency oscillating channel, and en-echelon tension-torsion fault. The intersection area of the main stream line of underwater distributary channel in a braided river delta and the No.2 fracture zone is identified as a favorable zone for structural-lithologic traps. Additionally, composite structural-lithologic traps are predominantly found in the near-source intersection area, while isolated structural-lithologic traps are more common in the far-source intersection area, leading to the formation of an accumulation model involving axial channel sand control, fault, and sand body composite control. The fault-lithologic trap model and accumulation model have demonstrated effective application in practice. Several favorable fault-lithologic composite trap groups with distinct fault sealing and sand body pinching orientations have been identified, particularly in the Wei B-E structure. Notably, well WB-E 1 has successfully drilled nearly 100 meters of oil layer, with subsequent wells yielding positive results. The exploration efforts in the third member of the Weizhou Formation within the No.2 fault zone of the Weixinan Sag have led to the discovery of geological reserves exceeding 10 million cubic meters, underscoring the significance of fault-lithologic composite traps in this region.

Understanding the paleoenvironment and phytogeographical history of the Tibetan Plateau, China relies on discovering new plant fossils. The Qaidam Basin has long been regarded as an ideal ‘field laboratory’ to investigate the paleoclimate and paleobiological evolution of the northern Tibetan Plateau. However, fossil angiosperms from the Qaidam Basin are rare, and our knowledge of its paleovegetation is poor. Here, we report fossil leaves and fruits of Betulaceae found from the Oligocene Shangganchaigou Formation of northwestern Qaidam Basin (Huatugou area). Comparative morphological analysis led us to assign the fruits to the Betula subgenus Betula and the leaves to Carpinus grandis. These findings, together with other reported fossil plants from the same locality, reveal a close floristic linkage between the Qaidam Basin and Europe during the Oligocene. The northern pathway of this floristic exchange may have crossed through the Qaidam Basin during the late Paleogene. This floristic linkage may have been facilitated by the continuous narrowing of the Turgai Strait and stronger westerlies, which transported moisture and provided favorable climatic conditions. Indeed, fossil plants collected from the Qaidam Basin suggest that during the Oligocene this region had warm and humid deciduous broad-leaf forest, which differs from the region’s modern vegetation and indicates that the Qaidam Basin may have been a suitable region for these plants to flourish and spread during the Oligocene.

Continental‐scale shear zones in Indochina record Cenozoic tectonic processes in SE Asia. Previous extrusion models link these shear zones to northward indentation of the Indian continent and conflict with distributed Oligocene conjugate strike‐slip pairs, formed by E‐W‐directed compression (present coordinates). This paper presents evidence of Oligocene shearing along the Mogok Metamorphic Belt in Myanmar, the western boundary of the Indochina block. The Kyanigan quarry at northern Mogok Metamorphic Belt exposes paragneiss, marble and quartzite schist with E‐W striking, which would be dragged from N‐S striking foliations of the main Mogok Metamorphic Belt by right‐lateral shearing of the brittle Sagaing Fault. After restoration, right‐lateral shearing 'σ' structures, cored with garnet, in paragneiss in the Kyanigan quarry are consistent with 'σ' and 'δ' structures in the Moulmein granitic mylonite to the south. U–Pb ages of metamorphic zircon of a sheared paragneiss and a leucogranite, cross‐cutting shear foliation in the Kyanigan quarry, and a biotite 39Ar‐40Ar age of mylonite at Moulmein constrain dextral shearing to 33–25.4 Ma, coeval with other 31–24.5 Ma shear zones in Indochina. The eleven NW‐striking left‐lateral shear zones and N‐S to NE‐striking right‐lateral shear zones define Oligocene conjugate fault patterns in Indochina. After restoration of ~80–45° clockwise rotation, these Oligocene conjugate shear zones, coupled with the anticlinal configuration of the Xuelongshan and Doi Inthanon‐Doi Suthep domes, reflect approximate N–S‐directed shortening. These structures to the north with coeval Myanmar‐Sumatra magmatic arc to the south demonstrate that they correspond to back‐arc contraction during northward subduction of the Indian Ocean. Oligocene continental‐scale intra‐continental shearing may be triggered by syn‐subduction compression in SE Asia. [ABSTRACT FROM AUTHOR]

The Musandam peninsula (northern part of the Oman thrust-and-fold belt), although flanked by a foreland basin rich in petroleum resources, has remained so far without a proven play. As part of an exploration project that covered partly the exposed external part of the peninsula made up of mainly Mesozoic carbonate platform, i.e., Arabian (including the equivalents of the producing reservoirs), the study of its outcrops, easily accessible along existing valleys, became the best opportunity to record details far beyond the resolution allowed by seismic surveys or wells and thus, to refine the structural model. The purpose of the paper is to update the general tectonic framework based on novel observations presented as series of outcrop pictures, supplemented with two interpreted seismic lines imaging the subsurface structure. These observations were made in around two hundred points where bed and/or fault/fold axis positions were measured or estimated, eventually modifying an existing geological map. Although it has been generally considered that in Musandam peninsula the fault systems affecting the Arabian platform were related in essence only to the continuing shortening since Late Cretaceous (after the obduction of the Semail ophiolite), the first outcomes of the fieldwork refer to those tectonic events pre-dating the contraction in the foreland plate which have not been previously noticed, namely a widespread Upper Triassic extension followed by inversion and development of a major angular unconformity at the Jurassic base (an equivalent of the "Old Cimmerian phase" encountered elsewhere along former Neo-Tethys margins). Within the newly installed carbonate platform, a second but milder angular unconformity occurs at the Dogger/Liassic boundary. Surprisingly, two ubiquitous ~ 20-m-thick reservoir beds—Upper Triassic and Lower Jurassic—leaked (everywhere accessible) hydrocarbons or hydrogen sulfide odor upon hammering. Other new outcomes are related to the structures and tectonic displacements induced during the shortening period, which appear far more complex and significantly larger than usually interpreted, as documented by series of thrusts making a duplex system, farther coupled within the foredeep to a triangle zone as supported by seismic data; these data also allowed to depict an offshore canyon initiated roughly at the Oligocene base which lies in continuity with a few small Paleogene clastic units cropping out just downstream the northern Musandam valleys (in UAE). The last (Late Miocene) major outcropping structure is a NW–SE-trending long and steep reverse fault running from near the confluence of valleys Shah and Bih in the south, up to at least the western parts of the Tibat and Bukha offshore hydrocarbon fields (Sultanate of Oman) in the north (called herein Bukha-Tibat-Ghalilah-Rahbah fault), which cuts obliquely the former nappe pile. As it appears to be synchronous with the orthogonal, also major, Dibba fault (SE margin of the Musandam platform), but of opposing kinematics (the latter is normal), one can infer that ~ E-W sinistral wrenching had acted upon the peninsula before the shortening was transferred to the Zagros system. Coeval with them or younger, a system of normal faults trending variously around N-S, with throws up to 100 m, was mapped. The main fieldwork results reported in the paper bring significant improvements to the understanding of the Musandam belt by highlighting previously overlooked tectonic events (particularly the early rifting), refining the structural geometry of the successive fault systems and adding new constraints on the regional kinematics and evolution. Furthermore, the onset of the Musandam nappe pile erosion can be placed confidently at around the beginning of the Oligocene, older than previously considered. Through the depiction of the aforementioned reservoir beds and a direct indication of a new perspective in terms of viable source rocks in the subsurface, the accompanying suggestions may trigger a rejuvenation of the prospectivity-oriented research. [ABSTRACT FROM AUTHOR]

Kuphus is a genus of teredinid bivalves whose modern counterpart, K. polythalamius, colonises oxygen-poor and restricted marine environments enriched in plant remains. In the Oligocene, Kuphus colonies are quite abundant worldwide, but their depositional setting has never been studied in detail. We describe the first report of Oligocene Kuphus beds from the Iberian Peninsula, cropping out in platform deposits of the Prebetic (Southeastern Spain). By means of anterior endings and taphonomic characters as orientation of Kuphus tubes, fragmentation, packing and mixing with other fauna, four skeletal concentrations were distinguished: SkC A represents in situ colonies with anterior endings well preserved and with local dolomitisation around the tubes and was recorded in the inner lagoon; SkC B, with parallel and horizontally reoriented tubes, was formed by tidal currents; SkC C records high-energy events breaking down the tubes and resedimenting them close to the source area; SkC D is characterised by fragmented tubes mixed with other bioclasts, deposited by storms in the outer platform. The recorded skeletal concentrations are consistent with the environmental setting of K. polythalamius, but the morphological differences and the absence of data on the presence of plant remains could possibly reflect adaptations to higher variety of palaeoenvironments. [ABSTRACT FROM AUTHOR]

The Oligocene Zhuhai sandstones are significant reservoirs for hydrocarbons in the Baiyun Sag, South China Sea. For effective appraisal, exploration and exploitation of such a deep-water hydrocarbon sandstone, samples of five wells from depths of 850 m to 3 000 m were studied. A series of comprehensive petrographic and geochemical analyses were performed to unravel the diagenetic features and their impact on the reservoir quality. Petrographically, the sandstones are dominated by feldspathic litharenites and lithic arenites with fine to medium grain sizes and moderate to good sorting. The reservoir quality varies greatly with a range of porosity from 0.2% to 36.1% and permeability from 0.016 × 10−3 µm2 to 4 301 × 10−3 µm2, which is attributed to complex diagenetic evolution related to sedimentary facies; these include compaction, cementation of calcite, dolomite, siderite and framboidal pyrite in eogenetic stage; further compaction, feldspar dissolution, precipitation of ferrocalcite and ankerite, quartz cements, formation of kaolinite and its illitization, precipitation of albite and nodular pyrite, as well as hydrocarbon charge in mesogenetic stage. The dissolution of feldspar and illitization of kaolinite provide internal sources for the precipitation of quartz cement, while carbonate cements are derived from external sources related to interbedded mudstones and deep fluid. Compaction is the predominant factor in reducing the total porosity, followed by carbonate cementation that leads to strong heterogeneity. Feldspar dissolution and concomitant quartz and clay cementation barely changes the porosity but significantly reduces the permeability. The high-quality reservoirs can be concluded as medium-grained sandstones lying in the central parts of thick underwater distributary channel sandbodies (>2 m) with a high content of detrital quartz but low cement. [ABSTRACT FROM AUTHOR]

Liquidambar L. is a significant constituent of the Cenozoic flora in the Northern Hemisphere. Currently, this genus exhibits a discontinuous distribution across Asia and North America, with the center of diversity being in southeastern Asia. This study presents the first occurrence of Liquidambar in the Oligocene of South China. Fossil sweetgum infructescences, associated pollen, and leaves have been found in the Nanning Basin, Guangxi. A new species, Liquidambar nanningensis sp. nov., is described based on the morphological and anatomical characteristics of three-dimensionally preserved infructescences. The Liquidambar fossils from the Nanning Basin show a combination of features indicative of the former genera of Altingiaceae, Altingia, Liquidambar s. str., and Semiliquidambar. The new occurrence expands the taxonomic and morphological diversity of the Paleogene Liquidambar species in South China. [ABSTRACT FROM AUTHOR]

Eomysticetidae (Chaeomysticeti clade) is an archaic family of baleen whales that originated and diversified during the Oligocene epoch. The fossil record of this family is represented by at least 11 formally described species, including records in Baja California Sur (Mexico), Kaiserswerth (Germany), Kitakyushu (Japan), South Carolina (United States), and South Island (New Zealand). Baja California Sur (BCS) possesses important marine deposits from the upper Oligocene, which document a rich diversity of fossil mysticetes, including members of the family Eomysticetidae. In this work, we report a whale specimen collected in the upper Oligocene San Juan Member, El Cien Formation, from the so-called "Ten Minute locality", San Hilario, about 100 km NW of La Paz, Baja California Sur. The studied specimen consists of an incomplete skull, in which most of the rostrum and part of the occipital shield are missing but preserving one tympanic bulla in situ. This specimen is identified as belonging to the family Eomysticetidae based on both an elongated skull and nasals and transversely narrow and long intertemporal region with a wide exposure of parietals and frontals. The lack of more diagnostic regions precludes its identification at generic/specific levels. The specimen represents the first description of an eomysticetid for the San Hilario area, increasing our knowledge of the evolution of this group of mysticetes and its record in the Pacific basin from the late Oligocene of BCS. [ABSTRACT FROM AUTHOR]

The Suborder Clupeoidei Bleeker, 1859 comprises mostly marine fishes, which form large schools feeding on plankton. The fossil record of the suborder in the Late Paleogene reveals that clupeoids were abundant in the Western, Central, as well as Eastern Paratethys. Clupeoid descriptions from the Polish Outer Carpathians (SE Poland, Central Paratethys) remain incomplete due to usage of 'collective species', taxonomical inaccuracies, and lack of clear links between extinct and extant representatives. In this paper we present a new clupeoid, †Beksinskiella gen. nov., from the Oligocene of the Outer Carpathians, Poland. The new genus encompasses the nominal species †Maicopiella longimana (Heckel, 1850). †Beksinskiella gen. nov. has a unique combination of characters (skull roof with frontoparietal striae; smooth opercle; 6-7 branchiostegal rays; 42-48 vertebrae; dorsal and anal fins with 21-23 rays; the last two rays of the anal fin being elongated, and the presence of a complete series of abdominal scutes with the postpelvic ones poorly developed), supporting recognition of a new genus of the Suborder Clupeoidei. Similarities and differences between fossil and extant genera of Cluepoidei are discussed to shed light on their relationship. [ABSTRACT FROM AUTHOR]

Well-preserved fossil assemblages provide valuable insights into the evolutionary history of biota and their environments. Here, we report on Rupelian (early Oligocene) siliceous nanoeukaryotes from diatomites in the Carpathian Mountains, southeastern Poland. These sediments yielded novel forms of parmaleans and parmalean-like fossils. Their cell wall structure differs from that of described genera. Instead of the generically specific separate dorsal plate and set of girdle plates, some of our taxa contain one upended, hollow, subspherical, perforated cup. To accommodate these differences, we propose a new division Parmaphyta, a new family Parmoligocenaceae, a new genus Parmoligocena and a new species Parmoligocena janusii. Other remains are reminiscent of the extant genus Pentalamina and for this we propose a new genus and species, Pentalaminamorpha radiata. The taxonomic affinity is less certain for other nannofossils found, as they are only somewhat similar to parmaleans, and so we only tentatively associate them with this group. All these fossils occur together with a diverse assemblage of diatoms (mostly from Leptocylindrales, Rhizosoleniales, Coscinodiscales, Cymatosirales, and Hemiaulales), silicoflagellates (mostly species from the genus Corbisema) and archaeomonads. Together they suggest the palaeoenvironmental context for the parmaleans, a neritic marine environment, thus similar to where silicified parmaleans can be found today.

Wireline log correlation panels of palynologically analysed boreholes illustrate lateral facies transitions within Rupelian age strata of the Dutch Rupel Formation across the southeastern North Sea Basin. The middle to upper part of the Rupel Formation consists of clays and silts of the Boom Member and the overlying sandier Steensel Member. In the Mill and Goirle boreholes in the Dutch Province of North Brabant, the Boom Member is thickly developed and represents the middle to upper Rupelian (biozones NSO3 to NSO5a), while the Steensel Member is rather thinly developed and only comprises the uppermost Rupelian (biozone NSO5a). Borehole log correlations show that towards the south (or more proximal to the palaeo-continent) the Rupel Formation becomes sandier and the clayey Boom Member thins in favour of the sandy superjacent Steensel Member. Palynological analyses confirm that the Boom Member is restricted to the middle Rupelian (biozone NSO3) age here, and that the superjacent Steensel Member is of middle to upper Rupelian age (biozones NSO3 to NSO5a). Geological models constructed for northern Belgium propose that this facies transition occurs rather sharply, along a WSW-ENE oriented zone parallel to the presumed shoreline at that time. The results of this study support this interpretation and extend the trend towards the Netherlands.

The results of the palynological study of the Kurshskaya Formation stratotype (Primorsky quarry, Kaliningrad Oblast) are presented. The lower part of the Kurshskaya Formation (Member of "chocolate" clays) contains an assemblage of latest Eocene dinoflagellate cysts Areosphaeridium diktyoplokum, Glaphyrocysta semitecta, and Cordosphaeridium funiculatum. The formation is characterized by four spore-pollen assemblages: (1) latest Eocene Pinuspollenites–Inaperturopollenites–Sciadopityspollenites assemblage in the "chocolate" clays and in the lower part of brown sands; (2) early Oligocene Sequoiapollenites–Betulaepollenites betuloides assemblage in the lower part of the brown sands member; (3) early Oligocene Boehlensipollis hohli–Carpinipites carpinoides in the middle part of brown sands member; (4) late Oligocene–early Miocene Alnipollenites–Corylopollis assemblage in the upper part of the brown sands of the Kurshskaya Formation. In total, the Kurshskaya Formation is terminal Eocene–early Miocene in age. The lower part of the Zamland Formation, which overlies the Kurshskaya Formation, contains the presumably middle Miocene Pinuspollenites–Tricolporopollenites pseudocingulum–T. euphorii assemblage. Based on the obtained palynological data, the depositional settings at the end of the Eocene–Oligocene–early Miocene in the South Baltic region are reconstructed. The regression of the marine basin began as early as the end of the Priabonian, the climate was still quite warm and humid, close to subtropical. Mesophytic mixed coniferous-broad-leaved forests grew along the shores of the strait, lowlands were occupied by marsh vegetation. Cooling at the Eocene/Oligocene boundary resulted in the appearance of hemlock in plant communities and increase in the proportion of catkins (alder, birch, hornbeam). Presumably, in the late Oligocene–early Miocene, the proportion of small-leaved trees, especially alder and hazel, sharply increased in mesophytic forests, while the number of pine trees decreased. Wetter and warmer climatic conditions are assumed for the early Miocene: this time is characterized by an increase in the number of walnut, cypress, and Cyrillaceae. In the middle Miocene, the climate was still quite warm, but drier, and such moisture-loving species as Podocarpus, spruce, Glyptostrobus, and swamp cypress disappeared from plant communities. [ABSTRACT FROM AUTHOR]

The article titled "Systematic Revision of Pre- and Post-Santacrucian Species of Protypotherium (Interatheriidae, Notoungulata)" provides a taxonomic revision of the species of Protypotherium, a genus of native ungulates from South America. The study focuses on the Interatheriidae family, which is considered one of the most diverse and abundant clades of South American native ungulates. The authors propose junior synonyms for certain species and conclude that Protypotherium includes several species. The article also presents a comprehensive phylogenetic analysis of Interatheriidae. [Extracted from the article]

Fossil teeth representing four species of Lophiomeryx are identified from early Oligocene strata in the Saint Jacques area of Nei Mongol, including L. shinaoensis, L. gracilis, L. cf. chalaniati, and L. triangularis sp. nov. This represents the highest species richness of this early traguline from a single stratigraphic sequence. The new materials expand the spatiotemporal ranges of L. shinaoensis and L. gracilis, which are previously known from the late Eocene of Guizhou, south China. We present further morphological details that support the validity of the original taxonomy for the Guizhou materials. L. cf. chalaniati resembles the type species morphologically but is smaller than European specimens. L. triangularis sp. nov. is the last to appear in the sequence, and it is notably larger and more high-crowned than all the other known species of Lophiomeryx. Aside from the dental materials, we report the first known skull of L. gracilis, collected from a nearby locality, Qianlishan. While the overall skull morphology is primitive for tragulines, the specimen preserves a closed postorbital bar, a derived feature that was previously thought to be absent in Lophiomeryx. Our new specimens shed light on the diversity, biogeography, and ecology of this basal ruminant as well as on the evolution of early tragulines. [ABSTRACT FROM AUTHOR]

Recently, the evolutionary history of the Caribbean mangroves has been reconsidered using partial palynological databases organized by the time intervals of interest, namely Late Cretaceous to Eocene for the origin, the Eocene–Oligocene transition for major turnover and Neogene to Quaternary for diversification. These discussions have been published in a set of sequential papers, but the raw information remains unknown. This paper reviews all the information available and provides the first comprehensive and updated compilation of the abovementioned partial databases. This compilation is called CARMA-F (CARibbean MAngroves-Fossil) and includes nearly 90 localities from the present and past Caribbean coasts, ranging from the Late Cretaceous to the Pliocene. Details on the Quaternary localities (CARMA-Q) will be published later. CARMA-F lists and illustrates the fossil pollen from past mangrove taxa and their extant representatives, and includes a map of the studied localities and a conventional spreadsheet with the raw data. The compilation is the most complete available for the study of the origin, evolution and diversification of Caribbean mangroves, and is open to modifications for adapting it to the particular interests of each researcher. [ABSTRACT FROM AUTHOR]

The early diverging, dolphin-sized, cetacean clade Xenorophidae are a short-lived radiation of toothed whales (Odontoceti) that independently evolved two features long thought to be odontocete synapomorphies: the craniofacial and cochlear morphology underlying echolocation and retrograde cranial telescoping (i.e., posterior migration of the viscerocranium). This family was based on Xenorophus sloanii, which, for the past century, has been known only by a partial skull lacking a braincase and tympanoperiotics, collected around 1900 from the Ashley Formation (28–29 Ma, Rupelian) near Ladson, South Carolina. A large collection of new skulls and skeletons (ChM PV 5022, 7677; CCNHM 104, 168, 1077, 5995) from the Ashley Formation considerably expands the hypodigm for this species, now the best known of any stem odontocete and permitting evaluation of intraspecific variation and ontogenetic changes. This collection reveals that the holotype (USNM 11049) is a juvenile. Xenorophus sloanii is a relatively large odontocete (70–74 cm CBL; BZW = 29–31 cm; estimated body length 2.6–3 m) with a moderately long rostrum (RPI = 2.5), marked heterodonty, limited polydonty (13–14 teeth), prominent sagittal crest and intertemporal constriction, and drastically larger brain size than basilosaurid archaeocetes (EQ = 2.9). Dental morphology, thickened cementum, a dorsoventrally robust rostrum, and thick rugose enamel suggest raptorial feeding; oral pathology indicates traumatic tooth loss associated with mechanically risky predation attempts. Ontogenetic changes include increased palatal vomer exposure; fusion of the nasofrontal, occipito-parietal, and median frontal sutures; anterior lengthening of the nasals; elaboration of the nuchal crests; and blunting and thickening of the antorbital process. The consistent deviation of the rostrum 2–5° to the left and asymmetry of the palate, dentition, neurocranium, mandibles, and vertebrae in multiple specimens of Xenorophus sloanii suggest novel adaptations for directional hearing driven by the asymmetrically oriented pan bones of the mandibles. A second collection consisting of a skeleton and several skulls from the overlying Chandler Bridge Formation (24–23 Ma, Chattian) represents a new species, Xenorophus simplicidens n. sp., differing from Xenorophus sloanii in possessing shorter nasals, anteroposteriorly shorter supraorbital processes of the frontal, and teeth with fewer accessory cusps and less rugose enamel. Phylogenetic analysis supports monophyly of Xenorophus, with specimens of Xenorophus simplicidens nested within paraphyletic X. sloanii; in concert with stratigraphic data, these results support the interpretation of these species as part of an anagenetic lineage. New clade names are provided for the sister taxon to Xenorophidae (Ambyloccipita), and the odontocete clade excluding Xenorophidae, Ashleycetus, Mirocetus, and Simocetidae (Stegoceti). Analyses of tooth size, body size, temporal fossa length, orbit morphology, and the rostral proportion index, prompted by well-preserved remains of Xenorophus, provide insight into the early evolution of Odontoceti. [ABSTRACT FROM AUTHOR]

Two new species of ctenodactylid rodents, Prodistylomys taatsinius sp. nov. and Prodistylomys mongoliensis sp. nov. , are described from the Valley of Lakes, Central Mongolia. They represent the first record of this genus in Mongolia. Prodistylomys is characterized by a simple dental pattern and high hypsodonty, reflecting an adaptation for tough vegetation in a dry environment, which is congruent with the aridification event that took place during the Late Oligocene and Early Miocene. We performed the most complete phylogenetic analysis combining the largest sampling in the family Ctenodactylidae and the best-represented stratigraphical distribution for the sample. This allowed us to propose that the origin of ctenodactylids lies in East Asia during the Eocene, and after that, the group dispersed through western Asia, Europe, and Africa. The presence of several similar rodent taxa in Mongolia, Kazakhstan, and China confirms that these areas were part of a large bioprovince covering most of central Asia during the Oligocene and Early Miocene. [ABSTRACT FROM AUTHOR]

Copyright of Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales is the property of Academia Colombiana de Ciencias Exactas, Fisicas y Naturales and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Some orogenic sedimentary basins are difficult to assign to a particular category. An example is the hydrocarbon‐bearing Thrace Basin in the northern Aegean. It has more than 9‐km‐thick Cenozoic clastic sediment, and is spatially associated with the Rhodope metamorphic core complex in the west, and with the Tethyan subduction‐accretion complexes in the south, and is cut by the North Anatolian Fault and its precursors. It has been interpreted variously as an intramontane, a forearc, or an orogenic collapse basin. Here, we provide new geochronological and biostratigraphic data to constrain the tectonic evolution of the Thrace Basin. The new data indicate that as an individual depocenter the Thrace Basin has a short age span (late Eocene—Oligocene, 36–28 Ma) and more than 90% of the basin fill consists of early Oligocene (34–28 Ma) siliciclastic turbidites, deposited at rates of 1.0 km/my. Paleocurrents and new detrital zircon U‐Pb ages show that the Rhodope Complex was the main sediment source. The exhumation of the northern Rhodope Complex (36–28 Ma) was coeval with the main subsidence in the Thrace Basin (34–28 Ma), and involved clockwise crustal rotation in the northern Aegean and possibly crustal flow from underneath the Thrace Basin. Crustal rotation is indicated by the paleomagnetic data, regional stretching lineations in the Rhodope Complex, and the triangular shape of the Thrace Basin. The rotating crustal block must have been bounded in the south by a sinistral fault zone; the location of which corresponds largely with the present day North Anatolian Fault. Key Points: Thrace Basin is a late Eocene ‐ Oligocene clastic basin with >90% of the sedimentary fill deposited in the early Oligocene at rates of 1.0 km/myThe main subsidence in the Thrace Basin (34‐28 Ma) was coeval with the exhumation of the northern Rhodope Complex (36‐28 Ma), which was the major sediment sourceThe exhumation of the Rhodope Complex and the formation of the Thrace Basin involved crustal rotation and possibly crustal flow [ABSTRACT FROM AUTHOR]

Copyright of Acta Sedimentologica Sinica is the property of Acta Sedimentologica Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study describes a new Paleogene Rotaliid genus Uvigerinelloides from the middle Oligocene, Septarienthon of Hermsdorf, near Berlin, Germany. It is characterized by fusiform triserial perforate calcareous test, chambers regularly triserial throughout, while the final chambers more loosely arranged, surface finely hispid to smooth, which the last-formed chambers often entirely smooth, aperture slender neck and slightly phialine lip. This genus differs from the other Uvigeriniid genera by its finely hispid to smooth surface, which the last-formed chambers often entirely smooth. [ABSTRACT FROM AUTHOR]

Background and Aims CAM photosynthesis is hypothesized to have evolved in atmospheres of low CO2 concentration in recent geological time because of its ability to concentrate CO2 around Rubisco and boost water use efficiency relative to C3 photosynthesis. We assess this hypothesis by compiling estimates of when CAM clades arose using phylogenetic chronograms for 73 CAM clades. We further consider evidence of how atmospheric CO2 affects CAM relative to C3 photosynthesis. Results Where CAM origins can be inferred, strong CAM is estimated to have appeared in the past 30 million years in 46 of 48 examined clades, after atmospheric CO2 had declined from high (near 800 ppm) to lower (<450 ppm) values. In turn, 21 of 25 clades containing CAM species (but where CAM origins are less certain) also arose in the past 30 million years. In these clades, CAM is probably younger than the clade origin. We found evidence for repeated weak CAM evolution during the higher CO2 conditions before 30 million years ago, and possible strong CAM origins in the Crassulaceae during the Cretaceous period prior to atmospheric CO2 decline. Most CAM-specific clades arose in the past 15 million years, in a similar pattern observed for origins of C4 clades. Conclusions The evidence indicates strong CAM repeatedly evolved in reduced CO2 conditions of the past 30 million years. Weaker CAM can pre-date low CO2 and, in the Crassulaceae, strong CAM may also have arisen in water-limited microsites under relatively high CO2. Experimental evidence from extant CAM species demonstrates that elevated CO2 reduces the importance of nocturnal CO2 fixation by increasing the contribution of C3 photosynthesis to daily carbon gain. Thus, the advantage of strong CAM would be reduced in high CO2, such that its evolution appears less likely and restricted to more extreme environments than possible in low CO2. [ABSTRACT FROM AUTHOR]

A series of early Oligocene Paratethyan manganese deposits occur in the shallow-marine sediments of the Maikop Series that surround the present-day Caspian Sea and Black Sea basins. These deposits are located either in former shallow-water seaways between the anoxic basins, where they typically occur as world-class deposits, or as much smaller deposits in shallow-water, shelf settings around the margins of the anoxic basins. The host rocks of the deposits are similar and are composed mainly of laminated marls, clays, and carbonates. The major-oxide compositions of the Paratethyan manganese deposits are similar and reveal a distinctive enrichment in Mn, Ca, and P, relative to Post-Archaean Australian Shale (PAAS). In addition, compared to the PAAS, the deposits typically show a trace element enrichment of Co, Ni, As, Ba, Sr, and strong depletion of Nb, Ta, Cr, Zr, Th, and Hf, which can be attributed to their similar processes of formation. Detrital-sourced elements of the Paratethyan deposits such as Nb, Ta, Cr, Zr, Th, Ti, and Hf are characteristically extremely low relative to the PAAS and indicate syn-sedimentary Mn-oxide and -carbonate deposition under conditions of low detrital input. Furthermore, a PAAS normalized positive Eu anomaly typically present in most deposits together with high contents of Co, Ni, As, Ba, and Sr in ores indicates a hydrothermal contribution into the basins. Besides the introduction of dissolved Mn and associated elements from rivers, this study shows that these elements may have been also discharged into the Paratethyan basins along the basin-margin growth faults. According to the geological and geochemical findings, Mn deposition is likely to have occurred from oceanic upwelling currents during periods of the high sea-level stand with syn-genetic precipitation of Mn-oxides and carbonates close to paleohighs between the deep anoxic basins. [ABSTRACT FROM AUTHOR]

Cyphostemma, with ca. 200 species, is the second‐largest genus after Cissus in the grape family Vitaceae. Cyphostemma exhibits a high degree of morphological variation both between and within species that confounds species delimitation. Additional questions remain due to limited taxon sampling, original reference specimens damaged or lost and incomplete descriptions of taxa. Previous molecular studies, with limited taxon sampling, suggested three major clades corresponding to their distribution in continental Africa, Madagascar and Asia. However, deep relationships and biogeographic history within Cyphostemma remain unresolved. We conducted phylogenetic analysis and morphological character reconstruction of Cyphostemma using 91 newly assembled plastomes, with a focus on resolving complex taxonomic issues in Madagascar. Our results strongly support the Malagasy Cyphostemma as non‐monophyletic for the first time. Biogeographic reconstructions reveal two independent dispersals from continental Africa to Madagascar. The first dispersal is dated to the Oligocene and has led to the diversification of species with pinnate leaves in Madagascar. The second dispersal is estimated to have occurred during the late Miocene and has given rise to the only species with digitate leaves in Madagascar. Ancestral state reconstructions reveal that several morphological innovations may have promoted adaptation of Cyphostemma to a diverse range of habitats in Madagascar. In particular, a group of species from southern Madagascar have evolved both succulent stems and leaves to cope with extreme aridification in this region. Finally, relationships within three species complexes from the "Sambirano domain", the southern spiny forest‐thicket and the northern limestone areas of Madagascar are clarified and four new taxa are proposed based on molecular and morphological evidence. [ABSTRACT FROM AUTHOR]

Well-preserved fossil assemblages provide valuable insights into the evolutionary history of biota and their environments. Here, we report on Rupelian (early Oligocene) siliceous nanoeukaryotes from diatomites in the Carpathian Mountains, southeastern Poland. These sediments yielded novel forms of parmaleans and parmalean-like fossils. Their cell wall structure differs from that of described genera. Instead of the generically specific separate dorsal plate and set of girdle plates, some of our taxa contain one upended, hollow, subspherical, perforated cup. To accommodate these differences, we propose a new division Parmaphyta, a new family Parmoligocenaceae, a new genus Parmoligocena and a new species Parmoligocena janusii. Other remains are reminiscent of the extant genus Pentalamina and for this we propose a new genus and species, Pentalaminamorpha radiata. The taxonomic affinity is less certain for other nannofossils found, as they are only somewhat similar to parmaleans, and so we only tentatively associate them with this group. All these fossils occur together with a diverse assemblage of diatoms (mostly from Leptocylindrales, Rhizosoleniales, Coscinodiscales, Cymatosirales, and Hemiaulales), silicoflagellates (mostly species from the genus Corbisema) and archaeomonads. Together they suggest the palaeoenvironmental context for the parmaleans, a neritic marine environment, thus similar to where silicified parmaleans can be found today. [ABSTRACT FROM AUTHOR]

The wood anatomy of Paradiospyroxylon kvacekii gen. et sp. nov. is described and illustrated based on material originating from the Ústí Formation's volcanic deposits of České středohoří Mts. (Paleogene, Czech Republic). The sample, identified earlier as Manilkaroxylon sp., was critically examined and is interpreted as root wood and proposed as the paratype of Paradiospyroxylon kvacekii. This paper discusses how wood anatomical variation needs to be considered when making systematic and palaeoecological interpretations. [ABSTRACT FROM AUTHOR]

Vast and geochemically diverse volcanic rocks from the western Alborz Magmatic Assemblage (AMA) represent the back-arc of the central Iran Neotethyan arc (Urumieh–Dokhtar Magmatic Assemblage; UDMA). Volcanic rocks of the west AMA record valuable information on the timing, source region(s) and geodynamic setting of magmatism. Over 30 days of field study and sampling, investigation of 170 thin sections, 30 whole-rock geochemical analyses, 13 whole-rock Sr–Nd isotopic ratios and U–Pb age dating of zircon separates from 7 samples furnished the present study data. Eocene (38.5 Ma) OIB-type volcanic rocks from South Kaleybar indicate an anorogenic (extensional) setting. This lithospheric-scale extensional event induced influx of asthenospheric mantle into the sub-arc wedge, of which the partial melts differentiated to produce OIB-type melts. The OIB-type melts incorporated some inherited zircons in their ascent through the Cadomian crust. A continued extensional regime led to asthenospheric upwelling and produced mafic melts that produced 27.5-Ma-old subalkaline series volcanics. The LILE-depleted signature of the South Kaleybar subalkaline volcanic rocks implies that their mantle source region experienced previous partial melting event(s), probably during OIB-type magmatism in the Eocene. Alkaline volcanism (24.4 Ma) and concurrent high-silica adakitic volcanism (24.3 Ma–23.4 Ma) followed subalkaline magmatism. The alkaline rock signature in the study area range from 'Nb–Ta depleted' to 'plume-type'. This is consistent with lithosphere–asthenosphere interaction in an arc-related setting. Simultaneous partial melts of delaminated lower crustal rocks reacted with the asthenosphere and produced adakitic melts. Asthenospheric, lithospheric and crustal contribution to the magmatism in South Kaleybar express the back-arc signature of magmatism in Eocene to Late Oligocene times. [ABSTRACT FROM AUTHOR]

Anthracotheres are generalised artiodactyls that have an extensive record in the Cenozoic of Eurasia and Africa. In North America they have been collected in middle Eocene to early Miocene localities from the California Coast, the Great Plains and the Gulf Coast of the United States, with a single record from the early Miocene of Panama. Here we report few specimens from the early Oligocene (Ar1) Iniyoo Local Fauna of north-western Oaxaca, and the earliest Miocene of Simojovel de Allende, in northern Chiapas. This material has diverse features that indicate they belonged to the bothriodontine Arretotherium , such as selenodont cristids associated with the protoconid and hypoconid, the absence of a premetacristid, and the crenulated enamel. They share with Arretotherium acridens and Arretotherium meridionale the absence of a mesiolingual metacristid, but their general morphology and size indicate a close relationship to Ar. meridionale. Nevertheless, in absence of better-preserved specimens, we decided not to assign the fossil material to this species. Specimens from Oaxaca and Chiapas are the first records of anthracotheres in Mexico. These new records link the previous ones from temperate North America and tropical Central America and indicate that Anthracotheriidae had a very wide geographical distribution in North America during the Palaeogene and the Neogene. Additionally, they represent the southern-most records of Arretotherium in North America during the Oligocene and the early Miocene. [ABSTRACT FROM AUTHOR]