Lower Miocene Research Articles

First Discinid Brachiopods (Brachiopoda: Lingulida) from the Cenozoic of Patagonia (Gaiman Formation, Lower Miocene, Argentina)

First Discinid Brachiopods (Brachiopoda: Lingulida) from the Cenozoic of Patagonia (Gaiman Formation, Lower Miocene, Argentina)

Electroderaeous crassicornis, a new genus and species of Deraeocorinae (Hemiptera: Heteroptera: Miridae) in Miocene Dominican amber.

The third fossil record of a deraeocorine species, preserved as an inclusion in late Lower Miocene, Burdigalian amber from Hispaniola (Dominican Republic) is presented with a description of Electroderaeous crassicornis gen. and sp. nov. based on a well-preserved specimen.

Sedimenty spodního a středního miocénu jihozápadně od Brna ve světle nových poznatků

New knowledge on the occurrence of Lower and Middle Miocene sediments in the southwestern surroundings of Brno has been acquired through geological mapping and documentation work during the recent years. Specific work was focused on: • preparation of the publication on the local national history of the cadastral territory of the village of Bohutice; • salvage study of the former reserved bentonite deposit Ivančice – Réna, which is being gradually remediated and turned into a recreational area; • the area in the foreground of the New Ivančice viaduct, which is susceptible to long-term slope instability; • the western edge of the village of Němčičky near Židlochovice, where extensive construction of family houses is underway; • the area between the municipalities of Moravany, Nebovidy and Ostopovice, where the excavations for new extra-high voltage pylons were documented. The detailed mapping, petrographic and biostratigraphic studies allowed to refine the distribution, lithological characteristics and age of Miocene sediments; specifically, a more extensive occurrence of Lower Miocene sediments compared to previous findings was confirmed (localities Ostopovice, Moravské Bránice – locality 5). These findings support earlier results from the area N of the City of Brno, where the known extent of Ottnangian sediments was expanded at the expense of Badenian sediments. The documentation and sampling of the new excavations (for family houses and extra-high voltage pylons) and old mining pits enabled the description and further study of the sediments. The acquired litho- and biostratigraphic data were correlated with engineering geological findings. In a construction pit in Bohutice, a completely new occurrence of tuffitic sediments of the Ottnangian age was discovered and geochemically verified. Furthermore, the Ottnangian gravels in Němčičky were newly discovered. These contain a large proportion of granitoid pebbles probably derived from the Brno Massif. It was found that the weakly consolidated lithologically variable Lower Miocene sediments are prone to landslides. In the case of the New Ivančice viaduct, extensive suffusion doline were identified, resulting from the ingress of rainwater from the wider area of the railway embankment foreground. Biostratigraphy of the sediments was based on micropaleontological analysis of foraminiferas. Ottnangian sediments were usually fossil- free and/or they contained reworked Cretaceous foraminiferas. Lower Badenian sediments are characterized by occurrence of abundant and diversified fauna represented by foraminifera species such as Martinotiella karreri (Cush.), Globigerinoides bisphericus Todd, Vaginulina legumen (L.), etc.

Drainage and sedimentary response of the Northern Andes and the Pebas system to Miocene strike‐slip tectonics: A source to sink study of the Magdalena Basin

AbstractMiocene strike‐slip tectonics was responsible for creating and closing short‐lived (ca. 6 Ma) passages and the emergence of isolated topography in the Northern Andes. These geological events likely influenced the migration and/or isolation of biological populations. To better understand the paleogeography of the Miocene hinterland and foreland regions in the Northern Andes, we conducted a source‐to‐sink approach in the Magdalena Basin. This basin is located between the Central and Eastern Cordilleras of Colombia and contains an ample Miocene record, which includes Lower Miocene fine‐grained strata and Middle Miocene to Pliocene coarsening‐up strata. Our study presents a new data set that includes detrital U–Pb zircon ages (15 samples), sandstone petrography (45 samples) and low‐temperature thermochronology from the Southern Central Cordillera (19 dates); which together with previously published data were used to construct a paleogeographical model of the Miocene hinterland and foreland regions in the Northern Andes. The evolution of the Magdalena Basin during the Miocene was characterized by playa and permanent lake systems at ca. 17.5 Ma, which may be related to a marine incursion into NW South America and western Amazonia. The appearance of Eocene to Miocene volcanic sources in the Honda Group after ca. 16 Ma suggests the development of fluvial passages, which connected the Pacific with the western Amazonia and Caribbean regions. These passages were synchronous with a time of Miocene exhumation and topographic growth (ca. 16 to 10 Ma) in the Central Cordillera and the transition from lacustrine to fluvial deposition in the Magdalena Basin. Middle to Late Miocene strike‐slip deformation promoted by oblique plate convergence and the oblique collision of the Panamá‐Chocó Block likely explains the synchronous along‐strike fragmentation and exhumation in the Central Cordillera.

A relict subterranean spider (Araneae: Linyphiidae: Troglohyphantes) reveals a unique component of the biogeography of Corsica

Abstract Spiders of the genus Troglohyphantes (Araneae: Linyphiidae) exemplify one of the largest subterranean adaptive radiation across European mountain ranges, counting over 130 species and representing about one fifth of total species richness of cave spiders in Europe. Despite the emerging potential of Troglohyphantes as a biogeographical model, no attempt has been made to reconstruct the geological events underlying the current distribution patterns of the genus. By coupling traditional taxonomy with target gene sequence data and comparative functional trait analyses, we describe a new species of Troglohyphantes, the first reported from the island of Corsica (France). The species is characterized by a high level of subterranean adaptation and distinct morphological affinities with geographically distant congenerics. By means of time-stamped phylogenies, we tested contrasting hypotheses about the origin of the new species. The most parsimonious explanation suggests that the species diverged from an ancestral group of species originating in the Adriatic plate in the lower Miocene (~19 Ma), colonizing Corsica from the east. In the absence of relevant fossil records, the well-known geochronology of Corsica and the Western Mediterranean basin can be used in future studies to reconstruct the biogeography of the whole genus and for inferring the timeline of its diversification.

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

Petrography and geochemistry of the Miocene Upper Red Formation sandstones in NW Iran; with an application to the origin and tectonic setting

Middle to Upper Miocene sedimentary successions in the Alborz sedimentary basin (northern Iran) form the caprock of the Lower Miocene gas reservoirs. Their stratigraphic and sedimentological studies have been of interest to geological studies. Due to their importance, in this research, two suitable stratigraphic sections in the Zanjan and Hashtroud regions (northwest of Iran) have been subjected to detailed sedimentological and stratigraphic study to determine the origin and tectonic setting. Clastic-evaporite sediments of the middle to upper Miocene (Upper Red Formation) in the northwest of Iran are about 950 m thick, which is placed on the hydrocarbon reservoirs of the Qom Formation (Lower Miocene) with a discontinuous and abrupt boundary, and are covered by conglomerate and unhardened sediments belong to Pliocene. These sediments in the northwest of Iran are divided into four lithostratigraphic units, including (1) green marls with gypsum, (2) red marls along with gray and red sandstones, (3) red and green marls, and (4) green marls. Based on microscopic studies, the sandstones of this formation are composed of sedimentary and metamorphic rock fragments, quartz, and to a lesser extent, feldspar, pyrite and chlorite, in order of importance. The matrix (carbonate mud) and, to a lesser extent, calcite and evaporite cements form the groundmass of studied sandstones. Based on petrographic studies, these fine-to medium-grained sandstones are litharenite to feldspathic litharenite with an average composition of Q38F13RF49. Also, based on the main constituent components of sandstones and geochemical analysis of major and minor elements, and by drawing different types of separating diagrams, the tectonic setting of these sandstones are considered as an active continental margins and foreland basins (collision belts between Arabia-Eurasia continental plates), which originate from fine-to medium-grained siliceous-clastic rocks, metamorphic, carbonate, and intermediate to felsic igneous rocks outcropped in the region. The data show that these sediments are influenced by arid to semi-arid climate and moderate degree of chemical weathering, mainly from the outcrops of Takab Complex and Qom Formation (Lower Miocene), which have significant outcrops and, to a lesser extent, from Eocene volcanics. The research results are consistent with the paleogeography of the region and previous studies and can be of interest to sedimentologists and other researchers related to petroleum geology.

New material of Parabrachyodus hyopotamoides from Samane Nala, Bugti Hills (Pakistan) and the origin of Merycopotamini (Mammalia: Hippopotamoidea)

Abstract Revision of the anthracothere Parabrachyodus hyopotamoides, endemic to the Lower Miocene of the Indian subcontinent and thus far confused with Brachyodus, is made possible by the description of unpublished specimens from the Samane Nala fossil-bearing deposits of the Bugti Hills (Pakistan). This is the first biochronologically constrained occurrence for a comprehensive series of this species. The analysis of cranial and dental morphological variations based on all known specimens of Parabrachyodus allows us to provide diagnostic characters for this monotypic genus. These include a four-crested upper molar protocone unique among artiodactyls and several convergences with subfamily Anthracotheriinae, like the two puzzling distal cristae on the last upper premolar protocone. A phylogenetic analysis at the hippopotamoid level, including Parabrachyodus and the enigmatic genera Telmatodon and Gonotelma (both also endemic to the Bugti Hills), is performed for the first time. These phylogenetically related taxa turn out to be basal to the tribe Merycopotamini, leading us to propose a more inclusive definition of the diagnosis of this tribe. Our results formally establish Elomeryx as the sister-group of Merycopotamini in Bothriodontinae, and definitely locate the early evolutionary history of Merycopotamini on the Indian subcontinent.

Seismic reservoir characterization of the syn-rift lower Miocene Rudeis Formation in the July oilfield, Gulf of Suez basin, Egypt: Implication for reservoir quality assessment

The Lower Miocene Rudeis Formation is among the most potential oil-bearing sedimentary sequences in the Gulf of Suez (GOS), representing the main producer of Egyptian oil. This study concerns primarily with revealing the reservoir characteristics and facies distribution, as well as the implication of the predominant diagenetic factors on the quality of the Lower Miocene syn-rift Rudeis reservoir in the July oilfield. Therefore, this study integrates 2D seismic, and wireline logs, as well as conventional and special core analyses to determine the reservoir characteristics and facies distribution. The interpreted data elucidate four different seismic facies in the Rudeis Formation with a net pay thickness ranging from 29 to 233 m in the studied wells of 16.3% average porosity, 62.9% average oil saturation, and 9.3% average shale volume. Four seismic facies (SF1-SF4) were interpreted and correlated with the Rudeis clastic deep-water turbiditic succession. The 3D static property models revealed that the best reservoir facies in terms of low shale content and water saturation, as well as high porosity, coincide with the submarine channels and fans containing coarse-grained, clean sandstones. From the core analysis, the Lower part of the Rudeis sequence is subdivided into five reservoir rock types (RRTs). The RRT1 is characterized by the best reservoir quality; it is composed of quartz arenites, sublithic arenites, and subfeldspathic arenites. In contrast, the RRT5 represents the lowest reservoir quality; it consists of very coarse siltstone, laminated glauconitic siltstone, and highly compacted dolomitic and calcareous quartz arenites. The poor reservoir characteristics of the RRT5 are attributed to tight compaction, cementation, and early dolomitization phase, whereas the highest quality of the RRT1 is related to fracturing and dissolution processes. The RRT1 rocks are mostly associated with the submarine channel and fan facies, whereas the poor quality RRT5 sediments were accumulated as hemipelagic/background. This integrated workflow study can be applied to further case studies in the Middle East, Africa, and the other analogues all over the world.

Petrology of Bengal Fan turbidites (IODP Expeditions 353 and 354): provenance versus diagenetic control

ABSTRACT High-resolution petrographic and heavy-mineral analyses of Bengal Fan turbidites from six cores drilled during IODP Expeditions 353 and 354 elucidate factors controlling their intersample compositional variability as a key to understanding sedimentary processes and erosional evolution of the Himalayan belt since the Miocene. Bengal Fan turbidites are feldspatho-quartzose to litho-feldspatho-quartzose with plagioclase > K-feldspar; slow-settling micas increase in abundance in very fine sand and coarse silt. The feldspar/quartz ratio and higher-rank metamorphic rock fragments notably increase from uppermost Miocene to Pleistocene deposits, which is ascribed to the onset of rapid exhumation of the Eastern Himalayan syntaxis since ∼ 5 Ma. The same trends are documented in Nicobar Fan turbidites, confirming that they belong to the same sedimentary system. Both Bengal and Nicobar fans record a pulse in mass accumulation rate at Tortonian times, when supply of sedimentary and very-low-grade metasedimentary detritus reflected accelerated exhumation of the Lesser Himalaya. In contrast to foreland-basin sediments, where ferromagnesian minerals have been completely dissolved in strata as young as Pliocene–Pleistocene, in both Bengal–Nicobar and Indus fans amphibole invariably represents about half of the moderately rich to rich transparent-heavy-mineral suite, demonstrating that amphibolite-facies Greater Himalaya metamorphic rocks were widely exposed in the Himalayan range well before the late Miocene and possibly since the late Oligocene, as indicated by a few sillimanite and kyanite grains in Bengal Fan sediments as old as 23 Ma and 28 Ma, respectively. Diagenetic dissolution strongly affected olivine and pyroxene in strata older than the middle and early Pleistocene, respectively, whereas amphibole decreases markedly through progressively older Miocene strata. Ferromagnesian minerals and sillimanite are almost completely dissolved in lower Miocene strata, where durable zircon, tourmaline, rutile, and apatite make up half of the strongly depleted heavy-mineral assemblage. Quaternary turbidites from the six studied cores have virtually the same compositional signatures, testifying to efficient homogenization by turbidite transport and reworking across the fan. Turbidites in western cores closer to peninsular India (U1444A and U1454B) are not different from those in eastern cores, indicating very minor supply from the subcontinent. Forward-mixing calculations based on integrated petrographic and heavy-mineral data indicate that sand supply from the Brahmaputra River to Quaternary turbidites was four times larger than supply from the Ganga River, indicating up to six times higher sediment yields and erosion rates in the Brahmaputra than in the Ganga catchment, largely reflecting superfast erosion of the Eastern Himalayan syntaxis.

Present‐Day Caribbean‐North American Oblique Convergence Through the Ocoa‐Bonao‐La Guacara Fault Zone, Southern Central Hispaniola: A Transition Zone Between Oceanic Subduction and Arc‐Oceanic Plateau Collision

AbstractAccording to GPS measurements, the Caribbean plate is moving east‐northeastward relative to the North American plate at a rate of ∼20 mm/a. This oblique motion is partly accommodated in southern Hispaniola by northward underthrusting/subduction bellow the Muertos submerged accretionary prism and the Peralta fold‐and‐thrust belt. This work investigates the active transition zone that connects Muertos and Peralta: the Ocoa‐Bonao‐La Guacara fault zone (OBFZ). Combined detailed structural analysis at macroscopic and mesoscopic scales, regional magnetic data and seismicity analysis, geomorphic observations, fault‐slip data inversion and geochronology of Quaternary deposits allow to establish the deformation pattern for the OBFZ along southern central Hispaniola. Distinct tectonic regimes have occurred successively in the Neogene, within a consistent regional NE‐trending horizontal shortening: (a) a lower Miocene to Early Pleistocene D1 regime characterized by SW‐directed thrusting that homogeneously affects the region; and (b) an Early/Middle Pleistocene to Holocene D2 regime of strike‐slip to transpressional faulting mainly located along the OBFZ. The change is coeval with the tectonic indentation of the Beata Ridge in the back‐arc region of the Hispaniola microplate. Finally, a Late Pleistocene to Holocene D3 extensional regime has a local development around the Ocoa Bay. Part of the present‐day stress‐field induced by the Beata Ridge collision is accommodated by the OBFZ within the Hispaniola microplate. This fault zone defines the onland transition between oceanic subduction and arc‐oceanic plateau collision. Due to its length and potential to generate large earthquakes, the OBFZ must be considered in the regional seismic hazard assessment.

Basin structure, depositional age, and paleostress of the lower Miocene Yoka Formation in the Tajima-Mihonoura area, Southwest Japan

山陰地方の中新統堆積盆地の成因の特定に向けて，本論は兵庫県北西部の但馬御火浦地域の中新統八鹿層と基盤の境界部周辺の調査研究を行った．八鹿層の軽石火山礫凝灰岩のジルコンU‒Pb年代測定を行い，19.63±0.15 Maの年代値を得た．この年代値は遠方地域の同層の年代制約と調和的であり，八鹿層の火成活動は広域的に同時期に起こったことが明らかとなった．基盤と八鹿層の境界には基底礫岩と判断される堆積性の角礫岩が点在し，境界部に断層は認められない．このことは八鹿層が基盤をアバット不整合に覆っていることを示している．本地域で見積もられるアバット不整合の比高は200 mを越え，山陰地方の中新統の層厚差には堆積時の古地形が寄与していた．八鹿層相当の岩脈群の方向解析によって，NNE-SSW方向に引張する応力比の低い正断層型応力を得た．この結果は，当時の山陰地方が多様な方向のグラーベンが形成されうる造構応力場にあったことを示唆する．

Exceptionally well‐preserved seed cones of a new fossil species of hemlock, Tsuga weichangensis sp. nov. (Pinaceae), from the Lower Miocene of Hebei Province, North China

AbstractTsuga (hemlock) is a small genus of 10 extant species in the Pinaceae, with a disjunct distribution in East Asia and eastern and western North America. Reliable species‐level identification of Tsuga fossils depends on the discovery of seed cones with intact bracts, but such cones are rare in the fossil record. Here we describe a new fossil species of hemlock as T. weichangensis sp. nov. based on exquisitely preserved seed cones with nearly complete bracts from the Lower Miocene of Weichang, Hebei Province, North China. This fossil species displays a mosaic of characters between Tsuga and Nothotsuga. The well‐developed and slightly exserted bract scales of T. weichangensis are reminiscent of Nothotsuga, but other characters, such as nonleaved peduncles and tongue‐shaped bract scales, in addition to monosaccate pollen found at the same fossil locality, suggest an affinity closer to Tsuga. Cladistic analysis based on 15 morphological characters and a molecular backbone constraint supports the assignment of these fossil cones to Tsuga rather than Nothotsuga, and places the fossil species of T. weichangensis in an unresolved polytomy within the genus Tsuga. The occurrence of Tsuga seed cone fossils indicate the paleoclimate in the Miocene of Weichang was warmer and more humid than today's climate, which is consistent with the paleoclimate reconstructed by paleopalynology.

New evidence for Early Miocene palaeoenvironmental changes in the North Croatian Basin: Insights implicated by microfossil assemblages

An integrated stratigraphic study has been performed of the Lower Miocene deposits of the Poljanska and Mala sections (North Croatian Basin), coupled with 40Ar/39Ar dating, geochemical and mineralogical study of tuffitic and silty sand beds. The sedimentary record evidences deposition influenced by volcaniclastic input. The presence of marine, brackish and non–marine microfossils indicates complex palaeoenvironment, palaeoecology, and palaeobiogeography. Four different units were recognized based on their fossil content and sedimentological data. At the base of the Poljanska section (Unit P1), tuffitic sediments bear common endemic brackish, and rare marine to freshwater and terrestrial microfossils. Radiometric 40Ar/39Ar dating obtained on volcanic glass shards from this layer provided an age of 22.2 ± 1.9 Ma correlating with the earliest Early Miocene and indicating the existence of older volcanic activity in the NCB pro tempore. The succession transitions into the brackish-water lacustrine environments (Unit P2). This unit has two presumed different climatic events: a maximum temperature event in the lower part of the interval and one interruption with lower temperatures recognized in the upper part of the interval. The co-occurrence of limnic and marine species in the uppermost part of the investigated sediments (Unit P3) indicates a marine inflow into the coastal lake. It marks the beginning of a salina-type lake formation in Poljanska. In the Mala section (Unit M1), biostratigraphically dated to the NN4 Zone, a transgressive sequence is documented through the presence of marine calcareous nannoplankton, planktonic and benthic foraminifera, and ostracods.

Interpretation of Geochemical Data of Eocene Volcanism in Eastern Sivas Province (Central Anatolia, Türkiye)

The study area covers the eastern part of Zara district (Sivas) located in East-Central Anatolia. The units found in the region from bottom to top are characterized by the Upper Creataceous-Paleocene Refahiye Complex, the Middle-Upper Eocene Akıncılar Formation, the Karataş volcanics and Kösedağ Syenite, the Lower Miocene Onarı Formation, the Upper Miocene-Pliocene İsola volcanics, the Şerefiye volcanics, the Kadıköy Formation and the uppermost Quaternary sediments. In the frame of this study, the Karataş volcanics, which were formed as a result of the second magmatic activity of the Eocene period, are studied in detail. The Karataş volcanics are greenish black on their undisturbed clean surfaces, and some parts are brown-purple in color and have distinctive crack systems. It shows a reddish-pinkish color distribution in regions where degradation is observed intensely. The SiO2 content, which is the main criterion for determining the magma character of Karataş volcanics, is between 52.09 % and 58.45 %. MgO contents of similar importance are between 0.53 % and 2.21 %. Some of the light rare earth elements, La have 22.2-40.7 ppm, Ce 44.4-67.3 ppm, Pr 5.23-8.88 ppm, Sm 4.41-7.15 ppm, Eu 1.24-1.83 ppm; one of the heavy rare earth elements, Lu have 0.20-0.45 ppm and Yb 1.88-2.98 ppm values. The Karataş volcanics consist of basaltic-trachyandesite and trachyandesite. Evidence of liquid-crystal fractional crystallization (FC) in the phenocryst phase during the formation of the Karataş volcanics is clearly observed in the geochemical diagrams. Traces of partial melting and crustal contamination were found in geochemical studies. Following the closure of the Neo-Tethys ocean in the region, a widespread crustal thickening occurred in the region with the northward divergence of the northern branch of Neo-Tethys, and a suture zone was formed along this line. The Karataş volcanics were formed as a product of active volcanism after the collision in the region.

Neogene subsidence rates of the southern Peri Pannonian realm (1D basin modeling): Constraints on the extensional geodynamic drivers of the asymmetric Toplica basin (central-southern Serbia)

With the objective to quantify the Neogene extensional geodynamic drivers of the Peri Pannonian Realm s.l., a series of 1D basin models were carried out by integrating the available geological and geochemical data extracted from the landlocked Toplica Basin (central-southern Serbia; Serbo-Macedonian Unit). The modeling was conducted on four wells located immediately south of Jastrebac Mt., in the area of the Toplica Basin. The investigated southernmost point of the Peri Pannonian Ream s.l. (areas surrounding the basin, to the south of rivers Danube and Sava) underwent intense tectonically-driven subsidence episodes, which lasted from the Lower Miocene up to the Pliocene. The restored Neogene burial history (subsidence rates), paleotemperature, and calibrated paleo-heat fluxes (or changes in the ancient crustal or basal heat flow) indicated a two-staged crustal stretching of the wider Toplica area. The combined tectonic, i.e., thermal subsidence, resulted in a very high sedimentation rate, having an average ca. 300–400 m/Ma (Čučale unit). The intense tectonically-driven subsidence is consistent with the involvement of extensional processes, affecting the crustal and lithospheric layers of the retreating Adria/Dinarides, amplified by a distant Carpathian rollback stage. The regional extension led to the asymmetric opening and the formation of the Toplica Lower Miocene mesosaline to the freshwater lacustrine system. Higher participation of mixed microbiologically reworked/terrestrial organic matter incorporated in oil-prone Type II kerogen mainly characterized the investigated lacustrine sedimentary sequence. The latest Oligocene–earliest Neogene subsidence onset was characterized by elevated temperatures, affecting the early development of the oil window (ca. at 16 Ma). The 1D models also showed that the Lower Čučale unit achieved ca. 50% transformation ratio for the Type II organic matter. The two intra-Neogene extensional episodes suggested the existence of the Early Neogene “syn-rift” stage, followed by a thermal sagging. The Neogene continuous thinning of the overriding Serbo-Macedonian continental crust contributed to the “negative inversion” of the former pre-Neogene nappes. Therefore, Neogene tectonic reactivation induced contemporaneous subsidence, further allowing the extensional rise of the Jastrebac core complex.

Assessment of the petrophysical properties and hydrocarbon potential of the Lower Miocene Nukhul Formation in the Abu Rudeis-Sidri Field, Gulf of Suez Basin, Egypt

Lower Miocene rift sediments of the Nukhul Formation are one of the prominent hydrocarbon producers in the Gulf of Suez basin. In this study, we focused on the oil producing Nukhul sandstones of the Abu Rudeis-Sidri Field, located in the east central Gulf of Suez. Nukhul Formation is characterized by the prominent low amplitude seismic reflectors and represents the youngest identified reflector (Lower Miocene) in the study area. Petrophysical assessment was carried out using wireline logs to infer the reservoir characteristics. The Nukhul sandstone reservoir exhibits lower shale volume (< 0.1 dec dominantly), 0.07–0.16 dec total porosity and effective porosity up to 0.13 dec within the Nukhul sandstone interval. Bulk density-neutron porosity cross plot infers primarily sandstone matrix with the influence of carbonates, which characterizes the studied reservoir as calcareous sandstones. Spectral gamma ray data indicates montmorillonite as the principal clay phase along with minor kaolinite and illite. The calculated water saturation of the reservoir zone in the three productive wells ranges between 0.17 and 0.34 dec (i.e., the hydrocarbon saturation equals 0.66–0.87 dec). A small range of bulk volume of water (0.011–0.03 dec) indicates superior quality of the hydrocarbon-bearing sandstone intervals. Absence of productive sands in one of the studied wells, drilled in the hanging wall implied structural control on hydrocarbon accumulation in the study area. This study provides crucial insights regarding the quantitative petrophysical characteristics, reservoir quality distribution and hydrocarbon potential of the Lower Miocene Nukhul clastic reservoir.

A plastome phylogeny of Rumex (Polygonaceae) illuminates the divergent evolutionary histories of docks and sorrels

The genus Rumex L. (Polygonaceae) provides a unique system for investigating the evolutionary development of sex determination and molecular rate evolution. Historically, Rumex has been divided, both taxonomically and colloquially into two groups: ‘docks’ and ‘sorrels’. A well-resolved phylogeny can help evaluate a genetic basis for this division. Here we present a plastome phylogeny for 34 species of Rumex, inferred using maximum likelihood criteria. The historical ‘docks’ (Rumex subgenus Rumex) were resolved as monophyletic. The historical ‘sorrels’ (Rumex subgenera Acetosa and Acetosella) were resolved together, though not monophyletic due to the inclusion of R. bucephalophorus (Rumex subgenus Platypodium). Emex is supported as its own subgenus within Rumex, instead of resolved as sister taxa. We found remarkably low nucleotide diversity among the docks, consistent with recent diversification in that group, especially as compared to the sorrels. Fossil calibration of the phylogeny suggested that the common ancestor for Rumex (including Emex) has origins in the lower Miocene (22.13 MYA). The sorrels appear to have subsequently diversified at a relatively constant rate. The origin of the docks, however, was placed in the upper Miocene, but with most speciation occurring in the Plio-Pleistocene.

The origin of modern marlins (Teleostei: Istiophoridae): new fossil evidence from the Lower Miocene of Austria

ABSTRACT We report the oldest fossil record of Istiophoridae from the Northern Alpine Foreland Basin (Western Paratethys) in Pucking, Austria (Lower Miocene, lower Aquitanian, ∼22.4 Ma). The studied specimen consists of fragments of five articulated vertebrae and a partially preserved second dorsal fin. We found that the Pucking specimen is only surpassed in age by an isolated vertebra from the Chandler Bridge Formation (South Carolina, U.S.A.), with ∼24.7–23.5 Ma. Pucking and the Chandler Bridge Formation differ in age by ∼1.1–2.6 Ma. The fossil istiophorid from the Chandler Bridge Formation was considered controversial due to the large gap in the fossil record between the first appearance of Istiophoridae and the last appearance of any other extinct billfish clade. Here we report that Pucking (Lower Miocene) and South Carolina (Oligocene) share the occurrence of Istiophoridae, †Xiphiorhynchinae (Xiphiidae), and †Aglyptorhynchinae (†Palaeorhynchidae). Our finding demonstrates that the coexistence of different groups of billfishes is maintained over time and that the Chandler Bridge specimen is a reliable record. Our work closes a temporal gap of ∼4.4 Ma between the previously recognized oldest Istiophoridae (∼18 Ma) and the last appearance of †Xiphiorhynchinae and †Aglyptorhynchinae. This result supports a longer evolutionary history for Istiophoridae, establishes continuity in the billfish fossil record, and is significant for future time calibrated phylogenies.

New insight into Cenozoic Orbitestellidae (Gastropoda: Heterobranchia) from the Magellanic Region based on lower Neogene and Recent species

AbstractPatagorbitestella new genus is here proposed to include two extant and one fossil species: P. ponderi (Linse, 2002) new combination, P. patagonica (Simone and Zelaya, 2004) new combination, and P. leonensis new species, the last described from the Punta Entrada Member of Monte León Formation (50°21′25.4”S, 68°53′05.9″W, Aquitanian to lower Burdigalian, lower Miocene). A protoconch sculptured with distinctive microscopic spiral threads serves as a per se diagnostic shell character for the new genus. Patagorbitestella n. gen. constitutes a distinctive lineage of orbitestellid gastropods inhabiting exclusively the Magellanic Region at least since the early Miocene. This is the first fossil record of Orbitestellidae in South America.UUID: http://zoobank.org/e48a4b73-1c0a-4bf7-aceb-8a180ef7e039