Lower Miocene Sediments Research Articles

Palynostratigraphy, palynofacies and reservoir characteristics of Upper Oligocene - Lower Miocene sediments in the southwestern Cuu Long Basin, Vietnam

Palynostratigraphy, palynofacies and reservoir characteristics of Upper Oligocene - Lower Miocene sediments in the southwestern Cuu Long Basin, Vietnam

Benthic Foraminifera from the Lower Miocene Sediments of Murachbann, Western Kachchh, Gujarat, India: Implications for Inferring Palaeoenvironment

A thorough taxonomic study was carried out for the first time using high-resolution microscopy from Neogene sections of western Kachchh, India. In the present study, 25 species of benthic foraminifera belonging to 3 classes viz. Globothalamea, Tubothalamea, Nodosariata and 4 orders Rotaliida, Textulariida, Miliolida and Polytmorphinida have been identified from limestone and silty-claystone of Murachbann section belonging to lower Miocene. This taxonomic study provides the distribution of benthic foraminifera species from Murachbann section. The attempt is made to interpret depositional palaeoenvironment based on this distribution of the studied foraminifera. Keywords: Morphology, Taxonomy, Benthic Foraminifera, Limestone, Palaeoenvironment, Chhasra Formation

Bridging the extant and fossil record of planktonic foraminifera: implications for the Globigerina lineage

AbstractWe conducted a morphometric study and wall texture analysis on extant and fossil specimens of the planktonic foraminifera Globigerina falconensis plexus. Our global data reveal morphological inconsistencies between fossil and extant populations. Our results are significant as G. falconensis is widely used in palaeoceanographic studies in conjunction with its sister taxon G. bulloides. Morphologically these two species are similar, with the main difference being the distinctive apertural lip present in G. falconensis. We selected cores covering the entire stratigraphic range of G. falconensis, from the early Miocene to current day, spanning sites from high latitudes in the North Atlantic Ocean and the southern Indian Ocean to sites in equatorial regions. The morphology found in the modern ocean is not consistent with the Miocene holotype of Globigerina falconensis Blow described from lower Miocene sediments in Venezuela. A more lobate morphology evolved in the late Miocene, thus, a new name is required for this morphotype, coexisting in the modern oceans with G. falconensis s.s. We thus describe the new morphospecies, G. neofalconensis for the more lobate forms which evolved in the late Miocene and inhabit the modern oceans. Additionally, we report a pseudocancellate wall texture present in the G. falconensis plexus. We use the molecular sequences from the PR2 database to explore the generic attribution of the G. falconensis lineage, confirming its close relationship with G. bulloides and its retention in the genus Globigerina.

BIOSTRATIGRAPHY AND PALEOENVIRONMENTAL ANALYSIS OF THE LOWER MIOCENE QOM FORMATION (JAAM AREA, CENTRAL IRANIAN BASIN)

Lower Miocene sediments from a previously not investigated outcrop of the Qom Formation (Central Iranian Basin) were studied for their foraminiferal and calcareous nannofossil content. The studied stratigraphic record is assigned to the upper part of calcareous nannofossil NN2 Zone/CN1c Subzone and to the benthic foraminiferal Borelis melo melo Zone of Burdigalian age. The diversity indices, benthic foraminiferal morphogroups, and quantitative analyses of assemblages (principal component and cluster analysis) suggest an overall shallow-marine depositional environment. This interpretation is well constrained based on the dominance of the B1 benthic foraminifera morphotype with biconvex, trochospiral calcareous test, and epifaunal habitat. The identified six cluster groups of benthic foraminiferal assemblages are confirmed by the principal component analysis too, and their distribution along the studied section argue for dynamic changes of the environment. This is well exemplified by a more or less constant shallowing, then deepening trend of the environment as revealed by the shifting from the high diversity, shallow-shelf assemblages of Cluster 5 and 6 toward the low diversity, near-shore Ammonia tepida and Porosononion subgranosus assemblage (Cluster 1), and back.

Fault seal analysis for VS area, block 16 -1/15, Cuu Long Basin, Viet Nam

Fault-bound traps represent an important class of hydrocarbon-bearing structure. Whether a fault can seal hydrocarbons on a geological timescale may be controlled by one or more of three conditions: (1) sealing due to lithological juxtaposition, where reservoir rock is juxtaposed against sealing rock across the fault; (2) sealing by the fault damage zone, which forms a barrier composed of low-permeability clay within the fault zone and (3) the tectonic activity of the fault, as during faulting, hydrocarbon accumulations can be destroyed and leakage along the fault zone. This research employs an indirect method to establish a correlation between pressure and the sealing properties on fault surfaces, such as the SGR (Shale Gouge Ratio), across various formations under the same geological conditions from all fields within the region and around the world. This aids in assessing the sealing potential of the faults. Evaluate the fault seal capacity according to 3D model for the structures in Oligocene D, Oligocene C and Lower Miocene sediments to serve the assessment hydrocarbon potential in VS area and reduce the risk for further exploration - appraisal work in block 16-1/15, Cuu Long basin. Geology, seismic and petrophysical data were used to construct 3D structural frameworks, lithology model and Vclay model. Parameters such as fault throw, Vshale, lithology, bed thickness, burial depth history, fluid density and pressures, ect. are incorporated into fault seal analysis and also estimate the maximum hydrocarbon column height can be held by each fault in study area, therefore helping to assess the hydrocarbon potential in undrilled structures in VS area.

Calcareous-nannofossil biostratigraphy of the Miocene Fatha Formation at the Miryas section, Qaradagh Mountain Series, Sulaimaniyah, Kurdistan Region, Iraq

The middle Miocene Fatha Formation is a prominent cap rock for hydrocarbon accumulations in Iraq’s oil fields. It is widely distributed in the Low Folded Zone but less common in the High Folded Zone of Iraq. For the first time, a nannostratigraphic study has been conducted on the formation at the Miryas locality in the High Folded Zone of the Qaradagh Mountain Series, southwest of Sulaimaniyah, Kurdistan Region, Iraq. The Fatha Formation consists of claystone, siltstone, marlstone, gypsum and few limestone beds. Ten samples were taken from marl-rich strata in the upper part of the formation between the red claystones of the Miryas. On the basis of the identified calcareous nannofossils, three biozones are recorded from the upper part of the Fatha Formation: the NN1, NN2 and NN3 zones. The combined stratigraphic ranges of the calcareous nannofossils identified here support the early Miocene–Aquitanian age; Discoaster druggii, Sphenolithus belemnos, S. cometa, S. procerus, S. tintinnabulum, S. delphix and S. capricornutus are marker species of the Aquitanian that have been identified inside the Miryas’s smear slides. These genera/species are also accompanied by the occurrences of Sphenolithus moriformis, Cyclicargolithus floridanus, Reticulofenestra minuta, R. bisecta, S. minuta, S. dictyoda, Coccolithus pelagicus, Helicosphaera carteri and Coronocyclus nitescens. The appearance of Discoaster saundersi at the top of the formation indicates the last occurrence of the NN2 zone of the Aquitanian and first occurrence of the NN3 zone of the Burdigalian. Through this study, for the first time, the early Miocene biozones determined within the Fatha Formation indicate that lower Miocene sediments (facies) were not deposited at some locations in the Qaradagh Mountain Series. Instead, the equivalent cap rock sediments of the Fatha Formation were deposited in the High Folded Zone; this clarifies why accumulation of hydrocarbons is rare within the late Oligocene–earliest Miocene succession in the High Folded Zone rather than the reservoir rocks of the same age in the Low Folded Zone (such as Kirkuk Oil Fields). KEY POINTS First study of nannostratigraphy of the Fatha Formation in the High Folded Zone of Iraq. First study of early Miocene nanno-biozones within the Fatha Formation. First record of NN1, NN2 and NN3 zones within the Fatha Formation.

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.

Detrital zircon geochronology and heavy mineral composition constraints on provenance evolution in the western Pearl River Mouth basin, northern south China sea: A source to sink approach

Investigating the provenance evolution of sedimentary basins with complex tectonic histories is challenging because of the continuously evolving tectonic framework and changing source areas. Pearl River Mouth Basin (PRMB) in the northern South China Sea preserves a large volume of Cenozoic sediments derived from both intrabasinal and extrabasinal sources. However, rare study has been conducted to investigate the provenance evolution of the western PRMB. In this study, we report new detrital zircon U–Pb geochronological and heavy mineral data from the western PRMB, attempting to identify its potential sources and provenance evolution from Eocene to early Miocene. Our data from distinct structural units and formations reveal spatial-temporal differences in provenance. In the northern part, a similar age pattern with a major peak at ∼425 Ma and a subordinate peak at ∼230 Ma is preserved in the Eocene-late Oligocene sediments and suggests that sediments were mainly derived from the Yunkai Massif via Nanduhe River. By contrast, in the southern part, the Eocene-late Oligocene sediments display a dominant age population ranging from 100 Ma to 300 Ma, which implies that the sediments were mainly eroded from nearby Shenhu Uplift and Hainan Island. The heavy mineral data also record such spatial differences in provenance. However, during the early Miocene, the northern and southern parts show similar detrital zircon age patterns with multiple clusters at ∼245 Ma, ∼450 Ma, ∼850 Ma, 970–980 Ma, 1825–1845 Ma, and ∼2500 Ma, indicating that the Miocene sediments across the whole basin were mainly provided by the Pearl River system. The increase of Paleozoic and Precambrian zircons in the lower Miocene sediments suggests a profound provenance shift from multiple nearby sources to the South China Block via the Pearl River between Oligocene and Miocene in the western PRMB, and its timing is posterior to other regions of the PRMB. Finally, four-stage source-to-sink evolution for the PRMB is proposed, showing that sediment provenance in the PRMB is controlled by regional tectonic movement, drainage evolution, and basin architecture. This study suggests that the small-scale drainage system Nanduhe River sourced by Yunkai Massif contributed significantly to the PRMB between Eocene and Oligocene, and highlights its complex processes of provenance evolution that are relevant to the evolution of marginal sea basins globally.

Ultrastructure, composition, and 87Sr/86Sr dating of shark teeth from lower Miocene sediments of southwestern Peru

Bioapatite of fossil bone and teeth is susceptible to alteration and ion exchange during burial and diagenesis, varying its Sr content through the geological time. Nevertheless, fossil shark teeth are a powerful proxy for both chronostratigraphic and paleoecological reconstructions, thanks to the presence of the enameloid, a hard outer layer consisting of resistant fluorapatite crystallites. Here, we analyze fossil shark teeth from the Miocene sediments of the Chilcatay Formation of the Pisco Basin (southwestern Peru) with the aim of dating poorly constrained strata in this region. (Ultra)structural and compositional analyses of fossil lamniform and carcharhiniform teeth are performed through macroscopical observations, optical microscopy and SEM-EDS for evaluating the preservation state of the collected teeth. Shark teeth display a compact and well preserved outer enameloid layer formed by highly ordered bundles of crystallites that is distinctly separated by a more porous and heterogeneous inner core of dentine featuring diagenetic artefacts and microborings. Compositional mapping highlights differences in the distribution of Ca, P, F, and S in the enameloid and dentine, and chemical results show a Sr content that is consistent with the range reported for extant shark teeth. The best preserved teeth were selected for Strontium Isotope Stratigraphy (SIS), measuring the 87Sr/86Sr values in the enameloid and obtaining numerical (absolute) age estimates. In the Ica River Valley, SIS dates the Chilcatay strata to the Burdigalian (between 19.1 and 18.1 Ma), in agreement with previous radiometric, isotopic and biostratigraphic ages obtained in the same region. At Media Luna, the Chilcatay strata are dated herein for the first time, resulting in a slightly older age of 21.8–20.1 Ma (late Aquitanian–early Burdigalian). These results strengthen the notion that the Sr-ratio of shark teeth can be successfully applied for obtaining reliable age estimates via SIS.

Application of seismic attribute analysis in Lower Miocene reservoir characterization, northeast Bach Ho field, Vietnam

The Cuu Long basin is an Early Tertiary rift basin of southern Vietnam, and the most potential basin in the country with high productive for oil and gas. Special interest in the Lower Miocene reservoir in the Cuu Long basin is caused by the gradual depletion of unique oil-bearing in the fractured basement and the possibility of transferring production wells to overlying deposits in the terrigenous rocks of the sedimentary cover and entering new deposits into development. In recent years, seismic attributes analysis has emerged as an effective tool to predict ancient riverbeds where sand bodies may exist in nonstructural traps. Understanding the distribution of these sand bodies will be of great significance in the orientation of oil and gas exploration activities. The paper applied seismic attribute analysis method combined with artificial neural network (ANN) and well data to predict the distribution of sandstones reservoirs of Lower Miocene sediments in the Northeastern Bach Ho oil field. Seismic attributes selected as input for ANN training including Relative Acoustic Impedance, Root Mean Square, Sweetness. The attributes provide the most obvious opportunity to display geological features with varying seismic amplitude characteristics as well as predict lithofacies, petrology and the distribution of sand bodies. The research results have identified the potential reservoirs in the Northeastern area of Bach Ho field, which are deposited in the fluvial, marginal lacustrine and deltaic environments.

Temperature Estimates of Lower Miocene (Burdigalian) Coastal Water of Southern India Using a Revised Otolith “Clumped” Isotope Paleothermometer

AbstractCarbonate clumped isotope thermometry is based on the ordering of 13C and 18O in the carbonate lattice and is based on the relative abundance of 13C18O16O in CO2 produced through acid digestion of carbonate minerals. The major advantage of this technique is its non‐dependency on the δ18O value of water from which the carbonate precipitated. Ghosh et al. (2007, https://doi.org/10.1016/j.gca.2007.03.015) previously published calibration data for fish otoliths referenced to heated gases and used the Gonfiantini 17O parameter set in their data evaluation. Herein, we present a new clumped isotope (Δ47) calibration for aragonitic fish otoliths in the absolute reference frame using the International Union of Pure and Applied Chemistry 17O correction. Our revised calibration equation for otolith is: . To test the accuracy of this calibration, we apply it to otoliths of modern Lutjanus lutjanus from the Bay of Bengal. The estimated average temperature (22.3°C ± 4.2°C) for the Bay of Bengal and δ18OV‐SMOW composition of waters of −1.7‰ (±0.5) are consistent with the onsite observations. We also apply the new calibration to well‐preserved otoliths of “genus Ambassidarum” sp. and “genus Gobiidarum” sp. from lower Miocene (Burdigalian) sediments of the Quilon Formation, India to quantify coastal water conditions. Estimated average environmental water temperatures in their habitats were 12.9°C ± 1.7°C, and the average δ18OV‐SMOW of ambient waters calculated yielded a value between −3.5‰ and −2.6‰ (V‐SMOW) (mean: −2.9‰ ± 0.4) and −4.4‰, respectively. These results indicate δ18O values reflect the kinetic effects impacting the δ18O of fish otoliths independently of Δ47, although we cannot fully preclude diagenesis.

Nannofossil palaeoecology of Lower Miocene sapropels from IODP Expedition 359, the Maldives

During IODP expedition 359 multiple holes recovered Modern to Middle Miocene sediments from the Kardiva Drift which is strongly influenced by monsoonally-driven currents. Two holes continued below the drift into Lower Miocene sediments that were deposited under rather different conditions following Oligocene subsidence of the Maldives Ridge. These sediments are characterised by marked alternation between dark organic-rich sapropelic sediments and pale nannofossil oozes. This interval is also characterised by generally good to excellent nannofossil preservation. Nannofossil assemblages from the sapropel and non-sapropel intervals are broadly similar; both sediment types contain diverse normal marine assemblages and no taxa are confined to either sediment type. In the sapropels nannofossil abundance and diversity tends to be lower and Cyclicargolithus floridanus specimens are smaller. In addition Umbilicosphaera abundances are higher in the non-sapropel layers whilst Discoaster abundance is higher in most sapropels. These differences are more marked in the better developed sapropels. The nannofossil evidence supports the interpretation from geochemistry that sapropel formation was primarily driven by changes in bottom water ventilation linked to sea-level change rather than surface water productivity.

Combination of methodology on researching the petroleum formation process in Lower Miocene sediments, Cuu Long Basin

The process of formation and deposition of granular sedimentary formations containing oil and gas in sedimentary basins on the continental shelf of Vietnam is a key factor in the study to determine the distribution trend, characteristics and scale of the sedimentary formations in general and Miocene sediments in particular. Up to the present time, the majority of Vietnam's oil and gas exploitation basin are distributed on continental or coastal shelves, so the study of the origin and evolution of basins in general and components in particular (into reservoir system) still exists many gaps not only with geologists but also with petroleum research and exploration company on the continental shelf of Vietnam. The samples and data collected cover most of the onshore and offshore in Southeastern Vietnam, allowing the construction of the relationship boths the two areas that have traditionally been studied by the companys, with the lack of synchronous methods, closely links. The collection of research data, recently collected, created convenient conditions for linking and comparing the evolutionary history between the continental sediments and the continental shelf through the survey of collecting field samples and core samples at petroleum exploration drill wells come to clarify the origin, evolution, the trend of sedimentary materials transporting. The methodology conducted to research includes geotectonics, stratigraphic seismic analysis, borehole geophysical analysis, stress filed, core sample analysis, sedimentary lithological analysis, biostratigraphic analysis, analysis of U-Pb zircon isotope age and at last artificial intelligence. The study results can also be used to predict the presence and distribution of the Miocene sandstone petroleum formations in researching area.

A Salgótarjáni és Ózdi paleogén részmedence térképezése szeizmikus és gravitációs mérési adatok alapján, és az eredmények szénhidrogén-földtani vonatkozásai

Az Észak-magyarországi Paleogén-medence perspektivikus szénhidrogének kutatása szempontjából. A kutatási lehetőségek megítéléséhez azonban elengedhetetlen a medencealjzat domborzatának, ill. az üledékkitöltés szintjeinek helyes ábrázolása. A Salgótarjáni- és Ózdi-részmedence területén a medenceperemi kutatófúrások alapján készült, országos léptékű prekainozoos medencealjzat térképek a szeizmikus mélységszelvények alapján pontosíthatók. A Magyar Bányászati és Földtani Szolgálat (MBFSZ) szakemberei szeizmikus, gravitációs és mélyfúrási adatok újrafeldolgozása, újraértelmezése alapján elkészítették a terület részletes, nagyobb felbontású prekainozoos medencealjzat térképét, és az üledékkitöltés vezérszintjeinek térképeit. Az itt bemutatott eredmények alapján a paleogén medence aljzata a medenceperemektől Bárna település alatt (Salgótarjántól 10 km-re K felé) 3400 méter tengerszint alatti mélységig süllyed.
 A geofizikai adatok együttes értelmezése szerint a Salgótarjáni- és az Ózdi-részmedence között jelentős eltérés van mind az aljzat mélysége, mind a medencét kitöltő üledékrétegsor tekintetében. A gravitációs medencemodell két sűrűségmodellel közelíthető, amelyek között egy átmeneti zóna is van. A szeizmikus értelmezés alapján a részmedencék paleogén–alsó-miocén üledékkitöltésében öt vezérszint követhető, a nyugati részen (Salgótarjáni-részmedence) nagy vastagságban találhatók idősebb oligocén üledékek, míg az északkeleti területen (Ózdi részmedence) a fiatalabb oligocén és miocén képződmények dominálnak. A potenciálisan anyakőzetként számontartott összletekről mélység- és vastagságtérképek készültek. Ezek szerint a medence nyugati részének mélyzónája kiterjedtebb, mint azt a korábbi áttekintő térképek ábrázolják. A terület kőolaj és földgáz előfordulásai és indikációi azt jelzik, hogy a Salgótarjáni-részmedencében a szénhidrogének anyakőzetei érettek, a felhalmozódások pedig az anyakőzetekben, vagy azok szűk környezetében lehetnek, mert a szénhidrogén migráció korlátozott. A vitrinit reflexió adatok szerint a medenceperemeken a jelenleg felszín közelben lévő megmintázott kőzetrészek szerves anyaga korábban a jelenleginél mélyebben volt eltemetve, és a kőolajképződés kezdeti fázisának közelébe jutott.
 A Salgótarjáni-részmedencének a korábban várhatótól jelentősebb kiterjedése és mélysége, a várható szénhidrogén anyakőzetek mennyisége és érettsége alapján a terület CH potenciálja jelentősebb lehet a korábbi megítélésnél. A térképek, és a szakirodalomból ismert szénhidrogén-földtani adatok alapján becslés történt az anyakőzet összlet által generált szénhidrogén mennyiségre, amely az értékelés szerint a 100 millió m3-t is meghaladhatja.

Occurrence and Depositional Environment of the Genus Actinocythereis (Ostracod) from the Lower Miocene Sediments of Kachchh, Gujarat

ABSTRACT The genus Actinocythereis commonly occurs in the lower Miocene sediments of Kachchh, Saurashtra and Kerala basins. Among these basins, the genus thrives well in Kachchh basin, where it is represented by five species, including two new subspecies: Actinocythereis gujaratensis (Tewari and Tandon) karanpurensis n. subsp. and Actinocythereis vinjhanensis (Tewari and Tandon) lakhpatensis n. subsp., reported in this study. A. gujaratensis Tewari and Tandon, A. tumefaciens (Lyubimova and Guha) and A. vinjhanensis (Tewari and Tandon) have been previously described. The systematics along with paleoecological data of the genus presented.

Revised chronostratigraphy of DSDP Site 270 and late Oligocene to early Miocene paleoecology of the Ross Sea sector of Antarctica

Deep Sea Drilling Project (DSDP) Site 270, located in the central high of the Ross Sea, was cored to 422.5 m below seafloor (mbsf) and recovered a thick Oligocene to lower Miocene sequence of mudstone with varying amounts of ice rafted debris (IRD), overlain by ~20 m of Pliocene to Recent diatom silty clay with IRD. This site provides important temporal constraints on regional stratigraphy and insights into late Oligocene to early Miocene ice sheet dynamics; however, previous age models were based on limited data. Here we provide a revised age model using a combination of biostratigraphy (dinoflagellate cysts, pollen, calcareous nannofossils, foraminifers, and diatoms), magnetostratigraphy, Sr-isotope stratigraphy, and KAr dating of glauconite. We divide the sequence between 386 and 20 mbsf into four chronostratigraphic intervals (CSIs). CSI 1 (386–352 mbsf) is dated to between ~26 and 25 Ma based on glauconite KAr dating, the highest occurrence (HO) of the dinoflagellate Lejeunecysta rotunda (24.5 Ma), and a paleomagnetic reversal tied to the C8r/C8n.2r boundary (25.987 Ma). A distinct change in the benthic foraminifer assemblage at 352 mbsf marks an unconformity and the base of CSI 2. CSI 2 (352 to 149–146 mbsf) is dated to between 25.44 Ma and 23.13 Ma based on nannofossil biostratigraphy. Within this 200 m interval we correlate seven magnetic reversals to Chrons C8n.2n to C6Cr (25.3–23.3 Ma) and our line of correlation suggests rapid sedimentation (~80 m/m.y.). Microfossil and lithologic evidence indicate a distal marine setting with a paleo-water depth of ~200 m at 345 mbsf, with deepening above. Within CSI 2 is a diamictite overlain by grounding line proximal sandstone and laminated mudstone indicating glaciomarine deposition in a grounding-line proximal setting between 245 and 230 mbsf, followed by ice sheet grounding-line retreat into a more distal setting from 230 to 146 mbsf (~24.5–23.5 Ma), likely due to basin subsidence and incursion of relatively warm deep water onto the shelf. Another unconformity between 149 and 146 mbsf marks the boundary between CSI 2 and CSI 3. The thin CSI 3 (149–146 to 121/112 mbsf) is dated to ~23 Ma and we place the Oligocene/Miocene boundary at the base of the sequence, although we cannot rule out that the boundary is represented by an unconformity. Benthic foraminifers indicate continued deepening in the earliest Miocene and finer-grained mudstone with less IRD suggests that the site remained in a grounding line distal setting, although a decrease in abundance of calcareous plankton indicates cooling climatic conditions at that time. The boundary between CSI 3 and CSI 4 is marked by an unconformity spanning at least 2.5 m.y. based on the lowest occurrence of the dinoflagellate Batiacasphaera cooperi (<20.7 Ma) at 111 mbsf. Biostratigraphic data constrain CSI 4 to the early Miocene. We tentatively identify three magnetic reversals within CSI 4 (121/112–20 mbsf) that may tie this interval to Chrons C6An.2n to C6r (~20.6–19.7 Ma). A major unconformity at 20 mbsf separates the lower Miocene sediments from the overlying Pliocene and younger sediments. Late Oligocene to early Miocene pollen assemblages from Site 270 suggest a tundra landscape with low-growing Nothofagaceae, Podocarpaceae, and Proteaceae scrub in warmer locations with a relatively stable terrestrial environment during that time.

Provenance and palaeogeographic evolution of Lower Miocene sediments in the eastern North Alpine Foreland Basin

Detrital heavy mineral analysis and sediment chemistry of Lower Miocene sediments of the Lower Austrian Northern Alpine Foreland Basin generally indicate provenance from metapelitic source rocks. The sediments of the Traisen Formation (Ottnangian) were primarily derived from Alpine sources such as the Austroalpine crystalline units of the Eastern Alps and reworked and eroded siliciclastics strata on top of the Northern Calcareous Alps and, in addition, low-grade metamorphic rocks of the Bohemian Massif. Ottnangian and Karpatian sediments in the subground of the northern Lower Austrian Molasse basin were mainly fed from the same southern sources, from low-grade metamorphic rocks of the Bohemian Massif and via resedimentation of Lower Miocene and Palaeogene of the Waschberg–Ždanice Unit and the Vienna Basin. A large-scale input of material from the Rhenodanubian Flysch Zone and of higher-grade metamorphic units and granites of the Bohemian Massif in the Lower Miocene Molasse basin can be ruled out. A compilation of well sections and heavy mineral data point to the existence of a partly emerged, N–S oriented ridge during the Egerian.

Petrography and geochemistry of Oligocene to Lower Miocene sandstones in the Baiyun Sag, Pearl River Mouth Basin, South China Sea: Provenance, source area weathering, and tectonic setting

There is a controversy regarding the source area and weathering intensity of Oligocene to Lower Miocene sediments in the Baiyun Sag of the Pearl River Mouth Basin. Detrital modes, geochemistry, heavy mineral data, and detrital zircon U–Pb ages were analysed to understand the provenance, source area weathering, and tectonic setting of Oligocene to Lower Miocene sandstones in the Baiyun Sag. Petrographic data reveal that the sandstones were derived from a recycled orogen. With increasing transport distance, sediment maturity increased correspondingly. The Oligocene to Lower Miocene sandstones in the Baiyun Sag have low compositional maturity and have experienced low to moderate weathering. The sediments of the Zhuhai Formation have experienced relatively strong weathering intensity compared with those of the Enping and lower Zhujiang formations. Due to low degree of illitization and differences in the geochemical compositions of the sediments, the continental island arc data from different boreholes in the Baiyun Sag are more irregularly distributed in the A‐CN‐K plot. The modal composition (e.g., quartz, feldspar, and lithic fragments) and geochemical indices (Al2O3/TiO2 ratio; Al2O3‐TiO2 diagram; discriminant F1‐F2 diagram; Eu/Eu*, La/Sc, La/Co, Th/Sc, and Th/Co ratios; Hf‐La/Th and La/Sc‐Co/Th diagrams; and rare earth element patterns) indicate that the sediments in the Baiyun Sag are mainly derived from felsic source rocks. Although the uplift around the Baiyun Sag includes multistage magmatism and basic rocks, it has little influence on the sediment in the depression, and no sediments were transported by the Han River to the Baiyun Sag. Geochemical data and detrital zircon U–Pb ages suggest that the Pearl River was formed in the Early Oligocene and became the main source for the sediments in this area. The river carried felsic material from the South China Coast forming a large delta on the northern slope of the Baiyun Sag. The ratios of Eu/Eu*, La/Sc, La/Co, Th/Sc and Th/Co, and heavy mineral data indicate that the sediments transported by the Pearl River to the Baiyun Sag were changed from the arc‐dominated coastal zone to the interior of the South China Block during the Late Oligocene to Early Miocene and even reached the south‐eastern margin of the Tibetan Plateau (West Yunnan Plateau). The La‐Th‐Sc and Th‐Sc‐Zr/10 diagrams suggest that the provenance of these sandstones is evolved continental island arc or an active continental margin setting.

Oligocene and Lower Miocene source rocks in the Paratethys: palaeogeographical and stratigraphic controls

Abstract Oligocene and Lower Miocene deposits in the Paratethys are important source rocks, but reveal major stratigraphic and regional differences. As a consequence of the first Paratethys isolation, source rocks with very good oil potential accumulated during Early Oligocene time in the Central Paratethys. Coeval source rocks in the Eastern Paratethys are characterized by a lower source potential. With the exception of the Carpathian Basin and the eastern Kura Basin, the source potential of Upper Oligocene and Lower Miocene units is low. In general, this is also valid for rocks formed during the second (Kozakhurian) isolation of the Eastern Paratethys. However, upwelling along a shelf-break canyon caused deposition of prolific diatomaceous source rocks in the western Black Sea. Overall, Oligocene–Lower Miocene sediments in the Carpathian Basin (Menilite Formation) can generate up to 10 t HC m −2 . Its high petroleum potential is a consequence of the interplay of very high productivity of siliceous organisms and excellent preservation in a deep silled basin. In contrast, the petroleum potential of Oligocene–Lower Miocene (Maikopian) sediments in the Eastern Paratethys is surprisingly low (often &lt;2 t HC m −2 ). It is, therefore, questionable whether these sediments are the only source rocks in the Eastern Paratethys.

A new species of Plesiodimylus (Dimylidae, Eulipotyphla, Mammalia) from the Early Miocene of Spain

We report a new dimylid species, Plesiodimylus ilercavonicus sp. nov., from the Early Miocene locality of Mas d’Antolino B-5 (Ribesalbes-Alcora, Castelló, Spain). This new species of Plesiodimylus is an amblyodont form of the genus and exhibits some primitive characters. The phylogenetic and palaeoenvironmental implications of this southern occurrence of Plesiodimylus in Lower Miocene sediments are discussed.http://zoobank.org/lsid:zoobank.org:pub:E78DB979-6552-4BE2-BEC9-FA2EA05B7B39