Early Miocene Age Research Articles

Oldest Asian Record of Snapping Shrimps (Malacostraca: Alpheidae) from the Kutch Basin, Western India and Associated Biota: Biostratigraphic, Paleoenvironmental and Paleoecological Significance

AbstractThe oldest Asian record of alpheid shrimps, assigned to genus Alpheus, based on snapping claw fingertips from the Miocene Khari Nadi Formation in the Kutch Basin, western India reported herein, extends the fossil record of the family Alpheidae from Asia by ∼22 million years. An early Miocene (Aquitanian) age is estimated based on the associated assemblage of calcareous nannofossils, Sphenolithus disbelemnos, Cyclicargolithus floridanus, and Reticulofenestra haqii. The co‐occurring microbiota includes bony fish otolith remains, identified as “genus Gobiidarum”, isolated teeth of Dasyatis rays, Sphyrna sharks, and teleosts, ctenoid and placoid scales, ostracods, belonging to the genera Paractinocythereis, Alocopocythere, Ruggieria, Aglaiocypris, Bairdoppilata, and echinoid spines. Taken together, the microfossil assemblage and data from chemical analyses using Energy Dispersive Spectroscopy, X‐Ray Diffraction and Wavelength Dispersive X‐Ray Fluorescence of host and associated lithologies suggests prevalence of a shallow (neritic) to coastal marine (intertidal) depositional paleoenvironment. The present investigation also provides the oldest fossil evidence on the co‐occurrence of Alpheus and gobiids (based on otoliths) that strongly advocates that the mutualistic association between these animal groups had developed by the Aquitanian.

Early Miocene Sr-geochronology of Patagoniense marine units from southern Argentina: Implications for molluscan assemblages and interbasinal correlation

Early geological investigations in southern South America addressed the Oligocene-Miocene Patagoniense deposits, a fossiliferous marine succession distributed in several basins that had been flooded by three different transgressive events. Chronological calibration and correlation of these transgressive events, lithological units and fossil assemblages through the Patagonian basins still need further definitions in some areas. To tackle this problem, new Sr-isotope ages of pectinid shells from four early Miocene key sections located at the coastal sector of Patagonia, were obtained to improve correlations among the Magallanes-Austral (MAB), San Jorge (SJB) and Mazarredo (MB) basins. A bed in the middle part of the Punta Guanacos section (MAB) was dated in a mean age of 19.8 Ma allowing its correlation with the lower section of the Monte Leon Formation. In the SJB, the lowermost bed of the Chenque Formation at Punta Borja has an age of 19.6 Ma, while lower bed of Sequence 2 of this unit has an age of 17.7 Ma at Punta Delgada. Patagoniense deposits exposed along the cliffs of the southern San Jorge Gulf (MB), and overlying the continental Sarmiento Formation, are recognized herein as the Mazarredo Formation with a mean age of 20.9 Ma at Canadón El Lobo. It is younger than the San Julián Formation and correlates with the lower part of the Monte León Formation at Playa La Mina (MAB). The radiometric age of the Mazarredo Formation is of outstanding importance because the Mazarredo area constitutes a geographic link between the MAB and SJB and precludes the presence of the “Juliense” transgression in central Patagonia as had been proposed, supporting the early Miocene age previously provided by the authors for the Jorgechlamys centralis –Reticulochlamys borjasiensis Molluscan Assemblage. This assemblage is recorded in the Mazarredo Formation and in the lower section of the Chenque Formation (SJB). Moreover, faunal similarity with the Monte León Formation allows the identification of the Reticulochlamys zinsmeisteri - Struthiolarella patagoniensis - Pleuromeris cruzensis Assemblage at Punta Guanacos in the northeastern sector of the MAB.

Palynology, Paleoenvironment and Stratigraphy Relationship of Tungan Buzu Hill with Adjacent Valley Gwandu Formation, Sokoto Basin, Northwestern Nigeria

Palynological study of Tungu Buzum Hill was investigated with a view towards determining the age of the outcrop, compare its miospore content with the adjacent Tungu Buzu Valley of carbonaceous shale, their stratigraphic relationship and paleoenvironment of deposition of the litho-sequence. Field study involved litho-description and logging achieved by noting the rock type, mineralogical composition, bed thickness, texture, sorting, roundness, structure, fossil content and diagenetic effect. Palynological slide preparation involved decarbonisation, digestion, sieving, maceral separation using zinc bromide, mounting on slide and petrographic analysis. The litho-sequence is composed sequentially upward of claystone, siltstone, indurated silty claystone, mudstone and ferruginized ironstone characterized by loadcast, fracture, lithification and bioturbation. Palynologically, the litho-section exhibits few marker forms such as Belskipollis elegans, Peregrinipollis nigericus and Retibrevitricolporites obodoensis depictive of early Miocene age. The paleoenvironment was deduced based on the occurrence of peridinacean forms such as Andalusiella sp., Senegalinium sp., Lejeuncysta diversiforma and Paleocystodinium golzowense indicative of marginal marine, while deeper marginal marine forms of gonyaulacacean phytoplanktons present are Micrhystridium sp., Canningia capillata and Dinogymnium sp. There are similarities in palynomorph assemblages of this study and Tunga Buzu Valley section in terms of age and similarity to Gwandu Formation though varied in paleoenvironment in the valley litho-section, marked by continental to marginal marine settings. Field relationship suggests that the Tunga Buzu Hill is stratigraphically overlying the Tunga Buzu Valley, separated by a fault. The Tunga Buzu Hill section represents the footwall while the Tunga Buzu Valley is situated within the hanging wall of a normal fault structure.

New data on the Miocene vertebrate assemblage of the Zaysan Basin (Central Asia) with implications for biostratigraphy, paleoecology, and paleobiogeography

ABSTRACT The Zaysan Basin in Central Asia has a long geological history, and it has therefore seen major climatic and evolutionary transformations. The Miocene fossil record of this locality is remarkably rich representing all groups of vertebrates. A revision of fish remains has been carried out and new records of fishes, reptiles, and mammals recovered from Miocene deposits of the Zaysan Basin have been described. The study of fossils has revealed the existence of a quite diverse vertebrate assemblage in the basin during the Miocene. Representatives of the Percidae and Amiinae, and the species †Leobergia zaissanica predominated among fishes, whereas reptiles were supposedly represented in the assemblage by pan-trionychid turtles and crocodiles. No amphibians have been revealed, while the only mammalian taxa in the studied sample is a fossorial rodent of the genus †Tachyoryctoides. In contrast to previous views regarding the Middle Miocene age of the Zaysan Formation, the analysis of fish and mammal remains recovered from this locality strongly suggests an Early Miocene age. Findings of bowfin remains in the Zaysan Basin confirm that this group had existed outside of North America beyond the Paleogene/Neogene transition, and, at the same time, these specimens are the last known occurrences of the taxa Amiidae, Amiiformes, and Halecomorphi outside of North America. Data also indicate the existence of a lacustrine ecosystem in the Zaysan Basin during the Miocene with a taxonomically rich vertebrate assemblage and diverse trophic relations being an important center of biodiversity in the Miocene of Central Asia.

Biostratigraphy of Limestone based on Large Foraminifera in the Donggala Region, Central Sulawesi

The Sulawesi Molasa Formation is mostly composed of clastic and carbonate sediments which are widely distributed on the island of Sulawesi. Research on the Sulawesi Molasa Formation has been carried out by several researchers. However, there has been no detailed research on limestone biostratigraphy in the Donggala area, so it is very important to do it. This study aims to analyze the age and depositional environment of the Sulawesi Molasa Formation limestone based on the content of large foraminifera. The method used in data collection is measuring section. Field data collection was carried out by stratigraphic measurements including lithology identification, thickness and rock sampling. Laboratory observations were carried out using a polarizing microscope to observe a thin section of rock to determine the species of large foraminifera, their mineral and organic compositions. From the results of field observations found four types of lithology, namely wackestone, packstone, grainstone and floatstone. Based on the observation of large foraminifera fossils in a thin section of limestone in the study area, there are 24 species of large foraminifera identified. Among them, there are four index fossils, namely Miogypsinoides dehaarti (van der Vlerk), Paleomiogypsina bononensis (Matsumaru), Miogypsina sp, (Vaughan), Paleomiogypsina sp, and Miogypsinella sp, (Aquitanian). Based on age withdrawal and description of large foraminifera fossils, it is known that the limestones of the study area are Early Miocene-Middle Miocene age with the depositional environment in the lagoon zone to the forereef shelf

Controls on Early Miocene carbonate and siliciclastic deposition in eastern Java and south Makassar Straits, Indonesia

The Early Miocene stratigraphy of NE Java and the southern Makassar Straits is examined in the context of siliciclastic sediment supply and subsidence (creation of accommodation space), as indicated by biohermal carbonate growth. Stratigraphic variation is examined geographically and assessed quantitatively, using geohistory analysis. During the Oligocene through to basal Miocene times, basin development had been dominated by extension with local transtension. This changed within the Early Miocene to regional compression, increasing in magnitude with time. Three tectonic events, at about 24 Ma (base of section studied), at 21 Ma, and roughly 16 Ma are described in terms of the influence they had on stratigraphy. Most significant was the concentration of siliciclastics on the proximal side of the Oligo-Miocene axis of subsidence, which caused isostatic loading and nearby pinnacle reefs to achieve high relief, but ultimately an acceleration in siliciclastic input at about 16 Ma caused simultaneous reef extinction. Carbonates of Early Miocene age are important hydrocarbon reservoirs, and the siliciclastics are a geographically variable part of the overburden and seal, as well as causing the thermal maturation of hydrocarbon source rocks. The stratigraphic framework described here will have implications for facies and exploration risk prediction into under-explored regions around the study area. The tectono-stratigraphic framework is carefully constrained for age and facies inputs, and the resulting palaeogeographic history indicates a new model of basin development. This dynamic framework correlates to coeval tectonic processes over a large region and has important implications for Sundaland plate tectonics.

Pollen and Spores Recovery in Tunga Buzu Carbonaceous Shale Type Section Member: Significance in Sequence Stratigraphy, Age Dating and Paleoenvironment Deduction of the Early Miocene Gwandu Formation, Sokoto Basin, Northwestern Nigeria

Feld samples were collected from an outcrop at Tunga Buzu with the intention of comparing field relationship between the claystone member and the underlying carbonaceous shale Type Section for palynological study. The study was carried out in order to determine the geologic age relationship of the facies sequence, sequence stratigraphy and paleoenvironment of deposition of the sediments. Lithological description of the beds follows notation of colour, facies composition, texture, fossil content, structure and post depositional diagenetic effects. Laboratory preparation of palynological slides involved decarbonisation, sample digestion using hydrofluoric acid, sieving with 10µm mesh, bleaching of organic debris with nitric acid, maceral separation with zinc bromide, rinsing of separated maceral with ethanol and final mounting of the organomaceral on the slides for microscopic analysis.The carbonaceous shale is light grey in colour, fissile, carbonaceous, slightly bioturbated and ferruginized. Pollen, spores, dinoflagellates and algae were recovered from samples N1-N4. The samples N1-N3 are claystone samples characterised by relatively low assemblage assemblage of miospores with downhole increase in dinoflagellate cysts. The carbonaceous shale (sample N4) is relatively rich in palynomorphs with corresponding high palynomorph population and diversity compared with the claystone facies. Both the claystone and carbonaceous shale contain marker fossils such as Striamonocolpites sp., Retibrevitricolporites obodoensis, Verrutricolporites sp., Praedapollis sp., Belskipollis elegans and Peregnipollis nigericus; indicative of Early Miocene age. The litho-sequence of claystone and carbonaceous shale indicated alternation of continental and marginal marine deposits characterised by paucity and preponderance of peridinacean dinocysts. This suggests eustatic change in sea level of continental Lowstand Systems Tract (LST) and marginal marine Transgressive Systems Tract (TST) deposits respectively. The Tunga Buzu Carbonaceous Shale Type Section constitutes a member of the Early Miocene Gwandu Formation of the Sokoto Basin, Nigeria.

Geology of parts of the central and eastern Clarion Clipperton Zone

ABSTRACT The Clarion Clipperton Zone (CCZ) hosts the most valuable deposit of polymetallic nodules yet discovered. International Seabed Authority exploration contractors, such as Tonga Offshore Mining Limited, Nauru Ocean Resources Incorporated and Marawa Research and Exploration Limited, routinely conduct ship-based 12 kHz multibeam echosounder surveys over all or parts of their exploration contract areas. This is often supported by physical seabed samples, side-scan sonar, sub-bottom profile sonar and seabed photographs. Geological maps for seven discrete mapped areas are presented. Basaltic abyssal plains of mid-Eocene to early Miocene age are overlain by 75–100 m of mid-Eocene and younger deep-sea chalks of the Marquesas Oceanic Formation. In turn, the chalk is overlain by up to 27 m of early Miocene to present, often mobile, siliceous clay-ooze sediment of the Clipperton Oceanic Formation. This stratigraphy is crosscut by a very wide variety of mostly volcanic magmatic rock units.

A new, Late Cretaceous gonorynchiform fish in the genus †Notogoneus from drill core of crater-lake deposits in a kimberlite maar, Northwest Territories, Canada

The Gonorynchiformes are a group of mostly marine fishes that are the sister group to the Otophysi (e.g., carps, tetras, catfishes). They include milkfishes (family Chanidae) and beaked sandfishes (family Gonorynchidae) among extant taxa. The only freshwater genus is the strictly fossil †Notogoneus, which until now contained eight species of Late Cretaceous to early Miocene age. A ninth species, †Notogoneus maarvelis, sp. nov., is described here from a single, small specimen found in a diamond-exploration drill core into strata deposited in a kimberlite maar lake in northern Canada. The maar crater was formed by the explosive emplacement of the “Wombat” kimberlite pipe, one of many in the nearby region. The new species is the oldest known member of the genus †Notogoneus and is dated by U–Pb geochronology on associated tephras as early Campanian or about 82 Ma. Although very small, the type and only specimen is very similar in morphology, meristics, and body proportions to the type species †N. osculus. The most important difference is that the origin of the pelvic fin in the new species is beneath vertebral centrum 26, whereas the origin of the dorsal fin is above vertebral centrum 20. In †N. osculus, in contrast, the two fins both originate opposite centrum 22 or 23. The new species is the only one known among those of †Notogoneus or the extant Gonorynchus in which the pelvic fin origin is well behind that of the dorsal fin. The new species agrees with †N. osculus and other congenerics in key attributes of the genus †Notogoneus, including subopercular clefts and, in the caudal skeleton, autogenous parhypural plus hypurals 1 and 2. The bones of the new species ossified at a much smaller size than did those of young individuals of †N. osculus, suggesting that the new species likely attained a much smaller adult size as well. This small, new species, as well as other unidentified fish fragments, was discovered in a core into maar-lake deposits within otherwise fossil-poor areas of the North American craton. Such discoveries highlight the potential importance of maar lakes and similar crater-lake settings for revealing more about fish diversity in the Late Cretaceous than has been previously known.

Geochronological characterization of Llallagua altered porphyry and hydrothermal vein assemblages from selected phosphate minerals and zircon

Llallagua is one of the world's biggest tin deposits and part of the metallogenic Bolivian Tin Belt, which occurs in the inner arc of the Central Andes. The Llallagua deposit formed through emplacement of a subvolcanic porphyry stock, of intermediate dacitic to rhyodacitic composition, metasomatism, and hydrothermal mineralization. The deposit is the subject of a well-established geochronologic controversy that includes contradictory ages (≈40 and 20 Ma) from multiple geochronometers. Geochronological characterization of phosphate minerals from the metasomatized igneous porphyry and hydrothermal vein assemblages, along with detailed petrography and chemical analyses, are used to reconcile the age controversy. The new interpretation is further supported by existing textural and geochemical data. The UPb ages of unaltered igneous fluorapatite (e.g. 21.2 ± 2.9 Ma), monazite (e.g. 21.22 + 0.80/−0.66 Ma), and zircon (e.g. 21.15 ± 0.39 Ma) from the Llallagua porphyry are all equivalent within error at ≈20 Ma, and are interpreted to represent the age of porphyry stock emplacement. Ages determined from altered portions of these minerals (e.g. apatite, 18.8 ± 8.0 Ma) are within error the same as unaltered portions, suggesting alteration of the porphyry soon after emplacement. UPb ages from unaltered fluorapatite (e.g. 21.4 ± 6.7 Ma), altered and unaltered monazite (e.g. 19.4 ± 1.4 Ma and 20.29 ± 0.30 Ma respectively), and unaltered xenotime (e.g. 19.32 ± 0.67 Ma) from the hydrothermal veins are also ≈20 Ma, indicating a very short hiatus or temporal continuity between stock emplacement and hydrothermal vein formation. The early Miocene age for tin mineralization at Llallagua is consistent with neighboring mineralization centers at the Morococala, Colquechaca, Japo, and Santa Fe mines, and with regional trends observed across the Bolivian Tin Belt, including stratigraphy, magmatic, and tectonic history of the Andean Eastern Cordillera.

Deformation and Sedimentary Responses to Top‐to‐North Shear Along the Range Front of the Big Bend of the Ailao Shan–Red River Shear Zone, SE Edge of the Tibetan Plateau, and Its Tectonic Implications

AbstractUnderstanding the mountain–basin coupling relationship is fundamental to placing constraints on the tectonic evolution of the Ailao Shan mylonite shear zone, the key feature accommodating relative movement between the Tibetan Plateau and SE Asia, because a contemporary basin, namely Red River, bounds its middle segment on the northeast, along which the shear zone is bent from northwest–southeast to roughly east–west (The Big Bend). The basin comprises two units: the Mubang Breccia and the Lengdun Conglomerate of Early Oligocene and Late Oligocene–Early Miocene age, respectively. This study reveals evidence indicating that the Wubang Breccia marks a high‐strain zone, resulting from top‐to‐north shear (range‐front detachment (RFD), along which the mylonite on the footwall experienced northward bending in the form of creeping. Moreover, the Lengdun Conglomerate on the hanging wall was deposited as growth strata, overlying a thrust belt to the north. The latter marks the southern rim of the Yangtze block, composed of extensional fault blocks, whose northward displacement along the toe of the RFD was synchronized with the north–south extension across the Red River basin. The spatial and temporal relationships between the Red River basin and the Ailao Shan shear zone indicate that basin formation was controlled by the change in geometry of the shear zone. The Red River basin can be viewed as an extensional step‐over in the left‐lateral strike‐slip field, in which all sedimentary and deformation processes were controlled by the extension and subsequent topographic spreading, accommodated by the RFD. This indicates that the extensional crustal materials, including both Langdun Conglomerate and underlying extensional fault blocks, were all shed from the top of the Ailao Shan mylonite belt. The cause of bending of the shear zone is attributed to the northward movement of India with respect to South China and the bending process came to an end as the left‐lateral movement ceased.

Variation of sediment provenance at the 09 - 1 Block, Cuu Long Basin: their significance in assessing the Oligocene - Miocene reservoir quality

The Cuu Long Basin is one of the Tertiary sedimentary basins situated on the continental shelf of Vietnam, which demonstrates the high potential of oil and gas. Apart from fractured granite reservoirs, the Oligocene - Miocene sand bodies are thought to have significant potential for forming non - structural traps. The results of the study on the composition and physical properties of the sediments derived from wells "X" and "Y", block 09 - 1, Cuu Long Basin show that there is a clear difference between the Late Oligocene and Early Miocene sandstone in the well "X", namely the Miocene sandstone shows larger particle size, higher roundness and sortness (TB: 434.2; Ro: 0.69; So: 2.22) than those of the Late Oligocene sandstone (TB: 104.28; Ro: 0.64; So: 1.46). This difference is likely attributed to the fact that the Miocene sandstone was influenced by the marine environment, which intensified the roundness and sortness. Meanwhile, the well "Y" did not show much difference in the physical parameters of the sediments between the Late Oligocene and Early Miocene age ranges. However, the grain size was slightly increased and the roundness was less during the Early Miocene. It is possible that the “Y” well is located closer to the local source. The variation in the physical parameters of the sediments, proportion of sand grains and clay minerals shows that the quality of late Oligocene reservoir is better than that of Early Miocene reservoir, and the Late Oligocene reservoir quality in the "X" well is better than that in the borehole "Y".

Miocene adakitic volcanism in eastern Lhasa Terrane, Tibet: perspective from zircon U–Pb geochronology, whole-rock geochemistry and Sr–Nd–Hf isotopes

ABSTRACT The Riduo intermediate-felsic volcanic rocks are located in the eastern Lhasa terrane in southern Tibet. Zircon U–Pb dating, geochemical and Sr–Nd–Hf isotope analyses were carried out to constrain the age, petrogenesis and magma source of the Riduo magma suite, including andesite, dacitic tuff, and quartz diorite. Zircon U–Pb dating yielded Early Miocene ages of 19.5 ± 0.5 Ma (andesite), 17.6 ± 0.3 Ma (dacitic tuff), and 15.6 ± 0.5 Ma (quartz diorite). Geochemically, this early Miocene suite is adakitic with high SiO2 (55.76–69.46 wt.%), Al2O3 (15.21–16.61 wt.%), Na2O (3.82–4.83 wt.%), Sr (427–1033 ppm), and Sr/Y (24.5–145), but low Y (< 17.8 ppm) and Yb (< 1.82 ppm). The rocks also have low to high K2O (0.44–3.82 wt.%). They are enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs, e.g. K, Rb, Th and U), but depleted in high-field strength elements (e.g. Nb, Ta) and heavy rare earth elements (HREEs), and have weakly negative to positive Eu anomalies. Isotope analyses reveal that most samples have high whole-rock initial 87Sr/86Sr ratios (0.705611–0.708807), low εNd(t) (−2.25 to −1.15), and positive zircon εHf (t) (+1.29 to +6.49). We suggest that the early Miocene magmas in the eastern Lhasa terrane were likely sourced from post-collisional partial melting of the juvenile lower crust with minor mantle input. The magmas may have been crustal-contaminated during their ascent to the upper crust along the N-S-trending Cona-Riduo rift.

&lt;i&gt;Califrapana&lt;/i&gt;: a new genus of California and Bája California late Oligocene to early Miocene muricids previously attributed to the genus &lt;i&gt;Rapana&lt;/i&gt; (Mollusca: Gastropoda: Muricidae)

Califrapana n. gen., is proposed for California late Oligocene to early Miocene muricids attributed previously to the possibly Paleocene to modern western Pacific and Indian oceans genus Rapana. Four fossil species have been assigned to Rapana in the eastern Pacific. One of these species, R. perrini Clark and Arnold (1923), should be placed in another genus, the other species Purpura vaquerosensis Arnold (1907), R. imperialis Hertlein and Jordan (1927), and R. serrai Wiedey (1928) are synonymized here with the morphologically variable species Califrapana vaquerosensis n. comb. We confirm C. vaquerosensis is an index fossil for the lower and middle “Vaqueros” California provincial molluscan stage of late Oligocene to early Miocene age in southern California and Bája California, México, although the lack of numerical dating and the misuse of lithostratigraphic and biostratigraphic names had made that difficult to determine. Califrapana is distinguishable from similar genera by 1) its heavier shell, 2) an aperture that is pointed at its anterior and posterior ends, 3) more numerous fine to coarse spiral cords on the ultimate whorl, 4) less numerous nodes at the top of the ultimate whorl, which are commonly larger and more pronounced, and 5) the siphonal fasciole, which is large and broad, with a large, open channel.

New material of Aprotodon lanzhouensis (Perissodactyla, Rhinocerotidae) from the Early Miocene in Northwest China

Aprotodon is an extinct genus of the family Rhinocerotidae with a peculiar morphology that is mainly embodied in the wide mandibular symphysis and a pair of prominent second low incisors. The genus once lived on the vast grasslands of Asia, from Pakistan, and Kazakhstan to China, during the Late Eocene to the Early Miocene. The scarcity and incompleteness of the record, however, make the morphological characteristics of Aprotodon rather perplexing. Here, we report on a better mandible fossil with an intact second right incisor from the Xianshuihe Formation from the Early Miocene age (approximately 21–20 Ma) in the Lanzhou Basin, Gansu Province, China. Several important features, notably the elongated strongly curved tusk‐like incisors and mandibular symphysis, which widens sharply in the anterior part of the mandible, support attribution to A. lanzhouensis. Compared with previous specimens, the material described here is distinct in the lack of p1, horizontal ramus, and the ventral morphology of the mandible symphysis. Based on the new fossil specimen, we provide new material for the understanding of this extinct peculiar rhinoceros.

Biostratigraphy, Paleoecology, Microfacies and Depositional environment of the Asmari formation (Oligocene-Early Miocene) in Karanj oil field, SW Iran

Core data analysis of one well from the Karanj oil field, southwestern Iran, allowed us to precise the biostratigraphy, microfacies and paleoecology of the Asmari Formation. Analysis of thin section from this cored well permitted identification of 28 genera and 20 species of benthic and planktic foraminifera respectively. Subsequently four benthic foraminiferal assemblage biozones were identified, as follows: (1) Lepidocyclina-Operculina-Ditrupa Assemblage zone, (2) Archaias asmaricus-Archaias hensoni-Miogypsinoides complanatus Assemblage zone, (3) Miogypsina-Peneroplis farsensis–Elphidium sp. 14 Assemblage zone and (4) Borelis melo curdica-Borelis melo melo Assemblage zone; indicating an Oligocene (Rupelian-Chattian) to early Miocene (Aquitanian to Early Burdigalian) age for the Asmari Formation. Microfacial study of depositional textures led to characterizing 12 microfacies types, indicating environments in five different settings: restricted lagoon, open lagoon, shoal, slope, and basin mostly in the upper Asmari Formation. These sediments had been deposited under 3 different salinity levels (from 34 to more than 50 psu) in an environment ranging from aphotic to oligophotic and to euphotic zones, and under oligotrophic to eutrophic conditions from the Chattian to the Burdigalian on a carbonate platform (homoclinal ramp). In the studied well, the Asmari Formation had been deposited in a marine environment with normal salinity during the Rupelian-Chattian interval and in a marine environment with high salinity during the Aquitanian to the Burdigalian times.

Dinoflagellate cyst assemblages of the Cunga - Quifangondo cenozoic formations in the Cabo São Brás section, Kwanza Basin (Angola): towards a first stratigraphic and paleoenvironmental interpretation

This work introduces one of the first palynostatigraphic study conducted on formations from the Eocene and overlying lowermost Miocene successions (Cunga and Quifangondo formations) exposed in the Onshore Kwanza Basin, Angola.To improve the Cunga and Quifangondo formations age, new biostratigraphic correlations and palaeoenvironmental interpretations based on qualitative and quantitative analyses of organic walled dinoflagellate cysts from sedimentary rocks sampled in the Cabo de São Brás section were obtained.Those works have revealed that the Cunga Formation could be assigned to a middle Eocene - early Oligocene age, with a palynomorph signature typical of outer neritic to oceanic environments (dominance of dinocysts with microforaminiferal linings and radiolarian pyritized fragments).The lower Quifangondo Formation could be assigned to late Oligocene (latest Chattian) - early Miocene (Aquitanian) ages. This assumption is based on the first occurrence of Ectosphaeropsis burdigalensis, and the last occurrence of Deflandrea spp. and Chiropteridium galea. Additionally, the Chiropteridium, Distatodinium, Homotryblium, Hystrichokolpoma and Lingulodinium acme endorses a latest Chattian-early Aquitanian age to these samples. The palynomorph signature of this unit reflects an outer neritic environment.The latest Oligocene/early Miocene Quifangondo Formation overlaps unconformably on strata of the middle Eocene to early Oligocene Cunga Formation, pointing out a hiatus between the two units.

Selective colonization after storm events in a delta environment: applied ichnology from the early Miocene of Taiwan

The sedimentological and palaeoecological interpretation of early Miocene age shallow marine deposits from one of the most emblematic geological areas of Taiwan – Yehliu peninsula – is not easy to approach in detail, and several contrasting proposals can be found in the literature. The present ichnological study helps to corroborate a delta environment as the most likely palaeoenvironmental setting, and to recognize the different sub-environments and hydrodynamic processes involved. The distal delta front displays the greatest trace fossil diversity, assigned to the Cruziana ichnofacies, including Ophiomorpha, Phycosiphon, Planolites, Rosselia, Schaubcylindrichnus, Scolicia, Thalassinoides and vertical equilibrium adjustment structures. The delta front records predominantly vertical traces attributable to the Skolithos ichnofacies. Amalgamated shell beds (most likely related to storm events) show concentrations of broken bivalve shells. After storm a selective colonization is interpreted, firstly by bioerosive tracemakers during times of decreasing sedimentation rate, followed by a dominance of trophic generalists such as those producing Ophiomorpha during post-storm sedimentation.

Stratigraphy of the Oligocene-Early Miocene successions, Sangaw area, Kurdistan Region, NE- Iraq

Lithostratigraphy and biostratigraphy of the Darzila section from Low Folded Zone, Ashdagh Mountain, Sangaw area, Kurdistan Region, Northeastern Iraq, is investigated. Forty-three species from twenty-nine genera of large benthic foraminifera (LBF) in addition to non-foraminifera fossils such as echinoid fragments, bryozoan, red algae, green algae, bivalve, and coral are recognized from the studied section. Based on the recognized large benthic foraminifera, it is subdivided into six biozones: Nummulites vascus - Nummulites fichteli Assemblage Zone, Eulepidina dilatata - Nephrolepidina marginata Concurrent-Range Zone, Praerhapydionina delicata- Peneroplis evolutus- Concurrent Range Zone, Meandrospina anahensis - Austrotrillin asmariensis Interval Zone, Ammonia beccarii –Austrotrillina howchini Assemblage Zone, and Dendritina rangi- Rotalia viennoti Assemblage Zone. Both suggest an Oligocene to Early Miocene age. Each of these biozones represents certain lithostratigraphic units, which are Sheikh Alas, Baba, Bajwan, Anah, Jeribe, and Fatha formations. The recognized biozones were correlated with comparatively well-known biozones from other parts of the tethys region which showed a good comparison between the biostratigraphic zones established in this study with other studies.

A tuffaceous volcaniclastic turbidite bed of Early Miocene age in the Temburong Formation of Labuan, North‐West Borneo and its implications for the Proto‐South China Sea subduction in the Burdigalian

AbstractA 2 m thick bed of smectite‐rich clay within a sequence of distal deep water turbidites and marine mudstones of the Temburong Formation on the island of Labuan, Sabah, North‐West Borneo, is an altered, re‐sedimented pyroclastic tuff which is geochemically of rhyolite‐dacite composition. The tuff bed was deposited in deep water, although probably &lt;1,000 m, by traction currents and retains relic siliceous shards, feldspar phenocrysts and biotite crystals but was dominated by ash‐grade material. The tuff is interpreted as a turbidite deposit and most probably records long distance sub‐marine transport down the depositional slope from an active volcanic system in the hinterland. It has a zircon U–Pb weighted mean age of 19.6 ± 0.1 Ma whilst combined forminiferal and nannofossil ages from the enclosing marine mudstones range from 21.5 to 19.4 Ma; together these indicate an early Miocene age for the Temburong Formation. The tuff is the result of a very short‐lived volcanic arc magmatic episode and was either related to similar aged volcanics of the Sintang Suite in central Borneo or a product of the Proto‐South China Sea subduction beneath the Cagayan arc north‐east of Borneo. The age indicates that deep water sedimentation in North‐West Borneo continued into the Burdigalian suggesting the subduction trench of the Proto‐South China Sea was active into the early Miocene, beneath the depocentre of the Temburong turbidite fan. By contrast, sandstones representative of the typical marine Temburong Formation yield abundant zircons which are dominately Cretaceous in age indicating an important switch in source provenance during the Early Miocene from the Crocker Formation that is dominated by Permian‐Triassic zircons. This difference in zircon populations likely reflects an important tectonic event in the early Miocene that resulted in uplift of central Borneo to supply sediment to the Sabah Trough whilst the input of material derived from the western terrains diminished. The Temburong Formation was sourced by reworking of uplifted Rajang Group, Sapulut or Trusmadi formations.