Oligocene Sediments Research Articles

Some characteristics of sediments in Cenozoic basins in Northern Vietnam: implication for Oligocene paleoclimate

Oligocene sediments in northern Vietnam have been extensively studied in terms of geology, stratigraphy, paleogeography, formation environments, tectonics, etc. However, relatively little attention has been paid to the paleoclimate. The Oligocene climate interpreted herein is based on features recorded in sediments taken from the Dong Ho (Hoanh Bo basin), Na Duong (Na Duong basin), and Co Phuc (Red River Trough) formations. These sediments were analyzed using thin-section microscopy, X-ray diffraction, and palynology with the Coexistence Approach. The sediments primarily consist of conglomerate, gritstone, sandstone, siltstone, claystone, and coal shale, deposited in continental environments and dated to the Oligocene based on palynomorph assemblages. The Oligocene paleoclimate is generally warm subtropical, with intermittent hot-humid or cold-dry periods and a slight influence of monsoons. An alternation of hot-humid and cold-dry climates was recorded in the Hoanh Bo basin. In the Red River Trough, the Oligocene climate exhibited a Mean Annual Temperature (MAT) of 9.3-22.2°C and a Mean Annual Precipitation (MAP) of 1122 to 1857 mm, based on the majority of palynological samples, indicating more continental, drier and colder conditions than present. In the Na Duong basin, a warm subtropical climate with a MAT of 9.3-21.7°C and MAP of 1122-1724 mm in the majority of samples was occasionally replaced by hot and humid subtropical periods; the variations in temperature and precipitation followed a similar pattern, suggesting an alternation between dry-cold and humid-hot phases.

An unexpected late paroxyclaenid (Mammalia, Cimolesta) out of Europe: dental evidence from the Oligocene of the Bugti Hills, Pakistan

AbstractEight isolated mammal molars were discovered in lower Oligocene deposits of the Bugti Hills, Pakistan (Paali Nala, DB‐C2; lower Chitarwata Formation). Because of their unusual morphology, these molars have long remained enigmatic. Extensive comparisons with fossil eutherian and metatherian mammals and the recent description of new paroxyclaenids (Mammalia, Cimolesta) from the lower Eocene (Ypresian) of Europe have highlighted the plausible affinities of these teeth from the Oligocene of Pakistan and suggest a referral to Paroxyclaenidae. The dental morphology of this taxon is singular among Paroxyclaenidae, and as such it allows us to propose here a new species and a new genus: Welcommoides gurki. The occurrence of a paroxyclaenid in the Oligocene of Pakistan remains somewhat unexpected inasmuch as these mammals have so far been known only from the Eocene of Europe. At c. 4.2 kg, W. gurki is the largest paroxyclaenid ever discovered, and is assigned to the subfamily Merialinae, which became extinct in Europe around the Ypresian–Lutetian transition, long before the occurrence of this new taxon from Pakistan. Welcommoides has a suite of unusual characters compared with merialines, suggesting that this South Asian lineage had diverged for some time from its European Ypresian counterparts. Such a hypothesis is supported by the faunal similarities between European and Indian subcontinent faunas during the Ypresian. Moreover, our discovery strengthens support for the hypothesis that low latitudes of South Asia were a tropical refugium, at least during the first steps of the global climatic deterioration started at the Eocene–Oligocene transition.

Mineralogy and Major Element Geochemistry of the Oligocene Barail Group Sandstones from the Sylhet Trough, Bengal Basin: Provenance and Tectonic Implications

The origin of Oligocene sediments in the Bengal Basin and associated tectonic setting remain poorly understood. This study investigates the framework mineralogy and major element geochemistry of the Barail Group sandstones from the Sylhet Trough within the Bengal Basin to clarify the provenance and tectonic history of the Oligocene. Modal analysis (Q83F7L10) and geochemical data support a classification of sublitharenite to subarkose, some with Fe enrichment. The heavy mineral assemblage is dominated by opaque minerals, followed by ultrastable minerals with zircon > tourmaline > rutile. The sub-angular to sub-rounded sand grains with a compositionally moderate mature nature suggest that the sediments were deposited close to the source area. The mineralogical and geochemical provenance discrimination diagram suggests contributions from felsic igneous, sedimentary/metasedimentary, and low-grade metamorphic sources, with detritus derived from the Indian craton and proto-Himalaya region. Data suggest moderate to intense chemical weathering, indicative of low relief and a sub-humid to humid climate in the source area. The tectonic analyses indicate that the Bengal Basin transitioned from a predominantly passive margin to an active tectonic margin setting during the Oligocene.

Coupling of X-ray fluorescence and Strontium isotopes to track brine influences in continental deposits: study of the Oligocene sediments in the Digne area (SE basin, France)

Deciphering past salt tectonics events is often difficult in orogenic domains. The southwestern Alpine foreland in France presents a long Mesozoic extensive salt tectonics history, inverted during the Cenozoic Alpine orogeny. Syn-orogenic Cenozoic salt-related deformations are rather difficult to identify because of the contemporaneous shortening experienced by the foreland. This study is based on sedimentologic and geochemical approaches (Sr concentration and 87 Sr/ 86 Sr ratio) of the Oligocene non-marine succession of St Geniez (Digne region, France. Oligocene salt influences are highlighted by (1) high strontium concentrations (>1000 ppm) in most of the series, (2) the occurrence of Halophyticgastropods and (3) the deposit of two gypsum beds. 87 Sr/ 86 Sr ratio measured in the limestones and the gypsum beds confirm a Triassic origin for the strontium, originating from the diapir of Sorine, located to the south-west for the first part of the series, and from the Authon Thrust, located to the north, for the upper part. Geochemical values also suggest the occurrence of two Triassic evaporite levels, one already known and attributed to the Carnian-Norian (Late Triassic) and one attributed to the Olenekian-Anisian (Ealy-Middle Triassic). These results support that combined use of field geology and geochemistry can provide information on erased past salt-tectonics.

New pollen taxon Syncolpraedapollis angolensis nov. gen. sp. nov.: A noteworthy discovery reported in the preliminary investigation of the latest Eocene-latest Oligocene deposits in the Kwanza Basin, Angola

A palynostratigraphic study of the upper Cunga and lower Quifangondo deposits in the Cabo de São Brás section, Kwanza Basin, Angola, has revealed a new pollen named Syncolpraedapollis angolensis nov. gen. sp. nov. This finding was part of a wider survey in the upper Cunga and lower Quifangondo deposits of the Cabo de São Brás section, Kwanza Basin, Angola, covering the latest Eocene to the latest Oligocene.The novel pollen features unique characteristics, notably a 3-syncolporate structure with well-defined and distinctive pores. The pollen grain is adorned with a free but irregular reticulum with an irregular polygonal mesh. Syncolpraedapollis angolensis nov. gen. sp. nov. is sporadically but consistently observed within the latest Eocene-latest Oligocene interval, conspicuously absent in the underlying Eocene sediments (lower Cunga Formation) and occurring infrequently in the latest Oligocene sediments (lower Quifangondo Formation). Thus, it is plausible to infer a limited age range, likely restricted to the latest Eocene-latest Oligocene, as previous studies in the Kwanza Basin have not documented this pollen.

Geochemical and palynological characteristics of the Maykop sections in the north-west of the Shamakha-Gobustan region (Azerbaijan)

The article provides a comparative analysis of the results of complex palynological and geochemical studies of rocks from natural outcrops of Lagich, Angekharan and Agsu in the north-west of the Shamakhi-Gobustan region. A comparison of the distribution features of palynomorph species with the lithofacies variability of sediments made it possible to reveal the conditions of sedimentation during the formation of the described sections. In addition, the age of the units identified in the Maikop deposits in Lagich and Angekharan was clarified by analogy with the formations and horizons of similar ages in the Western and Central Ciscaucasia. The boundary of Eocene and Oligocene deposits in the Lagich section is assumed to be in the interval of 80–115 m. Late Eocene deposits occurring at the base of the section are apparently an analogue of the boundary deposits of the Beloglinskaya and Pshekhskaya formations of the Ciscaucasia. The presence of cold-water dinocysts of the species I.recurvus and calcareous nannofossils Coccolithus pelagicus in the boundary interval corresponds to the existing ideas about climate cooling at the end of the Eocene - beginning of the Oligocene. The formation of sediments in the upper intervals of the section probably occurred in more open marine conditions, relatively warm water, but with low levels of nutrients (nitrates). This interval of sediments with a characteristic phytoplankton complex can be correlated with the middle part of the Khadum horizon, an analogue of the Nizhny Morozkinsky subformation and, possibly, with the upper clayey part of the Polbinsky formation of Western and Central Ciscaucasia. The accumulation of the lower units of the studied part in the Angekharan, dated to the Early Oligocene, most likely occurred in a marine, shallower environment with possible short-term transgressive impulses. Overall, it is possible to suggest a proximal environment of high nutrient content in well-mixed waters within the inner neritic zone. An analogue of the deposits of this interval can be the Lower Morozkinsky Formation and the lower parts of the Upper Morozkinsky Formation of the Ciscaucasia. The significant increase in deflandroids in the upper part of the Angekharan section is similar to the changes noted during the transition to the zone of Deflandrea spinulosa f. Majkopica in the upper part of the Batalpashinskaya Formation of the late Oligocene in Ciscaucasia. The accumulation of sediments probably occurred in a marine basin with signs of stagnation in brackish, eutrophic environment, with a short-term supply of material from the photic zone. The conclusions about the peculiarities of changes in the depositional conditions in the study area are also confirmed by the results of geochemical studies. The deposits of the studied sections are represented by both terrestrial and aquatic types of organic matter (OM). Terrigenous OM was more typical in rocks from the Lagich and Agsu outcrops. The OM of rocks from the Lagich section varies from marginally mature to mature. In the Angekharan section the OM is thermally immature, as evidenced by the low Tmax values. Despite the small thickness of the Agsu outcrop, rock samples from this section contain kerogen of various stages of transformation from immature to mature. The carbon isotope composition (CIC) of Corg in sediments within the studied sections is in the δ13C range, characteristic of Oligocene sediments in the Paratethys. There is a higher enrichment of the 13C isotope in OM in sediments from the Agsu section.

Digital skull anatomy of the Oligocene North American tortoise Stylemys nebrascensis with taxonomic comments on the species and comparisons with extant testudinids of the Gopherus–Manouria clade

The anatomy of North American tortoises is poorly understood, despite a rich fossil record from the Eocene and younger strata. Stylemys nebrascensis is a particularly noteworthy turtle in this regard, as hundreds of specimens are known from Oligocene deposits, and as this species is one of the earliest fossil turtles to have been described in the scientific literature. Since its initial description based on a shell, many specimens with more complete material have been referred to Stylemys nebrascensis. Here, we review and confirm the referral of an important historic specimen to Stylemys nebrascensis, which includes shell, non-shell postcranial, and skull material. This allows us to document unique skull features of Stylemys nebrascensis (e.g., an unusual ‘poststapedial canal’ that connects the posterior skull surface with the cavum acustico-jugulare) and to refer another well-preserved skull to the species. Based on computed-tomography scanning of these two skulls, we provide a detailed description of the cranial and mandibular osteology of Stylemys nebrascensis. Stylemys nebrascensis has a combination of plesiomorphic skull characteristics (e.g., retention of a medial jugal process) and derived traits shared with extant gopher tortoises (e.g., median premaxillary ridge) that suggest it may be a stem-representative of the gopher tortoise lineage. This supports the hypothesis that extant and fossil tortoises from North America form a geographically restricted clade that split from Asian relatives during the Paleogene.

FORAMINIFERA FROM THE CLAY PULP OF MUD VOLCANOES IN THE KERCH-TAMAN REGION: SEMIGORSKY, ANDRUSOV, BORUKH-OBA

The stratigraphy of the Kerch-Taman region has been refined by the foraminiferal assemblages from the clay pulp of the Semigorsky, Andrusova, and Borukh-Oba mud volcanoes. By comparison with the fauna from the reference section of the Paleogene along the river Belaya (Republic of Adygea) deposits of the Middle Eocene (Circassian, Kuma formations of the Lutetian and Bartonian) were revealed. Deposits of lower Oligocene (Pshekh Formation, Rupelian Stage), confirmed by finds of remains of pteropods. Middle Miocene (Konkian and Sarmatian stages of the Eastern Paratethys regional scale of the Miocene) were revealed too. Cretaceous deposits (Semigorsky volcano) belong to the late Campanian - Maastrichtian.

Research on treating inorganic salt deposition in production wells of Tho Trang oil field

The Tho Trang oil field, operated by the Russia"-"Vietnam Joint Venture"- Vietsovpetro, produced oil from the lower Miocene and upper Oligocene sediments. After a long time of exploitation, the production wells at the Tho Trang oil field have problems with salt deposition, which greatly affects the efficiency of exploitation, a matter of concern to Vietsopetro."Salt deposition, in general, has a complex composition. At the initial stage of production, the most common components of deposition are Calcite (CaCO<sub>3</sub>), Gypsum (CaSO<sub>4</sub>.2H<sub>2</sub>O), Anhydrite (CaSO<sub>4</sub>), Barite (BaSO<sub>4</sub>), Asentin (SrSO<sub>4</sub>), Halite which is a mineral of NaCl. In addition to the common minerals mentioned above, inorganic salt deposits may contain other inorganic minerals such as: MgCO<sub>3</sub>, MgSO<sub>4</sub>, Ca(OH)<sub>2</sub>, Mg(OH)<sub>2</sub>, Fe(OH)<sub>3</sub>, quartz"- SiO<sub>2</sub>, Biotite"- MgCl<sub>2</sub>.6H<sub>2</sub>O, CaF<sub>2</sub>,… and some organic substances such as asphaltenes, resins, paraffins, some aromatic compounds, high molecular weight compounds, etc."The phenomenon of inorganic salt deposition has reduced the ability to exploit and transport oil and gas due to reducing the permeability of the reservoir, causing blockage of production wells, pipelines, and suction pumping systems. There are many methods applied to control and deal with salt deposition. One of them is the use of chemicals with special structures inhibiting the formation and crystal growth of salt deposits."This paper presents solutions to improve the efficiency of inorganic salt deposition treatment at the Tho Trang oil field. The method of using chemicals to inhibit salt deposition is the preferred method to maintain oil production. This is considered to be the most advanced and effective method to keep production well without being stopped.

Oligocene reservoir-rocks within Krosno zone of Folded Carpathians

Increasing the production of natural hydrocarbons requires an increase in the volume of exploration and exploration for oil and gas, and this requires such work to be carried out in areas that were previously considered unpromising. In addition, it is necessary to pay attention to collectors in carbonate deposits, where fractured zones can be observed, which can be reservoirs of oil and gas. Considering this, the Oligocene carbonate layer of the Krosnen zone of the Folded Carpathians is one of the interesting objects for the search, exploration and devel?pment of hydrocarbon deposits. In order to assess the quality of reservoir rocks, which are composed of fractured limestones, it is necessary to conduct a more detailed study of their filtration and capacity properties. The article presents the results of the study of Oligocene limestones of Lutnyanska square, which is located within the Krosnen zone. A comprehensive approach was used for the study of reservoir rocks composed of fractured limestones, which included lithologic-stratigraphic, petrographic and geochemical analyses, as well as the study of fracturing and structural features of the rocks. The results of the researches indicate a high fracturing and a favorable mineral composition of the limestones, which indicates good filtration-capacity characteristics and confirms their belonging to reservoirs for hydrocarbons of industrial importance. In the results of the study and analysis of the produced grindings from the limestones of the Oligocene deposits, diagenetic changes were found in them, which affect the porosity and permeability, which makes it possible to assess the reliability of the natural reservoir for the accum?lation and preservation of hydrocarbon deposits. The practical value of the obtained results lies in their use for planning and high-quality conducting of exploration and exploration for oil and gas, which can increase the eficiency of the development of oil and gas fields in carbonate deposits

Influence of Soils Conditions on the Macroseismic Effects in the Dukagjin Area Based the Seismic Wave Propagation from Durres Earthquake 26/11/2019

Kosovo represents a region with relatively high seismic activity, it has been hit in the past and may be hit in the future by very strong indigenous earthquakes. Geographically, Kosovo is in the contact zone of two large tectonic plates, on one side of Africa that pushes the Euro-Asian and lies at its foundation. For these reasons, the countries in theMediterranean area belong to countries with high seismic risk, including the surrounding areas. The strongest earthquake recorded and documented in Kosovo is the earthquake of 1921, in the Viti-Ferizaj-Gjilan area with a magnitude of 6.1 on the Richter scale and an intensity of 8.5 on the Mercalli scale. During the recent geological period the region has been embraced from the neotectonic processes which have conditioned the formation of many structural units that are expressed by intensive uplifting and sinking movements. Are used macroseismic data to investigate the influence of local geological structure on earthquake intensities in Dukagjin area of Kosovo. The occurrence of earthquakes is connected with the geological and neotectonics characteristics of the individual regions. The territory of Kosovo is composed of rocks of Precambrian to Quaternary age. In addition soft sediments in the Kosovo basins have a strong influence on seismic ground motion. Macroseismic data are used to investigate Response of Soil class of Dukagjini basin with deposits of Oligocene, Pliocene and Quaternary, where the lake sediments continue during its Pleistocene, (epicenter distance 140 km, Durrës Earthquake 26/11/2019), which had shown, systematic Intensity increase.

Zeolitized fossil woods from alkaline volcaniclastic rocks: Unravelling an uncommon mineralization process

Mineralization of fossil woods with unusual mineral phases remains an underconstrained process despite its relatively common occurrences. Aside from common mineralization agents such as silica or carbonates, there are also atypical mineralization associations, such as zeolite-group phases, but the zeolitization process has not yet been investigated in detail. We studied zeolitized woods collected from two localities in the Cenozoic alkaline České Středohoří Volcanic Complex (Ohře Rift, Czech Republic), where fossil woods of diverse paleobotanical classification were deposited in volcaniclastic rocks of the same origin (lahar) and stratigraphic formation (Upper Oligocene). The identical geological setting allowed the investigation of potential variables influencing this type of mineralization by combining paleobotanical classification, detailed mineralogy, mineral chemistry, geochemistry, Sr isotope analysis and KAr chronology.The new results demonstrate the significant potential of fossil woods mineralized with zeolite-group minerals to be used to reconstruct the formation and deposition conditions of the lahars in which these woods are contained. The composition of zeolites is strongly dependent on thermal conditions and material exchange between wood and host rocks. Dominant mineral phases are phillipsite and chabazite in variable proportions. The phillipsite/chabazite ratio correlates well with the magnitude of the Eu anomaly, suggesting crystallization of phillipsite at a higher temperature under hot-lahar conditions of deposition. Chabazite lacking an Eu anomaly represents the later, colder mineralization stage. The 87Sr/86Sr ratios ranging 0.7042–0.7047 provide an additional line of evidence of fluid derivation from volcaniclastic deposits of the Upper Oligocene Děčín Fm.

Fish biostratinomy applied to lacustrine paleoenvironmental reconstructions: Oligocene deposits of Taubaté Basin, Brazil

Fish biostratinomy applied to lacustrine paleoenvironmental reconstructions: Oligocene deposits of Taubaté Basin, Brazil

Sequence stratigraphy and petrographic characteristics of Oligocene sediments in the West trough of the Cuu Long Basin, Vietnam

The Cuu Long Basin is the major source of Vietnam's oil and gas production. In clastic sediments, the Oligocene and Lower Miocene formations are the main objects of oil and gas exploration and exploitation activities. Oligocene sediments are both source and reservoir rocks; therefore, studying the petroleum system of these formations is of great interest. This paper discusses detailed stratigraphy and lithological properties to clarify the Oligocene sedimentary characteristics and their significance in the petroleum system. Study results show that Oligocene sediments are divided into three sequences, including eight parasequences and are dominated by the terrestrial sediments. Sequence E, mainly coarse-grained, contains low palynomorphs and rich organic matter with mainly palynomaceral 1 and is deposited in freshwater fluvial settings under high-energy conditions, showing sediments not so far from the original areas. The high level of detrital matrix materials is the main cause of poor or negligible porosity of the rock. The parasequences of Sequence D contain abundant palynomorph assemblages, characterized by swamp and freshwater alga taxa. They are deposited mainly in the shallow lake with a decreasing energy level pointing upward. The volume of organic matter in sediments is very rich, with sapropel organic matter (SOM) rates reaching up to 80%, indicating that the hydrocarbon generation potential is mainly oil-prone and some oil-gas mixtures. The porosity is poor and reservoir quality is affected by detrital matrix and authigenic minerals. The parasequences of Sequence C are characterized by the extreme abundance of freshwater algae, deposited mainly in the shallow-to-deep lake under moderate energy conditions, and rich sapropel organic matter, suggesting mainly oil-prone in hydrocarbon generation potentials. The porosity ranges from fair to good and the reservoir quality is estimated as the best in Oligocene sediments. A new finding of marker assemblages provides evidence to pinpoint the stratigraphic boundary between the Lower Miocene and Upper Oligocene. This finding helps to complete the stratigraphic framework of the area and to correlate the stratigraphy to adjacent sedimentary basins. This study provides information on depositional environmental conditions, organic matter content, hydrocarbon generation potential, and reservoir quality that relate to source rock, reservoir, and seal; these are the elements of a petroleum system. A complete petroleum system assessment requires a holistic view of all the petroleum system elements.

Middle-late Eocene to Early Miocene micropaleontology of the ANH–TIERRALTA–2–X–P well: Biostratigraphic implications for southwestern deposits of the Sinú-San Jacinto belt (Colombian Caribbean)

The Eocene and Oligocene deposits of the southwestern region of the Sinú-San Jacinto Belt (SSJB) in NW South America were formed in marine environments influenced by fluvial discharges from the northern Andes of Colombia. However, these deposits are not well-exposed on the surface, which has limited the study of micropaleontological assemblages that could improve our understanding of the chronostratigraphic and paleoenvironmental characteristics of these rocks. In this study, we analyzed two cores of one of the thickest Cenozoic stratigraphic sections in the Caribbean region, from the ANH-TIERRALTA-2-X-P stratigraphic well, using palynomorphs and calcareous nannofossils. Our analysis allowed us to determine the age of deposition and understand the biostratigraphic patterns of marine and terrestrial microfossils in these nearshore deposits. We found that the first cored interval, from 2122 m to 2026.9 m, corresponds to marine rocks accumulated between the middle and late Eocene. The second interval, from 1130 m to 731.6 m, showed patterns of terrestrial and marine microfossils, which indicate the middle-late Eocene to the Early Miocene age. Palynological and calcareous nannofossil biostratigraphy were consistent in the middle to upper Eocene and Lower Miocene deposits, but discrepancies were observed in the Oligocene deposits. We attributed this to reworking or broader biostratigraphic ranges of certain palynological markers used in the biozones. Determining the age of the middle to upper Eocene and upper Eocene to lower Oligocene deposits was challenging due to the limited number of well-calibrated biostratigraphic markers. As a result, accurate correlation with the late Eocene – early Oligocene stratigraphic record from other parts of the SSJB is hindered, demonstrating that regional stratigraphic correlations based on biostratigraphy alone are problematic.

Dinoflagellate-based age control and biostratigraphic correlations of the Eocene and Oligocene (Lutetian–Chattian) sediments in the El Habt tectonic Unit, western External Rif Chain, Morocco (NW Africa)

Dinoflagellate-based age control and biostratigraphic correlations of the Eocene and Oligocene (Lutetian–Chattian) sediments in the El Habt tectonic Unit, western External Rif Chain, Morocco (NW Africa)

Duabanga (Lythraceae) from the Oligocene of India and its climatic and phytogeographic significance

Understanding the evolutionary history of biodiversity hotspots has important implications for their future survival. India hosts four biodiversity hotspots: the Western Ghats of South India, the Andaman and Nicobar Islands, the Eastern Himalaya, and the Indo-Myanmar region. Northeast India (NEI) is an important region that hosts 43% of the total plant species occurring in India, of which ∼39% are endemic. This region also acts as a gateway for biotic exchange between India and southeast Asia. The area also receives exceptional rainfall during the pre-monsoon (March to May), in addition to the summer monsoon (June to September) season. In rainforests of NEI, forest-forming plant species make up a large proportion of the biodiversity. Understanding the evolutionary history of rainforests of NEI has implications for the conservation of biodiversity hotspots. Here we report the evergreen rainforest genus Duabanga Buch.-Ham. of the family Lythraceae from the late Oligocene sediments of Assam, NEI. Fossil records of this genus (from south and southeast Asia) suggest its Gondwanan origin, while its modern distribution is dominantly controlled by moisture availability.

Early Oligocene gravity-flow deposits at the base of the Meiji Reef system in the South China Sea, and their palaeoclimate significance

In this paper, we describe gravity flow facies that form the base of the Meiji Reef system in the South China Sea, and discuss their palaeoclimate significance. These Early Oligocene (26.1–23.5 Myr) deposits occur in Well NK1 and comprise a 110.6 m thick succession developed on top of volcanic basement. The deposits can be divided into two intervals, both of which are dominated by debris flow facies. The lower 17.6 m thick interval has a gravel content of 50–65% with parent rocks including dacite, basalt, tuff, and coral reef fragments. From base to top, these units coarsen upward and show increasing gravel contents. Gravel clasts are well-rounded but poorly sorted (diameter 10–350 mm), which, together with their complex composition, indicate transportation by the gravity flows from the near-shore volcanic rock basement to the slope. The upper 93 m thick interval comprises abundant bioclastic materials, including benthic foraminifera, crustal red algae, and red algae detritus, with a few volcanic gravel clasts. The content of volcanic rock gravels decreases towards the top, which may be attributed to the reduction or disappearance of volcanic rocks in the provenance area due to the establishment of coral reef facies that cap the succession and dominate the overlying interval from a core depth of 885.6 m to the seafloor. Based on U-Pb dating, the cap-shaped red algae laminae at the facies transition were formed at 24.6 ± 1.1 Ma, dating the earliest initiation of reef building to end-Oligocene times. The emergence of gravity flow sediments during the early Oligocene may be attributed to the onset of the Antarctic glaciation and concurrent regional tectonic activities that led to a shallowing of the sea. The origin of debris with high roundness characteristics is believed to be associated with transportation along the slope triggered by tectonic and climatic events, resulting in the formation of debris flow deposits. Studying the gravity flow facies at the Meiji Reef system is crucial for determining the onset of reef-building and helps establish the relationship between gravity flow deposition, paleoclimate, and regional tectonic evolution in the South China Sea.

NEW DATA ON PROMISING OIL AND GAS OBJECTS OF THE YAMNA SUITE OF THE PALEOCENE IN THE SOUTH-EASTERN PART OF THE SKІBA AND KROSNO COVERS OF THE UKRAINIAN CARPATHIANS

Thick sandstones of the Yamna suite are widespread throughout the Skіba cover, as well as in the south-eastern part of the Krosno cover. The research area is bounded by the Limnytsia River in the northwest and the Ukrainian-Romanian border in the southeast. Several promising structures comprising the Yamna sandstones (Brusturanska, Yanovetska, and Voronenkivska) are identified in this area. Among them, according to the number of positive indicators of oil and gas potential, the Voronenkivska structure (Nadvirna district of Ivano-Frankivsk region, near the settlements of Voronenka, Yablunytsya, Polyanytsya) is the most promising, localized in the Zelemyanka slice. The structure is divided by faults into four tectonic blocks and stretches for 8 km. Under the Oligocene rocks, crumpled into the anticlinal fold of the north-western extension, Paleocene-Eocene deposits are inferred according to the geological models, which contain thick sand strata of the Vyhoda (Middle Eocene) and Yamna suites of the total thickness over 300 m. Oil manifestations are documented in the Oligocene deposits on the surface. Potentially promising horizons may be in the depths range 1500-1800 m. The article extends the previous work devoted to the assessment of the oil and gas prospects of the Yamna suite of the Paleocene of the north-western part of the Skуba cover of the Ukrainian Carpathians. 4.2 million tons of oil were recovered from the Yamna sandstones of the Paleocene, which are characterized by good reservoir properties, in the fields localized in the north-western part of the Skiba cover. The Yamna sandstones in this sector of the Carpathians are also common in the Krosno cover. The uneven distribution of industrial oil potential between these two parts of the Carpathians is explained by lithological changes or the influence of structural and geochemical factors. A study of stratigraphy and reservoir properties of the Yamna sandstones, common in the deposits of the Skіba and Krosno covers, suggests that they comprise satisfactory reservoirs for hydrocarbons. Promising areas and structures have been identified and described.

Global sea level changes or local tectonics? Pliocene, Miocene and Oligocene biomarkers in cored sedimentary rocks from IODP Expedition 317, Canterbury Basin, New Zealand

The various influences of global sea level (eustasy) and local tectonic changes on sedimentation processes in continental margin deposits are important topics in sedimentary research. International Ocean Discovery Program Expedition 317 to the Canterbury Basin, on the eastern margin of the South Island of New Zealand, provided an opportunity to study sediment geochemistry in contrasting depositional settings, from mid-shelf to upper continental slope sedimentary rocks from the Eocene to the Holocene. This paper provides the first examination of the organic geochemical record from Pliocene, Miocene, and Oligocene sediment samples recovered during the expedition from the U1351, U1352, and U1353 sites, using bulk geochemistry and hydrocarbon distributions, including biomarkers. The main aim of this research was to correlate changes in organic accumulation with local tectonic activity and global climate changes that occurred in the Miocene. There is good preservation of C11 to C35n-alkanes, with varying predominance of odd-over-even chain length n-alkanes, and much variation in the terrigenous/aquatic ratio over the cores. Based on biomarker and Rock Eval parameters, thermal maturity varies from low in the Pliocene, to early oil window in the deeper Miocene and Oligocene sedimentary rocks. The pristane/phytane ratios for the three cores indicate anoxic to oxic depositional environments. Marine organic matter input is indicated by the high C30 sterane index, whilst high relative amounts of oleanane, C24 tetracyclic terpane, and C29 steranes indicates major terrigenous organic matter input. Local tectonic activity is suggested to have had a significant influence on the accumulation of the organic matter in the Canterbury Basin. The influence of eustasy and global sea temperature variations are suggested for the periods < 14 Ma, 12–7 Ma, and ∼ 6 Ma. An increase in terrigenous organic matter input during the late Miocene correlates with the uplift of the Southern Alps and an increase in the continental slope angle for the South Island of New Zealand.