Paleogene Age Research Articles

3D anatomy of the Cretaceous–Paleogene age Nadir Crater

The Nadir Crater offshore West Africa is a recently proposed near K-Pg impact structure identified on 2D seismic. Here we present 3D seismic data that image this crater in exceptional detail, unique for any such structure, which demonstrates beyond reasonable doubt that the crater-forming mechanism was a hypervelocity impact. Seismic mapping reveals a near-circular crater rim of 9.2 km and an outer brim of ~23 km diameter defined by concentric normal faults. An extended damage zone is evident across the region, well beyond the perceived limit of subsurface deformation for impact craters, except in a ‘sheltered zone’ to the east. The paleo-seabed shows evidence for widespread liquefaction because of seismic shaking, and scars and gullies formed by tsunami wave propagation and resurge. Deformation within the ~425 m high stratigraphic uplift and annular moat allows us to reconstruct the evolution of the crater, with radial thrusts at the periphery of the uplift suggesting a low-angle impact from the east. Structural relationships are used to reconstruct the deformation processes during the crater modification stage, with the central uplift forming first, followed by centripetal flow of surrounding sediments into the evacuated crater floor in the seconds to minutes after impact.

Reappraisal of the Cretaceous and Paleogene paleogeography of eastern Amazonia based on systematic paleocurrent measurements

Cretaceous and possibly Paleogene strata, originally defined as the Alter do Chão Formation, are extensively exposed in the Amazonas Basin. While theoretical considerations suggest that the eastern Amazon has been draining into the Atlantic since pre-Miocene times, the limited published field data indicate a significant continental-scale reversal of drainage, transitioning from westward flow during the Cretaceous to the current eastward regional flow. This hypothesis has a significant impact on accepted paleogeographic reconstructions and has implications for the origin of the Amazon River and the associated biotic environments. Nevertheless, the observational database to support that hypothesis is still very scarce. To address this problem, the present study presents data from a basin-transverse profile where the entire stratigraphic succession of Cretaceous and Paleogene ages in the Amazonas Basin is exposed, namely the Jazida da Fazendinha and Alter do Chão formations. Facies analysis of cliff outcrops along the Tapajós River margins, including the type area of the units, reveals associations interpreted as fluvial deposits dominated by sandy bars. Paleocurrents were interpreted from more than 2000 individual measurements of fluvial cross-strata from various stratigraphic levels. The findings indicate that the regional flow direction during the deposition of both units was eastward across the entire basin transect. Integrating our dataset into the existing data on provenance reveals that, unlike the modern Andean-derived system, the primary sources for the Alter do Chão Formation were limited to the Amazon Craton. Our findings offer compelling empirical evidence to support the scenario proposed by previous numerical models. The findings also suggest that the rock record does not support the poorly documented and highly influential model of a significant westward-flowing river in Amazonia during the Cretaceous and the Paleogene.

MORPHOLOGY AND EVOLUTION OF ALVEOLAR WEATHERING CAVITIES ON SANDSTONE TORS OF THE UKRAINIAN BESKIDS

The paper systematizes morphological forms of alveolar weathering cavities and presents patterns of their evolution. We have studied the forms of tafoni (cavities 2–10 cm in size), which are found in the crags in the Ukrainian Beskydy. The factors that caused the formation of tafoni in our latitudes are humidity and the inherent specificity of selective weathering in sandstones due to structural and textural features formed during the formation of sediments. In winter periods, the role of frost weathering increases. The crags are composed of sandstones of the Yamna suite of the Palaeocene of the Lower Paleogene age. The lithological composition of the sandstones is represented by quartz and feldspar, which allows us to classify them as typical feldspar-quartz sandstones. The cement is clay-siliceous, sometimes with chlorite, of the basal or contact cementation type. In research region tafoni are distributed on rock surfaces in two ways: locally in small areas or covering large areas e.g. whole crag surface of particular aspect. In the first case, the forms are located in small groups of 10–30 pieces in separate parts of a tor wall. In the second case, they occupy the entire plane of the tor surface or half of the surface of particular exposure. Local groups of tafoni can be divided into three shape varieties: 1) vertical bands, 2) horizontal bands, and 3) lenticular bands. Tafoni concentrations that occupy the entire one plane of the tor can be located on it: a) chaotically, b) in a chain-like manner. The following shapes of particular cavities can be distinguished in the Ukrainian Beskydy: 1) rounded, 2) ellipsoid, 3) vertically elongated, and 4) subtriangular. In the Beskyds, the largest length of ellipsoidal cavities is 20–30 cm, the diameter of rounded cavities reaches 10 cm, and the greatest depth is 15 cm. Investigating the morphology of tafoni in the Beskydy, we distinguished the following stages of their evolution: emergence – deepening – expansion – merging – degradation – re-emergence. On the walls of the Beskydy tors, one can observe tafonic forms at various stages of evolution. We identified morpho-evolutionary varieties of tafoni: A) with all four clear edges, B) with three clear and one leveled wall, C) with all unclear walls. The confinement of cavities to slope exposures was also investigated. Cavities in the Carpathians develop more actively on walls of warm exposures than on cold ones. Tafoni forms on tors, their morphology, evolution and formation factors can be the subject of expert interpretations during geotourism excursions. Key words: cavities, tafoni; morphology, evolution, alveolar weathering; tors; Beskydy, Ukrainian Carpathians.

Deciphering the U-Pb dates of sedimentary phosphates: A complex example from the Upper Cretaceous-Lower Paleogene series in northwestern Morocco

Uranium‑lead geochronology rapidly generates dates of rock deposition/formation with reasonable precision and accuracy using laser ablation inductively coupled plasma mass spectrometry, which is needed for bracketing stratigraphy. However, previous radiometric U-Pb dating of biogenic (i.e., bones and teeth) and sedimentary phosphate minerals have had limited success, probably because of the nanometric to micrometric crystallites that generate open system behavior. Sediment lithification inhibiting trace element exchange between minerals and porewaters and thus forcing phosphorus-rich crystallites to adopt a closed system behavior has been suggested for interpreting U-Pb dating of carbonate fluorapatite (CFA). Despite these insights, what remains lacking is extensive U-Pb CFA dating at the regional scale to test whether several processes influence the timing of U-Pb system closure by inhibiting U and Pb exchanges. Here, we report U-Pb CFA dating from four sampling sites in northwestern Morocco to understand better the meaning of U-Pb dates in CFA. The Upper Cretaceous-Lower Paleogene phosphate series yields anomalously low 207Pb/206Pb initial ratios and young dates ranging from 37.3 ± 2.4 Ma to 22.7 ± 0.7 Ma, which does not agree with the terrestrial lead model composition for Paleogene ages and the known biostratigraphic ages, respectively. We argue that ancient radiogenic Pb from leached polymetallic mineralizations of the regional environment have been incorporated into CFA and that a 25 to 40 Ma-long widespread resetting of the U-Pb system has affected the northwestern Moroccan phosphates. Neither CFA-hosted CO32− concentrations nor rare earth element and yttrium contents indicate post-depositional modifications of the chemical nature of phosphate-bearing rocks. Burial diagenesis promoting sediment lithification is one of the mechanisms that have triggered final closure of the U-Pb system of CFA minerals and, interestingly, the sedimentation rate was probably not a controlling factor. Unexpectedly, U-Pb dates of ∼23 Ma from three stratigraphic levels separated by several million years seem to be concomitant with the regional emersion and generalized continentalization of northwestern Morocco, allowing CFA to behave as a closed system. We conclude that the laser ablation inductively coupled mass spectrometry U-Pb dating of biogenic and sedimentary CFA minerals must be carefully employed to date the timing of fossilization or sediment deposition.

Использование метода главных компонентов для анализа геохимических данных и ассоциаций элементов Колумбинского перспективного участка (Кемский террейн, Сихотэ-Алиньский складчатый пояс)

Native manifestations and deposits of precious metals of folded belts of surrounding of the North Asian and Sino-Korean cratons are of lesser resources and areas; that requires growth of research and technological potential for discoveries of the mineralizations. In Sikhote-Alin folded belt, which is typical example of boundary folded belts developed over a subduction zone, terranes of different age are described. Basements of these terranes are of accretion, island arc and turbidite origin, intruded by magmatic rocks and overlain by volcanic-sedimentary cover. Conducted researches consider area of island arc Kema terrane, which occupies large territories of the Strait of Tartary continental coast. Au-Ag deposits here are related to the origin and development of the active volcanic boundary. Genesis of the ore objects here is epithermal and related to intrusive and effusive complexes of Upper Cretaceous and Paleogene ages. Detailed field lithogeochemical surveys were held on a prospective Kolumbe site where Upper Jurassic–Lower Cretaceous siliceous and terrigenous rocks are intruded by Cretaceous granites of Tatibinski and Olginsky complexes. Research of the geochemical features was done using Principal Component Analysis, the effective method of dimensional reduction and data filtration. Implementation of that method in geochemical data analysis facilitates outlining of the associations of the elements by unifying them into principal components and discover their spacial distribution related to geological complexes of the research area. Determining of the number of principal components used explained variance covered by these components. Derived maps of the spatial distribution of principal components that include elements associations allowed to determine the locations of the local geochemical extrema. Grouping of elements into principal components made it possible to assume the staging in ore deposition in a prospective Kolumbe site. Conducted studies could invigorate further more detailed researches of the minerageny of the considered area.

Diagenesis of fossil gar fish scales with implications for geochronology and paleoenvironmental applications

Fossil scales from gar fish are made of bioapatite and are common in the continental sedimentary record from the Cretaceous to the present, prompting interest in using these fossil scales as geochemical archives. We investigated the diagenetic characteristics of the two different components of gar scales: ganoine, which has similarities to tooth enamel, and bone. We examined microscopic textural characteristics, spatially resolved trace element patterns, and apparent gar scale ages using the (U-Th)/He and U-Th-Pb systems, in modern scales as well as fossil scales from Cretaceous to Paleogene age strata in the North American Williston and San Juan Basins. Structural and textural characteristics of modern and fossil gar scales suggest that ganoine is more resistant to diagenetic alteration than bone. Trace element concentrations in fossil bone are at least an order of magnitude higher than in ganoine and can be spatially heterogeneous, indicative of a complex and prolonged diagenetic history. Trace element concentrations in fossil ganoine often decrease systematically with distance from the ganoine surface, which may be consistent with a fossilization model in which trace element concentrations are controlled by an inwardly propagating recrystallization front. However, (U-Th)/He dates of ganoine are substantially younger than expected based on basin thermal histories and compared to conventional detrital apatite (U-Th)/He dates from the same localities. The ganoine (U-Th)/He dates are also older than a few Ma for only the lowest effective uranium concentrations. We interpret the young (U-Th)/He dates and the date-effective uranium pattern to be indicative of either protracted or late-stage incorporation of trace elements, which is inconsistent with a recrystallization front model alone. The young (U-Th)/He dates may also reflect microstructurally-controlled low helium retentivity in gar scale ganoine, although this does not explain the observed date- effective uranium systematics. Late-stage incorporation of trace elements is supported by the U-Th-Pb systematics of ganoine, which require addition of U and Th at a time significantly later than the depositional age. Late-stage, or protracted, diagenetic uptake of parent nuclides in gar scale ganoine contrasts with recent studies of bioapatite from conodont elements, which instead appear to exhibit late-stage parent nuclide loss. We conclude that the (U-Th)/He system in gar scale bioapatite is not currently useful as a chronometer and suggest that applications of other trace element proxies to gar scale bioapatite be approached with caution.

Результаты определения коэффициента пористости в нефтенасыщенных глинистых породах

The article studies the wells that opened clayey reservoirs of Paleogene age. When predicting the trajectory of a crack during hydraulic fracturing (HF), it is necessary to take into account the percentage of minerals in the rock, since cracks during hydraulic fracturing are formed at the contacts between mineral grains. This conclusion is indisputable, but obtaining complete information about the percentage of minerals in a rock is an expensive and not always feasible task. At the same time, the physical and mechanical characteristics of clayey rocks are no less significantly influenced by their porosity. Therefore, it is important to note that a reliable determination of the porosity coefficient from the exposed geological section will undoubtedly have a primary positive impact on the reliability of hydraulic fracturing modeling. Based on this, in wells that opened clayey reservoirs, the values of porosity coefficients determined by various methods were analyzed, including the direct one – analysis of core, cuttings and the indirect one – geophysical methods. During the work, a coincidence of the porosity coefficient in the core, cuttings and electrical logging was discovered. Based on the results of the study, it can be concluded that the porosity coefficient determined from acoustic logging (AL) significantly exceeds the values of the porosity coefficient determined from core, cuttings and induction logging. This is due both to the influence of clay content on the acoustic logging readings, and due to the low quality of AC materials induced by erosion of the wellbore. It should be noted that the calculations of porosity coefficients in the above-reference part – in the Batalpashinsky formation based on core and induction logging – coincide almost completely. However, in the sub-reference part of the formation the readings differ slightly. The porosity coefficient calculated is a maximum of 2% lower than the porosity coefficient determined from the core, which is quite acceptable.

A Maastrichtian insect assemblage from Patagonia sheds light on arthropod diversity previous to the K/Pg event

Insect faunas from the latest Cretaceous are poorly known worldwide. Particularly, in the Southern Hemisphere, there is a gap regarding insect assemblages in the Campanian-Maastrichtian interval. Here we present an insect assemblage from the Maastrichtian Chorrillo Formation, southern Argentina, represented by well-preserved and non-deformed, chitinous microscopic remains including head capsules, wings and scales. Identified clades include Chironomidae dipterans, Coelolepida lepidopterans, and Ephemeroptera. The assemblage taxonomically resembles those of Cenozoic age, rather than other Mesozoic assemblages, in being composed by diverse chironomids and lepidopterans. To the best of our knowledge, present discovery constitutes the first insect body fossils for the Maastrichtian in the Southern Hemisphere, thus filling the gap between well-known Early Cretaceous entomofaunas and those of Paleogene age. The presented evidence shows that modern clades of chironomids were already dominant and diversified by the end of the Cretaceous, in concert with the parallel radiation of aquatic angiosperms which became dominant in freshwater habitats. This exceptional finding encourages the active search of microscopic remains of fossil arthropods in other geological units, which could provide a unique way of enhancing our knowledge on the past diversity of the clade.

Deep-time Arctic climate archives: high-resolution coring of Svalbard's sedimentary record – SVALCLIME, a workshop report

Abstract. ​​​​​​​We held the MagellanPlus workshop SVALCLIME “Deep-time Arctic climate archives: high-resolution coring of Svalbard's sedimentary record”, from 18 to 21 October​​​​​​​ 2022 in Longyearbyen, to discuss scientific drilling of the unique high-resolution climate archives of Neoproterozoic to Paleogene age present in the sedimentary record of Svalbard. Svalbard is globally unique in that it facilitates scientific coring across multiple stratigraphic intervals within a relatively small area. The polar location of Svalbard for some of the Mesozoic and the entire Cenozoic makes sites in Svalbard highly complementary to the more easily accessible mid-latitude sites, allowing for investigation of the polar amplification effect over geological time. The workshop focused on how understanding the geological history of Svalbard can improve our ability to predict future environmental changes, especially at higher latitudes. This topic is highly relevant for the ICDP 2020–2030 Science Plan Theme 4 “Environmental Change” and Theme 1 “Geodynamic Processes”. We concluded that systematic coring of selected Paleozoic, Mesozoic, and Paleogene age sediments in the Arctic should provide important new constraints on deep-time climate change events and the evolution of Earth's hydrosphere–atmosphere–biosphere system. We developed a scientific plan to address three main objectives through scientific onshore drilling on Svalbard: a. Investigate the coevolution of life and repeated icehouse–greenhouse climate transitions, likely forced by orbital variations, by coring Neoproterozoic and Paleozoic glacial and interglacial intervals in the Cryogenian (“Snowball/Slushball Earth”) and late Carboniferous to early Permian time periods.b. Assess the impact of Mesozoic Large Igneous Province emplacement on rapid climate change and mass extinctions, including the end-Permian mass extinction, the end-Triassic mass extinction, the Jenkyns Event (Toarcian Oceanic Anoxic Event), the Jurassic Volgian Carbon Isotopic Excursion and the Cretaceous Weissert Event and Oceanic Anoxic Event 1a.c. Examine the early Eocene hothouse and subsequent transition to a coolhouse world in the Oligocene by coring Paleogene sediments, including records of the Paleocene–Eocene Thermal Maximum, the Eocene Thermal Maximum 2, and the Eocene–Oligocene transition. The SVALCLIME science team created plans for a 3-year drilling programme using two platforms: (1) a lightweight coring system for holes of ∼ 100 m length (4–6 sites) and (2) a larger platform that can drill deep holes of up to ∼ 2 km (1–2 sites). In situ wireline log data and fluid samples will be collected in the holes, and core description and sampling will take place at The University Centre in Svalbard (UNIS) in Longyearbyen. The results from the proposed scientific drilling will be integrated with existing industry and scientific boreholes to establish an almost continuous succession of geological environmental data spanning the Phanerozoic. The results will significantly advance our understanding of how the interplay of internal and external Earth processes are linked with global climate change dynamics, the evolution of life, and mass extinctions.

Cretaceous–Paleogene tectonic reconstructions of the South Scotia Ridge and implications for the initiation of subduction in the Scotia Sea

The Cenozoic development of the Scotia Sea and the opening of Drake Passage led to the dispersal of crustal blocks of the North and South Scotia ridges, which today have a strong influence on the pathway of the Antarctic circumpolar current. The pre-translation positions of the crustal fragments of the Scotia ridges are uncertain, with correlations to both the Antarctic and South American plates. We present direct geochronology results ( 40 Ar/ 39 Ar) from the Bruce and Jane banks of the South Scotia Ridge that yield Late Cretaceous–Paleogene ages, indicating a pre-translation magmatic history. The basaltic magmatism from Bruce Bank is calc-alkaline, akin to the Cenozoic magmatism of the South Orkney microcontinent and the South Shetland Islands, and agrees with pre-translation tectonic models that place the crustal blocks of the South Scotia Ridge adjacent to the northern Antarctic Peninsula arc. The intra-oceanic arc magmatism at Jane Bank is Late Cretaceous in age (97.2 ± 1.1 Ma) and is therefore inconsistent with models suggesting a Miocene origin as part of the ancestral South Sandwich arc. The development of westwards-directed subduction adjacent to Jane Bank is predicted in some tectonic models as a consequence of Late Cretaceous plate dynamics that developed prior to the Oligocene–Miocene ancestral arc. Supplementary material: Full 40 Ar/ 39 Ar datasets and GPlates reconstruction files are available at https://doi.org/10.6084/m9.figshare.c.6639909

SEDIMENTATION RATES AND CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY OF THE NANGGULAN FORMATION, KULON PROGO, INDONESIA

The Nanggulan Formation is the oldest sedimentary rock of Paleogene age that was deposited in the eastern part of the Southern Central Java Basin. A total of 103 nannofossil samples were taken from two traverses in the study area, i.e., the Watupuru and Jetis Routes. Based on the biodatum identified from the nannofossil samples, the biostratigraphy of the rock formation is divided into five zonations, namely the upper part of Zone NP16, Zone NP17, the lower part of Zone NP18, the upper part of Zone NP22, and the lower part of Zone NP23, expanding from 41.1 Ma to 32.2 Ma of age (Middle Eocene to Early Oligocene). Only Zone NP17 is identified as a complete zone, whereas the other four are observed as partial. The fluctuation of global sea level is believed to be an influence on the deposition of the Nanggulan Formation. The sedimentation rate and the change of nannofossil species shows a decrease of oligotrophic (Sphenolithus) and an increase of eutrophic (Reticulofenestra) taxa, especially in small reticulofenestrids (Reticulofenestra spp.). This occurrence suggests a shift in the environmental conditions from an oligotrophic condition around 41.1 Ma to a eutrophic one, particularly after 40.40 Ma. The enhanced eutrophication in the Watupuru and Jetis Routes was caused by an increasing terrigenous input in 40.40 Ma and after, consequently providing nutrient availability on the water surface. This interpretation is supported by the increase in the sedimentation rate when sea level slightly decreased in 40.40 Ma.

Hydrocarbon Generation and Accumulation in the South Junggar Basin, Northwest China: Insights From Basin Modeling

The South Junggar foreland basin (SJFB) is characterized by fold-and-thrust deformation caused by the Cenozoic India–Tibet collision and uplift of the Tianshan Mountains. The tectonic deformation and hydrocarbon accumulation in this region show east-west, north-south, and vertical zoning. Four sets of source rocks are present in the basin, which are middle Permian, Middle–Early Jurassic, Early Cretaceous, and Paleogene in age. The various source rocks are vertically stacked and thus form a composite petroleum system. Due to differences in source rock distribution, hydrocarbon generation, and structural trap formation, the accumulation and distribution of oil and gas is spatially variable. In this study, we presented a detailed analysis of hydrocarbon generation and accumulation in the SJFB based on a combined basin modeling work both in 1D, 2D, and 3D single-well 1D modeling with measured temperature, and Ro data provide the suggested parameters, especially heat flow and erosion thickness, and then a simple 3D model was established based on the thickness maps of each formation and previous work on heat flow distribution. After 3D modeling, the results are rechecked with measured data and finally the source rock maturity map is obtained. By using the advanced “Block” function, the 2D modeling of complicated compressional structural sections has been successfully carried out. Four types of burial and thermal evolution history have been classified, which correspond to the different hydrocarbon phase and maturity. The heterogeneous distribution of oil and gas reflects the variable source rock distribution and maturity evolution, relative timing of hydrocarbon generation, and formation of structural traps. The timing of structural trap formation in the second and third row of anticlines was later than the main phase of hydrocarbon generation, which may explain the poor exploration outcomes in the SJFB. The result indicates that Jurassic and Cretaceous formations in the middle segment of the fold-and-thrust belt in the SJFB are the most favorable combination for hydrocarbon accumulations and have high potential for gas exploration.

New mammals from the Naskal intertrappean site and the age of India’s earliest eutherians

The first Cretaceous mammals described from India were recovered from the Naskal locality, on the southeastern edge of the Deccan Traps Volcanic Province (DTVP), where it is preserved between two basalt flows. Because the DTVP eruptions spanned the Cretaceous-Paleogene boundary (KPB), it is often unknown whether trap-associated fossil sites are latest Cretaceous (Maastrichtian) or early Paleocene in age. The Naskal locality accounts for nearly half of published mammal records from DTVP-associated sediments as well as a host of other vertebrate microfossils. Its age takes on singular importance in the context of mammalian evolution in India and the effects of the end-Cretaceous mass extinction and subsequent evolutionary radiation of placentals. Here we describe two new mammal species, Indoclemensia naskalensis gen. et sp. nov. and I. magnus sp. nov., from Naskal and present evidence from 40 Ar/ 39 Ar geochronology, magnetostratigraphy, and chemostratigraphy of the over- and underlying basalt flows to refine the age of the Naskal locality and nearby Rangapur locality. In conjunction with palynostratigraphy and vertebrate biostratigraphy, these sites can be confidently restricted to a <100 kyr interval spanning the KPB. The most probable 40 Ar/ 39 Ar age is latest Cretaceous (66.136–66.056 Ma), but an earliest Paleogene age cannot be ruled out. We explore the implications of this age assignment for Deccan chemostratigraphy and Deccan volcanism, Cretaceous-Paleogene (K/Pg) mass extinction, Indian mammalian faunal evolution, and the timing of the origin of placental mammals. • New 40 Ar/ 39 Ar geochronology, magnetostratigraphy, chemostratigraphy, and palynofloras from the Naskal and Rangapur sites. • Age of Naskal and Rangapur are likely Maastrichtian, constrained to within 100 kyr of the Cretaceous-Paleogene boundary. • Two new eutherian mammal species from the Naskal site of India are described. • These sites are ‘transitional’ distinctive in biotic composition from older and younger infra - and intertrappean localities.

THE PALEOGENE SEDIMENT IN SOUTH SUMATRA - WHERE HAS IT GONE?

It has been widely known that South Sumatra Basin yields Paleogene successions (Ferdiyanto et al., 2003). These successions consist of Lemat and Talang Akar Formations (De Coster, 1974) or Lahat and Lower Talang Akar Formations (Clure et al., 2002). The regional stratigraphy of the South Sumatra Basin is shown in Figure 1. The Paleogene sediment is interpreted to form within the occurrence of horst and graben which was caused by the formation of Semangko dextral fault as a result of Late Cretaceous-Early Tertiary tectonism (Suwidiyanto, 2003). In its study, LEMIGAS (2001) classified these successions as the synrift deposit because they were deposited during rifting phase which presumably occurred in Oligo-Miocene age. In fact, finding the Paleogene synrift sediment in South Sumatra is a serious matter. Most studied wells provided by the client lacks biostratigraphic evidences of Paleogene age. The author contributed to this study by investigating the fossil contents of the studied sediment. The result of the biostratigraphic analysis of this sediment encourages the author to publish it as presented in this paper. Therefore, this paper is intended to disclose a comprehensive biostratigraphic data which is obtained from three different disciplines including foraminifer, nannoplankton and palynology. The Early Tertiary sediment in South Sumatra was generally deposited in the non-marine to transition (deltaic) environment (De Coster, 1973). The previous investigators show that this type of sediment contains rich palynomorph (Hasjim, 1993, Morley, 1995 and Lelono, 2003). Apparently, the age determination mostly referred to the occurrence of age diagnostic pollen. In this case, the appearance of peat swamp element of Meyeripollis naharkotensis is used to indicate the Oligocene sedi- ment (LEMIGAS, 1998). Unfortunately, it was lack of support from other microfossil study such as foraminifer and nannoplankton which resulted in least confidence to this interpretation. The occurrence of M. naharkotensis has been widely used to designate the Late Paleogene over the Southeast Asian Region (Morley, 1991 and Rahardjo et al., 1994). However, the stratigraphic range of M. naharkotensis is somewhat ambiguous as this pollen associates with the occurrence of coals indicating the ever-wet warm climate (Morley, 1991). In fact, this pollen ranges up as far as basal Late Miocene as recorded in the coaly succession of East Kalimantan (Lelono, 2003). On the other hand, in East Java, well section with least coal development shows the distribution of M. naharkotensis along the Oligocene section (Lelono, 2003). Nichols (1999) stated that the age indicators strongly controlled by facies reduce their stratigraphic value. This means that the occurrence of M. naharkotensis does not necessarily indicate the Late Paleogene. Therefore, it is suggested to consider the existence of coal lithology in applying M. naharkotensis for age interpretation. The occurrence of (?Late Oligocene)-Early Miocene rift sediments led to the conclusion that the rifting phase triggered by Late Cretaceous-Early Tertiary tectonism occurred slightly later in South Sumatra than that in Central Sumatra (LEMIGAS, 2001). Meanwhile, In Central Sumatra, rift deposit occurred during Eocene-Oligocene time (Williams et al., 1985 and Longley et al., 1990). Although De Coster (1974) assumed that South and Central Sumatra Basins had very similar and related history and could be considered as one large basin with many troughs and grabens, the recent biostratigraphic data suggest distinct period of basin development between South and Central Sumatra. This interpretation may not be obtained without accurate biostratigraphic data. Therefore, this paper is published to provide biostratigraphic information which allows explorationists to possess better understanding of the South Sumatra Basin.

Shakrook Anticline, a Very Complicated Structural Form, North Iraq, Kurdistan Region

The Shakrook anticline has very a complicated structural form, this is attributed to three thrust faults, and the presence of four anticlinal axes with the main anticlinal body. The most northwest existing anticline is called in the current study the Sisawa anticline, the main two anticlines are called the Shakrook East and Shakrook West, whereas the fourth one is called the Biluk anticline it is developed along the southwestern limb of the Shakrook East anticline. The exposed rocks in the Shakrook anticline range from Upper Jurassic to the Paleogene age. The bulk of the main Shakrook anticline is formed by the Bekhme Formation (Upper Cretaceous age), whereas the bulk of the Sisawa anticline is formed of the Shiranish Formation (Upper Cretaceous age) with Paleogene and Neogene aged rocks. Geological maps and high-quality satellite images were used to elucidate the complex structural form of the Shakrook anticline. The updated geological map is quite different from those existing geological maps. A field investigation was carried out to check the interpreted data and to implement photography to the interested structural and geomorphological forms. Different geomorphological forms also were interpreted; they all refer to the lateral growth of the Shakrook anticline.

Conditions and processes of precipitation of iron compounds upon discharge of high-mineralized artesian water from artesian borehole R-30, Staro Oryahovo, Bulgaria.

The artesian borehole R-30-Staro Oryahovo with total depth of 1740m gives waters of chlorine-sodium type with a mineralization of 31g/L from formations of Paleogene age. These waters contain high concentrations of iron and because of this, intense precipitation of iron compounds takes place at and around the wellhead. To clarify the ongoing processes, samples of precipitates and overflow water were taken. It was shown that the predominant form of iron in the water before reaching the surface is Fe2+-85-90% and FeCl+-4-11%. The calculated saturation index for a number of Fe2+-containing minerals showed that hydroxides and sulfates of Fe2+ are the possible candidates for sources of iron in the water. The reductive dissolution of wide spread Fe3+-containing minerals (hematite, goethite) was assumed as a possible alternative process releasing Fe2+ into water. At the surface, due to the contacts with the atmospheric oxygen, the environment is sharply changed to oxidizing one thus forming a geochemical barrier and causing mass precipitation of Fe3+ oxides. Simultaneous Fe2+ oxidation, hydrolysis of Fe3+ and co-precipitation with silica and other components are assumed as the major processes causing the formation of low-crystalline Si-containing ferrihydrite or ferrihydrite-like phase. After formation, the precipitated gels due to the processes of aging and continued interaction with the outflowing water have suffered the further change including the formation of goethite. It was shown that due to the intensive precipitation processes, the iron migration to the surface is limited to a very small area and does not affect adjacent agricultural territories with Fe.

Integrated geological and geophysical study of the Tagil river valley morphology in its middle course

Relevance. Integrated geological and geophysical studies of a bridge in the Makhnevo village area are considered in the frame of the Urals eastern slope geology. Research objective is to study the lithology of the underlying part of the valley floor, determine soil physical and mechanical characteristics, and study a complex of fluvial terraces. Results. Relief elevations across the river valley have been studied, and four main fluvial terrace levels typical of the Urals eastern slope have been identified. An unstable section of the streambed with a canyonshaped valley above the neotectonic unwarping zone has been identified. The geological section of the river’s floodplain and streambed were studied based on geological and geophysical data. A change in the physical properties of glauconite sandstones and clays of Paleogene age in the recent underlying part of the river valley has been established. Layers of sand and glauconite sandstone that can be developed have been found at the new bridge site near the existing sand and gravel deposit. Conclusions. A complex of terraces of the Tagil river valley in its middle course is typical for the Urals eastern slope. The paleovalley is cut into a Paleogene glauconite sandstone layer. In the underlying part of the valley floor, changes in sandstones and clays physical properties have been recorded, and the presence of hypogene minerals was revealed. These are the signs of possible neotectonic processes in the series of the Cenozoic and Quaternary deposits.

Technology of testing shale reservoirs of Paleogene age on the territory of the Eastern Ciscaucasia

The article demonstrates the technology of testing reservoir layers represented by fractured clay-carbonate rocks in the Eastern Ciscaucasia. Practice shows that if the saturation of permeable rocks is uniform, the reliability of the tests can be ensured if the tested interval does not exceed 25 m. The probability of obtaining an inflow during tests significantly decreases with the increase in the amount of repression of the washing liquid and the duration of its impact on the reservoir. This is caused by clogging of the near-well zone of the reservoir, which results in the hydrodynamic connection of the reservoir with the well deteriorates. Test results are the most reliable if they are performed no later than 3-5 days after opening the reservoir, however, even in this case, the reservoir may be contaminated. For high-quality testing of reservoir layers represented by fractured clay-carbonate rocks, the following processes are required: to make an individual selection of the depression on the formation, to have a priori accurate information about the strength characteristics of the well walls.

A Paleogene magmatic overprint on Cretaceous seamounts of the western Pacific

AbstractThe West Pacific Seamount Province (WPSP) represents a series of short‐lived Cretaceous hotspot tracks. However, no intraplate volcanoes in advance of petit‐spot volcanism erupted near a trench have been identified after the formation of the WPSP on the western Pacific Plate. This study reports new ages for Paleogene volcanic edifices within the northern WPSP, specifically the Ogasawara Plateau and related ridges, and Minamitorishima Island. These Paleogene ages are the first reported for basaltic rocks on western Pacific seamounts, in an area that has previously only yielded Cretaceous ages. The newly found Paleogene volcanisms overprint the Early–middle Cretaceous volcanic edifices, because the seamount or paleo‐island material‐covered reefal limestone caps on these edifices are uniformly older than the Paleogene volcanism identified in this study. This study outlines several possible causative factors for the Paleogene volcanism overprinting onto existing Cretaceous seamounts, including volcanism related to lithospheric stress, or a younger hotspot track within the northern part of the WPSP that records magmatism from ~60 Ma.

Channel to the Strait : the geological history of the Tamar Valley–Launceston area

The Tamar Valley occupies the Tamar Graben, a geological structure defined by a series of parallel NW-trending faults which have lowered the dolerite basement to below sea level. The resulting narrow trough, some 50 km long and 5 km wide, has been partially infilled with soft sands, clays and gravels, with intercalated basalt flows in places, of mainly Paleogene (lower Tertiary) age. Low hills of hard Jurassic dolerite define the structure on either side. The graben was formed during the break-up of Gondwana, the separation of Australia from Antarctica, and the making of Tasmania, in the Cretaceous-early Cenozoic period, some 70–140 million years ago (Ma). A spreading ridge had propagated eastwards through the Great Australian Bight but was unable to break through the Bass Strait area, and instead a large wedge of crust containing the future Tasmania was pulled away from the corner of Antarctica on a series of transcurrent faults. The associated crustal stretching in the Bass Strait area resulted in the formation of the deep ‘hole’ of Bass Basin, which had offshoots onto what became Tasmania, including the Tamar Graben. For much of its life, the Tamar River was a major feeder stream into the Bass Basin, carrying large volumes of sediment eroded from the Tasmanian highlands. The course of its major tributary, the South Esk River, within the southern part of the graben was completely blocked by basalt flows near the present Evandale about 35 Ma, forcing it into a new course to the west through the dolerite, to form the Cataract Gorge.