Oligocene Formations Research Articles

New insights on the Marseille-Aubagne Oligocene basins (France)

The Marseille-Aubagne Basins, which extend from Marseille to Roquevaire, occupy more than fifty per cent of the Marseille-Aubagne geological map, with approximately one million people living in this area. Despite this geological importance they are still poorly known. The first synthetic view was delivered in the 1935 geological map. Studied by Bonifay, the Quaternary deposits have been included in the 1969 geological map. Nevertheless, the Oligocene formations remained unmodified until Nury, who provided a lot of very detailed stratigraphic data. New studies have been carried out in the frame of the third issue of the 1:50,000 geological map. These studies allow us to distinguish between three different basins: the “Jarret basin” in the northern part, the “Prado basin” in the southwestern part and the “Aubagne basin” in the eastern part. Each of them contains its own stratigraphic succession, including several formations from the Rupelian to the Chattian. Globally, the Lower to Upper Rupelian formations are tectonically deformed, whilst deposits from the Latest Rupelian to the Latest Chattian show only slight deformation. Thus, two main geodynamic stages have been distinguished: the first beginning with the Early Oligocene extensive regime leading to the opening of NNE-SSW troughs all over the European platform and, the second, beginning with a NNW-SSE extensive regime coeval with the Western Mediterranean rifting. The key point that separates these two stages from each other is a possible Late Rupelian compressive regime. To sum up, this basin can be considered as a natural archive for the Oligocene events. Therefore, these basins should be considered as masterpieces for the Oligocene palaeogeographic and geodynamic reconstructions.

TRAKYA HAVZASINDA, DANİŞMEN FORMASYONU İÇİNDEKİ LİNYİT KATMANLARININ POTANSİYELİNİ KONTROL EDEN JEOLOJİK FAKTÖRLER

This project has been conducted for the General Directorate of Turkish Coal Enterprise. The aim of this study is to understand lignite potential of the basin. Subsurface data ( including numerous wells and several seismic lines) provided by TPAO, MTA and TKI were used. Structure and thickness maps of Oligocene-Miocene-Pliocene units prepared for the basin. Purpose of this work is to understand economical values of lignite seam beds interbedding in the Danismen Formation (Oligocene-Early Miocene). For this purpose, from bottom to top following maps were prepared: Structural map of the top Osmancik (Oligocene) Formation, thickness map of the Danismen Formation, paleo-topographic map of unconformity surface which is at the top of the Danismen Formation, total thickness map of Ergene-Kircasalih formations (Late Miocene-Pliocene). Finally total thickness map of the lignite layers was prepared. It was the main purpose of the work. Lignite seam layers are located in middle of the Danismen Formation. Also several stratigraphic correlations were conducted to understand lateral continuation of lignite layers. The first obstacle to reach lignite is thickness of the Ergene and Kircasalih formations which overlie lignite bearing Danismen Formation. Main structural event controlling the thickness variation of the Danismen Formation is Thrace Fault System (Perincek, 1991); it was active during Middle Miocene. Danismen Formation extensively or partially was eroded along the fault zone and on the en-echelon folds of the fault system. Amount of erosion is variable and in some areas Danismen Formation completely was eroded. As a result Ergene Formation lies directly on Osmancik Formation. Lignite layers are also eroded at these localities. Elevated areas related the Thrace Fault System partially was eroded; however these areas were still paleo-elevated areas during the accumulation of Ergene Formation. Onlapping sequence of Ergene Formation is thinner on these areas. At the end of this project, thicker lignite areas were delineated. Addition to this, thin overburden areas on lignite are located. Considering these result, new permit areas were selected.. In order to refine this work, a suggested facies map of Danismen Formation is advise to be prepared

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AbstractWe discuss the Andreani et al.’s tectonic interpretation of both la Nerthe and L’Etoile ranges, which form the western part of the southern Provence thrust defined by Aubouin and Chorowicz [1967]. Referring to previous works, emphasis is given to the structural independence of the two ranges. The western L’Etoile range is underthrusted beneath the southern La Nerthe tectonic unit along the Graffiane key-area Aptian corridor.In contrast with the autochthonous concept of La Nerthe range by Andreani et al., structural and paleogeographic data are presented, supporting the interpretation of the southern part of the range as an important north-verging thrust emplaced during the Bartonian major tectonic event. This one was followed by a shortening Ludian (Priabonian) event resulting in a strong refolding of the southern La Nerthe structures.Contrary to the Andreani et al’s interpretation, field facts provide evidence that the W-E trending fault systems affecting La Nerthe and L’Etoile ranges have formed during the N-S distensive regime that started from early Rupelian and that was accentuated during late Chattian and Aquitanian. However, stratigraphical and tectonic regional data suggest a Middle Oligocene strike-slip reactivation of the WE trending system faults of La Nerthe range, coeval to north-verging overthrusting and reverse faulting, affecting early Oligocene formations of the neighbouring Marseilles basin.

Morphology and geomorphological significance of relict landslides in the Tertiary basin of Puy-en-Velay (Massif Central, France)

The study of a set of relict landslides in the Tertiary basin of Puy-en-Velay (Massif Central, France) provides information about the types of landslide that affect a part of the hillslopes and the predisposing factors controlling their pattern. Two clusters of landslides were defined, located in similar morphostructural contexts, but characterised by basaltic covers of different ages. The first factor controlling pattern was lithological, in particular the occurrence of two sandy-clay geological formations. One, 'Sables de la Laussonne', is an Oligocene formation, and the other corresponds to the sandy-clay fraction of a Quaternary formation. The second factor was the age of the basaltic cover, which controls the degree of catchment dissection. The ‘old’ catchments are most strongly widening, with a more differentiate topography than younger ones, and the density of relict landslides was greater in these catchments. The main type in the set of relict landslides seems to be complex slides with a rotational component at the top and a slow-moving earthslide making up the body. So far we cannot advance any firm hypothesis about the kinetics of these landslides. These relict landslides constitute major processes underlying basaltic scarp back-tilting in the basin and are a key factor in catchment geomorphology development.

A record of continental collision and regional sediment flux for the Cretaceous and Palaeogene core of SE Asia: implications for early Cenozoic palaeogeography

Abstract: Palaeogene sedimentary rocks exposed in West Java were derived from local volcanic sources and central Sundaland, the continental core of SE Asia. Detrital zircons from seven sandstone samples contain U–Pb age populations with ages of 50–80 Ma, 74–145 Ma, 202–298 Ma, 480–653 Ma and 723–1290 Ma. Late Cretaceous and Palaeogene zircons in Middle Eocene forearc sandstones are interpreted as derived from two spatially and temporally discrete volcanic arcs located in Java and Sulawesi respectively. In contrast, all other populations have a Sundaland provenance. Most Permian–Triassic zircons were derived from granites of this age in the SE Asian Tin Belt. Mid-Cretaceous zircons in all Upper Eocene and Lower Oligocene formations were derived from the Schwaner Mountains of SW Borneo. The differences in zircon populations reflect changing Sundaland sources with time. In the Middle Eocene, sediment was derived mainly from the Tin Belt. From the Late Eocene onwards a Borneo source became more important. Older zircon ages are from SE Asia basement that once formed part of Gondwana. Zircons also record the timing of microcontinental collision at the Java margin ( c . 80 Ma) that halted Cretaceous subduction and probably resulted in the elevation of large parts of continental SE Asia. Supplementary material: Methods, sample locality list, tables for U–Pb zircon age measurements, point count data and heavy mineral assemblages, sandstone petrographic descriptions and palaeocurrent data are available at www.geolsoc.org.uk/SUP18489 .

ГЕОДИНАМІКА

In the article the first results of researches of joints and slickensides from outcroppings in the valley of the Sukil River are given. In 37 points of the flysh deposits of thrusts: Orivska, Skolivska and Parashka about 1100 intentions of joints and 90 intentions of slickensides are executed in the different deposits strata: from the Upper Cretaceous to Oligocene formations. By the complex (method of structural paragenesis and kinematics one) analysis of these mesostructures, with the use of the modern computer providing (StereoNett, Win-Tensor and other) the reconstruction of main parameters was carried out. Deformation regimes and orientations of main axes of the old and young stress fields which occur in Paleogene-Neogene time to and during and after fold formation in this area of Ukrainian Carpathians was specified.

Isotope age constraint for the Blue Dyke and Jardine Peak subvertical intrusions of King George Island, West Antarctica

The Blue Dyke and Jardine Peak are subvertical hypabyssal intrusions cutting a stratiform volcanic sequence in the Admiralty Bay area on King George Island (South Shetlands, Antarctica). The rocks are porphyritic, crystal−rich basaltic andesites. Tiny zir− con crystals were used for single grain SHRIMP U−Pb dating. The mean ages calculated for the zircon populations from both intrusions indicates Late Oligocene (Chattian) formations. Zircon grains from the Blue Dyke gave the mean age of 27.9±0.3 Ma, whereas those from the Jardine Peak are slightly younger displaying the mean age of 25.4 ± 0.4 Ma: a Late Oligocene (Chattian) crystallization age the inferred of both these intrusions. These are much younger than previous Eocene K−Ar and Ar−Ar ages for such rocks and suggest that formation of the King George Island intrusions can be related to tectonic processes that ac− companied the opening of the Drake Passage. Key wor ds: Antarctica, King George Island, Late Oligocene, U−Pb SHRIMP dating.

MATURE ZONE OF ORGANIC MATTER AND OIL AND GAS PROCESS OF CUU LONG BASIN

Geochemical parameters used popularly to define the level of maturation of organic matter are a vitrinite reflectance % Ro) combined with Tmax value defined at the peak Pic S2 by Pyrolysis (Rock-Eval). Moreover, model TTI method of Lopatin and Waple is applied to define the level of maturation of organic matter at any point where there is no well. By this way, mature process of organic matter will be estimated generally for a whole of study area. Results are that organic matters of lower Oligocene and upper Eocene formation and the bottom of upper Oligocene formation provide essentially oil and gas of Cuu Long basin. The bottom of lower Oligocene and the top of Eocene formation supplement wet and Condensat. Eocene formation at the depressions especially in the east and north BachHo is the dry gas. Oil and gas generated and migrated into traps occurred from early Miocene, but very intensively generated and migrated in period of Pliocene + Quaternary times. At the same time, the traps always are supplemented the wet gas, condensate and dry gas from Eocene formation.

The first Paleogene mammal record of Middle America: Simojovelhyus pocitosense (Helohyidae, Artiodactyla)

ABSTRACT Simojovelhyus pocitosense, gen. et sp. nov., is based on a mandibular fragment with m1-3 collected from an unnamed Late Oligocene formation, in an amber mine near Simojovel, in northwestern Chiapas. The source strata consist of black, very fossiliferous, shaley phyllarenitic sandstone and mudstone that were deposited in an estuarine to swampy lagoonal environment, dated in Chrons C10–C9 (~29.4–26.8 Ma), or early Late Oligocene. Simojovelhyus pocitosense possesses small, rectangular, bunodont molars that increase in size posteriorly. This combination of characters sets it apart from the Oligocene bunodont artiodactyls (entelodontids, tayassuids and leptochoerids), and bring it within the Helohyidae. It differs from recognized genera in having a tiny paraconid, and a unique combination of cristids and cuspulids as follows. Cristids: paracristid, anteromesocristid (neomorphic), and anterolingualcristid (neomorphic) on the trigonid anterior slope, cristid obliqua (short to remnant), and a robust postcristid in the talonid. Cuspulids (small, accessory): mesoconid, hypoconulid (large and blunt in m3), postmesoconulid (neomorphic), and pseudohypoconulid (neomorphic). This record extends the geochronologic range and geographic distribution of the Helohyidae from the Late Eocene of North America and Asia to the early Late Oligocene (Early Arikareean) of Middle America. Simojovelhyus pocitosense is also the southernmost record of Paleogene mammals, not only of Mexico, but of all North America. This record significantly adds to the meager, but important, record of Paleogene vertebrates in the tropics.

Late Cretaceous to Paleogene post-obduction extension and subsequent Neogene compression in the Oman Mountains

ABSTRACT After the obduction of the Semail ophiolitic nappe onto the Arabian Platform in the Late Cretaceous, north Oman underwent several phases of extension before being affected by compression in the framework of the Arabia-Eurasia convergence. A tectonic survey, based on structural analysis of fault-slip data in the post-nappe units of the Oman Mountains, allowed us to identify major events of the Late Cretaceous and Cenozoic tectonic history of northern Oman. An early ENE-WSW extensional phase is indicated by synsedimentary normal faults in the Upper Cretaceous to lower Eocene formations. This extensional phase, which immediately followed ductile extension and exhumation of high-pressure rocks in the Saih Hatat region of the Oman Mountains, is associated with large-scale normal faulting in the northeast Oman margin and the development of the Abat Basin. A second extensional phase, recorded in lower Oligocene formations and only documented by minor structures, is characterized by NNE (N20°E) and NW (N150°E) oriented extensions. It is interpreted as the far-field effect of the Oligocene-Miocene rifting in the Gulf of Aden. A late E-W to NE-SW directed compressional phase started in the late Oligocene or early Miocene, shortly after the collision in the Zagros Mountains. It is attested by folding, and strike-slip and reverse faulting in the Cenozoic series. The direction of compression changed from ENE-WSW in the Early Miocene to almost N-S in the Pliocene.

Microfacies Analysis of Oligocene Formations in Butmah and Rafan Areas Northwest Iraq.

Oligocene deposits in Butmah and Rafan areas northwestern Iraq were penetrated by three core holes (BW-CH1, BE-CH1 and RF-CH1). The depositional basin evolved through two stages, generating two sedimentary cycles, which were separated by exposure surface as represented by conglomerate beds in core holes BW-CH1 and RF-CH1. Six microfacies were recognized in the Oligocene formations (Shurau Fn., Sheikh Alas Fn. and Bajwan Fn.), comprising three microfacies association allocated to: reef (Sa1) and back reef (Sh1, Sh2) in the first cycle (Early Oligocene), and back reef (B1, B2, B3) in the second cycle (Late Oligocene). Oligocene rocks have been affected by many diagenetic processes of cementation, dissolution, dolomitization (by mixing process) and dedolomitization. The paleogeographic distribution of the microfacies in conjunction to the previous work elucidates that the studied area is representing the eastern margin of the Sinjar Oligocene basin. ــــــــــــــــ ـــــــــــــ ــــــــــــــــ ـــــــــــ ﻕﺍﺭﻌﻟﺍ ﺏﺭﻏ لﺎﻤﺸ ﻥﺎﻓﺍﺭﻭ ﺔﻤﻁﺒ ﻲﺘﻘﻁﻨﻤ ﻲﻓ ﻥﻴﺴﻭﺠﻴﻟﻭﻻﺍ ﺕﺎﻨﻴﻭﻜﺘﻟ ﻲﻨﺤﺴﻟﺍ لﻴﻠﺤﺘﻟﺍ

有孔虫化石からみた北海道西部の中部始新統〜下部漸新統の地史（再検討）

Geohistorical implications of several middle Eocene-lower Oligocene formations distributed in the western Hokkaido are restudied mainly from published data of foraminiferal assemblages. These formations are correlative to the Poronai and Momijiyama formations.Foraminiferal assemblages from the Utsunai and Magaribuchi formations in northernmost part of Hokkaido indicate paleobathymetric change from the upper bathyal to sublittoral zones. Those from the lower part of the Sankebetsu Formation in Chikubetsu-Haboro area indicate the shallower paleobathymetric zones than the upper bathyal zone, and those from the Shimokine and overlying Tappu formations indicate transgression from none-marine condition to the upper bathyal zone.These paleobathymetric changes and the geologic ages determined by calcareous nannofossil biostratigraphy show that the transgression which generated the Poronai Sea occurred from east to west and reached maximum depths in the late Eocene (CP 15b). Previous interpretation that paleo-topography of the Poronai Sea as an embayment can not be accepted, because there is no evidence that shallower bathymetric zones existed in the eastern part of this sea.

ABSTRACT: Eustatic Controls on Incised Valley Shape and Geometry: La Pascua Formation, Eastern Venezuela

Ten Fourth-order sequences in the Lower Oligocene La Pascua Formation were identified and mapped using over 700 wells in a 3500 km2 study area in eastern Venezuela. One third-order sequence (OR-2) and elements of another were identified on the basis of aggregate stacking patterns. Net sand maps for incised valleys for each sequence showed variations in geometry, width and thickness dimensions, and were related to their position on the constructed relative sea level curve. Unique incised valley geometries were common to each third-order sequence-set. Vshaped, coalesced and elongate-straight valleys were most often found in the lowstand sequence-set where they were widest (7.3 kilometers average.), and had highest width-tothickness ratios of between 220-277. Elongate-slightly-sinuous and elongate-sinuous geometries were most commonly found in transgressive sequence-sets. These contained narrowest valleys (2.2 kilometers average) for the entire sequence, with width-to-thickness ratios of between 76-150. The fourth-order sequence associated with maximum retrogradation showed no evidence of erosion or

Abstract: High-frequency sequence stratigraphy of the Lower Oligocene La Pascua Formation: Effect of relative sea level on the size, geometry and spacing of depositional systems

Abstract: High-frequency sequence stratigraphy of the Lower Oligocene La Pascua Formation: Effect of relative sea level on the size, geometry and spacing of depositional systems

La formation conglomératique du Vazzio près d'Ajaccio (Corse-du-Sud), un témoin des dépôts du Chattien supérieur continental synrift en Méditerranée occidentale

Evidence of Oligocene deposits was for the first time described in Corsica (near Ajaccio) within the Vazzio Formation. The succession is composed of a continental sedimentary sequence, mainly conglomerate, with a thickness of 250 to 300 m. Such conglomerates were deposited in torrential and lacustrine environments. Pollinic association and mammal data date the formation from Late Oligocene age (MP 29). The Vazzio Oligocene formation was deposited in a half-graben upon Hercynian granites. Within the Corsica-Sardinia block, the Vazzio Formation can be considered as an equivalent of the Ussana Formation of Sardinia. A Late-Oligocene palaeogeographic reconstruction is attempted, prior to the rotation of the Corsica-Sardinia block.

Eocene and Oligocene Otay-Type Waxy Bentonites of San Diego County and Baja California: Chemistry, Mineralogy, Petrology and Plate Tectonic Implications

AbstractOtay-type waxy bentonites of San Diego County are illite-smectite (I-S) with 85% dioctahedral smectite mixed with dioctahedral illite showing a Reichweite of 0. Primary or secondary waxy bentonite exposures are found in all Eocene and Oligocene formations of southwest San Diego County and western Baja California north of Ensenada. Primary waxy bentonites formed when hot volcanic ash fell into quiet marine or brackish coastal water. The transformation from glass to bentonite occurred within hours or days but consolidation of the bentonite into its waxy consistency took longer. Primary waxy bentonite consists of 95 wt% I-S with the remainder consisting of volcanic glass shards, sanidine fourling twins, hexagonal biotite crystals and amorphous manganese oxides and hydroxides. Secondary waxy bentonite is primary waxy bentonite that was mixed with nonvolcanic detritus either before consolidation or after consolidation and subsequent erosion. The hydrophobic character of primary waxy bentonite allows it to reflect, accurately, the chemistry and petrology of the original volcanic material. Chemical analysis of primary waxy bentonites shows that the original lava was subduction-related and exhibited petrologic variations nearly identical to those of the modern Cascades of the northern Pacific coast of the lower United States. Primary and secondary waxy bentonites as well as smectites derived from the weathering of volcanic ash that fell outside the waxy bentonite-producing environments are the previously unrecognized products of extensive Eocene and Oligocene subduction-related volcanic activity. Baja California exposures of waxy bentonite demonstrate pre-Pliocene subduction tectonics that gave way to rifting tectonics.

Evidence for the Early Oligocene formation of a proto-Subtropical Convergence from oxygen isotope records of New Zealand Paleogene brachiopods

Abstract Using the oxygen isotope record in fossil brachiopods, we reconstruct Late Eocene through Early Miocene paleotemperatures of an eastern New Zealand shelf environment. Our results show a decline in temperature to a low of ∼6°C in the Early Oligocene, of a magnitude similar to that of open-ocean isotopic studies from similar latitudes. However, the brachiopod-derived paleotemperatures are ∼ 10°C lower than those inferred from occurrences of warm-water fauna and flora (e.g., large foraminifera, mangrove and coconut palms), which suggest a subtropical (20–23°C) climate throughout most of the New Zealand Oligocene. We propose that a proto-Subtropical Convergence (pSTC), with cool subantarctic water flowing along the eastern coast of the South Island, first developed in the Early Oligocene. The subtropical fauna and flora distribution patterns are consistent with this hypothesis. Warm-water biota (e.g., larger foraminifera, and mangrove trees) occur primarily on the west and north coasts of New Zealand in warm subtropical water characteristic of water north of the pSTC, similar to the modern Subtopical Convergence. We explain the occurrence of occasional subtropical taxa in Early Oligocene strata of the east coast of the South Island as a result of the north-south migration of the pSTC or the colonization of relict Surtseyan-type seamounts in local waters warmed by volcanic eruptions.

Rifting actif ou passif en Éthiopie ? éléments de réponse apportés par l'étude des xénolites péridotitiques de la région du lac Tana

The comparative study of peridotitic xenoliths from Oligocene and Quaternary volcanic formations of north-western Ethiopia shows that the textural, mineralogical, thermal and geochemical characteristics of the lithospheric mantle of this region were acquired in Oligocene times. These data suggest that the impinging of the Afar plume beneath the Ethiopian lithosphere occurred prior to the traps emplacement and the Plio-Quaternary rifting. This favours a model of active rifting for the Afar triple junction.

New paleomagnetic results from the Aegean extensional province

Various Oligocene formations from NE Greece (ignimbrites from the Medousa area, rhyolites from Zagradenia, granodiorites from Elatia) show discordant paleomagnetic signatures, in each case indicating small cw (clockwise) rotation and also inclination flattening. Marls from Pithion were partly remagnetized in a present-day field. Samples that contain ancient magnetization components also indicate small cw rotation and inclination flattening. However, the magnetization of andesites from Peplos reflects a considerably larger rotation, likely owing to local tectonics. In the context of previous work in the area, these results are used to propose a subdivision of NE Greece into four structural zones of distinctive rotational behaviour (from east to west): sites in zone 1, east of the Kavala-Xanthi-Komotini fault (KXK), show various cw and ccw (counterclockwise) rotation angles owing to complex kinematics resulting from the interaction of the KXK and the north-Anatolian fault zone. However, zone 2, between the KXK and the Strymon valley, is structurally homogeneous (∼ 10° cw rotation). The paleomagnetic signature of the Vertiskos massif (zone 3) implies a larger (> 30°) cw rotation, whereas sites in the Vardar basin (zone 4) contain a paleomagnetic signature similar to that of zone 2. This suggests a motion of the Vertiscos massif, a meta-ophiolitic nappe, relative to underlying strata. Indeed, zones 2 and 4 may be parts of the same structural unit which underlies this nappe.

Trinovantedinium boreale Bujak-dominated dinoflagellate assemblages in Eocene-Oligocene stratified water in northern Japan

Dinoflagellate assemblages in marine late Middle Eocene to Early Oligocene formations in northern Japan are exceptionally limited in diversity and generally dominated by Trinovantedinium boreale. Other species in the assemblages include Bellatudinium hokkaidoanum Kurita and Matsuoka, sp. nov., Paralecaniella indentata, and Selenopemphix spp. The “restricted flora” developed particularly in Hokkaido, where earlier studies indicated a paleoenvironment of relatively shallow embayment with saline, stratified water. The persistent restriction in species composition was presumably influenced by the stratification and relatively low water temperature. The assemblages were also possibly influenced by high phytoplankton productivity which enhanced the dominance of peridiniacean forms. B. hokkaidoanum Kurita and Matsuoka, sp. nov. and the wide morphological variation of T. boreale are described.