Miocene Age Research Articles

Ebro Valley Gypsum Escarpment Near Zaragoza (NE Spain)—Combination of Highly Valuable Rock Record, Dynamic Geomorphosites and Associated Cultural Heritage

The 40-km-long escarpment of the Ebro River valley to the north-west of Zaragoza (NE Spain) is a remarkable geomorphological feature and an important geoheritage locality. Being 30 to 150 m high, the escarpment exposes a complex evaporate-clastic succession of Early to Middle Miocene age, with alternating gypsum and mudstone/marl units, as well as halite beds at depth. The escarpment is a highly dynamic feature, extensively shaped by mass movements of different types, especially in sections where it is directly undercut by the Ebro River. It also hosts abundant evidence of salt and gypsum dissolution, contributing to ongoing instability. Diverse cultural heritage is associated with the escarpment, including an ancient Celtiberian settlement, medieval castles, abandoned villages, rock-cut churches and dwellings and ancient salt mines. Twenty-six possible geosites are identified, with six considered as most representative described in detail. Opportunities to develop the area for geotourism are presented, but these will be associated with challenges of properly managing steep, dynamic and fragile terrain.

A wealth of P–T–t information from metasediments in the HP–UHP terrane of the Pohorje Mountains, Slovenia, elucidates the evolution of the Eastern Alps

AbstractContrasting views exist in regard of the evolution of metamorphic rocks in the southeastern Pohorje Mountains (Mts), located in the southeastern Eastern Alps. Major debated points are whether micaschists have experienced ultrahigh‐pressure metamorphism in the Late Cretaceous (Eo‐Alpine) and whether they were continuously exhumed or experienced a multiple subduction–exhumation process from that time on. Therefore, we studied micaschist sample 18Slo39 with two generations of garnet and phengitic muscovite from this area. Our detailed study of this rock included petrographic observations, chemical analyses of minerals with the electron microprobe, pseudosection modelling, conventional geothermometry, and monazite in‐situ U‐Th‐Pb dating using laser‐ablation inductively coupled plasma (ICP) mass spectrometry. The following results were obtained: The studied micaschist was subject to a peak pressure of 1.31 ± 0.14 GPa at 603 ± 26°C in Eo‐Alpine times: 90.62 ± 2.78 (2σ) Ma (Stage I). Contact metamorphism at pressure–temperature conditions of 0.66 ± 0.10 GPa and 577 ± 23°C was induced by the intrusion of the Pohorje pluton (Stage III). We determined an early Miocene age of 18.33 ± 0.43 (2σ) Ma for this intrusion. Based on this study and the previously reported data for a micaschist (16Slo12) taken in the vicinity of sample 18Slo39, a geodynamic model is proposed for the region of the Pohorje Mts considering Eo‐Alpine subduction of oceanic crust and European continental crust, of which the micaschist was part of. Another high‐pressure event in the Eocene (Stage II) was the result of intracontinental subduction because of transpression by the Periadriatic fault system that separates the Eastern Alps from the Southern Alps. This type of subduction gave rise to magma generation and ascent to form the Pohorje pluton, which caused contact metamorphism in its vicinity.

Tracing Oligocene−Miocene source-to-sink systems in the deep Levant Basin: A sandstone provenance study

The Levant Basin in the Eastern Mediterranean contains an ∼3-km-thick, predominantly siliciclastic section of Oligocene−Miocene age, which hosts large hydrocarbon reservoirs (“Tamar Sands Play”). Here, we present a provenance study of Oligocene−Miocene sandstones based on detrital zircon U-Pb-Hf and heavy mineral assemblages. Samples were retrieved from four boreholes across the Levant Basin: Myra-1, Dolphin-1, Leviathan-1, and Karish North-1. Our investigations revealed that the sediments are dominated by Neoproterozoic and older Precambrian zircons with variable Hf isotopic composition, indicating that they were mainly reworked from Paleozoic−Mesozoic sandstones of African-Arabian provenance, with minor derivation from the Neoproterozoic basement of the Arabian-Nubian Shield. Variations in the proportions of pre−900 Ma zircons were encountered in various levels of the siliciclastic section. These zircons were markedly enriched (44%−57%) in the Rupelian and Aquitanian−Burdigalian intervals, accompanied by abundant detrital apatite peloids in the heavy mineral fraction, and relatively sparse (21%−38%) in the Chattian−Aquitanian and Langhian−Tortonian intervals, alongside scarce Mesozoic−Cenozoic zircons. These findings allow us to associate the deep-basin detrital record with two sedimentary transport systems that reached the Levant Basin from both NE Africa and Arabia simultaneously until the late Miocene, when sediment transport from Arabia ceased. While Rupelian and Aquitanian−Burdigalian sediments, including the main section of the “Tamar Sands,” were derived mainly from Arabian sources via the Levant continental margin, Chattian−Aquitanian and Langhian−Tortonian sediments were primarily sourced from NE Africa via the Nile Delta. Detrital contribution from the Eurasian side of the Eastern Mediterranean was not identified, suggesting that sand originating in the Arabia-Eurasia collision belt did not reach the Levant Basin.

Eocene to Miocene palynology of the Amagá Basin (Cauca Valley, Colombia) compared to the Caribbean Region

The Cenozoic sedimentary basins of northwestern Colombia contain clues to understanding the evolution of past ecosystems and their possible relationship to regional events, such as the uplift of the northern Andes and the collision of the Panama-Chocó Block with the South American continent. However, these basins have not been thoroughly investigated. This work aims to fill this knowledge gap by performing a comprehensive palynological analysis of the Amagá Basin (Valle del Cauca). Three outcrops were studied to determine their depositional ages, paleoenvironments, and overall floral composition over time. To contextualize our analyses, a comparison was made with two drill holes (ANH-SSJ-Nueva Esperanza-1X and ANH-San Jacinto-1) in the Sinú-San Jacinto Basin in the Colombian Caribbean. The application of the palynological zonation from the Llanos Basin in eastern Colombia was also used to evaluate its suitability in the Amagá Basin. The age of deposition was determined by using several traditional palynostratigraphic markers, including Perisyncolporites pokornyi, Foveotriporites hammeni, Retibrevitricolporites speciosus, Magnastriatites grandiosus, Concavissimisporites fossulatus, Clavainaperturites microclavatus, and Polypodiaceoisporites pseudopsilatus. This assemblage indicates a Middle to Late Eocene, Oligocene, and Miocene age spanning from ~40 to 18 Ma (~22 Myr). However, there are also some differences with respect to the Llanos zonation, such as the absence of Cicatricosisporites dorogensis. Based on this age model, we question whether it is correct to include all these deposits in a single lithostratigraphic unit under the rank of a formation. In the Caribbean, stratigraphic units of similar age exhibit a greater number of key taxa than in the Llanos zonation. In addition, the presence of calcareous microfossils allows for a more detailed determination of the sedimentation age. Furthermore, the discovery of new pollen and spore species could improve the resolution of the biostratigraphy in western Colombia. In the Amagá Basin, only terrestrial palynomorphs were found, which, together with the sedimentary facies, suggest a humid lowland tropical vegetation in fluvial and lacustrine environments.

Stratigraphic context of Oligocene to Pliocene mammal-bearing deposits in Linxia Basin, Gansu Province, China: a historical review and a discussion of ongoing controversies

In this paper, we critically review the half-century (1962–2022) history of study of Oligocene to Pliocene mammal-bearing successions in the eastern Linxia Basin, Gansu Province, China. Despite great strides in our understanding of the regional geology and the discovery of a large quantity of mammal fossils, there remains major discrepancies concerning the definition and age assignment of the formations that comprise the Linxia Group. This has resulted in the development of two competing schemes for its subdivision: the first scheme was proposed by geologists of the Lanzhou University and the Institute of Tibetan Plateau Research, and the second scheme is associated with paleontologists of the Institute of Vertebrate Paleontology and Paleoanthropology. In an attempt to solve these discrepancies, a five year project was initiated in 2017, and herein we report the main findings as follows: (1) The Jiaozigou Formation does not extend into the Miocene, with its top calibrated at about 23 Ma; (2) The Liushu Formation, as defined in the Maogou section, should be considered as the penecontemporaneous shallow water facies of the coarse-grained Hujialiang Formation of Middle Miocene age; (3) The widespread Hipparion-bearing deposits along the Guangtong River, which have been also referred to the “Liushu” Formation represent a different stratigraphic unit and should be given another name to eliminate confusion following further stratigraphic analysis.

Middle Eocene Succession of Dammam Formation, Biostratigraphy and Microfacies Study, North Karbala Area, Western Iraq

Stratigraphic and sedimentary study to Dammam Formation (Eocene age) at well Kr-1, Karbala Government, Western Desert of Iraq. Lithologically, Dammam Formation consists of Nummulitic limestone and dolomitic limestone. The contact between the upper and lower of Dammam Formation is unconformable, the lower contact is represented by Umm Er-Radhuma Formation by the unconformable surface in the Upper Paleocene age, while the upper is an unconformable surface with Euphrates Formation in the Early Miocene age. The rock section of the well Kr-1 is divided into several beds depending on Petrographical and paleontological contents, the results of the identified foraminifera are indicated to several groups and genera which are: Nummulites, Lindrina, Lockhartia, Rotaliid, Miliolid, also other groups of fossils like Ostracoda, Echinoderms, Bryozoa, Gastropod, Pelecypod, and different fragments. Based on the petrographic study and type of microfacies, the formation was divided into three main and secondary microfacies which are: Nummulitic packstone, Dolomitic and Bioclastic Packstone, and Floatstone. One main biozone was recognized in the studied section which is Nummulites gizehensis- Nummulites planulatus - Nummulites discorbinus Assemblage Zone with age Middle Eocene (Lutetian), this biozone is divided into two secondary biozones: Nummulites millecaput Rang zone Middle Eocene (Middle-Upper Lutetian) age and Nummulites elevate Rang zone Middle Eocene (Late Upper Lutetian) age. After collecting all the sedimentary and planetology data for the studied section, the Dammam Formation was deposited in shallow warm marine, tropical water, as well as, the absence of planktonic foraminifera crowds is another evidence that the environment is a shallow basin close to the coast. The basin is located at the Interior Platform represented by the evaporites basin, the restricted, and then the open sea environments.

Igneous Rock Associations 29. The Nenana Magnetitite Lava Flow, Alaska Range, Alaska

Magnetitite deposits like El Laco (Chile) are rare and have controversial origins. An unusual magnetitite lava flow overlying a rhyolite unit occurs in the north-central Alaska Range and originally covered ~ 750 km2 of the Miocene Nenana basin. Dating of the rhyolite and relationships between the magnetitite and sedimentary rocks indicate that both are of Late Miocene age. The magnetitite flow is mainly magnetite with some post-eruptive alteration to hematite. Both the rhyolite flow and the magnetitite flow are vesicular, but the magnetitite flow also has small, millimetre-scale columnar jointing. The vesicular zones in the magnetitite flow grade into massive rock on the scale of a thin section, suggesting a degassing lava origin. Samples of the magnetitite flow contain between 12 and 26 wt.% SiO2 and between 45 and 75 wt.% FeO. Rare earth elements (REE) and trace elements from the magnetitite and rhyolite have similar patterns but with lesser abundance in the magnetitite. Both the rhyolite and the magnetitite have light-REE-enriched REE profiles with negative Eu anomalies. Electron microscopic analysis shows that most of the silica and trace element content of the magnetitite flow comes from very finely disseminated silicate minerals and glass in the magnetite. This suggests that the magnetitite was derived from a magma that had undergone unmixing into a silica-rich phase and an iron-rich phase prior to its eruption. Fractures and vesicles within the magnetitite flow contain minor rhyolitic glass and minerals suggesting that the rhyolite magma invaded columnar joints in the solidified magnetitite flow, and is a subvolcanic sill-like body at the studied locality. The magnetitite flow erupted prior to the emplacement of the rhyolite, which may be extrusive on a regional scale. The features of the Nenana magnetitite, and its geological relationships, are consistent with genetic models that invoke unmixing of magma into immiscible Fe-rich and Si-rich liquids during ascent.

Biostratigraphical investigation of middle-early Miocene sediments from a section of AK-1 well, onshore Niger Delta: Insights from calcareous nanofossils

Biostratigraphic analysis was carried out on KA-1 well, onshore Niger Delta Basin of Nigeria. A total of forty (40) ditch cutting samples were collected from the studied section at 30 feet depth intervals with the studied section ranging from 7590-4800feet. The objectives of this study are to determine the age and biozonation of the studied section. Using simple smear slide method, the samples were processed and analyzed for nannofossils using a reflected binocular microscope. Calcareous nannofossil assemblages from the well are of low diversity and abundance. Some depths yielded almost monospecific assemblages while some have no records of calcareous nannofossils. Species include Helicospharea ampliaperta, Sphenolithus heteromorphus, Cyclicargolithus floridanus, Helicospharea scissura and Discoaster deflander. These belong to the NN4 zone of middle to early Miocene age. Keywords: Biozonation, Calcareous nannofossils, Helicospharea ampliaperta, Oligotrophic, Niger Delta.

Biostratigraphy and Climate Change in the Late Miocene Age Based on Foraminifera in the Oyo Formation, Oyo River Section, Gunung Kidul, Yogyakarta

The date of the paleoclimate event was ascertained using a biostratigraphic analysis. The thickness of the Oyo Formation was measured using measurements with a Jacob stick method, yielding a thickness of 80.8 meters and 23 rock samples. In the Southern Mountains Zone, new result of the age of the upper part of the Oyo Formation by biostratigraphy investigation of the hill Late Miocene (9.79 Ma to 5.78 Ma). Biostratigraphic investigation in the Oyo River revealed 28 species and 9 genera, with two datums. The study area was classified into three biozonations based on the datum found Globorotalia acostaensis/M13a/N16 zone, the lower Globorotalia plesiotumida/M13b/N17 zone, and the upper Globigerinoides conglobatus/M14/N17 zone. The results of a paleoclimate analysis on the Oyo River Section show a general cooling tendency in the study area. Seven paleoclimate zones can be determined from these trends consisting of four warm and three cold zones. Zone I (warm), zone II (cold), zone III (warm), and zone IV (cold) have the coldest peak in the study region in 8.3 Ma, zone V (warm), and zone VI (cold), followed by zone VII (warm). Based on the correlation with other studies (South China Sea, Pacific Ocean, Oyo River, Ngalang River, and Ngioro Section), paleoclimate events in the study area occur globally.

Provenance of sandstone layered in Injana Formation from Zawita and Dekala areas Northern of Iraq

To interpret the provenance 0f Injana Formation, 20 sandstone samples of Injana Formation were collected from Zawita and Dekala areas north Iraq (10 for each sections ), then thin section have been done sildes. The petrographic study showed that the sedimentary, metamorphic and igneous rock fragments, quartz (mono&polycrystalline) and feldspars (microcline, orthoclase and plagioclase) make up the main grain components of the sandstone. Carbonate cement is more common cementing minerals, and the matrix is subordinate. The percentage of mono-quartz and sedimentary, igneous rock fragments are greater than the amounts of feldspar and poly-quartzand metamorphic fragments. A diagenetic processes were represented by the carbonate, iron oxides and evaporite cements, as well as compaction, cementation, and dissolution. The majority of the rocks of Injana Formation’s provenances are sedimentary and igneous, with minor amounts of subordinate metamorphic rocks. These sandstones are considered to be immature and classified as immature Litharenites type. The tectonic provenances that are extrapolated from petrographical results are transitional and lithic with effect of uplifting of Alpaine oroging recycled origin which are derived from the order rocks during the Miocene age.

Geology, mineralization, zircon U-Pb geochronology and Hf isotopes of Serenu porphyry copper prospect, Kerman Cenozoic magmatic arc, southeastern Iran

Serenu porphyry copper prospect is situated 22 km northwest of the Meiduk copper mine, Kerman Cenozoic magmatic arc in southeastern Iran. The study area is characterized by a simple lithology including Eocene volcanic and volcaniclastics, Neogene sediments, and sub-volcanic rocks (Hezar complex) which is intruded by a late Miocene porphyry diorite to quartz-diorite stock that has developed alteration and mineralization in the area. Phyllic, argillic, and propylitic alteration types are well-distributed in the Serenu prospect; potassic alteration is only locally observed. Hypogene mineralization occurs in the Serenu porphyry and the host Eocene volcanic rocks as scattered vein-veinlets, stockworks, and disseminated mineralization related to potassic and phyllic alteration types.The mineralogy and cross-cutting relationships, allow the vein-veinlets to be classified into five groups including (I) magnetite ± quartz, (II) quartz ± magnetite ± chalcopyrite ± pyrite ± chlorite ± anhydrite (III) quartz ± pyrite ± chalcopyrite ± anhydrite, (IV) pyrite, and (V) quartz ± calcite veinlets. Oxide and supergene enriched ores are poorly developed in the area. Zircon U-Pb dating on two samples from the Serenu porphyry provided consistent ages at 9.83 ± 0.4 Ma and 10.2 ± 0.17 Ma (±2σ) indicative of late Miocene emplacement of the intrusion. The zircons are characterized by positive εHf (t) values of 8.52 to 12.27 and TDM of 200–370 Ma and a TCDM of 310–590 Ma indicating that they originated from a juvenile mafic and thickened lower crust and depleted mantle-derived magma.The late Miocene age determined for the Serenu porphyry copper prospect is consistent with the ages reported for many other shallow intrusions related to porphyry-type mineralization in the Kerman belt and further emphasizes the Miocene metallogenic epoch as the preferred time for porphyry Cu-Mo-Au mineralization in this belt, coinciding with a significant stage of continental collision between the Arabian and Iranian plates. The results of this study reveal that the juvenile mafic lower crust together with input from a depleted mantle and older subduction-related magma has a very significant impact on the formation of the Serenu porphyry host magma.

Biostratigraphy and Paleoecology of the Anah Formation in Kurdistan Region, Iraq

In the current study, biostratigraphy and paleoecology of the Anah Formation have been investigated.The study area is located in the Sulaimanyah Governorate, Kurdistan Region, Northeast Iraqwhere the Darzila section hasbeen sampled. Twenty-five species of larger foraminifera and skeletal fragments of coral, echinoid spine, pelecypods,and gastropods are described in seven samples collected from the Darzila section. Based on the distribution of the larger-benthic foraminifera andother skeletal grains, two assemblage biozones of the Late Oligocene–Early Miocene age have been recognized. According to the paleoecological parameters,such as temperature, nutrients, depth, and salinity in the study area, the Anah Formation hasdeposited the euphotic zone, abundant imperforate foraminifera are present, sub-tropical waters under oligotrophic to mesotrophic middle ramp environment with normal to a higher salinity inner ramp setting and at water depths that ranged from 40 m to 80 m, anda temperature about 18–25ºC.

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.

Jizerka Gemstone Placer—Possible Links to the Timing of Cenozoic Alkali Basalt Volcanism in Jizera Mountains, Czech Republic

The Jizerka Quaternary alluvial placer in the Czech Republic has been a well-known source of gemstones since the 16th century, and the only one in Europe that has yielded a significant amount of jewel-quality sapphire. Besides Mg-rich ilmenite (“iserine”), which is the most common heavy mineral at the locality, some other minerals have been mined for jewellery purposes. These are corundum (sapphire and ruby varieties), zircon (“hyacinth” gemstone variety) and spinel. Here, we present a detailed petrological and geochronological investigation of the enigmatic relationship between the sapphires and their supposed host rocks, supporting their xenogenetic link. Our hypothesis is based on thermal resetting of the U–Pb isotopic age of the zircon inclusion found inside Jizerka blue sapphire to the estimated time of the anticipated host alkaline basalt intrusion. The host rocks of the gemstones (sapphire and zircon) and Mg-rich ilmenite are not yet known, but could be related to the Cenozoic volcanism located near the Jizerka gem placer (Bukovec diatreme volcano, Pytlácká jáma Pit diatreme and Hruškovy skály basalt pipe). The transport of sapphire, zircon and Mg-rich ilmenite to the surface was connected with serial volcanic events, likely the fast ascent of alkali basalts and formation of multi-explosive diatreme maar structures with later deposition of volcanoclastic material in eluvial and alluvial sediments in nearby areas. All mineral xenocrysts usually show traces of magmatic corrosion textures, indicating disequilibrium with the transporting alkali basalt magma. In order to constrain the provenance and age of the Jizerka placer heavy mineral assemblage, zircon inclusion and associated phases (niobian rutile, baddeleyite and silicate melts) in the blue sapphire have been studied using LA–ICP–MS (laser ablation–inductively coupled plasma–mass spectrometry) geochemistry and U–Pb in situ dating. Modification of the zircon inclusion into baddeleyite by exposure to temperature above 1400 °C in a basaltic melt is accompanied by zircon U–Pb age resetting. A zircon inclusion in a Jizerka sapphire was dated at 31.2 ± 0.4 Ma, and its baddeleyite rim at 31 ± 16 Ma. The composition of the melt inclusions in sapphire and incorporated niobian rutile suggests that the parental rock of the sapphire was alkali syenite. The Eocene to late Miocene (Messinian) ages of Jizerka zircon are new findings within the Eger Graben structure, as well as among the other sapphire–zircon occurrences within the European Variscides. Jizerka blue sapphire mineral inclusions indicate a provenience of this gemstone mineral assemblage from different parental rocks of unknown age and unknown levels of the upper crust or lithospheric mantle.

Miocene tropical storms: Carbonate framework approaches and geochemistry proxies in a reservoir model

The Bragantina Platform is an important sedimentary package that occurs in northwestern Brazil, typically around the equatorial western Atlantic coast. Most of the latest Neogene succession of this carbonate-siliciclastic platform consists of the Pirabas Formation of Miocene age (Burdigalian to Serravalian). High-energy coastal storms and hurricanes as a consequence of trade wind anomalies during the Neogene impacted the shallow-water inner marine heterozoan assemblage deposits of the Pirabas Formation. A chaotic overlap of benthic infauna and epifauna, and of demersal and pelagic species in the same section was analyzed using petrography, petrophysics, micro- and macropaleontology, taphonomy, and geochemistry in order to understand sedimentary and paleoenvironmental processes. The equatorial carbonate platform of Brazil reveals high-energy and multiple Miocene tropical storms. This high-energy wave environment caused severe damage to shallow-water heterozoan assemblages at the seafloor, resulting in chaotic faunal arrangements, and removing fine-grained particles thus improving the petrographic properties of the rock (porosity and permeability).

Sedimentological and palynostratigraphical modeling of sediments penetrated by KW field wells, onshore western Niger Delta Basin, Nigeria

Sedimentological and palynostratigraphical studies were performed on 189 ditch-cutting samples composited at 50 ft intervals from four well sections located in KW field, onshore western Niger Delta Basin, Nigeria, using sieving and visual microscopic observations, hydrochloric and hydrofluoric acids digestion methods to determine their lithological character and palynologic content of the sedimentary successions. The basis of these data is to interpret the lithofacies and biostratigraphy, establish the age of the strata, establish the palynological zones and infer the environments of deposition. Five lithofacies delineated based on the sedimentological study were very coarse sand, coarse to fine sand, shaly sand, muddy sand, and sandy to silty shale. The age of the sedimentary successions ranges from Early Miocene to Pliocene based on the bio-assemblages of these key species. The Early Miocene age is characterized by the occurrence of Magnastriatites howardi, Psilatricolporites triangularis, Praedapollis africanus, Pachydermites diederixi, Spirosyncoilpites spiralis, Praedapollis flexibility, Racemonocolpites hians, Verrutricolporites rotundiporus, Verrutricolporites microporus, and Psilatricolporites divisus. The Middle Miocene age is characterized by the FAD of Crassoretitriletes vanraadshooveni, the occurrence of Belskipollis elegans, in association with Striatricolporites catatumbus, Verrutricolporites rotundiporus, Verrutricolporites microporus, Crassoretitriletes vanraadshooveni, Racemonocolpites hians, Retibrevitricolpites obodoensis, and Retibrevitricolpites protrudens. The Late Miocene age is characterized by the occurrence of Multiareolites formosus, Cyperaceaepollis sp., Stereiosporites sp., Peregrinipollis nigericus, Gemmamonoporites sp. (Cleistopholis patens), Laevigatosporites sp., Verrutricolporites sp., Nymphaeapollis clarus, and Verrutricolporites usmensis. The Pliocene age is characterized by the basal occurrence of Retistephenocolpites gracilis in association with Nymphaeapollis clarus, Cyperaceaepollis sp., Laevigatosporites sp., Verrutricolporites sp., and Crassoretitriletes vanraadshooveni. The boundary between the Early Miocene and Middle Miocene from the studied oil well sections is marked by the first appearance datum (FAD) and numerical maximum occurrence of Striatricolporites catatumbus and Belskipollis elegans and FAD of Crassoretitrilettes vanraadshooveni. The boundary between the Middle and late Miocene is defined by the LAD of Verrutricolporites rotundiporus, the quantitative top and numerical maximum occurrence of Racemonocolpites hians, and the numerical maximum occurrence of Zonocostites ramonae. The boundary between the late Miocene and the Early Pliocene is marked by the first appearance datum (FAD) and the numerical maximum occurrence of Retistephenocolpites gracilis, the numerical maximum occurrence of Echiperiporites icacinoides, and the highest abundance of Monoporites annulatus. Four palynozones PAZ-1, PAZ-2, PAZ-3, and PAZ-4, and ten sub-zones were erected. Finally, Fluvial-coastal to shallow marine environments of deposition were inferred for the sedimentary successions using sedimentological study, nature of organic matter, and association of key environmentally-sensitive biomarker species.

Robust reservoir identification by multi-well cluster analysis of wireline logging data

A novel clustering method is applied to well logs for improved rock type identification in hydrocarbon formations. For grouping the objects in the multi-dimensional data space, we propose a Most Frequent Value (MFV) based clustering technique applied to natural gamma ray, bulk density, sonic, photoelectric index, and resistivity logs. The MFV method is a robust estimator, which assists in finding the cluster centers more reliably than a more noise sensitive K-means clustering approach. The result of K-means cluster analysis highly depends on the choose of the initial centroids. To reduce the risk of inappropriately chosen starting values, we apply a histogram-based selection method to give the best position of the initial cluster centers. We assure the robustness of the solution by calculating the centroid as the MFV of the cluster elements and defining the overall deviation of cluster elements from the center by a weighted Euclidean (Steiner-) distance. The proposed workflow relies on a fully automated weighting of the cluster elements, which does not require a constraint on the statistical distribution of the observed variables. The processing of synthetic data shows high noise rejection capability and efficient cluster recognition even beside considerable amount of outlying and missing data; the accuracy is measured by the difference between the estimated and the exactly known distribution of cluster numbers. The clustering tool is first applied to single borehole data, then the procedure is extended to multi-well logging datasets to reconstruct the multi-dimensional spatial distributions of clusters revealing the lithological and petrophysical characteristics of the studied formations. A large in situ dataset acquired from several boreholes traversing Hungarian gas-bearing clastic reservoirs of Miocene age is analyzed. The accuracy of the field results is confirmed by core permeability measurements, independent well log analysis and a gradient metrics characterizing the noise rejection capability of the clustering method.

Early-middle Miocene Inversion of the Abu Jir Fault in the Western Iraq: a Possible Consequence of the Arabian Plate Northward Movement

The Abu Jir fault zone in western Iraq that marks the western limit of the Zagros foreland basin merges with the Anah graben in the north. The northern segment of the Abu Jir fault zone and the western Anah graben are inverted structures. In this study, we investigated the timing and mechanism of the northern Abu Jir fault zone inversion in comparison with other inverted structures like Tel Hajar and Sinjar, which are located in the north and closer to Arabia–Eurasia collision zone. In the study area the Abu Jir fault zone is characterized by a local-scale northwestern-trending asymmetric fold, associated with inverted normal faults, positive flower structures, right–lateral strike-slip faults, and seismically induced early middle Miocene slump structures. Based on the structural synthesis of the surface geology and age constraints from syntectonic deposits at the northern Abu Jir fault area, the Abu Jir fault inversion and its western block northward movement were inferred to be resulted from forces that originated from the south to the north, unlike the northern younger inverted structures. This early middle Miocene age of the Abu Jir fault inversion is comparable to the arrival time of the Afar plume hot mantle material flow from the south to the north in western Arabia. Therefore, we argue that the Abu-Jir fault inversion is more likely to be due to dragging of the Arabian plate by mantle flow from the south to the north rather than shortening propagation from the north to the south.

A Three-Dimensional Geological Model of the R’Mel Aquifer, Northwestern Morocco

One of the challenges of 3D geological modelling is the spatial representation of heterogeneous sedimentary rocks. The R’Mel coastal basin located in northwestern Morocco is a very suitable area for the modelling of sedimentary rock formations. This basin is part of the external Pre-Rif area and is composed of rocks of Miocene to Quaternary age (principally sand, marl, sandstone, silt, and alluvia). Due to the impact of climate change, any increase in the abstraction of groundwater can accentuate its vulnerability to marine water intrusion. Therefore, understanding of geometry of this aquifer is so important. To achieve this, a 3D geological model was developed to determine the different HydroGeological Units (HGUs) of the R’Mel aquifer. The processing and the construction of a GIS database including a detailed geological map, 125 boreholes, and 50 vertical electrical soundings (VESs), as well as the development of five geological cross-sections, helped build this model using 3D modelling software. The model provides a detailed visualization of the spatial distribution of the eight HGUs. HGUs 3 and 6 consist of marly-clayey lenses and five HGUs of Plio-Quaternary age are composed of: sand or/and sandstone (HGU 1), calcarenites and lumachelles (HGU 2), sandstone and/or shelly marine sand (HGU 4), gravel with a sandy-clayey matrix (HGU 5), and shelly sandstone and gravelly sand (HGU 7). The eighth layer (HGU 8) is composed of marls and clays of Miocene age. The generation of several geological sections from the model made it possible to identify anticlines, synclines and faults trending NNW–SSE and NNE–SSW. Theses, support the tectonics of the Gharb basin during the Mio-Plio-Quaternary. Finally, a conceptual model of the R’Mel aquifer was developed.

Depositional and Sratigraphic Evolution of the Early-Middle Miocene Succession in Hamrin, Ajeel and Mansuriyha Oil Fields, Central Iraq

The Early-Middle Miocene succession in Iraq is represented by the Serikagni, Euphrates and Dhiban formations, which deposited during the Early Miocene. The Jeribe and Fatha successions were deposited during Middle Miocene age. This study includes microfacies analysis, depositional environments, sequence stratigraphy and basin development of Early – middle Miocene in Hamrin and Ajeel oil fields and Mansuriyha Gas Field. The study area includes four boreholes in three oil fields located in central Iraq: Hamrin (Hr-2) and Ajeel (Aj-13, and 19) oil feilds, and Mansuriyha (Ms-2) Gas Field. Five facies associations were distinguished within the studied fields: deep marine, slop, platform-margin, open marine, restricted interior platform, and evaporitic interior platform. The facies associations interpreted were based on texture and fauna. Deep marine facies association consists of planktonic foraminifera wackestone, it was observed in well Ms–2. Slope environment association is observed in Euphrates Formation in Hamreen-10, and it represented by bioclastic – planktonic mudstone – wackestone. The open marine association is observed in all studied wells in particular in Jeribe and Euphrates formations, and it includes bioclastic mudstone-wackestone, bioclastic peloidal wackestone-packestone and bioclastic foraminiferal wackestone- packestone. While the restricted interior platform association is dominated in all studied wells, it consists of ooidal packstone, foraminiferal peloidal packstone, dolomitic lime mudstone, dolomititic and evaporitic peloidal wackestone-packstone. In Ajil Oil Field the studied succession is consisting of two sequences (C1 and C2). The fist sequence (C1) was started with transgressive system tract (TST) reflected by open marine occupies the lower part of Euphrates Formation, the TST bounded below by SB and above by MFS. The second sequence (C2) was started with TST which is observed in the lower part of Jeribe Formation, represented by evaporitic and restricted interior platform. In Hamrin Oil Field, this succession is started with thin transgressive system tract (TST) as C1 reflected by toe of slope and it occupied a bit of lower part of Euphrates Formation. The highstand system tract (HST) is divided to five cycles (CE1, CE2, CE3, CE/Dh and CDh). Sequence C2 was started with relatively thin transgressive system tract (TST) occupies the lower part of Jeribe Formation represented by open marine environment. Two sequences are observed in Mansuriya Gas Field (C1 and C2). Sequence C1 started with thin transgressive system tract (TST) bounded below by SB1 and above by MFS which is corresponding with conformable boundary that separated between Serikagni Formation and Dhiban. Contrary, the second sequence (C2) was started with relatively thin transgressive system tract (TST) occupies the lower and middle parts of Jeribe Formation represented by restricted interior platform environment.