Eocene Formations Research Articles

Geochemical characteristics of the Upper Cretaceous to Lower Eocene sedimentary rocks from the Pieniny Klippen Belt (Western Carpathians, Slovakia): implications for tectonic setting, paleoenvironment and paleoclimate

This paper presents geochemical data on sedimentary rocks from the Upper Cretaceous to Lower Eocene formations of the Pieniny Klippen Belt (Western Carpathians, Slovakia). On the basis of geochemical analyses of 15 samples, the plate tectonic setting of sediment accumulation and paleodepositional environment were reconstructed, which may help to understand a part of evolution of this orographically remarkable zone. Four main rock groups were identified within the samples studied: fine- to medium-grained sandstones, siltstones or claystones, pebbly/sandy mudstones and shales. In the Al2O3*5-SiO2-CaO*2 ternary diagram, they displayed developed sand and mud flat characteristics with light rich clay content. According to high-silica and lowsilica multi-dimensional diagrams, the investigated rocks might have originated from a continental collision tectonic setting. The Zr/Rb values (0.76–6.47) mirrored a fluctuation of hydro energy during deposition of the sediments studied. Paleoclimate indexes, such as the C-value (0.03–0.49) and Sr/Cu (3.25–202.27), revealed arid to semiarid climatic conditions during deposition of the studied sediments. In addition, the chemical data were used to constrain paleoredox conditions of the depositional environment, which proved that these sediments had been deposited mainly beneath the oxic water column with relatively low paleoproductivity, as evidenced by P/Ti with an average of 0.13 and Ba/Al with an average of 34.30.

Architecture of the Great Pyramid of Giza Concept and Construction

Egyptian culture of the old kingdom was locally and regionally simple and efficient; belief was in the sky and humanism was regulated by Ma’at as the key concept in Egyptian mentality. IUNU was the capital of the black land KEMET where ”IUNU UNIVERSITY” is located. Physics were well studied; was already known; the right angle triangle of members 3, 4, and 5 with the 53o angle was in use. Supremacy was integrated on earth by multiple interpretations in architecture. The great pyramid of Giza was and still the best magnificent structure ever built on earth without having contemporary science’s final word been said. Massive lime stone blocks are now arranged there in a huge massive number of about two and half million pieces; their weight could reach 6.5 million tons. Conceptually there was a strong belief that symbolism connects hot spots on the Egyptian soil as it represented the known world, as well as the main stars were connected in multiple constellations on the dome of the observed sky. Pyramids of Giza plateau, Saqqara plateau, and Abusir plateau were all examples of that concept. Other pyramids of Iunu era were also related to the same concept. Structurally the Giza axis coincided on the Giza plateau. Giza plateau was a part of the Moqattam plateau during the Eocene formation. Pyramids on the worked out surface of the plateau were built with the local lime stone. Pyramids’ blocks were extracted, shaped and transported to its definite place within the precinct of the plateau. Chiseled pieces of stone - as waste from shaping blocks - were thrown out on the northern edge of the plateau. Constructional perception of what and why the Khufu pyramid took that shape shows some facts; two hundred courses composed the total existed mass where each group of courses composed a layer. Each layer started with thicker course and ended in thinner ones. Higher layers got lesser courses. So far, one should start thinking now why there were layers; why thicker and thinner courses existed. In the mean time as mortar was not in use by that time, pyramids –as in Saqqara- were formed in inclined walls, as shown in the adjacent photo. In addition, inclined walls must have formed the whole structure of Khufu pyramid.

The turtles from the upper Eocene, Osona County (Ebro Basin, Catalonia, Spain): new material and its faunistic and environmental context

Abstract. Eochelone voltregana n. sp. is a new marine cryptodiran cheloniid found at the Priabonian levels (latest Eocene) of the Vespella marls member of the Vic–Manlleu marls formation. It is the second cheloniid from Santa Cecília de Voltregà (Osona County, Spain), the first one being Osonachelus decorata from the same formation. Shell parameters indicate that the new species belongs to a branch of sea turtles including the Eocene Anglo–Franco–Belgian forms Argillochelys, Puppigerus and Eochelone (the shell of the latter was studied here for the first time) as well as Glarichelys from the Oligocene of Switzerland, all of them predating the worldwide living Miocene genera. The description of two other more littoral–continental Eocene species is given: Trionyx sp., from an older layer of the same formation; and the podocnemidid erymnochelyine, Cordichelys from a more basal layer of a middle Eocene (Lutetian) formation. The last one is identified as the only evidence of the Shweboemys subgroup in the European record, being distinct from the other known Osona County pleurodire Eocenochelus farresi, which is a member of the Erymnochelys group (same subfamily), from the younger Priabonian Sant Martí Xic layer. Thus, an update on the marine turtle fauna of the eastern Ebro Basin that variably opened in the east during Eocene times is provided. The turtles of Osona County belong to two suborders and five genera with three new species and extend the known distribution of their families (LSID urn:lsid:zoobank.org:act:48CE8676-7B82-4EF2-8165-27BEE90129F2).

Biological marker indicators of paleo-depositional environment for the Eocene formations around Zara-Bolucan region (central anatolia, Turkey)

Biological marker (biomarker) characteristics and paleo-depositional conditions of Eocene sediments around Zara-Bolucan northeast of Sivas Basin have been determined by means of detail organic geochemical studies such as gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) analysis. In the investigated area, northeast section of the Sivas Basin, the Eocene Bozbel and Kozluca Formations consist of a organic matter rich sedimentary rocks deposited within trangressive-regressive cycles. During the evaluation of paleoenvironment characteristics with biomarker data, data related to n-alkanes, isoprenoids, terpenoids and steroids were used. Especially, the marine environment features indicated by C23 tricyclic/C30 hopane, the C26 /C25 tricyclic terpanes, homohopane/C30 hopane and diasterane/regular sterane data. The ratios of Pr/Ph, Pr/n-C17 and Ph/n-C18 indicate that there is marine organic matter predominantly precipitated under reducing environmental conditions. In the studied samples, the algal-bacterial organic matter contribution was interpreted to be due to the superiority of the C23 tricyclic terpene to C24 , as well as larger than the C24 tricyclic terpane. However, the gammacerane index suggests that there is initially a low salinity environment. The significant terrestrial organic matter contribution is indicated by the isoprenoid and biomarker ratios, dominance of higher n-alkanes such as n-C29 , n-C31 , CPI, TAR values, n-C19 /n-C31, relative abundance of C27-C28-C29 regular steranes. Suboxic to anoxic palo-depositional conditions are confired by the isoprenoid and n-alkane ratios and T m /T s , C 29 T s /C 29 hopane ratios.

Two Dimensional Evolution Modeling of Source Rocks in the Chaluhe Basin, Yitong Graben

Yitong Graben in Jilin Province of China, hosts three basins, namely: Chaluhe, Luxiang and Moliqing basins. The Chaluhe basin, as the focal point of this study has five subdivisions, thus, Bo-Tai sag, Wanchang Structural high, Liangjia Structure high Xinanpu sag, and the Gudian slope, with a cumulative sedimentary rock thickness of about 6000 metres. The basin is supposed to be a potential hydrocarbon-producing basin with its better source rock distribution and more favorable maturation indicators than the adjacent Luxiang and Moliqing Basin. Determining whether the mudstone beds present in the Eocene Formations are matured enough to generate hydrocarbons, three (3) wells with Seismic Lines (clh02, clh05 and clh07) were used for the study. It is observed that the entire region from NW to SE in the source rocks is mature to produce oil and gas. At depths of about 2400 m and below show good maturity with vitrinite reflectance values averaging 1.02% Ro. The Eocene Shuangyang mudstone is the main petroleum source rock.

Nummulite biostratigraphy of the Eocene succession in the Bahariya Depression, Egypt: Implications for timing of iron mineralization

In the northern part of the Bahariya Depression (Western Desert, Egypt) the Eocene carbonate succession, unconformably overlying the Cretaceous deposits, consists of three main stratigraphic units; the Naqb, Qazzun and El Hamra formations. The Eocene carbonates are relevant as they locally host a large economic iron mineralization. This work revises the stratigraphic attribution of the Eocene formations on the basis of larger benthic foraminifers from both carbonate and ironstone beds. Eight Nummulites species spanning the late Ypresian – early Bartonian (SBZ12 to SBZ17) were identified, thus refining the chronostratigraphic framework of the Eocene in that region of Central Egypt. Moreover, additional sedimentological insight of the Eocene carbonate rocks is presented. The carbonate deposits mainly represent shallow marine facies characteristic of inner to mid ramp settings; though deposits interpreted as intertidal to supratidal are locally recognized.Dating of Nummulites assemblages from the youngest ironstone beds in the mines as early Bartonian provides crucial information on the timing of the hydrothermal and meteoric water processes resulting in the formation of the iron ore mineralization. The new data strongly support a post-depositional, structurally-controlled formation model for the ironstone mineralization of the Bahariya Depression.

Metre-scale cyclicity in Middle Eocene platform carbonates in northern Egypt: Implications for facies development and sequence stratigraphy

The shallow-water carbonates of the Middle Eocene in northern Egypt represent a Tethyan reef-rimmed carbonate platform with bedded inner-platform facies. Based on extensive micro- and biofacies documentation, five lithofacies associations were defined and their respective depositional environments were interpreted. Investigated sections were subdivided into three third-order sequences, named S1, S2 and S3. Sequence S1 is interpreted to correspond to the Lutetian, S2 corresponds to the Late Lutetian and Early Bartonian, and S3 represents the Late Bartonian. Each of the three sequences was further subdivided into fourth-order cycle sets and fifth-order cycles. The complete hierarchy of cycles can be correlated along 190 km across the study area, and highlighting a general “layer-cake” stratigraphic architecture. The documentation of the studied outcrops may contribute to the better regional understanding of the Middle Eocene formations in northern Egypt and to Tethyan pericratonic carbonate models in general.

New data on the tectonic evolution of the Khoy region, NW Iran

Abstract The Khoy region (NW Iran) is important in the clarification of the structural framework of the alpine belt between the Taurides, the Lesser Caucasus and the NW Iran belt. The area is well-known for these ophiolitic units. We present here new stratigraphic and structural data that can be used to reconstruct the tectonic evolution of this region and then try to establish connections between these belts. According to new dates from nannoplankton assemblages, the obducted ophiolite of the Khoy complex was thrust over a sheared Campanian olistostrome and lenses of amphibolite are included within the contact. The obduction event is also marked by erosion of the ophiolitic unit and the deposition of conglomerates, shales, sandstones and siltstones. Poorly extended Paleocene detrital deposits cover the Campanian–Maastrichtian rocks. The Eocene formations characterize a basin filled with volcanogenic and sedimentary layers. The Middle and Upper Eocene series unconformably overlie the ophiolites and their cover of Campanian–Maastrichtian and Paleocene deposits. This corresponds to a syn-orogenic basin formed after the collision between Eurasia and the Taurides–Anatolides–South Armenian microplate. The Oligocene–Miocene Qom Formation with basal conglomerates unconformably covers all the earlier formations, including the Palaeozoic formations, indicating intense shortening before its deposition. Compressional deformation continued and is manifested by numerous folds, mainly west-dipping thrusts and reverse faults cutting the Qom Formation, and by recent NW–SE dextral strike-slip faults. This illustrates the continuous shortening and uplift (with intense erosion) resulting from the advanced stage of the collision between Arabia and Eurasia. The structural location of the tectonic units suggests that the Khoy Gondwana-related basement was part of the South Armenian Block and that the Khoy allochthonous ophiolites were obducted on it from the Amasia–Stepanavan–Sevan–Hakari suture zone.

The calc-alkaline and adakitic volcanism of the Sabzevar structural zone (NE Iran): Implications for the Eocene magmatic flare-up in Central Iran

A major magmatic flare-up is documented along the Bitlis–Zagros suture zone in Eocene–Oligocene times. The Cenozoic magmatism of intraplate Central Iran is an integrant part of this tectono-magmatic scenario. The Cenozoic magmatism of the Sabzevar structural zone consists of mostly intermediate to felsic intrusions and volcanic products. These igneous rocks have calc-alkaline and adakitic geochemical signatures, with nearly coincident zircon U–Pb and mica Ar–Ar ages of ca. 45Ma. Adakitic rocks have quite low HREE and high Sr/Y ratio, but share most of their geochemical features with the calc-alkaline rocks. The Sabzevar volcanic rocks have similar initial Sr, Nd and Pb isotope ratios, showing their cogenetic nature. Nd model ages cluster tightly around ~0.2–0.3Ga. The geochemistry of the Sabzevar volcanic rocks, along with their isotopic signatures, might strangle that an upper mantle source, metasomatized by slab-derived melts was involved in generating the Sabzevar calc-alkaline rocks. A bulk rock trace element modeling suggests that amphibole–plagioclase–titanite-dominated replenishment-fractional crystallization (RFC) is further responsible for the formation of the middle Eocene Sabzevar adakitic rocks. Extensional tectonics accompanied by lithospheric delamination, possibly assisted by slab break-off and melting at depth was responsible for the Eocene formation of the Sabzevar magmatic rocks and, more in general, for the magmatic “flare-up” in Iran.

One Dimensional Evolution Modeling of Source Rocks in the Chaluhe Basin, Yitong Graben

Chaluhe Basin is in Jilin Province of China with a cumulative sedimentary rock thickness of about 6000 meters and has four subdivisions: Wanchang Structural High, Bo-Tai Sag, Xinanpu Sag, Liangjia Structure High and the Gudian Slope. The basin with its better source rock distribution and more favorable maturation indicators than the adjacent Moliqing and Luxiang Basins is expected to be a potential hydrocarbon-producing basin. Four (4) wells were used in determining the maturation hydrocarbon generating potential of the mudstone beds present in the Eocene Formations (Shuangyang, Sheling and Yongji). Obtained result revealed heat flow average of 71.8 mW/m2, oil generation between 3.15 mg/g TOC and 39.49 mg/g TOC with gas generation of 6.98 mg/g TOC to 92.83 mg/g TOC. In conclusion the Eocene Shuangyang mudstone is the main petroleum source rock.

Lithofacies and biofacies characteristics and whales skeletons distribution in the Eocene rock units of Fayoum Area, Egypt

At Wadi Al Hitan area, rapid lateral and vertical variation is observed among the exposed middle and upper Eocene rock units. The tradionally known formations (Gehannam, Briket Qaroun, Qasr El-Sagha formations) interfinger laterally and not chronologically stacked above each other in most areas. Fine siltstones and claystones characterize the Gehannam Formation, sandstones and calcareous sandstones are characteristic for Briket Qaroun Formation, dark gray claystones are attributed to Garet El-Naqb Formation and interbedded claystones are attributed to Qasr El-Sagha Formation, irrespective of their stratigraphic position. Within these formations large numbers of marine vertebrate and invertebrate fossils exist at different stratigraphic levels. Whales are classified into four species belonging to four genera, these include Basilosaurus isis, Dorudon atrox, Saghacetus Osiris and Anclacetus simonsi. Basilosaurus isis and Dorudon atrox are the most common whale species exist in these formations. No major break in sedimentation has been described within the Eocene formations in Fayoum region. Only a well marked low sea stand is indicated at the top of the Gehannam Formation where it overlain by Birket Qaroun Formation.

Eocene age of the Baranowski Glacier Group at Red Hill, King George Island, West Antarctica

AbstractRadiometric and geochemical studies were carried out at Red Hill in the southern part of King George Island (South Shetland Islands, northern Antarctic Peninsula) on the Bransfield Strait coast. The rock succession at Red Hill has been determined to represent the Baranowski Glacier Group that was previously assigned a Late Cretaceous age. Two formations were distinguished within this succession: the lower Llano Point Formation and the upper Zamek Formation. These formations have stratotypes defined further to the north on the western coast of Admiralty Bay. On Red Hill the Llano Point Formation consists of terrestrial lavas and pyroclastic breccia; the Zamek Formation consist predominantly of fine to coarse tuff, pyroclastic breccia, lavas, tuffaceous mud-, silt-, and sandstone, locally conglomeratic. The lower part of the Zamek Formation contains plant detritus (Nothofagus, dicotyledonous, thermophilous ferns) and numerous coal seams (vitrinitic composition) that confirm the abundance of vegetation on stratovolcanic slopes and surrounding lowlands at that time. Selected basic to intermediate igneous rocks from the succession have been analysed for the whole-rock K-Ar age determination. The obtained results indicate that the Red Hill succession was formed in two stages: (1) from about 51–50 Ma; and (2) 46–42 Ma,i.e.during the Early to Middle Eocene. This, in combination with other data obtained from other Baranowski Glacier Group exposures on western coast of Admiralty Bay, confirms the recently defined position of the volcano-clastic succession in the stratigraphic scheme of King George Island. The new stratigraphic position and lithofacies development of the Red Hill succession strongly suggest its correlation with other Eocene formations containing fossil plants and coal seams that commonly occur on King George Island.

Source and Reservoir Rock Potential of Tertiary Units in the Kozaklı Basin, Central Anatolia, Turkey

The authors present the hydrocarbon source rock potential and reservoir properties of the Eocene Formations in the Central Anatolian Kozaklı Basin. Potential source and reservoir rocks in the Kozaklı basin include transgressive-regressive bank carbonates, fore-bank, deep-marine shales and sandstones, and coal and bituminous facies. The organic geochemical data of the Middle Eocene shales (Sarılar Formation) show that inadequate to marginal source rock qualities, and marginally mature to overmature characteristics, resulting from heat flow regime of the studied area. Alemli Member of the İncik Formation is good to excellent according to TOC wt% and immature to mature source rock from Tmax values. Sedimentological features and age data indicate that the Uzunlu Formation was deposited under the control of antecedent topography. Reservoir properties of the Uzunlu Formation and Keklicek member indicate that the carbonate unit is not adequate for reservoir rock. However, siliciclastics of the Sarılar Formation could be reservoir potential due to its high porosity and permeability values.

New data on the stratigraphy and environment of the Eocene formation at the Aktolagay Plateau (West Kazakhstan)

Detailed geological description along with sedimentological and petromagnetic studies provided new data on the structure and formation environments of the Eocene key section at the Aktolagay Plateau (North Peri-Caspian, West Kazakhstan). The volumes of the Alashen and the Tolagaysor Formations were revised.

Geothermal bathing and recreation centres in Poland

Ten geothermal bathing and recreation centres have been established in Poland from 2006 to 2013. The largest number of geothermal bathing and recreation centres is located in the Podhale region and in the Polish Lowlands. These structural units have the best geothermal conditions. The maximum reservoir’s temperatures in the main aquifer of the Podhale Geothermal System can reach ca. 120–128 °C in the deeper parts of the system. The most prospective and exploited aquifers occur within the Middle Triassic formations and in overlaying Middle Eocene formations at the depth of 1,000–3,700 m. At present, five operating centres are located in the Podhale region. They use geothermal waters with the temperature of 27–82 °C (the lowest and the highest wellhead temperature of water from wells which are connected for recreational purposes) and total dissolved solids (TDS) of 0.4–3 g/dm3. In the Polish Lowlands, the reservoir’s temperatures vary from 20 to 130 °C at depths of 1–4 km. The most prospective geothermal aquifers of the Polish Lowlands occur within the Lower Cretaceous and the Lower Jurassic formations. Five geothermal recreation centres are currently operating. The centres use waters with the temperature of 38–72 °C and a wide range TDS from 0.4 to 79 g/dm3. Geothermal waters of the Polish Lowlands are generally high in Na and Cl concentrations. The new centres will use the waters of Lower Jurassic aquifers, the outflow temperatures of which vary from 27 to 82 °C and a TDS from 6 to 140 g/dm3.

Palaeobiogeographic relationships and palaeoenvironmental implications of an earliest Oligocene Tethyan ichthyofauna from Egypt

The Fayum Depression of Egypt has produced a great diversity of fossil material, including marine and freshwater fishes. In contrast to the Eocene formations of the Fayum, the Oligocene Jbel Qatrani Formation has been more or less consistently considered to be deposited in a freshwater environment; however, the ichthyofauna indicates a more complex picture. Cenozoic fishes have been convincingly used to interpret the palaeoenvironment in which sediments were deposited. Based on the elasmobranch and osteichthyan faunas of the Jbel Qatrani Formation, we interpret that this formation was not deposited entirely in fresh waters, but had some marine influence, particularly in the lower part of the formation. The mixture of freshwater elements, such as polypterids and alestids, with brackish and marine elements, including myliobatid stingrays, in the Quarry E site suggests a local palaeoenvironment that was very close to the shoreline, in a less protected area, or under more seasonal influence than the rest of the sites in the formation. Additionally, the early Oligocene elasmobranch fishes from Quarry E have a strong biogeographic relationship with sites in Oman and Pakistan, in the eastern Tethys, representing a restricted fauna possibly limited in distribution by cooling global temperatures.

Natural tracers in Senonian–Eocene formations for detecting interconnection between aquifers

Relatively high concentrations of dissolved bio-Barium and bio-silica in groundwater in Paleocene–Eocene carbonate aquifers caused by the Paleocene–Eocene thermal maximum are proposed as tracers for delineating zones of leakage into adjacent aquifers. In fresh, oxidized and not thermal groundwater (within a narrow range of temperatures) these tracers can be considered as conservative. In addition, certain trace elements (U, Mo, Se and Tl) of phosphates widespread in Senonian carbonate strata are suggested to serve as tracers of water originating from these sediments. The locally increased concentrations of these trace elements in groundwater of a carbonate aquifer underlying the Senonian strata were also proposed as tracers of water leakage from above. The proposed tracers of water in Eocene and Senonian strata have been used for delineating zones of local leakage into the underlying Turonian aquifer in the Yarkon-Taninim basin (YTB) of Israel. Results of geochemical survey of 208 wells in the Turonian aquifer of the YTB were used for Pearson’s correlation and Principal Component Analysis (PCA) for detection of interconnection zones. PCA revealed 4 factors explaining up to 86% of variance in groundwater chemistry in the Turonian carbonate aquifer. Two factors, first – with high loadings of Ba and SiO2, and second – with high loadings of U, Mo, Se and Tl, were interpreted to be related to local groundwater leakage from Eocene strata into the Turonian aquifer, fast and slow, respectively. Mapping of these two factors enabled delineation of areas where local inflow of water from the Eocene aquitard exists.

The Steck Site (41WD529), a Titus Phase Settlement in the Lake Fork Creek Drainage Basin, Wood County, Texas

The Steck site (41WD529) is a 15th to early 16th century A.D. Caddo settlement situated in the far western margins of the modern Pineywoods of East Texas, in the upper Sabine River basin in Wood County. The site is specifcally situated in the uplands more than 12m above the Dry Creek foodplain, in the upper part of the Lake Fork Creek drainage basin. Two natural springs emerge from the Queen City Eocene formation immediately below the site. There are two midden deposits at the Steck site, as well as evidence for structures arranged around an open plaza in a small community. The archaeological investigations reported on in this article took place in 1976 in a ca. 9 m diameter trash midden deposit along the edge of the upland landform; the trash midden was ca. 30 cm in thickness. Available notes and analysis records have been used to reconstruct what was accomplished at the site and the kind and range of recovered artifacts.

Organic geochemical study of source rocks and natural gas and their genetic correlation in the central part of the Polish Outer Carpathians

Geochemical characteristics of organic matter (quantity, genetic type, maturity and petroleum potential) were determined in profiles of Lower Cretaceous–Miocene strata of the Dukla and Silesian units of the Polish Outer Carpathians in the Tarnów-Dębica-Nowy Sącz-Gorlice-Jasło area. This determination was based on Rock-Eval, isotopic, and biomarker analyses of 159 rock samples. Oligocene Menilite beds reveal the best hydrocarbon potential within the investigated formations (depositional units of the so-called flysch strata) and can be considered as primary source rock in the study area. Marine and mixed marine–terrestrial kerogen present in these rocks is immature in Silesian Unit and mature (oil window) in Dukla Unit, respectively. The Lower Cretaceous–Eocene formations (Veřovice, Lgota, Godula and Istebna beds, Variegated Shales, and Ciężkowice beds) of the Silesian Unit reveal variable amounts of mostly gas-prone kerogen and can be considered as additional source of hydrocarbons. The Upper Oligocene–Lower Miocene Krosno beds and Miocene Chaotic beds have a variable organic matter content, usually over 1 wt%, but very low maturity and low hydrocarbon potential predispose them as a source of microbial methane. Ten natural gas samples from sandstone reservoirs of the Upper Cretaceous–Lower Miocene strata in the Silesian Unit of the Outer Carpathians were analysed for molecular and isotopic compositions in order to establish their origin and role of thermogenic and microbial processes. Thermogenic gases without the admixture of microbial methane were encountered only in one well (Bystra-4) in the block A of Szalowa-Heddy-Bystra gas deposit. Thermogenic gas component was generated at a maturity level of 0.7 to 1.0% of vitrinite reflectance (Ro) scale from mixed Type II/III kerogen dispersed in the Oligocene Menilite beds from a few fields within the Silesian Unit. Microbial methane had been generated earlier from the same organic matter, during microbial carbon dioxide reduction process. A significantly high microbial component occurs mainly in the gases from Kobylanka (gas horizon), Gorlice-Glinik, and blocks C and B of the Szalowa-Heddy-Bystra fields. The microbial gases were generated within the Oligocene Menilite beds and/or Miocene Chaotic beds within local zones in the study area. Carbon dioxide originated both from thermogenic and microbial processes.

Sequence stratigraphy of Aqra Formation (Late Upper Campanian–Maastrichtian) in Geli Zanta corge, Northern Iraq

The Aqra Formation represents a succession that was deposited over most of Northern Iraq and adjacent regions. In north Iraq, in the core of NW–SE trending Aqra anticline, a 438-m-thick section of the Aqra Formation crops out at Geli Zanta corge. The base of the Aqra Formation is not exposed here. The upper contact is unconformably overlain by Paleocene–Lower Eocene formations (Kolosh and Khurmala formations). A hundred and one samples were collected from the section and used for biostratigraphic and microfacies analysis. According to the occurrence of larger Foraminifera (Orbitoides media and Orbitoides apiculata) and planktonic Foraminifera (Abathomphalus mayaroensis), Late Upper Campanian–Maastrichtian age was determined for Aqra Formation. Fifteen facies were distinguishable throughout the formation, representing tidal flat (supratidal), restricted marine shelf (lagoon) and shelf margin rudist reef, and its related debris. These environments were used to interpret three depositional sequences which correlate with those of Aruma Formation (KSA), Simsima Formation (UAE) in Arabian Plate, and with Iraqi formation sequences. Three maximum flooding surfaces were recognized as MFS 175, MFS 180, and MFS 190.