Thick-bedded Limestone Research Articles

Research on orthotropic anisotropy characteristics of thick bedded limestone based on in situ deformation tests

The orthotropic anisotropy of sedimentary rocks has a significant impact on the force and deformation behavior of the project. In this paper, radial pressurization tests were carried out in the borehole in a typical northern karst area to obtain the deformation properties and orthotropic anisotropy of the rock masses. The test results showed that the deformation modulus and elastic modulus of the limestone rocks in the dam site area obeyed normal distribution. The deformation modulus was basically larger than the proposed deformation modulus of Class II rocks (10 GPa). The deformation behavior and anisotropy degree of the limestone showed a weak correlation with the elevation, but a strong correlation with the development density of the rock joints. The larger development density of the rock in the right bank test section leads to a larger degree of orthotropic anisotropy and frequency of occurrence.

Microfacies correlation, analysis and palaeoecological reconstruction of Rupelian–Aquitanian succession in the central part of Lorestan Province, Northwestern Iran

The Oligocene–Miocene Asmari Formation is a sequence of shallow-water carbonate carbonates in the Zagros Basin. This formation is a significant oil reservoir that was formed in the Zagros foreland basin in southwestern Iran. The Razan section, located in the northwest of Zagros in the Lorestan province, was investigated to study microfacies types and evaluate the sedimentary environment. This section was then compared with the MakhmalKuh and Dehloran sections. It comprises limestone units with thin to medium strata, sometimes thick-bedded limestone, and other skeletal and non-skeletal components. Based on the biostratigraphy studies, 24 foraminifer genera and species have been identified. Among the foraminifera, the species of Peneroplis farsensis, Peneroplis evolutus, Austrotrilina howchini, Austrotrilina asmarensis, Dendritinarangi, Quinqueloculina sp., Triloculina trigonula, Pyrgo sp., Polymorphinids, Spiroluculina sp. and Meandropsina anahensis are the most important specimens. Based on identified co-occurrence taxa, the Austrotrilina howchini–Peneroplis evolutus assemblage zone has been recognised in the study area, which indicates early Miocene (Aquitanian). Texture analysis and faunal assemblages led to the recognition of fourteen microfacies. Based on the petrographic analysis, five depositional settings were determined in the studied section: (a) the outer ramp settings dominated by pelagic foraminifera, bryozoan, echinoid and benthic foraminifera such as Nummulites, Rotalia, Dendritina and Meandropesina iranica as a proxy for relatively deep marine conditions; (b) the mid ramp, characterised by sizeable perforate foraminifera such as Amphistegina, Operculina, Heterostegina and planktonic foraminifera; (c) the barrier, marginal marine environment dominated by foraminifera such as Miogypsinoides sp., Peneroplis, Meandropsina, Dendritina and Neoalveolina, as well as peloid and corallinacean algae; (d) the lagoon dominated by benthic foraminifera Austrotrillina, Dendritina, Peneroplis, Miogypsinoides, Borelis, Archaias, miliolids and red algae and (e) the tidal flat, the shallowest part of the inner ramp, dominated by fenestral dolo-mudstone without any fossils. The faunal assemblages represent warm tropical waters under euphotic and mesophotic conditions in a homoclinal ramp.

Palaeobiogeography, palaeoecology, and sequence stratigraphy of the Upper Jurassic carbonate succession of the Lar Formation, central Alborz Zone, Iran

Foraminifera, ammonites, and calcareous dinoflagellates were used for stratigraphy and, together with microfacies, for the assessment of the palaeoenvironmental conditions of the Upper Jurassic deposits in the central Alborz Zone of northern Iran. The Lar Formation (Lar Fm.) in the Polur section is of latest Oxfordian to early Kimmeridgian age. The ammonite Subnebrodites planula and the calcareous dinoflagellate Colomisphaera nagyi have been introduced as new biomarkers of the lower Kimmeridgian in the central Neo-Tethys. The distribution of calcareous dinoflagellates reflects possible dispersal routes along a narrow seaway between the western Neo-Tethys and the Alborz Zone in the central Neo-Tethys. The Terebella-Crescentiella associations of the Lar Fm. represent a low-energy setting under dysoxic conditions in the Central Neo-Tethys Ocean. The benthic foraminiferal assemblages in this formation show a high dominance of infaunal taxa and r-selected strategists. This assemblage is reminiscent of eutrophic conditions and low oxygen levels in the lower part of the Lar Fm. Good preservation of the hexactinellid sponges in the upper part of the Lar Fm. also indicates an oxygen-minimum zone. Three third-order depositional sequences can be distinguished in the study area based on six microfacies. Depositional sequence 1 (DS1) is composed mainly of argillaceous limestone and medium- to thick-bedded limestone, corresponding to an outer ramp-to-middle ramp environment. Depositional sequence 2 (DS2) comprises breccia limestone and thick-bedded limestone facies in its lower part and thin-bedded limestone to massive limestone in its upper part. The breccia limestone facies may be associated with subaerial exposure and reworking of previously deposited sediment during a relative sea level fall. The thin-bedded limestone to massive limestone of DS2 consists mainly of bioclastic mudstone to wackestone (outer ramp). These represent an deep-water outer homoclinal ramp facies. Depositional sequence 3 (DS3) consists mainly of massive limestone to thick-bedded limestone with a bioclastic peloidal microbial Crescentiella packstone (middle ramp). The relative stratigraphic positions of DSs1–3 and sequence boundaries in the uppermost Oxfordian to lower Kimmeridgian of the Polur area show a fair match to the upper Oxfordian to lower Kimmeridgian sequences (JOx7, JOx8, JKi1 and JKi2) on the global sea level curve.

Development and Application of Methodology for Quantification of Overbreaks in Hard Rock Tunnel Construction

A methodology for determining overbreaks in hard rock tunnel construction using the drill-and-blast technique is presented in this paper. The methodology was developed for and applied to crystalline medium- to thick-bedded limestone, but it can be used in any jointed hard rock mass. Overbreaks are inevitable in hard rock tunnelling in a low-confinement environment (shallow tunnels up to several hundred meters deep) as a result of wedge failures along unfavourably oriented discontinuities caused by blasting. It is widely accepted in engineering practise that overbreaks will be inevitable even if smooth contour blasting is applied. If not controlled, overbreaks can result in extreme financial and time costs; and determining, predicting, and mitigating them is the key to successful tunnel construction in hard rock. Technological overbreaks, which are caused by the inappropriate use of drill-and-blast excavation, are not easily distinguished from the inevitable overbreaks dictated by the geological conditions with which they interfere and overlap. A methodology was developed with the aim of distinguishing the two causes of overbreaks, which can be applied in any phase of tunnel construction for evaluation or mitigation. The analysis of key inputs, including geological face mapping, shear strength tests along discontinuities of the rock mass, and their spatial orientation relative to tunnel advancement and survey overbreak measurements, is presented in this paper. Due to the stochastic and statistical nature of the problem, a probabilistic concept was also applied as part of the method so that the probability of failure around unprotected tunnel sections could be determined. The so-called stability criterion is introduced to distinguish between stable and unstable sections in terms of the probabilistic safety factor. The quantification of overbreaks, including the threshold value distinguishing technological from geological overbreaks, is proposed. The application of the methodology, demonstrated on an 8.1 km long section of a 12 km long pressure tunnel in hard rock, is presented in the paper.

Biostromal unit from the Middle Devonian Jinbaoshi Formation, Sichuan, Southwest China: Implications for ecological structure of coeval reef communities

This study provides a comprehensive palaeontological and palaeoecological analysis of a middle Givetian (Middle Devonian) coral-stromatoporoid biostromal unit from the upper member of the Jinbaoshi Formation, northern Sichuan Province, Southwest China. The biostromal unit is 17.7 m of medium- to thick-bedded limestones, and lacks observable morphological relief in the field. Diverse shallow marine benthic fossils are common elements of the biostromal unit encompassing stromatoporoids (7 genera), tabulate corals (4 genera), brachiopods (2 genera), plus unidentified rugose corals, chaetetids, bryozoans, tubeworms, ostracods, gastropods, crinoids and calcimicrobes. In terms of the biotic composition and biostrome-building contributors, three ecological units are recognized: Alveolites–Clathrocoilona community (EU 1), Salairella–Pseudotrupetostroma community (EU 2) and Scoliopora–Idiostroma community (EU 3). High fragmentation of bioclasts partially with micritic envelopes in wackestone, packstone to grainstone matrix and the dominance of low-profile stromatoporoids indicate deposition in shallow water conditions with episodic high sedimentation rate and frequent turbulent periods. Muddy silt- to sandstone facies overlie the biostromal unit, and are interpreted to represent a shallowing-up sequence, together with terrigenous input, thus triggering termination of the biostromal unit. This biostromal unit is similar to the other early to middle Givetian reefs of South China, East Australia, West Europe, East Europe and North Africa in relation to their fossil composition and reef-building characteristics. The stability of the reef communities (i.e. no conspicuous extinction) and common occurrence of unusual reef structures (e.g. coverstone) are thus interpreted as significant biotic factors for the expansion of large-scale ecosystems during the Phanerozoic reef-building acme.

Uppermost Triassic Halstätt-like cephalopod limestone (Lilu Facies) and Foraminifera, Timor-Leste

Ammonoid-rich wackestone beds forming a ca 2 m section between shallow-marine limestones of the Bandeira Group (Norian to possibly Rhaetian) and a wackestone–calcareous mudstone succession belonging to the Lower Jurassic Wailuli Group are recorded from the western part of Timor Leste. They are included in the Halstätt-like Lilu Facies of the Bandeira Group. Age-diagnostic involutinid foraminiferal species, not previously recorded from Timor, include Involutina liassica, Trocholina sp. ex. gr. Trocholina turris and Lamelliconus permodiscoides, which collectively indicate a Rhaetian age, possibly ranging down to the Sevatian. The conodont Norigondolella steinbergensis, recorded low in the section, is consistent with this age determination. The Lilu Facies was deposited at a water depth of a few tens of metres, as suggested by the presence of extensive cyanobacterial borings into shell fragments and the presence of microbial laminations including the presence of stromatolites and bacinellid-like fabrics. Among macrofossils, common ammonoids are present in the section, and marine reptile bones are conspicuous in the lower beds. Other biogenic components of the rock observed in acetate peels and thin sections are abundant echinoderm debris (including pentacrinoid columnal plates), bivalve fragments and micro-gastropods, rare siliceous sponge spicules, solitary corals, and brachiopod debris. In the studied region, a major drowning of a shallow-marine carbonate platform took place probably in the Rhaetian or possibly latest Norian. Similar ‘ammonitico rosso limestone’ interbedded with thick-bedded limestones of a shallow-marine carbonate platform is present in the uppermost Triassic of Seram. More detailed biostratigraphical comparisons and correlations of similar units in Timor and other nearby islands may indicate a general marine drowning of Late Triassic carbonate platforms, at least in the northern part of the East Gondwana Interior Rift system, during the Rhaetian or possibly latest Norian.

Spatial heterogeneity in carbonate-platform environments and carbon isotope values across the Paleocene–Eocene thermal maximum (Tethys Himalaya, South Tibet)

The Paleocene–Eocene Thermal Maximum (PETM, ~56 Ma) is a large negative carbon isotope excursion (CIE) that testifies to a massive perturbation of the global carbon cycle and has been considered to be an ancient, deep-time analogue for present and future climate change. However, the environmental and carbon isotopic response to the PETM in shallow-water carbonate platforms has remained largely elusive. This study presents new sedimentological, biostratigraphic, and carbon isotopic data to evaluate the impact of the PETM on a shallow-water carbonate platform from more proximal southern parts of the northern Indian continental margin. Detailed biostratigraphy and carbon isotope data indicate that the PETM occurs 3 m below the boundary between nodular and thin-bedded limestones, is maintained up to the thin-bedded limestone and calcareous marl interval, and is followed by recovery at the base of thick-bedded limestone interval. Microfacies analysis testifies to a regression from open to restricted shallow-marine environments at the transition from PETM onset to PETM core, and shallowing continued through the PETM core. Restricted lagoonal deposition was renewed during PETM recovery. These environmental changes were associated with two major turnovers of shallow-water biota. We infer that the first sudden biotic change at the PETM onset may relate to intensified continental weathering, whereas the second biotic change at PETM recovery may have been caused by sea-level fall. The smaller magnitude of the CIE observed in proximal, shallower-water than in distal, deeper-water environments is ascribed to increased primary productivity due to increased nutrients' supply associated with intensified continental weathering. • A regression at the PETM onset from open to restricted shallow-marine environments, and restored to restricted lagoon at the recovery • The sudden environmental changes across PETM were associated with major changes of shallow-water biota • The smaller magnitude of the CIE observed in shallower-water than in deeper-water strata is ascribed to increased primary productivity

Microfacies Analysis And Depositional Environment Of Pila Spi Formation (Middle - Late Eocene) In The Nerwa Section, Berat Anticline, High Folded Zone, Kurdistan Region, Northern Iraq

Microfacies analysis and depositional environment of the Pila Spi Formation (Middle-Late Eocene) were studied in the Nerwa outcrop, Berat anticline, High Folded Zone in Iraqi Kurdistan Region. The total thickness of the formation is 13.5 m composed of medium to thick bedded yellow to white limestone and thick bedded grey to white dolomitic limestone. It is interbedded with thin beds of yellow marl in the lower part and have chert nodules in the upper part. The petrographic study of 17 thin sections of the Pila Spi carbonate showed that the majority of the carbonates are micritic mixed with some microspar. The skeletal grains involve benthonic foraminifera, ostracods, mollusca, dasycladacean green algae, pelecypods, gastropods, rare planktonic foraminifera and bioclasts. Non skeletal grain included peloids, intraclasts and extraclasts which is mainly monocrystalline quartz grain. Based on field observations and petrographic analysis, three different lithological units were distinguished in the Pila Spi Formation in the studied section. They are in ascending order: medium to thick bedded limestone interbedded with marl unit, thick bedded dolomitic limestone unit and, cherty limestone unit. Depending on detailed microfacies analysis of carbonate rocks, three main microfacies and twelve submicrofacies were recognized in the studied section of the Pila Spi Formation. From the sum of all petrographic, facies and textural analyses, it is here concluded that Pila Spi Formation in the Nerwa section was deposited at subtidal semi-restricted lagoon, in lower part gradually changed to open lagoon environment toward the upper part.

Mechanical characteristics of thick-bedded limestone with different bedding angles subjected to acid corrosion

Mechanical characteristics of thick-bedded limestone with different bedding angles subjected to acid corrosion

New Middle Permian (Capitanian) fusulinid genera from the Karakaya Complex, central Anatolia, Turkey: Taxonomic remarks

The Karakaya Complex widely exposed in the north of Turkey can be differentiated into two units as the Lower Karakaya Complex and Upper Karakaya Complex. A tectonic slice composed of medium to thick-bedded limestone belonging to the Upper Karakaya Nappe is located to the south of Ankara near Gokcehuyuk village. A very diverse fusulinid fauna from this slice has two new taxa of Middle Permian (Capitanian) age. As a result of the study of the fusulinids from the strata of the Upper Karakaya Nappe, two new genera Postkwantoella and Kahlerinella are proposed as well as two subfamilies: Kwantoellinae subfam. nov. (Postkwantoella) and Kahlerininae (Kahlerinella). The new genus Postkwantoella differs from the similar genus Kwantoella by well-developed axial fillings and fewer volutions. Wall structure and completely straight coiling of these latter two genera indicates that they should be classified under the Kwantoellinae subfam. nov. The other new genus, Kahlerinella, is differentiated from the closely related genus Kahlerina by having lenticular early whorls, globular test shape and by the absence of chomata.

Macrofaunal communities in the Cenomanian-Turonian strata of Kasserine area (west central Tunisia, North Africa)

ABSTRACT The Cenomanian/Turonian strata of the Kasserine area: Tunisia exhibit a unique sedimentological and palaeontological pattern. Five lithological units have been identified: 1) lower unfossilferous black shale; 2) well-bedded marly unit with thin limestone interbeds; 3) marl unit, 4) same as 2, and 5) unfossilferous dolomitic thick-bedded limestone. The middle three units contain low diversity macrofaunal communities dominated mainly by oyster bivalves with few gastropods and echinoids. Fortunately, three marker ammonite species were identified and are used to subdivide the studied interval into three biozones, including 1) Calycoceras cenomanense, 2) Pseudaspidoceras pseudonodosoides and 3) Neoptychites Cephalotus. Based on constrained clustering and ordination techniques, three distinct macrofaunal associations were identified: 1) Ceratostreon flabellatum, 2) Ilymatogyra africana and 3) Tylostoma (Tylostoma) globosum. In general, the macrofaunal diversity decreases at the Cenomanian-Turonian boundary, which is interpreted to be a consequence of a global sea-level rise and the destruction of shallower habitats. Based on the life habits of the macrofaunal communities, a change from a high-energy (Ceratostreon and Ilymatogyra) to a low-energy (Tylostoma) shallow marine environment was indicated. The dominance of oysters in these nutrient-rich sediments was attributed to their ability to tolerate high turbidity water and to colonise soft-substrate sea bottoms.

Biostratigraphy, microfacies and sedimentary model of the Qom Formation in the Posht- Darband section, northwest of Hamadan

In order to determination of biozones, facies types and sedimentary model, the Posht Darband stratigraphic section of the Qom Formation with thickness of 330 meters located in the northwest of Hamedan, structural zone of the Sanandaj- Sirjan, has been considered. On the basis of field observations, Qom Formation is composed of medium to thick-bedded limestone (Member a) and alternation of sandy limestone, sandstone and green marl (Member b). According to paleontological study, seventeen genera and nine species of benthic foraminifera and other skeletal components are introduced from the Posht Darband section and consequently, Lepidocyclina - Operculina - Ditrupa Assemblage zone has been recognized in the Qom Formation. Facies analysis (Variety in fauna features, fabrics, and sedimentary textures) has produced eight microfacies related to the four facies belts of tidal flat, reef, slope and open marine. Base on abundance in reef facies deposits including coral boundstone, algae and bryozoan, an open shelf is proposed for the Qom Formation. The vertical distribution column of the facies types (without considering the possible erosion phenomenon) suggests that the facies changes in member a are gradual, but in member b they were rapidly, with facies retrogradation and progradation.

Microfacies analysis and depositional environments of the Upper Cretaceous Fort Munro Formation in the Rakhi Nala Section, Sulaiman range, Pakistan

The Fort Munro Formation is 200-m-thick mixed carbonate–siliciclastic succession of Late Cretaceous (Campanian) age exposed at the Rakhi Nala Section, Sulaiman Range, Lower Indus Basin, Pakistan. The Fort Munro Formation is representing thin- to thick-bedded limestone with interbedded marls, shale and sandstone. Detailed microfacies analysis revealed the recognition of 15 microfacies types (11 carbonate and 4 sandstone). These facies were deposited on both inner and middle ramp platform. The inner ramp sediments are more widespread than the corresponding middle ramp including open-marine, skeletal shoals, semi-restricted, carbonate sand shoals and banks and lagoon depositional environments. The uppermost part of the Fort Munro Formation has received sufficient amount of siliciclasts, thereby producing a sandstone texture. These siliciclasts indicate the tectonic uplift, which thereby increases the source area rejuvenation. Therefore, a mixed carbonate–siliciclastic, moderately storm-dominated homoclinal ramp depositional environment is suggested for the Fort Munro Formation.

Geological, geochemical and microthermometric characteristics of the Hakkari region Zn-Pb deposits, SE Turkey

The Hakkari region in SE Turkey contains large Zn-Pb deposits, primarily of non-sulfide ore in Upper Triassic passive margin carbonates. In the Karakaya, Meskantepe and Üzümcü Zn-Pb deposit, the 3 main and >15 ore layers alternate with a thick-bedded limestone. The feeder in the region veins are well defined, containing both non-sulfide and sulfide ore. Primary sulfide ore contains between 1 and 37 % Zn, has transformed to “non-sulfide” ore containing Zn > 10%. Both non-sulfide and sulfide ore is associated with As, Se, Hg, Tl, Mn and Sb, which is similar to other SEDEX deposits. The average δ34S of the stratiform and feeder zone sulfides are 2.1‰ and 1.67‰, respectively. Sulfur isotope data of sphalerite, galena and pyrite (from −3.4 to 8.8‰) indicates that sulfur came from a homogeneous large source. Sulfate was reduced by the process of thermochemical sulfate reduction (TSR) rather than bacterial sulfate reduction (BSR). Lead isotope values (206Pb/204Pb ≈ 18.49, 207Pb/204Pb ≈ 15.66 and 208Pb/204Pb ≈ 38.69) reflect an evolved upper crustal source. The homogenisation temperature (Th) and salinity of fluid inclusions is from 165 to 289 °C, and from 1 to 22% equiv. NaCl salinity. Such a wide range of Th and salinity, and Cl/Br ratio (409 from sphalerite and galena; 662 from barite) of fluid inclusions may indicate mixing of basinal brines and seawater.Successive ore levels, laminated with shale-carbonate rich in organic matter, formed on the seafloor as banded and replacement ore. Trace element associations, fluid inclusion and isotope data indicate that the Zn-Pb deposits were formed as synsedimentary processes associated with feeder systems during the initiation of the Triassic rifting as a vent-proximal SEDEX-type. The metals (Pb, Zn, Fe) were leached from Palaeozoic and older clastic rocks in the Arabian platform by seawater sourced fluids, and ascended through deep fractures. The metalliferous fluids should have formed vein type mineralization in feeder zone, sub-seafloor replacement type ore under the ocean floor, and stratiform ore on the seafloor.

The regional facies analysis and depositional environments of the Oligocene and Lower Miocene deposits; Zagros Basin, SW of Iran

A regional transect is selected to study the paleoenvironment of the Oligocene and Lower Miocene deposits in the Zagros Basin (Persian Gulf Foreland Basin to the High Zagros). This study rebuilds the sedimentary environments and paleogeography of the Zagros basin deposits in the Oligocene and the Lower Miocene. A transect consists of two stratigraphic subsurface sections at the Persian Gulf Foreland Basin, five stratigraphic subsurface sections at the Dezful Embayment, two stratigraphic outcrop sections at the Zagros Simply Folded and one exposure section at the High Zagros. The sediments are included Asmari Formation and the Pabdeh Formation. Lithostratigraphy studies show that the Pabdeh Formation has been composed of an alternation of marls and medium-bedded argillaceous limestone. The Asmari Formation is generally composed of medium- to thick-bedded limestone. Micropaleontology studies offer Early Oligocene for Pabdeh Formation and Early–Late Oligocene to Early Miocene age for Asmari Formation. Variety in fabrics, textures and fauna features has produced 13 microfacies and based on geometry, lateral and vertical facies relationships, the homoclinal ramp is proposed for the Oligocene and Lower Miocene deposits. Hence, corresponding to this research, the Rupelian sedimentation has occurred in the Dezful Embayment and Zagros Simply Folded, so that a systematic progradation suggests from Zagros Simply Folded (N/NE) (Asmari/Pabdeh Formation) to the Dezful Embayment (S/SW) (Asmari carbonate system). Following a regression system during the Late Oligocene to the Early Miocene, continuing sedimentation uniformly has been felt out in the shallow water system throughout the study area.

Facies control on selective dolomitization and its impact on reservoir heterogeneities in the Samana Suk Formation (middle Jurassic), Southern Hazara Basin (NW Himalaya, Pakistan): an outcrop analogue

This studied rocks form part of the southern Hazara basin in the NW Himalayan Fold and Thrust belt, Pakistan. Thick inner to mid ramp carbonate platform deposits of Samana Suk Formation (Bajocian-Callovian) mostly composed of medium to thick bedded limestone with occasional dolostone beds are exposed in various localities. In the present studies, attempt has been made to understand degree of diagenetic alterations (i.e., dolomitization) within various limestone facies due to fluid-rock interaction phenomenon, and its impact on the reservoir behavior of altered rocks based on field investigations, petrographic studies, stable isotope signatures and porosity/permeability analysis. Field observations revealed various limestone types (oolitic, burrowed, fossiliferous, micritic and sandy), whereas dolomite occurs as completely replacive phase (Dol-I), and partially replacive patchy bodies (Dol-II) respectively. Petrographic studies showed various limestone and dolomite facies, which include: (i) Grainstone facies (bioclastic grainstone, peloidal grainstone, ooidal grainstone and pel-bioclastic grainstone), (ii) Packstone facies (bioclastic packstone and peloidal packstone), (iii) Wackestone facies (bioclastic wackestone), (iv) Mudstone facies (lime mudstone, and (v) Dolomite facies (coarse crystalline strata-bound Dol-I, and fine crystalline patchy Dol-II) respectively. O/C isotope analysis revealed that Dol-I shows signatures of δ18O (−5.84 to −3.91‰ V-PDB), and δ13C (+0.6 to +2.37‰ V-PDB) are within the limit of the carbonate marine seawater signatures, hence originated from sea-water or modified sea-water, whereas Dol-II exhibited depleted δ18O values (−6.88 to −5.87‰ V-PDB) and slightly depleted δ13C signatures (+0.968 to +1.85‰ V-PDB), indicating high temperature dolomitizing fluids. During early stage of marine diagenesis, which resulted in the cementation of pores within the grainstone-packstone facies, whereas mudstone-wackestone facies remained unaltered due to low porosity and permeability. Late stage dolomitization caused partial to complete alteration of mudstone-wackestone facies, in contrast grainstone-packstone facies are not affected by dolomitizing fluids due to the fact that the pore network of these coarser facies had already been occluded by the preceding marine cementation event. Porosity and permeability analyses revealed relatively high porosity values (4–8%) and permeability values (11.5 mD) in the dolomitized facies, whereas unaltered limestone facies showed considerably low porosity/permeability values (> 1%). In conclusion, less porous/permeable fine-grained facies evolved into more porous and permeable units due to the interaction of dolomitizing fluids of hydrothermal origin, which confirms that the original sedimentary texture of rock has implications on the selectivity of any diagenetic alteration.

Benthic foraminifera of the Maastrichtian sediments from the Maliboğazi (Kalecik, Ankara) and Irmak (Kırıkkale) areas in Türkiye

The investigation focuses on benthic foraminifera and their paleoecology, particularly on the Orbitoides genus in the Maaastrichtian sediments from the northern and western Ankara City (Turkey). The hard and soft rock samples from two measured sections, namely as Malibogazi (N Ankara) and Daryaka-Irmak (W Ankara, Kirikkale) were evaluated. More than one hundred equatorial and axial sections of the Orbitoides genus were prepared. The benthic foraminifera of the Maastrichtian sediments are as follows: Dorothia sp., Marssonella sp., Lenticulina sp., Saracenaria sp., Oolina sp., Cibicides sp., Gavelinella sp., Orbitoides apiculatus, O. gruenbachensis, O. medius, Pseudomphalocyclus sp., Omphalocyclus macroporus, Lepidorbitoides sp., Sirtina sp., Sulcoperculina globosa, S. vermunti, Siderolites calcitrapoides, Laffitteina mengaudi, Laffitteina sp. In the Malibogazi area, biometric data based on the internal and external parameters of the Orbitoides genus present reliable interpretations for paleoecological approaches of the Maastrichtian time. The calcareous siliciclastics comprise abundant Orbitoides apiculatus and O. gruenbachensis species. We have identified two ichnospecies as Maeandropolydora osmaneliensis and Curvichnus semorbis in the Orbitoides tests. It is thought that meandered microboring activity are related to parasitic life modes while cave shaped ones are associated with hermit type life modes. Orbitoides bearing siliciclastics overlies reefal sediments including biostromal limestones with rich rudist fauna, Thalassoniodes rich carbonates and massive, thick bedded limestones in the Maliboğazi area. In contrast, siliciclastics indicating open sea sediments outcrop widespreadly in the Irmak area. The obtained stratigraphical, sedimantological and paleontological data show that northern part of the Ankara was shallower than western part of the Ankara during the late Maastrichtian.

New Planktonic Foraminifera Data from the Upper Cretaceous Pelagic Limestones of the Yuksekova Complex in the Maden Area (Southeast of Elazig, Eastern Turkey)

The units situated in Southeast Anatolian Orogenic Belt within the Bitlis-Zagros suture zone, are still controversial. Therefore, it is important to obtain new data from the subduction/accretion complexes along the southeast Anatolian-Zagros suture belt in the Eastern Mediterranean. Hence, this study was carried out to find out whether the pelagic limestones overlying the volcanogenic rocks in the Maden area (southeast of Elaziğ) belong to Yüksekova Complex or Maden Complex. The lavas intercalated with pelagic limestones are dark-colored, pillow shaped and massive basalts. They are commonly amygdaloidal structured showing surface cavities filled with secondary minerals. The thick-bedded limestones are mainly represented by rare planktonic foraminifera bearing wackestone and mudstone depositional texture. Rare planktonic foraminifera in the rocks are mainly represented by double keeled marginotruncanids, which are characteristic organisms of the Turonian-Santonian interval of the Late Cretaceous. Poor planktonic foraminifera assemblages obtained from the micritic limestones comprise Marginotruncana aff. marginata and M. cf. paraconcavata. According to these taxa, the age of the volcanogenic formation is Turonian-Santonian. The volcaniclastic sequence discussed in this study, were considered to be part of the Middle Eocene Maden Complex in previous studies. But, the results show that the studied volcaniclastic succession belong to the Yüksekova Complex as the age of the micritic limestones is Late Cretaceous but not Middle Eosen.

Polygnathids (Conodonta) around the Pragian/Emsian boundary from the Dacun-1 section (central Guangxi, South China)

AbstractThe base of the Emsian, which is defined by the first appearance of the conodont Polygnathus kitabicus, has never been successfully demonstrated in the South China Block (including Guangxi and eastern Yunnan). As a result, we studied conodonts from the lowermost part of the Shizhou Member of the Yukiang Formation at the Dacun-1 section in the Liujing area, Guangxi. This new investigation has revealed a conodont fauna only consisting of Polygnathus pireneae, P. sokolovi, P. kitabicus, P. sp. and Pandorinellina exigua philipi, which can be assigned to the uppermost part of the pireneae Zone and the lowermost part of the kitabicus Zone in ascending order. The Pragian/Emsian boundary at the Dacun-1 section is located in the highest thick-bedded limestone bed that can be observed in the lowermost part of the Shizhou Member. Therefore, this is the first time that the lower boundary of the Emsian defined by the lowest occurrence of P. kitabicus is reported in the South China Block. However, the scarcity of suitable limestone samples for conodont analysis in the middle and upper parts of the Shizhou Member precludes definitive identification of the upper boundary of the kitabicus Zone in the Liujing area.

Structural controls on distribution of dolines on Mount Anamas (Taurus Mountains, Turkey)

Solution dolines are characteristic landforms on the high plateaus of the Taurus Mountains. In this study, the effects of tectonic structures, drainage and slope conditions on the distribution and morphometric properties of dolines in the western part of the Central Taurus are explained. To delimit the dolines, 1/25000 scale topographic maps were used. The uppermost closed contour lines were digitized as polygons and the elevation, long and short axes, elongation ratios, orientation angles of the polygons were calculated. The doline density is compared with drainage density and mean slope values. A total of 111 rose diagrams were created in order to illustrate the superficial distribution of orientation. As a result, a total of 10,652 dolines were detected in a 711 km2 doline area and maximum density reaches 123 dolines/km2. However, according to the doline density, two distinct regions were detected, high density (R1) and low density (R2). Correlations between drainage density, slope angle and doline density are negative in the two regions. According to negative correlations, the drainage density is not a determinant factor in R1, while it is a determinant factor in R2. A 30° slope angle (in km2) limits doline distribution on the plateau surface.The orientation of all doline long axes is NW-SE, which is parallel to the general orographic extent of Mount Anamas. However, different orientations were detected and these orientations were showed in farther sub-regions according to the 111 gridded rose diagrams. The overall result of this study is that the fault and joint systems that developed on the thick-bedded limestone between thrust faults affected the doline density, while lateral strike-slip, normal faults and joint systems in front of the thrust belt were more effective on the geometric shapes of dolines.