© Author(s) 2025. CC Atribution 4.0 License Stratigraphic-genetic complexes of the bedrock of Lviv city and their geotechnical properties Stratigrafsko-genetski kompleksi kamninske podlage mesta Lviv in njihove geotehnične lastnosti Pavlo ZHYRNOV1 & Petro VOLOSHYN2 1Faculty of Natural Sciences, Comenius University in Bratislava, str. Ilkovičova 6, 842 15 Bratislava, Slovakia; *corresponding author: zhyrnov1@uniba.sk 2Geological Department of Ivan Franko National University of Lviv, str. Hrushevskoho, 4, 79005 Lviv, Ukraine; e-mail: petro.voloshyn@lnu.edu.ua Prejeto / Received 22. 9. 2025; Sprejeto / Accepted 6. 11. 2025; Objavljeno na spletu / Published online 10. 12. 2025 Key words: stratigraphy, genetic complexes, facies, geotechnical properties, soils, Lviv Ključne besede: stratigrafija, genetski kompleksi, facies, geotehnične lastnosti, tla, Lviv Abstract The geological basis of engineering geological surveys is based on age and genetic factors. The age is determined by the regional stratigraphic scheme. Identification of specific features and criteria of genetic subdivisions of rocks is the main task of studying the geological structure of the territory of Lviv city for geotechnical purposes. Stratigraphic and genetic complexes should be identified for this purpose based on the stratigraphic-genetic scheme of bedrock dissection. The bedrock of the Cretaceous and Neogene systems was separated into independent stratigraphic-genetic complexes by this principle and dissected into engineering-geological elements based on the application of stratigraphic and geotechnical research methods. The article describes each engineering-geological element with characteristic geotechnical properties and concludes their use as a basis for foundations of buildings and structures. The soils that are the most difficult in geotechnical terms are also analyzed, recommendations on foundation construction on problematic soils are given, and a set of engineering preparation measures aimed at improving the general engineering-geological situation in Lviv city are defined. Izvleček Geološka podlaga inženirsko-geoloških raziskav temelji na starosti in genetskih dejavnikih. Starost se določa z regionalno stratigrafsko shemo. Opredelitev specifičnih značilnosti in meril genetske delitve kamnin je glavna naloga pri preučevanju geološke zgradbe območja mesta Lviv za geotehnične namene. V ta namen je treba, na podlagi stratigrafsko- genetske sheme razčlenitve kamnin, opredeliti stratigrafske in genetske komplekse. Kamnine krednega in neogenskega sistema so bile po tem načelu razdeljene na samostojne stratigrafsko-genetske komplekse in razčlenjene na inženirsko- geološke elemente na podlagi uporabe stratigrafskih in geotehničnih raziskovalnih metod. Članek opisuje vsak inženirsko- geološki element z značilnimi geotehničnimi lastnostmi ter podaja zaključke o njihovi uporabi kot osnovi za temeljenje stavb in objektov. Analizirana so tudi tla, ki so v geotehničnem smislu najzahtevnejša, podana so priporočila glede gradnje temeljev na problematičnih tleh in opredeljen je nabor inženirskih pripravljalnih ukrepov, namenjenih izboljšanju splošnega inženirsko-geološkega stanja v mestu Lviv. Article GEOLOGIJA 68/2, 287-306, Ljubljana 2025 https://doi.org/10.5474/geologija.2025.013 Introduction Lviv is one of the most dynamically developing cities in Ukraine in terms of construction, in con- nection with which there is a need for a detailed study of the geotechnical properties of soils as the basis for the foundations of buildings and struc- tures. The territory of Lviv city is geostructurally located within the Lviv Paleozoic Trough, cor- responding to a deeply submerged section of the crystalline basement of the southwestern margin of the East European Platform. Paleozoic, Meso- zoic, and Cenozoic rocks take part in the geolog- ical structure of the area. Of the extensive rock complexes developed within the study area, three different-aged and different-genesis rock complex- es are of decisive importance for prospective con- struction: Upper Cretaceous, Neogene and Qua- ternary. We will focus on the description of the bedrock Upper Cretaceous and Neogene rocks in this paper and their geotechnical properties. 288 Pavlo ZHYRNOV & Petro VOLOSHYN Geotechnical characterization of soils is based on the identification and mapping of stratigraph- ic-genetic complexes of rocks, accordingly, the geological basis of engineering-geological surveys should be based on two factors – age (stratigraph- ic) and genetic. If the age factor with sufficient completeness to fulfill the tasks is strictly regulat- ed by regional stratigraphic schemes adopted by the Interdepartmental Stratigraphic Committee, there is no accepted scheme for the genetic divi- sion of rocks. The main task of studying the geo- logical structure of Lviv city from the point of view of geotechnical use and development of the territo- ry was to identify specific features and criteria of the genetic division of rocks corresponding to the specialization of works. This article presents the results and bases of the adopted stratigraphic-genetic scheme of bed- rock dissection, necessary for the allocation of stratigraphic-genetic complexes of the territory of Lviv city. Therefore, this scheme, especially in its genetic part, cannot have regional significance but is only adapted to a specific area according to the intended purpose of the works (Gruzman, 1980). Study area Lviv is located in the central part of the Lviv Region between Yavoriv, Zhovkva and Pustomyty Districts, in the Eastern European time zone at the 24th meridian. The city is located approximately 540 km west of Kyiv, at a distance of about 70 km from the border with Poland (Fig. 1). Bedrocks are confined to certain geomorpho- logical units, so it makes sense to brief ly present the geomorphological zoning of the territory of Lviv city. It is also necessary to designate individu- al landforms that will be encountered in the text of this article. Lviv city belongs to the Volhynian-Po- dolian Region of strata-denudation upland by the map of geomorphological zoning. The territory of the Lviv city is located within two geomorpholog- ical subregions – the Podolian structural-denuda- tion upland on Cretaceous and Neogene deposits and the Lower Polissia strata-accumulative plain on Cretaceous deposits. Geomorphological subre- gions are further divided into districts and subdis- tricts (Gruzman, 1980) (Figs. 2, 3). Fig. 1. Administrative location of the Lviv city. 289Stratigraphic-genetic complexes of the bedrock of Lviv city and their geotechnical properties Materials and methods The basis for the genetic dissection of rocks was the available facies-ecological studies of the Paleo- gene and Neogene of Lviv city (Kudrin, 1966) and the experience of large-scale (1:50 000) geological survey. To describe the stratigraphic-genetic com- plexes of Lviv city’s bedrock deposits we used the works on the stratigraphy of the loess formation of Ukraine (Veklych, 1968), stratotypes and bio- stratigraphy of Miocene deposits of the Volhyn- ian-Podolian plate (Venglinsky & Horetsky, 1979), stratigraphy of the Tortonian deposits of Volhyn- ia-Podolia (Vyalov & Horetsky, 1965), Stratigraph- ic Code of Ukraine (Hozhyk, 2012), stratigraphic schemes and legends for the Carpathian region (Biryuleva et al., 1972), geological atlas of Lviv city and its surroundings (Lomnicki, 1897), stra- tigraphy of the Middle Miocene deposits of Opillia (Kazakova, 1952). As for geotechnical studies of the territory of Lviv city, the existing information is based on the materials of reports on engineering-geological surveys for residential-civil and industrial ob- jects. 357 geotechnical reports were analyzed, and those materials were collected and systematized Fig. 2. Scheme of geomorphological zoning of Lviv city. 290 Pavlo ZHYRNOV & Petro VOLOSHYN at the Lviv Branch of the “Ukrainian Institute of Engineering Technical Exploration for Construc- tion” (SE “LF UKRIINTR”). Also the main ideas on engineering-geological assessment of strati- graphic-genetic complexes were taken from sev- eral scientific works of Ukrainian (Mokritskaya, 2012, 2019; Budkin & Cherkez, 2000) and foreign scientists (Hataullin, 1991; Kopylov & Melchako- va, 2020; Arkhipov et al., 1980; Slavinskaya & Ly- ubimova, 2008; Bogomolov, 2011). Lithological, paleontological and chronostrati- graphic research methods were applied in the study of the stratigraphy of the bedrock of Lviv city. The group of lithological methods included dissection and correlation based on visual features (estab- lishing sediment types, colour, density, strength, structure, texture, presence of inclusions, second- ary alteration, signs of cyclicity, etc.). Mineralog- ical-petrographic methods included microscopic diagnosis of the minerals that make up the rocks and structural analysis using X-rays. The paleontological method was used to de- termine the relative ages, stratigraphic separa- tions and correlations of sedimentary rocks based on the sequence of fossil assemblages contained within them, as a result of biological evolution and changes in environmental conditions. For the pa- leontological method the groups of organisms with high abundance, rapid evolution and wide distri- bution, whose remains are well preserved, in our case these were red algae and several shell cepha- lopod mollusks, were of greatest importance. The use of chronostratigraphic methods solved the problem of comparing sections (private and composite) with the general stratigraphic scale and global correlation of sedimentary strata. The Fig. 3. Geomorphological zoning and individual landforms of Lviv city. 291Stratigraphic-genetic complexes of the bedrock of Lviv city and their geotechnical properties method is based on a comprehensive substantia- tion of the age of the lower strata boundary, link- ing it to the anchored “golden nail” tier boundary, and tracing this “isochronal boundary” within the basin and beyond based on a guiding correlation event (Zorina, 2015) (Fig.4). Geotechnical research methods included bore- hole drilling and mining, field and laboratory studies of the soils (engineering-geological ele- ments) identified within each stratigraphic-genet- ic complex. All strength and deformation charac- teristics of both rocks and soils were determined in the field. The compressibility of soils was stud- ied by die methods, pressiometers, and dynamic and static probing. To realize die loads in the borehole, bore- holes with a diameter of more than 320 mm were drilled. Soil testing was carried out by special in- stallations, which make it possible to work at a borehole depth of up to 20 m. A 600 cm2 die was lowered to the bottom of the borehole. The load on the die was transmitted through a rod on which a platform with a load was placed. The modulus of deformation was determined by the formula. Pressiometric studies were carried out in clayey soils using exploratory boreholes. The pressiome- ter is a rubber cylindrical chamber that is lowered into the borehole to a predetermined depth. The chamber is expanded by liquid or gas pressure. In the process, radial ground displacement and pressure are measured in the borehole walls. This makes it possible to determine the modulus of de- formation of the soils. Probing was used to study rock strata up to a depth of 15–20 m. The essence of the method was to determine the resistance to penetration of the probe into the ground. Probing gave an idea of the density and strength of soils at a certain depth and characterized changes in the vertical section. The shear resistance of soils in the field was assessed in both rocks and soils. The shear resis- tance of soils was determined by the stress limits at which they begin to fracture. In rocks, the experiments were carried out in construction pits, in which the pillars of undis- turbed soil of columnar type are left. A horizon- tal shear force was applied to the pillars. At the same time, the experiments were carried out on at least three columnar pillars for the correct de- termination of internal friction and specific cohe- sion. Shifting in soils was performed in two ways: 1) on targets; 2) using rotary shears with impel- ler torsion. The operation on targets is similar to rocks. The impeller is a paddle device and is used to determine shear resistance in dusty clay soils. A four-bladed impeller probe was lowered into the borehole bottom, pressed into the soil and rotated. The torque was measured and the shear resistance was calculated (Ananyev & Potapov, 2005). Fig. 4. Stratigraphic methods of the current study. 292 Pavlo ZHYRNOV & Petro VOLOSHYN Laboratory soil testing is also an important geotechnical method. Soil samples for laboratory investigations were collected from soil layers in boreholes located at the construction sites under investigation. Soil samples were delivered to the laboratory as monoliths or loose samples. All physical-mechanical and physical-chemical properties of soils can be determined in laboratory conditions. Each characteristic of these properties is defined according to its SSU, e.g. physical-me- chanical, physical-chemical characteristics are defined according to SSU B V.2.1-3-96, particle size distribution is defined according to SSU ISO 11277:2005, tensile strength is defined according to SSU B V.2.1-4-96, etc. (Fig. 5). Geotechnical research methods included bore- hole drilling and mining, field and laboratory stud- ies of the soils (engineering-geological elements) identified within each stratigraphic-genetic com- plex. All strength and deformation characteris- tics of both rocks and soils were determined in the field. The compressibility of soils was studied by die methods, pressiometers, and dynamic and static probing. In-situ and laboratory investiga- tions were performed using Ukrainian standards Today laboratory tests remain the main type of determination of physical-mechanical and physi- cal-chemical properties of soils. A number of char- acteristics, for example, natural moisture content, density of soil particles and some others are de- termined only in laboratory conditions and with high enough accuracy. The names and values of indicators of geotechnical properties of soils will be displayed further in the article in the relevant tables (Trofimov et al., 2005). Results The Upper Cretaceous complex (k2m2) devel- oped within the city of Lviv is part of the so-called Lviv Cretaceous trough, composing the uppermost part of the Cretaceous rocks (Figs. 6, 7, 8). It is covered everywhere by Neogene and Quaternary deposits, exposed on the daytime surface only on the sides of deeply incised ravines in the southeast of the territory within the Lysennytska Upland. Cretaceous rocks reach the subquaternary sur- face in the areas of the Poltva River valley, where they form the bottom of the valley, and also form the bedrock base of the loess cover of the Vynny- ky ridge and eastern spurs of hilly ridge Roztocze. Cretaceous rocks are lithologically represented by gray, light-gray, and greenish-gray marls, weakly sandy, weakly layered with interlayers of marly limestone, in some areas with a high content of sponge opicules, fragments of inoceramol shells and other detritus. The bulk of the rock under a microscope is composed of the finest silty parti- cles of carbonate-clayey composition, their size does not exceed 0.01 mm, which determines its pelitomorphic structure. Structurally, the rock is characterized by the alternation of thin layers en- riched to varying degrees in the detrital eleuritic component, which determines the eleuritic-pel- itic structure and thin-layered texture of the rock. Clastic material (up to 17 %) whose grain size does not exceed 0.1 mm is represented mainly by quartz and glauconite, with minor amounts of feldspars, sericite, zircon, and rutile. Fig. 5. Geotechnical methods of the current study. 293Stratigraphic-genetic complexes of the bedrock of Lviv city and their geotechnical properties Fig. 6. Symbols for the lithological-geological map of the bedrock of Lviv city. 294 Pavlo ZHYRNOV & Petro VOLOSHYN Fig. 7. Stratigraphic column. 295Stratigraphic-genetic complexes of the bedrock of Lviv city and their geotechnical properties The marls of Lviv contain an extensive complex of micro- and macrofauna, based on which it has been established that they belong to the upper part of the Maastricht stage, and the so-called Belem- nitella junior zone. (Gruzman, 1980). The described Cretaceous complex stands out as an independent stratigraphic-genetic complex in engineering-geological terms. Its importance for future construction is especially great in the vast valley of the Poltva River, where intensive civil and residential construction is currently tak- ing place, and where it forms a bearing base (up to 20 m deep) for all types of foundations. The Cre- taceous age marls composing this complex have several specific geotechnical properties, which are the object of study during engineering-geological surveys in the Poltva River valley. It has no impact on design and survey work in other areas due to the deep burial of this complex. Fig. 8. Lithological-geological map of the bedrock of the city of Lviv. 296 Pavlo ZHYRNOV & Petro VOLOSHYN Clay complex of the weathering crust (ek2m2). This complex is widespread in the northern and central parts of Lviv (Figs. 6, 7, 8). This is the Pol- tva River valley and the dissected northern slope part of the Lviv plateau according to the taxonomy of geomorphological zoning. The thickness of sed- iments is mainly 1-2 m and only at the sides of the Poltva valley, and in some cases of the valley itself, it increases up to 10-11 m. This is explained by the fact that from the valley sides, the sediments were partially swept away by denudation processes, while in the Poltva Valley, they are developed and preserved intact in the near-slope areas and some parts of the valley. The deposits are characterized by the content of clastic material, which varies from single inclusions in the roof to 30-40 % at the bottom. Different CaCO3 content in soils de- termines their different dispersibility and plastici- ty, and consequently their classification indices. It was not possible to establish any regularity in the spatial distribution of hard and half-hard loams, and hard and half-hard clays. The geotechnical properties of the selected nomenclature soil types are described below (Gruzman, 1980). The Neogene complex (N) is lithologically the most complex and consists of a motley mix of a significant number of sedimentary rocks from dif- ferent facies zones of the open sea. Neogene rocks are ubiquitously developed within the Lviv Pla- teau, the Roztocze Ridge, the Bilohiria-Malchyts- ka Valley, the Zubra River Valley, and are absent in the Poltva River valley and on the loess Vynnyky and Malekhivska ridges. Table 1. Engineering-geological elements of the Upper Cretaceous complex. EGE Description Marl The sedimentary rocks is grey, weakly weathered, low-strength, softening, swelling, fractured, fractures without filler, fracture walls tinny, massive texture, fracture smooth, and mostly watered. The marl often delaminates and disintegrates when saturated with water. Table 2. Geotechnical properties of rocks of the Upper Cretaceous complex. № Indicators of geotechnical properties Marl 1 Density, ɣo (t/m 3) 2.63 2 Bulk density, ɣc (t/m³) 2.12 3 Soil carbonate, (%) 48 4 Tensile strength in uniaxial compression at water-saturated state, Rc (MPa) 7 5 Tensile strength in uniaxial compression at natural water content, Rc (MPa) 9 6 Tensile strength in uniaxial compression at air-dried state, Rc (MPa) 15 7 Weathering coefficient 0.90 8 Softening coefficient 0.15 9 Degree of saturation, Sr (%) 0.89 10 Swelling coefficient, (%) 3.7 Table 3. Geotechnical properties of clayey soils of the weathering crust. № Indicators of geotechnical properties Half-hard loam Hard loam Half-hard clay Hard clay 1 Bulk density, ɣc (t/m³) 1.93 1.85 1.89 1.92 2 Porosity, e – 0.80 – – 3 Degree of saturation, Sr (%) 0.28 0.22 0.29 0.25 4 Modulus of deformation, Eo (MPa) 4.9 6.4 5.3 6.9 5 Specific adhesion, C (KPa) 39.2 41.1 37.5 38.2 297Stratigraphic-genetic complexes of the bedrock of Lviv city and their geotechnical properties The Neogene complex is traditionally divided in age into two parts, corresponding to the supra-Er- vilian and sub-Ervilian layers of the Lomnicki For- mation (Lomnicki, 1897). The lower part belong- ing to the Lower Tortonian Substage is combined into the Opolian horizon, and the upper part com- prising the Upper Tortonian Substage is allocated to the Tyrassic horizon. These strata are separated by a peculiar Ervilian horizon, which in the con- ditions of Lviv city serves as a marking age refer- ence. However, it should be noted that the position of this horizon in the regional plan for the Neogene complex of the Ciscarpathian region contradicts many factors and its marking position was not rec- ognized by several geologists. The most complete section of the Neogene complex was uncovered by a borehole on the Ozarlivska Cliff (Fig. 9) and this section was the reference for mapping the Neogene strata of the Lviv city. The Lower Tortonian deposits (N1t1) on the ter- ritory of Lviv city include deposits of the following facies zones (Figs. 6, 7, 8): - The lower part of the sublittoral zone of the sea – quartz sands; - The upper part of the sublittoral zone of the sea is quartz sandstones; - The lower part of the littoral zone of the sea – lithothamnium sandstones and limestones; - Deposits of the desalinated sea – sandstones and limestones with Ervilia pusilla Phil. 1. Deposits of the lower part of the subtidal zone, known in previous schemes as the Mykolaev or Opillia layers, are represented by sands of var- ious grain sizes and make up most of the low- er Tortonian section. The greatest thickness of sandy sediments is confined to the eastern and south-eastern parts of the territory – on the Sykh- ivska Plain, it reaches 32–40 m (Fig. 10). Geologist Leonid Kudrin divided the entire thickness of sandy sediments into two parts, formed in different facies conditions: the facies of sandy sediments of the open sea and the com- plex of submarine deltaic facies (Kudrin, 1966). The Lower Tortonian sands on the territory of the city of Lviv are considered by many research- ers as submarine deltaic deposits. The basis for this conclusion is the presence of cross-bedding and fragments of silicified wood, devoid of bark, which is considered a sign of river transport of sands. However, a more or less detailed study of cross-bedding in numerous quarries in Lviv city showed that the layered formations of sublittoral sandy sediments are distinguished by internal structure features that contradict their classifica- tion as submarine deltaic textures. Vertical alter- nation of a series of different thicknesses without visible or significant changes in the granulometry and thickness of the constituent layers is quite common for cross-bedded deposits. The rule is a subparallel horizontal occurrence of serial seams. Although there are relatively frequent cases of dis- placement of the boundaries of obliquely layered series, in which the series has the appearance of concave, less often convex inclined lenses with a larger or smaller radius of curvature. Bedding is either unidirectional or alternately multidirection- al; S-shaped cross-bedding is widespread along the direction of layers in adjacent series. All these features are not characteristic of deltaic layering, Fig. 9. Reference section of the Neogene strata of the Lviv city “Ozarlivska Cliff”. 298 Pavlo ZHYRNOV & Petro VOLOSHYN and even in the description of the latter, which is given by geologist Leonid Kudrin, one of the main features of submarine deltaic accumulation is missing – the cross, imbricated shape of serial sutures of cross-bedded units. There were no cases of confinement to the surfaces of the boundaries of a series of plant detritus, so common for the lay- ering of river fans. Also unusual for deltaic forma- tions is a typical detail of the internal structure of the Lower Tortonian sands: the separation of layers of the same order in thickness into packs or series, which alternate with non-layered stra- ta, sometimes reaching impressive thicknesses of 12–15 m. Thus, the nature of the internal structure of the Lower Tortonian sands on the territory of Lviv city makes us consider this entire sequence to be a sin- gle genetic formation, formed under conditions of quiet sedimentation of the open sea, in some ar- eas of which the bottom currents arose with the formation of an inclined-layered texture. Bottom sediments reach their greatest thickness in the south and southeast of the territory, where they are 35–40 m. Among the sands of the Sykhivska Plain, the light fraction is about 99.9 %, and the heavy frac- tion is 0.1 %. The light fraction is practically mo- nomineral: the quartz content ranges from 99.4 to 100 %. Glauconite, feldspars, and carbonates with a total content of 0 to 0.6 % are present as impuri- ties. Particles of carbonate material and fractions with a grain size of up to 0.5 mm are absent or present in negligible quantities in the form of a ce- menting mass. Feldspars contained in sands are essentially potassium in composition. The lithologic-facies isolation of sandy deposits as part of the Lower Tortonian cycle made it pos- sible to identify them as an engineering-geological element of the Lower Tortonian stratigraphic-ge- netic complex. 2. The upper part of the sublittoral zone in- cludes quartz sandstones, which in some areas form rock and bedrock outcrops such as armored surfaces. They make up the Lower Tortonian sec- tion within the Western planning area, replacing a thick layer of sand. They are covered everywhere by Upper Tortonian clays and gypsum. In all other sections, they occur in the form of frequent inter- layers of varying thickness (from 0.1 m to 10 m) among the quartz sands of the lower Tortonian. The colour of the rocks varies from light yel- low, and gray to greenish-gray. Studies of sand- stones in thin sections using the immersion meth- od showed that their composition is monomineral sandstones. The grain size is 0.01–0.1 mm, which determines the silty structure of the rocks. The composition of the clastic part includes glauconite. Fine- and medium-grained sandstones predomi- nate according to mechanical analyses. A feature of the rocks of this facies is the almost universal, but extremely uneven content of coarse clastic material of black chert. In some areas, there is a spotty alternation of interlayers and lenses of different sorting of grains, up to the identification of gravel packs. Quite often in sandstones, there is an accumulation of broken shells or large fragments of thick-walled fauna, as well as single fibrous con- cretions of red algae. As the amount of the latter in- creases, the sandstones are replaced by shallower formations compared to the previously described sands and were deposited in the intermediate zone between the sublittoral (quartz sands) and littoral (lithothamnium limestones) facies. Sublittoral sandstones stand out as a strong en- gineering-geological element in engineering-geo- logical terms. Their importance in this regard is increased by the fact that in several places they emerge on the daylight surface and can serve as a rock foundation for building structures. Fig. 10. Reference section of Neogene strata of Lviv city “Sykhivska Plain”. 299Stratigraphic-genetic complexes of the bedrock of Lviv city and their geotechnical properties 3. The main feature of the deposits of this fa- cies zone is the presence of organic remains from the class of red algae. The traditional name of these rocks (lithothamnium limestones and sandstones) is because it was initially believed that the red algae in them were represented only by the Lithotham- nium species. But later, geologist Vladimir Maslov showed the widespread distribution of other repre- sentatives of red algae – Lithophyllum and Meso- phyllum. Therefore, geologists began to call them red-algal limestones and sandstones. Red-algal rocks occupy very different positions in the sec- tions of the Lviv Tortonian – at the base of the Opil- lia horizon (the central part of the Lviv plateau), at the top of the horizon (Roztocze ridge), sometimes completely composing the section of the Lower Tor- tonian (eastern part of the Lviv plateau). Red-algal rocks are present both at the base and at the top of the Lower Tortonian in the most complete Neo- gene section (in the borehole near the Ozarlivska Cliff ). Three layers of lithothamnium limestones were found in sections of the Northern planning area. The thickness of the rocks is generally small (up to 4 m), except for those sections where red-al- gal rocks entirely compose the Lower Tortonian section, and then their thickness increases to 18 m. The sediments of this facies are composed of concretionary red-algal limestones and sandstones. Coarse layering is often observed in them due to the different nature of cementation of the underlying nodules or their coarseness. Massive varieties oc- cur besides concretionary varieties, connected by gradual transitions. The rocks are generally light grey to yellowish grey in colour, usually coarsely slabbed. The diameter size of red-water nodules reaches sometimes 10 cm. The histological struc- ture of the algae, consisting of pelitomorphic cal- cite and characterized by sheaf-like arrangements of sieve-like rows, is visible in the splits. The bot- tom rocks are characterized by a constant admix- ture of clastic material consisting of poorly sorted and variously fossilized sandy fragments of quartz, glauconite, feldspars, and f lints. Red algal rocks were formed in areas of shal- low water, in the zone of tidal action at a depth of not more than 60 m, accessible to the inf luence of solar radiation, as evidenced by the lithological composition of rocks and ecological features of red algae. In addition, the red-algal rocks were depos- ited on uplands of the chalk substrate, where sun- light penetrated and in this case, they are charac- terized by the presence of uncemented or weakly cemented nodule varieties. Red-algal (lithotham- nium) limestones along with the described sand- stones form another class of rocks in the Lower Tortonian complex. Although they are connected by various transitions, their engineering-geologi- cal properties are sharply different, which neces- sitates their separation. Sandy-calcareous rocks with a massive accumu- lation of internal cores and shells of Ervilia pussila Phil belong to the deposits of a desalinated, regres- sive basin. These sediments have been given an important stratigraphic position since Lomnický’s time and are usually isolated as an independent stratum. Certain facts emerged in the process of large-scale surveying that contradict the marking significance of the layers with the Ervilian fauna. These rocks occur everywhere on the boundary of the Upper and Lower Tortonian on the territory of the Lviv city and therefore they were considered as a separate horizon during the works. Ervilian de- posits are distributed only in the eastern part of the studied area – on the Lysennytska and Ratyn uplands and the northern planning area. The maxi- mum thickness of Ervilian deposits was recorded in the section of Zamkova Hill (1.1 m), in other places it varies between 0.1–0.7 m. The poverty and spec- ificity of the species composition of the fauna of the Ervilian layers indicate unfavorable living condi- tions associated with the sharp shallowing and sig- nificant desalination of the basin at the end of the Lower Tortonian time. The water salinity was no lower than 17 ‰. The lithological composition of the deposits and the large accumulation of remains of sessile benthos indicate a slow rate of sediment accumulation and conditions of sea regression. Deposition of the Ervilian layers ends the Lower Tortonian sedimentation cycle (Gruzman, 1980). The identified lithological-facial features of the Lower Torton sediments allowed the engineer- ing-geological survey to segregate them into a sep- arate stratigraphic-genetic complex consisting of several engineering-geological elements. Although the Lower Tortonian soils act directly as a bearing basement in a limited area (mainly on the slopes of uplands), they are involved in the sphere of the im- pact of engineering structures in most of the ter- ritory of Lviv, which predetermined the need for stratigraphic and lithological-facial study of these rocks for geotechnical purposes. Upper Torton (N1t2). The next cycle of sedimen- tation in the study area is associated with the Up- per Tortonian transgression, which completely cov- ered the studied area of Lviv and had the greatest development here (Figs. 6, 7, 8). On the territory of Lviv city, there are several reference sections, which formed the basis of the classical scheme of stratifi- cation of the Upper Torton – Ratynska Upland, Kar- tumova Hill, Zamkova Hill, and Snopkivsky Range. 300 Pavlo ZHYRNOV & Petro VOLOSHYN The dissection of the Upper Torton deposits in the area of Lviv city is presented as follows: І. Facies of the open sea: - Upper part of the sublittoral – reefogenic faci- es: shallow lithothamnium limestones, - The lower part of the sublittoral – quartz and glauconite-quartz sands. II. Lagoon facies: - The phase of sulfate sediments – gypsums, anhydrite. - Carbonate sediments – chemogenic lime- stones. III. Transitional facies: - Sandy-clayey sediments - dense clays with in- terlayers and nests of sandstones, with frag- ments of karst rocks (limestone, gypsum). 1. The presence of reefogenic deposits in the Up- per Torton in the territory of Lviv city confirmed the existence of a reef ridge in the southwest of the East European Platform. In the area of works, this facies is represented mainly by fine concre- tionary lithothamnium limestones of grey colour on clay cement and consists of a heterogeneous ac- cumulation of small nodules and their fragments Table 4. Engineering-geological elements of the Lower Torton deposits. EGE Description Limestone Organogenic, organogenic-clastic, strong, fractured, cavernous, white with a greenish tinge, 8-10 m thick. Sandstone Sandstones are fine-grained, greenish grey on clayey cement, carbonate, and fractured, with the inclusion of freshwater fauna in the southwest. Sandstones are grey and light grey, weathered, and fractured, with interbeds of strongly fractured sandstone within the Kleparivska Upland. Sandstones can be used as a natural foundation for buildings and structures. Fine sand Sand is fine with thin interlayers and nests of dusty and medium, low-moisture, medium density, yellow- ish-grey, and light grey, quartz, in the lower part of the layer with crushed limestone and sandstone up to 40 %, up to 8.5 m thick. The sands can serve as a natural foundation for buildings and structures, as well as a bearing layer for pile foundations. Dusty sand The sands are greenish and light yellow, weakly yellow, medium to dense, homogeneous, low-moisture, up to 5.1 m thick. The sands can be used as a natural foundation for structures. Medium sand The sands are yellowish and bluish-grey, water-saturated, medium density, quartz-feldspar, semi-calca- reous, and homogeneous. The sands can be used as a natural base for buildings and structures. Table 5. Geotechnical properties of rocks of the Lower Torton. № Indicators of geotechnical properties Limestone Sandstone 1 Coefficient of non-uniformity, Cu 0.11 0.19 2 Density, ɣo (g/cm 3) 2.72 2.67 3 Bulk density, ɣc (g/cm³) 2.39 2.4 4 Porosity, e 12.5 8.3 5 Water absorption, wabs (%) 5.05 – 6 Tensile strength in uniaxial compression at dry state, Rc (MPa) 15.8 13.7 7 Tensile strength in uniaxial compression at water-saturated state, Rc (MPa) 13.8 10.8 Table 6. Geotechnical properties of sandy soils of the Lower Torton. № Indicators of geotechnical properties Fine sand Dusty sand Medium sand 1 Coefficient of non-uniformity, Cu 0.24 0.25 0.25 2 Water content, W (%) – 26 – 3 Degree of saturation, Sr (%) 0.28 0.30 0.83 4 Theoretical resistance index, Ro (MPa) 13.8 – – 5 Porosity, e 0.7 0.64 0.59 6 Internal friction’s angle, φ (°) 35 26 35 7 Bulk density, ɣc (g/cm³) 1.70 1.91 1.99 8 Specific adhesion, C (KPa) 1.96 1.72 1.98 9 Modulus of deformation, Eo (MPa) 24.5 14.3 17.2 301Stratigraphic-genetic complexes of the bedrock of Lviv city and their geotechnical properties of 0.5 to 5 mm size cemented by clay-carbonate mass. Occasionally, limestones gradually change to layered grey and greenish-grey clays and small nodule red algae. Under the microscope it can be seen that the rock consists of small nodules and fragments of red algae, to which foraminifer shells and fragments of corals and mollusks are mixed in subordinate quantities. The thicknesses of these deposits vary from 1.0 to 5–6 meters. These rocks compose the most elevated parts of the relief and can be traced in a discontinu- ous band, starting in the south-east of the terri- tory (Sykhivska Plain and Ratynska Upland) at 360–370 m and ending in the northern spurs of Kleparivska Upland at 350–380 m. The width of the strip in the widest part reaches 2.5–2.8 kilo- meters and the narrowest (Zamkova Hill and the western part of the Northern planning area) is 0.5–0.8 kilometers. A large deposit of bioherm-type riffogenic rocks was identified during the works, located within the northern spurs of the Kleparivska Upland and the western part of the Goloskivska Upland and confined to an anticlinal uplift of the Cretaceous substrate. The central part of the bioherm, located at the maximum elevations of the territory, forms an armored site. It is composed of slabby recrys- tallized fine lithothamnium limestones with sub- horizontal positions of planes of separateness. The identification of reefogenic deposits in the cycle of the Upper Tortonian transgression makes geotechnical sense in that in several places they serve as a rock base for housing and civil engineer- ing. Therefore, the geotechnical properties of these soils due to genetic features are important for the engineering-geological characterization of these areas. 2. As a single genetic formation, the Upper Tortonian sublittoral sediments consist of a var- iegated combination of essentially clastic sedi- ments. The main role in this complex is played by multigrain quartz sands, always well pelletized, greyish-green due to insignificant but notable ad- mixture of glauconite. Compacting, the sands are replaced by sandstones of the same composition, which in some cases represent the entire section of the sublittoral zone. Often the composition of sandstones changes towards an increase in car- bonateness and an increased role of cement in the rock texture. These varieties are distinguished by an increased content of organic and plant detritus and an accumulation of internal lamellar gill nu- clei. Rapidly disappearing interlayers and lenses of gravel and pebble material are observed in some sections. Having a similar material composition, the Up- per Tortonian sands on the territory of Lviv city differ in the conditions of occurrence. They have a continuous area distribution in the east of the territory, on the elevated side of the Lysennytska tectonic zone. In the central part of the district, in the area enclosed between two faults (Lysen- nytsky and Zubrovsky), sands lie in a complex interlacing with reefogenic lithothamnium lime- stones and lagoonal “ratynsky” limestones, never- theless quite often forming independent fields. In the western part of the studied area, sands have no independent position and are subordinate to the clayey stratum, forming more or less extended and thick interlayers. 3. Sulfate deposits of gypsums and anhydrites are of particular importance for the assessment of the area for prospective construction. Long-term studies of sulfate rocks in the Precarpathian re- gion have revealed a great variety of petrographic varieties: anhydrites, gypsums, gypsoanhydrites, sulphate-carbonate rocks, sulphur-bearing and ore-free limestones. Even greater diversity is re- vealed in the morphological structure of rocks – up to 12 types of structures are distinguished. The sulfate strata on the territory of Lviv are spread in the west and south: starting at the head- waters of the Bilohiria-Malchytska valley it cov- ers the western and southern outskirts of the city in a giant semicircle, composing the territory of the South-Western planning district, the Southern planning district and the outskirts of the Sykhivs- ka Plain. In its composition anhydrites are dom- inant, and gypsums and transitional varieties – gypsoanhydrites – are much less widespread. There are no indications of other petrographic varieties. The thickness of sulfate rocks naturally increases to the west, where it reaches 13 meters. There is no zoning of lithological and petro- graphic types of gypsum-bearing formations and data of specialized studies of sulfate rocks on the territory of Lviv city. It follows from descriptive works that of petrographic varieties gypsums have the greatest predisposition to karst formation, and of textural-structural types – coarse-crystalline types – columnar, sheaf-shaped, radial-radiate, needle-shaped, twin-like. But at the same time, anhydrides are subject to hydration processes, which can also cause karst formation. 4. The studied area contains a stratotypic sec- tion of sediments of lagoonal carbonate facies, the location of which gave the name to these rocks – Ratyn Hill. Here the greatest thickness of these limestones on the territory of Lviv (14 m) was un- covered. Ratyn limestones form dense hard rocks 302 Pavlo ZHYRNOV & Petro VOLOSHYN of grey, creamy- and brownish-grey colour, often with significant clay admixture, detectable by dark grey colouring and the earthy surface of fresh chipping. Very often they bear traces of marked calcification. Limestones are characterized by a pelitomorphic structure and their grain size does not exceed 0.01 mm. Very often limestones reveal various kinds of clotted structures characterized by sometimes complex textural patterns. The usu- al clot structure consists of the presence of pelito- morphic lumpy clots with vague outlines of calcite. Sometimes the clots have the character of vein-like formations, intricately branching in the rock mass. Connecting, they form a fine-mesh network, the cells of which are made of fine-grained calcite. 5. The characteristics and conditions of sandy-clay deposits have been reported previous- ly. It should be added that under the microscope the main mass of these rocks is composed of clay- ey material with an admixture of carbonate and is characterized by a pelitic structure. It contains thin phenocrysts of pyrite and carbonized plant detritus. The sulphate component gives lenticular and rounded formations revealing an aggregate structure. At the same time, the carbonate-clay matter of the main mass seems to f low around anhydrite inclusions, which determines the glass structure of clays (Gruzman, 1980). Genetic peculiarities and stratigraphic inde- pendence allowed the described rocks to be iden- tified as an independent stratigraphic-genetic complex. The lithological diversity of the Upper Tortonian rocks ensured the separation of a large number of engineering-geological elements with different geotechnical properties in this complex. The Upper Tortonian marine stratigraphic-genet- ic complex is not only the most complex, where all engineering-geological types of soils are com- bined, except for peat soils but also has the largest area distribution on the territory of Lviv. Table 7. Engineering-geological elements of the Upper Torton deposits. EGE Description Sandy limestone Moderately weathered, strongly fractured, fractures 0.1–1 cm in size are randomly orientated and filled with sandy-clayey material with faunal remains. The thickness of sandy limestone is 1.8–2.8 m. Chemogenic limestone Low-strength, homogeneous, fractured, on clay cement, whitish grey. The thickness is from 0.8 to 4.0 m. Gypsum Crystalline, smoky, moderately weathered, and fractured – fractures up to 5 cm wide, watered along the fractures, karst phenomena are developed. Caverns are sometimes filled with tight and soft plastic clay with lenses of dusty sand. Gypsum thickness ranges from 1.8 to 13 meters. Fractured pressure waters are found in gypsums. Gypsum under load can cause uneven settlement of foundations due to uneven cavernousness in the plan. Sandstone Fine-grained, dense, on clay and lime cement, fractured, fractures of different densities, mainly vertical. Fractures of different widths – hair-like and thin up to 1 mm, less often 2-5 mm, and single fracture 5–20 mm. The fractures are closed, and some are filled with clayey material. The thickness of sand- stones is up to 8.2 m. It is a water-bearing rock, fractured water is present. Sandstones occur below the active zone of buildings. Medium sand Medium-sized, water-saturated, medium-density, heterogeneous, yellowish-grey sands. They occur in the roof of Upper Tortonian deposits, and underlying gypsums, occur among gypsums. It can serve as a natural foundation for buildings and structures. Fine sand Sands are yellowish and light grey, fine with thin interlayers and nests of dusty and medium, low-mois- ture, medium density. The sands can serve as a natural foundation for buildings and structures, as well as a bearing layer for pile foundations. Dusty sand The sands are greenish-yellow, dense, water-saturated, glauconite-quartz, with interlayers and lenses of sandy loam up to 10 cm thick. The sands are water-bearing rocks. Underground waters are not aggres- sive in all types of corrosion. The sands can be used as a natural foundation for buildings and structures. Hard clay The clay is greenish-grey, lumpy with sandstone fragments. Clays can serve as a natural foundation for buildings and structures. Half-hard clay Clays are greenish and bluish-grey, strongly sandy, with interlayers of weakly cemented sandstone, with fragments of limestone, with nests of bentonite. The clays can serve as a natural foundation for buildings and structures. Stiff-plastic clay Medium compressible clays of greenish-grey colour, lumpy, heterogeneous in composition, with frequ- ent bentonite inclusions. The clays can serve as a natural foundation for buildings and structures. Hard loam Loams can serve as a natural foundation for buildings and structures.Half-hard loam Stiff-plastic loam 303Stratigraphic-genetic complexes of the bedrock of Lviv city and their geotechnical properties Table 8. Geotechnical properties of rocks of the Upper Torton. № Indicators of geotechnical properties Sandy limestone Chemogenic limestone Gypsum Sandstone 1 Tensile strength in uniaxial compression at air-dried state, Rc (MPa) – – – 0.4 2 Tensile strength in uniaxial compression at dry state, Rc (MPa) – 18.5 13.0 24.5 3 Tensile strength in uniaxial compression at water-saturated state, Rc (MPa) 28.4 12.6 8.2 0.15 4 Softening coefficient – – – 0.50 Table 9. Geotechnical properties of sandy soils of the Upper Torton. № Indicators of geotechnical properties Medium sand Fine sand Dusty sand 1 Degree of saturation, Sr (%) – 0.24 – 2 Porosity, e – 0.63 0.59 3 Natural slope’s angle dry (°) 32 33 39 4 Natural slope’s angle underwater (°) 29 32 35 5 Bulk density, ɣc (g/cm³) 1.65 – 2.0 6 Specific adhesion, C (KPa) 1.96 1.96 4.0 7 Modulus of deformation, Eo (MPa) 27.9 – 23.6 Table 10. Geotechnical properties of clayey soils of the Upper Torton. № Indicators of geotechnical properties Hard clay Half-hard clay Stiff- plastic clay Hard loam Half-hard loam Stiff- plastic loam 1 Plasticity index, PI – 25 – 11 13 13 2 Water content, W (%) – 27.4 23.8 18.8 22.6 3 Density, ɣo (g/cm³) 1.89 1.95 1.95 2.02 2.03 1.90 4 Bulk density, ɣc (g/cm³) 1.44 1.54 1.60 1.70 1.63 1.49 5 Porosity, e 0.9 0.5 0.7 0.6 0.6 0.81 6 Degree of saturation, Sr (%) 0.96 0.93 – 0.87 0.95 0.93 7 Soil compaction index, kcom (KPa) 2.3 2.0 2.5 – – 8 Modulus of deformation, Eo (MPa) 9.1 9.9 9.6 9.8 – – 9 Internal friction’s angle, φ (°) 15 19 18 21 18 19 10 Specific adhesion, C (KPa) 42.9 42.5 43.7 54.9 32.6 27.5 The Upper Cretaceous complex is represented by marl, whose geotechnical properties include a tendency to swell. The peculiarity of swelling soils is their ability to decompact and increase in volume when moistened. Subsequent decrease of humidity in such soils leads to shrinkage. De- formations of the foundation soil as a result of swelling and shrinkage may cause damage to con- struction objects. Water protection measures are implemented first of all to eliminate the negative impact of swelling soil on structures: site planning for drainage of rain and melt water and organized drainage of water from the roof of buildings. One method of eliminating swelling properties of the soil is pre-soaking, which results in raising the soil before construction to a level above which swelling deformations are eliminated. It is also allowed to Lower Sarmatian (N1S1). Sarmatian deposits are known only on the Ozarlivska Cliff, where they form rock outcrops up to 30 m high. In general, their thickness here is up to 50 m and they are rep- resented by quartz sandstones of light grey colour, dense, multigrained with individual large quartz grains. The cement of the rocks is carbonate, the character of basal-type cementation (Figs. 6, 7, 8). Discussion Having characterized the geotechnical proper- ties of stratigraphic-genetic complexes of bedrock in Lviv, it is proposed to discuss the most difficult in geotechnical respect engineering-geological el- ements, which require certain measures during construction development and organization of en- gineering preparation of the territory. 304 Pavlo ZHYRNOV & Petro VOLOSHYN build compensating sand cushions, for which sand of any coarseness is used, except for dusty sand. The compaction of sand in the cushions is carried out to the dry density (ɣo = 1.6 t/m³). The weathering crust is represented by clayey soils characterized by low values of deformation modulus (Eo = 4.9-6.9 MPa). In addition, these types of soils are mainly confined to f looded and non-f looded terraces of the Poltva River, which are characterized by high levels of groundwater table from the day surface. Sand cushions and slab foundations are recommended for these soils (Shutenko et al., 2015). The gypsum column is identified among the engi- neering-geological elements of the Upper Torton de- posits, which have a propensity for karst formation. Special engineering surveys for karst were carried out in the southern planning area of Lviv in 2020. Gypsum was found to be present in the geological section of the southern part of the city and sau- cer-shaped waterlogged depressions of karst origin were found on the surface. In this connection, the possibility of deformation of the earth’s surface as a result of the collapse of karst cavity vaults or suffu- sion of loose material of overlying deposits into the cavity and expansion of fractures in gypsum is not excluded, especially if the natural regime of ground- water is disturbed. However, there is little evidence of karst on the earth’s surface. No karst failures have been observed in the Southern planning area. Com- plications in the construction and operation of build- ings and structures related to karst in Lviv and its immediate vicinity are practically unknown. There- fore, the following activities are recommended: 1. Do not locate buildings and structures over identified underground cavities of signifi- cant size or grout these cavities, do not locate buildings and structures on or near identified surface and buried sinkholes; 2. It is necessary to choose to strip monolithic or prefabricated monolithic reinforced con- crete foundations, to use foundations with support on rocks below the karst zone, to use pile-stocks and deep piles when supporting non-karst rocks (Tolmachev, 1986); 3. To prevent the activation of karst-suffosion phenomena it is extremely important to or- ganize a thorough drainage of the storm and waste water from the construction area, to ef- fectively control water leaks from utilities and to eliminate all boreholes exploiting the Neo- gene horizon, the zones of inf luence of which cover the territory of the southern planning area, as well as to prohibit the operation of new boreholes in the future (Gruzman, 1980). Conclusions 1. Geotechnical characterization of soils is based on the identification and mapping of strati- graphic-genetic complexes of rocks, accordingly, the geological basis of engineering-geological sur- veys should be based on two factors – age (strati- graphic) and genetic. The age factor is regulated by regional stratigraphic schemes, there is no ac- cepted scheme of genetic division of rocks. The main task of studying the geological structure of Lviv for geotechnical purposes is to identify spe- cific features and criteria of the genetic division of rocks, corresponding to the specialization of works. It is necessary to distinguish stratigraph- ic-genetic complexes based on the adopted strati- graphic-genetic scheme of bedrock dissection. 2. Bed rocks are confined to certain geomor- phological units, in connection with which at the primary stage it is necessary to geomorphological zoning of the territory of Lviv. Lviv belongs to the Volhynian-Podolian Region of strata-denudation uplands, in turn, within Lviv city there are two geomorphological subregions - Podolian structur- al-denudation upland on Cretaceous and Neogene deposits and Lower Pollisia strata-accumulative plain on Cretaceous deposits. These subregions are divided into 6 geomorphological districts and 13 subdistricts. 3. Lithological, paleontological and chronos- tratigraphic research methods were applied in the study of the stratigraphy of the bedrock of Lviv. Geotechnical methods included drilling and sink- ing of mine workings, f ield tests, and laboratory studies of soils. 4. The Cretaceous system is represented by rocks of the Upper Cretaceous complex (k2m2): clayey fractured marls with a high content of sponge spicules, fragments of inoceram shells and other detritus. The marls contain an exten- sive complex of micro- and macrofauna, based on which it was established that they belong to the up- per part of the Maastricht Stage, and the so-called Belemnitella junior zone. The marl has specific swelling properties, therefore, rain and meltwater drainage, sand cushions, and preliminary soaking are necessary to eliminate this phenomenon. The clay complex of the weathering crust (ek2m2) litho- logical complex is represented by loams and clays. Clay soils are characterized by a small deforma- tion modulus value and occurrence in waterlogged conditions, which requires sand cushions and the choice of slab foundations. 5. The Neogene system is represented by rocks of the Lower Torton, (N1t1) Upper Torton (N1t2), and Lower Sarmatian (N1S1). The Lower Torton 305Stratigraphic-genetic complexes of the bedrock of Lviv city and their geotechnical properties rocks are a thickness of interchangeable marine sediments: the lower part of the sublittoral zone is lithologically represented by laminated, quartz sands; the upper part of the sublittoral zone is rep- resented by carbonate plate sandstones; the lower part of the littoral zone is represented by red-algal sandy limestones. The geotechnical characteristic of the rocks of the Lower Torton is satisfactory, all soils can serve as a natural base for buildings and structures. The rocks of the Upper Torton are a thickness of intermixed marine and lagoonal sed- iments: reef facies are represented by organogenic f ine-lithothamnium limestones; the lower part of the sublittoral is represented by quartz and glauco- nite-quartz sands, fine-grained with sandstone in- terbeds; lagoonal facies is represented by gypsum and anhydrite facies; carbonate sediments facies is represented by chemogenic limestones; sandy-clay sediments facies is represented by dense clays with bentonite and rock fragments. Geotechnical characteristics of the rocks of the Upper Torton are as follows: gypsum is characterized by karst formation; sandstones lie below the active zone of buildings; sands, clays, and loams can serve as natural foundations for buildings and structures. The Lower Sarmatian rocks are represented by quartz fine-grained carbonate sandstones with organic detritus, which may well serve as natural foundations for buildings and structures, as they are quite strong. 6. 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