Bedrock Basins Research Articles

Interpretation and mapping of geologic structure in the Bali Basin based on integrated gravity, magnetic, and seismic data analysis

The Bali Basin is located in the Sunda-Banda back-arc from subduction along the Sunda Arc to continental collision along the Banda Arc. Still, its geologic structural patterns have yet to be mapped and discussed in detail as the transition zone. An integrated approach involving magnetic, gravity, and seismic data analysis was undertaken to discover these structures that potentially impact the surrounding area. The magnetic anomalies indicate that the thrust fault structure beneath the north coast of the islands of Bali and Lombok vertically displaces the basement on the seabed. The interpretation, verified with gravity and seismic reflection profiles, indicates a significant, tight, and well-developed expression of blind thrust faulting. Gravity data delineate the basin bedrock surface 6 km beneath the south Bali Basin, where seismic sections show five Cenozoic sedimentary sequences more than 2000 m thick, filling a highly deformed and faulted Cretaceous bedrock sequence. The seismic-gravity model shows sedimentation-related subsidence from basin filling followed by tectonics inversion.

Spatial distribution and enrichment mechanisms of high fluoride groundwater in geotherm-affected Pliocene aquifers of the Guide basin, China

Native high fluoride (F−) groundwater is one of the most serious environmental problems facing China and even the international society, which seriously threatens human health. The confined aquifer in the Guide basin contains high concentrations of F− and is subject to multifaceted influences, stemming not only from the geothermal activity present at the basin's bedrock but also from distinctive attributes such as elevated alkalinity, significant burial depths, and limited water circulation. Consequently, the precise mechanisms governing the enrichment of F− within the groundwater in this confined aquifer remain inadequately understood. This study aims to elucidate the migration and enrichment mechanism of F− in aquifers and assess the relative contributions of different control mechanisms responsible for high F− groundwater through systematic sampling, analysis and statistical calculations. Chemical types of confined groundwater and unconfined groundwater are Na-HCO3-Cl and Ca-HCO3, respectively. High-F− groundwater mainly exists in confined aquifers, and the content of F− gradually increases along the flow path. High content of HCO3− in confined groundwater promotes the precipitation of Ca2+, then enhances the dissolution of F−-containing minerals, resulting in F− being continuously released into groundwater. High pH, high Na/Ca molar ratios, geothermal and long residence time of groundwater are the additional factors to accelerate the release and migration of F− in groundwater. Results of redundancy analysis showed that competitive adsorption is the primary mechanism for F− enrichment in confined groundwater, followed by the geothermal effect, precipitation of carbonate minerals and residence time of groundwater time. The results of potential health risk assessment indicate that the potential health risks associated with confined groundwater are notably higher across all age groups compared to unconfined groundwater. The research results are not only helpful for the local government in reducing the threat of drinking-water fluorosis, but also provide a reference for other high-F− groundwater research with similar geological conditions in China and around the world.

The Salt Lake Basin Bedrock Weathered Crust Gas Reservoir in the Altun Mountains Front of the Qaidam Basin, China

AbstractThe bedrock weathered crust in front of the Altun Mountains in the Qaidam Basin is different from other bedrock weathered crust, because the Qaidam Basin is a salt lake basin, the saline water fluid is infiltrated and deposited in the overlying strata, and a large amount of gypsum is filled in bedrock weathered crust, the pore structure is changed. Use core observation, polarized light microscopy, Electron probe, physical property analysis and field emission scanning electron microscopy experiments. Cracks and a small number of dissolved pores in the interior of the weathered crust, the matrix micropores are widely developed. The characteristics of matrix micropores and cracks have been studied, especially the various matrix cracks formed by tectonic and weathered, as well as the stress characteristics of small dissolved pores, physical properties such as porosity and permeability, This “dual structure” developed in the bedrock is important for guiding the exploration of the lake basin bedrock natural gas.

Distribution and Morphology of the Bedrock Basins Known as Pans in a Granitic Inselberg Landscape

In 2008, Pogue and Katz reported that on granitic exposures in the Cassia City of Rocks, Idaho, the larger pans (shallow flat-floored gnammas or rock basins with overhanging sidewalls) are developed and preserved high in the local relief. They related this aspect of pan distribution to duration of exposure. This working hypothesis is tested by examining pan distribution on granitic inselbergs located on northwestern Eyre Peninsula, in semiarid southern South Australia. Pans in numbers have developed on sensibly level surfaces and have been shaped by pools of standing water. The larger—and more complex—forms are situated high in the local relief, as concluded by Pogue and Katz, but where water supply is limited to direct precipitation, by contrast with lower sites, where rainfall is augmented by runoff.

Volcanical and surficial process constraints on the formation of a lake basin in Jan Mayen, Norway

The volcanic island of Jan Mayen, located in the Norwegian – Greenland Sea, has very few lake basins out of which only one, Lake Nordlaguna, holds a permanent lake throughout the year. The island is volcanic and has been glaciated, but the lake basin is not genetically typical for volcanic crater lakes or other common types of volcanic lakes. Nor is it typical for ice-scoured glacial lakes. Instead, the lake basin originated from a series of hydromagmatic and subglacial volcanic eruptions, which over time yielded an irregularly horseshoe-shaped chain of small mountains to form flanks of a bedrock basin. Potassium–Argon and Argon–Argon dates from these rock walls facing the lake yield ages ranging from about 564 to 21 ka. Subsequent glacier overriding only had a minor influence on the basin morphology, but contributed, as did other surface processes to its sediment infill. Following deglaciation, relative sea-level change led to the formation of a beach barrier that connects between the rock walls. Tectonic uplift recorded in sections and ground penetrating radar profiles around the lake perimeter and dated using radiocarbon and tephra geochemistry, is attributed to a historical eruption in 1732 CE that took place on the opposite side of the island, some 4–5 km away. The uplift blocked the last remaining passage between the basin and the ocean, leading to the present landlocked lacustrine environment.

Three-Dimensional Numerical Analysis and Engineering Evaluation of Stilling Basin and Foundation Bedrock of Kala Hydropower Station, China

Kala reservoir is a large hydropower station, which will be built on the Yalong River in Sichuan Province, China. The topography and geomorphology at the project area of the hydropower station are characterized by high mountains and a deep V-shaped valley, where the engineering geological conditions are complex. The stilling basin of the Kala reservoir is planned to be built on a weak rock mass called a sericitized slate. Therefore, the safety of stilling basin structure has an important impact on the regular operation of the Kala hydropower station. To evaluate the working state of the stilling basin structure, a three-dimensional numerical model was built, including the valley, mountains and stilling basin structure. FLAC3D (A three-dimensional finite-difference simulation software) was used to simulate engineering and mechanical responses of the stilling basin structure and the foundation rock mass under various working conditions. Based on the simulation results, the structural layout of stilling basin and the rationality of sericitized slate treatment measurements were verified. It was determined that the engineering properties of the sericitized slate would generally meet the engineering requirements. However, considering that the characteristics of sericitized slate are easy to weaken with water, it was suggested to carry out necessary foundation improvement for sericitized slate to strengthen its engineering mechanical properties.

Coupling SWAT Model and CMB Method for Modeling of High-Permeability Bedrock Basins Receiving Interbasin Groundwater Flow

This paper couples the Soil and Water Assessment Tool (SWAT) model and the chloride mass balance (CMB) method to improve the modeling of streamflow in high-permeability bedrock basins receiving interbasin groundwater flow (IGF). IGF refers to the naturally occurring groundwater flow beneath a topographic divide, which indicates that baseflow simulated by standard hydrological models may be substantially less than its actual magnitude. Identification and quantification of IGF is so difficult that most hydrological models use convenient simplifications to ignore it, leaving us with minimal knowledge of strategies to quantify it. The Castril River basin (CRB) was chosen to show this problematic and to propose the CMB method to assess the magnitude of the IGF contribution to baseflow. In this headwater area, which has null groundwater exploitation, the CMB method shows that yearly IGF hardly varies and represents about 51% of mean yearly baseflow. Based on this external IGF appraisal, simulated streamflow was corrected to obtain a reduction in the percent bias of the SWAT model, from 52.29 to 22.40. Corrected simulated streamflow was used during the SWAT model calibration and validation phases. The Nash–Sutcliffe Efficiency (NSE) coefficient and the logarithmic values of NSE (lnNSE) were used for overall SWAT model performance. For calibration and validation, monthly NSE was 0.77 and 0.80, respectively, whereas daily lnNSE was 0.81 and 0.64, respectively. This methodological framework, which includes initial system conceptualization and a new formulation, provides a reproducible way to deal with similar basins, the baseflow component of which is strongly determined by IGF.

A subglacial hydrologic drainage hypothesis for silt sorting and deposition during retreat in Pine Island Bay

AbstractLate Holocene sediment deposits in Pine Island Bay, West Antarctica, are hypothesized to be linked to intensive meltwater drainage during the retreat of the paleo-Pine Island Ice Stream after the Last Glacial Maximum. The uppermost sediment units show an abrupt transition from ice-proximal debris to a draped silt during the late Holocene, which is interpreted to coincide with rapid deglaciation. The small scale and fine sorting of the upper unit could be attributed to origins in subglacial meltwater; however the thickness and deposition rate for this unit imply punctuated- rather than continuous-deposition. This, combined with the deposit's location seaward of large, bedrock basins, has led to the interpretation of this unit as the result of subglacial lake outbursts in these basins. However, the fine-scale sorting of the silt unit is problematic for this energetic interpretation, which should mobilize and deposit a wider range of sediment sizes. To resolve this discrepancy, we present an alternative mechanism in which the silt was sorted by a distributed subglacial water system, stored in bedrock basins far inland of the grounding line, and subsequently eroded at higher flow speeds during retreat. We demonstrate that this mechanism is physically plausible given the subglacial conditions during the late Holocene. We hypothesize that similar silt units observed elsewhere in Antarctica downstream of bedrock basins could be the result of the same mechanism.

Geophysical and geochemical analysis of shallow gas and an associated pockmark field in Bantry Bay, Co. Cork, Ireland

An integrated geophysical, geological, and geochemical investigation of seabed fluid venting was carried out in upper Bantry Bay, a large marine inlet on the southwest coast of Ireland. The results provide evidence of the seafloor venting of gas rich fluids, resulting in the formation of a pockmark field identified here for the first time. The pockmarks occur in an area where sub-bottom profiles provide evidence of chimney-like features interpreted to record upward gas migration through Quaternary sediments to the seafloor. Three vibrocores up to 6 m long were acquired in water depths of 24–34 m, two from the pockmark field and one from outside. Methane of predominantly biogenic origin was quantified in all three cores by headspace analysis of sediment sub-samples. Well-defined sulfate methane transition zones (SMTZs) were observed in two of the cores, the shallowest (1.25 m below sea floor (mbsf)) inside the pockmark field and the other (3.75 mbsf) outside. It is likely that an SMTZ occurs at the location of the third core, also within the pockmark field, although deeper than the samples obtained during this study. Gas migration towards the seafloor is suggested to involve both diffuse pore fluid migration across wide areas and focused flow through the pockmarks, together driven by methanogenesis of pre-glacial lacustrine sediments preserved in a bedrock basin, and possible gas release from the Owenberg River Fault. Analysis of phospholipid fatty acids (PLFAs) and archaeal isoprenoid hydrocarbons was used to investigate the microbial ecology of these sediments. Anaerobic oxidation of methane (AOM) may play a role in controlling release of CH4 to the water column and atmosphere in this shallow gas setting, potentially mediated by syntrophic sulfate reducing bacteria (SRB) and anaerobic methanotrophic archaea (ANME).

Using permutational and multivariate statistics to understand inorganic well water chemistry and the occurrence of methane in groundwater, southeastern New Brunswick, Canada

Concerns over possible impacts from the rapid expansion of unconventional oil and natural gas (ONG) resource development prompted a regional domestic well sampling program focusing on the Carboniferous Maritimes Basin bedrock in southeastern New Brunswick, Canada. This work applies recent developments in robust multivariate statistical methods to overcome issues with highly non-Gaussian data and support the development of a conceptual model for the regional groundwater chemistry and the occurrence of methane. Principal component analysis reveals that the redox-sensitive species, DO, NO3, Fe, Mn, methane, As and U are the most important parameters that differentiate the samples. Permutation-based MANOVA and ANOVA testing revealed that geology was more important than geographic location and topography in influencing groundwater composition. The statistical inferences are supported by chemistry trends observed in relation to road de-icing salt and other saline sources. However, source differentiation between Carboniferous brines, entrapped post-glacial marine water and modern seawater cannot be made. Furthermore, Cl:Br ratios lower than those of seawater or regional brines suggest an origin related to the diagenesis of organic-rich sediment and that the groundwater may be influenced by local low permeability units.Combined spatial, statistical and chemical analysis shows that, while trace or low levels of methane, <1 mg/L, are found ubiquitously throughout the Maritimes Basin, elevated concentrations, >1 mg/L, are associated with the Horton Group, consistent with it being the host and inferred source of ONG resources in the province. The highest methane concentrations (14–29 mg/L) were detected in the region with a complex history of cycles of uplift and erosion which, in some locations, resulted in the juxtaposition at the surface of the Horton Group with several other groups of the Maritimes Basin. It is thought that proximity to the Horton Group can lead to naturally high methane concentrations in non-ONG-bearing units.

An approach for deformation modulus mechanism of super-high arch dams

The reservoir basin bedrock produced significant impact on the long-term service safety of super-high arch dams. It was important for accurately identifying geomechanical parameters and its evolution process of reservoir basin bedrock. The deformation modulus mechanism research methods of reservoir basin bedrock deformation modulus for super-high arch dams was carried out by finite element numerical calculation of the reservoir basin bedrock deformation and in-situ monitoring data analysis. The deformation modulus inversion principle of reservoir basin bedrock in a wide range was studied. The convergence criteria for determining the calculation range of reservoir basin of super-high arch dams was put forward. The implementation method was proposed for different layers and zones of reservoir basin bedrock. A practical engineering of a super-high arch dam was taken as the example.

Geomorphic History of the Beaver Creek Drainage Basin as Determined from Topographic Map Evidence: Eastern Montana and Western North Dakota, USA

The Beaver Creek drainage basin is located along the North Dakota-Montana border slightly to the south of a recognized continental ice sheet margin and immediately to the east of the deep northeast-oriented Yellowstone River valley with Beaver Creek flowing in a north and northeast direction to join the north-oriented Little Missouri River. The Beaver Creek drainage basin originates on an escarpment-surrounded upland and its erosional history was determined by analyzing detailed topographic maps aided by previously made field observations that showed coarse-grained and distinctive alluvium had been transported in an east direction across the Beaver Creek drainage basin and across what is now the deep Little Missouri River valley to sediments making up southwest North Dakota high points containing both the distinctive alluvium and Oligocene age fossils. Drainage divides surrounding the Beaver Creek drainage basin show numerous divide crossings (or notches) linking northwest-oriented Yellowstone River tributary valleys with east-oriented Beaver Creek tributary valleys and west- or northwest-oriented Beaver Creek tributary valleys with southeast- or east-oriented Little Missouri River tributary valleys and suggest the Beaver Creek valley eroded headward across a large-scale flood formed anastomosing channel complex. Buttes located just to the east of the Beaver Creek-Little Missouri River drainage divide suggest the east-oriented water removed as much as 150 meters, or more, of Beaver Creek drainage basin bedrock, and even greater amounts of bedrock from regions to the south of the Beaver Creek drainage basin. Topographic map evidence and routes traveled by the distinctive alluvium suggest a continental ice sheet blocked a large and high-level northeast-oriented river and diverted at least some of the water along the ice sheet margin with the east-oriented floodwaters being captured in a progressive sequence by headward erosion of the Little Missouri River, Beaver Creek, and Yellowstone River valleys (in that order).

Microbial community changes during a toxic cyanobacterial bloom in an alkaline Hungarian lake.

The Carpathian Basin is a lowland plain located mainly in Hungary. Due to the nature of the bedrock, alluvial deposits, and a bowl shape, many lakes and ponds of the area are characterized by high alkalinity. In this study, we characterized temporal changes in eukaryal and bacterial community dynamics with high throughput sequencing and relate the changes to environmental conditions in Lake Velence located in Fejér county, Hungary. The sampled Lake Velence microbial populations (algal and bacterial) were analyzed to identify potential correlations with other community members and environmental parameters at six timepoints over 6weeks in the Spring of 2012. Correlations between community members suggest a positive relationship between certain algal and bacterial populations (e.g. Chlamydomondaceae with Actinobacteria and Acidobacteria), while other correlations allude to changes in these relationships over time. During the study, high nitrogen availability may have favored non-nitrogen fixing cyanobacteria, such as the toxin-producing Microcystis aeruginosa, and the eutrophic effect may have been exacerbated by high phosphorus availability as well as the high calcium and magnesium content of the Carpathian Basin bedrock, potentially fostering exopolymer production and cell aggregation. Cyanobacterial bloom formation could have a negative environmental impact on other community members and potentially affect overall water quality as well as recreational activities. To our knowledge, this is the first prediction for relationships between photoautotrophic eukaryotes and bacteria from an alkaline, Hungarian lake.

Preliminary Estimation of Engineering Bedrock Depths from Microtremor Array Measurements in Solo, Central Java, Indonesia

In the last decade the city of Solo, located in Central Java, Indonesia, has grown significantly and become a major city. Many industries and hotels have been built in the city and its surroundings. This study aimed to determine the engineering bedrock depths in Solo, an important parameter in seismic hazard analysis. The microtremor array method was used to obtain 1D S-wave velocity profiles and construct layer depth maps. The spatial autocorrelation (SPAC) method was used to calculate the dispersion curves, while the S-wave velocity structure was derived using a genetic algorithm (GA). The results of the S-wave velocity structure in Solo show that there are four stratigraphic layers, where the engineering bedrock depths in Solo exist within the range from 145 to 185 m. The shape of the bedrock basin is elongated in an east-west direction.

Evidence for a palaeo-subglacial lake on the Antarctic continental shelf

Subglacial lakes are widespread beneath the Antarctic Ice Sheet but their control on ice-sheet dynamics and their ability to harbour life remain poorly characterized. Here we present evidence for a palaeo-subglacial lake on the Antarctic continental shelf. A distinct sediment facies recovered from a bedrock basin in Pine Island Bay indicates deposition within a low-energy lake environment. Diffusive-advection modelling demonstrates that low chloride concentrations in the pore water of the corresponding sediments can only be explained by initial deposition of this facies in a freshwater setting. These observations indicate that an active subglacial meltwater network, similar to that observed beneath the extant ice sheet, was also active during the last glacial period. It also provides a new framework for refining the exploration of these unique environments.

Stratified glacimarine basin-fills in West Greenland fjords

Acoustically stratified sediments that infill glacially eroded bedrock basins are common in fjords (Seramur et al. 1997; Gilbert et al. 1998; Hogan et al. 2012; Dowdeswell & Vasquez 2013). Internally, such stratified sediments are often characterized by relatively smooth reflections that parallel the seafloor. Sills between basins usually comprise bedrock, sometimes covered by a thin veneer of glacimarine sediment and/or till. Fjords in West Greenland, including Rink Fjord and Vaigat, contain bedrock basins infilled by acoustically stratified sediment (Fig. 1). The basin fills are a product of rain-out from turbid meltwater plumes, probably supplemented by iceberg-rafting and downslope resedimentation. Fig. 1. Multibeam bathymetry and acoustic sub-bottom profiles of submarine basins close to the coast of West Greenland. ( a ) Multibeam bathymetry from Rink Fjord, West Greenland, with water depths >1000 m. ( b ) 3.5 kHz sub-bottom profile from Rink Fjord showing stratified, conformable basin fill (Facies 2) between basement pinnacles (Facies 1). VE×96. ( c , d ) Multibeam bathymetry in Vaigat strait and a coastal basin, West Greenland, respectively; arrows indicate ice-flow directions during the last glacial based on the orientation of sculpted …

Modeling of earth fissures caused by land subsidence due to groundwater withdrawal

Abstract. Land subsidence and earth fissures are phenomena related to groundwater withdrawal in a sedimentary basin. If the rock basement or basin lithology is irregular, both vertical and horizontal displacements can be induced due to differential settlement and tensile stresses appearing in the soil mass. If the differential settlement is of sufficient magnitude, earth fissuring can occur within tensile zones. The magnitudes of compaction and fissure geometry are closely related to the thickness and skeletal compressibility of fine-grained sediments within the aquifer system. Land subsidence and earth fissuring were modeled by employing a two-dimensional (2-D) coupled seepage and stress-strain finite element analysis. The basin bedrock geometry, lithological variation, measurements of surface displacements, and changes in hydraulic head were the critical input parameter for the subsidence modeling. Simulation results indicate that strain had exceeded the approximate threshold for fissure formation of 0.02 to 0.06 % in the area of the identified fissures. The numerical model was used to predict future subsidence and potential earth fissures for flood control structures within the metro Phoenix area.

Athens Subepisode (Wisconsin Episode) non-glacial and older glacial sediments in the subsurface of southwestern Michigan, USA

We describe the first complete sediment core to bedrock in southwestern Michigan of a radiocarbon defined sequence of Michigan Subepisode (Marine Oxygen Isotope Stage [MIS] 2) glacial sediments, Athens Subepisode (MIS 3) non-glacial sediments, and two older tills using sedimentological, lithological, and radiocarbon analyses. Organics from Athens Subepisode lacustrine and palustrine sediments yield radiocarbon ages of 41,920–42,950 and 43,630–45,340, and >43,500 14C yr BP. We propose the name Port Sheldon Formation for these organic-bearing sediments. We interpret the underlying diamictons as two basal tills separated by glaciolacustrine fines. The youngest till (Hemlock Crossing till) lying below the Port Sheldon Formation is a dark gray, gravel-poor clay loam to loam with a mean kaolinite–illite ratio of 0.98±0.04. The oldest till (Glenn Shores till) is a dark grayish brown, gravel-rich, clay loam to sandy loam with mean kaolinite–illite ratio of 1.22±0.08. About 130 water-well records demonstrate that organic sediments and underlying diamictons are common in the subsurface of Ottawa County. These tills are likely Illinois Episode (MIS 6) or older, but an Ontario Subepisode (MIS 4) age cannot be ruled out. Deep bedrock basins in Lower Michigan provide an untapped archive of pre-Michigan Subepisode history.

Floodplain Change in the Glenmalure Valley, South-east Leinster

The Glenmalure Valley is one of several U-shaped valleys which drain the eastern flanks of the Wicklow Mountains, 45km south west of Dublin. Five channel and floodplain reaches are recognised along a 25km stretch of the Glenmalure River on the basis of spatial changes in stream power and sediment load characteristics. The downvalley sequence of floodplain types within the river is atypical of that commonly associated with decreasing slope and sediment calibre downstream. Radiocarbon dating together with the use of anomalous concentrations of heavy metals, which are used as stratigraphic indicators of alluvial deposition post 1800, also reveal temporal changes in the rate of Holocene floodplain development within the valley. Downstream changes in floodplain processes within the valley are explained, therefore, in terms of spatial and temporal changes in the river's ability to adjust its slope, form and bed texture within the constraints of geological and Pleistocene geomorphic inheritance. The presence of a bedrock basin in the valley floor profile, infilled by Pleistocene lacustrine deposits, is believed to have caused a local change in base level leading to a significant reduction in valley slope and local stream power in the middle reaches of the valley. The subsurface bedrock form and the Pleistocene palaeolake also had a significant impact on coarse sediment transport, storage and transfer through the river system and hence on the ability of the Holocene river to regrade its slope and laterally rework Pleistocene valley fills for floodplain construction.

The Petřkovice Member (Ostrava Formation, Mississippian) of the Upper Silesian Basin (Czech Republic and Poland)

The Petřkovice Member (Carboniferous, Mississippian, Early Namurian) is in many ways the most interesting lithostratigraphic unit of the paralic part of the Carboniferous coal-bearing Upper Silesian Basin (described as the Ostrava Formation in the Czech part or as the Paralic Series in the Polish part). Petřkovice Member represents a transition between the non-coal-bearing Carboniferous flysch sedimentation of the Moravian-Silesian Basin and the coal-bearing sedimentation of the Upper Silesian Basin. The paper includes maps of the basic sedimentological parameters of this unit — thickness, sand content and coal-bearing capacity. The thickness of the Petřkovice Member ranges from approximately 50m in the east of the basin to around 770m in the west and has a clear polarity in the NNW-SSE direction. Sand content ranges from 23% in the west of the basin to more than 90% in the east. Its polarity is approximately the same as its thickness. The greatest coal-bearing capacity, expressed as total thickness of the coal layers with a thickness greater than 10cm, is known from the Czech part of the basin, where it exceeds 25m in places. In the majority of the Polish part of the basin the Petřkovice Member's total coal content is less than 5m, at times up to 7m. However, in this part of the basin their level of recognition is very low. On the basis of the above parameters 3 assumed zones of differing mobility in the basin's bedrock are defined in the Petřkovice Member's area.