NE Poland Research Articles

Nowe gatunki obce i rodzime rozprzestrzeniające się w północno-wschodniej Polsce poza granicami swoich pierwotnych zasięgów

The paper presents data on 32 alien plant species as well as seven ones native for other regions of the country which had not been recorded in NE Poland before or were known so far from only a few sites. The most important source of the spread of alien species in the initial stages of colonization is their intentional introduction into cultivation. Ornamental plants constitute 48.7% of recorded new species. The railway routes allowed spontaneous colonization of nine species (23%). The remaining species (28%) were most likely introduced by road transport of people and goods. The vast majority of alien species (77%) begin colonization in highly disturbed man-made habitats, especially ruderal ones in urban areas, as well as roadsides and embankments along communication routes, and so far they have appeared only in the sites of such types in the region. Only a few plants of alien origin are able to colonize forest habitats (i.a. trees and shrubs spreading by birds: Crataegus coccinea, Malus toringo and Rubus laciniatus). The expansion of Miscanthus sacchariflorus may pose the greatest risk of entering semi-natural habitats and naturally valuable areas in the near future. Predictions regarding the possibility of an explosive spread of Iva xanthiifolia did not come true. This may also apply to Erechtites hieraciifolius.

Microhabitat Conditions and Inter-Species Competition Predict the Successful Restoration of Declining Relict Species Populations.

The local populations of relict plant taxa living near the limits of their geographical range are particularly vulnerable to extinction. For example, Salix lapponum is one of the rarest and most endangered glacial relicts in Western and Central Europe. In Poland, the number of its sites has dramatically decreased over the past few decades, prompting us to take conservation measures focused on saving endangered populations. During a field experiment aimed at the reconstruction of the downy willow population in the Knyszyn Forest (NE Poland), 730 individuals of the species were planted in four different natural sites. The seedlings were obtained by micropropagation from parts of vegetative individuals taken from the most abundant population of this species in eastern Poland (Lake Bikcze). The success of the reintroduction, measured by the number of individuals that survived 2-3 years in the wild and took up growth, was about 67%, however, with low flowering efficiency (7.5%). Additionally, monitoring showed significant differences in plant survival and growth rates under different habitat conditions prevailing at the site and with different cover from competing species, especially tall grasses. However, the restoration projects for relict shrub species should include periodic removal of competing plants and protection of plants from trampling and browsing by herbivorous mammals to increase reintroduction success.

Technological study of the lithic materials from the site Wołkusz 3 in NE Poland. The concept of the preferential blades' production

The article aims to present the results of the technological analysis of the lithic artefacts from the site Wołkusz 3. This comprises a detailed characterisation of one of the two reconstructed flint knapping strategies described as the concept of preferential blades. The Wolkushian culture inventory consisting of almost 3000 pieces was subjected to the analyses. The collection includes the debitage products – cores, flakes and blades, as well as the products of debitage modification – retouched tools and the spalls connected with the process of their production and repairing. The conclusions are based on refitting studies supported by the analyses of the relief of negatives and the morphological attributes.

The Białowieża Forest as a Key Area for Understanding the History of European Forest Bird Communities

The last remnants of pristine forests in Europe, especially in the nemoral belt of deciduous and mixed deciduous coniferous trees, are unique for understanding the history, composition and structure of plant and animal communities. This is especially true for the Białowieża forest, NE Poland. The biogeographical history of emblematic forest clades of birds, e.g. woodpeckers, tits and nuthatches, is analyzed from molecular phylogenies which allow to determine their pace and mode of origination and differentiation. The flyways which connect temperate and tropical realms played a major role in the origination and differentiation of many extant lineages. Then, large differences in the structure of bird communities between North American and European forests are discussed and explained in the light of the geographic configuration of major land masses and past climatic changes and upheavals throughout the Neogene. From long term in depth studies in this forest, the composition and structure of bird communities may be used as references for understanding and measuring the processes and mechanisms of change in communities of the western managed forests.

Stratigraphy and Sedimentary Record of the Ordovician System in Poland: a Review

Abstract This report provides insight into the main stratigraphic and sedimentary aspects of the Ordovician System in major tectonic units of Poland: (1) East European Craton, (2) Pomeranian Block, (3) Łysogóry Block, (4) Małopolska Block, (5) Upper Silesian Block, and (6) the Sudetes. The first studies of the Ordovician rocks in Poland were conducted as early as the second half of the nineteenth century in outcrops of the Holy Cross Mountains (SE Poland). Moreover, the Ordovician rocks are exposed in the Sudetes, where they are incorporated into the tectonostratigraphic units accreted during the Variscan orogeny. Significant progress has been made since the 1950s in the recognition of the Ordovician stratigraphic and facies architecture due to numerous drilling cores, which have been mostly made in NE Poland (East European Craton). The temporal and spatial facies pattern in the Polish part of the East European Craton indicate that in the Early and Middle Ordovician this area was a part of large, epicontinental carbonate platform replaced in the Late Ordovician by fine-grained clastics of distal shelf. The Ordovician sedimentary record in the Łysogóry and Małopolska blocks (SE Poland) reveals numerous similarities to the facies architecture in the neighbouring East European Craton, especially its marginal localities. Thus, it is possible to distinguish the same eustatic events in these units corresponding to sea-level changes reported in Baltica, although locally a regional tectonic activity masked their effects. The evolution of the sedimentary basin in NW Poland (Pomeranian Block) was influenced by the collision of Baltica with Avalonia in the Late Ordovician, which resulted in the development of the Caledonian fold-and-thrust belt.

Mobility, activity and migration ability of Strigillaria cana (Stylommatophora: Clausiliidae)

Strigillaria cana mobility was observed in natural conditions in lowland mixed forest in NE Poland. Adult individuals cover a mean distance of 164 mm per hour when moving on a tree trunk. Their average speed was 4.76 mm/min and 19 mm/min maximum. Strigillaria cana activity depends on humidity. The distance covered by snails and the percentage of active individuals increase at high air humidity. The time of the day (day/night) did not influence Strigillaria cana activity. Strigillaria cana specimens show limited dispersal. Of 485 observed adults, 59% never changed the tree on which they were present. Specimens that migrate did not move far from their original location, and most of them (86.2%) cover distances of less than 10 m between trees.

The avoidance of living in the vicinity of a top predator: the coexistence of the black stork and the white-tailed eagle in NE Poland

The black stork Ciconia nigra is a rare species of bird that inhabits old forests near wetlands. The early 21st century has brought a regress of its population in north-eastern Poland. We verified the assumption that an important reason for the observed changes was the colonization of the study area by white-tailed eagle Haliaeetus albicilla, because we observed a correlation between decreasing numbers of the black stork and increasing numbers of the eagle. Based on the long-term monitoring, we analyzed changes in the numbers and distribution of the black storks’ nests and compared the colonization of the study area by the white-tailed eagle in the most extensive forest complex in Poland. We found 42 occupied territories of storks and no eagles in 1989 within the study area. In 2019, there were just 23 stork pairs, but the population of eagles increased to 13. We found a correlation between the rate of decline of the black storks population and the increase in the white-tailed eagles. In the first half of study period, storks’ nests have been distributed randomly, after which they became clustered. The pattern of nests distribution was influenced by the increase in the population of the eagle over time, with this ensuring the aggregation of the nests of storks in places more distant from the nests of eagles. Similarly, the nearest neighbor distance of storks’ nests was dependent on distances from the nests of eagles and the shares of territory accounted for by forests. We surmise that changes in the population size of storks were induced mainly by the growth of population of eagles. Storks avoided occupying nests less than 4.6 km from the eagles’ nests. Our study suggests that the determining role can be played by fear of the predator. Overall, it must be concluded that the protection of top predators can affect other co-occurring species in unexpected ways.

The Role of the Catchment Area in Shaping Water Quality in the Lowland Springs of the Knyszyn Forest (NE Poland)

The Puszcza Knyszyńska springs are an important element of the environment, conditioning the high geo- and biodiversity in the region. These springs are layered outflows that drain the waters of the Quaternary level. More than 200 outflows have been cataloged, and 80 of them have measured/estimated yields and analyses of their water qualities. During periods of low water levels, the discharge efficiency most often fluctuated within a range of 0.5–2.0 dm3·s–1. In light of the applicable legal standards, the tested waters were of excellent quality. They belonged to the two hydrochemical types HCO3-Ca and HCO3-Ca-Mg, indicating the Quaternary aquifer’s homogeneity in the post-glacial areas. Small concentrations of most of the chemical parameters of water were found in the forest springs. Larger transformations in the chemical composition of water occurred in the outflows located in agricultural land and rural areas. A characteristic feature of the chemical composition of the water in the region’s lowland springs was an increased concentration of biogenic compounds (nitrogen, phosphorus, and carbon compounds), both organic and inorganic. The average concentration of dissolved organic carbon in the water of the lowland springs in summer exceeded 4 mg·dm−3. In some outflows, most often of a swamp nature or located in peat areas, the concentration of dissolved organic carbon even exceeded a dozen or so mg·dm−3.

Late Pleniglacial – Late Glacial climate oscillations detected in the organic lacustrine succession at the Lipowo site, north‐eastern Poland

AbstractThe profile of the Lipowo palaeolake (NE Poland) preserves a record of environmental and climate changes from the Last Glacial Termination (16.5k cal ka BP), stretching from the Oldest Dryas to the youngest Allerød warm oscillation. In this interdisciplinary study of the lacustrine succession at Lipowo, we used biological and geochemical indicators and multiproxy analyses to reconstruct environmental changes in the lake ecosystem, such as mollusc, zooplankton and vegetation development, trophic state, water temperature and water level. Four cold and four warm climate oscillations of different durations were identified on this basis: the Older Dryas climate deterioration and two short‐term coolings within the Allerød Interstadial, separated by warm periods in the Bølling and Allerød. The covering of the lake series by diamicton deposits from the melting of dead‐ice blocks is a particularly interesting and rare phenomenon for a postglacial area. The hydrological system of the catchment was generally closed, with a periodically opening and existing flow‐through lake. Over the period of the lake's existence, vegetation changed in general from steppe tundra to forest with birch and pine. For most of this time, the palaeolake was mainly oligotrophic, with increased productivity and a higher trophic level only notable during the middle Bølling.

Supplement to the checklist of Macromycetes (Fungi) from the village of Wyskok in the Masurian Lakeland, NE Poland

Supplement to the checklist of Macromycetes (Fungi) from the village of Wyskok in the Masurian Lakeland, NE Poland

Long-term changes in the diversity of amphibian communities inhabiting small water bodies in the urban area of Olsztyn (NE Poland)

Long-term research has become increasingly important in predicting ecological changes, although only a few studies have reported changes in amphibian communities over long time scales in urban areas. The main aim of the research was to determine the changes in the number and species composition of amphibian communities in small water bodies of two Olsztyn (NE Poland) settlements in the period between 1997 and 2015. The examined settlements are characterized by a high concentration of small water bodies and different degrees of urbanization. A decrease in the diversity index of reproducing amphibian communities was found between the years 1997 and 2015 at both settlements. Over the period of 18 years, one species – the northern crested newt – disappeared from both settlements, and another – the fire-bellied toad – disappeared from one of the two settlements. We demonstrate a significant relationship between the probability of occupancy of a water reservoir by fire-bellied toad, common frog, edible frog, and pool frog and the degree of isolation of these water reservoirs. Moreover, a decrease in the average number of species in a single water body and in the average values of diversity was also observed. The diversity of amphibian communities in water reservoirs depended mainly on the distance to the nearest water reservoir, the nearest building and the area of vegetation in the water reservoir. Available data suggests that the newly created water reservoirs play a positive role in the protection of amphibians in urban spaces, but the restoration of local amphibian communities is related to the degree of urbanization, and mostly applies to generalist species.

Atheta (Dimetrota) knabli G. Benick, 1938 (Coleoptera: Staphylinidae) – a new species for the Polish fauna

In 2021, two specimens of Atheta knabli, a rare beetle species known mostly from subalpine/alpine regions in Europe, were discovered with dung-baited traps in a lowland habitat of Białowieża Forest, NE Poland. To our knowledge, this is the first record of this species for Poland and the first confirmed for a lowland habitat.

Linking the formation of varves in a eutrophic temperate lake to meteorological conditions and water column dynamics

Despite varved sediments being widely used for paleolimnological studies, little information is available about how climate and meteorological signals are recorded in varves at sub-seasonal to annual scale. We investigate links between meteorological and limnological conditions and their influence on biochemical varve formation and preservation of sub-seasonal climate signals in the sediments. Our study site is postglacial Lake Żabińskie located in NE Poland, in which thick and complex varved sediments have been studied for the last decade. These sediments provide an excellent material for studying the influence of short-term weather conditions on geological records. For this, we use an almost decade-long (2012–2019) series of observational data (meteorological conditions, physicochemical water parameters, and modern sedimentation observations) to understand varve formation processes. Then we compare these results with a high-resolution biogeochemical proxy dataset based on μXRF and hyperspectral imaging (HSI) measurements of a varved sediment core spanning the same period. Here we show direct links between the meteorological and limnological conditions and varve formation processes. This is particularly the case for air temperature which governs calcite laminae formation and primary production. We further show that calcite grain size is influenced by lake mixing intensity resulting from the wind activity, and that holomixis events lead to the formation of distinct manganese (Mn) peaks in the typically anoxic sediments. Our findings show that high-resolution non-destructive spectroscopy methods applied to complex biochemical varves, in combination with long observational limnological datasets, provide useful information for tracking meteorological and limnological processes in the past.

The role of the river in the functioning of marginal fen: a case study from the Biebrza Wetlands.

Study regionThe area of interest is the Upper Biebrza Valley, located in NE Poland.Study focusWe examined water exchange at the river-fen interface in a near-natural wetland system using the combined field research-modeling approach. The authors chose the Biebrza River as the research object: it is a specific case of fen marginal valley rivers, and it flows in the peat layer without direct connection to the mineral soil layer. Our case study introduces two new aspects not yet considered in the scientific literature: (1) the riparian aquifer is fen and (2) the river has no direct contact with the mineral layer. The following research questions were investigated: What is the role of the river in feeding and draining a fen? Which drainage paths are important for water exchange in a near-natural river-fen system? How important are the morphological settings for the river-fen relations? We applied a systematic hydrological research approach based on field measurements and observations of the river and surrounding fen hydrological characteristics, as well as on the modelling results.New hydrological insights for the regionWe demonstrated that morphological settings have a significant influence on river-fen relations. We also demonstrated that due to the undeniable need to introduce increased protection and restoration of marginal fens, we may focus on river status in narrow valleys; however, in the wide valleys, the limitation of the drainage layer by decreasing the intensity of evapotranspiration is more promising. We propose to distinguish zones in the fen river valley to include them when proposing protection or conservation plans.

Vanadium and Cobalt Occurrence in the Fe-Ti-V Oxide Deposits Related to Mesoproterozoic AMCG Complex in NE Poland

On the basis of geochemical whole-rock and mineralogical point analyses, the concentrations of V and Co were determined in magnetite-ilmenite oxide ores, associated with sulphides, at the Krzemianka and Udryn deposits in the Mesoproterozoic Suwałki Anorthosite Massif (SAM) in NE Poland. EPMA analyses showed that the main carrier of vanadium was magnetite (mean = 0.42 wt%) and, to a lesser extent, ilmenite (mean = 0.14 wt%) and minor Al-spinels (mean = 0.04 wt%). In turn, cobalt was found mainly in the form of isomorphic substitutions in magmatic sulphides such as pentlandite (mean = 4.41 wt% Co), pyrrhotite (mean = 0.16 wt%), and chalcopyrite (mean = 0.11 wt%). Moreover, Co-enrichments were also recognized in the secondary sulphides, such as pyrite and bravoite, replacing pyrrhotite (means = 1.6 and 2.7 wt% Co, respectively), and in the form of different thiospinels ((Fe, Ni) (Co, Ni)2S4), mainly siegenite (mean = 22.0 wt% Co), replacing pyrrhotite and pentlandite. Vanadium cations were substituted in Fe, Ti oxide minerals in place of Fe+3 cations, and in the case of cobalt, Fe+2 cations were substituted in sulphides and thiospinels. Vanadium and cobalt showed high Person’s correlation coefficients (r = 0.70), indicating their close spatial coexistence and a common source, which was parental anorthosite-norite magma of the SAM suites. The common magma genesis of magnetite-ilmenite and sulphide mineralization was also confirmed by the very similar shapes of the curves of REE content in the oxide-sulphide ores in relation to chondrite, in which negative Eu anomalies and positive Sm anomalies are clearly visible. Although the average contents of vanadium and cobalt were low (arithmetic means = 960 ppm, and 122 ppm, respectively), the resources of these metals were estimated to be large due to the enormous reserves of magnetite-ilmenite ores hosted by the SAM. However, the Fe-Ti-V ores associated with Fe, Ni, Co, and Cu sulphides were considered to be sub-economic because of their depth of occurrence (mainly 1.0 km below the surface level); their metal contents, which were usually too low; and additionally the fact that the location is in a highly environmentally protected landscape and lake area.

Forest ecosystem development in European nemoreal-boreal forest (NE Poland) over the last 2200 years: Impact of human activity and climate change

Long-term ecological studies can provide useful information on forest ecosystem resilience against past climatic change and human caused disturbances. Here, we present a high-resolution 2200-year-long record of forest development in north-eastern Poland, Suwalki region, using paleobotanical proxies (pollen, plant macrofossils, and charcoal). We show that the pollen abundance of deciduous trees was higher than that of coniferous trees, indicating a near pristine state until 900 AD and a semi-natural forest state until 1500 AD. After 1500 AD, the proportion of coniferous tree taxa surpassed that of deciduous trees and have since remained the dominant forest component. The 17th century experienced massive deforestation coupled with a new phase of human colonization in the area that led to the continued and significant decline of deciduous tree cover, for example, Carpinus, Quercus, and Tilia. Cooling associated with the Little Ice Age may have played a role in Picea’s expansion in this area after 1450 AD. Despite significant climatic shifts associated with the warmer Roman Period or Medieval Climate Anomaly and colder Migration Period, as well as a more sustained human impact, Quercus remained a stable forest component until 1500 AD. The stability of Quercus is an important aspect for forest management strategies as future projections suggest warmer conditions and increased frequency of climate extremes will impact forest composition and structure. Our long-term data suggest that forests in the Suwałki region should contain more abundant deciduous tree species, that is, Quercus, whereas conifer cover should be reduced. We also show clear regional differences in the forest development in the Suwałki region, highlighting the importance of local hydrology, geomorphology, and degrees of human activity on the forest composition.

3D geological and potential field modelling of the buried alkaline-carbonatite Tajno massif (East European Craton, NE Poland)

Geological and geophysical data are used to model the 3D geometry of the Tajno alkaline massif intruded during the Early Carboniferous in NE Poland. The massif consists mainly of pyroxenite, mafic intrusive and volcanic rocks, and carbonatites containing rare earth elements (REE) and other important mineral resources. The deep structure of the massif, and its thickness, shape and internal structure, has been poorly known making it impossible to properly search for useful mineral resources. In order to better constrain the distribution, geometries and relationships between the main rock types, a 3D geological model of the Tajno massif has been developed. The input data comprise a set of geological cross-sections built on an updated subsurface geological map, and borehole, magnetic and gravity data. 3D Geomodeller software was applied to integrate geological data into a coherent and geologically feasible model of the massif using geostatistical analysis. The magnetic and gravity data were used to constrain the 3D geological modelling results. The final 3D model is thus compatible with the geological data, as well as with geophysical data. The most important conclusions obtained from the modelling are as follows: (i) a higher proportion of nepheline syenites or tuffs and pyroclastic breccia in relation to pyroxenites; and, (ii) a smaller proportion of chimney breccia relative to chimney-hosted tuffs and volcanic breccia than proposed in previous geological interpretation. These results are important for further studies on the evolution of the Tajno massif and its associated carbonatites.

First Report of Fusarium lateritium Causing Shoot Dieback of Acer negundo in Europe.

Box elder (Acer negundo) is a tree native to North America. In Europe it is considered a dangerous invasive species, and assigned to the highest (4th) category of environmental hazard (Tokarska-Guzik et al. 2012). The tree can threaten a wide range of ecosystems and compete with the native flora. The shoot dieback was observed on 20% of boxelder in July 2018 and 2019 in Bryzgiel (N53°59.963' E23°04.324') in NE Poland (Europe). Young trees (10-15 yr. old) with visible symptoms were observed in a small group on the rural roadside. Infected shoots were chlorotic. There were visible shallow cracks on the bark and brown discoloration in sapwood inside infected branches. Symptomatic shoots were collected in sterile envelopes, surface disinfected with 95% ethanol. Twelve fragments of wood were cut from the border of living and dead tissue, and then divided into 3-5 mm pieces, placed on PDA medium and incubated at 21°C. After 10 days ten Fusarium spp. strains were obtained. Pure cultures were derived by monosporic isolation. The identification of the isolates was initially based on morphology and molecular genotyping (Leslie & Summerell 2006). On PDA, strains produced white, dense, floccose aerial mycelium with a pink surface. The underside of the petri dish was brown. Growth of the colony was relatively slow and reached Ø 3.5 cm after two weeks. Microscopic observation revealed the presence of macroconidia located in a few orange sporodochia. Macroconidia were slightly curved, with dimensions of 38-45 µm × 3.2-3,5 µm, 4-5 septate, with well-formed foot cell and beak on the apex. On aerial hyphae, single intercalary chlamydospores were present. Microconidia were not found. Morphological identification was confirmed by sequencing the ITS regions, the TEF-1α and β-tubulin genes for representative isolates. Mycelia were grown on PDB and freeze dried prior to genomic DNA extraction using the CTAB method. Sequences of two isolates were deposited in GenBank as MN186748 and MN588156 for ITS; MZ191070 and MZ191072 for TEF-1α; and MZ191069 and MZ191071 for TEF-1α. BLASTn search in the NCBI database revealed 100, 98 and >99% similarities of ITS, TEF-1α and β-tubulin with F. lateritium isolates LC171689, KT350607 and FN554618 respectively. A pathogenicity test was conducted on five first year Ø 0.6-0.8cm shoots from a 10-year-old tree. Before inoculation their surface was disinfected with 95% ethanol. Then, bark of the twigs was split longitudinally with a sterile blade and pieces of 10-day-old aerial mycelium grown on PDA were applied on the wound sites. Control samples were inoculated with sterile distilled water only. Inoculated areas were covered with parafilm. First sign of infection was observed after three weeks, as a dark lesion in the place of inoculation and chlorosis. Three weeks later the brown ring on the sapwood was marked in the shoot cross-section. Morphologically identical to the original, F. lateritium isolate was reisolated from the infected tissues, thus fulfilling Koch's postulates. F. lateritium is a species closely associated with trees and shrubs (Leslie & Summerell 2006). However, it has not been recorded on boxelder and this is the first report of F. lateritium causing dieback of boxelder maple. According to the Enemy Release Hypothesis (Elton 1958), new pathogens appearing on alien species can be an indicator of developing environmental resistance to the outlander, which indicate the grade of their domestication. This kind of notification poses a crucial role in invasion monitoring and the search for new biocontrol methods of invasive plant species.

Effective and environmental half-lives of radiocesium in game from Poland

For the first time changes in the 137Cs activity in game throughout Poland, including its most contaminated part known as the Opole Anomaly, were analyzed. Due to its long physical half-life, 137Cs continuously demonstrates high activity both in soil and biota. The species of game mammals, along with forest fruit and mushrooms, tend to accumulate this radionuclide, becoming one of the main sources of secondary contamination in people. In this study the 137Cs activity in roe deer, wild boar and red deer muscle tissue samples, within the years of 1986–2019, were studied. The effective and environmental half-lives were determined for each of the mentioned species for four regions including NE Poland and the Opole Anomaly placed in SW Poland. In all examined species at least two different phases of changes in the 137Cs activity were distinguished, therefore the values of effective half-lives for the researched period since the Chernobyl accident do not correspond with the values from within last ten years. It was proven for the first time that within the anomalous area, featuring the highest values of gamma surface activity in Poland, the 137Cs activity increases with time in the muscle tissues of all three species. No intraspecies, nor interspecies differences of 137Cs activity among the studied species were found. In the light of the collected data, monitoring game considering the 137Cs activity appears to be valid, as, due to not completely clear trophic dependencies, this radionuclide currently increased its migration to the game species despite passing its physical half-life period.

Ordovician and Silurian Formations of the Baltic Syneclise (NE Poland): An Organic Geochemistry Approach

Abstract The Baltic Syneclise is one of the Paleozoic basins along the western margin of the East European Craton. Commercial amounts of hydrocarbons have been found onshore and offshore in the Middle Cambrian sandstones and Upper Ordovician limestone reefs. The Middle-Upper Cambrian and Tremadocian bituminous shales have been identified as good quality effective source rocks. The existence of good quality source rocks in the Ordovician and Silurian profiles provides an impetus for conventional and unconventional hydrocarbon explorations in this region. Geochemical analyses revealed that the rocks of the Middle–Late Ordovician and Early Silurian horizons exhibit overall good to very good source rock quality. Within the Ordovician strata, the Sasino and Prabuty formations exhibit the highest amounts of organic carbon with the median total organic carbon (TOC) values of 1.96 and 1.23 wt. %, respectively. The Pasłęk and Pelplin formations in the lowest parts of the Lower Silurian stand out clearly from other formations with the median TOC values of 0.91 and 1.15 wt. % and median total hydrocarbon content (S1+S2) of 2.46 and 1.54 mg HC/g rock, respectively. The analyzed successions are dominated by immature/early mature, algal (oil-prone) type II, and mixed II/I kerogen deposited in a marine paleoenvironment with anoxic conditions at the bottom and oxic conditions in the photic zone. Immature organic matter prevails in the eastern and central parts of the study area (Gołdap–Kętrzyn–Olsztyn area), and the western part (Darżlubie–Hel–Gdańsk area) has mature kerogen.