The Holocene alluvia within the Wisłok River valley were described for the first time more than 100 years ago by Friedberg (1903). Between Rzeszów and Trzebownisko L. Starkel (1960) distinguished several alluvial fills from the Late Glacial and the Holocene dated by the palynological method by K. Mamakowa. The current recognition of the stratigraphy of the Vistulian (Weichselian) and the Holocene alluvia of the lower Wisłok River valley is based on more than 30 radiocarbon and palynological age determinations of the sequences located mostly between Łukawiec and Łąka villages and the town of Łańcut (Gębica
Maps with location and geomorphology of study area. General location of the study area. The Wisłok River valley and the Late Glacial and Holocene alluvia with sites sampled for the radiocarbon datings (elaborated by P. Gębica). Explanation of symbols: 1 – Kolbuszowska Plateau covered with sediments of the Elsterian Glaciation, 2 – Kańczucka Plateau covered with Saalian 2 (Wartanian) and Vistulian loess, 3 – fluvioglacial plain, Elsterian 2 Glaciation, 4 – river terrace 13–18 m high, Saalian 2 (Wartanian), 5 – loess terrace 15–20 m high, Vistulian, 6 – Vistulian (sandy) terrace 8–12 m high, with dunes, 7 – erosional-denudation valley, 8 – Pleistocene alluvial fan, 9 – Holocene alluvial fan, 10 – Holocene floodplain 7–8 m high and systems of palaeochannels, 11– study area, 12 – sites of the Late Glacial sediments, 13 – sites of the Early Holocene sediments, 14 – sites of the Last Millenium sediments. List of the sites dated by radiocarbon and palynological methods: SŁ – Słocina, KW – Krasne-Wólka, Ła1 – Łąka 1, Ła4 – Łąka 4, T – Terliczka, Ła 74 – Łąka archaeological site No. 74, ŁkIV – Łukawiec IV, Łk3 – Łukawiec 3, CzP – Czarna Podbór, D-Cz – Dąbrówki-Czarna, WM – Wola Mała, BI – Białobrzegi, BŁ – Budy Łańcuckie, GŁ2 – Gniewczyna Łańcucka 2, GŁ11 – Gniewczyna Łańcucka 11, GN1 – Grodzisko Nowe 1, GN2 – Grodzisko Nowe (Dolne) 2. Wola Dalsza gravel pit and the location of sequences described in the text (elaborated by S. Superson). Explanation of symbols: 1 – Vistulian sandy terrace 8–12 m high, 2 – Holocene terrace 7–8 m high, 3 – floodplain 5–6 m high, 4 – palaeochannels, 5 – erosional edges higher than 1 m, 6 – erosional edges up to 1 m high, 7 – extent of gravelpit, 8 – study sites, Sm – Smolarzyny site.Fig. 1
The study of recently outcropped depositional sequences located in the erosional undercuts of the Wisłok riverbed and in the gravel pits recently opened due to the construction of the A-4 highway, made it possible to recognise the structure and the stratigraphy of the Wisłok River valley alluvia between the towns of Łańcut and Przeworsk (Gębica
The Wisłok River is the longest tributary of the San River. In the 40 km long section it flows along the latitudinal erosional depression named the Fore-Carpathian Trough (Rynna Podkarpacka) (Starkel, 1972), through which during the San 2 (Elsterian) glaciation glacial waters flowed eastward toward the Dniester River basin. The bottom of the valley, eroded in Miocene clays is covered with Vistulian (Weichselian) and Holocene alluvia. The terraced floor of the valley is framed from the south and the north by the edges of the plateaus (
The study area is situated in the northern part of the Fore-Carpathian Trough, in the village of Wola Dalsza, about 5 km north-east of Łańcut (
After an initial survey of the accessible outcrops, 8 sequences located using the GPS (Global Positioning System) system were selected for further detailed examination and sampling. At the selected sites the sequences up to 7–8 m long in the outcrops were described and supplemented with archival bore-hole data up to the length of 11–13 m. Moreover, the sequences at the neighbouring sites in the village of Smolarzyny were examined in detail. 13 samples of peat, organic silt, charcoal as well as fragments of wood and tree trunks were collected. Five of these samples were dated by the radiocarbon method in the Department of Radioisotopes, Silesian University of Technology in Gliwice (Lab. code begins with GdS). One sample of fossil tree trunk, taken from the outcrop in the Wisłok floodplain at a distance of 1 km west of the gravel pit (
Radiocarbon datings of samples from the sequence in the Wola Dalsza gravel-pit.Sample no. Name of the profile Terrace level (m) Dated material Depth (m) Laboratory no. Age 14C (BP) Calendar Age (calibrated) range 68% Calendar Age (calibrated) range 95% 1 Wola Dalsza Vb 7–8 charcoals 0.60–0.80 ---------- no dated ---------- ---------- 2 Wola Dalsza Va 7–8 coal dust 1.50–1.60 ---------- no dated ---------- ---------- 3 Wola Dalsza Vc 7–8 wood 4.60–4.65 GdS-1920 10100±140 11960–11860 cal BP (11.2%) 11845–11395 cal BP (57.0%) 12370–12350 cal BP (0.3%) 12235–12205 cal BP (0.5%) 12170–11235 cal BP (94.5%) 4 Wola Dalsza IX 7–8 trunk 5.80–5.90 MKL-2786 9290±50 8619–8466 cal BC (68.2%) 8699–8679 cal BC (1.8%) 8641–8337 cal BC (93.6%) 5 Wola Dalsza IV 5–6 peat 3.20–3.25 GdS-3233 8900±95 10195–9885 cal BP (68.2%) 10230–9695 cal BP (95.4%) 6 Wola Dalsza VI 5–6 trunk 3.00–3.10 GdS-3230 7390±80 8335–8155 cal BP (64.8%) 8365–8030 cal BP (95.4%) 8085–8065 cal BP (3.4%) 7 Wola Dalsza VII 5–6 peat 4.70–4.80 GdS-3056 9085±65 10370–10355 cal BP ( 2.9%) 10490–10455 cal BP (1.5%) 10300–10185 cal BP (65.3%) 10440–10155 cal BP (93.9%) 8 Wola Dalsza VIII 5–6 peat 4.50–4.60 GdS-3228 9575±95 11095–10915 cal BP (37.0%) 11195–10655 cal BP (95.1%) 10910–10755 cal BP (31.2%) 10615–10605 cal BP ( 0.3%)
Consequently, the following 8 samples of organic deposits were selected for conventional radiocarbon dating (LSC) of: one sample of charcoal, 3 peat samples, 3 wood samples and one sample of fired clay with coal dust. However, the content of organic material in this last sample was too small for dating using the conventional technique. Furthermore, the charcoal sample of a weight of 1 g was too small for reliable conventional dating. Therefore finally, the reliable results of 6 age determinations were taken into account and are presented in
All samples underwent the standard procedure of initial preparation acid-alkali-acid, and then they were decomposed and converted into benzene (Pazdur
The palynological analysis was used for the verification of the age of the sediments determined by radiocarbon dating. Therefore, this analysis was performed for 6 samples taken from 6 depositional sequences of the 7–8 m high terrace and the floodplain, which were also dated by the radiocarbon method. Furthermore, the tree species composition of charcoal fragments in the overbank sediments was examined. The species identification of charcoal fragments was based on anatomic wood structure. The charcoal fragments were prepared for microscopic observation by cutting them along three anatomic cross-sections characteristic for botanic material: transversal, longitudinal-radial and tangential longitudinal. In order to record all anatomic details characteristic for particular tree species examination of fragments larger than 4 mm3 is recommended, nevertheless, smaller but accurately preserved particles are usually also identifiable (Chabal
Moreover, in the south-east face of the gravel pit in the profie WD IV the organic (peat) sequence of undisturbed fabric (vertical column) 57 cm long was sampled in order to perform palynological analysis. From the sequence WD IV four samples were analysed (
Geological cross-section of the floodplain (5–6 m high) and terrace 7–8 m high with the location of the sequences and samples dated by the radiocarbon and palynological methods (elaborated by S. Superson). Explanation of symbols: 1 – gravel, 2 – sand with single pebbles, 3 – sand, 4 – silt, 5 – flood rhytmithe, 6 – clay, 7 – tree trunks, 8 – wood fragments, 9 – peat, 10 – charcoal fragments, 11 – fired clay bearing coal dust, 12 – anthropogenic embankment; PAL-palynological dating, AT-Atlantic, SB-Subboreal, SA-SubatlanticFig. 2
The structure of floodplain 5–6 m high bearing peat, eroded in the sequence IV (elaborated by S. Superson and P. Gębica). Explanation of symbols: 1 – sand, 2 – silty sand, 3 – laminated sand, 4 – silt with sand, 5 – silt, 6 – organic silt, 7 – clayey silt, 8 – clay, 9 – peat, 10 – anthropogenic embankment, 11 – palynological analysis, 12 – number of the sequence; Bo-Boreal, AT-Atlantic.Fig. 3
Palynological diagrams of the Wola Dalsza and Smolarzyny sequences (analysed by P. Kołaczek).Fig. 4
Furthermore, the cartographic materials that were produced in 1878, 1900, 1938 in the scale 1 : 100 000 (Topographic map, 1938) and 1 : 75 000 (Special map 1878, 1900), illustrate the changes in the Wisłok River channel development in 19th and 20th centuries.
The structure of the 7–8 m high terrace is tripartite. Its substratum is formed of Miocene clays (Laskowska-Wysoczańska, 1971; Gębica, 2004). At a depth of 11–13 m these clays are overlain by 5–7 m thick sand-gravel channel alluvia that bear overbank silt inserts and wood fragments (
The peat samples taken in the outcrops of the floodplain sediments (sequences WD IV, VII, VIII and Sm I) (
The results of palynological analysis (amount of pollen grain) of six samples of organic sediments from the Wola Dalsza site (analysed by K. Szczepanek).Profile number Sample number depth (m) Vb 1 0.6–0.8 Va 2 1.5–1.6 VIII 3 4.5–4.6 IV 4 3.20–3.25 VII 5 4.7–4.8 Vc 6 4.60–4.65 Pinus sylvestris t. no pollan grains, charcoal: Quercus, Fraxinus, Carpinus no pollan grains, coal dust 213 210 160 no pollan grains Betula sp. 25 101 72 Ulmus 11 65 46 Quercus 106 3 9 Salix 46 48 58 Corylus 17 5 4 Alnus 1 1 0 Picea 3 3 2 Tilia 2 0 0 Larix 0 1 0 Poaceae 20 17 35 Cyperaceae 4 3 5 Artemisia 4 4 5 Brasicaceae 10 5 1 Rosaceae 8 6 1 Rubiaceae 1 1 0 Chenopodiaceae 0 1 0 Caryophyllaceae 3 1 0 Asteraceae 0 1 1 Apiaceae 16 15 9 Sparganium 8 8 9 Myriophyllum 0 23 14 Nuphar, Nymphaceae 0 1 2 Lemna 1 0 0 Humulus-Cannabis t. 2 3 3 Equisetum 2 0 0 Lycopodium 1 0 0 Polypodiaceae 14 5 8 Varia 8 2 4
At a depth of 1.5 m, under the flood rhythmite layer, coal dust occurs on the surface of and inside hard clay aggregates that resemble fossilized/carbonized wood (
Up to now four samples taken from WD-IV sequence of the peat have been analysed. The sample from a depth of 3.79 m is characterised by low pollen concentration, but by high content of redeposited pine pollen grains (see
The sediment sample bearing charcoal fragments, taken from the Vb sequence at the Wola Dalsza site at a depth of 60–80 cm, was used for the anthracological analysis (
Consequently, the qualitative analysis of such specimen of charcoal seems to be more adequate than quantitative one.
In regard to the result of the anthracological analysis, particularly, on the basis of hornbeam occurrence that is characteristic for the Neoholocene forests, the sample age was ascribed to the Subboreal or/and Subatlantic Phases.
Six samples from the eight ones have sufficient weight for radiocarbon dating. The content of organic material in the samples bearing coal dust and charcoal was too small for the dating using the conventional technique (
The amount of charcoal in the clay layer at the top of the 7–8 m high terrace, sampled at a depth of 0.6–0.8 m was too small for the conventional radiocarbon dating (
In the northern part of the gravel pit within the floodplain,
Analysis of cartographic materials proves that in the 70-ties of the 19th century the meandering Wisłok River channel of a width of 80–120 m, undercut the edge of the Vistulian terrace in a distance of
Changes of the Wisłok River channel during the 19th and 20th centuries (elaborated by S. Superson). A. Changes of the Wisłok Rivet channel between Wola Dalsza and Białobrzegi, B. The area presented on Fig. 1C in detail.Fig. 5
In the valley section between the villages of Trzebownisko and Łukawiec the floodplain occupies the area of a width of 200–300 m, whereas to the east of Łańcut its width increases up to 1.5 km. The organic sediments occurring in its bottom at a depth of 3–4 m represent the Interplenivistulian and are overlain by the Late Glacial and the Holocene alluvia (Gębica, 2004). To the east of the sites in the villages of Łąka and Łukawiec the Plenivistulian sediments are absent in the bottom of the 7 m high terrace, which suggests intensive downcutting of the Wisłok River in this part of the valley.
The preservation of the Early Holocene organic sediments forming the erosional bench of the floodplain (
The palynological analysis and the radiocarbon dating made it possible to determine the Early Holocene age (Preboreal and Boreal Phases) of the organic oxbow-lake sediments situated in the northern part of the Wisłok River valley. The attempts to perform the conventional radiocarbon dating of the horizons with charcoal fragments failed owing to the small amount of organic material sampled and subsequently obtained after the benzene preparation in the laboratory. The anthracological analysis of the charcoal sample reveals the occurrence of the tree taxa typical for the Neoholocene, which suggests that the deposition of clay sediments occurred during the Subboreal and/or Subatlantic Phases. The preservation of the Early Holocene organic sediments within the floodplain indicates the predomination of lateral migration of the river channel and the consequent erosion of the wide plain aggraded with flood (overbank) alluvia during the last 200 years. In the 20th century the aggradation of the floodplain was synchronous with the deepening of the Wisłok River channel. The radiocarbon ages obtained for the channel alluvia with tree trunks and peat horizons indicate the synchronicity of the organic deposition and the functioning of the active channel in the Early Holocene, which only partly confirm the hypothesis of L. Starkel (1995), that postulates the stabilisation of fluvial systems in that period.