Progress report on the stratigraphy, sedimentology and significance of the Kimerot and Bear Creek groups, Kilohigok Basin, District of Mackenzie

Some results of ongoing field investigations of the Kimerot and Bear Creek groups are summarized as they pertain to several topics, including: (1) revision of stratigraphic nomenclature for Kilohigok Basin; (2) vertical and lateral distribution of facies/fabrics of disconformities developed in the lower Bear Creek group; ( 3) stratigraphy and sedimentology of the Beechey Formation; (4) diagenesis studies of the Peg Formation (new name); and (5) constraints on the stratigraphy, sedimentology, and provenance of the Burnside Formation

Chemostratigraphy of Neoproterozoic carbonates: implications for 'blind dating'

The delta C-13(carb) and Sr-87/Sr-86 secular variations in Neoproteozoic seawater have been used for the purpose of 'isotope stratigraphy' but there are a number of problems that can preclude its routine use. In particular, it cannot be used with confidence for 'blind dating'. The compilation of isotopic data on carbonate rocks reveals a high level of inconsistency between various carbon isotope age curves constructed for Neoproteozoic seawater, caused by a relatively high frequency of both global and local delta C-13(carb) fluctuations combined with few reliable age determinations. Further complication is caused by the unresolved problem as to whether two or four glaciations, and associated negative delta C-13(carb) excursions, can be reliably documented. Carbon isotope stratigraphy cannot be used alone for geological correlation and 'blind dating'. Strontium isotope stratigraphy is a more reliable and precise tool for stratigraphic correlations and indirect age determinations. Combining strontium and carbon isotope stratigraphy, several discrete ages within the 590-544 Myr interval, and two age-groups at 660-610 and 740-690 Myr can be resolved

Roslinnosc Jeziora Zbaszynskiego [Pojezierze Lubuskie] na tle stanu jego trofii

The macrovegetation of a large shallow lake (Lake Zbąszyńskie, Lubuskie Lakeland) was characterized against the background of its physico-chemical properties. The question of interest was whether the phytocoenotic composition and structure of macrophyte vegetation reflect abiotic and trophic conditions of the studied lake. The results are discussed in the context of the theory of alternative stable states in shallow lakes

Nitella opaca [Bruzelius] Agardh [Characeae] w Wielkopolsce

This paper presents historical and new localities of Nitella opaca, a rare charophyte species whose distribution in the light of published data and herbarium material was restricted to a few localities in the Wielkopolska region. The basic information on the species ecology and detailed characteristics of phytocoenotic interrelation are provided. So far, the occurrence of Nitelletum opacae in the Wielkopolska region has not been reported

Transformation and simplification of aquatic vegetation structure and reoligotrophication of a lake during the last 40 years

The recovery or reconstruction of aquatic vegetation has recently been reported as a result of water quality improvement aer anthropogenic eutrophication. The objectives of this study were: to investigate long-term trends in aquatic vegetation abundance in relation to decreasing water fertility and to present new directions in changes of the submerged aquatic vegetation structure, species richness, and biodiversity in Lake Kuźnickie (western Poland) with the perspective of the last 40 years (1978–2018). Lake Kuźnickie is an example of water quality improvement taking place without any additional reclamation measures, except a reduction in nutrient discharge into the lake from its direct catchment. Currently, the study lake represents a mesotrophic status. The Trophy State Index evidenced a decrease in the lake’s fertility compared to previous decades. The water quality improvement manifests in a significant reduction in the total phosphorus concentration. An analysis of the spatial changes in the phytolittoral evidenced a decrease in rush vegetation between 1978 and 2018 by over 2 ha. In the period 1978–2018, the aquatic vegetation structure in Lake Kuźnickie underwent significant reconstruction. Currently, charophytes play a much greater role in the lake compared to the last 40 years, contributing to the maintenance of the lake’s high water quality. Moreover, the endangered charophyte Lychnothamnus barbatus has recovered. Concurrently, however, the biodiversity and species richness of the submerged vegetation has decreased. At present, only four species dominate in the lake, including two charophytes L. barbatus, Nitellopsis obtusa, and two vascular plants Ceratophyllum demersum and Myriophyllum spicatum. Over 40 years, Lake Kuźnickie has changed from a eutrophic lake dominated by vascular plants to a mesotrophic lake with a codominant contribution by charophytes. The lake is characterized by good water quality, optimal for the development of aquatic vegetation, especially charophytes