REMAINS OF PALEOFLORA IN THE BRECCIAS OF THE ONAPING FORMATION, SUDBURY IMPACT STRUCTURE, ONTARIO, CANADA

Electron microscopic investigations of four breccia samples of the Onaping Formation, Sudbury impact structure, Canada, have been carried out for the search of possible remains of paleoflora and identification of the nature of organic matter and their composition. Two forms of plant remains were discovered in the breccias. The first form is represented by single plant particles scattered in the matrix of breccias and included in gas vesicles in devitrified glasses. These particles are leaf-shaped, stem-shaped, tubular, and spherical objects, ranging from 5-10 to 200-300 µm in size. It is supposed that algal flora inhabiting the sea basin before the Sudbury impact was the source of this form of plant residues in breccias. The second form of plant remains in breccias is represented by plant detritus in carbon-bearing fragments of mudstones included in the breccia matrix. These fragments, reaching a size to 1000-1200 µm, have irregular shapes and complicated rugged contacts with the host breccia. Plant residues in mudstones are mainly ribbon-like scraps from 3-5 to 200-300 µm long, some while rare particles have a more complex shape. The matrix of the mudstones is a heterogeneous fine-grained clay-like substance with a network of micron-wide open joint fissures. The carbon content in mudstone matrix ranges from 7-10 to 20-25 wt%. Muddy bottom sediments of the pre-impact sea basin are supposed to be a source of mudstone fragments in breccias, while the algal flora inhabited the sea during their sedimentation served as a source of plant detritus in mudstones. Fragments of mudstones and floral residues are an important source of organic carbon in breccias of the Onaping Formation. The discovery of paleofloral remains in the breccias indicates the existence of a previously unknown complex algal flora that inhabited the pre-impact sea before the impact event 1.85 billion years ago at the very end of the Paleoproterozoic. The Sudbury impact structure is comparable in size to the Chicxulub impact structure, the formation of which caused the Cretaceous-Paleogene mass extinction. We assume that the formation of the Sudbury structure had a catastrophic impact on the paleoflora of the late Paleoproterozoic, the remnants of which were preserved in the breccias of the Onaping Formation.

Effects of litter and root manipulations on soil carbon and nitrogen in a Schrenk’s spruce (Picea schrenkiana) forest

Plant detritus represents the major source of soil carbon (C) and nitrogen (N), and changes in its quantity can influence below-ground biogeochemical processes in forests. However, we lack a mechanistic understanding of how above- and belowground detrital inputs affect soil C and N in mountain forests in an arid land. Here, we explored the effects of litter and root manipulations (control (CK), doubled litter input (DL), removal of litter (NL), root exclusion (NR), and a combination of litter removal and root exclusion (NI)) on soil C and N concentrations, enzyme activity and microbial biomass during a 2-year field experiment. We found that DL had no significant effect on soil total organic carbon (SOC) and total nitrogen (TN) but significantly increased soil dissolved organic carbon (DOC), microbial biomass C, N and inorganic N as well as soil cellulase, phosphatase and peroxidase activities. Conversely, NL and NR reduced soil C and N concentrations and enzyme activities. We also found an increase in the biomass of soil bacteria, fungi and actinomycetes in the DL treatment, while NL reduced the biomass of gram-positive bacteria, gram-negative bacteria and fungi by 5.15%, 17.50% and 14.17%, respectively. The NR decreased the biomass of these three taxonomic groups by 8.97%, 22.11% and 21.36%, respectively. Correlation analysis showed that soil biotic factors (enzyme activity and microbial biomass) and abiotic factors (soil moisture content) significantly controlled the change in soil C and N concentrations (P < 0.01). In brief, we found that the short-term input of plant detritus could markedly affect the concentrations and biological characteristics of the C and N fractions in soil. The removal experiment indicated that the contribution of roots to soil nutrients is greater than that of the litter.

ISOTOPIC COMPOSITION OF CARBON AND OXYGEN IN SEDIMENTATION AND EPIGENETIC CARBONATES OF THE LOWER TRANSITIONAL MEMBER OF THE VERKHNEKAMSKOE SALT DEPOSIT

In contrast to the carbonate-sulfate evaporites of the Syukeevskoe deposit and the salts of the Starobinskoe deposit, the formation of the salt stratum of the Verkhnekamskoe deposit is assumed to involve melt water formed between the P2 and P3 glacial events. Comparison of host rocks and newly formed mineralization made it possible to show that the process of diagenesis in carbonate-argillaceous strata alternating with rock salt was difficult. Initially, there was a decomposition of dispersed plant detritus, which is confirmed by the lightening of the isotopic composition of carbon. After the interaction of sulfate-containing sediment with desalinated waters, the anhydrite was replaced by 16O-enriched calcite. The complete lithification and stratification of clay strata led to the formation of exfoliation cavities, in which halite-calcite veins of columnar structure were formed associated with the influx of brines from neighboring salt strata enriched in 18O.

Organické uloženiny fluviální výplně údolního dna řeky Bečvy u Oseku nad Bečvou a jejich vztah k vývoji sedimentace

Organic matter, like pollen, plant detritus or subfossil woods can be found in sequences of fluvial sediments. Detail study of these remains help to assess age of accumulation processes, especially during the Holocene erosion/accumulation cycle. Two localities with exposed infill of the Bečva River valley were found near Osek nad Bečvou. The first outcrop is a gravel pit 1 km south of Osek nad Bečvou village. The second one is a river-cliff on the left bank of the Bečva River, 1 km westward of Oldřichov village, formed mostly during the extreme flood in 1997. Fluvial sediments, 4–5 m thick, of the the so called “lower flood-plain level” were exposed on both localities. At the base of the Oldřichov river-cliff was encountered a horizon of boggy soil with subfossil trunk at the base. In the gravel pit near Osek nad Bečvou was exposed layer of clay/silt with plant detritus. Up to 2 m thick middle/coarse grained gravel, situated beneath underground water level, underlie the organic-rich sediments in both localities. Badenian clay represents the bedrock of the river valley. Organic-rich layers are overlaid by middle/coarse grained gravel sediments passing gradually to sandy silt of the flood plain. Pollen analyses were made from the organic-rich layers and dendrological analysis, dendrochronology and radiometric dating from subfossil trunk.Organic-rich layer from Osek (sample LS001) was assigned to the early Holocene based on pollen analysis and represents the oldest age found. The Oldřichov samples come from oxbow sediment. The sample LV030V was poor in pollen grains and inconclusive. The sample LV030Z indicates Holocene climate optimum (Atlantic). This supposed age is compatible with radiometric dating of the subfossil trunk from the base of the layer. Radiocarbon dating using wiggle matching method gave age of 7 070–6 775 BC.Based on these data, repeated erosion/accumulation events during Late Pleistocene and Holocene are evident in Bečva River valley fill. Late Pleistocene accumulation was replaced with erosion during Late Pleistocene-Holocene transition. Erosion on the break of the Pleistocene and Holocene partly removed upper Pleistocene gravels so in places left reached level 2 m above the bedrock. The first third of Holocene (time of all interpreted data) seems to be very stable from erosion/accumulation evolution point of view. More dynamic evolution started with accumulation of “higher flood-plain level” (from cca 214 m a. s. l. up to 221 m a. s. l.). Subsequent erosion formed relatively deep cut in the northwest part of the flood plain which was filled relatively quickly by sediments as consequence of deforestation connected with a colonization of upper parts of Bečva River drainage area. This is supported by finds of much younger subfossil trunks dated from 1 century BC up to top of Middle-Age period in this accumulation (Vít et al. 2009). The surface of this accumulation is the so called “lower flood plain level” where periodicity of the inundation during floods is more regular then on the upper one.