organic-inorganic interaction. This localized and incipient maturation can be related to diabase sills of the Serra Geral Formation. Similar maturation due to heating also affected the distribution of the norcadalenes by thermally stabilizing their α -isomers with an isopropyl substituent, in addition to the formation of related compounds with an ethyl substituent. Based on this, a norcadalene ratio is proposed, which is the sum of the 1,6-dimethyl-4-ethylnaphthalene and 1,6-dimethyl-3-ethylnaphthalene over the sum of the 1-isopropyl-4- methylnaphthalene and 1-isopropyl-7-methylnaphthalene. The results of this ratio and the established cadalene ratio resemble each other whereas samples from the São Mateus do Sul Quarry (central eastern basin) were not affected by thermal maturation and are characterized by a uniform distribution of the cadalenes and norcadalenes.

Martins, L.L., Schulz, H.-M., Severiano Ribeiro, H.J.P., Nascimento, C.A.d., Souza, E.S.d., Cruz, G.F.d., 2020. Organic geochemical signals of freshwater dynamics controlling salinity stratification in organic-rich shales in the Lower Permian Irati Formation (Paraná Basin, Brazil). Organic Geochemistry 140, 103958.

http://www.sciencedirect.com/science/article/pii/S0146638019301950 The Lower Permian Irati Formation in the northeastern and central eastern Paraná Basin (southern Brazil) was investigated in terms of bulk and molecular organic geochemistry in order to enlighten the complex depositional paleoenvironment during deposition of Irati black shales. The geochemical data reflect temporal and spatial variations of freshwater incursions promoting salinity stratification and high primary productivity in surface waters with the establishment of photic zone euxinia. Overall, highly concentrated C long-chain 17 alkylnaphthalenes point to algal blooms as a result of freshwater inflows into the Irati Sea, mostly in the central n eastern basin segment, and resemble concentration variations of pristane, phytane and C . The freshwater 17 inflows were also retraced by increasing chroman ratios toward the top of the investigated units along with the general decrease of further palaeosalinity indicators, e.g., gammacerane, tetracyclic (C ), β -carotane, and the 24 herein suggested γ -carotane and lexane indexes. The existence of a water column stratification promoting organic matter preservation is supported by the detection of tetrahydrophenanthrene at high concentrations, in addition to the known prominent occurrence of gammacerane. The detection of C to C aryl isoprenoids in 10 31 addition to C and C pseudohomologue aryl isoprenoids points to the presence of photic zone euxinia. In 16 18 general, samples from the central eastern basin were deposited in a deeper marine setting with lower salinity than samples from the northeastern basin, which displays signals of a shallower marine environment with reducing bottom water conditions, both deposited under freshwater influxes.

Maßmig, M., Lüdke, J., Krahmann, G., Engel, A., 2020. Bacterial degradation activity in the eastern tropical South Pacific oxygen minimum zone. Biogeosciences 17, 215-230.

https://www.biogeosciences.net/17/215/2020/ Oxygen minimum zones (OMZs) show distinct biogeochemical processes that relate to microorganisms being able to thrive under low or even absent oxygen. Microbial degradation of organic matter is expected to be reduced in OMZs, although quantitative evidence is low. Here, we present heterotrophic bacterial production 3 β ( H leucine incorporation), extracellular enzyme rates (leucine aminopeptidase/ -glucosidase) and bacterial cell abundance for various in situ oxygen concentrations in the water column, including the upper and lower oxycline, of the eastern tropical South Pacific off Peru. Bacterial heterotrophic activity in the suboxic core of - 1 - 3 - 1 the OMZ(at in situ ≤ 5 µmol O kg ) ranged from 0.3 to 281 µmol Cm d and was not significantly lower 2 - 1 than in waters of 5 -60 µmol O kg . Moreover, bacterial abundance in the OMZand leucine aminopeptidase 2 - 1 activity were significantly higher in suboxic waters compared to waters of 5 -60 µmol O kg , suggesting no 2 impairment of bacterial organic-matter degradation in the core of the OMZ. Nevertheless, high cell-specific bacterial production was observed in samples from oxyclines, and cell-specific extracellular enzyme rates were especially high at the lower oxycline, corroborating earlier findings of highly active and distinct micro-aerobic bacterial communities. To assess the impact of bacterial degradation of dissolved organic matter (DOM) for oxygen loss in the Peruvian OMZ, we compared diapycnal fluxes of oxygen and dissolved organic carbon (DOC) and their microbial uptake within the upper 60 mof the water column. Our data indicate low bacterial growth efficiencies of 1 %-21 %at the upper oxycline, resulting in a high bacterial oxygen demand that can