High sedimentation-rate basins are characteristic of the continental margins, where sedimentation ratesup to 500m/Ma and more are no exception. The sediments are rich in organic matter and undergo awell-established sequence of bacterial oxidation reactions, starting at the sediment/water interface with:(1)the oxidation zone (absent in euxinic basins), which is followed downwards by (2) the nitrate reduction zone,(3) the sulfate reduction zone, (4) the carbonate reduction zone, (5) the fermentation zone and (6) thedecarboxylation zone, which marks the onset of thermocatalytic reactions characteristic of the intermediatestage (and deeper stages) of diagenesis. This sequence of bacterially mediated organic-matter decomposition reactions in rapidly depositedsediments on the continental margins is well reflected in the vertical trends of pore-water chemistry. Carbonisotopic fractionation permits to distinguish between zones (1) to (3) with negative δ~(13)C values for the CO_2generated, and between zones (4) and (5) with increasingly heavier carbon-isotopes in CO_2 (up to + 15 to+ 25‰δ~(13)C). The formation of gas-hydrates causes characteristic chemical and isotopic signatures in porewaters retrieved from hydrate-beating sediments. After hydrate decomposition (in the sampling process orat the base of hydrate zones) marked chlorimity decreases accompanied by increases in heavy oxygenisotopes are observed. These are distinctly different from the effects of meteoric water influx, which are notaccompanied by positive δ~(18)O values. The opposite trend of increasing salinity at shallow burial depths,rather than pore-waters freshening, is observed in the vicinity of evaporites. High sedimentation-rate basins are characteristic of the continental margins, where sedimentation rates up to 500m / Ma and more are no exception. The sediments are rich in organic matter and undergo awell-established sequence of bacterial oxidation reactions, starting at the sediment / water interface (1) the oxidation zone (absent in euxinic basins), which is followed by downwards by (2) the nitrate reduction zone, (3) the sulfate reduction zone, (4) the carbonate reduction zone, and (6) thedecarboxylation zone, which marks the onset of thermocatalytic reactions characteristic of the intermediate stage (and deeper stages) of diagenesis. This sequence of bacterially mediated organic-matter decomposition reactions in rapidly deposited sediments on the continental margins is well reflected in the vertical trends of pore-water chemistry. Carbonisotopic fractionation permits to distinguish between zones (1) to (3) with negative δ ~ (13) C values ​​for the CO_2generated, and between zones (4) and (5) with increasingly heavier carbon-isotopes in CO_2 (up to +15 to +25 ‰ δ ~ (13) C). The formation of gas-hydrates causes characteristic chemical and isotopic signatures in porewaters retrieved from hydrate -beating sediments. After hydrate decomposition (in the sampling process orat the base of hydrate zones) marked chlorimity decreases accompanied by increases in heavy oxygenisotopes are observed. These are distinctly different from the effects of meteoric water influx, which are notaccompanied by positive δ ~ (18) O values. The opposite trend of increasing salinity at shallow burial depths, rather than pore-waters freshening, is observed in the vicinity of evaporites.