Porosity-depth plots for sandstones commonly show a decrease in porosity with depth. In more deeply buried sandstones, this reflects an increase in the amount of mineral cement. This correlation is often thought to indicate a causal relationship; however, in this paper, we examine data that argue against a direct depth control on cementation. In sandstones from the Garn Formation, Haltenbanken, the homogenization temperatures of primary fluid inclusions in quartz cement are correlated with depth over the entire basin. The inclusions do not appear to have stretched or leaked so the correlation suggests a widespread cementation event affecting large parts of the basin at about the same time. K-Ar ages of illite cements from eolian sandstones of the Rotliegend Formation (Vil age Fields area, southern North Sea) all fall within the Middle to Late Jurassic and show no correlation with depth at time of cementation. There is, however, a weak correlation between illite oxygen isotope ratio and depth at time of illite growth. Both ages and isotope ratios again suggest a widespread cementation phase taking place within a restricted time period. Published data from other sandstones, including the Brent sandstone reservoirs of the North Sea, tell a similar story, indicating cementation at a particular time rather than temperature or depth. In the case of quartz, cementation seems to coincide with rapid subsidence and heating, while in the Southern North Sea, illite growth is approximately synchronous with rifting and consequent rapid subsidence and heating. These eff cts may have influenced fluid flow and/or precipitation mechanisms in such a way that regional cementation occurred.

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