From mud to shale: rock stiffening by micro-quartz cementation

Quartz cementation in Late Cretaceous mudstones, northern North Sea: Changes in rock properties due to dissolution of smectite and precipitation of micro-quartz crystals

“…A similar velocity contrast at 85 C has been documented in well 6505/10-1 ( Fig. 4 and Peltonen et al, 2009;Thyberg et al, 2009). …”

“…6b, c and 7). This type of quartz cement in consistent with the findings of Thyberg et al (2009). The micro-sized neoformed quartz crystals appear to have inter-grown with the mixed layered minerals and illite.…”

“…3 and Peltonen et al, 2009;Thyberg et al, 2009). The authigenic micro-quartz crystals identified in this study are interpreted to be sourced from local release of Si from the dissolution of smectite and precipitation of illite.…”

“…3. The Late Cretaceous mudstones section in well 6505/10-1 display similar mineralogical trends and petrophysical well log readings, including the smectite to illite thermal transformation associated with abrupt increase in velocity close to 2500 m (2430 m/85 C; Peltonen et al, 2009;Thyberg et al, 2009). A close-up and comparison of well log data of p-wave velocity (Vp) and bulk density (RHOB) in the 1800-2800 m depth interval of well 33/5-2 and 6505/10-1 display also similar trends showing the abrupt velocity change close to 2500 m (85 C; Fig.…”

Open-system chemical behaviour of Wilcox Group mudstones. How is large scale mass transfer at great burial depth in sedimentary basins possible? A discussion

“…Mineralogical analyses of initially smectite rich rocks heated to more that 80e100 C has shown that the silica has been precipitated as small quartz crystals which develop into sheets of quartz producing a distinct schistocity (Thyberg et al, 2009(Thyberg et al, , 2010Thyberg and Jahren, 2011). Day-Stirrat et al (2010) found that here is a decrease in the content of quartz, K-feldspar and kaolinite and an increase in illite and smectite with depth.…”