Summary The petrography and diagenesis of calcite cements in the Lower Jurassic, Bridport Sands (southern England) and Upper Jurassic, Viking Group sandstones (Troll Field, offshore Norway) have been investigated in order to assess their geometry and effect on hydrocarbon recovery. In the Bridport Sands, sediment texture and mineralogy controlled carbonate cementation. Clay-rich fairweather sediments were weakly cemented and are now compacted. Bioclast-rich storm deposits were stabilized mechanically by early fringing cements. During burial bioclasts and fringing cements were replaced or dissolved, and pores were filled by simultaneously precipitated ferroan calcite. Thus, cemented beds are laterally continuous for several kilometres in the Bridport Sands as a consequence of the sheet-like geometry of the storm beds in which they developed. In the Viking Group sandstones, carbonate cementation was controlled by rate of burial. Fringing cements formed locally during non-deposition or emergence. Cementation continued with non-ferroan calcite incorporating bacterially derived bicarbonate generated during prolonged residence in near surface zones of bacterial activity. Cement geometries will reflect the distribution of emergent surfaces and the longevity of residence near the surface. These two cases demonstrate the potential for laterally extensive carbonate cements to develop in shelf sandstones. The cements in these examples have different origins but in both cases their distribution is related to the episodic nature of deposition in the shelf environment.

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Bryant, Ian D., 1982: Loess deposits in lower Adventdalen, Spitsbergen. Polar Research 2 : 93-103.Aeolian deposits are described in terms of their areal distribution, sedimentary and pedological characteristics. These deposits, which have accumulated at the valley margins, result from deflation of fluvian sediments deposited in the valley bottom. Fine horizontal lamination in the upper horizons is tentatively attributed to winnowing of primary depositional units following partial cementation by salt precipitates. This stratification breaks down at depth and is replaced by a gleyed horizon, resulting from drainage impedance by permafrost. Proximal aeolian accumulations on fluvially inactive areas of the valley bottom may typify many other valleys in Spitsbergen.

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