Cretaceous chalk

Central and Eastern England is almost entirely underlain by sedimentary rocks that young from west to east. Four major geological sub-divisions are presented in Figure 1. Permian and Triassic mudstone and sandstone dominate the East Midlands and parts of Yorkshire Jurassic clays crop out within the centre of the study area and Cretaceous chalk underlies most of Central East Anglia. 

Mimran Y. (1975) Fabric deformation induced in Cretaceous chalks by tectonic stresses. Tectonophysics 26, 309-316. 

Whiting. Finely-ground Cretaceous chalk, CaC03. British whiting is 97-98% pure and practically all finer than 25 pm. It is used as a source of lime in pottery bodies and glazes, and to a small extent in glasses and vitreous enamels. 

Perch-Nielsen (1973) Perch-Nielsen, K. Fossil coccohths as indicators of late Cretaceous chalk used in Mediaeval Art Oldsaksamlingens Arbok (1973) 161-169 Perez et al. (1999) Perez, F.R. Edwards, H.G.M. Rivas, A. Drummond, L. Fourier transform Raman spectroscopic characterization of pigments in the mediaeval frescoes at Convento de la Peregrina, Sahagun, Leon, Spain Part 1 Preliminary Study Journal of Raman Spectroscopy 30 (1999) 301-305 Perez-Llano (1944) Perez-Llano, G.A. Lichens, their biological and economic significance The Botanical Review 10 1 (1944) 1-65... 

Northwestern Ohio Niagaian dolomitic stone 6 = New York magnesian stone 7 = Virginia high calcium stone and 8 = Kansas Cretaceous high calcium stone (chalk). 

Kreide-papier, n. enameled paper, art paper, -paste,/, a cement of chalk and glue, -piilver, n. chalk powder, -stein, m. chalkstone. -stift, m. crayon, kreldlg, a. chalky, cretaceous. 

The marine formations of late Cretaceous-Paleogene age on the southern part of the Russian Platform can be traced along strike for more than 2500 km and across it for more than 1000 m. They consist mostly of siliceous rocks (gaizes), clays, marls, chalk, and a small amount of sandstones and siltstones of quartzose composition. The rocks abound in glauconite and often contain phosphorites the clays are of a montmoril-lonitic composition, and a few pure bentonites have been found. Clinoptilolite occurs in almost all types of rocks of these formations. It fills pores and chambers of foraminifera and radiolaria and varies from fractions of a percent to 2-3% of the rock. It commonly makes up 70-80% of the 0.01- to 0.001-mm fraction. 

Chalk consists almost entirely of calcite. formed principally by shallow-water accumulation of (l) calcareous tests of floating microorganisms and (2) comminuted remains of calcareous algae. The most widely distributed chalks are of Cretaceous age. as exemplified by the cliffs on both sides of the English Channel. Although an unallered deposit, chalk masses may contain nodules of chen and pyrite. 

E12740 547A-16-3, 90-105 216.5 Cretac. slump ( ) clayey nannofos. chalk 0.30 12 0 ... 

Lamboy M. (1990) Microbial mediation in phos-phatogenesis new data from the Cretaceous phosphatic chalks of northern France. In Phosphorite Reserarch and Development. Geol. Soc. Spec. Publ. No. 52 (eds. A. J. G. Notholt and I. Jarvis), pp. 157-167. 

Second to water in quantity is chalk exactly the same material that schoolteachers use to write on blackboards. It is collected from the crushed remains of long-dead ocean creatures. In the Cretaceous seas chalk particles served as part of the wickedly sharp outer skeleton that these creatures had to wrap around themselves to keep from getting chomped by all the slightly larger other ocean creatures they met. Their massed graves are our present chalk deposits. 

Fig. 7. The typical pore-pressure profile of a well drilled within the GEA. Stepped increases in pore-pressure are recorded within the basal Chalk Group and underlying section. The maximum increase in pore-pressure coincides with Lowermost Cretaceous to Upper Jurassic organic-rich clay-stones where it approaches minimum values of LOT/FIT fracture pressure.

The cyclic Lower Cretaceous shelf carbonates of the Edwards Group dip into the Gulf of Mexico Coast geosyncline , and can be considered, to a first approximation, as part of a complex aquifer contained by Paleozoic basement beneath, and by relatively impermeable Upper Cretaceous clay and chalk above. The hydrodynamic character of this carbonate system is strongly controlled by major fault systems. Major fault systems serve as pathways for vertical movement of basinal brines into the Lower Cretaceous section. Formation water movement in this sytem has strong upfault and updip components. 

Fig. 7. Schematic north—south cross-section through San Antonio and the Muil Field (see Fig. 1). Jurassic and Lower Cretaceous sediments (the aquifer ) are shown by the limestone Pattern since most are carbonates. They are overlain by Upper Cretaceous clay and chalk. The northern-most outcrops are associated with the Balcones Fault zone near San Antonio. The shallow part of the section is underlain by Paleozoic basement , or by Triassic rocks further south. Jurassic salt is shown by solid hatchures. Darkened areas at A, B and C depict the three producing zones, the Stuart City Reef Trend (the carbonate platform margin), the Karnes Trough and the Atascosa Trough, respectively. Note the faulting associated with them. The temperature axis is speculative below 5 km.

Kennedy, W.J. Garrison, R.E. (1975) Morphology and genesis of nodular chalks and hardgrounds in the Upper Cretaceous of southern England. Sedimentology, 22, 311-386. 

Fig. 6.23 (a) Cretaceous oceanic anoxic events (OAEs) and their relationship to global isotopic trends (afterVeizer et al. 1999 Jones Jenkyns 2001 Leckie et al.2002) (b) 813Ccaibomte excursion associated with OAE2 in the Chalk ofEast Kent, UK (after Jenkyns et al. 1994). 

Abstract There is considerable diversity in petroleum type within the Judy and Joanne Fields of the Central Graben. Superficially, the three major reservoir systems can be considered to contain the following fluid types gas-condensates in the Pre-Cretaceous, undersaturated black oils in the Chalk and gas-condensates in the Palaeocene. Reality is, however, quite different. 

The Judy and Joanne fields comprise three major reservoir intervals Triassic/Jurassic sands, Cretaceous/Palaeocene chalks and Palaeocene sands. Figure 4 shows the generalized stratigraphy of the area. The deepest of the three reservoirs comprises the fluvial sandstones of the Triassic Skaggerak Formation (Joanne and Judy Sandstone Members), overlain unconformably by Upper Jurassic shallow marine sandstones of the Fulmar Formation. The Joanne Sands are the major reservoir unit in the Judy Field. The productive chalk intervals are the Upper... 

The considerable diversity in fluid type within the J Block area can be seen on the petroleum occurrence map (Fig. 5), which is colour-coded both by reservoir age and fluid type. Four gross reservoir intervals are shown Triassic, Jurassic, Cretaceous (including the Danian Chalk) and Palaeocene. 

The Chalk reservoired petroleums of J Block are predominantly undersaturated black oils. The model developed to explain the variation in petroleum type within the Chalk is heavily influenced by the understanding of fluid distribution within the Pre-Cretaceous, as discussed above. 

Geochemical characterization. The tested petroleums from the Chalk reservoirs are moderately mature and form an intermediate group between the low maturity Palaeocene condensates and high maturity Pre-Cretaceous fluids (Fig. 7). Within the Chalk group itself, there are clear differences between the Joanne oils and the oils from wells 30/7a-4a and 30/7a-6. 

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