Shales, marine, organic-rich

HaUam A. (1987b) Mesozoic marine organic-rich shales. In Marine Petroleum Source Rocks, Geological Society of London, Special Publication 26 (eds. J. Brooks and A. J. Fleet), pp. 251-261. 

Although sandstone dominated, the Ballycastle-Murlough Bay section contains subordinate marine to brackish shales rich in organic detritus (Fig. 4). Microbial reactions in shallow-buried organic-rich mudrocks can produce solutes that, upon diffusion into adjacent sandstones, may precipitate small amounts (c. 10 vol%) of carbonate cement (McMa-... 

The Bossier shale is not only the basal formation for much of the Cotton VaUey Group, but is also interbedded with isolated sands throughout most of eastern Texas and northwestern Louisiana. These shales are typically black, organic-rich, calcareous, fossiliferous, marine deposits which are the primary source rock for much of the entire Upper Jurassic and Lower Cretaceous vertical section. Thinner shale intervals in the western part of the basin thicken to the east correlative to general depositional patterns in the East Texas Basin. Source rock quality is generally poorer in the western and northwestern parts of the basin, but improves significantly easterly towards the basin centre. From west to east, the near-shore sand and low-stand fan deposits are usually completely encased in the marine Bossier shale. 

Moldowan et al (5) investigated a sediment core, spanning a depth range of 5m, of Lower Toarcian shales from W. Germany specifically at a transition zone from a rather oxidized, shallow-marine, marly sediment to an organic matter-rich, black shale. Variations in distributions of isoprenoid hydrocarbons, steranes and monoaromatic steroids were observed and were related to variations in oxidation/reduction conditions during and shortly after sedimentation. 

OC and K series), non-marine (D, Ca and C series) and transitional (B series) deposits. Within each series organic matter is often found in quite different facies, for instance acid treatment (Table III) indicates that within the Lothians Upper Oil Shale group samples Cal and Ca6 are carbonate rich (>40%) whereas Cal5 is carbonate poor (2.5%) 5 these differences are obvious within other series as noted in Table III. Microscopical analysis of polished blocks in white and blue light allowed the data in Table II to be compiled. 

The Kettle Point Formation subcrops in southwestern Ontario. It is up to 60 m thick, with organic carbon values usually in the range 5%-16% and Fischer Assay oil yields up to 70 1/t (17 gal/ton). The organic matter is dominantly kerogen of marine origin and has attained only an immature thermal maturation stage. A particularly rich upper zone is present over much of the subcrop area and its thickness seems to be controlled by post-Kettle Point erosion. Although studies are still preliminary, especially for the Devonian shales, the Kettle Point Formation appears to have the most potential for shale oil production in southern Ontario. 

Uraniferous black shales are of marine origin and, in addition to colour, are characterized by high sapropelic organic content, abundant pyrite or marcasite in thin lenses, nodules or disseminated particles, and the paucity of calcium and magnesium carbonates. The shales also contain small quantities of such other metals as Mn, Ti, V, Cu, Cr, Mo, P and REE. Most of these metals are dispersed in the shale, but phosphate may also occur as nodules or phosphate-rich layers. ... 

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