SECT. 3] BASIN SEDIMENTATION AND DIAGENESIS 609 



high density paraffinic type. Evidence from recent basin sediments can be used 

 to support either hyjjothesis. 



Petroleum is generally found in porous rocks or in strata containing fissures, 

 faults and voids, mainly in sands or limestones. Such sediments are known to be 

 poor in organic matter. Shales, on the other hand, have high contents of 

 organic matter but are poor reservoirs for petroleum. It is concluded that 

 petroleum generally does not remain where it originates, but is transported 

 either laterally or vertically as a result of compaction. This introduces the factors 

 of selection and transformation through transf)ortation. The recent mechanisms 

 proposed by Baker (1959) and Meinschein (1959) for the accumulation of sub- 

 stances with the general characteristics of petroleum suggest that the trans- 

 porting agent is of vital importance. It may be that this is the reason for the 

 apparent absence of petroleum in continental-type sediments. 



The production of organic matter in modern basins is usually high enough to 

 account for the accumulation of hydrocarbons in large quantities. From a 

 comparison of the Los Angeles Basin with the still submerged Santa Monica 

 Basin, Emery (1960) concluded that for every barrel of petroleum formed, 

 19,000 barrels of equivalent organic matter had to be produced by plankton 

 and 1200 barrels deposited on the basin floor; the present annual extraction 

 of petroleum in the Los Angeles Basin is 100 million barrels per year. Suffi- 

 ciently long cores are still lacking in present marine basins to determine 

 whether petroleum is currently being formed in them. 



B. Metal Sulfides 



Iron sulfides are known constituents of reducing basin sediments. The two 

 tyjDes most commonly met are the black hydrated iron monosulfide, hydro- 

 troilite, and pyrite. The fkst is highly unstable and decomposes during drying or 

 heating to iron oxides and elementary sulfur. Sulfides of other heavy metals 

 have not yet been described as occurring in modern basin sediments, but this is 

 probably due to their relative scarcity compared with the detrital material and 

 they have ]3robably been overlooked. There appears to be no reason why copper, 

 manganese, zinc and other cations which form highly insoluble sulfides should 

 not coexist with iron sulfide. Many such metals are present in living systems 

 (e.g. copper in the blood of Crustacea) and are liberated on the death of the 

 organism. 



The geological literature contains many descriptions of sedimentary pjnrite 

 and marcasite deposits. Coals sometimes have as much as 10% sulfur in the form 

 of pyrite. Shales are particularly rich in pyrite, as for example the Wabana 

 District of Newfoimdland which contains oolitic pyrite beds of 1 cm to about 

 30 cm in thickness. Sandstones and limestones also contain pyrite as found in 

 the Upper Cretaceous of Wyoming. The large deposits of Nairne, South Aus- 

 tralia, have been described as sedimentary by Skinner (1958) and LaGanza 

 (1959). Copper, lead and zinc sulfides are also found in sedimentary rocks but 

 their origin is not well established. The Kupferschiefer Basin in the Permian of 



