South Florida Basin—A Prime Example of Carbonate Source Rocks of Petroleum

A new and working petroleum source rock on the UK Continental Shelf (Upper Permian, offshore Yorkshire)

“…The values of Pr/n-C versus Ph/n-C in Figure indicate primary accumulation of marine OM under reducing conditions (Connan and Cassou, 1980;Palacas et al, 1984) for the source rock of the Boulby oil. It should also be noted that short and long molecular weight n-alkanes are reduced in some samples due to biodegradation (from non-to slight to moderate biodegradation and presence of an unresolved complex mixture illustrated in Figure 7), thermal maturity (cracking), water washing or evaporative fractionation (Thompson, 1987(Thompson, , 1983Holba et al, 1996;Akinlua et al, 2006).…”

“…7). An EOP in the range of >n-C 22 is typical of biomass deposited in restricted marine carbonate/evaporite facies (Dembicki et al, 1976;Shen et al, 1980;Palacas et al, 1984;Ten Haven et al, 1985) and can also be attributed to some specific bacteria or fungi (Han and Calvin, 1969;Jones, 1969;Fisher et al, 1972).…”

“…8, Table 3b), which are believed to indicate suboxic (high C 32 )/anoxic (high C 34 or C ) source-rock depositional environments (Peters and Moldowan, 1991). The dominance of 17αβ-C 32 over C 31 and C homologues and 17αβ-C 34 over C 33 and C 35 homologues (Table 3b) indicates a carbonate lagoonal and evaporitic environment source (Palacas et al, 1984;Jiamo et al, 1986;Brassell et al, 1988;Waples and Machihara, 1991) or a depositional setting for oil shale (Kara-Gülbay and Korkmaz, 2008). However, elevated 17αβ-C 34 and C 35 hopanes are also characteristic for Late Permian (Zechstein) oil from south-central Germany derived from a carbonate-evaporite source rock (Słowakiewicz et al, 2018).…”

“…The absence or low abundance of isorenieratene derivatives in the other oil samples is likely a result of the thermal maturity effect (Requejo et al, 1992). High C 29 /H (>0.8) in oil is commonly reported as derived from anoxic carbonate or a marl source rock (Palacas et al, 1984;Clark and Philp, 1989). In oil sample 1 the C 29 /H ratio is 0.27 and in KAF dolomite samples this ranges from 0.5 to 1.2 (mean 0.74) (Table 3a) and, in tandem with C 35 S/C 34 S, suggests a clay-rich source rock (Peters et al, 2005).…”

“…The diasterane/sterane ratio also helps to distinguish oil from carbonate versus clastic source rock (Mello et al, 1988). High diasterane/sterane ratios are typically interpreted to be derived from a clay-rich source rock but high ratios have also been observed in extracts from organic-lean and clay-poor carbonate rock (Palacas et al, 1984;Moldowan et al, 1991), or they might result from high thermal maturity or heavy biodegradation Moldowan, 1978, 1979), also in the case of coals (Killops et al, 1994). The diasterane/sterane ratio (C 27 and C 29 ) in all oil samples of between 0.3 and 0.9 and in KAF dolomite samples (0.3 -4) suggests a carbonate-evaporite source rock with an abundant clay (marl) content (Table 3b).…”