A. Racey et al., Palynological and geochemical analysis of carboniferous borehole and outcrop samples from the Isle of Man, J PETR GEOL, 22(3), 1999, pp. 349-362
Palynological and geochemical analyses were performed on Namurian (mid-Carb
oniferous) samples from the Ballavaarkish and Shellag Point boreholes from
the north of the Isle of Man, and on Dinantian/Namurian outcrop samples fro
m Black Marble Quarry in the south of the island.
The boreholes yielded a rich and diverse (over 60 species) Namurian B-C (Ki
nderscoutian-Yeadonian) palynomorph assemblage equivalent to the KV/FR Zone
s of Clayton et al. (1977). Reworked Brigantian-Namurian A palynomorphs of
the NC/TK Zones were recorded in the Shellag Point borehole. Offshore seism
ic data indicates a period of major fault activity in the early Namurian wh
ich may support this concept of early Namurian reworking. Amorphous organic
matter indicating anoxic/dysoxic depositional conditions together with pra
sinophyte algae and goniatites suggesting a marine environment were recorde
d in the Shellag Point borehole.
Vitrinite reflectance and spore colouration measurements coupled with Tmax
data from Rock-Eval pyrolysis indicate that the Namurian shades from the Sh
ellag Point borehole are currently in the oil window. Rock-Eval data and ke
rogen analyses indicate that these shades represent moderate to good gas-pr
one source rocks which have yet to attain full maturity. The Namurian sampl
es from Ballavaarkish are mainly in the oil window or late mature zone and
have poor gas potential. Extract chromatography indicates a relatively matu
re product and the possible onset of hydrocarbon biodegradation, particular
ly in the Ballavaarkish borehole samples.
Outcrop samples from near the top of the succession at Black Marble Quarry
underwent thermal alteration as a result of dyke intrusion and subsequent v
olcanism. Although previously believed to be Brigantian (end-Dinantian) in
age based on goniatites, corals and conodonts, the samples have produced a
sparse palynological-assemblage indicating an apparent age no older than Na
murian. The samples are late- to post-mature in terms of hydrocarbon genera
tion and have no remaining source potential.
The results indicate that where Namurian sediments are preserved beneath th
e base-Permian unconformity,for example in the Solway Basin, hydrocarbons a
re likely to have been generated.