Abstract Proven Infracambrian hydrocarbon plays occur in various parts of the world, including Oman, the former Soviet Union, India, Pakistan and Australia. Organic-rich strata also occur in NW Africa, and gas shows originating from Infracambrian hydrocarbon source rocks are known from well Abolag-1 in the Mauritanian part of the Taoudenni Basin. The distribution of Infracambrian source rocks in North Africa is patchy and deposition commonly occurred in half-graben and pull-apart basins. In these intra-shelf basins, marine, organic-rich shales and limestones were deposited beneath the turbulent wave zone, away from the coarse siliciclastic Pan-African molasse detritus. On the West African Craton (including the Taoudenni Basin) organic-rich horizons were also deposited earlier, in pre- and syn-Pan-African times between 0.5 and 2 Ga (Ga is 10 9 years). The long-lasting sedimentation history in this area contrasts with that of the Pan-African regions, such as Oman, which lies in the Pan-African province of the East African Orogen, where preserved sediments are rarely older than 640 Ma. Infracambrian black phyllites in the Anti-Atlas region of Morocco were deposited on a continental slope of a short-lived ocean lying to the north of the West African Craton. Hydrocarbons generated during Infracambrian times from these deposits, however, have a low preservation potential. Infracambrian organic-rich and/or black-pyritic deposits in North Africa are proven in the Taoudenni Basin, the Anti-Atlas and the Ahnet Basin. Thick carbonate successions exist in the Taoudenni Basin, indicating deposition in areas some distance from contaminating coarse siliciclastic hinterland influx. Infracambrian strata may also occur in the Tindouf Basin. However, their deep burial and consequent early maturation history may be unfavourable for the preservation of Infracambrian-sourced hydrocarbons in this area. Local development of Infracambrian source facies may also occur in the Reggane, Ahnet, Mouydir and Iullemeden basins, as indicated by black shales in wells MKRN-1 and MKRS-1 in the Ahnet Basin. Generally, however, these basins appear to be close to the active Pan-African orogenic belt and, consequently, probably received large quantities of coarse siliciclastic sediment, largely of continental facies, which may have diluted any significant hydrocarbon source potential.

Abstract The recently published groundwater vulnerability map of Fife is the first in a series of maps for the Scottish Environment Protection Agency (SEPA), which includes the unpublished maps of the areas around Dumfries and Strathmore. Based on the methodology used on the Environment Agency maps of England and Wales, the lithology and permeability of the geological formations, and the physical and chemical properties of the soils are classified to produce 15 groundwater vulnerability classes. However, the Scottish maps incorporate several modifications that improve their accuracy and usefulness. These are: (a) the geological formations are classified solely on the basis of their permeability and do not also incorporate aquifer potential; (b) the occurrence of low permeability drift deposits at the surface are shown over the whole of the map area instead of only where they overlie aquifers; (c) areas where borehole data indicate that significant thicknesses of low permeability deposits are present in the drift sequence are shown. In these areas groundwater in the underlying solid rock formations may have a lower risk of contamination than indicated by the vulnerability zones. This is particularly useful information where the clay occurs beneath permeable drift deposits. The borehole distribution is shown to give an indication of the reliability of the boundaries; (d) nitrate vulnerable zones are shown; (e) the leaching potential classification of soils with organic surface layers has been improved.

Thick marine sedimentary and volcanic sequences accumulated in northern Venezuela and Trinidad during ?Late Jurassic and Cretaceous time. By latest Cretaceous time, the northern part of this sequence had been regionally metamorphosed and rapidly uplifted. Flysch troughs developed to the south which received exotic masses and turbidite sands until early Eocene time. These events are interpreted as resulting from southward movement of the Caribbean crust and its subduction into a south-dipping Benioff zone located north of Venezuela. This postulated Benioff zone is believed to have become inactive in latest Cretaceous time, and the resulting isostatic rebound apparently caused overthrusting which initiated the flysch troughs. Mid-Eocene orogeny caused major changes in basin geometry and initiated crustal shortening, overthrusting, uplift, and strike-slip faulting in Venezuela and Trinidad. These events are believed to be related to east-west right-lateral transcurrent movement between the Caribbean and Americas Plate, which appears to have begun in Eocene time. Initially, the Caribbean Plate was offset a minimum of 35 km along faults which extended into western Venezuela and Colombia, but later the Andes also became involved in the relative movements between the plates.

Palinspastic reconstructions of the central part of the Venezuelan Coast Ranges combined with sedimentary data indicate that deep water marine deposits accumulated in east-west-trending troughs which were located successively farther south through time. From north to south, four such troughs are recognized. Regional metamorphism accompanied downbuckling in the two northern troughs, and allochthonous material slid southward into the two southern troughs. The emplacement of the allochthonous sequences is thought to be due to gravity sliding promoted by uplift in the north and downwarping in the south. Metamorphic grade and estimated sedimentary thicknesses suggest that the amount of downwarping decreased through time as the troughs migrated southward. In the eastern part of the East Venezuela Basin, this trough migration is reflected in the southward displacement of depositional axes between Late Cretaceous and Pliocene time. The structure of the Venezuelan Coast Ranges is interpreted as resulting from a linear downwarped zone, followed by an upwarped zone immediately to the north, migrating southward across the northern edge of the Guayana Shield at a rate of 1 to 2 km per m.y. from Jurassic until latest Tertiary time.