Resumé
A stratigraphic well was cored continuously to a total depth of 660 m in the town Vestmanna in the northwestern part of the Faeroe Islands in Sept.-0ct. 1980. The well is situated in the middle basalt series about 12 km ENE of the outcrop area of the lower basalt series on Vagar and far north of the lower basalts on Suduroy.
The well was drilled by the Icelandic National Energy Authority for the Faeroese Government and the Carlsberg Foundation with the special purpose of exploring the coal-bearing sequence between the lower and middle basalt series and the temperature increase with depth in the basalt plateau.
This preliminary report is based on the macroscopic core description and other work made at the well-site.
The drilling was stopped 101 m down in the lower basalt series. The lower basalt section consists of 12 flow-units 1.7-37-7 m thick separated by 6 tuffaceous beds making up 15% of the series. The basalts are near-aphyric to aphyric tholeiites, poor to moderately rich in olivine (-5-7% MgO) and similar to the uppermost 200 m of the lower basalts on Vagar and Suduroy.
The 'coal-bearing' sequence at 555-7-558-5 m depth consists of 0.5 m basaltic conglomerate overlain by dark grey to brownish grey tuffaceous sediments exhibiting cross bedding at the top and bottom, but is devoid of coal. The sediments were probably deposited at or near the shore of a lake and therefore the presence of thicker coal-bearing sediments close to the well cannot be excluded. The sequence occurs close to the expected depth suggesting that the dip of the sequence is very similar to the dip of the middle basalt flows, i.e. 2.5-3 degree to the east.
The middle basalt series lacks tuff-agglomerates and irregular intrusions at the base which suggests that no eruption fissures similar to that observed on Vagar and Suduroy occur close to the well. The middle basalt flow-units have an arithmetic average thickness of only 2. 2 m but range in thickness from a few centimeters to 14 m. Most units probably form part of compound flows. The flows are separated by only 10 tuffaceous beds forming 0. 5% of the series. The middle basalts are olivine-tholeiitic (picritic) to tholeiitic in composition. They are predominantly olivine-phyric up to 107 m depth but plagioclase-phyric at higher levels in the well though most flows contain phenocrysts of both minerals. the olivine-phyric section shows a remarkable cyclic variation in the phenocryst content. Three cycles, about 120 m thick each, are present. In each cycle the amount of olivine phenocrysts gradually builds up with time from less than 5% to 20-30% and then drops abruptly again.
The well was drilled by the Icelandic National Energy Authority for the Faeroese Government and the Carlsberg Foundation with the special purpose of exploring the coal-bearing sequence between the lower and middle basalt series and the temperature increase with depth in the basalt plateau.
This preliminary report is based on the macroscopic core description and other work made at the well-site.
The drilling was stopped 101 m down in the lower basalt series. The lower basalt section consists of 12 flow-units 1.7-37-7 m thick separated by 6 tuffaceous beds making up 15% of the series. The basalts are near-aphyric to aphyric tholeiites, poor to moderately rich in olivine (-5-7% MgO) and similar to the uppermost 200 m of the lower basalts on Vagar and Suduroy.
The 'coal-bearing' sequence at 555-7-558-5 m depth consists of 0.5 m basaltic conglomerate overlain by dark grey to brownish grey tuffaceous sediments exhibiting cross bedding at the top and bottom, but is devoid of coal. The sediments were probably deposited at or near the shore of a lake and therefore the presence of thicker coal-bearing sediments close to the well cannot be excluded. The sequence occurs close to the expected depth suggesting that the dip of the sequence is very similar to the dip of the middle basalt flows, i.e. 2.5-3 degree to the east.
The middle basalt series lacks tuff-agglomerates and irregular intrusions at the base which suggests that no eruption fissures similar to that observed on Vagar and Suduroy occur close to the well. The middle basalt flow-units have an arithmetic average thickness of only 2. 2 m but range in thickness from a few centimeters to 14 m. Most units probably form part of compound flows. The flows are separated by only 10 tuffaceous beds forming 0. 5% of the series. The middle basalts are olivine-tholeiitic (picritic) to tholeiitic in composition. They are predominantly olivine-phyric up to 107 m depth but plagioclase-phyric at higher levels in the well though most flows contain phenocrysts of both minerals. the olivine-phyric section shows a remarkable cyclic variation in the phenocryst content. Three cycles, about 120 m thick each, are present. In each cycle the amount of olivine phenocrysts gradually builds up with time from less than 5% to 20-30% and then drops abruptly again.
| Originalsprog | Engelsk |
|---|---|
| Udgivelsessted | Copenhagen |
| Forlag | DGU |
| Antal sider | 79 |
| DOI | |
| Status | Udgivet - feb. 1983 |
Emneord
- Faroe Islands
Programområde
- Programområde 3: Energiressourcer