Pittenweem Formation

From Earthwise
Jump to navigation Jump to search

Pittenweem Formation (PMB), Carboniferous, Midland Valley of Scotland[edit]

The Pittenweem Formation is part of the Strathclyde Group in the Fife area.

Name[edit]

From Pittenweem, east Fife. The unit was originally described by Forsyth and Chisholm (1977)[1] and given formation status by Browne (1986)[2].

Lithology[edit]

The Pittenweem Formation consists dominantly of mudstone and siltstone. Beds of nonmarine limestone and dolostone are less common than in the Anstruther Formation. Marine mudstone (including ‘marine bands’), siltstone and limestone occur as minor, but important, components. A few algal-rich oil-shale beds are also present. Generally fine- to medium-grained sandstone is subordinate to the argillaceous rocks, but locally thick, upward-fining, multistorey sandstones occur as well as thin beds of coal and ironstone. The formation is distinguished from those adjacent to it by the comparative diversity of the marine faunas, which probably all belong to the Macgregor Marine Bands (see Browne et al. 1999, p.10, table 3)[3].

Genetic interpretation[edit]

The pattern of sedimentation is of upward-coarsening deltaic cycles, with thinner upward-fining fluvial units erosively capping them, and minor marine incursions.

Stratotype[edit]

Type sections in the Pittenweem Formation occur on the shore near Pittenweem at Cuniger Rock (basal contact) (NO 5566 0271 to NO 5510 0249) and from 700 m (top contact) to 830 m depth in the Kilconquhar Bore No. 79/1 (BGS Registration Number NO40SE/26) (NO 4845 0305) near Elie. A good section of the full succession is also exposed on the shore at St Andrews (NO 506 173 to NO 513 169).

Lower and upper boundaries[edit]

The conformable base of the Pittenweem Formation lies in a transitional sequence, and is drawn at the base of the Cuniger Rock Marine Band above the mudstone, siltstone and sandstone of the Anstruther Formation (Figure 6, Column 4C). The top of the formation is at the top of the St Andrews Castle Marine Band (SCMB), which is overlain by mudstone and siltstone of the Sandy Craig Formation.

Thickness[edit]

The maximum thickness of the formation is now known to be more than 260 m in east Fife based on its development in the partial type sections (see above). Forsyth and Chisholm (1977, table 1)[1] state that the formation is over 220 m thick.

Distribution and regional correlation[edit]

Fife.

Age and biostratigraphical characterisation[edit]

Visean (Asbian). The marine faunas, which occur in thin ‘marine bands’, are usually diverse and sometimes abundant. The abundant but restricted nonmarine faunas are dominated by the bivalve Naiadites obesus.

References[edit]

  1. 1.0 1.1 Forsyth, I H, and Chisholm, J I. 1977. The geology of east Fife. Memoir of the Geological Survey of Great Britain, Sheets 41 part 49 (Scotland)
  2. Browne, M A E. 1986. The classification of the Lower Carboniferous in Fife and Lothian. Scottish Journal of Geology, Vol. 22, 422-425
  3. Browne, M A E, Dean, M T, Hall, I H S, McAdam, A D, Monro, S K, and Chisholm, J I. 1999. A lithostratigraphical framework for the Carboniferous rocks of the Midland Valley of Scotland. British Geological Survey Research Report, RR/99/07