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The Arbroath Field was discovered by the Amoco operated group comprising Amoco (UK) Exploration Company, Gas Council (Exploration), Amerada Hess Ltd and Texas Eastern (UK) Ltd with the 22/18-1 well in May 1969 and was the first commercial oil field to be discovered in any sector of the northern North Sea. Two years later in 1971, the adjacent Montrose Field was discovered. Both Arbroath and Montrose are located 130 miles east of Aberdeen towards the northern end of the Central Graben area. The two fields have simple non-faulted, anticlinal structures separated by a structural saddle with only 15 ft of relief. The structures are a product of Alpine tectonism combined with differential compaction of the reservoir section. The hydrocarbons have a Kimmeridge Clay source and occur wholly within the Forties Sandstone interval. The oil is trapped by mudstones of the Sele Formation. The reservoir sandstones were deposited in a prograding submarine fan complex and have maintained an average porosity of 23% and a permeability of 80 md.To date only the Montrose Field has been produced. The main recovery mechanism is natural bottom water drive supplemented by water injection. First oil was produced in 1976 via a tanker mooring system, replaced by a dedicated pipeline in 1984. The Arbroath Field is under development and first oil was produced in April 1990.

The Austell Gneiss is a metamorphosed biotite granite in the northeastern closure of the Austell-Frolona anticlinorium, a major northeast-trending early fold on the northwestern side of the Brevard fault zone. The anticlinorium is a structural window that exposes rocks of a parautochthonous continental-margin assemblage beneath rocks of an allochthonous oceanic assemblage. The Austell Gneiss and the Austell-Frolona anticlinorium were deformed by younger en echelon folds during dextral wrench faulting along the Brevard and Olley Creek fault zones. The Austell Gneiss has intruded the Bill Arp Formation and the Gothards Creek Gneiss, but is in fault contact with other units.The Austell Gneiss has yielded Pb-U ages on older zircon fractions and a six point Rb-Sr whole-rock isochron that are interpreted to indicate a crystallization age as a granite of about 430 Ma (Early Silurian). A still older zircon fraction is interpreted to be inherited from ~1.1 Ga basement. Younger zircon fractions yield ages interpreted to indicate synmetamorphic deformation during strike-slip and thrust faulting throughout the Silurian and Early Devonian. The Early Silurian crystallization age of the Austell indicates (1) that the thrusting that placed the allochthonous assemblage upon the parautochthonous assemblage took place prior to Early Silurian; we postulate that it took place during the Middle Ordovician, the time of slope reversal in the Valley and Ridge province. All rocks involved in that thrusting must be older than Early Silurian.(2) The early folding that produced the Austell-Frolona anticlinorium and folded the Austell Gneiss took place during and/or after the Early Silurian. (3) Most of the dextral wrench and strike-slip faulting and wrench folding along the Brevard and Olley

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