Notes on the geology of the Esk Valley, Canterbury

Abstract

Two new occurrences of Tertiary rocks in the Esk Valley each consist of about 2,000 ft of steeply dipping beds (35–45°) of which the lower 500 ft consists of marine sediments and volcanic rocks and the upper 1,500 ft of non-marine greywacke gravel. A third occurrence consists only of about 100 ft of tilted greywacke gravel. These beds range in age from Dannevirke Series (Waipawan to Heretaungan) to lower Nukumaruan, and the tilted greywacke gravels are correlated with the Kowai Gravels of North Canterbury. The occurrences lie in a north-east-trending faultangle depression tilted to the south-east, which can be traced from the Waimakariri River to Grant Stream in the north-east. Undermass rocks consist of steeply dipping (50-80°) north-north-east-trending unrnetarnorphosed greywacke and argillite in which good younging directions from scour casts and graded bedding can be obtained in several places. Two outwash surfaces, of probable Blackwater and possible Avoca ages, are present in the Esk Valley. The Blackwater surface (an be traced back to the outer of two closely spaced moraines in the Nigger Stream, but the Avoca (?) surface is represented only by a high isolated tableland. The inner moraine is tentatively correlated with the Poulter Advance.