Abstract
Summary. Palaeomagnetic and K-Ar whole rock age studies are reported from samples of the Camaraca Formation exposed near Arica (18.6S, 70.3' W), Chile. The Camaraca Formation is composed of andesites and interbedded marine shales which yield a fauna placing the formation in the Bajocian-Callovian stages of the Jurassic. Our sampling sites span a stratigraphic thickness of 2 km and yield a reversal stratigraphy of: N-R-N. The K-Ar isochron method, applied to least altered samples from the formation, gives a sharply defiied age of 157 Myr which is in agreement with the palaeontologically assigned age of the formation. Normal and reversed directions of remanent magnetization, isolated by af and thermal demagnetization methods, are statistically antiparallel. The pole position, computed from these directions of magnetization, is at 010 E, 70%S (Ag5= 6.0'). This pole position, when compared with the wellstudied Chon Aike Formation of Argentina, suggests that the sampling region has undergone a 28 ? 28 counter-clockwise rotation about a local vertical axis. The large uncertainty (between 0' and 56) in this estimate is due to the large scatter in the South American reference data. When compared with African Jurassic palaeopoles, with allowance made for the opening of the South Atlantic, a counter-clockwise rotation of 44 -I 14 is indicated.
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