The origin of Canada Hill — A result of strike-slip deformation and hydraulically powered uplift at the Pleistocene/Holocene border?

Abstract

Canada Hill, located in the centre of Miri City in Sarawak, is roofed by terrace deposits of Pleistocene/Holocene age, which implies a very young uplift of this complex anticline. The present-day Canada Hill structure is explained by strike-slip deformation, in conjunction with a semi-liquid pillow of Setap Formation clay. Horizontal pressure acting in NW-SE direction, and the likely presence of a strike-slip system with late inversion triggered a 'diapiric' remobilization of the clay reservoir. The flow of liquefied clay was refocused upwards, namely in direction of the lowest pressure. Miri Formation remnants, the roof of forming clay pillow, and overlying Quarternary terrace deposits, were subsequently uplifted and emerged from the Pleistocene peneplain. However, the adjacent country rock, including the main part of the Miri Field, was hardly affected. Assuming a hydraulic uplift in the order of 400 feet and a lithostatic pressure gradient of 0.9 psi/foot, lateral pressure above the 360 psi equilibrium pressure would have prompted the clay core to move. It is noted that all current oil seepages in the hill area are related to fault systems that were reactivated at the Pleistocene/Holocene border, and an extinct mud volcano of the Canada Hill was also sighted at Tanjong Lobang, this being an obvious indication that overpressured fluids had escaped from the centre of Canada Hill. In addition, other potential areas of hydraulic uplift located in Brunei and Sabah, particularly the well-documented Jerudong and Belait Anticlines are also discussed for comparison with the observations derived from Canada Hill to support the new structural model proposed in this study.