Sedimentation of the alternating greywacke and argillite strata in the Porirua district

The Lower Mesozoic alternating greywackes and argillites in the Porirua district exhibit graded bedding, lamination, convolute lamination, cross lamination, mud flakes, and current markings. The sediments, rapidly derived from a plutonic terrain, were rapidly transported and deposited by turbidity currents in the New Zealand Geosyncline. The orientation of cross lamination and Current markings suggests that the turbidity currents flowed north-north-east, sub-parallel to the present regional tectonic trend. At Porirua, sedimentation was in deep water, a considerable distance from the supplying land mass, and not far from the axis of the geosyncline.