Alternating sandstones and muddy siltstones at Takapuna are interpreted as a marine turbidite facies of the Lower Miocene Waitemata Group. The sandstone-siltstone alternation is described in terms of the following rhythmic sequence: a turbidite consisting of (1) massive sand, with a very abrupt base on siltstone, and occasional erosional sole structures, grading upwards into (2) laminated, (3) convoluted, and (4) ripple-drift-bedded sand; followed by interturbidite beds consisting of a variable number of alternations of (5) fine, muddy siltstone with (6) ripple-drift-bedded, very fine sand. Siltstone inclusions are common in the turbidites, and carbonised plant matter, in all stages of comminution, is abundant in all lithologies. Other sedimentary structures include intraformational slumping.Grain-size analyses are presented. All lithologies are positively skewed and very poorly sorted. Petrographically the turbidites are lithic subgreywackes, with abundant fine-grained sedimentary rock fragments and subordinate quartz and plagioclase feldspar, and a fine detrital matrix. They are mostly uncemented and highly porous. The interturbidite rippled sand is lithologically identical with, but finer-grained than, turbidite sand; it is interpreted as turbidite sand redistributed by bottom currents. Diagenetic features include carbonate nodules in the turbidites, and limonite staining.The rocks are unfossiliferous, apart from plant debris, a few planktonic Foraminifera in the siltstone, and traces of at least six types of burrowing, sedimenteating organism.The depositional environment is interpreted as a marine basin within a continental borderland, with weak bottom currents, receiving muddy, fine silt. South-eastflowing traction currents periodically moved thin, rippled layers of fine sand, posisibly derived from turbidites deposited elsewhere in the basin. South-east-flowing, high-density turbidity currents deposited sand beds averaging 18 in. in thickness; they arrived at irregular intervals, and occasionally may have flowed north-north-east. A preliminary discussion of some regional aspects of Waitemata sedimentation is given.