The warder formation: Cyclic fluvial sedimentation during the ngaterian (late Albian-Cenomanian) of Marlborough, New Zealand

Abstract

The Warder Formation of Ngaterian (late Albian‐Cenomanian) age crops out in southern Marlborough, New Zealand. Outcrops are characterised by fining‐upward alluvial cycles deposited by easterly flowing rivers on a coastal plain. Within‐channel deposits include clast‐supported conglomerate and trough cross‐bedded sandstone, overlain by alternating sandstone and siltstone, lateral accretion (inclined heterolithic stratification) beds, in turn overlain by siltstone and claystone. The fine‐grained units are interpreted as lacustrine sediments deposited in ox‐bow lakes through meander loop cut‐off. All outcrops are fault bounded, so a complete pattern of fluvial reconstruction cannot be made. The rivers which deposited the Warder Formation had a mean sinuosity of 1.5 and a discharge of 72–102 m3/s. Sedimentation was terminated by the eruption of alkaline basalts related to regional sea‐floor spreading. © The Royal Society of New Zealand 1993.