Lacustrine sedimentation – ancient rift fill tectonic control on alternating lacustrine and coal

Date: 31 January – 4 February 2026
Cost (NZD inc 15% GST): Approx $1,200 per person
Leader: Dr. Kari Bassett (University of Canterbury)

The Greymouth Basin on the West Coast of the South Island of New Zealand formed during the Cretaceous rifting that separated Zealandia from Gondwana.  The basin is part of the larger West Coast – Taranaki Rift System and has spectacular coastal outcrop of the conglomerates deposited along the faulted basin margin. The depocentre of the basin is filled with organic-rich lacustrine mudstones that transition through large mires to meandering axial rivers, a cycle repeated 3 times in the basin’s history.  The final 4^th phase opens the basin to the sea allowing deposition of limestones during a regional transgression.  Features included in this trip include lacustrine mudstones and muddy deltaic channel sandstones and coals deposited in the basin centre, as well as fan delta polymictic conglomerates with large scale soft sediment deformation and tight packing of clasts delineating subaqueous delta slope and mouth bar deposition.  The distribution of facies and the cyclic alternation of basin axis facies indicates deposition in a half-graben rift basin that progressively widened over time.  The spectacular coastal outcrops allow a detailed look at fan delta deposition into a large deep rift lake. We will also visit the bioclastic limestones formed during the regional transgression which host modern blowholes that are active at high tide. Geotourist stops on the drives over and back will showcase active tectonic, mountain building sedimentology and geomorphology and a deep lake analog.

Fitness level needed is moderate to high with one outcrop access being a steep path down to the beach.  Sturdy footwear/boots are necessary. Wet weather gear is a must for the West Coast of New Zealand where torrential rains are possible all months of the year.  Summer time temperatures range between 12-25C and be prepared for variability.  A backpack to hold all the field gear is useful.

You will need to organise your own travel from Wellington to Christchurch following the Congress (due to time available flying from Wellington to Christchurch is recommended). We will have two pick up times and locations, 9.00 am from the University of Canterbury and 10.00 am from the Christchurch airport, more detailed instructions to follow.

From Christchurch will will drive over the mountains to Greymouth where we will spend 4 nights.  We will drive back to Christchurch on the last day and will arrive approximately 6 or 7 pm.  You will need to arrange your own accommodation in Christchurch for the nights before and after the trip.  We will do our best to return to Christchurch on time but, as with any field work, we can’t guarantee to arrive on time for tight flight connections.  Best to be safe and book your flights out for the following day.