Wolf River Fieldwork Mar 2-5

Frontispiece: Young fossil (Taloclamys gemmulata) found in marine silts 580m above sea level, uplifted by the Alpine Fault.

With a narrow but promising weather window forecast over Fiordland, I quickly geared up at the last minute for what regrettably may have been my last bit of PhD fieldwork. This would be the first PhD fieldwork where I did not directly study the Alpine Fault. Rather the goal of this work was to re-find a deposit of young fossiliferous marine silts and sands exposed in large slips at the head of the Wolf River (580m/2000ft elevation) and drainages southward. We would collect any and all shells we found so that a paleontologist collaborator could determine the diversity, environment and water depth the shells were deposited in. I would then give a few of the broken fragments to another collaborator who would be able to date the shells so that I could determine an Alpine Fault-related uplift rate here. For the fieldwork I was fortunate to be joined by one of New Zealand's great field geologists who originally found the shell deposit almost 15 years ago.

An early start from Dunedin had us flying out out of Milford just after noon under overcast skies. We had a great but short flight up the Harrison and over into the John O'Groats to spiral into grassy "flats" near the head of the Wolf River, a large creek between the John O'Groats and Kaipo. In seconds we were out of the chopper and watching it fly out of sight and out of sound. A thorough search for a campsite found sparsely any flat ground but we settled on a sloping spot just inside the bush and set about making it comfortable.

We then walked up the creek towards the towering slip, noticing the occasional chunk of weathered marine silt in the creek. We followed deer tracks to the head of the slip where we found the marine deposit sitting on basement rock. The rock was strongly weathered with all the calcareous fossils gone from the rocks leaving only the imprints, which would be useless to me and of only minor interest to the paleontologists. Things were not looking promising and I began to think we had poorly gambled a helicopter flight to come here. I continued searching the area for fresher material and marking a stratigraphic section through the deposit. A couple hours later I heard a triumphant hoot- Mo had found shell material! I joined him to attack the more promising bluish gray silt outcrop where he found the shell. After digging in about 20cm we began finding fossils with regularity- apparently the calcareous shells had only been leached near the surface and were well-preserved (though delicate) within. A couple hours of careful work revealed over 15 species of molluscs including ones that would be useful for dating! Many were so well preserved they still had their iridescent  mother-of-pearl. Uncovering the fossils was great fun compared to my usual activities of structural measurements and oriented samples and reminded me of my early rock collecting days. Nearing the end of the day, we carefully wrapped up our finds and walked back to camp. We cooked dinner over an open fire in the creekbed as trails of smoke spun into the sky. I was much relieved by the day's eventual success.

The next morning we happily awoke to a cloudless sky and got an early start climbing up the slip past the previous day's outcrops and then headfirst into the bush to gain a well-deer tracked moraine ridge that we could travel to reach the edge of the Wolf River Tablelands, an extensive flat glacial surface beneath which lie the marine silts. We traveled about 1.5km to reach the rim of the next drainage to the west of the Wolf to take in the sobering view- a huge slip complex 700m across lined by 20-40m cliffs of moraine with waterfalls pouring over in places. Below we could see the marine silts we hoped to reach but it was not obvious how we were going to get down the cliffs to reach them. We continued for quite a distance along the rim before eventually finding a sketchy deer trail down through the cliffs to eventually reach the creek and walk up the next branch. Here we found a near perfect section through the entire silt unit with a 35m cliff towering overhead. I set about describing and measuring the base of the section. This time it was I that found the fossil-rich zone in the middle of the steep slope with well-preserved scallops in abundance on the surface. Here the exposure was so good that we could spend most of the time collecting the fossils off of the surface instead of digging through the silt looking for them. Over several hours we found a diverse fauna including scallops, clams, bivavles, gastropods, urchin, barnacles, chiton, mussel and others.

        Here be fossils.

As the day started to get on we headed back. To avoid the long circuitous route back up the cliffs we opted to try our chances at finding a more direct route. This went well for a while but the most promising place still had a 15m high bush clad cliff we would need to scale, including vertical roof-clinging for the last 5m. It looked do-able with care, though definitely with bad consequences if one of us fell. Using quite a bit of strength I pulled myself up the tree roots and shrub stems while wedging myself between a tree and the cliff. Eventually I reached the top and Mo followed, both of us feeling more than a bit triumphant. If only health and safety police could have seen us! We made great time heading back so collected a few more fossils at the Wolf outcrop before yet another great campfire evening.

The following morning we packed up camp and walked down the Wolf River to reach the coast. The day was beautiful and the going down the Wolf remarkably good thanks to low waters, good deer trails and grassy terraces lining the river. At the last turn in the river we abruptly received a beautiful view of Madagascar Beach guarded by a gateway of rock with a nice swimming pool beyond. We reached the beach without incident 2.5 hours after setting out. The sandflies were mostly civil and the warm sun exceedingly welcome on this beautiful and remote beach. We found a campsite and spent the rest of the day walking the bouldery coastline, examining old wave cut terraces that had been uplifted and abandoned. Nothing useful to date but it was worth a try. We had a great little driftwood-fed fire on the beach as the sun set and clouds rolled in from the horizon.

        Exiting the Wolf River

        Above and below: Several views of the remote Madagascar Beach

We had a lazy last day with a prolonged breakfast, then moved on to boredom fighting activities like moving rocks to make a good helipad and untying knotted crayfish pot lines. When those were succeeded we resorted to walking around in circles to avoid a cloud of sandflies landing on us. Eventually the chopper landed and we were whisked away on another beautiful flight back to Milford Sound with many kilograms of precious fossils carefully packed away.

Goodbye sandflies!

It was exceedingly pleasant fieldwork without complaints. Easy, beautiful, productive. Many thanks to Mo, my very keen, capable and accomplished field assistant for the trip.