Day 10 (February 25, 2017): One last day on Antigua and the end of a wonderful trip.
After another early start in paradise part II, we were on the road to Willoughby Bay. Here, we could see some beautiful outcrops of the Central Plains Group (CPG). The group studied outcrops both by the shore of the bay and at a road cutting. These were very different rocks to what we had seen up until them, as they were of sedimentary origin. A number of the horizons contained pebble sized clasts of metamorphic rock. This was an interesting find as it helped constrain the order of events; the metamorphism occurred before the fluvial erosion. We saw beds dipping to the northeast, following the trend we’ve seen so far. A small number of fossils, were found in the section, and the packet of beds was interpreted as forming by outward lobe building by a river channel.
Our next stop took us to the C.O Williams limestone quarry where we were excited to hunt for fossils. Right from the moment we arrived at the blast face, everyone was finding fossils. The first ones we found were tubes of calcareous material that had been built with algae, something very few members of the group had seen before. A number of bivalve shells were observed, as well as some beautiful examples of colonial corals. An unexpected find was the irregular heart shaped echinoderm Ed found at the base of a cut section. As we worked up the sequence, we found some limestone that was more grey in colour as opposed to the pale rock we had been searching through. This is thought to have formed from erosional sediment coming off the volcanic hills.
Our stop for lunch was very relaxed and accompanied by a reggae band practising their music. We then stopped at a nearby bridge to look out over Willoughby Bay. From here we could see evidence of modern day patch reefs along with the fringing reef that protects the bay. The flattened topography of the hills was also very clear to see, putting into context everything we had learned about Antigua so far.
Finally we arrived at Half Moon Bay for one last outcrop and then some well deserved snorkelling! The rocks in this area are the stratigraphically highest unit, though we suspect there would originally have been more sediments on top. The distance from these limestone beds to the base of the volcanic units is 2000 m, with maximum elevation of the current land surface at 400 m. Hence, we can assume that for these marine units to be exposed at the surface, there must have been 2400 m of uplift. The uplift is likely to be the effect of sediment accumulation on top of the ocean floor. Where the Caribbean and Atlantic tectonic plates collide, a wedge is created. Moreover, the limestone was also fossiliferous, with a large number of 5 mm diameter discs being found. These were a type of foraminifera named nummulites. Our last task of the day was to investigate the modern day coral reefs found around Antigua, a task none of us were complaining about! Unfortunately, most of the corals were bleached and have died as a result of rising ocean temperatures.
All in all it was a great last day, and I think all of us are sad to leave. Tomorrow we fly home and should land in Toronto in the evening. At least it’s not another early start! We can’t wait to get back and share our experiences with everyone. It has been a blast.
~written by: Amy Myers and Joshua Nguyen.