e-Science : October 2015 Issue 15
FOSSIL FLOWERS FROM VOLCANIC LAKES What is a maar? A maar lake forms when superhot (1200°C) volcanic magma such as basalt intercepts water on its way to the Earth's surface. The result is an extremely violent but localized eruption that leaves a small (0.1–2 km diameter) and correspondingly deep (50–300 m) crater surrounded by a rim of volcanic debris. The crater quickly fills with water and then slowly, over a very long period, it accumulates finely laminated organic sediment made up of micro-organisms such as algae living within the lake and other organic material, mostly from plants blown in from the surrounding environment. Little other terrestrial sediment can enter the lake due to the rim of debris and RESOURCES the bottom of the lake is anoxic (oxygendeprived) because it is so deep relative to its diameter. Because of these factors, maar lakes have become some of the world's most important sites for terrestrial fossils: when a leaf, flower or fruit is blown or falls into the lake it sinks to the bottom and is effectively “pickled” on a quiet, undisturbed bedding plane on the anoxic lake floor. Foulden Maar formed during a violent volcanic eruption about 23 million years ago which left a 200 m deep and 1000 m diameter crater. Over the next 100,000 years, billions of tiny siliceous plants known as diatoms bloomed seasonally in the surface waters of the deep lake that infilled the crater and drifted down to the anoxic lake bed. Eventually, the lake filled up with white, fine-grained laminated diatomite which has proven to be an exceptionally good material to preserve fossil leaves, fruits, seeds, flowers and pollen. Click to enlarge Foulden Maar reveals its secrets Our research team goes fossil-hunting in small diatomite quarries on the surface of the long-filled in lake that have revealed a treasure-trove of fossil flowers. So far, we have discovered and described flowers and fruits from 30 genera and 23 different angiosperm families. All are first records for New Zealand and Australia and in some cases globally.
July 2015 Issue 14
Feb 2016 Issue 16