Fig. 4

Transmission electron microscope (TEM) images of magnetic extracts from seven depth horizons shown in Fig. 2. Samples from a 1.00 m, b, c 1.14 m, d–f 1.18 m, g, h 1.23 m, i, j 1.27 m, k 1.36 m, and l 1.49 m. Magnetofossils in (a, b) have sharp crystal edges, whereas those of (c) through (j) are partially etched. Grains in k, l are likely silicates with magnetic inclusions. Scale bar: 50 nm (c–e, g, i, j), 100 nm (a, b, f, h), and 200 nm (k, l)