The dataset contains experimental data from two Cambrian igneous sequences: the approximately 505 Ma Bourinot volcanic rocks of Cape Breton Island, Nova Scotia, Canada, and the approximately 525 Ma Itabaiana mafic dyke swarm of northeastern Brazil. It includes specimen-level paleointensity measurements, paleomagnetic directional data, experiment-step references and file-level metadata. Bourinot samples were analysed using thermal Thellier paleointensity experiments. Itabaiana samples were analysed using thermal and microwave Thellier, modified Shaw, and continuous Triaxe/Wilson methods. The deposited files include upload-ready data for Paleomagnetism.org and Paleointensity.org and supporting files needed to interpret the laboratory treatment steps and directional measurements. The data relate to two study areas: the Bourinot volcanic belt on Long Island, Cape Breton Island, Nova Scotia, eastern Canada; and the Itabaiana mafic dyke swarm in northeastern Brazil, within the Borborema Province. The Bourinot data come from sites BV5, BV7 and BV8, while the Itabaiana data include sites IT1, IT2, IT7 and IT8. These data provide new constraints on Cambrian geomagnetic field strength and were used to show that weak field conditions persisted for tens of millions of years after the Cambrian radiation. The data support the manuscript “Earth’s magnetic field remained weak for 40 million years after the Cambrian radiation”
