It wasn’t the shot heard ’round the world but it was a blast heard across much of southwest Iowa. The state Fire Marshal’s office and the Union County Sheriff’s Department are investigating and explosion near Thayer. Officials have confirmed a building housing explosives at the Shildberg Rock Quarry exploded this morning around 5. Shockwaves from the blast were felt as far away as Osceola. No injuries are reported and the incident is under investigation.