Step-over fault zones controlling geothermal fluid-flow and travertine formation (Denizli Basin, Turkey)

•We document a permeable step-over zone in a normal fault setting.•Meters-thick (6,5 m) banded Ca-carbonate veins filled the fractures in the step-over zone.•We describe the root of an hydrothermal system feeding travertine deposits.•Fissure ridge-type travertine deposits are related to the step-over zone.