Evaporites were deposited widely during early Mesozoic rifting between northwestern Africa and northeastern North America. Their stratigraphy, petrography and geochemistry characterize their depositional milieux and constrain the timing and paleogeography of the opening of the Atlantic Ocean. Geochemical analyses group into two sets, reflecting evaporite formation in two distinct provinces. Evaporites from the Atlas province (the Atlas Mountains) are characterized by low bromide concentrations and widely variable sulfur and strontium isotope ratios. These early Liassic evaporites were deposited in continental sabkhas or playa lakes, where local weathering or hydrothermal activity controlled evaporite chemistry. In contrast, evaporites from the Atlantic province (Moroccan Meseta, Pre-Rif and DSDP Site 546) are characterized by high bromide concentrations, potash mineralization, and co-varying sulfur and strontium isotope ratios. In the Atlantic province, a system of mixing between marine and continental sources controlled the brine chemistry. Mixing of marine and fluvial waters in a marginal marine lagoon, or hydrothermal cycling of seawater through granitic crust, explains the geochemical and petrographic observations. Two cycles of evaporite deposition during Rhaetian too Sinemurian time reflect the progressively increasing marine conditions during rifting. The age and stratigraphy of evaporites from the Essaouira-Argana basin compare well with those of the Atlantic province. The geochemistry of the Essaouira-Argana evaporites, however, is dominated by continental input. This basin lay farther from the Atlantic shoreline during Rhaetian time, but by Sinemurian time saw greater marine influence, as the early Atlantic sea transgressed southward along the rifted continental margins.