Basalt stratigraphy of southern Mare Serenitatis

The major features of the stratigraphic and structural sequence are summarized for Mare Serenitatis. The dark oldest basalts include flows coextensive with Mare Tranquillitatis and also flows and pyroclastic deposits (dark mantles) that erupted from the edge of the Serenitatis basin. The basin sagged, possibly isostatically, as basalts of intermediate age were emplaced. Sagging had nearly ceased by the time the youngest flows were deposited. Compressive movements including thrusting followed, and small extensional fissures formed in late Copernican time. The revised stratigraphic sequence that was elaborated has implications for lunar stratigraphy that transcend the boundaries of Mare Serenitatis. Dark mantle deposits and the darkest maria have commonly been assumed in geologic mapping to be relatively youthful. These assumptions must now be reevaluated and perhaps discarded.