Dolostones from the Louisiade Plateau and Norfolk Ridge

Dolostones have been dredged from ∼2 km water depth on the Louisiade Plateau, offshore from northeast Australia and ∼1.5 km water depth on the Norfolk Ridge, a submerged part of Zealandia. The Louisiade dolostone has porous, sucrosic textures indicating complete diagenetic recrystallisation. An association with probable gypsum points to an evaporitic marginal-marine setting. The δ18O value of +21‰ VSMOW indicates dolomite crystallisation from mixed marine–meteoric waters at 25 °C, or from seawater at elevated temperatures (80–90 °C) while the δ1³C value of −31‰ VPDB indicates incorporation of isotopically light carbon derived from organic matter. The 87Sr/86Sr ratio is consistent with a Late Cretaceous age if precipitation occurred from seawater-dominated fluids. In contrast, the Norfolk Ridge dolostone occurs as dense nodular aggregates that likely formed during shallow submarine burial. Its δ18O value of +31‰ VSMOW indicates formation in equilibrium with seawater at ∼25 °C. Its moderately depleted δ1³C value of −8‰ VPDB indicates early diagenetic incorporation of some organic carbon, and its 87Sr/86Sr ratio suggests earliest Oligocene formation. These interpretations support the Louisiade Plateau being a formerly emergent continental fragment and reinforce stratigraphic connections between the Norfolk Ridge and New Zealand’s sedimentary basins.