ALBERT

Description: We have discovered evidence of a previously unrecognized, large-scale rotation of the Ontong Java Plateau (OJP) recorded in its basement palaeolatitudes. When palaeolatitude differences computed among Ocean Drilling Program Sites 807 and 1183–1187 are plotted versus their present-day site latitude differences, a systematic 2:1 slope bias is evident. While it is possible to resolve this bias by introducing ad hoc tilt corrections at all six sites, drilling records indicate relatively undisturbed conditions at Sites 1183 and 1185–1187. Of the possible causes of the bias, only whole plateau rotation resolves it while honouring the majority of published palaeolatitudes. This implies that only Sites 807 and 1184 palaeolatitudes, both questioned in the literature, are erroneous. A 9° northward dip previously reported at Site 1184 appears to stem from inclined deposition rather than post-emplacement deformation. We also estimate an 8° southward tilt correction at Site 807 to make the data set self-consistent. Based on the six sites analysed, we find that OJP may have experienced ~40° of clockwise rotation since its formation at ~123 Ma. In contrast, available Pacific absolute plate motion (APM) models predict less than 10° of rotation. If our analysis is correct, it suggests that the plateau moved independently of the Pacific Plate early in its history or that Pacific APM models for the Lower Cretaceous are unreliable. While our corrections to Sites 807 and 1184 combined with ~40° rotation resolve the internal inconsistencies, the mean palaeolatitude value of Ontong Java remains largely unchanged and is still anomalous with respect to the Pacific apparent polar wander path at ~123 Ma.