At the time when the disintegration of Laurasia is thought to have taken place, block faulting, marine transgression, and basalt extrusion marked the geologic evolution of northern West Greenland.

The downfaulting of the western seaboard of the area probably began in Cretaceous time. Considerable thicknesses of limnic arkose accumulated rapidly in the newly-formed depression, and coarse conglomerate was deposited at the foot of the fault scarps. Pauses in sedimentation allowed substantial accumulation of plant debris which gave rise to coal layers.

In late Turonian time a marine sea carrying a North American ammonite fauna transgressed outer Svartenhuk, and, during the Coniacian, reached Nugssuaq. Later the sea must have joined that covering Western Europe, as indicated by the European affinities of the molluscan fauna which became particularly marked in the early Tertiary.

Intercalations of tuff in Danian marine sedimentary strata are the first indications of volcanism which later led to the extrusion of subaqueous basalt breccia and pillow lava followed by the accumulation of about 8 km of picrite, olivine basalt, and plagioclase-porphyritic basalt.

Although there was probably intermittent faulting throughout the Cretaceous and early Tertiary, the greatest movements occurred in three phases--at the end of the Maestrichtian, in mid-Danian time, and after the extrusion of the basalts. The net result was a downthrow of several hundred meters on the seaward side of the faults.