Sponge Cliffs are a series of exposed rock layers, many of which are Mn-phos pavement.
The dark rocks in the photo are Mn-phos , broken into tabular slabs.
The lighter, brown rock is limestone (see Rock 5).

Photograph taken by L. Sautter from within sub, JSLII Dive 3461, showing
terraced Mn-phosphorite pavement of Sponge Cliff, Blake Plateau (1700 ft).