Kiritehere Beach.

The rocks at Kiritehere are part of what geologists call the Murihiku Supergroup (deposited 260 to145 million years ago). These rocks extend from port Waikato all the way down and round to the southeast coast of the South Island. They were laid down in a vast depression that had a chain of volcanoes alongside it. A lot of the sediments contain volcanic ash washed into them. The shellbed containing the fossils is called the Arawi formation which is only one of many formations in the Murihiku Supergroup. The fossils are dominated by scallop-like clams that belong to an extinct genus called monotis, but there are also other types too, such as brachiopods (lamp shells), occasional ammonites, or extremely rare marine reptile bones.

You will see that the rocks have been tilted and contorted. When sedimentary rocks pile up on the sea floor, they are initially soft and the layers can slump or buckle as more sediment piles up above them. Tectonic movements have added to this deformation as the rocks were squeezed by plate collision, then uplifted and exposed by erosion.
If you want to collect fossils, look for them in small boulders, or use a hammer and chisel. But don't forget safety goggles as the rocks are very hard. Watch the video link below to get good advice on fossil collecting in these rocks.