One of the earliest geologists to work in the area,
McKay, understood that the Manuherikia Group was probably originally continuous. Although some workers came to believe the sediments were deposited in a series of small, interconnected basins between the mountain ranges, e.g. Park, later workers, like
Cotton argued that the sediments had been isolated by later mountain growth. Douglas placed the Manuherikia Group sediments into a coherent genetic context. He drew attention to Manuherikia Group sediments on the top of mountain ranges, and to the observation that sequences in distinct basins were similar. His conclusion was that the Manuherikia Group is the result of
sedimentation in a single (except for the earliest stages) very large basin that was later intruded by the growth of the mountain ranges. This basin ultimately grew into a single huge lake –
Lake Manuherikia – that extended over some . Mildenhall, Mildenhall and Pocknall has indicated that the Manuherikia Group is basically
Miocene in age. The plant
macrofossils, common in the lower Manuherikia Group, are mostly
Early Miocene, perhaps with some in the earliest
Middle Miocene. == Stratigraphy ==