The Clarence River is on northeast South Island of New Zealand. It is 230 kilometres (140 mi) long, which makes it the eighth longest river in New Zealand.
For its first 50 kilometres (31 mi), the river runs in a generally southeastern direction. It then turns northeast, running down a long straight valley between the Inland and Seaward Kaikoura Ranges. At the end of the Seaward Kaikouras, the river meanders through undulating hill country before draining into the Pacific Ocean near the town of Clarence.
Northern tributaries along the middle segment of Clarence River (e.g., Mead Stream, Dee Stream, Branch Stream, Muzzle Stream) cut through an uplifted, folded and rotated block of limestone and marl that accumulated on the seafloor from the late Cretaceous through the Paleocene and middle Eocene (75–45 million years ago). Exposures of this limestone—the Amuri Limestone—provide some of the most complete records for this time interval of Earth's history. They have provided important insights to our understanding of the Paleocene-Eocene Thermal Maximum (PETM), Eocene Thermal Maximum 2 (ETM-2), and other Paleogene hyperthermal events 
^Hollis, C.J.; Gerald R. Dickens; Bradley D. Field; Craig M. Jones; C. Percy Strong (2005). "The Paleocene-Eocene transition at Mead Stream, New Zealand: a southern Pacific record of early Cenozoic global change". Palaeogeography, Palaeoclimatology, Palaeoecology, 215, 313-343.
^Nicolo, M.J.; Gerald R. Dickens; Christopher J. Hollis; James C. Zachos (2007). "Multiple early Eocene hyperthermals: Their sedimentary expression on the New Zealand continental margin and in the deep sea". Geology35: 699–702.
^Slotnick, B.S.; Gerald R. Dickens; Micah J. Nicolo; Christopher J. Hollis; James S. Crampton; James C. Zachos; Appy Sluijs (2012). "Large-amplitude variations in carbon cycling and terrestrial weathering during the Latest Paleocene and Earliest Eocene: The record at Mead Stream, New Zealand". Journal of Geology, 120, 487-505.