Reprint: Cretaceous–Palaeogene ocean and climate change in the subtropical North Atlantic

RICHARD D. NORRIS¹, DICK KROON², BRIAN T. HUBER³ & JOCHEN ERBACHER⁴

ABSTRACT: Ocean Drilling Program (ODP) Leg 171B recovered continuous sequences that yield evidence for a suite of 'critical' events in the Earth's history. The main events include the late Eocene radiolarian extinction, the late Palaeocene benthic foraminiferal extinction associated with the Late Palaeocene Thermal Maximum (LPTM), the Cretaceous- Palaeogene (K-P) extinction, the mid-Maastrichtian event, and several episodes of sapropel deposition documenting the late Cenomanian, late Albian and early Albian warm periods. A compilation of stable isotope results for foraminifera from Leg 171B sites and previously published records shows a series of large-scale cycles in temperature and ¹³C trends from ¹⁸O gradients between planktic and benthic foraminifera suggests that the North Atlantic evolved from a circulation system similar to the modern Mediterranean during early Albian time to a more open ocean circulation by late Albian-early Cenomanian time. Sea surface temperatures peaked during the mid-Cretaceous climatic optimum from the Albian-Cenomanian boundary to Coniacian time and then show a tendency to fall off toward the cool climates of the mid-Maastrichtian. The Albian- Coniacian period is characterized by light benthic oxygen isotope values showing generally warm deep waters. Lightest benthic oxygen isotopes occurred around the Cenomanian- Turonian boundary, and suggest middle bathyal waters with temperatures up to 20^oC in the North Atlantic. The disappearance of widespread sapropel deposition in Turonian time suggests that sills separating the North Atlantic from the rest of the global ocean were finally breached to sufficient depth to permit ventilation by deep waters flowing in from elsewhere. The Maastrichtian and Palaeogene records show two intervals of large-scale carbon burial and exhumation in the late Maastrichtian-Danian and late Palaeocene-early Eocene. Carbon burial peaked in early Danian time, perhaps in response to the withdrawal of large epicontinental seas from Europe and North America. Much of the succeeding Danian period was spent unroofing previously deposited carbon and repairing the damage to carbon export systems in the deep ocean caused by the K-P mass extinction. The youngest episode of carbon exhumation coincided with the onset of the early Eocene Warm Period and the LPTM, and has been attributed to the tectonic closure of the eastern Tethys and initiation of the Himalayan Orogeny.

Cretaceous and Palaeogene marine deposits provide the opportunity to study Earth system processes during partly to entirely deglaciated states. Certain key intervals are marked by rapid climate change and massive carbon input. These intervals are the Late Palaeocene Thermal Maximum (LPTM) and Oceanic Anoxic Events (OAEs) in early Aptian-Albian time and at the Cenomanian-Turonian boundary. These time intervals are particularly significant to current earth science objectives because focused research has the potential to considerably improve the understanding of the general dynamics of the Earth's climate during rapid perturbation of the carbon cycle.

Deep ocean sections that are continuously cored provide the high-resolution records to document complex sequences across unique events in the geological record that show global biogeochemical variations. These records are needed to register major steps in climate evolution: burial of excess carbon, changes in global temperatures, nutrient cycling, etc. Stable isotope records are fundamental in showing the sequence of events and the amplitude of change in the system. Most Cretaceous stable isotope records are based on bulk carbonate. Here, we present a compilation of known planktonic and benthic foraminiferal stable isotope records to highlight long-term trends in surface and deep ocean palaeoceanography. We present this stable isotope record to provide a palaeoceanographic context to the 14 papers presented in this Special Publication. Several portions of the stable isotope record were compiled from Ocean Drilling Program (ODP) Leg 171B results. This ODP Leg was dedicated to drill Cretaceous- Palaeogene sequences at Blake Nose, northwestern Atlantic, in 1998. The scientific crew on the JOIDES Resolution decided to compile a set of papers based on drilling results, in a Special Publication of the Geological Society of London. The focus would be western Atlantic Cretaceous-Palaeogene palaeoceanography and the results are now in front of you. Before we present the compilation of stable isotope results, we would like to introduce you to ODP Leg 171B drilling results.

¹Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA

²Department of Geology and Geophysics, University of Edinburgh, Grant Institute, West Mains Road, Edinburgh EH9 3JW, UK

³Department of Palaeobiology, Smithsonian Institution, MRC:NHB 121, National Museum of Natural History, Washington, DC 20560, USA

⁴Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover, Germany

From: KROON, D., NORRIS, R.D. & KLAUS, A. (eds). 2001 Western North Atlantic Palaeogene and Cretaceous Palaeoceanography. Geological Society, London, Special Publications, 183, 1-22. 0305-8719/01/$15.00 © The Geological Society of London 2001.