More than 200 m of black shale and limestone representing the upper Albian and lower Cenomanian was recovered in Hole 1052E during ODP Leg 171B. An equivalent sequence of black shale was drilled in Hole 1050C at paleowater depths of ~1200 m greater than in Hole 1052E (Norris, Kroon, Klaus, et al., 1998). Biostratigraphic and cyclostratigraphic work suggests that the section in Hole 1052E accumulated at rates of ~10 cm/k.y. for much of the late Albian, providing a remarkably expanded record of the onset and development of OAE 1d (Lehmann, 2000; Bellier et al., Chap. 3, this volume; Norris et al., 2001a; Wilson and Norris [N1]). Equally important, planktonic and benthic foraminifers are very well preserved, frequently with glassy shells and original tabular microstructure (Norris and Wilson, 1998), and are accompanied by ammonites (Lehmann, 2000) and gastropods preserved with primary aragonitic skeletons. The exquisite preservation of foraminifers has allowed some of the first stable isotopic studies of the paleoceanographic development of OAE 1d (Norris and Wilson, 1998; Wilson and Norris [N1]).
Norris and Wilson (1998) showed that Albian sea-surface temperatures (SSTs) were warmer than those measured anywhere in the modern oceans. Recently, these results have been confirmed in a more exhaustive study of OAE 1d. Wilson and Norris [N1] found that SSTs vary considerably throughout the ~1-m.y. interval leading up to OAE 1d and finally dropped abruptly at the onset of black shale deposition. The thermal gradient through the upper water column remained low throughout the interval of black shale deposition which straddles the Albian/Cenomanian boundary. These data provide some of the first direct evidence for the model of black shale deposition associated with increased overturning in the upper ocean and the expansion of organic carbon deposition under high productivity surface waters. Barker et al. (2001) have shown that the organic carbon associated with OAE 1d is mostly terrestrial in origin at Blake Nose.
The long-term oceanographic record of the Albian and Cenomanian has been discussed by Norris et al. (2001a) using stable isotope data from ODP Sites 1050 and 1052. Reconstructions of SSTs suggest that the Cretaceous greenhouse climate began in the late Albian rather than the late Cenomanian as suggested in previous climate reconstructions. Following organic shale deposition associated with OAE 1d, a second phase of black shale deposition took place during the Rotalipora reicheli Biozone followed by another phase of black shale formation at the Cenomanian/Turonian (C/T) boundary. Huber et al. (1999) have shown that the C/T boundary in ODP Hole 1050C is associated with the highest intermediate water temperatures (~17°C at a paleo-water depth of ~2300 m) at any time in the Cretaceous. It is currently unclear whether these high temperatures reflect elevated temperatures at the sites of high-latitude deep-water formation or represent deep thermocline waters filling a temporarily silled North Atlantic near the C/T boundary. However, stable isotope data suggest that these warm intermediate waters were relatively short lived because temperatures tended to fall in the Turonian and remainder of the Late Cretaceous (Norris et al., 2001a).