Table T4. Average ages of events defined and effectively used in present age-depth graphs, Congo and Angola sites.
Age (Ma)
Biostratigraphic event
Shipboard defined
Effectively used weighted
Effectively used unweighted
N
N FO Emiliania huxleyi acme
0.09 0.09 0.09 7
N FO Emiliania huxleyi
0.26 0.30 0.30 6
N Gephyrocapsa caribbeanica acme
0.26 0.30 0.30 6
N LO Pseudoemiliania lacunosa
0.46 0.41 0.43 4
R LO Axoprunum angelinum
0.46 0.38 0.38 3
N Small Gephyrocapsa acme
0.6 0.59 0.58 3
S LO Bachmannocena quadrangula
0.8 0.87 0.86 2
N LO Reticulofenestra asanoi
0.83 0.82 0.82 3
D LO Nitzschia fossilis
0.92 1.07 1.07 1
N Small Gephyrocapsa acme
0.96 0.91 0.93 3
N FO Reticulofenestra asanoi
1.06 1.07 1.07 1
R LO Lamprocyrtis neoheteroporos
1.07 1.43 1.37 2
N LO Helicosphaera sellii
1.25 1.29 1.30 4
N LO Calcidiscus macintyrei
1.67 1.52 1.56 2

Notes: N = nannofossil, R = radiolarian, S = silicoflagellate, D = diatom. FO = first occurrence, LO = last occurrence. N = number of samples. Estimated age weighted according to narrowness of age range, and unweighted. Average effective ages of biostratigraphic events are as used in the age models. Weighted = estimated age weighted according to narrowness of age range, unweighted = not so weighted. (Differences between shipboard-assigned age and effectively used age arise from a number of sources such as sampling interval vs. sedimentation rate, intensity of search for presence and absence of a nannofossil, and problems of preservation. Thus, the data do not necessarily reflect real differences in assigned ages of events and their occurrence at the sites occupied. They do give an idea about the consistency of biostratigraphic shipboard assignments in the circumstances of Leg 175.)