Table 3. Summary of biostratigraphic use, biochronology, occurrence in Leg 167 material, and reliability of Pliocene (1.80-5.33 Ma) calcareous nannofossil biohorizons.

Table 3. Summary of biostratigraphic use, biochronology, occurrence in Leg 167 material, and reliability of Pliocene (1.80-5.33 Ma) calcareous nannofossil biohorizons.

Code

Biohorizon

Previous use

Previous biochronology

Occurrence in sites

Reliability and biochronology in the study area

Pl16
D. brouweri D. triradiatus LOs Definition of the bottom of Zones NN19 and CN13 MIS 71/72 transition (11), in the lowermost of Olduvai (C2n), at an age of 1.95/1.97 Ma (11) 1010, 1011B, 1012, 1013, 1014, 1016, 1018, 1020, 1021, 1022 Calibrated at the bottom of C2n at Sites 1010 (1.935 ± 0.055 Ma) and 1021 (1.955 ± 0.1 Ma). At Site 1020 (California current), it occurs together with D. pentaradiatus and D. surculus. Diachronous, reliable only regionally.

Pl15
D. triradiatus AB Evidenced by (5) as useful event MIS 82 (11); in lowermost reversed Matuyama (C2r), at an age of 2.15 Ma (11) 1010, 1012,1014 Poorly reliable: present in low-latitude sites and calibrated at Site 1010 in the upper part of C2r (2.29 ± 0.1 Ma). Missing in mid- to high-latitude sites.

Pl14
D. pentaradiatus LO Definition of the bottom of Zone NN18 and Subzone CN12d Upper part MIS 100 (12); strongly diachronous (MIS 87-100) for (10); close to the Matuyama/Gauss boundary (C2r/C2An), at an age of 2.52 Ma (12) 1010, 1011, 1012, 1013, 1014, 1016, 1018, 1020, 1021, 1022 Fairly good, notwithstanding the species is rare and discontinuous; calibrated at the bottom of C2r.2r (Sites 1010 [2.44 ± 0.05 Ma] and 1021 [2.51 Ma]).

Pl13
D. surculus LO Definition of the bottom of Zone NN17 and Subzone CN12c Apparently synchronous and associated with MIS 98-100 (10) in the lowermost Matuyama Chron (C2r.2r), at an age of 2.53 Ma (10) (12) 1010, 1011, 1012, 1013, 1014, 1016, 1018, 1020, 1021,1022 Good and synchronous with previous evaluations. It occurs at Site 1010 in the lowermost C2r.2r (2.54 ± 0.05 Ma) and at Site 1021 (2.55 ± 0.04 Ma).

Pl12
D. tamalis LO Definition of the bottom of Subzone CN12b Apparently synchronous over wide latitudes and associated with MIS G10/11 transition (12) in the mid part of Chron C2An.1n, at an age of 2.83 Ma (12) 1010, 1011,1012, 1013, 1014, 1016, 1018, 1020, 1021, 1022 Fairly good, occurring in lower part of C2An.1n, at an age of 2.97 Ma, at Sites 1010 and 1021.

Pl11
Sphenolithus spp. LO Proposed as definition of the bottom of Subzone CN12aB (8) Near the base of Gauss (C2An.3n) (13), at an age of 3.66 Ma (14) 1021B The marker is rare to absent in its final range.

Pl10
D. pentaradiatus PE First proposed by (6) as useful subzonal boundary in the Mediterranean. Close to the base of the Gauss Chron (C2An.3n) in the Mediterranean (15), at an age 3.61 of Ma (16) 1010, 1011, 1012,1014, 1016, 1020, 1021 Useful in the area and occurring at Site 1010 at the base of C2An.3n (3.55 ± 0.05 Ma) and at Site 1021 (3.57 ± 0.02 Ma).

Pl9
R. pseudoumbilicus LO Definition of the bottom of Subzone CN12a In uppermost part of C2Ar (13), at an age of 3.82 Ma (14) 1011,1012, 1014, 1016, 1020, 1021 Apparently good and synchronous occurring in the upper part of C2Ar at an age of 3.83 ± 0.03 Ma (Site 1021).

Pl8
A. delicatus LO Definition of the bottom of Subzone CN11a (2)
1011, 1012, 1014, 1016, 1020, 1021 Apparently good and synchronous, in the study area, occurring in the lower part of C2Ar at an age of 3.96 ± 0.03 Ma (Site 1021).

Pl7
D. pentaradiatus PB First evidenced by (3) as useful event in the Mediterranean. In lower part of C2Ar in the Mediterranean (9), at an age of 3.93 Ma (16) 1011, 1014, 1016, 1020, 1021 Fairly good; calibrated within C2Ar at an age of 4.055 ± 0.065 Ma (Site 1021).

Pl6
P. lacunosa FCO Used as alternative event to recognize the base of Subzone CN12a (1, 7)
1011, 1014, 1016, 1020, 1021 Moderately reliable as FCO. Calibrated within C2Ar at an age of 3.96 ± 0.03 Ma (Site 1021).

Pl5
D. asymmetricus FCO Definition of the bottom of Subzone CN11b Age 4.12 Ma (16), near the top of Cochiti (oceanic area); in upper Gilbert (Mediterranean) (13) 1011, 1014, 1016, 1020, 1021 Moderately reliable as FCO. Calibrated within C2Ar at an age of 3,925 ± 0,065 Ma (Site 1021).

Pl4
H. sellii FO Proposed as useful event in the Mediterranean (7)
1021B Not reliable: the species is rare and discontinuous. Calibrated within C2Ar at an age of 4,15 ± 0,03 Ma (Site 1021).

Pl3
A. primus LO Definition of the bottom of Subzone CN11a Near the top of Sidufjal (oceanic area); within Nunivak Subchron (Mediterranean) (13) 1011, 1014, 1016, 1021 Poorly reliable, most probably for taxonomic problems. Calibrated at Site 1021 at the base of C3n.1n.

Pl2
C. rugosus FO Definition of the bottom of Subzone CN10c Within Thvera Subchron (C3n.4n), at an age of 5.089/5.23 Ma (12) (17) 1014, 1010, 1021B Not reliable; the genus is underrepresented.

Pl1
T. rugosus LO Definition of the bottom of Subzone CN10b At the base of Thvera (C3n.4n), at an age of 5.23 Ma (17) 1010, 1021 Poorly reliable; present at low-latitude Site 1010 and associated with C3r as last rare occurrence at an age of 4.995 ± 0.055 Ma, associated with Zone CN9a in high-latitude Site 1021B.

Code	Biohorizon	Previous use	Previous biochronology	Occurrence in sites	Reliability and biochronology in the study area
Pl16	D. brouweri D. triradiatus LOs	Definition of the bottom of Zones NN19 and CN13	MIS 71/72 transition (11), in the lowermost of Olduvai (C2n), at an age of 1.95/1.97 Ma (11)	1010, 1011B, 1012, 1013, 1014, 1016, 1018, 1020, 1021, 1022	Calibrated at the bottom of C2n at Sites 1010 (1.935 ± 0.055 Ma) and 1021 (1.955 ± 0.1 Ma). At Site 1020 (California current), it occurs together with D. pentaradiatus and D. surculus. Diachronous, reliable only regionally.
Pl15	D. triradiatus AB	Evidenced by (5) as useful event	MIS 82 (11); in lowermost reversed Matuyama (C2r), at an age of 2.15 Ma (11)	1010, 1012,1014	Poorly reliable: present in low-latitude sites and calibrated at Site 1010 in the upper part of C2r (2.29 ± 0.1 Ma). Missing in mid- to high-latitude sites.
Pl14	D. pentaradiatus LO	Definition of the bottom of Zone NN18 and Subzone CN12d	Upper part MIS 100 (12); strongly diachronous (MIS 87-100) for (10); close to the Matuyama/Gauss boundary (C2r/C2An), at an age of 2.52 Ma (12)	1010, 1011, 1012, 1013, 1014, 1016, 1018, 1020, 1021, 1022	Fairly good, notwithstanding the species is rare and discontinuous; calibrated at the bottom of C2r.2r (Sites 1010 [2.44 ± 0.05 Ma] and 1021 [2.51 Ma]).
Pl13	D. surculus LO	Definition of the bottom of Zone NN17 and Subzone CN12c	Apparently synchronous and associated with MIS 98-100 (10) in the lowermost Matuyama Chron (C2r.2r), at an age of 2.53 Ma (10) (12)	1010, 1011, 1012, 1013, 1014, 1016, 1018, 1020, 1021,1022	Good and synchronous with previous evaluations. It occurs at Site 1010 in the lowermost C2r.2r (2.54 ± 0.05 Ma) and at Site 1021 (2.55 ± 0.04 Ma).
Pl12	D. tamalis LO	Definition of the bottom of Subzone CN12b	Apparently synchronous over wide latitudes and associated with MIS G10/11 transition (12) in the mid part of Chron C2An.1n, at an age of 2.83 Ma (12)	1010, 1011,1012, 1013, 1014, 1016, 1018, 1020, 1021, 1022	Fairly good, occurring in lower part of C2An.1n, at an age of 2.97 Ma, at Sites 1010 and 1021.
Pl11	Sphenolithus spp. LO	Proposed as definition of the bottom of Subzone CN12aB (8)	Near the base of Gauss (C2An.3n) (13), at an age of 3.66 Ma (14)	1021B	The marker is rare to absent in its final range.
Pl10	D. pentaradiatus PE	First proposed by (6) as useful subzonal boundary in the Mediterranean.	Close to the base of the Gauss Chron (C2An.3n) in the Mediterranean (15), at an age 3.61 of Ma (16)	1010, 1011, 1012,1014, 1016, 1020, 1021	Useful in the area and occurring at Site 1010 at the base of C2An.3n (3.55 ± 0.05 Ma) and at Site 1021 (3.57 ± 0.02 Ma).
Pl9	R. pseudoumbilicus LO	Definition of the bottom of Subzone CN12a	In uppermost part of C2Ar (13), at an age of 3.82 Ma (14)	1011,1012, 1014, 1016, 1020, 1021	Apparently good and synchronous occurring in the upper part of C2Ar at an age of 3.83 ± 0.03 Ma (Site 1021).
Pl8	A. delicatus LO	Definition of the bottom of Subzone CN11a (2)		1011, 1012, 1014, 1016, 1020, 1021	Apparently good and synchronous, in the study area, occurring in the lower part of C2Ar at an age of 3.96 ± 0.03 Ma (Site 1021).
Pl7	D. pentaradiatus PB	First evidenced by (3) as useful event in the Mediterranean.	In lower part of C2Ar in the Mediterranean (9), at an age of 3.93 Ma (16)	1011, 1014, 1016, 1020, 1021	Fairly good; calibrated within C2Ar at an age of 4.055 ± 0.065 Ma (Site 1021).
Pl6	P. lacunosa FCO	Used as alternative event to recognize the base of Subzone CN12a (1, 7)		1011, 1014, 1016, 1020, 1021	Moderately reliable as FCO. Calibrated within C2Ar at an age of 3.96 ± 0.03 Ma (Site 1021).
Pl5	D. asymmetricus FCO	Definition of the bottom of Subzone CN11b	Age 4.12 Ma (16), near the top of Cochiti (oceanic area); in upper Gilbert (Mediterranean) (13)	1011, 1014, 1016, 1020, 1021	Moderately reliable as FCO. Calibrated within C2Ar at an age of 3,925 ± 0,065 Ma (Site 1021).
Pl4	H. sellii FO	Proposed as useful event in the Mediterranean (7)		1021B	Not reliable: the species is rare and discontinuous. Calibrated within C2Ar at an age of 4,15 ± 0,03 Ma (Site 1021).
Pl3	A. primus LO	Definition of the bottom of Subzone CN11a	Near the top of Sidufjal (oceanic area); within Nunivak Subchron (Mediterranean) (13)	1011, 1014, 1016, 1021	Poorly reliable, most probably for taxonomic problems. Calibrated at Site 1021 at the base of C3n.1n.
Pl2	C. rugosus FO	Definition of the bottom of Subzone CN10c	Within Thvera Subchron (C3n.4n), at an age of 5.089/5.23 Ma (12) (17)	1014, 1010, 1021B	Not reliable; the genus is underrepresented.
Pl1	T. rugosus LO	Definition of the bottom of Subzone CN10b	At the base of Thvera (C3n.4n), at an age of 5.23 Ma (17)	1010, 1021	Poorly reliable; present at low-latitude Site 1010 and associated with C3r as last rare occurrence at an age of 4.995 ± 0.055 Ma, associated with Zone CN9a in high-latitude Site 1021B.

Notes: MIS = marine isotopic stage. FO = first occurrence, LO = last occurrence, FCO = first common and continuous occurrence. AB = acme beginning, PB = paracme beginning, PE = paracme end. Underline = site with magnetostratigraphy, bold = reference site. References: (1) = Wise, 1973; (2) = Bukry, 1981; (3) = Driever, 1981; (4) = Rio, 1982; (5) = Backman and Shackleton, 1983; (6) = Driever, 1988; (7) = Rio, Raffi, et al. 1990; (8) = Bukry, 1991; (9) = Rio et al., 1991; (10) = Wei, 1993; (11) = Raffi et al., 1993; (12) = Tiedeman et al., 1994; (13) = Berggren, Hilgen, et al., 1995; (14) = Shackleton et al., 1995; (15) = Cita et al., 1996; (16) = Lourens et al., 1996; (17) = Backman and Raffi, 1997.