<<

Jørgensen, B.B., D’Hondt, S.L., and Miller, D.J. (Eds.) Proceedings of the Ocean Drilling Program, Scientific Results Volume 201

16. DATA REPORT: AND CORRELATION IN PELAGIC SEDIMENTS, ODP SITE 1225, EASTERN EQUATORIAL PACIFIC1

Sachiko Niitsuma,2 Kathryn H. Ford,3 Masao Iwai,4 Shun Chiyonobu,2 and Tokiyuki Sato5

1Niitsuma, S., Ford, K.H., Iwai, M., Chiyonobu, S., and Sato, T., 2006. Data report: Magnetostratigraphy and biostratigraphy correlation in pelagic ABSTRACT sediments, ODP Site 1225, eastern equatorial Pacific. In Jørgensen, B.B., D’Hondt, S.L., and Miller, D.J. (Eds.), Shipboard investigation of magnetostratigraphy and shore-based in- Proc. ODP, Sci. Results, 201, 1–19 vestigation of diatoms and calcareous nannofossils were used to iden- [Online]. Available from World Wide tify datum events in sedimentary successions collected at Ocean Web: . [Cited YYYY- magnetic record previously studied at the same site, ODP Leg 138 Site MM-DD] 851, and provide a comprehensive model for Site 1225. Two high– 2Graduate School of Science, Tohoku magnetic intensity zones at 0–70 and 200–255 meters below seafloor University, Sendai 980-8578, Japan. (mbsf) were correlated with lithologic Subunits IA and IC in Hole Correspondence author: 1225A. Subunit IA (0–70 mbsf) contains the magnetic reversal record [email protected] 3Graduate School of Oceanography, until the Cochiti Subchronozone (3.8 Ma) and has a sedimentation rate University of Rhode Island, South of 1.7 cm/k.y. This agrees with previous work done at Site 851. Subunit Ferry Road, Narragansett RI 02882, IC (200–255 mbsf) was not sampled at Site 851. Diatom and nannofos- USA. sil biostratigraphy constrained this subunit, and we found it to contain 4Department of Natural the magnetic reversal record between Subchrons C4n.2r and C5n.2n Environmental Science, Kochi University, Kochi 780-8520, Japan. (8.6–9.7 Ma), yielding a sedimentation rate of 2.7 cm/k.y. Biostrati- 5Faculty of Engineering and Resource graphy was used to establish the sedimentation rates within Subunits IB Science, Akita University, Akita 010- and ID (70–200 mbsf and 255–300 mbsf, respectively). These subunits 0851, Japan. had higher sedimentation rates (~3.4 cm/k.y.) and coincide with the late Miocene–early Pliocene biogenic bloom event (4.5–7 Ma) and the Initial receipt: 3 January 2005 Acceptance: 1 February 2006 Miocene global cooling trend (10–15 Ma). High biogenic productivity Web publication: 18 May 2006 Ms 201SR-110 S. NIITSUMA ET AL. DATA REPORT: CORRELATION 2 associated with these subunits resulted in the pyritization of the mag- netic signal. In lithologic Subunit ID, basement flow is another factor that may be altering the magnetic signal; however, the good correlation between the biostratigraphy and magnetostratigraphy indicates that the magnetic record was locked-in near the seafloor and suggests the age model is robust.

INTRODUCTION

Site 1225 is located in the eastern equatorial Pacific near the bound- ary between the South Equatorial Current and the North Equatorial Countercurrent west of the East Pacific Rise (Fig. F1). The site lies in the F1. Site locations, p. 10.

20° topographic high created by the rain of biogenic debris from the rela- N tively high productivity equatorial ocean. Site 1225 is adjacent to

Ocean Drilling Program (ODP) Leg 138 Site 851. The main features of 10° the sedimentary succession were documented during Leg 138 (Ship- NECC Site 851 Site 1225 board Scientific Party, 1992; Pisias, Mayer, Janacek, Palmer-Julson, and 0° van Andel, 1995). However, magnetostratigraphy at Site 1225 was not SEC measured or interpreted below 150 meters below seafloor (mbsf) based 10° on the assumption that diagenesis had destroyed the magnetic signal

20° (Shipboard Scientific Party, 1992). More efficient shipboard measure- S 120°E 110° 100° 90° 80° 70° ments at Site 1225 illustrated a second zone containing magnetic polar- 6000 5000 4000 3000 2000 1000 0 Water depth (m) ity below 200 mbsf (Shipboard Scientific Party, 2003). The goal of this project is to refine the chronology of this site using both magnetostrati- graphic and biostratigraphic techniques.

METHODS

Sampling

For the paleomagnetic and biostratigraphic analyses, samples were collected from Holes 1225A and 1225C. From Hole 1225A, all core catcher samples except those from Cores 201-1225A-28X and 29P were collected. The total volume of each core catcher sample was 50 cm3. This volume was subsampled to 10 cm3 for paleontological analyses. These samples were stored at 4°C until analyzed. From Hole 1225C, 29 discrete 7-cm3 samples were collected for paleomagnetic analysis and stored at room temperature.

Paleomagnetism

A 2G Enterprises superconducting rock magnetometer was used for shipboard pass-through measurements of natural remanent magnetiza- tion (NRM) and alternating-field (AF) demagnetization of split archive halves from the high–magnetic susceptibility intervals (Cores 201- F2. , p. 11.

Diatoms Geomagnetic polarity Nannofossils (Barron, 1985a, 1985b; 1225A-1H through 11H and 21H through 34H; 0–90 and 190–300 mbsf, (Cande and Kent, 1995) (Martini, 1971) Baldauf and Iwai, 1995) Zone Event (Ma) Zone Event (Ma) 0 NN21 F Emiliania huxleyi (0.25) P. n NN20 L Pseudoemiliania lacunosa (0.41) Brunhes L Reticulofenestra asanoi (0.85) doliolus F Gephyrocapsa parallela (0.95) L Nitzschia 0.78 C1 F Reticulofenestra asanoi (1.16) reinholdii (0.62) 1 Jaramillo L large Gephyrocapsa spp. (1.21) respectively) (Shipboard Scientific Party, 2003). An automatic paleo- Pleist. r NN19 LHelicosphaera sellii (1.27) N. F large Gephyrocapsa spp. (1.45) reinholdii F Gephyrocapsa oceanica (1.65) 1.77 n Olduvai F Gephyrocapsa caribbeanica (1.73) 2 LDiscoaster brouweri (1.97) F Pseudoeunotia C2 r Reunion NN18 Matuyama L Discoaster pentaradiatus (2.38) N. doliolus (2.00) NN17 magnetic processor NP2 (Niitsuma and Koyama, 1994) was used to 2.58 L Discoaster surculus (2.54) marina L Nitzschia L Discoaster tamalis (2.74)

late jouseae (2.77) 3 n Kaena L Reticulofenestra ampla (2.78) Manmmoth NN16 C2A Gauss 3.58 r N. Pliocene L Reticulofenestra pseudoumbilicus measure NRM and anhysteretic remanent magnetization (ARM) in sam- 4 4.18 L Sphenolithus abies (3.85) (3.85) jouseae Cochiti NN15 n Nunivak NN13-14 L Amaurolithus spp. (4.50) early Sidufjall F Ceratolithus rugosus (4.7) 5 C3 Gilbert Thvera NN12 F Nitzschia ples from Hole 1225C. NRM measurements were made with 10-mT jouseae (5.12) r LDiscoaster quinqueramus (5.6) T. 5.89 6 convexa n

Age (Ma) C3A L small Reticulofenestra int. (6.5) r F Thalassiosira stepwise AF demagnetization to 40 mT. ARM was measured with 10-mT convexa (6.57) 6.94 N. 7 n v. aspinosa NN11 miocenica C3B r F Nitzschia 7.43 miocenica s.l. n N. (7.30) 8 porteri steps up to 40 mT AF and a 29-µT steady direct field. The geomagnetic C4 r F Discoaster berggrenii (8.6) L Thalassiosira late 8.70 yabei (8.23) Miocene n NN10A 9 L Reticulofenestra T. pseudoumbilicus yabei C4A r NN10B L Denticulopsis L Discoaster hamatus (9.4) polarity timescale used in this study is the same as that presented by simonsenii (9.45) 9.74 L Actinocyclus 10 NN9 moronensis n (9.76) A. F Discoaster hamatus (10.7) C5 moronensis Cande and Kent (1995; CK95) (Fig. F2). 11 NN8 L Craspedodiscus r L Catinaster coalitus (11.3) C. coscinodiscus

middle (11.44) NN7 coscinodiscus 12 S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 3

Diatom Analysis

Core catcher samples from Hole 1225A were prepared for diatom analysis using a slide preparation technique modified from Koizumi and Tanimura (1985). Each sample was dried in a 60°C oven for 24 hr. The dried sample (~50 mg) was treated with hydrogen peroxide solu- tion (15% H2O2), decanted, and rinsed with deionized water. This rins- ing and decanting process was repeated until the solution no longer reacted to the H2O2. A 1.0-mL aliquot was taken from the shaken sus- pension and spread evenly onto an 18-mm2 coverslip. The aliquot was diluted with deionized water when the suspension was too concen- trated. The coverslip was oven dried at <40°C and then mounted on a glass slide with mounting medium (refractive index = 1.78). Random field traverses of the slide were examined under the Normarskii differ- ential interference contrast microscope at 630×. Higher magnification (1000×) was also used for taxonomic identification. Relative diatom fre- quencies are designated by one of the following codes (Winter and Iwai, 2002):

A = abundant (>10 valves per field of view [FOV]). C=common (>1 valve per FOV). F = few (>1 valve per 10 FOVs and <1 valve per FOV). R = rare (>3 valves per transverse of coverslip and <1 valve per 10 FOVs). + = present (<3 valves per transverse of coverslip, including frag- ments).

The diatom zonation used in this study is that of Barron (1985a, 1985b) with a few modifications by Baldauf and Iwai (1995) (Fig. F2).

Nannofossil Analysis

A total of 32 samples were processed and examined using commonly accepted techniques as described by Stradner and Papp (1961). The slides were examined under an Olympus binocular polarizing micro- scope at a magnification of 1500× with an oil-immersion objective lens. Several thousand coccolith and Discoaster specimens were identified. In addition, 200 specimens were randomly counted to determine relative frequencies and stratigraphic changes of species occurrences. Relative nannofossil frequencies are designated by one of the follow- ing codes (Takayama and Sato, 1987):

A = abundant (>32% of the species in the total assemblage). C = common (32%–8%). R = rare (<8%). + = present (found but not counted).

The calcareous nannofossil zonation used in this study is the same as that presented by Martini (1971), Takayama and Sato (1987), and Sato et al. (1999) (Fig. F2). S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 4 RESULTS

Drilling Disturbance

Coring using the ODP advanced piston corer (APC) intro- duces large vertical isothermal remanent magnetization (IRM) over- prints on the NRM of sediments (e.g., Acton et al., 2002). Downward and upward drilling overprints were recognized at Site 1225. Downward drilling overprints on archive-half and discrete samples were removed by <20-mT AF demagnetization (Fig. F3). Occasionally, drilling distur- F3. Demagnetization, p. 12.

ABAF demagnetization ARM aquisition C bance also introduces metal filings into the top of the cores. Such mate- 0 Core 201-1225C-1H, 2.43 mbsf

N W Up 30 mT SN rial was identified in Hole 1225A (Shipboard Scientific Party, 2003). 50 20 mT 40 mT 10 mT

1.0

This caused upward overprints that could not be removed by <20-mT 100 NRM

50 NRM 10 mT Div.= 1.0e-3 A/m E Dn Jo= 8.4e-3 A/m 10 mT 20 mT 20 mT AF demagnetization. Therefore, when the core catcher overlapped with 30 mT 30 mT 150 40 mT 40 mT D Depth (mbsf) Core 201-1225C-18H, 166.77 mbsf

N the top of the next core, the uncontaminated core catcher sections were W Up 200 20 mT 30 mT NRM used for analysis. SN40 mT 250 1.0

10 mT 50 E Dn Jo= 4.8e-4 A/m Div.= 2.0e-4 A/m 300 10-4 10-3 10-2 10 -1 10-5 10-4 10-3 10-2 10-1 1 Magnetostratigraphy Intensity (A/m) Intensity (A/m)

Polarity changes in lithologic Subunits IA (0–70 mbsf) and IC (200– 255 mbsf) were observed in the declination of NRM after 15-mT AF de- magnetization (Figs. F4, F5). The correlation between the observed F4. Paleomagnetic measurements, magnetic polarities in Subunit IA of Hole 1225A and the CK95 geomag- 0–90 mbsf, p. 13.

Intensity (A/m) Inclination (°) Declination (°) CK95 -5 -4 -3 -2 -1 10 10 10 10 10 1 -90 -60 -30 0 30 60 90 0 90 180 270 Chron Age (Ma) Polarity Chron zone 0 0.000 netic polarity timescale was made carefully under the age constraints 1H C1n 2H Brunhes 0.780 C1r.1r C1r.1n Jaramillo determined at Site 851 and confirmed by biostratigraphy. The Brunhes 3H 20 C1r.2r

4H 1.770 C2n Olduvai Matuyama 1.950 to Cochiti Subchronozone was identified in the upper 70 C2r.1n Reunion C2r.2r 5H C2r.2r-1# 40 2.581

6H C2An.1n mbsf (Fig. F4). The Brunhes/Matuyama (Chron C1n/Subchron C1r.1r) C2An.1r Kaena

C2An.2n Gauss Manmmoth

Depth (mbsf) C2An.2r 7H C2An.3n 60 3.580

C2Ar 8H polarity boundary in Hole 1225A at 11.44 mbsf was in agreement with Gilbert C3n.1n Cochiti C3n.1r 9H the same boundary in Holes 851B (12.75 mbsf) and 851E (11.58 mbsf). 80 10H

11H The Olduvai Subchronozone (Chron C2n) in Hole 1225A (29.2–31.36 100 mbsf) correlated with that in Holes 851B (28.10–30.48 mbsf) and 851C (27.80–29.85 mbsf). The magnetic directions and intensities varied in the Matuyama Chronozone (Subchrons C1r.1r–C2r.2r), so other events F5. Paleomagnetic measurements, were unclear. The onset of the Gauss Chronozone (Subchron C2n.1n) 190–320 mbsf, p. 14.

Intensity (A/m) Inclination (°) Declination (°) 10-5 10-4 10-3 10-2 10-1 1 -90 -60 -30 0 30 60 90 0 90 180 270 and the termination of the Cochiti Subchronozone (Subchron C3n.1n) 180 21H CK95 Polarity Chron Age (Ma) C4r.2r-1# 200 22H C4r.2r 8.699 in Hole 1225A (60.18 and 67.36 mbsf, respectively) correlated with the C4An 23H

C4Ar 220 24H C4Ar.1n C4Ar.1r C4Ar.2n 25H C4Ar.2r 9.740 same events in Hole 851B (59.72 and 67.40 mbsf), Hole 851C (59.25 C5n.1n C5n.1r

240 26H C5n.2n and 67.95 mbsf), and Hole 851E (59.60 and 67.80 mbsf). The magnetic 27H 28H Depth (mbsf) 260 29P reversal horizons in Subunit IA of Hole 1225A were well correlated with 30H 31H 280

32H

33H those in Holes 851B, 851C, and 851E, although they are ~1.5 m shal- 300

34H

35X lower than at Site 851. 320 The biostratigraphic zonation, described in detail in the next section, provided age control, enabling correlation of the polarity reversals in Subunit IC (200–255 mbsf) with CK95 (Fig. F5). The last occurrence (LO) of Discoaster hamatus (9.4 Ma) and the LO of Denticulopsis simonse- nii (9.45 Ma) occur between Samples 201-1225A-24H-CC and 25H-CC (224.82 and 234.30 mbsf). We defined a critical polarity boundary at 221.88 mbsf, above 224.82 mbsf, as the onset of Chron C4Ar (9.308 Ma). This definition then allows correlation of other magnetic events with CK95: terminations of Chron C4An (8.699 Ma) at 203.36 mbsf, Subchron C4Ar.2n (9.580–9.642 Ma) between 226.88 and 228.74 mbsf, and Subchron C5n.1n (9.740 Ma) at 230.06 mbsf. Figures F4 and F5 show the magnetostratigraphic interpretation for Hole 1225A. Subunits IB and ID did not contain a magnetic reversal record and the magnetic intensity dropped to ~1 × 10–4 A/m (Fig. F3). Pyrite was a S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 5 common feature of these subunits, as recorded by the lithologic de- scriptions (Shipboard Scientific Party, 2003). Samples from these inter- vals had not acquired any ARM (Fig. F3), which suggests an absence of magnetic iron sulfide minerals (pyrrhotite or greigite). X-ray diffraction analyses confirmed the visual identification of pyrite in Cores 201- 1225C-22H (199.01 mbsf), 27H (251.43 mbsf), and 201-1225A-33H (294.48 mbsf) (Shipboard Scientific Party, 2003).

Biostratigraphy (Hole 1225A)

Diatoms

Diatom datums and their depths in Hole 1225A are listed in Table T1. Diatoms are present in the Quaternary (Fragilariopsis doliolus Zone) T1. Diatom events, p. 18. through upper middle Miocene (Craspedodiscus coscinodiscus Zone) sedi- ments recovered from Hole 1225A. Although the LO of Nitzschia rein- holdii is commonly used to identify the boundary between the F. doliolus and N. reinholdii Zones, it is not well constrained at this site be- cause of the scattered occurrence of this species. Therefore, the LO of Fragilariopsis fossilis was used. Samples 201-1225A-1H-CC and 2H-CC were assigned to the F. doliolus Zone based on the occurrence of F. dolio- lus stratigraphically above the LO of F. fossilis. The first occurrence (FO) of F. doliolus, the F. doliolus/Nitzschia marina zonal boundary, was placed between Samples 201-1225A-4H-CC and 5H-CC, allowing Samples 3H- CC and 4H-CC to be assigned to the N. reinholdii Zone. The co-occur- rence of Rhizosolenia praebergonii and Thalassiosira convexa without Nitzschia jouseae in Sample 201-1225A-5H-CC allowed us to assign this sample to Subzone A of the N. marina Zone. The presence of N. jouseae in Samples 201-1225A-6H-CC through 10H-CC placed these samples in the N. jouseae Zone. Stratigraphic floral events observed in this interval included the FO of R. praebergonii, placed between Samples 201-1225A- 6H-CC and 7H-CC, the FO of T. convexa var. convexa between Samples 7H-CC and 8H-CC, and the LO of Nitzschia cylindrica between Samples 9H-CC and 10H-CC, all within the N. jouseae Zone. The FO of T. convexa var. aspinosa in Sample 201-1225A-15H-CC de- fined the base of the T. convexa Zone. The FO of Nitzschia miocenica was placed in Sample 18H-CC, allowing placement of the interval from Sample 16-CC to 18H-CC in the N. miocenica Zone. Samples 16H-CC and 17H-CC contain Thalassiosira praeconvexa without T. convexa, sug- gesting placement of these samples in Subzone B of the N. miocenica Zone. The presence of Nitzschia porteri without N. miocenica and the Thalas- siosira yabei group in Samples 201-1225A-19H-CC through 21H-CC sug- gests that these samples correspond to the N. porteri Zone. The presence of T. yabei in Samples 22H-CC through 24H-CC allowed placement of these samples in the T. yabei Zone. The last continuous occurrence (LCO) of Denticulopsis simonsenii s.l. and the LO of Actinocyclus moronen- sis between Samples 24H-CC and 25H-CC allowed placement of the boundary between the T. yabei and A. moronensis Zones in this interval. The sediments from Hole 1225A have a continuous diatom biostratigra- F6. Diatom biostratigraphy, p. 15.

Age (Ma) Abundance 02468101214RFCA phy with a minimal age of ~11.5 Ma at the basaltic basement, the same 0 age as Site 851. The age model based on diatoms compares favorably 50 with the magnetic record (Fig. F6). 100 150

200 Depth (mbsf)

250

300

350 S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 6

Nannofossils

Nannofossil datums and their depths in Hole 1225A are listed in Ta- ble T2. Sample 201-1225A-1H-CC was assigned to the upper Pleis- T2. Zonation summary, p. 19. tocene–Holocene Emiliania huxleyi Zone (NN21). E. huxleyi, Calcidiscus leptoporus, Helicosphaera carteri, Reticulofenestra spp. (small), and gephy- rocapsids were dominant. Rhabdosphaera clavigera, Syracosphaera pul- chra, and Umbilicosphaera sibogae were frequent. The presence of Pseudoemiliania lacunosa in Samples 2H-CC to 7H-CC indicates an early –late Pliocene age (Zones NN19–NN16) for these samples. Sample 2H-CC included Reticulofenestra asanoi, which indicates calcare- ous nannofossil Datum 7 in the Quaternary (Sato et al., 1999). The Pliocene/Pleistocene boundary was placed between Samples 201- 1225A-3H-CC and 4H-CC. Sample 7H-CC was assigned to Zone NN18 (Discoaster brouweri Zone). D. brouweri, Discoaster pentaradiatus, and Dis- coaster surculus were present in Sample 5H-CC, which was placed in Zone NN16 (D. surculus Zone). Below this sample, discoasters gradually increased in number of species. Discoaster tamalis was found below Sam- ple 6H-CC. Sample 8H-CC contained Reticulofenestra pseudoumbilicus to- gether with Sphenolithus abies. The occurrence of Amaurolithus spp. and Ceratolithus rugosus in Samples 10H-CC and 11H-CC indicates the lower Pliocene (Zones NN13~NN14). The presence of Discoaster quinqueramus places Sample 14H-CC within the upper Miocene D. quinqueramus Zone (Subzone NN11B). Samples 18H-CC to 22H-CC were characterized by small coccolith and Discoaster assemblages. R. pseudoumbilicus was once again present below Sample 23H-CC. Samples 25H-CC and 26H-CC may belong to Zone NN9 (D. hamatus Zone) on the basis of the occur- rence of D. hamatus. The occurrence of Discoaster kugleri in Samples 33H-CC and 34H-CC indicates the middle Miocene (Zones NN7~NN8). The age model based on nannofossils compares favorably with the magnetic record (Fig. F7). F7. Nannofossil biostratigraphy, p. 16.

Age (Ma) 0 2468101214 0

DISCUSSION 50

100 The age model based on magnetostratigraphy and biostratigraphy in 150 200 Hole 1225A is very consistent (Fig. F8). In Subunit IA (0–70 mbsf), po- Depth (mbsf) 250 larity reversals are consistent with diatom and nannofossil datums 300 through the last 4.2 m.y., yielding a sedimentation rate of 1.7 cm/k.y. 350 In the low–magnetic intensity interval (70–200 mbsf), diatom zona- tion was useful for age determination between 5 and 9 Ma, with a sedi- F8. Combined age-depth plot, mentation rate of 3.3 cm/k.y. Within Subunit IC, from 200 to 230 mbsf, p. 17. polarity reversals are well correlated with diatoms and nannofossils Age (Ma) 0 2468101214 from 8.6 to 9.7 Ma, with a sedimentation rate of 2.7 cm/k.y. In Subunit 0 50

ID (255–300 mbsf), a low–magnetic intensity unit, diatom and nanno- 100 events coincide within a range of 1 to 2 m.y. The sedimentation 150

200 rate is ~3.6 cm/k.y., based on diatom zonation. Depth (mbsf) Subunits IB and ID have higher sedimentation rates and correspond 250 300 to the late Miocene–early Pliocene biogenic bloom event (4.5–7 Ma) 350 and the Miocene global cooling trend (10–15 Ma) (Farrell et al., 1995; Cortese et al., 2004). The higher sedimentation rates and prevalence of pyrite in these subunits suggest that high biogenic productivity led to the pyritization of magnetic minerals and the destruction of the mag- netic signal. There is also evidence that basement fluid is penetrating Subunit ID (Oyun et al., 1995; Shipboard Scientific Party, 2003), which could result in the dissolution of iron minerals. S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 7 CONCLUSIONS

The magnetostratigraphy from Subunits IA and IC (0–70 and 200– 255 mbsf, respectively) in Hole 1225A correlates well with diatom and nannofossil biostratigraphy. Subunit IA contains magnetic reversals un- til the termination of the Cochiti Subchronozone (Subchron C3n.1n; 3.8 Ma). Subunit IC was constrained by the LOs of D. hamatus (9.4 Ma) and D. simonsenii (9.45 Ma) and contains magnetic reversals between Chrons C4n.2r and C5n.2n (8.6 and 9.7 Ma). The consistency of the biostratigraphy and magnetostratigraphy indicates that reversals are ad- equately preserved for the age model. Subunits IB and ID (70–200 and 255–300 mbsf, respectively) were dominated by pyrite and had no reversal record. These subunits corre- spond to higher sedimentation rates, which suggests that high biogenic productivity in relation to global climatic events led to the destruction of the magnetic signal. In Subunit ID, basement flow is another factor that may be altering the magnetic signal.

ACKNOWLEDGMENTS

We would like to thank Prof. J. King (University of Rhode Island), Prof. T. Kakegawa (Tohoku University), and Prof. B. Musgrave (La Trobe University) for their suggestions and the Leg 201 Co-Chief Scientists, Staff Scientist, shipboard sedimentologists, and other scientists for their partnerships. This research used samples and/or data supplied by the Ocean Drill- ing Program (ODP). ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Join Oceanographic Institutions (JOI), Inc. This study was performed under the cooperative research program of the Center for Advanced Marine Core Research, Kochi University (04B003). S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 8 REFERENCES

Acton, G.D., Okada, M., Clement, B.M., Lund, S.P., and Williams, T., 2002. Paleomag- netic overprints in ocean sediment cores and their relationship to shear deforma- tion caused by piston coring. J. Geophys. Res., 107. doi:10.1029/2001JB000518 Baldauf, J.G., and Iwai, M., 1995. Neogene diatom biostratigraphy for the eastern equatorial Pacific Ocean, Leg 138. In Pisias, N.G., Mayer, L.A., Janecek, T.R., Palmer-Julson, A., and van Andel, T.H. (Eds.), Proc. ODP, Sci. Results, 138: College Station, TX (Ocean Drilling Program), 105–128. Barron, J.A., 1985a. Late Eocene to Holocene diatom biostratigraphy of the equatorial Pacific Ocean, Deep Sea Drilling Project Leg 85. In Mayer, L., Theyer, F., Thomas, E., et al., Init. Repts. DSDP, 85: Washington (U.S. Govt. Printing Office), 413–456. Barron, J.A., 1985b. Miocene to Holocene planktic diatoms. In Bolli, H.M., Saunders, J.B., and Perch-Nielsen, K. (Eds.), Plankton Stratigraphy: Cambridge (Cambridge Univ. Press), 763–809. Cande, S.C., and Kent, D.V., 1995. Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and . J. Geophys. Res., 100:6093–6095. doi:10.1029/94JB03098 Cortese, G., Gersonde, R., Hillenbrand, C.-D., and Kuhn, G., 2004. Opal sedimenta- tion shifts in the World Ocean over the last 15 Myr. Earth Planet. Sci. Lett., 224:509– 527. doi:10.1016/j.epsl.2004.05.035 Farrell, J.W., Raffi, I., Janecek, T.C., Murray, D.W., Levitan, M., Dadey, K.A., Emeis, K.-C., Lyle, M., Flores, J.-A., and Hovan, S., 1995. Late Neogene sedimentation patterns in the eastern equatorial Pacific Ocean. In Pisias, N.G., Mayer, L.A., Jan- ecek, T.R., Palmer-Julson, A., and van Andel, T.H. (Eds.), Proc. ODP, Sci. Results, 138: College Station, TX (Ocean Drilling Program), 717–756. Koizumi, I., and Tanimura, Y., 1985. Neogene diatom biostratigraphy of the middle latitude western north Pacific, Deep Sea Drilling Project Leg 86. In Heath, G.R., Burckle, L.H., et al., Init. Repts. DSDP, 86: Washington (U.S. Govt. Printing Office), 269–300. Martini, E., 1971. Standard Tertiary and Quaternary calcareous nannoplankton zona- tion. In Farinacci, A. (Ed.), Proc. 2nd Int. Conf. Planktonic Microfossils Roma: Rome (Ed. Tecnosci.), 2:739–785 Niitsuma, N., and Koyama, M., 1994. Paleomagnetic processor: a fully automatic por- table spinner magnetometer combined with an AF demagnetizer and magnetic susceptibility anisotropy meter. Shizuoka Univ. Geosci. Rep., 21:11–19. Oyun, S., Elderfield, H., and Klinkhammer, G.P., 1995. Strontium isotopes in pore waters of east equatorial Pacific sediments: indicators of seawater advection through oceanic crust and sediments. In Pisias, N.G., Mayer, L.A., Janecek, T.R., Palmer-Julson, A., and van Andel, T.H. (Eds.), Proc. ODP, Sci. Results, 138: College Station, TX (Ocean Drilling Program), 813–819. Pisias, N.G., Mayer, L.A., Janecek, T.R., Palmer-Julson, A., and van Andel, T.H. (Eds.), 1995. Proc. ODP, Sci Results, 138: College Station, TX (Ocean Drilling Program). Sato, T., Kameo, K., and Mita, I., 1999. Validity of the latest Cenozoic calcareous nan- nofossil datums and its application to the tephrochronology. Earth Sci., 53:265– 274. Shipboard Scientific Party, 1992. Site 851. In Mayer, L., Pisias, N., Janecek, T., et al., Proc. ODP, Init. Repts., 138 (Pt. 2): College Station, TX (Ocean Drilling Program), 891–965. Shipboard Scientific Party, 2003. Site 1225. In D’Hondt, S.L., Jørgensen, B.B., Miller, D.J., et al., Proc. ODP, Init. Repts., 201, 1–86 [CD-ROM]. Available from: Ocean Drill- ing Program, Texas A&M University, College Station TX 77845-9547, USA. [HTML] Stradner, H., and Papp, A., 1961. Tertiäre Discoasteriden aus Österreich und deren stratigraphischen Bedeutung mit Hinweisen auf Mexico, Rumänien und Italien. Jahrb. Geol. Bundesanst. (Austria), 7:1–159. S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 9

Takayama, T., and Sato, T., 1987. Coccolith biostratigraphy of the North Atlantic Ocean, Deep Sea Drilling Project Leg 94. In Ruddiman, W.F., Kidd, R.B., Thomas, E., et al., Init. Repts. DSDP, 94 (Pt. 2): Washington (U.S. Govt. Printing Office), 651– 702. Winter, D., and Iwai, M., 2002. Data report: Neogene diatom biostratigraphy, Antarc- tic Peninsula Pacific margin, ODP Leg 178 rise sites. In Barker, P.F., Camerlenghi, A., Acton, G.D., and Ramsay, A.T.S. (Eds.), Proc. ODP, Sci. Results, 178 [Online]. Available from World Wide Web: [Cited 2005-01-03]. S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 10

Figure F1. Location of ODP Leg 201 Site 1225 (black circle) and Leg 138 Site 851 (white circle). Site 1225 was adjacent to Leg 138 Site 851. NECC = North Equatorial Countercurrent, SEC = South Equatorial Cur- rent.

20° N

10°

NECC

Site 851 Site 1225

SEC

10°

20° S 120°E 110° 100° 90° 80° 70°

6000 5000 4000 3000 2000 1000 0 Water depth (m) S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 11

Figure F2. Summary of the Neogene chronostratigraphy adopted for Hole 1225A. F = first occurrence, L = last occurrence.

Diatoms Geomagnetic polarity Nannofossils (Barron, 1985a, 1985b; (Cande and Kent, 1995) (Martini, 1971) Baldauf and Iwai, 1995) Epoch Zone Event (Ma) Zone Event (Ma) 0 NN21 F Emiliania huxleyi (0.25) P. n NN20 L Pseudoemiliania lacunosa (0.41) Brunhes L Reticulofenestra asanoi (0.85) doliolus F Gephyrocapsa parallela (0.95) L Nitzschia 0.78 C1 F Reticulofenestra asanoi (1.16) reinholdii (0.62) 1 Jaramillo L large Gephyrocapsa spp. (1.21) Pleist. r NN19 LHelicosphaera sellii (1.27) N. F large Gephyrocapsa spp. (1.45) reinholdii F Gephyrocapsa oceanica (1.65) 1.77 n Olduvai F Gephyrocapsa caribbeanica (1.73) 2 LDiscoaster brouweri (1.97) F Pseudoeunotia C2 r Reunion NN18 Matuyama L Discoaster pentaradiatus (2.38) N. doliolus (2.00) 2.58 NN17 L Discoaster surculus (2.54) marina L Nitzschia L Discoaster tamalis (2.74)

late jouseae (2.77) 3 n Kaena L Reticulofenestra ampla (2.78) Manmmoth NN16 C2A Gauss 3.58 r N. Pliocene L Reticulofenestra pseudoumbilicus 4 4.18 L Sphenolithus abies (3.85) (3.85) jouseae Cochiti NN15 n Nunivak NN13-14 L Amaurolithus spp. (4.50) early Sidufjall F Ceratolithus rugosus (4.7) 5 C3 Gilbert Thvera NN12 F Nitzschia jouseae (5.12) r LDiscoaster quinqueramus (5.6) T. 5.89 6 convexa n

Age (Ma) C3A L small Reticulofenestra int. (6.5) r F Thalassiosira 6.94 N. convexa (6.57) 7 n v. aspinosa NN11 miocenica C3B r F Nitzschia 7.43 miocenica s.l. n N. (7.30) 8 porteri C4 r F Discoaster berggrenii (8.6) L Thalassiosira late 8.70 yabei (8.23) Miocene n NN10A 9 L Reticulofenestra T. pseudoumbilicus yabei C4A r NN10B L Denticulopsis L Discoaster hamatus (9.4) simonsenii (9.45) 9.74 L Actinocyclus 10 NN9 moronensis n (9.76) A. F Discoaster hamatus (10.7) C5 moronensis 11 NN8 L Craspedodiscus r L Catinaster coalitus (11.3) C. coscinodiscus

middle (11.44) NN7 coscinodiscus 12 S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 12 N N 50 50

1.0 Jo= 4.8e-4 A/m NRM 1.0 Jo= 8.4e-3 A/m 40 mT 30 mT W Up E Dn 10 mT om Subunit IB that showed downward drilling showed IB om that Subunit W Up E Dn 30 mT 40 mT NRM 20 mT SN Div.= 2.0e-4 A/m Div.= 20 mT Stepwise acquisition of anhysteretic remanent magnetiza- of anhysteretic acquisition Stepwise 10 mT SN Div.= 1.0e-3 A/m Div.= Core 201-1225C-1H, 2.43 mbsf Core 201-1225C-1H, 2.43 mbsf Core 201-1225C-18H, 166.77 mbsf D B. 1 -1 10 10 mT 20 mT 30 mT 40 mT -2 10 -3 10 Demagnetization plot of typical sample fr sample plot of typical Demagnetization Intensity (A/m) ARM aquisition C. -4 10 l remanent magnetization (NRM). magnetization (NRM). l remanent -5 10 -1 10 NRM 10 mT 20 mT 30 mT 40 mT -2 10 -3 Intensity (A/m) 10 AF demagnetization Stepwise demagnetization of natura demagnetization Stepwise Demagnetization plot of typical sample from Subunit IB that did not show magnetic direction. magnetic show not did IB that Subunit from sample typical of plot Demagnetization A. D.

-4 10 0

AB C 50

100 150 200 250 300 Depth (mbsf) Depth tion (ARM) for 29 discrete samples from Hole 1225C. 1225C. from Hole samples discrete 29 for (ARM) tion overprint. Figure F3. S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 13 ion

Age (Ma)

2.581 Jaramillo Olduvai Reunion Cochiti Kaena Manmmoth

0.000 0.780 1.770 1.950 3.580

Brunhes Matuyama Gauss Gilbert zone Chron C2Ar CK95 C1n C2r.2r C3n.1r C1r.2r C2An.1n C2An.1r C1r.1r C1r.1n C2n C2r.1n C2An.2n C2An.2r C2An.3n C3n.1n C2r.2r-1# Polarity Chron magnetostratigraphic interpretat magnetostratigraphic Declination (°) AF demagnetization (15 mT) with with (15 mT) demagnetization AF Inclination (°) -90 -60 -30 0 30 60 90 0 90 180 270 1 1H 2H 3H 4H 5H 6H 7H 8H 9H 11H 10H -1 10 -2 10 -3 10 Intensity (A/m) -4 10 Magnetic intensity, declination, and inclination of NRM after of NRM after and inclination declination, intensity, Magnetic -5 10

0

60 80 20 40 Depth (mbsf) Depth 100 Figure F4. timescale. polarity geomagnetic (1995) Kent and = Cande CK95 mbsf. 0–90 at 1225A Hole for S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 14 ion 8.699 9.740 Age (Ma) CK95 C4r.2r C4An C4Ar C4Ar.1n C4Ar.1r C4Ar.2n C4Ar.2r C5n.1n C5n.1r C5n.2n C4r.2r-1# Polarity Chron magnetostratigraphic interpretat magnetostratigraphic Declination (°) AF demagnetization (15 mT) with with (15 mT) demagnetization AF Inclination (°) -90 -60 -30 0 30 60 90 0 90 180 270 1 29P 35X 21H 22H 23H 24H 25H 26H 27H 28H 30H 31H 32H 33H 34H -1 10 -2 10 -3 10 Intensity (A/m) -4 10 Magnetic intensity, declination, and inclination of NRM after of NRM after and inclination declination, intensity, Magnetic -5 10

180 200 220 240 260 280 300 320 Depth (mbsf) Depth Figure F5. timescale. polarity geomagnetic (1995) Kent and Cande = CK95 mbsf. 190–320 at 1225A Hole for S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 15

Figure F6. Age-depth plot based on diatom biostratigraphy in Hole 1225A. Solid black and red triangles show bottom and top of each diatom event. Open black and red triangles show oldest and youngest ages of each samples. Open squares show paleomagnetic stratigraphy points. A = abundant, C = common, F = few, and R= rare.

Age (Ma) Abundance 02468101214RFCA 0

50

100

150

200 Depth (mbsf)

250

300

350 S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 16

Figure F7. Age-depth plot based on nannofossil biostratigraphy (red triangles) and magnetostratigraphy (open squares) in Hole 1225A.

Age (Ma) 0 2 4 6 8 10 12 14 0

50

100

150

200 Depth (mbsf)

250

300

350 S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 17

Figure F8. Age-depth plot based on magnetostratigraphy (black squares) diatom (blue triangles) and nan- nofossil (red triangles) biostratigraphy at Hole 1225A. Solid triangles show bottom and top of each diatom event. Open triangles show oldest and youngest ages of diatoms and nannofossils for each sample.

Age (Ma) 0 2 4 6 8 10 12 14 0

50

100

150

200 Depth (mbsf)

250

300

350 S. NIITSUMA ET AL. DATA REPORT: STRATIGRAPHY CORRELATION 18

Table T1. Stratigraphically useful diatom events, Hole 1225A.

Core, section Depth Age* (top/bottom) (mbsf) Event (Ma)

201-1225A- 1H-CC/2H-CC 4.26–14.30 LO Nitzschia reinholdii 0.62 2H-CC/3H-CC 14.30–23.62 LO Nitzschia fossilis 0.70 LO Rhizosolenia matuyamai 1.05 FO Rhizosolenia matuyamai 1.18 3H-CC/4H-CC 23.62–33.08 LO Rhizosolenia praebergonii var. robusta 1.73 4H-CC/5H-CC 33.08–42.93 FO Pseudoeunotia doliolus 2.00 LO Thalassiosira convexa s.l. 2.41 5H-CC/6H-CC 42.93–52.38 LO Nitzschia jouseae 2.77 6H-CC/7H-CC 52.38–61.72 FO Rhizosolenia praebergonii s.l. 3.17 7H-CC/8H-CC 61.72–71.28 FO Thalassiosira convexa var. convexa 3.81 FO Asteromphalus elegans 3.99 9H-CC/10H-CC 80.79–90.34 LO Nitzschia cylindrica 4.88 10H-CC/11HCC 90.34–99.79 FO Nitzschia jouseae 5.12 12H-CC/13H-CC 109.23–118.81 FO Thalassiosira oestrupii 5.64 11H-CC/13H-CC 99.79–118.81 LO Thalassiosira miocenica 5.84 13H-CC/14H-CC 118.81–128.50 LO Nitzschia miocenica s.s. 6.08 LO Nitzschia miocenica var. elongata 6.08 14H-CC/15H-CC 128.50–137.75 LO Thalassiosira praeconvexa 6.18 16H-CC/17H-CC 147.50–156.33 LO Rossiella praepaleacea 6.54 FO Thalassiosira miocenica 6.55 15H-CC/17H-CC 137.75–156.33 FO Thalassiosira convexa var. aspinosa 6.57 17H-CC/18H-CC 156.33–166.05 FO Thalassiosira praeconvexa 6.71 18H-CC/19H-CC 166.05–175.75 LO Nitzschia porteri 7.16 FO Nitzschia miocenica s.l. 7.30 LO Rossiella paleacea 7.40 19H-CC/20H-CC 175.75–185.23 FO Nitzschia reinholdii 7.64 LO Actinocyclus ellipticus var. javanicus 7.79 21H-CC/22H-CC 194.39–204.23 LO Thalassiosira burckliana 7.85 20H-CC/21H-CC 185.23–194.39 FO Nitzschia marina 7.95 19H-CC/20H-CC 175.75–185.23 FO Nitzschia cylindrica 8.07 21H-CC/22H-CC 194.39–204.23 LO Thalassiosira yabei 8.23 LO Coscinodiscus loeblichii 8.86 22H-CC/23H-CC 204.23–215.38 FO Thalassiosira burckliana 8.91 24H-CC/25H-CC 224.82–234.30 LO Denticulopsis simonsenii 9.45 FO Coscinodiscus loeblichii 9.65 24H-CC/25H-CC 224.82–234.30 LO Actinocyclus moronensis 9.76 31H-CC/32H-CC 283.79–293.17 FO Actinocyclus ellipticus f. lanceolata 10.45 LO Denticulopsis 11.02 LO Coscinodiscus gigas var. diorama 11.23 32H-CC/33H-CC 293.17–302.70 FO Rossiella paleacea var. elongata 11.23 31H-CC/32H-CC 283.79–293.17 LO Craspedodiscus coscinodiscus 11.44 ——LO Synedra jouseana 11.51 ——FO Hemidiscus cuneiformis 11.80 ——LCO Actinocyclus ingens s.s. 12.18 ——LO Cestodiscus pulchellus 12.23 ——FO Thalassiosira brunii 12.28 ——FO Nitzschia porteri 12.32 ——LO Crucidenticula 12.47 ——LO Annellus californicus 12.53

Notes: Datums occur in the cores within the interval listed for each species. * = Cande and Kent (1995). LO = last occurrence datum, FO = first occurrence datum, FCO = first common occurrence datum, LCO = last common occurrence datum. Events in bold designate boundaries of each diatom zone. — = interval drilled but not cored or not drilled. S. NIITSUMA ET AL.

DATA REPORT: STRATIGRAPHY CORRELATION 19

Umbilicosphaera sibogae Umbilicosphaera

Syracosphaera pulchra Syracosphaera

Sphenolithus moriformis Sphenolithus

Sphenolithus abies Sphenolithus

Rhabdosphaera clavigera Rhabdosphaera

spp. (small) spp. Reticulofenestra

Reticulofenestra pseudoumbilicus Reticulofenestra

Reticulofenestra asanoi Reticulofenestra

Pseudoemiliania lacunosa Pseudoemiliania = present (found but not

Helicosphaera wallichii Helicosphaera

Helicosphaera sellii Helicosphaera

Helicosphaera intermedia Helicosphaera

Helicosphaera hyalina Helicosphaera

Helicosphaera granulata Helicosphaera

Helicosphaera carteri Helicosphaera

spp. (small) spp. Gephyrocapsa

ACR+A Gephyrocapsa parallela Gephyrocapsa

–8%), R = rare (<8%), + (<8%), R = rare –8%), Gephyrocapsa oceanica Gephyrocapsa

Gephyrocapsa carribeanica Gephyrocapsa

Emiliania huxleyi Emiliania ation from Barron(1985a, 1985b) andBaldauf and Iwai

CCCCAC R CR RR

spp. Discolithina

Discolithina multipora Discolithina Discolithina japonica Discolithina

+RAARCCRR

spp. Discoaster

Discoaster variabilis Discoaster

Discoaster triradiatus Discoaster

Discoaster tamalis Discoaster

Discoaster surculus Discoaster

Discoaster quinqueramus Discoaster

Discoaster quadramus Discoaster

Discoaster pentaradiatus Discoaster

Discoaster loeblichii Discoaster

Discoaster kugleri Discoaster

Discoaster hamatus Discoaster

Discoaster exilis Discoaster Discoaster challengeri Discoaster

et. al. (1999), and diatom biostratigraphic zon biostratigraphic and diatom (1999), al. et. Discoaster calcaris Discoaster

Discoaster brouweri Discoaster Discoaster bellus Discoaster

RRRR + C CC C

Discoaster asymmetricus Discoaster Cyclithella annulus Cyclithella

dant (>32% of the species in total assemblage), C = common (32% = C assemblage), total in species the of (>32% dant

Coccolithus miopelagicus Coccolithus

Coccolithus pelagicus Coccolithus

spp. Ceratolithus

Catinaster coalitus Catinaster

Calcidiscus macintyrei Calcidiscus Calcidiscus leptoporus Calcidiscus

RR + R R +RR R C AA C + R+ C + R +C R R CR CR R+C+++R+R C + CACR +RRRC C CACC C+ RC R+ R R RR RRC C +C R A R CR RC R R R RR C R+R A + C+ ++ C C + R + C RR RA RR RA A +

spp. Amaurolithus +C+ +R+C+ R C + R + C+ CA + +R R RA RR C R CA A R CA C nnofossils, Hole Hole 1225A. nnofossils, NN16 NN19 NN11B R C R R R R R R A C R C A A NN10B~11A from Martini (1971), bioevents datum from Sato bioevents (1971), Martini from Age (Ma) Zone

2.00~2.40 NN182.75~3.66 3.66~4.50 R R4.50~4.70 NN15 + NN13~14 C4.70~5.60 NN12 R5.60~8.70 R + R R C C + R A + + 8.70~9.40 NN10A 9.40~10.70 NN9

10.70~13.20 NN7~8

early middle late late

Pleistocene

Pliocene Miocene Summary of Neogene na Neogene of Summary Depth Depth (mbsf) Epoch counted). (1995). Relative frequencies (Takayama and Sato, 1987): A = abun and 1987): Sato, (Takayama frequencies Relative (1995). Core, Core, 7H-CC8H-CC C 61.31 R 71.06 R R + + C + + R C C R R + A + 5H-CC 2.56~2.75 42.59 6H-CC 52.14 9H-CC10H-CC R 80.39 11H-CC 90.09 12H-CC R 99.54 108.97 C13H-CC R R 118.56 14H-CC + C 128.09 + C R R C C R + R R C + C A + + C A R + R R R A R R C R + C + C A C A + C C R C + A A 2H-CC 0.85~1.16 14.10 1H-CCC ~0.25 3.94 3H-CC4H-CC 1.16~1.65 23.39 NN21 32.85 C 30H-CC + 272.81 31H-CC R 283.43 32H-CC R 292.88 33H-CC R 302.40 34H-CC C 313.48 C + R C R C R R C R C + + R R R + + R + R R C C + C C + A R R R R R R + + C R + + + A C C C C A A A R A R A R R R R R 15H-CC 137.48 16H-CC C 147.20 17H-CC C 156.16 18H-CC R C 165.80 19H-CC R C 175.47 20H-CC C C 184.94 21H-CC C R C 194.39 22H-CC C R R 203.96 23H-CC R C 215.13 24H-CC C R 224.62 25H-CC + R C 234.03 26H-CC C R C 243.53 C R R + R R R R R C R R R R + R R R + R + + R + R R R R R + + R R + + R C R + R + C R R C C C A R R A C R R C A + R + C R + R C C C + R + + C R C A A + C A A + A A C A C A C R A A C R C A C C 27H-CC 252.98 section Table T2. 201-1225A- Notes: Biostratigraphic zonation