9. INTEGRATED AGE MODELS EARLY MIOCENE, SITES 1168 FOR THE EARLY OLIGOCENE AND ABSTRACT. Helen A. Pfuhl 2 and I.

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1 Exon, N.F., Kennett, J.P., and Malone, M.J. (Eds.) Proceedings of the Ocean Drilling Program, Scientific Results Volume INTEGRATED AGE MODELS FOR THE EARLY OLIGOCENE EARLY MIOCENE, SITES 68 AND 7 Helen A. Pfuhl and I. Nicholas McCave ABSTRACT The aim of this study is to assess the viability of age models based on shipboard and postcruise bio- and magnetostratigraphic datums, as of August, using independently derived control points. The control points are based on matching between-site trends in stable isotope records, carbonate content, and weight percent sand. Site 7 on the western South Tasman Rise has a good record of magnetic reversals, which suggests a hiatus prior to ~ Ma (early Oligocene) relating to the Marshall Paraconformity, followed by strongly reduced sedimentation in the late Oligocene. Preservation of the Mi- event at this site is evidence for continued sedimentation across the Oligocene/Miocene boundary. Correlation of the Mi-a event to the record at Site 9 on the Agulhas Ridge confirms the usefulness of the magnetostratigraphic record at this site. However, the timing of the Mi- event at Site 7 appears different from that at Site 9, but is constrained by four magnetic reversals. At Site additional control points are consistent with biostratigraphic datums. Site is marked by the lowest sedimentation rates of all sites. Additional control points before Ma are more consistent with the biostratigraphy than with the magnetostratigraphy. At Site 68 we suggest that the magnetic reversal record MR provides the best match with the biostratigraphy and additional control points, as well as changes in the biogenic and lithogenic composition of the sedimentary record. Pfuhl, H.A., and McCave, I.N.,. Integrated age models for the early Oligocene early Miocene, Sites 68 and 7. In Exon, N.F., Kennett, J.P., and Malone, M.J. (Eds.), Proc. ODP, Sci. Results, 89, [Online]. Available from World Wide Web: < publications/89_sr/volume/ CHAPTERS/8.PDF>. [Cited YYYY- MM-DD] Max Planck Institute for Biogeochemistry, Hans Knöll Strasse, 775 Jena, Germany. hapfuhl@yahoo.com University of Cambridge, Department of Earth Sciences, Downing Street, Cambridge CB EQ, United Kingdom. Initial receipt: December Acceptance: 9 July Web publication: November Ms 89SR-8

2 meters H.A. PFUHL AND I.N. MCCAVE EARLY OLIGOCENE EARLY MIOCENE AGE MODELS The late Eocene/early Oligocene Marshall Paraconformity (base = ~ Ma at the type location) is evident at Sites 7, and low sedimentation rates occur at the two eastern sites ( and ) in the early Oligocene. A change in sedimentation just after the early late Oligocene transition appears to reduce rates at Site 7 and strongly affect the biogenic composition of sediments at Site 68, which is less exposed to the flow of the Antarctic Circumpolar Current. The Oligocene Miocene transition finally is marked by reduced sedimentation at Sites 7, but a relatively stronger decrease is noticeable at Site 68. Above this boundary sedimentation rates are identical at Sites 68 and 7 above.5 Ma and at Sites and above 7 Ma. APPROACH A robust age model is essential to evaluate the changes in the hydrographic and sedimentary regime across the Oligocene/Miocene boundary (OMB) (Pfuhl et al., in press). Combined biostratigraphic and magnetostratigraphic age models for Ocean Drilling Program (ODP) Sites 68 and 7, as of August, were used in an initial comparison between sites. However, close study of records of percent CaCO, weight percent sand (>6 µm), and stable oxygen and carbon isotopes (bulk sediment and benthic foraminifers) provides additional information that is crucial in recognizing hiatuses, especially the Marshall Paraconformity in the early Oligocene (~ 9 Ma) (Fulthorpe et al., 996) and sedimentary sequences. A detailed lithologic description of Sites 68 and 7 (Fig. F) is given in the Leg 89 Initial Reports volume (Exon, Kennett, Malone, et al., ). As a first step we attempt to correlate the benthic stable isotope records from Site 7, with special focus on the Mi- and Mi-a events (Miller et al., 985) with those at Site 9 (Billups et al., ) on the Agulhas Ridge south of Africa. A second step is to compare the results with the bio- and magnetostratigraphic data as of August, but also see the study of Stickley et al. (this volume) and additional information on hiatuses/condensed sections or changes in sedimentation rate that are indicated by the measurements obtained during postcruise work (this study and Pfuhl et al., in press). The revised age model for Site 7 incorporates the best fit between additional control points (this study) and the biomagnetostratigraphy (as of August ). This age model forms the basis for paleoceanographic correlation of Sites 7 and development of individual age models using the same overall approach as at Site 7. In a final step we identify additional control points for Site 68, which differs in its location on the continental margin from the open-ocean situation of Sites 7. A more recent version of the age models is presented by Pfuhl et al. (in press); however, the principles outlined here remain unchanged. F. Map of drill sites (Site 69 was abandoned), p METHODS Sites 7 Carbonate Content and Stable Isotope Composition Bulk sediments from Sites 7 were analyzed for their carbonate content and stable isotope composition in an Analytical Precision

3 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS AP mass spectrometer. Benthic isotope measurements were performed on ~ specimens of Cibicidoides mundulus (in very rare cases on a mix of Cibicidoides bradyi and Cibicidoides kullenbergi) from the >- µm size range. This genus is generally accepted as living within the sediment surface ( cm), although C. bradyi might prefer a slightly more infaunal habitat. Analyses were performed using standard procedures for Prism mass spectrometers. Precision is better than ±.6 for δ C, ±. for δ 8 O, and ±% for carbonate. All stable isotope results were calibrated to the international standard Vienna Pedee belemnite through standard laboratory carbonates including correction for vital effects (Shackleton and Hall, 997). A number of outlying measurements were subjected to repeat analysis. All measurements were performed at the Godwin Laboratory, Cambridge University. Carbon Content Site 68 Fine-fraction carbon content (C total ) was measured by CHN analysis in a Carlo Erba EA6 at the Godwin Laboratory, Cambridge University, UK. Additional measurements of total carbon and inorganic carbon content (TIC) were performed in an Elementar VarioMAX at the Max Planck Institute for Biogeochemistry, Jena, Germany. Samples for inorganic carbon content were combusted at ~ C for 6 hr, as combustion of only hr did not remove all nitrogen. In order to use both measurements of C total we calculated a linear regression based on parallel measurements from various intervals at Site 68, arriving at a regression coefficient of R =.95. All CHN measurements were subsequently converted to VarioMAX-equivalent values of C total (y =.99x +.67), where y = VarioMAX-equivalent C total and x = CHN value of total C. Total organic carbon (TOC) was approximated by TOC = C total TIC. Benthic Stable Isotope Composition Four to eight C. mundulus specimens from the >5-µm size fraction were analyzed in VG Optima or Prism gas-source mass spectrometers at the University of California, Santa Cruz. All values are reported in permil notation relative to Vienna Peedee belemnite standard, with δ 8 O measurements including a correction for vital effects (+.5 ) (Shackleton and Hall, 997). Analytical precision for both δ C and δ 8 O averaged better than.. No interlaboratory corrections were applied, as these are usually constant and should not affect our interpretations; however, we do concede that these offsets exist. Faunal and Lithogenic Reconnaissance Faunal and lithogenic reconnaissance is based on random order inspection of the >6-µm fraction at 75- to -cm resolution. We distinguished between = common/dominant, = frequent, = present,

4 Mi-a Mi t MR NF PF D 5 RD DF MR 5 Alt. MR Control points Error early late early late Miocene Oligocene Eocene H.A. PFUHL AND I.N. MCCAVE EARLY OLIGOCENE EARLY MIOCENE AGE MODELS = rare, and = absent (), the same scheme as applied in shipboard benthic foraminiferal studies at 9-m resolution (Exon, Kennett, Malone, et al., ). RESULTS All ages given in this study are based on Cande and Kent (99; 995) (CK95) unless stated otherwise (i.e., the OMB is placed at.8 Ma). Although the astronomically tuned age of the OMB is.9 Ma (Shackleton et al., ), the older Oligocene part of the section does not have a revised age scale; thus, we prefer to stick with CK95 for the time being. Data in the older parts are available only at low resolution (identified by gray backgrounds in figures), whereas resolution in the younger parts is 75 cm for Site 68, cm for Sites 7 and, and cm for Site. All biomagnetostratigraphic datums (as of August ) and additional control points used for our age models are listed in Table T (see also Stickley et al., this volume). Site 7 The benthic stable isotope records of Site 7 on the South Tasman Rise and Site 9 on the Agulhas Ridge, both located in the Southern Ocean, suggest some similarities despite different paleolatitudes. The benthic isotope record for Site 9 was established by Billups et al. (), who developed their age model by matching the excellent magnetic polarity stratigraphy to the geomagnetic polarity timescale of CK95. A comparison of their results with the astronomically tuned record of Shackleton et al. () yielded a constant offset of ~9 k.y. between the two approaches. We focus on the timing of the Mi- and Mi-a event in the benthic δ 8 O records, which are identifiable at both sites despite relatively low sedimentation rates (Fig. FA). The Mi- event appears in benthic foraminiferal δ 8 O records as a cold interval lasting from ~. to.66 Ma, centering around a double peak of extremely heavy (cold) values from.89 to.79 Ma (cf. Billups et al., ). One important difference between this event at Site 7 relative to Site 9 (as well as 99) (Paul et al., ) is that the second peak appears to be as strong, if not even slightly stronger than the first peak. A second difference is that this double peak appears to begin and end later at Site 7 (Fig. FB). At Site 7 timing of the Mi- event is constrained by four magnetostratigraphic datums across a depth of only.5 m, including one at.8 Ma, giving evidence for a strongly condensed section. It is this reversal at.8 Ma (onset of Subchron C6Cn.n at 8.9 meters below seafloor [mbsf]), which is in conflict with an alignment of the Mi- double peak at both sites (.88 Ma [8.6 mbsf] and.8 Ma [8.96 mbsf]). Matching the timing of the Mi-a event at Site 7 with Site 9 provides two additional control points (Fig. FA). Additional information evident in the record of weight percent sand for Site 7 indicates a change in the pattern of sedimentation (increase in the coarse fraction) between 6.69 and 5. mbsf (Fig. F). This is consistent with the correlation indicated by the magnetostratigraphy (Fig. F). The weight percent sand record further suggests placement of the Marshall Paraconformity (~ 9 Ma) (Fulthorpe et al., T. Fossil, magnetic reversal, and additional datums, p.. F. Comparison of Mi-a and Mi- events, p.. A 7 benthic δ 8 O ( ) 9 benthic δ 8 O ( ) 7 depth (mbsf) 9 age (Ma) B 7 benthic δ 8O ( ) Age (Ma) F. Bio- and magnetostratigraphic data, p Sed. rate (cm/k.y.) Age (Ma) Marshall Paraconformity 9 benthic δ 8 O ( )

5 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS 5 996) somewhere between and 6.6 mbsf (no samples) at a drop in average values (see also Site, p. 5, Site, p. 6, and Site 68, p. 6). This hiatus is common in sedimentary records from the southwest Pacific Ocean and is a logical explanation for an early Oligocene hiatus in the Leg 89 sites. At Site 7 this hiatus is constrained by three biostratigraphic markers ( Ma [ mbsf] and.6/. Ma [ mbsf]) and one magnetic reversal (.58 Ma [7 mbsf]) (Fig. F). We use the center of the youngest datum (. Ma; first occurrence [FO] of Rocella vigilans) for the purpose of interpolation downward from the last control point (Fig. F). These data raise an interesting conundrum in correlation, as one would not expect to find the isotope signature of a significant glacial event (Mi-) with different ages at separated locations (i.e., they should occur at the same time worldwide), but the same is also true of magnetic reversal ages. Closer examination is required. See also more recent age model information in the papers by Stickley et al. (this volume) and Pfuhl et al. (in press). Additional records of bulk δ C and benthic δ 8 O and δ C presented in Figure F will be referred to in Site below and Site, p. 6. Site The biomagnetostratigraphy for Site suggests a transition from a heavily condensed Oligocene (sedimentation rates <.5 cm/k.y.) to slightly increased sedimentation rates in the Miocene (.5 cm/k.y.) (Fig. F). Unfortunately, magnetic reversals are less frequently observed than at Site 7 and we fail to detect a complete Mi- event in the benthic δ 8 O record (Fig. F5), but we do observe a number of characteristic markers in the records obtained. Our oldest observation is a dramatic (~6%) and instantaneous (between 7 and 7.8 mbsf [79.68 and 79.8 meters composite depth (mcd)]) increase in CaCO accompanied by a drop in weight percent sand similar to the one observed at Site 7 (Fig. F). We once again suggest that this transition marks the Marshall Paraconformity. This is in good accordance with six biostratigraphic datums (Fig. F). We use the same diatom datum as at Site 7 to mark the top of the hiatus at. Ma (FO of R. vigilans) and our suggested depth of 7.9 mbsf (error of datum = mbsf). It is followed by a rapid transition to heavier values in both benthic and bulk δ C ( and mbsf) (Fig. F5). The lack of variability and the transition over 6 cm in the case of the bulk record suggests a strongly condensed section rather than a few hiatuses. We observe similar shifts in the δ C records at Site 7 at ~ mbsf (~6.9 Ma) and 98 mbsf (~6. Ma) followed by a strongly condensed interval ending at ~.78 Ma (Fig. F). Three biostratigraphic control points at Site suggest the same pattern for this site. Unfortunately, this interval is also marked by poor recovery. However, in order to relate these observations to the age model we decided to add control points centering on the two δ C increases and ignore the biostratigraphic datums. The magnetic reversal at 68 mbsf, assigned an age of.8 Ma (onset of Subchron C6Cn.n), implies a very strong increase in sedimentation rate, which appears most unlikely based on our present understanding of the sedimentary regime at all Leg 89 sites. Considering both poor recovery and low sedimentation rates before and after this datum, we suggest this datum also be ignored. A further control F. Sand, carbonate, and benthic and bulk δ C, Site 7, p.. A B Benthic δ 8 O ( ) Bulk δ C ( ) Sand (wt%).8.. Site 7 Mi-a Mi F5. Sand, carbonate, and benthic and bulk δ C, Site, p.. A B C Benthic δ 8 O ( ) Bulk δ C ( ) Sand (wt%) Site onset Mi Benthic δ C ( ) Bulk CaCO (%) Bulk CaCO (%) Benthic δ C ( )

6 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS 6 point, which we place at mbsf (.88 Ma), is based on the increase in benthic δ 8 O, which we identify as the onset of the Mi- event (Fig. F5). The remainder of this event was not recovered during drilling of Hole C (core gap at mbsf). Connection of this and the previous control points are consistent with the biostratigraphy (Fig. F). Above this gap we observe a low in benthic δ C and matched increases in bulk δ C and CaCO (5.9 and mbsf) (Fig. F5). Based on similarities with Site 7, we assign ages of.5 and.8 Ma (increase at Site 7 between samples at 77.6 and 76.5 mbsf across a core gap) (Fig. F). The ensuing low sedimentation rates lasting ~ m.y. following the OMB at Site are consistent with biostratigraphic datums at this site and a similar trend at Site 7. An additional control point is placed at. Ma (9.6 mbsf) based on correlation with the benthic δ 8 O record at Site 7. A last control point is placed at.7 Ma (. mbsf) based on the benthic δ C record. Two more gaps in recovery in Hole C are evident at and mbsf. Site Site has a greater number of magnetostratigraphic control points than Site across the interval studied (Fig. F). However, the Oligocene interval is marked by very few additional biostratigraphic datums. We estimate that sedimentation resumes above the Marshall Paraconformity at.98 Ma (magnetic reversal onset of Subchron Cn.n [58.6 mbsf]), but sedimentation rates remain very low, as suggested by three closely spaced magnetic reversals. As at Sites 7 and, we observe a sharp drop in weight percent sand at the Marshall Paraconformity (i.e., between and 58.6 mbsf) (Fig. F6). This constrains placement of the hiatus to within 6 cm ( mbsf). Our records suggest two additional control points based on correlation with Sites 7 and. At Site the bulk δ C record shows two strong increases ( and mbsf) (Fig. F6) that we match with the respective control points for the other two sites. Whereas these datum levels are close to the error given for two biostratigraphic datums, they are inconsistent with the magnetostratigraphy. However, in a strongly condensed section with potential hiatuses, identification of reversals is severely compromised. We are confident in the placement of these two δ C datums and suggest two additional points based on similarities between the benthic δ 8 O (onset of the Mi- event) and benthic δ C records from.7.7 and.56.6 mbsf, respectively (Fig. F6). The second control point is more difficult to define at Site 7 where the decrease in benthic δ C occurs over a number of samples from to 75.6 mbsf (Fig. F). However, we place our control point based on the turning point in the δ C record. Two final control points are based on the benthic and bulk δ C records at.5 Ma (.6 mbsf) and.79 Ma (9.86 mbsf). F6. Sand and bulk and benthic δ C, Site, p. 5. A B C Benthic δ 8 O ( ) Bulk δ C ( ) Sand (wt%) 6... Site onset Mi Benthic δ C ( ) Bulk CaCO (%) Site 68 Although the general trends observed in the records at Sites 7 reveal numerous similarities, we have difficulty in detecting

7 H.A. PFUHL AND I.N. MCCAVE EARLY OLIGOCENE EARLY MIOCENE AGE MODELS 7 matching patterns at Site 68 (Fig. F7). In this we are also constrained by lack of comparable data (i.e., the only stable isotopes available were measured on benthic foraminifers at very low resolution) (Dr. S. Schellenberg, pers. comm., ; but see also Pfuhl et al., in press). CaCO was measured on the fine fraction only, but a comparison with bulk values at this site (Dr. C. Kelly, unpubl. data) and between bulk and fine values at Sites 7 suggest that the records can be overlaid (Fig. F7). Our data reveal a strong transitional interval from ~765 to 75 mbsf marked by decreasing weight percent sand and organic carbon content, as well as increasing carbonate content (Fig. F8). We suggest that this interval marks the Eocene Oligocene transition similar to Sites 7, possibly without the development of the Marshall Paraconformity at this rather protected site on the continental margin of Tasmania. Following this transition we note a number of changes in the biogenic and lithogenic composition of the coarse fraction (>6 µm) at this site (Fig. F9). The first two occur at ~699 and 58 mbsf. At ~9 mbsf we note the end of a strongly condensed interval (shipboard observation on benthic foraminifers). Between 5. and.98 mbsf the carbonate content increases (Fig. F8) followed by an increase in dissolution and weight percent sand at 86. mbsf (Fig. F9). All these datums are matched closely by changes in sedimentation suggested by the biomagnetostratigraphy based on magnetic reversal interpretation MR (Fig. F). If we assume the timing of the Mi- event recognized isotopically to be identical at all Leg 89 sites, we would have to tentatively place the peaks of this event at.9 Ma ( mbsf) and.75 Ma ( mbsf). This is consistent with the biomagnetostratigraphy (based on magnetic reversal interpretation MR) within the error resulting from very low resolution (.5 m) of measurements available at present. In comparison with the other three sites the changes in sedimentation rates across the Oligocene Miocene transition are relatively strongest at this site. We suggest ignoring the planktonic foraminiferal datum at.8 Ma (79.6 mbsf; last occurrence [LO] of Dentoglobigerina globularis) because of its proximity to an event at Ma (7.97 mbsf; FO of Globoturborotalita woodi) and place the FO of Globoquadrina dehiscens (planktonic foraminifers) at its upper limit of error (7.6 mbsf). The extreme increase in sedimentation rate at Site 68 prior to the Oligocene Miocene transition is fixed by two magnetic reversals and has to be accepted at this point. F7. Overlap of bulk and fine-fraction carbonate, p CaCO (%) 7 CaCO (%) CaCO (%) CaCO (%) 6 Bulk Fine F8. Sand, carbonate, and TOC, Site 68, p. 7. Sand (wt%) Fine TOC (%) pt run. ave. 5-pt run. ave. 5-pt run. ave. Site F9. Changes in sedimentation, Site 68, p. 8. Pyrite Glauconite Clear spicules -pt run. ave. Bulk Fine Site F. Records used to define control points vs. revised ages, p. 9. A Bulk CaCO (%) B 8 6 Benthic δ 8 O ( ) CaCO (%) Quartz Dissolution Opaque spicules All Sites In Figure F we show the results of our measurements of lithologic and isotopic parameters at Sites 7 against their revised ages on the timescale of Cande and Kent (99, 995). Figure F shows a histogram of the sedimentation rates. SUMMARY The age models for the early Oligocene early Miocene interval for ODP Sites 68 and 7 were independently tested on the basis of a number of paleoceanographic data sets, including stable isotopes and carbonate content. With the exception of Site, our integrated approach proves largely consistent with the magnetostratigraphic out- C Age (Ma) Benthic δ C ( ) D Age (Ma) Bulk δ C ( ) F. Changes in sedimentation rates, p.. Sed. rate (cm/k.y.) Age (Ma)

8 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS 8 line (as of August, we propose to follow magnetic reversal hypothesis in the case of Site 68). The development of these integrated age models forms the basis for a study of the hydrographic system around Tasmania. One of the questions addressed is the relationship between the sites and their respective location on the Pacific Ocean (Sites ) or Indian Ocean (Sites 68 and 7) side of the South Tasman Rise. Changes in sedimentation rates (Figs. F, F) suggest that Site 68 s location is rather different in character from Sites 7, due to its continental margin location. The Marshall Paraconformity in the early Oligocene is one of the most important hiatuses in the Southern Ocean region. The base of this hiatus is generally at ~ Ma in deepsea sections (Shipboard Scientific Party, 999a, 999b) and is at. Ma at the onland type location (Fulthorpe et al., 996). Its duration at the type area is. m.y. (up to 9 Ma), but at Site it lasts until ~ Ma (Shipboard Scientific Party, 999a). Despite the significance of this hiatus for other sites, and here at Sites 7 from ~ to Ma, at Site 68 it is apparently represented only by an interval of reduced sedimentation rate. Sedimentation rates return to high values throughout the Oligocene and Miocene. Sites on the east South Tasman Rise and in the Tasman Sea are clearly most strongly affected by the Marshall Paraconformity. Even though the hiatus appears to end at ~ Ma, sedimentation rates remain low for most of the Oligocene. At Site 7 on the west South Tasman Rise, sedimentation in the early Oligocene is relatively high. However, this does change following the early/late Oligocene boundary, when we observe a decrease similar to but more pronounced than that at Site 68. At Site 68 we observe a change in the biogenic components of the sediment. The transition from opaque and sometimes branched spicules to clear, tiny, straight spicules with a canal might imply a change in water depth or ocean circulation. The Oligocene/Miocene boundary is marked by a strongly condensed section or small hiatus/core gap in Sites 7 from just before the boundary to ~.8 Ma, but the overall decrease in sedimentation rate across this interval is greatest at Site 68. The problem of the mismatch of the Mi- event (and/or the adjacent magnetic reversals) at Sites 68 and 7 requires closer investigation, as two key tenets of deep-sea stratigraphy appear to be in conflict. ACKNOWLEDGMENTS Special thanks go to Mike Hall, Patrizia Ferretti, James Rolfe, and Benoit Vautravers at Cambridge University for excellent sample preparation, and the Leg 89 time-team (the micropaleontologists and magnetic stratigraphers) for their efforts in providing the necessary age control. We would also like to thank Bob Carter and Ken Miller for their careful reviews and Clay Kelly for unpublished data. This research used samples and/or data provided by the Ocean Drilling Program (ODP). The ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. Research funding was provided through special ODP postcruise and small research grants by the UK Natural Environmental Research Council.

9 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS 9 REFERENCES Billups, K., Channell, J.E.T., and Zachos, J.C.,. Late Oligocene to early Miocene geochronology and paleoceanography from the subantarctic South Atlantic. Paleoceanography, 7:. Cande, S.C., and Kent, D.V., 99. A new geomagnetic polarity time scale for the Late Cretaceous and Cenozoic. J. Geophys. Res., 97:97 95., 995. Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic. J. Geophys. Res., : Exon, N.F., Kennett, J.P., Malone, M.J., et al.,. Proc. ODP, Init. Repts., 89 [CD- ROM]. Available from: Ocean Drilling Program, Texas A&M University, College Station TX , USA. Fulthorpe, C.S., Carter, R.M., Miller, K.G., and Wilson, J., 996. The Marshall Paraconformity: a mid-oligocene record of inception of the Antarctic circumpolar current and coeval glacio-eustatic lowstand. Mar. Pet. Geol., :6 77. Miller, K.G., Aubry, M.P., Khan, M.J., Melillo, A.J., Kent, D.V., and Berggren, W.A., 985. Oligocene Miocene biostratigraphy, magnetostratigraphy, and isotopic stratigraphy of the western North Atlantic. Geology, :57 6. Paul, H.A., Zachos, J.C., Flower, B.P., and Tripati, A.,. Orbitally induced climate and geochemical variability across the Oligocene/Miocene boundary. Paleoceanography, 5:7 85. Pfuhl, H.A., McCave, I.N., Schellenberg, S.A., and Ferretti, P., in press. Changes in Southern Ocean circulation in late Oligocene to early Miocene time. In Exon, N.F., Kennett, J.P., and Malone, M.J. (Eds.), Cenozoic Paleoceanography and Tectonics in the Expanding Tasmanian Seaway. Am. Geophys. Union, Geophys. Monogr. Shackleton, N.J., and Hall, M.A., 997. The late Miocene stable isotope record, Site 96. In Shackleton, N.J., Curry, W.B., Richter, C., and Bralower, T.J. (Eds.), Proc. ODP, Sci. Results, 5: College Station, TX (Ocean Drilling Program), Shackleton, N.J., Hall, M.A., Raffi, I., Tauxe, L., and Zachos, J.,. Astronomical calibration age for the Oligocene/Miocene boundary. Geology, 8:7 5. Shipboard Scientific Party, 999a. Site : North Chatham Drift a -Ma record of the Pacific Deep Western Boundary Current. In Carter, R.M., McCave, I.N., Richter, C., Carter, L., et al., Proc. ODP, Init. Repts., 8, 8 [CD-ROM]. Available from: Ocean Drilling Program, Texas A&M University, College Station, TX , U.S.A., 999b. Site : Rekohu Drift from the K/T boundary to the Deep Western Boundary Current. In Carter, R.M., McCave, I.N., Richter, C., Carter, L., et al., Proc. ODP, Init. Repts., 8, 7 [CD-ROM]. Available from: Ocean Drilling Program, Texas A&M University, College Station, TX , U.S.A.

10 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS Figure F. Map of the South Tasman Rise and adjoining areas indicating the drill sites studied. Site 69 was abandoned and is not discussed meters

11 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS Figure F. A. Comparison of the benthic stable isotope records for Sites 7 and 9 (Billups et al., ) across the late Oligocene early Miocene providing the basis for matching up the Mi-a and Mi- events. B. A detailed comparison of the Mi- events including the magnetic reversal points at Site 7 show that the pattern of the characteristic double-peak of this event is different between sites. Ages are after Cande and Kent (995). MR = magnetic reversal. A 7 depth (mbsf) benthic δ 8 O ( ) 9 benthic δ 8 O ( ) Mi-a Mi t B 7 benthic δ8o ( ) MR Age (Ma) 9 benthic δ 8 O ( ) 9 age (Ma)

12 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS Figure F. Bio- and magnetostratigraphic data for Sites 68 and 7, as of August (errors given based on lower and upper samples confining biostratigraphic datums) (see also Pfuhl et al., in press; Stickley et al., this volume), for the interval from 8 to Ma including additional control points for the Oligocene and early Miocene interval based on similarities between the records (see Table T, p., and text for details). At all four sites we follow largely the sedimentation pattern suggested by the magnetostratigraphy (MR = magnetic reversals). Our control points are consistent within the magnetostratigraphic outline including a few biostratigraphic datums (NF = nannofossils, PF = planktonic foraminifers, D = diatoms, RD = radiolarians, and DF = dinoflagellates), with the exception of Site. Here extremely low sedimentation rates suggest difficulties in identifying the magnetic reversals across the Oligocene/Miocene boundary. Our age models suggest there is no hiatus at the level of the Marshall Paraconformity at Site 68, but a relatively strong reduction in sedimentation rate across the Oligocene/Miocene boundary (see text for discussion). Scales for all four sites are identical. Ages are after Cande and Kent (995) NF PF D RD DF MR Alt. MR Control points Error Sed. rate (cm/k.y.) Marshall Paraconformity early late early late Miocene Oligocene Eocene Age (Ma)

13 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS Figure F. A. The record of weight percent sand (>6 µm) indicates two important changes between and 7.6 mbsf (no samples) and 6.69 and 5. mbsf, while the carbonate content increases across the core gap from 77.6 to 76.5 mbsf. B. Increases in benthic and bulk δ C occur over a number of samples from ~ to 98 mbsf, while a decrease in benthic δ C from to 75.6 mbsf appears more gradual. A Site 7 B Benthic δ 8 O ( ) Bulk δ C ( ) Sand (wt%).8.. Mi-a Mi Bulk CaCO (%) Benthic δ C ( )

14 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS Figure F5. A. The record of weight percent sand experiences a strong decrease matching the increase in carbonate content from 7 to 7.8 mbsf ( mcd). A second increase in carbonate content occurs at mbsf. B. Increases in benthic and bulk δ C occur over a number of samples from 69.6 to 69.6 and 69.6 to mbsf. C. The strong increase in benthic δ 8 O at mbsf is identified as the onset of the Mi- event. A 5 Site B C Benthic δ 8 O ( ) Bulk δ C ( ) Sand (wt%) onset Mi Benthic δ C ( ) Bulk CaCO (%)

15 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS 5 Figure F6. A. The record of weight percent sand experiences a sharp drop at ~58.6 mbsf. B. The bulk δ C record shows two strong increases at and mbsf, while the benthic δ C record experiences a strong decrease at.56.6 mbsf. C. A strong increase in the benthic δ 8 O record at.7.7 mbsf resembles the onset of the Mi- event at the other sites. A 6 Site B C Benthic δ 8 O ( ) Bulk δ C ( ) Sand (wt%).... onset Mi Benthic δ C ( ) Bulk CaCO (%)

16 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS 6 Figure F7. Comparison of records of carbonate content obtained on the bulk and fine fraction of the sediment showing strong overlap. Bulk Fine 68 CaCO (%) 7 CaCO (%) CaCO (%) CaCO (%)

17 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS 7 Figure F8. Sand, carbonate content, and organic carbon content (TOC) indicate a strong transitional interval from ~765 to 75 mbsf. An increase in carbonate content at mbsf is closely followed by a decrease in sand at 86. mbsf. 6 7-pt run. ave. Site 68 Sand (wt%) 5-pt run. ave. Bulk Fine 8 6 CaCO (%) Fine TOC (%) 8 5-pt run. ave

18 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS 8 Figure F9. Biogenic and lithogenic composition of the coarse fraction (>6 µm) of the sediment suggests two changes in sedimentation at ~699 and 58 mbsf. An increase in dissolution occurs at 86. mbsf. -pt run. ave. Site 68 Pyrite Quartz Glauconite Dissolution Clear spicules Opaque spicules

19 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS 9 Figure F. A D. Comparison of the different records used in defining additional control points between Sites 7 against their revised ages. The records reveal good matches at different times depending on the parameter. Ages from Cande and Kent (995). A 95 Bulk CaCO (%) 7 B Benthic δ 8 O ( ) C.6 Benthic δ C ( ) 7 D..8 Bulk δ C ( ) Age (Ma) Age (Ma)

20 EARLY OLIGOCENE EARLY MIOCENE AGE MODELS Figure F. Histogram depicting changes in sedimentation rates based on interpolation between datums listed in Table T, p.. Ages from Cande and Kent (995). Sed. rate (cm/k.y.) Age (Ma)

21 Table T. Overview of the fossil, magnetic reversal and additional datums used in developing the age models for the Leg 89 sites. Age (Ma) Event 7 (mbsf) Age (Ma) Event (mbsf) Age (Ma).76 MR-Onset C5ACn MR-Onset C5ACn MR-Onset C5ACn 85.. NF-FO Triquetrorhabdulus rugosus..78 MR-Termination C5ADn MR-Termination C5ADn MR-Termination C5ADn PF-FO Orbulina suturalis D-FO Actinocyclus ingens 9..6 MR-Onset C5ADn MR-Onset C5ADn PF- FO Praeorbulina curva 6.9 var. nodus.6 MR-Onset C5ADn MR-Termination C6n 7..8 MR-Termination C5Bn.n NF-FO Calcidiscus premacintyrei MR-Termination C5Bn.n 9.. MR-Onset C6n MR-Onset C5Bn.n NF-FO Sphenolithus heteromorphus MR-Onset C5Bn.n benthic δ C. 5. MR-Termination C5Bn.n NF-LO Sphenolithus belemnos MR-Termination C5Bn.n 97.5 Top of gap MR-Onset C5Bn.n NF-FO Sphenolithus belemnos.9 6. MR-Termination C5Cn.n 8. Bottom of gap MR-Termination C5Cn.n.. PF-LO Tenuitella munda. 6.9 MR-Onset C5Cn.n.5. 7-benthic δ 8 O MR-Onset C5Cn.n. PF-FO Globoturborotalita woodi MR-Termination C5Cn.n..8 7-bulk δ C MR-Termination C5Dn 6.9. PF-FO Globoquadrina dehiscens MR-Onset C5Cn.n..5 7-benthic δ C MR-Termination C5En.75 7-Mi peaks MR-Onset C5Dn. Top of gap MR-Onset C5En..9 7-Mi peaks MR-Onset C5En 8. Bottom of gap MR-Termination C6n MR--Termination C7n.n MR-Termination C6n benthic δ 8 O MR-Onset C6n. 5.8 MR--Onset C7n.n Mi-a Top of gap bulk δ C MR--Termination C7An Mi-a Bottom of gap benthic δ C MR--Termination C9n MR-Onset C6AAn bulk δ C bulk δ C MR--Onset C9n MR-Termination C6AAr.n benthic δ C benthic δ C MR--Termination Cn.n MR-Termination C6AAr.n 7.9. D-FO Rocella vigilans-~top MPC benthic δ 8 O MR--Onset Cn.n MR-Onset C6AAr.n bulk δ C MR--Termination Cn.n MR-Termination C6Bn.n MR-Termination Cn.n MR--Termination Cn.n 76. Top of gap MR-Onset Cn.n MR--Onset Cn.n MR-Termination C6Bn.nbottom MR-Termination Cn.n MR--Termination Cn.n 78.8 of gap.55 MR-Onset C6Cn.n MR-Onset Cn.n-~top MPC MR--Onset Cn.n MR-Termination C6Cn.n MR--Termination Cn MR-Onset C6Cn.n MR--Onset Cn 7..8 MR-Onset C6Cn.n MR-Termination C7n.n MR-Onset C7n.n MR-Termination C7An MR-Onset C7An MR-Termination C8n.n NF-LO Chiasmolithus altus MR-Onset C8n.n MR-Termination C9n MR-Onset C9n. 8.8 MR-Termination Cn.n MR-Termination Cn.n.. D-FO Rocella vigilans - ~top MPC Notes: FO = first occurrence, LO = last occurrence. D = diatom, DF = dinocyst, NF = nannofossil, PF = planktonic foraminifer, RD = radiolarian. MR = magnetic reversal. MPC = Marshall Paraconformity. Gap = recovery gap. Event (mbsf) Age (Ma) Event 68 (mbsf) H.A. PFUHL AND I.N. MCCAVE EARLY OLIGOCENE EARLY MIOCENE AGE MODELS