Bralower, T.J., Premoli Silva, I., and Malone, M.J. (Eds.) Proceedings of the Ocean Drilling Program, Scientific Results Volume 198
1. LEG 198 SYNTHESIS: A REMARKABLE 120-M.Y. RECORD OF CLIMATE AND OCEANOGRAPHY FROM SHATSKY RISE, NORTHWEST PACIFIC OCEAN1
Timothy J. Bralower,2 Isabella Premoli Silva,3 and Mitchell J. Malone4
1Bralower, T.J., Premoli Silva, I., and ABSTRACT Malone, M.J., 2006. Leg 198 synthesis: A remarkable 120-m.y. record of climate and oceanography from Samples collected from a depth transect of eight sites during Ocean Shatsky Rise, northwest Pacific Ocean. Drilling Program Leg 198 to Shatsky Rise contain a remarkable sedimen- In Bralower, T.J., Premoli Silva, I., and tary record of surface and deepwater circulation in the tropical Pacific Malone, M.J. (Eds.), Proc. ODP, Sci. over the past 120 m.y. In addition, basement sills recovered provide Results, 198, 1–47 [Online]. Available valuable constraints on the age and origin of the volcanic foundations from World Wide Web:
INTRODUCTION
The sedimentary record recovered over the course of several decades of deep-sea drilling has yielded a wealth of information on Earth’s cli- mate system. Pelagic sedimentary sections provide some of the most faithful time series of climate states from the Middle Jurassic to the Ho- locene. Potentially more significant, however, are the clues within the sedimentary archives of the mechanisms and processes that drive cli- mate change and the effect of that change on biotic evolution and geochemical cycling (e.g., Schlanger et al., 1987; Dickens et al., 1995; Leckie et al., 2002). The early decades of deep-sea drilling, largely associated with the Deep Sea Drilling Project (DSDP), involved a great deal of exploratory coring in locations where the stratigraphy of the sedimentary section was undocumented and poorly constrained. More recently, however, knowledge from previous drilling expeditions combined with the avail- ability of high-resolution multichannel seismic reflection data have al- lowed us to target particular time slices at locations where the sedimentary section looks essentially complete. In addition, hydraulic piston coring technology developed during the Ocean Drilling Program (ODP) allows us to obtain high-quality records when these locations are revisited. F1. Bathymetric map of Shatsky Shatsky Rise, a medium-sized large igneous province (LIP) in the Rise, p. 26. west-central Pacific (Fig. F1) was the target of three DSDP expeditions, 1207 (3101 m)
2000 Legs 6, 32, and 86, and ODP Leg 132 (Fischer, Heezen et al., 1971; Lar- 4000 1208 (3346 m) Depth (m)
ο 39 son, Moberly, et al., 1975; Heath, Burkle, et al., 1985; Natland, Storms, ο 38 1209 (2387 m) 1212 (2681 m) ο 1210 (2573 m) 37
ο 1211 (2907 m) ο 36 164 1214 (3402 m) ο 3 Latitu ο 1213 (3883 m) 16 et al., 1993). The quality of the records from the older legs was ham- 35 ο de 162 ο ο 34 161 ο ο 160 33 ο 159 ο ο gitude 32 on pered by rotary and spot-coring as well as low recovery in the Creta- 158 L ο ο 31 157 ο 56 ShatskyShatsky RiseRise ο 1 ceous because of the presence of persistent chert. Yet these legs revealed 30 the potential of Shatsky Rise sediments to provide high-quality records T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 3 of Cretaceous and Paleogene climate. This interval is located at shallow burial depths on the rise and thus is relatively unaltered by burial dia- genesis (e.g., Schlanger and Douglas, 1974). Leg 198 was designed to re- cover high-quality sedimentary records of this age along a depth transect (Bralower, Premoli Silva, Malone, et al., 2002). The transect has the potential to provide two-dimensional reconstructions of ocean tem- F2. Generalized climate curve for perature, chemistry (i.e., carbonate solubility and oxygenation), circula- Cretaceous and Paleogene, p. 27. tion, and biology through some of the most fundamentally interesting Benthic δ18O (‰) -1.5 -0.5 0.5 1.5 2.5 3.5 20 Mio. 25 intervals of climate change during the entire Phanerozoic. 30 Eocene/Oligocene Transition Oligocene 35
The mid-Cretaceous (~120–80 Ma) and early Paleogene (~60–45 Ma) 40
45 Eocene were characterized by equable climates including low latitudinal ther- 50 55 PETM Paleocene 60 biotic event Paleocene mal gradients, lack of extensive cryosphere, a relatively warm deep 65 K/T
MME 70 Maast. ocean, and high atmospheric pCO2 levels (Fig. F2) (e.g., Barron and Age (Ma) 75 80 Campanian
85 Sant. Washington, 1985; Berner, 1994). These “greenhouse” intervals also Coniac. 90 Tur. 95 Cenom. contain significant abrupt and transient warming events that led to ma- 100
105 OAEs Albian jor changes in oceanic environments, profound turnovers in marine 110 115 Aptian 120 OAE1a communities including extinctions, and perturbations to global chemi- 125 Barrem. cal cycles. Examples include the Paleocene/Eocene Thermal Maximum Warm Cold (PETM) (e.g., Kennett and Stott, 1991; Dickens et al., 1995; Katz et al., 1999; Norris and Röhl, 1999) and Cretaceous Oceanic Anoxic Events F3. Stratigraphy and lithology, (OAEs) (e.g., Schlanger and Jenkyns, 1976; Jenkyns, 1980; Arthur et al., Sites 1207–1214, p. 28.
Northern Central Southern High High High 1985, 1988). Leg 198 was designed to understand the causes, nature, 1207 1208 12091210 1212 1211 1214 1213 Water depth (m) 3101 3346 2387 2573 2681 2907 3402 3883 Age 0 Pleistocene late Plio. 5 early and mechanics of the long-term Cretaceous and Paleogene “green- late 10 middle
20 Miocene early
? house” as well as of the transient events during this period. The loca- late
30 Oligo. early E/O transition late 40 tion of Shatsky Rise in the tropical Pacific during the interval of interest middle Eocene 50 early PETM late Paleocene biotic event 60 is fundamentally significant—the aerial extent and importance of the Paleoc. early K/T Maast. 70 MME Age (Ma) Camp. Pacific in global circulation make this a critical target for investigation 80 Sant. Coniac.
90 Late Cretaceous Tur. of warm climatic intervals. Yet, this ocean basin contains far less com- Cenom. 100
Albian 110 plete records than the Atlantic, Indian, and Tethyan Oceans. During Aptian 120 OAE1a Barrem.
Early Cretaceous Haut. 130 Leg 198, one site was drilled on each of the North and Central Highs of Val. Berrias. 140 L. Jur. Tith. Shatsky Rise (Sites 1207 and 1208, respectively) and six sites were Nannofossil ooze Clay Chalk Chert Porcellanite drilled on the Southern High (Sites 1209–1214) (Bralower, Premoli Silva, Malone, et al., 2002). F4. Stratigraphic summary for An impressive 140-m.y. package of pelagic sediment was recovered at 145–130 Ma, p. 29. the eight sites (Figs. F3, F4, F5, F6, F7, F8, F9). In addition, the first Biozones 1207 1214 1213 Age Paleomag. Epoch (Ma) Foraminifers Nannofossils Radiolarians 3100 m 3402 m 3883 m G. ferreolensis UAZ 95 NC7 NC7a Leupoldina cabri NC6b
120 Aptian NC6 22 NC6a cores from the basement of Shatsky Rise were recovered at Site 1213. CM0 (121) Globigerinelloides blowi 20 m 23 m 1213B-7R-1 CM1 NC5d-e 1214A-21R to 21 to 9R-1, 18 cm CM2 Acanthocircus carinatus 24R-1, 47 cm H. similis- NC5 carinatus c. A. perforatus c. A. CM3 H. kuznetsovae A.c.transi 125 torius Detailed descriptions and preliminary interpretations of the cores are 75 m (126) NC5c CM4 1207B-42R- 20 CM5 CC to 1214A-24R-1, CM6 NC5a-b 49R-CC 72 cm, to CM7 1213B-9R-1, 25R-1, 22 cm CM8 Hedbergella sigali - 47 cm, to 27R-1, 38 cm CM9 "H. delrioensis" NC4b 19 TD - 1207B CM10 622.8 m provided in Bralower, Premoli Silva, Malone, et al. (2002) and Bralower 130 NC4 >15 m CM10N NC4a 18 TD - 1214A (131.5) 235.9 m CM11 17 NK3b CM11A Early Cretaceous CM12 Hedbergella sigali- NK3 CM12A H. aptica 16
et al. (2002). A broad array of exciting investigations have been con- Depth (mbs) CM13 NK3a 135 CM14 (135.8) NK2b CM15 NK2 15 NK2a CM16 Conoglobigerina gulekhensis NK1
ducted on the Leg 198 cores, resulting in a number of publications in Berriasian Valanginian Hauterivian Barremian CM17 140 14 NJKd CM18 (141.6) 174 m NJKc CM19n-1 NJK ? CM19 NJKb the open literature and in this volume. This summary is organized in CM20n-1 NJKa 46.5 m Not zoned TD - 1213A Pseudodictyomitra carpaticaPseudodictyomitra Cecrops septenforatus CM20 13 494.4 m 145 NJ20b Tithonian NJ20 Late Jurassic CM21 NJ20a Chalk OAE1a terms of the chronological history of Shatsky Rise, beginning with erup- Chert Volcanics
Porcellanite Hiatus tion of its basement foundation and followed by the progressive deposi- Claystone tion of its sedimentary carapace. F5. Stratigraphic summary for 130–80 Ma, p. 30.
CONSTRAINTS ON THE ORIGIN Biozones 1207 1208 1212 1214 1213 Age Paleomag. Epoch (Ma) Foraminifers Nannofossils 3100 m 3345 m 2681m 3402 m 3883 m 80 0.4 m C33r 1208A-41X- 1207B-10R- 2, 120 cm, (83.5) CC to to 41X-CC 19R-CC 1213A-7R- C34n CC (85.8) 86 m OF SHATSKY RISE 1212B-24H- 6, 30 cm <0.1 m
(89.0) 90 0.01 m Late Cretaceous
(93.5) 1212B-24H-6, 30.5 cm, to 27H-CC
1213A-
Cenomanian Turonian Coniac. Sant. Camp. 8R-CC to 1213B- At Site 1213, a series of at least three basaltic sills with a total thick- (98.9) 10 m 9R-1, 1214A-2R 18 cm 100 TD - 1212B to 10R-CC 207.6 m ness of 46 m was recovered at the base of the sedimentary section. The 1208A-42X 1207B-19R- 84.5 m Albian CC to <9 m Depth (mbsf) 49R-CC TD - 1208B 392.3 m 1214A-11R to 19R-CC 110 units underlie limonitic breccias, evidence for hydrothermal activity as- 87 m
(112.2)
1214A-20R to 24R-1, 47 cm sociated with sill intrusion. The sills are interpreted as a widespread plu- Early Cretaceous 200 m
120 CM0 (121) 39 m
CM1 tonic event associated with the latest stages in the construction of the 287.5 m CM2
CM3 Barremian Aptian TD - 1207B (126) CM4 622.8 m 1214A-24R-1, CM5 CM6 72 cm, to CM7 25R-1, 22 cm CM8 1213B-9R-1, CM9 47 cm Southern High of Shatsky Rise. Sediment interbedded in the sills yields CM10 130 Hauterivian >15 m TD - 1214A 235.9 m Nannofossil Chalk Chert Porcellanite ooze
Claystone OAE1a Hiatus T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 4 an earliest Berriasian age based on radiolarian and nannofossil assem- F6. Stratigraphic summary for 85– blages (H. Kano, pers. comm., 2005; Bown, this volume) and the sills 60 Ma, p. 31.
Age Biozones 1207 1208 1209 1210 1212 1211 1213 40 39 Paleomag. Epoch (Ma) Foraminifers Nannofossils 3100 m 3345 m 2387 m 2573 m 2681 m 2907 m 3883 m 60
themselves yield a mean Ar- Ar incremental heating age of 144.6 ± late Selan 1209A-24H- 1210A-23H- 1212B-10H- 1211A-15H- 5, 26 cm, 3, 100 cm, 5, 145 cm, 2, 27 cm, to 1209C- to 24H-4, to 11H-7, to 15H-4, 15H-3, 51 cm 24 cm 146 cm 96 cm early Paleocene 0.8 Ma (Mahoney et al., 2005). These data provide a constraint for the Danian
13 m 11 m 11 m 4 m 65 (65.0) 1212B-11H- CC to 1211A-15H- 1212B-24H-6, 4, 146 cm, 1209A-25H- 1210A-24H- to 1211B- age of the origin of Shatsky Rise and a minimum estimate for the age of 6,125 cm, 4, 51 cm 0 cm 19H-CC to 1209C- to 1210B- 22X-7, 42H-6, 56 cm 121 cm
the Jurassic/Cretaceous boundary that is slightly older than recent esti- Maastrichtian 36 m 70 62.5 m TD - 1211B 169.9 m
(71.3) TD - 1209C mates of ~141 Ma published by Bralower et al. (1990) and Pálfy et al. 307 m
96 m
(2000) but consistent with the 145.5-Ma estimate of Gradstein et al. 75
Late Cretaceous ?
1213A-7R-1, 0-84 cm 157 m 1212B-24H-6, 1 cm 1208A-36X-3, 50 cm, to 0.01 m <1 m 41X-CC TD - 1210B 377 m (2004). The new Jurassic/Cretaceous boundary age combined with mag- ? Campanian 1207A-18H-5 115 cm, to 1207B-15R-CC netism data (e.g., Nakanishi et al., 1999; Sager et al., 1999) suggest that 80 54 m
(83.5) Nannofossil Nannofossil Chalk the largest part of the rise was emplaced at rates between 1.2 and 4.6 ooze ooze with clay 134 m Condensed
Sant. Chert Hiatus sequence 85 km3/yr, rates similar to other large flood basalt provinces (Coffin and El- The whole interval is missing at Site 1214 dholm, 1994; Sager, in press; Sager et al., this volume; Tominaga et al., this volume) (Fig. F10). F7. Stratigraphic summary for 65– Various models have been proposed for LIPs including Shatsky Rise. 40 Ma, p. 32.
These include a mantle plume model involving rapid eruption at a Biozones 1208 1209 1210 1212 1211 Age Paleomag. Epoch (Ma) Foraminifers Nannofossils 3345 m 2387 m 2573 m 2681 m 2907 m 40 0.5 m
CP14 1209A-15H- 1210B-16H-4, 1211C-10H-6, plume head tapering off to slower eruption at a plume tail (Sager and CC to 101 cm, to 0 cm, to 1209C-11H- 1210A-20H-3, 1211A-11H-4, Han, 1993). A mantle plume model is supported by the fact that 2, 2 cm 46 cm 46 cm
45 middle CP13 Lutetian Bart. Shatsky Rise formed very rapidly at a triple junction of ocean ridges af- 3.75 m
Eocene 1211A-11H-4, 1212B-7H-6, 46 cm, to 1211B-12H-5, CP12 135 cm, to 9H-5, 46 cm 50 cm >4 m
50 ter the triple junction had jumped 800 km (e.g., Nakanishi et al., 1999; 1208A-36X- 1211B-12H-5, 46 cm, to CP11 2, 41 cm, to 12H-6, 46 cm 36X-CC, 42 cm 1.5 m
CP10 54 m 40 m 1211B-12H-6,
early 46 cm, to 1211A-13H-5, Sager et al., 1999) and by the rapid rates of the initial emplacement fol- 128 cm 1209C-11H- 1210A-20H-3,
Depth (mbsf) 2, 2 cm, to 46 cm, to CP9 1209B-22H- 1210B-20H-2, 1, 70 cm 50 cm 0.75 m 17 m 6.5 m 55 (55.0) 2 m 2 m lowed by gradually diminishing volcanism. A second alternative, the CP8 ? 1211A-13H- ? 5, 128 cm, to 1211C-15H- CP7 8 cm 4, 81cm barren CP6 1209B-22H- 1210B-20H-2, 1212B-9H-5, 1, 70 cm, to 50 cm, to 50 cm, to ? 1209C-15H- 1210A-24H-4, 1212B-11H-7, CP5 3, 96 cm 51 cm 24 cm “perisphere” model, involves a large asteroid impact on oceanic crust late CP4 16 m 60 Selandian Ypresian 1211A-15H-2,
Paleocene CP3 that excavates the underlying mantle, leading to eruption of an LIP 27 cm, to 15H-4,146 cm
CP2 early (Rogers, 1982). This model has recently been proposed for Ontong Java Danian Thanetian 38 m 22 m 4 m CP1 40 m 65 The whole interval is missing at Sites 1207, 1213, and 1214 Nannofossil Condensed Hiatus Plateau (OJP) by Ingle and Coffin (2004) and Tejada et al. (2004). The ooze with clay sequence two origin models should generate different sill geochemistry. Nd-Pb-Sr isotope values of the sills exhibit a Pacific mid-ocean-ridge F8. Stratigraphic summary for 45– basalt (MORB) signature (Fig. F11) (Mahoney et al., 2005) that is consis- 20 Ma, p. 33.
Biozones 1208 1209 1210 1211 tent with a perisphere origin but not a plume-head origin, which would Age Paleomag. Epoch (Ma) Foraminifers Nannofossils 3345 m 2387 m 2573 m 2907 m 20 Burdigal. N5 1208A-35X-4, (part) 10 cm, to 1209A-12H-5, 35X-5, 12 cm 1 cm, to 12H-6, 52 cm
be associated with ocean island-like rather than MORB-like isotopic sig- early
Miocene N4
(23.8) <1.1 m 1.5 m natures. Although a contemporaneous impact to that which formed the 25 P22 late Chattian Aquitanian
>70-km-diameter Morokweng crater in South Africa dated at 144.7 ± 1.9 P21b
P21a Oligocene and 146.2 ± 1.5 Ma (Koeberl et al., 1997) may have led to the formation 30 P20 P19 early
1208A-35X-5, P18 12 cm, to 1210A-13H-2, 1211C-8H-7, 36X-2, 40 cm 1209A-13H-4,,
Depth (mbsf) (33.7) 70 cm, to 30 cm, to P17 45 cm, to of Shatsky Rise, such an impact would have caused massive disruption 14H-2, 46 cm 1211A-10H-2, <5 m 1209C-3H-6, 134 cm 31 cm P16 5 m 35 late
Priabonian ? 8 m of the seafloor that is not observed on seismic lines near the Southern P15
1211A-10H-4, <5 m 1210A-14H-4, 108 cm, to 45 cm, to 1211C-10H-6, 1210B-16H-4, 1 cm 1209A-15H-3, 101 cm P14 127 cm, to 1209A-17H-2,
Bartonian Rupelian 7 m
High. Moreover, an impact would have caused near-instantaneous LIP Eocene 40 51 cm P13 1211A-10H-4, 108 cm, to
middle 11H-3, 46 cm formation, which is clearly not the case for Shatsky Rise. A third, com- P12 Lutetian P11 >20 m 23 m 7.5 m 45 The whole interval is missing at Nannofossil Condensed promise model is that a large impact (i.e., Morokweng) may have Sites 1207, 1212, 1213, and 1214 Hiatus ooze sequence strengthened existing mantle plumes on the other side of Earth from the impact site (Abbott and Isley, 2002), but once again this scenario would not produce a MORB basement signature. F9. Stratigraphic summary for 25– An alternative to the perisphere and plume models is that the ridge 0 Ma, p. 34. Age Biozones 1207 1208 1209 1210 1212 1213 1211 Paleomag. Epoch (Ma) Foraminfers Nannofossils 3100 m 3345 m 2387 m 2573 m 2681 m 2883 m 2907 m 0
Pleist. Calabrian jump that occurred around the time that Shatsky Rise formed led to a 1213A-1R 1211A-1H (1.77) to 1207A-1H 1208A-1H 1209A-1H 1210A-1H 1212A-1H 6R-4, to Gelasian to to to to to 95 cm 7H-2, 17H-2, 34X-CC 10H-2 10H-CC 8H-3, 9 cm late 107 cm Piacenz. 10 cm
change in the stress regime (i.e., decompression), which promoted Plioocene 54.6 m early 5 55 m (5.32)
melting of anomalously warm lithosphere (Sager, in press). This alterna- Messinian Zanclean 86.4 m 91 m 52 m
1210A-11H tive would explain the MORB geochemical signature and avoid poten- 1209A-10H-3 to 12H- 150 m 10 to CC 11H-CC tial difficult explanations of the coincidence of the ridge jump and 16.8 m
Depth (mbsf) 1207A-17H- 315 m 1212A-8H-3,
Serravallian 2, 107 cm, 1209A-12H-1, 10-100 cm middle late to 18H-4, 1 cm, to 80 cm ? 12H-4, 0.90 m 15 90 cm 1211A-7H-2, either mantle plume activity or impact. However, the notion that de- 12 m 10-20 cm Miocene 5.4 m
Langhian 0.10 m 1208A-35X- 1 cm, to 35X-5, compression could cause such significant melting is untested. Clearly, 12 cm 19 m
1207A-18H- 1209A-12H- 5, 25 cm, 4, 91 cm, to 18H-5, ? Burdigalian Tortonian to 102 cm 12H-6, 20 52 cm 3.8 m additional basement sampling and model testing are required to resolve early barren ?
0.75 m 2.6 m the origin of Shatsky Rise. Aquitanian (23.80) 6.20 m Chattian late 25 Oligo. Nannofossil Condensed At Site 1214 Holocene-Pleistocene = 6.9 m. Hiatus Mn crust ooze with clay sequence T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 5
Cretaceous Oceanic Anoxic Events: Production F10. Magnetic polarity interpreta- of Highly Organic Rich Horizons tion of Lower Cretaceous sedi- ments, p. 35.
Inclination (°) -20 0 20 40 60 80 Polarity Greenhouse climate conditions in the mid-Cretaceous led to a trans- 360 formation of marine environments that caused rapid turnover of eco- 19R 370 systems and profound changes in biogeochemical cycles. One of the 20R 380 most remarkable consequences of the changes in climate and ocean cir- 21R CM16? 390 22R culation was the widespread deposition of organic carbon (Corg)-rich Depth (mbsf) CM17? 400 sediments, also known as “black shales,” during OAEs (Schlanger and 23R CM18?
410 Jenkyns, 1976; Jenkyns, 1980; Sliter, 1989; Arthur et al., 1988; Bralower 24R
420 et al., 1993; Erbacher and Thurow, 1997; Wilson and Norris, 2001; 25R Leckie et al., 2002). Although the ultimate trigger(s) of OAEs remain elusive, there is growing evidence for a link with massive volcanism as- sociated with the emplacement of LIPs (e.g., Vogt, 1989; Larson, 1991; F11. Geochemistry of diabase sills, Sinton and Duncan, 1997; Larson and Erba, 1999; Snow et al., 2005). p. 36.
206 204 A ( Pb/ Pb)t 17.5 18.0 18.5 19.0 19.5 20.0 Thus, one of the goals of Shatsky Rise drilling was to determine the +12
+10 East Pacific record of OAEs in the northwest Pacific and their stratigraphic relation- Rise +8 Manihiki Easter-Nazca
(t) Ridge +6 Ontong Nd ship with increasingly well constrained ages for LIPs. ε Java +4 1179D Hess Rise, 464
+2 Shatsky Rise Highly carbonaceous sedimentary rocks that correlate to early Aptian Manihiki 1213B 0 D9, D14 B 39.5 Easter-Nazca OAE1a were recovered at Sites 1207 and 1213 (Fig. F12). At Site 1207, Ridge
39.0
t Manihiki
OAE1a is found within 45 cm of finely laminated, dark brown radiolar- Pb) 38.5 204 Ontong Pb/ Manihiki Java 38.0 208 ian claystone. Organic carbon contents in these horizons (up to 35 ( East 37.5 Pacific Rise wt%) are among the highest values measured from OAEs and are similar 37.0 C 10
Avg. Ontong Java, to values measured in contemporaneous units from other Pacific deep- Kwaimbaita Avg. N-MORB 1 1213B 1213B Concentration/ primitive mantle 1213B sea sites (e.g., Baudin et al., 1995; Jenkyns, 1995). A detailed analysis of Cs Rb Ba Th U Nb Ta La Ce Pr Pb Sr Nd P Hf Zr Sm Eu Ti Gd Tb Dy Y Ho Er Tm Yb Lu carbon isotopes measured on the organic fraction of the sediments at Site 1207 (Dumitrescu and Brassell, submitted [N1]) allows precise cor- relation to detailed features in curves from other sections (e.g., Mene- F12. Carbonate, Corg, and hydro- gatti et al., 1998). These data demonstrate that the lower part of OAE1a gen index for lower Aptian sedi- was not recovered at Site 1207 but the upper part of the event is rela- mentary rocks, p. 37. Cores of early Aptian OAE1a interval recovered on Leg 198
198-1207B-44X-1 198-1214A-23R-1 198-1213B-8R-1 tively complete. 3100 mbsl 3402 mbsl 3883 mbsl 0 •0.75 •1.38 •NA The Site 1213 Corg-rich units include clayey porcellanites and radio- •0.42 •0.10 •NA larian porcellanites with associated minor tuff containing Corg as high Chert and radiolarian porcellanite as 25 wt%. At Site 1214, a black laminated claystone unit contains a dis- Bioturbated radiolarite and radiolarian porcellanite
•0.5 •10.2 50 •501 tinctive radiolarian assemblage that suggests the recovered sediments Bioturbated limestone
•0.00 •34.7 •0.75 •423 •25.2 correlate to the OAE1a interval (e.g., Erbacher and Thurow, 1997), but Radiolarian claystone with thin, altered tuffs •506 Bioturbated olive-black to Bioturbated olive-black claystone green-black
•0.00 •10.4 low Corg contents (<1.4 wt%) indicate the peak of the event was not re- •523 Length (cm) •0.58 •0.00 •NA covered (Bralower, Premoli Silva, Malone, et al., 2002). Finely laminated radiolarian claystone •0.42 •2.87 •365 •0.00 100 •1.70 Sedimentology of the lower Aptian interval from Sites 1207, 1213, •438 Laminated to bioturbated porcellanite and 1214 was studied in detail by Marsaglia (this volume). She attrib- bioturbated Porcellanite, to laminated, and homogeneous claystone uted a pulse of ash input just below the Corg-rich horizon to the same Dark claystone laminated to bioturbated volcanic event that caused the emplacement of OJP at this time, al- •CaCO3 (wt%) •Corg (wt%) though the ash probably did not originate on OJP or Shatsky Rise. Vol- 150 •HI (mg HC/g OC) canic material in the organic-rich horizon suggests that it cooled and altered in subaerial environments, indicating the presence of nearby emergent volcanoes. Intervals of organic-rich sediments are finely lami- nated and alternate with slightly bioturbated sediments, indicating al- ternating anoxia and oxygenated conditions. The close association of organic-rich and volcanic rocks provides additional evidence of a tem- poral relationship, but not necessarily a direct causal link, between an- oxia and volcanism.
Corg contents of lower Aptian intervals from Sites 1207 and 1213 (up to 35 wt%) are the highest levels recorded for OAE1a and are among the highest recorded for any OAE. These levels attest to extraordinary envi- ronmental conditions during OAE1a. Rock-Eval and gas chromatogra- T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 6 phy–mass spectrometry (GC-MS) analyses of extractable hydrocarbons and ketones indicate that the organic matter in the Corg-rich units is al- most exclusively algal and bacterial in origin. GC-MS data show biom- arkers associated with cyanobacteria. The prevalence and character of bacterial biomarkers suggest the existence of microbial mats at the time of deposition (Dumitrescu and Brassell, 2005). Compounds identified in Leg 198 sediments also include the oldest known alkenones, a char- acteristic biomarker of haptophyte algae (Brassell et al., 2004), extend- ing the geologic record of these compounds by 15 m.y. The high Corg content and its nearly pristine nature suggest highly favorable deposi- tional conditions including high primary productivity, anoxic deepwa- ter environments, and subsequent shallow burial. Organic geochemical data indicate that profound changes in prokaryote and protistan popu- lations were involved in sequestration of Corg during OAE1a (Dumi- trescu and Brassell, 2005). Recovery of mid-Cretaceous sediments at all of the Leg 198 sites was hampered significantly by the presence of widely disseminated chert (e.g., Fontilea et al., this volume). In the poorly recovered intervals, geophysical logs integrated with sedimentological, biostratigraphic, and physical property data are critical to interpreting depositional his- tory. The geophysical logs confirm the presence of a signal from OAE1b even though no organic-rich sediments were recovered in this interval (Fig. F13) (Robinson et al., 2004). This is significant because OAE1a and F13. Correlation of the Hauteri- OAE1b are thought to have had extremely widespread or global extents, vian–Albian between Sites 1207 whereas the other Albian events (OAE1c and OAE1d) are more regional and 1213, p. 38.
(Bralower et al., 1993; Erbacher and Thurow, 1997; Leckie et al., 2002). Logging unit Stage Nanno- zone fossil Hole 1207B 340 UC8
360 UC3-4 UC1-2 It is therefore surprising that OAE2 at the Cenomanian/Turonian 380 Cenom. Hole 1213B Nanno- zone fossil Stage Logging unit 180 400 3 UC0 190 Chalk with thin chert beds (<10 cm 420 NC9b thick) boundary, an event widely regarded as global in extent (e.g., Schlanger NC8c- 200 440 NC9a 1 210
460 Albian NC8b
NC8a-b 220 Chalk with common chert, et al., 1987), does not appear to be present in the logs. This interval is 480 4 porcellanite, and silicified carbonate NC8a 230
Depth (mbsf) 500 240 Depth (mbsf) Chalk with thin chert beds (<10 cm 2 thick); chalk becoming more lithified 520 5 NC7 250 either unconformable or highly condensed on Shatsky Rise. Geophysi- Chalk with common chert, 540 NC7 3 porcellanite, and silicified carbonate;
Aptian 260 NC6 chalk becoming more lithified; ash Aptian layers and black shale also present 560 270 NC6 NC4b 6 580 cal logs suggest that lower Aptian and lower Albian carbonates are rela- 0246810 Haut.e. Albian NC5 Ω 600 Resistivity ( m) ?
620 Haut-Barr. u. ? 0246 8 10 12 tively lithified compared to surrounding sediments, likely a result of Biostrat. correlation Resistivity (Ωm) "Selli" level correlation (gamma ray peak) increased siliceous cementation (Robinson et al., 2004). Increased bio- siliceous production during OAEs in the early Aptian (OAE1a) and early Albian (OAE1b) suggest widespread increased productivity and delivery of biolimiting nutrients from hydrothermal sources.
Late Cretaceous and Paleogene Deepwater Circulation: Identifying Switches in Source Regions
One of the major objectives of drilling the Leg 198 depth transect was to establish deepwater circulation patterns for the Late Cretaceous and Paleogene and elucidate changes over long timescales (millions of years) along with those that took place abruptly in a geologic sense (thousands of years). Drilling recovered a number of abrupt events as well as a nearly complete Campanian–Oligocene section at sites from a range of water depths (Bralower, Premoli Silva, Malone, et al., 2002; 2002). These events and the long-term section have been the subject of a host of investigations aimed at unraveling changes in deepwater cir- culation patterns. A number of techniques including stable isotopes, neodymium isotopes, trace elements, and micropaleontology have been used to pursue these objectives. The predominant ooze and chalk lithology at relatively shallow burial depths contains moderately well preserved foraminifers throughout that are suitable for detailed stable isotope and other geochemical investigations. T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 7
Frank et al. (2005) applied stable and neodymium isotope studies to reconstruct Pacific deepwater circulation patterns in the Maastrichtian. These data suggest that during the early Maastrichtian the source re- gions for deep waters at the paleodepths of Shatsky Rise (strictly speak- ing, intermediate waters) changed from the northern Pacific to the Southern Ocean. An abrupt warming event in the mid-Maastrichtian at ~69 Ma that led to the extinction of inoceramid clams is associated with changes in benthic foraminiferal isotopic values. This mid-Maas- trichtian event (MME) was recovered at three sites on Shatsky Rise and is graphically represented in cores by the abrupt appearance and disap- pearance of abundant inoceramid shells and prisms (Bralower et al., 2002). The MME has previously been interpreted in terms of changing deepwater source regions (MacLeod and Huber, 1996; MacLeod et al., 1996). Data from Shatsky Rise cores reveal a sudden 2°–3°C intermedi- ate water warming, consistent with a switch to a low-latitude source re- gion (Fig. F14) (Frank et al., 2005). Neodymium isotope analyses show F14. Carbon, oxygen, and neody- abrupt excursions during the MME, also indicating a different interme- mium isotope records, p. 39. diate water source. Together, neodymium and benthic isotope data sug- 66
67 gest a temporary Tethyan Sea source for intermediate waters. Tethys has 68
69 been proposed as the source of intermediate and deep waters in other Age (Ma) 70 warm intervals including the mid-Cretaceous (e.g., Brass et al., 1982), 71 72 Site 1209 PETM (e.g., Kennett and Stott, 1991), and early Eocene (Scher and Mar- 66 Site 1210 67 tin, 2004) but has not previously been implicated for the MME. 68
69 Planktonic foraminiferal oxygen isotope values indicate that the Age (Ma) 70 MME is characterized by an abrupt rise (~2°–3°C) in sea-surface temper- 71 72
-5.0 -4.0 -3.0 66 Site 1212 atures (SSTs). Increased productivity during the event is suggested by a εNd 67 δ13 collapse in the surface water C gradient (Fig. F14) (Frank et al., 2005). 68
69 Age (Ma) Changes in planktonic and benthic foraminiferal assemblages also sug- 70
Planoglobulina multicamerata 71 Globotruncana stuartiformis gest higher productivity. Leg 198 data show for the first time a clear sur- Rugoglobigerina rugosa 72 Gavelinella beccariiformis Nuttalides truempyi 0.5 1.5 2.5 1.0 0.0 -1.0 face water perturbation during the MME. Although the exact details δ13C (‰, V-PDB) δ18O (‰, V-PDB) remain to be elucidated, the significant surface water response during the MME suggests that the ultimate origin of the event was climatic and that changes in surface water oceanography were responsible for modi- fied intermediate water circulation and, ultimately, for the inoceramid extinctions. Dutton et al. (2005) investigated long-term changes in surface and deepwater properties and circulation patterns using a combination of δ18O measurements of planktonic foraminifers and coupled δ18O and Mg/Ca analyses of benthic foraminifers (Fig. F15). Interpretation of Mg/ F15. Paleogene stable isotope re- Ca values helps determine how much of the δ18O change is associated sults, p. 40.
25 20 15 10 5°C δD 20 15 10 5°C δD δ δ 25 20 15 10°C s 25 20 15 10°C s 35 with temperature and how much with variation in the isotopic compo- Site 865 Site 1209 Site 865 Site 1209 Mg/Ca-temp (ºC) 28 26 24 40
sition of seawater due to fluctuation in local or regional salinity or in 45 Eocene
SAL 50 ice volume. HTM? Age (Ma) PETM 55
SST trends are similar to those proposed for other Paleogene sections 60 Paleocene early late early middle 65 -3.5 -2.5 -1.5 -0.5 0.5 1.5 -2.5 -1.5 -0.5 0.5 1.5 0.0 2.0 4.0 -2.0 0.0 2.0 4.0 6.0 such as Site 577 on Shatsky Rise (e.g., Corfield and Cartlidge, 1991) and δ18O (‰) δ18O (‰) δ13C (‰) δ13C (‰) Site 865 on Allison Guyot (Mid-Pacific Mountains) (Bralower et al., 1995). Stable SSTs of ~22°C are proposed for the Paleocene and early Eocene. Considerable intersample variability during this interval is used as evidence for significant seasonality, whereas the lower–middle Eocene interval shows less variability and is interpreted to have been characterized by less seasonality. SSTs began to decrease in the late early Eocene and reached 17°C in the middle Eocene. Intermediate water temperatures determined from benthic δ18O values remained steady at 9°–11°C in the Paleocene but increased to 13°C in the latest Paleocene and early Eocene. Cooling of intermediate waters began in the middle Eocene and temperatures decreased to 3.5°C by the late Eocene (Fig. T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 8
F15). Benthic foraminiferal Mg/Ca values help constrain the proportion of the δ18O change that can be attributed to temperature change and to changes in the isotopic composition of seawater as a result of Antarctic glaciation. These data suggest intensification of glaciation in the middle Eocene with accumulation of continental ice sheets of up to ~50% of modern volume. Stable isotope data reveal interesting changes in surface-thermocline and thermocline-deepwater gradients. Notably, there is a collapse in the gradient between thermocline and deepwater δ18O values in the early Eocene (52 Ma) at the peak of the Early Eocene Climatic Optimum (EECO) and at the time when seasonality decreases abruptly. Dutton et al. (2005) proposed that the decreased gradient preconditioned the wa- ter column for a brief switch in intermediate water circulation. This in- terval is marked by one sample with an extremely negative benthic δ13C value and increased δ18O values of planktonic and benthic foraminifers that is tentatively correlated to the “Chron 24n” event, also known in- formally as the “ELMO” event (53 Ma) at Walvis Ridge (Zachos, Kroon, Blum, et al., 2004; Lourens et al., 2005). Dutton et al. (2005) speculated that the event was associated with a transient low-latitude, saline inter- mediate water source. Neodymium isotope measurements of fish teeth provide an indepen- dent means of tracking Late Cretaceous and Paleogene intermediate and deepwater circulation patterns (Fig. F16) (Thomas, 2004, 2005). Site F16. Paleogene neodymium iso- 1209 and 1211 Nd isotope data contain evidence for two end-member tope records, p. 41.
δ18O (‰) sources of deep waters: the Southern Ocean and the North Pacific 3 2 1 0 Ocean. Data from both sites suggest a gradual change in the dominant 35 source of deep waters on Shatsky Rise in the latest Cretaceous from the 40 Southern Ocean to the North Pacific. North Pacific waters continued to 45 bathe Shatsky Rise through the EECO, the time of warmest deep-sea conditions during the Cenozoic. Thomas (2004) proposed that climate 50 Age (Ma) change altered precipitation patterns in source regions of the Southern 55
Ocean and North Pacific Ocean, rendering the latter waters denser than 60 the former. These data demonstrate a 20-m.y. interval of fundamentally 65 different circulation from that of the modern day (Fig. F16). As global
70 deep waters continued to cool starting in the middle Eocene, the source -6 -5 -4 -3 -2 εNd(t) of deep waters shifted back to the Southern Ocean. Deepwater proper- ties changed fundamentally in the Eocene/Oligocene boundary inter- val, which demonstrates a significant lithologic transition at the Shatsky Rise sites (Bralower, Premoli Silva, Malone, et al., 2002; Averyt et al., this volume).
New Interpretations for Extinction Events at the Cretaceous/Tertiary Boundary
The origin of extinctions at the Cretaceous/Tertiary (K/T) boundary (65 Ma) is well understood; however, the effect of the event on marine ecosystems is not well constrained. A remarkable set of cores was taken F17. K/T boundary sections on across the K/T boundary on the Southern High at Sites 1209, 1210, Shatsky Rise, p. 42. 1211, and 1212 (Fig. F17) that has promoted studies aimed at address- Site 1212
Site 1209 Hole A Hole A Site 1210 Site 1211 ing these issues. Hole C Hole B Hole A Hole A The K/T boundary succession is similar at all of these sites (Fig. F17). Hole B Hole C Hole B The boundary lies between uppermost Maastrichtian (nannofossil Zone
CC26) white to very pale orange slightly indurated nannofossil ooze White layer and an 8- to 12-cm-thick layer of basal Paleocene (foraminiferal Zone Pa) grayish orange foraminiferal ooze. The substantial thickness of the Basal Danian ooze T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 9 uppermost Maastrichtian Micula prinsii (CC26) Zone and the lowermost Danian Parvularugoglobigerina eugubina (Pα) Zone indicates that the K/T boundary is relatively expanded on the Southern High of Shatsky Rise compared to other deep-sea sites. The Leg 198 sections represent some of the best preserved and least disrupted deep-sea records of the K/T ex- tinction event and subsequent biotic radiation. The boundary between the uppermost Maastrichtian and the lower- most Paleocene is clearly bioturbated, with an irregular surface contact and pale orange burrows extending 10 cm into the white Maastrichtian ooze. The deepest sections of these burrows yielded highly abundant, minute (<75 µm), planktonic foraminiferal assemblages dominated by triserial Guembelitria with rare Hedbergella holmdelensis and Hedbergella monmouthensis, which suggest the presence of the lowermost Paleocene Zone P0. In the uppermost Maastrichtian (Abathomphalus mayaroensis Zone), faunal preservation is variable from layer to layer, ranging from fair to progressively poorer approaching the top of the Cretaceous: faunas be- come chalky in aspect and tend to dissolve and specimens are highly fragmented, in contrast to the excellent preservation of the minute as- semblages of Zone P0 recovered in the deepest part of the burrows (Pre- moli Silva et al., this volume). Similar good preservation characterizes the still minute Guembelitria-dominated assemblage, containing very rare, minute five-chambered P. e ugu b ina at the top of the burrows and in the millimeter-thick depressions on the irregular surface of the up- permost Maastrichtian white ooze. One centimeter above the lithologic change, planktonic foraminifers start to diversify, acquiring abundant biserial heterohelicids and very subordinate trochospiral taxa (Eoglobige- rina, Globoconusa, and still rare P. eu gu bi na ). Planktonic foraminiferal as- semblages of Zone Pα = total range of P. e u gu bin a ), still dominated by triserial Guembelitria and biserial chiloguembelinids and woodringinids, also contain common larger-sized hedbergellids that disappear some 20 cm above the base of the zone. Such a range of hedbergellids is anoma- lously higher than that known in the literature (i.e., Keller, 1988; Ols- son et al., 1999) and may be an artifact resulting from either reworking or sampling procedure. Quantitative analysis shows that Guembelitria displays an opposite trend with respect to both biserial heterohelicids and P. e ugu bi na . Moreover, at Shatsky Rise biserial and triserial hetero- helicids continue to dominate the assemblages well within Zone P1, and only ~1.5 m above the lithologic change (233.45 meters below sea floor [mbsf]) trochospiral taxa make up 25% of the assemblage concom- itantly with the near total absence of triserial Guembelitria. High-resolution nannofossil assemblage studies across the boundary at Site 1210 by Bown (2005) demonstrate that 10 Late Cretaceous spe- cies survived the K/T boundary extinction, including two species previ- F18. K/T survivor and incoming ously thought to have gone extinct (Fig. F18). Although it is well Cenozoic nannofossils, p. 43.
Survivor species established that ~93% of species went extinct at the boundary, we have Cyclagelo. reinhardtii Watznaueria sp. M. inversus Ne. fossus Zeugrhab. sigmoides 2040 60 80 100 20 40 60 2040 20 2040 60 80 100 215 a poor understanding of the ecological preferences of the taxa that sur- % 216
NP2 N. vived and whether these preferences differed from those of species that 217 cruci.
6 64.5 218 5 went extinct. Bown (2005) proposed that the extinctions were highly Depth (mbsf)
NP1 219 %Cretaceous selective and related to trophic strategy and habitat preference. Survi- 4
3 65.0 K/T UC20 2 220 vors include neritic taxa that are adapted to unstable environments, 1510 5 1 Incoming Cenozoic species Neobisc. parvulum Cruciplac. primus Cocco. pelagicus Praeprinsius tenuiculus 2040 60 80 2040 60 80 20 40 60 2040 60 80 whereas the species that went extinct were largely open-ocean taxa that 215 % have lower tolerance to environmental stress. Some survivors also may 216 NP2 Praeprinsius sp. have possessed a cyst stage that allowed them to temporarily escape 217 6 218 64.5 5 Depth (mbsf) Co. pelagicus from hostile surface water conditions. (small) NP1 219 Futyania petalosa
4
3 65.0 K/T UC20 2 220 1 T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 10
Paleocene/Eocene Thermal Maximum on Shatsky Rise: Biotic, Climatic, and Oceanographic Signatures
The PETM (55 Ma) was a profound yet transient (~120–200 k.y.) warming event with a geologically abrupt onset (several thousand years). A number of different causal mechanisms have been proposed for the event, all of which involve input of a massive amount of green- house gas into the ocean-atmosphere system (e.g., Dickens et al., 1995; Kent et al., 2003; Svensen et al., 2004). The magnitude and rate of envi- ronmental change during this event led to transformation of marine and terrestrial communities (e.g., Hooker, 1996; Kelly et al., 1998; Crouch et al., 2001; Bralower, 2002), including the most severe deep-sea extinction event in the last 90 m.y. (e.g., Thomas, 1990, 1998) and sig- nificant shifts in continental weathering patterns and marine geochem- ical cycling (Gibson et al., 1993; Ravizza et al., 2001). The PETM has intrigued paleontologists and paleoceanographers be- cause the event serves as a worst-case scenario for modern global warm- ing and its effect on ocean circulation and its implication for biotas (e.g., Bains et al., 1999; Norris and Röhl, 1999). However, the lack of high-quality tropical records has prevented a thorough understanding of the physics of the event. Oxygen isotope data from high-latitude sites indicate SST increases of as much as 10°C, and data from a range of latitudes suggest that bottom water temperatures increased by 5°C (Kennett and Stott, 1991; Bralower et al., 1995). One of several existing quandaries in the interpretation of the PETM is the lack of a clear signal for warming at tropical latitudes. The event has been attributed to a rapid rise in greenhouse gas levels that should lead to warming at all latitudes (e.g., Huber and Sloan, 1999; Bice and Marotzke, 2001). A number of tropical records, including ODP Sites 999 and 1001 from the Caribbean Sea and Site 1051 from Blake Nose (western North Atlantic Ocean), are deeply buried and are thus unsuitable for foraminiferal sta- ble isotope analyses. Existing shallow sections, including DSDP Site 577 on Shatsky Rise and ODP Site 865 from Allison Guyot, are stratigraphi- cally incomplete (e.g., Pak and Miller, 1992; Bralower et al., 1995). The PETM interval was cored in nine holes at Sites 1209, 1210, 1211, and 1212 on the Southern High and Site 1208 on the Central High (Fig. F19). At the Southern High sites, the PETM is stratigraphically complete F19. PETM sections on Shatsky and corresponds to an 8- to 23-cm-thick layer of yellowish brown Rise, p. 44.
Site 1209 clayey nannofossil ooze with a sharp base and a gradational upper con- (2387 m) Hole B Hole C Site 1210 (2573 m) Hole A Hole B Site 1212 tact. These sediments have been the subject of a host of geochemical (2681 m) Site 1211 Hole A (2907 m) Hole A Hole A Hole C and paleontological investigations. Site 1208 (3346 m) Hole A Hole B
Combined measurements of oxygen isotopes and Mg/Ca ratios from Hole B the same planktonic foraminifers from Site 1209 imply a 4.5°–5.0°C in- crease in tropical Pacific SSTs during the PETM (Fig. F20) (Zachos et al., 2003), the first definitive evidence for warming in the tropics during the event. Mg/Ca ratios indicate that the oxygen isotope signal is af- fected by a substantial change in sea-surface salinity (SSS). The warming trends at Site 1209 combined with those from high-latitude sites are F20. Stable isotopes and trace ele- consistent with a two- to threefold increase in atmospheric pCO2 over ments from the PETM, p. 45.
ABCD E F G background levels. 13 18 δ δ Core CaCO3 Magnetic Fragmentation C O Mg/Ca Sr/Ca Age photo (wt%) susceptibility (%) (‰) (‰) (mmol/mol) (mmol/mol) (Ma) 85 90 95 100 5 10 15 20 20 40 60 0 1 2 3 4 5 -2.5 -2.0 -1.5 -1.0 -0.5 3 4 5 6 0.5 1.0 1.5 0.85 54.85 The PETM environmental change caused dramatic turnover in plank- 0.90 0.95
1.00 tonic marine faunas and floras. One of the dominant nannolith genera, 1.05 1.10
1.15 Fasciculithus, was replaced by Zygrhablithus bijugatus, a holococcolith 1.20 1.25
1.30
Depth in Section 198-1209B-22H-1 (m) 1.35 55.00 species that is often a highly abundant component of Eocene assem- 1.40
1.45 blages. The genus Discoaster is highly abundant, likely as a result of 1.50 warming or increased oligotrophy (Bralower, 2002). Planktonic fora- T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 11 miniferal assemblages contain an ephemeral group of ecophenotypes or short-lived species of the genera Acarinina and Morozovella (Kelly et al., 1996). Gibbs et al. (2006) investigated nannofossil assemblage changes at Site 1209 in detail. They observed a prominent increase in species of Biantholithus, Markalius, Braarudosphaera, and Thoracosphaera at the base of the event, followed by an increase in Z. bijugatus and species of Dis- coaster and Sphenolithus some 10 cm above the event base (Fig. F21). F21. Nannofossil diversity and The former genera are well-established disaster taxa that thrived in abundance for the PETM, p. 46.
Planktonic foraminiferal Indet./Ident. % total Discoaster % total % total Biantholithus % Zygrhablithus % total Age δ 13 C (‰) Toweius and Sphenolithus Thoracosphaera and % Markalius bijugatus Toweius (Ma) stressful environments in the immediate aftermath of the Cretaceous/ 0240 51015 0 20 40 60 0010 20 240102020 40 0 Heliolithus 195.6 Low High Dissolution 195.8 F. sidereus Tertiary boundary event (e.g., Thierstein and Okada, 1979; Pospichal, D. diastypus F. alanii 196.0 54.85
C. 196.2 N. modestus robusta
Depth (mbsf) 196.4 1996; Bown, 2005). The latter taxa are known to prefer warm and olig- F. schaubii 55.00 N. junctus Prinsius FCO F. lillianae 196.6 L. nascens LCO F. sidereus N. protenus otrophic surface water conditions (e.g., Aubry, 1998; Bralower, 2002). 196.8 1.7 2.1 2.5 0123 Nannofossil diversity (S-W) % Braarudosphaera bigelowii Although there are a number of possible explanations for the peaks in 3 point running average (gray) abundance of the disaster taxa, the preferred explanation is extremely oligotrophic conditions resulting from an increasingly stratified water column (Gibbs et al., 2006). The PETM coincides with the most significant benthic foraminiferal extinction event of the last 90 m.y. (Tjalsma and Lohmann, 1983; Tho- mas, 1990). A great deal of attention has been devoted to understand- ing the detailed assemblage changes and elucidating the selectivity of the extinction. For example, the extinction was exclusive to epifaunal rather than infaunal taxa and shelf taxa appear to have been much less affected than those in the deep sea (e.g., Thomas and Shackleton, 1996; Thomas, 1998; Spiejer and Schmitz, 1998). A significant question—the cause of the extinction—remains largely unanswered. The timing and pattern of the extinction are remarkably similar between sites, and this is hard to explain using most viable extinction mechanisms (e.g., Tho- mas, 2003). High-resolution studies of benthic foraminiferal assem- blages from the Leg 198 PETM sections show that the onset of the event was characterized by extinction of ~30% of species and a low-diversity assemblage dominated by dwarfed specimens of Bolivina advena (Kahio et al., submitted [N2]). This assemblage persisted for ~30 k.y. and was followed by a shift to an assemblage dominated by dwarfed specimens of Quadrimorphina profunda that lasted for 55 k.y. The low diversity and small size of the assemblage are possibly a result of lower deepwater ox- ygen conditions that resulted from PETM warming. At the same time as benthic foraminiferal size decreased, the size of surface water plank- tonic taxa increased significantly, possibly in response to increased thermal stratification and decreased nutrient supply (Kahio et al., sub- mitted [N2]). The depth transect of sections can be used to elucidate the response of the lysocline and calcite compensation depth (CCD) during the
PETM. Input of a massive amount of greenhouse gas (i.e., CO2 or CH4) at the onset of the event should result in rapid shoaling of the lysocline and CCD (e.g., Dickens et al., 1997; Dickens, 2000). The Shatsky Rise PETM sections show clear evidence for lysocline shoaling including an abrupt change in the nature of sediments from nannofossil ooze to clay-rich nannofossil ooze and a rapid decrease in CaCO3 content. De- tailed investigation of PETM sediments by Colosimo et al. (this vol- ume) shows a sharp increase in foraminiferal fragmentation at the base of the event corresponding to deterioration in visual preservation. Comparison of sites suggests a minimum lysocline shoaling of ~500 m in the tropical Pacific Ocean during the PETM. The sites also show evi- dence of CaCO3 dissolution within the sediment column, carbonate “burn down,” a predicted response to a rapid change in deepwater satu- T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 12 ration (Walker and Kasting, 1992). The magnitude of this shoaling is far less than that in the Atlantic Ocean (e.g., Zachos et al., 2005), suggest- ing that a substantial amount of greenhouse gas was mixed via the deep ocean and that circulation patterns were broadly similar to those of the present day.
Abrupt Warming Events: “Hyperthermals” in the Paleogene
The PETM is recognized as the most significant short-term warming event. However, the event may not be unique and a number of other intervals of rapid temperature increase, although smaller in magnitude, may also exist in the warm early Paleogene (Thomas et al., 2000; Bral- ower et al., 2002). One of these so-called “hyperthermals” in the early late Paleocene at ~58.4 Ma corresponds to a prominent clay-rich ooze at Sites 1209, 1210, 1211, and 1212 (Hancock and Dickens, this volume) and may have had evolutionary significance. The clay-rich layer con- tains common crystals of phillipsite, fish teeth, and phosphatic micron- odules. This event coincides with the evolutionary first occurrences of the nannoplankton Heliolithus kleinpellii and primitive discoasters. H. kleinpellii is an important late Paleocene zonal marker; the discoasters are dominant components of tropical and subtropical assemblages for most of the remainder of the Cenozoic. Planktonic foraminifers in the clay-rich layer are characterized by a low-diversity, largely dissolved as- semblage dominated by the genus Igorina. Two species of Igorina, I. pu- silla and I. tadjikistanensis, dominate samples (Petrizzo, this volume). The abundance of phillipsite and fish teeth suggests pervasive disso- lution of carbonate resulting from prolonged seafloor exposure or at least very slow sedimentation. A critical question remains as to whether the foraminiferal assemblages that are clearly altered by dissolution also reflect a significant perturbation in surface waters. Although Petrizzo (this volume) concluded that the foraminiferal assemblage shifts result primarily from dissolution, nannofossil assemblages (T. Bralower, un- publ. data) suggest that the event corresponds to an abrupt surface wa- ter warming. Clearly, more research is required to answer this question. Nevertheless, it is of note that the early late Paleocene “hyperthermal” event was also recovered on Walvis Ridge in the South Atlantic Ocean and this interval is characterized by similar lithologic composition and planktonic foraminiferal assemblages to the contemporaneous interval on Shatsky Rise (Zachos, Kroon, Blum, et al., 2004). Magnetic susceptibility records from the Southern High transect show a strong orbital cyclicity dominated by eccentricity (100- and 400- k.y. frequencies) (Westerhold and Röhl, this volume). The early late Pa- leocene event corresponds to an eccentricity minimum, suggesting that it is a response to an orbital change in climate. Other susceptibility minima also correspond to horizons characterized by increases in clay content, some of which also contain phillipsite and fish debris. These events may also turn out to be hyperthermals. The cycles appear to be controlled by variations in the amount of dissolution as indicated by variations in foraminiferal fragmentation and benthic/planktonic fora- miniferal ratios (Hancock and Dickens, this volume). Moreover, Han- cock and Dickens (this volume) found an increase in the amount of dissolution between 45 and 33.7 Ma at Sites 1209 and 1211. T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 13
Neogene
The Neogene–Holocene succession was recovered at seven sites drilled on Shatsky Rise along a latitudinal transect that spans ~6° of lat- itude from 37°N on the Northern High to 31°N on the Southern High. The most expanded section, which spans the interval from the upper middle Miocene to the Holocene and has a sedimentation rate as high as 42 m/m.y., was recovered at Site 1208 on the Central High. A similar section with a lower sedimentation rate (28 m/m.y.) was recovered at Site 1207 on the Northern High. Sedimentation rates at Southern High sites (Sites 1209–1213) are <14 m/m.y., at least partially as a result of the lower production of biosiliceous and carbonate materials. Moreover, the Central and Northern High sites appear to have received a large sup- ply of fine sediment from bottom water currents and eolian transport. The upper Miocene and younger sections at all Leg 198 sites rests un- conformably on middle Miocene sediments. The middle Miocene and most of the lower Miocene are represented by incomplete, highly con- densed sequences that are dark in color, enriched in clay content, and may be capped by manganese crusts. These unconformities from the lower to middle Miocene and the lower Miocene to lower Oligocene are partially equivalent from site to site and suggest that regional oceano- graphic processes controlling erosion and dissolution had a major affect on sedimentation. Today, Shatsky Rise lies in a subtropical water mass toward the north end of the range of the warm-water Kuroshio Extension Current. North of the Northern High lies a significant front, a transition region be- tween subtropical and subarctic water masses. The transition zone wa- ters are derived from off the coast of northern Japan, where the cold, nutrient-rich Oyashio Current mixes with the warm, nutrient-poor Kuroshio Current. Even though at 10 Ma in the late Miocene the North- ern High was located father south at ~32°N paleolatitude (R. Larson, pers. comm., 2001), because of its proximity to the transition zone the northern part of Shatsky Rise was a location highly sensitive to past cli- matic variations. Significant oceanographic changes occurred during the Neogene that had profound effects on circulation and distribution of water masses in the Pacific Ocean; these changes appear to be reflected in the sedimen- tary record recovered at Shatsky Rise. An event at 14.5 Ma has been as- sociated with the formation of the East Antarctica Ice Sheet (Kennett et al., 1985); another event at 11 Ma is related to closure of the Indo- Pacific Seaway (Romine and Lombari, 1985). These events led to a steepening of temperature gradients and intensification of North Pacific gyral circulation including the ancestral Kuroshio Current. The modi- fied circulation resulted in development of a distinct North Pacific tran- sitional water mass, separated from the northern subpolar region, and northward displacement of temperate organisms. Moreover, these events may be responsible for hiatuses and/or condensed intervals of variable duration that characterize sediment deposition throughout the rise during the late early and middle Miocene. The decrease in carbonate content at the shallowest Site 1209 on the Southern High in the middle Miocene is accompanied by the presence of several more clay rich intervals (Malone, this volume). This pattern is similar to those observed at the deeper Sites 1207 and 1208. Based on biostratigraphic data, these clay horizons are condensed intervals, most likely produced by dissolution of carbonate at the seafloor during the middle and late early Miocene. Such a phenomenon would be consis- T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 14 tent with the reported shoaling of the global lysocline and CCD through the early and middle Miocene (Rea and Leinen, 1985). Studies of previously drilled sites suggest that the lysocline was as shallow as 3 km during the early Miocene. Leg 198 data indicate that the lysocline might have been even shallower (<2.4 km) during much of this period. The alternating carbonate- and clay-rich lithologies suggest that the process(es) responsible for slow sedimentation was somewhat cyclic, perhaps related to fluctuating CCD levels (discussed above) and/or in- tensity of erosional currents. Northward migration of Shatsky Rise by 5° latitude since the late Miocene (R. Larson, pers. comm., 2001) is accompanied by changes in biogenic components of the sediments as well as their state of preserva- tion. Although the middle Miocene record displays slightly different ages from site to site, calcareous plankton assemblages are rather uni- form and diverse across Shatsky Rise and display warm, subtropical af- finities. Since the late Miocene, however, a faunal and floral gradient has been established across Shatsky Rise. Calcareous plankton assem- blages progressively lose the warmest taxa from southern to northern sites, including discoasters and sphenoliths among calcareous nanno- fossils and Globigerinoides and keeled globorotaliids among planktonic foraminifers. The resulting marked decrease in diversity is reflected in assemblages that assume temperate (occasionally cold-temperate) affin- ities at the more northern Sites 1207 and 1208. The changes in calcare- ous plankton assemblages are paralleled by a progressive decrease in preservation. Over the same interval, diatoms become progressively more abundant toward the north. Based on magnetostratigraphic age constraints (see Evans et al., this volume), the first occurrence of biosil- iceous organisms at Shatsky Rise is dated at ~12 Ma in the late middle Miocene at Sites 1207 and 1208 but at ~6.5 Ma in the latest Miocene at Site 1209 or ~5 Ma in the earliest Pliocene at Site 1210 on the Southern High. Diatoms increase markedly in abundance at ~8 Ma, just after a change in Pacific Ocean circulation associated with the closure of the Indonesian Seaway that caused intensification of North Pacific gyral cir- culation (Kennett et al., 1985); a strengthened west wind drift likely in- creased upwelling along this boundary and created a more well- established North Pacific transitional water mass separated from the northern subpolar region. The amount of diatoms observed in the sedi- ments is variable from layer to layer, probably as a function of the de- gree of carbonate dissolution. However, peaks in abundance of biosiliceous material occur in the latest Miocene, late early Pliocene, and late Pliocene. Based on magnetostratigraphic age models (Evans et al., this volume), the highest abundance of biosiliceous material across Shatsky Rise was recorded between ~3.2 and 2.6 Ma. A significant peak in opal accumulation rates also occurs between 3.2 and 2.75 Ma at other sites from the northern Pacific (Haug et al., 1995; Maslin et al., 1995). The origin of this peak and subsequent decline is uncertain, but the base of this peak corresponds to the beginning of long-term global cooling, which culminated in Northern Hemisphere glaciation, and the top of the peak corresponds to the rapid advance of Northern Hemi- sphere glaciers. Regional studies (e.g., Natland, 1993) of ash distribution across Shatsky Rise suggest that ash beds present in the last 2.6 m.y. at Site 1208 are wind-borne sediments that likely were carried to the site from volcanic eruptions along the Japan and/or Kurile magmatic arc systems. The maximum and subsequent waning of ash input expressed in the T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 15 frequency of ash beds (see Gadley and Marsaglia, this volume) could be linked to changes in volcanic activity along the arc systems or to changes in wind patterns over time. Isolated pumice clasts were most likely rafted to the site by the Kuroshio Current, which passes across the submerged pumice-producing calderas of the Izu-Bonin magmatic arc to the west (see Taylor, Fujioka, et al., 1990) and flows directly over Shatsky Rise. Changes in the geographic distribution of water masses through time also affected other fossil groups. In particular, Neogene planktonic fora- minifers show distinct stratigraphic changes between assemblages dom- inated by subtropical and tropical taxa and those dominated by taxa with cool, temperate affinities. Moreover, faunas at Site 1208 are con- siderably richer in warmer, tropical taxa than those at Site 1207, which is located only ~1° to the north. This suggests that for much of the Neo- gene, Sites 1207 and 1208 were located in a region with sharp tempera- ture gradients. The Pliocene–Pleistocene at Site 1207 on the Northern High is partic- ularly rich in siliceous microfossils, most likely due to cool, productive waters, which were also responsible for the paucity of tropical–subtrop- ical species of planktonic foraminifers at this location. The influx of warmer-water planktonic foraminifers and reduction of biosiliceous plankton to the south at Sites 1209 to 1213 show the paleobiogeo- graphic and paleoceanographic importance of the Shatsky Rise drill sites near the path of the Kuroshio Current. One of the most significant features of the upper Miocene through Pleistocene sections recovered at Shatsky Rise is the decimeter- to meter-scale cycles between darker and lighter horizons. The darker-col- ored intervals in general contain higher amounts of very well preserved biosiliceous material, whereas calcareous plankton assemblages have suffered a greater amount of dissolution and are of cold-water nature. Calcareous plankton preservation is considerably better in the light-col- ored layers that have fewer diatoms. The darker layers are interpreted as probably representing intervals of higher surface water productivity as well as periods of higher carbonate dissolution. This interpretation is supported not only by the richness in diatoms in the darker layers but also by the abundance of some planktonic foraminifers such as Globige- rina bulloides, a taxon that typifies the subpolar bioprovince and/or pro- liferates in upwelling regimes. Based on average sedimentation rates of 18.4 m/m.y. over the last 8 m.y. at Site 1207, the cycle frequency ap- pears to be similar to that of glacial–interglacial cycles, with the darker beds representing glacials and the lighter beds representing intergla- cials. It is worth mentioning that prior to the onset of cyclic patterns at 8 Ma, calcareous plankton were definitely warmer in character than in the Pliocene–Pleistocene. The ~5° of latitude that separates the Northern High drill site from those drilled on the Southern High is such a distance that one can ex- pect significant change in oceanographic regime especially during un- stable climatic conditions at the various sites. The most distinct cycles in terms of color variation and other physical properties occur in the upper Neogene. These are best represented by the total color reflectance (L*) records from Sites 1207–1209. The Pleistocene–Holocene color data at these sites exhibit the “classic” asymmetric glacial–interglacial cycle pattern. The transitions are mostly gradational, although several gla- cial/interglacial contacts are sharp. Interglacials are characterized by carbonate-rich, light-colored nannofossil ooze with clay, whereas gla- cials are characterized by clay- and diatom-rich, dark-colored clayey T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 16 nannofossil ooze or nannofossil clay. For most of the upper Miocene– Holocene section at Site 1208, the cycles are predominantly between nannofossil clay with diatoms and nannofossil ooze with clay and dia- toms. The darker gray to green interbeds tend to have more abundant diatoms and clay, more dissolved calcareous plankton assemblages, and more abundant reduced iron minerals (i.e., pyrite). The lighter gray, tan, and white interbeds contain fewer diatoms, less clay, and a better- preserved calcareous plankton assemblage. Upper Miocene–Holocene sediments recovered at Site 1208 contain few to common diatoms (up to 20%)—lower percentages than in sedi- ments recovered at Site 1207 but higher percentages than contempora- neous units from sites on the Southern High of Shatsky Rise, where diatoms are usually <5%. Site 1208 is ~1° south of Site 1207 and ~4° north of the Southern High sites. As at Site 1207, diatom-rich layers are thought to represent intervals during which colder, more productive, transitional, and subarctic water masses shifted southward over the site. Lighter-colored layers that are poorer in diatoms represent warmer in- tervals during which Site 1208 was located in a subtropical water mass, similar to its location today and similar to sites on the Southern High through most of the Neogene. As the site is considerably higher than the surrounding deep-ocean floor, there may also be a topographic con- trol on productivity. Cyclic variations in the position of the lysocline and CCD have ex- erted a strong influence on the composition of sediment in the Pacific through the Cenozoic. At present, Site 1209, the shallowest on the Southern High, is situated well above the lysocline and CCD, which are at 3.5 and 4.1 km, respectively, in the region. As such, the uppermost Holocene sediments at Site 1209 have a relatively higher carbonate con- tent than the Holocene of Sites 1207 (3.5 km) and 1208 (3.3 km). Be- cause the CCD generally deepens in the Pacific during glacials (Farrell and Prell, 1989), its role in driving the Pleistocene lithologic cycles is probably minor. Instead, productivity and sediment transport may be more important. As with the deeper-water Sites 1207 and 1208, the darker-colored intervals generally contain higher amounts of biosili- ceous material and clay and probably represent intervals of higher sur- face water productivity and increased in situ carbonate dissolution (e.g., Robinson and Jenkyns, this volume). Even though the frequency of cycles in color reflectance through the Pleistocene are also related to glacial–interglacial cycles, the cycle am- plitudes are smaller at Site 1209 than at deeper Site 1208 (Gylesjö, this volume), owing to a lower contribution of clay and siliceous microfos- sils to the sediment. Moreover, despite the shallower water depth, the sedimentation rate is significantly lower at Site 1209, ~13–14 m/m.y. over the Pleistocene compared to 42.4 m/m.y. at Site 1208. This indi- cates that carbonate production and preservation may have played a more important role in driving the Pleistocene lithologic cycles. As at the other sites, the dominant period of the cycles corresponds to eccen- tricity (100 k.y.) subsequent to 0.6 Ma and obliquity (41 k.y.) for the pe- riod from 0.6 to 2.5 Ma. The cycle wavelength at Site 1209, however, is much more irregular, suggesting that accumulation rates were highly variable through time. Biostratigraphic age constraints suggest that the dominant cycle fre- quency over the last 0.6 m.y. is near that of the 100-k.y. eccentricity cy- cle. From 0.6 to 2.6 Ma, the dominant period shifts toward a higher frequency close to that associated with the 41-k.y. obliquity cycle. Throughout the last 2.6 m.y., the cycle amplitudes in reflectance re- T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 17 main remarkably similar between the Southern and Central Highs, al- though the mean total reflectance is higher on the Southern High. Climate-driven variations in opal and carbonate production and preser- vation and in clay fluxes are responsible for these changes. Analysis of the frequency of the dark–light cycles, calibrated to a well-established magnetostratigraphy throughout the rise, demonstrates that the domi- nant period of the cycles corresponding to obliquity (41 k.y.) extends back to 8 Ma (Evans et al., this volume). However, in the earlier Neo- gene section prior to the onset of Northern Hemisphere glaciation at 2.6 Ma, the amplitude of obliquity cycles is noticeably reduced, particu- larly at sites on the Southern High. The decrease results primarily from the absence of the low-carbonate “glacial” end-member of the cycles, despite a relative increase in silica content in the mid-Pliocene. The re- duction in the high-frequency cycle amplitude is accompanied by an apparent increase in low-frequency cycle amplitude. In the Site 1209 color reflectance record (over the period 3–5 Ma), for example, there ap- pears to be a long-wavelength oscillation with a period of roughly 1.0– 1.25 m.y. Comparison with the derived orbital curves (Laskar, 1990) suggests that this cycle may be in phase with the long-period 1.25-m.y. obliquity cycle. The peak in siliceous microfossil deposition at Site 1209 occurred in the mid-Pliocene, at roughly the same time as in regions of the North Pacific (Rea et al., 1995). The cyclic sedimentation during the Pleis- tocene and Pliocene is similar at Sites 1210 and 1211 and is character- ized by relatively low amplitude cyclicity compared to the cyclic sedimentation recorded in the sediment farther north (e.g., Site 1209). This may be attributable to overall lower surface water productivity on the southern flank of the Southern High, as indicated by the dimin- ished abundance of siliceous microfossils compared to sites farther north on the Southern, Central, and Northern Highs. In addition, the average sedimentation rate for the Pleistocene and Pliocene (8.6 m/ m.y.) is significantly lower than those recorded at the Central and Northern Highs (up to 42 m/m.y.), also suggesting lower surface water productivity. However, despite the lower rates of primary productivity, the cyclicity was most likely dictated by small-scale changes in the in- tensity of surface water productivity. Relative biogenic silica enrich- ment occurs within the darker, more olive-green lithologies (up to 15% diatoms), with the lighter gray intervals remaining depleted in opal (~1%). It is unlikely that the light–dark sediment cycles resulted from glacial–interglacial fluctuations in deepwater corrosiveness given the relatively shallow water depth of ~2900 m, which lies above the sub- tropical northern Pacific CCD (Rea et al., 1995). In the Pleistocene Pa- cific Ocean, “glacial” intervals were generally times of higher productivity. Thus, the prominent color and compositional cycles are similar to those observed elsewhere in the North Pacific (Haug et al., 1995). Systematic changes in cycle amplitude and frequency are consis- tent from site to site, suggesting that these changes reflect regional pale- oceanographic processes. The cycle packages (in all physical properties) are sufficiently distinct to allow for detailed correlation between sites. Koizumi (1985) correlated fluctuations in Pliocene–Pleistocene dia- tom communities at DSDP sites in the abyssal plain northwest of Shatsky Rise to climatic fluctuations controlling the location of subarc- tic water masses at these sites. In colder intervals of the late Miocene to Pleistocene, the Northern High may have been within the transition zone between the subtropical water mass and the subarctic water mass, even though the site was well to the south of its current location. Thus, T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 18 fluctuations in the proportion of diatoms, which are more abundant in subarctic than subtropical waters, may reflect latitudinal shifts in the position of the transition zone. If the darker layers correspond to cool intervals as argued, then the pattern of preservation is opposite that of most sites in the Pacific (e.g., Farrell and Prell, 1991; Zahn et al., 1991). A body of evidence suggests that during glacial stages intermediate deep waters were produced in the Pacific and that these young, nutrient-poor waters caused little dis- solution close to their source. An opposite pattern was noted at a site on Emperor Seamount by Haug et al. (1995), who argued that the up- welling of nutrient- and CO2-rich waters during glacial stages increased carbonate dissolution. Microfossils suggest a similar mechanism for dis- solution patterns in the upper Miocene–Pleistocene at the Northern High site. With the exception of Site 1214, all sites include complete and rap- idly deposited Pliocene–Pleistocene sections in which the noncarbonate fraction forms a significant proportion, including the particularly ex- panded drift-deposit succession (200 m and 42.4 m/m.y. sedimentation rate) recovered at Site 1208. These sections, displaying visible cyclic sed- imentary patterns, allowed better age assignments of magnetic chrons using astrochronology since 8 Ma (Evans et al., this volume, and study in progress).
ACKNOWLEDGMENTS
We thank the highly capable drilling operations team, the rough- necks, and the technicians who sailed on Leg 198 for their outstanding support. We are very grateful to all of the scientists who sailed with us for their hard work onboard ship and their subsequent productivity. We thank Mitch Lyle and Larry Peterson for their constructive reviews. This research used samples and data provided by the Ocean Drilling Program (ODP). ODP is funded by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. Funding for this research was provided by the U.S. Science Support Program, administered by JOI and by NSF EAR- 0120727. T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 19 REFERENCES
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Figure F2. Generalized climate curve for the Cretaceous and Paleogene derived from deep-sea benthic ox- ygen isotope data (from Zachos et al., 1993, 2001). Also shown are locations of events discussed including Eocene/Oligocene transition, Paleocene/Eocene Thermal Maximum (PETM), late Paleocene biotic event, Cretaceous/Tertiary boundary (K/T), mid-Maastrichtian event (MME), and early Aptian Oceanic Anoxic Event (OAE1a) (modified from Bralower, Premoli Silva, Malone, et al., 2002).
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Figure F3. Summary of stratigraphy and lithologic succession from Sites 1207–1214. Lithology is plotted against time to show duration of periods of deposition and location of unconformities. Southern High Sites 1209–1214 are ordered by water depth. Arrows show stratigraphic position of transient events discussed: Eocene/Oligocene (E/O) transition, Paleocene/Eocene Thermal Maximum (PETM), late Paleocene biotic event, Cretaceous/Tertiary boundary (K/T), mid-Maastrichtian event (MME), and early Aptian Oceanic An- oxic Event (OAE1a) (modified from Bralower, Premoli Silva, Malone, et al., 2002).
Northern Central Southern High High High 1207 1208 12091210 1212 1211 1214 1213 Water depth (m) 3101 3346 2387 2573 2681 2907 3402 3883 Age 0 Pleistocene late Plio. 5 early late 10 middle
20 Miocene early
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Nannofossil ooze Clay Chalk Chert Porcellanite T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 29
Figure F4. Stratigraphic synthesis for Shatsky Rise sites from 145 to 130 Ma plotted against the biostrati- graphic scheme used in Bralower, Premoli Silva, Malone, et al. (2002). Biostratigraphy after Bralower, Pre- moli Silva, Malone, et al. (2002) and Bown (this volume). Condensed pattern annotates intervals in which some biozones could not be identified with certainty and/or may comprise short hiatuses or unconformi- ties. Note that in the Cretaceous sections older than Campanian the recovery was very poor due to diffuse chert layers alternating with softer chalk. OAE = Ocean Anoxic Event, TD = total depth.
Age Biozones 1207 1214 1213 Paleomag. Epoch (Ma) Foraminifers Nannofossils Radiolarians 3100 m 3402 m 3883 m G. ferreolensis UAZ 95 NC7 NC7a Leupoldina cabri NC6b
120 Aptian NC6 22 NC6a CM0 (121) Globigerinelloides blowi 20 m 23 m 1213B-7R-1 CM1 NC5d-e 1214A-21R to 21 to 9R-1, 18 cm CM2 Acanthocircus carinatus 24R-1, 47 cm H. similis- NC5 carinatus c. A. perforatus c. A. CM3 H. kuznetsovae A.c.transi 125 torius (126) NC5c 75 m CM4 1207B-42R- 20 CM5 CC to 1214A-24R-1, CM6 NC5a-b 49R-CC 72 cm, to CM7 1213B-9R-1, 25R-1, 22 cm CM8 Hedbergella sigali - 47 cm, to 27R-1, 38 cm CM9 "H. delrioensis" NC4b 19 TD - 1207B CM10 622.8 m 130 NC4 >15 m CM10N NC4a 18 TD - 1214A (131.5) 235.9 m CM11 17 NK3b CM11A Early Cretaceous CM12 Hedbergella sigali- NK3 CM12A H. aptica 16
Depth (mbs) CM13 NK3a 135 CM14 (135.8) NK2b CM15 NK2 15 NK2a CM16 Conoglobigerina gulekhensis NK1
CM17 Berriasian Valanginian Hauterivian Barremian 140 14 NJKd CM18 (141.6) 174 m NJKc CM19n-1 NJK ? CM19 NJKb
CM20n-1 NJKa 46.5 m Not zoned TD - 1213A Pseudodictyomitra carpaticaPseudodictyomitra Cecrops septenforatus CM20 13 494.4 m 145 NJ20b Tithonian NJ20 Late Jurassic CM21 NJ20a Chalk OAE1a
Chert Volcanics
Porcellanite Hiatus
Claystone T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 30
Figure F5. Stratigraphic summary for 130–80 Ma. Biostratigraphy after Bralower, Premoli Silva, Malone, et al. (2002), Bown (this volume), and Lees and Bown (this volume). Condensed pattern annotates intervals in which some biozones could not be identified with certainty and/or may comprise short hiatuses or un- conformities. Note that in the Cretaceous sections older than Campanian the recovery was very poor due to diffuse chert layers alternating with softer chalk. OAE = Ocean Anoxic Event, TD = total depth.
Age Biozones 1207 1208 1212 1214 1213 Paleomag. Epoch (Ma) Foraminifers Nannofossils 3100 m 3345 m 2681m 3402 m 3883 m 80 0.4 m C33r 1208A-41X- 1207B-10R- 2, 120 cm, (83.5) CC to to 41X-CC 19R-CC 1213A-7R- C34n CC (85.8) 86 m 1212B-24H- 6, 30 cm <0.1 m
(89.0) 90 0.01 m Late Cretaceous
(93.5) 1212B-24H-6, 30.5 cm, to 27H-CC
1213A-
Cenomanian Turonian Coniac. Sant. Camp. 8R-CC to 1213B- (98.9) 10 m 9R-1, 1214A-2R 18 cm 100 TD - 1212B to 10R-CC 207.6 m
1208A-42X
1207B-19R- 84.5 m Albian CC to <9 m Depth (mbsf) 49R-CC TD - 1208B 392.3 m 1214A-11R to 19R-CC 110 87 m
(112.2)
1214A-20R to 24R-1, 47 cm Early Cretaceous
200 m
120 CM0 (121) 39 m
CM1 287.5 m CM2
CM3 Barremian Aptian TD - 1207B (126) CM4 622.8 m 1214A-24R-1, CM5 CM6 72 cm, to CM7 25R-1, 22 cm CM8 1213B-9R-1, CM9 47 cm CM10 130 Hauterivian >15 m TD - 1214A 235.9 m Nannofossil Chalk Chert Porcellanite ooze
Claystone OAE1a Hiatus T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 31
Figure F6. Stratigraphic summary for 85–60 Ma. Biostratigraphy after Bralower, Premoli Silva, Malone, et al. (2002), Lees and Bown (this volume), Bralower (this volume), Petrizzo et al. (this volume), and Pre- moli Silva et al. (this volume). Condensed pattern annotates intervals in which some biozones could not be identified with certainty and/or may comprise short hiatuses or unconformities. Note that in the Creta- ceous sections older than Campanian the recovery was very poor due to diffuse chert layers alternating with softer chalk. OAE = Ocean Anoxic Event, TD = total depth.
Age Biozones 1207 1208 1209 1210 1212 1211 1213 Paleomag. Epoch (Ma) Foraminifers Nannofossils 3100 m 3345 m 2387 m 2573 m 2681 m 2907 m 3883 m 60 late Selan 1209A-24H- 1210A-23H- 1212B-10H- 1211A-15H- 5, 26 cm, 3, 100 cm, 5, 145 cm, 2, 27 cm, to 1209C- to 24H-4, to 11H-7, to 15H-4, 15H-3, 51 cm 24 cm 146 cm 96 cm early Paleocene Danian
13 m 11 m 11 m 4 m 65 (65.0) 1212B-11H- CC to 1211A-15H- 4, 146 cm, 1209A-25H- 1210A-24H- 1212B-24H-6, 0 cm to 1211B- 6,125 cm, 4, 51 cm 19H-CC to 1209C- to 1210B- 22X-7, 42H-6, 56 cm 121 cm Maastrichtian 36 m 70 62.5 m TD - 1211B 169.9 m
(71.3) TD - 1209C 307 m
96 m
75
Late Cretaceous ?
1213A-7R-1, 0-84 cm 157 m 1212B-24H-6, 1 cm 1208A-36X-3, 50 cm, to 0.01 m <1 m 41X-CC TD - 1210B 377 m ? Campanian 1207A-18H-5 115 cm, to 1207B-15R-CC 80
54 m
(83.5) Nannofossil Nannofossil Chalk ooze ooze with clay 134 m Condensed
Sant. Chert Hiatus sequence 85 The whole interval is missing at Site 1214 T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 32
Figure F7. Stratigraphic summary for 65–40 Ma. Biostratigraphy after Bralower, Premoli Silva, Malone, et al. (2002), Bralower (this volume), Petrizzo et al. (this volume), and Premoli Silva et al. (this volume). The Paleocene/Eocene boundary was set at 55 Ma (see discussion in Aubry and Ouda, 2003). Condensed pattern annotates intervals in which some biozones could not be identified with certainty and/or may com- prise short hiatuses or unconformities. OAE = Ocean Anoxic Event, TD = total depth.
Age Biozones 1208 1209 1210 1212 1211 Paleomag. Epoch (Ma) Foraminifers Nannofossils 3345 m 2387 m 2573 m 2681 m 2907 m 40 0.5 m
CP14 1209A-15H- 1210B-16H-4, 1211C-10H-6, CC to 101 cm, to 0 cm, to 1209C-11H- 1210A-20H-3, 1211A-11H-4, 2, 2 cm 46 cm 46 cm
45 middle CP13 Lutetian Bart.
3.75 m
Eocene 1211A-11H-4, 1212B-7H-6, 46 cm, to 1211B-12H-5, CP12 135 cm, to 9H-5, 46 cm 50 cm >4 m
50 1208A-36X- 1211B-12H-5, 46 cm, to CP11 2, 41 cm, to 12H-6, 46 cm 36X-CC, 42 cm 1.5 m
CP10 54 m 40 m 1211B-12H-6,
early 46 cm, to 1211A-13H-5, 128 cm 1209C-11H- 1210A-20H-3,
Depth (mbsf) 2, 2 cm, to 46 cm, to CP9 1209B-22H- 1210B-20H-2, 1, 70 cm 50 cm 0.75 m 17 m 6.5 m 55 (55.0) 2 m 2 m
CP8 ? ? 1211A-13H- 5, 128 cm, to 1211C-15H- CP7 8 cm 4, 81cm barren CP6 1209B-22H- 1210B-20H-2, 1212B-9H-5, 1, 70 cm, to 50 cm, to 50 cm, to ? 1209C-15H- 1210A-24H-4, 1212B-11H-7, CP5 3, 96 cm 51 cm 24 cm late
CP4 16 m 60 Selandian Ypresian 1211A-15H-2, Paleocene CP3 27 cm, to 15H-4,146 cm
CP2 early Danian Thanetian
38 m 22 m 4 m CP1 40 m 65 The whole interval is missing at Sites 1207, 1213, and 1214 Nannofossil Condensed Hiatus ooze with clay sequence T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 33
Figure F8. Stratigraphic summary for 45–20 Ma. Biostratigraphy after Bralower, Premoli Silva, Malone, et al. (2002), Bown (this volume), Bralower (this volume), and Petrizzo et al. (this volume). Condensed pat- tern annotates intervals in which some biozones could not be identified with certainty and/or may com- prise short hiatuses or unconformities. TD = total depth.
Age Biozones 1208 1209 1210 1211 Paleomag. Epoch (Ma) Foraminifers Nannofossils 3345 m 2387 m 2573 m 2907 m 20 Burdigal. N5 1208A-35X-4, (part) 10 cm, to 1209A-12H-5, 35X-5, 12 cm 1 cm, to 12H-6, 52 cm early
Miocene N4
(23.8) <1.1 m 1.5 m
25 P22 late Chattian Aquitanian
P21b
P21a Oligocene 30 P20
P19 early
1208A-35X-5, P18 12 cm, to 1210A-13H-2, 1211C-8H-7, 36X-2, 40 cm 1209A-13H-4,,
Depth (mbsf) (33.7) 70 cm, to 30 cm, to P17 45 cm, to 14H-2, 46 cm 1211A-10H-2, <5 m 1209C-3H-6, 134 cm 31 cm P16 5 m 35 late
Priabonian ? 8 m P15
1211A-10H-4, <5 m 1210A-14H-4, 108 cm, to 45 cm, to 1211C-10H-6, 1210B-16H-4, 1 cm 1209A-15H-3, 101 cm P14 127 cm, to 1209A-17H-2,
Bartonian Rupelian 7 m 40 Eocene 51 cm P13 1211A-10H-4, 108 cm, to
middle 11H-3, 46 cm P12 Lutetian P11 >20 m 23 m 7.5 m 45 The whole interval is missing at Nannofossil Condensed Hiatus Sites 1207, 1212, 1213, and 1214 ooze sequence T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 34
Figure F9. Stratigraphic summary for 25–0 Ma. Biostratigraphy after Bralower, Premoli Silva, Malone, et al. (2002) and Bown (this volume). Magnetostratigraphy after Evans et al. (this volume). Condensed pattern annotates intervals in which some biozones could not be identified with certainty and/or may comprise short hiatuses or unconformities. TD = total depth.
Age Biozones 1207 1208 1209 1210 1212 1213 1211 Paleomag. Epoch (Ma) Foraminfers Nannofossils 3100 m 3345 m 2387 m 2573 m 2681 m 2883 m 2907 m 0
Pleist. Calabrian 1213A-1R 1211A-1H (1.77) to 1207A-1H 1208A-1H 1209A-1H 1210A-1H 1212A-1H 6R-4, to Gelasian to to to to to 95 cm 7H-2, 17H-2, 34X-CC 10H-2 10H-CC 8H-3, 9 cm late 107 cm Piacenz. 10 cm Plioocene 54.6 m early 5 55 m (5.32) Messinian Zanclean 86.4 m 91 m 52 m
1210A-11H 1209A-10H-3 to 12H- 150 m 10 to CC 11H-CC
16.8 m
Depth (mbsf) 1207A-17H- 315 m 1212A-8H-3,
Serravallian 2, 107 cm, 1209A-12H-1, 10-100 cm middle late to 18H-4, 1 cm, to 80 cm ? 12H-4, 0.90 m 15 90 cm 1211A-7H-2, 12 m 10-20 cm Miocene 5.4 m
Langhian 0.10 m 1208A-35X- 1 cm, to 35X-5, 12 cm 19 m
1207A-18H- 1209A-12H- 5, 25 cm, 4, 91 cm, to 18H-5, ? Burdigalian Tortonian to 102 cm 12H-6, 20 52 cm 3.8 m
early barren
?
0.75 m 2.6 m Aquitanian
(23.80) 6.20 m Chattian late 25 Oligo. Nannofossil Condensed At Site 1214 Holocene-Pleistocene = 6.9 m. Hiatus Mn crust ooze with clay sequence T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 35
Figure F10. Magnetic polarity interpretation of Hole 1213B Lower Cretaceous sediment samples between 360 and 424 mbsf. Solid circles = inclination values for samples; subbottom depth has been recalculated to expand recovered core to fill the cored intervals. Polarity interpretation is shown at right: black = normal polarity, white = reversed polarity, and gray = uncertain polarity (from Sager et al., this volume).
Inclination (°) -20 0 20 40 60 80 Polarity 360
19R
370 20R
380 21R
CM16? 390 22R Depth (mbsf)
CM17? 400 23R
CM18?
410 24R
420 25R T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 36
Figure F11. Geochemistry of diabase sills recovered at Site 1213. A, B. Age-corrected isotope data. Fields for Pacific mid-ocean ridge basalt (MORB) and the Easter-Nazca Ridge hotspot chain are adjusted for radiogenic ingrowth to the estimated 144-Ma positions of the mantle sources (see Tejada et al., 2004). Pb isotope data for Holes 1213B and 1179D (and Easter-Nazca Ridge) were acquired using a double spike. Fields are from Mahoney and Spencer (1991), Tejada et al. (2004), and Ray et al. (2003), and references therein. C. Incom- patible element patterns. Ontong Java pattern is from Fitton and Godard (2004); average normal-MORB (N- MORB) pattern and normalizing values are Sun and McDonough’s (1989) (from Mahoney et al., 2005).
206 204 A ( Pb/ Pb)t 17.5 18.0 18.5 19.0 19.5 20.0 +12
+10 East Pacific +8 Rise Manihiki Easter-Nazca
(t) Ridge +6 Ontong Nd
ε Java
+4 1179D Hess Rise, 464
+2 Shatsky Rise Manihiki 1213B 0 D9, D14 B 39.5 Easter-Nazca Ridge
39.0
t Manihiki Pb) 38.5 204 Ontong Pb/ Manihiki Java 38.0 208 (
East 37.5 Pacific Rise
37.0
C 10
Avg. Ontong Java, Kwaimbaita
Avg. N-MORB 1 1213B 1213B Concentration/ primitive mantle 1213B Cs Rb Ba Th U Nb Ta La Ce Pr Pb Sr Nd P Hf Zr Sm Eu Ti Gd Tb Dy Y Ho Er Tm Yb Lu T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 37
Figure F12. Core photo, carbonate, Corg contents, and hydrogen index (HI) for lower Aptian sedimentary rocks recovered at Sites 1207, 1213, and 1214. Note that Sites 1207 and 1213 recovered Corg-rich intervals that represent OAE1a (from Bralower, Premoli Silva, Malone, et al., 2002). NA = not analyzed.
Cores of early Aptian OAE1a interval recovered on Leg 198
198-1207B-44X-1 198-1214A-23R-1 198-1213B-8R-1 3100 mbsl 3402 mbsl 3883 mbsl 0 •0.75 •1.38 •NA
•0.42 •0.10 •NA Chert and radiolarian porcellanite Bioturbated radiolarite and radiolarian porcellanite
•0.5 •10.2 50 •501 Bioturbated limestone
•0.00 •34.7 •0.75 •423 •25.2
Radiolarian claystone with thin, altered tuffs •506 Bioturbated olive-black to Bioturbated olive-black claystone green-black
•0.00 •10.4 •523 Length (cm) •0.58 •0.00 •NA Finely laminated radiolarian claystone •0.42 •2.87 •365 •0.00 100 •1.70 •438 Laminated to bioturbated porcellanite Porcellanite, bioturbated Porcellanite, to laminated, and homogeneous claystone Dark claystone laminated to bioturbated
•CaCO3 (wt%) •Corg (wt%) 150 •HI (mg HC/g OC) T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 38 ation
Chalk with thin chert beds (<10 cm chalk becoming more lithified thick); Chalk with thin chert beds (<10 cm thick) Chalk with common chert, and silicified carbonate porcellanite, Chalk with common chert, and silicified carbonate; porcellanite, ash chalk becoming more lithified; shale also present and black layers Depth (mbsf) Depth
180 190 200 210 220 230 240 250 260 270
unit
Logging 3 1 2
.Hu.Albian Aptian Haut. e. Stage
fossil zone fossil
NC8a-b Nanno- NC7 NC6 NC4b m) Ω 6810 Hauterivian–Albian interval between Sites 1207 and 1213. Correl 1213. and 1207 Sites between interval Hauterivian–Albian Hole 1213B Resistivity ( Biostrat. correlation Biostrat. peak) correlation (gamma ray "Selli" level 024 m) ? Ω 6 8 10 12 ? Hole 1207B Resistivity (
024 fossil zone fossil
UC3-4 Nanno-
NC6 UC8 UC0 NC7 NC5
NC9b NC9a NC8b NC8a NC8c- UC1-2
Cenom. Albian Aptian Haut-Barr. u. Stage unit
Summary of sedimentological interpretations and correlation of and correlation interpretations Summary of sedimentological Logging 3 4 5 6
340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 Depth (mbsf) Depth Figure F13. is based upon nannofossil biostratigraphy and geophysical and lithological data (from Robinson et al., 2004). al., et Robinson (from data lithological and geophysical and biostratigraphy nannofossil upon based is T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 39
Figure F14. Carbon (left column), oxygen (middle column), and neodymium (right column) isotope records for 66–72 Ma interval from Sites 1209, 1210, and 1212. Shaded bars across Site 1209 and 1210 records indicate chronostratigraphic extent of the inoceramid event (from Frank et al., 2005). V-PDB = Vi- enna Pedee belemnite.
66
67
68
69 Age (Ma) 70
71
72 Site 1209
66 Site 1210
67
68
69 Age (Ma) 70
71
72
-5.0 -4.0 -3.0 66 Site 1212 εNd
67
68
69 Age (Ma) 70
Planoglobulina multicamerata 71 Globotruncana stuartiformis Rugoglobigerina rugosa 72 Gavelinella beccariiformis Nuttalides truempyi 0.5 1.5 2.5 1.0 0.0 -1.0 δ13C (‰, V-PDB) δ18O (‰, V-PDB) T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 40
Erez
Age (Ma) Age ific (Bral- ific 35 40 45 50 55 60 65 , 2003); open , 2003); . Site 1209 C (‰) 13 δ Bralower and Mutterlose (1995), re-
-2.0 0.0 2.0 4.0 6.0 e scales are calculated using the equation of equation the using calculated are e scales this volume). this (this volume) and volume) (this Site 865 = –0.1‰. SAL = salinity event, HTM = hyperthermal event, = hyperthermal HTM event, = –0.1‰. SAL = salinity S δ C (‰) Bralower Dutton et al., 13
δ 0.0 2.0 4.0 te 1209 in the subtropical Pacific and Site 865 in the equatorial Pac in the equatorial 865 and Site Pacific in the subtropical te 1209 SAL s D HTM? δ δ PETM 10°C 15 O (‰) 18 spp.; solid circles = benthics. Paleotemperatur = benthics. circles solid spp.; δ 20 for foraminifers from Si for foraminifers = –0.98‰, and dw of surface water = water dw of surface and = –0.98‰, D 20 15 10 5°C δ mum event (from Dutton et al., 2005; mum event (1995) timescale. Open squares = surface planktonic Mg/Ca data at Site 865 (Tripati et al et (Tripati 865 at Site data Mg/Ca planktonic = surface squares Open timescale. (1995) 25 . Subbotina -2.5 -1.5 -0.5 0.5 1.5 s D δ δ 5°C Site 865 Site 1209 10°C Berggren et al Berggren
15 O (‰) 18 20 δ Paleogene stable isotope stable results Paleogene 25 , 1995) plotted relative to age using the nannofossil stratigraphies of stratigraphies nannofossil age using the to relative plotted , 1995) . 26 24 -2.5 -1.5 -0.5 0.5 1.5 28
25 20 15 10
Mg/Ca-temp (ºC)
al aeerymiddle early late early
-3.5
Eocene Paleocene and Luz (1983) with dw of deep water = water dw deep of with Luz (1983) and spectively, relative to the relative spectively, circles = surface planktonics; crosses = crosses planktonics; = surface circles ower et al ower et Figure F15. PETM = Paleocene/Eocene Thermal Maxi = Paleocene/Eocene PETM T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 41
Figure F16. Paleogene neodymium isotope records from Sites 1209 and 1211. Diamonds = Site 1209, trian- gles = Site 1211. Error bars represent two standard deviations. Benthic foraminiferal oxygen isotope values (green dots; from Zachos et al., 2001) provide an estimate of deep-sea temperature. The vertical line repre- sents a deep-sea temperature of 7°C (from Thomas, 2004).
δ18O (‰) 3 2 1 0
35
40
45
50 Age (Ma) 55
60
65
70
-6 -5 -4 -3 -2
εNd(t) T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 42 nic Hole A this volume). this cognized by plankto Site 1212 Hole B Premoli Silva et al., et Silva Premoli gical boundary as re Hole C Hole B Site 1211 al., 2002; Bralower et al., al., Hole A atsky Rise. atsky Arrows show level paleontolo of Hole B Site 1210 Hole A alower, Premoli Silva, Malone, et et Malone, Silva, Premoli alower, Hole A Site 1209 Cretaceous/Tertiary from Cretaceous/Tertiary boundary sections Sh
Hole C
White layer White ooze Danian Basal Figure F17. Figure F17. (from Br biostratigraphy foraminiferal T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 43
Figure F18. Abundances of principal Cretaceous/Tertiary boundary (K/T) survivor and incoming Cenozoic nannofossils. Survivor species counts are percentages of survivor assemblage. Incoming Cenozoic species counts are percentages of total assemblage. Line plots = additional taxa; dashed line = interval of mixed- reworked nannofossil taxa, and heavy dashed line = K/T boundary level (after Bown, 2005).
Survivor species Cyclagelo. reinhardtii Watznaueria sp. M. inversus Ne. fossus Zeugrhab. sigmoides 2040 60 80 100 20 40 60 2040 20 2040 60 80 100 215 %
216
NP2 N. 217 cruci.
6 64.5 218 5 Depth (mbsf)
NP1 219 %Cretaceous 4
3 65.0 K/T UC20 2 220 1510 5 1
Incoming Cenozoic species Neobisc. parvulum Cruciplac. primus Cocco. pelagicus Praeprinsius tenuiculus 2040 60 80 2040 60 80 20 40 60 2040 60 80 215 %
216
NP2 Praeprinsius sp. 217
6 218 64.5 5 Depth (mbsf) Co. pelagicus (small)
NP1 219 Futyania petalosa
4
3 65.0 K/T UC20 2 220 1 T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 44 cognized by pres- jor in carbon- changes this volume). Sites Sites are this volume). Hole A (3346 m) Site 1208 Bown, Hole B is recognized by ma by recognized is n). The PETM at Site 1208 is re 1208 is Site PETM at The n). Hole C (2907 m) Site 1211 Hole A Hole B sediment carbon isotope excursio carbon isotope sediment (2681 m) Site 1212 sections on Shatsky Rise. Onset of event Rise. Onset of on Shatsky sections Hole A (2573 m) Site 1210 bulk sediment carbon isotope stratigraphy and nannofossil biostratigraphy ( biostratigraphy and nannofossil stratigraphy carbon isotope sediment bulk Hole A Hole B Hole A The Paleocene/Eocene Thermal Maximum (PETM) The Thermal Paleocene/Eocene (2387 m) Site 1209 Hole B Hole C Figure F19. ate content and preservation (confirmed by the presence of bulk ervational change and is confirmed by confirmed and is change ervational organizedpresent by (and paleo) water depth. T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 45 ) C Age 54.85 55.00 (Ma) Acarinina soldadoen- Acarinina Sr/Ca (mmol/mol) (circles) and (circles) ) bulk magnetic susceptibility; ( magnetic susceptibility; ) bulk B Mg/Ca (mmol/mol) (after Zachos et al., 2003). Zachos et al., (after of bulk sediment; ( sediment; of bulk Morozovella velascoensis 3 ) CaCO O A 18 (‰) δ Acarinina soldadoensis and C Ospecimens of individualof 13 (‰) δ 18 δ C and C and 13 δ ) Morozovella velascoensis ts from the PETM in Hole 1209B. ( 1209B. from the PETM in Hole ts (%) D, E Fragmentation CD G Magnetic susceptibility ) Mg/Ca and Sr/Ca of and Sr/Ca Mg/Ca ) 3 F, G (wt%) CaCO Stable isotopes and trace elemen Stable 85 90 95 100 5 10 15 20 20 40 60 0 1 2 3 4 5 -2.5 -2.0 -1.5 -1.0 -0.5 3 4 5 6 0.5 1.0 1.5 Core photo AB E F
0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50 (triangles); and ( and (triangles); Depth in Section 198-1209B-22H-1 (m) 198-1209B-22H-1 Section in Depth sis Figure F20. fragmentation of planktonic foraminifers; ( foraminifers; of planktonic fragmentation T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 46 - 54.85 55.00 Age (Ma) % total Toweius 0 F. alanii F. F. schaubii F. lillianae F. F. sidereus F. 20 40 bijugatus Zygrhablithus LCO % nce (after Gibbs et al., 2006). et al., Gibbs nce (after 01020
FCO L. nascens Markalius Biantholithus (gray) 24 F. sidereus F. Heliolithus and % % total 0123 Braarudosphaera bigelowii % spp. The number of nannofossil fragments relative to 100 whole nannofossils whole 100 to relative fragments nannofossil of number spp. The N. modestus 10 20 N. protenus % total D. diastypus Prinsius Thoracosphaera Toweius ence, LCO = last common occurre 00
Discoaster Sphenolithus 20 40 60 and % total C. robusta N. junctus 0 fractionexcept for 15 High Coccolithus Toweius - 510 Indet./Ident. Low Dissolution 0 2.5 Toweius (‰) C 13 δ
Nannofossil diversity and abundance plots for the PETM in Hole 1209B. Nannofossil abundance records are percent abundances rel abundances are percent records abundance Nannofossil 1209B. in Hole PETM the for plots and abundance diversity Nannofossil 1.7 2.1 3 point running average 024 Planktonic foraminiferal Nannofossil diversity (S-W)
195.6 195.8 196.2 196.4 196.6 196.0 196.8 Depth (mbsf) Depth Figure F21. ative to the totalnon- is used as a preservation index. FCO = first common occurr common index. FCO = first preservation as a used is T.J. BRALOWER ET AL. LEG 198 SYNTHESIS: SHATSKY RISE CLIMATE AND OCEANOGRAPHY 47 CHAPTER NOTES
N1. Dumitrescu, M., and Brassell, S.C., submitted. Compositional and isotopic char- acteristics of organic matter for the early Aptian oceanic anoxic event at Shatsky Rise, ODP Leg 198. Palaeogeogr., Palaeoclimatol., Palaeoecol. N2. Kaiho, K., Takeda, K., Petrizzo, M.R., and Zachos, J.C., submitted. Anomalous shifts in tropical Pacific planktonic and benthic foraminiferal test size during the Paleocene–Eocene Thermal Maximum. Palaeogeogr., Palaeoclimatol., Palaeo- ecol.
*Dates reflect file corrections or revisions.