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Wilson, P.A., Lyle, M., and Firth, J.V. (Eds.) Proceedings of the Ocean Drilling Program, Scientific Results Volume 199

24. BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES IN A MIDDLE DIATOM-RICH UNIT FROM THE EASTERN EQUATORIAL PACIFIC: ODP LEG 199, SITE 12191

Torsten H. Steiger2

ABSTRACT

Quantitative analysis of radiolarian assemblages at Ocean Drilling Program Leg 199 Site 1219 provides new information on ocean temper- ature variations during a significant productivity event. This event (which occurs within radiolarian Zone RP-15) is marked by the accumu- lation of diatoms in association with highly diverse radiolarian faunas. The data collected for this present work include (1) counts of radiolar- 1Steiger, T.H., 2006. Biogenic ian diversity and (2) estimates of the abundance ratio of the radiolarian sedimentology of radiolarian groups Spumellaria and . The radiolarian assemblages within assemblages in a middle Eocene the diatom-rich unit do not differ greatly from one another in their diatom-rich unit from the eastern composition. There are, however, some long-term trends in faunal equatorial Pacific: ODP Leg 199, Site 1219. In Wilson, P.A., Lyle, M., and abundances, as indicated by changes in the nassellarian:spumellarian Firth, J.V. (Eds.), Proc. ODP, Sci. Results, ratio. Particular changes in this ratio that possibly are related to the dia- 199, 1–19 [Online]. Available from tom event involve (1) the increase of the abundance of actinommids World Wide Web: . [Cited YYYY-MM-DD] nal phase of diatom production. These changes can tentatively be inter- 2Silberbornstrasse 4, D-38889 preted as a reaction of specific radiolarian groups to the increase of Blankenburg . diatom productivity in shallow waters. Taken together with the earlier [email protected] onset of nannoplankton deposition, the diatom-rich unit can be interpreted as marking a short-term gradual change in sea-sur- Initial receipt: 26 April 2004 Acceptance: 29 September 2005 face temperature, together with a change in the equatorial current sys- Web publication: 10 April 2006 Ms 199SR-217 T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 2 tem that involved the introduction of cold waters by lateral transport rather than the vertical of water masses derived from the southeastern regions of the Pacific Ocean.

INTRODUCTION

Scientific ocean drilling in the central equatorial Pacific Ocean has concentrated on obtaining fundamental information about sedimen- tary successions and developing an overall biostratigraphic framework. As drilling techniques have improved, the research goals have changed somewhat—moving away from basic investigations and toward special- ized objectives such as the reconstruction of changing climatic condi- tions and ocean-current patterns since the onset of deposition. In addition to its general-interest objectives (those pre- sented in the Ocean Drilling Program [ODP] Leg 199 Scientific Prospec- tus), Leg 199 focused on the sequence of calcareous and siliceous in the area of the paleoequator during the early Tertiary (be- tween 56 and 40 Ma) and on the evolution of biota there at that time. Of particular interest were (1) the effects of temperature on the position of the carbonate compensation depth and the stability of marine sili- ceous components and (2) the effects of the Late Paleocene Thermal Maximum on productivity. Previous drilling in this area was carried out during Deep Sea Drilling Project (DSDP) Leg 8 (Tracey, Sutton, et al. 1971), DSDP Leg 16 (van Andel, Heath, et al., 1973), and DSDP Leg 85 (Mayer, Theyer, Thomas, et al., 1985). Improved drilling techniques al- lowed the collection of high-recovery cores and almost undisturbed sediment sequences for most of Leg 199. In addition, multiple coring of several holes allowed continuous sedimentological analysis by letting gaps in the sediment record that were the result of drilling disturbances be filled with corresponding sediments from other holes at the same site. Leg 199 Sites 1215–1222 (a north–south oriented transect) were drilled on 56-Ma basaltic crust; an exception was Site 1218, which was drilled on 40-Ma crust. The sedimentary record obtained from Leg 199 sites showed predictable variations from north to south. Significant thicknesses of sediment were intersected at the southern sites for those sites that were at the equator between 40 and 25 Ma. Three sites (Sites 1219, 1220, and 1221) contained signals of both southern and northern hemisphere positions (Shipboard Scientific Party, 2002). The sediments studied from Leg 199 sites range in age from the late middle Eocene to the Eocene/Oligocene boundary. During that time, the ecological and productivity conditions changed from those charac- teristic of an oceanic, deepwater milieu to those that marked the change from siliceous to carbonaceous lithologies at the Eocene/Oli- gocene boundary. The drilled sediments spanned a 20-m.y. time period that covers the passage of the equator over the Inter-Tropical Conver- gence Zone (ITCZ). The sediments that were deposited contain accumu- lations of radiolarians, diatoms, and nannofossils that are characteristic of specific productivity conditions within the Eocene ITCZ. This paper is the result of a pilot study of 30 samples from Hole 1219A, from a dia- tom-rich unit that is both underlain and overlain by radiolarian-rich sediments. T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 3 GEOGRAPHIC SETTING

Site 1219 is located at 7°48.019′N, 142°00.940′W, 3° north of the Clipperton Fracture Zone (Fig. F1). The drill site represents the south- F1. Leg 199 drill sites, p. 13.

160°W 150° 140° 130° 30° ernmost location of a north–south oriented transect drilled on 56-Ma N Leg 199 sites DSDP sites

Site 1215 . crust. The distance from Site 1219 northward to Site 1220 is ~400 km, ai F.Z Molok Honolulu Site 1216 20° and the distance to Leg 8 Sites 70 and 71 is ~300–400 km (Tracey, Sut- Site 40 Site 43 Site 1217 .Z. rion F Cla Site 162 ton, et al., 1971). Site 1222 Site 42 Site 1221 Site 160 Site 163 Site 1220 Site 161 10° Site 1219 was evidently situated in the southern hemisphere until 29 Site 1218 Site 1219 Site 69 Site 70 Site 575 Site 71 Z. Site 574 ton F. Ma (late Oligocene equator crossing); equatorial and tropical conditions lipper km C 0 500 1000 Site 573 Site 72 0° existed there between the middle Eocene and the early (Ship- 150°W 145° 140° 135°

board Scientific Party, 2002). These conclusions are based on recon- Site 1215 ne ° re Zo 25 ai Fractu Molok N struction of equator passage and paleogeographic position using a fixed Site 1216 20° 40 43 Site 1217 ne ture Zo hotspot model (Gripp and Gordon, 1990; Engebretson et al., 1985). n Frac ° io 15 Clar 162 42 one Site 1222 cture Z ahi Fra Mahi M Site 1221 Site 1219 sediments contain numerous levels of diatom-bearing sedi- 163 161 10° Site 1220 Site 1219 Site 1218 70 575 ments that are related to the high-productivity events at 40 Ma and 574 5° one 71 ture Z Frac erton Clipp 72 573 during the equator passage (Fig. F2). Neighboring sites are not included 0° in this pilot study, either because of the scarcity of diatoms in the smear slides from Site 1220 or because of the poor sediment recovery at neigh- boring sites. Floral and faunal changes in the corresponding diatom- F2. Diatom events, p. 14. S N

Site 1219 rich unit at Site 1218 will be compared with the present results in a sep- 5063.3 m

N Site 1220 5217.9 m Site 1222 arate study. 4988.8 m Site 1217 Site 1216 5342.1 m Site 1215 S Site 1221 5147.2 m Oligocene 5175.3 m 5395.6 m

Eocene N ? ? RP-15 ? RP-15 N ? ? S N

S Basalt S basement Basalt basement Basalt basement SCIENTIFIC PURPOSE Clipperton Mahi Clarion Molokai F.Z. Mahi F.Z. F.Z. F.Z.

Clay, clay with zeolite, zeolitic clay Clayey nannofossil ooze Equator crossing based on shipboard Clay with Nannofossil ooze paleomagnetism results

Thin chert layers Nannofossil chalk Equator crossing based on backtrack calculation Radiolarite Nannofossil chalk with increasing dolomite >5% diatoms Radiolarian ooze and clay, clayey radiolarian ooze Nannofossil chalk with increasing diatoms Radiolarian ooze with increasing clay content Metalliferous oxide ooze Previous investigations on siliceous organisms in the central equato- Nannofossil clay Basalt rial Pacific Ocean have concentrated on radiolarian- and diatom-based biostratigraphic zonation, using as their basis sediments cored during DSDP and ODP legs and others obtained from box cores and piston cores (Moore, 1971; Dinkelman, 1973; Schrader, 1976; Fenner, 1984; Nigrini, 1985). Oceanographic research related to the occurrence of ra- diolarians and diatoms has focused on their lateral distribution relative to the present current system, sea-surface temperatures, temperature gradients, thermocline influences, salinity, and nutrient supply (comp. Blueford et al., 1990; Goll, 1976). Radiolarian depth zonations (Kling, 1979) have been obtained from different water masses and for low and high latitudes, and radiolarian associations have been recognized that represent specific temperature and bathymetric regimes (Petrush- evskaya, 1971; Casey, 1993). Recent paleoceanographic research has investigated depositional patterns of siliceous and calcareous micro- organisms and nannoorganisms with the purpose of delineating the spatial distribution of productivity zones and (in combination with ocean-climate models) of investigating the recycling of silica (Leinen, 1985; Ragueneau et al., 2000; Moore et al. 2001; Huber, 2002). The primary scientific goal of the present study is to describe and in- terpret the changes in radiolarian associations from the Zone RP-15 dia- tom-rich unit at Site 1219. The “radiolarites” underlying this unit are composed either of hard radiolarian chert that could not be penetrated, drilled, or recovered without problems or of soft brownish to pink ra- diolarian accumulations that are identified as radiolarites. These under- lying radiolarian deposits range from middle to late Eocene in age and represent the overall signal of unique oceanic conditions described and modeled by Huber (2002). From an ecological standpoint, the radiolar- ian mass accumulations are a result of the evolutionary potential of ra- diolarians, the supply of silica into the ocean system, and the T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 4 availability of nutrients. After the high temperatures of the early Eocene, radiolarians increased both in their diversity and in their indi- vidual abundance (hence in their biomass); the result was that every- where at lower latitudes there was deposited a radiolarian-rich sediment interval (Zones RP-14 through RP-16). The mass accumulation rate of radiolarian silica is constant throughout this interval, suggesting that stable oceanic conditions existed for most of the middle Eocene. Within this radiolarian-rich interval is the diatom-rich unit that forms the subject of this present work; it represents an intercalation of parti- cles produced by photoautotrophic phytoplankton and marks an im- portant change in the eastern equatorial Pacific Ocean current system. This diatom-rich unit is related to a high-productivity belt deposited in the ITCZ during the equator crossing of Hole 1219A and nearby Site 1220. Backtracking and paleomagnetic investigations indicate that the southern sites of the transect crossed the equator at ~29 Ma. This tim- ing favors the hypothesis that the diatom accumulation at Site 1219 is part of the southern productivity lobe of the ITCZ, which was moving southward and transporting the productivity signal in younger sedi- ments of the southern sites. Above the diatom-rich unit are normal ra- diolarites that are almost lithologically identical to those from the middle Eocene; these occur up to the Eocene/Oligocene boundary. This pilot study concentrates on the changes in biological associa- tions from the onset to the end of the deposition of the diatom-rich unit. Because other siliceous organisms (e.g., ) are almost unde- tectable in the radiolarite, the analysis is limited to radiolarians. The main point of interest concerns the sedimentological or, possibly, bio- logical relationship between spherical radiolarians (spumellarians) and monopylid radiolarians (nassellarians); this relationship has been used to interpret changes in water depth, temperature, and productivity at other times in earth history (Steiger, 1998). A secondary point concerns the question of whether the faunal development was induced by pro- ductivity or whether it was simply a long-term reaction of the radiolar- ians to gradual changes in oceanic conditions and the geographic location of the depositional area; this question is investigated by ana- lyzing counts of subgroups on the family level or counts of groups of comparable morphotypes from base to top of the diatom-rich unit. Fi- nally, the study tries to determine what were the major radiolarian as- semblages, to identify the predominant species in these, and to estimate the degree to which compositional changes in the associations reflect alterations within the water column.

METHODS

Thirty sediment samples were obtained from the diatom-rich unit. The disaggregated sediment was simply suspended in water on a slide and observed. This was sufficient to identify differences in radiolarian occurrences and to allow determination of the ratio of diatoms to radio- larians and the percentage of radiolarian families (Fig. F3). It must be F3. Vertical distributions of con- stressed that the aim of the study was not to quantify fluxes of radiolar- tents, Hole 1219A, p. 15. ian and diatom tests to characterize paleoproductivity in this time in- Zone Physical properties LAS mineralogy Siliceous biota groups Hole 1219A SI) ) 3 -6 Color reflectance (L*) Bulk density (g/cm Magnetic susceptibility (x 10 Calcite (%) Illite (%) Smectite (%) (%) Diatoms Porifera Nassellarians Spumellarians

20 40 80 1.2 1.6 2.0 40 60 80 40 80 20 40 40 80 20 40 60 40 80 20 40 40 80 20 40 60 terval but only to determine radiolarian maxima, typical radiolarian Core Recovery Samples Lithology Age Calcareous nannofossils Radiolarians Magnetic stratigraphy RP-17 Barren 170 C17n 19H ) f CP15 RP-16 assemblages, and specific occurrences of taxon groups or growth forms s

b 180 20H CP14b C18n m (

h

t Barren p e CP14b D 190 21H

above and below the diatom-rich unit (cf. Cortese and Bjørklund, middle Eocene RP-15 CP14a

C19n 200 22H

1999). Thus it was not necessary in this case to use sophisticated meth- Nannofossil Radiolarian Interbedded ooze ooze diatom, Radiolarian ooze nannofossil, and with decreasing clay content ods of radiolarian preparation (e.g., Locker, 1996) in order to obtain radiolarian oozes T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 5 randomly distributed individuals. The quantitative data set was based on a 300-point grid for the diatom:radiolarian ratio and on the count- ing of 300 radiolarian individuals in determining the percentages of ra- diolarian families.

LITHOLOGIES OF DIATOMACEOUS SEDIMENTS AND RADIOLARITES AT SITE 1219

The diatom-rich unit occurs from the lower part of Sections 199- 1219A-20H-4 through 22H-2. The interval of maximum diatom content is clearly revealed by a color change from reddish brown sediments dominated by radiolarians to grayish green diatomaceous sections. The color change is gradual in the lower part of the unit and more abrupt (but still gradual) in the upper part of the unit. The sediments are in- tensely bioturbated. Preservation of diatom flora is moderate to poor because of intense dissolution of the tests (J. Fenner, pers. comm.). Dissolution of diatoms is species-selective (see discussion in Berger, 1976). Robust species of the Centrales group are predominant, whereas other taxa are almost impos- sible to identify, mostly because of their fragmented occurrence. In con- trast to this, radiolarians are mostly well preserved, although dissolution features are present in delicate shells. Some of the robust ra- diolarians show rounded protuberances (e.g., the spines of the actinom- mids or periphaenas), and the ragged outlines of many spongodiscids is also evidence of dissolution. Artostrobids are typically dissolved at their collarlike base. The radiolarian shells settled gently to the bottom, in water that may evidently have been moving slowly; afterward came bioturbation and compaction of the sediment. The reason for suggesting that there may have been slow-moving currents is that there is evidence in some places of both original layering and size-sorting of shells. This layering has been modified by differential compaction, forming small lenses in which grains are concentrated. The lenticular spaces of low grain den- sity are filled with long-spined radiolarians and ornamented forms. Be- tween the larger radiolarians, the rock matrix is composed of small radiolarians, diatoms, calcareous nannofossils, and clay. The entire diatom-rich unit is composed of three parts. The basal part, above the color change from the reddish radiolarites to grayish to greenish diatom-radiolarian mixed lithologies, is characterized by thin- layered banding. The central part of the unit begins at a relatively abrupt color change, with thick color bands retaining the color of the basal part. The unit terminates with a gradational color change from greenish gray to reddish gray and reddish, returning to the normal Eocene-type radiolarite. The upper part of the unit still contains consid- erable numbers of diatoms in Core 199-1219A-20H. Smear slides of older samples show that there is a precursor diatom event within Section 199-1219A-23H-4 (middle Eocene; radiolarian Zone RP-14; Podocyrtis mitra Zone) (cf. Sanfilippo and Riedel, 1985). Above Zone RP-15, the diatom content of late Eocene radiolarian sedi- ments is 0%–5%, which does not represent a distinct diatom interval. The Zone RP-15 diatom episode is important because high numbers of calcareous nannoplankton are present. The sedimentologic overview (Fig. F3) demonstrates that calcareous nannoplankton occurs earlier than the diatoms that start just at the beginning of the Podocyrtis cha- T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 6 lara Zone in Section 199-1219A-24H-2. The alternating layers of diatom and radiolarian deposits are characterized by a distinct color banding (Fig. F4). F4. Lithologic sequence of RP-15 diatom-rich interval, p. 16.

Core, section, interval (cm) 199-1219A-21H- 1, 20-24 Low diatom BIOSTRATIGRAPHIC BOUNDARIES AND 1 m Eocene-type content; radiolarite end of productivity 1, 140-142 phase 2, 14-16 2, 27-29 2, 40-42 Diatomaceous 2, 67-69 interval, upper part: DURATION OF DEPOSITION Decreasing 2, 120-122 color banding decreasing in diatom thickness of content, 3, 30-32 layers and Si MAR, and 3, 63-65 color change from greenish productivity gray to reddish OF DIATOM-RICH UNIT 4, 28-30 brown

4, 100-102

Diatomaceous Highest interval, middle diatom part: content, color bands with Si MAR, 5, 100-102 thick light and The late middle Eocene radiolarites of Hole 1219A are composed of 5, 120-122 colored layers productivity 6, 30-32 6, 60-62 6, 85-87 Diatomaceous 6, 100-102 Increasing interval, lower diatom part: taxa belonging to radiolarian Zones RP-16 (Podocyrtis goetheana Zone), 6, 140-142 content, color bands with Si MAR, 7, 30-32 short sections and of light and dark productivity RP-15 (Podocyrtis chalara Zone), and RP-14 (Podocyrtis mitra Zone). Based 7, 60-62 colored layers 8, 33-36 Eocene-type 8, 49-51 on age calculations using data from the multisensor track (Pälike et al., radiolarite this volume), the diatom-rich unit was deposited ~1.8 m.y. ago (39.554– 41.358 Ma). Linear rates for Hole 1219A of ~4.8 m/m.y. indicate the end of a 4-m.y. period of relatively fast sedimentation (Shipboard Scientific Party, 2002). Bulk mass accumulation rates (MARs) are very high at ~41 Ma. MARs of silica for Hole 1219A peak at 41 and 43 Ma, corresponding to both of the middle Eocene diatom intervals. The basal part of the diatom-rich unit in Zone RP-15 corresponds to the base of the lower Si MAR peak, and the middle part of Zone RP-15 shows stepwise decreasing Si MAR. A similar trend can be recognized at Site 1218 and, with weaker intensity, at Site 1217 (Shipboard Scientific Party, 2002).

QUANTITATIVE ANALYSIS OF RADIOLARIANS IN ZONE RP-15 DIATOM INTERVAL

The methodological approach to the particle analyses of the Zone RP-15 diatom interval depends strongly on preparation procedures that provide the basis for reproducible results. Considering the sedimentary fabric of the radiolarites described under “Lithologies of Diatoma- ceous Sediments and Radiolarites at Site 1219,” p. 5, the vertical dis- tribution of the particles is influenced by reworking processes that are strong enough that high-resolution sampling would not yield more de- tailed information about the radiolarian deposition. Therefore, radiolar- ians were counted in the original sediment taken from suspended samples treated with hydrogen peroxide. The counting results are calcu- lated as percentage of groups in the sample. Another problem with the counting procedure is the high dissolution rate and selective dissolu- F5. Ratios of siliceous organisms, tion of the observed particles. The preservation of the diatomaceous p. 17. sediments is characterized by the fact that diatoms are severely affected A 100 Diatoms by dissolution, whereas radiolarians show specific dissolution features, 90 80

70 restricting the possibility of comparing diatom accumulation and depo- 60

50

40 sition of radiolarians. After counting, particles in the original sediment Radiolarians (%) 30

20 slides were prepared for identification of predominant taxa in the radio- 10

0 9 -65 larian assemblages. 85-87

199-1219A-20H-5,199-1219A-21H-1, 91-93199-1219A-21H-2, 20-24199-1219A-21H-2,199-1219A-21H-2, 14-16 27-29 40-42199-1219A-21H-3,199-1219A-21H-3,199-1219A-21H-4, 30-32 63 28-30 199-1219A-21H-6,199-1219A-21H-6,199-1219A-21H- 30-32 60-62 6, 199-1219A-21H-7,199-1219A-21H-7,199-1219A-21H-8, 30-32199-1219A-21H-8, 60-62 33-36199-1219A-22H-1, 49-51199-1219A-22H-2, 92-94 27-2 199-1219A-19H-1,199-1219A-19H-4,199-1219A-19H-6, 102-104199-1219A-20H-4, 130-132 144-146 133-135199-1219A-21H-1, 140-142 199-1219A-21H-2W,199-1219A-21H-2, 67-69 120-122 199-1219A-21H-4,199-1219A-21H-5,199-1219A-21H-5, 100-102 100-102 120-122 199-1219A-21H-6,199-1219A-21H-6, 100-102 140-142 199-1219A-22H-1W, 35-37 Core, section, interval (cm) The calculated results of radiolarian quantities vs. diatom content B 120

Nassellarians (Fig. F5) indicate that the diatom interval starts with a rapid decrease in 100 the radiolarian content. Above the diatom maximum (at the boundary 80 60

40

between narrower and wider color banding represented by darker gray Spemullarians (%) layers), there is a stepwise decrease in the diatom content, correspond- 20 0

, 14-16

199-1219A-20H-5,199-1219A-20H-7,199-1219A-21H-1, 91-93 36-38199-1219A-21H-2 20-24199-1219A-21H-2,199-1219A-21H-2,199-1219A-21H-2, 27-29 40-42199-1219A-21H-3, 67-69199-1219A-21H-3,199-1219A-21H-4, 30-32 63-65 28-30 199-1219A-21H-6,199-1219A-21H-6,199-1219A-21H-6, 30-32 60-62 85-87199-1219A-21H-7,199-1219A-21H-7,199-1219A-21H-8, 30-32199-1219A-21H-8, 60-62199-1219A-22H-1, 33-36199-1219A-22H-1, 49-51199-1219A-22H-2, 35-37 92-94 27-29 199-1219A-19H-1,199-1219A-19H-4,199-1219A-19H- 102-104199-1219A-20H-4, 130-132 6, 144-146 133-135199-1219A-21H-1, 140-142 199-1219A-21H-2, 120-122199-1219A-21H-4,199-1219A-21H-5,199-1219A-21H-5, 100-102 100-102 120-122199-1219A-21H-6,199-1219A-21H-6, 100-102 140-142 Core, section, interval (cm) T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 7

ing to a parallel stepwise reduction of the Si MAR, which indicates that diatoms are mostly responsible for the fluctuations in the Si MARs. Radiolarian counts provide two important values:

1. The ratio of nassellarians to spumellarians indicates changes in the temperature regime. 2. The percentage of radiolarian families compared to the bulk fauna monitors significant form groups that possibly indicate evolutionary trends or more favorable conditions in the water column, such as changes in the food structure, light, or salinity.

Figures F5 and F6 show the results of nassellarian:spumellarian counting F6. Percentages of major radiolar- and radiolarian family counts. These raw data show trends in the radio- ian families, p. 19.

Coccodiscids Theoperids 60 larian faunal distribution. 30 50 25

40 20

30 15

20

Percentage 10 Percentage

10 5

0 0

H-8, 49-51 H-1, 92-94

A-21H-8, 33-36

199-1219A-20H-5,199-1219A-20H-7,199-1219A-21H-1, 91-93 199-1219A-21H-2,36-38 199-1219A-21H-2,22-24 199-1219A-21H-2, 199-1219A-21H-2,14-16 27-29 199-1219A-21H-3,40-42 199-1219A-21H-3,67-69 199-1219A-21H-4, 30-32 63-65 28-30 199-1219A-21H-6,199-1219A-21H-6,199-1219A-21H-6, 30-32 60-62 199-1219A-21H-7,85-87 199-1219A-21H-7,199-1219A-21H-8, 199-1219A-21H-8,30-32 199-1219A-22H-1,60-62 199-1219A-22H-1,49-51 199-1219A-22H-2,33-36 35-37 92-94 27-29 199-1219A-20H-5,199-1219A-20H-7,199-1219A-21H-1, 91-93 199-1219A-21H-2,36-38 199-1219A-21H-2,22-24199-1219A-21H-2, 199-1219A-21H-2,14-16 27-29 199-1219A-21H-3,40-42 199-1219A-21H-3,67-69199-1219A-21H-4, 30-32 63-65 28-30199-1219A-21H-6,199-1219A-21H-6,199-1219A-21H-6, 30-32 60-62 199-1219A-21H-7,85-87199-1219A-21H-7,199-1219A-21 199-121930-32 199-1219A-22H-1,60-62199-1219A-22199-1219A-22H-2, 35-37 27-29 199-1219A-21H-2 120-122 RADIOLARIAN ASSEMBLAGES RECOGNIZED 199-1219A-20H-4, 133-135199-1219A-21H-1, 140-142 199-1219A-21H-4,199-1219A-21H-5,199-1219A-21H-5, 100-102 100-102 120-122199-1219A-21H-6,199-1219A-21H-6, 100-102 140-142 199-1219A-20H-4, 133-135199-1219A-21H-1, 140-142 199-1219A-21H-2, 120-122199-1219A-21H-4,199-1219A-21H-5,199-1219A-21H-5, 100-102 100-102 120-122199-1219A-21H-6,199-1219A-21H-6, 100-102 140-142 Core, section, interval (cm) Core, section, interval (cm)

Actinommids Artostrobids 25 30

25 20

IN ZONE RP-15 DIATOM INTERVAL 20 15

15 Percentage

Percentage 10 10

5 5

0 0 5 2 2 -24 -42 -94 -29 02 42 0-42 0-102

H-6, 60-62 H-5, 120-12 Radiolarian counts demonstrate that recognizable assemblages in de- 1H-6, 140-1 199-1219A-20H-5,199-1219A-20H-7,199-1219A-21H-1, 91-93199-1219A-21H-2, 36-38199-1219A-21H-2, 22199-1219A-21H-2,199-1219A-21H-2, 14-16 27-29199-1219A-21H-3, 40199-1219A-21H-3, 67-69199-1219A-21H-4, 30-32 63-65 28-30199-1219A-21H-6,199-1219A-21H-6,199-1219A-21H-6, 30-32 60-62199-1219A-21H-7, 85-87199-1219A-21H-7,199-1219A-21H-8,199-1219A-21H-8, 30-32199-1219A-22H-1, 60-62199-1219A-22H-1, 49-51199-1219A-22H-2, 33-36 35-37 92 27 199-1219A-20H-5,199-1219A-20H-7,199-1219A-21H-1, 199-1219A-21H-2,91-93 199-1219A-21H-2,36-38 199-1219A-21H-2,22-24199-1219A-21H-2, 14-16 199-1219A-21H-3,27-29 199-1219A-21H-3,4 199-1219A-21H-4,67-69 30-32 63-65 199-1219A-21H-6,28-30199-1219A-21199-1219A-21H-6, 30-32199-1219A-21H-7, 199-1219A-21H-7,85-87199-1219A-21H-8,199-1219A-21H-8, 199-1219A-22H-1,30-32 199-1219A-22H-1,60-62 199-1219A-22H-2,49-51 33-36 35-37 92-94 27-29 199-1219A-20H-4, 133-13199-1219A-21H-1, 140-142199-1219A-21H-2, 120-122199-1219A-21H-4,199-1219A-21H-5,199-1219A-21H-5, 100-102 100-102 120-122199-1219A-21H-6,199-1219A-21H-6, 100-102 140-142 199-1219A-20H-4, 199-1219A-21H-1,133-135 140-142199-1219A-21H-2, 199-1219A-21H-4,120-122199-1219A-21H-5,199-1219A-21 10 100-1199-1219A-21H-6,199-1219A-2 100-10 Core, section, interval (cm) posits underlying Zone RP-15 are different from those in deposits over- Core, section, interval (cm) lying Zone RP-15. Furthermore, the radiolarian assemblage composition obviously changes through the diatom interval, which possibly repre- sents a linear faunal evolution pattern. The radiolarian assemblage beneath the diatom accumulation is a coccodiscid–theoperid–artostrobid assemblage. The radiolarian assem- blage in the uppermost section of diatom-rich sediments is a theoperid– coccodiscid–actinommid assemblage. There are also distinct faunal as- semblage compositions in the lowermost sediments of Zone RP-15 and at the diatom maximum in the diatomaceous interval. The coccodiscid–theoperid–artostrobid assemblage is characterized by large coccodiscid shells, mostly represented by Lithocyclia ocellus E. and various species of Periphaena and Heliodiscus. The artostrobid group is composed of smaller and robust forms represented by Dictyoprora mongolfieri (E.). The radiolarian assemblage from the uppermost part of the diatom interval, grading into the normal Eocene radiolarian sediment, is char- acterized by a reversal in the theoperid:coccodiscid ratio and a clear in- crease in actinommids. Artostrobids decrease above the diatom maximum.

DETAILED FAUNAL CHANGE

The general pattern of radiolarian faunal change through the diatom interval is a change in the nassellarian:spumellarian ratio; there is an increase in nassellarian shells above the diatom maximum (Fig. F5). In detail, the radiolarian families reacted as follows (Fig. F6):

1. Actinommids increased above the diatom maximum to a point where spumellarians and nassellarians are equal during the latest stage of the event. 2. Higher contents of theoperids in the upper sections of the dia- tom interval indicate a minor decline in artostrobids. 3. The artostrobids show two maxima: a smaller peak at the base of the diatom event and a second peak above the diatom maximum T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 8

but in the diatom zone. The peak at the base of the interval prob- ably represents a generally high artostrobid content, mostly rep- resented by D. mongolfieri (E.), which is interrupted by one sample with fewer specimens. The upper peak could also be seen as a sedimentologic effect but is located at the top of a gradual increase of artostrobids during the diatom event.

There is no dramatic change in the radiolarian composition during the Zone RP-15 diatom interval. The major groups, such as coccodiscids and theoperids, display a long-term trend that does not seem to be in- fluenced by the diatom occurrences. It is difficult to interpret these find- ings. Actinommids comprise the only group that clearly contributes to the composition of the radiolarian assemblage as a reaction to the dia- tom event and probably represent faunal elements that originated in the upper parts of the water column (cf. Casey, 1993). Actinommids proba- bly show minimum occurrences because of the diatom impact in the up- permost part of the water column. Other radiolarian groups, which are not affected by the diatom event, belong to tropical warm-water assem- blages that, especially in the Eocene, were located in deeper bathymetric zones. The artostrobids seem to react in colder and deeper zones of the water column. In the literature, robust forms of this group are inter- preted as belonging to cold-water upwelling faunal assemblages (Casey, 1993); therefore, it is of interest to recognize them at both the base and top of the diatom interval. Consequently, the artostrobids together with the diatoms could be interpreted as representatives of a cooling event, but they dominated only for short periods of time.

CONSEQUENCES FROM FAUNAL ANALYSIS

Radiolarian counts from the diatom interval sequence indicate that the deposition of radiolarian shells at Site 1219 is probably not con- nected to the production of diatoms or the occurrence of a high-pro- ductivity event. The changing nassellarian:spumellarian ratio is either a result of a long-term trend of slight deepening of the oceanic environ- ment or of a temperature change with cooling and subsequent warming of the entire water column in the equatorial area during the middle to late Eocene. Also, there are some observations that could be interpreted as reactions to the onset of both diatom deposition and a new oceanic circulation pattern (comp. Blueford et al., 1990). This reaction is illus- trated in the vertical distribution of radiolarian groups and specific dis- solution features in radiolarian shells traced from base to top of the diatom sequence. The general Eocene-type radiolarian fauna is mostly composed of warm-water, tropical, low-latitude forms as interpreted by Casey et al. (1990). The lateral distribution of the middle Eocene radiolarites indi- cates a very broad tropical zone, where similar assemblages of radiolar- ians are deposited. The cosmopolitan radiolarian composition in the Central Pacific region is influenced by the open Isthmus of Panama during the Eocene. It is not possible to interpret a maximum zone of ra- diolarian production in this area. McGowran’s (1989) interpretation of radiolarian development at the end of the early Eocene, after maximum temperature regimes (Zachos et al., 2001) and during the following cooling period, is reasonable. As long as radiolarians are used as indica- tors of increased productivity, the widespread occurrence of thick radio- larian deposits can be interpreted as a biologic reaction of siliceous T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 9 organisms in an oceanic environment without steep gradients but with a slight tendency toward cooling. The permanent El Niño model intro- duced by Huber (2002) supports this interpretation. Interruptions of the middle Eocene oceanic conditions in terms of temperature changes and availability of silica could immediately modify the geometry of the circulation system with a consequent change in the configuration of productivity areas. The three-lobed productivity zone of the ITCZ in the equatorial Pacific Ocean could have developed under these conditions, reaching shallow water levels, transporting cold-water biota (such as ra- diolarians from the southeastern Pacific area), and initiating the growth of diatoms. This picture does not take into account specific oceanic in- fluences produced by limiting factors like Fe (cf. Ragueneau et al., 2000) or special wind systems. The mass accumulation of diatoms is an indicator and part of the Zone RP-15 productivity event. The change in the oceanic circulation regime is documented by the occurrence of calcareous nannoplankton followed by diatoms that indicate maximum productivity for this 2-Ma interval. Only a few radiolarian groups, or even single taxa, reacted un- der these changing conditions. The artostrobids possibly represent such cold-water forms having bloomlike evolution episodes in the initial and terminal stages of the diatom productivity event. Another group of ra- diolarians, the actinommids, represent tropical warm-water faunas and are indicators of a warming phase after the diatom event when the former middle Eocene radiolarian assemblage composition returns. It is possible that the elongated occurrence of the diatom mass accu- mulations (also found at Site 1218) belongs to the southern productiv- ity lobe of the ITCZ in the middle Eocene. Site 1219 sediments continuously contain varying amounts of diatoms throughout the Oli- gocene. Greater diatom content coincides with the equator passage at ~29 Ma.

SUMMARY

The primary results of this study on the depositional patterns of ra- diolarians during a diatom event in the equatorial Pacific Ocean during the middle Eocene are as follows:

1. Most radiolarian groups were not affected by the mass produc- tion of diatoms and the deposition in the area of the ITCZ, indi- cating major radiolarian taxa distribution in deeper marine tropical environments and a deep thermocline with tempera- tures similar to surface temperatures. 2. Changing environmental conditions are responsible for rapidly evolving distinct zones of higher productivity in the equatorial area. The Eocene radiolarian sedimentation, which is character- ized by an extended marine zonation lacking steep gradients, is controlled by slight cooling of the circulation system and rich input of nutrients and silica after an extremely warm period (early Eocene). 3. Radiolarian assemblage compositions indicate that lateral trans- port, together with the increasing South Equatorial Current, in- duced an overprint from above, adding diatoms and shallow marine radiolarians (actinommids) to the faunal spectrum dur- ing and immediately after maximum diatom production. T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 10

4. Some specific forms of radiolarians (“robust” artostrobids; Casey, 1993) seem to react at the beginning and end of the diatom oc- currence. Nassellarians, mostly occurring in intermediate zones between the warm- and cold-water levels at greater depths, could be specialized to collect food and silica from the sinking diatom tests, which are mostly dissolved at these bathymetric levels.

ACKNOWLEDGMENTS

The author is greatly indebted to the Co-Chief Scientists and all col- leagues of the Shipboard Scientific Party as well as the ship’s crew, who provided a friendly and cooperative atmosphere during the cruise. The German Science Foundation is acknowledged for funding the 2 months of cruise participation and 2 months of postcruise work (DFG project Al-331/9). Many thanks go to Alexander Altenbach, University of Mu- nich, Germany, for supporting this research subject. For scientific dis- cussions many thanks go to Juliane Fenner, Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Hannover, Germany. The En- glish text of the manuscript was reviewed by John Tipper (Freiburg/Bre- isgau) and Ian Lerche (Halle/Saale). Many thanks go to them for their friendly help. This research used samples and/or data provided by the Ocean Drilling Program (ODP). ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under the man- agement of Joint Oceanographic Institutions (JOI), Inc. T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 11 REFERENCES

Berger, W.H., 1976. Biogenous deep-sea sediments: production, preservation, and interpretation. In Riley, J.P., and Chester, R. (Eds.), Chemical Oceanography (Vol. 5): London (Academic Press), 265–388. Blueford, J.R., Gonzales, J.J., and Van Scoy, K., 1990. Comparing radiolarian and dia- tom diversity and abundance from the northeast Pacific. Mar. Micropaleontol., 15:219–232. Casey, R.E., 1993. . In Lipps, J.H. (Ed.), Prokaryotes and : Boston (Blackwell Scientific), 249–284. Casey, R.E., Weinheimer, A.L., and Nelson, C.O., 1990. radiolarian evolu- tion and zoogeography of the Pacific. Bull. Mar. Sci., 47(1):221–232. Cortese, G., and Bjorklund, K.R., 1999. Radiolarians from the cyclic Messinian diato- mites of Falconara (, Italy). In De Wever, P., and Caulet, J.P. (Eds.), InterRad VIII, Paris/Bierville 8–13 Septembre 1997. Geodiversitas, 21(4):593–624. Dinkelman, M.G., 1973. Radiolarian stratigraphy: Leg 16, Deep Sea Drilling Program. In van Andel, T.H., Heath, G.R., et al., Init. Repts. DSDP, 16: Washington (U.S. Govt. Printing Office), 747–813. Engebretson, D.C., Cox, A., and Gordon, R.G., 1985. Relative Motions between Oceanic and Continental Plates in the Pacific Basin. Spec. Pap.—Geol. Soc. Am., 206. Fenner, J., 1984. Middle Eocene to Oligocene planktonic diatom stratigraphy from Deep Sea Drilling sites in the South Atlantic, equatorial Pacific, and Indian Oceans. In Hay, W.W., Sibuet, J.-C., et al., Init. Repts. DSDP, 75 (Pt. 2): Washington (U.S. Govt. Printing Office), 1245–1271. Goll, R.M., 1976. Morphological intergradation between modern populations of Lophospyris and Phormospyris (Trissocyclidae, Radiolaria). Micropaleontology, 22(4):379–418. Gripp, A.E., and Gordon, R.G., 1990. Current plate velocities relative to the hotspots incorporating the NUVEL-1 global plate motion model. Geophys. Res. Lett., 17:1109–1112. Huber, M., 2002. Straw man 1: a preliminary view of the tropical Pacific from a global coupled climate model simulation of the early Paleogene. In Lyle, M., Wilson, P.A., Janecek, T.R., et al., Proc. ODP, Init. Repts., 199, 1–30 [CD-ROM]. Available from: Ocean Drilling Program, A&M University, College Station TX 77845-9547, USA. [HTML] Kling, S.A., 1979. Vertical distribution of polycystine radiolarians in the central North Pacific. Mar. Micropaleontol., 4:295–318. Leinen, M., 1985. Techniques for determining opal in deep-sea sediments: a compari- son of radiolarian counts and x-ray diffraction data. Mar. Micropaleontol., 9:375– 383. Locker, S., 1996. Quantitative radiolarian slides prepared from soft marine sediments. Micropaleontology, 42(4):407–411. Mayer, L., Theyer, F., Thomas, E., et al., 1985. Init. Repts. DSDP, 85: Washington (U.S. Govt. Printing Office). McGowran, B., 1989. Silica burp in the Eocene Ocean. Geology, 17:857–860. Moore, T.C., 1971. Radiolaria. In Tracey, J.I., Jr., Sutton, G.H., et al., Init. Repts. DSDP, 8: Washington (U.S. Govt. Printing Office), 727–775. Moore, T.C., Jr., Rea, D.K., Lyle, M., and Liberty, L.M., 2002. Equatorial ocean circula- tion in an extreme warm climate. Paleoceanography, 17(1):51–56:10.1029/ 2000PA000566. Nigrini, C., 1985. Radiolarian biostratigraphy in the central equatorial Pacific, Deep Sea Drilling Project Leg 85. In Mayer, L.A., Theyer, F., Thomas, E., et al., Init. Repts. DSDP, 85: Washington (U.S. Govt. Printing Office), 511–551. T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 12

Petrushevskaya, M.G., 1971. Radiolaria in the and recent sediments from the Indian Ocean and Antarctic. In Funnell, B.M., and Riedel, W.R., The Micropalae- ontology of Oceans: Cambridge (Cambridge Univ. Press), 319–329. Ragueneau, O., Tréguer, P., Leynaert, A., Anderson, R.F., Brzezinski, M.A., DeMaster, D.J., Dugdale, R.C., Dymond, J., Fischer, G., Francois, R., Heinze, C., Maier-Reimer, E., Martin-Jézéquel, V., Nelson, D.M., and Quéguiner, B., 2000. A review of the Si cycle in the modern ocean: recent progress and missing gaps in the application of biogenic opal as a paleoproductivity proxy. Global Planet. Change, 26:317–365. Sanfilippo, A., and Riedel, W.R., 1985. radiolaria. In Bolli, H.M., Saunders, J.B., and Perch-Nielsen, K. (Eds.), Plankton Stratigraphy: Cambridge (Cambridge Univ. Press), 573–630. Schrader, H.-J., 1976. Cenozoic planktonic diatom biostratigraphy of the southern Pacific Ocean. In Hollister, C.D., Craddock, C., et al., Init. Repts. DSDP, 35: Wash- ington (U.S. Govt. Printing Office), 605–671. Shipboard Scientific Party, 2002. Leg 199 summary. In Lyle, M., Wilson, P.A., Janecek, T.R., et al., Proc. ODP, Init. Repts., 199: College Station TX (Ocean Drilling Program), 1–87. [HTML] Steiger, E., 1998. Die Radiolarien des Campans der kalkalpinen Gosau (Lattengebirge, Bayern) [Ph.D. dissert.]. Ludwig Maximilians Univ., Munich. Tracey, J.I., Jr., Sutton, G.H., et al., 1971. Init. Repts. DSDP, 8: Washington (U.S. Govt. Printing Office). van Andel, T.H., Heath, G.R., et al., 1973. Init. Repts. DSDP, 16: Washington (U.S. Govt. Printing Office). Zachos, J., Pagani, M., Sloan, L., Thomas, E., and Billups, K., 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science, 292:686–693. T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 13

Figure F1. Location of Leg 199 drill sites. Site 1219 is situated north of the Clipperton Fracture Zone (F.Z.) on 56-Ma-old crust at seafloor depths of >5000 mbsl (Shipboard Scientific Party, 2002).

160°W 150° 140° 130° 30° N Leg 199 sites DSDP sites

Site 1215 . ai F.Z Molok Honolulu Site 1216 20° Site 40

Site 43 Site 1217 .Z. rion F Cla Site 162 Site 1222 Site 42

Site 1221 Site 160 Site 163 Site 1220 Site 161 10° Site 1218 Site 1219 Site 69 Site 70 Site 575 .Site 71 Site 574 n F.Z perto km Clip 0 500 1000 Site 573 Site 72 0°

150°W 145° 140° 135°

Site 1215 e ° re Zon 25 ai Fractu Molok N

Site 1216 20° 40 43 Site 1217 one cture Z ion Fra 15° Clar 162 42 one Site 1222 cture Z ahi Fra Mahi M Site 1221 163 161 10° Site 1220 Site 1219 Site 1218 70 575 574 5° one 71 ture Z Frac erton Clipp 72 573 0° T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 14 in g the Oligocene— the g n N o i t a ? l u c 5 l m a 1

c

2 6 d k . r 1 c

a 5 a o r e 9 t b t k i 3 p i c i a 5 S h a s b .

k ? n n Z o o o l .

? s F d d o t l e e u s s M s a a e b b r

g g 6 m m n n i i 1

s i s s t 2 2 s s e . o o 1 t n r r

7 g c c n

e a 4 r r t e o o i 1 m t t o a a m 5 S e u u l e q q a s >5% diatoms p E E a b

t l P-15 a R s 7 a m 1

B 2 1 . 1

2 e 4 e t s t i 3 i ides compared to the estimated positions of the equator crossing the equator of positions the estimated compared to ides m n 5 S m o . o t o l i a o i Z r . d d

a ? F l g g n n i i C s s t a a n e e t r r 2 l e c c m 2

a n n e e i i

m 2 z z s 8 h h . o o e t t 1 a i i o o

8 s

w w l B i

e e 8 a s k k k t d l l l e i i 9 s b z a a a x o 4 f S o h h h o i i

o c c c o

.

s l l l l n h h i i i i ? u n Z s s s s a a o . a s s s s r F n o o o o e

f f f f F.Z. = Fracture Zone. N = nassellarians, S = spumellarians. S = = Fracture Zone. N nassellarians, F.Z. f M M i t y l o o o o l l e n n n n a a y t n n n n s a e a a a a l a 1 m N S N N N B N M C 2

2 3 . 1

5 e 7 t i 1 5 S t S N n S e N 0 m m 2

e 2 9 s . 1 a

7 b e 1

t t t i l 2 n e a 5 S t s n o a c

B y a l c

N S g n i 9 s m a 1

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3

h e 6 t t i i 0 w

5 S n e s y r z o t a e l t r o y c r . e o RP-15

a l h l i e n Z

Occurrence of diatom events (>5% diatoms) observed in smear sl smear in observed diatoms) (>5% events of diatom Occurrence c s e t .

t a r p s i i h F r r e e o t p i f a a h i l l n o l w c o o

n i i e e y n C n d d i a c n a a l a h o e Radiolarian ooze and clay, clayey radiolarian N T R Clay, clay with zeolite, zeolitic C R c g i l o O E Figure F2. Leg 199 dill sites (Shipboard Scientific Party, 2002). Site 1219 shows two diatom levels—one in the Middle Eocene and one durin one and Eocene Middle the in levels—one diatom two shows 1219 Site 2002). Party, Scientific (Shipboard sites dill 199 Leg along with theequator crossing of the site ~29 m.y. ago. S T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 15 color

60 Spumellarians 40 20

80 Nassellarians 40

40 Porifera 20

Siliceous biota groups Diatoms

40 80

(%) 60 Opal 40

20

(%) 80 Smectite

40 (%)

Radiolarian ooze with decreasing clay content Illite

s (Shipboard Scientific Party, 2002). Party, Scientific s (Shipboard LAS mineralogy

(%) 80 20 40 Calcite

40 (L*)

80 reflectance

Color

(g/cm )

3

Bulk density Bulk Interbedded diatom, nannofossil, and radiolarian oozes

SI) (x 10 (x

-6 80 1.2 1.6 2.0 40 60 susceptibility

40 Magnetic

Physical properties 20

stratigraphy Magnetic C17n C18n C19n

as well as biostratigraphic zonation biostratigraphic as well as Radiolarians Radiolarian ooze

RP-17 RP-16 RP-15 nannofossils

Zone Calcareous

CP15 Barren Barren CP14b CP14b CP14a

middle Eocene middle Age

Lithology Samples

Nannofossil ooze

Hole 1219A between Cores 199-1219A-22H and 19H, containing vertical distributions of contents of siliceous biota, mineralogy, mineralogy, biota, siliceous of contents of distributions vertical containing 19H, and 199-1219A-22H Cores between 1219A Hole Recovery

Hole 1219A Core 19H 20H 21H 22H

170 180 190 200 ) f s b m ( h t p e D Figure F3. reflectance, and physical properties T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 16

Figure F4. Lithologic sequence of the Zone RP-15 diatom-rich interval. Composite core images clearly show color changes and banding representing three diatom-rich intervals and their interpretation with respect to productivity and Si mass accumulation rates (Shipboard Scientific Party, 2002). MAR = mass accumula- tion rate. Core, section, interval (cm) 199-1219A-21H- 1, 20-24 Low diatom 1 m Eocene-type content; radiolarite end of productivity 1, 140-142 phase 2, 14-16 2, 27-29 2, 40-42 Diatomaceous 2, 67-69 interval, upper part: 2, 120-122 color banding Decreasing decreasing in diatom thickness of content, 3, 30-32 layers and Si MAR, and 3, 63-65 color change from greenish productivity gray to reddish 4, 28-30 brown

4, 100-102

Diatomaceous Highest interval, middle diatom part: content, color bands with Si MAR, 5, 100-102 thick light and 5, 120-122 colored layers productivity

6, 30-32 6, 60-62 6, 85-87 Diatomaceous 6, 100-102 Increasing interval, lower diatom part: 6, 140-142 content, color bands with Si MAR, 7, 30-32 short sections and of light and dark productivity 7, 60-62 colored layers

8, 33-36 Eocene-type 8, 49-51 radiolarite T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 17

Figure F5. Ratios of siliceous organisms between Cores 199-1219A-22H and 19H. A. Diatom:radiolarian ra- tio shows the general trends of diatom development and stepwise reduction in Core 199-1219A-21H. B. Impression of radiolarian fluctuations during the diatom interval, mostly reflecting the high occurrences of artostrobids in the samples. (Continued on next page.) A 100 Diatoms 90

80

70

60

50

40 Radiolarians (%)

30

20

10

0 9 -65 85-87

199-1219A-20H-5,199-1219A-21H-1, 91-93199-1219A-21H-2, 20-24199-1219A-21H-2,199-1219A-21H-2, 14-16 27-29 40-42199-1219A-21H-3,199-1219A-21H-3,199-1219A-21H-4, 30-32 63 28-30 199-1219A-21H-6,199-1219A-21H-6,199-1219A-21H- 30-32 60-62 6, 199-1219A-21H-7,199-1219A-21H-7,199-1219A-21H-8, 30-32199-1219A-21H-8, 60-62 33-36199-1219A-22H-1, 49-51199-1219A-22H-2, 92-94 27-2 199-1219A-19H-1,199-1219A-19H-4,199-1219A-19H-6, 102-104199-1219A-20H-4, 130-132 144-146 133-135199-1219A-21H-1, 140-142 199-1219A-21H-2W,199-1219A-21H-2, 67-69 120-122 199-1219A-21H-4,199-1219A-21H-5,199-1219A-21H-5, 100-102 100-102 120-122 199-1219A-21H-6,199-1219A-21H-6, 100-102 140-142 199-1219A-22H-1W, 35-37 Core, section, interval (cm) B 120

Nassellarians

100

80

60

40 Spemullarians (%)

20

0

199-1219A-20H-5,199-1219A-20H-7,199-1219A-21H-1, 91-93 36-38199-1219A-21H-2, 20-24199-1219A-21H-2,199-1219A-21H-2, 14-16199-1219A-21H-2, 27-29 40-42199-1219A-21H-3, 67-69199-1219A-21H-3,199-1219A-21H-4, 30-32 63-65 28-30 199-1219A-21H-6,199-1219A-21H-6,199-1219A-21H-6, 30-32 60-62 85-87199-1219A-21H-7,199-1219A-21H-7,199-1219A-21H-8, 30-32199-1219A-21H-8, 60-62199-1219A-22H-1, 33-36199-1219A-22H-1, 49-51199-1219A-22H-2, 35-37 92-94 27-29 199-1219A-19H-1,199-1219A-19H-4,199-1219A-19H- 102-104199-1219A-20H-4, 130-132 6, 144-146 133-135199-1219A-21H-1, 140-142 199-1219A-21H-2, 120-122199-1219A-21H-4,199-1219A-21H-5,199-1219A-21H-5, 100-102 100-102 120-122199-1219A-21H-6,199-1219A-21H-6, 100-102 140-142 Core, section, interval (cm) T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 18

Figure F5 (continued). C. General shift of the nassellarian:spumellarian distribution compared to diatom quantities. Because of the increase of actinommids, the nassellarian:spumellarian ratio equals during the final phase of the diatom interval. C 250

200

Nassellarians Spumellarians

150

100 Diatoms (number of individuals) Diatoms (number 50

0 5 2 2 6

199-1219A-20H-5,199-1219A-20H-7,199-1219A-21H-1, 91-93 36-38199-1219A-21H-2, 20-24199-1219A-21H-2,199-1219A-21H-2, 14-16199-1219A-21H-2, 27-29 40-42199-1219A-21H-3, 67-69199-1219A-21H-3,199-1219A-21H-4, 30-32 63-6 28-30 199-1219A-21H-6,199-1219A-21H-6,199-1219A-21H-6, 30-32 60-6 85-87199-1219A-21H-7,199-1219A-21H-7,199-1219A-21H-8, 30-32199-1219A-21H-8, 60-62199-1219A-22H-1, 33-3199-1219A-22H-1, 49-51199-1219A-22H-2, 35-37 92-94 27-29 199-1219A-19H-1,199-1219A-19H-4,130-132199-1219A-19H-6, 102-104199-1219A-20H-4, 144-146 133-135 199-1219A-21H-1, 140-142 199-1219A-21H-2, 120-122 199-1219A-21H-4,199-1219A-21H-5,199-1219A-21H-5, 100-102 100-102 120-12 199-1219A-21H-6,199-1219A-21H-6, 100-102 140-142

Core, section, interval (cm) T.H. STEIGER BIOGENIC SEDIMENTOLOGY OF RADIOLARIAN ASSEMBLAGES 19 nd, the

ly also depend also ly

H-1, 92-94 H-1,

199-1219A-22H-2, 27-29 199-1219A-22H-2,

-94

199-1219A-22

A-21H-8, 33-36 A-21H-8,

H-8, 49-51 H-8,

199-1219A-22H-1, 35-37 199-1219A-22H-1,

199-1219A-22H-2, 27-29 199-1219A-22H-2, 199-1219

199-1219A-22H-1, 92 199-1219A-22H-1,

199-1219A-21

199-1219A-22H-1, 35-37 199-1219A-22H-1,

199-1219A-21H-7, 60-62 199-1219A-21H-7,

199-1219A-21H-8, 33-36 199-1219A-21H-8,

199-1219A-21H-7, 30-32 199-1219A-21H-7, 199-1219A-21H-8, 49-51 199-1219A-21H-8,

199-1219A-21H-7, 60-62 199-1219A-21H-7,

199-1219A-21H-6, 140-142 199-1219A-21H-6,

199-1219A-21H-7, 30-32 199-1219A-21H-7,

199-1219A-21H-6, 100-102 199-1219A-21H-6,

199-1219A-21H-6, 140-142 199-1219A-21H-6,

199-1219A-21H-6, 85-87 199-1219A-21H-6,

199-1219A-21H-6, 100-102 199-1219A-21H-6,

199-1219A-21H-6, 60-62 199-1219A-21H-6, 199-1219A-21H-6, 85-87 199-1219A-21H-6,

199-1219A-21H-6, 60-62 199-1219A-21H-6,

199-1219A-21H-6, 30-32 199-1219A-21H-6, 199-1219A-21H-6, 30-32 199-1219A-21H-6,

Theoperids

Artostrobids

199-1219A-21H-5, 120-122 199-1219A-21H-5,

199-1219A-21H-5, 120-122 199-1219A-21H-5,

199-1219A-21H-5, 100-102 199-1219A-21H-5, 199-1219A-21H-5, 100-102 199-1219A-21H-5,

Core, section, interval (cm) Core, Core, section, interval (cm) Core,

199-1219A-21H-4, 100-102 199-1219A-21H-4, 199-1219A-21H-4, 100-102 199-1219A-21H-4,

199-1219A-21H-4, 28-30 199-1219A-21H-4,

199-1219A-21H-4, 28-30 199-1219A-21H-4,

-42

199-1219A-21H-3, 63-65 199-1219A-21H-3,

199-1219A-21H-3, 63-65 199-1219A-21H-3,

199-1219A-21H-3, 30-32 199-1219A-21H-3,

199-1219A-21H-3, 30-32 199-1219A-21H-3,

199-1219A-21H-2, 120-122 199-1219A-21H-2,

199-1219A-21H-2, 67-69 199-1219A-21H-2,

199-1219A-21H-2, 120-122 199-1219A-21H-2,

199-1219A-21H-2, 40 199-1219A-21H-2,

199-1219A-21H-2, 67-69 199-1219A-21H-2,

199-1219A-21H-2, 27-29 199-1219A-21H-2,

199-1219A-21H-2, 40-42 199-1219A-21H-2,

199-1219A-21H-2, 14-16 199-1219A-21H-2,

199-1219A-21H-2, 27-29 199-1219A-21H-2, 5 0 140-142 199-1219A-21H-1,

30 25 20 15 10 199-1219A-21H-1, 22-24 199-1219A-21H-1,

199-1219A-21H-2, 14-16 199-1219A-21H-2,

Percentage

199-1219A-20H-7, 36-38 199-1219A-20H-7,

199-1219A-20H-5, 91-93 199-1219A-20H-5, 199-1219A-21H-1, 140-142 199-1219A-21H-1, 199-1219A-21H-1, 22-24 199-1219A-21H-1,

5 0

199-1219A-20H-4, 133-135 199-1219A-20H-4,

30 25 20 15 10

199-1219A-20H-7, 36-38 199-1219A-20H-7, Percentage 199-1219A-20H-5, 91-93 199-1219A-20H-5,

act as a response to the diatom deposition. Artostrobids probab Artostrobids deposition. diatom the to response a as act

199-1219A-20H-4, 133-135 199-1219A-20H-4,

199-1219A-22H-2, 27-29 199-1219A-22H-2,

199-1219A-22H-1, 92-94 199-1219A-22H-1,

199-1219A-22H-1, 35-37 199-1219A-22H-1,

199-1219A-21H-8, 33-36 199-1219A-21H-8,

199-1219A-22H-2, 27-29 199-1219A-22H-2,

199-1219A-21H-8, 49-51 199-1219A-21H-8, 199-1219A-22H-1, 92-94 199-1219A-22H-1,

199-1219A-22H-1, 35-37 199-1219A-22H-1,

199-1219A-21H-7, 60-62 199-1219A-21H-7, 42

199-1219A-21H-8, 33-36 199-1219A-21H-8, 2

199-1219A-21H-7, 30-32 199-1219A-21H-7,

199-1219A-21H-8, 49-51 199-1219A-21H-8,

1H-6, 140-1 1H-6,

199-1219A-21H-7, 60-62 199-1219A-21H-7,

199-1219A-21H-6, 140-142 199-1219A-21H-6,

199-1219A-21H-7, 30-32 199-1219A-21H-7,

199-1219A-21H-6, 100-102 199-1219A-21H-6,

H-6, 60-62 H-6, 2

199-1219A-2 199-1219A-21H-6, 85-87 199-1219A-21H-6,

02

199-1219A-21H-6, 100-10 199-1219A-21H-6,

199-1219A-21H-6, 60-62 199-1219A-21H-6, 199-1219A-21H-6, 85-87 199-1219A-21H-6,

H-5, 120-12 H-5,

0-102 199-1219A-21

199-1219A-21H-6, 30-32 199-1219A-21H-6, 199-1219A-21H-6, 30-32 199-1219A-21H-6,

Actinommids

Coccodiscids

199-1219A-21H-5, 120-122 199-1219A-21H-5,

199-1219A-21

199-1219A-21H-5, 100-102 199-1219A-21H-5, 199-1219A-21H-5, 100-1 199-1219A-21H-5,

Core, section, interval (cm) Core, Core, section, interval (cm) Core,

199-1219A-21H-4, 10 199-1219A-21H-4,

199-1219A-21H-4, 100-102 199-1219A-21H-4,

199-1219A-21H-4, 28-30 199-1219A-21H-4,

199-1219A-21H-4, 28-30 199-1219A-21H-4,

0-42

199-1219A-21H-3, 63-65 199-1219A-21H-3,

199-1219A-21H-3, 63-65 199-1219A-21H-3, 199-1219A-21H-3, 30-32 199-1219A-21H-3,

199-1219A-21H-3, 30-32 199-1219A-21H-3,

199-1219A-21H-2, 120-122 199-1219A-21H-2,

199-1219A-21H-2, 67-69 199-1219A-21H-2,

199-1219A-21H-2 120-122 199-1219A-21H-2 199-1219A-21H-2, 4 199-1219A-21H-2,

199-1219A-21H-2, 67-69 199-1219A-21H-2, 199-1219A-21H-2, 27-29 199-1219A-21H-2,

199-1219A-21H-2, 14-16 199-1219A-21H-2, 199-1219A-21H-2, 40-42 199-1219A-21H-2,

5 0 199-1219A-21H-1, 140-142 199-1219A-21H-1,

199-1219A-21H-2, 27-29 199-1219A-21H-2,

25 20 15 10 199-1219A-21H-1, 22-24 199-1219A-21H-1,

Percentage

199-1219A-21H-2, 14-16 199-1219A-21H-2, 199-1219A-20H-7, 36-38 199-1219A-20H-7,

Percentages of major radiolarian families in the Zone RP-15 diatom-rich unit. Coccodiscids are distributed without general tre general without distributed are Coccodiscids unit. diatom-rich RP-15 Zone the in families radiolarian of major Percentages

199-1219A-20H-5, 91-93 199-1219A-20H-5,

199-1219A-21H-1, 140-142 199-1219A-21H-1,

199-1219A-20H-4, 133-135 199-1219A-20H-4, 199-1219A-21H-1, 22-24 199-1219A-21H-1, 0

60 50 40 30 20 10

199-1219A-20H-7, 36-38 199-1219A-20H-7,

Percentage

199-1219A-20H-5, 91-93 199-1219A-20H-5, 199-1219A-20H-4, 133-135 199-1219A-20H-4, Figure F6. re seem to and actinommids increases, slightly content theoperid on theoccurrence of diatoms, withmaximum contents at thebeginning and in the terminal phase of diatom deposition.