The three holes at Site 1258 yielded primarily middle Eocene–early Albian marine sediments that contain planktonic foraminifers, calcareous nannofossils, and radiolarians in abundances and states of preservation that vary widely with lithology and sediment induration. Shipboard examination of these microfossil groups in core catcher samples, supplemented as necessary by additional samples from the cores, permitted zonal or stage assignments to be made for the entire sequence. Datum levels are summarized in Figure F10 and in Tables T3, T4, T5, T6, T7, and T8.
A veneer of middle Miocene ooze at the top of the section overlies a sliver of lower Oligocene calcareous ooze rich in diatoms and radiolarians. All microfossil groups are abundant and well preserved.
About 25 m of middle Eocene biosiliceous chalk disconformably overlies a 143-m lower Eocene chalk as measured in the nonfaulted portion of Hole 1258B. The P/E boundary is present in Cores 207-1258A-19R, 207-1258B-21R, and 207-1258C-8R. Radiolarians cannot be identified to species in the Paleocene section, where the conspicuous presence of zeolites and locally abundant opal-CT lepispheres evident in nannofossil smear slides (see also "Lithostratigraphy") indicate that these and other siliceous microfossils, formerly present, have been largely destroyed by sediment diagenesis. The secondary silica was sufficiently disseminated in the expanded chalk section, however, that porcellanites did not form to the extent that they impeded good core recovery.
The K/T boundary ejecta layer is present in Core 207-1258B-27R. The uppermost Maastrichtian nannofossil Micula prinsii was identified immediately below the ejecta horizon, and overlying strata contain the lowermost Danian planktonic foraminifers in Zone P. Site 1258 captured an especially thick (~20 m) uppermost Maastrichtian section (planktonic foraminiferal Zone KS31 [nannofossil Zones CC25C–CC26]).
The entire Maastrichtian–lower Campanian zeolitic chalk section at the present site is considerably expanded. The virtual absence of holococcoliths, however, indicates that this chalk represents relatively deepwater deposition with consequent dissolution of nonresistant calcareous nannofossils. Nannolith preservation does improve somewhat in the lower Campanian. Radiolarians in this Campanian interval show moderate–good preservation.
A condensed glauconite-rich horizon visible in Core 207-1258B-44R separates the Campanian chalk from the ~56 m of black shales below (lithostratigraphic Unit IV) that compose or represent the lower part of OAEs 3 and 2. The contact between the glauconite-rich layer and black shale is best displayed in Section 207-1158B-44R-1, where the heavily bored top of the black shale is a light tan color. Laminated strata in Section 207-1158B-44R-2 have been dated by sparse calcareous nannofossils as Coniacian (Zone CC14). A debris flow in Section 207-1158B-44R-3 contains a mixture of Turonian and Coniacian nannofossils that includes an unusually high abundance of the normally rare but dissolution-resistant Martasterites furcatus.
Calcareous microfossils are generally present throughout the black shales, although foraminifers are often poorly preserved and of low diversity. Both upper Turonian and middle–lower Turonian microfossil assemblages were distinguished. In the latter interval the distinctive evolutionary radiation that occurs among the eprolithids, a calcareous nannofossil group, appears to be well represented by exceptionally well preserved (i.e., long rayed) specimens.
The bulk of the black shale sequence is Cenomanian in age. The preservation and abundance of the Cenomanian calcareous microfossils is better than at the other Leg 207 sites, although these remain spotty in distribution, particularly for the planktonic foraminifers. Fish scales are common, and a fish vertebra ~1 cm in diameter was recovered in Sample 207-1258B-45R-4, 75 cm (Fig. F9) (see "Lithostratigraphy").
A disconformity may be present in Cores 207-1258B-55R and 207-1258C-27R that separates the lower Cenomanian from underlying middle Albian black shales. Clay-rich beds of early Albian age below these shales yielded some of the best-preserved microfossils at the site, including nannofossils pristine in appearance and "glassy" planktonic foraminifers that compare well visually with Holocene assemblages. In addition, ammonites as small as 1 cm in diameter are abundant in some laminae.
The calcareous microfossil groups in combination allowed the base of Hole 1258C to be dated as early Albian (foraminiferal and nannofossil Zone KS13 and Subzone NC8a–NCb, respectively; the latter as correlated to substage by Bown et al., 1998 [figs. 5.2, 5.4]).
Three holes at Site 1258 recovered primarily Paleogene–mid-Cretaceous sediments that generally contain common to abundant calcareous nannofossils of moderate to good preservation. These allowed for zonal or stage assignments that are summarized in Figure F10 and Tables T3 and T6. Core catcher samples were examined for all holes and supplemented as necessary by samples from the cores to further refine the zonal assignments. Major disconformities are observed separating the following sedimentary packages:
From the above, hiatuses, unconformities, and/or condensed sequences may be derived for the following:
In the more detailed descriptions that follow, the assemblages and ages pertain to Hole 1258A unless noted otherwise.
Sample 207-1258A-1R-CC recovered a nannofossil assemblage of middle Miocene age (Zone NN7 of the Martini, 1971 scheme), including Discoaster exilis, Discoaster variabilis, Discoaster challengeri, and Discoaster kugleri. Samples 207-1258A-2R-CC to 4R-CC are of middle Eocene age (Zone NP15) as indicated by the presence of Nannotetrina fulgens, Chiasmolithus grandis, Chiasmolithus gigas, Dictiococcites bisecta, and Ericsonia formosa. The presence of C. gigas here and in Sample 207-1258B-2R-CC denotes Okada and Bukry (1980) Subzone CP13b (middle NP15); a specimen of Chiphragmalithus calathus in Sample 207-1258B-4R-CC is considered reworked.
Sections 207-1258A-5R-CC to 6R-CC contain a middle Eocene assemblage (Zone NP14) that includes Sphenolithus radians, Zygrhablithus bijugatus, Discoaster barbadiensis, Discoaster sublodoensis, and Discoaster lodoensis. The subjacent Sections 207-1258A-7R-CC to 8R-CC have an early Eocene age (Zone NP13), yielding D. lodoensis, E. formosa, and S. radians. Specimens of overgrown Orthorhabdus tribrachiatus at this level in Hole 1258B (Cores 207-1258B-7R and 8R) are considered reworked, as they lie well above the foraminiferal Planorotalites palmerae datum for the base of Zone P9 (see "Planktonic Foraminifers").
Based on the presence of Discoaster tani nodifer, Discoaster saipanensis, S. radians, D. lodoensis, and Tribrachiatus orthostylus, Sections 207-1258A-9R-CC to 13R-CC have been assigned an early Eocene age (Zone NP12). The underlying Samples 207-1258A-14R-CC to 15R-CC are of earliest Eocene age (Zone NP10) based on the presence of Discoaster multiradiatus, Toweius eminens, Campylosphaera eodela, Discoaster diastypus, and Rhomboaster spp.
Relative to Hole 1258A, downhole offsets in Holes 1258B and 1258C of the boundaries of Zone NP10 are attributed to the fault that cut both holes. Faulting apparently reduced the stratigraphic section in Hole 1258A by ~20 m relative to Hole 1258B (see "Composite Depths").
Samples 207-1258A-16R-CC to 22R-CC contain D. multiradiatus, Discoaster mohleri, Neochiastozygus junctus, and Fasciculithus tympaniformis and are thus of earliest Eocene to latest Paleocene age (Zone NP9). In that zone but above the P/E boundary in Cores 207-1258A-19R, 207-1258B-21R, and 207-1258C-8R, N. junctus and Z. bijugatus are abundant, whereas fasculiths replace the latter as dominant taxa below the P/E boundary (see Bralower, 2002).
A nannofossil assemblage consisting of D. mohleri, Heliolithus riedelii, and F. tympaniformis in the absence of D. multiradiatus characterizes Sample 207-1258A-23R-CC as late Paleocene age (Zone NP8). A late Paleocene age (Zone NP7) is also assigned to Samples 207-1258A-24R-CC and 25R-CC based on the presence of Chiasmolithus consuetus, Heliolithus kleinpellii (Sample 24R-CC only), Ellipsolithus macellus, and Discoaster splenditus, along with common to abundant D. mohleri. Discoaster mohleri, however, is absent in Sample 207-1258A-26R-CC but Fasciculithus involutus (few), small E. macellus, and abundant large Cruciplacolithus tenuis (up to 10 Ám long) denote Zone NP5.
Sample 207-1258A-27R-CC contains primarily C. tenuis but no fasciculiths and thus has an earliest Paleocene age (Zone NP2). This sample also yielded a rich reworked nannoflora of Maastrichtian age.
Samples 207-1258A-28R-CC to 32-CC yield nannofossil assemblages of late Maastrichtian age (Zone CC25 of the Sissingh, 1977, scheme) including Micula murus and Arkhangelskiella cymbiformis. In the expanded uppermost Maastrichtian section of Hole 1258B (Cores 207-1258B-30R and 32R), Ceratholithoides kamptneri is present in the absence of M. murus (i.e., in an order of first appearances opposite that given for "Tethyan-intermediate" province zones by Burnett , figs. 6.6 and 6.7).
Sample 207-1258A-33R-CC is of early Maastrichtian age (Zone CC24) as indicated by the presence of Reinhardtites levis. Samples 207-1257A-34R-CC to 40R-CC contain an early Maastrichtian to late Campanian assemblage (Zones CC23 and CC22), including Uniplanarius trifidum, R. levis, A. cymbiformis, and Uniplanarius sissinghi. The subjacent Sample 207-1258A-41R-CC yielded Reinhardtites anthoporus, Aspidolithus parcus constrictus, Micula concavata, Micula decussata, and Eiffellithus eximius but no Eprolithus floralis, allowing an early Campanian age assignment (Zones CC20 to upper CC18).
The black shales of Hole 1258A underlie a sharp erosional contact with the overlying Campanian chalk. An impoverished flora of Turonian age with Radiolithus planus and Stoverius achylosus is present in Samples 207-1257A-42R-CC to 44R-CC.
In Hole 1258B, the top of the black shales was encountered at a greater subbottom depth than in either Holes 1258A or 1258C. It is also the only one of the three that preserves the top of the sequence, which appears to be younger than in the other two holes. The upper strata in Hole 1258B are light tan and heavily burrowed (Sample 207-1258B-44R-2, 58 cm). A black-colored sample below that (Sample 207-1258B-44R-2, 64 cm) contains Eiffellithus turriseiffelii and E. floralis and is therefore no younger than late Coniacian. A debris flow at Sample 207-1258B-44R-3, 96 cm, yielded abundant M. furcatus, a dissolution-resistant form normally rare in chalks but here possibly concentrated by dissolution. Other taxa include abundant E. turriseiffelii, E. eximius, Gartnergo cf. costatum, common to few M. decussata, a possible specimen of Lithastrinus moratus, and rare but well-preserved Eprolithus eptapetalus. Assuming the latter specimen is reworked, this somewhat mixed assemblage is considered to be Coniacian in age. Sample 207-1258B-44R-4, 19 cm, contains common E. floralis, E. turriseiffelii, and rare E. eptapetalus and is assigned to the Turonian. In Hole 1258C, the upper Turonian is well represented in Sample 207-1258C-15R-CC, which contains E. eximius and several specimens of Quadrum gartneri.
In all holes, a definite Cenomanian age (Zone CC10) is assigned to Samples 207-1257A-45R-CC to 49R-CC, based on the combined presence of Corollithion kennedyi and Axopodorhabdus albianus. Sample 207-1257A-50R-CC has a late middle–early late Albian age based on the absence of E. turriseiffelii and the presence of Tranolithus orionatus and A. albianus.
The Albian section was drilled deepest in Hole 1258C. Eiffellithids are absent in Sample 207-1258C-27R-CC, but A. albianus is present; therefore, the sample is referred to middle Albian Subzone NC9a. Axopodorhabdus albianus, in turn accompanied by Prediscosphaera columnata, Rhagodiscus angustus, Microstaurus chiastus, E. floralis, Eprolithus apertior, R. planus, and occasional Watznaueria britannica and Heliolithus trabeculatus range downhole to Sample 207-1258C-32R-CC and denote middle Albian Subzone NC9a.
Prediscosphaera columnata, few in number but found amidst rich and well-preserved Albian nannoflora, continue to the bottom of the hole in Sample 207-1258C-34R-CC. It is accompanied by Rhagodiscus achlyostarius, R. angustus, common L. floralis, and rare Nannoconus truitti and Lapediocassis coronuta. These date the assemblage and the bottom of the hole as early Albian (Subzone NC8a–NC8b).
Planktonic foraminifer biostratigraphy at Site 1258 was based on a combination of core catchers from all three holes and samples taken from every section in Hole 1258A. Zonal assignments are summarized in Figure F10 and Tables T4, T7, and T8. Planktonic foraminifer Zone M9 through Albian Zone KS13 were identified in Hole 1258A along with significant breaks in the biozonation in the middle Oligocene–middle Miocene, middle Eocene–middle Oligocene, upper Danian, Santonian–lower Campanian, and upper Albian–lower Cenomanian. Planktonic foraminifers were present in nearly all samples but varied widely in preservation and abundance. Preservation was best in clay-rich parts of the Cenomanian–Turonian sequence and middle Albian, although foraminifers were difficult to extract and completely clean in the organic marls. Foraminifers in the light-colored bands in the organic marls were frequently filled with calcite spar. Good preservation was found in the Miocene, Oligocene, middle Eocene, and lower Danian, whereas preservation was moderate or poor in the chalk of the lower Eocene and Maastrichtian–Campanian sequences.
Sample 207-1258A-1R-1, 0–2 cm, contains a mixture of modern diatoms with Pleistocene planktonic foraminifers such as Globorotalia tumida. Pleistocene sediments are only a few centimeters thick and were nearly entirely washed off the core top in Hole 1258B, where surficial foraminiferal sands are of middle Miocene age. Yellow calcareous ooze in Section 207-1258A-1R-1 contains a diverse middle Miocene assemblage that includes Fohsella fohsi, Fohsella robusta, Menardella praemenardii, Globoconella miozea, and Dentoglobigerina altispira and indicates middle Miocene Zone M9.
The top of Section 207-1258A-2R-1 contains an Oligocene assemblage assigned to the Subzone P21a/P21b boundary. Subzone P21b is represented in Section 207-1258A-2R-1 and Sample 2R-2, 50–53 cm, by a diverse assemblage containing Globigerina angulisuturalis, Globigerina ouachitensis, Globoquadrina euapertura, and Globigerina ciperoensis without Chiloguembelina cubensis. A similar assemblage is present in Sample 207-1258A-2R-3, 50–55 cm, but with abundant C. cubensis, indicating Subzone P21a.
Sample 207-1258A-2R-3, 50–55 cm, also contains abundant middle Eocene foraminifers belonging to Zone P12, including Turborotalia pomeroli, Morozovella lehneri, and Acarinina bullbrooki. In contrast, the next sample below this (Sample 207-1258A-2R-4, 50–55 cm) contains Morozovella aragonensis and Guembelitrioides nuttali without Globigerinatheka kugleri, which suggests Zone P10 of early middle Eocene age. Although the sample does not contain Hantkenina, it does contain Clavigerinella eocanica, which makes its first appearance just below the base of Zone P10. The presence of A. bullbrooki also suggests the sample cannot be older than latest Zone P9.
Guembelitrioides nuttali associated with Clavigerinella akersi and C. eocanica are present together as low as Sample 207-1258A-3R-5, 50–55 cm, which we suggest approximates the P9/P10 zonal boundary. Sample 207-1258A-3R-6, 50–54 cm, contains small specimens that may record the evolutionary origin of G. nuttali along with a typical lower middle Eocene assemblage that includes M. aragonensis, Acarinina praetopilensis, Igorina broedermanni, Acarinina pentacamerata, and Subbotina inaequispira.
Zone P9 occurs between Samples 207-1258A-3R-5, 50–55 cm, and 9R-2, 49–51 cm. Globigerina lozanoi, a species ancestral to the globigerinathekids, makes its last occurrence (LO) in Sample 207-1258A-5R-CC. Sample 207-1258A-6R-CC contains specimens of M. aragonensis, strikingly similar to modern Globorotalia truncatulinoides, as well as examples of Pseudohastigerina micra that are notably evolute and have more chambers in the final whorl than is typical for this species. Otherwise, the Zone P9 planktonic foraminifers are typical of tropical assemblages and include A. pentacamerata, Acarinina aspensis, Planorotalites renzi, and G. lozanoi. Planototalites palmerae ranges between Samples 207-1258A-7R-CC and 9R-2, 49–51 cm, suggesting that these samples represent the lower part of Zone P9. Sample 207-1258A-9R-3, 45–47 cm, contains transitional forms between P. renzi and P. palmerae that have deeply lobate chambers without terminal spines. Transitional forms between S. inaequispira and clavigerinellids are present over an extended interval in Zone P9 between Samples 207-1258A-7R-CC and 8R-CC.
Zone P8 occurs in the interval from the extinction of Morozovella formosa between Samples 207-1258A-11R-2, 50–53 cm, and 11R-3, 50–53 cm, and the first appearance of P. palmerae between Samples 207-1258A-9R-3, 45–47 cm, and 9R-2, 49–51 cm. In Zone P8, there are a number of last appearances, including that of Morozovella subbotinae between Samples 207-1258A-10R-5, 48–50 cm, and 10R-4, 50–52 cm, and that of Acarinina quetra between Samples 207-1258A-9R-5, 50–53 cm, and 9R-6, 50–53 cm, just below the top of Zone P8. The first appearance of A. pentacamerata occurs between Samples 207-1258A-10R-1, 50–54 cm, and 10R-2, 51–56 cm. Typical species in Zone P8 include A. quetra, M. aragonensis, Globigerina praecentralis, and M. subbotinae.
The first occurrence (FO) of M. aragonensis between Samples 207-1258A-13R-7, 49–53 cm, and 13R-CC marks the base of Zone P7. A well-developed transition occurs in the base of Core 207-1258A-13R with the overlap of large five-chambered Morozovella lensiformis and even larger six- or seven-chambered M. aragonensis. Assemblages in Zone P7 include few to common A. quetra, Morozovella gracilis, M. formosa, M. subbotinae, Acarinina wilcoxensis, and Acarinina coalingensis with subordinate M. lensiformis and Morozovella aequa. Poor preservation in Zone P6 made it difficult to subdivide this zone with confidence using the FO of M. formosa. However the base of Zone P6 could be established between Samples 207-1258A-17R-CC and 18R-CC using the LO of Morozovella velascoensis, Morozovella acuta, and Morozovella occlusa. The P/E boundary is believed to be located in Core 207-1258A-19R in an interval of green claystone. Sample 207-1258A-19R-CC contains rare specimens of Gavelinella beccariiformis, a benthic foraminifer that became extinct at the P/E boundary, suggesting that this sample is of late Paleocene age.
A thick Paleocene succession is found between Samples 207-1257A-19R-CC and 27R-CC. The Zone P4/P5 boundary can be located between Samples 207-1258A-20R-CC and 21R-CC based on the LO of Globanomalina pseudomenardii. We were not able to reliably subdivide Zone P4 owing to the near absence of Acarinina subspherica and Parasubbotina variospira. Assemblages characteristic of Zone P4 contain M. acuta, M. velascoensis, Subbotina triangularis, Subbotina triloculinoides, and Igorina albeari. Parasubbotina varianta, Acarinina nitida, Morozovella pasionensis, and M. aequa are rare constituents in most samples. Core 207-1258A-26R contains a mixture of Zone P4 and Subzone P3a assemblages. Praemurica uncinata and Morozovella praeangulata are present, suggesting Zone P2 or Subzone P3a, but most samples also contain G. pseudomenardii, M. velascoensis, and acarininids, all of which are more typical of Zone P4 or younger assemblages.
Core 207-1258A-27R contains a lower Danian foraminifer assemblage between the core catcher and Sample 207-1258A-27R-3, 0–2 cm. A sample from the top of Core 207-1258A-27R yielded a mixed fauna of Morozovella angulata, Eoglobigerina edita, Igorina pusilla, and G. pseudomenardii. This last species is indicative of Zone P4, whereas the others are found in Zone P1 or P3. Hence, the top of Core 207-1258A-27R appears to contain an extensive collection of reworked species as seen in the overlying core. In contrast, Sample 207-1258A-27R-3, 0–2 cm, contains Praemurica pseudoinconstans, Eoglobigerina eobulloides, S. triloculinoides, and Praemurica taurica that together suggest Subzone P1c. The next sample below this, Sample 207-1258A-27R-4, 0–2 cm, includes Woodringina claytonensis, E. eobulloides, Parvulorugoglobigerina eugubina, and P. taurica in the absence of S. triloculinoides, suggesting a P zonal assignment. Samples 207-1258A-27R-5, 112–114 cm, and 27R-CC have only a dwarfed fauna with Guembelitria cretacea, P. eugubina, Parvulorugoglobigerina extensia, and P. taurica, indicating Zone P. The >150-Ám fraction in both samples contains only reworked Cretaceous species and benthics. Hence, Core 207-1258A-27R appears to contain a relatively complete sequence of biozones between the K/T boundary and Danian Subzone P1c. The apparently complete K/T section in Core 207-1258B-27R was not sampled in detail for foraminifers other than to confirm the Maastrichtian age of the core catcher, but lithostratigraphy suggests this core forms part of a spliced section between Cores 27R and 28R.
Maastrichtian foraminifer assemblages were identified between the top of Core 207-1258A-28R and 33R-CC. Tan and white chalk clasts at the top of Core 207-1258A-28R were sampled and found to contain only upper Maastrichtian species (Zone KS31) based on the occurrence of Abathomphalus mayaroensis in the >250-Ám fraction and the absence of Danian species from the <150-Ám fraction. Zone KS31 extends to Sample 207-1258A-29R-CC given the continued rare occurrence of A. mayaroensis. Typical species in the upper Maastrichtian include Globotruncanita stuarti, Rugoglobigerina rugosa, Rugoglobigerina rotundata, Abathomphalus intermedius, and Pseudoguembelina palpebra. Zone KS30 was identified in Samples 207-1258A-30R-CC to 33R-CC. Samples 207-1258A-30R-CC to 32R-CC all contain Contusotruncana contusa, suggesting that they belong to the Racemiguembelina fructicosa–C. contusa Subzone of Zone KS30. Assemblages in Zone KS30 are composed in part of C. contusa, R. rugosa, Gansserina gansseri, and Rugoglobigerina hexacamerata with subordinate Rugotruncana subcircumnodifer, Pseudoguembelina costillifera, and Heterohelix globulosa. Below the FO of C. contusa, assemblages change to include few to common G. stuarti, Globotruncana arca, Globotruncanella pschadae, and Rosita fornicata. Planktonic foraminifers were absent from Samples 207-1258A-34R-4, 0–2 cm, to 41R-CC.
Cenomanian and Turonian foraminifers are present between Samples 207-1258A-42R-CC and 49R-CC. These samples have mostly low species diversity, with few taxa diagnostic of particular zones. An assemblage of Whiteinella baltica, Whiteinella inornata, Heterohelix moremani, Hedbergella delrioensis, and Hedbergella planispira is present in Samples 207-1258A-42R-CC to 43R-CC and between Samples 45R-CC and 49R-CC. Globigerinelloides caseyi tends to become more common downhole, whereas biserial foraminifers tend to become less so. An interval with extremely small foraminifers is present in Sample 207-1258A-44R-CC, an interval that was also noted at similar depths in Holes 1258B and 1258C, which probably corresponds to the K/T boundary. The first distinctive foraminifer datum occurs in Sample 207-1258A-47R-CC with the occurrence of both Rotalipora globotruncanoides and Praeglobotruncana delrioensis, both suggesting a Cenomanian age.
A distinct change in the composition of the fauna occurs between Samples 207-1258A-49R-CC and 50R-CC. The presence of Ticinella primula and Biticinella breggiensis in Sample 207-1258A-50R-CC provides a date in the B. breggiensis Zone of the late middle Albian (Zone KS14) and suggests that much if not all of the upper Albian and possibly part of the lower Cenomanian is missing at Site 1258. Albian sediments are also present between Cores 207-1258C-27R and 34R. The contact between the B. breggiensis Zone and the underlying T. primula Zone occurs between Samples 207-1258C-27R-1, 85–89 cm, and 27R-2, 89–92 cm, which includes the first appearance of B. breggiensis. Species present in the B. breggiensis Zone include Globigerinelloides bentonensis, T. primula, Ticinella roberti, and Hedbergella simplex. Four-chambered hedbergellids are also present, some of which show a pattern of aligned pustules reminiscent of the lower Cenomanian species Costellagerina lybica. These costellate species continue into the underlying T. primula Zone and are joined by Clavihedbergella subcretacea, Clavihedbergella moremani, Ticinella madecassiana, and Ticinella raynaudi, which represent Zone KS13. The assemblage dominated by various species of Ticinella sp. continues to the bottom of Hole 1258C in Sample 207-1258C-34R-CC.
Radiolarians were found in most of the Tertiary and Cretaceous sediments at Site 1258, but were abundant and adequately preserved for identification and age assignment only in particular stratigraphic intervals (i.e., middle Eocene, Campanian, and Albian). Core catcher samples were examined systematically from Hole 1258A. A limited number of samples were also taken from Holes 1258B and 1258C, mainly to examine the presence or absence of radiolarians in the Cretaceous sediments. Occurrences are summarized in Figure F10.
Radiolarians appear to be absent in the veneer of Miocene sediments at the top of the site. On the other hand, they are abundant and well preserved in Eocene sediments, which also contain some diatoms and occasionally siliceous sponge spicules. Cores 207-1258A-2R to 4R yielded middle Eocene radiolarian assemblages. They are assigned to Zones RP11 and RP12 based on the presence of Theocotyle conica and Thyrsocyrtis triacantha in Sample 207-1258A-2R-CC and Dictyoprora mongolfieri and Thyrsocyrtis tensa in Sample 207-1258A-4R-CC. Both T. tensa and T. triacantha were observed in Sample 207-1258A-2R-CC, but the former species outnumbers the latter. As the evolutionary transition of T. tensa to T. triacantha is approximately synchronous with the lower limit of Zone RP12, the boundary between Zones RP11 and RP12 is placed in Sample 207-1258A-3R-CC.
Radiolarians are rare and poorly preserved (often transformed into zeolites) farther below. The presence of Buryella clinata in Samples 207-1258A-10R-CC and 12R-CC suggests an assignment to Zones RP8–RP10 (lower part). Samples 207-1258A-14R-CC and 16R-CC are assigned to Zones RP7–RP8 based on the presence of Pterocodon ampla, Podocyrtis papalis, and Thyrsocyrtis tarsipes. Farther downhole, radiolarians are rare and poorly preserved in general. However, Buryella tetradica was observed in Samples 207-1258A-23R-CC and 24R-CC and allows assignment to Zones RP5–RP8.
Age-diagnostic Cretaceous radiolarians were observed in Cores 207-1258A-36R and 40R and 207-1257C-10R. Preliminary identifications were made on board on the basis of observations with a stereoscopic microscope, but they will need to be confirmed with the use of the scanning electron microscope. The assemblage in Sample 207-1258A-36R-CC is characterized by the presence of the Campanian species Amphipyndax pseudoconulus (Sanfilippo and Riedel, 1985), whereas the presence of the marker species Crucella cachensis in Sample 207-1258A-40R-CC allows an assignment to the lower Turonian Zones C. cachensis (Erbacher and Thurow, 1998) or Alievum superbum (O'Dogherty, 1994) or to a higher interval.
Pyritized Cretaceous radiolarians are present in the lowermost cores of Hole 1258C. As Thanarla broweri was observed in both Samples 207-1258C-32R-CC and 34R-CC and Triactoma paronai in the latter sample, they are assigned to the Mallanites romanus Subzone of O'Dogherty (1994).