An apparently continuous middle Miocene to Pleistocene section of nannofossil ooze, chalk, and clay was cored in Hole 1208A. Calculated sedimentation rates are high for the Pleistocene to Pliocene (42.4 m/m.y.) but decrease in the lower Pliocene to upper Miocene (22.3 m/m.y.) and are low in the upper to middle Miocene (5.9 m/m.y.) (see "Sedimentation and Accumulation Rates"). The middle Miocene (Sections 198-1208A-31X-CC through 34X-CC) overlies a predominantly condensed lower? Miocene to Paleogene claystone section (interval 198-1208A-35X-4, 50 cm, through 36X-CC, 24 cm), which is thought to contain at least three unconformities, separating lower Miocene to upper Oligocene (interval 198-1208A-35X-4, 50 cm, to 35X-5, 10 cm), lower Oligocene to uppermost Eocene (interval 198-1208A-35X-5, 50 cm, to 36X-2, 40 cm), and lower Eocene to upper Paleocene (interval 198-1208A-36X-2, 42 cm, to 36X-CC, 24 cm) sequences. The upper Paleocene brown claystone lies unconformably on white Campanian nannofossil ooze at the bottom of Section 198-1208A-36X-CC. A relatively complete mid- to lower Campanian section, in turn, lies unconformably on a middle Albian chalk and chert horizon recovered at the base of Hole 1208A.
The Miocene sediments overlying the uppermost condensed section and unconformity, and the Campanian sediments underlying the penultimate unconformity are identical in age to sediments observed on either side of the major unconformity at Site 1207, suggesting a sedimentation and/or erosional history of regional significance.
All core catcher samples were examined, and supplementary samples were used to refine the stratigraphy of the condensed intervals and unconformities. Calcareous nannofossils are generally abundant and moderately to well preserved in Neogene and Cretaceous sediments. The condensed claystone intervals generally yield etched assemblages dominated by robust taxa or occasional barren samples. In general, Neogene planktonic foraminifers are moderately to well preserved, but foraminiferal abundances are relatively low, due to selective dissolution and fragmentation. Cretaceous planktonic foraminifers are well preserved and abundant.
Studies of benthic foraminifers were conducted on selected core catcher samples. Neogene benthic foraminifers are well preserved and rare to common in abundance; Paleogene and Cretaceous forms are moderately well preserved and rare. The 125- to 250-µm size fraction was examined when specimens were too rare in the 250-µm size fraction.
The Neogene section ranges from upper Pleistocene (Zone CN15) to lower Miocene (Zone CN1) and appears to be relatively complete, at least within the biostratigraphic resolution achieved on board ship (Table T3). Nannofossils are abundant throughout, and preservation is moderate to good. A short hiatus may be present at the base of the Miocene. Most of the zones of Okada and Bukry (1980) were recognized, but division at subzonal level was not always possible. Though they were relatively rare, sphenoliths and discoasters occur in greater abundance relative to the Site 1207 assemblages. This slight increase in abundance may be due to closer proximity to tropical latitudes.
The thick Pliocene-Pleistocene section was subdivided using the standard Okada and Bukry (1980) markers. We were not able to identify the Pleistocene Gephyrocapsa subzonal events (first occurrence [FO] Gephyrocapsa caribbeanica and Gephyrocapsa parallela), due to difficulties in discerning these two taxa from the other species of Gephyrocapsa and Reticulofenestra that are present in the assemblages. Notably, Reticulofenestra asanoi and small reticulofenestrids are particularly abundant in Samples 198-1208A-6H-CC and 7H-CC; the former has a short range across the CN13/CN14 boundary.
The middle to upper Miocene section was divided using datums based on species of Catinaster, Discoaster, and Amaurolithus, but Discoaster kugleri, Discoaster hamatus, and Discoaster loeblichii were not observed.
The oldest Neogene section is difficult to date and subdivide, because of the paucity of the sphenoliths, which are used to define the top and bottom of Zone CN2 and the bottom of CN5. These assemblages are directly comparable with those from the lower Neogene of Holes 1207A and 1207B, being characterized by low diversity, high abundances of Discoaster deflandrei and Cyclicargolithus floridanus, the presence of Calcidiscus premacintyrei, and occasional occurrences of the marker taxon Sphenolithus heteromorphus. Samples 198-1208A-32X-CC and 33X-CC contain both Cyclicargolithus floridanus and large (<7 µm) Reticulofenestra pseudoumbilicus, indicating a Subzone CN5a age; the former taxon may be somewhat unreliable but is not thought to range above Zone CN5 (Young, 1998). Samples 198-1208A-34X-CC and 35X-4, 12 cm, contain Sphenolithus heteromorphus, indicating Zones CN3 and CN4. Sample 198-1208A-35X-4, 50 cm, was assigned to Zone CN1 based on the presence of Triquetrorhabdulus carinatus and the absence of Cyclicargolithus abisectus (Young, 1998); rare specimens of Reticulofenestra bisectus and R. umbilica in this sample and a number of underlying samples are considered to be reworked.
The Paleogene is represented by etched assemblages dominated by robust taxa but generally including useful marker species. The nannofossil biostratigraphy indicates a number of condensed intervals including the upper Oligocene, lower Oligocene-uppermost Eocene, and lower Eocene-upper Paleocene, bounded by short unconformities.
Samples 198-1208A-35X-4, 99 cm, to 35X-4, 10 cm, are correlated to Subzone CN1a-Zone CP19 (basal Miocene to upper Oligocene) based on the presence of Cyclicargolithus abisectus; however, precise dating of the interval is hampered by the absence of sphenoliths and the presence of reworked taxa, such as Reticulofenestra umbilica. Zones CP17 and CP18 (lower Oligocene) were not identified, and a short unconformity may be present in this interval.
Interval 198-1208A-35X-5, 50-51 cm, to 36X-2, 30 cm, is assigned to Zone CP16 (lowermost Oligocene to uppermost Eocene) with all three subzones identified by the absence of Discoaster saipanensis and Discoaster barbadiensis, the top acme of Ericsonia subdisticha (Sample 198-1208A-36X-1, 70 cm), the LO of Coccolithus formosus (Sample 198-1208A-35X-CC), and the continued presence of common Reticulofenestra umbilica, respectively. Zones CP12 to CP15 (middle to upper Eocene) were not identified, and an unconformity is likely to correspond to this interval.
The deepest Paleogene interval is restricted to Sections 198-1208A-36X-2 and 36X-CC and rests unconformably on Campanian sediment at the base of Section 36X-CC (Fig. F17). The assemblages are poorly to moderately preserved and pervasively etched and consequently dominated by large and robust taxa. Within this interval, the FO of Discoaster lodoensis defines the base of Zone CP10 and the LO of Tribrachiatus orthostylus occurs toward the top of Zone CP11.
The assemblages in samples toward the base of the Paleogene show some degree of mixing that may be due to downhole contamination during drilling or core handling and/or a small amount of reworking. The contaminated component can be separated from the in situ component by observing continuity of ranges; contaminated taxa tend to be more abundant upsection and are discontinuously present. Three events that are thought to lie close to the Paleocene/Eocene boundary, the LO of the genus Fasciculithus and the FOs of Tribrachiatus bramlettei and Discoaster diastypus, are present within 6 cm of each other in Section 198-1208A-36-CC (Fig. F17). These events lie just within or just above the PETM and are separated by ~330 k.y. (Bralower et al., 1995; Aubry et al., 1996). The lowermost 10 cm of the Paleocene section is barren.
The Cretaceous section ranges from upper Campanian (Zone CC22) to middle Albian (Subzone NC8c). Much of the mid- to lower Campanian was recovered; drilling was terminated below an unconformity in a chert-rich interval of middle Albian age. The nannofossils are generally abundant and moderately well preserved, but the single Albian sample (198-1208A-42X-CC) displayed poor to moderate preservation. Moderate overgrowth is present in all samples of Cretaceous age, and etching is prevalent in the Albian sample.
The relatively common and consistent presence of the Aspidolithus parcus coccoliths and Ceratolithoides and Uniplanarius nannoliths in the upper part of the Upper Cretaceous section allowed confident subdivision of the Campanian (Table T3). Zones CC18 to CC19 could not be completely subdivided, due to the absence of the nannolith Marthasterites furcatus.
The single Albian sample (198-1208A-42X-CC) is placed in Subzone NC8c based on the presence of Tranolithus orionatus, Eprolithus floralis, and Prediscosphaera columnata and the absence of Axopodorhabdus albianus.
Planktonic foraminiferal abundance varies from abundant to common through the Pleistocene and upper Pliocene but declines in the Miocene to few to rare relative to siliceous microfossils and clay. Like Site 1207, temperate-water species dominate many of the Neogene planktonic foraminiferal assemblages at Site 1208. The abundance of the upwelling indicator species Globigerina bulloides, together with an abundance of diatoms, radiolarians, and a diverse benthic fauna consisting of benthic foraminifers, echinoderms, ostracodes, and sponges, suggest that (seasonal) productivity was high over this site during much of the Pliocene and Pleistocene. Productivity may have also varied cyclically, as suggested by the pronounced decimeter-scale lithologic cycles observed in lithologic Unit I (see "Lithostratigraphy").
Many biostratigraphically useful tropical-subtropical taxa are present in low to moderate abundances, including Globorotalia menardii, Globorotalia tumida, Globorotalia plesiotumida, and Paragloborotalia mayeri (Table T4). In addition, secondary marker taxa are used to make biostratigraphic assignments and/or confirm zonal assignments. For example, the LOs of Globigerinoides extremus, Dentoglobigerina altispira, Sphaeroidinellopsis seminulina, Globorotalia margaritae, and Globoturborotalita nepenthes, and the FOs of Globorotalia crassaformis, Globoconella puncticulata, and Globoconella conomiozea are used to delineate positions within Zones N21 and N19-N20. The FOs of Globorotalia margaritae and Globigerinoides conglobatus are useful within Zone N17.
Common Pliocene-Pleistocene taxa include Globigerina bulloides, Globorotalia inflata, G. crassaformis, G. puncticulata, G. conomiozea, Neogloboquadrina dutertrei, and Neogloboquadrina pachyderma (dextral). Persistent late Miocene taxa include Orbulina universa, Neogloboquadrina acostaensis, Sphaeroidinellopsis seminulina, and Globoturborotalita nepenthes. A marked decrease in the number of taxa and specimens characterizes the middle Miocene sediments (Sections 198-1208A-32X-CC to 34X-CC), which contain few orbulinids, Globoquadrina dehiscens, Globigerina venezuelana, S. seminulina, Sphaeroidinellopsis disjuncta, and rare Globoconella conoidea, Globoconella miozea, and Paragloborotalia mayeri. Based on the absence of G. nepenthes and the presence of O. universa, this assemblage is interpreted to lie within Zones N13 to N9. The underlying Section 198-1208A-35X-CC yields rare Tenuitella gemma, Globorotaloides suteri, and Tenuitellinata angustiumbilicata, suggesting the lower Oligocene Zone P18.
The mid- to lower Campanian nannofossil ooze and chalk recovered at Site 1208 contains generally abundant and well-preserved assemblages of planktonic foraminifers. The composition of the assemblages is similar to those recovered at Site 1207. The upper boundary of the Campanian at both sites is truncated at the same age, ~75.7-76.0 Ma, based on the absence of Radotruncana calcarata and presence of Globotruncanita atlantica. Common taxa through this Campanian sequence include Archaeoglobigerina cretacea, Contusotruncana fornicata, Contusotruncana patelliformis, Globigerinelloides messinae, G. cf. Globigerinelloides prairiehillensis, Globotruncana arca, Globotruncana linneiana, Globotruncana orientalis, Globotruncanita stuartiformis, Globotruncanita subspinosa, Hedbergella holmdelensis, Heterohelix carinata, Heterohelix globulosa, Laeviheterohelix pulchra, Pseudoguembelina costulata, Pseudotextularia nuttalli, and Rugoglobigerina rugosa. The FO of Globotruncanita atlantica serves to distinguish the Globotruncana ventricosa Zone (Zone KS26) in Sections 198-1208A-36X-CC to 39X-CC from the Globotruncanita elevata Zone (Zone KS25) in Sections 198-1208A-40X-CC to 41X-CC. A major unconformity separates the lower Campanian and middle Albian strata.
Site 1208 terminated in middle Albian chert-bearing chalk of the Ticinella primula Zone (Zone KS13). Common taxa include T. primula, Ticinella roberti, Ticinella raynaudi, Hedbergella planispira, Hedbergella delrioensis, and Hedbergella rischi in the absence of Biticinella breggiensis. A similar assemblage was recovered at Site 1207. The large size and diversity of the ticinellids indicates that these sediments represent the upper part of the T. primula Zone.
In the interval representing the Pleistocene to early Pliocene (Samples 198-1208A-1H-CC through 21X-CC), the main components of benthic foraminifers are calcareous trochospiral and planispiral species (Oridorsalis tener, Pullenia bulloides, cibicidoidids, Nonion spp., and gyroidinoidinids), uvigerinids (Uvigerina hispidocostata and Uvigerina hispida), miliolids (Pyrgo lucernula and Pyrgo murrhina), and Eggerella bradyi (Table T5).
In Sample 198-1208A-23X-CC, uvigerinids are absent. Trochospiral forms, together with abundant Globocassidulina subglobosa, Pyrgo murrhina, and Eggerella bradyi, characterize the benthic assemblage. The benthic assemblage in Sample 198-1208A-24X-CC is dominated by Oridorsalis tener, Cibicidoides cicatricosus, Cibicidoides wuellerstorfi, Cibicidoides spp., Gyroidinoides girardanus, Gyroidina neosoldanii, Nonion spp., Melonis barleanus, Pullenia bulloides, and abundant Globocassidulina subglobosa, Pyrgo murrhina, and Eggerella bradyi. Uvigerinids are present again and dominate the benthic assemblage in Sample 198-1208A-25X-CC. Other characteristic forms are Stilostomella abyssorum, Stilostomella subspinosa, O. tener, C. cicatricosus, Cibicidoides spp., G. girardanus, G. neosoldanii, and Eggerella bradyi.
Abundant stilostomellids (Stilostomella abyssorum, Stilostomella spp., and S. subspinosa) replace uvigerinids in Sample 198-1208A-29X-CC. Other components are generally the same as in Sample 198-1208A-25X-CC, although the miliolids decrease in abundance.
In Sample 198-1208A-31X-CC, the stilostomellids (Stilostomella abyssorum, Stilostomella spp., and S. subspinosa) are again common. Other characteristic species are Oridorsalis tener, Anomalinoides globulosus, Cibicidoides praemundulus, Cibicidoides spp., Gyroidinoides neosoldanii, G. girardanus, Pullenia bulloides, Dentalina spp., Pyrgo murrhina, Martinottiella sp., and Eggerella bradyi. In Sample 198-1208A-34X-CC, the stilostomellids remain dominant, but some changes are observed in the representatives of the calcareous trochospiral and planispiral taxa (Anomalinoides globulosus, Oridorsalis umbonatus, O. tener, Cibicidoides mundulus, and Pullenia bulloides) and the agglutinated species Vulvulina spinosa.
In Sample 198-1208A-36X-2, 18-20 cm, only Vulvulina spinosa and Vulvulina mexicana are present in the >250-µm size fraction. In the 125- to 250-µm size fraction, trochospiral species (Nuttallides truempyi, Cibicidoides bradyi, C. praemundulus, Cibicidoides subspiratus, Cibicidoides spp., Oridorsalis umbonatus, and O. tener), Stilostomella subspinosa, and Stilostomella spp. characterize the benthic assemblage. The LO of N. truempyi slightly precedes the Eocene/Oligocene boundary, and therefore its presence in Sample 198-1208A-36X-2, 18-20 cm, indicates that the top of the condensed interval is older than the Oligocene.
Pleistocene to middle Miocene benthic foraminifers indicate upper abyssal paleowater depths (2000-3000 m) (Pflum et al., 1976; Tjalsma and Lohmann, 1983; Woodruff, 1985; van Morkhoven et al., 1986).
No benthic foraminifers were found in Sample 198-1208A-36X-CC (Campanian age). In Sample 198-1208A-37X-CC, the benthic assemblage is characterized by Oridorsalis umbonatus, osangulariids (Osangularia plummerae, O. mexicana), Nuttallides truempyi, and Sliterella lobulata), Dentalina spp., Pleurostomella spp., Gaudryina pyramidata, and Marssonella trochoides. Abundant Pyramidina szajnochae and trochospiral forms such as O. umbonatus, S. lobulata, Gyroidinoides globosus, Gyroidinoides infracretaceus, Conorbinoides hillebrandti, and Serovaina spissiformis dominate Sample 198-1208A-39X-CC. In Sample 198-1208A-41X-CC, the benthic assemblage is represented by trochospiral forms (C. hillebrandti, O. umbonatus, N. truempyi, Nuttallinella florealis, S. spissiformis, and Osangularia plummerae), Aragonia velascoensis, Aragonia ouezzanensis, Bulimina spp., Lenticulina spp., and Pleurostomella spp., together with abundant agglutinated taxa, including G. pyramidata and M. trochoides.
Sample 198-1208A-42X-CC of middle Albian age is characterized by abundant trochospiral benthic forms of Protosangularia albiana, G. infracretaceus, and Pseudoclavulina rugolosa. Other components are Protosangularia cenomaniana, buliminids, nodosariids, and Remesella spp.
The Cretaceous benthic assemblages at Site 1208 are similar to those recorded at Site 1207 and suggest the same deepening trend from upper lower bathyal (~1000- to 1500-m paleowater depth) in the Albian to upper abyssal (~2000- to 3000-m paleowater depth) by the Campanian.