An apparently continuous upper Miocene to Pleistocene section of siliceous nannofossil ooze and nannofossil ooze was cored with the APC at Hole 1207A based on calcareous plankton biostratigraphy. An unconformity in Section 198-1207A-17H-2, 107 cm, separates the upper Miocene and middle Miocene and is marked by a sharp color change. A thin interval of middle Miocene nannofossil ooze (interval 198-1207A-17H-2, 107 cm, to 18H-5, 43 cm) overlies a 59-cm-thick condensed lower Miocene section containing reworked Paleogene and Cretaceous nannofossils. This condensed interval consists of darker-colored nannofossil clay capped by a manganese crust in interval 198-1207A-18H-5, 43-102 cm. An unconformity spanning nearly 60 m.y. is present at the bioturbated contact between dark yellow-brown lower Miocene nannofossil clay and dusky yellow-brown Campanian nannofossil ooze at 102 cm in Section 198-1207A-18H-5. The mid-Campanian to Barremian section cored at Site 1207 appears to be biostratigraphically complete.
All core catcher samples were examined, and additional samples were used to refine datums and zonal boundaries. Calcareous nannofossils are generally abundant and moderately to well preserved in Neogene and Cretaceous sediments of Holes 1207A and 1207B. Despite poor recovery in the Cretaceous section, diverse nannofossil assemblages were recovered in almost all intervals, from small sediment chips or from chalk/limestone scraped off chert pieces. In general, Neogene planktonic foraminifers are also moderately to well preserved, but foraminiferal abundances are relatively low because of selective dissolution and fragmentation. Foraminiferal abundance shows an inverse relationship to siliceous microfossil abundance. Moderately well preserved planktonic foraminiferal assemblages occur where calcareous ooze or chalk was recovered.
Studies of benthic foraminifers were conducted on selected core catcher samples. Benthic foraminifers are generally well preserved but rare or few in abundance. The >250-µm size fraction was examined for the Neogene samples, and the >125-µm size fraction was examined for the Cretaceous samples.
The Neogene section ranges from lower Miocene (Subzone CN1b-Zone CN3) to upper Pleistocene (CN15) and appears to be relatively complete, at least within the biostratigraphic resolution achieved shipboard (Table T5). Nannofossils are abundant throughout, and preservation is moderate to good but deteriorates in the lower to middle Miocene nannofossil ooze. A number of short hiatuses may be present in the lower to middle Miocene interval. Most of the zones of Okada and Bukry (1980) were recognized, but division at subzonal level was not always possible. In particular, the rarity or absence of sphenoliths and the rarity of discoasters prevented the recognition of a number of zones and subzones. The rarity of these two important nannolith groups suggests a common paleoenvironmental cause, the most likely being enhanced surface water productivity and cooler temperatures as supported by planktonic foraminiferal assemblages. Such conditions would have supported high abundances of r-selected noelaerhabdacean coccoliths, such as Reticulofenestra, Gephyrocapsa, and Emiliania, and excluded or reduced k-selected nannoliths, such as the discoasters and sphenoliths.
The thick Pliocene-Pleistocene section was subdivided using the standard Okada and Bukry (1980) markers; however, because the discoasters are rare throughout, their last occurrence (LO) should be viewed with caution. 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 other species of Gephyrocapsa and Reticulofenestra that were present in the assemblages. Notably Reticulofenestra asanoi (Section 198-1207A-2H-CC) and small reticulofenestrids were particularly abundant. The former taxon 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 the subzonal marker species Amaurolithus amplificus was not observed and the ranges of Discoaster kugleri, Discoaster hamatus, and Discoaster loeblichii could not be satisfactorily resolved due to inconsistent ranges and poor preservation. The LO of the genus Amaurolithus was recorded at an anomalously low stratigraphic level relative to the FOs of Discoaster asymmetricus and Ceratolithus rugosus, and it plots off the age-depth line (Fig. F32). Rare Amaurolithus specimens may have been overlooked due to the abundance of siliceous material, which has similar birefringence and relief.
The oldest Neogene section is difficult to date and subdivide due to the absence of the sphenoliths, which are used to define the top and bottom of Zone CN2 and the bottom of Zone CN5. The exception was Sample 198-1207A-18H-4, 45-46 cm, which yields common Sphenolithus heteromorphus (Zone CN3-CN4). Samples below this level are tentatively dated as Subzone CN1b-Zone CN3, based on the exceptional abundance of Discoaster deflandrei (acme top within Zone CN3; Young, 1998) and the absence of older, robust taxa, such as Cyclicargolithus abisectus, Reticulofenestra bisecta, and Zygrhablithus bijugatus, which have LOs in Subzone CN1a and lower Subzone CN1b. The lowermost Miocene assemblage was observed in Sample 198-1207A-18H-5, 126 cm, just below the major color change within a clearly bioturbated interval and, notably, 83 cm below the prominent manganese crust. Our interpretation of the mixed zone is that the Campanian/Miocene boundary lies at the color change in Section 198-1207A-18H-5, 102 cm. The lowermost 60 cm of Miocene sediment contains prevalent Cretaceous (Campanian) reworking, which decreases upward from the color change. Consistent but rare Paleogene reworking was also encountered in an interval from 198-1207A-18H, 50 to 102 cm, consisting of late Paleocene-early Eocene taxa such as Discoaster multiradiatus and Tribrachiatus orthostylus.
The Cretaceous section ranges from upper Campanian (Zone CC22) to Barremian (Subzones NC5d and NC5e) and appears to be complete, at least within the biostratigraphic resolution achieved shipboard. Nannofossils are generally abundant but variable in preservation. Overgrowth is prevalent in the Barremian and Turonian to Campanian intervals; good to pristine preservation was encountered in the Aptian and Albian.
A near-complete succession of nannofossil zones was recognized, and those that were not identified are most probably absent as a result of biogeographic and preservational factors or poor core recovery rather than incomplete stratigraphy. Many of the Sissingh (1977) CC Zones were recognized in the Upper Cretaceous section (Table T5). The relatively common and consistent occurrence 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, and the youngest Cretaceous assemblages were placed in Zone CC22/Subzone UC15d (lower upper Campanian). Zones CC14 to CC19 could not be completely subdivided as a result of the absence of the holococcolith marker species of Lucianorhabdus and Calculites, the nannolith Marthasterites furcatus, and the coccolith Reinhardtites anthophorus. The latter two species are notoriously unreliable markers, and their absence is not entirely surprising. Holococcoliths are known to display shelf affinities (e.g., Burnett, 1998), which may explain their absence at this oceanic site. In addition, this interval yields the poorest preservation of the entire hole, and absences may be due to dissolution.
Zones NC6 to NC10 are all present, but the subzonal markers Conusphaera rothii and Micrantholithus hoschulzii were absent, almost certainly because of biogeographic exclusion, and we were unable to divide the Hayesites irregularis-albiensis plexus, thus missing the Hayesites albiensis datum. Subzone NC9a was not recognized as the FOs of Eiffellithus monechiae and Axopodorhabdus albianus corresponded to the same sample (198-1207B-29R-CC).
The age of the oldest sediments is problematic because of the lack of low-latitude datums in the Barremian interval. The age is given as Subzones NC5d and NC5e, based on the absence of Hayesites irregularis (FO in Sample 198-1207B-44R-CC) and absence of Calcicalathina oblongata (LO at 126.9 Ma). Inference of the latter datum is highly suspect because C. oblongata is rarely encountered outside the Tethyan biogeographic region. However, the presence of Assipetra terebrodentarius (FO mid-Subzone NC5c, close to the Barremian/Hauterivian boundary) in the deepest sample (198-1207B-49R-CC) provides a secondary datum that supports the Barremian age determination. The organic-rich horizon recovered in Core 198-1207B-44R lies within Zone NC6, between the FO of Eprolithus floralis (198-1207B-43R-CC) and the FO of Hayesites irregularis (44R-CC), strongly supporting the correlation of this interval with OAE1a.
Planktonic foraminiferal abundance generally is low in the Neogene of Hole 1207A. Relatively low abundances of whole, moderately to well-preserved specimens of foraminifers and high abundances of foraminiferal fragments show that differential dissolution has modified the assemblages, particularly in the Pliocene-Pleistocene part of the section. Dissolution of planktonic foraminifers is likely to be at least partially responsible for the observed abundance of radiolarians and benthic organisms in the >63-µm sediment assemblages.
Temperate water species dominate many of the Neogene planktonic foraminiferal assemblages of Hole 1207A. The abundance of cool water taxa is the consequence of differential dissolution of the less heavily calcified and more porous tropical-subtropical species, as well as strong seasonality and/or high productivity. The abundance of the upwelling-indicator species Globigerina bulloides, together with an abundance of diatoms, radiolarians, and a healthy benthic fauna consisting of benthic foraminifers, echinoderms, ostracodes, and sponges, suggest that (seasonal) productivity was high at this site during much of the Pliocene and Pleistocene. Productivity may have also varied cyclically as suggested by the pronounced decimeter-scale color/lithologic cycles observed in lithologic Unit I (see "Lithostratigraphy"). For example, dark-colored bands of siliceous nannofossil ooze in Samples 198-1207A-5H-1, 80-82 cm, and 5H-CC contain relatively few planktonic foraminifers and an abundance of the mat-forming diatom genus Thalassiothrix, whereas the white band in Sample 198-1207A-5H-4, 80-82 cm, contains a very similar assemblage of planktonic foraminifers but with very few diatoms and few radiolarians.
Common Pliocene-Pleistocene taxa include Globigerina bulloides, Globorotalia inflata, Globorotalia crassaformis, Globorotalia puncticulata, Globoconella conomiozea, Neogloboquadrina dutertrei, and Neogloboquadrina pachyderma (dextral). Persistent late Miocene taxa include Orbulina universa, Neogloboquadrina acostaensis, Sphaeroidinellopsis seminulina, and Globoturborotalita nepenthes. In general, species of the genus Globigerinoides are rare but persistent through the Neogene. No species of the tropical, dissolution-resistant Pulleniatina were observed. A 15- to 20-m-thick interval of the lower Pliocene (Sections 198-1207A-9H-4 to 11H-1), in particular, is marked by a low diversity assemblage dominated by G. puncticulata, G. conomiozea, and S. seminulina.
Many biostratigraphically useful tropical-subtropical taxa occur sporadically or in low abundances, including Sphaeroidinella dehiscens, Globorotalia menardii, Globorotalia tumida, Globorotalia plesiotumida, Globorotalia merotumida, and Paragloborotalia mayeri (Table T6). As a consequence, secondary marker taxa are used to make biostratigraphic assignments and/or confirm zonal assignments based on rare or sporadic primary marker taxa. For example, the FO of G. crassaformis, FO G. puncticulata, FO G. conomiozea, and the LO of Globoturborotalita nepenthes are used to delineate positions within Zone N19; the FOs of Globorotalia margaritae, Globoconella cibaoensis, and Globigerinoides conglobatus are useful within Zone N17.
A sharp lithologic break in Section 198-1207A-17H-2 marks an unconformity of ~2.5-3.5 m.y. that spans planktonic foraminiferal Zones N15 (upper Miocene) to lower N12 or upper N11 (middle Miocene). Reworked Late Cretaceous planktonic foraminifers occur sporadically in the middle Miocene sediments (Sections 198-1207A-17H-4 to 18H-4) below this unconformity. Fohsella peripheroacuta, Fohsella peripheroronda, Globorotalia praemenardii, Globorotalia miozea, Orbulina universa, and Globoquadrina dehiscens are characteristic taxa of middle Miocene Zones N9-N11 in Hole 1207A. Sample 198-1207A-18H-4, 78-80 cm, is assigned to Zone N9 based on the co-occurrence of O. universa, Praeorbulina glomerosa, and Globigerinatella insueta in the absence of F. peripheroacuta.
Few small-sized Cretaceous planktonic foraminifers including Heterohelix spp., Hedbergella holmdelensis, and schackoinids, together with rare Miocene taxa, occur in Sections 198-1207A-18H-5 and 18H-6 below the horizon with manganese nodules. The underlying Cretaceous assemblages (Sample 198-1207A-19H-1, 26-28 cm, to 21X-3, 26-28 cm, and Core 198-1207B-2R) are characterized by the absence of age-diagnostic taxa and are dominated by small-sized heterohelicids, hedbergellids, globigerinelloidids, and juvenile globotruncanids. A moderately well preserved mid-Campanian assemblage occurs in Sections 198-1207A-21X-3 through 23X-CC and 198-1207B-3R-CC through 9R-CC (Table T6). Globotruncana arca, Globotruncana orientalis, Globotruncanita elevata, Globotruncanita atlantica, and Globotruncanita stuartiformis are common in the large size fraction (>250 µm), whereas Hedbergella holmdelensis, Globigerinelloides messinae, Globigerinelloides ultramicrus, Heterohelix globulosa, Heterohelix dentata, and Heterohelix planata dominate the small size fractions (45-250 µm). Few specimens of Schackoina cenomana and Schackoina multispinata are also present. Based on the presence of G. atlantica, this latter interval is assigned to the mid-Campanian Globotruncana ventricosa Zone (KS26). The lower Campanian Globotruncanita elevata Zone (KS25) is recorded at the bottom of Hole 1207A (Sample 198-1207A-24X-CC) based on the absence of G. atlantica and presence of common G. elevata.
In the remainder of the Cretaceous sequence, planktonic foraminifers could only be collected in a few cores because the very low recovery was dominated by chert fragments with rare carbonates. Consequently, few biozones are recognized. The biostratigraphic resolution based on planktonic foraminifers may improve with the study of indurated lithologies in thin section. Sample 198-1207B-18R-CC, 37-39 cm, yielded a few specimens of Hedbergella holmdelensis and rare specimens of the long-ranging Hedbergella planispira and G. ultramicrus. Because H. holmdelensis seems to appear in the Dicarinella concavata Zone (KS23), this assemblage is probably not older than Coniacian.
Few Rotalipora appenninica, Ticinella madecassiana, and Praeglobotruncana delrioensis are recorded from Cores 198-1207B-22R through 24R, indicating correlation of this stratigraphic interval to the upper Albian R. appenninica Zone (KS16). The presence of Biticinella breggiensis together with rare to few Ticinella praeticinensis, Ticinella roberti, T. madecassiana, Globigerinelloides bentonensis, and Hedbergella delrioensis in Sample 198-1207B-28R-CC, 11-16 cm, in the absence of Ticinella subticinensis, indicates the T. praeticinensis Subzone of the Biticinella breggiensis Zone (KS14) of early late Albian age. Samples 198-1207B-30R-CC and 33R-1, 103-104 cm, contain Ticinella primula, Ticinella raynaudi, T. roberti, Hedbergella rischi, and H. planispira. These two levels are assigned to the middle Albian Ticinella primula Zone (KS13) based on the presence of T. primula and the absence of B. breggiensis.
Rare Globigerinelloides barri, Globigerinelloides blowi, Globigerinelloides aptiense, and "Hedbergella delrioensis" are recorded in Sample 198-1207B-40R-CC, 15-17 cm. This level is assigned to the upper Aptian Globigerinelloides algerianus Zone (KS9) based on the presence of G. barri, whose range closely overlaps with that of the nominate taxon (Sigal, 1977). The presence of "H. delrioensis" and G. blowi, which both first occur in Sample 198-1207B-43R-CC, 20-21 cm, may indicate the G. blowi Zone (KS6). In the oldest sample studied (Sample 198-1207B-47R-3, 79-81 cm), the presence of Clavihedbergella eocretacea, Clavihedbergella semielongata, Hedbergella sigali, Hedbergella similis, and Gubkinella graysonensis indicates the Hedbergella similis-Hedbergella kuznetsovae Zone of Barremian age according to Coccioni and Premoli Silva (1994).
Planktonic foraminifers have been studied in a number of thin sections cut from indurated Cretaceous sedimentary rocks, mainly chert and porcellanite. Planktonic foraminiferal abundance and preservation vary from sample to sample depending on the degree of rock silicification. Planktonic foraminifers may become visible with crossed nicols or brightfield or both. Calcitic foraminiferal tests are frequently preserved and often recrystallized. The calcitic wall rarely is replaced by silica, but frequently both types of preservation occur in the same sample.
The biostratigraphy of certain intervals can be constrained, and some biozones were recognized. The distribution of planktonic foraminifers identified in thin section is shown in Table T7 along with abundance estimates of benthic foraminifers, radiolarians, and other fossil groups.
The occurrence of Dicarinella asymetrica in Sample 198-1207B-15R-CC, 12-15 cm, identifies the base of the nominal zone (KS24) of Santonian age. The top of the zone, which lies very close to the Santonian/Campanian boundary, corresponds to the disappearance level of the marginotruncanids in Sample 198-1207A-28N-1, 3-4 cm.
Core 198-1207B-16R is attributed to the D. concavata Zone (KS23) of Coniacian age, based on the presence of the nominal species. The D. concavata Zone is extended to include Sample 198-1207B-18R-CC, 14-15 cm, which yields common whiteinellids, along with Globigerinelloides bollii, Hedbergella flandrini, Marginotruncana coronata, and Marginotruncana tarfayaensis. The occurrence of the latter taxon supports this zonal assignment, as M. tarfayaensis is known to appear just prior to the base of the D. concavata Zone close to the base of the upper Turonian.
Core 198-1207B-37R is assigned to the latest Aptian Ticinella bejaouaensis Zone (KS11) based on the presence of the nominal species along with Hedbergella trocoidea and a possible Planomalina cheniourensis. The occurrence of Globigerinelloides ferreolensis, together with rare Hedbergella trocoidea, "H. delrioensis," and G. aptiense, indicates that the assemblage from Sample 198-1207B-42R-CC, 40-41 cm, may correlate to the late Aptian G. ferreolensis Zone (KS8) or possibly to the Globigerinelloides algerianus Zone (KS9).
The oldest foraminiferal fauna observed in thin section from Hole 1207B occurs in Sample 198-1207B-46R-1, 96-98 cm, and is assigned to the Globigerinelloides blowi Zone (KS6) of late Barremian age.
In Sample 198-1207A-1H-CC, ~50% of the benthic foraminifers belong to spinose uvigerinids such as Uvigerina hispida and Uvigerina hispidocostata (Table T8). Other characteristic components are Cibicidoides wuellerstorfi, Melonis sphaeroides, Pyrgo lucernula, and Pyrgo murrhina. Melonis sphaeroides represents more than 30% of the assemblage in Sample 198-1207A-4H-CC. Other important components are Pyrgo lucernula, P. murrhina, Oridorsalis umbonatus, U. hispida, and Eggerella bradyi. In Sample 198-1207A-6H-CC, the assemblage is characterized by abundant C. wuellerstorfi, P. lucernula, P. murrhina, and U. hispida.
The main components of benthic foraminifers in Sample 198-1207A-8H-CC are C. wuellerstorfi, gyroidinoids, Pullenia bulloides, Oridorsalis umbonatus, Pyrgo lucernula, and P. murrhina, along with agglutinated forms such as Eggerella bradyi, Haplophragmoides spp., and Karreriella bradyi.
Sample 198-1207A-11H-CC contains well-preserved and diverse benthic foraminifers. The assemblage is mainly composed of Gyroidinoides neosoldanii, Gyroidinoides girardanus, O. umbonatus, P. bulloides, P. lucernula, P. murrhina, Stilostomella abyssorum, U. hispida, U. hispidocostata, Haplophragmoides spp., and K. bradyi. Smaller numbers of Cibicidoides cicatricosus, Cibicidoides incrassatus, and Cibicidoides subhaidingeri are also included. Sample 198-1207A-12H-CC of late Miocene age is characterized by such taxa as O. umbonatus, G. girardanus, Nonion spp., P. bulloides, P. lucernula, P. murrhina, and E. bradyi. In Sample 198-1207A-15H-CC, benthic foraminifers show moderate preservation and low abundance. The most common taxa in this sample are O. umbonatus and S. abyssorum. P. lucernula and P. murrhina, the dominant species in overlying samples, are markedly less abundant.
The middle Miocene Sample 198-1207A-17H-CC contains common, well-preserved benthic foraminifers. The main taxa are Anomalinoides globulosus, C. wuellerstorfi, C. subhaidingeri, O. umbonatus, P. bulloides, and Stilostomella subspinosa. Sample 198-1207B-1R-CC yields few moderately preserved benthic foraminifers, including A. globulosus, Pullenia bulloides, S. abyssorum, and S. subspinosa.
Neogene benthic foraminifers indicate upper abyssal paleowater depths (2000-3000 m) (Woodruff, 1985; van Morkoven et al., 1986) at Site 1207.
In the interval representing the early to middle Campanian (Samples 198-1207A-18H-CC through 23X-CC and 198-1207B-2R-CC through 6R-CC), benthic foraminifers show moderate to good preservation but are rare to few in abundance (Table T9). Calcareous trochospiral benthic taxa (Conorbinoides hillebrandti, Nuttallides truempyi, O. umbonatus, Osangularia plummerae, and gyroidinoids), Dentalina spp., and Lenticulina spp. generally characterize the assemblage, although Gaudryina pyramidata is absent in the lower Campanian. Most specimens are small (125-250 µm).
Sample 198-1207B-9R-CC contains benthic foraminiferal components similar to those observed higher in the Campanian, except for the absence of O. umbonatus. Because of the presence of chert and poor recovery, no useful core catcher samples were available from Sample 198-1207B-10R-CC through 21R-CC. In Samples 198-1207B-22R-CC and 24R-CC, benthic foraminifers are poor to moderately preserved and rare to few in abundance. Most specimens are small (125-250 µm). Calcareous trochospiral forms such as Gavelinella sp., Gyroidinoides globosus, Gyroidinoides infracretaceus, Hanzawaia ammophila, Protosangularia albiana, and Protosangularia cenomaniana, along with Serovaina lobulata, Dentalina spp., Lenticulina spp., Saracenaria spp., Spiroplectammina excolata, and Pseudoclavulina globulifera characterize the benthic assemblage.
Samples 198-1207B-28R-CC, 30R-CC, and 33R-1, 103-104 cm, are middle to late Albian in age. The samples are characterized by calcareous trochospiral such as H. ammophila, P. albiana, P. cenomaniana, Serovaina lobulata, G. infracretaceus, and agglutinated taxa (Pseudoclavulina globulifera, Remesella sp., Dorothia spp., and Gaudryina dividens). Test preservation is poor to moderate and abundance is few. Almost all specimens are small (125-250 µm).
In the Aptian to Barremian interval, useful benthic foraminifers are found in only two core catcher samples (198-1207B-43R-CC and 47R-CC). Sample 198-1207B-43R-CC contains poorly preserved but abundant benthic foraminifers. The main components are quite different from those observed upsection and are dominated by nodosariids, unilocular forms, and G. dividens. In Sample 198-1207B-47R-CC, benthic foraminifers show poor preservation but high abundance. The assemblage is represented by Dentalina spp., Lenticulina spp., Oolina spp., Pyrulina spp., and abundant Marssonella sp.
Benthic foraminiferal evidence suggests a deepening upward trend from upper lower bathyal (~1000-1500 m water depth) in the Barremian-Aptian to upper abyssal depths (~2000-3000 m) by Campanian time.