In the three holes at Site 1257, we recovered primarily Paleogene–mid-Cretaceous marine sediments that contain calcareous nannofossils, planktonic foraminifers, 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 F7 and in Tables T3, T4, T5, T6, T7, and T8.
A veneer of Pleistocene and upper Miocene ooze at the top of the section overlies an expanded lower Oligocene calcareous ooze rich in diatoms and radiolarians. All microfossil groups are abundant and well preserved. About 20 m of middle Eocene biosiliceous chalk disconformably overlies a 15-m-thick lower Eocene chalk. Core 207-1257C-1R contains the P/E boundary (see Fig. F9, in the "Leg 207 Summary" chapter). Radiolarians cannot be identified to the species level in the Paleocene section, where the conspicuous presence of zeolites and occasional porcellanites indicates that these and other siliceous microfossils have been largely destroyed by sediment diagenesis.
The K/T boundary sequence is incomplete, as the lower Danian and upper Maastrichtian are missing in all holes and a slump is evident in the lower Paleocene of Hole 1257A. The lower Maastrichtian–lower Campanian zeolitic chalk (lithostratigraphic Subunit IIIB) is similar to the Paleocene, but radiolarians could be zoned in only a few samples and disappear from the section completely below this level. A condensed glauconite-rich horizon in Core 207-1257A-20X separates the Campanian chalk from the ~57 m of black shale below (lithostratigraphic Unit IV) that comprises OAEs 3 and 2. Calcareous microfossils are generally present throughout this unit, although preservation of foraminifers varies from often poorly preserved to pristine ("glassy"). The diversity of foraminifers is low. Cenomanian planktonic foraminifers near the base of the black shale indicate an environment shallower than that noted upsection; calcareous nannofossils are too few to yield an age. A sharp contact between the laminated black shales and the underlying clayey carbonate siltstone (lithostratigraphic Unit V) was recovered in Core 207-1257C-15R. Calcareous microfossils provide a middle–late Albian age for the bottom of the drilled section.
In the three holes at Site 1257, we recovered primarily Paleogene–mid-Cretaceous sediments that contain generally common to abundant calcareous nannofossils of moderate to good preservation, thereby permitting zonal or stage assignments to be made as summarized in Figure F7 and Tables T3 and T6. Core catcher samples were examined for all holes and supplemented by samples from the cores to further refine the zonal assignments. The following description is based on Hole 1257A, which was sampled in the most detail.
Samples 207-1257A-1H-1, 26 cm, to 1H-2, 45 cm, yielded a nannofossil assemblage of late Miocene age (Zone NN11 of the Martini, 1971, zonal compilation) that included Discoaster brouweri, Discoaster braarudii, Discoaster quinqueramus, and Amaurolithus delicatus. Samples 207-1257A-2H-1, 24 cm, to 2H-7, 23 cm, are of early Oligocene age (Zone NP23), as indicated by the presence of Dictyococcites bisectus, Sphenolithus distentus, and Sphenolithus predistentus. Samples 207-1257A-2H-CC to 3H-7, 25 cm, contain an early Oligocene–age assemblage (Zone NP22), including Reticulofenestra umbilica and S. predistentus. Samples that follow downhole from Samples 207-1257A-3H-CC to 6H-2, 65 cm, are earliest Oligocene age (Zone NP21), yielding D. bisectus, R. umbilica, Ericsonia formosa, Sphenolithus pseudoradians, and Reticulofenstra oamaruensis. Based on the presence of Discoaster tanii ssp. nodifer, Discoaster saipanensis, Reticulofenestra reticulata, and Coccolithus eopelagicus, Samples 207-1257A-6X-2, 104 cm, to 6X-2, 143 cm, were assigned a late Eocene age (Zone NP20). An interesting taxon found in this interval in Hole 1257B was Isthmolithus recurvus, a "cool-water" species seldom reported from the low latitudes. Its presence may indicate the upwelling of cooler waters. Also noted in this interval in Hole 1257B were slumps with darker-colored clasts relative to the matrix; the zonal age of these clasts and matrix, however, were all the same, indicating that the slump was intraformational.
A sharp disconformity at Section 207-1257A-6X-2, 137 cm, marked by a change from light to darker green sediment, separates the upper from the middle Eocene. The middle Eocene spans the interval from Samples 207-1257A-6X-3, 24 cm, to 9X-5, 25 cm, and comprises Zones NP17 and NP16, based on the presence of Chiasmolithus grandis, S. distentus, D. tanii ssp. nodifer, Sphenolithus radians, R. umbilica, and D. bisectus. Subjacent samples from Samples 207-1257A-9X-CC to 10X-CC contain Chiasmolithus solitus, Discoaster kueperi, Chiasmolithus consuetus, Discoaster multiradiatus, Discoaster diastypus, Zygrhablithus bijugatus, and S. radians and are thus of early Eocene age (Zone NP11).
A nannofossil assemblage consisting of D. multiradiatus, Toweius pertusus, and Fasciculithus tympaniformis characterizes Sections 207-1257A-11X-2 (bottom) to 12X-CC, which have a late Paleocene–early Eocene age (Zone NP9). A late Paleocene age (Zone NP8) is assigned to Sections 207-1257A-13X-CC to 15X-CC, based on the presence of Heliolithus riedelii, Discoaster mohleri, D. multiradiatus, and Discoaster nobilis. Chiasmolithus bidens, Fasciculithus ulii, Ericsonia subpertusa, and Cruciplacolithus tenuis in Sample 207-1257A-16X-CC indicate the presence of the early late Paleocene nannofossil Zone NP5.
Samples 207-1257A-17X-1, 25 cm, to 17X-1, 102 cm, yielded a nannofossil assemblage of mid-Maastrichtian age (Zone CC24 of the Sissingh, 1977, zonal scheme), including Reinhardtites levis, Arkhangelskiella cymbiformis, and Ceratolithoides aculeus (internal angle of the horns = <90°). The interval from Samples 207-1257A-17X-5, 102 cm, to 20X-2, 102 cm, is mid-Campanian–early Maastrichtian in age (Zones CC22–CC23), as indicated by the presence of Uniplanarius trifidum, R. levis, and A. cymbiformis. Sections 207-1257A-20X-3 to 22X-CC contain a Coniacian–early Campanian assemblage (Zones CC13–CC18), including Quadrum gartneri and Marthasterites furcatus. The subjacent Samples 207-1257A-23X-CC to 24X-CC yielded an impoverished nannoflora presumably of Turonian age (Zones CC10–CC12) with Eprolithus floralis, Lithastrinus septentrionalis, and Eiffellithus eximius.
Based on the absence of Eiffellithus turriseifelii and the presence of Tranolithus orionatus, Rhagodiscus asper, Rhagodiscus angustus, and Corollithion achylostaurion in Samples 207-1257A-27X-4, 143 cm, to 31X-CC, they were assigned an Albian age (Zone NC8).
Planktonic foraminifer biostratigraphy at Site 1257 was based upon a combination of core catchers from all three holes and samples taken in every section in Hole 1257A. Zonal assignments are summarized in Figure F7 and Tables T4, T5, T7, and T8. Planktonic foraminifer Zone M14/M13b through Albian Zone KS13 were identified in Hole 1257A, along with significant breaks in the biozonation of the lower Oligocene–upper Miocene, the lower–middle Eocene, the lower Maastrichtian–Danian, and the Albian–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–Santonian sequence, although foraminifers were difficult to extract and completely clean in the organic-rich calcareous claystones (black shales). Foraminifers in the light-colored bands in the black shales were frequently filled with calcite spar. Good preservation was found in the Miocene, Oligocene, middle Eocene, and Paleocene, whereas preservation was moderate or poor in the hard chalk of the lower Eocene, Campanian–Maastrichtian sequence, and Albian marls.
Sample 207-1257A-1H-1, 0–2 cm, contains Pleistocene planktonic foraminifers, including Globorotalia menardii, Globigerinoides ruber, and Globigerinoides sacculifer. Brown and green calcareous ooze in Section 207-1257A-1H-1 contains an upper Miocene assemblage of Globigerinoides siegliei, Globorotalia plesiotumida, and Globorotalia juani, which suggests uppermost Miocene Zone M14. Sample 207-1257A-1H-1, 50–52 cm, contains reworked middle Miocene Fohsella fohsi, which represents Zones M8–M9. A lower Oligocene Zone P19 assemblage, including Turborotalia ampliapertura without Pseudohastigerina sp., is present in the light yellow nannofossil ooze in Sample 207-1257A-1H-2, 50–52 cm. Typical species belonging to lower Oligocene Zone P19 include common T. ampliapertura, Subbotina galavisi, Subbotina globularis, Subbotina euapertura, and Globorotaloides suteri in the >150-µm fraction. Cassigerinella chipolensis, Tenuitella gemma, Tenuitella munda, Chiloguembelina cubensis, and Globigerina praebulloides are common constituents of the <150-µm fraction. The boundary between Zones P18 and P19 is located between Samples 207-1257A-3H-2, 50–54 cm, and 3H-1, 50–54 cm, and is marked by the last occurrences of Pseudohastigerina micra and Pseudohastigerina naguewichiensis.
The E/O boundary is present between Samples 207-1257A-6X-1, 46–48 cm, and 7X-1, 52–54 cm, recording the contact between the lowermost Zone P18 and upper Zone P14. A more complete boundary section was recovered from Hole 1257B between Samples 207-1257B-1R-2, 1–2 cm (Zone P18), and 1R-2, 47–48 cm (Zone P16–P15). Upper Eocene foraminifers include well-preserved Turborotalia pseudoampliapertura, Hantkenina alabamensis, Subbotina yeguaensis, Subbotina gortani, and Turborotalia cerroazulensis without Globigerinatheka sp. The absence of Globigerinatheka index or Globigerinatheka semiinvoluta suggests a latest Eocene age for this sample, but the absence of Cribrohantkenina inflata or Turborotalia cunielensis suggests the sample is from Zone P15. Hantkeninids include strongly inflated H. alabamensis that closely resemble the holotype of this species and are ancestral to Cribrohantkenina in the upper part of Zone P15. Assemblages in Hole 1257A representing Zone P14 include Globigerinatheka tropicalis, which evolved late in Zone P14, as well as typical upper middle and upper Eocene species such as Turborotalia cerraozulensis, Acarinina rohri, and Morozovella spinulosa. The presence of morozovellids and acarininids below Sample 207-1257A-7X-1, 52–54 cm, shows that the fauna predates the extinction of these groups in the lower part of Zone P15.
A regular succession of middle Eocene biozones is present between Cores 207-1257A-7X and 9X. The P14/P13 boundary occurs between Samples 207-1257A-7X-3, 49–52 cm, and 7X-4, 47–51 cm, based upon the last occurrence of Orbulinoides beckmanni. Zone P13 assemblages are species rich and include Acarinina praetopilensis, Turborotalia pomeroli, P. micra, M. spinulosa, Muricoglobigerina senni, and A. rohri. The boundary between Zones P12 and P13 is located between Samples 207-1257A-8X-2, 47–48 cm, and 8X-3, 51–53 cm, based on the first occurrence of O. beckmanni. The evolution of O. beckmanni involves the gradual envelopment of the test by the last two chambers of the final whorl, which eventually results in a spherical shell completely enclosed by the last chamber. This evolutionary transition is well represented at Site 1257. The last appearance of Morozovella aragonensis between Samples 207-1257A-8X-CC and 9X-5, 50–54 cm, marks the Zone P11/P12 boundary. Typical assemblages from Zone P11 include Acarinina bullbrooki, M. aragonensis, Igorina broedermanni, Acarinina topilensis, and Turborotalia griffinae. Specimens of Clavigerinella akersi were found in Sample 207-1257A-9X-4, 50–54 cm.
The lower/middle Eocene boundary is present between Samples 207-1257A-9X-5, 50–54 cm, and 9X-CC, juxtaposing faunas of Zone P11 (or possibly Zone P10) and Subzone P6b. The base of Zone P6 was not found in Hole 1257A but has been located between Samples 207-1257C-1R-3, 123–125 cm, and 1R-CC. These samples span a green clay bed in interval 207-1257C-1R-5, 48–51 cm, which may represent the P/E boundary. Sample 207-1257C-1R-CC contains a typical Zone P5 assemblage with Morozovella velascoensis, Morozovella subbotinae, Morozovella occulsa, Igorina albeari, Globonomalina planoconica, Acarinina coalingensis, and Subbotina velascoensis. Unusual elements include Igorina broadermanni, Acarinina wilcoxensis, and Chiloguembelina wilcoxensis, all of which appear just above to the P/E boundary. A latest Paleocene age for Sample 207-1257C-1R-CC is further suggested by the very rare occurrence of the benthic foraminifer Gavelinella beccariiformis, which becomes extinct at the onset of the 
13C event associated with the P/E boundary. The P/E boundary is difficult to define precisely in Hole 1257A, owing to very poor preservation in Sample 207-1257A-11X-CC, but is known to occur between Samples 207-1257A-11X-2, 27–32 cm, and 12X-1, 50–54 cm, most likely in the core break.
A thick Paleocene succession is found between Cores 207-1257A-11X and 16X. These cores contain a typical assemblage from Zone P4 that includes M. velascoensis, Morozovella aequa, Morozovella occlusa, Globanomalina pseudomenardii, and Acarinina mckannai. Zone P4 faunas are partly contaminated by foraminifers from Zones P2 and P3 as well as Maastrichtian foraminifers in Core 207-1257A-16X, where species such as Morozovella conicotruncata (Zones P3–P4), Praemurica inconstans (Zones P2–P3), and Pseudoguembelina costulata (Cretaceous) are mixed into faunas containing G. pseudomenardii (index species for Zone P4). In Core 207-1257A-16X, a slumped interval includes white limestone containing P. inconstans from Zone P2 and lower Maastrichtian chalk belonging to Zone KS30.
Beginning in Sample 207-1257A-17X-1, 50–54 cm, and continuing to the base of the hole, the succession of planktonic foraminifers indicates a series of biozones between lower Maastrichtian Zone KS30 and middle Albian Zone KS13. Campanian–lower Maastrichtian Zone KS30 (Gansserina gansseri) extends from Samples 207-1257A-17X-1, 50–54 cm, to 18X-CC. The Maastrichtian assemblages contain common to few Rugotruncana subcircumnodifer, Globigerinelloides prairiehillensis, P. costulata, Heterohelix puncticulata, and Rugoglobigerina macrocephala, with occasional Abathomphalus intermedius, Globotruncanella pschadae, Rosita fornicata, and Globotruncana aegyptiaca. Gansserina gansseri is absent, so differentiation of the Maastrichtian part of Zone KS30 from the subadjacent Campanian part of Zone KS30 relies on a combination of the foraminifer data with nannofossil datums (see "Calcareous Nannofossils"). Between Sample 207-1257A-19X-CC and the base of the glauconitic calcareous chalk in Core 20X, planktonic foraminifers are absent and the faunas are represented by diverse benthic foraminifer assemblages.
Dark black shales in Sample 207-1257A-20X-CC contain a low-diversity assemblage of Heterohelix globulosa, Hedbergella delrioensis, Hedbergella planispira, and Dicarinella canaliculata. This foraminifer fauna, together with nannofossil data (see "Calcareous Nannofossils"), suggest a Coniacian–Santonian age (Zones KS23–KS24). Samples between 207-1257A-21X-CC and 25X-2, 45–47 cm, could not be dated precisely, owing to the absence of marker species. These samples were mostly dominated by small foraminifers representing only four to five species, none of which are useful in differentiating between Cenomanian and Santonian ages. However, Sample 207-1257A-25X-CC contains Whiteinella inornata and Rotalipora greenhornensis, suggesting that the fauna dates from the late Cenomanian.
Preservation varies markedly through the organic marl sequence. Foraminifers are typically larger and more likely to be filled with sparry calcite in the lighter-colored interbeds and are typically better preserved, even with glassy shells, in the darker, more clay-rich interbeds. Benthic foraminifers are nearly absent, but both the abundance of benthic foraminifers and species diversity of planktonic foraminifers are highest in the Coniacian–Santonian interval and decrease toward the upper Cenomanian interval.
The green silty calcareous claystone in Samples 207-1257A-26X-2, 96–98 cm, to 36X-CC contain only rare foraminifers, when they are present at all. All foraminifers are recrystallized and filled with calcite spar. Sample 207-1257A-27X-CC contains a few specimens of Ticinella raynaudi, along with fragments of fish bones and echinoderm debris. Sample 207-1257A-29X-CC contained the highest-diversity fauna of any samples examined in the claystone, with Favusella washitensis, H. delrioensis, H. planispira, and Ticinella sp. The assemblage broadly suggests an age of middle–late Albian. The low species diversity and abundance in most claystone samples suggests that the depositional environment was not favorable to planktonic foraminifers, perhaps because the waters were shallow or of unusually high salinity. The paleogeography of Demerara Rise in the Albian suggests the region was part of a large epicontinental sea between Africa and South America (Gouyet et al., 1994; Benkhelil et al., 1995) and supports the hypothesis that the low taxonomic diversity of Albian species at Site 1257 is related to shallow-water habitats.
Site 1257 radiolarians were found in most of the recovered Tertiary material as well as in the uppermost Cretaceous (lower Maastrichtian–Campanian). Core catcher samples were examined systematically from Hole 1257A. A limited number of samples were also taken from Holes 1257B and 1257C to examine radiolarian presence/absence in the Upper Cretaceous black shales or to better constrain the age of some cores.
The radiolarian fauna is well preserved and abundant in the Oligocene and Eocene parts of the site. Samples 207-1257A-2H-CC and 3H-CC are considered to have an early Oligocene age, as they can be assigned with confidence to Zone RP20 based on the presence of Lithocyclia crux.
Radiolarian preservation is relatively poor in Samples 207-1257A-4H-CC and 5H-CC. Based on the presence of Theocyrtis tuberosa and Dictyoprora mongolfieri, these samples can be assigned to an interval between the lower part of Zone RP20 and the upper part of Zone RP18. Radiolarian preservation greatly improves in Sample 207-1257A-6X-CC, in which the abundant presence of Podocyrtis goetheana and Eusyringium fistuligerum suggests an age between the lower part of Zone RP18 and the base of Zone RP16.
Sample 207-1257A-7X-CC is assigned to Zone RP16, as P. goetheana (marker species of the base of this zone) co-occurs with Spongatractus pachystylus. This is younger than calcareous nannofossil and foraminiferal datums of this interval, which suggest lower Zones NP17 and P13, respectively. The absence of S. pachystylus in Sample 207-1257A-6X-CC (containing an abundant and well-preserved radiolarian fauna) implies that the boundary between Zones RP16 and RP17 may be placed in Core 207-1257A-7X. The abundant presence of Podocyrtis chalara in Sample 207-1257A-8X-CC (largely outnumbering the few specimens of Podocyrtis mitra) suggests that the boundary between Zones RP16 and RP15 can be placed in Core 207-1257A-8X.
Finally, Samples 207-1257A-10X-CC to 11X-1, 49–54 cm, can be assigned to Zone RP7 or RP8, based on the presence of Podocyrtis papalis and Pterocodon ampla. Further below, poor preservation prevented identification of any age-diagnostic radiolarians.
Cretaceous radiolarians were observed in Cores 207-1257A-17X, 18X, and 20X as well as in Core 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 a scanning electron microscope. Sample 207-1257A-18X-CC may be assigned to the upper Campanian–Maastrichtian Amphipyndax tylotus Zone and Sample 207-1257C-20R-CC to the Campanian Amphipyndax pseudoconulus Zone, based on the presence of their respective marker species. No radiolarians were identified from the Albian–Santonian interval.
