The two holes at Site 1261 document a 370-m-thick sequence of Pleistocene–late Miocene sediments overlying 300 m of middle Eocene–Cenomanian marine deposits. These yielded calcareous nannofossils, planktonic foraminifers, and radiolarians in varying abundances and states of preservation, depending on lithology and sediment induration. The shipboard examination of these microfossil groups from core catcher samples was supplemented by additional samples from the cores. The biostratigraphic data permitted zonal or stage assignments to be made for the entire sequence. The upper 230 m of the succession (i.e., most of the Neogene) was only recovered by six spot cores; thus, biostratigraphic boundaries encountered in this interval are loosely defined. Datum levels are summarized in Figure F8 and in Tables T3, T4, T5, T6, and T7.
A 13-m-thick nannofossil ooze (Samples 207-1261A-1R, 0 cm, to 2R-CC) at the top of the section has a Pleistocene age. This unit overlies a 205-m-thick nannofossil clay (Samples 207-1261A-3R, 0 cm, to 6R-CC) of middle Pliocene age. The boundary to the underlying late Miocene nannofossil clays (Core 207-1261A-7R to Section 20R-5) is not present because of isolated spot coring in the upper part of the succession. The lower part of the Miocene succession (Cores 207-1261A-14R to 20R) is heavily slumped and reworked. The subsequent 165 m of calcareous chalk (Sections 207-1261A-20R-6 to 37R-CC) are of middle Eocene–Paleocene age. A pronounced hiatus at the top of this unit represents the middle Miocene–late Eocene. The P/E boundary, present in Sample 207-1261A-33R-4, 105 cm, is overlain by ~30 cm of radiolarian claystone that may represent the PETM. The lowermost Paleocene (planktonic foraminifer Zone P1 and calcareous nannofossil Zones NP1 and NP2) is missing as well as the earliest Danian boundary clay and the spherule layer, indicating an unconformity across the Cretaceous/Tertiary (K/T) boundary.
The subjacent, highly condensed 33-m section of upper Maastrichtian–lower Campanian nannofossil chalk (Sections 207-1261A-38R-CC to 41R-1) is similar to that of the Paleocene, with moderately or poorly preserved calcareous microfossils. The lowermost part of the Maastrichtian/Campanian chalk facies, enriched in glauconite, overlies an 89-m-thick Santonian–Cenomanian black shale succession (Sections 207-1261A-41R-2 to 50R-3). Calcareous microfossils are generally present throughout this unit, with planktonic foraminifers often poorly preserved. Calcareous nannofossils and planktonic foraminifers of Cenomanian age are present near the base of the black shale. Samples 207-1261A-47-CC, 49-CC, and 50-CC supplied nannofossils and planktonic foraminifers of mid- to late Cenomanian age. A sharp contact between the laminated black shale and quartz sandstone (lithostratigraphic Unit V) occurs in Sample 207-1261A-50R-3, 32 cm. The latter unit did not provide any calcareous microfossils and is not dated. However, oysters and ammonites are present in these sandstones and may provide biostratigraphic information during shore-based studies.
Unlike the sections from other Leg 207 sites, the two holes at Site 1261 recovered a considerable amount of Neogene sediment as well as Paleogene to mid-Cretaceous deposits. These materials contain generally common to abundant calcareous nannofossils of moderate to good preservation that vary with lithology. These fossils allowed for zonal or stage assignments, summarized in Figures F8A and F8B and Tables T3 and T4. Core catcher samples were examined for all holes and supplemented as time permitted by samples from the cores to further refine zonal assignments.
Sample 207-1261A-1R-CC, 12–17 cm, yielded upper Quaternary sediment with well-preserved nannofossils assigned to Zone NN21. The core catcher contained very abundant Emiliania huxleyi, abundant Gephyrocapsa oceanica, Rhabdosphaera clavigera, Helicosphaera carteri, and common Ceratolithus cristatus. The abundance and preservation is similar in the next core (also Quaternary), where Sample 207-1261A-2R-CC contained Pseudoemiliania lacunosa and belongs to Zone NN19.
The middle–lower Pliocene is indicated by a variety of discoasters in Samples 207-1261A-3R-CC to 4R-CC, namely Discoaster brouweri, Discoaster pentaradiatus, Discoaster variabilis, Discoaster tamalis, and Sphenolithus sp. If none of these taxa are reworked, the assemblage should be assigned to Zone NN16. Reticulofenestra pseudoumbilica in Cores 207-1261A-5R and 6R denotes Zones NN13–NN15.
Uppermost Miocene sediments in Sample 207-1261A-7R-CC contain Amaurolithus delicatus (Messinian [Zone NN11 or Subzone CN9b]). Sample 207-1207-261A-8R-CC yielded Discoaster quinqueramus, which is abundant in the subjacent Sample 207-1261A-9R-CC, as is D. pentaradiatus, R. pseudoumbilica, Sphenolithus moriformis, and a few well-preserved Nicklithus amplificus. A single specimen of Eiffellithus turriseiffelii is reworked from the Cretaceous. This sample is assigned to Zone NN11 or, more precisely, to Subzone CN9bB of the augmented Okada and Bukry (1980) scheme. The next four cores (through Sample 207-1261A-13R-CC) also belong to Zone NN11 or, more precisely, to Subzone CN9bA, as there are few to rare A. delicatus and the generally rare N. amplificus is not observed.
Triquetrorhabdulus rugosus is rare in Sample 207-1261A-11R-CC, whereas D. quinqueramus is abundant, and late-evolved forms of Discoaster berggrenii (stellate knobs covering ~80% of the central area) are present in Sample 207-1261A-12R-CC. Three-rayed focus of D. quinqueramus are common in the subjacent core catcher in addition to a reworked specimen of Discoaster calcaris.
Initially, Sample 207-1261A-14R-CC appeared straightforward, although slightly older (~Zone NN10 or Subzone CP8a) than overlying samples, with little clay to dilute discoasters such as abundant Discoaster challengeri and a few specimens of D. calcaris, T. rugosus, Minylitha convallis, and Pontosphaera multipora. The sample contains a reworked specimen of Coronocyclus nitescens. The next two core catchers were considerably older (middle–lower Miocene Zones NN6 and NN4), but Sample 207-1261A-17R-CC was considerably younger (upper Miocene Zone NN11 again), indicating an age inversion.
The lower half of Core 207-1261A-14R shows a variety of clasts of different colors swirled in a dark brown upper Miocene (Zone NN11) matrix (Fig. F8A). The clasts include pieces such as that found in Sample 207-1261A-15R-CC, a coarse foraminifer-rich limestone with abundant Discoaster exilis, R. pseudoumbilica, and C. nitescens but no Cyclicargolithus floridanus or Discoaster kugleri; hence, it belongs to middle Miocene Zone NN6. The subjacent Sample 207-1261A-16R-CC contains a greenish calcareous ooze with C. floridanus, Sphenolithus heteromorphus, C. nitescens, Calcidiscus premacintyrei, D. exilis, and abundant Discoaster petaliformis but no Helicosphaera ampliaperta, an assemblage equivalent to Zone NN5. The same assemblage was noted in a small clast (Sample 207-1261A-14R-5, 42 cm) as a minor admixture to a Messinian (Subzone CN9bB) assemblage, whereas a light green clast at 131 cm in this section was dated as lower Miocene Zone NN4 (CN3) (see below for similar dates for these two sampled provided by planktonic foraminifers). A Zone NN4 assemblage was also detected as a minor admixture to Zone NN11 material in Sample 207-1261A-14R-5, 35 cm.
The middle Miocene clast lithologies and/or microfossil assemblages were not found in situ in the remainder of the Miocene section at this site. They, therefore, provide some indication of the nature and extent of the original stratigraphic sequence in the source area(s) from which they came.
Sample 207-1261A-17R-CC contains D. quinqueramus, D. berggrenii, Discoaster neohamatus, D. calcaris, and one heavily overgrown reworked specimen of Discoaster deflandrei and was assigned to Zone NN11 (approximately Subzone CN9a). This Zone NN11 assemblage evidently represents the matrix for this portion of the slumped material. A similar matrix age is indicated by Sample 207-1261A-18R-CC, which is a green glauconitic clay studded with numerous small (5 mm) round whitish coarse-grained clasts. Both the green and white lithologies yielded nannoliths of two ages: Zone NN11, as indicated by D. quinqueramus, and Zone NN5, denoted by common S. heteromorphus, C. floridanus, and Helicosphaera wilcoxonii. Sample 207-1261A-19R-CC, on the other hand, contains a calcite-cemented, mottled, light green nannofossil chalk with Discoaster hamatus, Catinaster coalitus, Catinaster calyculus, Hayaster perplexus, Calcidicus macintyrei, and R. pseudoumbilica, indicative of Zone NN9, an assemblage not seen elsewhere in the sequence here.
The base of the slumped upper Miocene section rests on middle Eocene chalk, as displayed in Section 207-1261A-20R-5, 118 cm. The well-indurated core catcher contains a sparse, poorly preserved assemblage characteristic of upper Zone NP17 with Chiasmolithus grandis, Reticulofenestra umbilica, and small Dictyoccocites bisectus (9 µm long, representing an early evolutionary stage of development).
The abundance of opal-CT lepispheres in the nannofossil smear slides indicates that the biogenic silica usually seen in Eocene chalks at previous Leg 207 sites has been largely altered under the considerably thicker overburden here. The Eocene at this site is overlain by ~370 m of strata, as opposed to ~70 m at Site 1257, 5 m at Site 1258, 130 m at Site 1259, and 40 m at Site 1260. This, plus heavy overgrowth on the discoasters, indicates a relatively advanced state of diagenesis at the present site that has considerably reduced the diversity and abundance of the nannofossils and diminished their utility for age control. Nevertheless, Sample 207-1261A-21R-CC could still be assigned to upper Zone NP17.
Abundant Chiasmolithus solitus accompanied by few R. umbilica date Sample 207-1261A-22R-CC as upper Zone NP16 (Subzone CP14a), whereas the absence of R. umbilica in the subjacent core catcher suggests lower Subzone NP14b. Preservation of nannofossils is too poor to allow reliable dating of the next two core catchers downhole, but these also appear to belong to Zone NP16. The presence of the total range marker, Chiasmolithus gigas, however, indicates Zone NP15 (Subzone CP13b) for Sample 207-1261A-27R-CC, and Rhabdosphaera inflata suggests upper Zone NP14 for Sample 207-1261A-28R-CC.
Poor preservation prevented precise dating of Samples 207-1261A-29R-CC to 31R-CC. Discoaster multiradiatus, Neochiastozygus junctus, and Zygrhablithus bijugatus with only scattered fasciculiths date Sample 207-1261A-32R-CC as upper Zone NP9, above the P/E boundary. That boundary lies in Sample 207-1261A-33R-4, 105 cm, where it is marked by a clay band. The reversal in dominance downhole across this epoch boundary from Z. bijugatus/N. junctus to fasciculiths was confirmed in the core catcher, which is assigned to Subzone NP9a. Subzone NP9a continues downhole through Sample 207-1261A-34R-CC. No samples were analyzed for nannofossils from Cores 207-1261-35R and 36R.
The K/T contact was not recovered in Hole 1261A. Sample 207-1261A-37R-CC contains mostly Cretaceous taxa (such as Micula murus), but two samplings of the core catcher also disclosed a sparse but persistent representation of the Tertiary taxa Coccolithus pelagicus, Chiasmolithus danicus, and moderate-sized (6.25 µm) Ericsonia subpertusa. This assemblage belongs to the Danian Zone NP3. Essentially the same assemblage with large Cruciplacolithus edwardsii (12.5 µm) occurs upcore (Samples 207-1261A-37R-5, 0–1 cm, and 37R-1, 0–1 cm). The next core returned only a modest-sized core catcher sample and no other material; hence, the contact was not observed.
A disconformity at the K/T contact is clearly visible in Hole 1261B at a color change upsection from light to darker green chalk at Section 207-1261B-2R-3, 83 cm. One centimeter below the contact is a purely Cretaceous nannolith assemblage with abundant M. murus, whereas 1 cm above is a Tertiary assemblage with abundant C. pelagicus (up to 7.25 µm) and some reworked Cretaceous taxa. A sample 17 cm farther upcore contains Cruciplacolithus tenuis (8.75 µm), moderate-sized E. subpertusa, and no chiasmoliths, all of which denote Zone NP2.
In Hole 1261A, the core catcher below the K/T contact (Sample 207-1261A-38R-CC) contains M. murus and a characteristic upper Maastrichtian assemblage assigned to Zones CC26/upper CC25, as does the subjacent core. Close to this stratigraphic level in Sample 207-1261B-3R-3, 150 cm, the abundant nannolith assemblage includes rare to few Lithraphidites quadratus, Rhagodiscus splendens, and some Kamptnerius magnificus with large flanges that indicate moderately good preservation.
Rare to few and rather poorly preserved Uniplanarius trifidum in Sample 207-1261B-4R-CC (roughly equivalent to Sample 207-1261A-40R-CC) signal upper Campanian Zone CC23, provided they are not reworked at this shallow end-member of the Leg 207 depth transect. This fact plus the site's relatively close proximity to the continental margin could account for the abbreviated Maastrichtian/Campanian section at this locality.
Returning to Hole 1261A, the black shales are present in Sample 207-1261A-42R-CC. In smear slides this gritty sample contains large zeolites but only moderately preserved nannofossils, including common Eiffellithus eximius (bar angle < 9°), Gartnerago obliquum, Tranolithus orionatus, and the dissolution-resistant Marthasterites furcatus, here apparently in acme proportions. As Micula decussata is absent, the sample belongs to the lower Coniacian Zone CC13. Eiffellithus eximius remains present, however, in the subjacent samples (Samples 207-1261A-43R-CC and 44R-CC), which are accordingly assigned to the upper Turonian Zone CC12. Nannoliths are abundant, but preservation ranges from poor to good. Preservation improves downhole in Sample 207-1261A-45R-3, 136 cm, which contains Eprolithus apertior, Eprolithus floralis, and Eprolithus eptapetalus but not E. eximius, and therefore belongs to the lower Turonian Zone CC11. Sample 207-1261A-46R-CC is barren of nannoliths.
Sample 207-1261A-47R-CC yields Eprolithus octopetalus, Corollithion signum, and Radiolithus planus in the absence of E. eptapetalus and was referred to the upper Cenomanian Zone CC10. The secondary Cenomanian marker taxon Axopodorhabdus albianus was encountered in Samples 207-1261A-48R-CC and 49R-CC, and the exclusively Cenomanian species Corollithion kennedyi is present in the equivalent Sample 207-1261B-14R-2, 1 cm, despite a rare and poorly preserved nannoflora.
A clean homogeneous massive sandstone was encountered at the base of both holes (Cores 207-1261A-51R and 207-1261B-15R and 16R). Interbedded with the sandstone in the latter core, however, is ~10 cm of apparently in situ black silty claystone. A sparse but moderately well preserved nannoflora in Sample 207-1261B-16R-1, 95 cm, contains abundant E. turriseiffelii (which can range in time no lower than the mid- to late Albian), along with rare E. apertior, E. floralis, and abundant zygoliths. This sample could be Cenomanian or late Albian in age.
Planktonic foraminifer biostratigraphy at Site 1261 was based upon core catchers in Holes 1261A and 1261B. We examined one sample per section in the Miocene and Paleocene–Cenomanian but looked only at core catchers in the extremely poorly preserved assemblages of the lower and middle Eocene. Zonal assignments are summarized in Figure F8 and Tables T4, T5, and T7. Planktonic foraminifers from Pleistocene Zone PT1 through Cenomanian Zone KS19 were identified in Hole 1261A, along with significant breaks in the biozonation between the late Miocene and middle Eocene, the early Eocene to middle Eocene, the middle Paleocene, and the K/T boundary.
Planktonic foraminifers were present in nearly all samples but varied widely in preservation and abundance. Preservation was best in clay-rich parts of the Miocene–Pleistocene sequence and in parts of the upper Paleocene. Foraminifers were frequently filled with calcite spar in the Paleogene and Cretaceous parts of the sequence and, in the majority of cases, were also recrystallized. In contrast to other Leg 207 sites, even selective sampling of black and olive-green claystones in the Cenomanian–Santonian sequence failed to produce foraminifers that are not filled with calcite spar, and nearly all specimens have entirely recrystallized skeletons. The poor preservation of foraminifers in the Cenomanian–Santonian black shales is unfortunate because this section appears to be one of the most expanded and completely recovered intervals through the upper Turonian and Santonian obtained during Leg 207. Foraminifer preservation in the black shales is generally sufficient for biostratigraphic studies. Foraminifers in the lower and middle Eocene hard chalks are particularly poorly preserved, often consisting of little more than pieces of rocks that are vaguely shaped like foraminifers even after ultrasonic cleaning. Slightly better preservation may be present in more clay-rich bands in the Eocene sequence, and any future foraminifer biostratigraphy should selectively sample such beds.
Sample 207-1261A-1R-1, 0–2 cm, contains modern planktonic foraminifers such as Orbulina universa, Globigerinoides sacculifer, Globorotalia menardii, Globorotalia truncatulinoides, Neogloboquadrina dutertrei, and Globigerinoides ruber (pink). Pteropods are present in Sample 207-1261A-1R-CC along with scattered grains of glauconite. Pleistocene sediments are also found in Sample 207-1261A-2R-CC.
The contact between Pleistocene sediments and those of middle Pliocene Zone PL3 occurs between Samples 207-1261A-2R-CC and 3R-CC. Both of these are short cores and are highly disturbed by rotary coring, so we did not attempt to refine the stratigraphy. Samples 207-1261A-3R-1, 49–52 cm, to 4R-CC contain Globigerinoides fistulosus, Sphaeroidinellopsis seminulina, and Dentoglobigerina altispira altispira, which indicate Zone PL3. Specimens of G. fistulosus have short knobs on the final chamber and are rare, as is also the case at Ocean Drilling Program (ODP) Site 925 on nearby Ceara Rise. Typical species in Zone PL3 include very well preserved Globorotalia multicamerata, Globorotalia crassaformis, Globigerinoides extremus, S. seminulina, D. altispira, and G. sacculifer.
Sample 207-1261A-5R-CC contains an assemblages characteristic of lower Pliocene Zone PL2, such as Globorotalia margaritae, D. altispira, S. seminulina, Globorotalia plesiotumida, and Globigerinoides conglobatus. Sphaeroidinellopsis paenedehiscens, Globorotalia miocenica, and G. multicamerata are regular constituents as well. As at Ceara Rise (see Chaisson and Pearson, 1997), we find G. plesiotumida ranges well into the lower Pliocene. These range extensions for G. plesiotumida suggest that this species did not evolve without branching (via anagenesis) into Globorotalia tumida near the Miocene/Pliocene boundary, as maintained by Malmgren et al. (1983).
Continuous coring in Hole 1261A began with Core 207-1261A-7R, which we assign to uppermost Miocene Zone M14. We did not find Sphaeroidinella dehiscens in any samples from this core, suggesting that all these samples predate the Miocene/Pliocene boundary. The presence of Globoquadrina dehiscens (whose last appearance is near the Miocene/Pliocene boundary) also suggests that Core 207-1261A-7R is of late Miocene age. Additional species in Zone M14 include G. margaritae, Globorotalia limbata, Globigerina nepenthes, Globorotalia cibaoensis, D. altispira, and G. extremus. G. tumida is present as low as Sample 207-1261A-9R-2, 50–54 cm.
The top of Subzone M13b, defined by the last appearance of Globorotalia lenguaensis, occurs in Sample 207-1261A-9R-CC. Foraminifer assemblages are characterized by G. extremeus, D. altispira, Globigerinoides obliquus, G. menardii, G. plesiotumida, and S. seminulina. Fragmentation is common. The base of Subzone M13b occurs at an abrupt contact with underlying Eocene chalks between Samples 207-1261A-20R-5, 113–116 cm, and 20R-5, 120–122 cm. Core photographs show that the Eocene/Miocene contact occurs at ~118 cm in Section 207-1261A-20R-5.
The Miocene is pervasively slumped between Cores 207-1261A-14R and 20R. Diverse clast types and colors in this section represent a spectrum of early, middle, and late Miocene ages. No pre-Miocene clasts were found. Many clasts represent discrete foraminifer assemblages from single biostratigraphic zones. The oldest clasts representing a single zone are found near the top of the slumped section. Zone M4 (late early Miocene) is present in a dark green clast (e.g., Sample 207-1261A-14R-5, 35–36 cm) and in a light green clast (Sample 14R-5, 131–133 cm) where Globigerinatella insueta occurs together with Globigerinoides bisphericus. A white foraminifer sand clast in Sample 207-1261A-14R-5, 42–43 cm, yielded a Zone M9 (middle Miocene) assemblage with Fohsella robusta and Paragloborotalia mayeri. Other clasts in Cores 207-1261A-14R to 20R yielded faunas from Subzone M13b (upper Miocene) that are indistinguishable from those of the overlying undisturbed sedimentary sequence.
Lower in the slumped section, several clasts produce mixed assemblages with index species for Subzones M5a and M5b and Zones M8 and M11 (e.g., Sample 207-1261A-18R-2, 24–26 cm [white clast]) and Zones M4 and M11 and Subzone M13b (e.g., Sample 18R-2, 27–30 cm [chocolate brown clast]), but a few clasts also have only Zone M8–M9 assemblages (e.g., Samples 15R-CC, 16R-CC, and 17R-1, 129–131 cm), a Zone M11 fauna (e.g., Sample 17R-6, 123–127 cm [large yellowish green clast]), and one has a Subzone M5a assemblage (e.g., Sample 20R-4, 97–100 cm). Evidently there were several intervals of extensive reworking and winnowing during the middle and late Miocene before final redeposition of winnowed sediments in debris flows during Subzone M13b.
There is no clear progression in clast ages with depth at Site 1261. Nearly all clasts in Cores 207-1261A-18R to 20R contain at most a few middle or lower Miocene foraminifers mixed into an assemblage characteristic of Subzone M13b, whereas many clasts in Cores 14R to 17R produced assemblages representing single lower and middle Miocene zones. Apparently, both lower and middle Miocene strata cropped out in the vicinity of the site throughout the period of debris flow deposition. The lack of Eocene- and Oligocene-age clasts suggests that strata of these ages were not exposed in the source areas for the debris flows at any time in the Miocene.
The middle Eocene rests below a sharp contact with the overlying Miocene slumps. Sample 207-1261A-20R-5, 120–122 cm, immediately below the Miocene slumps, contains an assemblage that includes Turborotalia pomeroli, Acarinina rohri, Globigerinatheka mexicana (the barri morphotype), Globigerinatheka index, Morozovella spinulosa, and Acarinina collactea, indicating Zone P14. Similar faunas are present in Sample 207-1261A-20R-CC. In contrast, Sample 207-1261A-21R-2, 84–86 cm, contains large specimens of Orbulinoides beckmanni, including completely spherical forms in which the final chamber constitutes more than two-thirds of the shell. The presence of O. beckmanni indicates Zone P13. Sample 207-1261A-21R-CC contains an assemblage similar to that in overlying Zone P13 but without O. beckmanni and therefore belongs to Zone P12. Assemblages in Samples 207-1261A-22R-CC to 25R-CC are very poorly preserved and could not be dated beyond assigning them to the interval between Zones P11 and P14. Globigerinathekids in these samples show that all belong to Zone P11 or younger Eocene zones.
Zone P11 is indicated in Samples 207-1261A-26R-CC and 27R-CC, based upon the presence of Morozovella aragonensis and G. index along with Acarinina bullbrooki, A. rohri, Guembelitriodes nuttali, and Igorina broedermanni. Samples 207-1261A-28R-CC and 29R-CC are assigned to Zones P10–P11 based upon the presence of A. bullbrooki, which makes its first appearance near the Zone P9/P10 boundary. In contrast, Sample 207-1261A-30R-CC contains a limited assemblage of M. aragonensis, Acarinina pentacamerata, and Acarinina aspensis, which probably reflects Zone P9, but could be younger (possibly Zone P10).
There is a hiatus between Samples 207-1261A-30R-CC and 31R-CC, as the succession crosses abruptly from Zone P9–P10 to P7. Species representative of Zone P7 include Acarinina quetra, M. aragonensis, Morozovella lensiformis, Morozovella formosa, and Acarinina coalingensis. Zone P7 is probably separated from the underlying succession by another hiatus because Sample 207-1261A-32R-CC contains the species Morozovella velascoensis, which is indicative of the top of Zone P5.
The P/E boundary occurs in Zone P5 at Section 207-1261A-33R-4, 130 cm. Typical assemblages in Zone P5 include M. velascoensis, Morozovella aequa, Acarinina soldadoensis, A. coalingensis, Morozovella subbotinae, and Morozovella occlusa. The lower boundary of Zone P5 could not be determined precisely owing to the absence of Globanomalina pseudomenardii in very poorly preserved assemblages from Samples 207-1261A-33R-CC and 34R-CC. Large flattened globanomalinids are present beginning in Sample 207-1261A-35R-1, 50–54 cm, and may indicate the top of Zone P4, but the poor preservation makes it difficult to confirm this zonal assignment. The base of Zone P4 occurs between Samples 207-1261A-36R-5, 50–54 cm, and 36R-6, 50–54 cm. These earliest assemblages in Zone P4 are nicely preserved, in contrast to virtually all of the remaining Paleocene and Cretaceous faunas, and include M. velascoensis (with extremely well developed umbilical muricae), Morozovella acutispira, Acarinina subspherica, and Morozovella apanthesma as well as very large specimens of Igorina albeari. A similar assemblage is present in Sample 207-1261A-36R-6, 50–54 cm, but lacks acarininids.
The Danian/Selandian contact and most of the upper Danian biozones are present in a condensed sequence in Hole 1261A. Subzone P3b is present from Sample 207-1261A-36R-6, 50–54 cm, to 37R-1, 50–54 cm, whereas Samples 37R-2, 50–54 cm, to 37R-3, 50–54 cm, may belong to Subzone P3a because they do not appear to contain I. albeari or M. velascoensis. However, preservation is very poor so we can only recognize Zone P3 (undifferentiated), pending further study. The boundary between Zones P3 and P2 occurs between Samples 207-1261A-37R-3, 50–54 cm, and 37R-4, 50–54 cm, accompanied by a distinct change in foraminifer assemblage to one dominated by Praemurica uncinata and Morozovella praeangulata, with subordinate Praemurica inconstans, Parasubbotina varianta, Subbotina triloculinoides, and Parasubbotina pseudobulloides.
The K/T boundary is apparently unconformable at Site 1261. Samples 207-1261A-37R-CC, 24–29 cm, and 207-1261B-2R-CC both yielded upper Maastrichtian faunas, although a few Danian calcareous nannofossils were found in Sample 37R-CC (see "Calcareous Nannofossils"). A series of samples was taken in Core 207-1261B-2R, and these showed that faunas representing Danian Zone P2 with P. uncinata are present from the top of Core 207-1261B-2R to Sample 207-1261B-2R-3, 78–79 cm, where a mixed assemblage of Zones P2 and KS31 is observed. The interval between 70 and 80 cm in Section 207-1261B-2R-3 is lithostratigraphically similar to Sample 37R-CC and consists of pyrite-rich interbeds of light greenish gray chalk and darker greenish chalk that represent the eroded remains of the K/T boundary sequence.
The Maastrichtian–Campanian succession is highly condensed and probably contains undocumented hiatuses. Uppermost Maastrichtian Zone KS31 is recorded in Samples 207-1261A-37R-CC and 38R-CC. Zone KS31 is represented by poorly preserved foraminifer assemblages including Abathomphalus mayaroensis, Contusotruncana contusa, Rugoglobigerina rugosa, Globotruncana aegyptiaca, and Globotruncanita stuarti. Sample 207-1261A-39R-CC may belong to Zone KS29 of the upper Campanian because it lacks C. contusa and Gansserina gansseri and has a very poorly preserved fauna of G. aegyptiaca, Globotruncanella havanensis, and R. rugosa, similar to Campanian assemblages at other Leg 207 sites. Finally, Sample 207-1261A-40R-6, 55–60 cm, yields only a few poorly preserved specimens of Heterohelix globulosa and Heterohelix striata that do not provide a conclusive zone assignment. This nearly barren sample contains a few radiolarians and benthic foraminifers similar to upper Campanian samples from other sites drilled during Leg 207.
Black shale in Sample 207-1261A-41R-CC contains a moderately species-rich assemblage of Dicarinella concavata, Contusotruncana fornicata, Whiteinella inornata, Whiteinella brittonensis, Dicarinella canaliculata, and Marginotruncana pseudolinneiana, representing Coniacian/Santonian Zones KS24–KS23. The overlap of C. fornicata and D. concavata indicates that these samples cannot be older than the middle Coniacian but could be as young as Santonian. Calcareous nannofossil evidence also suggests that the upper part of the black shale sequence is primarily Coniacian or lowermost Santonian in age (see "Calcareous Nannofossils"). Coniacian foraminifers are found in Samples 207-1261A-42R-5, 5–8 cm, and 42R-CC and include W. inornata, W. archaeocretacea, Marginotruncana sinuosa, and Archaeoglobigerina blowi, which probably represents Coniacian Zone KS23, although the zone markers are absent.
The Turonian/Coniacian boundary is in the vicinity of Samples 207-1261A-43R-CC and 44R-CC, both of which contain W. inornata and W. archaeocretacea, as well as a diverse assortment of clavate and stellate planktonic foraminifers such as Hastigerinelloides watersi and Hastigerinelloides alexanderi.
Dicarinella hagni in Sample 207-1261A-44R-CC and Dicarinella primitiva in Sample 43R-CC suggest uppermost Turonian Zone KS22 and lower Coniacian Zone KS23, respectively, in the absence of the zone markers, D. concavata and Helvetoglobotruncana helvetica. All foraminifers in the core catchers and samples taken from sections (typically one per section) yielded foraminifers with recrystallized skeletons and chambers filled with calcite spar.
The upper part of the Turonian includes an abundance of whiteinellids, such as W. inornata with weak imperforate bands, W. archaeocretacea, and Whiteinella baltica, along with the nearly ever-present Hedbergella delrioensis. The clavate species Clavihedbergella amabilis, H. watersi, and H. alexanderi are also rare components. Low species diversity foraminifer assemblages range from Sample 207-1261A-45R-3, 136 cm, to 47R-CC and consist of little more than H. globulosa, Heterohelix moremani, H. delrioensis, W. archaeocretacea, and W. baltica, which could indicate either a Turonian or latest Cenomanian age. Foraminifers are often small (<180 µm) and rare in Samples 207-1261A-46R-CC to 47R-1, 132–133 cm, which we believe may approximate the Cenomanian/Turonian boundary.
Cenomanian assemblages can be found between Sample 207-1261A-48R-CC and 50R-CC. Rotalipora greenhornensis in Sample 207-1261A-48R-CC indicates Zone KS19 along with H. moremani, Globigerinelloides sp., H. delrioensis, and Praeglobotruncana gibba. Whiteinellids range as low as Sample 207-1261A-50R-CC and indicate that the black shales above the first of the quartz sandstone beds near the base of Hole 1261A cannot be older than the middle of Zone KS19. A black silty claystone sample interbedded between quartz sandstone in Sample 207-1261B-15R yielded only a few well-rounded quartz grains.
The radiolarian record at Site 1261 consists of long barren intervals and, in general, poor preservation. Core catcher samples were processed systematically only from Hole 1261A. The Pleistocene and Pliocene are entirely barren of radiolarians. Only two samples of the late Miocene interval (Samples 207-1261A-10R-CC and 11R-CC) contained some non–age diagnostic radiolarians. In the Paleogene, radiolarians are present nearly throughout the entire interval but generally are poorly preserved. The consistent occurrence of Dictyoprora mongolfieri and species of the Lithocyclia ocellus group in Samples 207-1261A-20R-CC through 27R-CC allows assignment of this interval to Zones RP11 to RP15, as the evolutionary transition of the latter species to the Lithocyclia aristotelis group is approximately synchronous with the base of Zone RP16. The presence of Sethochytris triconiscus in Sample 207-1261A-22R-CC and Eusyringium lagena in Sample 26R-CC allows recognition of Zones RP12–RP14 and RP14–RP15, respectively.
Radiolarian occurrence is very patchy in the Cretaceous. In the undistinguished Campanian–Maastrichtian interval, a few poorly preserved radiolarians are present in Sample 207-1261A-40R-CC. Preservation improves in the Cenomanian–Turonian interval (Sample 207-1261A-43R-CC), but the rare radiolarians encountered were not age diagnostic.