Previous   |    Next

doi:10.2204/iodp.proc.342.108.2014

Biostratigraphy

Coring at Site U1407 recovered a 300 m thick sequence of Pleistocene to upper Albian nannofossil ooze with varying amounts of clay and foraminifers. Minor black shale, calcareous sandstone, and limestone lithologies are present in the mid-Cretaceous section. Nannofossils, planktonic foraminifers, and smaller benthic foraminifers are present in all but the mid-Cretaceous black shale, sandstone, and limestone lithologies, which contain larger benthic foraminifers and macrofossils. Radiolarians are only present in the middle Eocene, lower Eocene, and Paleocene. Thin Pleistocene and lower Oligocene intervals overlie a middle Eocene through upper Albian succession, with significant hiatuses between the lower Eocene and uppermost Paleocene, the lowermost Paleocene and uppermost Maastrichtian, and the uppermost Maastrichtian and Campanian. Sedimentation rates are relatively high (~0.4–1.5 cm/k.y.) through the Paleogene and mid-Cretaceous but low (~0.1–0.5 cm/k.y.) through the Maastrichtian to Turonian.

The uppermost brown foraminifer sandy clay and nannofossil ooze (Core 342-U1407A-1H; 0–6.81 mbsf) contains nannofossils and planktonic foraminifers that indicate Pleistocene ages (nannofossil Zones NN21–NN19). Below this (Sample 342-U1407A-1H-CC; 6.78 mbsf), nannofossils and planktonic foraminifers provide a well-defined biostratigraphy indicating a lower Oligocene to upper Albian succession. Benthic foraminifers are generally rare (the “present” category) but increase in abundance during short intervals of the Paleocene and Cretaceous. Benthic foraminifer preservation is good to very good through most of the recovered sequence, although poor to moderate preservation is seen in the Oligocene interval and occasionally in the Cretaceous succession.

An integrated calcareous and siliceous microfossil biozonation is shown in Figure F18. Datum and zonal determinations from nannofossils, planktonic foraminifers, and radiolarians are in close agreement. An age-depth plot including biostratigraphic and paleomagnetic datums is shown in Figure F19. A summary of calcareous and siliceous microfossil abundances and preservation is given in Figure F20.

Calcareous nannofossils

Calcareous nannofossil biostratigraphy is based on analysis of core catcher and additional working section half samples from Holes U1407A–U1407C. Depth positions and age estimates of biostratigraphic marker events are shown in Table T3. Calcareous nannofossil occurrence data are shown in Table T4. Note that the distribution chart is based on shipboard study only and is therefore biased toward age-diagnostic species.

At Site U1407, the preservation of calcareous nannofossils is generally moderate and good. The uppermost sediment in Hole U1407A contains abundant nannofossils of Pleistocene Zones NN21–NN19, as indicated by the presence of abundant Emiliania huxleyi in Sample 342-U1407A-1H-1, 37 cm (0.37 mbsf), and the top of Pseudoemiliania lacunosa in Sample 1H-4, 20 cm (4.70 mbsf).

The short interval from Sample 342-U1407A-2H-5, 60 cm, to 3H-1, 110 cm (12.28–17.41 mbsf), can be assigned to lower Oligocene Zones NP23–NP21 based on the top of Reticulofenestra umbilicus and the top of Coccolithus formosus. The identification of Zone NP21 in Sample 342-U1407A-3H-1, 110 cm (17.41 mbsf), and Subzone NP15a in Sample 3H-2, 110 cm (18.91 mbsf), indicates the presence of a hiatus of ~11 m.y., representing the upper middle Eocene to lowermost Oligocene.

The interval from Sample 342-U1407A-3H-2, 110 cm, to 15H-CC (18.91–121.82 mbsf) is assigned to middle to lower Eocene nannofossil Subzone NP15c to Zone NP11. All primary zonal marker species are present and listed in Table T3.

The identification of Zone NP11 in Sample 342-U1407A-15H-CC (121.82 mbsf) and Subzone NP9a in Sample 16X-1, 8 cm (121.98 mbsf), indicates the presence of a hiatus of ~2 m.y., incorporating the lowermost Eocene and uppermost Paleocene, including the PETM.

The interval from Sample 342-U1407A-16X-1, 8 cm, to 23X-2, 125 cm (121.98–186.65 mbsf), is assigned to nannofossil Zones NP9–NP2, with all primary marker species present apart from Heliolithus riedelii, which prevents the formal differentiation of Zone NP8. The intra-Zone NP8 event, base of Discoaster backmanii, confirms the presence of Zone NP8, with equivalent sediment in Samples 342-U1407A-18X-2, 113 cm, through 18X-CC (138.53–142.90 mbsf) (Table T3).

The identification of Zone NP2 in Sample 342-U1407A-23X-2, 125 cm (186.65 mbsf), and Subzone UC20c in Sample 23X-2, 135 cm (186.75 mbsf), indicates the presence of a hiatus of ~2.5 m.y., incorporating the lowermost Paleocene and uppermost Maastrichtian, including the K/Pg boundary. The presence of Campanian sediment assigned to Zone UC16 in Section 342-U1407A-22H-CC indicates that a short interval of older sediment has been incorporated into the lowermost Paleocene section, possibly by drilling disturbance. The identification of Subzone UC20c in Sample 342-U1407A-23X-3, 74 cm (187.64 mbsf), and the Subzone UC14d/UC15b boundary in Sample 23X-6, 97 cm (192.37 mbsf), indicates the presence of a hiatus of ~10 m.y., incorporating the lower Maastrichtian and upper Campanian.

The interval from Sample 342-U1407A-23X-6, 97 cm, to 31X-CC (192.37–268.60 mbsf) is assigned to Cretaceous nannofossil Zone UC20–Subzone UC0a based on the following biohorizons: base of Nephrolithus frequens, base of Ceratolithoides kamptneri, top of Reinhardtites levis, base of Broinsonia parca constricta, base of Lithastrinus grillii, base of Micula staurophora, base of L. septenarius, base of Q. gartneri, top of Helenea chiastia, base of Lithraphidites acutus, base of C. kennedyi, top of Hayesites, and presence of Eiffellithus turriseiffelii in the lowermost nannofossiliferous sediment (Table T3). Core 342-U1407A-28X contains a striking black shale lithology, and the presence of Turonian nannofossil Zone UC6 above and Cenomanian Zone UC5/UC4 below is strong evidence that this lithology is equivalent to OAE 2 black shale, such as the Italian Bonarelli level. Further high-resolution sampling is required to establish the succession of nannofossil extinction events across this interval.

The lowermost Cores 342-U1407A-32X through 35X (270.35–299.13 mbsf) are composed of calcareous sandstone and limestone lithologies that contain no nannofossils, most likely because of shallow water depths indicated by the presence of larger benthic foraminifers, corals, and molluscan shell fragments.

Radiolarians

Radiolarian biostratigraphy is based on analysis of all core catcher samples from Hole U1407A and selected section samples from Cores 342-U1407A-21X and 22X. No samples from Hole U1407B or U1407C were examined. Radiolarians are abundant and well preserved in the lower middle Eocene and the Paleocene but are either absent or indeterminate in both the upper Pleistocene–upper middle Eocene and lowermost Paleocene–Cretaceous intervals in Hole U1407A. Strong faunal affinities are noted with coeval assemblages described from Blake Nose ODP Site 1051 (Sanfilippo and Blome, 2001) and J-Anomaly Ridge Deep Sea Drilling Project Site 384 (Nishimura 1992). Depth positions and age estimates of biostratigraphic marker events are shown in Table T5, and the radiolarian distribution is shown in Table T6. Note that the distribution chart is based on shipboard study only and is therefore biased toward age-diagnostic species.

Samples 342-U1407A-1H-CC through 6H-CC (6.78–54.7 mbsf) are barren of radiolarians. Samples 7H-CC through 9H-CC (64.16–83.16 mbsf) contain only poorly preserved spumellarian radiolarians that cannot be assigned to species.

Samples 342-U1407A-10H-CC through 11H-CC (92.32–102.04 mbsf) contain abundant and well-preserved middle Eocene radiolarians. This interval is correlated to radiolarian Zone RP11 based on the presence of primary index species Dictyoprora mongolfieri and the absence of the primary index for Zone RP12, Eusyringium lagena. Correlation with Zone RP11 is supported by three additional bioevents that are known to occur with the zone; the tops of Buryella clinata, Calocyclomma castum, and Lamptonium fabaeforme fabaeforme occur within Sample 342-U1407A-11H-CC (102.04 mbsf).

Samples 342-U1407A-12H-CC through 15H-CC (102.84–121.82 mbsf) contain rare, poorly preserved radiolarians of likely Eocene age based on the presence of probable Podocyrtis papalis s.s.

Interval 342-U1407A-16X-CC through 22X-1, 24–25 cm (124.61–174.55 mbsf), contains abundant, well-preserved Paleocene radiolarians. Samples 342-U1407A-16X-CC through 18X-CC (124.61–142.90 mbsf) are correlated to Zone RP7 based on the common occurrence of primary index species Bekoma bidartensis. As at Site U1406, this interval would be assigned to the lowermost Eocene part of Zone RP7 based on the presence of P. papalis, Theocorys? phyzella, and Theocorys? aff. phyzella (sensu Sanfilippo and Blome, 2001). However, nannofossils indicate that Samples 342-U1407A-16X-1, 8 cm, through 19X-2, 32 cm (121.98–147.45 mbsf), are late Paleocene in age (nannofossil Subzone NP9a to Zone NP7/NP8). The faunal crossover from Bekoma campechensis to B. bidartensis occurs abruptly between Samples 18X-CC and 19X-CC (142.9–149.25 mbsf). A short hiatus of ~1 m.y. may occur between these two samples because uppermost Subzone RP6c has not been identified. This is a well-defined subzone at nearby Site 384, where the gradual faunal crossover between B. campechensis and B. bidartensis is observed. Only Subzones RP6b and RP6a are present in Hole U1407A. Sample 342-U1407A-19X-CC (149.25 mbsf) is assigned to Subzone RP6b based on the occurrence of Stichocampe? caia, a distinctive species restricted to this subzone. The subzone is also bracketed by the bases of B. bidartensis and Pterocodon? poculum in overlying Sample 342-U1407A-18X-CC (142.90 mbsf) and the top of Orbula comitatas in underlying Sample 20X-CC (164.85 mbsf). Interval 342-U1407A-20X-CC through 22X-1, 24–25 cm (164.85–174.55 mbsf), is the lowermost interval that contains age-diagnostic radiolarians in Hole U1407A and is assigned to Subzone RP6a based on the co-occurrence of B. campechensis and O. comitatas. The lowermost sample is inferred to be low in this subzone, as it contains the top of Anthocyrtis mespilus, a species with a range that extends no higher than nannofossil Zone NP4 at Site 384 (Nishimura, 1992). We estimate an age of 62 Ma for this last occurrence datum.

Radiolarians are absent from all samples examined from Sample 342-U1407A-22X-CC through 35X-CC (182.27–299.11 mbsf). A dark claystone in Sample 342-U1407A-28X-1, 18–20 cm (232.09 mbsf) within the Cenomanian/Turonian boundary interval was examined for radiolarians and benthic foraminifers but proved to be barren of microfossils. Radiolarians were observed in thin sections from three chert layers above the Cenomanian/Turonian boundary in Core 342-U1407B-24X (Fig. F21). All radiolarian tests are infilled or replaced by microcrystalline quartz, but in some specimens the test outline is preserved. This suggests that these cherts may be suitable for processing for radiolarians using the hydrofluouric acid method.

Planktonic foraminifers

Core catchers and additional samples from working section halves were examined in Hole U1407A. Samples contain diverse and well-preserved assemblages of planktonic foraminifers from the Pleistocene to the mid-Cretaceous. Depth positions and age estimates of biostratigraphic marker events are shown in Table T7. The stratigraphic distribution of planktonic foraminifers is shown in Table T8.

The uppermost interval from Samples 342-U1407A-1H-CC through 2H-1, 50–52 cm (6.78–7.31 mbsf), contains Globorotalia truncatulinoides, indicative of Pleistocene age. Samples 2H-2, 70–72 cm, through 2H-4, 50–52 cm (9.01–11.61 mbsf), contain poorly preserved assemblages containing no index markers except Globorotalia inflata and Neogloboquadrina pachyderma, suggesting an age of Pliocene–Pleistocene. A poorly preserved Oligocene assemblage (mainly comprising Catapsydrax spp. and Dentoglobigerina galavisi) was recovered from Samples 342-U1407A-2H-5, 60–62 cm, through 2H-CC (12.28–15.95 mbsf). Samples 2H-7, 40–42 cm, through 3H-1, 110–112 cm (15.07–17.42 mbsf) contain poorly preserved specimens of Acarinina bullbrooki, Globigerinatheka index, and Globigerinatheka mexicana, suggesting a middle Eocene age.

Well-preserved and taxonomically diverse planktonic foraminifers of Eocene age are found in Samples 342-U1407A-3H-2, 110–112 cm, through 15H-CC (18.91–121.84 mbsf). Sample 3H-2, 110–112 cm (18.91 mbsf), contains Guembelitrioides nuttalli but lacks Morozovella aragonensis and Morozovella crater, indicating Zone E10. The top of M. aragonensis (the base of Zone E10), base of G. nuttalli (base of Zone E8), top of Morozovella subbotinae (base of Zone E6), and base of M. aragonensis (base of Zone E5) are found in Samples 342-U1407A-4H-1, 100–102 cm (26.81 mbsf), 10H-2, 110–112 cm (85.41 mbsf), 12H-1, 25–27 cm (102.11 mbsf), and 15H-CC (121.82 mbsf), respectively.

The interval from Sample 342-U1407A-16X-1, 35–37 cm, to 22X-CC, 10–12 cm (122.29–181.92 mbsf), contains planktonic foraminifers spanning upper to middle Paleocene Zones P5–P3. The top and base of Globanomalina pseudomenardii mark the respective top and base of Zone P4. The Paleocene/Eocene boundary is not recognized because of the absence of “excursion taxa” such as Acarinina sibaiyaensis and Morozovella allisonensis. Planktonic foraminifers of early Paleocene (Zone P1) age occur from Sample 342-U1407A-23X-2, 33–35 cm, to 23X-2, 126–127 cm (185.74–186.67 mbsf). An apparent inconsistency between the planktonic foraminiferal Zone P3/P4 boundary and the identification of nannofossil Zone NP2 is likely explained by the coarser resolution of the planktonic foraminiferal sampling in this particular interval.

Relatively diverse assemblages of Cretaceous planktonic foraminifers occur from Samples 342-U1407A-22H-CC, 30–32 cm, through 31X-CC (182.12–268.60 mbsf), in which preservation varies from good to occasionally poor. The base of the Campanian Radotruncana calcarata Zone occurs in Sample 23X-6, 12–15 cm (191.54 mbsf). The top and base of the lowermost Campanian to Santonian Dicarinella asymetrica Zone are found in Samples 342-U1407A-24X-CC (199.40 mbsf) and 25X-CC (206.61 mbsf). The base of Dicarinella concavata, denoting the upper Turonian, occurs in Sample 27X-1, 33–35 cm (222.64 mbsf). The Cretaceous sequence at Site U1407 may thus contain the Campanian/Santonian, Santonian/Coniacian, and Coniacian/Turonian boundaries. The top and base of Helvetoglobotruncana helvetica (lower to upper Turonian) occurs in Samples 342-U1407A-27X-3, 29–30 cm (225.60 mbsf), and 27X-4, 65–67 cm (227.46 mbsf), respectively. Samples 28X-2, 14–15 cm, through 29X-3, 85–86 cm (233.53–245.mbsf), contain Rotalipora cushmani, marking the upper Cenomanian. The short Thalmanninella reicheli Zone occurs in Sample 342-U1407A29X-4, 85–86 cm (246.86 mbsf). The base of Thalmanninella globotruncanoides, indicating the lowermost Cenomanian, occurs in Sample 342-U1407A-31X-5, 70–71 cm (267.41 mbsf), and the upper Albian marker species Planomalina buxtorfi is found in Samples 31X-6, 36–37 cm, through 31X-CC (268.17–268.60 mbsf). An apparent inconsistency between the base of the D. asymetrica Zone with the identification of nannofossil Zone UC9 is likely explained by the coarser resolution of the planktonic foraminiferal sampling in this particular interval.

Benthic foraminifers

Benthic foraminifers were examined semiquantitatively in core catcher samples from Hole U1407A. Additional working section half samples taken from Cores 342-U1407A-2H through 31X and 342-U1407B-21X through 24X were examined for preservation and relative abundance of benthic foraminifers. Benthic foraminifers at this site are rare (the “present” category) relative to total sediment particles >150 µm in the Oligocene–Paleocene and slightly more abundant in parts of the Cretaceous (Fig. F20; Table T9).

Although preservation of benthic foraminifer tests is generally good to very good in the Eocene to Cretaceous, the Oligocene and parts of the Cretaceous succession contain some moderately or poorly preserved samples (Fig. F20). The occurrences of benthic foraminifers at this site are shown in Tables T9 and T10.

Sample 342-U1407A-1H-CC yields a well-preserved Pleistocene fauna containing mainly Bolivina sp., Cassidulina subglobosa, Cibicidoides spp., and Pullenia spp.

Samples 342-U1407A-2H-CC through 15H-CC (15.95–121.82 mbsf) are dominated by an Eocene assemblage of the calcareous taxa Bulimina spp., C. subglobosa, Dentalina sp., Gyroidinoides spp., Nuttallides truempyi, Oridorsalis umbonatus, and stilostomellids (including Stilostomella gracillima, Stilostomella lepidula, Stilostomella subspinosa, and Stilostomella sp.). Agglutinated benthic foraminifers are minor constituents only. Overall, the Eocene assemblages show fluctuations between intervals of high abundance of infaunal taxa, indicating a high organic matter flux to the seafloor and intervals of dominantly epifaunal species.

Samples 342-U1407A-16X-CC through 22X-CC (124.61–182.27 mbsf) contain diagnostic Paleocene assemblages. Abundant calcareous taxa include Bulimina sp., Dentalina sp., gavelinellids (Gavelinella beccariiformis, Gavelinella hyphalus, and Gavelinella sp.), Gyroidinoides spp., Lenticulina cf. adenalensis, N. truempyi, and Pullenia coryelli. The agglutinated benthic foraminifer Gaudryina pyramidata occurs frequently to abundantly in these samples.

Benthic foraminifer assemblages of the Upper Cretaceous sediment from Samples 342-U1407A-23X-CC through 25X-CC (193.13–206.61 mbsf) are almost comparable to the overlying Paleocene assemblages, with additional species such as Lenticulina rotulata, Marssonella oxycona, and Reussella sp. occurring frequently to abundantly.

Sample 342-U1407A-27X-CC (230.88 mbsf) shows an assemblage that is typical of the black shale facies associated with OAE 2 (e.g., Holbourn and Kuhnt, 2002; Friedrich, 2010). The assemblage is dominated by the agglutinated species Spiroplectinata annectens. Abundant calcareous taxa are Bolivina anambra, Pleurostomella reussi, and Tappanina laciniosa, indicating low oxygen concentrations at the seafloor.

Underlying Cores 342-U1407A-28X through 31X show a lower Cenomanian to upper Albian benthic foraminifer assemblage characterized by Astacolus sp., gavelinellids (including Gavelinella cenomanica, Gavelinella intermedia, and Gavelinella sp.), Gyroidinoides spp., L. rotulata, Osangularia schloenbachi, and S. annectens.

The sandstone facies of Sample 342-U1407A-33X-CC (280.00 mbsf) contains few specimens of the larger benthic foraminifer genus Orbitulina (probably Orbitulina concava and Orbitulina texana), indicative of an Albian age (Fig. F22).

Macrofossils

Macrofossil remains such as algae, bivalves, cephalopods, corals, and gastropods are found in lithostratigraphic Unit VI (Fig. F23). Although calcareous hard parts of most specimens are not preserved, outer molds are found in the limestone.

Sample 342-U1407A-31X-CC (268.54 mbsf) yields two belemnites (possibly Neohibolites) (Fig. F23A). Well-preserved rostrums were horizontally embedded within this core catcher. Those two individuals are aligned side-by-side with adapical ends pointing in the same direction indicative of relatively strong bottom water current.

Although mostly preserved as outer molds, diverse shallow-marine macrofossil fauna were observed in Sample 342-U1407A-35X-CC (299.10 mbsf). Hermatypic corals, bivalves, and gastropods (Fig. F23D, F23E, F23F) are predominant, and coralline algae are subordinate (Fig. F23B).

Top of page   |    Previous   |    Next