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doi:10.2204/iodp.proc.302.104.2006

Micropaleontology

During Integrated Ocean Drilling Program (IODP) Expedition 302, four closely spaced sites (Sites M0001–M0004) were drilled along a single seismic profile, and cores from the various holes could be confidently spliced and correlated. The different sequences are treated as a single succession. Among the holes, only Holes M0002A and M0004A reached significant depths; the others captured parts of the Pleistocene. Hole M0002A penetrated into the middle Miocene and upper middle Eocene, with a marked hiatus separating these units. Hole M0004A continued from where Hole M0002A ended, recovered portions of the underlying middle and lower Eocene and the Paleocene/Eocene transition, and bottomed in lower Campanian basement at ~410 mbsf.

Onboard micropaleontology included the analysis of calcareous nannofossils, diatoms, silicoflagellates, ebridians, radiolarians, calcareous and agglutinated benthic foraminifers, planktonic foraminifers, ostracodes, organic-walled dinoflagellate cysts (dinocysts), other palynomorphs, and fish remains. Only core catcher samples were analyzed during the offshore phase.

All but one of the studied samples were barren of calcareous nannofossils. A single productive sample is reported from the Holocene in Hole M0001A. Siliceous microfossils, notably diatoms, silicoflagellates, and ebridians, are most abundant and well preserved in the middle Eocene interval. Calcareous planktonic and benthic foraminifers and ostracodes are rare in the Pleistocene and absent in older parts. Agglutinated benthic foraminifers are generally scarce but are locally abundant and well preserved in the Campanian and the Paleocene to lower Eocene intervals. Organic-walled dinoflagellate cysts (dinocysts) are patchy in the Quaternary–Neogene but are abundant and well preserved in the Paleogene and Cretaceous intervals. Other palynomorphs, notably pollen and spores, and remains of aquatic algae (chlorophytes) are common in most intervals. An acme of the remains of the hydropterid fern Azolla marks the basal middle Eocene.

Preliminary age-depth relationships are based on dinocyst, ebridian, and silicoflagellate datums and the Azolla event. Dinocysts represent the only group that by and large is present throughout the entire Cenozoic section. Paleogene dinocyst events have been calibrated to magnetostratigraphy by Eldrett et al. (2004) from Hole 913B in the Norwegian-Greenland Sea. Additional age information is derived from silicoflagellates and ebridians in the middle Eocene and a few benthic foraminifer events in the older Paleogene.

During Expedition 302, cores ranging in age from the Campanian (basement) to the Holocene were recovered. Major hiatuses occur between the Campanian and the Paleocene, the middle Eocene and early Miocene, and within the Pliocene.

Paleoenvironments ranged between marginal marine neritic settings in the Campanian through earliest Eocene to an enclosed marginal basin setting marked by episodic brackish to possible freshwater conditions in the middle Eocene, as indicated by the Azolla event. The upper part of the Miocene through the Pleistocene is characterized by deep marine conditions. The palynological assemblage in Samples 302-M0002A-44X-CC and 45X-CC resembles that of a coastal, restricted marine, brackish setting. Reworking of Cretaceous through late Eocene elements is common in this interval. The Oligocene elements may be reworked as well, tentatively placing this succession in the Miocene. Non-fossil-bearing strata, provisionally assigned to the Miocene, overlie this interval. Paleoenvironmental information is not available for this interval (Samples 302-M0002A-38X-CC through 43X-CC).

Calcareous nannofossils

During the offshore phase of IODP Expedition 302, 124 smear slides made with the core catcher sediments from each of the four sites were studied for calcareous nannofossils. All of the studied samples were barren, except for one sample from Hole M0001A. Although calcareous nannofossils are poorly represented in high-latitude sediments (Perch-Nielsen, 1985a), this result was striking. Studies carried out in recent years on several piston cores from the Arctic Ocean (e.g., Gard, 1993; Jakobsson et al., 2000, 2001) have shown that calcareous nannofossils are present in low abundances only in short intervals during the present and the last interglacial periods. Expedition 302 recovered a long Cretaceous to Cenozoic stratigraphic record, and so it was a surprise not to find calcareous nannofossils, a fossil group that normally is well represented in marine sediments.

After the cores were split at the IODP Bremen Core Repository (BCR), the upper 19 m of Hole M0004C and the top 3 m of Hole M0002A were sampled at varying intervals downcore, using a strategy based largely on visual observations of core coloration. Although many of the samples subsequently proved to be barren, a surprising large number did contain poor–moderate–well-preserved calcareous nannofossil assemblages. Moreover, a few of the samples from Hole M0004C equate to 18 mbsf. Although some of these nannofossils are undoubtedly reworked from Mesozoic–Cenozoic sediments and transported over long distances to the core sites (Gard and Crux, 1994), others may have been produced in situ.

Hole M0001A

Four samples from Section 302-M0001A-1H-CC (collected at depths of 10, 12, 14, and 26 cm) were analyzed for calcareous nannofossils. Only the sample collected in a brown interval at 14 cm contains an impoverished assemblage of calcareous nannofossils. The following forms have been determined: Coccolithus pelagicus (small form), Calcidiscus leptoporus, and a species of Gephyrocapsa. All of them are rare. This assemblage has been previously recorded in Holocene sediments from the Arctic Ocean (Gard, 1993).

Hole M0002A

Seventy-nine samples from the core catchers were analyzed on board for calcareous nannofossils, but all of them were barren (Table T5). Samples taken from the first core opened proved to be more fruitful. The coccoliths in the top 10 cm were moderately preserved and largely comprised Emiliania huxleyi and small–medium Gephyrocapsa species, the latter being absent in the top two samples (Sections 1X-1, 2.0 cm, and 1X-1, 3.5 cm). The samples in the top 10 cm also included a number of unidentified coccoliths, and a few specimens of C. pelagicus, C. leptoporus, and thoracospheres were found. Some coccoliths were found in deeper samples from Cores 1X and 2X but were poorly preserved and very rare.

Hole M0003A

Three core catcher samples (1H-CC, 3 cm, 2H-CC, 16 cm, and 3H-CC, 24 cm) were analyzed on board for calcareous nannofossils, but all were barren. Fifteen samples were analyzed onshore, most of which were barren, but with a gephyrocapsid specimen in Section 1H-1, 11 cm, two reworked coccoliths in Section 1H-1, 12 cm, and a coccolith of C. pelagicus in section 1H-2, 59 cm.

Holes M0004A, M0004B, and M0004C

Thirty-two core catcher samples from Hole M0004A (Table T6), two from Hole M0004B (302-M0004B-3X-CC, 2 cm, and 13 cm), and four samples from Hole M0004C (302-M0004C-1H-CC through 4H-CC and 6X-2, 149 cm) were analyzed on board for calcareous nannofossils, but all samples were barren.

Samples taken from the opened cores of Hole M0004C yielded significant numbers of coccoliths. The top 35 cm of Section 302-M0004C-1H-1 contained good to moderately preserved specimens of E. huxleyi, small to medium Gephyrocapsa spp., and C. pelagicus, as well as a few C. leptoporus and Syracosphaera species. Unidentified coccoliths were also present. Below this, most of the samples were either barren or contained rare and poorly preserved coccoliths of small to medium Gephyrocapsa spp., C. pelagicus, and C. leptoporus. In Section 302-M0004C-1H-2, 2 cm, there were many small and medium Gephyrocapsa spp. as well as a few E. huxleyi, whereas another sample at 4H-3, 3 cm, comprised a few specimens of moderately preserved small to medium Gephyrocapsa species. It should be pointed out that samples from the same core depth but from different horizontal locations often yielded dissimilar results.

Nannofossil stratigraphy

The findings in Hole M0004C suggest that coccolithophorids were living in the Arctic prior to the last interglacial. However, their rare presence in the lower core sections does not allow us at this time to assign an age or zone with any confidence. On the other hand, the “dominance” of E. huxleyi in the uppermost part of the first section indicates that the sediments represent the Holocene, prior to which (i.e., before the beginning of the E. huxleyi acme) there is a “dominance” of small to medium Gephyrocapsa species. The presence of large specimens (>4 µm) of E. huxleyi, reportedly indicative of the last glacial period at lower latitudes (Colmenero-Hidalgo et al., 2002), occur in the Arctic sediments presumably during the warmer Holocene. The presence of large specimens (9–15 µm). of C. pelagicus indicates that temperate waters infiltrated the Arctic region during the Holocene (Young et al., 2003)

Diatoms

Hole M0001A

Samples 1H-CC, 18 and 25 cm, were studied, but diatoms were not observed in these samples.

Hole M0002A

A total of 87 samples (about one sample per section) in interval 1X-1, 3 cm, through 47X-2, 37 cm, were prepared, but these were barren of diatoms and other siliceous microfossils (silicoflagellates, ebridians, and archaeomonads), apart from Sample 46X-CC, 6 cm, which yielded rare diatoms (Table T7). Samples 47X-2, 50 cm, to 49X-3, 31 cm, contained few diatoms but generally abundant ebridians. Samples 51X-1, 25 cm, to 62X-3, 50 cm, contained a diverse siliceous assemblage with abundant diatoms, common to abundant ebridians, and few to common silicoflagellates. Sediments of this interval are dominated by diatoms.

Based on qualitative analysis of smear slides and some quantitative counts, the diatoms in the biosiliceous interval can be divided into different assemblages. Given the sparsity of published information on middle Eocene diatoms in northern high latitudes, most of the species recorded in these samples have been identified only to generic level. Diatoms in the ebridian-dominated interval 47X-2, 50 cm, to 49X-3, 31 cm, are dominated by Pyxilla spp. The diatom assemblage in interval 51X-1, 25 cm, to 53X-3, 100 cm, is mainly composed of species of Hemiaulus and Huttonia. In interval 53X-4, 38 cm, to 57X-3, 60 cm, the assemblage is composed of species of Goniothecium, Eunotogramma, Hemiaulus, and Huttonia. We have specifically sampled some of the white layers of the laminated interval. One of these samples (57X-4, 50 cm) is a pure diatomite composed mainly of species of Eunotogramma. The other three samples (58X-2, 69 cm, 58X-3, 5 cm, and 59X-3, 79 cm) are composed mainly of species of Hemiaulus. The diatom assemblage in interval 60X-1, 39 cm, to 62X-3, 50 cm, is composed of species of Eunotogramma, Trinacria, and Odontotropis. Within this diatom-dominated interval there is one sample (61X-2, 20 cm) that is dominated by ebridians.

The diatom species assemblages in Hole M0002A show some similarities to those reported from Deep Sea Drilling Project (DSDP) Leg 38, Sites 338–340 (e.g., Schrader and Fenner, 1976; Dzinoridze et al., 1978; Fenner, 1985), Ocean Drilling Program (ODP) Leg 151 from the middle Eocene to the late Oligocene in the Norwegian-Greenland Sea (Scherer and Koç, 1996), Core Fl-422 from the Alpha Ridge of the central Arctic Ocean assigned to early to middle Eocene by Dell’Agnese and Clark (1994), the Eocene of the Urals (Strelnikova, 1974), and to the early Eocene Moler/Für Formation of Denmark (Homann, 1991). Because of the sparsity of sediments of this age and consequently a poorly established high-latitude northern hemisphere Eocene diatom biostratigraphy, it is not possible to provide a more detailed age assessment to the interval 47X-2 to 62X-3 in Hole M0002A other than middle Eocene. However, the present material yielded significant changes in the presence and abundance of species that may potentially be useful for the establishment of a diatom biostratigraphy for the Arctic Ocean. Counts of species in Samples 51X-2, 117–118 cm, through 62X-CC show some significant changes in the species composition of this interval (Table T7; Fig. F8).

There are three peaks in the abundance of Hemiaulus sp. 1 between interval 51X-2, 117–118 cm, and 62X-CC, namely in Samples 62X-CC through 61X-CC, 59X-CC, and the interval from 57X-CC through 55X-CC. Similar changes are also recognized in the patterns of Hemiaulus danicus, Hemiaulus incisus, Hemiaulus kittonii, and Hemiaulus spp. indet., which have abundance maxima in Samples 54X-CC and 51X-2, 117–118 cm. Pseudopyxilla spp. are abundant from Sample 62X-CC through 59X-CC, whereas Cymatosira spp. show a maximum abundance in the upper part of Sample 59X-CC. Goniothecium is abundantly present in all samples that yielded diatoms. Among representatives of this genus, Goniothecium loricatum has two peaks (i.e., from Samples 60X-CC through 57X-CC and from 54X-CC through 52X-CC). Goniothecium odontella var. danica also has two peaks, in Samples 60X-CC and 52X-CC. Abundant occurrences of Costopyxis trochlea were also recognized. This species was formerly known as “Trochosira trochlea” from middle Eocene sediments in high and low latitudes (Dzinoridze et al., 1978; Fenner, 1985; Scherer and Koç, 1996).

The Eocene Chaetoceros resting spore assemblages are of low diversity, represented only by two species, resting spore sp. 1 and Syndendrium diadema? Resting spore sp. 1 is common only in Sample 52X-CC.

Paleoenvironment

The diatom species of Hole M0002A are all marine. The presence of abundant diatoms (and other biosiliceous organisms) indicates extremely productive surface ocean conditions in the interval 51X-1 through 62X-CC. Presence of laminations with pure diatom assemblages in the light layers throughout the interval is a further confirmation of the extremely productive nature of the surface waters. A large number of the observed species, such as Pseudotriceratium radiosoreticulatum, which occurs from Samples 48X-CC through 57X-CC, is especially common in neritic environments (Fenner, 1985).

Diatom resting spore assemblages, including Pterotheca aculeifera, resting spore sp. 1, and S. diadema?, are common in Sample 52X-CC. Their presence may indicate proximity to the shelf edge, as only neritic planktonic diatoms form resting spores in the modern oceans. The abundance of resting spores also suggests a highly productive environment.

Hole M0003A

Three core catcher samples (1H-CC, 22 cm, 2H-CC, 14 cm, and 3H-CC, 1 cm), in addition to Samples 1H-1, 12 cm, 1H-2, 59 cm, 3H-3, 12 cm, 3H-3, 70 cm, and 3H-3, 85 cm, were investigated for diatoms. All of these samples were barren.

Hole M0004A

Fifty-seven core samples from Hole M0004A (i.e., between Sections 4X-1, 10 cm, and 42X-CC) were investigated for biosiliceous components (diatoms, ebridians, silicoflagellates, and archaeomonads). Well-preserved and abundant diatoms are recognized in Samples 4X-1 through 12X-CC, whereas rare, poorly preserved specimens occur in Sections 15X-CC through 19X-CC. Samples between 20X-CC, 5 cm, and 42X-CC were barren (Table T8; Fig. F9).

Biosiliceous sediments in the interval 4X-1, 10 cm, through 7X-1, 60 cm, are mostly dominated by diatoms. Only in Samples 5X-1, 15 cm, and 5X-2, 30 cm, are the sediments dominated by ebridians. The rest of the biosiliceous interval between 7X-2, 80 cm, and 15X-1, 10 cm, is mainly dominated by ebridians.

Based on the qualitative analysis of smear slides, the diatom record can be grouped into different assemblages. In the interval 4X-1, 10 cm, through 6X-3, 70 cm, the assemblage is mostly composed of species of Eunotogramma, Trinacria, and Odontotropis. Species of Pterotheca and Trinacria are the most common elements of the diatom assemblage in the interval 6X-4, 30 cm, through 10X-CC. In the interval 11X-1, 40 cm, through 11X-3, 100 cm, the assemblage is mainly composed of Pseudostictodiscus picus and species of Trinacria. In Sample 11X-3, 20 cm, an especially common occurrence of Odontotropis ex gr. carinata/hyalina is observed. Pyxilla oligocaenica var. oligocaenica and species of Trinacria make up most of the assemblage in the interval 11X-4, 5 cm, through 15X-1, 10 cm.

Counting of species in nine samples between Sections 4X-1 and 12X-CC showed the presence of abundant well-preserved resting spores in this interval (Table T8). In these samples, representatives of 24 genera, comprising 26 species and 12 unidentified species, including two unknown resting spore species, were observed. Samples 15X-CC and 18X-CC included rare and poorly preserved small-sized diatom valves of Goniothecium spp., Hemiaulus spp., P. picus, and P. aculeifera. In addition, a few well-preserved large-size diatom valves in the >45 µm fraction, including Odontotropis carinata, Stephanopyxis spp., and Trinacria cornuta, were recognized. The abundance of Hemiaulus sp. 1 (>70%) and Pseudopyxilla spp. (>20%) and absence of Anaulus spp. and Cymatosira spp. resemble diatom assemblages in the lower part of the diatomaceous sediments in Hole M0002A.

Few age-diagnostic taxa are recorded in Hole M0004A. Sample 6X-CC contained rare but well-preserved Brightwellia hyperborea, which is an age-diagnostic taxon from the middle Eocene of the North Atlantic Ocean (Fenner, 1985). Samples 11X-4, 5 cm, and 11X-4, 40 cm, contained few P. oligocaenica var. oligocaenica indicating an early Eocene age for these samples (Fenner, 1985). Species recorded in Hole M0004A show some similarities to those reported from DSDP Leg 38, Site 338 (Schrader and Fenner, 1976; Dzinoridze et al., 1978), and from ODP Leg 151, from the middle Eocene to the late Oligocene in the Norwegian-Greenland Sea (Scherer and Koç, 1996), Core Fl-422 from the Alpha Ridge of the central Arctic Ocean assigned to early to middle Eocene by Dell’Agnese and Clark (1994), Eocene of the Urals (Strelnikova, 1974), and early Eocene Moler/Für Formation of Denmark (Homann, 1991).

Paleoenvironment

All diatoms observed in Hole M0004A are marine species. Most species occurring abundantly at this site, like Hemiaulus spp., Goniothecium spp., and Stephanopyxis spp., indicate a neritic environment (Fig. F10). Resting spore assemblages (notably P. aculeifera and Pseudopyxilla sp.) are abundant and also indicate a nearshore, coastal setting. The abundance of biosiliceous organisms together with diatom resting spores may suggest a highly productive environment, possibly associated with active upwelling in the interval 4X-1, 10 cm, through 15X-1, 10 cm.

Correlation of Holes M0002A and M0004A

Diatom assemblages of Hole M0002A in interval 60X-1, 39 cm, through 62X-3, 50 cm, and Hole M0004A in interval 4X-1, 10 cm, through 6X-3, 70 cm, are very similar. Both are composed of species of Eunotogramma, Trinacria, and Odontotropis. Furthermore, even though both intervals are primarily dominated by diatoms, there is a short interval in both holes where ebridians dominate over diatoms and where the two holes overlap. These are Sample 302-M0002A-61X-2, 60 cm, and interval 302-M0004A-5X-1, 15 cm, through 5X-2, 30 cm.

Hole M0004B

Two core catcher samples, 1H-CC, 2 cm, and 3X-CC were investigated. The former sample was barren. The latter contained poorly preserved, small-size diatom valves, including Pyxilla spp. and some fragments, and few but well-preserved large-size diatom valves in the >45 µm fraction, including Pseudotriceratium radiosoreticulatum, Paralia crenulata, Actinoptychus spp., Stephanopyxis spp., Hemiaulus spp., and Pseudopyxilla spp. This assemblage is not age diagnostic. The occurrence of Pseudotriceratium radiosoreticulatum indicates neritic conditions (Fenner, 1985).

Hole M0004C

A total of 24 samples including the seven core catcher samples, 1H-CC, 2H-CC, 3H-CC, 4H-CC, 6X-2, bottom, 8X-CC, and 9X-CC were studied but did not contain diatoms.

Diatom and paleoenvironment summary, Holes M0002A and M0004A

The biosiliceous sediments in Cores 302-M0002A-47X through 62X as well as 302-M0004A-4X through 15X indicate productive surface ocean conditions in the Arctic during the early Eocene through the middle Eocene. The start and end of this biosiliceous interval is dominated by ebridians, possibly indicating a nearshore environment with moderate productivity, whereas the middle part of the interval, which is dominated by diatoms, indicates highly productive surface waters with neritic to pelagic conditions (Figs. F10, F11). The recovered diverse diatom assemblages show high temporal variability in their composition, indicating significant climate variability within the recovered time interval.

Silicoflagellates and ebridians

Seventeen samples above 33.9 mbsf from all holes were processed, and all were barren of silicoflagellates and ebridians. These include samples from Holes M0001A (Core 302-M0001A-1H), M0002A (Cores 302-M0002A-1X-CC and 3X-CC), M0003A (Cores 302-M0003A-1H, 2H, and 3H), M0004A (Samples 302-M0004A-2X-1, 149–151 cm, 2X-2, 0–2 cm, and 3X-1, 149–151 cm), and M0004C (Cores 302-M0004C-1H through 4H, 6X, 8X, and 9X).

Below 33.9 mbsf, a total of 104 cores were recovered from Holes M0002A (59 cores), M0004A (42 cores), and M0004B (3 cores). Here, we briefly discuss the silicoflagellate and ebridian biostratigraphy, after splicing Holes M0002A and M0004A and inserting data from Hole M0004B (Core 302-M0004B-3X).

Holes M0002A and M0004B

In Hole M0002A, silicoflagellates and ebridians were absent in all samples between Samples 302-M0002A-1X-CC and 46X-CC. Samples 302-M0002A-47X-CC through 62X-CC, 9–11 cm, yielded well-preserved, abundant, and highly diversified (~40 taxa) silicoflagellate and ebridian assemblages, permitting preliminary age assignments (Table T9).

Both the silicoflagellate and ebridian assemblages are similar to those reported in Core Fl-422 from the Alpha Ridge in the Arctic Ocean (Ling, 1985), a core whose age was considered to be early Paleogene. All 18 taxa illustrated by Ling (1985) are present in Samples 302-M0002A-47X-CC through 62X-CC, 9–11 cm, in addition to at least a dozen more taxa in Hole M0002A. The two most critical taxa for biostratigraphy (Corbisema hexacantha and Dictyocha frenguellii, see below) were not reported by Ling (1985).

Using samples from the same Alpha Ridge core, Bukry (1984) gave an age range of late middle Eocene to late Eocene. Based on his photomicrographs, six taxa occur in the present cores (Samples 302-M0002A-47X-CC through 62X-CC, 9–11 cm) from the Lomonosov Ridge, although the taxonomic nomenclature of a few taxa differs from ours. More recently, Dell’Agnese and Clark (1994) provided an age estimate of early to middle Eocene for Alpha Ridge Core Fl-422. There are thus three possible ages for Core Fl-422: early Paleogene, early to middle Eocene, and late middle to late Eocene.

Samples 302-M0002A-47X-CC (207.35 mbsf) and 48X-CC (210.64 mbsf) belong to the silicoflagellate C. hexacantha Zone, which ranges from the middle Eocene to the late Eocene. In terms of calcareous nannofossil zonation, this represents the upper part of Zone NP15 to Zones NP19/NP20. An age of ~44.1 Ma is estimated between Samples 302-M0002A-48X-CC and 49X-CC, where the first occurrence (FO) datum of C. hexacantha occurs. Note that abundant C. hexacantha occurred in Sample 302-M0002A-48X-CC (362 specimens) followed by rare occurrences of this taxon in Sample 48X-2, 139–151 cm, and Core 47X-CC.

Samples 302-M0002A-49X-CC through 62X-CC, 9–11 cm, belong to the silicoflagellate Corbisema spinosa and Naviculopsis robusta Zones. The zonal ranges of these species correspond to the middle part of nannofossil Zones NP15 (middle Eocene) to NP12 (lower Eocene). Age information from dinoflagellate cysts (see “Palynology, organic-walled dinoflagellate cysts”) combined with silicoflagellate data constrains the age of Cores 302-M0002A-49X through 62X to the middle Eocene. The following is a preliminary discussion of silicoflagellate age determinations for Hole M0002A.

Sample 302-M0002A-47X-CC contains moderately preserved and abundant C. hexacantha and D. frenguellii, which are the most age-diagnostic taxa. Less diagnostic taxa with long stratigraphic ranges include Dictyocha crux parvus, Dictyocha lockerii, Dictyocha deflandrei, Corbisema hastata hastata, Corbisema hastata globulata, Corbisema apiculata, Distephanus quinquengellus, Distephanus quinarius, Ammodichium rectangulare, and Pseudoammodochium dictyoides. Sample 302-M0002A-48X-CC contains the key species C. hexacantha, C. hastata globulata, C. hastata hastata, Corbisema sp. aff. toxeuma, and P. dictyoides.

Based on the material from Leg 151 Site 913 from the Greenland Basin, Locker (1996) provided the FO and last occurrence (LO) of C. hexacantha as 44.1 and 37.4 Ma, respectively. The range of D. frenguellii in the C. hexacantha Zone was discussed by Perch-Nielsen (1985b). Thus, Samples 302-M0002A-47X-CC and 48X-CC are assigned to the C. hexacantha Zone of the middle to upper Eocene.

About two samples per core were investigated between Cores 302-M0002A-49X and 62X (Table T9). Samples 302-M0002A-49X-CC through 62X-CC, 9–11 cm, contained well-preserved and abundant silicoflagellate and ebridian assemblages, except for Samples 302-M0002A-49X-CC and 50X-CC, which contained few specimens. Samples 302-M0002A-49X-CC through 62X-CC, 9–11 cm, may belong to the C. spinosa and N. robusta Zones, which correlate to nannoplankton Zone NP15 (middle Eocene). Several taxa such as Distephanus crux and Dictyocha quinquengellus may have biostratigraphic value pending further study. Broadly age diagnostic (early to middle Eocene) taxa include D. frenguellii, D. deflandrei, Corbisema glezerae, Corbisema toxeuma, Corbisema ovalis, C. apiculata, C. hastata hastata, and C. hastata globulata. As Samples 302-M0002A-49X-CC through 50X contained few silicoflagellates, an effort was made to count as many specimens as possible using more than the standard eight traverses at 400×. This resulted in the recognition of >70 specimens in each sample and confirmed that the index taxon C. hexacantha was absent in Samples 302-M0002A-48X-CC and 49X-CC. Single specimens of C. spinosa, an important age-diagnostic taxon, which ranges from the upper part of the Naviculopsis foliacea Zone to the C. hexacantha Zone (Perch-Nielsen, 1985b), was present in Samples 302-M0002A-49X-CC, 2–4 cm, and 52X-CC. This concurs with an age assignment of Cores 302-M0002A-49X through 62X that correlates to Zone NP15. A single specimen of Corbisema lamellifera, which occurs in the C. hexacantha Zone, was found in Sample 302-M0002A-62X-CC, 9–11 cm. Single specimens of Naviculopsis foliacea tumida, Naviculopsis constricta, and Naviculopsis punctilia were present in Sample 302-M0002A-50X-CC, 8–10 cm. A single specimen of N. robusta, which is characteristic of the N. foliacea Zone, was present in Sample 302-M0002A-62X-CC, 9–11 cm, in the >45 µm fraction.

Small (14–20 µm equatorial diameter) silicoflagellate taxa reported by Ling (1985) from the Alpha Ridge were observed in several samples below Core 302-M0002A-52X-CC to the bottom of the hole (Table T9). These taxa include Dictyocha curta and Dictyocha sp. cf. rotundata. The silicoflagellate Dictyocha sp. cf. carentis incerta (diameter of basal ring = 17–24 µm) illustrated by Ling (1985) also was continuously present between Samples 302-M0002A-52X-1, 0–2 cm, and 62X-CC, 9–11 cm, except in Samples 52X-CC and 53X-CC. Samples 302-M0002A-61X-CC, 0–1 cm, and 62X-CC, 9–11 cm, yielded eight and six specimens, respectively. These small, rare taxa suggest a similarity between Alpha Ridge Core Fl-422 and Samples 302-M0002A-52X-1, 0–2 cm, through 62X-CC, 9–11 cm, and an age of early to middle Eocene for both cores.

Distephanus speculum speculum was present sporadically between Cores 302-M0002A-49X and 57X. Today, this taxon is a typical temperate to cold-water form. Distephanus antiqua was present continuously from Cores 302-M0002A-49X through 57X, except in Section 56X-CC.

A single specimen of Mesocena apiculata inflata was present at the top of Sample 302-M0002A-57X-CC (<45 µm fraction), which ranges from the N. foliacea Zone of the lower to the middle Eocene to the C. apiculata Zone of the Oligocene. Abundant and well-preserved specimens of the undescribed species Dictyocha sp. A and Dictyocha sp. B were found throughout Samples 302-M0002A-49X-CC through 59X-CC and 60X-1, 0–2 cm. In particular, high numbers of Dictyocha sp. B were recorded from Samples 302-M0002A-54X-CC through 55X-CC and Dictyocha sp. A in Samples 53X-CC through 51X-CC.

Paleoenvironment

Abundant Corbisema in the >45 µm fraction and ebridians in the <45 µm fraction of Sample 302-M0002A-62X-CC suggest the following paleoenvironmental conditions favorable to these groups: warm waters, nearshore habitats, and high productivity.

Hole M0004A

Cores 4X (265.03 mbsf) through 18X (318.96 mbsf) yielded silicoflagellates and ebridians with variable abundance and states of preservation. No silicoflagellates and ebridians were found below Core 18X. The silicoflagellate assemblages from this site are similar to those at Site M0002 but differ lower in the section. These cores are assigned to the C. spinosa and N. robusta Zones, analogous to cores from Hole M0002A (Cores 302-M0002A-49X through 62X).

C. glezerae was consistently present in the lower section of this hole except in Cores 302-M0004A-6X, 9X, and 10X. According to Perch-Nielsen (1985b), this taxon ranges from the Corbisema hastata Zone to the N. constricta Zone. However, observations from this site and Site M0002 suggest that the range of C. glezerae extends to the top of the C. spinosa Zone in the Arctic Ocean.

Well-preserved specimens of C. ovalis were found in Samples 4X-CC, 15X-CC, and 18X-CC. In contrast to C. glezerae, C. ovalis was known to be present only in the C. hexacantha Zone (Perch-Nielsen 1985b), but this taxon was found in Cores 56X, 61X, and 62X; therefore, the range of C. ovalis can be extended into the C. spinosa Zone in the Arctic Ocean.

About two dozen specimens of Mesocena were found in Section 7X-CC and Cores 10X through 12X (Table T10). As the size of Mesocena is large (~90–110 µm), scanning the >45 µm size fraction at 100× magnification readily provides common specimens in addition to those observed in the standard census at 400× magnification. The following taxa also were encountered: M. apiculata inflata (with and without spines), Mesocena apiculata apiculata, and Mesocena occidentalis. Their ranges suggest a middle Eocene age. One exception is the presence (two specimens) of M. apiculata apiculata, which ranges from the upper Eocene to the middle Miocene (Perch-Nielsen, 1985b). The Arctic range of this taxon is hereby extended into the C. spinosa Zone of the lower to middle Eocene. The genus Mesocena is present approximately at the maximum abundance of the spores of the freshwater fern Azolla, which has an age of 49.2 Ma (see “Palynology, organic-walled dinoflagellate cysts”).

Paleoenvironment

Fluctuations in the abundances of Corbisema and ebridians are present in Hole M0004A and are similar to those present in Sample 302-M0002A-62X-CC. These two groups tended to occur in high numbers in Cores 302-M0004A-8X through 12X. Variable abundances of these taxa may be related to paleoenvironmental changes in the Arctic Ocean.

Silicoflagellate and paleoenvironment summary, Holes M0002A, M0004A, and M0004B

Based on the assemblages in Cores 302-M0002A-47X through 62X as well as 302-M0004A-4X through 18X, paleoclimatic conditions for the early Eocene through the middle Eocene were warm relative to those in the Arctic today. The presence of sporadic and rare (<1% of population) presences of Distephanus (cold-water hexagonal forms) and quadrate forms of the genus Dictyocha (e.g., Dictyocha crux crux; temperate water) may also have paleoclimatic significance.

The relatively high diversity of well-preserved distinctive silicoflagellate and ebridian assemblages appears to indicate that the Eocene environment in the central Arctic ranged from coastal neritic to hemipelagic (Fig. F12). It is possible that brackish water conditions existed with intrusions of pelagic waters indicated by the sporadic presence of radiolarians.

Radiolarians

Samples taken at Sites M0001–M0004 were barren of radiolarians except Samples 302-M0002A-49X-CC, 50X-CC, and 52X-CC. By treating samples for 20 s in an ultrasonic bath and resieving at 45 µm, the coarse residue was sufficiently concentrated to identify approximately a dozen specimens in four slides made from Sample 302-M0002A-49X-CC and fewer than six specimens in two slides from Sample 302-M0002A-50X-CC. A single unidentifiable specimen was seen in the fine fraction (<45 µm) in Sample 302-M0002A-52X-CC during the silicoflagellate census. The presence of Calocyclas talwanii and Botryostrobis joides indicates an age of middle to late Eocene (C. talwanii to Artostrobus quadriporus Zones) (Table T11), based on the work of Bjørklund (1976).

Work on modern radiolarians indicates that many of the species can live at depths below the pycnocline, but they do not generally tolerate salinities less than ~20 ppt (Bjørklund and Swanberg, 1987; Boltovskoy et al., 2003). Thus, the trace amount of radiolarians in Eocene samples, combined with the results from the dinocysts, silicoflagellates, ebridians, and diatoms, suggests a relatively brief incursion of pelagic waters may have occurred, perhaps at depths below the upper brackish waters of the Arctic Ocean.

Planktonic and benthic foraminifers and ostracodes

Hole M0001A

Shipboard analyses of foraminifers at Site M0001 were conducted using five core catcher samples from Section 1H-CC. Foraminifers from Samples 1H-CC, 0–2 cm, and 1H-CC, 14–16 cm, contained the planktonic species Neogloboquadrina pachyderma (sinistral) and several ostracode species. Sample 1H-CC, 26–28 cm, contained the agglutinated species Cyclammina pusilla and unidentified fragments of other species. Two additional Samples (1H-CC, 10–12 cm, and 1H-CC, 20–22 cm) contained C. pusilla and other agglutinated species.

Hole M0002A

Shipboard analyses of benthic foraminifers at Site M0002 were conducted using core catcher samples. Benthic foraminifers from Hole M0002A range in age from Miocene to Holocene and consist of both calcareous and agglutinated taxa. Calcareous benthic foraminifers were found only in Sample 1X-CC, where they were rare. The agglutinated benthic foraminiferal record recovered from Hole M0002A can be subdivided into the following four informal stratigraphic assemblage zones:

• Zone 1: Samples 1X-CC through 10X-CC contained rare to common abundances of agglutinated foraminifers dominated by C. pusilla, with lesser numbers of Recurvoides, Alveolophragmum, and Trochammina spp. intermittently present. The preservation state varies from fair to excellent. A reworked specimen of Haplophragmoides from either the Paleocene or Eocene was found in Sample 4X-CC.

• Zone 2: Samples 12X-CC through 34-X-CC contained no agglutinated foraminifers except very occasional fragments of unidentified genera.

• Zone 3: Samples 35X-CC through 42X-CC contained few to common agglutinated foraminifers including C. pusilla, Cyclammina aff. cancellata, Recurvoides, and Trochammina.

• Zone 4: Samples 44X-CC through 62X-CC were barren of benthic foraminifers.

The assemblages in the upper part of Zone 1 represent the agglutinated foraminiferal assemblages observed in numerous short cores from various ridges in the Arctic at ~2–7 mbsf (Ishman et al., 1996; Jakobsson et al., 2001; Backman et al., 2004). The agglutinated foraminiferal facies underlies sediments rich in calcareous microfossils deposited during and since about marine isotope Stage 5 (~127 ka). These agglutinated assemblages usually have been assigned ages of Pliocene to early Pleistocene. However, rigorous confirmation of their ages is usually lacking. Site M0002 is therefore important in extending the available record of agglutinated foraminifers from short cores down to at least 45 mbsf (Core 10X), which includes the Pleistocene and perhaps part of the Pliocene.

The analysis of assemblages in Zone 2 requires additional sampling to obtain more abundant foraminifers.

The assemblages in Zone 3 (Table T12) represent middle Miocene material. At present, the agglutinated assemblages cannot be correlated with other Miocene faunas from the region (in particular Leg 151 Site 909).

In summary, the material from Site M0002, when combined with that of Site M0004, offers an opportunity to develop a Cenozoic agglutinated foraminiferal biozonation for the Lomonosov Ridge region of the central Arctic Ocean.

Hole M0003A

Shipboard analyses of benthic and planktonic foraminifers at Site M0003 were conducted using core catcher samples. Benthic foraminifers from Sample 2H-CC, 14–19 cm, included the agglutinated taxa C. pusilla, Haplophragmoides sp., Trochammina sp., and Saccammina sp., which are typical of Pleistocene sediments containing common agglutinated foraminifers, which usually underlie the uppermost 1–2 m containing calcareous foraminifers.

Four samples from Section 3H-CC were examined, yielding the following results from different lithofacies:

• 3H-CC, 0–1 cm = olive layer, containing unidentified agglutinated foraminiferal fragments.

• 3H-CC, 2–3 cm = olive layer, containing rare Trochammina sp.

• 3H-CC, 2–5 cm = olive layer, with darker streaks of manganese, agglutinated foraminifers C. pusilla and Alveolophragmium polarensis, planktonic foraminifer N. pachyderma (sinistral), and fragments of ostracodes Polycope and Cytheropteron.

• 3H-CC, 4–5 cm = dark manganese layer containing agglutinated foraminifers C. pusilla, Haplophragmoides sp., and Recurvoides sp.; planktonic foraminifers N. pachyderma (sinistral) and Turborotalia quinqueloba; and calcareous benthic foraminifer Cassidulina.

These results suggest that well-preserved foraminifers are present in some lithofacies of Pleistocene sediments of the Lomonosov Ridge as deep as 19.3 meters composite depth (mcd) (see below).

Hole M0004A

Shipboard analyses of benthic foraminifers at Site M0004 were conducted using core catcher samples. Benthic foraminifers from Hole M0004A range in age from Campanian to early Eocene and consist entirely of agglutinated taxa. No calcareous microfossils were found in the samples, probably owing to dissolution (Table T13).

The agglutinated benthic foraminiferal record recovered from Hole M004A can be subdivided into three stratigraphically significant assemblages, discussed below from top to bottom:

1. Samples 4X-CC through 24X-CC were barren of any foraminifers. The uppermost sample containing foraminifers is Sample 27X-CC. This sample, along with the next deeper core catcher (28X-CC), contained a moderately diverse assemblage of agglutinated foraminifers containing the species Ammodiscus planus, Convallina spp., Haplophragmoides excavatus, Haplophragmoides perexilis, Psammosphaera eocenica, and Trochammina spp. and common Verneuilinoides subtilis and Verneuilinoides macintyrei. The assemblage is assigned an early Eocene age based on superposition and the presence of V. subtilis, which was described from the Paleocene–lower Eocene Aklak Formation of the Beaufort Sea (McNeil, 1997). The genus Verneuilinoides is also a frequent component of early Eocene assemblages in the Barents Sea described by Nagy et al. (2000). The genus is characteristic of neritic environments.

   Sample 29X-CC contains an unusual type of agglutinated foraminiferal assemblage in sediment with a large amount of quartz sand. The dominant taxa are coarsely agglutinated species of Lagenammina, Reophax, and Psammosphaera. The tubular form of Jaculella and a finely agglutinated species of Trochammina are also present. The taxa recorded in this sample are not age diagnostic but are characteristic of a shallow-marine environment. Assemblages with common Psammosphaera are known from the Paleogene of Spitsbergen, and Reophax-dominated assemblages are known from the Eocene of western Siberia (Podobina, 1998). Based on these comparisons, the environment is interpreted as inner neritic. Samples 30X-CC and 31X-CC are barren of foraminifers.

2. Beneath a barren interval containing only pyrite and fish remains, a diverse assemblage of agglutinated foraminifers is present in Sample 32X-CC. This assemblage is distinctive, containing three species of primitive Reticulophragmium that dominate the assemblage. The species Reticulophragmium ministicoogense, Reticulophragmium arcticum, and Reticulophragmium boreale are known from the upper Paleocene in the Beaufort Sea (McNeil, 1997). R. arcticum is known from Paleocene strata in Alaska and Spitsbergen. Primitive species of Reticulophragmium are also known from the Paleocene of the North Sea and Western Siberia. The genus may have evolved in the northern hemisphere during the middle Paleocene and is not known from Cretaceous strata. This “Reticulophragmium assemblage” also contains tubular forms such as Nothia and Rhabdammina, as well as A. planus, Haplophragmoides raindeerensis, Recurvoides sp., and Trochammina spp. The assemblage is present downhole to Sample 35X-CC. The age of the interval from Samples 32X-CC through 35X-CC is regarded as late Paleocene based on the FO of Reticulophragmium in Sample 35X-CC.

3. A completely different assemblage of agglutinated foraminifers was found in Samples 39X-CC through 42X-CC beneath an interval with no recovery. Agglutinated foraminifers in this assemblage are stained a medium yellowish brown color, perhaps indicating a higher level of thermal maturation of the enclosing sediment. The assemblage displays a high dominance of one Trochamminoides species. The assemblage is accompanied by rare specimens of Glaphyrammina spirocompressa, a species known from the Santonian to Campanian Smoking Hills sequence of the Beaufort-MacKenzie Basin. Another species present in Sample 41X-CC is Recurvoides cf. obskiensis, a taxon known from mid–Upper Cretaceous strata in the Norwegian offshore. Based on the low diversity, high dominance, and lack of any tubular forms, the environment is interpreted as inner neritic.

Hole M0004B

Shipboard analyses of benthic and planktonic foraminifers in Hole M0004B were conducted using two core catcher samples. Benthic foraminifers from Sample 1X-CC, 0–2 cm, contained rare C. pusilla and a single specimen of the planktonic foraminifer N. pachyderma (sinistral). Sample 3X-CC, 2–5 cm (~219 mbsf), was barren of foraminifers but contained many pyritized diatoms and other pyritized material, fish parts, and large unidentified spores.

Hole M0004C

Shipboard analyses of benthic and planktonic foraminifers in Hole M0004C were conducted using two core catcher samples. Benthic foraminifers from Sample 1X-CC, 0–2 cm, contained no foraminifers. Samples 2X-CC and 3X-CC, 0–2 cm, contained the agglutinated foraminifers C. pusilla, Reophax, Rhizammina, Ammodiscus, and Recurvoides. Sample 4X-CC contained a single specimen of the planktonic foraminifer N. pachyderma (sinistral); Sample 6X-CC was barren of foraminifers. Samples 8X-CC and 9X-CC contained the agglutinated taxon C. pusilla and unidentified fragments of agglutinated species. The sequence of foraminifers at this site is generally similar to those recovered from Holes M0002A and M0003A.

Pliocene and Pleistocene results summary

Previous studies have found that calcareous microfossils (benthic, planktonic foraminifers, and ostracodes) characterize the uppermost 1–2 m of sediments on ridges in various locations in the Arctic Ocean including the Lomonosov Ridge (Scott et al., 1989; Stein et al., 1994; Cronin et al., 1994, 1995; Evans and Kaminski, 1998).

The calcareous facies is underlain by predominantly agglutinated foraminiferal assemblages in many regions of the Arctic. The calcareous–agglutinated transition has been dated within marine isotope Stage 7 (Backman et al., 2004).

The calcareous–agglutinated transition was present at several sites and extended the depth of the predominantly agglutinated fauna to ~12–45 mbsf in Hole M0002A, >15 mbsf in Hole M0003A, and >14 mbsf in Hole M0004C (Table T14). However, sparse planktonic foraminifers are present in thin layers to 15 mbsf (= 19.3 mcd). By sampling a 1 cm dark layer in Sample 302-M0003A-3X-CC, 4–5 cm, we found N. pachyderma (sinistral) and T. quinqueloba. A single specimen of N. pachyderma was observed in Sample 302-M0004C-4H-CC (~18.4 mbsf = 17.1 mcd). Based on recent studies of N. pachyderma (sinistral) morphology, genetics, and stratigraphy, it is possible that the recent forms of this species had their first appearance at ~1.1 Ma and those from the earlier Pleistocene represent a different species (Kucera and Kennett, 2002).

Carbonate fossil preservation is intermittent at best down to 15 mbsf, and, as is the case with the uppermost few meters of Arctic sediments, fine-scale sampling is required to obtain calcareous material. The downcore appearance of what appear to be spherical (carbonate?) concretions begins near 20–30 mbsf. These first appear as small (~0.5 mm) rare barbell-shaped objects that increase in abundance and size downcore, often forming cemented accumulations of spheres. Peak abundances in these concretions occur in Hole M0002A at ~20–30, 50–63, and 117–123 mbsf before disappearing at ~155–170 mbsf, where major lithologic changes occur.

Cretaceous–Paleocene–Eocene results summary

The sequence of agglutinated foraminiferal assemblages found in Hole M0004A includes several distinct biofacies that have been recognized in circum-Arctic exposures and deep onshore and offshore wells. They can be used to reconstruct shallow-water marine depositional environments from prodeltaic–inner neritic to outer neritic–uppermost bathyal environments.

Palynology, organic-walled dinoflagellate cysts

In total, 98 samples were processed for organic-walled microfossils. Palynomorphs were distinguished in different categories, but only dinoflagellate cysts (dinocysts) were identified to genus and species level. Assignment of some species must be considered provisional because of poor preservation and strong morphological variability and because safety considerations precluded the use of hydrofluoric acid. The abundance of dinocysts from Neogene and Pleistocene sediments is particularly low because of dilution by siliciclastic components. Despite the variable abundances, a tentative biostratigraphy could be established based on the presence of a few age-diagnostic species.

Hole M0001A

Two samples from Hole M0001A were analyzed for palynomorphs. Sample 1H-CC, 0 cm, contained pollen (Pinus and Picea) and a few dinocysts assignable to the genus Brigantedinium. This assemblage may be indicative of the modern conditions in the area. Sample 1H-CC, 24 cm, was barren (see Table T15).

Hole M0002A

Core catcher samples and a few additional samples were processed for palynological studies, allowing the recognition of four intervals in Hole M0002A. The upper ~160 m has a rather patchy record, as almost half of the samples were barren of palynomorphs. Following a barren interval (~23 m), an interval spanning ~1 m (Samples 44X-CC through 45X-CC) contained a dominant organic-walled dinoflagellate cyst (dinocyst) with some reworking of older dinocysts and massively abundant terrestrial pollen and spores, in addition to probably freshwater to brackish water algal cysts. Below that unit, the remainder of the drilled succession (down to Sample 62X-CC) contained both marine and terrestrial palynomorphs in high abundances. Preservation was moderate to fair in most samples containing dinocysts. Reworked dinocysts, pollen, and spores were present in almost all samples. Some of these may be as old as Carboniferous.

The uppermost 50 m of Hole M0002A lacks true age-diagnostic taxa. The presence of abundant Filisphaera microornata in Sample 12X-CC (51.26 mbsf) indicates a late Miocene to early Pleistocene age for this interval (cf. Head, 1993). The specimens recorded on the Lomonosov Ridge are morphologically different from Filisphaera filifera s.s. but may contain specimens of the subspecies Filisphaera filifera pilosa. Relatively high abundances of Filisphaera filifera s.l. are reported from the Middle to Upper Pliocene sediments of Yermak Plateau, Fram Strait, and East Greenland (e.g., Matthiessen and Brenner, 1996; Smelror, 1999; Bennike et al., 2002), indicating a Pliocene age for Sample 12X-CC. The age of the uppermost 50 m (Core 1X through Section 12X-3) cannot be resolved further (see Table T16).

Evittosphaerula sp. 2 of Manum et al. (1989) was recorded in Samples 17X-CC, 18X-CC, and 23X-CC (76.08–101.32 mbsf). It has a widespread distribution in Miocene sediments from the Norwegian-Greenland Seas and the Labrador Sea (Manum et al., 1989; Head et al., 1989; Poulsen et al., 1996). The total stratigraphic range in the high northern latitudes appears to be from the uppermost Serravallian to the lower Messinian, but higher abundances seem to be restricted to the Tortonian. Poulsen et al. (1996) recorded its first occurrence and subsequent acme interval in Core 151-908A-20X. That interval may correlate to the base of Chron C3Bn (Hull et al., 1996). This species has its last occurrence at the base of Core 151-908A-19X, approximating the top of Chron C3An (see Hull et al., 1996), giving a total age range of its acme from 5.9 to 7.1 Ma. It is here assumed that Evittosphaerula sp. 2 of Manum et al. (1989) migrated northward into the Arctic Ocean at the time of the acme in the Fram Strait, suggesting a similar age for its occurrence in Hole M0002A. The presence of Bitectatodinium? serratum confirms a late Miocene age for Sample 23X-1, 11–13 cm. It has previously been described from the Labrador Sea only (Leg 105 Hole 646B), from an interval assigned to nannoplankton Zones NN10 to mid-NN11 (Head et al., 1989a), which is consistent with our results based on dinocyst biostratigraphy.

As Samples 13X-CC, 14X-CC, and 15X-CC were barren of dinocysts, except for a single specimen of Filisphaera sp., the upper Miocene/Pliocene boundary must be placed between Cores 12X-CC and 17X-CC.

Habibacysta tectata is present from Sections 23X-1 through 35X-1, between 101.32 and 154.06 mbsf. This species has its first occurrence in the northern mid-latitudes during the middle Miocene at 14 Ma (Williams et al., 2004), suggesting an age not older than Serravallian for Section 35X-1. The presence of a single specimen of Operculodinium janduchenei in Sample 35X-1 is consistent with this assignment because it has a recorded range from lower Miocene to Upper Pliocene (e.g., Head et al., 1989a). The LO of H. tectata is not well defined, but it had its last appearance on the Yermak Plateau in Leg 151 Hole 911A in the lower Pleistocene (Matthiessen and Brenner, 1996). Its co-occurrence with Evittosphaerula sp. 2 of Manum et al. (1989) in Sample 23X-CC indicates that its range may be restricted in the central Arctic Ocean to the middle and upper Miocene (see Table T16).

The presence of a single specimen of B.? serratum in Sample 35X-1 may extend its range into the middle Miocene. Species of Impagidinium (Impagidinium japonicum, Impagidinium major, Impagidinium pallidum, and Impagidinium velorum) that occur in the same interval as H. tectata are not age diagnostic, but I. major has previously been recorded (only once) from nannoplankton Zone NN10 (Tortonian) in the Labrador Sea (Head et al., 1989a). Samples 302-M0002A-38X-CC through 44X-1 are palynologically barren.

The age assessment of the interval represented by Samples 44X-CC and 45X-CC is problematic. Although some taxa present in Sample 44X-CC suggest a Rupelian (early Oligocene) or, more likely, Chattian (late Oligocene) age, others indicate older intervals. Moreover, Sample 45X-CC yielded a monotypic assemblage of a new peridinioid taxon (genus et sp. indet. B) of which no age indication is available. The same sample thus has apparently reworked elements ranging in age from Cretaceous, earliest Eocene, middle Eocene, late Eocene, to early Oligocene (e.g., isolated specimens of Cribroperidinium muderongense, Apectodinium augustum, Glaphyrocysta semitecta, Phthanoperidinium amoenum, Svalbardella cooksoniae, and Wetzeliella gochtii). Thus, the age of the interval 44X-CC to 45X-CC may not be older than (early) Oligocene but is more likely to be much younger (late early Miocene?). Significantly, the reworked taxa suggest that sediments of late middle Eocene to Oligocene age were once present in the area (see Table T16).

Interval 46X-CC through 62X-CC has a similar palynological composition throughout, including massive abundances of the Phthanoperidinium echinatum group and Senegalinium spp., with isolated Thalassiphora delicata, Cerodinium depressum, and Phthanoperidinium clithridium (with the exception of Sample 47X-CC, which is dominated by Impagidinium spp.). In addition, there are consistent occurrences of an intermediate form between Lentinia wetzelii and Lentinia serrata. Combined provisional evidence thus suggests an age of ~45.5 Ma (Chron C20r) and older for this interval, applying the scheme of Eldrett et al. (2004) from Leg 151 Hole 913B. Alternatively, if the form described above can be attributed to L. serrata and the specimens of P. clithridium and C. depressum are reworked, then the age may be as young as mid-Bartonian (middle Eocene, ~40 Ma). However, many typical Bartonian species, also known from an interval of that age from Leg 151 Hole 913B (e.g., Firth, 1996), are conspicuously missing in Hole M0002A.

The interval between Samples 46X-CC and 62X-CC is also characterized by high abundances of terrestrial palynomorphs in addition to abundant, remarkably large (>500 µm) spherical phycomata(?) of Tasmanites spp. (= gen. et sp. indet. A in Table T17). From Sample 60X-CC downhole, the moderately diversified dinocyst assemblage is joined by a new distinctly elongated and large species of Operculodinium—Operculodinium cf. microtriainum. The biostratigraphic significance of this taxon is unknown.

The bottom age of Hole M0002A (Sample 62X-CC) is, in view of only minor compositional changes from the interval between Samples 46X-CC and 62X-CC, thought to be comparable (i.e., on the order of ~45–46 Ma). The FO of P. clithridium is reported to be at 46.2 Ma (Eldrett et al., 2004) (see Table T16).

Preliminary paleoenvironmental interpretation

Most dinocyst taxa recorded in the Neogene sediments of Hole M0002A have a restricted geographic distribution in the northern high latitudes. Filisphaera spp., Evittosphaerula sp. 2 of Manum et al. (1989), I. japonicum, I. major, and I. pallidum prefer cool–temperate to cold (ice margin) waters. H. tectata lived in cool–temperate to subtropical conditions but apparently preferred cooler conditions (e.g., Head, 1994). I. velorum and O. janduchenei are more widely distributed in northern hemisphere Paleogene, Neogene, and Quaternary sediments but are mainly associated with cooler intervals (e.g., Brinkhuis and Biffi, 1993; Versteegh et al., 1996).

Nematosphaeropsis labyrinthus and Spiniferites ramosus are cosmopolitan species (e.g., Marret and Zonneveld, 2003). Thus, the ecological preferences of the taxa suggest that cold to cool-water but seasonally ice-free conditions occurred during the Neogene at the Lomonosov Ridge or were influenced by such settings. Barren samples might be indicative of perennial sea ice cover, postmortem degradation, or absence of cyst-forming species.

The presence of freshwater algae of the genera Botryococcus and Pediastrum is a distinct signal in some Neogene and Quaternary sediments. In particular, Sample 1X-CC contains abundant freshwater algae. Comparable acmes of Pediastrum have been found in a sediment core from the Alpha Ridge (Mudie, 1985). The occurrence of freshwater algae is clearly related to river run-off from large rivers draining into the Arctic Ocean (Matthiessen et al., 2000). These algae are incorporated into sea ice during formation in autumn and winter and are further transported via the Transpolar Drift or the Beaufort Gyre.

The monotypic assemblages of gen. et sp. indet. B in Samples 44X and 45X, together with the pronounced terrestrial and freshwater and/or brackish water algal components, strongly indicate restricted marine, brackish water (estuarine?) conditions for this interval.

In general, the only moderately diversified assemblages below Sample 45X-CC (down to the bottom of the hole) are mainly composed of typical high-latitude Eocene taxa and mainly represent heterotrophic dinoflagellates (Brinkhuis et al., 2004a, 2004b). The concomitant abundance of siliceous microfossils throughout indicates a highly eutrophic setting (Reichart and Brinkhuis, 2003). Meanwhile, runoff-related low salinity might be indicated by the abundance of terrestrial palynomorphs and the phycomata of chlorophytes such as Tasmanites. The absence of benthic biota (see “Planktonic and benthic foraminifers and ostracodes”) and the high organic matter content indicate suboxic to anoxic bottom conditions at this time, such as the highly stratified, restricted marine, poorly ventilated waters of the modern Black Sea.

The exception to this is Sample 47X-CC, which is dominated by Impagidinium spp., roughly assignable to the cosmopolitan Eocene taxon Impagidinium dispertitum. In modern oceans, most Impagidinium consistently occur in tropical to subtropical, oligotrophic oceanic environments (e.g., Wall et al., 1977; Rochon et al., 1999; Marret and Zonneveld, 2003). Only I. pallidum characterizes polar environments today. The composition of the dinocyst assemblage of Sample 47X-CC is thus indicative of warm and oligotrophic surface water conditions. Yet, terrestrial palynomorphs and the phycomata remain prominent in this sample, suggesting the continual influence of runoff.

The anomalous Sample 47X-CC may thus reflect a short-lived phase of warm conditions at the end of the middle Eocene. Bohaty and Zachos (2003) have recently documented such a phase, occurring at ~41.5 Ma in the Southern Ocean, coined the Middle Eocene Climatic Optimum.

Hole M0003A

Three core catcher samples (1H-CC, 22–27 cm, 2H-CC, 14–19 cm, and 3H-CC, 3–5 cm) were analyzed for palynomorphs. All samples were barren except for a single specimen of bisaccate pollen (Pinus) in the uppermost and lowermost samples (see Table T18).

Hole M0004A

Samples from core catchers (4X-CC through 42X-CC) and a few additional samples yielded well-preserved and generally rich palynological associations. A number of dinocyst and other events have reasonably well constrained age calibrations (Table T19), providing an age model for the cored succession (Table T20). Hole M0002A was abandoned after reaching levels assignable to the mid-Lutetian. Despite overall poor recovery, Hole M0004A represents its continuation and penetrated the older Arctic Paleogene and even the Upper Cretaceous record.

The middle/lower Eocene (Lutetian/Ypresian) and Paleocene/Eocene (Thanetian/Ypresian) boundaries may be recognized using abundance peaks of the freshwater fern Azolla spp. and dinocysts assignable to the (sub)tropical genus Apectodinium (particularly A. augustum), respectively. Note that here we follow the recently revised concept of the position of the Paleocene/Eocene boundary (i.e., the base of the carbon isotope event [CIE] at the Global Stratotype Section and Point [GSSP] in Egypt). This means that the oldest Apectodinium acme, and the range of A. augustum, is now placed in the lowermost Eocene.

The FO and LO of the acme of Azolla spp. have been calibrated against magnetostratigraphy in ODP Leg 151 Hole 913B (Eldrett, 2003; Eldrett et al., 2004), indicating that the base of the middle Eocene must be placed between Sections 10X-CC and 11X-CC. The entire (short) range of A. augustum marks the lowermost Eocene interval and its well-known “thermal maximum,” called the Paleocene/Eocene Thermal Maximum (PETM) (cf. Zachos et al., 2001) throughout the northern hemisphere (i.e., sensu the new GSSP). The base of the Eocene thus occurs in Core 32X. An overlying continuous and expanded lower Eocene record is demonstrated by the subsequent Cerodinium wardenense and Deflandrea oebisfeldensis acme intervals, which, in turn, are overlain by the FO of the Wetzeliella articulata-hampdenensis complex (Table T20). This succession is well known from among other places (e.g. the entire North Sea Basin) and the entire North Atlantic region, including the Norwegian, Greenland, Beaufort, and Barents Basins, albeit mostly from industry wells (H. Brinkhuis, unpubl. data; J.P. Bujak, pers. comm., 2004). The PETM is calibrated against the lower part of Chron C24r. Its onset has an age of 54.98 Ma, and the PETM spans ~200 k.y. (Röhl et al., 2000). The underlying succession does not truly yield age-diagnostic dinocysts. Yet, because no sedimentological break is apparent downhole until Sample 35X-CC, it appears that the interval underlying the PETM may tentatively be regarded as representing the uppermost Paleocene (see Tables T19, T20).

Stratigraphically below the PETM, the assemblage from Sample 34X-CC has a Paleocene character, with the occurrence of Deflandrea denticulata and Membranosphaera spp. (e.g., Heilmann-Clausen, 1985). This contrasts with assemblages from the underlying Sample 35X-CC, where isolated specimens of the late Cretaceous dinocysts Chatangiella verrucosa and Palaeohystrichophora infusorioides and the lack of typical Paleocene dinocysts in the midst of rich but non-age-diagnostic sporomorphs may well indicate a (early) Campanian age. Alternatively, these specimens may represent late Paleocene reworking of the underlying sedimentary bedrock.

Samples also rich in sporomorphs but totally dominated by typical mid–Late Cretaceous species of Chatangiella have been recorded from Sample 39X-CC and further downhole. Despite a few co-occurring Paleogene dinocysts, this aspect, including major changes in palynofacies and organic maturity, strongly suggests that Sample 39X-CC is early Campanian or older in age and that a major unconformity sits above it (see Tables T19, T20).

Conspicuously, there was no core recovery between Samples 35X and 39X. The agglutinated benthic foraminifer assemblage (see “Planktonic and benthic foraminifers and ostracodes”) of Sample 35X-CC is apparently of Paleocene aspect and indicative of shallow-marine environments. This agrees with a palynological assemblage dominated by sporomorphs, although it is remarkable that no Paleocene dinocysts were found. The few Cretaceous dinocysts found in Sample 35X-CC may thus indeed represent reworking from the directly underlying sedimentary bedrock during the late Paleocene. It therefore appears that the latter sample marks the base of the Paleocene succession overlying the unconformity because cores could not be retrieved from the underlying 20 m (see Tables T19, T20).

Preliminary paleoenvironmental interpretation

The rather mature Campanian assemblages are dominated by sporomorphs, notably spores, and comprise many representatives of the probable heterotrophic dinocyst Chatangiella. This aspect suggests nearshore conditions at this time, in agreement with the interpretation of the co-occurring agglutinated benthic foraminifer assemblages (see “Planktonic and benthic foraminifers and ostracodes”). Both the lithology and the palynomorph assemblages are distinctly different from those in the organic-rich black muds of Core Fl-533 and the laminated biosiliceous ooze of Cores Fl-437 and the Canadian Expedition to Study the Alpha Ridge (CESAR) 6 that were deposited at the Alpha Ridge in high-productivity environments (perhaps due to upwelling) in the Campanian to Maastrichtian (e.g., Firth and Clark, 1998).

The upper Paleocene–lower Eocene palynological associations are generally dominated by sporomorphs and only occasionally by dinocysts. The dinocyst assemblages are usually dominated by Senegalinium spp., except for the Apectodinium-dominated PETM interval (Samples 30X-CC and 31X-CC). Additional elements in the lower Eocene are D. oebisfeldensis, C. wardenense, and, in younger strata, the Cerodinium striatum–D. denticulata complex. Environmental conditions apparently did not vary significantly during the later Paleocene to the early middle Eocene.

Sporomorphs disappear completely at about the end of the early Eocene (Ypresian) only to return by early middle Eocene (Lutetian) times. The dominance of cysts of probable heterotrophic dinoflagellates (mainly Senegalinium spp. and Cerodinium/Deflandrea spp.), some of them possibly being tolerant of freshwater conditions, and the concomitant abundance of diatoms and silicoflagellates from Samples 4X-CC through 18X-CC overall indicate eutrophic conditions. The low diversity of the dinocyst assemblages may indicate reduced sea-surface salinities. In the middle of this succession (Cores 11X and 12X), there is an extremely dense concentration of remains of the hydropterid (freshwater) fern Azolla—unprecedented in other Eocene sections yielding Azolla. The event testifies to an extreme change in environmental conditions at the base of the lower middle Eocene (Lutetian). A distinct acme of Azolla spp. has previously been recognized across northern high and mid-latitudes from many marine and even deep marine settings (as transported elements) (e.g., Boulter and Manum, 1989; Eldrett, 2003; Eldrett et al., 2004; J.P. Bujak and H. Brinkhuis, unpubl. data). In an unpublished Ph.D. thesis concerning Leg 151 Site 913, J.S. Eldrett showed that the Azolla maximum can be calibrated to mid-Chron C22n (~49.2 Ma). Note that the concentrations of Azolla remains recovered during Expedition 302 are several orders of magnitude higher than those recorded elsewhere. Yet, apparently microfossils indicative of marine environments (dinocysts, silicoflagellates, and diatoms) continue to occur in the assemblages in samples studied to date.

The acme of (sub)tropical Apectodinium spp. is of global paleoenvironmental significance because it reflects a pronounced short-term warming at the onset of the Eocene (i.e., the PETM) (e.g., Bujak and Brinkhuis 1998; Crouch et al., 2001, 2003a, 2003b; Röhl et al., in press). It has been shown to occur synchronously across hemispheres and to precisely coincide with the onset of the so-called PETM CIE and benthic extinction event. Dinocyst assemblages containing common Apectodinium were also recovered from intrabasaltic sediments of the lower basalt series at ODP Leg 104 Site 642 (Boulter and Manum, 1989) that were dated by a single radiometric age at 57.8 ± 1.0 Ma. This suggests a similar age range in the arctic regions. Multiple acmes of Apectodinium have been reported from the late Paleocene and early Eocene in the literature (e.g., Iakovleva et al., 2001; Crouch et al., 2003a, 2003b), but a large number of published and unpublished (oil exploration) studies have shown that A. augustum is strictly confined to the PETM itself (see summary in Bujak and Brinkhuis, 1998).

Hole M0004B

Samples 1X-CC and 3X-CC were analyzed for palynomorphs. Sample 1X-CC was barren. Sample 3X-CC contains an assemblage comparable to that found in cores of Hole M0002A (see Table T21).

Hole M0004C

Six core catcher samples and one additional sample were analyzed for palynomorphs. All samples were barren of dinocysts except for Sample 6X-2, which contained rare H. tectata. The last occurrence of H. tectata is not well defined, but it has its last appearance on the Yermak Plateau in Leg 151 Hole 911A in the lower Pleistocene, approximately at the base of the Jaramillo Subchron (Matthiessen and Brenner, 1996). Based on lithologic correlation to Hole M0002A, the base of Hole M0004C is not older than Pliocene. Therefore, Samples 1H-CC through 4H-CC are probably younger than 1 Ma (see Tables T22, T23).

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