Cenozoic planktonic foraminifera of the Falkland Plateau and Argentine Basin

Sites 511 and 512 (Falkland Plateau) and 513 (Argentine Basin) penetrated calcareous-siliceous oozes of the middle and upper Eocene and lower Oligocene with rather numerous planktonic foraminifers. Upper Oligocene, Miocene, Pliocene, and Quaternary sections are composed mostly of siliceous sediments (Sites 511-514) where planktonic foraminifers are rare or absent. High-latitude planktonic foraminifers of the Austral Province are characterized by impoverished assemblages - only representatives of Globigerina, Globigerinita, Globorotaloides, and Globorotalia with a rounded peripheral margin are found. In the Paleogene, these species are supplemented, in lesser amounts, by representatives of Globigerapsis, Acarinina, Pseudogloboquadrina, Pseudohastigerina, and Chiloguembelina. Assemblages of planktonic foraminifers have low stratigraphic resolution, especially in the upper Oligocene-Quaternary. This reflects the generally deteriorating Cenozoic climate, which evinced a sharp change in the upper Oligocene that is connected with initiation of the circum-Antarctic current near the Paleogene/Neogene boundary. Comparison of Paleogene and Neogene planktonic foraminifers of the South Atlantic (Falkland Plateau, Argentine Basin, 46-51°S) and the North Atlantic (Rockall Plateau, 55-56°N) indicates that the South Atlantic climate was much colder than that of the same latitudes of the North Atlantic. Paleogene oozes of the Falkland Plateau rest unconf ormably on Maestrichtian sediments and in their turn are overlain unconformably by Neogene-Quaternary oozes. Cenozoic sections are stratigraphically discontinuous: periods of intensive biogenic sedimentation resulting in a thick succession of sediments alternated with periods of nondeposition and strong erosion that resulted in hiatuses and unconformities. In the Argentine Basin, Oligocene calcareous-siliceous oozes rest on basalts of the oceanic basement; they are replaced upward in the section by Neogene-Quaternary siliceous oozes with some hiatuses. Planktonic foraminifers here clearly demonstrate the processes of oceanic subsidence and CCD fluctuations as well as Polar Front migrations during Cenozoic time. Fifty species of planktonic foraminifers are discussed and illustrated.

Planktic foraminifera from the Paleocene-Eocene Thermal Maximum at Shatsky Rise, Pacific Ocean

High-resolution biostratigraphic and quantitative studies of subtropical Pacific planktonic foraminiferal assemblages (Ocean Drilling Program, Leg 198 Shatsky Rise, Sites 1209 and 1210) are performed to analyse the faunal changes associated with the Paleocene-Eocene Thermal Maximum (PETM) at about 55.5 Ma. At Shatsky Rise, the onset of the PETM is marked by the abrupt onset of a negative carbon isotope excursion close to the contact between carbonate-rich ooze and overlying clay-rich ooze and corresponds to a level of poor foraminiferal preservation as a result of carbonate dissolution. Lithology, planktonic foraminiferal distribution and abundances, calcareous plankton and benthic events, and the negative carbon isotope excursion allow precise correlation of the two Shatsky Rise records. Results from quantitative analyses show that Morozovella dominates the assemblages and that its maximum relative abundance is coincident with the lowest delta 13C values, whereas subbotinids are absent in the interval of maximum abundance of Morozovella. The excursion taxa (Acarinina africana, Acarinina sibaiyaensis, and Morozovella allisonensis) first appear at the base of the event. Comparison between the absolute abundances of whole specimens and fragments of genera demonstrate that the increase in absolute abundance of Morozovella and the decrease of Subbotina are not an artifact of selective dissolution. Moreover, the shell fragmentation data reveal Subbotina to be the more dissolution-susceptible taxon. The upward decrease in abundance of Morozovella species and the concomitant increase in test size of Morozovella velascoensis are not controlled by dissolution. These changes could be attributed to the species' response to low nutrient supply in the surface waters and to concomitant changes in the physical and chemical properties of the seawater, including increased surface stratification and salinity. Comparison of the planktonic foraminiferal changes at Shatsky Rise to those from other PETM records (Sites 865 and 690) highlights significant similarities, such as the decline of Subbotina at the onset of the event, and discrepancies, including the difference in abundance of the excursion taxa. The observed planktonic foraminifera species response suggests a warm-oligotrophic scenario with a high degree of complexity in the ocean structure.

Planktonic foraminiferal stratigraphy of sediments from ODP Leg 173 sites

Planktonic foraminifers recovered from five sites drilled off western Portugal during Ocean Drilling Program Leg 173 are documented. Hole 1065A yielded planktonic foraminifers from Miocene sediments in Sections 173-1065A-1R-1 through 6R-2. Hole 1067A penetrated middle Eocene sediments containing planktonic foraminifers in Section 173-1067A-1R-1 through Lower Eocene planktonic foraminiferal horizons to Section 12R-CC. Hole 1068A yielded planktonic foraminiferal assemblages from middle Eocene sediments at Section 173-1068A-1R-1 to Maastrichtian sediments at Section 173-1068A-15R-3, whereas Hole 1069A contained middle Eocene taxa in Section 173-1069A-1R-1 through Campanian/Maastrichtian forms in Section 173-1069A-15R-2. All of the planktonic foraminifers recovered from these sites are of poor to moderately good preservation and are variable in abundance. Hole 1070A yielded only six planktonic foraminifers, with the assemblages being dominated by benthic foraminifers and fish teeth. The co-occurrence of other microfossil groups, including benthic foraminifers, are only briefly discussed here. The lower Miocene biosiliceous facies recorded in Hole 1065A is considered to be coeval with a similar facies found in onshore sections farther to the east, in southern Spain.

Stable carbon and oxygen isotope ratios of Paleogene planktonic foraminifera from the Maud Rise

The oxygen and carbon isotopic composition has been measured for numerous Paleogene planktonic foraminifer species from Maud Rise, Weddell Sea (ODP Sites 689 and 690), the first such results from the Antarctic. The results provide information about large-scale changes in the evolution of temperatures, seasonally, and structure of the upper water column prior to the development of a significant Antarctic cryosphere. The early Paleocene was marked by cooler surface-water conditions compared to the Cretaceous and possibly a less well developed thermocline. The late Paleocene and early Eocene saw the expansion of the thermocline as Antarctic surface waters became warm-temperate to subtropical. The late Paleocene to early Eocene thermal maximum was punctuated by two brief excursions during which time the entire Antarctic water column warmed and the meridional temperature gradient was reduced. The first of these excursions occurred at the Paleocene/Eocene boundary, in association with a major extinction in deep sea benthic foraminifers. The second excursion occurred within the early Eocene at ~54.0 Ma. These excursions are of global importance and represent the warmest intervals of the entire Cenozoic. The excursions were associated with fundamental changes in deep-water circulation and global heat transport. The thermal maximum of the early Eocene ended with the initiation of a long-term cooling trend at 52.0 Ma. This cooling trend was associated with reduced seasonality, and diminished structure and/or duration of the seasonal thermocline. The cooling trend was punctuated by three major cooling steps at 43.0, 40.0, and -36.0 Ma.

Late Campanian and Maastrichtian benthic foraminifera of El Kef, Tunesia

Late Campanian through Maastrichtian sea-level changes are examined based on lithology, macrofossils and benthic foraminifera at the Elles and El Kef sections in Tunisia. Six major sea-level regressions are identified during the late Campanian (74.4-74.2 Ma, 74.0-72.5 Ma), the Campanian-Maastrichtian transition (72.2-70.3 Ma), early Maastrichtian (69.6-69.3 Ma, 68.9-68.3 Ma), and late Maastrichtian (~65.5 Ma). Correlation of the Maastrichtian sea-level regressions with the oxygen isotope record of DSDP Site 525 in the middle latitude South Atlantic reveals that they coincide with episodes of high latitude cooling and appear to be of eustatic origin.

Cretaceous stable isotopic record and sea surface temperture estimation for ODP Site 207-1259

The Turonian (93.5 to 89.3 million years ago) was one of the warmest periods of the Phanerozoic eon, with tropical sea surface temperatures over 35°C. High-amplitude sea-level changes and positive d18O excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth. New d18O data from the tropical Atlantic show synchronous shifts ~91.2 million years ago for both the surface and deep ocean that are consistent with an approximately 200,000-year period of glaciation, with ice sheets of about half the size of the modern Antarctic ice cap. Even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets, calling into question the common assumption that the poles were always ice-free during past periods of intense global warming.

Calcareous nannofossil stratigraphy and datums of sediments from ODP Leg 198 sites

During Ocean Drilling Program Leg 198, Sites 1207, 1208, 1212, 1213, and 1214 were drilled on Shatsky Rise, coring Lower to mid-Cretaceous successions of nannofossil chalk, porcellanite, and chert. Although recovery was poor, these sites yielded an outstanding record of calcareous nannoplankton, providing valuable data concerning the evolutionary succession and paleobiogeography of the largest Cretaceous marine habitat. Mid-Cretaceous sections (Aptian-Cenomanian) were recovered at all sites, and Site 1213 includes an apparently complete Berriasian-Hauterivian section. Biostratigraphic dating is problematic in places because of the absence or rarity of zonal fossils of both Boreal and Tethyan affinity. The majority of nannofossil assemblages are relatively typical of this age, but there are clear differences that set them apart from coeval epicontinental assemblages: for example, Lithraphidites carniolensis is common to abundant throughout and was most likely an oceanic-adapted taxon; the cold- to temperate-water species Crucibiscutum salebrosum, Repagulum parvidentatum, and Seribiscutum primitivum are entirely absent, indicating the persistence of tropical, warm surface water temperatures; and the warm-water species Hayesites irregularis is common. Most striking, however, is the virtual absence of Nannoconus and Micrantholithus, both taxa that were conspicuous and often common components of many Tethyan and Atlantic nannofloras. These forms were almost certainly neritic adapted and usually absent in deep open-ocean settings away from guyots and platforms. Other Tethyan taxa are also absent or rare and sporadically distributed (e.g., Calcicalathina oblongata, Conusphaera spp., Tubodiscus verenae, and Lithraphidites bollii), and factors related to neritic environments presumably controlled their distribution. Site 1213 also records extended Early Cretaceous ranges for species previously thought to have become extinct during the Late Jurassic (e.g., Axopodorhabdus cylindratus, Hexapodorhabdus cuvillieri, and Biscutum dorsetensis), suggesting these species became Pacific-restricted prior to their extinction. Watznaueria britannica may also have been a species with Pacific affinities before reexpansion of its biogeography in the early Aptian. One new genus (Mattiolia) and thirteen new species (Zeugrhabdotus clarus, Zeugrhabdotus petrizzoae, Helicolithus leckiei, Rhagodiscus amplus, Rhagodiscus robustus, Rhagodiscus sageri, Rhagodiscus adinfinitus, Tubodiscus bellii, Tubodiscus frankiae, Gartnerago ponticula, Haqius peltatus, Mattiolia furva, and Kokia stellata) are described from the Shatsky Rise Lower Cretaceous section.

Planktonic foraminifera in late Eocene to Pleistocene sediments of ODP Hole 120-747A and 120-749B

Late Eocene to Pleistocene planktonic foraminifers from Leg 120 Holes 747A and 749B on the Kerguelen Plateau were quantitatively analyzed. Microperforate tenuitellid forms dominate the Oligocene to middle Miocene, and 17 species (including the new species Tenuitella jamesi and Tenuitellinata selleyi) are recorded. A lineage zonation of tenuitellid foraminifers is proposed as an alternative scheme for refinement of the Oligocene-Miocene biostratigraphy in high latitudes. Progressive or abrupt alterations in morphological characters within this lineage, producing different morphotypes or species, coincided with prolonged or sudden changes in paleoclimate. These microperforate planktonic foraminifers thus appear to have potential as indicators of cold-water masses and temperature fluctuations in post-Eocene oceans.

Cretaceous planktonic foraminifera of the Kerguelen Plateau

An almost complete Upper Cretaceous sedimentary sequence recently recovered on the Kerguelen Plateau (southern Indian Ocean) during ODP Leg 183 was analysed for planktonic foraminifera in order to refine and integrate the zonal schemes previously proposed for the Southern Ocean area. Detailed biostratigraphic analysis carried out on holes 1135A, 1136A and 1138A (poleward of 50°S palaeolatitude during Late Cretaceous time) has allowed recognition of low and mid-high latitude bioevents, useful for correlation across latitudes, in addition to known Austral bioevents. The low latitude biozonation can be applied to Turonian sediments, because of the occurrence of Helvetoglobotruncana helvetica, which marks the boundary between Whiteinella archaeocretacea and Helvetoglobotruncana helvetica zones. The base of the Whiteinella archeocretacea Zone falls within the uppermost Cenomanian-Turonian black shale level in Hole 1138A. The stratigraphic interval from upper Turonian to uppermost Santonian can be resolved using bioevents recognized in the mid-high latitude sections. They are, in stratigraphic order: the last occurrence of Falsotruncana maslakovae in the Coniacian, the first occurrence of Heterohelix papula at the Coniacian/Santonian boundary, the extinction of the marginotruncanids in the late Santonian, and the first occurrence of Globigerinelloides impensus in the latest (?) Santonian. The remainder of the Late Cretaceous fits rather well in the Austral zonal scheme, except that Globigerinelloides impensus exhibits a stratigraphic range in agreement with its record at the mid-high latitude sections and extends further downwards than previously recorded at southern sites. Therefore, despite the poor recovery in certain intervals and the presence of several hiatuses of local and regional importance as revealed by correlation among holes, a more detailed zonal scheme has been obtained (mainly for the less resolved Turonian-Santonian interval). Remarks on some species often overlooked in literature are also provided.

Foraminiferal assemblages and stable isotopes across the early Paleogene carbonate facies of Perth Abyssal Plain off Western Australia

Bulk carbonate content, planktic and benthic foraminiferal assemblages, stable isotope compositions of bulk carbonate and Nuttallides truempyi (benthic foraminifera), and non-carbonate mineralogy were examined across ~30 m of carbonate-rich Paleogene sediment at Deep Sea Drilling Project (DSDP) Site 259, on Perth Abyssal Plain off Western Australia. Carbonate content, mostly reflecting nannofossil abundance, ranges from 3 to 80% and generally exceeds 50% between 35 and 57 mbsf. A clay-rich horizon with a carbonate content of about 37% occurs between 55.17 and 55.37 mbsf. The carbonate-rich interval spans planktic foraminiferal zones P4c to P6b (~57-52 Ma), with the clay-rich horizon near the base of our Zone P5 (upper)-P6b. Throughout the studied interval, benthic species dominate foraminiferal assemblages, with scarce planktic foraminifera usually of poor preservation and limited species diversity. A prominent Benthic Foraminiferal Extinction Event (BFEE) occurs across the clay-rich horizon, with an influx of large Acarinina immediately above. The delta13C records of bulk carbonate and N. truempyi exhibit trends similar to those observed in upper Paleocene-lower Eocene (~57-52 Ma) sediment from other locations. Two successive decreases in bulk carbonate and N. truempyi delta13C of 0.5 and 1.0? characterize the interval at and immediately above the BFEE. Despite major changes in carbonate content, foraminiferal assemblages and carbon isotopes, the mineralogy of the non-carbonate fraction consistently comprises expanding clay, heulandite (zeolite), quartz, feldspar (sodic or calcic), minor mica, and pyrolusite (MnO2). The uniformity of this mineral assemblage suggests that Site 259 received similar non-carbonate sediment before, during and after pelagic carbonate deposition. The carbonate plug at Site 259 probably represents a drop in the CCD from ~57 to 52-51 Ma, as also recognized at other locations.

Oligocene and lowermost Miocene diatom stratigraphy and datums of ODP Site 199-1220 sediments

Completion of studies on material collected during Ocean Drilling Program Leg 199 at Site 1220 in the equatorial Pacific allows calibration of the ranges of >35 stratigraphically important diatoms to paleomagnetic stratigraphy for the Oligocene and earliest Miocene (~33.5-21.5 Ma). The taxonomy of these taxa is reviewed, and age estimates of their first and last occurrences are compiled. The diatom zonation for the Oligocene and earliest Miocene of the equatorial Pacific is revised and correlated with paleomagnetic stratigraphy. This biostratigraphy is likely to be applicable throughout the low-latitude regions of the world's oceans.

(Table 5) Distribution of benthic foraminifers in the late Cretaceous of DSDP Hole 71-511

The book is devoted to stratigraphy of Cretaceous deposits from high latitudes of the southern hemisphere (subantarctic part of the ocean), as well as to geological and climatic Cretaceous history of the area. Correlation with Cretaceous sediments from warm water regions is carried out. Description and photos of characteristic species of planktonic and benthic foraminifera and calcispherulides are given.

Paleogene planktonic foraminifera of DSDP Hole 29-277

Stratigraphy of Paleogene deposits from high latitudes of the Pacific region (Koryak Highland, Kamchatka Peninsula, Karaginsky Island - in the northern hemisphere, Australian-Antarctic region - in the southern hemisphere) on planktonic foraminifera are under consideration in the book. Correlation with Paleogene of the warm Pacific belt is given. On the basis of geographic and stratigraphic distributions of planktonic foraminifera climatic zonation and the Paleogene climatic curve are analyzed. Description and photos of 115 species and varieties of planktonic foraminifera are given in the palaeontological part of the book.