Planktonic foraminifera in the Maastrichtian of Hor-Hahar

The lengthy warm, stable climate of the Cretaceous terminated in the Campanian with a cooling trend, interrupted in the early and latest Maastrichtian by two events of global warming, at ~70-68 Ma and at 65.78-65.57 Ma. These climatic oscillations had a profound effect on pelagic ecosystems, especially on planktic foraminiferal populations. Here we compare biotic responses in the tropical-subtropical (Tethyan) open ocean and mesotrophic (Zin Valley, Israel) and oligotrophic (Tunisia) slopes, which correlate directly with global warming and cooling. The two warming events coincide with blooms of Guembelitria, an extreme opportunist genus best known as the main survivor of the Cretaceous-Paleogene (K-Pg) catastrophe. In the Maastrichtian, Guembelitria bloomed in the uppermost surface water above shelf and slope environments but failed to reach the open ocean as it did at K-Pg. The coldest interval of the late Maastrichtian (~68-65.78 Ma) is marked by an acme of the otherwise rare species Gansserina gansseri, a deep-dwelling keeled globotruncanid. The G. gansseri acme event can be traced from the deep ocean even onto the Tethyan slope, marking copious production and circulation of cold intermediate water. This acme is abruptly terminated by extinction of the species, a dramatic reversal attributed to a short-term global warming episode. This extinction corresponds precisely with the second bloom of Guembelitria that began ~300 kyr prior to the K-Pg event. The antithetical relationship between blooming of Guembelitria and the G. gansseri acme reflects planktic foraminiferal sensitivity to warm-cool-warm-cool climatic oscillations marking the end of the Cretaceous.

Eocene-Oligocene nannofossils from the Labrador Sea

During Ocean Drilling Program (ODP) Leg 105, a thick sequence of lower Eocene to lower Oligocene sediments was recovered from Hole 647A in the southern Labrador Sea. These sediments contain diverse, well-preserved, high-latitude calcareous nannofossil flora. The nannofossil biostratigraphy of the hole indicates the presence of a minor hiatus between Zones NP 16 and NP 17 in the upper middle Eocene and a barren interval separating Zones NP 13 and NP 15. Species abundance is highest within the lower to middle Eocene and starts to decline near the base of the upper Eocene. No major change in the nannoflora was observed across the Eocene/Oligocene boundary, although a slight decrease in species abundance was recorded. The Paleogene calcareous nannofossils of nearby DSDP Site 112 were reexamined and compared with those of Site 647. Several cores were reassigned to different nannofossil zones. The calcareous nannoflora are dominated by high-latitude indicative species and also exhibit a high diversity, which suggests the influence of more temperate water masses in this region during Eocene and Oligocene time. One new subspecies from the middle Eocene, Sphenolithus furcatolithoides labradorensis, is described.

Cretaceous and Paleogene calcareous nannofossils from ODP Leg 123

Two of five holes drilled at two separate sites during Leg 123 of the Ocean Drilling Program intersected thick and relatively complete sections of Upper Cretaceous-Paleogene nannofossiliferous sediments. Although dominated by turbidite deposition in the upper part, Hole 765C contains a thick and relatively complete Albian-Oligocene section, including a particularly thick Aptian interval, with abundant and fairly well-preserved nannofossils. Several unconformities are confidently interpreted in this section that span much of the Santonian, late Campanian, Maestrichtian, late Eocene, and early Oligocene. Hole 766A contains a thick and relatively complete Albian-lower Eocene section having generally abundant and well-preserved nannofossils. Several unconformities also have been identified in this section that span much of the Coniacian, early Campanian, Maestrichtian, and late Eocene through early Pliocene. The chronostratigraphic position and length of all these unconformities may have considerable significance for reconstructing the sedimentary history and for interpreting the paleoceanography of this region. A particularly thick section of upper Paleocene-lower Eocene sediments, including a complete record across the Paleocene/Eocene boundary, also was cored in Hole 766A that contains abundant and diverse nannofossil assemblages. Although assemblages from this section were correlated successfully using a standard low-latitude zonation, difficulties were encountered that reduced biostratigraphic resolution. Several lines of evidence suggest a mid-latitude position for Site 766 during this time, including (1) high assemblage diversity characteristic of mid-latitude zones of upwelling and (2) absence of certain ecologically controlled markers found only in low latitudes.

Pollen records from two outcrop profiles in the Kakitu Mountain of Tibet

There is a great similarity between pollen types which occur in the early Holocene NE Tibetan pollen spectra and those which are commonly considered to be typical for the Würm Late Glacial period in Central Europe and for the Würm Pleniglacial period in Southern Europe. Evidently, this similarity is due to a remarkable general conformity of plant taxa growing in cold-arid regions of the northern hemisphere. The improvement of the climate and the retreat of the glaciers that commenced at the end of the Würm period had already terminated definitely before 9500 BP. In addition, the climatic situation as well as the vegetation belts must have remained rather constant during the following 3000 yr, i.e. through most parts of the climatic optimum of the Holocene.

Maastrichtian planktic foraminifera of the South Atlantic Ocean

Stratigraphic, faunal and isotopic analyses of the Maastrichtian at DSDP sites 525A and 21 in the South Atlantic reveal a planktic foraminiferal fauna characterized by two major events, an early late Maastrichtian diversification and end-Maastrichtian mass extinction. Both events are accompanied by major changes in climate and productivity. The diversification event which occurred in two steps between 70.5 and 69.1 Ma increased species richness by a total of 43% and coincided with the onset of major cooling in surface and bottom waters and increased surface productivity. The onset of the terminal decline in Maastrichtian species richness began at 67.5 Ma and the first significant decline in surface productivity occurred at 66.2 Ma, coincident maximum cooling to 13°C in surface waters and the reduction of the surface-to-deep temperature gradient to less than 5°C. Major climatic and moderate productivity changes mark the mass extinction and the last 500 kyr of the Maastrichtian. Between 200 and 400 kyr before the K-T boundary surface and deep waters warmed rapidly by 3-4°C and cooled again during the last 100 kyr of the Maastrichtian. Surface productivity decreased only moderately across the K-T boundary. Species richness began to decline during the late Maastrichtian cooling and by K-T boundary time, the mass extinction had claimed 66% of the species. Viewed within the context of Maastrichtian climate and productivity changes, the K-T mass extinction could have resulted from extreme environmental stress even without the addition of an extraterrestrial impact.

Characterization of late Campanian and Maastrichtian planktonic foraminiferal depth habitats and vital activities based on stable isotopes

Depth habitats of 56 late Cretaceous planktonic foraminiferal species from cool and warm climate modes were determined based on stable isotope analyses of deep-sea samples from the equatorial Pacific DSDP Sites 577A and 463, and South Atlantic DSDP Site 525A. The following conclusions can be reached: Planoglobulina multicamerata (De Klasz) and Heterohelix rajagopalani (Govindan) occupied the deepest plankton habitats, followed by Abathomphalus mayaroensis (Bolli), Globotruncanella havanensis (Voorwijk), Gublerina cuvillieri Kikoine, and Laeviheterohelix glabrans (Cushman) also at subthermocline depth. Most keeled globotruncanids, and possibly Globigerinelliodes and Racemiguembelina species, lived at or within the thermocline layer. Heterohelix globulosa (Ehrenberg) and Rugoglobigerina, Pseudotextularia and Planoglobulina occupied the subsurface depth of the mixed layer, and Pseudoguembelina species inhabited the surface mixed layer. However, depth ranking of some species varied depending on warm or cool climate modes, and late Campanian or Maastrichtian age. For example, most keeled globotruncanids occupied similar shallow subsurface habitats as Rugoglobigerina during the warm late Campanian, but occupied the deeper thermocline layer during cool climatic intervals. Two distinct types of "vital effect" mechanisms reflecting photosymbiosis and respiration effects can be recognized by the exceptional delta13C signals of some species. (1) Photosymbiosis is implied by the repetitive pattern of relatively enriched delta13C values of Racemiguembelina (strongest), Planoglobulina, Rosita and Rugoglobigerina species, Pseudoguembelina excolata (weakest). (2) Enriched respiration 12C products are recognized in A. mayaroensis, Gublerina acuta De Klasz, and Heterohelix planata (Cushman). Isotopic trends between samples suggest that photosymbiotic activities varied between localities or during different climate modes, and may have ceased under certain environmental conditions. The appearance of most photosymbiotic species in the late Maastrichtian suggests oligotrophic conditions associated with increased water-mass stratification.

Planktic foraminiferal assemblage turnover at the Cretaceous-Tertiary boundary

Three uppermost Cretaceous through basal Paleocene stratigraphic sequences are examined for planktic foraminiferal assemblage stability and temporal succession patterns. These sequences are at mid-latitude South Atlantic DSDP Site 528, then-equatorial Pacific DSDP Site 577 and the Tethyan shelf Ben Gurion section of the Negev, Israel. In order to better estimate biogeographic patterns and habitat preferences, the results of these analyses are compared to previous Cretaceous biogeographic studies and to previous analyses of Cretaceous-Tertiary (K/T) boundary shelf and epicontinental sections. Results indicate that immediately following the K/T boundary, the examined epicontinental and open-ocean sites were exploited primarily by previously epicontinental planktic foraminiferal assemblages. This pattern of K/T boundary assemblage dominance suggests the geologically instantaneous break-down of Late Cretaceous epicontinental and open-ocean biogeographic provincialization. This shift in open-ocean foraminiferal assemblages is not consistent with models of nonselective K/T boundary extinctions, but is consistent with models of extinction resistence and offshore expansion of nearshore taxa. The re-establishment of stable biogeographic differences between open-ocean and epicontinental planktic foraminiferal assemblages occurs by the basal Parvularugoglobigerina eugubina Zone. At open-ocean sites 528 and 577 and the outershelf Ben Gurion section, P0 and P. eugubina Zone faunal records are marked by a pronounced alternation between Paleocene biserial- and non-biserial-dominated assemblages, This alternation appears strongly damped at shelf and epicontinental sections previously examined. The first appearance and peak magnitude of abundant earliest Paleocene trochospiral forms (Parvularugoglobigerina, Eoglobigerina, Morozovella, Globoconusa) also vary from site to site and may depend closely on levels of primary carbonate productivity.

Correlation of Bolboforma zonation and nannoplankton stratigraphy in the Neogene of the North Atlantic

The Neogene Bolboforma zones established in the North Atlantic have been correlated with the calcareous nannoplankton stratigraphy obtained by investigation of the same samples from DSDP Sites 12-116 (44 samples), 49-408 (76 samples), 81-555 (43 samples) and 94-608 (103 samples). The absolute ages for the zonal boundaries were determined by the paleomagnetic record of Site 94-608. This correlation and the age determinations are additional useful tools to develop a precise biostratigraphy of Neogene sediments in the Northern Atlantic.

Pedogeomorphology, geochronology and paleobotany of soil profiles obtained in the Kyichu River catchment, sourthern Tibet

Results of pedogeomorphological, geochronological and paleobotanical investigations are presented covering the last ca. 4,000 years. The study sites are located in the heavily degraded Kyichu River catchment around Lhasa at 3,600-4,600 m a.s.l. Repeatedly, colluvial sediments have been recorded overlying paleosols. These deposits can be divided into i) coarse-grained sediments with a high proportion of stones and boulders originating from alluvial fans and debris flows, ii) matrix supported sediments with some stones and boulders originating from mudflows or combined colluvial processes such as hillwash plus rock fall, and iii) fine-grained sediments originating from hill wash. The IRSL multi-level dating of profile QUG 1 points to a short-time colluvial sedimentation between 1.0 ± 0.1 and 0.8 ± 0.1 ka. In contrast, dated paleosols of profile GAR 1 (7,908 ± 99 and 3,668 ± 57 BP) encompass a first colluvial episode. Here, the upper colluvial sedimentation took place during several periods between 2.6 ± 0.3 and 0.4 ± 0.1 ka. For the first time in Tibet, a systematic extraction, determination and dating of charcoals from buried paleosols was conducted. The charcoals confirm the Late Holocene presence of juniper forests or woodlands in a now treeless, barren environment. A pollen diagram from Lhasa shows a distinct decline of pollen of the Jumperus-type around 4,140 ± 50 BP, which is interpreted as indicating a clearing of forests on the adjacent slopes. It is assumed that the environmental changes from forests to desertic rangelands since ca. 4,000 BP have been at least reinforced by humans.

Late Albian foraminiferal carbon and oxygen isotope data and biostratigraphic datums from ODP holes 171-1050C and 171-1052E

A late Albian-early Cenomanian record (~103.3 to 99.0 Ma), including organic-rich deposits and a d13C increase associated with oceanic anoxic event 1d (OAE 1d), is described from Ocean Drilling Program sites 1050 and 1052 in the subtropical Atlantic. Foraminifera are well preserved at these sites. Paleotemperatures estimated from benthic d18O values average ~14°C for middle bathyal Site 1050 and ~17°C for upper bathyal Site 1052, whereas surface temperatures are estimated to have ranged from 26°C to 31°C at both sites. Among planktonic foraminifera, there is a steady balance of speciation and extinction with no discrete time of major faunal turnover. OAE 1d is recognized on the basis of a 1.2 per mill d13C increase (~100.0-99.6 Ma), which is similar in age and magnitude to d13C excursions documented in the North Atlantic and western Tethys. Organic-rich "black shales" are present throughout the studied interval at both sites. However, deposition of individual black shale beds was not synchronous between sites, and most of the black shale was deposited before the OAE 1d d13C increase. A similar pattern is observed at the other sites where OAE 1d has been recognized indicating that the site(s) of excess organic carbon burial that could have caused the d13C increase has (have) yet to be found. Our findings add weight to the view that OAEs should be chemostratigraphically (d13C) rather than lithostratigraphically defined.

Diatoms in Paleocene sediments of the southwestern South Atlantic

The taxonomy and stratigraphy of pelagic Paleocene diatoms from ODP Sites 698, 700, and 702 and DSDP Site 524 in the South Atlantic and DSDP Site 214 in the Indian Ocean are presented, as well as paleogeographic and paleoecologic implications. Eleven new species and one new variety are described and one new combination is proposed: Coscinodiscus cruxii sp. nov. Grunowiella palaeocaenica var. alternans var. nov. Hemiaulusl beatus sp. nov. Hemiaulusl ciesielskii sp. nov. Hemiaulusl conicus sp. nov. Hemiaulus kristoffersenii sp. nov. Hemiaulus nocchiae sp. nov. Hemiaulusl oonkii sp. nov. Hemiaulusl velatus sp. nov. Triceratium gombosii sp. nov. Trochosira gracillima comb. nov. Trochosira marginata sp. nov. Trochosira radiata sp. nov. Hole 700B provides one of the most continuous diatomaceous Paleocene profiles known. Stratigraphic ranges of diatom species from this and other Southern Hemisphere sites are calibrated against calcareous microfossil zones. The first-appearance datums of Triceratium gombosii, Hemiaulus incurvus, and Triceratium mirabile in Paleocene deep-sea sediments are useful for regional stratigraphic correlations. Quantitative analysis of the biosiliceous microfossil groups (diatoms, silicoflagellates, radiolarians, and archaeomonadaceae) shows that preservation of diatoms is confined primarily to the upper Paleocene (planktonic foraminifer Zones P3 and P4 and calcareous nannofossil Zones upper NP5 to lower NP9). In the lower Paleocene only short intervals in Hole 700B are diatomaceous. A correlation between the degree of silica diagenesis and the calcium carbonate content of the sediment is not obvious. Diatom species analysis reflects changes in the paleoenvironment between island-related upwelling conditions with highly diverse and well-preserved diatom assemblages and less productive periods resulting in less wellpreserved diatom assemblages with a higher content of robust neritic diatoms.

Macrobenthos from the Novaya Zemlya Trough, Kara Sea

During Cruise 54 of R/V Akademik Mstislav Keldysh macrobenthos of the Novaya Zemlya Trough was studied with use of a Sigsby trawl along a submeridional transect near 75°30'N at depth range from 68 to 362 m. In total 140 species of bottom animals were found. Relative role of taxons was assessed using three parameters: abundance, biomass, and energy flow. Similarity of the parameters was used for comparison of samples. New material greatly contributes to data on composition of fauna and structure of communities of the studied region. It was revealed that small scyphozoid polyps and sipunculoids play an important role in the trough's community. Presence of a community dominated by Ophiocten sericeum (with important role of small bivalves) was revealed for the first time not only at the eastern by also at the western slope of the Novaya Zemlya Trough. The sharpest changes in composition and structure of the bottom community were confined to a zone of transition from the trough floor to the slope. These changes are determined by specificity of the macrorelief (of the floor and slope), composition of ground (soft brown silts abound in rhizopods and dense gray silts with admixture of pebbles), and possibly by hydrodynamic processes near the bottom.