Benthic foraminifera

Short sediment cores (up to 44 cm long) taken from salt marshes regenerated during the last 60 years in the Urdaibai Biosphere Reserve have been interpreted on the basis of microfaunal and geochemical determinations and historical data. Agricultural soils in the middle and upper estuary reaches were abandoned during the 1950s and entrance of estuarine water provoked a rapid natural environmental transformation of these anthropogenic areas. Increasing amounts of sand and benthic foraminifera were deposited at a very high sedimentation rate (average 16 mm yr −1 ) during the 1950s and 1960s allowing well developed regenerated salt marshes to be rapidly established in these formerly occupied areas. During recent decades much lower sedimentation rates (average 2.5 mm yr −1 ), abundant agglutinated foraminiferal assemblages and enrichment of heavy metals (Pb, Zn, Cu, Ni and Cr) due to industrialization are characteristic of these already regenerated environments. This rapid regeneration process (less than 10 years) is of great interest for environmental management of modern coastal zones where extensive reclaimed land could be easily restored to tidal wetlands under the current scenario of accelerating sea-level rise. .es (A. Cearreta), [email protected] (A. García-Artola), [email protected] (E. Leorri), [email protected] (M.J. Irabien), [email protected] (P. Masque).

In order to assess the response of benthic foraminifera to trace element pollution, a study of benthic foraminiferal assemblages was carried out into sediment samples collected from the Santa Gilla lagoon (Sardinia, Italy). The lagoon has been contaminated by industrial waste, mainly trace elements, as well as by agricultural and domestic effluent. The analysis of surficial sediment shows enrichment in trace elements, including Cr, Cu, Hg, Ni, Pb and Zn. Biotic and abiotic data, analyzed with multivariate techniques of statistical analysis, reveal a distinct separation of both the highly polluted and less polluted sampling sites. The innermost part of the lagoon, comprising the industrial complex at Macchiareddu, is exposed to a high load of trace elements which are probably enhanced by their accumulation in the finer sediment fraction. This area reveals lower diversity and higher percentages of abnormalities when compared to the outermost part of the lagoon.

The global warming and major perturbation of the global carbon cycle that occurred during the Paleocene-Eocene Thermal Maximum (PETM) have been investigated in the lower bathyal-upper abyssal Alamedilla section (Spain). Geochemical anomalies and dramatic faunal changes (including the globally recognized extinction event of deep-sea benthic foraminifera and the rapid evolutionary turnover of planktic foraminifera and calcareous nannofossils) are associated with the PETM at Alamedilla.

1] The paleoclimatology and paleoceanology of the Late Jurassic and Early Cretaceous are of special interest because this was a time when large amounts of marine organic matter were deposited in sediments that have subsequently become petroleum source rocks. However, because of the lack of outcrops, most studies have concentrated on low latitudes, in particular the Tethys and the ''Boreal Realm,'' where information has been based largely on material from northwest Germany, the North Sea, and England. These areas were all south of 40°N latitude during the Late Jurassic and Early Cretaceous. We have studied sediment samples of Kimmeridgian ($154 Ma) to Barremian ($121 Ma) age from cores taken at sites offshore mid-Norway and in the Barents Sea that lay in a narrow seaway connecting the Tethys with the northern polar ocean. During the Late Jurassic-Early Cretaceous these sites had paleolatitudes of 42-67°N. The Late Jurassic-Early Cretaceous sequences at these sites reflect the global sea-level rise during the Volgian-Hauterivian and a climatic shift from warm humid conditions in Volgian times to arid cold climates in the early Hauterivian. The sediments indicate orbital control of climate, reflected in fluctuations in the clastic influx and variations in carbonate and organic matter production. Trace element concentrations in the Volgian-Berriasian sediments suggest that the central part of the Greenland-Norwegian Seaway might have had suboxic bottom water beneath an oxic water column. Both marine and terrigenous organic matter are present in the seaway sediments. The Volgian-Berriasian strata have unusually high contents of organic carbon and are the source rocks for petroleum and gas fields in the region. The accumulation of organic carbon is attributed to restricted conditions in the seaway during this time of low sea level. It might be that the Greenland-Norwegian segment was the deepest part of the transcontinental seaway, bounded at both ends by relatively shallow swells. The decline in organic matter content of the sediments in the Valanginian-Hauterivian indicates greater ventilation and more active flow through the seaway as the sea level rose. The same benthic foraminifera assemblages are encountered throughout the seaway. Endemic assemblages of arenaceous foraminifera in the Volgian-Berriasian give way to more diverse and cosmopolitan Valanginian-Hauterivian benthic communities that include calcareous species. The foraminiferal assemblages also suggest low oxygen content bottom waters during the earlier Cretaceous, changing to more fully oxygenated conditions later. The calcareous nannoplankton, particularly Crucibiscutum salebrosum, which is rare at low latitudes and abundant in high latitudes, reflect the meridional thermal gradient. They indicate that the Greenland-Norwegian segment of the seaway was north of a subtropical frontal zone that acted as a barrier between the Tethyan and Boreal Realms. This implies the existence of stable climatic belts during the early Valanginian and Hauterivian, significant meridional temperature gradients, and moderate ''ice house'' conditions.

This paper deals with the algal assemblage described from lower-middle Ilerdian sediments in the Kışlatepe section, Seyitgazi Region, Central Turkey. Eocene Dasycladalean flora from this region prevailingly contains species of the tribus Thyrsoporelleae, with genera Belzungia, Anatolia (type area) and Thyrsoporella. It is a unique area, a rich, diversified population of Belzungia occurs in a foraminifera limestone containing Alveolina, Nummulites, Orbitolites. Belzungia barattoloi spec. nov. is introduced. The list of the genus Belzungia in the Kışlatepe section, as in the Sarıbayır and Kozyaka sections, includes B. terquemi Morellet, B. silvestrii (Pfender), B. pfenderae Radoičić & Özgen-Erdem, B. barattoloi sp. nov. and some undetermined Belzungia specimens.

The Barremian and Aptian were times of global plate reconfiguration and profound changes in the ocean–climate system, culminating in the worldwide deposition of lower Aptian black shale layers (OAE 1a). Based on high-resolution lithostratigraphic and micropaleontological analyses, precursor conditions and timing of the anoxia are here reconstructed along a 33.06 m thick section in the proposed Barremian/Aptian boundary GSSP stratotype at Gorgo a Cerbara (Umbria–Marche Basin, Italy). A non-uniform history of benthic foraminiferal diversification is interrupted by the Selli Level (= OAE 1a) and by three turnover points for both benthic and planktic organisms, each highlighted by prominent breaks in lithology and outcrop morphology. The first two points, at ~ 1.1 Myr and ~20–50 kyr prior to the onset of the OAE 1a, correspond respectively to the nannoconid (=bathypelagic calcareous nannofossils) 'decline' and 'crisis' events, and separate: (a) pelagic limestone/chert-claystone lithological cycles of the uppermost Maiolica Formation, showing frequencies reminiscent of orbital eccentricity and containing an oligotrophic Barremian benthic and planktic assemblage, dominated by k-selected nannoconids and Rhizammina; (b) greenish-grey cherty marls of the lowermost Marne a Fucoidi Formation, associated to declining sedimentation rates and eutrophic early Aptian assemblages dominated by radiolarians and lituolid benthic foraminifera; and (c) anoxic radiolarites and shales of the carbonate-free Selli Level. High magnitude and frequency assemblage fluctuations occur between the nannoconid crisis (~ 25 cm below the lowermost OAE 1a black shale layer) and the Selli Level base, with suggestions of bottom-water acidification. At ~800 kyr after the OAE 1a end, a third turnover point in the basal reddish member of the Marne a Fucoidi highlights 'middle' Aptian assemblages characterized by a bloom of early macroperforate planktic foraminifera (Hedbergella spp.) and appearances of new benthic species, marking a shift towards better oxygenation. OAE 1a oxygen and pelagic carbonate factory crises are here suggested to have been step-wise and linked to global warming conditions.

1] Eocene Thermal Maximum 2 (ETM2; ∼53.7 Ma) occurred approximately 2 Myr after the Paleocene-Eocene Thermal Maximum (∼55.5 Ma) and was characterized by a deep-sea warming of >3°C, associated with massive release of carbon into the ocean-atmosphere system. We performed single-specimen stable isotope analyses of the planktic foraminiferal genera Acarinina (surface dweller) and Subbotina (thermocline dweller) from Ocean Drilling Program Sites 1265, 1267, and 1263 (Walvis Ridge, SE Atlantic Ocean) and compared high-resolution planktic and benthic stable isotope records to constrain the surface warming and the bathymetric pathway of the carbon isotope excursion during ETM2. Tests of the thermocline dweller Subbotina are absent from sediment deposited during the peak of ETM2. The Acarinina carbon and oxygen isotope records of Sites 1263, 1265, and 1267 are strikingly similar, despite some test recrystallization and large differences in burial depths. Sea surface temperature (SST) estimates based on d 18 O isotope values of Acarinina indicate a SST increase of ∼2°C, significantly less than the >3°C estimated for bottom water warming. The maximum negative carbon isotope excursion for Acarinina was ∼1.7‰, slightly more than in the deep sea (∼1.4‰). The planktic and benthic isotope records do not show time lags, indicating that during ETM2 the isotopically depleted carbon injected into the ocean-atmosphere system was rapidly mixed within all oceanic carbon reservoirs.

One of the most enigmatic features of long-term Cenozoic climatic evolution, with some analog potential for present/future global climate change, is the last sustained warm and high-atmospheric CO 2 interval in Earth's history, which started after the end of the Messinian Salinity Crisis (5.971–5.332 Ma) in the Mediterranean Sea. We present high-resolution, astronomically-tuned climate (Mg/Ca, δ 18 O) and productivity (Ba/Ca, δ 13 C) proxy records from the planktonic foraminifera Globigerinoides obliquus in the Kalamaki section (Zakynthos Island, Greece), which sheds new light on the early Pliocene Mediterranean hydrographic dynamics, and the associated climatic transition from 5.33 to 5.11 Ma. We recognized four distinct climatic phases with variable amplitude changes: (1) very warm climate interval prior to 5.28 Ma characterized by minimum ice volume, large salinity fluctuations, enhanced productivity, and intense river runoff, (2) stable paleoceanographic conditions from 5.28 to 5.23 Ma, which reflect a relatively warm and mesotrophic to eutrophic open-marine environment with improved ventilation, (3) a brief interval (20 ky) characterized by the most pronounced ice growth and intense cooling (∼5 °C) coupled with the abrupt decrease of ventilation and primary productivity, and (4) reinstate-ment of relatively stable conditions (warm and well-ventilated mesotrophic upper water column) in conjunction with relatively stable sea-level after 5.21 Ma. Overall, the succession of these phases provides an explanation for the more variable Mediterranean climate and stronger hydrographic variability with respect to other regions during the early Pliocene.

The impact of an asteroid at the Cretaceous/Paleogene (K/Pg) boundary triggered dramatic biotic, biogeochemical and sedimentological changes in the oceans that have been intensively studied. Paleo-biogeographical differences in the biotic response to the impact and its environmental consequences, however, have been less well documented. We present a high-resolution analysis of benthic foraminiferal assemblages at Southern Ocean ODP Site 690  (Maud Rise, Weddell Sea, Antarctica).
At this high latitude site, late Maastrichtian environmental variability was high, but benthic foraminiferal assemblages were not less diverse than at lower latitudes, in contrast to those of planktic calcifiers. Also in contrast to planktic calcifiers, benthic foraminifera did not suffer significant extinction at the K/Pg boundary, but show transient assemblage changes and decreased diversity. At Site 690, the extinction rate was even lower (~3%) than at other sites. The benthic foraminiferal accumulation rate varied little across the K/Pg boundary, indicating that food supply to the sea floor was affected to a lesser extent than at lower latitude sites. Compared to Maastrichtian assemblages, Danian assemblages have a lower diversity and greater relative abundance of heavily calcified taxa such as Stensioeina beccariiformis and Paralabamina lunata. This change in benthic foraminiferal assemblages could reflect post-extinction proliferation of different photosynthesizers (thus food for the benthos) than those dominant in the Late Cretaceous, therefore changes in the nature rather than in the amount of the organic matter supplied to the seafloor. However, severe extinction of pelagic calcifiers caused carbonate supersaturation in the oceans, thus might have given competitive advantage to species with large, heavily calcified tests. This indirect effect of the K/Pg impact thus may have influenced the deep-sea dwellers, documenting the complexity of the effects of major environmental disturbance.

In this paper, microfacies and sedimentary environment of the Asmari Formation are investigated at the northwest of Deris village, located at 7 km northwest of Kazerun city (west of Fars province). The Asmari Formation in this section consists of 460 m massive, thick, medium and thin bedded gray and cream to gray limestone, slightly dolomitic with interbeds nodular and marly limestone. More than 270 thin sections from this Oligocene carbonate interval have been prepared, studied and analyzed. Facies analysis on the basis of depositional texture, benthic foraminifera and non-foraminifera caused to distinguish 14 microfacies and 4 subfacies: O1-Bioclastic nummulitidae floatstone-rudstone, O1-1-Bioclastic nummulitidae echinoids floatstone-rudstone, O2-Bioclastic lepidocyclinidae nummulitidae Neorotalia rudstone, O3-Bioclastic nummulitidae Neorotalia packstone-rudstone, O3-1-Bioclastic nummulitidae Neorotalia corallinacean packstone-rudstone, O4-Bioclastic lepidocyclinidae Neorotalia packstone, O4-1-Bioclastic lepidocyclinidae Neorotalia corallinacean packstone, O5-Bioclastic Neorotalia corallinacean packstone, O6-Bioclastic coral corallinacean Neorotalia packstone-rudstone, Sh-Neorotalia corallinacean echinoids packstone-grainstone, L1-Coral benthic foraminifera floatstone-rudstone, L2-Benthic foraminifera (perforate and imperforate) peloidal packstone, L3-Bioclastic imperforate foraminifera corallinacean packstone, L4-High diversity imperforate foraminifera bioclastic packstone-grainstone, L5-Bioclastic miliolids wackestone-packstone, L5-1-Bioclastic miliolids Valvulinid wackestone-packstone, L6-Small rotaliids Discorbis bioclastic wackestone, and T-Sandy mudstone. Based on these facies association lagoon and open marine environments related to inner and middle parts of a homoclinal ramp have been considered for deposition of the Asmari Formation. Middle ramp fauna are mostly characterized by hyaline benthic foraminifera specially nummulitidae and lepidocyclinidae, and inner ramp is dominated by imperforate foraminifera.

Large benthic foraminifers are considered to be good indicators of shallow marine carbonate environments in fossil series. Over the last 50 years, the palaeoenvironment of Tertiary Nummulites accumulations has been a matter of debate, particularly because of difficulties in interpreting these deposits, and in this way, the absence of analogues in present-day seas does not help. The aim of this paper is to insight the different ways Nummulites tests and clasts may accumulate according to their hydrodynamic behaviour. Based on experimental measurements and on SEM observations, it appears that the high primary skeletal porosity of Nummulites made them easily transportable. The calculated threshold shear velocities confirm that large-sized Nummulites can be moved by weak wave-driven currents. This peculiar hydrodynamic behaviour of Nummulites could explain the diversity of depositional models. Depending on local hydrodynamic conditions, autochthonous Nummulites deposits can be preserved as in situ winnowed bioaccumulations or be accumulated offshore, onshore or alongshore, away from the original biotope.