Benthic Foraminiferal Oxygen Index Research Articles

Benthic Foraminifera Across the Cretaceous/Paleogene Boundary in the Eastern Tethys (Northern Alborz, Galanderud Section): Extinction Pattern and Paleoenvironmental Reconstruction

AbstractExtinction patterns, paleobathymetric inferences, and paleoenvironmental changes based on benthic foraminifera were investigated across the Cretaceous/Paleogene (K/Pg) boundary at the Galanderud section (Northern Alborz, Iran), which contains one of the most continuous and expanded K/Pg transitions in the eastern Tethys. On the basis of benthic foraminiferal taxa abundance and distribution, an outer neritic to uppermost bathyal paleo-depositional setting is inferred. In addition, benthic foraminiferal assemblages and planktic/benthic ratios do not indicate any major change in relative sea level during latest Maastrichtian-early Danian time.Changes in benthic foraminiferal assemblages, morphotypes, diversity, heterogeneity, and benthic foraminiferal oxygen index, coupled with statistical analyses, define three intervals. In the first interval (uppermost Maastrichtian Plummerita hantkeninoides Zone), benthic foraminiferal assemblages are moderately to well preserved and highly diverse, with a combination of epibenthic and endobenthic taxa indicating stable, mesotrophic to weakly eutrophic, normal marine conditions. A major change in benthic foraminiferal assemblages at the K/Pg boundary defines a second interval (basal Danian Guembelitria cretacea and lower part of Parvularugoglobigerina eugubina Zones) that is marked by a decrease in the endobenthic morphogroups as well as a decrease in diversity, heterogeneity, genus and species richness. This second interval denotes highly oligotrophic conditions and a collapse in productivity and food availability due to the extinction of some primary producers, with the exception of the three chalk beds representing short-lived blooms of calcareous dinoflagellates. Benthic foraminifera do not show significant extinction at the end of the Cretaceous at this section with only about an 8% loss of species. Additionally, the abundance of some opportunistic species, including Cibicidoides pseudoacutus and Tappanina selmensis, may reflect instability in the benthic foraminiferal assemblages. The third interval (middle-upper part of the Pv. eugubina Zone) is characterized by the dominance of epibenthic morphogroups (up to 70% of the assemblages) with a partial recovery of endobenthic groups. The characteristics of the benthic foraminiferal assemblages indicate that the flux of food to the benthos had not fully recovered during the early Danian.

The evolution of deepwater dissolved oxygen in the northern South China Sea since 400 ka

The dissolved oxygen (DO) content of the ocean provides potential evidence and clues for the waxing and waning of marine productivity, ocean circulation, global climate change, and the evolution of ecological communities. On the basis of the analysis of the Benthic Foraminiferal Oxygen Index (BFOI), the percentage of epifaunal benthic foraminifers, and the redox-sensitive trace elements (Mo/Al) in Core MD12-3432, we reconstruct the evolution of deep water DO content in the northern South China Sea (SCS) during the past 400ka and discuss the mechanisms of variable DO content. The results show that the changes of BFOI, Mo/Al, and the percentage of epifaunal benthic foraminifer present a similar pattern, which may reflect the variations of the DO content in seawater since 400ka. Both variations in BFOI and Mo/Al indicate that the DO content was high during most time of marine isotope stage (MIS) 11 to mid-MIS 6, then decreased in late-MIS 6, and remained stable in MIS 5. It increased in MIS 4 and decreased until MIS 2, and then rose again. The non-synchronous variations between bottom water DO and benthic foraminiferal δ18O indicate that the DO content is not controlled by glacial-interglacial cyclic environmental variations. Comparing the biomarker productivity index with the DO content of water, we find that the DO content is affected mainly by productivity. Bulimina, Uvigerina and Chilostomella oolina are high productivity species. The accumulation rates of Bulimina and Uvigerina are higher during 61–15kyr interval, but the accumulation rate of C. oolina is higher during 168–130kyr. The results infer that different intensity of primary productivity and DO during these two periods. The DO and phytoplankton total (PT) show the opposite relation, which also indicates that the DO is affected by primary productivity, and the combined action of productivity and DO decides the growth of Bulimina, Uvigerina, and C. oolina. Besides the influences of productivity, the change of DO in the ocean is also affected by oceanic circulation.

The Eocene-Oligocene climate transition in the Central Paratethys

We studied two boreholes (Cserépváralja-1 and Kiscell-1) with continuous sedimentary records across the Eocene-Oligocene climate transition from the Central Paratethyan area. Assemblages of benthic foraminifera display a shift in dominance by epifaunal taxa in the late Eocene to shallow and deep infaunal taxa in the early Oligocene. Using the benthic foraminiferal oxygen index (BFOI), a decreasing trend of bottom-water oxygen levels is established across the Eocene-Oligocene transition (EOT), leading to the development of dysoxic conditions later in the early Oligocene.Trends in δ18O and δ13C values measured on tests of selected benthic and planktic foraminifera roughly parallel those of the global record of stepped EOT δ18O increase and deviate only later in the early Oligocene, related to the isolation of the Paratethys. The overall similarity of the isotope curves and the presence of a planktic-benthic ecological offset suggest that the original isotope trends are preserved, despite the systematically more negative δ18O values. Of different scenarios, a quasi-uniform diagenetic overprint by fluids with low δ18O values, during burial or uplift, appears best supported. We conclude that the globally established isotopic expression of Antarctic ice sheet growth across the EOT may be recognizable in the Paratethys. Deviations from the global trends after the EOT were caused by regional paleoceanographic changes induced by the progressing Alpine orogeny and sea-level change, which led to a restricted connection with the open ocean, freshwater influx from increased precipitation, and gradual development of bottom-water oxygen depletion.

Cenomanian‐Coniacian Sea‐level Change and Dissolved Oxygen Fluctuations in Tethys‐Himalaya: Evidences from Benthic Foraminifera of Gamba, Tibet

Abstract:Benthic foraminifera, preserved in the Late Cretaceous organic carbon‐rich sediments of Gamba, southern Tibet, provide high‐resolution proxies for sea‐level changes and dissolved oxygen fluctuations of southeastern Tethys. The fossils were statistically analyzed and divided into three faunas of “Cenomanian fauna”, “Turonian fauna”, and “Coniacian fauna”. A middle neritic‐upper bathal environment (50–250m) was estimated considering the ratios of planktonic and epifaunal benthic foraminifera (P/(P+E)), the morphological analysis according to the studies of recent foraminifera and the abundant distributions of depth‐related species such as Alabamina creta, Laevidentalina sp., Praebulimina spp., Pleurostomella cf. naranjoensis, Pyrulina sp., Quinqueloculina spp., Haplophragmoides spp., etc. The result shows an almost parallel trend with the global transgressive and regressive cycles, but the former fluctuates more frequently at upper Cenomanian, which probably indicates tectonic instability of the continental margin. According to the benthic foraminiferal richness (BFN), Shannon‐Weiner diversity (H(s)), as well as benthic foraminiferal oxygen index (BFOI), five periods of oxygen depleted conditions (dysoxic‐anoxic) have been recognized. They correspond to the OAE2, the lower Turonian, the upper Turonian, the Turonian‐Caniacian boundary event and the probably OAE3. In addition, the oxygen fluctuations in Gamba might be controlled directly by sea‐level changes, while the paleoproductivity and oxygen conditions interacted with each other under oxygen deficiency environments.

Calibration of the Benthic Foraminiferal Oxygen Index in the Marmara Sea

Benthic foraminifera (total assemblages) were studied from 30 sea-floor samples collected along a bathymetric transect on the southern shelf of the Marmara Sea from depths of 15–350 m. At each station, Kaiho’s Benthic Foraminiferal Oxygen Index (BFOI) was calculated based on species abundances using the methods outlined by Kaiho (1994). The calculated BFOI values were converted to analogue oxygen values, and calibrated to the dissolved oxygen values measured 1 m above the sea floor at each station.  In the surface waters and central part of the Marmara Shelf transect, the BFOI values reproduce the measured dissolved oxygen values with a remarkable degree of accuracy. Beneath the pycnocline at depths of 30 to 75 m , the BFOI underestimated the measured oxygen values. This discrepancy is attributed to seasonally higher summer oxygen values within the chlorophyll maximum, corresponding to the position of the Mediterranean Inflow Water (MIW) present during summer. In the deeper part of the transect ( below 140 m) , BFOI values overestimated the measured oxygen values.  This discrepancy is attributed to the presence of denser MIW that cascades down the submarine canyon beneath the Marmara ship channel during winter, ventilating the deep Marmara Sea.  The BFOI accurately points out the seasonal differences in the position and depth of the MIW in the southwestern Marmara Sea. The BFOI likely reflects the longer-term oxygen values averaged over the span of many years.&nbsp

The oxygen and carbon isotopic composition of Langhian foraminiferal tests as a paleoecological proxy in a marginal part of the Carpathian Foredeep (Czech Republic)

The oxygen and carbon isotopic composition of Langhian foraminiferal tests as a paleoecological proxy in a marginal part of the Carpathian Foredeep (Czech Republic)Foraminiferal assemblages from three locations of the Moravian part of the Carpathian Foredeep (Kralice, Přemyslovice, Židlochovice) have been studied in order to determine the paleoenvironmental conditions during the Early Badenian (Middle Miocene). Paleobiological characteristics (plankton/benthos-ratio, relative abundances of warm-water plankton species, five-chamberedGloboturborotalitaspp.,Coccolithus pelagicusand high nutrient markers [benthos], test sizes and ranges ofGlobigerinasp. and cibicidoids, Benthic Foraminiferal Oxygen Index) were determined along with stable C and O isotope compositions. The stable isotope compositions show large variabilities indicating sample inhomogeneity in well preserved foraminiferal samples, interpreted as a sign of primary environmental variation and postmortem mixing of tests of different populations and sources. Based on the combined interpretation of paleobiological indicators and isotopic compositions, two theoretical models were established to describe the observed paleobiological and stable isotope data, that were used to categorize the locations studied. Several types of near-shore paleoenvironment were distinguished using the theoretical models: (i) bay influenced by seasonal phytodetritus supply from the continent (Kralice); (ii) dynamic shore characterized by variable isotopic compositions probably due to mixing of indigenous, transported and reworked tests (Přemyslovice); (iii) shore of alternating normal marine and continentally influenced environments (Židlochovice).

Integrated biostratigraphy and palaeoenvironments of an upper Santonian – upper Campanian succession from the southern part of the Eastern Carpathians, Romania

Study of an upper Santonian to upper Campanian hemipelagic succession from the southern part of the Romanian Eastern Carpathians enables us to establish an integrated biostratigraphy based on planktonic foraminifera and calcareous nannofossils and to compare this record with the agglutinated foraminiferal biozonation used for the Carpathians. Benthic foraminiferal assemblages were investigated using several methods, such as agglutinated and calcareous benthic foraminiferal morphogroups, and the benthic foraminiferal oxygen index in order to determine their response to environmental parameters in the basin (correlated with sea-level maxima documented by regional sea-level curves for the Tethys). A pattern of changes in benthic foraminiferal communities associated with increased organic carbon flux and rising sea-levels can be summarized as follows in the studied succession. As sea-level begins to rise there is an increase in the proportion of calcareous benthic foraminifera at the expense of agglutinated foraminifera within the benthic assemblages (earliest Campanian, mid-late Campanian). Once sea-level rises, an increase in the elongate keeled morphotype of agglutinated foraminifera (shallower water forms) can be observed, and if sea-level remains high for an extended period (as in the early Campanian) then an invasion of both agglutinated and benthic calcareous foraminifera characteristic of outer shelf-upper slope environments take place in the basin. The variations in tubular and deep infaunal morphotypes of agglutinated foraminifera are ascribed to varying levels of organic carbon flux.

Paleoceanographic changes on the Farallon Escarpment off central California during the last 16,000 years

New benthic and planktic foraminiferal assemblage census data and Benthic Foraminiferal Oxygen Index (BFOI) values, previously published marine climate proxy data (stable isotopes and Ca/Cd), and unpublished results of total carbon, organic carbon, and calcium carbonate analyses of sediments recovered off central California on the Farallon Escarpment (1605 m water depth; 37°13.4′N, 123°14.6′W; core F-8-90-G21) document paleoceanographic changes during the latest Quaternary which reflect the intensity and source of North Pacific Intermediate Water (NPIW) and surface productivity. Accelerator mass spectrometry radiocarbon dates of both benthic and planktic species provide an excellent age-depth model for the last 16,000 years, covering the latest glacial, Bølling–Allerød, Younger Dryas, and early, middle, and late Holocene intervals. A Q-mode cluster analysis separated the benthic fauna into three clusters, one Pleistocene and two Holocene, whereas the planktic fauna was divided only into Pleistocene and Holocene clusters. Stable oxygen isotope values show an increase in water temperature of ∼1 °C from the late glacial to late Holocene and a change in faunal composition of the planktic assemblage implies surface waters warmed as well. A general trend of decreasing dissolved oxygen concentration from the Pleistocene (high oxic; 3.0–6.0+ ml/l O 2) to the Holocene (low oxic; 1.5–3.0 ml/l O 2) suggested by the BFOI and Cd/Ca data reflect decreased ventilation as the source of the NPIW shifted from the Sea of Okhotsk to the tropical east Pacific at ∼11,000 cal BP. The middle Holocene cooling reported in other central and northern California margin studies is not apparent in F-8-90-G21, which compares more favorably with studies from southern California and British Columbia. Total carbon and organic carbon values are highest in the Bølling–Allerød, early Holocene, and late Holocene. Similarly, calcium carbonate values are high in the Bølling–Allerød and peak in the early Holocene, but decrease significantly in the latest middle and late Holocene which coincides with a depauparate planktic foraminiferal fauna in the upper 60 cm (∼70000–0 cal BP) of the core and poor preservation of the benthic foraminiferal fauna at 40 cm (∼3000 cal BP). Decoupling is evident between the planktic and benthic faunal response to changing climatic conditions, with the surface-dwelling assemblage often leading the bottom-dwelling assemblage by several millennia.

A multiproxy approach of the Holocene evolution of shelf–slope circulation on the NW Iberian Continental Shelf

Textural, mineralogical, geochemical and microfaunal data (benthic foraminifera) were studied along the OMEX core KSGX 40 recovered in the Galicia Mud Deposit, of the NW Iberian outer continental shelf, off the Ría de Vigo (North of Spain). This core included the records of the last ca. 4.8 ka cal BP and consists, from the base to the top, of a sedimentary sequence exhibiting gradual upward decrease in grain size. Sediments of this core are mainly siliciclastic, largely composed of quartz, K-feldspars, plagioclases, and phyllosilicates (mica/illite, kaolinite and chlorite) showing a great continental influence in this zone. Two periods of deposition of finer sediments are registered between ∼ 2.2–1.2 ka cal BP and ∼ 0.5–0 ka cal BP. Since the last ∼ 2.2 ka BP, but mainly during both muddy intervals, the Galicia Mud Deposit was nourished with a lower and finer supply of detrital minerals compensated by higher amounts of organic matter, as it is suggested by a Benthic Foraminifera High Productivity (BFHP) proxy. Processes involved in organic matter degradation by aerobic organisms led to depressed levels of oxygen in the sediments, as shown by a Benthic Foraminiferal Oxygen Index (BFOI). Peaks of redox-sensitive elements, like Mn, Fe, Cu, Ni, Cr, Co, Zn, Ni and Pb as well as the presence of diagenetic minerals, such as pyrite, suggest the development of anoxic conditions beneath the sedimentary surface and early diagenetic changes due to high organic matter flux, in both muddy intervals. Two different hydrodynamic regimes were inferred through the analysis of the different proxies (textural, mineralogical, geochemical and benthic foraminifera): (1) A strong hydrodynamic regime between ∼ 4.8 and 2.2 ka cal BP characterized by the prevalence of winter storms, which gave rise to a deep mixed layer on the shelf. (2) Weak hydrodynamic regime between ∼ 2.2–1.2 ka cal BP and ∼ 0.5–0 ka cal BP with a high predominance of upwelling and an increase in oceanic stratification.

Extension of carbon flux estimation to oxic sediments based on sulphur geochemistry and analysis of benthic foraminiferal assemblages: A case history from the Eocene of Hungary

The amount and type of organic matter (OM), chemical and mineralogical compositions, and the amount and isotopic ratio of sulphur were measured and benthic foraminiferal assemblages were analysed in a 70 m thick core section comprising marine marls from the Eocene of Hungary. On the basis of Benthic Foraminiferal Oxygen Index (BFOI), the studied sediments were deposited under a range of anoxic to oxic bottom water conditions. The amount of C org mineralised during early burial was calculated in two steps. First, carbon mineralised by sulphate reduction was calculated from the amount of sedimentary sulphur, corrected for escaped/oxidised H 2S by taking into account the isotopic composition of sulphur. Then, on analogy of recent sediments which are deposited with a similar rate of sedimentation and beneath bottom waters of similar O 2 content, carbon loss by aerobic respiration was estimated. A good stratigraphic control and knowledge of variation of mineralogical composition along the section permitted to estimate past variation of local organic carbon flux (C flux) from calculated original C org contents. During deposition of the studied strata, C flux first decreased from 1.16 to 0.41 g C org/m 2/y, then it progressively increased to 1.81 g C org/m 2/y. Changes in local C flux are explained by changes in water depth, flux of terrestrial organic components and availability of nutrients liberated by alteration of products of the coeval pyroclastic activity.

Cyclic changes in oxygenation based on foraminiferal microhabitats: Early–Middle Pleistocene, Lucania Basin (southern Italy)

Abstract. In the Pleistocene Montalbano Jonico composite section (southern Italy) the microhabitat preferences of the benthic foraminifera have been determined by comparison with data on living forms. The stratigraphic distribution of the different living positions seems to be related to the cyclic oxygen fluctuations recorded in the succession. In the high-oxygenated phases, when the oxygenated zone within the sediment column is wide, the assemblages show a distinct vertical microhabitat distribution. In the low-oxygenated phases, when the minor oxygen availability at the bottom–water interface reduces the oxygen penetration within the sediment, infaunal microhabitat is the preferred living depth.In order to quantify the oxygen fluctuations recorded in the succession, a palaeo-oxygen curve is reconstructed testing Kaiho’s benthic foraminiferal oxygen index (BFOI) in the equation: y=1.686+ 0.033337x. In general, good correlations are observed between the dissolved oxygen regimes and the benthic assemblage composition. The low-oxygenated phases are identified with the low-medium oxic regime and the high-oxygenated phases with the high oxic regime.In the deeper part of the composite section, oxygen has played an important role on the foraminiferal assemblage composition. In contrast, in the shallower part, a combination of oxygen and sea-level changes regulates the distribution and composition of the assemblages.

Last glacial–Holocene paleoceanography of the Black Sea and Marmara Sea: stable isotopic, foraminiferal and coccolith evidence

Multi-proxy data and radiocarbon dates from several key cores from the Black Sea and Marmara Sea document a complex paleoceanographic history for the last ∼30 000 yr. The Marmara Sea was isolated from both the Black Sea and the Aegean Sea during glacial periods when global sea-level lowering subaerially exposed the shallow sills at the Straits of Bosphorus and Dardanelles (i.e. lake stage), and reconnected through both straits during interglacial periods, when rise of global sea level breached the shallow sills (i.e. gateway stage). Micropaleontological data show that during the ‘lake stage’ the surface-water masses in both the Marmara Sea and Black Sea became notably brackish; however, during the ‘gateway stages’ there was a low-salinity surface layer and normal marine water mass beneath. Two sapropel layers are identified in the Marmara Sea cores: sapropels M2 and M1 were deposited between ∼29.5 and 23.5 ka, and ∼10.5 and 6.0 ka, respectively. Micropaleontological and stable isotopic data show that the surface-water salinities were reduced considerably during the deposition of both sapropel layers M2 and M1, and calculation using planktonic foraminiferal transfer functions shows that sea-surface temperatures were notably lower during these intervals. The presence of fauna and flora with Black Sea affinities and the absence of Mediterranean fauna and flora in sapropels M1 and M2 strongly suggest that communication existed with the Black Sea during these times. A benthic foraminiferal oxygen index shows that the onset of suboxic conditions in the Marmara Sea rapidly followed the establishment of fully marine conditions at ∼11–10.5 ka, and are attributed to Black Sea outflow into the Marmara Sea since 10.5 ka. These suboxic conditions have persisted to the present. The data discussed in this paper are completely at odds with the ‘Flood Hypothesis’ of Ryan et al. (1997), and Ryan and Pitman (1999).

Effect of organic carbon flux and dissolved oxygen on the benthic foraminiferal oxygen index (BFOI)

Variations in oceanic primary productivity, flux of organic carbon to the sediments, and dissolved-oxygen levels in the water column are thought to be important in the control of benthic foraminiferal test size, wall thickness, morphology, and species composition of assemblages by many foraminiferal paleontologists. Aspects of these processes should be reflected by the benthic foraminiferal oxygen index (BFOI) based on these foraminiferal characteristics. However, analyses indicate that the BFOI correlates most strongly with dissolved-oxygen levels in overlying water ( R 2=0.81), weakly with oceanic primary productivity ( R 2=0.55), and weakly with organic carbon flux to the sediments ( R 2=0.51). Although both dissolved oxygen and organic carbon flux are main controlling factors for benthic foraminiferal assemblages, the BFOI is a useful indicator extracted from benthic foraminiferal assemblages for estimating the condition of dissolved oxygen in Cretaceous and Cenozoic oceans.