Planktic Foraminifers Research Articles

Late Maastrichtian–early Danian high-stress environments and delayed recovery linked to Deccan volcanism

Deccan volcanism occurred in three intense phases of relatively short duration: phase 1 spanning the paleomagnetic chron C30r/C30n boundary (planktic foraminiferal CF4), phase 2 in the latest Maastrichtian C29r (zones CF1–CF2), and phase 3 in the early Danian C29n (P1b). This study explores the nature of paleoenvironmental changes correlative with the three volcanic phases in central Egypt and the Sinai based on planktic foraminifers, stable carbon and oxygen isotopes.Results show that high-stress assemblages dominated by Guembelitria blooms are prominent in, but not exclusive to, all three volcanic phases. These blooms are well known from the aftermath of this mass extinction in zones P0–P1a, the intertrappean interval between volcanic phases 2 and 3. Guembelitria blooms in CF4 (phase 1) are relatively minor (<45%) although they comprise a substantial component of the planktic foraminiferal assemblages. Maximum Guembelitria blooms (>80% of the total assemblage) are observed in CF1, which spans the last 160 ka of the Maastrichtian marked by rapid global climatic warming and cooling correlative with phase 2. Major Guembelitria blooms (50–75%) are also observed in P1b, which is marked by climate warming (Dan-C2 event) and a major negative carbon isotope excursion correlative with phase 3. This high-stress event precedes full marine biotic recovery after the mass extinction.

A Cretaceous chronostratigraphic database: construction and applications

Timing and rates of tectonic events, evolutionary processes, and oceanographic and paleoclimatic changes must be based on high-precision numerical age calibration of stages defined in Global Stratotype and Section Points (GSSPs). The Cretaceous Chronostratigraphic Database (CRETCSDB3) is an objective, testable database that calibrates select Cretaceous events and enables high-resolution chronostratigraphic correlations. CRETCSDB3 is a compilation of more than 3500 taxa and marker beds in nearly 300 published sections calibrated to a mega-annum (Ma) scale. The database spans the Jurassic/Cretaceous and the Cretaceous/Paleogene boundaries. Construction of CRETCSDB3 began by plotting bioevents in the Kalaat Senan, Tunisia, Cenomanian-Turonian section to the 1989 time scale. The sedimentology, sequence stratigraphy, and biostratigraphy of this section were precisely documented and stage boundaries defined biostratigraphically. Additional sections with radiometrically dated beds were graphed to constrain the accuracy of the numerical scale. Ranges of first and last occurrences are calibrated to mega-annums of Cretaceous stages defined by GSSPs or reference sections. This database serves as a look-up table for interpolation and age calibration of other stratigraphic sections. The age ranges of some taxa and marker beds are preliminary and may be extended as new sections are added to the database. CRETCSDB3 tested the numeric age calibration of the Albian/Cenomanian boundary. This boundary in North Texas accurately correlates with the GSSP in France by ammonites, planktic foraminifers and dinoflagellates. This stage boundary in North Texas correlates with the 97.88±0.69 Ma Clay Spur Bentonite in Wyoming by sequence stratigraphy and cosmopolitan dinoflagellates. The inconsistency between this age and the current 100.5 Ma date of the 2012 Geologic Time Scale remains to be evaluated independently.

FOSSIL PSAMMOBIONTIC SPONGES AND THEIR FORAMINIFERAL RESIDENTS, CENTRAL APENNINES, ITALY

ABSTRACT Sponges generally live firmly attached on firm- and hardgrounds but a few species are known to colonize mobile sediments in shallow water. These psammobiontic sponges are anchored to the bottom by incorporating sediment particles at their base. Herein we relate so-far enigmatic bowl-shaped structures from seagrass deposits of the lower Miocene (Burdigalian) Calcari a Briozoi e Litotamni Formation on the Latium-Abbruzzi carbonate platform (Central Apennines, Italy) to the in-ground parts of psammobiontic sponges. The sponge fossils yield a peculiar foraminiferal assemblage with an increased abundance of Bulimina and Bolivina compared to the surrounding sediments as well as with planktic foraminifers and spirillinids (Spirillina, Patellina), which are not recorded outside the sponges. Drifting planktic foraminifers became trapped on the sponge surface exposed to the water column before agglutination. In contrast, high quantities of Bulimina, Bolivina, and spirillinids indicate commensalistic relati...

EVOLUTION AND TAXONOMIC STUDY OF THE CRETACEOUS PLANKTIC FORAMINIFERAL GENUS HELVETOGLOBOTRUNCANA REISS, 1957

The evolution and taxonomy of the planktic foraminifer genus Helvetoglobotruncana Reiss, 1957, are investigated to improve stability in the concepts of the biomarker species Hv. praehelvetica and Hv. helvetica , which have been used to correlate uppermost Cenomanian–middle Turonian (Upper Cretaceous) marine sediments worldwide. The study focuses on exquisitely preserved specimens obtained from Turonian marine claystones drilled on the coastal margin of Tanzania, and these are compared with specimens reported from a number of Cenomanian/Turonian boundary sequences worldwide. Absence of discernable shell recrystallization in the Tanzanian specimens provides an unprecedented opportunity for detailed observations of the external wall texture and wall microstructures, allowing for a more concise characterization of similarities and differences between the two species. Abundance counts of Turonian planktic foraminifer assemblages from one Tanzania borehole reveals that Hv. helvetica occurs in trace abundance early in its range and reaches maximum abundance of 35–45% of the total assemblage shortly before the simultaneous and abrupt extinction of both helvetoglobotruncanid species. The ratio between Hv. helvetica and Hv. praehelvetica increases gradually up-section, with a 1:1 ratio reached nearly halfway above the lowest occurrence level of Hv. helvetica and 9:1 dominance by Hv. helvetica near the top of its range. The helvetoglobotruncanid and mixed whiteinellid species yield δ 13 C and δ 18 O values that are nearly identical and slightly more enriched in δ 18 O than co-occurring Globoheterohelix paraglobulosa, and they are slightly more enriched in d 13 C and more depleted in δ 18 O than co-occurring species of Dicarinella and Praeglobotruncana. These isotopic results indicate that helvetoglobotruncanids lived at relatively shallow depths in the mixed layer. Using an age model developed for the Rock Canyon Anticline Cenomanian/Turonian Global Stratotype Section and Point (GSSP) sequence near Pueblo, Colorado, the age of the first occurrence of Hv. helvetica is calculated as 93.52 Ma. The extinction of Hv. helvetica has not been properly calibrated, but it must be younger than 92.77 Ma, which is the age of its occurrence at the top of the Rock Canyon Anticline GSSP section.

Biostratigraphic Revision of Middle-Cretaceous Biostratigraphy Succession in South Zagros Basin

Cenomanian succession (Sarvak Formation) is well distributed along Zagros area particularly in the south portion of the Zagros (Fars area). This study attempts to determine the precise biostratigraphic biozones of four stratigraphic sections selected from the Cenomanian strata south Zagros basin, including the sections of Nour Abad, Samghan, Doroodzan, and Arsanjan. The vertical distribution of the index foraminifers confirms a faunal assemblage of benthic and planktic foraminifers in the mentioned stratigraphic sections. The received Biostratigraphic data of this work reveals well developed benthic foraminifers and well distributed Cenomanian planktons in the uppermost lithostratigraphic part of the studied Sarvak exposures. However, the established biozones of the Sarvak Formation represent the Cenomanian age, which is similar to many recognized Cenomanian biozones in the Tethyan realm, whereas the foraminiferal biostratigraphy of the Arsenjan stratigraphic column is assigned to the Late Albian to Early Cenomanian age. Since benthic foraminifers are well expanded in studied section of Sarvak Formation, the presence of pelagic biofacies is a proof of transgression in some studied sections. However, the established biozones support that geologic setting is the most factor which controls vertical distribution of foraminifers and other microfossils during the deposition of Sarvak Formation. The received biostratigraphic data of the Sarvak Formation determines subdivision of Cenomanian age in the South Zagros basin clearly.

Migrations of the North Atlantic Polar Front during the Last 300 ka: Evidence from Planktic Foraminiferal Data

Migrations of the North Atlantic Polar Front during the Last 300 ka: Evidence from Planktic Foraminiferal Data

Late Quaternary productivity changes in the equatorial Indian Ocean (ODP Hole 716A)

The equatorial Indian Ocean is swept by the Indian Ocean equatorial westerlies (IEW) which intensify in monsoon transitions during April–May and October–November, driving Eastward Equatorial Current (EEC) to the upper ocean. The EEC brings significant changes in the surface productivity in the equatorial region influencing the life style of the surface and deep-sea fauna. This study is aimed at understanding ~300Kyr record (~450–150Kyrs ago) of productivity changes linked to variations in IEW–EEC in the equatorial Indian Ocean using high resolution microfaunal record from Integrated Ocean Drilling Program (IODP) Hole 716A, Maldives Ridge. In total, 451 core samples of 10cm3 volume from the ~300Kyr long sequence (ranging ~450–150Kyrs ago) were analyzed at every 1cm interval to generate census data of the benthic foraminiferal fauna. Factor and cluster analyses using percentages of 53 highest-ranked benthic foraminiferal species were run that enabled us to identify five biofacies, indicating the varied nature of deep-sea environments during the late Quaternary. The results show a major shift roughly 300Kyr ago, across Marine Isotope Stages 9 and 8 (MIS 9/8), recorded in this study as mid-Brunhes transition at Hole 716A. The present study also combines published planktic foraminiferal fauna and pteropod records from Hole 716A to understand if the surface to shallow and intermediate water paleoenvironments were coupled with deep-water changes during the late Quaternary in the Maldivian Archipelago. Biofacies Robulus nicobarensis–Trifarina reussi (Rn–Tr), Uvigerina porrecta–Reussella simplex (Upo–Rs) and Cymbaloporetta squammosa–Bolivinita sp. (Cs–Bsp) dominate before the mid-Brunhes transition and document high organic flux with relatively low oxygen paleoenvironment, similar to the planktic foraminifer Globigerina bulloides population, while benthic foraminiferal biofacies Hoeglundina elegans–Miliolinella subrotunda (He–Ms) and Uvigerina peregrina–Quinqueloculina seminulum (Upe–Qs) record high seasonality in food supply with well-oxygenated deep water following the mid-Brunhes climatic transition (~300Kyr ago at Hole 716A). These changes are also recorded in the population of planktic foraminiferal species Globigerinoides ruber and Neogloboquadrina dutertrei as well as pteropods. Organic carbon flux linked to changes in the IEW–EEC strength appears to be the most plausible factor controlling faunal assemblages and hence paleoproductivity dynamics in the Maldivian region. Our results suggest that the strength of the IEW is inversely related with the Indian Ocean Dipole (IOD). The IOD strengthened across MIS 9/8 during which time the IEW weakened, leading to major changes at Hole 716A.

Sub sea surface temperatures in the Polar North Atlantic during the Holocene: Planktic foraminiferal Mg/Ca temperature reconstructions

Holocene sea surface temperatures in the eastern Fram Strait are reconstructed based on Mg/Ca ratios measured on the planktic foraminifer Neogloboquadrina pachyderma (sin). The reconstructed sub sea surface temperatures (sSSTMg/Ca) fluctuate markedly during the earliest Holocene at ~11.7 and 10.5 kyr BP. This is probably in response to the varying presence of sea-ice and deglacial meltwater. Between ~10.5–7.9 kyr BP, the sSSTMg/Ca values are relatively high (~4°C) and more stable reflecting high insolation and intensified poleward advection of Atlantic Water. After 7.9 kyr BP, the sSSTMg/Ca values decline to an average of ~3°C throughout the mid-Holocene. These changes can be attributed to a combined effect of reduced poleward oceanic heat advection and a decline in insolation as well as a gradually increased influence of eastward migrating Arctic Water. The sSSTMg/Ca values increase and vary between 2.1°C and 5.8°C from ~2.7 kyr BP to the present. This warming is in contrast to declining late-Holocene insolation and may instead be explained by factors including increased advection of oceanic heat to the Arctic region possibly insulated beneath a widening freshwater layer in the northern North Atlantic in conjunction with a shift in calcification season and/or depth habitat of N. pachyderma (sin).

LA‐ICP‐MS depth profiling perspective on cleaning protocols for elemental analyses in planktic foraminifers

Measurements of trace metal ratios in foraminiferal calcite are routinely used to reconstruct paleoceanographic conditions. Analyses using solution‐based inductively coupled plasma mass spectrometry (ICP‐MS) require dissolution of the entire foraminifer shell. The potential exists for contamination from adherent clays, mineralized coatings, and other diagenetic components that confound the biogenic trace metal signal. We present results from a cleaning experiment on fossil specimens of the planktic foraminifer Orbulina universa that were cracked into several shell fragments and subjected to different cleaning protocols. We use laser ablation ICP‐MS (LA‐ICP‐MS) depth profiling to evaluate the effects of reductive, oxidative, and chelating (diethylene‐triamine pentaacetic acid) cleaning protocols on shell Mg/Ca and Ba/Ca ratios. Using the natural pattern of intrashell Mg/Ca heterogeneity exhibited by O. universa, we demonstrate that reductive and oxidative cleaning can dissolve shell calcite from available surfaces, although intrashell Mg/Ca minima and maxima are unaffected. High‐resolution depth profiles can be used to identify areas of heterogeneous intrashell Ba/Ca, which can be excluded from computations of whole‐shell Ba/Ca. The size and density of shell pores plays a major role in the degree of contamination from sedimentary material. We demonstrate an approach for computing whole‐shell Me/Ca ratios from LA‐ICP‐MS depth profiles that accounts for potential contamination and diagenetic overprinting.

The influence of salinity on Mg/Ca in planktic foraminifers – Evidence from cultures, core-top sediments and complementary δ18O

The Mg/Ca ratio in foraminiferal calcite is one of the principal proxies used for paleoceanographic temperature reconstructions, but recent core-top sediment observations suggest that salinity may exert a significant secondary control on planktic foraminifers. This study compiles new and published laboratory culture experiment data from the planktic foraminifers Orbulina universa, Globigerinoides sacculifer and Globigerinoides ruber, in which salinity was varied but temperature, pH and light were held constant. Combining new data with results from previous culture studies yields a Mg/Ca-sensitivity to salinity of 4.4±2.3%, 4.7±1.2%, and 3.3±1.7% per salinity unit (95% confidence), respectively, for the three foraminifer species studied here. Comparison of these sensitivities with core-top data suggests that the much larger sensitivity (27±4% per salinity unit) derived from Atlantic core-top sediments in previous studies is not a direct effect of salinity. Rather, we suggest that the dissolution correction often applied to Mg/Ca data can lead to significant overestimation of temperatures. We are able to reconcile culture calibrations with core-top observations by combining evidence for seasonal occurrence and latitude-specific habitat depth preferences with corresponding variations in physico-chemical environmental parameters. Although both Mg/Ca and δ18O yield temperature estimates that fall within the bounds of hydrographic observations, discrepancies between the two proxies highlight unresolved challenges with the use of paired Mg/Ca and δ18O analyses to reconstruct paleo-salinity patterns across ocean basins. The first step towards resolving these challenges requires a better spatially and seasonally resolved δ18Osw archive than is currently available. Nonetheless, site-specific reconstructions of salinity change through time may be valid.

Foraminiferal and radiolarian biostratigraphy of the youngest (Late Albian through Late Cenomanian) sediments of the Tatra massif, Central Western Carpathians

Abstract Bąk, K. and Bąk M. 2013. Foraminiferal and radiolarian biostratigraphy of the youngest (Late Albian through Late Cenomanian) sediments of the Tatra massif, Central Western Carpathians. Acta Geologica Polonica, 63 (2), 223-237. Warszawa. The foraminiferal and radiolarian biostratigraphy of selected sections of the Zabijak Formation, the youngest sediments of the Tatra massif (Central Western Carpathians), have been studied. Benthic foraminifers, mainly agglutinated species, occur abundantly and continuously throughout the studied succession, while planktic foraminifers are generally sparse. Five planktic and two benthic foraminiferal zones have been recognized. The marly part of the Zabijak Formation comprises the Pseudothalmanninella ticinensis (Upper Albian) through the Rotalipora cushmani (Upper Cenomanian) planktic foraminiferal zones, and the Haplophragmoides nonioninoides and Bulbobaculites problematicus benthic foraminiferal zones. The radiolarians were recognized exclusively in the Lower Cenomanian part of the formation.

Atlantic Water advection versus sea‐ice advances in the eastern Fram Strait during the last 9 ka: Multiproxy evidence for a two‐phase Holocene

A sediment core from the West Spitsbergen continental margin was studied to reconstruct climate and paleoceanographic variability during the last ~9 ka in the eastern Fram Strait (FS). Our multiproxy evidence suggests that the establishment of the modern oceanographic configuration in the eastern FS occurred stepwise, in response to the postglacial sea‐level rise and the related onset of modern sea‐ice production on the shallow Siberian shelves. The late Early and Mid‐Holocene interval (9 to 5 ka) was generally characterized by relatively unstable conditions. High abundance of the subpolar planktic foraminifer species Turborotalita quinqueloba implies strong intensity of Atlantic Water (AW) inflow with high productivity and/or high AW temperatures, resulting in a strong heat flux to the Arctic. A series of short‐lived cooling events (8.2, 6.9, and 6.1 ka) occurred superimposed on the warm late Early to Mid‐Holocene conditions. Our proxy data imply that simultaneous to the complete postglacial flooding of Arctic shallow shelves and the initiation of modern sea‐ice production, strong advance of polar waters initiated modern oceanographic conditions in the eastern FS at ~5.2 ka. The Late Holocene was marked by the dominance of the polar planktic foraminifer species Neogloboquadrina pachyderma, a significant expansion of sea ice/icebergs, and strong stratification of the water column. Although planktic foraminiferal assemblages as well as sea subsurface temperatures suggest a return of slightly strengthened advection of subsurface AW after 3 ka, a relatively stable cold‐water layer prevailed at the sea surface, and the study site was probably located within the seasonally fluctuating marginal ice zone during the Neoglacial period.

Cenomanian–Turonian carbon isotope stratigraphy of the Western Canadian Sedimentary Basin

The Cenomanian–Turonian boundary was characterized by distinctive positive carbon isotope excursions that were related to the formation of widespread oceanic anoxia. High-resolution geochemical proxies (TOC, CaCO3, δ13Corg, and δ13Ccarb) obtained from bulk rock, planktic foraminifers, and inoceramids from four marine marlstone-dominated stratigraphic sections in the Western Canada Sedimentary Basin (WCSB) were used to establish a regional carbon isotope stratigraphic framework and to investigate paleoenvironmental variability in four different depositional settings. Compared to background δ13Corg, (<−27‰) and δ13Ccarb (<2‰) values which were correlative to stable isotope excursions during Oceanic Anoxic Event (OAE) II worldwide, the δ13Corg (>24‰), and δ13Ccarb (>4‰) derived from inoceramid prisms in the studied sections within WCSB, were elevated during the Late Cenomanian–Early Turonian. During this interval, TOC and CaCO3 values which increased sporadically to >40% and 7%, respectively, were not consistent enough to be used for stratigraphic correlations. Based on the δ13Corg excursions, two bentonite beds were regionally correlated across this portion of the Western Interior Seaway (WIS). The eruption associated with the “Red” bentonite occurred approximately coeval with the maximum δ13Corg-excursion during OAE II in the Neocardioceras juddii Zone, whereas the “Blue” bentonite coincides with the termination of OAE II in the latest Watinoceras devonense zone. During the Late Cenomanian–Early Turonian in the WCSB, benthic foraminifers were sparse or totally absent, indicating the existence of fully anoxic bottom-water conditions. Planktic foraminifera were common in the well-oxygenated surface waters. A benthic oxic zone characterized by several agglutinated species occurs in the eastern part of the WSCB at the beginning of OAE II in the Sciponoceras gracile zone. The termination of the OAE II in the WCSB coincides with the first occurrence of small ammonites (Subprionocyclus sp.) in the western part of the basin.

Changes in planktic and benthic foraminifer assemblages in the Gulf of Lions, off south France: Response to climate and sea level change from MIS 6 to MIS 11

AbstractA multidisciplinary study involving micropaleontological and geochemical tools was carried out in borehole PRGL1 (Promess 1), with the aim of reconstructing the impact of climate change and sea level variation between 133 ka and 406 ka in the upper slope of the Gulf of Lions. We used factor analysis to obtain three main benthic assemblages related to eutrophic, mesotrophic, and oxygenated environments; planktic foraminifers were grouped as warm‐water and cold‐turbulent species. These results were compared with records of CaCO3 and major and trace elements (Al, Ca, K, Sr) as well as the C/N ratio of organic matter. Power and cross‐spectral analysis showed a straightforward relationship between precession minima and thermal stratification of the water column as well as the occurrence of eutrophic bottom conditions during lowstand periods and mesotrophic environments at times of highstand. These eutrophic‐mesotrophic oscillations, usually driven by global eustatic change, also involved regional variations in CaCO3 source to this environment. During periods of precession maxima, enhancement of northwesterly winds increased primary productivity by mixing, enhancing the percentage of cold‐turbulent species in the water column and the proportion of oxygenated benthic species on the bottom. During interglacial stages, these events were recorded by lower biogenic carbonate at the expense of higher silicate‐related components most likely due to a higher supply from Pyrenees rivers. The record of oxygenated benthic species can be a good proxy to monitor past changes in Winter Intermediate Water dynamics driven by northwesterly winds.

Deglacial–Holocene environmental changes at the Pacific entrance of the Strait of Magellan

We show environmental and nitrogen cycle changes between 13 and 2.5kyr BP (from the latest deglaciation to the Holocene) based on biogeochemical records in a sediment core from the Pacific entrance of the Strait of Magellan. Organic carbon, total nitrogen, and C37 alkenone contents were low during 13–9kyr BP but increased rapidly at 8kyr BP. The relative contribution of tetra-unsaturated C37 alkenone, used as a salinity proxy, suggests low salinity during 13–9kyr BP changing to high salinity at 8kyr BP. Planktic foraminifer data showed that Globigerina bulloides was more abundant during the deglacial–early Holocene than in the mid–late Holocene, whereas abundances of Neogloboquadrina pachyderma showed the opposite pattern. This evidence plus biogenic opal data suggest that sea level rose, surface waters were relatively stratified, and in situ productivity was low except for organisms with opal tests from 13 to 9kyr BP. Bulk δ15N values were high (9–11‰) relative to present-day values during the deglacial–early Holocene, with consistently lower values (~7‰) after ~8kyr BP. These relatively high δ15N values most likely reflect increased nutrient utilization in the Southern Ocean, which resulted in high-δ15N water being advected to the Patagonian fjords, although local denitrification caused by the delivery of copious terrestrial materials and organic matter to the ocean cannot be ruled out. By ~8kyr BP continental influences and surface stratification were reduced and characteristic Holocene conditions were established, with increased influence of Southern Ocean water in the western Strait of Magellan. Sea surface temperatures showed millennial-scale changes during the deglaciation and early Holocene, with relatively warm temperatures (11–12°C) corresponding to the Antarctic counterpart of the Younger Dryas cooling event of the Northern Hemisphere. The longer term pattern (~10kyr time scale) in alkenone-derived sea surface temperatures generally follows orbital changes in insolation during austral spring, suggesting a controlling influence of austral spring insolation on southern Patagonian climate.

Reprint of: Benthic and planktic community changes at the North Siberian margin in response to Atlantic water mass variability since last deglacial times

Abstract The eastward penetration of Atlantic-derived water (ADW) into the Eurasian Basin of the Arctic Ocean was investigated at the western Laptev Sea continental margin for the time since c. 17.6 ka. Using a high-resolution investigation of the lithology, geochemistry, planktic and benthic foraminifers, and ostracods on a sediment core from 270 m water depth major steps in the environmental evolution of the region are recognized. In general, ADW was continuously present in the study area. Between 17.6 and 15.4 ka ADW manifested itself through open-water polynyas and associated upwelling events. Comparison between the Laptev Sea and northern Svalbard shelf using Cassidulina neoteretis allows assuming an unmodified subsurface inflow of ADW within its northern branch between 15.4 and 13.2, which was strongest after 14.7-ka and in line with the overall climate amelioration. A local freshwater event at 13 ka followed by shelf flooding and the establishment of a freshened shelf water mass resulted in an off-shelf displacement of ADW from the studied site as suggested by the disappearance of C. neoteretis between 12 and 7 ka. As evidenced by an abundance peak in Nonion labradoricum , the sea-ice marginal zone was located at the site around 12–11 ka but then shifted northward during the early Holocene warming. Enhanced ADW inflow since 7 ka correlated with climate cooling and southward retreat of the seasonal drift-ice margin. The inflow of ADW during mid–late Holocene differed from deglacial times because of the combined influence of northern and eastern ADW branches.

The Cenomanian–Turonian boundary on the Saharan Platform (Tunisia and Algeria)

Several transects made of correlated stratigraphic sections and well logs have been constructed spanning southern Tunisia and the Algerian Sahara (Tinrhert) for comparison with earlier results obtained in the Saharan Atlas. The study is based on facies analysis, sedimentology, biostratigraphy focused on ammonites and foraminifers) as well as whole rock geochemistry (δ13C). These suggest that the entire northern Sahara Platform underwent marine flooding that commenced just prior to the onset of the global positive δ13C shift documented for the Cenomanian–Turonian boundary. This flooding occurred in two phases. The first phase is expressed by the deposition of deeper-water, light-coloured bioturbated mudstones overlying the shallow-water deposits comprising the local Cenomanian successions. But in some places in the Central Sahara (Hassi Messaoud area, Tihemboka Arch) as well as in the Saharan Atlas, shallow-water carbonates kept up locally with the relative sea-level rise to build up isolated carbonate platforms. The topographic lows or saddles between these areas could have been formed through differential accumulation rates. During the second phase, flooding resumed and black shales were deposited over the mudstones in the saddles. The occurrence of black shales in these saddles is limited to the northern edge of the platform (Saharan Atlas of Algeria, Gafsa Trough in southern Tunisia). On the platform, this phase is represented by the same kind of mudstones deposited during the first phase of the flooding (southern Tunisia), or by ammonite-rich chalks in the intra-cratonic basin of the Tinrhert (southern Algeria). Black-shale deposition ceased in the early Turonian. Based on the δ13C curve, the latest Cenomanian flooding of the Sahara Platform is roughly coeval with that documented for the US Western Interior.During the first phase of the transgression, that is before the occurrence of the large Whiteinella of the W. archeocretacea Zone in the black shale unit, planktic foraminifers are dominated by small globulose forms of the Hedbergella delrioensis type, associated with Heterohelicidae. Keeled forms (rotaliporids, dicarinellids) are scarce and always very small when present. Perhaps these dwarfed forms were adapted to the restricted environments of the extensive intracratonic seaways crossing the Saharan Platform to the Benoué Trough in Nigeria.

In search of the Latest Danian Event in a paleobathymetric transect off Kasserine Island, north-central Tunisia

Danian (lower Paleocene) sequences in north-central Tunisia are dominantly composed of marls and shales but a conspicuous, indurated glauconite-bearing marker bed is associated with the P3a–P3b transition. This glauconite bed is considered to correlate with the Latest Danian Event (LDE) described from the Nile Basin in Egypt, with the ‘top Chron C27n event’ (Atlantic and Pacific Oceans) and with the ‘CIE-DS1’ (Zumaia, Spain). The LDE is thought to reflect a short period of global warming, similar to the Paleocene Eocene Thermal Maximum, but of lesser magnitude. The presence of a glauconitic bed at the P3a/P3b transition in Tunisia suggests that the sequence is condensed, which is confirmed by planktic foraminifer and nannofossil biostratigraphy, and by the absence of the typical LDE beds found in most Egyptian sections. Benthic foraminiferal assemblages were quantitatively analyzed in three sections in north-central Tunisia (Sidi Nasseur, Garn Halfaya, Elles) in order to characterize the paleoenvironmental evolution during the late Danian and compare this with sections in Egypt. The benthic foraminiferal assemblages indicate that the Tunisian sections were located along a depth- and a paleoenvironmental gradient on the shelf north of Kasserine Island. The reconstructed depth range is comparable with sections in Egypt, and encompasses middle neritic (Sidi Nasseur section) to shallow upper bathyal depths (Elles section, with up to 16% Gavelinella beccariiformis below the P3a/P3b). Like in Egypt, assemblage shifts across the P3a/P3b subzonal transition indicate shallowing and a transition to a more eutrophic paleoenvironment, characterized by relatively high abundances of buliminids and Stainforthia sp. The δ13C and δ18O records generated on well-preserved specimens of the ostracode species Bairdia failed to demonstrate the presence of the carbon isotope excursion (CIE) associated with the LDE at the base of Subzone P3b. A condensed section or a hiatus associated with the glauconite bed would explain why the CIE is not recorded in the Tunisian sections.

Micron-scale intrashell oxygen isotope variation in cultured planktic foraminifers

In this study, we show that the rate of shell precipitation in the extant planktic foraminifer Orbulina universa is sufficiently rapid that 12h calcification periods in 18O-labeled seawater can be resolved and accurately measured using secondary ion mass spectrometry (SIMS) for in situ δ18O analyses. Calcifying O. universa held at constant temperature (22°C) were transferred every 12h between ambient seawater (δ18Ow=−0.4‰ VSMOW) and seawater with enriched barium and δ18Ow=+18.6‰ VSMOW, to produce geochemically distinct layers of calcite, separated by calcite precipitated with an ambient geochemical signature. We quantify the position of the Ba-labeled calcite in the shell wall of O. universa via laser ablation ICP-MS depth profiling of trace element ratios, and then measure intrashell δ18Ocalcite in the same shells using SIMS with a 3μm spot and an average precision of 0.6‰ (±2 SD). Measured δ18Ocalcite values in O. universa shell layers are within ±1.1‰ of predicted δ18Ocalcite values. Elemental and oxygen isotope data show that LA-ICP-MS and SIMS measurements can be cross-correlated within the spatial resolution of the two analytical techniques, and that δ18Ocalcite and elemental tracers appear to be precipitated synchronously with no measurable spatial offsets. These results demonstrate the capability of SIMS to resolve daily growth increments in foraminifer shells, and highlight its potential for paleoceanographic and biomineralization applications on microfossils.

Seasonal Flux and Assemblage Composition of Planktic Foraminifers from a Sediment-Trap Study in the Northern Gulf of Mexico

ABSTRACT Poore, R.Z.; Tedesco, K.A., and Spear, J.W., 2013. Seasonal flux and assemblage composition of planktic foraminifers from a sediment-trap study in the northern Gulf of Mexico. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 6–19, Coconut Creek (Florida), ISSN 0749-0208. Sediment-trap samples from the northern Gulf of Mexico reveal that Globorotalia truncatulinoides, Neogloboquadrina dutertrei, Pulleniatina spp. (includes P. obliquiloculata and P. finalis), and the Globorotalia menardii group (includes Gt. menardii, Gt. tumida, and Gt. ungulata) generally occur in cold months. Globigerinoides ruber (white and pink varieties) and Globigennoides sacculifer occur throughout the year. The seasonal occurrence of individual taxa of planktic foraminifers in the Gulf of Mexico have important differences with the seasonal occurrence of the same taxa ...