South Atlantic Site Research Articles

Maastrichtian to Eocene Subsurface Stratigraphy of the Cauvery Basin and Correlation with Madagascar

Abstract: Late Maastrichtian through middle Eocene planktic foraminiferal biostratigraphy and erosion patterns from three Cauvery basin wells are compared with the Krishna-Godavari basin, Madagascar and South Atlantic Site 525A. Maastrichtian sedimentation appears continuous at DSDP site 525A and substantially complete in the Cauvery basin and Madagascar for the interval from ~70.3 to 66.8 Ma (zones CF6-CF3). But the latest Maastrichtian through early Paleocene record is fragmented, except for some Krishna-Godavari and Cauvery basin wells protected from erosion by Deccan traps or graben deposition, respectively. Hiatuses are observed correlative with sea level falls at 66.8, 66.25, 66.10, 65.7, 63.8 and 61.2 Ma with erosion amplified by local tectonic activity including doming and uplift due to Deccan volcanism. Throughout this region the Cretaceous-Paleogene transition (magnetochron C29r-C29n, 66.25-65.50 Ma) is preserved only in deep wells of the Krishna-Godavari basin where Deccan Traps protected intertrappean sediments from erosion. The late Paleocene to middle Eocene marine record was recovered from two Cauvery basin wells with hiatuses correlative with low sea levels at ~49.0-56.5 Ma (zones P4c-E6) and ~53.0-55.3 Ma (zones E1-E4) at the ridge well KALI-H. A nearly complete record was recovered from well AGA, including the PETM event (zones E1-E2), which marks this an excellent reference section for India. Similarity in erosion and sedimentation patterns of the late Maastrichtian to middle Paleocene from India to Madagascar and South Atlantic is mainly attributed to climate changes and sea level falls, regional tectonic activity from the Bay of Bengal to Madagascar, and uplift and doming in the Cauvery and K-G basins as a result of Deccan volcanism. Directly correlative with Deccan volcanism are high stress environments for marine calcifiers, as observed by species dwarfing, reduced diversity and blooms of the disaster opportunist Guembelitria cretacea in magnetochron C30n (zones CF4-CF3) correlative with Deccan phase-1 and Ninetyeast Ridge volcanism, in C29r (zones CF2-CF1) correlative with Deccan phase-2 and in C29n (zone P1b) correlative with Deccan phase-3 marking volcanism as the most important stress factor in the end-Cretaceous mass extinction and delayed evolution of planktic foraminifera.

Emerging questions from the discovery of the long term presence of Acipenser oxyrinchus in France

Sturgeon remains have been identified in several French archaeological sites. Accurate observation has led to a new finding: the presence of another sturgeon species by side of Acipenser sturio. This investigation, mostly a reevaluation, was conducted by using the morphological characteristics of dermal bones (bony plates and scutes) that allow discriminating between the two sturgeon species A. sturio from A. oxyrinchus. A. oxyrinchus was found present in several archaeological sites on the French Atlantic coast, dating from the end of the Neolithic Age until the 2nd century AD (C.R. Palevol., 8, 2009, 717); in the Loire River in Roman Times and in the 11th century AD; in the Seine River drainage between the 2nd century BC and first half of 17th century AD, as well as in the Scarpe River flowing into the Scheldt River (France, Belgium and the Netherlands) between the 10th and 11th century AD. In one site, up to 65 sturgeon remains were identified and are attributable to one or the other species. In two out of the four South Atlantic sites, both species were recorded, as well as in one site (Paris-Grand Louvre) of the Seine River. The two species were in sympatry for a long time in several French drainages and sometimes up until recent times. The sympatry of the two species in France gives additional support for this characteristic as a quasi-general rule concerning sturgeons world-wide. The present findings suggest A. oxyrinchus as a native French sturgeon species and new key-issues should be addressed.

Response of South Atlantic deep waters to deglacial warming during Terminations V and I

New deep-sea core data from the Atlantic sector of the Southern Ocean, covering MIS12 to MIS10 and the last deglaciation, show a clear lag of the changes in deep water properties with respect to changes in surface conditions. The development of a chronology based on the correlation of Southern Ocean sea surface temperature with air temperature over Antarctica allows the quantification and comparison of phase lags within the marine records during Termination V (TV) and Termination I (TI). Deglacial changes in the South Atlantic are interpreted as the response to changes in the state of the Atlantic meridional ocean circulation (AMOC). The warming of South Atlantic surface waters and air temperature over Antarctica at the beginning of both TV and TI is attributable to a reduction in interhemispheric heat transport due to the weakening of the AMOC. Comparison of our results with CLIMBER-2 simulations indicates that the response of bottom waters seen in the benthic isotopic records, delayed with respect to South Atlantic surface warming, can be explained by the increased inflow of North Atlantic Deep Water (NADW) to the South Atlantic site at the time of the AMOC recovery. Reconstructed sea surface temperature at our South Atlantic site exhibits a cold spell at the end of TV, resembling the Antarctic Cold Reversal of the last deglaciation. The presence of cold spells during TV and TI may be explained by the fact that the recovery of the AMOC took place early during the termination in both cases. The sequence of events is similar during both terminations; however, the magnitude of the phase shifts between South Atlantic surface and deep waters conditions differs from one termination to the other, suggesting variations in the magnitude and duration of the AMOC perturbation.

Variability in oceanic dissolved iron is dominated by the colloidal fraction

Oceanic surface and deep iron distribution and size fractionation were investigated on three cruises in the sub-tropical and tropical Atlantic Ocean. Detailed profiles and transects were collected and analyzed for “dissolved” Fe (DFe, 0.4 μm filtered) and “soluble” Fe (SFe, 0.02 μm filtered). The difference between DFe and SFe is inferred to be the “colloidal” fraction of Fe (CFe). SFe concentration distributions and profiles showed little variability in the Atlantic Ocean with slightly lower concentrations of SFe in the upper ocean than the relatively uniform concentrations observed in deep-water (≈0.3 to 0.4 nmol/kg). In contrast, variability in the Atlantic DFe was dominated by variability in CFe. DFe and CFe followed dust deposition trends, and observed surface maxima in DFe profiles were always due to maxima in the CFe fraction. Where dust deposition and surface DFe were low (i.e., the South Atlantic), the CFe fraction of DFe was low and frequently negligible in surface waters. Below the surface maxima in CFe and DFe, CFe always decreased to negligible levels at 30–80 m, remained low or negligible throughout the pycnocline, and increased with depth below the pycnocline. At a site located on the edge of the equatorial system (10°N), high DFe and CFe concentrations were associated with an oxygen minimum zone (OMZ) at depths of 130 to 1100 m. Deep-water DFe and CFe concentrations varied between water masses depending on the source, age, and path of the water masses. DFe in NADW decreased by 30% from the North Atlantic to the South Atlantic site with most of the decrease due to loss of CFe. At the South Atlantic site, NADW had higher DFe and a higher fraction of CFe than the Antarctic water masses.

Dissolved iron in the tropical and subtropical Atlantic Ocean

Detailed depth profiles and surface transects of dissolved iron (DFe defined by 0.4‐μm filtration) were investigated on three cruises in the subtropical and tropical Atlantic Ocean where dust deposition varied by 3 orders of magnitude. Surface DFe and dissolved Mn concentrations reflected dust deposition trends, but are not proportional to the estimated inputs. Using estimates of the atmospheric flux of DFe, surface DFe residence times were calculated to be on the order of 1 to 5 months. Deepwater DFe concentrations varied with water masses depending on their source, age, and transit pathways. At a site located on the edge of the equatorial system (10°N, 45°W), high DFe (>1 nmol/kg) was associated with an oxygen minimum zone at depths of 130 to 1100 m. DFe concentrations in North Atlantic Deep Water (NADW) decreased by 30% from sites in the North Atlantic to a site in the South Atlantic (24.5°S, 37°W), and DFe was lower in the Antarctic derived water masses (∼0.4 nmol/kg) than in NADW at the South Atlantic site. An estimate of deepwater scavenging residence time for DFe was 270 ± 140 years based on decreasing DFe along the NADW flow path.

Competition, mortality and diversity in South Atlantic coastal boulder communities

Boulder shores are common at all latitudes and dominate the intertidal and subtidal zones of sub-Antarctic coastlines. The encrusting benthos of boulders was examined on similar shore types at four locations: Tierra del Fuego, East Falkland, West Falkland and Bird Island (off South Georgia). Bird Island is unusual in experiencing high trampling and organic enrichment from fur seals. The results were compared to a Patagonian site and a non-trampled South Georgia site (Husvik) and other sites taken from the literature. Principal Component Analysis revealed South Atlantic/Southern Ocean encrusting faunas formed a distinct cluster when compared to assemblages from elsewhere at similar latitudes. Bray Curtis cluster analysis of the South Atlantic-Southern Ocean sites showed the major division was between Southern Ocean and South Atlantic Ocean sites, beyond which there were three distinct clusters centred around Patagonia (Magellanic), the Falklands and Southern Ocean sites. The organisation of competitive interactions between species was mostly determinate and transitive (essentially hierarchical). The transitivity index scores were higher than most similar assemblages studied to date. The diversity of encrusting assemblages ranged from Shannon Weaver H values of 2.38–0.77 (East Falkland and Bird Island, respectively) in the intertidal to 1.27–0.73 (Patagonia and South Georgia, respectively) in the subtidal zone. Annual mortality (of bryozoan colonies) varied from 85–97% in the intertidal to 65–92% in the subtidal, being higher in the Southern Ocean than South Atlantic sites, largely due to ice scour and wave action. The Bird Island mortality values may be high even for a Southern Ocean site.

An analysis of ozonesonde data for the troposphere: Recommendations for testing 3‐D models and development of a gridded climatology for tropospheric ozone

I present an analysis of ozonesonde data, synthesizing what is known about the distribution of tropospheric ozone. Major features of the distribution are highlighted, and recommendations are given for testing three‐dimensional models of tropospheric chemistry and transport with these data. The data are analyzed on pressure surfaces and relative to the height of the thermal tropopause. A minimum of 20 soundings are required for 95% confidence intervals of the ozone monthly means to be less than ±30% near the extratropical tropopause. Twenty soundings also ensures means reliable to better than ±15% for 800–500 hPa for the extratropics and for 800–100 hPa in the tropics. Ozone variability is higher in the upper troposphere for subtropical locations than for tropical locations, and 35 soundings are required for 400–100 hPa for the means to be defined to better than ±15%. For northern middle and high latitudes, the broad summer maximum in ozone in the middle troposphere extends all the way up to the tropopause. Median concentrations at the tropopause are highest in June and July, typically 125–200 ppb, and are a factor of 2 smaller in winter. Highest values of ozone are in spring 2 km above the tropopause. The change in the phase of the annual cycle of ozone between the tropopause and the region immediately above it, and the steep concentration gradients across the tropopause, suggest that high vertical resolution (∼1 km) will be required in models to simulate this behavior. Mean ozone values in the middle troposphere are approximately constant from 30° to 75° in the winter in both hemispheres, while there is a maximum from 35° to 50°N in summer. In the northern subtropics, there is a summer minimum in middle tropospheric ozone over the Pacific and a summer maximum over the Atlantic which appear to be related to differences in circulation. Mean ozone values over Samoa are similar to those measured 20–30 years ago over Panama. Ozone is higher over the tropical South Atlantic (Natal) than over the western Pacific (Samoa) all year from about 800 hPa to the tropopause; ozone is most similar in May and June over the Atlantic and Pacific, the months with minimum burning in the tropics. The ozone maximum at Samoa in the middle and upper troposphere in October is caused by long‐range transport of ozone and its precursors from biomass burning, with the peak lagging that at Natal by about a month. The secondary peak in ozone in January and December at South Atlantic sites reflects transport of biomass burning effluents from the Northern Hemisphere. The sonde data were used in combination with surface and satellite data to derive a gridded climatology for tropospheric ozone.

Last-glacial-maximum North Atlantic deep water: on, off or somewhere in-between?

Various papers have been published during the past decade concerning Last Glacial Maximum (LGM) North Atlantic Deep Water (NADW) flow. Using somewhat different methods, they have produced somewhat contradictory results. This review considers both apparent and real conflicts concerning the data and their interpretation, and attempts to resolve them. Despite the earlier (contradictory) interpretations, currently there is a widespread belief that nutrient concentrations in deep cores from the North Atlantic increased during glacial times and that concentrations in the upper-deep and intermediate waters decreased at least slightly. It is also clear that further north in the basin (particularly at upper-deep and intermediate depths), nutrient concentrations were as low or perhaps even lower than those seen today. Data from the Caribbean Sea, ventilated by intermediate waters through an approximately 1800 m sill, indicate that lower nutrient levels were also found at intermediate depths in the North and Tropical Atlantic; this data is supported by continental margin data. The recontoured 8 13 C data of Duplessy et al. ( Paleoceanography 3, 343—360 (1988)) remain a valid expression of the broadscale LGM Atlantic nutrient distribution. Data from the South Atlantic has been the most contradictory to date, but recent 8 13 c evidence from a low-productivity South Atlantic site supports Cd data indicating a relative stability in the nutrient chemistry of waters that are presently influenced by low-nutrient NADW. Sedimentary 231 Pa/ 230 Th data appear to require the continued export of Atlantic-generated 231 Pa from the Atlantic into the Southern Ocean. Finally, radiocarbon evidence from paired planktonic/benthic foraminifera indicates that the ventilation time of the North Atlantic remained low and that the ventilation time of the entire ocean did not change much beyond the uncertainty of the 14 C data. Taken together, this evidence suggests that the NADW became ‘Glacial North Atlantic Deep/Intermediate Water’ (GNAIDW) during glacial times, with perhaps a greater flux through intermediate waters than currently combined with a lesser flux through deeper waters. Although one cannot say much with confidence about the total GNAIDW flux, the data are consistent with a persistent but perhaps somewhat diminished role for NADW in the global thermohaline circulation during glacial times. A review of recent evidence concerning the response of the deep North Atlantic during the Younger Dryas concludes that there is no inconsistency between the new evidence and the occurence of a Younger Dryas NADW event in the deep western North Atlantic.

Biogeography of terminal Cretaceous deep-sea benthic foraminifera from the Atlantic and Pacific Oceans

Most species of Late Cretaceous deep-sea benthic foraminifera are believed to be cosmopolitan and therefore to exhibit only minor biogeographical differences. In this preliminary report, six Deep Sea Drilling Project (DSPD) sites from different oceans, paleolatitudes, and paleodepths were analyzed for terminal Cretaceous abyssal-bathyal benthic foraminifera in order to investigate their assumed cosmopolitan distribution and the question of whether different faunal compositions are related to time, different paleolatitudes, and/or different paleodepths. The material studied was obtained from the low-latitude Site 465 (Pacific Ocean), and the intermediate-latitude Sites 384 (North Atlantic) and 356, 516, 525, and 527 (South Atlantic). The material analyzed represents a time slice encompassing the last 20–50 k.y. of the Cretaceous. The faunas contain numerous “Velasco-type” species, such as Gavelinella beccariiformis (White), Cibicidoides velascoensis (Cushman), Nuttallides truempyi (Nuttall), Gaudryina pyramidata Cushman, and various gyroidinoids and buliminids. The results contradict the general assumption of the cosmopolitan nature of Late Cretaceous deep-sea benthic foraminifera advocated in the literature. Only about 9% of the taxa identified were found to be truly “cosmopolitan” through their occurrence at all the sites analyzed. On the basis of correspondence analysis and relative abundance data, three assemblages and three subassemblages were recognized: (1) a bathyal-abyssal assemblage [ Nuttallinella sp. A, Cibicidoides hyphalus (Fisher), Valvalabamina sp. evolute form, and Gyroidinoides spp.] at the South Atlantic Sites 356, 516, 525, and 527, divided into three subassemblages, namely (a) a middle bathyal subassemblage [ Eouvigerina subsculptura McNeil and Caldwell, Tritaxia aspera (Cushman), and G. pyramidata] at Sites 516 and 525, (b) a lower bathyal subassemblage [ Osangularia? sp., Pyramidina rudita (Cushman and Parker), and Quadrimorphina camerata (Brotzen)] at Site 356, and (c) an abyssal subassemblage [ Gyroidinoides sp. C, Hyperammina-Bathysiphon, Gyroidinoides beisseli (White), and Globorotalites sp. B] at Site 527; (2) an abyssal assemblage [ Buliminella cf. plana (Cushman and Parker) and Bulimina incisa Cushman] at the North Atlantic Site 384; and (3) a middle bathyal assemblage [ Vulvulina sp. A, Osangularia navarroana (Cushman), Alabamina? sp., Bulimina velascoensis (Cushman), Spiroplectammina spp. calcereous forms, and Bulimina trinitatensis Cushman and Jarvis] at the Pacific Site 465.

Miocene benthic foraminiferal Cd/Ca records: South Atlantic and western equatorial Pacific

Cadmium‐to‐calcium records in benthic foraminifera, interpreted in conjunction with carbon isotope records, reflect oceanic circulation patterns and oceanic inventories of Cd, carbon 13/carbon 12, and indirectly, phosphorus. Cd/Ca ratios have been determined in benthic foraminifera Cibicidoides spp. for the late, middle, and early Miocene from a site in the South Atlantic (Deep Sea Drilling Project (DSDP) site 525, leg 74, ∼2500 m, Walvis Ridge) and from a site in the western equatorial Pacific (DSDP site 289, leg 30, ∼2200 m, Ontong‐Java Plateau). Both sites have well‐established carbon isotope records for benthic foraminifera typical of the global record dominated by inventory changes. Cd/Ca ratios and carbon isotope values were averaged for the Miocene in time intervals substantially longer than estimated oceanic residence times of Cd, C, or P. Oceanic mean Cd/Ca and carbon isotopes were estimated as weighted means of the values from both sites using weighting factors based on replicating modern oceanic means; this may tend to underestimate oceanic inventories earlier than the late Miocene because of changing water mass dominance at the South Atlantic site. From these means, the oceanic Cd inventory appears relatively stable during the Miocene, while there are large changes in carbon isotope inventories. Miocene Cd inventory estimates are at least 20% lower than published estimates for Quaternary stages 1 and 2. Increasing oceanic Cd inventories over the past 10 m.y. are consistent with hypotheses of increased river fluxes in the recent geologic past. Cd/Ca differences between sites may be indicative of the extent of basin‐basin fractionation from bottom water circulation, although the validity of this comparison depends on how representative each of these two sites is through time for its respective ocean basin. The Pacific‐Atlantic Cd/Ca difference based on these two sites was larger in the late Miocene compared to the middle and early Miocene. The relationship between Cd/Ca and carbon isotope inventories and intersite gradients for these sites suggests that either oceanic phosphorus inventories or parameters related to marine organic matter composition must have been different in the Miocene than at present. Large changes in the carbon isotope balance, reflected as both positive and negative excursions in the carbon isotope inventories, occurred with little effect on Cd inventories. Changes in phosphorus fluxes associated with these carbon isotope flux changes may have been compensated for by changing deposition fluxes to other phosphorus sinks. Phosphorus inventories may have increased from the middle to late Miocene with increasingly negative oceanic carbon isotope inventories. However, confirmation of these suggestions depend on collecting more Cd/Ca (and δ13C) data throughout the Miocene oceans and on developing the application of other constraints for these interpretations.

Regional variations in spinel compositions: An important key to the Cretaceous/Tertiary event

Research Article| June 01, 1986 Regional variations in spinel compositions: An important key to the Cretaceous/Tertiary event Frank T. Kyte; Frank T. Kyte 1Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar Jan Smit Jan Smit 1Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar Author and Article Information Frank T. Kyte 1Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024 Jan Smit 1Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1986) 14 (6): 485–487. https://doi.org/10.1130/0091-7613(1986)14<485:RVISCA>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Frank T. Kyte, Jan Smit; Regional variations in spinel compositions: An important key to the Cretaceous/Tertiary event. Geology 1986;; 14 (6): 485–487. doi: https://doi.org/10.1130/0091-7613(1986)14<485:RVISCA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Spinel found in spherules from Cretaceous/Tertiary boundary sediments exhibits a wide range in composition and is distinguished from typical igneous spinel by high Mg, Al, and Ni, relatively low Ti and Cr, and high Fe2O3/FeO. Solid-solution compositions range from nearly pure magnetite to magnesioferrite to relatively pure MgAl2O4 spinel. The Ni-spinel trevorite is also a common component. A regional variation in composition is also observed: spinel from two North Pacific sites has higher Mg and Al and lower Ni and Fe than spinel from two European sites and one South Atlantic site. The most probable source of the spinel is crystallization from molten silicate droplets produced from a major impact event. The regional variations may provide a key to locating the impact site(s). First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

DSDP Leg 73: Contributions to Paleogene stratigraphy in nomenclature, chronology and sedimentation rates

DSDP Leg 73 was successful in determining magnetostratigraphic—biostratigraphic correlations throughout much of the Paleogene. This paper treats three aspects of the data analysis. The first section treats the development of a chron nomenclature which facilitates the precise correlation of arbitrary events with respect to the geomagnetic polarity history. The second section analyzes the accuracy of radiometric dates for the Paleogene. The conclusion is that despite the recent advances in radiochronology ‘South Atlantic Standard’ remains the most convenient and probably the most reliable chronological standard. The final section studies the correlation in sedimentation rates between the Umbrian and South Atlantic sites. The conclusion is that sedimentation rate changes determined from magnetostratigraphy provide a high-resolution source of paleoenvironmental information. Strong correlations are noted between sites and with respect to other paleo-environmental studies involving oxygen isotope ratios, biogeography and CCD fluctuations within the Paleogene marine sediments.