Occurrence of late Aptian/earliest Albian radiolaria from ODP Hole 113-693A (Table 2)

Unusually well preserved Cretaceous radiolarians are observed in the subsurface sections from two drilled sites in the Weddell Sea collected during Leg 113 of the Ocean Drilling Program. Radiolarians from the lithified calcareous chalk of Hole 689B represent the first Campanian-Maestrichtian assemblage which is characterized by abundant Cromyodruppa Iconcentrica, Dictyomitra multicostata, and Protostichocapsa stocki. Abundant Pseudodictyomitra pentacolaensis and Diacanthocapsa sp. 1, on the other hand, are the main constituents of the assemblage from the latest Aptian/earliest Albian diatomite of Hole 693B. These represent the oldest and the highest-latitude reported radiolarian occurrences from the Atlantic sector of the Antarctic Ocean. The assemblages are marked by their low diversity and an absence of low- to mid-latitude zonal indices.

(Table 1) Organic carbon isotopic composition in Cretaceous sediments at DSDP Hole 75-530A

Cretaceous sediments from DSDP Site 530 have been analyzed for organic carbon isotopic composition. The d13C values in the sediments decrease from -22.7 per mil to -27.5 per mil in the following order: light-olive green mudstone/claystone, dark brown-red mudstone/siltstone/claystone, and black shale. This large range is primarily the result of variation in the relative amounts of terrestrial organic carbon superimposed on that derived from marine organisms. The black shales have an average d13C value of -25.9 per mil (range is from -23.7 per mil to -27.5 per mil). These values indicate that they originated primarily in terrigenous organic materials. The average d13C value present throughout the Cretaceous suggests that a large amount of terrestrial organic matter was supplied into this paleoenvironment, except during the Campanian, when an average d13C of -23.9 per mil is found near the marine end of the range.

Age model and Nd isotope ratios of DSDO Hole 43-386 and ODP Hole 210-1276A

Modern thermohaline circulation plays a role in latitudinal heat transport and in deep-ocean ventilation, yet ocean circulation may have functioned differently during past periods of extreme warmth, such as the Cretaceous. The Late Cretaceous (100-65 Ma) was an important period in the evolution of the North Atlantic Ocean, characterized by opening ocean gateways, long-term climatic cooling and the cessation of intermittent periods of anoxia (oceanic anoxic events, OAEs). However, how these phenomena relate to deep-water circulation is unclear. We use a proxy for deep-water mass composition (neodymium isotopes; e-Nd) to show that, at North Atlantic ODP Site 1276, deep waters shifted in the early Campanian (~78-83 Ma) from e-Nd values of ~-7 to values of ~-9, consistent with a change in the style of deep-ocean circulation but >10 Myr after a change in bottom water oxygenation conditions. A similar, but more poorly dated, trend exists in e-Nd data from DSDP Site 386. The Campanian e-Nd transition observed in the North Atlantic records is also seen in the South Atlantic and proto-Indian Ocean, implying a widespread and synchronous change in deep-ocean circulation. Although a unique explanation does not exist for the change at present, we favor an interpretation that invokes Late Cretaceous climatic cooling as a driver for the formation of Southern Component Water, which flowed northward from the Southern Ocean and into the North Atlantic and proto-Indian Oceans.

Geochemistry and mineralogy at DSDP Holes 61-462, 61-462A and 33-315A

Sedimentary rocks of Barremian through early Maestrichtian age recovered on Deep Sea Drilling Project Leg 61 had their principal source in the complex of igneous rocks with which they are interlayered in the Nauru Basin. Relict textures and primary sedimentary structures show these Cretaceous sediments to be of hyaloclastic origin, in part reworked and redeposited by slumps and currents. The dominant composition now is smectite, but locally iron, titanium, and manganese oxides, plagioclase, pyroxene, analcime, clinoptilolite, chalcedonic quartz, cristobalite, amphibole, nontronite, celadonite, and pyrite are also present. The mineral assemblages and the geochemistry reflect the original basaltic composition and its subsequent alteration by one or more processes of submarine weathering, authigenesis, hydrothermal circulation, and contact metamorphism. Hyaloclastitic sandstone, siltstone, and breccia within the sheet flows below 729 meters sub-bottom depth have Barremian fossils, thus establishing the age of the lower, or extrusive, complex of post-ridge-crest volcanism. Similar hyaloclastites between 564 and 729 meters are invaded by hypabyssal sills of the upper igneous complex, and fossil ages of Albian or Cenomanian set an older limit to the age of that second post-ridge-crest episode. Cenomanian to early Campanian sedimentary rocks between 490 and 564 meters have a substantial contribution of clays of submarine-weathered-basalt origin, as well as hydrothermal and pelagic components. The interval of reworked hyaloclastitic siltstone, sandstone, and breccias between 450 and 490 meters is of late Campanian and early Maestrichtian age. These sediments probably formed from glassy basalt that fragmented upon eruption nearby, when sills were being emplaced. In addition to pelagic elements, these Upper Cretaceous volcanogenic sediments include redeposited material of shallow-water origin, apparently derived from the Marshall Islands.

(Appendix) Benthic foraminifera distribution of upper Creatceous and Paleocene at DSDP Hole 72-516F

Benthic foraminifers of the Coniacian-Santonian through the Paleocene were recovered from a continuous pelagic carbonate section from Hole 516F on the Rio Grande Rise. Sixty-five genera and 153 species have been identified, most of which have been reported from other localities. Bathyal depths are reflected in the benthic assemblages dominated by gavelinellids (Gavelinella beccariiformis, G. velascoensis), Nuttallides truempyi, and various gyroidinids and buliminids. Rapid subsidence during the Coniacian-Santonian from nearshore to upper to middle bathyal depths was followed by much reduced subsidence, with the Campanian-Paleocene interval accumulating at middle bathyal to lower bathyal depths. A census study based on detailed sampling reveals major changes in benthic faunal composition at the Cretaceous/Tertiary boundary transition. It was a time of rapid turnover, with the extinctions of numerous species and the introduction of many new species. Overall, species diversity decreases about 20%, and approximately one-third of latest Maestrichtian species do not survive to the end of the Cretaceous. This shift indicates a significant environmental change in the deep sea, the precise nature of which is not apparent from the foraminifers or their enclosing sediments.

Magnetostratigraphy of ODP Leg 207 sediments

Ocean Drilling Program (ODP) Sites 1257-1261 recovered thick sections of Upper Cretaceous-Eocene oceanic sediments on Demerara Rise off the east coast of Surinam and French Guiana, South America. Paleomagnetic and rock magnetic measurements of ~800 minicores established a high-resolution composite magnetostratigraphy spanning most of the Maastrichtian-Eocene. Magnetic behavior during demagnetization varied among lithologies, but thermal demagnetization steps >200°C were generally successful in removing present-day normal polarity overprints and a downward overprint induced during the ODP coring process. Characteristic remanent magnetizations and associated polarity interpretations were generally assigned to directions observed at 200°-400°C, and the associated polarity interpretations were partially based on whether the characteristic direction was aligned or apparently opposite to the low-temperature "north-directed" overprint. Biostratigraphy and polarity patterns constrained assignment of polarity chrons. The composite sections have a complete polarity record of Chrons C18n (middle Eocene)-C34n (Late Cretaceous).

Detailed analysis of the organic carbon content in sediment cores M0002 and M0004

During IODP Expedition 302 (Arctic Coring Expedition-ACEX), the first scientific drilling campaign in the permantly ice-covered central Arctic Ocean, a 430 m thick sequence of upper Cretaceaous to Quaternary sediments has been drilled. The lower half of this sequence is composed of organic-carbon-rich (black shale-type) sediments with total organic carbon contents of about 1-14%. Significant amounts of the organic matter preserved in these sediments is of algae-type origin and accumulated under anoxic/euxinic conditions. Here, for the first time detailed data on the source-rock potential of these black shales are presented, indicating that most of the Eocene sediments have a (fair to) good source-rock potential, prone to generate a gas/oil mixture. The source-rock potential of the Campanian and upper Paleocene sediments, on the other hand, is rather low. The presence of oil or gas already generated in situ, however, can be ruled out due to the immaturity of the ACEX sediments.

Late Cretaceous to Eocene calcareous nannofossil distribution near Gubbio, Italy

Using a modified sample preparation technique, we have been able to establish a detailed lower Campanian to upper Eocene nannofossil stratigraphy in the Bottaccione and Contessa Highway sections near Gubbio. Appearance and extinction levels of virtually all the commonly used calcareous nannofossil zonal markers have been recognized and can now be closely correlated with the planktonic foraminifera zonation and the magnetic reversal stratigraphy previously established in these sections. Comparisons with the nannofossil calibrations of the oceanic magnetic anomaly sequence in Deep Sea Drilling Project (DSDP) sites suggest that magmetic Subchrons C17N and C25N are missing in the Bottaccione section. The observed variability of the relative stratigraphic position of most plankton events is confirmed to less than one magnetic subchron. Absolute abundance, paleobiogeographic restriction, and differential preservation render some of the traditionally used biostratigraphic events less reliable than others.

Palinoestratigrafía, paleoambientes y cambios climáticos durante el Cretácico final y Paleógeno de la Cuenca del Grupo Salta, República Argentina

El objetivo principal de la presente tesis es la búsqueda de nuevos registros palinológicos para las formaciones del Grupo Salta, especialmente para aquellas que cuentan con poco o ningún registro de palinomorfos, tales como las Formaciones La Yesera, Las Curtiembres, Yacoraite y Olmedo. Los resultados palinológicos permitieron evaluar algunos aspectos geológicos como las relaciones estratigráficas, edad y ambientes de depósito. El muestreo se centró principalmente en el período comprendido entre el Neocomiano y Daniano, correspondiente a los subgrupos con mayor escasez de datos (Pirgua y Balbuena). 157 muestras palinológicas de la Cuenca del Grupo Salta y áreas relacionadas se trataron en laboratorio, 31 resultaron fértiles. Se brindan los primeros registros palinológicos de la Formación La Yesera (localidad valle de Pucará) que consisten en 35 especies. Las inferencias aleoambientales obtenidas a partir de la palinoflora apoyan las conclusiones que provienen de los datos sedimentológicos: presencia de un lago perenne al momento de la depositación del Miembro Brealito y sequías estacionales cuando se acumuló el Miembro Don Bartolo. La palinoflora indica un clima subtropical con presencia de cierta aridez. A partir de los rangos estratigráficos de algunas especies y de las dataciones radimétricas del Basalto de Isonza, se estima una edad entre el Albiano y el Cenomaniano. Para la Formación Las Curtiembres (Miembro Morales) se describen 19 especies provenientes de la quebrada de Palo Seco, que constituyen la primer asociación palinológica registrada. El predominio de Ephedraceae y Cheirolepidiaceae, junto a la escasa representación de pteridofitas, sugieren condiciones ambientales de aridez a semiaridez, en coincidencia con la sedimentología que indica que la sección superior del Miembro Morales es transicional con las capas rojas de la parte superior de la Formación Las Curtiembres. La asociación palinológica contiene representantes de amplia distribución espacial y temporal. Es relevante la presencia de Peninsulapollis gillii que indica una edad no mayor al Campaniano para la asociación estudiada. Sólo una muestra de la Formación Yacoraite en la localidad de Tres Cruces fue productiva en cuanto al contenido de palinomorfos. La asociación consta solamente de los géneros Leiosphaeridia y Pediastrum que se asocian a condiciones de agua dulce o mixtas. Para la Formación Olmedo se registran 34 especies de palinomorfos y 39 especies para la Formación Tunal (localidades de Garabatal y El Chorro respectivamente). Ambas formaciones comparten un 49 % de taxa. El marcado predominio de algas clorococales indica condiciones lacustres y un ambiente palustre se infiere por la presencia de Pandaniidites texus y Mtchedlishvilia saltenia. El elevado porcentaje de Verrustephanoporites simplex indica que la selva de ulmáceas, era la unidad fitogeográfica más ampliamente distribuida, comparable con la actual Selva de Transición de la Provincia de Yungas. La coincidencia de facies y contenido palinológico indicarían similares condiciones ambientales para las Formaciones Olmedo y Tunal. Mtchedlishvilia saltenia permiten circunscribir las Formaciones al Daniano. Los cambios climáticos acontecidos durante el desarrollo de la Cuenca del Grupo Salta quedaron evidenciados en la palinoflora. Durante el Cretácico Tardío, habrían prevalecido condiciones de aridez y a partir del Maastrichtiano, el clima se torna más húmedo. Las asociaciones del Daniano se caracterizan por una palinoflora de clima subtropical húmedo. Entre el Paleoceno Superior y hasta el Eoceno Inferior, continúa el registro de la flora de clima subtropical pero con una leve disminución en la humedad. Las especies Peninsulapollis gillii, Rhoipites sp. A, Rousea patagonica, Spinitricolpites jennerclarkei, Verrustephanoporites simplex y Azolla sp., pasan el límite Cretácio-Paleógeno registrándose en sedimentos pre- y post-danianos. Se requieren mayores estudios de detalle en aquellos niveles donde está contenido el límite para esclarecer los posibles cambios vegetacionales que hayan ocurrido.

Benthic and planktic foraminiferal stable isotope records combined with Nd isotope ratios of ODP Hole 198-1210B

The Pacific Ocean is the largest water body on Earth, and circulation in the Pacific contributed significantly to climate evolution in the latest Cretaceous, the culmination of a period of long-term cooling. Here, we present new high-resolution late Campanian to Maastrichtian benthic and planktic foraminiferal stable isotope data and a neodymium (Nd) isotope record obtained from sedimentary ferromanganese oxide coatings of Ocean Drilling Program Hole 1210B from the tropical Pacific Ocean (Shatsky Rise). These new records resolve 13 million years in the latest Cretaceous, providing insights into changes in surface and bottom water temperatures and source regions of deep to intermediate waters covering the carbon isotope excursions of the Campanian-Maastrichtian Boundary Event (CMBE) and the Mid-Maastrichtian event (MME). Our new benthic foraminiferal d18O and Nd isotope records together with published Nd isotope data show markedly parallel trends across the studied interval over a broad range of bathyal to abyssal water depths interpreted to reflect changes in the intensity of deep-ocean circulation in the tropical Pacific. In particular, we observe a three-million-year-long period of cooler conditions in the early Maastrichtian (72.5 to 69.5 Ma) when a concomitant change toward less radiogenic seawater Nd isotope signatures probably marks a period of enhanced admixture and northward flow of deep waters with Southern Ocean provenance. We suggest this change to have been triggered by intensified formation and convection of deep waters in the high southern latitudes, a process that weakened during the MME (69.5 to 68.5 Ma). The early Maastrichtian cold interval is closely related to the negative and positive carbon isotope trends of the CMBE and MME. The millions-of-years long duration of these carbon cycle perturbations suggests a tectonic forcing of climatic cooling, possibly related to changes in ocean basin geometry and bathymetry.

Cretaceous planktonic foraminifera of DSDP Hole 71-511

Lower and Upper Cretaceous sediments of the Maurice Ewing Bank, Site 511 (black shales, mudstones, zeolitic clays, and nannofossil chalk and ooze, 361 m thick) are characterized by an assemblage of planktonic foraminifers of low systematic diversity, including over 50 species. Representatives of Hedbergella, Globigerinelloides, Archaeoglobigerina, Whiteinella, Rugoglobigerina, and Heterohelix are predominant; species of Ticinella, Praeglobotruncana, Globotruncana, Schackoina, and Planoglobulina associated with some interbeds occur in smaller numbers. Planktonic foraminifers enable us to subdivide the Cretaceous sediments into Barremian-Aptian, Albian, upper Cenomanian, Turonian, Coniacian-Santonian, Santonian, Campanian, and upper Campanian-Maestrichtian intervals. The Lower Cretaceous (Albian) and Upper Cretaceous (upper Cenomanian-Turonian) are separated by a distinct hiatus and unconformity. In the Upper Cretaceous section, a hiatus may be present at the top of the Campanian. The upper Cenomanian-Santonian sediments are reduced in thickness, whereas the Campanian-Maestrichtian interval is expanded. In the Barremian-Aptian black shales, planktonic foraminifers are very rare: they were deposited in shallow water under anoxic conditions. In the Albian, when sedimentation conditions became oxidizing and the depth increased to 200-400 meters, they became more common. By the end of the Upper Cretaceous, depths appear to increase to 2000 meters. In the interbeds of calcareous sediments, planktonic foraminifers are common; in interbeds of zeolitic clays they are rare or absent (dissolution facies). Alternation of these types of sediments is especially characteristic of the Coniacian-lower Campanian, testifying to abrupt CCD fluctuations. The planktonic foraminifers of the Falkland Plateau belong to the Austral Province of the Southern Hemisphere. In their systematic composition they are extremely similar to microfauna of the Boreal Province of the Northern Hemisphere.

Magnetic susceptibility, XRF and color reflectance data of DSDP Hole 72-516F, cores 113 and 114

Deep marine successions of early Campanian age from DSDP site 516F drilled at low paleolatitudes in the South Atlantic reveal distinct sub-Milankovitch variability in addition to precession and eccentricity related variations. Elemental abundance ratios point to a similar 5 climatic origin for these variations and exclude a quadripartite structure - as observed in the Mediterranean Neogene - of the precession related cycles as an explanation for the inferred semi-precession cyclicity in MS. However, the semi-precession cycle itself is likely an artifact, reflecting the first harmonic of the precession signal. The sub-Milankovitch variability is best approximated by a ~ 7 kyr cycle as shown by 10 spectral analysis and bandpass filtering. The presence of sub-Milankovitch cycles with a period similar to that of Heinrich events of the last glacial cycle is consistent with linking the latter to low-latitude climate change caused by a non-linear response to precession induced variations in insolation between the tropics.

Stable carbon and oxygen isotope composition of Late Cretaceous benthic foraminifera from the southern South Atlantic

The stable carbon and oxygen isotope composition of different benthic foraminiferal species of the latest Campanian and earliest Maastrichtian from Ocean Drilling Project Hole 690C (Weddell Sea, southern South Atlantic, ~1800 m paleowater depth) have been investigated. The total range of measured isotope values of all samples exceeds ~4 per mil for delta 13C and 1.1 per mil for delta 18O. Carbon isotope values of proposed deep infaunal species are generally similar or only slightly lower when compared to proposed epifaunal to shallow infaunal species. Interspecific differences vary between samples probably reflecting temporal changes in organic carbon fluxes to the sea floor. Constantly lower delta 13C values for Pullenia marssoni and Pullenia reussi suggest the deepest habitat for these species. The strong depletion of delta 13C values by up to 3 per mil within lenticulinids may be attributed to a deep infaunal microhabitat, strong vital effects, or different feeding strategy when compared to other species or modern lenticulinids. The mean delta 18O values reveal a strong separation of epifaunal to shallow infaunal and deep infaunal species. Epifaunal to shallow infaunal species are characterized by low delta 18O values, deep infaunal species by higher values. This result possibly reflects lower metabolic rates and longer life cycles of deep infaunal species or the operating of a pore water [CO3]2- effect on the benthic foraminiferal stable isotopes. Pyramidina szajnochae shows an enrichment of oxygen isotopes with test size comprising a total of 0.6 per mil between 250 and 1250 µm shell size. Although delta 13C lacks a corresponding trend these data likely represent the presence of changes in metabolic rates during ontogenesis. These results demonstrate the general applicability of multi-species stable isotope measurements of pristine Cretaceous benthic foraminifera to reconstruct past microhabitats and to evaluate biological and environmental effects on the stable isotope composition.

Calcareous nannofossils of ODP Holes 114-699A and 114-700B

Ocean Drilling Program (ODP) Leg 114 recovered nannofossil-bearing sediments from seven sites in the high latitudes of the South Atlantic Ocean. Cretaceous sections were recovered from Sites 698 and 700, located on the Northeast Georgia Rise and its lower flanks, respectively. These contain distinctive high-latitude nannofossil floras similar to those from high-latitude areas of the Northern Hemisphere. Most of the biostratigraphic datums used to date the upper Campanian to Maestrichtian interval appear to lie at approximately the same level in both hemispheres. The FAD of Nephrolithus frequens is confirmed to be diachronous with an earlier occurrence in high latitudes. The LAD of Monomarginatus primus n. sp. also appears to be diachronous with a later LAD in the high latitudes of the Southern Hemisphere. Fossiliferous Paleocene to lowermost Miocene sediments were recovered at all seven sites, from the Northeast Georgia Rise in the west to the Meteor Rise in the east. These nannofossil floras, although restricted in diversity and only poorly preserved, are sufficiently distinctive to allow the recognition of 19 zones and three subzones, which are used to date and correlate the cores recovered. Only Site 704 on the Meteor Rise yielded a substantial section of Miocene to Quaternary nannofossil-rich sediments. The nannofossil floras of this section are of very low diversity, with usually fewer than eight species present. Some stratigraphic ranges of important biostratigraphic datum species are observed to be different in the high-latitude sections from those recorded from low-latitude areas. The LAD of Reticulofenestra bisecta, when calibrated by magnetostratigraphy, appears to occur earlier in Hole 699A (within Chron C6CR) than in Hole 703A and possibly Hole 704B and in other published accounts of lower latitude sites in the South Atlantic. The FAD of Nannotetrina fulgens/N. cristata appears to occur later in Hole 702B (Chron C20R) than it does in other published accounts of lower latitude sites in the South Atlantic. Diachroneity is also suspected in the stratigraphic ranges of Chiasmolithus solitus and Chiasmolithus oamaruensis, although poor magnetostratigraphic results through the critical interval prevent confirmation of this. Differences in the relative stratigraphic ranges of lsthmolithus recurvus and Cribrocentrum coenurumlC. reticulatum at Sites 699 and 703 are noted. These possibly suggest warmer surface waters on the eastern side (Site 703) of the middle to late Eocene South Atlantic than those on the western side (Site 699). The diversities of the nannofossil floras and the presence of the warm-water genera Discoaster, Sphenolithus, Helicosphaera, and Amaurolithus reflect the changing surface water temperatures throughout the Cenozoic. Warmer periods are inferred for the late Paleocene to early middle Eocene, late middle Eocene to late Eocene, latest Oligocene to earliest Miocene, and possibly the Pliocene. Colder periods are inferred for the middle Eocene, most of the Oligocene, and the Miocene. Dramatic changes in the nannofossil floras of the Pleistocene of Site 704 are thought to reflect a rapidly changing environment. Monomarginatus primus, a new species from the Upper Cretaceous strata of Hole 700B, is described.