Geochemical and stable isotope composition of Middle Campanian marl-limestone rhythmites of the Lehrte West Syncline near Hannover (Lower Saxony, northern Germany)

A cyclic marl-limestone succession of Middle-Late Campanian age has been investigated with respect to a Milankovitch-controlled origin of geochemical data. In general, the major element geochemistry of the marl-limestone rhythmites can be explained by a simple two-component mixing model with the end-members calcium carbonate and 'average shale'-like material. Carbonate content varies from 55 to 90%. Non-carbonate components are clay minerals (illite, smectite) and biogenic silica from sponge spicules, as well as authigenically formed zeolites (strontian heulandite) and quartz. The redox potential suggests oxidizing conditions throughout the section. Trace element and stable isotopic data as well as SEM investigations show that the carbonate mud is mostly composed of low-magnesium calcitic tests of planktic coccolithophorids and calcareous dinoflagellate cysts (calcispheres). Diagenetic overprint results in a decrease of 2% d18O and an increase in Mn of up to 250 ppm. However, the sediment seems to preserve most of its high Sr content compared to the primary low-magnesium calcite of co-occurring belemnite rostra. The periodicity of geochemical cycles is dominated by 413 ka and weak signals between 51 and 22.5 ka, attributable to orbital forcing. Accumulation rates within these cycles vary between 40 and 50 m/Ma. The resulting cyclic sedimentary sequence is the product of (a) changes in primary production of low-magnesium calcitic biogenic material in surface waters within the long eccentricity and the precession, demonstrated by the CaCO3 content and the Mg/Al, Mn/Al and Sr/Al ratios, and (b) fluctuations in climate and continental weathering, which changed the quality of supplied clay minerals (the illite/smectite ratio), demonstrated by the K/Al ratio. High carbonate productivity correlates with smectite-favouring weathering (semi-arid conditions, conspicuously dry and moist seasonal changes in warmer climates). Ti as the proxy indicator for the detrital terrigenous influx, as well as Rb, Si, Zr and Na, shows only low frequency signals, indicating nearly constant rates of supply throughout the more or less pure pelagic carbonate deposition of the long-lasting third-order Middle-Upper Campanian sedimentary cycle.

Chemical composition of ferromanganese nodules from the Western Sicily Jurassic limestone beds

The stratigraphic study focuses on the description of lithofacies and geological sections of secondary, tertiary and quaternary formations in different parts of western Sicily. The tectonic analysis derived from field studies is used to trace the history and effects of the Alpine orogeny on the geology of Western Sicily. During his field study the author conducted several chemical element analysis on fossil manganese nodules extracted from Jurassic limestone beds.

Tab. 1: Semi-quantitative estimations of mineral composition

Paleontological and petrological studies of clay beds in the Basilika Formation (Tertiary age) are the subject of this paper. The petrology of the beds indicates that their main constituents were derived from volcanic activity and represent bentonites. Differing composition of the beds may suggest several spatially separated eruptions. The volcanic source area probably lay towards the north of the present Tertiary outcrops of Svalbard. Two foraminiferal assemblages are found in the bentonites: the lower is dominated by arenaceous forms while the upper consists of calcareous species.

Investigation of Pliocene foraminifera on sediment core CRP-1 from the Ross Sea, Antarctica

Mixed assemblages of Pliocene and Quaternary foraminifera occur within the Quaternary succession of the CRP-1 drillhole. Pliocene foraminifera are not present in the lowermost Unit 4.1. are rare in Unit 3.1 and 2.3, are relatively common in Units 2.2 and 2.1, and are absent in Unit 1.1. Fifteen and twelve species were documented in two of the samples from Units 2.2 and 2.1 respectively. A census count of foraminifera in a sample at 26.89 mbsf (Unit 2.2) indicated that 39% of the tests were from a Pliocene source, with the remaining 61% tests assigned to the in situ Quaternary assemblage. There appears to be a close correlation between the stratigraphic distribution of ice-rafted sediments and the test number and diversity of Pliocene taxa. It is concluded that Pliocene assemblages were not derived from submarine outcrops on Roberts Ridge, but are more likely to have been rafted to the site via major trunk valley drainage systems such as operated within the Mackay and Ferrar glacial valleys. The co-occurrence of marine biota (including foraminifera), fossil wood, pollen, and igneous clasts in the Quaternary succession of CRP-l, points to the marine and terrestrial facies of the Pliocene Sirius Group as a likely source. A major episode of erosion and transport of sediment into the offshore marine basins at about ~1 Ma may have been triggered by dynamism in the ice sheet-glacier system, an episode of regional uplift in the Transantarctic Mountains, sea level oscillations and associated changes in the land-to-sea drainage baselines, or some combination of these factors.

Grain size distribution in surface sediments samples of the continental shelf and slope of southeast Greenland

During "Meteor" Cruise 6/1966 in the northwest Atlantic a systematic survey of the bottom topography of the southeast Greenland continental margin was undertaken. Eighty-seven profiles transverse to the shelf edge at distances of 3-4 nautical miles and two longitudinal profiles parallel to the coast were carried out with the ELAC Narrow Beam Echo-Sounder giving a reliable record of even steep slopes. On the basis of the echo soundings the topography and morphology of the continental shelf and slope are evaluated. A detailed bathymetric chart and a serial profile chart were designed as working material for the morphological research. These maps along with the original echograms are morphometrically evaluated. The analysis of the sea bottom features is the basis of a subsequent morphogenetical interpretation, verified and extended by means of interpretation of magnetic data and sediment analysis (grain size, roundness, lithology). The results of the research are expressed in a geomorphological map. The primary findings can be summarized as follows: 1) The southeast Greenland shelf by its bottom topography can be clearly designated as a glacially formed area. The glacial features of the shelf can be classified into two zones nearly parallel to the coast: glacial erosion forms on the inner shelf and glacial accumulation forms on the outer shelf. The inner shelf is characterized by the rugged and hummocky topography of ice scoured plains with clear west/east slope asymmetry. On the outer shelf three types of glacial accumulation forms can be recognized: ice margin deposits with clearly expressed terminal moraines, glacial till plains and glaciomarine outwash fans. Both zones of the shelf can be subdivided into two levels of relief. The ice scoured plains, with average depths of 240 meters (m), are dissected to a maximum depth of 1060 m (Gyldenloves Trough) by trough valleys, which are the prolongations of the Greenland fjords. The banks of the outer shelf, with an average depth of 180 m, surround glacial basins with a maximum depth of 670 meters. 2) The sediments of the continental shelf can be classified as glacial due to their grain size distribution and the degree of roundness of the gravel particles. The ice margin deposits on the outer shelf can be recognized by their high percentage of gravels. On the inner shelf a rock surface is suggested, intermittently covered by glacial deposits. In the shelf troughs fine-grained sediments occur mixed with gravels. 3) Topography and sediments show that the southeast Greenland shelf was covered by an ice sheet resting on the sea floor during the Pleistocene ice-age. The large end moraines along the shelf edge probably indicate the maximum extent of the Wurm shelf ice resting on the sea floor. The breakthroughs of the end moraines in front of the glacial basins suggest that the shelf ice has floated further seaward over the increasing depths. 4) Petrographically the shelf sediments consist of gneisses, granites and basalts. While gneisses and granites occire on the nearby coast, basalt is not known to exist here. Either this material has been drifted by icebergs from the basalt province to the north or exists on the southeast Greenland shelf itself. The last interpretation is supported bythe high portion of basalt contained in the sediment samples taken and the strong magnetic anomalies probably caused by basaltic intrusions. 5) A magnetic profile allows the recognition of two magnetically differing areas which approximately coincide with the glacial erosion and accumulation zones. The inner shelf shows a strong and variable magnetic field because the glacially eroded basement forms the sea floor. The outer shelf is characterized by a weak and homogenous magnetic field, as the magnetized basement lies at greater depthy, buried by a thick cover of glacial sediments. The strong magnetic anomalies of the inner shelf are probably caused by dike swarms, similar to those observed further to the north in the Kangerdlugssuaq Fjord region. This interpretation is supported by the high basalt content of the sediment samples and the rough topography of the ice scoured plains which correlates in general with the magnetic fluctuations. The dike structures of the basement have been differentially eroded by the shelf ice. 6) The continental slope, extending from the shelf break at 313 m to a depth of 1270 m with an average slope of 11°, is characterized by delta-shaped projections in front of the shelf basins, by marginal plateaus, ridges and hills, by canyons and slumping features. The projections could be identified as glaciomarine sediment fans. This conclusion is supported by the strong decrease of magnetic field intensity. The deep sea hills and ridges with their greater magnetic intensities have to be regarded as basement outcrops projecting through the glaciomarine sediment cover. The upper continental rise, sloping seaward at about 2°, is composed of wide sediment fans and slump material. A marginal depression on the continental rise running parallel to the shelf edge has been identified. In this depression bottom currents capable of erosion have been recorded. South of Cape Farvel the depression extends to the accumulation zone of the "Eirik" sedimentary ridge. 7) By means of a study of the recent marine processes, postglacial modification of the ice-formed relief can be postulated. The retention effect of the fjord troughs and the high velocity of the East Greenland stream prevents the glacial features from being buried by sediments. Bottom currents capable of active erosion have only been found in the marginal depression on the continental rise. In addition, at the time of the lowest glacio-eustatic sea level, the shelf bottom was not situated in the zone of wave erosion. Only on the continental slope and rise bottom currents, sediment slumps and turbidity currents have led to significant recent modifications. Considering these results, the geomorphological development of the southeast Greenland continental terrace can be suggested as follows: 1. initial formation of a "peneplain", 2. fluvial incision, 3. submergence, and finally 4. glacial modification.

Maps of surface sediment distribution in the northern Wadden Sea, North Sea

From 1978 to 1981, intensive sedimentological investigations were carried out on the Northfrisian intertidal shoals between the small island of Gröde and Nordstrand lsland as a part of an interdisciplinary research projekt. The objective of this sedimentological study was to reveal long and short term tendencies in sedimentation and erosion in the environment. The presented study mainly concentrated on surface mapping in the tidal flats which based on more than 5000 sediment samples. The relative amounts of the grain-size fractions <0.063 mm and >0.125 mm are presented on maps. Predominant sediment typs are well sorted fine sands ("Wattsand") and muddy sands ("Schlicksand"), pure muds covering only small areas. The fine-grained deposits are either found in the lee-side of an island in elongated bays having a low waterdepth during high tide near the shore or near exposed "Klei" outcrops as well as sporadically on the edge of tidal rills. Together with standardized fields observations of biological and physical properties, the maps indicate a slight erosive tendency in large sections of the investigated area.

Determination of sulfite and manganese in sediments from the K/T boundary

The solid-state-physics technique of electron spin resonance (ESR) has been employed in an exploratory study of marine limestones and impact-related deposits from Cretaceous-Tertiary (KT) boundary sites including Spain (Sopelana and Caravaca), New Jersey (Bass River), the U.S. Atlantic continental margin (Blake Nose, ODP Leg 171B/1049/A), and several locations in Belize and southern Mexico within -600 km of the Chicxulub crater. The ESR spectra of SO3(1-) (a radiation-induced point defect involving a sulfite ion substitutional for CO3(2-) which has trapped a positive charge) and Mn(2+) in calcite were singled out for analysis because they are unambiguously interpretable and relatively easy to record. ESR signal strengths of calcite-related SO3(1-) and Mn(2+) have been studied as functions of stratigraphic position in whole-rock samples across the KT boundary at Sopelana, Caravaca, and Blake Nose. At all three of these sites, anomalies in SO3(1-) and/or Mn(2+) intensities are noted at the KT boundary relative to the corresponding background levels in the rocks above and below. At Caravaca, the SO3(1-) background itself is found to be lower by a factor of 2.7 in the first 30,000 years of the Tertiary relative to its steady-state value in the last 15,000 years of the Cretaceous, indicating either an abrupt and quasi-permanent change in ocean chemistry (or temperature) or extinction of the marine biota primarily responsible for fixing sulfite in the late Cretaceous limestones. An exponential decrease in the Mn(2+) concentration per unit mass calcite, [Mn(2+)], as the KT boundary at Caravaca is approached from below (1/e characteristic length =1.4 cm) is interpreted as a result of post-impact leaching of the seafloor. Absolute ESR quantitative analyses of proximal impact deposits from Belize and southern Mexico group naturally into three distinct fields in a twodimensional [SO3(1-)]-versus-[Mn(2+)] scatter plot. These fields contain (I) limestone ejecta clasts, (II) accretionary lapilli, and (III) a variety of SO3(1-) -depleted/Mn(2+) enriched impact deposits. Data for the investigated non-impact-related Cretaceous and Tertiary marine limestones (Spain and Blake Nose) fall outside of these three fields. With reference to thes enon-impact deposits, fields I, II, and III can be respectively characterized as Mn(2+) -depleted, SO3(1-) -enhanced, and SO3(1-) -depleted. It is proposed that (1) field I represents calcites from the Yucatin Platform, and that the Mn(2+) -depleted signature can be used as an indicator of primary Chicxulub ejecta in deep marine environments and (2) field II represents calcites that include a component formed in the vapor plume, either from condensation in the presence of CO2/SO3(1-) -rich vapors, or reactions between CaO and CO2/SO3 rich vapors, and that this SO3(1-) -enhanced signature can be used as an indicator of impact vapor plume deposits. Given these two propositions, the ESR data for the Blake Nose deposits are ascribed to the presence of basal coarse calcitic Chicxulub ejecta clasts, while the finer components that are increasingly represented toward the top are interpreted to contain high- SO3(1-) calcite from the vapor plume. The apparently-undisturbed Bass River deposit may contain even higher concentrations of vapor-plume calcite. None of the three components included in field III appear to be represented at distal, deep marine KT-boundary sites; this field may include several types of impact-related deposits of diverse origins and diagenetic histories.

Stable isotope composition of carbonate components of Rhaetian shallow-water limestones of the Wombat Plateau

Stable oxygen- and carbon-isotope ratios of Rhaetian (upper Triassic) limestone samples from the Wombat Plateau, northwest Australia, were measured to explore possible diagenetic pathways that the material underwent after deposition in a shallow-water environment, before plateau submergence in the Early Cretaceous. Host sediment isotopic values cluster near typical marine carbonate values (d18O ranging from -2.57 per mil to +1.78 per mil and d13C, from +2.45 per mil to +4.01 per mil). Isotopic values of equant clear calcite lining or filling rock pores also plot in the field of marine cements (d18O = +1.59 per mil to -2.24 per mil and d13C = +4.25 per mil to +2.57 per mil), while isotopic values for neomorphic calcites replacing skeletal (megalodontid shell) carbonate material show a wider scatter of oxygen and carbon values, d18O ranging from +2.73 per milo to -6.2 per mil and d13C, from +5.04 per mil to +1.22 per mil. Selective dissolution of metastable carbonate phases (aragonite?) and neomorphic replacement of skeletal material probably occurred in a meteoric phreatic environment, although replacement products (inclusion-rich microspar, clear neomorphic spar, etc.) retained the original marine isotopic signature because transformation probably occurred in a closed system dominated by the composition of the dissolving phases (high rock/water ratio). The precipitation of late-stage equant (low-Mg?) calcite cement in the pores occurred in the presence of normal marine waters, probably in a deep-water environment, after plateau drowning. Covariance of d18O and d13C toward negative values indeed suggests influence of meteorically modified fluids. However, none of the samples shows negative carbon values, excluding the persistence of organic-rich soils on subaerial karstic surfaces (Caribbean-style diagenesis). Petrographical and geochemical data are consistent with the sedimentological evidence of plateau drowning in post-Rhaetian times and with a submarine origin of the >70-m.y.-long Jurassic hiatus.

Magnetic susceptibility dataset from the early Givetian to early Frasnian in the La Thure section

Recent advances in radiometric dating result in significant improvements in the geological timescale and provide better insight into the timing of various processes and evolutions within the Earth's system. However, no radiometric ages are contained within the Givetian. Consequently, the absolute ages of the Givetian Stage boundaries, as well as the stage's duration, remain poorly constrained. As an alternative, the analysis of sedimentary cycles allows for the estimation of the duration of this stage. We examined the high-resolution magnetic susceptibility signals of four Givetian outcrops in the Givet area for a possible astronomical imprint, to fully understand the rates of evolutionary and environmental change. All four sections are firmly correlated and wavelet analyses of the magnetic susceptibility signals reveal the imprint of astronomical eccentricity forcing. The highly stable 405 kyr cycles constrain the duration of the Givetian Stage at 4.35±0.45 Myr, which is in good agreement with the International Chronostratigraphic Chart (5.0 Myr). The studied sections also exhibit an imprint of obliquity, suggesting a climatic teleconnection between low and high latitudes. The corresponding microfacies curves demonstrate similar astronomical imprint, and thereby indicate that the observed 10**5 year-scale cyclicity is the result of climatic and environmental change.

Cretaceous-Paleogene biomagnetostratigraphy of ODP Leg 121 sites

Broken Ridge, in the eastern Indian Ocean, is a shallow-water volcanic platform which formed during the Early to middle Cretaceous at which time it comprised the northern portion of the Kerguelen-Heard Plateau. Rifting during the middle Eocene and subsequent seafloor spreading has moved Broken Ridge about 20?N to its present location. The sedimentary section of Broken Ridge includes Turonian-lower Eocene limestone and chalk with volcanic ash, an interval of detrital sands and gravels associated with middle Eocene rifting and uplift, and a middle-late Oligocene unconformity overlain by a thin section of Neogene-Holocene pelagic calcareous ooze. This paper summarizes the available post-cruise biostratigraphic and magnetostratigraphic data for the Cretaceous-Paleogene section on Broken Ridge. The synthesis of this information permits a more precise interpretation of the timing of events in the history of Broken Ridge, in particular the timing and duration of the middle Eocene rifting event. Paleontologic data support rapid flexural uplift of Broken Ridge in response to mechanical rather than thermal forces. Other highlights of the section include a complete Cretaceous/Tertiary boundary and an opportunity for first-order correlation of Paleogene diatom stratigraphy with that of the calcareous groups.

Iridium contents and microprobe analyses of DSDP Leg 77 samples

Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater.

Petrology and diagenesis of sandstones at DSDP Hole 58-445

The sandstone succession in the lower 240 meters of DSDP Site 445, on the Daito Ridge, provided an opportunity to evaluate the effect of burial diagenesis of sandstones in a deep hole in a tectonic environment (remnant arc) characterized by a history of high heat flow. This report provides preliminary data concerning the petrology and diagenesis of these sandstones and records diagenetic changes which have occurred with increasing depth of burial. Methods used for this study included grain-size analysis (measured from thin sections using the method of Friedman, 1958), polarizing microscopy, X-ray diffraction, and scanning electron microscopy. A JEOL scanning electron microscope fitted with an energydispersive- X-ray detector was used for obtaining qualitative chemical data on certain minerals to aid in identification.