X-ray fluorescence scanning of discrete samples on the Schwalbenberg II loess-paleosol sequence, raw data, magnetic susceptibility, organic carbon and U-ratio as grainsize index

The Schwalbenberg II loess-paleosol sequence (LPS) denotes a key site for Marine Isotope Stage (MIS 3) in Western Europe owing to eight succeeding cambisols, which primarily constitute the Ahrgau Subformation. Therefore, this LPS qualifies as a test candidate for the potential of temporal high-resolution geochemical data obtained X-ray fluorescence (XRF) scanning of discrete samplesproviding a fast and non-destructive tool for determining the element composition. The geochemical data is first contextualized to existing proxy data such as magnetic susceptibility (MS) and organic carbon (Corg) and then aggregated to element log ratios characteristic for weathering intensity [LOG (Ca/Sr), LOG (Rb/Sr), LOG (Ba/Sr), LOG (Rb/K)] and dust provenance [LOG (Ti/Zr), LOG (Ti/Al), LOG (Si/Al)]. Generally, an interpretation of rock magnetic particles is challenged in western Europe, where not only magnetic enhancement but also depletion plays a role. Our data indicates leaching and top-soil erosion induced MS depletion at the Schwalbenberg II LPS. Besides weathering, LOG (Ca/Sr) is susceptible for secondary calcification. Thus, also LOG (Rb/Sr) and LOG (Ba/Sr) are shown to be influenced by calcification dynamics. Consequently, LOG (Rb/K) seems to be the most suitable weathering index identifying the Sinzig Soils S1 and S2 as the most pronounced paleosols for this site. Sinzig Soil S3 is enclosed by gelic gleysols and in contrast to S1 and S2 only initially weathered pointing to colder climate conditions. Also the Remagen Soils are characterized by subtle to moderate positive excursions in the weathering indices. Comparing the Schwalbenberg II LPS with the nearby Eifel Lake Sediment Archive (ELSA) and other more distant German, Austrian and Czech LPS while discussing time and climate as limiting factors for pedogenesis, we suggest that the lithologically determined paleosols are in-situ soil formations. The provenance indices document a Zr-enrichment at the transition from the Ahrgau to the Hesbaye Subformation. This is explained by a conceptual model incorporating multiple sediment recycling and sorting effects in eolian and fluvial domains.

Tab. 1: Geochemical analysis and age dating of Kap Washington Group volcanites and related dykes

The bimodal, alkaline volcanic suite of the Kap Washington Group (KWG) at the northern coast of Greenland was investigated during the BGR CASE 2 expedition in 1994. Geochemical and Nd and Sr isotopic data are presented for basalts to rhyolites of the KWG and of related basaltic dykes cutting Lower Paleozoic sediments. In the evd(t) vs. (87Sr/86Sr)t diagram, the KWG basalts and rhyolites follow a common mixing trend with increasing crustal contamination from basic to acid volcanites. Assimilation of pre-existing crustal rocks during formation of the rhyolitic melt is documented by Nd model ages of 0.9-1.2 Ga and by different fractionation trends for the basalts and the rhyolites in the Y vs. Zr diagram. Petrographical and geochemical features indicate intra-plate volcanism which was active most probably during a continental rifting phase. A new Rb/Sr whole rock age on rhyolites of 64 ±3 Ma, corresponding to the result of LARSEN (1982), confirms that the volcanic activity lasted until the Cretaceous-Tertiary boundary. 40Ar139Ar dating on amphibol separates from a comendite yielded strongly disturbed age spectra with a minimum age of 37.7 ±0.3 Ma. This age is interpreted to date a hydrothermal overprint of the volcanic rocks related to compressive tectonics which led to the overthrust of basement rocks over the Kap Washington Group.

Chemical and isotope composition of rocks from the Omgon Range, Western Kamchatka coastal area

Hypabyssal rocks of the Omgon Range, Western Kamchatka that intrude Upper Albian-Lower Campanian deposits of the Eurasian continental margin belong to three coeval (62.5-63.0 Ma) associations: (1) ilmenite gabbro-dolerites, (2) titanomagnetite gabbro-dolerites and quartz microdiorites, and (3) porphyritic biotite granites and granite-aplites. Early Paleocene age of ilmenite gabbro-dolerites and biotite granites was confirmed by zircon and apatite fission-track dating. Ilmenite and titanomagnetite gabbro-dolerites were produced by multilevel fractional crystallization of basaltic melts with, respectively, moderate and high Fe-Ti contents and contamination of these melts with rhyolitic melts of different compositions. Moderate- and high-Fe-Ti basaltic melts were derived from mantle spinel peridotite variably depleted and metasomatized by slab-derived fluid prior to melting. The melts were generated at variable depths and different degrees of melting. Biotite granites and granite aplites were produced by combined fractional crystallization of a crustal rhyolitic melt and its contamination with terrigenous rocks of the Omgon Group. The rhyolitic melts were likely derived from metabasaltic rocks of suprasubduction nature. Early Paleocene hypabyssal rocks of the Omgon Range were demonstrated to have been formed in an extensional environment, which dominated in the margin of the Eurasian continent from Late Cretaceous throughout Early Paleocene. Extension in the Western Kamchatka segment preceded the origin of the Western Koryakian-Kamchatka (Kinkil') continental-margin volcanic belt in Eocene time. This research was conducted based on original geological, mineralogical, geochemical, and isotopic (Rb-Sr) data obtained by the authors.

Geochemistry of ODP Leg 115 basalts

Melting-phase relations at high pressures and Sr-Nd isotopic compositions are reported for basalts collected from the western Indian Ocean during Ocean Drilling Program Leg 115. Based on the concentrations of high-field-strength elements, we have subdivided the basalts into eight groups. A tholeiitic primary magma estimated using an olivine maximum fractionation model is representative of depleted lavas. This melt is in equilibrium with lherzolite minerals at 1.3 GPa and 1330°C under dry conditions. Also, an alkaline primary magma, representative of enriched lavas, is not saturated with orthopyroxene under dry conditions, but it is saturated with lherzolite minerals under CO2-saturated conditions at 1.7 GPa and 1350°C. These results imply that the tholeiitic magmas were segregated from mantle diapirs at shallower levels than the alkaline magmas. The highest 143Nd/144Nd value is obtained for the most depleted tholeiitic basalts, and the lowest value corresponds to the enriched alkaline basalt. The Sr isotopes of the basalts range from 0.70378 to 0.70449 and are inversely correlated with the Nd isotopic values. The present experimental and geochemical data suggest that depleted mantle material is underlain by the enriched material in the upper mantle beneath the region.

Strontium isotope ratios of planktonic foraminifera from sediment samples acroos the K/T boundary

Seawater 87Sr/86Sr values increase abruptly by 28 * 10**-6 across the Cretaceous/Tertiary boundary (KTB). This small, but rapid shift is superimposed on the larger scale structure of the seawater Sr isotope curve. The time scale of radiogenic Sr addition appears to be too rapid to reconcile with sources associated with volcanism, and we show that the amount of Sr required to produce even this small increase is too large to be derived from: (1) a KT bolide of the size constrained by the Ir anomaly, (2) continental crust ejecta from the impact of such a bolide, (3) soot from global wildfires initiated by an impact, or (4) any combination of these sources. The probable source of the radiogenic Sr is enhanced continental weathering, but the high rate of increase appears to rule out processes such as sea level regression, glaciation or tectonism. A plausible mechanism for rapid addition of radiogenic Sr to the oceans is enhanced weathering associated with globally distributed acid rain (pH c. 1) which is a proposed by-product of a bolide impact (Prinn and Fegley, 1987, doi:10.1016/0012-821X(87)90046-X).

Major, trace and rare earth element concentrations of sediments from ODP Leg 207 sites

The Cretaceous and Paleogene sediments recovered during Ocean Drilling Program Leg 207 can be divided into three broad modes of deposition: synrift clastics (lithologic Unit V), organic matter-rich, laminated black shales (Unit IV), and open-marine chalk and calcareous claystones (Units III-I). The aim of this study is to provide a quantitative geochemical characterization of sediments representing these five lithologic units. For this work we used the residues (squeeze cakes) obtained from pore water sampling. Samples were analyzed for bulk parameters (total inorganic carbon, total organic carbon, and S) and by X-ray fluorescence for major (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, and P) and selected minor (As, Ba, Co, Cr, Cu, Mo, Ni, Pb, Rb, Sr, U, V, Y, Zn, and Zr) elements. Inductively coupled plasma-mass spectrometry analyses for rare earth elements (REEs) were performed on acid digestions of the squeeze cake samples from Site 1258. The major element composition is governed by the mixture of a terrigenous detrital component of roughly average shale (AS) composition with biogenous carbonate and silica. The composition of the terrigenous detritus is close to AS in Units II-IV. For Unit I, a more weathered terrigenous source is suggested. Carbonate contents reach >60 wt% on average in chalks and calcareous claystones of Units II-IV. The SiO2 contribution in excess of the normal terrigenous-detrital background indicates the presence of biogenous silica, with highest amounts in Units II and III. The contents of coarse-grained material (quartz) are enhanced in Unit V, where Ti and Zr contents are also high. This indicates a high-energy depositional environment. REE patterns are generally similar to AS. A more pronounced negative Ce anomaly in Unit IV may indicate low-oxygen conditions in the water column. The Cretaceous black shales of Unit IV are clearly enriched in redox-sensitive and stable sulfide-forming elements (Mo, V, Zn, and As). High phosphate contents point toward enhanced nutrient supply and high bioproductivity. Ba/Al ratios are rather high throughout Unit IV despite the absence of sulfate in the pore water, indicating elevated primary production. Manganese contents are extremely low for most of the interval studied. Such an Mn depletion is only possible in an environment where Mn was mobilized and transported into an expanded oxygen minimum zone ("open system"). The sulfur contents show a complete sulfidation of the reactive iron of Unit IV and a significant excess of sulfur relative to that of iron, which indicates that part of the sulfur was incorporated into organic matter. We suppose extreme paleoenvironmental conditions during black shale deposition: high bioproductivity like in recent coastal upwelling settings together with severe oxygen depletion if not presence of hydrogen sulfide in the water column.

Age and strontium isotope composition for Cretaceous in DSDP Hole 74-525

Firm stratigraphic correlations are needed to evaluate the global significance of unconformity bounded units (sequences). We correlate the well-developed uppermost Campanian and Maestrichtian sequences of the New Jersey Coastal Plain to the geomagnetic polarity time scale (GPTS) by integrating Sr-isotopic stratigraphy and biostratigraphy. To do this, we developed a Maestrichtian (ca. 73-65 Ma) Sr-isotopic reference section at Deep Sea Drilling Project Hole 525A in the southeastern Atlantic Ocean. Maestrichtian strata can then be dated by measuring their 87Sr/86Sr composition, calibrating to the GPTS of S. C. Cande and D. V. Kent (1993, personal commun.), and using the equation Age (Ma) = 37326.894-52639.89 (87Sr/86Sr). Sr-stratigraphic resolution for the Maestrichtian is estimated as +-1.2 to +-2 m.y. At least two unconformity-bounded units comprise the uppermost Campanian to Maestrichtian strata in New Jersey. The lower one, the Marshalltown sequence, is assigned to calcareous nannofossil Zones CC20/21 (~NC19) and CC22b (~NC20). It ranges in age from ~74.1 to 69.9 Ma based on Sr-isotope age estimates. The overlying Navesink sequence is assigned to calcareous nannoplankton Zones CC25-26 (~NC21-23); it ranges in age from 69.3 to 65 Ma based on Sr-isotope age estimates. The upper part of this sequence, the Tinton Formation, has no calcareous planktonic control; Sr-isotopes provide an age estimate of 66 +- 1.2 Ma (latest Maestrichtian). Sequence boundaries at the base and the top of the Marshalltown sequence match boundaries elsewhere in the Atlantic Coastal Plain (Owens and Gohn, 1985) and the inferred global sea-level record of Haq et al. (1987); they support eustatic changes as the mechanism controlling depositional history of this sequence. However, the latest Maestrichtian record in New Jersey does not agree with Haq et al. (1987); we attribute this to correlation and time-scale differences near the Cretaceous/Paleogene boundary. High sedimentation rates in the latest Maestrichtian of New Jersey (Shrewsbury Member of the Red Bank Formation and the Tinton Formation) suggest tectonic uplift and/or rapid progradation during deposition of the highstand systems tract.

Age determination of Paleogene sediments from the Prysz Bay

Age dating of Paleogene diamictites from ODP Site 739 in Prydz Bay with marine microfossils (diatoms and calcareous nannofossils) suggests the build-up of a major East Antarctic ice shield in latest Eocene to earliest Oligocene time, about 35-38 m.y. ago. Strontium isotopic analyses of small mollusk remains found within these diamictites, however, yield younger ages ranging from 29 to 23 Ma (i.e., latest early Oligocene to earliest Miocene). These age discrepancies could be caused by repeated glacial reworking of microfossils, macrofossils, and sediment clasts through the late Oligocene or, alternatively, by ion exchange in the still aragonitic mollusk shells.

Isotopic composition and major and trace element concentrations of mafic rocks obtained from western Dronning Maud Land

On the basis of new bulk major and trace element (including REE) as well as Sm-Nd and Rb-Sr isotope data, used in conjunction with available geochronological data, a post-tectonic mafic igneous province and four groups of pre- to syntectonic amphibolite are distinguished in the polymetamorphic Maud Belt of western Dronning Maud Land, East Antarctica. Protoliths of the Group 1 amphibolites are interpreted as volcanic arc mafic intrusions with Archaean to Palaeoproterozoic Nd model ages and depletion in Nb and Ta. Isotopic and lithogeochemical characteristics of this earliest group of amphibolite indicate that the Maud Belt was once an active continental volcanic arc. The most likely position of this arc, for which a late Mesoproterozoic age (c. 1140 Ma) is indicated by available U-Pb single-zircon age data, was on the southeastern margin of the Kaapvaal-Grunehogna Craton. The protoliths of Group 2 amphibolites are attributed to the 1110 Ma Borgmassivet-Umkondo thermal event on the basis of comparable Nd model ages and trace element distributions. Group 3 amphibolite protoliths are characterized by mid-ocean ridge basalt-type REE patterns and low Th/Yb ratios, and they are related to Neoproterozoic extension. Group 4 amphibolite protoliths are distinguished by high Dy/Yb ratios and are attributed to a phase of syntectonic Pan-African magmatism as indicated by Rb-Sr isotope data.

Major and trace element content of the 17 lithostratigraphic units recovered during DSDP Leg 49 (Table 1)

IPOD Leg 49 recovered basalts from 9 holes at 7 sites along 3 transects across the Mid-Atlantic Ridge: 63°N (Reykjanes), 45°N and 36°N (FAMOUS area). This has provided further information on the nature of mantle heterogeneity in the North Atlantic by enabling studies to be made of the variation of basalt composition with depth and with time near critical areas (Iceland and the Azores) where deep mantle plumes are thought to exist. Over 150 samples have been analysed for up to 40 major and trace elements and the results used to place constraints on the petrogenesis of the erupted basalts and hence on the geochemical nature of their source regions. It is apparent that few of the recovered basalts have the geochemical characteristics of typical "depleted" midocean ridge basalts (MORB). An unusually wide range of basalt compositions may be erupted at a single site: the range of rare earth patterns within the short section cored at Site 413, for instance, encompasses the total variation of REE patterns previously reported from the FAMOUS area. Nevertheless it is possible to account for most of the compositional variation at a single site by partial melting processes (including dynamic melting) and fractional crystallization. Partial melting mechanisms seem to be the dominant processes relating basalt compositions, particularly at 36°N and 45°N, suggesting that long-lived sub-axial magma chambers may not be a consistent feature of the slow-spreading Mid-Atlantic Ridge. Comparisons of basalts erupted at the same ridge segment for periods of the order of 35 m.y. (now lying along the same mantle flow line) do show some significant inter-site differences in Rb/Sr, Ce/Yb, 87Sr/86Sr, etc., which cannot be accounted for by fractionation mechanisms and which must reflect heterogeneities in the mantle source. However when hygromagmatophile (HYG) trace element levels and ratios are considered, it is the constancy or consistency of these HYG ratios which is the more remarkable, implying that the mantle source feeding a particular ridge segment was uniform with respect to these elements for periods of the order of 35 m.y. and probably since the opening of the Atlantic. Yet these HYG element ratios at 63°N are very different from those at 45°N and 36°N and significantly different from the values at 22°N and in "MORB". The observed variations are difficult to reconcile with current concepts of mantle plumes and binary mixing models. The mantle is certainly heterogeneous, but there is not simply an "enriched" and a "depleted" source, but rather a range of sources heterogeneous on different scales for different elements - to an extent and volume depending on previous depletion/enrichment events. HYG element ratios offer the best method of defining compositionally different mantle segments since they are little modified by the fractionation processes associated with basalt generation.

Chemical composition and dated ages of detrital smectites in sediments at DSDP Legs 43, 48 and 50

Mineralogical, morphological and isotopic (Rb-Sr and K-Ar) determinations were made on some detrital smectites of Palaeocene and Cenomanian ages from DSDP. drillings in the Atlantic Ocean. These minerals are not inert in their depositional environment; authigenic laths grow on detrital sheets with sharp borders. This authigenesis could occur slightly after deposition in a closed system, for some of these smectites. It has been tentatively quantified by the Rb-Sr and K-Ar isotopic methods, which seem also well suited to evaluate the chemical extent of this authigenesis. At least, no preferential loss of 40Ar vs. 87Sr could be detected in the minerals, even in those which are smaller than 0.2 ?m.

Geochemistry of metasedimentary units of the Cambro-Ordovician Ross Orogen in North Victoria Land and Oates Land, Antarctica

Metasediments in the three early Palaeozoic Ross orogenic terranes in northern Victoria Land and Oates Land (Antarctica) are geochemically classified as immature litharenites to wackes and moderately mature shales. Highly mature lithotypes with Chemical Index of Weathering values of >=95 are typically absent. Geochemical and Rb-Sr and Sm-Nd isotope results indicate that the turbiditic metasediments of the Cambro-Ordovician Robertson Bay Group in the eastern Robertson Bay Terrane represent a very homogeneous series lacking significant compositional variations. Major variations are only found in chemical parameters which reflect differences in degree of chemical weathering of their protoliths and in mechanical sorting of the detritus. Geochemical data, 87Sr/ 86Sr t=490 Ma ratios of 0.7120 - 0.7174, epsilonNd, t=490 Ma values of -7.6 to -10.3 and single-stage Nd-model ages of 1.7 - 1.9 Ga are indicative of an origin from a chemically evolved crustal source of on average late Palaeoproterozoic formation age. There is no evidence for significant sedimentary infill from primitive "ophiolitic" sources. Metasediments of the Middle Cambrian Molar Formation (Bowers Terrane) are compositionally strongly heterogeneous. Their major and trace element data and Sm-Nd isotope data (epsilonNd, t=500 Ma values of -14.3 to -1.2 and single-stage Nd-model ages of 1.7 - 2.1 Ga) can be explained by mixing of sedimentary input from an evolved crustal source of at least early Palaeoproterozoic formation age and from a primitive basaltic source. The chemical heterogeneity of metasediments from the Wilson Terrane is largely inherited from compositional variations of their precursor rocks as indicated by the Ni vs TiO2 diagram. Single-stage Nd-model ages of 1.6 -2.2 Ga for samples from more western inboard areas of the Wilson Terrane (epsilonNd, t=510 Ma -7.0 to -14.3) indicate a relatively high proportion of material derived from a crustal source with on average early Palaeoproterozoic formation age. Metasedimentary series in an eastern, more outboard position (epsilonNd, t=510 Ma -5.4 to -10.0; single-stage Nd model ages 1.4 - 1.9) on the contrary document stronger influence of a more primitive source with younger formation ages. The chemical and isotopic characteristics of metasediments from the Bowers and Wilson terranes can be explained by variable contributions from two contrasting sources: a cratonic continental crust similar to the Antarctic Shield exposed in Georg V Land and Terre Adélie some hundred kilometers west of the study area and a primitive basaltic source probably represented by the Cambrian island-arc of the Bowers Terrane. While the data for metasediments of the Robertson Bay Terrane are also compatible with an origin from an Antarctic-Shield-type source, there is no direct evidence from their geochemistry or isotope geochemistry for an island-arc component in these series.

Geochemistry of volcanic rocks from the Hikurangi and Manihiki Plateaus

Here we present the first radiometric age data and a comprehensive geochemical data set (including major and trace element and Sr-Nd-Pb-Hf isotope ratios) for samples from the Hikurangi Plateau basement and seamounts on and adjacent to the plateau obtained during the R/V Sonne 168 cruise, in addition to age and geochemical data from DSDP Site 317 on the Manihiki Plateau. The 40Ar/39Ar age and geochemical data show that the Hikurangi basement lavas (118-96 Ma) have surprisingly similar major and trace element and isotopic characteristics to the Ontong Java Plateau lavas (ca. 120 and 90 Ma), primarily the Kwaimbaita-type composition, whereas the Manihiki DSDP Site 317 lavas (117 Ma) have similar compositions to the Singgalo lavas on the Ontong Java Plateau. Alkalic, incompatible-element-enriched seamount lavas (99-87 Ma and 67 Ma) on the Hikurangi Plateau and adjacent to it (Kiore Seamount), however, were derived from a distinct high time-integrated U/Pb (HIMU)-type mantle source. The seamount lavas are similar in composition to similar-aged alkalic volcanism on New Zealand, indicating a second wide-spread event from a distinct source beginning ca. 20 Ma after the plateau-forming event. Tholeiitic lavas from two Osbourn seamounts on the abyssal plain adjacent to the northeast Hikurangi Plateau margin have extremely depleted incompatible element compositions, but incompatible element characteristics similar to the Hikurangi and Ontong Java Plateau lavas and enriched isotopic compositions intermediate between normal mid-ocean-ridge basalt (N-MORB) and the plateau basement. These younger (~52 Ma) seamounts may have formed through remelting of mafic cumulate rocks associated with the plateau formation. The similarity in age and geochemistry of the Hikurangi, Ontong Java and Manihiki Plateaus suggest derivation from a common mantle source. We propose that the Greater Ontong Java Event, during which ?1% of the Earth's surface was covered with volcanism, resulted from a thermo-chemical superplume/dome that stalled at the transition zone, similar to but larger than the structure imaged presently beneath the South Pacific superswell. The later alkalic volcanism on the Hikurangi Plateau and the Zealandia micro-continent may have been part of a second large-scale volcanic event that may have also triggered the final breakup stage of Gondwana, which resulted in the separation of Zealandia fragments from West Antarctica.

Geochemistry of altered phases, basalts and sediments of ODP Site 136-843

40Ar-39Ar incremental heating experiments on a relatively unaltered basalt from Site 843 yield a crystallization age of 110 ± 2 Ma for the central Pacific Ocean igneous basement near Hawaii. Previous estimates of the age of the basement inferred by indirect methods and from radiometric dates of the South Hawaiian Seamounts are too young by 20-30 m.y. Phyllosilicate alteration minerals from veins in the Site 843 basalts define a Rb/Sr isochron with an age of 94.5 ± 0.5 Ma. The isochron records the last equilibration of the phyllosilicate minerals with a hydrothermal fluid at about 16 m.y. after the formation of the igneous basement. The last event recorded by calcite veins is the sealing of the crust by a sufficient thickness of sediment to impede the free circulation of seawater into the crust. The chemistry of the alteration minerals indicates the rare earth elements in the hydrothermal solutions were derived from alteration of the basalts and, furthermore, were transported in solution as metal species and carbonate complexes. Calcite with approximately seawater 87Sr/86Sr, but Sr contents too low to precipitate directly from seawater, is suggested to have formed at a late stage in the alteration history of the crust by the reaction of seawater with calcite precipitated earlier from basalt-dominated hydrothermal fluids.