Chemical analysis of various geological samples from Northern Victoria Land, Antarctica

This paper reports the results of a preliminary palaeomagnetic investigation of the Admiralty Intrusives complex of northern Victoria Land, Antarctica. The samples were collected at Mt. Supernal and Inferno Peak, two pinions mainly formed of granodiorite and minor tonalite and emplaced at ab. 350 Ma at a high crustal level, as shown by amphibole geobarometric data and occurrence of miarolitic cavities. Microprobe and isothermal remanence analyses showed that magnetite. characterized by low coercivity and Curic point in the range 550-570 °C is the only primary ferromagnetic mineral. Stepwise thermaldemagnetization succeeded in isolatingamagnetization component. stable up to 530 °C. The virtual geomagnetic poles (VGPs) of the two plutons are different. That of Inferno Peak is consistent with the Australian palaeopoles of late Devonian-early Carboniferous age, whereas the location of the Mt. Supernal VGP probably results from the tectonic activity which affected the Ross Sea region during the Cenozoic.

delta13Corg of Paleozoic land plants

Based on the evaluation of 1323 carbon isotope values for Silurian to Permian terrestrial organic carbon, measured on plant fossils, cuticules, humic coals and bulk terrestrial organic matter (TOM), we conclude that the temporal trend in d13CTOM records variations in the global carbon cycle, notably an increase in the fractional burial of light (terrestrial) organic matter in Late Palaeozoic sediments. d13CTOM values suggest that the Late Palaeozoic pO2 peak could have been restricted to a time frame of ca. 40 Ma. Carbon isotope data from four taxonomic groups reveal small differences that could be a consequence of habitat conditions. No significant differences in organic carbon isotopic composition in relation to variable climatic conditions are discernible. The carbon isotopic composition solely reflects C3 plant metabolism.

(Table 1, page 146) Iron, manganese and nickel contents of 21 ferromanganese nodules from Combe D'Izame and Mont Peyroux, Montagne Noire

Ferromanganese nodules (equivalent to Recent manganese nodules) are described from the Upper Devonian griotte (red pelagic limestone) of the Montagne Noire (S. France) and the Cephalopodenkalk of the Rheinisches Schiefergebirge, West Germany. They occur as encrustations, commonly exhibiting colloform structures, around skeletal material and limestone clasts. The nodules are associated with encrusting foraminifera and a development in the sublittoral environment is envisaged. Chemically, the ferromanganese nodules are depleted in manganese relative to iron, compared with Recent nodules, a loss which is attributed to diagenetic migration of manganese. Electron probe studies show that manganese covaries positively with calcium, but negatively with iron and silicon. Diagenetic enrichment of hematite occurs in the griotte at hardground horizons where two periods of mineralization can be established. The Devonian ferromanganese nodules show that solution of nodules has not occurred on burial.

Sediment composition in NE Greenland Fjords, Shelf, and Slope

In order to document changes in Holocene glacier extent and activity in NE Greenland (~73° N) we study marine sediment records that extend from the fjords (PS2631 and PS2640), across the shelf (PS2623 and PS2641), to the Greenland Sea (JM07-174GC). The primary bedrock geology of the source areas is the Caledonian sediment outcrop, including Devonian red beds, plus early Neoproterozoic gneisses and early Tertiary volcanics. We examine the variations in colour (CIE*), grain size, and bulk mineralogy (from X-ray diffraction of the <2 mm sediment fraction). Fjord core PS2640 in Sofia Sund, with a marked red hue, is distinct in grain size, colour and mineralogy from the other fjord and shelf cores. Five distinct grain-size modes are distinguished of which only one is associated with a coarse ice-rafting signal - this mode is rare in the mid- and late Holocene. A sediment unmixing program (SedUnMixMC) is used to characterize down-core changes in sediment composition based on the upper late Holocene sediments from cores PS2640 (Sofia Sund), PS2631 (Kaiser Franz Joseph Fjord) and PS2623 (south of Shannon Is), and surface samples from the Kara Sea (as an indicator of transport from the Russian Arctic shelves). Major changes in mineral composition are noted in all cores with possible coeval shifts centred c. 2.5, 4.5 and 7.5 cal. ka BP (±0.5 ka) but are rarely linked with changes in the grain-size spectra. Coarse IRD (>2 mm) and IRD-grain-size spectra are rare in the last 9-10 cal. ka BP and, in contrast with areas farther south (~68° N), there is no distinct IRD signal at the onset of neoglaciation. Our paper demonstrates the importance of the quantitative analysis of sediment properties in clarifying source to sink changes in glacial marine environments.

Chemical composition of a manganese nodule from the Pacific Ocean

By means of spectrographic analysis 96 samples of marine sediments were analyzed quantitatively for V, Ti, Zr, Co, Ni, Sc, Cr, and La, and semi-quantitatively for Ba and Sr. Ca has been estimated by visual comparison of spectrographic plates, and several Fe values have also been determined in the same way. Geographically 40 of these samples are from the Pacific Ocean basin, one of which is a manganese nodule, 21 from the Gulf of Mexico, 11 from Atchafalaya Bay, 8 from American Devonian to Miocene sedimentary rocks, 4 from the Mississippi Delta, 3 from the San Diego trough, 3 from off Grand Isle, 3 from Lake Pontchartrain, from Bay Rambour, 1 from Laguna Madre off the Texas coast, and 1 from the Guadalupe River, Texas. The afore-mentioned elements were sought using PdCl2 as an internal standard, after the method developed by Ahrens (1950) and his co-workers. Samples were run in duplicate, and standard deviations varied from 5 to 14 percent. Working curves, from which final values were obtained, were constructed with the use of standard granite, G1, and the standard diabase, W1, as standards. See Fairbairn and others (1951). An experiment was carried out to determine the effect of matrix change, involving CaCO3, on the spectral line intensities of the quantitatively analyzed elements. The distribution of each of the elements is discussed separately, and particular emphasis is given to oceanic "red clay", in which many elements are enriched. A general discussion is given to mineralogy of the sediments, cation exchange in its bearing on this thesis, and a brief recount of the two hypotheses of origin of oceanic "red clay". An application of the findings of this thesis to aid in the choice of the more likely hypothesis is made.

(Table 2) d13C from the Lusklint section

The carbon isotope composition (d13C) of bulk organic matter and two palynomorph groups (scolecodonts and chitinozoans) from the Llandovery-Wenlock strata of Gotland (E Sweden) are compared to gain knowledge about carbon cycling in the Silurian (sub)tropical shelf environment. The d13C values of the palynomorphs are mostly lower than the d13C values of the bulk organic matter, and the d13C values of the benthic scolecodonts are lower than those of the planktonic chitinozoans. While the difference between bulk and palynomorph d13C may be in part a function of trophic state, the lower values of the scolecodonts relative to those of chitinozoans, which are assumed to live in the well-mixed water column, might imply an infaunal mode of life for the polychaetes that carried the scolecodonts. Lower d13C for the scolecodonts in the middle of the section may represent variations in primary marine productivity (supported by acritarch abundance data), oxidation of organic matter in the bottom waters, or genera effects. In general, however, trends between the three data sets are parallel, indicating similarities in the low frequency, environmentally forced controls. The d13C data show a decreasing trend from the base of the section, up to a horizon well below the base of the Upper Visby Formation. At this level, and therefore probably several 10 kyr before the d13C increase in the carbonates, the d13C organic values increase by ~1 per mil. This perhaps is an expression of a changed composition of the bulk organic matter associated with the extinction events prior to the Llandovery-Wenlock boundary.

(Table 1) List of samples with carbonate mineralogy, stable isotope, and accessory-mineral information

Petrographic and stable-isotope (d13C, d18O) patterns of carbonates from the Logatchev Hydrothermal Field (LHF), the Gakkel Ridge (GR), and a Late Devonian outcrop from the Frankenwald (Germany) were compared in an attempt to understand the genesis of carbonate minerals in marine volcanic rocks. Specifically, were the carbonate samples from modern sea floor settings and the Devonian analog of hydrothermal origin, low-temperature abiogenic origin (as inferred for aragonite in serpentinites from elsewhere on the Mid-Atlantic Ridge), or biogenic origin? Aragonite is the most abundant carbonate mineral in serpentinites from the two modern spreading ridges and occurs within massive sulfides of the LHF. The precipitation and preservation of aragonite suggests high Mg2+ and sulfate concentrations in fluids. Values of d18OPDB as high as +5.3 per mill for serpentinite-hosted aragonite and as high as +4.2 per mill for sulfide-hosted aragonite are consistent with precipitation from cold seawater. Most of the corresponding d13C values indicate a marine carbon source, whereas d13C values for sulfide-hosted aragonite as high as +3.6 per mill may reflect residual carbon dioxide in the zone of methanogenesis. Calcite veins from the LHF, by contrast, have low d18OPDB (-20.0 per mill to -16.1 per mill) and d13C values (-5.8 per mill to -4.5 per mill), indicative of precipitation from hydrothermal solutions (~129°-186°C) dominated by magmatic CO2. Calcite formation was probably favored by fluid rock interactions at elevated temperatures, which tend to remove solutes that inhibit calcite precipitation in seawater (Mg2+ and sulfate). Devonian Frankenwald calcites show low d18O values, reflecting diagenetic and metamorphic overprinting. Values of d13C around 0 per mill for basalt-hosted calcite indicate seawater-derived inorganic carbon, whereas d13C values for serpentinite-hosted calcite agree with mantle-derived CO2 (for values as low as -6 per mill) with a contribution of amagmatic carbon (for values as low as -8.6 per mill), presumably methane. Secondary mineral phases from the LHF for which a biogenic origin appears feasible include dolomite dumbbells, clotted carbonate, and a network of iron- and silica-rich filaments.

(Tables 1-2) Composition of red coloured tills from Schobuell, Schleswig-Holstein and Møn Island, Denmark

The stratigraphic position of the glacially transported 'Scholle' (large-size erratic block) at Schobüll near Husum (Schleswig-Holstein) is now considered to be Devonian rather than 'Rotliegendes'. The 'Scholle', consisting of red clay and dolomite, is overlain by red-colored till without any flint but with up to 90% carbonate clasts (containing 15% dolomite), which indicates an eastern Baltic origin. The relationship of the 'Scholle' with the glacial till also points to an eastern Baltic origin for it, with up to 1 000 km transport distance.

Electron microprobe results of clay minerals from samples of the Frankenwald and the Thüringer Wald

Late Devonian (Frasnian) pillow basalts from the Frankenwald and Thüringer Wald within the Saxothuringian zone in Germany were found to contain abundant putative biogenic filaments, indicating that the volcanic rocks once harbored microbial life. The mineralized filaments are found in calcite-filled amygdules (former vesicles), where they started to form on internal surfaces of vesicles after seawater ingress. The filaments postdate an early fibrous carbonate cement but predate later equant calcite spar, revealing syngenetic formation. A biogenic origin of filaments is indicated by their size and morphology resembling modern microorganisms, their independence of crystal faces and cleavage plans, complex branching patterns, and internal segmentation. The filamentous microorganisms represent cryptoendoliths that lived in structural cavities of the basalt. They became preserved upon microbial clay authigenesis similar to the encrustation of modern prokaryotes in iron-rich environments. Filaments consist of clay minerals with the endmember composition berthierine-chamosite and illite-glauconite. Based on the discovery of fossilized filamentous microorganisms in Late Devonian pillow basalts of the Saxothurigian zone that are similar to filaments previously found in Middle Devonian pillow basalts of the Rhenohercynian zone, it is apparent that cryptoendolithic life was more widespread than previously recognized. Structural cavities within seafloor basalt may thus represent a common, perhaps universal niche for life in the oceanic crust.

(Table 1) Detrital modes for sand grains in sediment core CRP-3

Detrital modes determined on 68 sandstone samples from CRP-3 drillcore indicate a continuation of the dynamic history of uplift-related erosion and unroofing previously documented in CRP-1 and CRP-2/2A. The source area is identified very strongly with the Transantarctic Mountains (TAM) Dry Valleys block in southern Victoria Land. Initial unroofing of the TAM comprised removal of much of a former capping sequence of Jurassic Kirkpatrick basalts, which preceded the formation of the Victoria Land Basin. Erosion of Beacon Supergroup outcrops took place during progressive uplift of the TAM in the Oligocene. Earliest CRP-3 Oligocene samples above 788 metres below the sea floor (mbsf) were sourced overwhelmingly in Beacon Supergroup strata, including a recognisable contribution from Triassic volcanogenic Lashly Formation sandstones (uppermost Victoria Group). Moving up-section, by 500 mbsf, the CRP-3 samples are depauperate quartz arenites dominantly derived from the quartzose Devonian Taylor Group. Between c. 500 and 450 mbsf, the modal parameters show a distinctive change indicating that small outcrops of basement granitoids and metamorphic rocks were also being eroded along with the remaining Beacon (mainly Taylor Group) sequence. Apart from enigmatic fluctuations in modal indices above 450 mbsf, similar to those displayed by samples in CRP-2/2A, the CRP-3 modes are essentially constant (within a broad data scatter) to the top of CRP-3. The proportion of exposed basement outcrop remained at < 20 %, indicating negligible uplift (i.e. relative stability) throughout that period.

Biomarker in Heinrich event layers

There are controversies regarding the origin of Heinrich layer 3 (H3), the massive ice-rafting and meltwater event in the North Atlantic during the last glacial cycle spanning a time window between 29 and 30 kyr B.P. Some argue in favor of a Laurentide Ice Sheet source similar to other Heinrich layers, while a contending view argues for the European ice sheet source. Existing geochemical proxies such as 40Ar/39Ar, 206Pb/204Pb, or epsilon-Nd, etc., could not be used to distinguish among various sources of ice-rafted debris in H3 because of their low abundances, suggesting a background glacial sediment signal. In order to circumvent this problem a biomarker-based approach is used to characterize the provenance of H layers 2, 3, and 4 and other non-Heinrich layers. The presence of hopanes and steranes and their aromatic counterparts in the H layers is incompatible with Recent sediments and is attributed to the transportation of organic matter because of the glacial erosion of source rocks. The most diagnostic and useful signatures of this ancient organic matter in the H layers are the dominance of C34 hopanoids over C33 and the occurrence of isorenieratane along with palaerenieratane. Biomarkers signatures in H layers 2 and 3 of the Labrador Sea suggest no difference in their source. Hydrocarbon distributions suggest that these sediments were derived from the Middle to Late Ordovician and Silurian source rocks of the Hudson Bay of eastern Canada. Biomarker data of the H layer 4 from the northwest Atlantic reveal that the sediments of this layer have a similar source to the H layers in the Labrador Sea.

Age determination of the Vendian intrusions in the polar Urals

The Precambrian basement beneath the Pechora Basin of northern Russia is known from deep (up to approx. 4.5 km) drill holes to be largely composed of Neoproterozoic successions, variously deformed and metamorphosed and intruded by magmatic suites of Vendian age. Presented here are new single- zircon, Pb-evaporation (Kober method) ages from eight intrusions across the Izhma, Pechora and Bolshezemel'skaya Zones, all from below the Lower Ordovician (locally Middle Cambrian) unconformity. The majority of the intrusions (six) yield remarkably similar ages of 550-560 Ma, apparently dating a widespread pulse of late- to post-tectonic magmatism. An early Vendian granite (618 Ma) has been identified in the northeasternmost region (Bolshezemel'skaya zone) and a Devonian granodiorite (380 Ma) in the Pechora Zone, where mid to late Palaeozoic magmatism has been previously reported. Evidence of inheritance in the zircon populations suggests the presence of Mesoproterozoic crust beneath the Neoproterozoic complexes.

Germanium content in marine sediments

In the geosphere, germanium (Ge) has a chemical behavior close to that of silicon (Si), and Ge commonly substitutes for Si (in small proportions) in silicates. Studying the evolution of the respective proportions of Ge and Si through time allows us to better constrain the global Si cycle. The marine inventory of Ge present as dissolved germanic acid is facing two main sinks known through the study of present sediments: 1) incorporation into diatom frustules and transfer to sediments by these "shuttles", 2) capture of Ge released to pore water through frustule dissolution by authigenic mineral phases forming within reducing sediments. Our goals are to determine whether such a bio-induced transfer of Ge is also achieved by radiolarian and whether Ge could be trapped directly from seawater into authigenic phases with no intervention of opal-secreting organisms (shuttles). To this end, we studied two Paleozoic radiolarite formations and geological formations dated of Devonian, Jurassic and Cretaceous, deposited under more or less drastic redox conditions. Our results show that the Ge/Si values observed for these radiolarites are close to (slightly above) those measured from modern diatoms and sponges. In addition, our results confirm what is observed with some present-day reducing sediments: the ancient sediments that underwent reducing depositional conditions are authigenically enriched in Ge. Furthermore, it is probable that at least a part of the authigenic Ge came directly from seawater. The recurrence and extent (through time and space) of anoxic conditions affecting sea bottoms have been quite important through the geological times; consequently, the capture of Ge by reducing sediments must have impacted Ge distribution and in turn, the evolution of the seawater Ge/Si ratio.