Authors' Reply

Abstract— Jull et al. propose an alternative interpretation of our depth vs. ¹⁴C data measured on a peat core from the central Tunguska impact site (Rasmussen et al., 1999). We find that the proposed alternative is untenable.     

The carbon isotopic response of algae, (cyano)bacteria, archaea and higher plants to the late Cenomanian perturbation of the global carbon cycle: Insights from biomarkers in black shales from the Cape Verde Basin (DSDP Site 367)

The stable carbon isotopic compositions of free and sulfur (S)-bound biomarkers derived from algae, (cyano)bacteria, archaea and higher plants and total organic carbon (TOC) during the first phase of the late Cenomanian/Turonian oceanic anoxic event (OAE) were measured in black shales deposited in the southern proto-Atlantic Ocean in the Cape Verde basin (DSDP Site 367) to determine the response of these organisms to this major perturbation of the global carbon cycle resulting from widespread burial of marine organic matter. The average positive isotope excursions of TOC and biomarkers varied from 5.1‰ to 8.3‰. The δ¹³C values were cross correlated to infer potential common sources of biomarkers. This revealed common sources for C₃₁ and C₃₂ hopanes but no 1:1 relationship for pristane and phytane. The correlation of δ¹³C_TOC with the δ¹³C value of sulfur (S)-bound phytane is the strongest. This is because S-bound phytane is derived from phytol that originates from all marine primary producers (algae and cyanobacteria) and thus represents a weighted average of their carbon isotopic compositions. The δ¹³C values of S-bound phytane and C₃₅ hopane were also used to estimate pCO₂ levels. Before the OAE burial event, pCO₂ levels are estimated to be ca. 1300 ppmv using both biomarkers and the independent maximum Rubisco fractionation factors. At times of maximum organic carbon burial rates during the OAE, reconstructed pCO₂ levels are estimated to be ca. 700 ppmv. However, compared to other C/T OAE sections the positive isotope excursion of S-bound phytane is also affected by an increased production during the OAE. When we compensate for this, we arrive at pCO₂ levels around 1000 ppmv, a reduction of ca. 25%. This indicates that burial of organic matter can have a large effect on atmospheric CO₂ levels.     

Thermal stability of ladderane lipids as determined by hydrous pyrolysis

Anaerobic ammonium oxidation (anammox) has been recognized as a major process resulting in loss of fixed inorganic nitrogen in the marine environment. Ladderane lipids, membrane lipids unique to anammox bacteria, have been used as markers for the detection of anammox in marine settings. However, the fate of ladderane lipids after sediment burial and maturation is unknown. In this study, anammox bacterial cell material was artificially matured by hydrous pyrolysis at constant temperatures ranging from 120 to 365 °C for 72 h to study the stability of ladderane lipids during progressive dia- and catagenesis. HPLC-MS/MS analysis revealed that structural alterations of ladderane lipids already occurred at 120 °C. At temperatures >140 °C, ladderane lipids were absent and only more thermally stable products could be detected, i.e., ladderane derivatives in which some of the cyclobutane rings were opened. These diagenetic products of ladderane lipids were still detectable up to temperatures of 260 °C using GC-MS. Thus, ladderane lipids are unlikely to occur in ancient sediments and sedimentary rocks, but specific diagenetic products of ladderane lipids will likely be present in sediments and sedimentary rocks of relatively low maturity (i.e., C₃₁ hopane 22S/(22S + 22R) ratio <0.2 or ββ/(αβ + βα + ββ) ratio of >0.5).     

Stratigraphy and sedimentation rates of Upper Cretaceous deep-water systems of the Rhenodanubian Group (Eastern Alps, Germany)

In the Bavarian Alps (Germany), west of the Isar River, the abyssal deposits of the Lower Barremian to Upper Campanian Rhenodanubian Group consist of siliciclastic and calcareous turbidites alternating with hemipelagic non-calcareous mudstones. The up to 1500-m-thick succession, deposited in the Penninic Basin to the south of the European Plate, is characterized by a low mean sedimentation rate (c. 25 mm kyr⁻¹) over 60 million years. Palaeocurrents and turbidite facies distribution patterns suggest that sedimentation occurred on a weakly inclined abyssal plain. The highest sedimentation rates (up to 240 mm kyr⁻¹) were associated with the calcareous mud turbidites of the newly defined Röthenbach Subgroup, which includes the Piesenkopf, Kalkgraben and Hällritz formations (Middle Coniacian to Middle Campanian). These calcareous turbidites prograded from the west, and interfinger towards the east with red hemipelagic claystone. A high sea level presumably favoured pelagic carbonate production and accumulation on the shelves and on internal platforms in the western part of the basin, whereas siliciclastic shelves with steep slope angles have bordered the eastern part of the basin, where a dearth of turbidite sedimentation and increased Cretaceous oceanic red beds deposition occurred. In contrast to the eustatically-induced Middle Coniacian to Lower Campanian Cretaceous oceanic red beds (calcareous nannoplankton zones CC14 to CC18), red hemipelagites of Early Cenomanian age (upper part of calcareous nannoplankton zone CC9) and early Late Campanian age (upper part of zone CC21 and zone CC22) are interpreted as the result of regional tectonic activity.     

Calcareous nannoplankton, planktonic foraminiferal, and carbonate carbon isotope stratigraphy of the Cenomanian–Turonian boundary section in the Ultrahelvetic Zone (Eastern Alps, Upper Austria)

Ultrahelvetic units of the Eastern Alps were deposited on the distal European continental margin of the (Alpine) Tethys. The Rehkogelgraben section (“Buntmergelserie”, Ultrahelvetic unit, Upper Austria) comprises a 5 m thick succession of upper Cenomanian marl-limestone cycles overlain by a black shale interval composed of three black shale layers and carbonate-free claystones, followed by lower Turonian white to light grey marly limestones with thin marl layers. The main biostratigraphic events in the section are the last occurrence of Rotalipora and the first occurrences of Helvetoglobotruncana helvetica and Quadrum gartneri. The thickest black shale horizon has a TOC content of about 5%, with predominantly marine organic matter of kerogen type II. Vitrinite reflectance and Rock-Eval parameter T_max (<424 °C) indicate low maturity. HI values range from 261 to 362 mg HC/g TOC. δ¹³C values of bulk rock carbonates display the well documented positive shift around the black shale interval, allowing correlation of the Rehkogelgraben section with other sections such as the Global Boundary Stratotype Section and Point (GSSP) succession at Pueblo, USA, and reference sections at Eastbourne, UK, and Gubbio, Italy. Sediment accumulation rates at Rehkogelgraben (average 2.5 mm/ka) are significantly lower than those at Pueblo and Eastbourne.     

Baryt und ankerit aus Ammoniten des Berner Juras (Schweiz)

Barite has been found for the first time in the Swiss Jura (Hirni, Passwang). Small, white crystals of barite with yellow ankerite grow on calcite in different chambers of a Bajocian ammonite. Chemical data (by microprobe analysis) and lattice parameters (refined by leastsquares from powder patterns) are given for the two minerals. There is a distinct correlation between the cell dimensions and the chemical composition for both of them. The genesis is discussed.     

Zum Jahresgang der relativen Feuchte über dem Mittelmeer

Zusammenfassung Abweichend von der in einem früheren Aufsatz versuchten Erklärung der sommerlichen Feuchtezunahme über dem Mittelmeer wird plausibel gemacht, daß im wesentlichen die normale Erhöhung der Temperatur der Meeresoberfläche dafür verantwortlich ist.

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Summary Earlier in this journal an article was published, which suggested that the increase of the relative humidity in the warmer season of the Mediterranean was effected by subsiding of dry air from above and therefore increasing evaporation. But now it seems to the author that only the normal annual variation of the sea surface temperature is responsible for the observed phenomenon.