Werner Ricken

Carbon–sulfur–iron relationships and δ13C of organic matter for late Albian sedimentary rocks from the North Atlantic Ocean: paleoceanographic implications

Abstract Cores from six Deep Sea Drilling Project Sites (367, 369, 137, 386, 387 and 603) of the late Albian North Atlantic Ocean were investigated for organic carbon content, δ13C values of the kerogens, maceral composition of the organic matter, C/S ratios, Fe–TOC–S relationships and framboidal pyrite size distribution in order to evaluate processes that led to the accumulation of organic matter-rich black shale deposits. The results show a clear separation of the Albian North Atlantic into an anoxic eastern part and a mostly oxic western part. The eastern North Atlantic is dominated by organic matter-rich deposits. Sulfate reduction occurred in an oxygen-free water column and resulted in characteristic C/S ratios, Fe–TOC–S relationships and framboidal pyrite size distribution patterns. Elevated productivity, anoxia and high sedimentation rates supported the formation of black shale deposits. For most of the western and central parts, organic matter sedimentation took place through an oxygenated water column. The accumulated organic matter is dominantly of terrigenous origin. The deposition of marine derived organic matter was most likely controlled by productivity, paleobathymetry and low sedimentation rates.

Interhemispheric ice-sheet synchronicity during the last glacial maximum

Part of the East Antarctic Ice Sheet advanced and retreated in synchrony with Northern Hemispheric ice sheets. The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood. We develop a chronology for the Weddell Sea sector of the East Antarctic Ice Sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of Northern Hemisphere ice sheets. Surface climate forcing of Antarctic mass balance would probably cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Our new data support teleconnections involving sea-level forcing from Northern Hemisphere ice sheets and changes in North Atlantic deep-water formation and attendant heat flux to Antarctic grounding lines to synchronize the hemispheric ice sheets.

Recent and historical discharge of a large European river system – oxygen isotopic composition of river water and skeletal aragonite of Unionidae in the Rhine

Abstract Seasonal variations in the oxygen isotopic composition of Rhine River water were analyzed in detail and compared with the oxygen isotopic record from recent and historical specimens of freshwater bivalves (Unionidae). The purpose of this study was to investigate the potential use of these aragonitic bivalves as proxy recorders for varying amounts and sources of discharge, and thereby infer climate change. Seasonal variations in the river water δ 18 O are on the order of 1–2‰. During summer, Alpine melt-water contributes significantly to the total discharge, resulting in average values of −10 to −10.5‰, whereas the non-Alpine contribution is higher during winter, as indicated by mean δ 18 O values of −8.5 to −9‰. The basic pattern of the modern seasonal variation of δ 18 O of river water can be described by a numerical mass balance approximation of the various contributions from the Alpine and non-Alpine catchments with their average δ 18 O composition. The δ 18 O of growth increments in the prismatic shell layer of Anodonta corresponds perfectly to what is predicted by known fractionation of 18 O between water and aragonite. Shell growth is restricted to water temperatures above 8–10°C, so variations in δ 18 O and the river water temperature are faithfully recorded by relatively large growth increments during summer. The distinctive isotopic signatures of individual flood events during summer and autumn are also recorded in the shells.

BMPix and PEAK tools: new methods for automated laminae recognition and counting Application to glacial varves from Antarctic marine sediment

We present tools for rapid and quantitative detection of sediment lamination. The BMPix tool extracts color and gray-scale curves from images at pixel resolution. The PEAK tool uses the gray-scale curve and performs, for the first time, fully automated counting of laminae based on three methods. The maximum count algorithm counts every bright peak of a couplet of two laminae (annual resolution) in a smoothed curve. The zero-crossing algorithm counts every positive and negative halfway-passage of the curve through a wide moving average, separating the record into bright and dark intervals (seasonal resolution). The same is true for the frequency truncation method, which uses Fourier transformation to decompose the curve into its frequency components before counting positive and negative passages. We applied the new methods successfully to tree rings, to well-dated and already manually counted marine varves from Saanich Inlet, and to marine laminae from the Antarctic continental margin. In combination with AMS14C dating, we found convincing evidence that laminations in Weddell Sea sites represent varves, deposited continuously over several millennia during the last glacial maximum. The new tools offer several advantages over previous methods. The counting procedures are based on a moving average generated from gray-scale curves instead of manual counting. Hence, results are highly objective and rely on reproducible mathematical criteria. Also, the PEAK tool measures the thickness of each year or season. Since all information required is displayed graphically, interactive optimization of the counting algorithms can be achieved quickly and conveniently.

Bedding rhythms and cyclic sequences as documented in organic carbon-carbonate patterns, Upper Cretaceous, Western Interior, U.S.

Abstract A three-component sedimentation model is introduced for estimating the relative effects of major changes in sediment flux. Coupled organic carbon-carbonate changes, reflecting different dilution-concentration styles are utilized to detect the changing flux between the carbonate, siliciclastic and organic matter components. The three-component model is then applied to Upper Cretaceous rhythmically bedded units of the Greenhorn and Niobrara cycles of the Western Interior Seaway. The cycles are related to third-order sea-level changes. The Western Interior Seaway was sensitive to small-scale climatic cycles only during periods of maximum flooding, due to combined variations in carbonate productivity, redox conditions and siliciclastic supply from continental sources. Rhythmic deposition is different for different parts within the periods of maximum flooding for each of the two investigated third-order sea-level cycles. Section intervals reflecting peak flooding show variations in carbonate productivity and variations in redox conditions. Slightly more regressive intervals show variations in calcareous productivity and siliciclastic dilution with stagnant dysaerobic bottom waters. For most of the investigated bedding rhythms, persistent dysaerobic bottom waters are largely uninfluenced by variations in pelagic carbonate productivity, except for section intervals representing peak flooding. This suggests the existence of a circulation pattern in which a mixed surface water zone was underlain by more stratified, oxygen-depleted water masses with slow circulation.

Orbital Control on Carbonate-Lignite Cycles in the Ptolemais Basin, Northern Greece - An Integrated Stratigraphic Approach

Establishing the time frame is crucial for most geoscientific investigation. Without proper time control, past geologic processes cannot be inferred appropriately, nor can their dynamics be understood adequately. Rhythmic changes in sedimentary cycles hold the key to establishing precise and high-resolution chronologies. The concept goes back to theoretical considerations first published by Milankovitch (1941). His calculations showed that changes in earth’s orbital geometry lead to changes in the seasonal and latitudinal distribution of incoming solar radiation (insolation). Three main periods are responsible for these insolation changes, eccentricity (the shape of the orbit around the sun; with periods of 413 kyr, 123 kyr, and 95 kyr), obliquity (the tilt of the axis; changing at a period of 41 kyr), and precession (the wobbling spin of the axis with periods of 19 kyr and 23 kyr). He argued that these changes caused the waning and waxing of polar ice sheets. More than three decades later, Hays et al. (1976) and Imbrie et al. (1984) provided proof the cyclic changes of the earth energy budget were large enough to be preserved in marine sediment. Theoretical calculation of Berger (1976) and Berger and Loutre (1991) supported the Milankovitch theory and provided templates for orbital variability for the last couple of million yeas. Henceforth, cyclic changes in sediment strata were used to develop detailed orbital chronologies by assigning sedimentary cycles to orbital cycles.