Tobias Kluge

Assessing the use of 3H–3He dating to determine the subsurface transit time of cave drip waters

3H–3He measurements constitute a well-established method for the determination of the residence time of young groundwater. However, this method has rarely been applied to karstified aquifers and in particular to drip water in caves, despite the importance of the information which may be obtained. Besides the determination of transfer times of climate signals from the atmosphere through the epikarst to speleothems as climate archives, 3H–3He together with Ne, Ar, Kr, Xe data may also help to give new insights into the local hydrogeology, e.g. the possible existence of a perched aquifer above a cave. In order to check the applicability of 3H–3He dating to cave drips, we collected drip water samples from three adjacent caves in northwestern Germany during several campaigns. The noble gas data were evaluated by inverse modelling to obtain recharge temperature and excess air, supporting the calculation of the tritiogenic 3He and hence the 3H–3He age. Although atmospheric noble gases were often found to be close to equilibrium with the cave atmosphere, several drip water samples yielded an elevated 3He/4He ratio, providing evidence for the accumulation of 3He from the decay of 3H. No significant contribution of radiogenic 4He was found, corresponding to the low residence times mostly in the range of one to three years. Despite complications during sampling, conditions of a perched aquifer could be confirmed by replicate samples at one drip site. Here, the excess air indicator ΔNe was about 10 %, comparable to typical values found in aquifers in mid-latitudes. The mean 3H–3He age of 2.1 years at this site presumably refers to the residence time in the perched aquifer and is lower than the entire transit time of 3.4 years estimated from the tritium data.

Deccan volcanism caused coupled pCO2 and terrestrial temperature rises, and pre-impact extinctions in northern China

Evaluating the terrestrial climate record provides a critical test of the roles of Chicxulub impact and Deccan Traps volcanism during the Cretaceous-Paleogene (K-Pg) mass extinction. Most evidence came from marine records, but our new clumped isotopes data from paleosol carbonates in the Songliao Basin provide a terrestrial climate history from northern China. This reveals there was a pre-impact warming caused by the onset of Deccan Traps volcanism, whereas the following short-term cooling then another warming episode were likely caused by Chicxulub impact and post-boundary volcanism. Our study suggests that the pCO₂ levels were probably the main control on the latest Cretaceous cooling and the climatic fluctuations across the K-Pg boundary interval in northern China. In the Songliao Basin, the pre-impact Deccan Traps volcanism links to losses of half of the lacustrine algae species (charophytes) and almost all of the lacustrine ostracodes; this suggests that the Deccan Traps volcanism had already destabilized the ecosystem and caused extinctions prior to the Chicxulub impact.

Carbonate Reservoir Analogues and Clumped Isotopes: How Combined Geometries and Geochemistry of Outcrops Help Reservoir Management in the Middle East

Petroleum geologists working in carbonate plays are facing two common and inter-connected challenges linked to optimizing production. First, constraining the geometry, spatial distribution and inter-connectivity of reservoir geobodies is crucial as these properties can control the permeability anisotropy of reservoirs zones. This is difficult to do at the inter-well scale due to the limited resolution of seismic methods (20 meters or higher) compared to the size of typical reservoir geobodies (tens of centimers to meters and higher) and the very heterogeneous nature of carbonate reservoirs. Furthermore, diagenetic transformations are very important in carbonate reservoirs. Being able to fingerprint the process and timing of diagenetic transformation is crucial to a correct assessement of the distribution of cemented zones in the subsurface. The issue of diagenesis is also important for organic matter maturation and the timing of oil migration, and therefore the second challenge faced by reservoir geologists in carbonate plays is one of constraining as well as possible the thermal history of the targeted basin. This paper reports on the results of a major long-term research effort that addresses some aspects of this double challenge in the Middle East, and that focused on novel isotopic methods to constrain the thermal history of carbonate phases in the context of the geometry of geobodies measured at the outcrop. Geological work under the Qatar Carbonates and Carbon Storage Centre (QCCSRC), funded jointly by Qatar Petroleum, Shell and the Qatar Science & Technology Park, has as its long-term research goals to improve characterization of subsurface anisotropies in carbonate reservoirs, notably for CCS operations.

Verschlossene Vergangenheit. Tropfsteine als Klimaarchive

Das Klima der Vergangenheit hinterlasst Spuren im Innern von Objekten, die als Klimaarchive genutzt werden konnen. Ein Beispiel sind Tropfsteine: Langsam und geschutzt wachsen sie uber die Jahrhunderte hinweg in Hohlen und schliesen dabei Informationen der Ausenwelt in sich ein. Heidelberger Wissenschaftler haben Methoden entwickelt, um die im Stein verschlossenen Klimazeugnisse zu lesen. Was die Tropfsteine von vergangenen Zeiten berichten, lasst auch unser heutiges Klima besser verstehen.