Conference Agenda

Overview and details of the sessions of this conference. Please select a date or location to show only sessions at that day or location. Please select a single session for detailed view (with abstracts and downloads if available).

Session Overview
1.9 Depositional and diagenetic processes in carbonate systems
Wednesday, 22/Sept/2021:
1:30pm - 3:00pm

Session Chair: Lars Reuning, CAU Kiel, Institute of Geosciences

Session Abstract

Modern carbonate systems such as reefs provide livelihood and ecosystem services, such as coastal protection and food security, for hundreds of millions of people. Fossil carbonate systems are important archives of environmental change and form a valuable resource for renewable energy exploration and exploitation such as geothermal heat but also for CO2 sequestration. Over the past decades, our understanding of carbonate systems has improved by the combination of traditional fieldwork with new techniques such as 3D seismic analysis, modeling, high-resolution 3D microscopy, and advanced geochemical methods. This session seeks to present studies applying state of the art methodologies in addressing open questions in the broad field of carbonate sedimentation and diagenesis. We especially encourage contributions to the following themes: 1) Anthropogenic influences on modern carbonate systems or carbonate secreting organisms, 2) Impact of diagenesis on palaeo-environmental and palaeoclimatological carbonate archives, (3) Biogeochemical and physicochemical processes driving carbonate precipitation and alteration processes, and (4) Petrophysical and geophysical characterization of carbonate systems.

1:30pm - 2:00pm
Session Keynote

Changing carbonate budgets and the maintenance of coral reefs and reef islands

Chris T Perry

University of Exeter, United Kingdom

The ecology and structure of many tropical coral reefs have altered markedly over the past few decades. Drivers of this degradation range from direct local damage from destructive human practices to global scale climate stressors, and especially those associated with elevated sea‐surface temperature anomalies. A major consequence of these climatic and pervasive local stressors has often been a rapid decrease in the abundance of habitat building corals, which has consequently reduced reef structural complexity and coral carbonate production rates. Equally, many reefs have been impacted by changes (both increases and decreases) in the abundance of bioeroding taxa such as parrotfish, urchins, sponges and microendolithic organisms. The collective effect has been to alter the rates and relative balance of carbonate producing and eroding processes on many reefs. Such changes are of increasing interest because these processes directly regulate net rates of reef carbonate production and sediment generation, and collectively can impact upon multiple geo‐ecological functions on reefs. These functions include reef‐building and the capacity of reefs to accrete vertically in response to sea‐level rise, and the supply of sands necessary to sustain beaches and reef islands. This talk will discuss recent progress in developing methodologies to estimate rates of reef carbonate production, reef growth and sediment generation. It will then use selected recent field examples to highlight changes in these processes in response to ecological disturbance, and highlight the potential to integrate these data into numerical and lab-based modelling approaches than be used to predict coastal wave exposure under future sea level rise scenarios.

2:00pm - 2:15pm

Dynamic as always – Sedimentary evolution of a coral reef island from the Spermonde Archipelago, Indonesia

Yannis Kappelmann1,2, Hildegard Westphal1,2, Dominik Kneer1, André Wizemann1,3, Thomas Mann1,4

1Leibniz Centre for Tropical Marine Research (ZMT), Fahrenheitstraße 6, Bremen, Germany; 2University of Bremen, Bibliothekstraße 1, Bremen, Germany; 3Bioplan GmbH, Strandstraße 32a, 18211 Ostseebad Nienhagen, Germany; 4Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Stilleweg 2, Hannover, Germany

The effects of changing climate and environmental conditions on coral reef islands have received a lot of attention, and the findings are discussed broadly. The low elevation of such islands above mean sea level and the largely unconsolidated sediment is exposing them to hydrodynamic processes. Coral reef islands are formed by sediment sourced from the surrounding reef systems and depend on these reef systems as continuous material suppliers. Shifts in these governing conditions may affect these landforms, however the results of such shifts remain controversial as island-response is likely to be regionally specific. The present sedimentological study addresses the formation of a reef island in the Spermonde Archipelago, Sulawesi, and its development through time. Sediment cores of 10 m length taken on the island allowed to reconstruct the sedimentary history of this mid-shelf island. The carbonate facies from these cores reflects the development of the island and thus allows for inferring the evolution of the surrounding ecosystem as well as the hydrodynamic regime that governed sedimentation. While sediment from the maximum depth of the cores mirror parautochthonous accumulation in a lagoonal environment, subsequent sedimentation is thought to be the result of hydrodynamic events with oscillating intensity.

2:15pm - 2:30pm

Shallow-marine carbonate cementation in Holocene segments of the calcifying green alga Halimeda

Thomas Mann1,2, André Wizemann1,3, Marleen Stuhr1,4,5, Yannis Kappelamann1,6, Alexander Janßen1,6, Jamaluddin Jompa7, Hildegard Westphal1,6

1Leibniz Centre for Tropical Marine Research (ZMT), Fahrenheitstraße 6, Bremen, Germany; 2Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Stilleweg 2, Hannover, Germany; 3Bioplan GmbH, Strandstraße 32a, 18211 Ostseebad Nienhagen; 4Interuniversity Institute for Marine Sciences (IUI), Eilat, Israel; 5Bar-Ilan University (BIU), Ramat Gan, Israel; 6University of Bremen, Bibliothekstraße 1, Bremen, Germany; 7Hasanuddin University, Jl. Perintis Kemerdekaan KM.10, Makassar, Indonesia

Early-diagenetic cementation of tropical carbonates results from the combination of numerous physico-chemical and biological processes. In the marine phreatic environment it represents an essential mechanism for the development and stabilization of carbonate platforms. However, many early-diagenetic cements that developed in the marine phreatic environment are likely to become obliterated during later stages of meteoric or burial diagenesis. In this contribution, a petrographic microfacies analysis of Holocene Halimeda segments collected on a coral island in the Spermonde Archipelago, Indonesia, is presented. Through electron microscopical analyses of thin sections, this study shows that segments are characterized by intragranular cementation of fibrous aragonite, equant Mg calcite (3.9 – 7.2 Mol% Mg), bladed low Mg calcite (0.4 – 1.0 Mol%) and mini-micritic Mg calcite (crystal size < 0.1 µm; 3.2 – 3.3 Mol% Mg). The consecutive development of (1) fibrous aragonite, (2) equant Mg calcite and (3) bladed low Mg calcite is explained by shifts in pore water pH and alkalinity through fluid kinetics and microbial sulfate reduction. Microbial activity appears to be the main trigger for the precipitation of mini-micritic Mg calcite, as inferred from the presumable detection of an extracellular polymeric matrix. Radiocarbon analyses of five Halimeda segments furthermore indicate that intragranular aragonite and Mg calcite cementation of microstructurally complex carbonate constituents in the shallow marine phreatic environment is a slower process than intergranular ooid cementation, characterized by relatively smooth surfaces.

2:30pm - 2:45pm

Magnesium and calcium isotope fractionation during microbial dolomite formation

Michael Tatzel1,2, Adina Paytan2, Samantha Carter2, Daniel A. Frick3, Francisca Martinez-Ruiz4, Zach A. DiLoreto5, Maria Dittrich5, Tomaso R. R. Bontognali6, Mónica Sanchez-Román7

1Universität Göttingen; 2University of California, Santa Cruz, USA; 3GFZ Deutsches Geoforschungszentrum, Potsdam; 4Universidad de Granada; 5University of Toronto; 6Space-X Switzerland; 7Vrije Universiteit Amsterdam

Microbial mediation is considered an important process for the formation of primary dolomite at ambient temperature. Yet, no structural, mineralogical, chemical or isotopic means exist to discern this mode of dolomite formation from secondary dolomite. To explore the utility of metal isotopes in allowing this distinction we characterize magnesium and calcium stable isotope ratios in primary (proto)dolomites from a modern hypersaline environment.

Samples from the Khor Al-Adaid sabkhas in Qatar show consistent isotopic differences of Ca isotopes (Δ44/40Ca) of -1.1 and -1.8 ‰ between solution and (proto-)dolomite and -0.3 to -0.7 ‰ between solution and organic phases, consistent with a previously postulated two-step fractionation process that enriches microbially mediated dolomite in 40Ca (Krause et al., 2012). Mg isotopes reveal a more complex picture with varying magnitudes of fractionation across different microbial zones in the shallow subsurface in agreement with a wide range of Δ26/24Mg-values previously observed in the sabkahs of Abu Dhabi (Geske et al., 2015) and suggested impact of microbial activity on δ26Mg (Riechelmann et al., 2020). The high variability is moreover modulated by authigenic palygorskite formation close to the water-sediment interface that yields consistently 26Mg-enriched signatures.

While clay-free sites suggest simple Mg precipitation from seawater into dolomite (Shalev et al., 2020), our data shows that Mg uptake into clay minerals does not allow a straightforward identification of a characteristic isotopic fingerprint in ancient primary dolomite, but shows potential to obtain a detailed picture of specific microbial involvement.

2:45pm - 3:00pm

Host influenced geochemical signature in the parasitic foraminifer Hyrrokkin sarcophaga

Nicolai Schleinkofer1,2, David Evans1,2, Max Wisshak3, Janina Vanessa Büscher4,5, Jens Fiebig1,2, André Freiwald3, Sven Härter1, Horst Marschall1,2, Silke Voigt1,2, Jacek Raddatz1,2

1Goethe Universität Frankfurt, Institut für Geowissenschaften, Frankfurt am Main, Germany; 2Goethe Universität Frankfurt, Frankfurt Isotope and Element Research Center (FIERCE), Frankfurt am Main, Germany; 3Senckenberg am Meer, Marine Research Department, Wilhelmshaven, Germany; 4National University of Ireland Galway, Department of Earth and Ocean Sciences, Galway, Ireland; 5GEOMAR Helmholtz Centre for Ocean Research Kiel, Department of Biological Oceanography, Kiel, Germany

Here, we present element to Ca ratios (Mg/Ca, Sr/Ca, Na/Ca and Mn/Ca) and stable isotope data (δ18O, δ13C) of the parasitic foraminifer Hyrrokkin sarcophaga, collected from two different host organisms, Desmophyllum pertusum - a cold-water coral commonly found in cold-water coral reefs and Acesta excavata - a bivalve associated with cold-water coral reefs.

Our results reveal that the geochemical signature in H. sarcophaga is influenced by the host organism. Sr/Ca ratios are 1.1 mmol mol-1 higher in H. sarcophaga that infest D. pertusum, which could be an indication that dissolved host carbonate material is utilised in shell calcification. Similarly, we measured 3.1 ‰ lower δ13C and 0.3 ‰ lower δ18O values in H. sarcophaga that lived on D. pertusum, which might be caused by the direct uptake of the host’s carbonate material with a more negative isotopic composition. Moreover, we observe higher Mn/Ca ratios in foraminifera that lived on A. excavata but did not penetrate the host shell compared to specimen that did.

H. sarcophaga is therefore, unlikely to be a reliable indicator of paleoenvironmental conditions using Sr/Ca, Mn/Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for. Still, these results provide interesting insights in the calcification process of these specialized foraminifera.