The Arabian/Persian Gulf
Most recently, I co-lead a collaborative research study in which we looked at carbonate mineralisation in the coastal sabkha of Abu Dhabi, United Arab Emirates. Our aim was to document microbial, carbonate and evaporite facies as they occur at the surface and in the shallow subsurface, and to monitor temporal and spatial changes in environmental parameters such as temperature, salinity and oxygen consumption due to their effect on the growth, demise and/or preservation of the observed facies. While the microbial mats are important economically as modern analogues to ancient carbonate reservoirs of the Persian Gulf and as hosts to fish schools, the ultimate purpose of this research was to archive as much information as possible about this diverse and unique but threatened environment, and to create conceptual and numerical models that characterise rates and timescales of biotic and abiotic mineralisation pathways and the impact of external factors on the spatial and temporal development of this system.
Methodically, we established four transects perpendicular to the shoreline based on a preliminary field survey and satellite imagery. Relative elevation differences along each of the transects were surveyed with a differential GPS unit. In the following 1.5 years and often accompanied by graduate students, I carried-out field work once or twice per week to map and document changes in microbial and sedimentary facies at the surface and in the upper 1 to 1.5 metres of the subsurface. Environmental data loggers were deployed every 100 to 250 metres along each transect; the loggers continuously measured parameters including temperature, salinity, dissolved oxygen and water level, both at the surface and in the subsurface. In addition, a weather station was deployed at a strategic location for calibration and observation purposes. Sediment and microbial samples were recovered in syringes at the surface and in trenches, as well as in core tubes of 1 to 2 metres in length. Pore water samples were recovered with rhizons.
In the laboratory, detailed descriptions were completed for all samples and cores, after which they were prepared for a variety of sedimentological, mineralogical, geochemical and geomicrobiological analyses. Most notably, these included scanning electron microscopy and electron-dispersive spectroscopy, X-ray diffractometry for mineralogical characterisation, X-ray fluorescence element analysis and ICP-MS analyses of pore water. Macrocosm experiments (aquariums) were constructed that hosted microbial mat samples in controlled environments which simulated daily temperature changes, constant day-night cycle, daily tidal variations and sea-water chemistry. The programming and statistical analysis languages Python and R were used to analyse and visualise datasets from weather stations and environmental data loggers.
With the data collected, we were able to significantly advance the current state of knowledge in regard to microbial mats and the rates and timescales of associated biotic and abiotic mineralisation processes: conceptual models were developed that explain the formation of marine carbonate hardgrounds as the result of the complex interplay between mineralisation and sea-level variations during the Holocene, the formation of modern stromatolites was explained as the result of the interaction between erosion and microbial mineralisation and growth and conceptualised their continued development in the future into similar structures as found in Shark Bay, the preservation potential of environmentally diagnostic sedimentary structures was documented, a model presented that explains the formation of microbial polygons, and the results of a combined remote sensing – field-based study was used to quantify and predict the impact of sea-level rise on the coastal sabkha of Abu Dhabi during the 21st century.
Despite our best efforts, however, many questions remain to be answered and a lot of opportunities for field and/or laboratory-based studies are available. For example, I would like to rebuild the microcosms and closely monitor the development of the microbial mats and associated authigenic minerals in this controlled environment, in order to test and further quantify the rates and timescales in which they respond to environmental change. Part of this study would also be colonisation experiments in the lab and in the field where the rates and timescales of migration and colonisation of exposed sedimentary rocks by microbial communities will be observed. The results of this study would be important for making predictions about the behaviour of this sensitive system in the future, especially in light of global climatic change.
Another exciting study to do would be to spatially monitor geochemical proxies such as stable isotope ratios and to create maps that show the distribution and evolution of these ratios in space and time, covering quantitative variations over timescales from mere hours to months. The results of this study would be important for palaeoenvironmental reconstructions of similar systems, but will also help to develop machine learning models that predict rates of change in these parameters and help identify similar systems in the geologic record. Naturally, this study can be conducted in many places around the world, most notably some of the coral reefs of Taiwan including the Qixingyan group of islands, the Bahamas, Shark Bay in Western Australia, or in the coastal sabkha Abu Dhabi as part of a collaboration with Khalifa University. Ideally, the results will be applied to data from ancient analogue(s) elsewhere in the world or to data from extra-terrestrial systems.
Besides my research on microbial mats in the coastal sabkha of Abu Dhabi, I also conceptualised and later co-advised graduate research projects. Of the two projects, for which we were able to find students willing to participate in the intensive fieldwork campaign, one was about the mangroves of Abu Dhabi and the other about microbial mats deposits in continental sabkhas of the Liwa oasis, respectively.
The Santos Basin
In my post-doctoral research fellowship, funded by Total S.A., I aimed at reconstructing the sedimentary evolution of the terrestrial carbonate and microbial deposits that form the deep-water reservoirs of the Santos Basin, offshore Brazil. This basin remained largely unexplored until recently when vast hydrocarbon reserves were discovered that lead to a surge in petroleum exploration and development activities in this region.
Initially, we interpreted an approximately 150 km long seismic section and reconstructed the tectono-stratigraphic evolution of this transect. I conducted a study of modern analogues based on the scientific literature, which focussed on spatial facies distributions and the tectono-stratigraphic evolution of other terrestrial environments such as the East-African rift lakes and the Pamukkale travertine terraces in Turkey, which are thought to be largely similar to the Santos Basin deepwater reservoir facies. Subsequently, I constructed comprehensive two-dimensional facies models based on the analogue study, available well data and the tectono-stratigraphic framework. Lastly, I developed a stratigraphic forward model in the software package DionysosFlow . This forward model incorporated input parameters that were derived from the analogue study, the tectono-stratigraphy, facies models and well data, including lateral and vertical thickness variations of facies groups, and the rates of burial and tectonic movements. This model is currently being successfully used in follow-up studies by Total to enhance petroleum recovery in the study area.
The results of this project were presented to peers and shareholders in the form of two classified technical reports and I aim to publish a paper about this research in 2019 or 2020 after a non-disclosure agreement expires.
The Maldives carbonate platform
In my PhD research project, which was funded by the Vrije Universiteit Amsterdam, I looked at the impact of the Indian Monsoon system on carbonate production and sediment distribution pathways on the Maldives carbonate platform. The overarching aim of my project was to investigate shallow-water carbonate sedimentation in an environment dominated by the monsoon and its seasonal reversals in the wind & current directions and to shed light on the causes for the ‘missing sediment’ paradox of Maldivian atolls.
As sedimentologist, I initially took part in leg M74/4 of the German research vessel Meteor in late 2007. During this cruise, 12 piston cores were recovered from the Inner Sea sedimentary basin of the Maldives, several hundreds of kilometres of seismic lines were recorded, and a continuous hydroacoustic record was created. I selected three of the piston cores and the associated hydroacoustic data for my research. I did this in such a way as to be able to compare deposition of shallow-water carbonates between the eastern and western side of the Maldives and to link both seasonal and long-term variations in ocean current strength and direction to the deposits. In the laboratory, each of the at minimum 10 meters long cores was scanned with a multi-sensor core logger to gather petrophysical data, and with an X-ray fluorescence core scanner to gather data about the chemical composition of the sediments. Subsequently, sediment samples were taken with syringes every 5 cm, which resulted in an excitingly large but challenging amount of sedimentological, geochemical and mineralogical analyses that I carried-out over a time interval of approximately 3 years. Inclusive to these measurements was the selection and picking of planktonic foraminifers ( Globigerinoides ruber white) to create a record of stable isotope values (δ18O, δ13C) in order to be able to construct an age model for each of the cores through comparison and wiggle matching with other local stable isotope records and the benthic stack. Other analytical methods included grain size analysis with laser granulometry, wet and dry sieving and image analysis, thermo-gravimetric analysis, CNS analysis with Flash EA 1112 analysers, X-ray diffractometry to identify and quantify carbonate minerals, and X-ray fluorescence core scanning to reconstruct variations in elements, particularly Sr , through space and time. In the course of these analyses, I used the programming language Python to carry-out data analyses and numerical modelling, including the development of synthetic seismograms from the petrophysical data. I also used the geomodelling package Surfer to create 3-dimensional representations of bathymetric data.
Through my research, we were able to make significant contributions to advancing the state-of-knowledge about the Maldives and other carbonate platforms on our planet. For example, through the reconstruction of the sedimentation history at the location of one of the three piston cores, we were able to model the vertical movement of the local carbonate production window as a result of sea-level variations. We were also able to identify gaps in the sedimentary records of the three cores and linked these gaps to erosive events that resulted from current amplification during glacial periods and led to the ‘missing sediment’ paradox. Lastly, we identified and quantified terrestrial dust flux from the Sahara desert and the Chinese Loess Plateau using a machine learning model developed from X-ray fluorescence core scanning data. Lastly, we showed that ocean currents controlled the growth of the carbonate platform of the Maldives to a larger extent than previously thought.
As with my most recent project, many questions and unexplored opportunities remain on the Maldives. For example, during our research cruise in 2007, we discovered a multitude of submerged terraces on the slopes of larger atolls on the Maldives such as Ari Atoll. While these terraces were interpreted to be drowned coral reefs, based on limited hydroacoustic data, no actual sedimentary data is available to confirm or deny this interpretation. If these terraces are no reefs at all, or if the composition of coral species differs from the composition of the coral reefs of today, this would have significant implications for the climatic development after the last glacial maximum, including rates of sea level rise, changes in the local current system, or in the availability of nutrients. Ultimately, this might have consequences for the reconstruction of post-glacial monsoonal changes in the region, and help to better characterise the period after the LGM.
The Tibetan Plateau
In my graduate research project, which was funded by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research in Potsdam, Germany, I worked with sediment samples collected on the Tibetan Plateau. My aims were to use an unsupervised, dimensionality reducing algorithm, principal component analysis combined with redundancy analysis, to create a model that predicts the precipitation distribution on the Tibetan Plateau from geochemical proxy data, and to apply this model to a sediment core to reconstruct variations in erosion and precipitation since the last glacial maximum.
In the laboratory, I focussed on analyses of core material and lake surface sediment samples and conducted a variety of sedimentological and geochemical analyses. Most importantly, this included 3-acid pressure dissolution of sediments and subsequent measurements of the resulting solution in an ICP-AES unit in order to obtain element concentrations. The element concentration data of the lake surface sediment samples were then fed into the predictive algorithm which in turn created a set of linearly uncorrelated variables, principal components, from the previously large set of possibly correlated variables. Each of the resulting components represented an environmental gradient, in this case, conductivity and elevation; the correlation of individual sample points with the conductivity-component indicated the relative amount of precipitation as compared to other samples. This model of the recent distribution of precipitation was then applied to the core sedimentary record to reconstruct precipitation through time.
As before, this project leaves open many opportunities for future research. For example, an expansion of the record of surface samples will help improve the model of spatial distribution of precipitation. New core records from the Tibetan Plateau will help to better constrain the model and also establish a link between the past and the present. Lastly, it is important to conduct similar analyses in other regions on our planet, such as e.g. southern Oman. In this region, in southern Oman near Salalah, every summer a strong monsoonal influence is developing in this region, changing the whole region from a brown rocky desert into the “Shire of the Middle-East”. Hence, the idea would be to sample ponds and lakes during and immediately after this rainy season and, combined with weather stations that recorded the precipitation, develop the same models of spatial precipitation as I did for the Tibetan Plateau.