On the Enrichment of Magnetic Heavy Minerals in a Coastal Environment : Exploration, Examination, Explanation

In this thesis, an approach for the detailed assessment of magnetic heavy mineral enrichments in a coastal environment using integrated geophysical and sedimentological data is developed, the observed enrichment patterns are interpreted, and their formation mechanisms discussed. Used methods are electromagnetic profiling of the subsurface, close-up seafloor photography, various laboratory techniques to analyze bulk and magnetic grain sizes and mineralogy, and numerical modelling of bi-fractional sediment transport. The studies take place in an exemplary study area in the western Bay of Plenty (New Zealand) with dimensions of 60 km x 7 km in water depths from 2-35 m. Primary instrument is the benthic profiler MARUM NERIDIS III. Overall, the findings of this thesis demonstrate an innovative, effective way to approach an unmapped area and reach detailed results with conclusive interpretations in a relatively short time. It shows the conditions under which natural sorting patterns due to size and density develop along the coast. The basic formation mechanisms are applicable to other areas in similar coastal settings and for a diverse range of heavy minerals

Lithofacies distribution and sediment dynamics on a storm-dominated shelf from combined photographic, acoustic and sedimentological profiling methods (Bay of Plenty, New Zealand)

Sediment dynamics on a storm-dominated shelf (western Bay of Plenty, New Zealand) were mapped and analyzed using the newly developed multi-sensor benthic profiler MARUM NERIDIS III. An area of 60 km × 7 km between 2 and 35 m water depth was surveyed with this bottom-towed sled equipped with a high-resolution camera for continuous close-up seafloor photography and a CTD with connected turbidity sensor. Here we introduce our approach of using this multi-parameter dataset combined with sidescan sonography and sedimentological analyses to create detailed lithofacies and bedform distribution maps and to derive regional sediment transport patterns. For the assessment of sediment distribution, photographs were classified and their spatial distribution mapped out according to associated acoustic backscatter from a sidescan sonar. This provisional map was used to choose target locations for surficial sediment sampling and subsequent laboratory analysis of grain size distribution and mineralogical composition. Finally, photographic, granulometric and mineralogical facies were combined into a unified lithofacies map and corresponding stratigraphic model. Eight distinct types of lithofacies with seawards increasing grain size were discriminated and interpreted as reworked relict deposits overlain by post-transgressional fluvial sediments. The dominant transport processes in different water depths were identified based on type and orientation of bedforms, as well as bottom water turbidity and lithofacies distribution. Observed bedforms include subaquatic dunes, coarse sand ribbons and sorted bedforms of varying dimensions, which were interpreted as being initially formed by erosion. Under fair weather conditions, sediment is transported from the northwest towards the southeast by littoral drift. During storm events, a current from the southeast to the northweast is induced which is transporting sediment along the shore in up to 35 m water depth. Shorewards oriented cross-shore transport is taking place in up to 60 m water depth and is likewise initiated by storm events. Our study demonstrates how benthic photographic profiling delivers comprehensive compositional, structural and environmental information, which compares well with results obtained by traditional probing methods, but offers much higher spatial resolution while covering larger areas. Multi-sensor benthic profiling enhances the interpretability of acoustic seafloor mapping techniques and is a rapid and economic approach to seabed and habitat mapping especially in muddy to sandy facies

Über die Anreicherung magnetischer Schwerminerale im Küstenraum : Erkundung, Untersuchung, Erklärung

In this thesis, an approach for the detailed assessment of magnetic heavy mineral enrichments in a coastal environment using integrated geophysical and sedimentological data is developed, the observed enrichment patterns are interpreted, and their formation mechanisms discussed. Used methods are electromagnetic profiling of the subsurface, close-up seafloor photography, various laboratory techniques to analyze bulk and magnetic grain sizes and mineralogy, and numerical modelling of bi-fractional sediment transport. The studies take place in an exemplary study area in the western Bay of Plenty (New Zealand) with dimensions of 60 km x 7 km in water depths from 2-35 m. Primary instrument is the benthic profiler MARUM NERIDIS III. Overall, the findings of this thesis demonstrate an innovative, effective way to approach an unmapped area and reach detailed results with conclusive interpretations in a relatively short time. It shows the conditions under which natural sorting patterns due to size and density develop along the coast. The basic formation mechanisms are applicable to other areas in similar coastal settings and for a diverse range of heavy minerals

Lithofacies distribution in the western Bay of Plenty, New Zealand

Sediment dynamics on a storm-dominated shelf (western Bay of Plenty, New Zealand) were mapped and analyzed using the newly developed multi-sensor benthic profiler MARUM NERIDIS III. An area of 60 km × 7 km between 2 and 35 m water depth was surveyed with this bottom-towed sled equipped with a high-resolution camera for continuous close-up seafloor photography and a CTD with connected turbidity sensor. Here we introduce our approach of using this multi-parameter dataset combined with sidescan sonography and sedimentological analyses to create detailed lithofacies and bedform distribution maps and to derive regional sediment transport patterns. For the assessment of sediment distribution, photographs were classified and their spatial distribution mapped out according to associated acoustic backscatter from a sidescan sonar. This provisional map was used to choose target locations for surficial sediment sampling and subsequent laboratory analysis of grain size distribution and mineralogical composition. Finally, photographic, granulometric and mineralogical facies were combined into a unified lithofacies map and corresponding stratigraphic model. Eight distinct types of lithofacies with seawards increasing grain size were discriminated and interpreted as reworked relict deposits overlain by post-transgressional fluvial sediments. The dominant transport processes in different water depths were identified based on type and orientation of bedforms, as well as bottom water turbidity and lithofacies distribution. Observed bedforms include subaquatic dunes, coarse sand ribbons and sorted bedforms of varying dimensions, which were interpreted as being initially formed by erosion. Under fair weather conditions, sediment is transported from the northwest towards the southeast by littoral drift. During storm events, a current from the southeast to the northweast is induced which is transporting sediment along the shore in up to 35 m water depth. Shorewards oriented cross-shore transport is taking place in up to 60 m water depth and is likewise initiated by storm events. Our study demonstrates how benthic photographic profiling delivers comprehensive compositional, structural and environmental information, which compares well with results obtained by traditional probing methods, but offers much higher spatial resolution while covering larger areas. Multi-sensor benthic profiling enhances the interpretability of acoustic seafloor mapping techniques and is a rapid and economic approach to seabed and habitat mapping especially in muddy to sandy facies

Electromagnetic and related benthic profiles from the Bay of Plenty, New Zealand

Processed electromagnetic parameters (magnetic susceptibility and electric conductivity) along 33 profiles in the Bay of Plenty, New Zealand. Measurements were taken with the benthic profiler MARUM NERIDIS III. Related parameters are the porosity (according to Archie equation using standard values), concentration of stochiometric magnetite equivalent to the measured susceptibility, electric conductivity and temperature of bottom water (measured with on-board CTD), turbidity (measured with connected turbidity sensor), depth (two measurements with NERIDIS CTD and ship-mounted multibeam where available), relative backscatter (where available, measured with sidescan sonar), lithofacies (based on samples, see Kulgemeyer et al., 2016), distance along the profile, date (according to UTC) and time of the given day in ms (0 = UTC midnight), linenumber, location of points and individual point ID