Characteristics of migrating submarine canyons from the middle Miocene to present: Implications for paleoceanographic circulation,northern South China Sea

Previously undocumented, migrating submarine canyons have developed in the Pearl River Mouth Basin along the northern continental margin of the South China Sea from the middle Miocene to present. A grid of high-resolution, 2-D multi-channel seismic profiles calibrated by borehole information permits documentation of these northeastward migrating submarine canyons, as the result of the interplay of gravity flows and bottom currents. The modern canyons have lengths of 30–60 km, widths of 1–5.7 km, and relief of 50–300 m in water depths of 450–1500 m. Buried ancient submarine canyon successions were originally eroded by basal erosional discontinuities and partially filled by canyon thalweg deposits. These are overlain by lateral inclined packages and hemipelagic drape deposits. Basal erosional discontinuities and thalweg deposits are probably created principally by turbidity currents and filled with turbidites. Lateral inclined packages likely were formed by along-slope bottom currents. The evolution of these migrating submarine canyons reveals that northeastward bottom currents have consistently occurred at least from the middle Miocene to present in the study area. It might further imply that thermohaline intermediate water circulation of the South China Sea has been anti-cyclonic from the middle Miocene to present. The initiation of migrating submarine canyons possibly signals commencement of strong bottom currents after the middle Miocene in the South China Sea. The intensification of bottom currents also possibly may reflect shoaling of the major ocean seaways and increased vigor in oceanic circulation forced by global cooling after the middle Miocene.     

The international global navigation satellite systems service (IGS): development and achievements

Since 21 June 1992 the International GPS Service (IGS), renamed International GNSS Service in 2005, produces and makes available uninterrupted time series of its products, in particular GPS observations from the IGS Global Network, GPS orbits, Earth orientation parameters (components x and y of polar motion, length of day) with daily time resolution, satellite and receiver clock information for each day with different latencies and accuracies, and station coordinates and velocities in weekly batches for further analysis by the IERS (International Earth Rotation and Reference Systems Service). At a later stage the IGS started exploiting its network for atmosphere monitoring, in particular for ionosphere mapping, for troposphere monitoring, and time and frequency transfer. This is why new IGS products encompass ionosphere maps and tropospheric zenith delays. This development became even more important when more and more space-missions carrying space-borne GPS for various purposes were launched. This article offers an overview for the broader scientific community of the development of the IGS and of the spectrum of topics addressed today with IGS data and products.     

From bone to pixel—fossil restoration and reconstruction with digital techniques

Fossils represent the only physical evidence for the existence of extinct life, and hold a vast potential to reconstruct organisms and ecosystems vanished a long time ago. Yet fossils are not as complete as they might appear in museum exhibits, documentaries or Hollywood blockbusters. Millions of years of fossilization have left their marks on the fossils, which might no longer resemble the condition of the organism when it was alive. A key challenge in palaeontology is therefore to restore and reconstruct the morphology of fossils. Luckily, novel digital visualization and reconstruction techniques offer powerful tools to bring extinct organisms back to life in unprecedented detail.     

Geschichte und Ursachen des Röhrichtrückgangs am Ammersee (Deutschland)

The development of aquatic reed stands at Lake Ammersee was documented by using vertical airborne photographs which were taken during four partial and five complete flights beginning in 1944. A dramatic decline of reed, especially of those parts which stood in deep water, was demonstrated. Between the years 1963 and 1969 60% and until 1992 another 30% of the Phragmitetum disappeared. Only at the east bank did the lake reed beds slightly expand.The examination of possible factors affecting the development of reed at Lake Ammersee lead to the following scenario: Until 1940 reed stands at Lake Ammersee spread and covered large aquatic areas. Only the east bank of the lake, where the influence of wind and waves was high, and banks near towns and recreation areas remained uncovered. Since the regulation of the River Ammer between 1920 and 1938 flood occurrence increased enormously. The flood disaster of the year 1965 coincided with the period of the highest rate of reed decline. The peak of eutrophication in the lake was reached in 1975. Huge carpets of green algae caused further retreat of reeds.At the present time recovery is not possible because of the negative influence of human recreation and of reed consuming waterfowl. Interestingly enough an expansion of reed has been observed at the east bank of Lake Ammersee at places were there was no Phragmites previously.     

Modern and historical tropical cyclone and tsunami deposits at the coast of Myanmar: Implications for their identification and preservation in the geological record

The catastrophic storm surge of tropical cyclone Nargis in May 2008 demonstrated Myanmar's exposure to coastal flooding. The investigation of sediments left by tropical cyclone Nargis and its predecessors is an important contribution to prepare for the impact of future tropical cyclones and tsunamis in the region, because they may extend the database for long-term hazard assessment beyond the relatively short instrumental and historical record. This study, for the first time, presents deposits of modern and historical tropical cyclones and tsunamis from the coast of Myanmar. The aim is to establish regional sedimentary characteristics that may help to identify and discriminate cyclones and tsunamis in the geological record, and to document post-depositional changes due to tropical weathering in the first years after deposition. These findings if used to interpret older deposits will extend the existing instrumental record of flooding events in Myanmar. Evaluating deposits that can be related to specific events, such as the 2006 tropical cyclone Mala and the 2004 Indian Ocean tsunami, indicates similar sedimentary characteristics for both types of sediments. Landward thinning and fining trends, littoral sediment sources and sharp lower contacts allow for the differentiation from underlying deposits, while discrimination between tropical cyclone and tsunami origin is challenging based on the applied methods. The modern analogues also demonstrate a rather low preservation potential of the sand sheets due to carbonate dissolution, formation of organic top soils, and coastal erosion. However, in coastal depressions sand sheets of sufficient thickness (>10 cm) may be preserved where the shoreline is prograding or stable. In the most seaward swale of a beach-ridge plain at the Rakhine coast, two sand sheets have been identified in addition to the deposits of 2006 tropical cyclone Mala. Based on a combination of optically stimulated luminescence, radiocarbon and ¹³⁷Cs dating, the younger sand layer is related to 1982 tropical cyclone Gwa, while the older sand layer is most probably the result of an event that took place prior to 1950. Comparison with historical records indicates that the archive is only sensitive to tropical cyclones of category 4 (or higher) with landfall directly in or a few tens of kilometres north of the study area. While the presented tropical cyclone records are restricted to the last 100 years, optically stimulated luminescence ages of the beach ridges indicate that the swales landward of the one investigated in this study might provide tropical cyclone information for at least the past 700 years.     

Testing the preservation potential of early diagenetic dolomites as geochemical archives

Early marine diagenetic dolomite is a rather thermodynamically-stable carbonate phase and has potential to act as an archive of marine porewater properties. However, the variety of early to late diagenetic dolomite phases that can coexist within a single sample can result in extensive complexity. Here, the archive potential of early marine dolomites exposed to extreme post-depositional processes is tested using various types of analyses, including: petrography, fluid inclusion data, stable δ¹³C and δ¹⁸O isotopes, ⁸⁷Sr/⁸⁶Sr ratios, and U-Pb age dating of various dolomite phases. In this example, a Triassic carbonate platform was dissected and overprinted (diagenetic temperatures of 50 to 430°C) in a strike-slip zone in Southern Spain. Eight episodes of dolomitization, a dolostone cataclasite and late stage meteoric/vadose cementation were recognized. The following processes were found to be diagenetically relevant: (i) protolith deposition and fabric-preservation, and marine dolomitization of precursor aragonite and calcite during the Middle–Late Triassic; (ii) intermediate burial and formation of zebra saddle dolomite and precipitation of various dolomite cements in a Proto-Atlantic opening stress regime (T ca 250°C) during the Early–Middle Jurassic; (iii) dolomite cement precipitation during early Alpine tectonism, rapid burial to ca 15 km, and high-grade anchizone overprint during Alpine tectonic evolution in the Early Eocene to Early Miocene; (iv) brecciation of dolostones to cataclasite during the onset of the Carboneras Fault Zone activity during the Middle Miocene; and (v) late-stage regression and subsequent meteoric overprint. Data shown here document that, under favourable conditions, early diagenetic marine dolomites and their archive data may resist petrographic and geochemical resetting over time intervals of 10⁸ or more years. Evidence for this preservation includes preserved Late Triassic seawater δ¹³C_DIC values and primary fluid inclusion data. Data also indicate that oversimplified statements based on bulk data from other petrographically-complex dolomite archives must be considered with caution.     

Highlights of the Messel Oil Shale

The Messel oil shale, Germany, was deposited in a maar crater that formed 47 million years ago. Since 1975 the Senckenberg Research Institute in Frankfurt am Main, has conducted systematic scientific excavations of this oil shale with much success. Besides plants and insects, more than 130 species of well - preserved fossil vertebrates like reptiles, fishes, birds and mammals have been found and have made Messel worldfamous. Some examples of these vertebrates are presented.     

Rock physics model for seismic velocity & fluid substitution in sub-resolution interbedded sand–shale sequences

The measured geophysical response of sand – shale sequences is an average over multiple layers when the tool resolution (seismic or well log) is coarser than the scale of sand – shale mixing. Shale can be found within sand – shale sequences as laminations, dispersed in sand pores, as well as load bearing clasts. We present a rock physics framework to model seismic/sonic properties of sub-resolution interbedded shaly sands using the so-called solid and mineral substitution models. This modelling approach stays consistent with the conceptual model of the Thomas–Stieber approach for estimating volumetric properties of shaly sands; thus, this work connects established well log data-based petrophysical workflows with quantitative interpretation of seismic data for modelling hydrocarbon signature in sand – shale sequences. We present applications of the new model to infer thickness of sand – shale lamination (i.e., net to gross) and other volumetric properties using seismic data. Another application of the new approach is fluid substitution in sub-resolution interbedded sand–shale sequences that operate directly at the measurement scale without the need to downscale; such a procedure has many practical advantages over the approach of “first-downscale-and-then-upscale” as it is not very sensitive to errors in estimated sand fraction and end member sand/shale properties and remains stable at small sand/shale fractions.     

The impact of internal waves on upper continental slopes: insights from the Mozambican margin (southwest Indian Ocean)

Evidences of sedimentation affected by oceanic circulation, such as nepheloid layers and contourites are often observed along continental slopes. However, the oceanographic processes controlling sedimentation along continental margins remain poorly understood. Multibeam bathymetry and high-resolution seismic reflection data revealed a contourite depositional system in the Mozambican upper continental slope composed of a contourite terrace (a surface with a gentle seaward slope dominated by erosion) and a plastered drift (a convex-shape sedimentary deposit). A continuous alongslope channel and a field of sand dunes (mainly migrating upslope), formed during Holocene, were identified in the contourite terrace at the present seafloor. Seismic reflection data of the water column show internal waves and boluses propagating in the pycnocline near the upper slope. The channel and the dunes are probably the result of the interaction of the observed internal waves with the seafloor under two different conditions. The alongslope channel is located in a zone where intense barotropic tidal currents may arrest internal solitary waves, generating a hydraulic jump and focused erosion. However, upslope migrating dunes may be formed by bottom currents induced by internal solitary waves of elevation propagating landwards in the pycnocline. These small-scale sedimentary features generated by internal waves are superimposed on large-scale contouritic deposits, such as plastered drifts and contourite terraces, which are related to geostrophic currents. These findings provide new insights into the oceanographic processes that control sedimentation along continental margins that will help interpretation of palaeoceanographic conditions from the sedimentary record. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd