Late Triassic dinosaur tracks from Penarth, south Wales

Evidence of Late Triassic large tetrapods from the UK is rare. Here, we describe a track-bearing surface located on the shoreline near Penarth, south Wales, United Kingdom. The total exposed surface is c. 50 m long and c. 2 m wide, and is split into northern and southern sections by a small fault. We interpret these impressions as tracks, rather than abiogenic sedimentary structures, because of the possession of marked displacement rims and their relationship to each other with regularly spaced impressions forming putative trackways. The impressions are large (up to c. 50 cm in length), but poorly preserved, and retain little information about track-maker anatomy. We discuss alternative, plausible, abiotic mechanisms that might have been responsible for the formation of these features, but reject them in favour of these impressions being tetrapod tracks. We propose that the site is an additional occurrence of the ichnotaxon Eosauropus, representing a sauropodomorph trackmaker, thereby adding a useful new datum to their sparse Late Triassic record in the UK. We also used historical photogrammetry to digitally map the extent of site erosion during 2009–2020. More than 1 m of the surface exposure has been lost over this 11-year period, and the few tracks present in both models show significant smoothing, breakage and loss of detail. These tracks are an important datapoint for Late Triassic palaeontology in the UK, even if they cannot be confidently assigned to a specific trackmaker. The documented loss of the bedding surface highlights the transient and vulnerable nature of our fossil resources, particularly in coastal settings, and the need to gather data as quickly and effectively as possible.

Assessing the representative elementary volume of rock types by X-ray computed tomography (CT) – a simple approach to demonstrate the heterogeneity of the Boda Claystone Formation in Hungary

X-ray computed tomography (CT) can reveal internal, three-dimensional details of objects in a non-destructive way and provide high-resolution, quantitative data in the form of CT numbers. The sensitivity of the CT number to changes in material density means that it may be used to identify lithology changes within cores of sedimentary rocks. The present pilot study confirms the use of Representative Elementary Volume (REV) to quantify inhomogeneity of CT densities of rock constituents of the Boda Claystone Formation. Thirty-two layers, 2 m core length, of this formation were studied. Based on the dominant rock-forming constituent, two rock types could be defined, i.e., clayey siltstone (20 layers) and fine siltstone (12 layers). Eleven of these layers (clayey siltstone and fine siltstone) showed sedimentary features such as, convolute laminations, desiccation cracks, cross-laminations and cracks. The application of the Autoregressive Integrated Moving Averages, Statistical Process Control (ARIMA SPC) method to define Representative Elementary Volume (REV) of CT densities (Hounsfield unit values) affirmed the following results: i) the highest REV values corresponded to the presence of sedimentary structures or high ratios of siltstone constituents (> 60%). ii) the REV average of the clayey siltstone was (5.86 cm3) and (6.54 cm3) of the fine siltstone. iii) normalised REV percentages of the clayey siltstone and fine siltstone, on the scale of the core volume studied were 19.88% and 22.84%; respectively. iv) whenever the corresponding layer did not reveal any sedimentary structure, the normalised REV values would be below 10%. The internal void space in layers with sedimentary features might explain the marked textural heterogeneity and elevated REV values. The drying process of the core sample might also have played a significant role in increasing erroneous pore proportions by volume reducation of clay minerals, particularly within sedimentary structures, where authigenic clay and carbonate cement were presumed to be dominant.

Deep-Learning-Based Automated Sedimentary Geometry Characterization From Borehole Images

Sedimentary geometry on borehole images usually summarizes the arrangement of bed boundaries, erosive surfaces, crossbedding, sedimentary dip, and/or deformed beds. The interpretation, very often manual, requires a good level of expertise, is time consuming, can suffer from user bias, and becomes very challenging when dealing with highly deviated wells. Bedform geometry interpretation from crossbed data is rarely completed from a borehole image. The purpose of this study is to develop an automated method to interpret sedimentary structures, including the bedform geometry resulting from the change in flow direction from borehole images. Automation is achieved in this unique interpretation methodology using deep learning (DL). The first task comprised the creation of a training data set of 2D borehole images. This library of images was then used to train deep neural network models. Testing different architectures of convolutional neural networks (CNN) showed the ResNet architecture to give the best performance for the classification of the different sedimentary structures. The validation accuracy was very high, in the range of 93 to 96%. To test the developed method, additional logs of synthetic data were created as sequences of different sedimentary structures (i.e., classes) associated with different well deviations, with the addition of gaps. The model was able to predict the proper class in these composite logs and highlight the transitions accurately.

Barrier Island Sediments Reveal Storm Surge and Fluvial Flood Events in the Past Centuries at Thua Thien Hue, Central Vietnam

Sedimentary evidence of storms and fluvial floods (FFs) is crucial for a better understanding of such events in coastal zones. In this study, we analyzed the sedimentary characteristics of the coastal storm and FF deposits at the Hoa Duan barrier, Thua Thien Hue, central Vietnam. Analyses of the sedimentary structures and properties (grain size distribution, composition, roundness, and sphericity) and loss on ignition revealed that the storm sediments were comprised of coarser grains with a low organic and carbonated content, and with sedimentary structures, including parallel and inclined landward lamination, multiple sets of normal and reverse grading, mud rip-up clasts, and sharp and erosional contacts (both top and bottom) with finer-grain layers. Conversely, the FF sediments had only fine to very fine grains, with dominant high organic and carbonate contents, and only exhibited sedimentary structures of sharp erosional top and bottom contacts with coarser-grained layers. The clearest differentiation to distinguish coastal storm layers from inland FF layers was obtained by plotting the mean grain size against the sorting. The results of optically stimulated luminescence dating suggested that two storm layers and one FF layer were deposited during the last 130 ± 10 years. Moreover, two layers were deposited by storms and one by a FF prior to that (>130 ± 10 years). The identification of the sedimentary diagnostic key of these two hazards can help to improve the understanding of the geomorphological evolution of the studied site and the other parts of this coastal region in order to remind the coastal community to prepare for future coastal hazards well.

Some Aspects of Sedimentology of the Wanganui Basin, North Island, New Zealand

<p>The thesis comprises studies of the marine Pleistocene sediments of the Wanganui Basin, North Island, New Zealand. Part I deals with the chronology of the sediments and correlation of horizons within and outside the basin, by dating glass shards from tephra horizons using the fission-track method. Correlation to similar tephras from Hawke's Bay, to deep-sea cores taken 1000km east of New Zealand and to the central North Island volcanic district is attempted. These fission-track ages fill a dating gap that previously existed in the New Zealand marine Quaternary sequence. Thirteen tephras were examined in the Wanganui Basin and were found to range in age from 1.50 [plus or minus] 0.21m.y.B.P. (Ohingaiti Ash) to 0.28 [plus or minus] 0.05m.y.B.P. (uppermost Finnis Road Ash). These tephras record major rhyolitic eruptive phases in the central volcanic region. The most significant eruptive phase began 1.06 [plus or minus]0.16m.y.B.P. with the deposition of the Makirikiri Tuff sediments, continued to 0.88 [plus or minus]0.13m.y.B.P. and is tentatively associated with the older ignimbrites of the King Country, west of Lake Taupe. A volcanically quiet period followed when no volcanic glass was deposited in the sediments, until 0.74 [plus or minus] 0.09m.y.B.P. Several large eruptions then occurred between 0.74 and 0.28m.y.B.P. The age of the Plio-Pleistocene boundary, at the base of the Hautawan Stage in the Wanganui Basin is 1.87m.y.B.P. The age of the base of the Nukumaruan is 1.55m.y.B.P., the Okehuan, 1.06m.y.B.P., the Castleclifflan 0.45m.y.B.P., and the Hawera Series is less than 0.38m.y.B.P. Palaeomagnetic stratigraphy was determined for the upper Nukumaruan and lower Okehan sequence in the Rangitikei River. Viscous components of magnetism were removed from the samples by thermal demagnetising, extreme care being needed to obtain consistent results. Independent dates from the palaeomagnetic stratigraphy substantially confirm the fission-track dates. The Bruhnes-Matuyama boundary is clearly defined between the Rewa and Potaka Pumice Members (aged 0.74 and 0.61m.y.B.P. respectively) of the Kaimatira Pumice Send Formation. The Jaramillo event was not recognised and is probably represented in part of the sequence where sediments are too coarse and friable to yield palaeomagnetic cores. Part II deals with the detailed sedimentology of the lower Okehuan Stage sequence which is composed of two volcaniclastic formations, the Makirikiri Tuff and Kaimatira Pubmice Sand, separated by a non-volcaniclastic siltstone formation, the Okehu Siltstone. Interpretations of the Sedimentary structures in the Makirikiri Tuff and the Kaimatira Pumice Sand Formation confirm previous conclusions of shallow water deposition based on palaeontological evidence. Some structures also indicate the high rate of sediment accumulation during deposition of the volcancic sediments. Size analysis statistics show influence of source material and processes acting on the sediment during transport and deposition. Rapid sediment accumulation is emphasised by poor sorting, and processed inferred from the sedimentary structures are confirmed by the grain size analyses of the same structures. Analysis of the attitude of large and small scale cross-stratification reveals a complex polymodal palaeocurrent pattern, as might be expected of shallow water to intertidal sequences. Although often bipolar-bimodal, the dominant sediment transport appears to have been from west to east, similar to the direction of current movement along the Wanganui coast today. Size and petrography of clasts from the conglomeratic horizons indicated sediment sources both from the central volcanic region of North Island and from the Mesozoic "greywackes" of the axial mountain ranges which were emergent and probably significantly elevated at the time when the sediments were accumulating. No volcanic debris was deposited with the Okehu Siltstone. The mineralogy of the sands points to the same sediment sources but also indicates that some metamorphic material was being introduced most likely from South Island. Part III of the thesis represents a pilot study undertaken to determine whether isotopic differences in fossil shell composition could be used to distinguish shells that grew in fully marine water from those that grew in less saline conditions. Carbon and oxygen isotope ratios were determined on shells from three formations whose environments had been adequately studied by paleontologists. The horisons chosen were the Waipuru Shellbed, the Tewkesbury Formation and the Tainui Shellbed. Agreement with the palaeontological evidence and thus distinction between the fully marine and the fresh water contaminated marine environments was possible with the technique.</p>

Some Aspects of Sedimentology of the Wanganui Basin, North Island, New Zealand

<p>The thesis comprises studies of the marine Pleistocene sediments of the Wanganui Basin, North Island, New Zealand. Part I deals with the chronology of the sediments and correlation of horizons within and outside the basin, by dating glass shards from tephra horizons using the fission-track method. Correlation to similar tephras from Hawke's Bay, to deep-sea cores taken 1000km east of New Zealand and to the central North Island volcanic district is attempted. These fission-track ages fill a dating gap that previously existed in the New Zealand marine Quaternary sequence. Thirteen tephras were examined in the Wanganui Basin and were found to range in age from 1.50 [plus or minus] 0.21m.y.B.P. (Ohingaiti Ash) to 0.28 [plus or minus] 0.05m.y.B.P. (uppermost Finnis Road Ash). These tephras record major rhyolitic eruptive phases in the central volcanic region. The most significant eruptive phase began 1.06 [plus or minus]0.16m.y.B.P. with the deposition of the Makirikiri Tuff sediments, continued to 0.88 [plus or minus]0.13m.y.B.P. and is tentatively associated with the older ignimbrites of the King Country, west of Lake Taupe. A volcanically quiet period followed when no volcanic glass was deposited in the sediments, until 0.74 [plus or minus] 0.09m.y.B.P. Several large eruptions then occurred between 0.74 and 0.28m.y.B.P. The age of the Plio-Pleistocene boundary, at the base of the Hautawan Stage in the Wanganui Basin is 1.87m.y.B.P. The age of the base of the Nukumaruan is 1.55m.y.B.P., the Okehuan, 1.06m.y.B.P., the Castleclifflan 0.45m.y.B.P., and the Hawera Series is less than 0.38m.y.B.P. Palaeomagnetic stratigraphy was determined for the upper Nukumaruan and lower Okehan sequence in the Rangitikei River. Viscous components of magnetism were removed from the samples by thermal demagnetising, extreme care being needed to obtain consistent results. Independent dates from the palaeomagnetic stratigraphy substantially confirm the fission-track dates. The Bruhnes-Matuyama boundary is clearly defined between the Rewa and Potaka Pumice Members (aged 0.74 and 0.61m.y.B.P. respectively) of the Kaimatira Pumice Send Formation. The Jaramillo event was not recognised and is probably represented in part of the sequence where sediments are too coarse and friable to yield palaeomagnetic cores. Part II deals with the detailed sedimentology of the lower Okehuan Stage sequence which is composed of two volcaniclastic formations, the Makirikiri Tuff and Kaimatira Pubmice Sand, separated by a non-volcaniclastic siltstone formation, the Okehu Siltstone. Interpretations of the Sedimentary structures in the Makirikiri Tuff and the Kaimatira Pumice Sand Formation confirm previous conclusions of shallow water deposition based on palaeontological evidence. Some structures also indicate the high rate of sediment accumulation during deposition of the volcancic sediments. Size analysis statistics show influence of source material and processes acting on the sediment during transport and deposition. Rapid sediment accumulation is emphasised by poor sorting, and processed inferred from the sedimentary structures are confirmed by the grain size analyses of the same structures. Analysis of the attitude of large and small scale cross-stratification reveals a complex polymodal palaeocurrent pattern, as might be expected of shallow water to intertidal sequences. Although often bipolar-bimodal, the dominant sediment transport appears to have been from west to east, similar to the direction of current movement along the Wanganui coast today. Size and petrography of clasts from the conglomeratic horizons indicated sediment sources both from the central volcanic region of North Island and from the Mesozoic "greywackes" of the axial mountain ranges which were emergent and probably significantly elevated at the time when the sediments were accumulating. No volcanic debris was deposited with the Okehu Siltstone. The mineralogy of the sands points to the same sediment sources but also indicates that some metamorphic material was being introduced most likely from South Island. Part III of the thesis represents a pilot study undertaken to determine whether isotopic differences in fossil shell composition could be used to distinguish shells that grew in fully marine water from those that grew in less saline conditions. Carbon and oxygen isotope ratios were determined on shells from three formations whose environments had been adequately studied by paleontologists. The horisons chosen were the Waipuru Shellbed, the Tewkesbury Formation and the Tainui Shellbed. Agreement with the palaeontological evidence and thus distinction between the fully marine and the fresh water contaminated marine environments was possible with the technique.</p>