Paleotsunami Evidence in the Bahía Inglesa Coast (Atacama, Chile) Based on a Multi-Approach Analysis

The Atacama coast is located in an area with a current high risk of tsunami, and the sedimentary deposits found in the Bahía Inglesa area, in the Morro sector, clearly indicate that this was also the case in the past. Thisinvestigation analyzes a paleotsunami sedimentary deposit consisting of a block field associated with three sand lobes oriented towards land on top of a marine terrace at an altitude of 70–75 m, which originated from a tsunamigenic event occurred between interglacial periods MIS 7 (ca. 210 ± 10 ky) and MIS5e (ca.125 ± 5 ky). The deposits have been studied using a multiple approach combining geomorphological, sedimentological, biological, and geochemical criteria. The first type of criteria clearly indicate that the energy required to move the blocks and form the sand lobes could only have been generated by a tsunami. Sedimentological criteria constitute direct evidences of a marine origin due to the presence of siliceous remains from diatom species and spicules from strictly marine sponges, while geochemical criteria, such as the stable isotope signature and chemical composition, constitute evidence of a marine intrusion.

Marine terrace evolution of windward Barbados

ABSTRACT The geomorphic evolution of southeastern windward Barbados is embodied in the development of a terraced seaward island slope on a tectonically rising scarp. The island slope is wholly erosional and a product of marine and subaerial processes. Modulation of the slope by terraces has occurred fundamentally by marine erosion at eustatic stillstands but includes morphologic additions by limestone deposition. The ongoing phase of morphologic development and island emergence began at or before ca. 700 ka. Emergence has proceeded at an increasing rate northwestward along the island’s southeastern coastline. The terraced island slope is markedly affected by post-terrace denudation. As many as eight marine terraces are preserved on the windward island slope below the planed surface of the Central Highlands, which is counted as terrace 1. Relics of an upper set of terraces are perched on the face of Second High Cliff, the ancient erosional margin of the oldest limestone capping Barbados. Second High Cliff developed by successive marine incisions over a probably long duration preceding oxygen isotope stage 9. A lower terrace set was excised in stages 9 through 5a in the siliciclastic island foundation or (and) in limestone cover of preceding terraces. Marine terrace floors extend seaward from an erosional backcliff and shoreline angle to a younger erosional cutoff. The most broadly preserved terrace floors indicate the following systematic succession of seaward profile elements: narrow upper ramp; broad upper flat; lower ramp; and on one, a lower flat. Carbonate cover is chiefly clastic on the upper ramp and flat, and chiefly reefal on the lower ramp. Most shoal-water reefal facies appear to be in fringe reef blankets. Terrace profile geometries are explained by a simple theory of wave abrasion in proportion to duration of sea level at a shoreline. At stillstands, the wave impact caused large shoreline recession and development of flats, whereas in transgression and regression, rapid sea-level change permitted only minor recession. Corresponding differences in cover facies are explained as functions of duration of breaking waves and seabed stability. Widespread post-terrace denudation is attributed to floods of upland provenance, local overland flow, and marine flooding. Riverine processes have produced channelization and a high degree of terrace preservation on the interfluves in the steeper, foundation-based northern windward region. This differs markedly from the more diffuse, shallow gullying and stripping of the limestone-covered shallow slopes of the southern region. An intensely stormy spell is suggested between stages 5e and 5c.

Vulnerability of the Permafrost Landscapes in the Eastern Chukotka Coastal Plains to Human Impact and Climate Change

Permafrost landscapes are particularly susceptible to the observed climate change due to the presence of ice in the ground. This paper presents the results of the mapping and assessment of landscapes and their vulnerability to potential human impact and further climate change in the remote region of Eastern Chukotka. The combination of field studies and remote sensing data analysis allowed us to identify the distribution of landscapes within the study polygon, reveal the factors determining their stability, and classify them by vulnerability to the external impacts using a hazard index, H. In total, 33 landscapes characterized by unique combinations of vegetation cover, soil type, relief, and ground composition were detected within the 172 km2 study polygon. The most stable landscapes of the study polygon occupy 31.7% of the polygon area; they are the slopes and tops of mountains covered with stony-lichen tundra, alpine meadows, and the leveled summit areas of the fourth glacial-marine terrace. The most unstable areas cover 19.2% of the study area and are represented by depressions, drainage hollows, waterlogged areas, and places of caterpillar vehicle passage within the terraces and water-glacial plain. The methods of assessment and mapping of the landscape vulnerability presented in this study are quite flexible and can be adapted to other permafrost regions.

Formation and preservation of marine terraces during multiple sea level stands

<p>Marine terraces are a cornerstone for the study of paleo sea level and crustal deformation. Commonly, individual erosive marine terraces are attributed to unique sea level high-stands. This stems from early reasoning that marine platforms could only be significantly widened under moderate rates of sea level rise as at the beginning of an interglacial and preserved onshore by subsequent sea level fall. However, if marine terraces are only created during brief windows at the start of interglacials, this implies that terraces are unchanged over the vast majority of their evolution, despite an often complex submergence history during which waves are constantly acting on the coastline, regardless of the sea level stand.<span> </span></p><p>Here, we question the basic assumption that individual marine terraces are uniquely linked to distinct sea level high stands and highlight how a single marine terrace can be created By reoccupation of the same uplifting platform by successive sea level stands. We then identify the biases that such polygenetic terraces can introduce into relative sea level reconstructions and inferences of rock uplift rates from marine terrace chronostratigraphy.</p><p>Over time, a terrace’s cumulative exposure to wave erosion depends on the local rock uplift rate. Faster rock uplift rates lead to less frequent (fewer reoccupations) or even single episodes of wave erosion of an uplifting terrace and the generation and preservation of numerous terraces. Whereas slower rock uplift rates lead to repeated erosion of a smaller number of polygenetic terraces. The frequency and duration of terrace exposure to wave erosion at sea level depend strongly on rock uplift rate.</p><p>Certain rock uplift rates may therefore promote the generation and preservation of particular terraces (e.g. those eroded during recent interglacials). For example, under a rock uplift rate of ca. 1.2 mm/yr, Marine Isotope Stage (MIS) 5e (ca. 120 ka) would resubmerge a terrace eroded ca. 50 kyr earlier for tens of kyr during MIS 6d–e stages (ca. 190–170 ka) and expose it to further wave erosion at sea level. This reoccupation could accordingly promote the formation of a particularly wide or well planed terrace associated with MIS 5e with a greater chance of being preserved and identified. This effect is potentially illustrated by a global compilation of rock uplift rates derived from MIS 5e terraces. It shows an unusual abundance of marine terraces documenting uplift rates between 0.8 and 1.2 mm/yr, supporting the hypothesis that these uplift rates promote exposure of the same terrace to wave erosion during multiple sea level stands.</p><p>Hence, the elevations and widths of terraces eroded during specific sea level stands vary widely from site-to-site and depend on local rock uplift rate. Terraces do not necessarily correspond to an elevation close to that of the latest sea level high-stand but may reflect the elevation of an older, longer-lived, occupation. This leads to potential misidentification of terraces if each terrace in a sequence is assumed to form uniquely at successive interglacial high stands and to reflect their elevations.</p>

Hydrochemical composition of Holocene ice wedges near the town of Anadyr

The research is conducted on the Holocene ice wedges exposed in the outcrop of the first marine terrace near the town of Anadyr, on the east of the Chukchi Peninsula, on the coast of Onemen Bay. Polygonal Relief is clearly traced on the surface of the first sea terrace in the area of explorations, the size of the polygons is about 8x12 m. In the exposed terrace, turf with a capacity of about 1.5 m is striped, underlied with sand clay with  capacity up to 2 m; below is the horizontally-stratified and. Ice wedges are embedded the turf (head of wedges) and in the underlying clay sand. The ice of wedges is vertically stratifies, yellowish gray. Ice wedges are also striped in turf  outcrops with capacity of up to 2.5 m, embedded in form of a lens from the terrace surface. Ice from three most fully exposed ice wedges was sampled for hydrochemical analysis. A total of 20 ice samples were collected from Holocene ice wedges, as well as ice from modern ice veinlet and water from Onemen Bay. It was found that mineralization of the studied Holocene ice wedges is low, does not exceed 80 mg/L, Na+, Ca2+, and Cl- dominate. Similar values of mineralization and ionic composition were obtained for modern ice veinlet. The obtained data correspond with data on ice wedges studied in other regions of Chukotka, both continental and coastal. Mineralization of most of the previously studied ice wedges did not exceed 150 mg/L. Low values of mineralization of ice wedges near Anadyr demonstrate mainly meteoric source of water forming ice, i.e. winter precipitation, prevalence of sodium and chlorine indicates the capture of sea aerosols by precipitation or wind introduction of droplets from the water area of the Onemen Bay to the surface of the snow cover.

Tectonic uplift rate in the northern coast of the South China sea: insight from the 10Be exposure dating of marine terrace in southeastern China

<p>Along the northern coast of the South China Sea in southeastern China, marine terraces preserved on the widespread Cretaceous granite and recorded both Quaternary uplift and sea-level oscillation. However, because sediments or materials for dating are usually absent, it is difficult to date these paleo-shoreline, which cause great difficulties in early exploration. Fortunately, as great progress on terrestrial cosmogenic nuclide dating, it is possible to yield the exposure age of marine terrace and to calculate the uplift rate along coastal line. This study focuses on two typical sequences of preserved marine terraces lying on the coastal line adjacent the Taiwan Strait in southeastern China. These two sequences of marine terraces (denoted as NZS and HJC site, respectively) both locate on the footwall (uplifting wall) of normal NE-SW trending fault (the Coastal Normal Fault) but on separated blocks subdivided by a normal NW-SE fault. At least 5 terraces and 2 terraces developed on granite at HJC and NZS site, respectively. In particularly, T1 and T3 terrace at HJC site and T1 terrace at NZS site present typical abrasion wave-cut platform with preserved sea stacks. Hence, we collected both profile and surface quarts samples on these well-preserved marine terraces for <sup>10</sup>Be exposure dating and yielded exposure ages of 51.0±1.9 ka, 66.2±2.9 ka in T1 and T3 terrace at HJC site, and 87.9±3.5 ka in T1 terrace at NZS site. After subtracting eustatic sea-level changes from the relative sea-level curve, we measure high uplift rates of 1.13 mm/a at HJC site and 1.04 mm/a at NZS site during late Pleistocene. The similar uplift rates in different faulting blocks suggest that surface uplift can be directly linked to NE-SW fault system. Low difference of uplift rate between tow site suggest relative vertical motion of tow faulting blocks could be adjust by NW-SE faults. The regional uplift with high uplift rates is likely corresponding to the major collision between Luzon arc and the Chinese continental margin. However, because the contribution of by isostasy, e.g. surface erosion or ice-volume variation in Quaternary, remains uncertain, the calculated uplift rate maybe overestimated.</p>