Eemian marine terraces along the Pacific coast of South America (1°N-40°S) allow regional assessments of tectonic forcing from earthquake cycle to glacial-cycle timescales
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<p><strong>Abstract. </strong>Tectonically active coasts are dynamic environments characterized by the presence of multiple marine terraces formed by the combined effects of wave-erosion, tectonic uplift, and sea-level oscillations at glacial-cycle timescales. Well-preserved erosional terraces from the last interglacial sea-level highstand are ideal marker horizons for reconstructing past sea-level positions and calculating vertical displacement rates, which can be subsequently compared to short-term coastal deformation patterns associated with the earthquake cycle. We carried out an almost continuous mapping of the last interglacial marine terrace along ~5,000 km of the western coast of South America between 1&#176;N and 40&#176;S. We used quantitatively replicable approaches constrained by published terrace-age estimates to ultimately compare elevations and patterns of uplifted terraces with tectonic and climatic parameters in order to evaluate the controlling mechanisms for the formation and preservation of marine terraces, and crustal deformation. Uncertainties were estimated on the basis of measurement errors and the distance from referencing points. Overall, our results indicate a median elevation of 30.1 m, which would imply a median uplift rate of 0.22 m/ka averaged over the past ~125 ka. The patterns of terrace elevation and uplift rate display high-amplitude (~100&#8211;200 m) and long-wavelength (~10<sup>2</sup> km) structures at the Manta Peninsula (Ecuador), the San Juan de Marcona area (central Peru), and the Arauco Peninsula (south-central Chile). Medium-wavelength structures occur at the Mejillones Peninsula and Topocalma in Chile, while short-wavelength (< 10 km) features are for instance located near Los Vilos, Valpara&#237;so, and Carranza, Chile. We interpret the long-wavelength deformation to be controlled by deep-seated processes at the plate interface such as the subduction of major bathymetric anomalies like the Nazca and Carnegie ridges. In contrast, short-wavelength deformation may be primarily controlled by sources in the upper plate such as crustal faulting, which, however, may also be associated with the subduction of topographically less pronounced bathymetric anomalies and varying distances to the trench. Latitudinal differences in climate additionally control the formation and preservation of marine terraces. Based on our synopsis we propose that increasing wave height and tidal range result in enhanced erosion and morphologically well-defined marine terraces in south-central Chile. Conversely, river incision and lateral scouring in areas with high precipitation may degrade marine terraces. Our study emphasizes the importance of using systematic measurements and uniform, quantitative methodologies to characterize and correctly interpret marine terraces at regional scales, especially if they are used to unravel tectonic and climatic forcing mechanisms of their formation.</p>Keywords:
Terrace (agriculture)
Elevation (ballistics)
Tectonic uplift
Marine isotope stage
A critical study of the Pleistocene lake and terrace deposits in Colombia leads to the result, that, during the Quaternary, the climatic fluctuations in this country were the same as in Europe and in Northamerica, with the only exception that the glacial periods were also of high atmospheric precipitation. The presence of a lime crust in the 45 m. terrace near Aipe (fig. 2) indicates that the terrace sediments were deposited during a wetter climate with somewhat lower temperature than we observe today. The terrace sediments of this region are therefore interpreted as deposited during glacial-pluvial periods and not during interglacial-interpluvial periods. A cautious tentative correlation of the río Magdalena terraces near Garzón in alpine pleistocene terms (fig. 1) results in the conclusion, that the 145 m. terrace in which the opal objects and the Megatherium bones described by Bürgl (1958) were found, cannot be younger than Mindel.
Terrace (agriculture)
Pluvial
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Marine isotope stage
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Marine isotope stage
River terraces
Sea-Level Change
Isostasy
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Paleoclimate of interglacial Marine Isotope Stage 11 (MIS 11), about 400 ky ago was estimated using data from shallow-marine to terrestrial strata of the Japanese Islands. The reason of the estimation comes from that the paleoclimate gives analogs for the future climate, because the conditions of Milankovitch forcing of MIS 11 are similar to those of modern Holocene. The results show the MIS 11 of the Japanese Islands was warmer, with a longer interval of highstand, and higher sea levels than the other interglacials. Further investigation for the strata of MIS 11 of the Japanese Island is needed and will give us important information about our future climate.
Paleoclimatology
Marine isotope stage
Milankovitch cycles
Climate oscillation
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Similar orbital geometry and greenhouse gas concentrations during marine isotope stage 11 (MIS 11) and the Holocene make stage 11 perhaps the best geological analogue period for the natural development of the present interglacial climate. Results of a detailed study of core MD01‐2443 from the Iberian margin suggest that sea surface conditions during stage 11 were not significantly different from those observed during the elapsed portion of the Holocene. Peak interglacial conditions during stage 11 lasted nearly 18 kyr, indicating a Holocene unperturbed by human activity might last an additional 6–7 kyr. A comparison of sea surface temperatures (SST) derived from planktonic foraminifera for all interglacial intervals of the last million years reveals that warm temperatures during peak interglacials MIS 1, 5e, and 11 were higher on the Iberian margin than during substage 7e and most of 9e. The SST results are supported by heavier δ 18 O values, particularly during 7e, indicating colder SSTs and a larger residual ice volume. Benthic δ 13 C results provide evidence of a strong influence of North Atlantic Deep Water at greater depths than present during MIS 11. The progressive ocean climate deterioration into the following glaciation is associated with an increase in local upwelling intensity, interspersed by periodic cold episodes due to ice‐rafting events occurring in the North Atlantic.
Marine isotope stage
Holocene climatic optimum
Paleoclimatology
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Fringing reef
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Relative sea-level variability during the late Middle Pleistocene: New evidence from eastern England
Unravelling patterns of relative sea-level change during previous interglacials enhances our understanding of ice sheet response to changing climate. Temperate-latitude estuarine environments have the potential to preserve continuous records of relative sea level from previous interglacial (warm) periods. This is important because, currently, we typically only have snapshots of sea-level highstands from low-latitude corals and raised palaeoshoreline indicators while the (continuous) deep-sea oxygen isotope record only provides indirect evidence of sea-level changes. Here, we focus on the Nar Valley in eastern England, in which is preserved evidence of a late middle-Pleistocene marine transgression more than 20 vertical metres in extent. By applying a model of coastal succession and sea-level tendencies, as used in Holocene sea-level studies, we assess the mode (abrupt versus gradual) of sea-level change recorded by the interglacial Nar Valley sequences. Compiled palaeo-stratigraphic evidence comprising foraminifera, pollen and amino acid racemization dating, suggests that the mode of sea-level change in the Nar Valley interglacial sequence was gradual, with potentially two phases of regional transgression and relative sea-level rise occurring at two separate times. The first phase occurred during the latter part of marine Oxygen Isotope Stage (MIS) 11 from ∼8 to 18 m OD; and, the second phase potentially occurred during early MIS 9 from ∼-3 to 3 m OD (with long-term tectonic uplift included in these estimates). We cannot conclusively preclude an alternative MIS 11 age for these lower sediments. The lack of indicators for rapid sea-level oscillations in the Nar Valley adds weight to an argument for steady melt of the ice sheets during both MIS 11 and 9.
Marine transgression
Marine isotope stage
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Marine isotope stage
Orbital forcing
Eemian
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Post-glacial rebound
Marine isotope stage
Isostasy
Tectonic uplift
Elevation (ballistics)
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Estimating minimum ice volume during the last interglacial based on local sea-level indicators requires that these indicators are corrected for processes that alter local sea level relative to the global average. Although glacial isostatic adjustment is generally accounted for, global scale dynamic changes in topography driven by convective mantle flow are generally not considered. We use numerical models of mantle flow to quantify vertical deflections caused by dynamic topography and compare predictions at passive margins to a globally distributed set of last interglacial sea-level markers. The deflections predicted as a result of dynamic topography are significantly correlated with marker elevations (>95% probability) and are consistent with construction and preservation attributes across marker types. We conclude that a dynamic topography signal is present in the elevation of last interglacial sea-level records and that the signal must be accounted for in any effort to determine peak global mean sea level during the last interglacial to within an accuracy of several meters.
SIGNAL (programming language)
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