Evidence For Sea-level Changes Research Articles

Micropaleontological Evidence of A Submarine Fan in the Lower Coaledo Formation, Southwestern Oregon, USA

Abstract The middle Eocene lower Coaledo Formation was interpreted as ten shoaling upward delta-margin cycles based on sediments and macrofauna. The strata, however, contains deep-water foraminifers. Explanations to resolve this anomaly included reworking, bathymetric range extension, or upward migration of water masses. Paleoecology analysis of foraminifers indicates that the few shelf species are poorly preserved whereas the well-preserved lower bathyal species dominate, and planktic organisms are present. Evidence for reworking, bathymetric range extension, or upward migration of water masses was not found in any of the cycles. The paleoecologic utility of hummocky cross-bedded sandstones is questioned as these features are controversial. In addition, there is no evidence of sea-level changes or tectonic activity to accommodate the bathymetric changes needed. Deposition of the lower Coaledo Formation on a submarine fan at lower bathyal depths eliminates the need to explain bathymetric anomalies or lack of tectonic movement.

Mode and timing of the Early Cretaceous transgression in Iran: Insights from the stratigraphic evidence of sea-level changes and geodynamic events

The study of selected logs from the Central-Eastern Iran Microplate (CEIM; area of Arusan) and Sanandaj–Sirjan Zone (SSZ; areas of Esfahan east and Tiran) constrains timing and evolution of the Cretaceous successions, resting unconformably on older sediments or non-conformably on the metamorphic basement. The Cretaceous marine transgression occurred almost synchronously on a levelled topography, documenting a previous deep erosion. Above a basal siliciclastic unit, rudist- and orbitolinid-rich lower Aptian limestone (“Orbitolina Limestone”, Shak Kuh Formation, Taft Formation) were deposited. Later, the stratigraphic evolution of the three studied areas differentiates, documenting changes in the depositional environments, reflecting different subsidence rates. In the Tiran area, marls and cherty limestones covering shallow-water limestones record a deepening trend. A differentiation of depositional environment is observed at Arusan, where conglomerates to the west pass to basinal sandstone and marls to the east. Here, a Coniacian-Campanian reprise of the carbonate production (with skeletal limestones rich in rudists, ostreids, and abundant orbitoidids) is covered by cherty marls. In the Esfahan north area, glauconitic hardground marls covered by chert record important deepening during the early Cenomanian, followed by the reprise of shallow-water carbonate production (middle Cenomanian). The synchronous deposition of Aptian carbonate successions on large parts of the CEIM, SSZ and North-Iranian domains suggests a rapid regional transgression controlled by a sea-level rise. Stratigraphic differentiation occurring in late Aptian–Cenomanian times, recording the onset of tectonic events differently affecting the aforementioned domains, likely related to the opening of oceanic seaways in the CEIM and the SSZ.

A standardized database of Marine Isotope Stage 5e sea-level proxies in southern Africa (Angola, Namibia and South Africa)

Abstract. Evidence for sea-level change during and around Marine Isotope Stage (MIS) 5e (ca. 125 ka) in southern Africa derives from a wide variety of geomorphic and sedimentological sea-level indicators, supported in the past 2 decades by absolute chronological control, particularly on littoral deposits, some of which have a quantifiable relationship to former sea level. In addition to these proxies, data provided by both terrestrial (dune sediments and archaeological remains) and marine (lagoonal and nearshore littoral sediments) limiting points provide broad constraints on sea level. Here, we review publications describing such data points. Using the framework of the World Atlas of Last Interglacial Shorelines, we insert in a standardized database (https://doi.org/10.5281/zenodo.4459297, Cooper and Green, 2020) all the elements available to assess former palaeo-relative sea level (palaeo-RSL) and the chronological constraints associated with them (including uncertainties). Overall, we reviewed 71 studies, from which we extracted 39 sea-level indicators and 26 limiting points. As far as age attribution is concerned, early analysis of molluscs and whole-rock beachrock samples using U series allowed dating of several sea-level indicators during the 1980s, but the more widespread application of optically stimulated luminescence (OSL) dating since 2004 has yielded many more (and more accurate) sea-level indicators from several sites. This has helped resolve the nature and timing of MIS 5e shorelines and has the potential to further elucidate the apparent presence of two or more sea-level peaks at several South African sites during this interval. The standardized sea-level database presented in this paper is the first of its kind for this region. Future research should be directed to improve the stratigraphic description of last interglacial shorelines and to obtain better dating, high-accuracy elevation measurements with better palaeo-RSL interpretation.

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.

A geochemical framework for retrieving the linked depositional and diagenetic histories of marine carbonates

In modern shallow seawater carbonate platforms, successive changes in diagenetic zones are found as the result of a drop in sea level. Such a relationship is important in identifying diagenetic processes, in interpreting global carbon isotope shifts and in finding the reasons for positive correlations between C and O isotopes in marine carbonates. However, it is not readily recognized in ancient marine carbonates because evidence for sea level changes can be cryptic in the rock record. Because of the fall of sea level, fresh water may add to precipitating marine carbonates on continental substrates, resulting in geochemical mixtures between shallow seawater and fresh water. To resolve this issue, we carry out a combined study of rare earth elements and yttrium (REE+Y) and CO isotopes in Carboniferous–Triassic marine carbonates from the Lower Yangtze platform in China. The relationships between inter-REE+Y ratios such as Y/Ho vs. (Nd/Yb)PAAS for pure carbonates strongly indicate mixing between fresh water and shallow seawater. The REE+Y patterns for pure carbonates show temporal variations, reflecting changes in the proportion of fresh water addition into shallow seawater, which were likely due to changes in relative sea level. Changes in diagenetic zones indicated by the relationships between carbonate C and O isotopes as well as other evidence follow the changes in relative sea level suggested by the REE+Y patterns. Therefore, a combined study of the REE+Y and CO isotopes in marine carbonates can provide robust constraints on the changes in the linked depositional environments and diagenetic processes on continental substrates.

Comment on “The Badenian–Sarmatian Extinction Event in the Carpathian foredeep basin of Romania: Paleogeographic changes in the Paratethys domain” (Palcu et al., 2015)

Palcu et al. (2015) dated the Badenian-Sarmatian Extinction Event (BSEE) in the Tisa Valley section in Romania based on microfossils and magnetostratigraphy, concluding that there is no evidence of sea level change around the BSEE. In our short comment we show that the sampling resolution and the sample preparation method was not suitable to properly constrain the position of the BSEE in the exposure, and some conclusions are questionable. Additionally we propose an alternative interpretation of the foraminiferal assemblages recovered at the Tisa section.

High-Resolution Seismic Stratigraphy and Current-Induced Bed Forms in the Khoran Strait, South of Iran

Hosseinyar, G.; Behbahani, R.; Chaychizadeh, S.; Lak, R., and Chakeri, M., 2013. High-resolution seismic stratigraphy and current-induced bed forms in the Khoran Strait, south of Iran.The distribution of current-induced bed forms, shallow sub-seabed architecture, and geological development of the Khoran Strait, south of Iran, were investigated using subbottom profiler and side-scan sonar data. Current-induced bed forms in this area include a variety of dunes, such as simple large flood-dominated, composite medium to very large flood-dominated to simple-composite large to very large ebb-dominated, simple medium to very large ebb-dominated, and large symmetrical dunes. High-resolution shallow seismic profiling reveals two depositional sequences. The lower sedimentary sequence, which displays channel infills in the southern part of the study area, provides evidence of sea-level changes having resulted in the formation of four different units (A, B, C, and D). After deposition of unit D, sea-level fall led to erosion of the lower sequence. Further evolution of the basin and subsequent sea-level rise resulted in renewed inundation and formation of the upper sequence. The general seismic architecture of the area reveals both deposition and erosion along the margin of the strait, while sediment starvation prevails in the inner part of central areas.

Archaeological littoral sites on the northern coast of Santa Cruz: Valuable evidence of sea level changes on the continental Patagonian coasts (Argentina)

Geological studies are fundamental to archaeologists as they provide essential data to understand certain processes involved in the present archaeological record. When working on marine coastal archaeology, the information provided by geomorphologic studies with regards to the evolution and dynamics of coastal marine lines is essential to assess the availability and accessibility of certain marine coastal areas, and their resources, to human populations of the past. This is also the key to reach correct cultural interpretations. However, on certain occasions, archaeological information can also offer valuable alternative data for geologists to reach geological interpretations, for instance when working on the evolution and changes of coastal sea lines. In this case, spatial and temporal scales must be regarded. This idea is supported on the experience gained through research done on the Patagonian Atlantic coast at the two archaeological localities introduced in this paper: Cabo Blanco, where we evaluate models of evolution of the coastline with a number of radiocarbon dates from excavated sites; and Punta Medanosa, where we discuss the temporal depth of the formation of the coastal ridges for the mid-Holocene transgression.

Current topics in ESR dating

After over 25 years, the use of electron spin resonance (ESR) is well-established in dating sites of geological, paleontological and archaeological interest. Like any scientific technique, there have been changes in understanding and in methodology. Improvements have not, however, changed the observation that external dose calculations are still a significant source of uncertainty in ages. Examples from Europe, Africa and the Americans illustrate this point. For Pradayrol Cave (France), the occupation age, 330 ka, is unchallenged, making this the oldest known Neanderthal site in France. For Roc de Marsal, also in France, on the other hand, discrepancies between TL and sedimentary dose rates imply substantial differences in interpretation. In the Western Egyptian Desert, where artifacts and datable material are not well-correlated, the dating results show consistency with expectations based on global climate change, even in deflated sites. Climate change is also the question in geological studies in the Bahamas where, despite concerns about cosmic dose history, ESR dates confirm other evidence for sea level changes. We show that an uncertain age is not the same as an impossible one.

Palaeogeographic reconstruction of northern Tyrrhenian coast using archaeological and geomorphological markers at Pianosa island (Italy)

This paper provides new data and interpretations on the relative sea level change occurred at Pianosa island (Italy) since the last ∼125 ka, where the recent relative sea level changes have not yet been adequately constrained, based on geomorphological and archaeological research of tectonic movements. The MIS 5.5 deposits are characterized by a 2 m thick sandstone, cropping out at a maximum altitude of 4 m a.s.l. containing Strombus bubonius, and are associated with an abrasion platforms carved by lithodome holes. These deposits, considered one of the best long term sea level markers, establish that Pianosa was a stable area since 125 ka. Archaeological remains provide evidence of sea level change for the last ∼8 ka. Particularly useful are some fishtanks and a quarry cut around 2 ka BP (Roman age). The measurements, compared with predicted sea level curves, have established that Pianosa has remained stable during the last millennia. Based on this assumption, palaeomorphology variations since Palaeolithic age for this portion of the Tuscan Archipelago are reconstructed.

Coastal vegetation evidence for sea level changes associated with Heinrich Events

Coastal vegetation evidence for sea level changes associated with Heinrich Events

Reconstruction of Holocene Paleoenvironment and Evidence of Sea-level Changes in the Bengal Lowland

This paper provides a detailed description of sedimentary facies including pollen and diatom analyses, and 14C ages obtained from a hand-excavated outcrop in the central part of the Bengal Lowland. Based on this examination, seven sedimentary facies were recognized in relation to relative sea-level (RSL) changes since the mid Holocene. With the help of a standard reference datum, the required Mean Sea Level (MSL) has been calculated at the surface of the outcrop. The top of the outcrop was about 1.9 m above MSL and the base is 4.1 m below the MSL. The lowermost bioturbated sand flat facies, 3.75 m below the present MSL, contains mangrove pollen and represents an intertidal coastal-plain and estuarine-channel deposits that were dominated by tidal current. A 14C age of 7570-7430 cal BP was obtained for this unit. The evidence supports a transgressive mode in the Bay of Bengal during the middle-Holocene epoch. A subsequent regression interval was found in a salt marsh facies before 6670-6410 cal BP. The salt marsh facies has a sharp contact with an underlying (lower) mud flat facies, shaped by downcutting of the upper bed, indicating a regression. In response to this regression, the environment changed gradually from a mud flat to a salt marsh. The salt-marsh deposits contain abundant mangrove pollens and marine- and brackish-water diatoms, providing support for inflow of shallow-marine water into a supratidal, brackish-water mangal environment. The bioturbated mud flat facies indicates that the succession was dominated by tidal current, and the relative sea-level started to rise again after a small rebound. Hence, the transgressive conditions prevailed during the deposition of this mud flat facies in an intertidal coastal-plain environment. The underlying bluish-black medium-bedded peat layer contains grass pollen. This indicates that after the mid-Holocene the environment around the site changed gradually from mangrove to fresh-water swamp vegetation, in response to regression of the bay between 4080-4030 cal BP. The above evidence suggests that the central part of the Bengal Lowland represented as an intertidal to supratidal coastal-plain estuarine environment that experienced with mid-Holocene relative sea-level changes between 7570-7430 and 4080-4030 cal BP.

Evidence of sea level change at Guaratiba Mangrove, Sepetiba Bay, Brazil

Evidence of sea level change at Guaratiba Mangrove, Sepetiba Bay, Brazil

Holocene environmental reconstruction from deltaic deposits in northeast Greenland

AbstractTerraces of different age in the Zackenberg delta, located at 74°N in northeast Greenland, have provided the opportunity for an interdisciplinary approach to the investigation of Holocene glacial, periglacial, pedological, biological and archaeological conditions that existed during and after delta deposition.The raised Zackenberg delta accumulated mainly during the Holocene Climatic Optimum, starting slightly prior to 9500 cal. yr BP (30 m a.s.l.) and continued until at least 6300 cal. yr BP (0.5 m a.s.l.). Evidence of sea‐level change is based on conventional14C dates of shells from the marine delta bottomsets,14C AMS dating of macroscopic plant material from the foresets and of fluvial deposits. Arthropod and plant remains from 7960 cal. yr BP in the delta foresets include the oldest evidence of the arctic hare in Greenland and evidence of a rich herb flora slightly different from the modern flora.Empetrum nigrumandSalix herbacearemains indicate a summer temperature at least as high as today during delta deposition. Post‐depositional nivation activity, dated by luminescence, lichenometry and Schmidt Hammer measurements indicate mainly late Holocene activity, at least since 2900 yr BP, including Little Ice Age (LIA) avalanche activity. Pedological analyses of fossil podsols in the Zackenberg delta, including14C AMS dating of selected organic rich B‐horizons, show continued podsol development during the Holocene Climatic Optimum and into the subsequent colder period of the late Holocene, until 3000–2400 yr BP. A Neo‐Eskimo house ruin found on the lower part of the delta, presently being eroded by the sea, is dated toAD1800. It presumably was abandoned prior toAD1869, and suggests that some of the last Eskimos that lived in northeast Greenland might have occupied the Zackenberg delta. Copyright © 2002 John Wiley & Sons, Ltd.

ABSTRACT: Milankovitch Control on Sequence Formation; Evidence for Sea-Level Change Forced by the 400KYR Long Eccentricity Cycle in the Cretaceous and Paleogene

ABSTRACT: Milankovitch Control on Sequence Formation; Evidence for Sea-Level Change Forced by the 400KYR Long Eccentricity Cycle in the Cretaceous and Paleogene

Raised Coral Terraces at Malakula, Vanuatu, Southwest Pacific, Indicate High Sea Level During Marine Isotope Stage 3

The occurrence of a series of raised coral reefs from the uplifted island of Malakula (Vanuatu, SW Pacific) provide an opportunity to examine sea-level fluctuations over at least the past 120,000 years. Thirteen fossil coral samples from Malakula were analyzed by the thermal ionization mass spectrometry (TIMS) U/Th dating technique, yielding information on sea levels during late marine isotope stage 3 and early stage 4. Our findings are in good agreement with sea-level estimates from raised coral terraces in Papua New Guinea and the recent sea-level reconstruction from the deep-sea sedimentary δ 18O records. In particular, our coral data appear to confirm that sea levels at about 45,000–50,000 yr B.P. were only 30 to 60 m below the present level. Combined with other evidence of sea-level change, our data provide a strong case for much higher sea levels and therefore markedly reduced continental ice volume at 47,000 to 49,000 years ago.

EVIDENCE DELIMITING PAST GLOBAL CLIMATE CHANGES

Politicians and the media assume Earth's climate is warming as the result of human activity. Various types of evidence of previous climate changes were investigated as a means of testing the validity of assigning anthropogenic causes to this change. Data with broad geographic coverage indicative of temperature and climate were evaluated. It included records of glacial advance and retreat, sedimentologic evidence of sea level change and glacial activity, palynologic indications of species succession, dendrochronologic evidence of tree-growth response to environment, and continental-ice core parameters indicating accumulation rates as well as other climate surrogates. Also reviewed were historical sources such as explorers' journals, which document significant climate effects over time. Each type of evidence has particular value. Among these are preservation of regional versus local conditions, transport in or out of the system, age–date reliability, correlation between data types, and data (as well as human) bias. All the data indicate that the Holocene has been characterized by ten or more global “little ice ages” irregularly spaced. Each lasted a few centuries separated by sometimes sudden and dramatic global warming events. It is difficult to develop precise paleothermometry. Qualitative evaluations indicate frequent, sudden, and dramatic climate changes. Changes can be rapid, swinging from warmer than today to full glacial conditions within 100 years. The converse can be true. All available data indicate that current climate change is no greater in rate or magnitude, and probably less in both, than many changes that have occurred in the past.

Hoxnian interglacial freshwater and marine deposits in northwest Norfolk, England and their implications for sea-level reconstruction

An interglacial site is described from Tottenhill, in the Nar Valley in northwest Norfolk. A transgressive surface is recorded at this site with marine Nar Valley Clay overlying lacustrine Nar Valley Freshwater Beds. Biostratigraphical analyses indicate that these units span the latest part of the Anglian (Elsterian) glacial Stage and the first half of the Hoxnian (Holsteinian) Stage. Several other sites in the valley contain evidence for sea-level changes during the Hoxnian and the relevant information from these sites is briefly discussed. This gives an estimate of the timing of the Hoxnian maximum flooding surface, the maximum extent of the marine incursion and possible water depths attained. Evidence for Hoxnian sea-level changes at other sites in eastern England are briefly discussed. Although a regional sea-level highstand during the Hoxnian seems very likely, the details of the extent and timing of salt-water penetration are conflicting. It is suggested that post-depositional effects, particularly isostatic re-adjustment, may account for some of these differences and that the modern height of interglacial sediments can be misleading when depositional sea-levels are reconstructed.

Stratal Patterns, Sediment Composition, and Sequence Stratigraphy at the Margin of the Vercors Carbonate Platform (Lower Cretaceous, SE France)

ABSTRACT Conventional sequence-stratigraphic concepts relate the large-scale stratal architecture of sediment bodies to changes in relative sea level. This paper evaluates the relationship between stratal geometry and sea-level stand, based on a study of large, semicontinuous outcrops of Cretaceous carbonate platform strata in the Vercors (southeastern France). Multiple lines of evidence for sea-level change are combined, including stratal geometry, detailed quantitative microfacies analyses, and diagenetic patterns at platform-top hardground surfaces. The studied outcrops of the Cirque d'Archiane show two main prograding platform tongues, both over 100 m thick. The stratal geometries at the boundary between these platform tongues, including an apparent pinchout of a wedge of slope sediments, suggest the presence of a major lowstand unconformity. However, this stratal boundary does not coincide with the horizon containing the most extensive meteoric alteration. Furthermore, detailed platform-to-basin correlation shows that the wedge of slope sediments is not basin-restricted, but makes a thin drape over the platform top. The sedimentologic and diagenetic evidence suggest incipient drowning of the platform at the boundary between the two main platform tongues, preceded by a minor exposure event only. Internally, the main platform tongues consist of smaller (10-30 m thick) units that prograde towards the basin and aggrade on the platform top, and which are interpreted as stacked highstand wedges. These wedges are usually topped by hardground surfaces with minor evidence for subaerial exposure. The platform-top horizon with the most extensive subaerial diagenesis and erosion correlates with a distinct but relatively thin unit of lithoclastic debris on the slope. A pronounced scour in the clinoforms of the Vercors does not correlate with a major exposure surface on the platform top. This study shows that stratal geometries alone are a rather ambiguous guide to sea-level history. Without the accompanying sedimentologic and diagenetic evidence for sea-level change, most of the stratal architecture of the Vercors platform can be explained by either changes in accommodation or changes in carbonate production.

Evidence for sea level change from the cretaceous of Bornholm, Denmark

Abstract The Albian to Santonian succession of Bornholm, Denmark, is reviewed. The lithological data and major fossil groups encountered within the formations are examined, including new biostratigraphic data. Foraminifera, palynomorphs, belemnites, ammonites, and inoceramid bivalves are all important for the dating of the succession. Major transgressive phases are recognised in the Early Albian and Early Cenomanian, with an intervening regressive event. A highstand systems tract was formed during the Middle Cenomanian. A “mid‐Cenomanian” non‐sequence is noted and is equated to a major transgressive surface. Several transgressive surfaces are evident in the Late Cenomanian to earliest Coniacian, possibly with intervening regressive events. A second major highstand system tract is recognised in the Coniacian to Early?‐Middle Santonian, with a gradual decline in effective water depth up the succession. Packer, S.R. & Hart, M.B., 1994: Evidence for sea level change from the Cretaceous of Bornholm, Denmark. G...