Sea-level changes

Catastrophes and Lesser Calamities ◽

10.1093/oso/9780198524977.003.0008 ◽

2004 ◽

Author(s):

Tony Hallam

Keyword(s):

Sea Level ◽

Plate Tectonics ◽

Careful Study ◽

Intellectual Stimulation ◽

Sea Level Changes ◽

Rock Formations ◽

Global Correlation ◽

Sediment Types ◽

Ecological Aspects ◽

The Subject

In earlier times many geologists clearly became cynical about what they had learned as students about Earth history from their stratigraphy courses. ‘The sea comes in, the sea goes out.’ This is indeed one of the most striking signals that emerges from study of the stratigraphic record in a given region: a succession of marine transgressions and regressions on the continents. Little scientific rigour was, however, applied to the subject, and students were left with no overarching explanation to provide any intellectual stimulation. Since the 1970s things have begun to change for the better, as less emphasis has been placed on learning the names of rock formations and fossil zones and more on the dynamic aspects of what to many ranks as a fascinating subject. This entails studying changing geographies and climates within a framework supplied by plate tectonics, the successions of strata being subjected to ever-more-rigorous sedimentological and geochemical analysis, and global correlation continually improved by further study of stratigraphically useful fossils. How do we infer sea-level changes from a given succession of sedimentary rocks? In essence we use facies analysis, which is based upon a careful study of the sediment types and structures, together with a study of the ecological aspects of the contained fossils, or palaeoecology. These features can be compared with those of similar sediments that are being deposited today, or similar organisms living today. Comparisons of this kind were practised by the likes of Cuvier as well as Lyell. Consider, for example, the Cretaceous succession in southern England. The oldest strata, well exposed on the coast from Sussex to Dorset, are known as the Wealden, and consist mainly of sandstones and siltstones that were deposited in a coastal plain (non-marine) setting. They are overlain by the Lower Greensand, a sandy unit of Aptian–Lower Albian age laid down in a very shallow marine environment. These conditions are revealed, not just by the types of fossils, which include the exclusively marine ammonites, but also by the distinctive green clay mineral glauconite, which gives its name to the rock formation and occurs today only in marine settings.

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High-resolution isotope stratigraphy of the Lower Ordovician St. George Group of western Newfoundland, Canada: implications for global correlation

Canadian Journal of Earth Sciences ◽

10.1139/e09-032 ◽

2009 ◽

Vol 46 (6) ◽

pp. 403-423 ◽

Cited By ~ 14

Author(s):

Karem Azmy ◽

Denis Lavoie

Keyword(s):

High Resolution ◽

Sea Level ◽

Sea Level Changes ◽

Global Correlation ◽

Lower Ordovician ◽

Isotope Stratigraphy ◽

Platform Carbonates ◽

The Baltic ◽

Marine Platform ◽

Bottom To Top

The Lower Ordovician St. George Group of western Newfoundland consists mainly of shallow-marine-platform carbonates (∼500 m thick). It is formed, from bottom to top, of the Watts Bight, Boat Harbour, Catoche, and Aguathuna formations. The top boundary of the group is marked by the regional St. George Unconformity. Outcrops and a few cores from western Newfoundland were sampled at high resolution and the extracted micritic materials were investigated for their petrographic and geochemical criteria to evaluate their degree of preservation. The δ13C and δ18O values of well-preserved micrite microsamples range from –4.2‰ to 0‰ (VPDB) and from –11.3‰ to –2.9‰ (VPDB), respectively. The δ13Ccarb profile of the St. George Group carbonates reveals several negative shifts, which vary between ∼2‰ and 3‰ and are generally associated with unconformities–disconformities or thin shale interbeds, thus reflecting the effect of or link with significant sea-level changes. The St. George Unconformity is associated with a negative δ13Ccarb shift (∼2‰) on the profile and correlated with major lowstand (around the end of Arenig) on the local sea-level reconstruction and also on those from the Baltic region and central Australia, thus suggesting that the St. George Group Unconformity might have likely had an eustatic component that contributed to the development–enhancement of the paleomargin. Other similar δ13Ccarb shifts have been recorded on the St. George profile, but it is hard to evaluate their global extension due to the low resolution of the documented global Lower Ordovician (Tremadoc – middle Arenig) δ13Ccarb profile.

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WALIS - Towards a global database of Last Interglacial sea-level proxies.

10.5194/egusphere-egu21-9827 ◽

2021 ◽

Author(s):

Alessio Rovere ◽

Deirdre Ryan ◽

Matteo Vacchi ◽

Alexander Simms ◽

Andrea Dutton ◽

...

Keyword(s):

Sea Level ◽

Research Council ◽

Geological Data ◽

Sea Level Changes ◽

Last Interglacial ◽

Global Database ◽

The World ◽

First Results ◽

Data Points ◽

The Subject

<p>The standardization of geological data, and their compilation into geodatabases, is essential to allow more coherent regional and global analyses. In sea-level studies, the compilation of databases containing details on geological paleo sea-level proxies has been the subject of decades of work. This was largely spearheaded by the community working on Holocene timescales. While several attempts were also made to compile data from older interglacials, a truly comprehensive approach was missing. Here, we present the ongoing efforts directed to create the World Atlas of Last Interglacial Shorelines (WALIS), a project spearheaded by the PALSEA (PAGES/INQUA) community and funded by the European Research Council (ERC StG 802414). The project aims at building a sea-level database centered on the Last Interglacial (Marine Isotope Stage 5e, 125 ka), a period of time considered as an "imperfect analog" for a future warmer climate. The database is composed of 17 tables embedded into a mySQL framework with a total of more than 500 single fields to describe several properties related to paleo sea-level proxies, dated samples and metadata. In this presentation, we will show the first results of the global compilation, which includes nearly 2000 data points and will discuss its relevance in answering some of the most pressing questions related to sea-level changes in past warmer worlds.&#160;</p>

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Origin of the Late Ordovician Lepidocyclus brachiopod fauna in North America and its biogeographic significance

The Paleontological Society Special Publications ◽

10.1017/s2475262200007097 ◽

1992 ◽

Vol 6 ◽

pp. 149-149

Author(s):

Jisuo Jin

Keyword(s):

North America ◽

Sea Level ◽

North American ◽

Plate Tectonics ◽

Late Ordovician ◽

Sea Level Changes ◽

Stepping Stones ◽

Shell Size ◽

Larval Stages ◽

The North

Three rhynchonellid brachiopod genera, Hiscobeccus, Lepidocyclus, and Hypsiptycha, are the most diagnostic elements of the Lepidocyclus fauna of North America in Late Ordovician time. These are characterized by relatively large, strongly biconvex to globular shells with coarse imbricating growth lamellae and, internally, with septiform cardinal processes in brachial valves. Among the three genera, Hiscobeccus appears the earliest, now known from rocks of late Trentonian-Edenian age in the Canadian Rocky Mountains and Mackenzie Mountains. Morphologically, Hiscobeccus is distinguished from the other two genera by its open delthyrium in the pedicle valve. Early forms of Hiscobeccus show close morphological similarity to Rhynchotrema in their non-globular biconvex shells covered by strong growth lamellae only in the anterior portions. It has been suggested that Hiscobeccus evolved from the Rhynchotrema wisconsinense stock through increase in shell size, globosity, and strength of growth lamellae. Earliest species of Rhynchotrema has been documented convincingly from rocks of early Trentonian age, and the derivation of Hiscobeccus most likely took place during the mid-Trentonian. Lepidocyclus and Hypsiptycha evolved from either Rhynchotrema or Hiscobeccus by developing a pair of deltidial plates covering the delthyrium.Rhynchotrema and other rhynchonellids that evolved before mid-Trentonian time are common to the North American (Laurentian) and the Siberia-Kazakhstan paleocontinents. In contrast, Hiscobeccus, Lepidocyclus, and Hypsiptycha that evolved after the mid-Trentonian are virtually restricted to Laurentia. Therefore, Rhynchotrema marked the last successful intercontinental migration of rhynchonellids during their Llandeilian-Caradocian cosmopolitanism. The pronounced provincialism of the North American Lepidocyclus fauna may have been caused by a number of factors. Facies control is not likely the explanation because these rhynchonellids occur in nearly all the inland and marginal platform seas of Laurentia and commonly are found together in the same types of rocks. Plate tectonics and sea-level changes are considered major causes. The Ordovician rhynchonellids lived in shallow marine (intertidal-subtidal) environments and were incapable of crossing vast, deep oceanic barriers because of their sedentary mode of life and short-lived motile larval stages. The widening of the ocean between North America and Siberia, coupled with high sea-level stand, may have created a sufficiently wide oceanic barrier to interrupt faunal mixing between the two paleocontinents by late Trentonian time. Moreover, the rise in sea level would have resulted in the disappearance of island faunas, which could have served as stepping stones for intercontinental migration of shallow-water benthic faunas during low sea-level stand.

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Archaean plate tectonics revisited 2. Paleo-sea level changes, continental area, oceanic heat loss and the area-age distribution of the ocean basins

Tectonics ◽

10.1029/tc003i007p00709 ◽

1984 ◽

Vol 3 (7) ◽

pp. 709-722 ◽

Cited By ~ 14

Author(s):

Dallas H. Abbott

Keyword(s):

Sea Level ◽

Heat Loss ◽

Plate Tectonics ◽

Age Distribution ◽

Sea Level Changes ◽

Continental Area

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Stratigraphy, amino acid geochronology, and correlation of Quaternary sea-level and glacial events, Broughton Island, arctic Canada

Canadian Journal of Earth Sciences ◽

10.1139/e83-055 ◽

1983 ◽

Vol 20 (4) ◽

pp. 577-598 ◽

Cited By ~ 32

Author(s):

Julie K. Brigham

Keyword(s):

Amino Acid ◽

Sea Level ◽

Interglacial Period ◽

Major Advance ◽

Sea Level Changes ◽

Pollen Assemblage ◽

The North ◽

Sediment Types ◽

Outer Coast ◽

Glacial Advance

Raised marine and glaciomarine terraces on Broughton Island record regional isostatic adjustments and eustatic sea-level changes. Previous workers proposed three alternative glacial and sea-level chronologies of the region. These conflicts are resolved by the stratigraphic control provided by amino acid ratios (D-allo-isoleucine/L-isoleucine) in marine molluscs collected form cliff exposures. Amino acid ratios, radiometric dates, and relative weathering measurements on geomorphological features provide a basis for regional correlations.Based upon amino acid ratios, the coastal sedimentary sequences, all part of the Broughton Island Formation, can be subdivided into six units to which informal member names have been assigned. These units delimit at least four glacial episodes during which local ice advanced around Broughton Island to the outer coast. The youngest advance is correlative with deposits that are dated > 54 000 BP, and the absolute ages of older events have been estimated from minimum uranium-series dates and amino acid data. Glacial events previously recognized as the Foxe Glaciation represent a much greater portion of the Quaternary than was previously realized.The Tuneek member, the oldest sedimentary unit on Broughton Island, consists of a bouldery, sandy clay diamicton deposited by a major pre-Foxe glacial advance(s) that occurred possibly > 500 000 years BP when ice traversed the island. Subsequent advances were deflected along the southern coast of the island through Broughton Channel. The Anigatalik member, estimated to be between 300 000 and 500 000 years old, consists of a variety of sediment types including bouldery clay diamictons and bedded, coarse sands and gravels. The Platform member represents a subsequent and extensive pre-Foxe glacial advance. It consists of a bouldery, shelly till deposited over a wave-cut platform at the north end of Broughton Island between 250 000 and 350 000 years BP. Correlative tills were deposited along the east coast by glacial ice extending around the southeast corner of the island. Relative sea level was at least 72 m asl during this time.The Cape Broughton member consists of ice-proximal sediments deposited when fiord ice was retreating from Broughton Channel approximately 150 000 – 200 000 years BP. The macrofauna and microfauna within these sediments suggest that subarctic water masses, warmer than present, were adjacent to the northeastern Baffin coast subsequent to the glacial maximum. These deposits may be correlative with a prominent moraine system on either side of Broughton Channel.The Harbour member represents the beginning of the Foxe Glaciation (as it is redefined) and delineates the last major advance of ice to the outer coast. The current best estimate for the age of these sediments is 70 000 – 130 000 years BP. At one locale, Harbour sediments overlie an organic-rich, oxidized horizon containing a pollen assemblage strongly indicative of interglacial conditions. The stratigraphy suggests that a major interglacial period preceded the Harbour advance. Organic horizons near the top of the Harbour member contain a pollen assemblage that suggests a terrestrial climate similar to that of today.The Matsaja member consists of nearshore marine sands and beach facies deposited by an early Holocene transgression to between 7 and 8 m asl that occurred approximately 8000 – 10 000 years BP. A minor transgression of 1–2 m commenced approximately 1000 years BP.

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