Volume three

Donald R. Prothero , in Encyclopedia of Geology (Second Edition), 2021

Abstruse

The Paleogene Period spans the interval from 66 to 23  Ma. The Paleogene is further subdivided into the Paleocene, Eocene, and Oligocene epochs. Some time scales nonetheless employ the primitive term "3rd" for the Paleocene through Pliocene, and the Quaternary for the Pleistocene and Holocene.

During the Paleogene, Pangea continued to break upwardly, with India and Africa slamming into the southern role of Eurasia to uplift the Himalayas and Alps. The Atlantic opened wider, further separating the Americas from Europe. Enormous subduction zones formed a "Ring of Burn" around the Pacific Rim, consuming voluminous amounts of oceanic chaff and yielding many volcanoes and earthquakes.

During this fourth dimension, the climate of the Earth went from a greenhouse earth in the early on Eocene to an icehouse globe by the early Oligocene, when glaciers starting time appeared on Antarctica. Life of the Cenozoic responded to these climate changes when the tropical species of the Eocene were gradually replaced by more than common cold-tolerant species in the Oligocene.

The most hit changes were the considerable evolutionary radiation and diversification of groups which had been severely decimated by the Cretaceous extinction. In the oceans, there was a all-encompassing diversification of the planktonic foraminifera, which had only 2–3 lineages survive the Cretaceous, and lesser diversifications in the calcareous nannoplankton and other planktonic organisms, equally well as benthic groups like bivalves, gastropods, and echinoids. On country, the virtually remarkable issue was the explosive diversification of land mammals once their dinosaurian overlords had vanished. In ten million years, they went from mostly shrew-sized creatures to a wide assortment of large herbivores and carnivores, along with specialists like bats and whales. Notwithstanding, the dramatic climatic cooling and drying in the later on Eocene and early on Oligocene eliminated the tropical and subtropical forests that once covered the planet to the poles. In addition, the predominantly arboreal groups (lemur-like primates, insectivores, multituberculates) and primitive leaf eaters on the ground vanished. They were replaced by primitive members of many mod families of mammals (horses, rhinos, tapirs, pigs, peccaries, ruminants, dogs, etc.) by the Oligocene.

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Volume 5

Mario Luis Assine , Lucas Verissimo Warren , in Encyclopedia of Geology (Second Edition), 2021

Oligocene to Present (Cenozoic Glaciations)

The first one-half of the Paleogene Period was uncommonly warm, with merely sparse records of restricted glaciers in Northern and Southern Hemispheres during the Eocene Epoch ( Stickley et al., 2009). The global cooling initiated in the heart Eocene reached its maximum in the primeval Oligocene, induced by rapidly declining CO2 concentrations in the atmosphere (DeConto and Pollard, 2003). This cooling was characterized by rapid growth of the Antarctic ice sheet, followed past an eustatic body of water level fall of ~   fifty   m (~   34   Ma). In fact, paleotemperature reconstructions reveal that this glaciation began abruptly, as demonstrated by the accentuated decline of well-nigh four   °C (Ivany et al., 2000). Due to this effect, the extinctions of marine invertebrates at the Eocene-Oligocene boundary are commonly associated with the Early on Oligocene glaciation as is the onset of ice coverage of Antarctica (Zachos et al., 2001).

The long-term cooling was non reversed later the Early Oligocene glaciation, and the ice sheets and temperatures oscillated in a transition period until the late Miocene (Herbert et al., 2016). During the Tortonian to Messinian stages (vi–viii   Ma) a global decline of atmospheric CO2 produced an precipitous cooling of the sea surface temperatures by every bit much equally six   °C in both hemispheres, causing profound changes in the Earth'southward climate and ecosystems. The global cooling culminated vii.0   Ma agone, with the onset of glaciation in loftier latitudes and mountains marked by the appearance of alpine glaciers in Alaska (United States), Greenland, Republic of iceland, Patagonia (Argentine republic), and later in the Alps (Italy/French) and Andes (western Southward America).

The early to mid-Pliocene was a period considerably warmer than today. In different tropical regions, declines in sea surface temperatures betoken a transition from global warmth to ice ages over the Pliocene-Pleistocene, culminating with the North Hemisphere Fourth glaciations.

The global Cenozoic icehouse started in the latest Eocene (~   35   Ma) and is ongoing. The ice sheets that cover Antarctica became established in the Early Oligocene and progressively expanded during the Cenozoic. The Northern Hemisphere glaciations are essentially Quaternary events, when glaciers sometimes extended into mid-latitudes. This departure between the hemispheres demonstrates the importance of the distribution of continents beyond the world. In this complex paleogeographic and paleoclimatic puzzle, the presence of landmasses at the poles (Antarctica) and in high latitudes (Northern Europe, Asia and North America) played an of import function in the development and maintenance of glaciers, as well as the preservation of bear witness for glacial episodes in the geologic record.

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Volume 5

Scott A. Elias , in Encyclopedia of Geology (Second Edition), 2021

Paleogene Catamenia

The primeval part of the Cenozoic was the Paleogene Period, including the Paleocene, Eocene, and Oligocene epochs, spanning the interval of 64–23  mya. The start driblet in pCO2 levels marked in proxy records was during the transition from the Paleocene to the Eocene, most 56   mya. During the Paleocene-Eocene thermal maximum (PETM), bounding main surface temperatures (SST) rose by 5   °C in the torrid zone and as much as 9   °C in the high latitudes, and bottom-water temperatures increased past iv–5   °C. The initial SST rising was rapid, on the order of 1000   years, although the full extent of warming was non reached until some 30,000   years after (Zachos et al., 2005). The well-nigh probable cause of this dramatic warming was the addition of two trillion (2   ×   1015) metric tons of carbon into the temper, released from methane hydrates melted from deep-sea sediments (Fig. 6). Methane hydrate is an water ice-similar substance formed when CHiv and water combine at depression temperature and moderate force per unit area which corresponds to combined h2o and sediment depths of 300–500   m. Nominally, methane hydrate concentrates CH4 by about 164 times on a volumetric basis compared to gas at standard pressure and temperature. Warming a small-scale volume of gas hydrate thus liberates a large volume of gas. The big, negative carbon isotopic excursion (CIE) recorded in both marine and terrestrial sediments during the PETM has been interpreted as reflecting widespread release of isotopically-light, microbial carbon from dissociating marine methane hydrates (Zachos et al. 2005).

During the Paleogene, the Earth experienced a global greenhouse climate. Temperatures were much warmer and more humid than today. Reconstructions of pCOtwo levels for the Paleogene are by and large based on proxy evidence, such every bit stomatal indices of fossil leaves, boron isotope analysis, paleosol carbon isotopes, boron isotopes from marine calcium carbonate and carbon isotopes from phytoplankton. Every bit seen in Fig. seven (lower right), these proxies accept yielded inconsistent and oftentimes contradictory pCO2 reconstructions that range from about 280 to 4000 per mile.

Fig. 7

Fig. vii. Climate change and pCO2 levels during the last 65   million years. The climate reconstructions (upper panel and lower left panel) are based on a compilation of oxygen isotope measurements (δ18O) on benthic foraminifera by Zachos et al. (2001), reflecting a combination of local temperature changes in their environment and changes in the isotopic composition of seawater associated with the growth and retreat of continental ice sheets. Wikimedia Eatables, in the public domain. Proxy reconstructions of pCO2 levels (lower right panel) reflect relatively low levels, ranging from pre-industrial to modernistic levels from 64 until almost fifty   mya (Wang et al., 2020).

A study by Wang et al. (2020) establish that pCO2 levels during the Early and Middle Paleocene (ca. 64–60   mya) were similar to modernistic levels, and heart Eocene pCOtwo levels were equally much as double the mod level (Fig. 7, lower right). Their estimated pCO2 reconstruction, based on the stomatal alphabetize of Metasequoia needles, supports the hypothesis that Paleogene climate changes cannot be explained merely past atmospheric COii variations, which suggests that atmospheric COtwo might non have e'er played a critical role in climate change during these ancient epochs and therefore cannot be a direct analogy for the current global warming. As seen in Fig. 7 (Cenozoic in the upper console; accident-up of Paleogene record in the lower left panel), paleotemperature estimates based on δ18O analysis of benthic foraminifera (Zachos et al., 2001) indicate that the global temperatures from Paleocene through the Eocene were considerably warmer than modern, despite the afore-mentioned low pCOii levels. It appears that other factors may have played a more important function equally climate drivers in Early Cenozoic times, such as paleogeography, high latitude vegetation feedbacks, increased polar stratospheric clouds, and increased latent estrus transport. Accordingly, Wang et al. (2020) infer that pCO2 played a less crucial function in these ancient epochs.

Gehler et al. (2016) confirmed that the Paleocene-Eocene transition was marked by a rapid temperature ascent contemporaneous with a large negative carbon isotope excursion (CIE), both of which are well-documented by terrestrial and marine proxies. Nonetheless, different Zachos et al. (2005) and Gehler et al. (2016) consider that the source and quantities of CO2 and CH4 emissions associated with this climatic transition are poorly constrained and highly debated. They adult a new proxy for pCO2 through the assay of the bioapatite of terrestrial mammals. Bioapatite is a grade of calcium phosphate that is the major component in the mineralized part of vertebrate teeth. Their results suggest that COii levels during the PETM/CIE (carbon isotope excursion) remained close to the previous and subsequent levels. Their data thus back up a hypothesis that the CIE was triggered by marsh gas released from marsh gas hydrates on the seabed, rather than past changes in pCO2. Every bit discussed higher up, methane is an extremely potent GHG, equally the global warming potential of methane is 34 times that of carbon dioxide.

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Along-strike segmentation of the Farallon-Phoenix midocean ridge: Insights from the Paleogene tectonic development of the Patagonian Andes between 45° and 46°30′Southward

Guido K. Gianni , ... Andrés Folguera , in Andean Tectonics, 2019

Abstract

The kinematics of the Farallon-Phoenix-South America triple junction during the Cretaceous and Paleogene periods remain incompletely resolved. Geological studies have interpreted Paleocene-Eocene ridge subduction beneath Patagonia based on the documentation of slab window magmatism and close-off of the Andean arc. Nevertheless, a new regional synthesis of studies assessing the Paleogene tectonic development of Patagonia, focused on a primal Andean segment between 45°S and 46°xxx′Due south, shows inconsistencies in this estimation. In particular, the presence of two separate areas with simultaneous slab window-related magmatism and an intervening sector that registered plate-broad contraction, along with a spatiotemporal mismatch betwixt magmatism location and ridge kinematics, foreclose a single ridge-trench interaction. As reviewed here, it is likely that the oblique standoff of a segmented ridge accounts for the latitudinally variable tectonomagmatic evolution in Paleogene times. Finally, this study highlights the potential of the geological record for decoding the complex configurations of midoceanic ridges during subduction.

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Large Coal-Derived Gas Fields and Their Gas Sources in the Tarim Basin

Jinxing Dai , et al., in Giant Coal-Derived Gas Fields and their Gas Sources in Red china, 2017

five.5 Hydrocarbon Accumulation Stages

The Kuqa depression experienced 2 stages of hydrocarbon accumulation. The first was early oil generation on a large scale in Triassic lacustrine source rock from the cease of the Cretaceous to the Paleogene periods. Tectonic stress was small at that time, and some compressional structures began to take shape only at the front of South Tianshan. Therefore, oil and gas generated from Triassic formations could drift s for a great distance ( Zhu et al., 2013b) and accrue in tectonic zones such every bit Yaha and Yingmai7 to form hydrocarbon reservoirs. Late hydrocarbon aggregating occurred in the Neogene and Quaternary periods, when Jurassic and Triassic source rock became high-mature to postmature and mainly generated natural gas. Horizontal compressive stress from northward to south kept increasing with intensified Himalayan movement, and hydrocarbon charging took identify in the Yingmai7 tectonic zone. Thus, there were two stages of hydrocarbon aggregating in the Yingmai7 gas field: crude oil charging mainly occurred at the early phase from the end of Cretaceous to the Early Paleogene periods, and natural gas charging mainly occurred at the late stage, from the Late Neogene to the Quaternary periods.

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Large Gas Fields and Their Significance in the Natural Gas Industry

Jinxing Dai , et al., in Giant Coal-Derived Gas Fields and their Gas Sources in China, 2017

2.two.2 Gas Aggregating Stages

Virtually big gas fields in China are characterized by "later on gas accumulation" or "super-afterward gas aggregating." As shown in Effigy 1.twenty, autonomously from the large gas fields in the Ordos Basin being formed in the Jurassic-Cretaceous period, the latest gas accumulation of all other large gas fields in China occurred in the Cenozoic Paleogene, Neogene, and Quaternary periods. Based on the relations among gas generation peaks, reservoirs, and gas source rock of large gas fields, the gas accumulation history of big gas fields in China is summarized as follows (Wang, 2003a, 2003b):

Figure i.twenty. Gas accumulation stages of large gas fields in Prc
i.

Gas generation and aggregating occurred in the super-late menstruum (Neogene-Quaternary), for example, the chief gas accumulation flow of the Ya13−1 gas field in the Yingqiong Basin is Quaternary (5.2 Ma ago to today), and information technology is still in a gas aggregating catamenia (Hao & Chen, 1995); the main gas-charging menses of the Kela2 gas field in the Kuche depression of the Tarim Basin is three-1 Maago (Zhao & Dai, 2002).

2.

Gas generation and aggregating occurred in the late menstruum (Paleogene-Neogene), for case, the main source rock of the southern margin of the Junggar Basin consists of Jurassic coal measures, but the main gas accumulation took place in the Neogene.

3.

Gas generation and accumulation occurred in the early period (mainly in the Mesozoic), but reservoirs were fixed in the tardily period (Neogene-Quaternary), for example, the gas aggregating of the Xinchang gas field in the Sichuan Basin occurred mainly in the Late Jurassic–Early Cretaceous, merely it was finally formed in the Neogene-4th after multiphasic reconstruction of Himalayan motility.

4.

Gas generation and accumulation occurred in the early period (mainly in the Mesozoic), for example, the Ordos Basin is a stable cratonic basin that experienced weak tectonic movement over a long geological period, and the main gas accumulation period of major big gas fields in it is Jurassic-Cretaceous. Scholars had different views on the time of gas-charging and accumulation of the Sulige gas field, but they all concluded that the chief gas-charging period was 168–156 Ma or 190–154 Ma ago, and the main gas accumulation flow was 148–143 Ma or 137–96 Ma ago (Liu et al., 2005, 2007; Zhang et al., 2009; Li et al., 2012b).

Most basins in China have experienced multicyclic tectonic evolution (multiple folding, trap germination, uplifting and subsidence, structural faulting, magmation, multiple sets of source-reservoir-caprock assemblages, and multiple stages of gas accumulation). This resulted in the destruction of large gas fields formed in the early period, and but gas aggregating in the tardily menstruum is favorable for gas preservation and so large gas field formation (Dai, 2003). The Ordos Basin is an exception, due to its being one of the most stable basins in People's republic of china, with a dip bending of less than one degree within and very weak multicyclic tectonic evolution in the late period. Furthermore, the tight sand formation formed at an early phase provided the natural gas generated in the Carboniferous-Permian coal measures with a practiced reservoir.

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Book three

Donald R. Prothero , in Encyclopedia of Geology (2d Edition), 2021

The Cenozoic Fourth dimension Calibration

Originally, pioneering naturalists like Giovanni Arduino in 1759 regarded the soft horizontal beds of the Apennine Mountains (which overlaid the tilted and folded "Secondary" beds, and the hard granitic or metamorphic rocks below as "Primary") every bit the "Tertiary beds." Unconsolidated sands and gravels that lay above them were called "Quaternary." This terminology was in widespread usage until recently, when geologists have advocated dividing the Cenozoic into the Paleogene Flow (Paleocene, Eocene, and Oligocene epochs, 66–23  Ma), and the Neogene Period (Miocene and Pliocene epochs, 23–5   Ma). Originally, the Neogene of Moritz Hörnes (1853) likewise included the Pleistocene and the Holocene epochs, simply many fourth dimension scales place these time intervals in the Fourth. Currently, the about widely accepted timescale uses the Paleocene, Neogene, and 4th as the major subdivisions of the Cenozoic, but most geologists but use the names of the epochs, since we know these relatively recent events in then much more than detail than we do for the older parts of the geologic past.

The terms "Miocene" and "Pliocene" were proposed by Charles Lyell in 1833 in the third and last of book of his legendary volume Principles of Geology. Lyell wanted to subdivide the 3rd into smaller units based on the similarity of the fossil mollusks to species that are alive today. The Miocene ("less contempo" in Greek) supposedly had only 17% living species, and the older Pliocene (Greek for "more recent") had 33–l% modern species. The "newer Pliocene" (which was somewhen renamed the Pleistocene) had 90% living mollusks. This organization did not work very well when other geologists tried to apply this abstruse concept of steady molluscan modify through fourth dimension to the real fossils in local rock sections, and also did not piece of work with the existing organization, where "stages" were named based on actual rock sections in specific places. Eventually, the terms "Miocene" and "Pliocene" were converted into chronostratigraphic and thus geochronological terms, and no longer are divers past Lyell's original concepts.

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Introduction

F.M. Gradstein , in Geologic Time Scale 2020, 2020

1.4.three Cenozoic scales

The Cenozoic time scale from 66   Ma to Recent (set at CE 2000) contains stages that vary in duration from almost 8   Myr for the Lutetian to less than 1   Myr for the Gelasian, and with the Holocene Epoch of only eleven,800 years. Although the Cenozoic Era is known in much detail, standardization of stage boundaries with consensus definitions and GSSPs is not consummate (come across Affiliate 28 : The Paleogene Period and Chapter 29: The Neogene Catamenia). All Cenozoic standard stages are originally based on European stratotypes. In the face up of higher breadth climatic cooling, which increases provincialism and diachronism in faunal and floral events, the Neogene Mediterranean ones are more difficult to correlate world-wide. Selected Cenozoic time scales are compared to GTS2012 in Fig. i.6.

Figure 1.6. Comparison of selected Cenozoic time scales with GTS2020.

Since 1964, when B.F. Funnel presented the first, relatively detailed, and accurate Cenozoic time scale with radiogenic isotope age estimates, many marine time scales take been erected with a progressive enhancement of scaling methods. Berggren (1972) and NDS82 combined radiogenic isotope age dating stratigraphic reasoning, and biostratigraphic–geomagnetic calibrations. Hardenbol and Berggren (1978), GTS82, DNAG83 and EX88 added marine magnetic reversal calibrations.

Whereas the Paleozoic and Mesozoic time scales still lack single interpolation methods, the marine magnetic reversals contour (C-sequence) for many years provided a powerful interpolator for the Cenozoic time scale. The large number of geomagnetic field reversals since Tardily Santonian time, coupled with a wealth of seafloor magnetic profiles and detailed noesis of the radiogenic isotope age of selected magnetic polarity reversals in lavas and sediments, provide a finely spaced calibration. These are combined with orbital tuning and cubic splines to produce spreading-rate models for ocean basins and an associated magnetic polarity time calibration (come across Chapter 5: Geomagnetic Polarity Time Scale). An splendid account of the method and its early on applications is given past A.5. Cox in Harland et al. (1982).

The method itself dates back to Heirtzler et al. (1968), who selected a detailed profile in the Due south Atlantic from anomalies 2 to 32. The only calibrated tie indicate was magnetic anomaly 2   A at 3.4   Ma, based on the radioisotopically dated magnetic reversal calibration of Cox et al. (1964) in Pliocene through Pleistocene lavas. Assuming that ocean-floor spreading had a constant spreading rate of one.ix   cm/103 years dorsum through the Campanian (~80   Ma), ages were assigned to the chief Campanian through Pleistocene polarity chrons. This ambitious extrapolation has turned out to be within ~10% of later interpolations using a more than detailed composite seafloor profile, and an improved array of age-calibrated tie points (Hardenbol and Berggren, 1978, DNAG83, EX88, and GTS89).

Cande and Kent (1992a,b, 1995) synthetic a new geomagnetic reversal fourth dimension calibration using a blended of marine magnetic anomalies from the South Atlantic with brusque splices from fast-spreading Pacific and Indian Ocean segments, better estimates of anomaly width, nine age tie points, and a cubic-spline smoothing. Using an array of biomagnetostratigraphic correlations with the Cande and Kent spreading model, Berggren et al. (1995) compiled a comprehensive Cenozoic time scale.

Orbital tuning has become the dominant method for constructing detailed Neogene and at present as well Paleogene time scales, going back to Shackleton et al. (1990, 1999, 2000), Hilgen (1991), Hilgen et al. (1995, 1997), Lourens et al. in GTS2004, Pälike et al. (2006), and F. Hilgen in GTS2012. These Milankovitch cycles of climate oscillations are recorded in about all oceanic and continental deposits, and their presence has get a requirement for placement of stage purlieus stratotypes within the Neogene (encounter Chapter 29; The Neogene Period). In general, the Cande and Kent's (1995) geomagnetic polarity time scale for the Belatedly Neogene is slightly too immature. Cycle tuning relative to the well-dated base Paleogene has enabled scaling of Paleocene magnetic chrons (Röhl et al., 2001) and refined estimates of spreading rates for the Due south Atlantic profile (see Chapter 5: Geomagnetic Polarity Time Scale). The electric current state of astrochronology, marine magnetochronology, and selected radioisotopic dates for Paleogene and Neogene is dealt with in detail in Affiliate 4, Astrochronology, Affiliate 5, Geomagnetic Polarity Time Scale, Chapter 28, The Paleogene Flow, and Chapter 29, The Neogene Period.

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TERTIARY TO Nowadays | Eocene

J.J. Hooker , in Encyclopedia of Geology, 2005

Introduction

The Eocene epoch/series is the oldest of the four original subdivisions of the Third period/system proposed in 1833 by Sir Charles Lyell in his Principles of Geology. The name derives from the Greek 'eos', meaning dawn, and 'kainos', meaning recent. This is "… because the very small proportion of living species contained in those strata indicates what may be considered the starting time commencement, or dawn, of the existing state of the animate creation" (vol. iii, p. 55). The time covered past Lyell'due south 'existing state' is what we now empathize to be the Cenozoic era/erathem, which itself is broadly divided into either Tertiary and 4th or Paleogene and Neogene periods. Lyell subdivided the Third into four epochs based on the proportions of living and extinct species of shelled organisms (molluscs and foraminifera) encountered as fossils in different strata. He recognized 1238 Eocene species, of which he considered only 42 (or three.5%) remain alive today. Lyell's species are most equivalent to what modern marine biologists would rank as genera or even subfamilies. For this reason, no modern species of mollusc or foraminifer is currently recognized every bit occurring as far back as the Eocene.

The Eocene as recognized today has changed considerably in its definition and time-span since 1833. Its earliest parts accept get the Paleocene and its afterwards parts the Oligocene, both epochs that were described after 1833. The Eocene thus succeeds the Paleocene and precedes the Oligocene. It is currently estimated to accept lasted nearly 22 one thousand thousand years, from 55.eight to 33.9 Ma. The Eocene itself is divided into four ages/stages (in guild of decreasing historic period): the Ypresian, the Lutetian, the Bartonian, and the Priabonian (Figures 1 and 2). The starting time and end of the Eocene have merely recently been stabilized past the Paleogene Subcommission of the International Marriage of Geological Sciences (IUGS). Its beginning is marked past a sharp dip in the carbon isotope curve, named the Carbon Isotope Excursion (CIE), interpreted every bit a global warming event, the Paleocene–Eocene Thermal Maximum (PETM). This climate effect sparked major changes in both marine and continental biotas. The Global Stratotype Department and Point (GSSP) for the first of the Eocene is placed at Dababiya, Egypt. This geological section is the best bachelor for demonstrating the purlieus criteria and acts as a global reference. The stop of the Eocene is marked by extinction of the planktonic foraminiferal family Hantkeninidae, representing the concluding in a cumulative series of extinctions caused by long-term global cooling. The GSSP for the Eocene–Oligocene boundary is at Massignano, Italian republic.

Figure 1. Fourth dimension chart of the Eocene, showing how information technology is divided up past ages/stages, magnetochrons (chron C), and global calcareous nannoplankton (NP) and planktonic foraminiferal (P) biozones. Also shown are an isotope proxy temperature curve and the main biotic events in the sea and on land. Magnetochrons are divided into normal (blackness) and reversed (white) intervals; the normals (n), often composite, are younger than the reversals (r) that bear the same number. CIE, Carbon Isotope Excursion; EECO, Early Eocene Climatic Optimum; MDE, Mammalian Dispersal Event; PETM, Paleocene–Eocene Thermal Maximum. Data for the isotope curve from Zachos J, Pagani Yard, Sloan 50, Thomas E, and Billups K (2001) Trends, rhythms, and aberrations in global climate 65 Ma to nowadays. Science 292: 686–693. Absolute dates from Gradstein F, Ogg J, and Smith A (in press) A Geological Timescale 2004. Cambridge Academy Press, Cambridge.

Figure 2. Littoral section in Alum Bay, Island of Wight, Great britain, showing strata spanning about the entire Eocene. Oldest is to the right, youngest to the left. The ruby-red and brownish are Ypresian, the yellow with dark intercalations is Lutetian, the greyness below the house is Bartonian (all vertical), and the white (mainly horizontal) is Priabonian.

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Oxygen Isotope Stratigraphy

Due east.L. Grossman , M.Thousand. Joachimski , in Geologic Fourth dimension Calibration 2020, 2020

10.3.i Principles

Oxygen isotope stratigraphy depends on rapid changes in fossil δ18O in response to rapid changes in temperature and (or) global seawater δxviiiO, the latter as a result of changing glacial ice volume. During glacial intervals the storage of 18O-depleted h2o as glacial ice results in xviiiO enrichment (higher δ18O) in seawater and consequently in marine authigenic minerals. Lower temperatures during glacial intervals (e.thou., Lea et al., 2000) farther enrich marine authigenic minerals in 18O. Deglaciation lowers seawater δ18O and combines with warming to produce lower marine carbonate δ18O values during interglacial intervals. Glacial–interglacial cyclicity in the δ18O of marine foraminifera provides a high-definition oxygen isotope stratigraphy for the Neogene (Emiliani, 1955; Shackleton and Opdyke, 1973; Lisiecki and Raymo, 2005; Raffi et al., 2020, Chapter 29, The Neogene Period, this book) and holds hope for a refined Paleogene stratigraphy (Speijer et al., 2020, Chapter 28 , The Paleogene Period, this book). Because glacial–interglacial cycles respond predictably to variations in Earth'southward orbit and tilt (Milankovitch cycles; Hays et al., 1976), their chronology can exist tuned to the astronomical time scale. This has led to loftier-resolution cyclostratigraphy (see later word and Laskar, 2020, Affiliate 4, Astrochronology, this volume).

The principles used to develop the Neogene oxygen isotope stratigraphy are being applied to older sediments. Although the extension is limited by the availability of precise radioisotope ages, "floating" astronomical time scales (not yet calibrated to an absolute age) exist for the Paleogene and Mesozoic based on δeighteenO and other information (Hinnov and Hilgen, 2012; Laskar, 2020, Chapter iv, this volume). As the records reach further back in fourth dimension, the clarity of the glacial–interglacial δ18O cycles is reduced by diminishing ice book and decreased sample resolution and preservation.

The dual dependence of oxygen isotope values on seawater δ18O and temperature can hinder stratigraphic applications; however, this dual dependence can amplify the isotopic signal as discussed with respect to Neogene marine isotope stratigraphy. The aforementioned distension should apply for studies of other icehouse periods such as the latest Ordovician, Late Carboniferous, and Early Permian. For ice-free periods, global seawater δ18O will be constant over short (less than tectonic) time scales, simplifying the application of oxygen isotope stratigraphy. However, in marginal marine environments such as epicontinental seas, seawater δ18O can vary locally and complicate stratigraphic and paleoclimate applications. Nevertheless, advances are beingness made through the combined application of oxygen isotopes and other paleotemperature proxies such equally Mg/Ca (east.grand., Lear et al., 2000; McArthur et al., 2007) and clumped isotopes (Ghosh et al., 2006; Came et al., 2007; Henkes et al., 2018).

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