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Tertiary oxygen isotope synthesis, sea level history, and continental margin erosion
Abstract
Tertiary benthic and planktonic foraminiferal oxygen isotope records are
correlated to a standard geomagnetic polarity time scale, making use of
improved chronostratigraphic control and additional Oligocene isotope
data. Synchronous changes in both benthic and planktonic
δ18O values which occurred in the Oligocene to Miocene
(36-5.2 Ma) are interpreted, in part, to represent ice growth and decay.
The inferred ice growth events correlate with erosion on passive
continental margins as interpreted from seismic and chronostratigraphic
records. This association is consistent with a link between Oligocene to
Miocene erosional events and rapid (>15 m/m.y.) glacioeustatic
lowerings of about 50 m. High benthic foraminiferal
δ18O values suggest the presence of continental ice
sheets during much of the Oligocene to Recent (36-0 Ma). Substantially
ice-free conditions probably existed throughout the Paleocene and Eocene
(66-36 Ma). The mechanisms and rates of sea level change apparently were
different between the early and late Tertiary, with glacioeustatic
changes restricted to the past 36 m.y. Pre-Oligocene erosion on passive
continental margins was caused by eustatic lowerings resulting from
global spreading rate changes. We apply a model which suggests that
large areas of the continental shelves were subaerially exposed during
such tectonoeustatic lowstands, stimulating slope failure and submarine
erosion. The different mechanisms and rates of eustatic change may have
caused contrasting erosional patterns between the early and late
Tertiary on passive continental margins. This speculation needs to be
confirmed by examination of data from several passive margins.
... Global sea-level variations tied to shifts against an ellipsoidal reference ('eustasy'; Miller et al., 2005; can be precisely defined as global mean geocentric sea-level change (GMGSL; Gregory et al., 2019). Changes in the volume of ocean water, GMSL (global mean sea level; Fairbanks, 1989;Fairbanks & Matthews, 1978;Miller et al., 1987Miller et al., , 2005, and changes in the shape of the ocean basins combine to produce GMGSL. Most of the GMGSL change on geological timescales can be attributed to: (1) variations in ocean basin volume (OBVSL) due to mid-ocean ridge spreading rate variations (Kominz, 1984;Muller et al., 2008;Pitman, 1978); and (2) barystatic sea-level (BSL) changes stemming from ice-volume fluctuations (Fairbanks, 1989;Fairbanks & Matthews, 1978;Miller et al., 1987Miller et al., , 2005 SCHMELZ et al. et al., 2005;Westerhold et al., 2020). ...
... Changes in the volume of ocean water, GMSL (global mean sea level; Fairbanks, 1989;Fairbanks & Matthews, 1978;Miller et al., 1987Miller et al., , 2005, and changes in the shape of the ocean basins combine to produce GMGSL. Most of the GMGSL change on geological timescales can be attributed to: (1) variations in ocean basin volume (OBVSL) due to mid-ocean ridge spreading rate variations (Kominz, 1984;Muller et al., 2008;Pitman, 1978); and (2) barystatic sea-level (BSL) changes stemming from ice-volume fluctuations (Fairbanks, 1989;Fairbanks & Matthews, 1978;Miller et al., 1987Miller et al., , 2005 SCHMELZ et al. et al., 2005;Westerhold et al., 2020). These variations in GMGSL generate variations in accommodation through control on RSL and the equilibrium profile, and affect sedimentation across passive continental margins. ...
We produced a 10 Myr synthetic stratigraphic section using a forward stratigraphic model that generates marine deltaic stratigraphy over geological timescales. We recursively fit the model using a Bayesian inversion algorithm to test: (1) if it could be accurately reconstructed; (2) if the parameters used to create it could be recovered; and (3) the sensitivity of the model output to given model parameters and the attendant physical processes. The original synthetic stratigraphic section was produced with cyclical sea‐level variations of 40 and 30 m with 2.4 and 10 Myr periods respectively. Sediment was also supplied cyclically, in 2.4 and 10 Myr cycles with amplitudes of 30 and 80 tons/100 kyr, respectively, varying from a mean of 232 tons/100 kyr. Parameter values were sampled to fit the model using a Markov chain Monte Carlo algorithm, resulting in a ±5 m (1σ) variation between the experimental output and the original. Sea level varied by ±7 m (1σ) within the posterior distribution of parameters. As a result, both the 10 Myr and 2.4 Myr sea‐level cycles could be extracted from the original output. The variation in sediment supply was approximately ±38 tons/100 kyr (1σ) and, as a result, only the larger long‐term supply variations could be accurately recovered in refitting the model. The variation in thermal, flexural and total subsidence across those parameter sets is less than ±10 m (1σ). The original section experienced 150 m of total subsidence at the depocentre. Our results demonstrate the distinct and interpretable imprint of sea level and subsidence on continental margin stratigraphy can be quantified. Moreover, we conclude that sea‐level change produces a defined effect on the geometries of stratigraphic architecture, and that techniques applied for the purpose of delineating sea‐level variation from continental margin strata have a well‐founded conceptual basis.
... 12). Permanent ice sheets, evidenced by higher δ 18 O values, were established following long-term cooling during the Palaeocene-Eocene (Miller et al., 1987;Ditchfield et al., 1994;Zachos et al., 2001;Tripati et al., 2003;Allen and Armstrong, 2008), which led to the reorganisation of global ocean circulation and the climate system (Goldner et al., 2014). This led to various upwelling events and changes in ocean productivity globally (e.g., Shackleton and Kennett, 1975;Moore et al., 1978;Diester-Haass, 1996;Mallinson et al., 2003;Goldner et al., 2014;Villa et al., 2014), including the southeast Atlantic (Diester-Haass, 1996;Compton et al., 2004;Villa et al., 2014). ...
The sedimentary record of the western South African continental shelf is condensed compared to the continental slope and contains erosional unconformities, owing to periods of non deposition, eustatic sea-level fluctuations, episodic uplift and intensified continental aridity. Despite this, the sedimentary record of the continental shelf provides important information on the depositional history and palaeoenvironmental evolution of the region. A core retrieved from the western shelf of South Africa was analysed for its sedimentary composition, lithological variation, foraminiferal content and its relation to the palaeoenvironment of the region. Four depositional facies were identified along the core, namely quartzitic sand, sandy mud, and glauco phosphatic sand and a glaucophosphatic gravel. The basal facies consisting of quartzitic sand is interpreted to have been deposited between 15.90 and 14.60 Ma, corresponding to the timing of the Mid-Miocene Climatic Optimum (MMCO). The highly quartzitic nature of the sediments indicate a high terrestrial influence from fluvial sources. The overlying sandy mud facies was deposited between 14.60 and 13.90 Ma based on planktic foraminiferal biostratigraphy. Foraminiferal analyses of these two facies that were deposited in the Langhian stage of the middle Miocene point to subtropical sea surface conditions and mesotrophic benthic environments. Sea level was noticeably higher during the MMCO and part of the cooling period following the MMCO. An erosional surface that spans 10.77 Myr, equal to the late Miocene (13.90 Ma) to early Pliocene (3.13 Ma), marks the boundary between the two Langhian facies and the overlying two Pleistocene facies, consisting of coarser grained glauco-phosphatic gravelly sand units. The Pleistocene environment on the shelf is interpreted to contrast with the Langhian environment, where cooler, shallower conditions and a more eutrophic benthic environment was prevalent, during a time that Benguela upwelling intensified with higher frequency and higher amplitude sea level fluctuations. Palaeobathymetric interpretations indicate that middle Miocene sea-level in the region were up to 77 m higher than present day and 101 m lower in the Pleistocene, in-line with previous global studies. Glauco-phosphatic content that increase upcore also marks the shallowing of the environment under high productivity conditions.
... Throughout its history, Earth has undergone continuous changes in its climate, having fluctuated between 'greenhouse' (tropical sea-surface temperatures) and 'icehouse' (initiation of Antarctic glaciation) phases (Shackleton and Kennett, 1975;Miller et al., 1987). Since the start of the split of the Gondwana supercontinent ~180 Ma, Antarctica underwent a significant transformation from an equatorial environment to the current glacial state (Lurcock and Florindo, 2017). ...
... The P/E boundary was correlated on the base of the P5/E1 zones of planktonic foraminifera (Berggren and Pearson, 2005) and between the NP9/NP10 zonal boundary, that was determined by the LO of Tribrachiatus bramlettei (Martini, 1971), or the LO of Discoaster diastypus (Okada and Bukry, 1980). Many events took place through the P/E boundary including alterations in oceanic circulation (Miller et al., 1987;Thomas, 1990aThomas, , b, 1993, global warming (Stott and Kennett, 1990;Kennett and Stott, 1991), and reduction in atmospheric circulation (Rea et al., 1990). Major shifts in the bathyal and abyssal benthic foraminifera coincided with these PETM-related occurrences (Benthic Extinction Event BEE) (Tjalsma and Lohmann, 1983;Thomas, 1990a, b). ...
Member of the Brule Formation of the White River Group at Toadstool Geologic Park in Nebraska. Our approach combined descriptive and quantitative methods to reconstruct river flow, sediment transport, channel dynamics, floodplain behavior, and catchment-scale moisture variability and ecosystem function. We found that rivers were ephemeral, with peak flow depths and widths of approximately 2.5 m and 65 m respectively. Median peak discharges were approximately 168 cms, and base flows near zero, as indicated by subaerial exposure surfaces on river beds. Floodplains were dynamic and built by frequent floods able to suspend and deposit sand up to 200 microns, with relatively short intervening periods of stasis for soil development. Environmental information recorded in n-alkane δD, δ13C, average chain lengths (ACL) was similar and primarily inherited from transported plant material. The paleo-catchment relief, estimated from variability in δD values and modern altitude-driven lapse rates, was approximately 800 meters. River channels had a gradient of approximately 3 x 10-4, an order of magnitude less steep than modern rivers in the area. This difference is likely due to the eastward tilting of the Great Plains associated with dynamic topography that initiated during the Miocene. Modern river discharges are an order of magnitude lower and current mean annual precipitation is 100 - 220 mm less than during early Oligocene time; together, these estimates indicate greater moisture availability on early Oligocene landscapes relative to today, possibly due to lower paleo-landscape elevations at the time. Our study provides a detail-rich characterization of Early Oligocene landscapes in Nebraska, offering insights into the hydrology, morphology, paleo-elevation, and relief of rivers and catchments during this period. The coordinated approach we used integrates hydroclimatic reconstructions, river and floodplain dynamics, and sediment and water fluxes, thereby bridging the timescale gap between geological records and modern hydrological data and ensuring consistency in reconstructions across subdisciplines. Our approach can support improved predictive modeling of paired climate-river dynamics through time.
We estimate ice-volume driven (barystatic; BSL) sea-level changes for the Cenozoic using new Mg/Ca data from 58 to 48 Ma and a revised analysis of Mg/Ca trends over the past 66 Myr. We combine records of BSL, temperature-driven sea level, and long-term ocean basin volume variations to derive a new global mean geocentric sea level (GMGSL; “eustatic”) estimate. Bayesian analysis with Gaussian process priors shows that our BSL estimate shares a component that covaries on the Myr scale with “backstripped” relative sea-level (RSL) estimates (accounting for compaction, loading, and thermal subsidence) from the US Mid-Atlantic Coastal Plain, validating our method and estimates with errors of ±10 m. Peak warmth, elevated GMGSL and BSL, high CO 2 , and ice-free conditions occurred at times in the Paleocene to Eocene (ca. 64, 57.5, 35 Ma) and in much of the Early Eocene (55–48 Ma). However, our new results show that the Early Eocene was punctuated at specific times by several Myr-scale sea level lowerings (∼20–40 m) that require growth and decay of significant continental ice sheets even in the supposedly “ice-free” world. Continental-scale ice sheets waxed and waned beginning ca. 34 Ma (>50 m BSL changes), with near complete collapse during the Miocene Climate Optimum (17–14.8 Ma). Both the BSL and RSL estimates have markedly higher Oligocene to Early Miocene Myr-scale amplitudes (20–60 m) than recently published δ ¹⁸ O-based estimates (<20 m) and much lower estimates than those of Exxon Production Research (>100 m), leading us to reject those estimates. The US Mid-Atlantic margin RSL was dominated by GMGSL but was overprinted by changes in mantle dynamic topography on the several Myr scale, showing approximately 50 m higher Eocene estimates and regionally propagating Miocene RSL changes.
This study describes the paleoenvironmental evolution of the Middle-Upper Eocene succession exposed along the northern plateau of the Bahariya Depression (Western Desert, Egypt). Based on detailed field observations and facies analysis, twenty-one facies were recognized and grouped into five facies associations: tidal flat to restricted marine (FA1), lagoonal (FA2), ramp crest (FA3), middle ramp (FA4), and siliciclastic-dominated foreshore–shoreface (FA5). These facies associations were developed in a gently dipping mixed siliciclastic-carbonate ramp which was connected with siliciclastic coastal-shelf depositional system. The biogenic assemblages described in the Middle-Upper Eocene deposits show a mixing of photozoan and heterozoan associations, indicating euphotic to mesophotic inner to mid-ramp settings under mesotrophic-oligotrophic conditions. The succession shows a transition from photozoan to heterozoan carbonates and a shift towards inner ramp settings. The formation and the evolution of the northern Bahariya platform reflect the complex interplay of synsedimentary tilting due to post-Middle Eocene inversion phase, high-frequency sea-level changes, transition from warm to humid climate and paleoecological parameters. The sedimentation pattern including distinct lateral changes in facies and thicknesses are largely controlled by tectonics. Long-term sea level changes were responsible for the unconformities associated with major regressions. The Middle-Upper Eocene strata display a characteristic up-section increase in clastic input from the hinterlands through tectonic uplift and/or a change to a cooling climate. The shift to a colder climate, which was a result of a global temperature decrease, led to the maximum northward retreat of the Neo-Tethys Ocean. During the Eocene epoch, carbonates dominated by Larger Benthic Foraminifera (LBF) were prevalent along the entire Tethyan margins. This was linked to a decline in coral reef formations. Comparisons with other southern and western-central Tethyan sectors showed that small coral reef build-ups in widely scattered localities could exist in broad LBF-rich ramps. Consequently, zooxanthellate corals were only able to flourish locally in marginal environments under specific ecological conditions.
In this chapter we refer to the area of the Atlantic Ocean south of the Equator and north of the Polar Front (Antarctic Convergence). The main topographical feature in the South Atlantic is the Mid-Atlantic Ridge which runs between Africa and South America from approximately 58° South to Iceland in the north. A rift valley is associated with the Ridge. The Ridge is of volcanic origin and the development of transverse ridges creates a number of basins: the Argentine, Brazil, Guinea, Angola and Cape Basins.
The Atlantic coast of South America is influenced by three major rivers, Orinoco, Amazon and La Plata, that discharge large amounts of freshwater and sediment into the Atlantic Ocean. The Amazon discharges about one-fifth of the world’s total freshwater runoff into the Atlantic (Curtin, 1986) and it is transported offshore up to 500 km seaward (Lentz, 1995). The heavy sediment discharge (2.9 · 108 tons year)-1) is not deposited over the outer shelf, but is carried by the North Brazil Current to Guyana’s shelf, where it forms extensive mud deposits (Gratiot et al., 2008). The continental shelf is wider along its West Coast, both in the north at the Amazon (≈300 km) and in southern Argentina, where it reaches up to 600 kilometres (Miloslavich et al., 2011). The shelf is narrower along the East Coast of the Atlantic and also along the east coast of Brazil, where riverine muds give way to calcareous deposits and the shelf in some areas reaches a minimum of 8 km width (Miloslavich et al., 2011).
The continental slope is cut by deep canyons connecting shelf and deep waters. High benthic richness was reported at the head of the submarine canyons, and about half of the species are shared with the shelf-break community (Bertolino et al., 2007; Schejter et al., 2014b). The ~7500 km of the Brazil coasts comprise a combination of freshwater, estuarine and marine ecosystems, with diverse but poorly known habitats in its northern part and with sandy beaches, mangrove forests, rocky shores, lagoons and coral reefs to the south (Miloslavich et al., 2011). Uruguay’s coasts are dominated by sandy beaches; a narrow rocky portion has high biodiversity (Calliari et al., 2003). The coasts of Argentina are mostly sandy beaches, with some rocky formations located mainly at Mar del Plata, Peninsula Valdes and Tierra del Fuego; pebble beaches are common in Patagonia. The coasts of South Africa are part sandy beaches, rocks and rocks mixed with sand on the upper shore and a wave-cut rocky platform (Bally et al., 1984).
Major benthic foraminiferal changes occurred in the late Eocene at Site 549. A Nuttallides truempyi-dominated assemblage was replaced by a buliminid assemblage (approx 40-38.5 m.y. ago); this change in faunal abundance was apparently a circum-Atlantic event. The buliminid assemblage was replaced, in turn, by an assemblage dominated by stratigraphically long-ranging and bathymetrically wide-ranging taxa just below the Eocene/Oligocene boundary (approx 37.5 m.y. ago). A series of late Eocene to earliest Oligocene first and last appearances of taxa accompanied these abundance changes. Benthic foraminiferal delta 18O increased approx 1.0per mille in the late Eocene to earliest Oligocene (approx 38-36.5 m.y. ago) at Site 549. Most (approx 0.7per mille) of this increase occurred simultaneously with a 0.6per mille increase in benthic foraminiferal delta 13C as a geologically rapid event in the earliest Oligocene (approx 36.5 m.y. ago). The major benthic foraminiferal abundance change (approx 40-38 m.y. ago) predates the major isotopic enrichments. A prominent seismic horizon, Reflector R4, has been noted in the Labrador Sea, Rockall, and Biscay regions, and has been dated as latest Eocene to early Oligocene. This horizon marks the onset of increased intensity of abyssal circulation associated with the initial entry of bottom water from the Norwegian-Greenland Sea and/or Arctic Ocean into the North Atlantic. The interval during which Reflector R4 was formed may encompass both the faunal and isotopic changes; the best estimate for the age of this horizon and the associated circulation change suggests that it correlates with the delta 18O increase. Our interpretation of these data suggests that a temperature drop, decrease in age (increased O2, lowered CO2, increased pH, hence decreased corrosiveness) of bottom water, and an increase in intensity of abyssal circulation occurred in the late Eocene to earliest Oligocene of the North Atlantic. -from Authors
Documents regionwide stratigraphic gaps in the Paleocene and middle Miocene. Episodes of carbonate dissolution also occurred during the Paleocene at several sites. Several oceanographic factors, not just simple sea-level change, probably interacted to produce these regional unconformities. Differences in the stratigraphic record from site to site across the continental slope result from 1) location in separate half-graben structures, 2) varying location across the developing margin, and 3) difference in position relative to the seaward edge of the enclosing half-graben.-from Authors
Sediment samples taken at close intervals across four major unconformities (middle Miocene/upper Miocene, lower Oligocene/upper Oligocene, lower Eocene/upper Eocene, lower Pale/upper Paleocene) at DSDP-IPOD Site 548, Goban Spur, reveal that coeval biostratigraphic gaps, sediment discontinuities, and seismic unconformities coincide with postulated low stands of sea level. Foraminiferal, lithic, and isotopic analyses demonstrate that environments began to shift prior to periods of marine erosion, and that sedimentation resumed in the form of turbidites derived from nearby upper-slope sources. The unconformities appear to have developed where a water-mass boundary intersected the continental slope, rhythmically crossing the drill site in concert with sea-level rise and fall. -Authors
We have assumed that at most passive margins, the shelfedge lies at (or even seaward of) the ocean-continent boundary. Under these conditions it is not likely that the shoreline can move out over the shelfedge because the driving subsidence at the shelfedge is greater than the rate at which sealevel may fall. We have also shown that if by chance the rate of sealevel fall is several times greater than the rate of subsidence at the shelfedge it may take several M yr to displace the shoreline seaward to the shelfedge. Alternatively, at a starved margin, the shelfedge may lie well landward of the ocean-continent boundary (well up toward the hinge zone). In this case, rate of subsidence may be much less than 1 cm/1000 yr and rate of sealevel fall may be much greater than rate of subsidence at the shelfedge. In this case the coastline may move seaward over the shelfedge, but this will still require a time interval of a M yr or greater. If sealevel drops sufficiently to allow the coastline to move seaward over the shelfedge and if at the same time sealevel ceases falling, then within a time interval of less than 2 M yr the combined effects of both erosion and subsidence will generally cause the coastline to retreat onto the shelf and transgress toward the hinge zone. -from Authors
A simple relation exists between depth and age for ocean floor created at aspreading center. The depth for about 60 percent of the deep oceans can becharacterized by this relationship; areas whose depth differs significantly are calledresidual depth anomalies. They can be separated into two types: aseismic ridges, whichare excess crustal loads created at or near a spreading center; and mid-ocean swells,which are thought to be surface manifestations of convection cells in the upper mantlebeneath the lithospheric plate. The past position and depth of both types of feature arediscussed.A simple method is introduced for computing the past depth of sediment recoveredin individual Deep Sea Drilling Project holes. The method can be used for sites on bothnormal ocean floor and aseismic ridges. It is accurate from the beginning of the Neogene(25 Ma) to better than 100 m for almost all sites. Four specific examples are discussed inthe text.Charts showing the ages of the ocean floor and the positions of the major plateboundaries and continents are constructed by combining a digitized version of thesea-floor magnetic isochrons with published rotation poles and angles. This reportincludes constructions for the present, the time of anomaly 5 (9 Ma), and the time ofanomaly 6 (20 Ma). Additional charts which include predicted ocean depths are constructedfor the present and for three selected ages in the Neogene (22,16, and 8 Ma).The predicted bathymetries are derived by combining the depth-age relation for normalocean floor, simple models for aseismic ridges, and individual analyses for mid-oceanswells. A comparison between the predicted and observed bathymetry for the present ispresented as evidence that the predicted contours lie within ± 400 m of the observed forabout 80 percent of the deep oceans. The marginal basins are excluded.The paleogeographic position of the continents and the paleodepth contours areevidence that:1) There was a shallow water passage path around Antarctica well prior to theNeogene.2) Just before or just after the onset of the Neogene a deep water passage may havedeveloped around Antarctica.3) The closure of the equatorial circulation system in the late Neogene was proba-bly complex, starting with the closure of northern Australia and South East Asia, thenAfrica and Eurasia and finally the formation of the isthmus of Panama.The opening and closing of these seaways are in the correct direction to produceeffects which may be responsible for the major climatic events in the Cenozoic. Theseinclude the cooling of the high latitudes in the Late Eocene, the formation of an Antarcticice sheet in the Middle Miocene and, finally, formation of Northern Hemisphere icesheets in the Pliocene.