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Statistics For Strontium Isotope Stratigraphy: A Robust Lowess Fit to the Marine Sr‐Isotope Curve For 0 to 206 Ma, With Look‐Up Table For Derivation of Numeric Age
Abstract
We provide a best-fit curve to 1849 strontium isotope data for the period 0 to 206 Ma using the LOcally-WEighted
regression Scatterplot Smoother (LOWESS) method. This is a robust, nonparametric modern regression technique.
Since it does not yield an explicit mathematical equation relating 87Sr/86Sr to time, a look-up table to determine
numeric age has been generated in steps of 1 x 10-6 in 87Sr/86Sr. The calibration uses the timescales of Shackleton
and coworkers for 0–7 Ma; Cande and Kent for 7–72 Ma; Obradovich for 72–95 Ma and Gradstein and coworkers for
>95 Ma. The look-up table includes 95% confidence intervals on the predictions of numeric age. When using this
table, the uncertainty on the 87Sr/86Sr of the sample whose age is sought must be added to that inherent in the LOWESS
regression. We show how to determine the uncertainty in 87Sr/86, i.e., how best to obtain the 95% confidence bounds
on a single measurement of 87Sr/86 for a sample, and on the mean 87Sr/86 value for 2 or more replicate measurements
of 87Sr/86 in the sample; these confidence intervals reflect analytical-system reproducibility for routine samples (as
opposed to that of standard control materials, e.g., NIST 987) and are necessary to establish the final upper and lower
bounds on predicted numeric age.
... Thus, 87 Sr/ 86 Sr values in unaltered fossil carbonate skeletons reflect the 87 Sr/ 86 Sr isotopic composition of seawater at the time of precipitation. Since ~37 Ma, the 87 Sr/ 86 Sr isotopic composition of seawater has become increasingly radiogenic (Howarth and McArthur, 1997;McArthur et al., 2001McArthur et al., , 2012McArthur et al., , 2020. ...
... Only specimens that were 99-100% aragonite were selected for analysis. Because of the small changes in 87 Sr/ 86 Sr values over the course of the Quaternary (Howarth and McArthur, 1997;McArthur et al., 2020), analyses consisted of: (1) multiple shells (two to five individuals) from each locality; ...
... .gov/m-srmors/certificates/987.pdf) was used as a reference 87 Sr/ 86 Sr standard, with at least two samples of this standard in each barrel. Age estimates were made for each shell analyzed using the calibrated 87 Sr/ 86 Sr values of Howarth and McArthur (1997) and McArthur et al. (2001McArthur et al. ( , 2020, LOWESS Version 6. Numerous studies, summarized by Schneider et al. (2009), have shown that in addition to determination of primary mineralogy by XRD, there are chemical criteria useful in ascertaining the reliability of Sr isotopes in geochronology. The concentrations of certain trace elements found in marine carbonate shells (Mg, Sr, Ba) can be useful measures of whether there have been diagenetic alterations (usually element loss) of the original skeletal compositions. ...
Studies of marine terraces and their fossils can yield important information about sea level history, tectonic uplift rates, and paleozoogeography, but some aspects of terrace history, particularly with regard to their fossil record, are not clearly understood. Marine terraces are well preserved on Santa Rosa Island, California, and the island is situated near a major marine faunal boundary. Two prominent low-elevation terraces record the ~80 ka (marine isotope state [MIS] 5a) and ~ 120 ka (MIS 5e) high-sea stands, based on U-series dating of fossil corals and aminostratigraphic correlation to dated localities elsewhere in California and Baja California. Low uplift rates are implied by an interpretation of these ages, along with their elevations. The fossil assemblage from the ~120 ka (2nd) terrace contains a number of northern, cool-water species, along with several southern, warm-water species, a classic example of what has been called a thermally anomalous fauna. Low uplift rates in the late Pleistocene, combined with glacial isostatic adjustment (GIA) processes, could have resulted in reoccupation of the ~120 ka (MIS 5e), 2nd terrace during the ~100 ka (MIS 5c) high-sea stand, explaining the mix of warm-water (~120 ka?) and cool-water (~100 ka?) fossils in the terrace deposits. In addition, however, sea surface temperature (SST) variability during MIS 5e may have been a contributing factor, given that Santa Rosa Island is bathed at times by the cold California Current with its upwelling and at other times is subject to El Niño warm waters, evident in the Holocene SST record. Study of an older, high-elevation marine terrace on the western part of Santa Rosa Island shows more obvious evidence of fossil mixing. Strontium isotope ages span a large range, from ~2.3 Ma to ~0.91 Ma. These analyses indicate an age range of ~500 ka at one locality and ~ 600 ka at another locality, interpreted to be due to terrace reoccupation and fossil reworking. Consideration of elevations and ages here also yield low, long-term uplift rates, which in part explains the potential for terrace reoccupation in the early Pleistocene. In addition, however, early Pleistocene glacial-interglacial cycles were of much shorter duration, linked to the ~41 ka obliquity cycle of orbital forcing, a factor that would also enhance terrace reoccupation in regions of low uplift rate. It is likely that other Pacific Coast marine terrace localities of early Pleistocene age, in areas with low uplift rates, also have evidence of fossil mixing from these processes, an hypothesis that can be tested in future studies.
... Previous studies of the Lower Jurassic evolution of 87 Sr/ 86 Sr ratios from various macrofossils (e.g. belemnites, brachiopods and oysters) largely centred around outcropping strata of the Laurasian Seaway and westernmost Tethys (Jones et al., 1994;Howarth & McArthur, 1997;McArthur et al., 2000McArthur et al., , 2019Jenkyns et al., 2002;Woodfine et al., 2008;Comas-Rengifo et al., 2010;Armendáriz et al., 2012;Metodiev et al., 2014;Val et al., 2017;Rosales et al., 2018). These studies revealed a broadly troughshaped pattern, with 87 Sr/ 86 Sr ratios decreasing throughout the Hettangian, Sinemurian and Pliensbachian Stages from ~0.70775 to ~0.70705 and increasing throughout the Toarcian, with the inflection point near the Pliensbachian-Toarcian boundary. ...
... The marine 87 Sr/ 86 Sr curve is constructed by a statistical fit through 87 Sr/ 86 Sr ratios measured from well preserved fossils whose age is independently known at high precision (Howarth and McArthur, 1997;McArthur et al., 2001McArthur et al., ,2012 (Metodiev et al., 2014), as well as Germany (Parkinson, 1994;Jenkyns et al., 2002). Some further information from outside Europe supporting the global trends comes from the Queen Charlotte Islands, Canada . ...
... Regarding the weighting of individual techniques these methods fall between the extremes of treating every single datum as a true reflection of the marine 87 Sr/ 86 Sr ratio at one end, and statistical fits to a larger dataset smoothing out high frequency variability on the other. The former approach is often chosen where limited data are available whereas the latter has been adopted to generate the widely used look-up chart for the Phanerozoic marine 87 Sr/ 86 Sr trend (Howarth and McArthur, 1997;McArthur et al., 2001McArthur et al., , 2012. Both approaches and hybrids between them generate conceptual issues. ...
87Sr/86Sr ratios have been frequently used for correlating marine sedimentary units and its fossils, especially where high fidelity reference curves exist. The latter are usually constructed from macrofossil calcite samples which have been screened for post-depositional alteration. Here, belemnite rostra from Lower Jurassic (Upper Sinemurian–Upper Toarcian) siliciclastic and carbonate sediments of the Swabo-Franconian Basin, deposited at mid-latitudes in the Laurasian Seaway, were targeted to confirm the trends and absolute values of the marine 87Sr/86Sr reference curve throughout this interval.
87Sr/86Sr ratios are derived from 21 belemnite rostra from a wider set of fossil specimens for which preservation was controlled using Scanning Electron Microscopy (SEM) and element/Ca ratios. Taken together with published data, a compilation of >500 87Sr/86Sr datapoints is established that helps verifying the global significance of the reported trends and allows for the best-constrained reconstruction of marine 87Sr/86Sr across the late Sinemurian-Toarcian interval yet. The obtained results are in excellent agreement with earlier measurements from basins in Portugal, Spain, UK, Germany, and Bulgaria and Canada. 87Sr/86Sr ratios follow the well-known decreasing trend, from 0.70747 in the latest Sinemurian to lowest ratios of 0.70708 around the Pliensbachian–Toarcian boundary. Also the subsequent increase throughout the early Toarcian reaching values of >0.7072 in the early Late Toarcian is found to match previously established datasets.
The new results further corroborate a link between marine 87Sr/86Sr ratios and rifting related to the Central Atlantic Magmatic Province throughout the Early Jurassic and increased radiogenic influx, possibly linked to Karoo-Ferrar volcanism and associated climate change in the Early Toarcian which would have likely caused a weathering pulse. The very good agreement in trends and absolute values suggests that macrofossils tapped into an isotopically uniform Sr pool across the Laurasian Seaway even during phases of severe basinal restriction.
... Table 11. Such values are within the expected range for the Middle Jurassic (Jones et al., 1994;Howarth and McArthur, 1997;McArthur et al., 2000McArthur et al., , 2012Jenkyns et al., 2002;Wierzbowski et al., 2012Wierzbowski et al., , 2017Ullmann et al., 2013a). Chapter 5: Sample Preservation ...
... The 87 Sr/ 86 Sr ratio of seawater is uniform throughout the oceans because of the residence time of strontium which is much longer than the mixing time of seawater (DePaolo and Ingram, 1985;Elderfield, 1986;Veizer, 1989;McArthur, 1994;Jones and Jenkyns, 2001). The seawater 87 Sr/ 86 Sr can be recorded in well-preserved marine carbonates and phosphates and may be used for dating sedimentary rocks based on previously reconstructed seawater strontium isotope curves for the Jurassic (e.g., Jones et al., 1994;Howarth and McArthur, 1997;Jenkyns et al., 2002;McArthur, 1994;McArthur et al., 2001McArthur et al., , 2004McArthur et al., , 2012Wierzbowski et al., 2012Wierzbowski et al., , 2017. Strontium uniformity makes it possible, in some instances, to date and correlate geographically distant sedimentary sequences without involving biostratigraphic and radioisotopic data (e.g., Kuznetov et al., 2018). ...
... Using the full look-up table for the marine Sr-isotope curve for the last 206 million years (Howarth and McArthur, 1997) 1. the slope of the curve of 87 Sr/ 87 Sr against numeric age; ...
Here, I have investigated the stable isotope (δ13C, δ18O) and elemental
composition (Mg/Ca, Sr/Ca, Fe/Ca, Mn/Ca) of Jurassic belemnites from Cabo Mondego in Portugal (Bajocian-Bathonian) and Albstadt-Pfeffingen in southern Germany (Bathonian Callovian). Both localities are stratigraphically significant, with Cabo Mondego representing the Auxiliary Stratotype Section and Point (ASSP) for the Bathonian Stage and Albstadt-Pfeffingen being a potential Global
Stratotype Section and Point (GSSP) for the Callovian Stage.
Variations in the stable carbon-isotope ratios of macrofossil calcite can
reflect changes in fluxes between reservoirs in the palaeo carbon cycle. Cabo Mondego is an important site to link changes in stable isotope ratios directly to ammonite zones and subzones, and thereby allow chronostratigraphic
calibration. An abrupt positive δ13C isotope shift is observed in the belemnite stable isotope record from the bomfordi Subzone below the Bajocian-Bathonian boundary. The δ13C shift appears not to have been caused by temperature changes as δ
18O ratios remain stable throughout the studied section, nor is there a change in the δ13C values of coeval brachiopods. One possible cause of this shift in carbon-isotope ratios is a faunal turnover. Faunal turnovers of ammonites and belemnites are observed elsewhere in Europe within the bomfordi Subzone.
The potential of the Jurassic section at Albstadt-Pfeffingen (Baden-Württemberg, Germany) to become a GSSP, an internationally agreed reference point which defines the lower boundary of a stage on the geologic timescale, for the base of the Middle Jurassic Callovian Stage, makes detailed investigations, especially regarding the completeness of the strata, important. The ammonite
assemblages of this section have already been studied in detail, but few
chemostratigraphic data from the Bathonian and Lower Callovian fossils of the site have been published. Belemnite rostra are relatively abundant in the section and have undergone little diagenetic alteration according to chemical and optical screening techniques, making them a suitable target for isotopic analysis.
Chemostratigraphic signals in the rostra across the Bathonian-Callovian
boundary show comparatively little change in δ13C values, but a gradual decrease in δ18O may indicate a warming trend into the Callovian. Notably, a distinct step-change in 87Sr/86Sr ratios across the stage boundary suggests an unconformity,
or at least strongly condensed part of the section, confirming strong doubts on the site's suitability as a GSSP.
... 3.1.3. Strontium isotope stratigraphy Strontium isotopes can be utilized for assessing ages of fossil carbonate marine organisms in sediments because the Sr isotopic composition of seawater varies over geologic time (Howarth and McArthur, 1997;McArthur et al., 2001McArthur et al., , 2020. Marine organisms that precipitate Sr (which substitutes for Ca in CaCO 3 , whether aragonite or high-Mg calcite) in their skeletons do so without measurable fractionation of Sr isotopes. ...
... Thus, 87 Sr/ 86 Sr values in unaltered fossil carbonate skeletons reflect the 87 Sr/ 86 Sr isotopic composition of seawater at the time of precipitation. Since~37 Ma, the 87 Sr/ 86 Sr isotopic composition of seawater has been increasingly radiogenic, i.e., there has been a steady increase in the 87 Sr/ 86 Sr value, albeit at different rates in different time intervals (Howarth and McArthur, 1997;McArthur et al., 2001). ...
... The results, while uncertain for ages of specific units, do indicate that the entire sequence is likely of Pleistocene age, and some units could certainly date back to the early or middle Pleistocene. Given the ranges of measurements from each depth interval, the instrumental analytical uncertainties for each analysis, and the uncertainties in the Sr isotope calibration curve (Howarth and McArthur, 1997;McArthur et al., 2001McArthur et al., , 2020, all that can be said with certainty is that the aeolian sediment packages likely have an average age range that could span an interval from~950 ka to~400 ka. ...
Africa is the most important source of dust in the world today and dust storms from that continent frequently deposit sediment on the nearby Canary Islands. Many investigators have inferred African dust inputs to Canary Islands paleosols based only on the presence of quartz. However, some local rocks do contain this mineral, so quartz alone is insufficient proof of dust deposition. Further, it is not known whether the Sahara Desert or the Sahel region is more important as a dust source. We address these issues by study of sequences of Pleistocene aeolian sands on the islands of Lanzarote and Fuerteventura. Aeolian sands are composed mostly of marine carbonate minerals and locally derived volcanic minerals. They date from the early-middle Pleistocene to the Holocene. Trace element geochemistry shows that the soils formed from both locally derived basalt and African dust. Major element geochemistry and clay mineralogy indicate that dust additions to the Canary Islands likely come from both the Sahara and Sahel. Dust delivered from the Sahel indicates that droughts in that region have had a history extending through much of the Quaternary. Accretionary-inflationary profile development, from dust accretion, is evident in the upward growth of Canary Islands paleosols.
... Thus, 87 Sr/ 86 Sr values in unaltered fossil carbonate skeletons reflect the 87 Sr/ 86 Sr isotopic composition of seawater at the time of precipitation. Since~37 Ma, the 87 Sr/ 86 Sr isotopic composition of seawater has become increasingly radiogenic (Howarth and McArthur, 1997;McArthur et al., 2001McArthur et al., , 2012McArthur et al., , 2020. ...
... D.R. Muhs, R.R. Schumann, L.T. Groves et al. Geomorphology 389 (2021) 107826 Because of the small changes in 87 Sr/ 86 Sr values over the course of the Quaternary (Howarth and McArthur, 1997;McArthur et al., 2020), we analyzed (1) shells from four localities on the same terrace; ...
... was used as a reference 87 Sr/ 86 Sr standard, with at least two samples of this standard in each barrel. Age estimates were for each shell analyzed using the calibrated 87 Sr/ 86 Sr values of Howarth and McArthur (1997) and McArthur et al. (2001McArthur et al. ( , 2020, LOWESS Version 6. ...
Glacial isostatic adjustment (GIA) models hypothesize that along coastal California, last interglacial (LIG, broadly from ~130 to ~115 ka) sea level could have been as high as +12 m to +14 m, relative to present, substantially higher than the commonly estimated elevation of +6 m. Areas with low uplift rates can test whether such models are valid. Marine terraces on Santa Cruz Island have previously been reported to occur at low (<10 m) elevations, but ages of many such localities are not known. Using lidar imagery as a base, marine terraces on Santa Cruz Island were newly mapped, elevations were measured, fossils were collected for U-series dating (corals), strontium isotope compositions and amino acid geochronology (mollusks), and paleozoogeography (all taxa). Sr isotope compositions of mollusks from the highest of three marine terraces give ages of ~2.5 Ma to 1.9 Ma, along with Pliocene ages, from shells interpreted to be reworked. U-series ages of corals from the western part of the island indicate that low-elevation terraces north of the Santa Cruz Island fault correlate to the LIG. Where corals are lacking, amino acid ratios and faunal aspects support terrace correlation to the LIG high stand of sea. Elevations of most terrace localities north of the east-west trending Santa Cruz Island fault, in both the western and eastern parts of the island, range from 5.75 m to 8 m above sea level, well below the modeled paleo-sea-level range. Subsidence is ruled out as a mechanism for explaining the lower-than-modeled elevations, because higher-elevation terraces are present along much of the Santa Cruz Island coast north of the fault, indicating long-term tectonic uplift. The low elevations of the LIG terrace fragments are, however, consistent with a low rate of uplift derived from the higher, ~2.5-1.9 Ma terrace. A number of other localities on the Pacific Coast, also dated to the LIG, have marine terrace elevations below the modeled level. GIA models may have overestimated last interglacial sea level by a substantial amount and need to be revised if used for forecasts for future sea-level rise.
... The interception between the 87 Sr/ 86 Sr ratios of the analyzed samples and mixing curves defines seawater content and paleosalinity estimates. Freshwater and oligohaline-water salinity curves (0.5 and 5 psu) were calculated utilizing the previous binary-mixing models and calibrated with a seawater salinity curve (Howarth and McArthur, 1997). ...
... These samples present less negative δ 13 C and δ 18 O values, closer to those of the North Atlantic seawater range ( Fig. 4A; Table S2). (Howarth and McArthur, 1997), and present-day rivers (Palmer and Edmond, 1992) used by Vonhof et al. (1998Vonhof et al. ( , 2003 (left side). Same data from Santos et al. (2014) with cratonic freshwater and catchments data contribution from Allègre et al. (1996) (right side). ...
... For the Early Miocene Eastern Amazonian samples (Pirabas Formation, Marajó Basin and Belém area), a binary mixture between seawater and cratonic rivers is the most probable scenario since the deposition of Dashed blue (Andean water) and red (cratonic water) curves were calibrated based on the Miocene marine 87 Sr/ 86 Sr reference solid black curve (Howarth and McArthur, 1997) and the paleosalinity calculations respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) ...
Several studies have reported Miocene shallow-marine incursions in the Pebas Megawetland system (Western Amazonia) based on paleontological and sedimentological evidence. Only a few publications restricted to Middle and Late Miocene fossils outcropping in the Iquitos (Peru), Benjamin Constant and Eirunepé (Brazil) areas have provided isotopic evidence to test these incursions. In this study, we present new carbon, oxygen, and strontium (⁸⁷Sr/⁸⁶Sr ratios) isotopic data of macrofossils (pacu and ray teeth, crab claws and oysters), and microfossils (ostracods and foraminifera) from reported lower to lower upper Miocene sedimentary rocks of Western and Eastern Amazonian (Peru and Brazil), mainly from shallow-marine deposits. It was also analyzed present-day organisms from distinct environments (beach, sea, riverine, and estuary) and compared these results with Miocene fossils. While C and O isotopic compositions indicate that Western Amazonia fossils display an isotopic composition similar to the present-day continental, limnic and riverine, environments (−17‰ to −5.61‰ for δ¹³C and − 10.14‰ to −1.92‰ for δ¹⁸O), Eastern Amazonia fossils display C and O isotopic compositions comparable to those from seawater environments (−2.53‰ to −0.72‰ for δ¹³C and − 4.85‰ to −1.76‰ for δ¹⁸O). We further used the ⁸⁷Sr/⁸⁶Sr isotopic composition of the fossils to estimate paleosalinity conditions. The ⁸⁷Sr/⁸⁶Sr isotopic compositions indicates that Eastern Amazonian water bodies of the Pirabas Formation (Marajó Basin) varied from mesohaline to marine conditions. In contrast, Early Miocene Western Amazonian water bodies of the Pebas Megawetland System (PMWS) are characterized by freshwater conditions. Nonetheless, in Middle and Early Late Miocene, oligohaline conditions are found in the Peruvian part of the PMWS. Paleosalinity estimates of the Brazilian part of the PMWS are less constrained and might indicate a salinity range between freshwater or oligohaline conditions. Our isotopic data suggest the PMWS was occasionally submitted to oligohaline conditions during Middle and Early Late Miocene shallow-marine incursions. We suggest that Miocene shallow-marine incursions in Western Amazonia at this time were characterized by transitional paleoenvironments, reconciling isotopic, sedimentological and paleontological evidences.
... Dating Pliocene and especially Pleistocene sediments by means of Sr isotope stratigraphy has proved more difficult. The Sr isotope curves of Howarth & McArthur (1997, 2004 for the Pliocene and Pleistocene have in general lower gradients than the Oligocene and Miocene parts (Fig. 2). Small errors in the 87 Sr/ 86 Sr isotopic composition due to possible minor impurities in the calcareous tests, re-crystallisation of the tests, errors introduced during sample preparation and the mass spectroscopy analysis process, etc., have a much larger impact when calculating ages from low-gradient parts of the Sr isotope curves than from high-gradient parts (Eidvin et al., 2014). ...
... The parts of the curve for the Pleistocene which give ages of 2.75 to 1.6 Ma and 1.05 Ma to recent are somewhat steeper, and the part which gives ages between 1.6 and 1.05 Ma is the steepest part of the Sr isotope curve for the Pleistocene and consequently, theoretically, should provide the most reliable Pleistocene ages (Fig. 2). Howarth & McArthur (1997), which is based on the time-scale of Berggren et al. (1995) with the Pliocene/Pleistocene boundary at 1.85 Ma. However, we have used a Pliocene/Pleistocene boundary at 2.588 Ma according to the new time-scale of Cohen et al. (2013). ...
... As mentioned above, the 87 Sr/ 86 Sr ratios were converted to age estimates using the SIS look-up table of Howarth & McArthur (1997;2004; Tables 1-3 and 7-9). The look-up table of Howarth & McArthur (1997) is based on the time-scale of Berggren et al. (1995) and the look-up table of Howarth & McArthur (2004) is based on the time-scale of Gradstein et al. (2004). ...
Strontium (Sr) isotope data from cores and ditch-cutting samples from hydrocarbon wells from Pleistocene sediments from four areas on the Norwegian continental shelf have been compared with previously published biostratigraphic, lithostratigraphic, seismic and new micropaleontological and palynological data. The aim for this paper is also to provide a review of previous investigations of the use of Sr analysis on this margin, and to give a new assessment of some of the well samples by re-analysing these data and discuss the main limitations of the use of Sr isotopes to date Pleistocene sediments. It is important to obtain accurate dating of the Pleistocene sediments in order to constrain the age of glacial events, indicate the age of neotectonic periods and perform basin modelling. However, obtaining a good chronostratigraphy of the thick Pleistocene successions has proved to be very difficult. Since the sediments have been deposited
during a relatively short time, there are few recorded fossil events as first and last appearance datums. Sr isotope stratigraphy based on analyses of calcareous mollusc and microfossil tests (foraminifera and Bolboforma) have proven an effective dating method particularly for Oligocene and Miocene sections on the Norwegian continental shelf. Dating Pliocene and especially Pleistocene sediments by means of Sr isotope stratigraphy has proved more difficult. The Sr isotope curves for the Pliocene to Pleistocene, in general, have lower gradients than the Oligocene and the Miocene parts, and small errors in the 87Sr/86Sr isotopic composition have a much larger impact when calculating ages from low-gradient parts of the Sr isotope seawater curves than from high-gradient parts. In addition, possible error sources comprise reworked fossil tests since a large portion of the marine Pleistocene deposits on the Norwegian continental
shelf consists of redeposited older sediments originally deposited closer to the coast. These factors are probably the main reasons why the Sr isotope analyses of the investigated Pleistocene sections, with some exceptions, have not yielded very reliable ages.
... Some of the data have low radiogenic Pb and anchor the extrapolation to a lower intercept Concordia date with a relatively high radiogenic Pb content, but the small-scale isochron yields a realistic intercept age. Figure 6. Regional ammonite biostratigraphic correlation from Western North America, Northwest Europe, Andes, and Mediterranean [62,63], and absolute U-Pb age data [64,65] during the early Toarcian. ...
... Figure 6. Regional ammonite biostratigraphic correlation from Western North America, Northwest Europe, Andes, and Mediterranean [62,63], and absolute U-Pb age data [64,65] during the early Toarcian. ...
The Bilong Co oil shale is one of the most significant source rocks in the Mesozoic Qiangtang Basin (Northern Tibet); however, its absolute chronology remains controversial. In this study, in situ carbonate U-Pb isotope dating analysis was carried out for the first time. Detailed field geological investigations yielded some age-diagnostic ammonites, enabling a re-evaluation of the stratigraphic age of the Bilong Co oil shale. A total of 61 spots of U-Pb isotope dating from the middle part of the Bilong Co oil shale section suggests an average age of 181 ± 13 Ma. Elemental geochemistry and diagenetic analysis indicate that the proposed age represents the early deposition of the calcite, and the oil shale was deposited during the Early Jurassic time. This estimated age is further supported by the newly discovered ammonite assemblage of Hildoceratidae-Tiltoniceras sp. at the top part of the oil shale section, which confirms the deposition of the oil shale during the Toarcian age of the late Early Jurassic. Consequently, the Bilong Co oil shale can be assigned to the Quse Formation, which is attributed to the Lower Jurassic rather than the Middle Jurassic. The re-assessment of the stratigraphic age of the Bilong Co oil shale is of great significance for regional evaluation and exploration activities of hydrocarbon source rock layers in the Qiangtang Basin as well as for global stratigraphic correlation of the late Early Jurassic Toarcian oceanic anoxic event.
... In Core GS-2, the 87 Sr/ 86 Sr ratios vary between the minimum of 0.707321 ± 32 × 10 -6 and the maximum of 0.707805 ± 34 × 10 -6 ( Table Version 4: 08/ 03) 50,51 . The 87 Sr/ 86 Sr ratios of the studied intervals mostly fall between these end-members, except for those associated with the disconformities (Fig. 1). ...
... To understand the duration of hiatuses associated with disconformities, the Rb-corrected 87 Sr/ 86 Sr of reliable samples bracketing the desired disconformity are converted to the ages according to the Look-Up Table (Version 4: 08/ 03) (Fig. 7) 50,51 . Their derived numerical ages result in a duration time for the hiatus (Timespan A). ...
The mutual interplays between plate tectonic processes, orogenesis and continental uplift, high-flux magmatism, and high sedimentation rates can affect the geochemical signatures and composition of marine sediments. Here, we examine two major disconformities, the Cenomanian–Turonian boundary (CT-ES) and the middle Turonian (mT-ES) exposure surfaces, from the Upper Cretaceous sedimentary successions of the southeastern Neo-Tethys Ocean in the Zagros Basin (Iran). The disconformities are expressed as distinct positive peaks in rubidium (Rb) contents and 87Sr/86Sr isotopic ratios of carbonates. The 87Sr/86Sr values of samples bracketing the disconformities in seven well cores give average age ranges of 94.4–93.6 Ma for the CT-ES and 91–86 Ma for the mT-ES. These ages fall in the timespan of forearc/ophiolite formation through subduction initiation in the Neo-Tethys realm (southern margin of Eurasia), high convergence velocities between Arabia and Eurasia, and blueschist exhumation. All these processes involved buckling of the Neo-Tethyan lithosphere, initiating the Neo-Tethys closure and a high erosion rate on the Eurasian margin. The first two mechanisms exerted considerable compressional forces on the adjacent carbonate platforms, reactivated basement faults, and led to the uplift and erosion of the Arabian Plate, which provided the high contents of Rb and the high 87Sr/86Sr ratios in the carbonates.
... Une première courbe est proposée en 1997 par Howarth et McArthur (1997) pour illustrer l'évolution des rapports 87 Sr/ 86 Sr en fonction du temps (en Ma). Ce travail de compilation des rapports 87 Sr/ 86 Sr est lissé via une méthode de régression statistique non paramétrique appelée ''LOWESS'' (LOcally WEighted Scatterplot Smoother). ...
... Ce travail de compilation des rapports 87 Sr/ 86 Sr est lissé via une méthode de régression statistique non paramétrique appelée ''LOWESS'' (LOcally WEighted Scatterplot Smoother). Le traitement statistique établi par Howarth et McArthur (1997) offre une courbe sans vide qui couvre l'entièreté du Phanérozoïque de sorte que pour un rapport 87 Sr/ 86 Sr donné il y a toujours un âge correspondant. L'intervalle de confiance à 95% est un avantage considérable pour la fiabilité des datations effectuées sur la base de cette courbe. ...
Dans cette dernière décennie, des découvertes pétrolières importantes ont été faites au large du Liban dans les eaux est-méditerranéennes. Des études géologiques nombreuses en offshore (bassin du Levant) avec des acquisitions sismiques (2D et 3D) ont révélé des réservoirs d'hydrocarbures d'âge Miocène et suggèrent des perspectives prometteuses pour l'exploration. Par ailleurs, des modélisations de systèmes pétroliers à l'échelle de toute la région ont été réalisées, et montrent que les formations du Trias-Jurassique sont des roches-mères potentielles entrées à maturité thermique grâce à un fort contrôle tectonique à certaines périodes. Si celles-ci ont été très étudiées dans le Moyen Orient (Syrie, Jordanie, …) et ont permis de mettre en évidence leur potentialité pétrolière, la zone onshore libanaise a été quant à elle peu étudiée. L'approche stratigraphique complète et l'analyse du bassin sédimentaire onshore libanais font encore défaut sur certains aspects, ne permettant pas encore de définir parfaitement le rôle de la tectonique sur la géométrie, la nature et le calendrier des évènements sédimentaires et diagénétiques. Cette thèse a ainsi pour objectif de caractériser la géométrie des dépôts sédimentaires du bassin onshore et d'expliciter le contrôle tectonique sur son enregistrement stratigraphique. Un ensemble de données géologiques issues de la littérature sur la région (calages profondeurs, stratigraphie, etc.) est synthétisé dans un modeleur géologique 3D (SKUA-GoCad®). A partir de ces données géo-modelées, une approche interprétative permet de visualiser : i) les dépôts sédimentaires du bassin libanais ; ii) les structures tectoniques majeures le contrôlant ; iii) les surfaces d'érosion majeures et iv) les pièges pétroliers potentiels. Cette approche permet ensuite de générer des courbes de subsidence tectonique du bassin sédimentaire dans l'onshore libanais et une partie de l'offshore (sous PetroMod®) et de les interpréter. L'ensemble des résultats décrit les relations entre sédimentation et évolution tectonique à l'échelle régionale du Liban, de définir les failles majeures contrôlant l'enregistrement sédimentaire, d'identifier certaines phases clés dans l'évolution géodynamique et donc de retracer l'histoire tectonique du pays. D'une échelle régionale à une échelle plus locale, cette thèse se focalise sur une famille de failles ayant un rôle de contrôle sur l'enregistrement sédimentaire, en étudiant l'une d'entre-elles dans la région de Nahr Ibrahim. Ce travail se concentre sur la période initiale du Mésozoïque (Jurassique) présent sur le territoire libanais et d'un système structural peu étudié qui l'affecte : le système de failles normales mésozoïques NE-SO réactivées lors de la structuration du système de failles du Levant. Afin de caractériser le contrôle tectonique de ces failles sur la sédimentation (géométrie et diagenèse), une étude de terrain a été réalisée dans cette région, avec une approche sédimentaire, géochimique et diagénétique. Ainsi, trois coupes stratigraphiques dans la formation de Kesrouane (Jurassique) sont présentées. Une étude des faciès et de la diagenèse permet d'identifier les variations d'environnements, puis les principales phases diagénétiques qu'a subi cette formation jurassique. Par une approche chimio-stratigraphique (isotopes du strontium notamment), un calage par des âges absolus est proposé qui permet de corréler les coupes stratigraphiques et de mettre en évidence un rejet vertical de la faille régionale de Nahr Ibrahim de l'ordre de 800 m. Les résultats permettent de mettre en évidence le rôle important de ces failles sur le contrôle de la sédimentation jurassique, la structuration géométrique des formations mésozoïques et leur rôle potentiel joué sur la diagenèse. Aussi, cette approche locale a permis de revenir sur le modèle 3D régional et de l'améliorer en prenant en considération le rôle majeur de ces failles NE-SO réactivées (rejets de 800m) affectant la stratigraphie.
... This agrees with the fact that the samples from the terraces T6 are probably already too old to be dated by 230 Th/ 238 U chronology. is a relative dating technique applicable to coral samples (Figure 3-15). The principle is based on the analysis of the 87 Sr/ 86 Sr ratio within marine samples, to be compared to a calibrated curve (McArthur, 1994;Howarth and Mcarthur, 1997) in order to get the relative age of the sample analyzed (Figure 3-16). In fact, unlike of Sr, Rb in very poorly incorporated within coral skeletons. ...
... (C) Evolution curve of the 87 Sr/ 86 Sr ratio over the last 4 My. Extracted fromHowarth and Mcarthur (1997). ...
The Levant Fault, also known as the Dead Sea Fault, is a left-lateral strike-slip fault of about 1200 km long. It extends from north to south, from the Taurus Mountains and the East Anatolian Fault system, to the northern termination of the extensive Red Sea system. The sinistral activity of the Levant Fault, linked to the north- ward displacement of the Arabian Plate relative to the Sinai sub-plate, is now well constrained with a displacement of ∼ 5mm/yr and nearly 107 km of cumulative dis- placement over 20 My. However, the vertical component of this large fault system is still poorly defined. Based on the study of tectonic activity markers in the Gulf of Aqaba and the Strait of Tiran region, this work consists in constraining the archi- tecture of the fault system in its southern termination. Using new high-resolution multibeam bathymetric data collected during two marine campaigns, we have thus defined a new fault model in the Gulf of Aqaba. The uplift of coral terraces to nearly 100 m above the mean sea level in the Gulf of Aqaba and up to 500 m on the Tiran island, reflects a significant vertical motion over the last few million years. The corals collected on these surfaces during a field trip in March 2017, and analyzed by Uranium-Thorium dating and Strontium isotopy, reveal an establishment of these coral terraces during the interglacial periods. These levels thus serve as temporal markers to constrain the vertical uplift generated by the faults. The precise location of the coral terraces, determined using Pleiades satellite images, allows us to under- stand how the tectonic activity is structured in the Gulf of Aqaba and the Strait of Tiran areas. By correcting the current elevation of the terraces with the eustatic data available in the literature, and by knowing precisely their ages of formation, we deduced the uplift rates of the eastern coast of the Gulf of Aqaba and along the Tiran island. The uplift along the Gulf of Aqaba, estimated using the coral terraces, does not agree with the long-term uplift determined by thermochronology. Further analyses suggest that this uplift is distributed over the off-shore active structures, but also along the on-land structures which were previously considered inactive. This reactivation is due to the change in position of the Arabia-Sinai rotation pole there is 5 My ago. The conclusions of this work raises new questions as to how the de- formation is distributed along this fault section before the change in position of the rotation pole, and how the system is connected to the triple junction Red Sea - Gulf of Suez - Gulf of Aqaba. Is the basin south of the Tiran island is the last pull-apart basin before connecting to the extensive system, or do additional steps, now masked by large evaporite deposits in the Red Sea, propagate further south before connecting to the extensive system?
... Strontium isotope stratigraphy is used as an additional control for the biostratigraphic correlations. The method has best resolution for sediments older than 15 Ma (Howard and McArthur, 1997McArthur, , 2004. For samples with ages younger than 8 Ma, the Sr isotope ages have to be treated with more caution. ...
... For samples with ages younger than 8 Ma, the Sr isotope ages have to be treated with more caution. This is due to less variation in the Sr isotopic composition and a relatively flat curve especially between 4.6 and 2.75 Ma, but also to some extent between 8 and 6 Ma (Howard and McArthur, 1997McArthur, , 2004. ...
... The obtained 87 Sr/ 86 /Sr ratios were converted to numerical ages (Tab. 1) based on the works by Howarth and McArthur (1997), McArthur et al. (2001), andMcArthur et al. (2012), and using the Look-Up Table Version 3:10 / 99. 87 Sr/ 86 Sr ratios obtained in four portions of shell A go from 0.708869 to 0.708822. ...
... Since the mentioned sediments reach the Lavre region, located about 80 km far from the present coastline, they are related to one of the broadest transgressions that affected the basin. Notes: Sr isotope ratios were converted to numerical ages based on the works by Howarth and McArthur (1997), McArthur et al. (2001) and McArthur et al. (2012) and using the Look-Up Table Version ...
The Lower Tagus Basin was subjected to several marine transgressions along the Neogene, related to positive eustatic oscillations and also controlled by the regional tectonic activity. In the Alcácer do Sal-Sines region, previous studies identified an episode of marine sedimentation interpreted as having occurred during the late Serravalian to early Tortonian interval, based on biostratigraphic data. This episode is represented in the Alcácer do Sal Formation. The study of the SMS-12-01B borehole, drilled for mineral prospection purposes, located about 10 km NNE of Melides, allowed the identification of a 3 m thick layer of sediments containing marine fossils. 87 Sr/ 86 Sr determinations of oyster shells point to deposition about 11.5 Ma ago, validating previous proposals for the age of the formation. These data correspond to the first numerical ages obtained for the Alcácer do Sal Formation, allowing a solid correlation with other known marine units in the Lower Tagus and Algarve basins related to the same transgression episode.
... The standard results are consistent with published values and the long-term average values for the laboratory. The Sr Stratigraphy Age Dates were determined from the measured 87 Sr/ 86 Sr isotope ratios by reference to Howarth and McArthur (1997) Look-Up Table Version 4: 08/04 (latest version June 2006). The minimum and maximum age dates were based on the ±2SE of the measured 87 Sr/ 86 Sr isotope ratios and the confidence limits of the calibration curve. ...
... Recent studies have applied this method to fossils from older Quaternary marine terrace deposits of Santa Cruz Island and Santa Rosa Island, California (Muhs et al., 2021(Muhs et al., , 2023, as well as to Pliocene-Pleistocene and Miocene fossils in California (Buczek et al., 2021;Paces et al., 2023). Since~37 Ma, the 87 Sr/ 86 Sr isotopic composition of seawater has become increasingly radiogenic (Howarth and McArthur, 1997;McArthur et al., 2001McArthur et al., , 2020. ...
... From whole-rock carbonate 87 Sr/ 86 Sr data, Petermann et al. (1970), Veizer and Compston (1974), and Burke et al. (1982) compiled the first detailed Phanerozoic strontium evolution curves. Since then, additional data (e.g., compiled recently in McArthur et al. 2020), insights on the most suitable type of samples (e.g., McArthur 1994), and on the statistical treatment of the data (e.g., Howarth and McArthur 1997) led to progressive improvement of this curve. ...
In the Late Permian Zechstein Sea of Central Europe, up to 2000 m of evaporitic rocks were deposited in at least four consecutive cycles. The age of these evaporitic rocks could not yet be precisely determined, because they are virtually fossil-free and do not contain radiometrically datable volcanic layers. A chemostratigraphic age of the succession can be determined by comparing ⁸⁷ Sr/ ⁸⁶ Sr ratios of marine gypsum and anhydrite to the worldwide marine strontium evolution curve. Unfortunately, published ⁸⁷ Sr/ ⁸⁶ Sr data of the Zechstein succession are characterized by frequent outliers towards higher ratios, making an age assignment challenging. The scatter in ⁸⁷ Sr/ ⁸⁶ Sr ratios might be induced by different processes like the contribution of meteoric water to the brine, in-situ Rb decay, or post-depositional hydrothermal or diagenetic overprint. Here, we present a dataset of 26 new gypsum and anhydrite ⁸⁷ Sr/ ⁸⁶ Sr ratios from drill cores situated at “Alter Stolberg” in the northernmost Thuringian Basin. Evaporites of the Werra-, Staßfurt-, and Leine cycles were sampled. The close proximity of the drillings allows a very accurate assignment of the stratigraphic position of each sample, so that trends and outliers in ⁸⁷ Sr/ ⁸⁶ Sr ratios can easily be recognized. While the entire Werra Formation obviously revealed non-marine ⁸⁷ Sr/ ⁸⁶ Sr ratios, the lowermost ⁸⁷ Sr/ ⁸⁶ Sr ratios in the Staßfurt and Leine Formations can be assumed to represent marine ratios and allow estimating a chemostratigraphic age of 257‒254 Ma. The combination of the ⁸⁷ Sr/ ⁸⁶ Sr data with the mineral composition of the samples suggests a contribution of meteoric water, probably river water, to the Zechstein Sea as the main reason for the observed increase in ⁸⁷ Sr/ ⁸⁶ Sr ratios. Additional in-situ Rb decay, related to the riverine input of clay minerals, cannot be excluded. Modelling the amounts of sea water and meteoric water in the brine indicates that 83‒99% of meteoric water would be necessary to explain the highest ⁸⁷ Sr/ ⁸⁶ Sr ratios observed in the Werra Formation.
Graphical abstract
... Solution standards comprising NIST NBS-987 for Sr, and JNDi-1 for Nd were measured during the same MC-ICP-MS runs as the samples. Sr isotope ratios were corrected using the Factor 86 Sr/ 88 Sr = 0.1194, and then were normalized to the NBS-987 standard measurement result 0.710248 ± 7 (2σ) (Howarth and McArthur, 1997). Nd isotope ratios were corrected using the Factor 146 Nd/ 144 Nd = 0.7219, and then were normalized to the JNDi-1 standard measurement result 143 Nd/ 144 Nd = 0.512115 (Tanaka Neelum granite showing hypidiomorphic texture with a zoned plagioclase phenocrysts, (i) Perthite phenocryst displaying irregular albite blebs, Neelum granite, (j) Biotite flake, interstitial to perthites and partially altered into muscovite along the rim portions, (k-l) Plagioclases and alkali feldspar phenocrysts, slightly altered into sericite and clays. ...
This study presents detailed petrography, bulk rock geochemistry, U-Pb dating, and Sr-Nd isotopes of pre-Himalayan granite gneisses and granites exposed in the Neelum Valley, NW Pakistan. To understand pre-Himalayan crustal growth history in the Indian plate, basement granitoids provide useful constraints. Two granites (the Jura and Neelum granites) and two granitic gneisses (the Nauseri and Jura gneisses) were investigated with the goal of their petrogenesis and constraining their geotectonic settings. Petrographically both granites and gneisses contain plagioclase, K-feldspar, quartz with S-type granite paragenesis of muscovite, garnet and tourmaline. Geochemically granites and gneisses are characterized by strongly peraluminous (A/NK > 1.1) character with a distinct mafic metapelitic sources. Notable negative Ta, Nb, and Ti compared to La and K, and a pronounced positive Pb anomalies in the studied rocks indicate convergence related source with a similar rare earth element pattern of upper continental crust. Two U-Pb zircon age populations, ca. 2429 ± 17 Ma and 1844 ± 11 Ma were obtained from the Nauseri gneiss whereas Jura gneiss yielded 865 ± 5.6 Ma. In contrast, Neelum and Jura granites yielded ages of 736 ± 11 Ma and 459.1 ± 3.5 Ma, respectively. Sr-Nd isotopic composition ((⁸⁷Sr/⁸⁶Sr)i = 0.7099 to 0.7303; εNd(t) = -8.1 to −3.6) together with the major and trace element geochemistry indicate that parental magmas of granites and gneisses were derived from the partial melting of upper continental crust during syn-collision tectonic settings. The Sr-Nd isotopes coupled with two-stage model ages further suggest incorporation of Archean and Paleoproterozoic reworked continental material that contained some mafic metapelitic component as well. Tectonically the parental magma of gneisses and granites could be linked with the global-scale orogenic events that operated during the assembly and rifting of the supercontinents of Columbia to Pangaea. Protoliths of Nauseri gneiss was possibly formed during the assemblage of Columbia supercontinent (1.8 Ga). Later, the Pan-African Orogeny provided additional pulse of magmatism that resulted Jura gneiss and Neelum granite. Moreover, the Bhimphedian orogeny in the Indian plate during Ordovician times generated the Jura granite of ca. 460 Ma.
... Note that both benthic and nekto-benthic forms and calcitic and aragonitic shells were binned together due to the limited number of samples available. These values were used to determine a numerical age for the eight intervals and the uncertainty limits on each age using the newest version (V5, provided by J. McArthur, 2014 and2017, personal commun.) of the Locally Weighted Scatterplot Smoothing (LOWESS) look-up table (Howarth and McArthur, 1997). Following Crame et al. (1999), the uncertainty of each age includes the uncertainty inherent in the reference curve of Fig. 3). ...
A second K/Pg boundary interval in the northern sector of the Antarctic Peninsula on Vega Island has been proposed, yet current temporal resolution of these strata prohibits direct testing of this hypothesis. To not only test for the existence of a K/Pg boundary on Vega Island but also provide increased age resolution for the associated vertebrate fauna (e.g., marine reptiles, non-avian dinosaurs, and avian dinosaurs), the Vega Island succession was intensively re-sampled. Stratigraphic investigation of the Cape Lamb Member of the Snow Hill Island Formation, and in particular, the overlying Sandwich Bluff Member of the López de Bertodano Formation, was conducted using biostratigraphy, strontium isotope stratigraphy, magnetostratigraphy, and detrital zircon geochronology. These data indicate a Late Campanian−early Maastrichtian age for the Cape Lamb Member and present three possible correlations to the global polarity time scale (GPTS) for the overlying Sandwich Bluff Member. The most plausible correlation, which is consistent with biostratigraphy, detrital zircon geochronology, sequence stratigraphy, and all but one of the Sr-isotope ages, correlates the base of the section to C31N and the top of the section with C29N, which indicates that the K/Pg boundary passes through the top of the unit. A second, less plausible option conflicts with the biostratigraphy and depends on a series of poorly defined magnetic reversals in the upper part of the stratigraphy that also correlates the section between C31N and C29R and again indicates an inclusive K/Pg boundary interval. The least likely correlation, which depends on favoring only a single Sr-isotope age at the top of the section over biostratigraphy, correlates the section between C31N and C30N and is inconsistent with an included K/Pg boundary interval. Although our preferred correlation is well supported, we failed to identify an Ir-anomaly, spherules/impact ejecta, or other direct evidence typically used to define the precise position of a K/Pg boundary on Vega Island. This study does, however, confirm that Vegavis, from the base of the Sandwich Bluff Member, is the oldest (69.2−68.4 Ma) phylogenetically placed representative of the avian crown clade, and that marine vertebrates and non-avian dinosaurs persisted in Antarctica up to the terminal Cretaceous.
... Strontium isotope dating is based on the assumption that 87 Sr/ 86 Sr values measured in carbonate marine fossils reflect the seawater composition at the time of their test formation (Kuznetsov et al., 2012). Changing Sr ratios of seawater with time makes it possible to derive the ages of marine carbonate fossils from a global calibration curve (Howarth and McArthur, 1997;McArthur et al., 2001). In this study, 88 mono-specific and three mixed foraminiferal samples were selected from 81/26, 8903, and 5.1/5.2, and nine shell fragment samples from 16/1-8 were analyzed for Sr isotope dating (Table 2 and Appendix A). ...
Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka.
Sr ages suggest a hiatus of <2 million years (Ma) possibly due to non-deposition or low sedimentation between the Utsira Formation (Pliocene) and the Early Pleistocene. An increase in sedimentation rates around 1.5 ± 0.07 Ma (∼MIS 51) may partly be due to sediment supply from rivers from the south-east and partly due to the extension of ice sheet around 1.36 ± 0.07 Ma from the Norwegian coast to the central North Sea. A possible basin-wide glaciation occurred around 1.1 Ma (∼ MIS 32) (upper regional unconformity/top of unit Q4 in this study), resulting in erosion and regional unconformity. Two interglacials in the Norwegian Channel have been dated: the Radøy Interglacial to 1.07 ± 0.01 Ma (possibly MIS 31, the ‘super interglacial’), and the Norwegian Trench Interglacial to 0.50 ± 0.02 Ma (possibly MIS 13). A massive till unit identified at the same stratigraphic level in all shallow borings may partly represent an extensive MIS 12 glaciation. This study shows that the combined use of amino acid racemization data and Sr isotope chronology can refine the chronological ambiguities of Quaternary North Sea sediments related partly to the impact of glacial processes.
... A more promising isotopic method of age determination for fossils of pre-MIS 5e terraces on the Pacific coast is Sr isotope stratigraphy, a calibrated method of geochronology. Early experiments with this method in California showed promise (Ludwig et al., 1992), and since that time, better calibration curves have been developed (Howarth and McArthur, 1997). ...
The primary last interglacial, marine isotope substage
(MIS) 5e records on the Pacific coast of North America, from Washington
(USA) to Baja California Sur (Mexico), are found in the deposits of
erosional marine terraces. Warmer coasts along the southern Golfo de
California host both erosional marine terraces and constructional coral reef
terraces. Because the northern part of the region is tectonically active,
MIS 5e terrace elevations vary considerably, from a few meters above sea
level to as much as 70 m above sea level. The primary paleo-sea-level
indicator is the shoreline angle, the junction of the wave-cut platform with
the former sea cliff, which forms very close to mean sea level. Most areas
on the Pacific coast of North America have experienced uplift since MIS 5e
time, but the rate of uplift varies substantially as a function of tectonic
setting. Chronology in most places is based on uranium-series ages of the
solitary coral Balanophyllia elegans (erosional terraces) or the colonial corals Porites and
Pocillopora (constructional reefs). In areas lacking corals, correlation to MIS 5e often
can be accomplished using amino acid ratios of fossil mollusks, compared to
similar ratios in mollusks that also host dated corals. Uranium-series (U-series) analyses of
corals that have experienced largely closed-system histories range from
∼124 to ∼118 ka, in good agreement with ages
from MIS 5e reef terraces elsewhere in the world. There is no geomorphic,
stratigraphic, or geochronological evidence for more than one high-sea stand
during MIS 5e on the Pacific coast of North America. However, in areas of
low uplift rate, the outer parts of MIS 5e terraces apparently were
re-occupied by the high-sea stand at ∼100 ka (MIS 5c),
evident from mixes of coral ages and mixes of molluscan faunas with
differing thermal aspects. This sequence of events took place because
glacial isostatic adjustment processes acting on North America resulted in
regional high-sea stands at ∼100 and ∼80 ka
that were higher than is the case in far-field regions, distant from large
continental ice sheets. During MIS 5e time, sea surface temperatures (SSTs)
off the Pacific coast of North America were higher than is the case at
present, evident from extralimital southern species of mollusks found in
dated deposits. Apparently, no wholesale shifts in faunal provinces took
place, but in MIS 5e time, some species of bivalves and gastropods lived
hundreds of kilometers north of their present northern limits, in good
agreement with SST estimates derived from foraminiferal records and
alkenone-based reconstructions in deep-sea cores. Because many areas of the
Pacific coast of North America have been active tectonically for much or all
of the Quaternary, many earlier interglacial periods are recorded as
uplifted, higher-elevation terraces. In addition, from southern Oregon to
northern Baja California, there are U-series-dated corals from marine
terraces that formed at ∼80 ka, during MIS 5a. In contrast to
MIS 5e, these terrace deposits host molluscan faunas that contain
extralimital northern species, indicating cooler SST at the end of MIS 5.
Here I present a review and standardized database of MIS 5e sea-level
indicators along the Pacific coast of North America and the corresponding
dated samples. The database is available in Muhs et al. (2021b; https://doi.org/10.5281/zenodo.5903285).
... The 87 Sr/ 86 Sr values were corrected for instrumental bias to a NIST SRM 987 standard value of 0.710248 (McArthur et al., 2001) following the procedure of Howarth and McArthur (1997) and McArthur et al. (2001). ...
The occurrence of the opportunistic, oyster-like bivalve Chondrodonta is widely documented in late Cenomanian shallow-water carbonates of the Tethyan Realm. Despite its high abundance and widespread geographic distribution, the precise relationship between the time of its proliferation and the environmental perturbations that precede the Cenomanian – Turonian anoxic event, has not been yet investigated. Stratigraphic and geochemical analyses of the upper Cenomanian Chondrodonta accumulations within the inner platform limestones of the Adriatic Carbonate Platform (AdCP) are performed to assess the timing and the environmental controls on the Chondrodonta proliferation.
In the study area, Chondrodonta appears as sparse to common individuals within radiolitid rudist beds and reaches a phase of proliferation and predominance in the benthic community. This biotic event has been correlated via C- and Sr-isotopes to a late Cenomanian environmental stress phase, occurred in shallow-water settings and in the deep counterparts.
This environmental stress phase on the AdCP was characterized by high nutrient levels, fluctuating seawater oxygenation, and more terrigenous inputs that favored the flourishment of Chondrodonta and its transient predominance over the less resilient rudists. This bioevent seems to be recurrent at the central Tethys scale, allowing to consider the proliferation of Chondrodonta in shallow-water carbonate platforms as a stratigraphic marker for a late Cenomanian environmental stress phase preceding the anoxic event.
... The core lithostratigraphy is composed of a basal olive-green mud overlain by gravelly pelletal phosphorite sands that coarsen upwards (FIGURE 2). Components in core 2670 were dated using strontium isotope stratigraphy (SIS) (Howarth & McArthur, 1997). Picked foraminifera in the basal mud unit had a SIS middle Miocene age (14.4 to 16.1 Ma) and the overlying pelletal phosphorite units had SIS ages indicating a Plio-Pleistocene depositional age (Compton & Bergh, 2016). ...
This article documents the taxonomy and biostratigraphy of middle Miocene foraminifera from the Namibian continental shelf. The taxonomy of 51 benthic and 12 planktic foraminiferal species from the northern Namibian shelf are discussed, their stratigraphic significance given, and their ecological preferences and regional distribution summarised within this study. The identification of extinct planktic foraminifera provided key stratigraphic control for the middle Miocene strata of this region. A total of 47 species are identified and discussed for the first time from this region, with an attempt to resolve some of the discrepancies in the identification of taxa in previous literature. Nineteen
species recorded in this study are extinct and eleven taxa reported here have previously only been reported on the genus level on the southwestern shelf of South Africa.
... First, the magnetic susceptibility (χ lf ) values were sorted and resampled with median value. The data were then detrended using LOWESS (LOcally WEighted Scatterplot Smoothing) (Howarth and McArthur, 1997;McGuire et al., 1997) -a detrending method -to remove low-frequency, long-term trends (Huang, 2014). The 2π multitaper method (MTM) was then applied to the series to obtain spectral analysis graphs using the robust red noise model reported at the 50%, 90%, 95%, and 99% confidence levels for interpretation of spectral peak significance (Mann and Lees, 1996;Ghil et al., 2002). ...
The core monsoon zone (CMZ) is an ideal region for reconstructing the Indian summer monsoon rainfall (ISMR). Mineral magnetic and organic geochemical parameters have been measured for an AMS ¹⁴C-dated sediment core from the Anshupa Lake, situated in the eastern part of the CMZ, to reconstruct changes in the paleo-monsoonal precipitation on a sub-decadal scale during the past 600 years. Based on the data obtained, two phases may be recognised in the sedimentation history of the lake over the past six centuries: Phase-I (1397 to 1850 A.D.) comprising sediments deposited during the Little Ice Age (LIA), and Phase-II (1850 A.D. to the Present) comprising sediments deposited after the LIA. The measured proxies show decadal to sub-decadal scale variations. The relatively low values of mineral magnetic parameters (χlf,χhf,χfd, SIRM, χARM/χlf, χARM/SIRM, χARM/χlf, and χARM/SIRM) and more positive δ¹³C values during Phase-I suggest a weak ISMR compared to Phase-II. The variations in mineral magnetic parameters suggest that the ISMR was the lowest during the Spörer, Maunder and Dalton Minima, but strong during the intervening periods. This inference resonates with the δ¹³C and C/N profiles of the core. Bacterial magnetite is documented during the mid-16th to mid-17th century, suggesting warm and humid conditions in the intervening phase between the Spörer and Maunder Minima. The magnetic susceptibility (χlf) data exhibit a number of periodicities similar to those shown by cosmogenic nuclide-derived Total Solar Irradiance (TSI) data, reaffirming a solar influence on the Indian summer monsoon in the core monsoon zone of India.
... Depths correspond to the E-W trending stratigraphic section shown inFig. 2. The blue rectangle indicates the range of depositional 87 Sr/ 86 Sr values of seawater (SW) during the Devonian as indicated byHowarth & McArthur (1997). ...
A multi-proxy field and laboratory study was conducted to investigate the impact of a regional fault zone on Devonian
carbonate geothermal reservoir properties. The outcrop analogue chosen is exposed in the Steltenberg quarry (North
Rhine-Westphalia, Germany) and provides access to Devonian lime- and dolostone units affected by branches of the Ennepe
Thrust Fault zone. Data presented include (i) field evidence from sedimentological and structural data, (ii) petrographic and
mineralogical analyses, and (iii) geochemical and petrophysical data. Although the interpretation of the depositional environment
is not trivial, the carbonate facies present generally reflect the shedding of reefal material from large bioherms to
the west of the study areas as well as localised, small bioherms prone to storm disintegration. The inherited properties of
these carbonates at deposition, and a clear understanding of their diagenetic history, are the prerequisite for extrapolation
between outcrop analogues and their corresponding subsurface units. We document a detailed interpretation of the paragenetic
sequence that affected these rocks from deposition, burial, subsequent hydrothermal overprint related to rock disintegration
and fluid circulation along the fault zone, and finally, late-stage meteoric overprint. Emphasis is placed on various
forms of dolomitisation and its effect on rock properties and reservoir quality. The resulting scenario is complex, and when
comparing the data from the Steltenberg quarry with nearby outcrops, significant regional heterogeneity is observed. It is
important to separate between: (i) diffuse, locally distributed dolomitisation, (ii) replacive dolomitisation (fronts), spatially
separating lime- and dolostones, and (iii) fault-bound, hydrothermal dolomitisation. The Devonian carbonates in the Steltenberg
quarry examined here have higher thermal conductivity compared to the Jurassic (Malm) carbonate units in the Munich
area, with some even higher than the values of massive limestone facies of the Munich area. As a large portion of North
Rhine-Westphalia’s territory is underlain by Devonian carbonates, this is considered significant. However, emphasis is
placed on the fact, that data shown here document the spatially complex organisation of rock types and their reservoir properties.
This presents a warning against oversimplifications when extrapolating observations from outcrops into subsurface
rock bodies.
... The estimated range from local geology for Syracuse is 0.70800-0.70900, based on expected Sr isotopic compositions of Cenozoic (Oligocene to Pleistocene) carbonate rocks [64]. Based on precipitation estimates from OIPC and collected water samples, the δ 18 O baseline for Agrigento is -5.1‰ to -3.1‰ and Syracuse is -4.5‰ to -2.5‰ (Table 2). ...
Increased mobility and human interactions in the Mediterranean region during the eighth through fifth centuries BCE resulted in heterogeneous communities held together by political and cultural affiliations, periodically engaged in military conflict. Ancient historians write of alliances that aided the Greek Sicilian colony Himera in victory against a Carthaginian army of hired foreign mercenaries in 480 BCE, and the demise of Himera when it fought Carthage again in 409 BCE, this time unaided. Archaeological human remains from the Battles of Himera provide unique opportunities to test early written history by geochemically assessing the geographic origins of ancient Greek fighting forces. We report strontium and oxygen isotope ratios of tooth enamel from 62 Greek soldiers to evaluate the historically-based hypothesis that a coalition of Greek allies saved Himera in 480 BCE, but not in 409 BCE. Among the burials of 480 BCE, approximately two-thirds of the individuals are non-local, whereas among the burials of 409 BCE, only one-quarter are non-local, in support of historical accounts. Although historical accounts specifically mention Sicilian Greek allies aiding Himera, isotopic values of many of the 480 BCE non-locals are consistent with geographic regions beyond Sicily, suggesting Greek tyrants hired foreign mercenaries from more distant places. We describe how the presence of mercenary soldiers confronts prevailing interpretations of traditional Greek values and society. Greek fighting forces reflect the interconnectedness and heterogeneity of communities of the time, rather than culturally similar groups of neighbors fighting for a common cause, unified by “Greekness,” as promoted in ancient texts.
... Magnesium isotope compositions of seawater are controlled by the mass balance of the Mg flux, including the Mg influx of riverine runoff (F riv ) into the ocean, and the outflux of dolomite precipitation (F dol ) and secondary Mg silicate formation at mid-ocean ridges (F silicate ) (Tipper et al., 2006;Li et al., 2015), which are tightly linked to tectonic activity, global climate change, and weathering (Wimpenny et al., 2014;Higgins and Schrag, 2015;Hu et al., 2021). The reported seawater 87 Sr/ 86 Sr values during the late Albian (110-105 Ma) are relatively stable (Howarth and McArthur, 1997;Navarro-Ramirez et al., 2015), indicating no major changes in weathering inputs. The relatively invariant C-O isotopes in the dolomite layers also demonstrate a relatively stable marine environment (Fig. 6). ...
Marine dolomitization processes are characterized by complex variations in hydrological conditions and pore-fluid chemistry. Deposition of massive dolomitized carbonates on the Comanche Platform of south Texas, USA, during the Albian coincided with multiple fluctuations in sea level, thereby providing an ideal setting to study the response of magnesium isotopes to dolomitization during eustatic sea-level change. In this study, we conducted Mg, C, and O isotope analyses and complimentary mineralogical and petrographic investigations of dolomitized massive carbonates of the Albian Edwards Group in the Comanche Platform. Petrographic observations indicate that the carbonate rocks in the studied units were not altered by deep burial diagenesis or hydrothermal fluids. Based on our petrographic observations and the trace element and CO isotope data, we infer the dolomites were formed via syn-depositional dolomitization during a period of low sea level. The δ²⁶Mg values of the dolomites increase rapidly from −2.5‰ to −1.8‰ in the basal part of the unit, reflecting a change in fluid chemistry caused by dolomitization in a restricted marine environment. Subsequently, δ²⁶Mgdolomite values gradually decrease back to their initial value of approximately −2.5‰ due to seawater replenishment during transgression. The observed variability in dolomite δ²⁶Mg values reflects changes in the connectivity of the platform with the open ocean during marine transgressions. However, the δ²⁶Mgdolomite values do not vary with the high-frequency eustatic sea-level change recorded in the lithological variations, indicating uniform hydrologic conditions of the massive dolomitization system despite the hydrodynamic variations in the sedimentary environment. Therefore, we propose that massive dolomitization systems are mostly fluid-buffered and, as a result, Mg isotopes of dolomites can be used to trace changes in the paleo-marine environment, such as basin connectivity.
... Great care is required when carrying out strontium isotopic analyses to successfully correlate limestone and marl-type carbonate rocks that are younger than eight million years old (Howard and McArthur, 1997). Isotopic studies are more credible for sedimentary rocks that are older than fifteen million years. ...
Cenozoic sediments are spread across southeast and eastern Anatolia, including the Adıyaman–Malatya regions of southeast Turkey. This study presents the first detailed petrographic, micropaleontologic, and strontium isotope analyses of the Eocene marl, clayey limestone, and limestone units that outcrop unconformably above the Mesozoic Meydan and İspendere ophiolitic rocks in the Adıyaman and Malatya regions, respectively. These carbonate rocks contain abundant planktonic foraminifera, including Turborotalia frontosa, Subbotina senni, Subbotina eocaena, Acarinina bullbrooki, Guembelitrioides nuttalli, Globigerinatheka subconglobata, and G. curryi, and benthic taxa (Nummulites, Discocyclina, and Chapmanina).Two planktonic foraminiferal zones were defined: the Turborotalia frontosa zone representing the Early–Middle Eocene (Ypresian–Lutetian/Bartonian), and the Turborotalia possagnoensis zone representing the Middle Eocene (Lutetian–Bartonian). Strontium isotope ratios (87Sr/86Sr) calculated for four samples ranged between 0.707663 and 0.707784, indicating an age of 45.1–51.9 million years (Ypresian–Lutetian/Bartonian). The presence of echinoid thorns in the units indicates a shallow marine environment where carbonates developed on the seaward side of a reef. For the first time in the study region and southeast Anatolia, this study has revealed the stratigraphic position of the Nummulitic limestone of the Kırkgeçit Formation unconformably overlying the ophiolites. Therefore, based on strontium isotope analyses and planktonic foraminiferal micropaleontology, the Kırkgeçit Formation is estimated as Early–Middle Eocene (Ypresian–Lutetian/Bartonian) in age.
... Sr ratios were corrected to NIST 987 = 0.710248. The numerical ages were derived from the SIS Look-upTable Version 3:10/99 of Howardand McArthur (1997). NIST = National Institute for Standard and Technology. ...
... First, the magnetic susceptibility (χ lf ) values were sorted and resampled with median value. The data were then detrended using LOWESS (LOcally WEighted Scatterplot Smoothing) (Howarth and McArthur, 1997;McGuire et al., 1997) -a detrending method -to remove low-frequency, long-term trends (Huang, 2014). The 2π multitaper method (MTM) was then applied to the series to obtain spectral analysis graphs using the robust red noise model reported at the 50%, 90%, 95%, and 99% confidence levels for interpretation of spectral peak significance (Mann and Lees, 1996;Ghil et al., 2002). ...
Denudation rates are often estimated with high uncertainty using the average mass of material discharged through a drainage basin or considering the rate of surface processes. Estimating long-term denudation rates through these conventional methods requires the assumption that the surficial processes have remained constant throughout time. Since the earth's surface has been obliterated throughout the geological time by climate, tectonics, or the recent anthropogenic activities, the present rate of change may not represent past processes. This study presents changes in denudation rate using the 10Be (meteoric)/9Be ratio for the past 600 years from Anshupa Lake sediment record in the core monsoon zone of India. Paleodenudation rate estimated using 10Be (meteoric)/9Be varies from 392 ± 42 to 95 ± 6 t/km2/yr. Intense Indian Summer Monsoon (ISM) during the periods of solar maxima, which caused decadal-scale floods in the Indian sub-continent, favored a higher rate of denudation than the periods of solar minima, that experienced droughts in the Indian sub-continent due to weakening of ISM.
... 87 Sr/ 86 Sr values from some key samples are summarized in Table 2. These results indicate ages ranging from the Serpukhovian (330 Ma) to Asselian (earliest Permian) (296 Ma; Howarth and McArthur 1997;McArthur et al. 2001McArthur et al. , 2012. In the lower part of section 2, where fossils occurrences are poor, Sr isotope analysis was more important than biostratigraphy, but age dates based on isotopes and biostratigraphy consistently agreed in the middle and upper parts of the section (Fig. 4). ...
The Pennsylvanian is characterized by intense paleoenvironmental changes related to glacio-eustatic sea-level fluctuations and major tectonic events, which affected the evolution of biocommunities. Most known Pennsylvanian tropical reefs and mounds are predominantly composed of calcareous algae (e.g. phylloid algae, Archaeolithophyllum), calcareous sponges, fenestrate bryozoans, Tubiphytes, and microbialites. However, in Houchang (southern China), the Late Pennsylvanian carbonate platform records a large coral reef lacking any analogs in age (Gzhelian), size (80-100 m thick) and composition (high biodiversity). The large coral reef developed at the border of the Luodian intraplatform basin. The intraplatform basin is characterized by the deposition of green algal grainstone, coated grain grainstone and bioclastic packstone, grainstone, floatstone and rudstone in shallow-waters. In the deep-water shelf, lithofacies are composed of burrowed bioclastic wackestone, microbioclastic peloidal packstone, grainstone, and fine-grained burrowed wackestone and packstone. In this context, the coral reef developed on a deep-shelf margin, in a moderate to low energy depositional environment, below the FWWB.
The scarcity of Pennsylvanian coral reefs suggests global unfavorable conditions, which can be attributed to a complex pattern of several environmental factors, including seawater chemistry (aragonite seas), paleoclimatic cooling related to continental glaciation, and the biological competition with the more opportunistic and adaptive phylloid algal community that occupied similar platform margin paleoenvironments. The existence of the large Bianping coral reef in southern China, as well as a few additional examples of Pennsylvanian coralliferous bioconstructions, provides evidence that coral communities were able to endure the Late Paleozoic fluctuating paleoenvironmental conditions in specific settings. One of such settings appears to have been the deep shelf margin, where low light levels decreased competition with the phylloid algal community.
... The LOESS fit is a derivative of the LOWESS (Cleveland, 1979(Cleveland, , 1981Chambers et al., 1983;Thisted, 1988;Cleveland et al., 1992). Details of the fitting procedure matched closely those given in Howarth and McArthur (1997). Because of the complex shape of the fit, and the very uneven density of data points through time, the curve was optimized by being fitted in overlapping local segments. ...
The ⁸⁷Sr/⁸⁶Sr value of Sr dissolved in the world’s oceans has varied through time in a known way. When minerals, such as biogenic calcite, precipitate from seawater, they incorporate Sr from seawater and capture the ⁸⁷Sr/⁸⁶Sr value for marine-Sr at the time of precipitation. Measurement of the ⁸⁷Sr/⁸⁶Sr value in fossil precipitates, such as belemnites or foraminifera, can therefore be used to date and to correlate worldwide the marine sedimentary rocks in which the precipitates occur. Here, the theory and practice of the methodology is outlined.
The variation of marine-⁸⁷Sr/⁸⁶Sr through time is usually ascribed to changing fluxes of Sr from mid-ocean-ridge volcanism (⁸⁷Sr/⁸⁶Sr≈0.703) coupled with changing ⁸⁷Sr/⁸⁶Sr and flux through time of riverine inputs to the ocean of Sr with a high ratio (≈0.711).
... These data reflect that the biologically available strontium is mainly derived from geologically young igneous rocks, such as volcanic arc lavas, pyroclastic and volcaniclastic sediments, as well as some marine sedimentary rocks (Harmon et al., 2016). Seawater with an 87 Sr/ 86 Sr ratio of just below 0.7092 forms the upper limit of the biologically available strontium (Howarth and McArthur, 1997;Brand et al., 2003). In human coastal communities, this seawater value likely Table 4 Published data from historical contexts and osteological series with intentional dental modification. ...
Intentional dental modification is a widespread practice in both ancient and modern populations. In Panama, the modern practice is restricted to the Ngäbe indigenous people inhabiting the western provinces. Several researchers have posited that Ngäbe dental modification evidences cultural transfer of African origin due to the absence of post-contact records of this practice in the region, and based on the chipping technique used to create a pointed tooth shape. In this paper, we collate bioarchaeological data from human remains recovered from pre-contact and early colonial period contexts in Panama to evaluate this hypothesis. The results of our study found no evidence for intentional dental modification among the pre-contact sample, but several instances of artificially modified incisor teeth among the early colonial sample. The latter pertained exclusively to individuals of African ancestry, and whose teeth had been chipped to points in the same manner as reported from Ngäbe communities. Isotope data revealed that one individual was a first-generation immigrant who likely originated from the African continent. Based on these results, as well as an exhaustive review of the ethnohistorical and modern ethnographic literature, the original hypothesis of a late introduction of African origin for the practice of dental shaping among the Ngäbe was upheld.
... All 87 Sr/ 86 Sr ratios have been normalized to the accepted value of NBS987 = 0.710248 (McArthur et al., 1994). 87 Sr/ 86 Sr isotopic ratios were then converted to numerical ages using version 5 (26 March 2013; J.M. McArthur, 2013, personal commun.) of the LOWESS lookup table (Howarth and McArthur, 1997;McArthur et al., 2001). ...
Temporary storage of sediment between source and sink can hinder reconstruction of climate and/or tectonic signals from stratigraphy by mixing of sediment tracers with diagnostic geochemical or geochronological signatures. Constraining the occurrence and timing of intrabasinal sediment recycling has been challenging because widely used detrital geothermochronology applications do not record shallow burial and subsequent reworking. Here, we apply strontium isotope stratigraphy techniques to recycled marine shell material in slope deposits of the Upper Cretaceous Tres Pasos Formation, Magallanes Basin, Chile. Detrital 87Sr/86Sr ages from 94 samples show that the majority (>85%) of the shells are >1–12 m.y. older than independently constrained depositional ages. We interpret the gap between mineralization age (87Sr/86Sr age) and depositional age of host strata to represent the intrabasinal residence time of sediment storage at the million-year time scale. We also use specimen type to infer relative position of intrabasinal source material along the depositional profile, where oysters represent shallow-water (i.e., proximal) sources and inoceramids represent deeper-water (i.e., distal) sources. The combined use of detrital strontium isotope ages and specimen types from linked depositional segments provides an opportunity to identify and quantify sediment storage and recycling in ancient source-to-sink systems.
In areas of low uplift rate on the Pacific Coast of North America, reoccupation of emergent marine terraces by later high sea‐stands has been hypothesised to explain the existence of thermally anomalous fauna (mixtures of warm and cool species) of last interglacial age. If uplift rates have been low for much of the Quaternary, it follows that higher (older) terraces should also show evidence of reoccupation. Strontium isotope analyses of fossils from a high‐elevation marine terrace on Anacapa Island, California, yield ages ranging from ~2.4–2.3 Ma to ~1.4–1.5 Ma. These results indicate that terrace reoccupation and fossil mixing on Anacapa Island could have taken place over several interglacial periods in the early Pleistocene. Terrace reoccupation over this time period is likely a function of both a low uplift rate and the timing of orbital forcing of glacial–interglacial cycles. Climate change in the early Pleistocene was modulated by the 41 ka obliquity cycle, and glacial–interglacial cycles were much shorter than later in the Pleistocene. Nearby San Miguel Island also has evidence of terrace reoccupation, with Sr isotope ages of shells from several high‐elevation terraces ranging from ~1.21–1.25 Ma to ~0.43–0.50 Ma. However, the frequency of terrace reoccupation was lower than on Anacapa Island. The uplift rate of San Miguel Island is higher than that of Anacapa Island and terraces formed when glacial–interglacial cycles were longer. The frequency of marine terrace reoccupation is controlled by the rate of tectonic uplift and the timing of orbital forcing of sea level change during glacial–interglacial cycles.
Providing a chronostratigraphic framework often is problematic in shallow-marine carbonates with poor biostratigraphic resolution. In such cases, an integration of geochemical, sedimentological, and paleontological data can be used to construct a reliable sequence stratigraphic framework. This study focuses on elemental concentrations and isotopic ratios of Cenomanian–Santonian (C–S) neritic carbonates in SW Iran used to construct a sequence stratigraphic framework, asses sequence ages and durations of hiatus. The diagenetic and geochemical expression of two paleoexposure surfaces, representing type-I sequence boundaries (SBs), are discussed. Increase in Fe and Rb concentrations and decrease in Ca content are recorded at and/or below distinct erosional surfaces. Mg content shows a facies-dependent response with former LMC (low magnesium calcite) or aragonitic facies showing increase while HMC (high magnesium calcite) indicates decrease in response to SBs. Mn shows considerable changes apart from sequence surfaces that are strongly facies dependent. Sr concentrations show an increase in HMC and decrease in LMC in samples which experienced semi-closed meteoric diagenesis, far below the SBs. However, in samples characterized by open system diagenesis, directly underlying the SBs, Sr tends to decrease in all components. The Sr/Rb ratio is a reliable tool in detecting erosional SBs, shown as conspicuous negative excursions. C (carbon) and O (oxygen) isotopes show distinct negative excursions at erosional SBs and a slight increase at or around the MFSs. The ⁸⁷Sr/⁸⁶Sr ratio shows clear positive excursions at SBs probably due to ⁸⁷Rb decay in incorporated aluminosilicate detritus, which makes it as the most reliable proxy for the detection of SBs in the studied sections. Two main erosional SBs are marked by ⁸⁷Sr/⁸⁶Sr ratios including the CT-ES (Cenomanian–Turonian boundary exposure surface) and mT-ES (middle Turonian exposure surface) with hiatus durations of 0.53 and 2.7 Myr, respectively. These paleoexposure surfaces are correlated with other neritic sections of C–S sequences in SW Iran.
Late Cretaceous sea surface temperatures (SST) are, amongst others, traditionally reconstructed by compiling oxygen isotope records of planktonic foraminifera obtained from globally distributed pelagic IODP drill cores. In contrast, the evolution of Early Cretaceous SSTs is essentially based on the organic TEX 86 palaeothermometer, as oxygen-isotope data derived from well-preserved ‘glassy’ foraminifer calcite are currently lacking. In order to evaluate the extraordinary warm TEX 86 -derived SSTs of the Barremian to Aptian (130–123 Ma) subtropics, we present highly resolved sclerochemical profiles of pristine rudist bivalve shells from Tethyan and proto-North Atlantic shallow water carbonate platforms. An inverse correlation of seasonal ontogenetic variations in δ ¹⁸ O rudist and Mg/Ca ratios demonstrates the fidelity of oxygen isotopes as palaeotemperature proxy. The new data shows moderate mean annual SSTs (22–26 °C) for large parts of the Barremian and Aptian and transient warm pulses for the so-called Mid-Barremian Event and Oceanic Anoxic Event 1a (reaching mean annual SSTs of 28 to 30 °C). A positive shift in mean annual oxygen-isotope values (δ ¹⁸ O: ≤ − 0.3‰) coupled with invariant Mg/Ca ratios at the Barremian–Aptian boundary points to a significant net loss of ¹⁶ O in Tethyan shallow-marine settings. As the positive oxygen-isotope rudist shell values are recorded immediately beneath a major superregional hiatal surface, they are interpreted to be related to a major cooling phase and potential glacio-eustatic sea-level lowering. Our new sclerochemical findings are in clear contrast to open ocean SST records based on TEX 86 , which indicate exceptionally warm Barremian to earliest Aptian subtropical oceans and weak meridional SST gradients.
Cenozoic sediments are spread across southeast and eastern Anatolia, including the Adıyaman–Malatya regions of southeast Turkey. This study presents the first detailed petrographic, micropaleontologic, and strontium isotope analyses of the Eocene marl, clayey limestone, and limestone units that outcrop unconformably above the Mesozoic Meydan and İspendere ophiolitic rocks in the Adıyaman and Malatya regions, respectively. These carbonate rocks contain abundant planktonic foraminifera, including Turborotalia frontosa, Subbotina senni, Subbotina eocaena, Acarinina bullbrooki, Guembelitrioides nuttalli, Globigerinatheka subconglobata, and G. curryi, and benthic taxa (Nummulites, Discocyclina, and Chapmanina).Two planktonic foraminiferal zones were defined: the Turborotalia frontosa zone representing the Early–Middle Eocene (Ypresian–Lutetian/Bartonian), and the Turborotalia possagnoensis zone representing the Middle Eocene (Lutetian–Bartonian). Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) calculated for four samples ranged between 0.707663 and 0.707784, indicating an age of 45.1–51.9 million years (Ypresian–Lutetian/Bartonian). The presence of echinoid thorns in the units indicates a shallow marine environment where carbonates developed on the seaward side of a reef. For the first time in the study region and southeast Anatolia, this study has revealed the stratigraphic position of the Nummulitic limestone of the Kırkgeçit Formation unconformably overlying the ophiolites. Therefore, based on strontium isotope analyses and planktonic foraminiferal micropaleontology, the Kırkgeçit Formation is estimated as Early–Middle Eocene (Ypresian–Lutetian/Bartonian) in age.
The Late Neogene sedimentary sequence of the Murray Basin provides an excellent opportunity to examine paleoenvironmental change across southeastern Australia. A detailed stratigraphic analysis of sediments deposited within the basin in the last 10 Ma was undertaken to assess the influence of tectonic and eustatic processes on deposition.
Stratigraphic observations and radiogenic isotope analysis reveals the onset of deposition by 7.2 Ma with a transgressive episode that deposited the marine marls of the Bookpurnong Beds. Deposition was restricted to the central and eastern parts of the basin due to the Hamley Fault. In the west, subsurface elevation contours indicate the presence of incised paleodrainage channels above Miocene limestones, which facilitated the formation of a large estuary system at 5.3 Ma. The sediments of the Norwest Bend Formation were deposited within this western region, while further east, the Loxton-Parilla Sands strandplain deposited over 214 coastal ridges. The basal parts of this unit occur as lateral equivalents to the sediments of the Lower Norwest Bend Formation (in the west). Topographic and magnetic data reveal that tectonism was active during this period and resulted in the erosion and truncation of strandlines.
Tectonic evidence and an estimated minimum 28,037 year cyclicity between strandline sets, suggests that the Loxton-Parilla Sands strandlines do not represent an unbroken record of glacioeustatic change. The subaerial exposure of these sediments at approximately 3.0 Ma caused the formation of a calcareous karst above the Norwest Bend Formation and a ferruginous and/or silicious cap (the Karoonda Surface) above the Loxton-Parilla Sands. The stratigraphic position of these surfaces are indicative of a regional widespread unconformity.
The Douglas-Blackburn paleodrainage system in western Victoria was dammed during the Mid-Late Pliocene by uplift associated with the Padthaway High, which caused the formation of a 400,000 km2 lacustrine system, known as Lake Bungunnia. Topographic analysis indicates that Lake Bungunnia comprised at least four distinct sub-basins with water depths of up to 30 metres, with lake shorelines indicating that active tectonism occurred during this period. The resulting lack of sediment input to the coast caused the formation of the Kanawinka Escarpment, a large erosional scarp along the southern margin of the Padthaway High.
The geomorphology of the modern Murray Basin can be directly attributed to the demise of the Lake Bungunnia system. Movement along the Morgan Fault in the west at approximately 700 Ka, resulted in the draining and progressive drying of Lake Bungunnia as a breach was created along the Padthaway High. The Murray River gorge as observed today was incised following this episode. The modern Murray River (and playa lakes such as Lake Tyrell) occupy the lowest elevations along the former sub-basins of Lake Bungunnia.
The Late Neogene sedimentary sequence across the Murray Basin illustrates a complex interaction of eustatic and tectonic processes on deposition. Sedimentation within strandline, estuarine and lacustrine systems, particularly in the western Murray Basin, display evidence of significant tectonic control. This highlights the important role that neotectonic processes have played in shaping southeastern Australia.
Extensive carbonate crusts discovered forming on the slopes of seamounts in many parts of the world's oceans are providing extra stability to the volcanic edifices. These crusts are hardgrounds composed of mixtures of volcaniclastic debris and bioclastic material, in most cases cemented by calcite, in the form of isopachous coatings around grains and pore-filling spar. Such crusts, which have been collected by a remotely-operated vehicle (ROV), are described here from moderate-depth to deeper-water slopes (180–820 m) around the volcanic island of Montserrat in the Caribbean, and from the nearby Kick'em Jenny submarine volcano off Grenada. Radiogenic ⁸⁷Sr/86Sr isotope ratios from the carbonates give an indication of age (up to 0.4 Ma years old) but they also demonstrate that some samples have been altered by hydrothermal-volcanic processes, to give ages much older than expected (14 to 18 Ma) based on the foraminifera present. Such alteration is also supported by carbon and oxygen isotope (δ¹³C and δ¹⁸O) ratios, although most samples retain typical marine values. In many cases δ¹⁸O is usually a little more positive than expected from modern Caribbean shallow-water carbonates, likely reflecting cooler water at their moderate depths of lithification. Just one sample, from Kick'em Jenny, has very negative δ¹³C (−42‰) indicating methanogenesis. Crusts are also reported here from the Mediterranean Sea, with an example described from Kolumbo submarine volcano, northeast of the Santorini volcanic complex in the Hellenic subduction zone, that are similar in many respects to those from the Caribbean. Typically, the biota of the crusts consists of calcareous red algae (commonly encrusting volcanic clasts), foraminifera (benthic, some also encrusting, and planktic), subordinate serpulids, bivalves, pteropods and heteropods, and rare deeper-water corals. Some bioclasts are derived from shallower water, others from the moderate depths of the slope itself, and planktic fallout. In addition, there is evidence for the former presence of microbes from the occurrence of calcified filaments and peloids in intragranular cavities. Several generations of sponge borings are usually present as well as calcite cement. Dissolution and calcite replacement of aragonitic bioclasts and cement, and sponge spicules (originally opaline silica), have taken place. The carbonate crusts are attributed to seawater circulating within the surficial sediment, in some cases mixing with hydrothermal fluid driven by geothermal and volcanic processes. Submarine volcanic slopes clearly provide a location for moderate-depth carbonate production and cementation, but a further significance of these hardgrounds is in stabilising seamounts, enabling their slopes to avoid frequent collapse, dissection and readjustment. However, when failure does occur, larger-scale submarine landslides involving coherent slabs are more likely.
We present an integrated geomagnetic polarity and stratigraphic time scale for the Triassic, Jurassic, and Cretaceous periods of the Mesozoic Era, with age estimates and uncertainty limits for stage boundaries. The time scale uses a suite of 324 radiometric dates, including high-resolution Ar-40/Ar-39 age estimates. This framework involves the observed ties between (1) radiometric dates, biozones, and stage boundaries, and (2) between biozones and magnetic reversals on the seafloor and in sediments. Interpolation techniques include maximum likelihood estimation, smoothing cubic spline fitting, and magnetochronology. The age estimates for the 31 stage boundaries (in mega-annum) with uncertainty (millions of years) to 2 standard deviations, and the duration of the preceding stages (in parentheses) are Maastrichtian/Danian (Cretaceous/-Cenozoic) is 65.0 +/- 0.1 Ma (6.3 m.y.), Campanian/Maastrichtian is 71.3 +/- 0.5 Ma (12.2 m.y.), Santonian/Campanian is 83.5 +/- 0.5 Ma (2.3 m.y.), Coniacian/Santonian is 85.8 +/- 0.5 Ma (3.2 m.y.), Turonian/Coniacian is 89.0 +/- 0.5 Ma (4.5 m.y.), Cenomanina/Turonian is 93.5 +/- 0.2 Ma (5.4 m.y.), Albian/Cenomanian is 98.9 +/- 0.6 Ma (13.3 m.y.), Aptian/Albian is 112.2 +/- 1.1 Ma (8.8 m.y.), Barremian/Aptian is 121.0 +/- 1.4 Ma (6.0 m.y.), Hauterivian/Barremian is 127.0 +/- 1.6 Ma (5.0 m.y.), Valanginian/Hauterivian is 132.0 +/- 1.9 Ma (5.0 m.y., Berriasian/Valanginian is 137.0 +/- 2.2 Ma (7.2 m.y.), Tithonian/Berriasian (Jurassic/Cretaceous) is 144.2 +/- 2.6 Ma (6.5 m.y.), Kimmeridgian/Tithonian is 150.7 +/- 3.0 Ma (3.4 m.y.), Oxfordian/Kimmeridgian is 154.1 +/- 3.2 Ma (5.3 m.y.), Callovian/Oxfordian is 159.4 +/- 3.6 Ma (5.0 m.y.), Bathonian/Callovian is 164.4 +/- 3.8 Ma (4.8 m.y.), Bajocian/Bathonian is 169.2 +/- 4.0 Ma (7.3 m.y.), Aalenian/Bajocian is 176.5 +/- 4.0 Ma (3.6 m.y.), Toarcian/Aalenian is 180.1 +/- 4.0 Ma (9.5 m.y.), Sinemurian/Pliensbachian is 195.3 +/- 3.9 Ma (6.6 m.y.), Hettangian/Sinemurian is 201.9 +/- 3.9 Ma (3.8 m.y.), Rhaetian/Hettangian (Triassic/Jurassic) is 205.7 +/- 4.0 Ma (3.9 m.y.), Norian/Rhaetian is 209.6 +/- 4.1 Ma (11.1 m.y.), Carnian/Norian is 220.7 +/- 4.4 Ma (6.7 m.y.), Ladinian/Carnian is 227.4 +/- 4.5 Ma (6.9 m.y.), Anisian/Ladinian is 234.3 +/- 4.6 Ma (7.4 m.y.), Olenekian/Anisian is 241.7 +/- 4.7 Ma (3.1 m.y.), Induan/Olenekian is 244.8 +/- 4.8 Ma (3.4 m.y.), Tatarian/Induan (Permian/Triassic) is 248.2 +/- 4.8 Ma. The uncertainty in the relative duration of each individual stage is much less than the uncertainties on the ages of the stage boundaries.
Strontium-isotope ratios of Cretaceous shallow-water carbonates from two guyots in the Mid-Pacific Mountains are compared with high-resolution data derived from stratigraphically well-calibrated belemnites and oysters from sequences in England. The thickest section penetrated on Resolution Guyot can, with the aid of carbon-isotop e data, be divided into stages ranging from uppermost Hauterivian to the Albian/Cenomanian boundary. The section on Allison Guyot, although more ambiguous in interpre- tation, is exclusively Albian, and its upper limit is also close to the contact with the Albian/Cenomanian boundary. Comparison of age-vs.-thickness data on the two guyots suggests that Allison was subsiding at a rate at least twice that of Resolution Guyot during the Albian. The strontium-isotope data are compatible with the hypothesis of synchronous cessation of deposition of shallow-water carbonates at both sites.
It is recognized that effective quality control procedures are essential if analysis is to produce data that are fit for their purpose. This paper outlines the practical approaches to quality control, The control of random error using replication of analysis is described. Different types of reference materials are discussed as a means of controlling systematic error.
The Maastrichtian and Danian intervals of Ocean Drilling Program (ODP)
Hole 738C contain numerous microfossils above the level of their
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communities long after species turnover occurred across the rest of the
globe or (2) large-scale reworking. These interpretations have very
different paleoenvironmental implications, but discriminating between
them has proved difficult. To test the competing hypotheses, we measured
the 87Sr/86Sr ratios of taxon-specific separates
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lower Danian strata in ODP Hole 738C. We estimate that up to 30% of the
mass of foraminifers in any sample can be contributed by individuals
that have been reworked.
The Cenozoic strontium isotope (87Sr/86Sr) variation in seawater is largely defined using Deep Sea Drilling Project (DSDP) samples. Examination of non-DSDP results, particularly for the Paleogene, suggest that the original seawater curve of Burke et al. (1982) may lie above the true seawater ratio during this time. To investigate this possibility, we analyzed the 87Sr/86Sr for 230 Paleogene rock and shell samples from the 83 sites in Alabama, Mississippi, and Louisiana. Many of the samples are from classic sections on which the Gulf Coast Paleogene stratigraphy was originally defined. Multiple analyses of samples from these units show very little scatter, and in most cases, precise agreement is obtained among geographically separated collection sites. We believe that analysis of multiple samples from a unit of established age, collected at more than one site, yields results that most accurately define the actual seawater Sr isotope ratio at any given time. Results from these units define a seawater variation line that tracks well within the range of DSDP data, but is generally below the original seawater line of Burke et al. (1982). It is often assumed that samples from continental settings will exchange with high-ratio Sr thereby raising 87Sr/86Sr values. Our Gulf Coast samples, which are derived from a continental setting, yield individual 87Sr/86Sr values that are both higher and lower than the estimated contemporaneous seawater ratio. An analysis of our Gulf Coast data and DSDP results show that the direction of isotopic exchange cannot be confidently predicted for individual samples based solely on their derivation from either continental or oceanic settings.
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Geological time scales are constructed by combining the stratigraphic record with radiometric dates and their standard deviations. The stratigraphic record encompasses litho-, bio-, chrono-, and magnetostratigraphy. The statistical methods employed should embody concepts and data available for the systems considered. Recently, in order to estimate the ages of 31 Mesozoic stage boundaries, use was made of a database with chronostratigraphic classifications for 340 dates, biostratigraphic data including ammonite subzones, and information on seafloor spreading. This paper is primarily concerned with the propagation of errors through the successive steps of the data analysis. The following stepwise approach was taken for combining the different types of data: (1) maximum likelihood estimation with windows set around prior stage boundary estimates, (2) averaging of estimates with variable precision including magnetochronologic data, and (3) calibration by means of cubic smoothing splines assuming equal duration of ammonite subzones. The end product is a time-scale in which the stage boundary ages are accompanied by approximate 95 per cent confidence intervals.
Authigenic and replacement francolites in modern phosphorite have values of within error of that of modern marine Sr (0.70916 ± 2). During the phosphatisation of carbonate, Sr is not inherited from the carbonate but is totally exchanged with Sr in ambient water. The in shallow marine pore waters is indistinguishable from the value for modern marine Sr, so authigenic francolite, which precipitates from pore water, accurately records the isotopic ratio of contemporary marine Sr. By comparing the in francolite with published curves for the isotopic evolution of Tertiary marine Sr we have dated phosphogenetic events affecting the Chatham Rise (4.90 ± 0.35 Ma), the Nambian margin (1.15 ± 0.25 Ma and 4.70 ± 0.35 Ma), and the Sechura Desert, Peru (11.8 ± 0.5 Ma).
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