Jurassic Time Scale Research Articles

Calcite uranium–lead geochronology applied to hardground lithification and sequence boundary dating

AbstractHardground discontinuities within carbonate platforms form important stratigraphic surfaces which can be used at basin scale to correlate sequence boundaries. Although these surfaces are commonly used in sequence strati‐graphy, the timing and duration of hardground lithification and the crystallization of early cements remain unexplored. Here, early calcite cements were dated by U‐Pb geochronology for five Jurassic hardgrounds, interpreted as third‐order sequence boundaries, situated within a well‐constrained petrographic, sedimentological and stratigraphic framework. The consistency or the slight deviation between the age of the cements and the stratigraphic age of deposition of the formations illustrate that cementation occurred early in the diagenetic history. The ages obtained on dogtooth cements, replacing aragonite in gastropod shells and pendant cements in intergranular spaces, match those of the standard Jurassic biostratigraphic ammonite Zones, making calcite U‐Pb geochronology a promising method for dating third‐order sequence boundaries of depositional sequences and refining the Jurassic time scale in the future.

Astronomical constraints on the duration of the Early Jurassic Pliensbachian Stage and global climatic fluctuations

The Early Jurassic was marked by multiple periods of major global climatic and palaeoceanographic change, biotic turnover and perturbed global geochemical cycles, commonly linked to large igneous province volcanism. This epoch was also characterised by the initial break-up of the super-continent Pangaea and the opening and formation of shallow-marine basins and ocean gateways, the timing of which are poorly constrained. Here, we show that the Pliensbachian Stage and the Sinemurian–Pliensbachian global carbon-cycle perturbation (marked by a negative shift in δ13C of 2–4‰), have respective durations of ∼8.7 and ∼2 Myr. We astronomically tune the floating Pliensbachian time scale to the 405 Kyr eccentricity solution (La2010d), and propose a revised Early Jurassic time scale with a significantly shortened Sinemurian Stage duration of 6.9±0.4 Myr. When calibrated against the new time scale, the existing Pliensbachian seawater 87Sr/86Sr record shows relatively stable values during the first ∼2 Myr of the Pliensbachian, superimposed on the long-term Early Jurassic decline in 87Sr/86Sr. This plateau in 87Sr/86Sr values coincides with the Sinemurian–Pliensbachian boundary carbon-cycle perturbation. It is possibly linked to a late phase of Central Atlantic Magmatic Province (CAMP) volcanism that induced enhanced global weathering of continental crustal materials, leading to an elevated radiogenic strontium flux to the global ocean.

A new U–Pb zircon age for an ash layer at the Bathonian–Callovian boundary, Argentina

A U–Pb zircon age of 164.64 ± 0.2 Ma (95% confidence level) is reported for an ash bed, at the Bathonian–Callovian (late Middle Jurassic) boundary, determined by isotope dilution thermal ionisation mass spectrometry from individual, chemically abraded grains. The volcanic ash layer occurs within the Chacay Melehue Formation, Chacay Melehue section, Neuquén Province, central west Argentina, above the last record of ammonites of the regional Lilloettia steinmanni Standard Zone, and, stratigraphically, where the first of those of the regional Eurycephalites vergarensis Standard Zone appears, generally referred to as the uppermost Bathonian and the lowermost Callovian, respectively. This ash layer represents the only known datable horizon worldwide that is directly related to a well-documented ammonite faunal succession at this boundary. The U–Pb zircon age is older than one previously reported for the same bed and closer to an estimation of 164.7 ± 4 Ma for the boundary based on the scaling durations of ammonite zones to their subzones in the sub-boreal standard zonation. The new age agrees better with the age model for the Oxfordian through Bathonian M-sequence magnetic anomalies in the Pacific and contributes to the radioisotopic age calibration of the Jurassic time scale.

Astronomical calibration of the Early Oxfordian (Vocontian and Paris basins, France): Consequences of revising the Late Jurassic time scale

Magnetic susceptibility (MS) variations record Earth's orbital parameters in the clays and marls of the Early Oxfordian in the Paris and Vocontian basins of France. Climatically driven weathering of surrounding emergent areas and the resulting detrital input to the basins is a significant source of the MS signal. MS proves to be an effective tool for deciphering the orbital forcing signal in these sediments, and for assessing the chronology of these formations. The 405-kyr orbital eccentricity cycle is clearly visible in the MS signal and, consequently, is a valuable geochronometer for this portion of the Jurassic time scale. Astronomical calibration of the Mariae ammonite zone (basal Oxfordian stage) indicates a duration of ~ 2.2 myrs, whereas current time scales assign only 0.6 myrs to this biozone. However, the Late Jurassic time scale has large uncertainties in stage boundary ages (± 4 myrs), hence of interval durations. These results could lead to significant revisions in the M-sequence magnetic anomaly block model, and greatly improve the resolution of the Jurassic time scale.

The quest for refined calibration of the Jurassic time-scale

The Jurassic time-scale assigns numerical ages to boundaries of chronostratigraphic units. A well-established ammonite biochronology forms the basis of stage definitions that are being formalized by Global Stratotype Sections and Points. Two major updates of the Jurassic time-scale (referred to as JTS2000 and GTS2004) were published recently. JTS2000 relies heavily on U-Pb and 40 Ar/ 39 Ar dates, whereas GTS2004 emphasizes complementary scaling methods using strontium (Sr) isotope stratigraphy, cyclostratigraphy and magnetostratigraphy. U-Pb and 40 Ar/ 39 Ar dates remain the backbone of the time-scale; relevant new developments are reviewed briefly. Fourteen recently published ages are added to the database of calibration points. Floating cyclostratigraphies already cover a significant portion of the Jurassic, allowing measurements of durations that need to be anchored and linked to chronostratigraphy. Where tie-points are sparse, reliance on scaling methods remains necessary. Sr isotope stratigraphy and magnetostratigraphy are increasingly sophisticated and useful for both correlation and scaling. Further refinements of calibration are expected from more accurate and densely spaced radioisotopic age tie-points, especially in the Late Jurassic, and from an extended coverage of Jurassic astrochronology. In the computer era, time-scales increasingly are being delivered digitally, updated continuously and accessed interactively by their users.

A U-Pb and 40Ar/39Ar time scale for the Jurassic

Published time scales provide discrepant age estimates for Jurassic stage boundaries and carry large uncertainties. The U-Pb or 40Ar/39Ar dating of volcaniclastic rocks with precisely known stratigraphic age is the preferred method to improve the calibration. A radiometric age database consisting of fifty U-Pb and 40Ar/39Ar ages was compiled to construct a revised Jurassic time scale. Accepted ages have a precision of ±5 Ma (2σ) or better and are confined to no more than two adjacent stages. The majority of these calibration points result from integrated bio- and geochronologic dating in the western North American Cordillera and have not been previously used in time scales. Direct dates are available only for the Triassic-Jurassic boundary and the initial boundary of the Crassicosta chron and the Callovian stage. The chronogram method was used to estimate all Early and early Middle Jurassic zone boundaries (attempted here for the first time), late Middle Jurassic substage boundaries, and Late Jurassic stage boundaries. Significant improvement is achieved for the Pliensbachian and Toarcian, where six consecutive zone boundaries are determined. The derived zonal durations are disparate, varying between 0.4 and 1.6 Ma. The latest Jurassic isotopic database remains too sparse, therefore chronogram estimates are improved using interpolation based on magnetochronology. The initial boundaries of Jurassic stages are proposed as follows: Berriasian (Jurassic-Cretaceous): 141.8+2.5&#150 1.8 Ma; Tithonian: 150.5+3.4&#150 2.8 Ma; Kimmeridgian: 154.7+3.8&#150 3.3 Ma; Oxfordian: 156.5+3.1&#150 5.1 Ma; Callovian: 160.4+1.1&#150 0.5 Ma; Bathonian: 166.0+3.8&#150 5.6 Ma; Bajocian: 174.0+1.2&#150 7.9 Ma; Aalenian: 178.0+1.0&#150 1.5 Ma; Toarcian: 183.6+1.7&#150 1.1 Ma; Pliensbachian: 191.5+1.9&#150 4.7 Ma; Sinemurian: 196.5+1.7&#150 5.7 Ma; Hettangian (Triassic-Jurassic): 199.6 ± 0.4 Ma.

New U–Pb zircon ages integrated with ammonite biochronology from the Jurassic of the Canadian Cordillera

The accuracy of published Jurassic time scales is compromised by a paucity of sufficiently accurate and stratigraphically well-constrained isotopic dates. U–Pb dating of volcaniclastic rocks within fossiliferous marine successions is a method suitable of providing additional useful calibration points. Stikinia and Wrangellia, two of the major accreted terranes of the Canadian Cordillera, comprise volcanosedimentary assemblages of magmatic arc origin. Within them we selected sections from which we report 14 new U–Pb zircon ages that are integrated with ammonite biochronology at the zonal level. Poor zircon recovery and complex U–Pb systematics made it difficult to obtain precise ages for many of the samples. The following ages were determined (with 2σ errors): 194.0+9.1–1.8 Ma from the Plesechioceras? harbledownense Assemblage (upper Sinemurian), 191.5 ± 0.8 Ma from the Plesechioceras? harbledownense Assemblage (upper Sinemurian) to the Whiteavesi Zone (lower Pliensbachian), 185.6+6.1–0.6 Ma from the Freboldi Zone (lower Pliensbachian), 184.7 ± 0.9 Ma from the Kunae Zone (upper Pliensbachian), 180.4+8.0–0.4 Ma from the Kanense to Planulata zones (lower to middle Toarcian), 179.8 ± 6.3 Ma from the Yakounensis Zone (upper Toarcian) to the lower Bajocian, 167.2+10.5–0.4 Ma from the Rotundum Zone (upper Bajocian), 158.2+1.9–0.4 Ma from the upper Bathonian, and 162.6+2.9–7.0 from the upper Bathonian to lower Callovian. Five other dates are inferior in precision, but still provide some constraints for time-scale calibration. The U–Pb dates reported here together with a wealth of other recently obtained Cordilleran isotopic dates will be used for a significant revision of the Jurassic time scale.

New U–Pb zircon ages integrated with ammonite biochronology from the Jurassic of the Canadian Cordillera

The accuracy of published Jurassic time scales is compromised by a paucity of sufficiently accurate and stratigraphically well-constrained isotopic dates. U–Pb dating of volcaniclastic rocks within fossiliferous marine successions is a method suitable of providing additional useful calibration points. Stikinia and Wrangellia, two of the major accreted terranes of the Canadian Cordillera, comprise volcanosedimentary assemblages of magmatic arc origin. Within them we selected sections from which we report 14 new U–Pb zircon ages that are integrated with ammonite biochronology at the zonal level. Poor zircon recovery and complex U–Pb systematics made it difficult to obtain precise ages for many of the samples. The following ages were determined (with 2σ errors): 194.0+9.1–1.8 Ma from the Plesechioceras? harbledownense Assemblage (upper Sinemurian), 191.5 ± 0.8 Ma from the Plesechioceras? harbledownense Assemblage (upper Sinemurian) to the Whiteavesi Zone (lower Pliensbachian), 185.6+6.1–0.6 Ma from the Freboldi Zone (lower Pliensbachian), 184.7 ± 0.9 Ma from the Kunae Zone (upper Pliensbachian), 180.4+8.0–0.4 Ma from the Kanense to Planulata zones (lower to middle Toarcian), 179.8 ± 6.3 Ma from the Yakounensis Zone (upper Toarcian) to the lower Bajocian, 167.2+10.5–0.4 Ma from the Rotundum Zone (upper Bajocian), 158.2+1.9–0.4 Ma from the upper Bathonian, and 162.6+2.9–7.0 from the upper Bathonian to lower Callovian. Five other dates are inferior in precision, but still provide some constraints for time-scale calibration. The U–Pb dates reported here together with a wealth of other recently obtained Cordilleran isotopic dates will be used for a significant revision of the Jurassic time scale.

Cyclostratigraphy and the Early Jurassic timescale: Data from the Belemnite Marls, Dorset, southern England

Research Article| December 01, 1999 Cyclostratigraphy and the Early Jurassic timescale: Data from the Belemnite Marls, Dorset, southern England G. P. Weedon; G. P. Weedon 1Department of Environment, Geography and Geology, University of Luton, Park Square, Luton, Bedfordshire LU1 3JU, United Kingdom Search for other works by this author on: GSW Google Scholar H. C. Jenkyns H. C. Jenkyns 2Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, United Kingdom Search for other works by this author on: GSW Google Scholar GSA Bulletin (1999) 111 (12): 1823–1840. https://doi.org/10.1130/0016-7606(1999)111<1823:CATEJT>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation G. P. Weedon, H. C. Jenkyns; Cyclostratigraphy and the Early Jurassic timescale: Data from the Belemnite Marls, Dorset, southern England. GSA Bulletin 1999;; 111 (12): 1823–1840. doi: https://doi.org/10.1130/0016-7606(1999)111<1823:CATEJT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Time series based on determinations (wt%) of calcium carbonate and total organic carbon have been generated for the entire Lower Jurassic hemipelagic Belemnite Marls, Dorset, southern Britain. This formation was deposited during early Pliensbachian time, at a paleolatitude of about 35°N, in an epicontinental sea that was largely enclosed by the supercontinent of Pangea. The sequence contains compositionally diverse light and dark marl bedding couplets, the thicknesses of which are notably reduced in the upper third of the section. The regularity of the couplets in segments of the sequence, combined with a regular amplitude modulation, indicates an origin that is related to the orbital-precession cycle (i.e., one of the Milankovitch parameters). A timescale is developed by assigning a duration of 20 k.y. per couplet, and this suggests that the entire formation represents at least 1.78 m.y.Using the new timescale, bundles of bedding couplets are shown to have periods consistent with the 123 k.y. component of the orbital-eccentricity variations. The amplitude of the couplets varies at the same frequencies as the bundle cycles, in accordance with the interpretation that the couplets record precession and the bundles record eccentricity. However, despite having the same frequency of variation, there is no consistent relationship (coherence) between the variations in amplitude of the couplet cycle and the bundle cycles as would be predicted by the eccentricity-precession relationship. This mismatch can be explained in terms of nonlinear behavior of a climatic system characterized by a varying response time or nonlinear response of the sedimentary system itself. The data contain no evidence for orbital-obliquity cycles. Because the obliquity cycle affects insolation principally at high latitudes, the climatic factors that indirectly controlled the sedimentary cyclicity must have arisen at relatively low latitudes.The Belemnite Marls timescale indicates highly variable minimum durations for ammonite zones and subzones. True durations cannot be determined because it is possible that the succession is incomplete as a result of undetected erosion and/or nondeposition. A combination of the new results with cyclostratigraphic data from Yorkshire, northeast England, and the Southern Alps, Switzerland, indicates, based on cycle counts, that the Pliensbachian Stage lasted at least 4.82 m.y. Marine Sr-isotope ratios appear to have decreased linearly from the start of Jurassic time until the end of Pliensbachian time. The rate of decrease in 87Sr/86Sr established using the Belemnite Marls timescale was 0.000042/m.y. (or less if the main part of the formation is incomplete). Using this rate, with the observed changes in Sr-isotope ratios, gives minimum durations of 2.86 m.y. for Hettangian time, 7.62 m.y. for Sinemurian time, and 6.67 m.y. for Pliensbachian time. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Integrated ammonite biochronology and U-Pb geochronometry from a basal Jurassic section in Alaska

New results from integrated biochronologic and geochronometric studies on the basal Jurassic section at Puale Bay (Alaska Peninsula) improve the calibration of the Early Jurassic time scale. Previously, the interval around the Triassic-Jurassic system boundary was poorly dated, which hampered our understanding of geologic and biotic events, e.g., the end-Triassic mass extinction and subsequent recovery. Published suggestions for the presence of the earliest Hettangian (Planorbis Zone) and a continuous boundary section at Puale Bay are not substantiated. Although the Kamishak Formation is likely to contain an uninterrupted sedimentary record, pre‐middle Hettangian strata are locally faulted, resulting in an apparent Rhaetian to early Hettangian gap in the fossil record. The Hettangian ammonite zonal schemes developed locally for Nevada and the Queen Charlotte Islands permit reliable correlation with Alaska, but have limited applicability. The faunal succession recorded at Puale Bay is useful in the development of a regional zonation for North America. We obtained three U-Pb zircon dates that are tied into an ammonite biochronology at the zonal level. A middle Hettangian tuff layer from near the top of the Kamishak Formation is dated at 200.8 +2.7 / ‐2.8 Ma. Tuffs from the overlying Talkeetna Formation are bracketed by middle and late Hettangian ammonites and yield crystallization ages of 197.8 +1.2 / ‐0.4 and 197.8 ± 1.0 Ma. These new calibration points require that the Hettangian-Sinemurian boundary be younger than 199 Ma. The Triassic-Jurassic boundary is likely to fall between 200 and 205 Ma. Similar studies are needed for the uppermost Triassic to obtain tighter constraints. Zircon U-Pb systematics of two samples revealed strong Proterozoic and late Archean inheritance patterns that require revised tectonic models to account for the proximity of the Talkeetna arc to evolved crustal blocks.

Astronomical calibration of the Jurassic time-scale from cyclostratigraphy in British mudrock formations

Three British Jurassic mudrock formations have been investigated, via timeseries analysis, for evidence of sedimentary cyclicity related to orbitalclimatic (Milankovitch) cyclicity: the Blue Lias, ...

Long-period Milankovitch cycles from the Late Triassic and Early Jurassic of eastern North America and their implications for the calibration of the Early Mesozoic time–scale and the long–term behaviour of the planets

During the Late Triassic and Early Jurassic the Newark rift basin of the northeastern US accumulated in excess 5 km of continental, mostly lacustrine strata that show a profound cyclicity previousl...

Constraints on the Jurassic Time-Scale by40Ar/39Ar Dating of North Caucasian Volcanic Rocks

age measurements on biotites and high-temperature plagioclases of Jurassic basaltic to rhyolitic subvolcanic rocks from the Northern Great Caucasus (USSR) yielded plateau and total argon ages between 190 and 180 Ma. The dated rocks are intrusive sills, dikes and laccoliths in sediments of the middle to upper Pliensbachian and of the lower Toarcian (Lower Jurassic). Pebbles of the volcanic rocks exist in the basal conglomerates of the Aalenian (base of the Middle Jurassic). Thus, their stratigraphic age is restricted to the Lower Jurassic stages of middle to upper Pliensbachian and Toarcian. Because of the scarcity of tie-points in the Lower Jurassic, the isotopic ages of these volcanic rocks, in spite of their rather large stratigraphic range, may serve as new calibration points for the improvement of the Jurassic time-scale.

Jurassic Chronology and History of Atlantic Basins: ABSTRACT

Stratigraphic backbone for the eleven stages of the Jurassic period, 200 to 135 m.y. ago, are ammonite zonations with local resolution close to 1 m.y. Micropaleontologic zonations largely have stage-level resolution. Facies-dependence and provincialism limit universal application, and calibration to ammonite and (at the Jurassic-Cretaceous boundary) to calpionellid zonations is limited. The geomagnetic reversal scale (with few events only), stage designations, and linear time scale are not well integrated either. Uncertainty may be on the order of a stage. Two examples of recent progress in Jurassic stratigraphy are: (1) calibration of the Early Jurassic foraminifer and ostracod zonation for Portugal and Grand Banks to a standard ammonite scheme; it shows that the post-evaporite-dolomite marine transgression occurred at the Sinemurian-Pliensbachian boundary as in east Greenland and northwestern Europe; (2) acquistion of a continuously cored, fossiliferous Middle and Late Jurassic record in Deep Sea Drilling Site 534, Blake Bahama Basin, in the Jurassic magnetic quiet zone. Oceanic pillow basalt (31.5 m) occurs below a strong basement seismic reflector, which proves normal ocean crust exists under the Jurassic magnetic quiet zone. End_Page 1662------------------------------ The overlying dark shales are early-middle Callovian, which revises upward with 10 to 20 m.y., the age of the Blake Spur and M-28 anomalies, and the time of early spreading of the central North Atlantic. Widespread Callovian transgression may be an expression of rapid, early spreading. The new bio- and magneto-stratigraphic data are being integrated with local zonal schemes for Atlantic basins to provide an improved Jurassic time scale of events. End_of_Article - Last_Page 1663------------

A Jurassic Time Scale

Application of geologic ages expressed in numeric time (millions of years) is a recent but rapidly expanding factor in petroleum exploration (rates of tectonic movements; basin models; geohistory analysis; prediction of reservoir quality, source potential, and HC maturation; correlation of geophysics with geologic events, etc.). This paper proposes an emendation of published versions of the Jurassic time scale. The standard geochronologic subdivision is combined with a linear-numeric scale, with a biostratigraphic scheme (ammonites, calcareous nannofossils), and with the geomagnetic-reversal time scale. To this purpose, basement ages at some Deep Sea Drilling Project sites are evaluated and related to the geomagnetic-reversal scale. The numeric scale certainly cannot be r garded as precisely and firmly determined throughout the Jurassic, but it seems adequate as a broad framework.