The base of the Toarcian (Early Jurassic) in the Almonacid de la Cuba section (Spain). Ammonite biostratigraphy, magnetostratigraphy and isotope stratigraphy
Abstract:The Almonacid de la Cuba section, located in the Iberian Range, in central-eastern Spain, contains an outstanding record of the Pliensbachian-Toarcian boundary (Early Jurassic). Four ammonite assemblages, characterized respectively by the presence of Pleuroceras, Canavaria, Dactylioceras (Eodactylites) and Dactylioceras (Orthodactylites) have been distinguished. The base of the Toarcian is located at level CU35.2, based on the first occurrence of Dactylioceras. The presence of Boreal and Mediterranean taxa all… Show more
“…The obtained isotope values suggest a relatively cold climate period for the Spinatum Zone recorded in the Iberian Basin, consistent with the data from other basins (e.g., Asturian Basin: Gómez & Goy, 2011;Gómez et al, 2015; Basque-Cantabrian Basin: Rosales et al, 2004;Causses Basin: Mailliot et al, 2009;Lusitanian Basin: Suan et al, 2010). A comparison with previous stable isotope analyses in the relatively deeper section in the Iberian area (Almonacid de la Cuba section: -Rengifo et al, 2010) and the nearby Asturian (Gómez & Goy, 2011) and Basque-Cantabrian basins (Rosales et al, 2004;Quesada et al, 2005) indicates similar isotope values for Spinatum Zone (Fig.12), ranging between -0.5‰ to 2.5‰ for δ 18 O and -0.5‰ to 2‰ for δ 13 C, and displaying coeval increasing and decreasing trends respectively.…”
Section: Accepted Manuscriptsupporting
confidence: 58%
“…Four lower-order sequences (sets of bundles) have been defined. Rengifo et al, 2010), the Asturian Basin (Gómez et al, 2015) and the Basque-Cantabrian Basin (Rosales et al, 2004;Quesada et al, 2005). The dashed line delimits the Spinatum zone extension.…”
Section: Accepted Manuscriptmentioning
confidence: 99%
“…obtained byComas-Rengifo et al (2010) after extensive ammonite biostratigraphy and 87 Sr/ 86 Sr isotope data from the nearby Almonacid de la Cuba section(Fig. 9B).…”
Deposition of regressive successions and coeval positive trend in the oxygen stable isotope record in relatively deep marine successions of the upper Pliensbachian of western European basins have been related to a cooling interlude within the warm greenhouse conditions of the Pliensbachian. Sedimentological, cyclostratigraphic and chemostratigraphic analyses carried out in two upper Pliensbachian successions exposed in the Iberian Chain (Obón and San Pedro localities, Spain) allowed the characterization of the imprint of this cooling interlude on the relatively shallow areas of the Iberian carbonate ramp. The upper Pliensbachian succession is characterized by skeletal limestones and encompasses proximal mid-ramp to proximal outer-ramp facies, in which resedimentation and reworking by storm-induced flows controlled the accumulation of bioclastic debris. Two orders of high-frequency, metre-scale sequences have been identified: bundles of beds, and deepening-shallowing sets of bundles. According to the age calibration (previous biostratigraphic data and new strontium isotopes data) and correlation with nearby sections, these A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 2 sequences are suggested as formed in tune with the short-term and long-term eccentricity Milankovitch cycles. The isotopic data from brachiopod shells and belemnite rostra indicate progressively increasing δ 18 O and slightly decreasing δ 13 C trends for the uppermost PliensbachianSpinatum Zone, reflecting the influence of cooling conditions. However, facies analysis reflects that the expected coeval long-term regression was interrupted by a tectonically driven transgressive event in the uppermost part of the Spinatum Zone.
“…The obtained isotope values suggest a relatively cold climate period for the Spinatum Zone recorded in the Iberian Basin, consistent with the data from other basins (e.g., Asturian Basin: Gómez & Goy, 2011;Gómez et al, 2015; Basque-Cantabrian Basin: Rosales et al, 2004;Causses Basin: Mailliot et al, 2009;Lusitanian Basin: Suan et al, 2010). A comparison with previous stable isotope analyses in the relatively deeper section in the Iberian area (Almonacid de la Cuba section: -Rengifo et al, 2010) and the nearby Asturian (Gómez & Goy, 2011) and Basque-Cantabrian basins (Rosales et al, 2004;Quesada et al, 2005) indicates similar isotope values for Spinatum Zone (Fig.12), ranging between -0.5‰ to 2.5‰ for δ 18 O and -0.5‰ to 2‰ for δ 13 C, and displaying coeval increasing and decreasing trends respectively.…”
Section: Accepted Manuscriptsupporting
confidence: 58%
“…Four lower-order sequences (sets of bundles) have been defined. Rengifo et al, 2010), the Asturian Basin (Gómez et al, 2015) and the Basque-Cantabrian Basin (Rosales et al, 2004;Quesada et al, 2005). The dashed line delimits the Spinatum zone extension.…”
Section: Accepted Manuscriptmentioning
confidence: 99%
“…obtained byComas-Rengifo et al (2010) after extensive ammonite biostratigraphy and 87 Sr/ 86 Sr isotope data from the nearby Almonacid de la Cuba section(Fig. 9B).…”
Deposition of regressive successions and coeval positive trend in the oxygen stable isotope record in relatively deep marine successions of the upper Pliensbachian of western European basins have been related to a cooling interlude within the warm greenhouse conditions of the Pliensbachian. Sedimentological, cyclostratigraphic and chemostratigraphic analyses carried out in two upper Pliensbachian successions exposed in the Iberian Chain (Obón and San Pedro localities, Spain) allowed the characterization of the imprint of this cooling interlude on the relatively shallow areas of the Iberian carbonate ramp. The upper Pliensbachian succession is characterized by skeletal limestones and encompasses proximal mid-ramp to proximal outer-ramp facies, in which resedimentation and reworking by storm-induced flows controlled the accumulation of bioclastic debris. Two orders of high-frequency, metre-scale sequences have been identified: bundles of beds, and deepening-shallowing sets of bundles. According to the age calibration (previous biostratigraphic data and new strontium isotopes data) and correlation with nearby sections, these A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 2 sequences are suggested as formed in tune with the short-term and long-term eccentricity Milankovitch cycles. The isotopic data from brachiopod shells and belemnite rostra indicate progressively increasing δ 18 O and slightly decreasing δ 13 C trends for the uppermost PliensbachianSpinatum Zone, reflecting the influence of cooling conditions. However, facies analysis reflects that the expected coeval long-term regression was interrupted by a tectonically driven transgressive event in the uppermost part of the Spinatum Zone.
“…2 ). Figure 4 Comparison of Hg/TOC, [Hg], carbon isotopes, magnetostratigraphy and ammonite biostratigraphy from Chacay Melehue (this study), Peniche (Lusitanian Basin, Portugal) 2 , 6 , the Mochras Borehole including astronomical age of 183.70 ± 0.50 60 (Cardigan Bay Basin, UK) 45 , 58 , 60 , 61 , and the Almonacid de la Cuba section (Spain) 62 , 63 . Grey bands indicate the Pliensbachian–Toarcian boundary and the Toarcian carbon-isotope excursion.…”
Section: The Pliensbachian–toarcian Boundary Carbon-isotope Excursionmentioning
The Pliensbachian–Toarcian boundary interval is characterized by a ~ 3‰ negative carbon-isotope excursion (CIE) in organic and inorganic marine and terrestrial archives from sections in Europe, such as Peniche (Portugal) and Hawsker Bottoms, Yorkshire (UK). A new high-resolution organic-carbon isotope record, illustrating the same chemostratigraphic feature, is presented from the Southern Hemisphere Arroyo Chacay Melehue section, Chos Malal, Argentina, corroborating the global significance of this disturbance to the carbon cycle. The negative carbon-isotope excursion, mercury and organic-matter enrichment are accompanied by high-resolution ammonite and nannofossil biostratigraphy together with U–Pb CA-ID-TIMS geochronology derived from intercalated volcanic ash beds. A new age of ~ 183.73 + 0.35/− 0.50 Ma for the Pliensbachian–Toarcian boundary, and 182.77 + 0.11/− 0.15 for the tenuicostatum–serpentinum zonal boundary, is assigned based on high-precision U–Pb zircon geochronology and a Bayesian Markov chain Monte Carlo (MCMC) stratigraphic age model.
“…According to these authors, this interpretation is supported by ammonite migration pattern indicating a northward expansion of Tethyan fauna. Additionally, δ 18 O values measured in belemnite rostra in the Almonacid de la Cuba section (Spain; Comas-Rengifo et al, 2010), and TEX 86 data from La Cerradura section (Spain; also suggest seawater warming during the Pl/To event. This is in opposition to δ 18 O values measured in brachiopod shells from the Barranco de la Cañada (Spain) and Fonte Coberta/Rabacal (Portugal) sections that suggest relatively cool temperature during the earliest Toarcian (Ullmann et al, 2020).…”
Section: An Updated Scenario For the Pliensbachian/toarcian Boundary ...mentioning
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