Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)

Abstract

Abstract. One of the main controversial themes in palaeoclimatology involves elucidating whether climate during the Jurassic was warmer than the present day and if it was the same over Pangaea, with no major latitudinal gradients. There has been an abundance of evidence of oscillations in seawater temperature throughout the Jurassic. The Pliensbachian (Early Jurassic) constitutes a distinctive time interval for which several seawater temperature oscillations, including an exceptional cooling event, have been documented. To constrain the timing and magnitude of these climate changes, the Rodiles section of the Asturian Basin (Northern Spain), a well exposed succession of the uppermost Sinemurian, Pliensbachian and Lower Toarcian deposits, has been studied. A total of 562 beds were measured and sampled for ammonites, for biochronostratigraphical purposes, and for belemnites, to determine the palaeoclimatic evolution through stable isotope studies. Comparison of the recorded latest Sinemurian, Pliensbachian and Early Toarcian changes in seawater palaeotemperature with other European sections allows characterization of several climatic changes that are likely of a global extent. A warming interval partly coinciding with a δ 13 C bel negative excursion was recorded at the Late Sinemurian. After a "normal" temperature interval, with temperatures close to average values of the Late Sinemurian-Early Toarcian period, a new warming interval containing a short-lived positive δ 13 C bel peak, developed during the Early-Late Pliensbachian transition. The Late Pliensbachian represents an outstanding cooling interval containing a δ 13 C bel positive excursion interrupted by a small negative δ 13 C bel peak. Finally, the Early Toarcian represented an exceptional warming period, which has been pointed out as being responsible for the prominent Early Toarcian mass extinction.

New high resolution geochemistry of Lower Jurassic marine sections in western North America: A global positive carbon isotope excursion in the Sinemurian?

“…1), which shows a succession of Upper Sinemurian, Pliensbachian and Lower Toarcian (Lower Jurassic) deposits, offers an excellent opportunity to asses this statement, as several climatic oscillations have been identified (Gómez et al, 2016) and the record of the TOC content of the succession reveals the presence of several intervals of organic-rich and black shale deposits.…”

“…2). A total of 191 analyses of stable isotopes were performed on diagenetically screened belemnite calcite samples to determine the seawater palaeotemperatures and the carbon isotope variations in the time interval studied (see Gómez et al, 2008;Gómez and Goy, 2011 for the latest Pliensbachian and the Early Toarcian, and Gómez et al, 2016, for the all studied interval). In addition, a total of 146 samples were analyzed for TOC content and radioactivity (gamma-ray) of the rocks was measured bed by bed along the whole section.…”

“…The ammonite-based biochronostratigraphical subdivisions of these deposits in the Asturian Basin have been carried out by Suárez-Vega (1974), Gómez et al (2008), Goy et al (2010a, b), Comas-Rengifo and Goy (2010) and Gómez et al (2016) which are the subdivisions used in this work.…”

“…Comparison of the recorded changes in seawater palaeotemperature, using the δ 18 O bel from diagenetically screened belemnite calcite as a proxy, and the δ 18 O bel records obtained in several European sections has allowed the characterization of several climatic intervals probably of global extent (Gómez et al, 2016). A warming interval which partly coincides with a negative δ 13 C bel excursion was recorded at the Late Sinemurian.…”

The hydrocarbon source rocks of the Pliensbachian (Early Jurassic) in the Asturian Basin (Northern Spain): Their relationship with the palaeoclimatic oscillations and gamma-ray response.

“…3) (Gómez et al, 2016). A negative δ showing the lithological column, the sequence stratigraphy, the gamma-ray log, the ammonite taxa distribution, the profiles of the δ …”