Abstract
Some of the major Carbon cycle perturbations of the Phanerozoic occurred during the Aptian, in relation to magmatism. The highest temperatures reconstructed for the Cretaceous Period correspond to the Oceanic Anoxic Event of the early Aptian (OAE 1a), an episode of accelerated global change. Here we present a chemostratigraphic study based on osmium isotopes integrated with high-resolution Carbon-Oxygen stable isotope data from the Cau Core (Western Tethys, SE Spain), including a 6.4 Ma record from the early to the late Aptian. This high-resolution study of the continuous and expanded Cau section permits a thorough understanding of the duration of the Aptian events, as well as an evaluation of the mechanisms triggering the abrupt changes of the global carbon and osmium cycles and their interdependence. Here we show that the Large Igneous Province (LIP) Aptian magmatism initiated 550–750 kyr prior to the OAE 1a, and persisted for 1.4 Myr after the event, influencing the composition of seawater for 2.8 Myr. We show a continuous Os isotope record encompassing the OAE 1a and the late Aptian for the first time, and demonstrate that the recovery from the exceptionally unradiogenic composition of seawater Os produced by the dominance of the Ontong Java Plateau volcanism, was slow. Our results demonstrate the different time duration of some events, and the asynchronous relationship between the carbon and osmium cycles
Highlights
The Aptian (121.4–113.2 Ma, Gradstein et al, 2020), records major environmental perturbations at both global and local scales, reflected in prominent climatic changes and biotic turnovers both in continental and marine realms
The Osi profile has been subdivided into 5 segments (B to F), following previously defined segments (A to E; Bottini et al, 2012), for the OAE 1a interval, adding a division in segments B and C, and a new segment F extending up to the upper Aptian (Fig. 4).Overall, the Re and 192Os abundances of the 56 samples range from 0.37 to 29.63 ppb and
This zig-zag pattern is recorded in the δ13C data (Fig. 4)In subsegment B2 (137 to 130 m – middle part of δ13C zone Ap2), the Osi values show a gradual shift towards non-radiogenic values, from 0.84 to 0.27, which is paired with a slight increase in Re content from 0.37 to 3.76 ppb (Fig. 4), and this correlates with the onset of the C-isotope CIE predating the OAE 1a
Summary
The Aptian (121.4–113.2 Ma, Gradstein et al, 2020), records major environmental perturbations at both global and local scales, reflected in prominent climatic changes and biotic turnovers both in continental and marine realms. The most remarkable environmental changes during the Aptian are related to the early Aptian Oceanic Anoxic Event or OAE 1a (Schlanger and Jenkyns, 1976; Arthur et al, 1990) This major event was marked by intense global palaeoclimatic and palaeoceanographic change, related to a rise in temperature that led to a hyperthermal event, increased marine productivity, depleted oxy gen conditions in the oceans and widespread burial of organic matter in deep marine settings in a global context of sea-level rise (e.g., Weissert and Breheret, 1991; Erba, 1994; Erba and Tremolada, 2004; Erbacher et al, 1996; Weissert et al, 1998; Leckie et al, 2002; Jenkyns, 2010; Erba et al, 2015; Castro et al, 2019). The sources of carbon have been the subject of intense debate, and are considered to originate from different and possibly complementary sources: submarine volcanic degassing mostly from the Ontong-Java Plateau (OJP), methane emissions, and carbon emissions caused by the injection of magma into organic-rich sediments in the High Artic
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