Expression of the late Aptian cold snaps and the OAE1b in a highly subsiding carbonate platform (Aralar, northern Spain)

Abstract

Cretaceous climate records provide evidence that major volcanic pulses with duration of 103 to several 105yr triggered changes in climate and oceanography. Black shales of Oceanic Anoxic Event 1b (ca. 113–109Ma) are regarded as signatures of late Aptian greenhouse pulses associated with volcanic episodes. New TEX86 paleotemperature record indicates that warm Aptian climate was interrupted by repeated cold snaps alternating with described greenhouse pulses. An extraordinary thick shallow-water carbonate succession of the Aralar Platform from the southeastern Basque–Cantabrian Basin in Spain provides a unique opportunity to test the hypothesis that cold phases interrupted warm climate in the Aptian. Platform evolution is traced through time of the proposed Aptian cold snaps alternating with greenhouse episodes. New high-resolution C-isotope records established in the studied upper Aptian platform carbonates serve as chemostratigraphic tool providing a link between carbonate-platform evolution, basinal black-shale formation and associated changes in open ocean palaeotemperatures. The late Aptian cold snaps find their expression in a remarkably reduced neritic succession, punctuated by several emersion horizons formed during sea-level lowstands. The studied section bears evidence for several episodes of choked carbonate production related to increased runoff at times of sea-level rise, during which orbitolinids bloomed in a sediment-loaden lagoonal setting. These intervals coincide with the deposition time of organic-rich Kilian and Leenhardt levels belonging to OAE1b.