Chemo- and cyclostratigraphic records of the Albian from the Tethyan Himalaya of southern Tibet, China

Abstract

The Albian Age is characterized by frequent short-lived perturbations of the global carbon cycle, including a series of Oceanic Anoxic Events (OAEs). Carbon Isotope Excursions (CIEs) document these OAEs in detail. A strong influence of orbital forcing on oceanographic and climatic conditions in the Albian has been documented, but the relationship between orbital changes and the carbon cycle is still unclear. The Albian CIEs are well recorded globally, except in the eastern Tethys. The major forcing mechanisms of Mesozoic carbon cycling have long remained a conundrum. Here, we present bulk carbon (δ 13 C carb ) and oxygen (δ 18 O carb ) isotope data, magnetic susceptibility (MS) and total organic carbon (TOC) data from the Nirang Section in the Tethyan Himalaya of southern Tibet, China. The δ 13 C carb record for the first time documents the long-term secular variations in δ 13 C during the Albian in the Tethyan Himalaya in high resolution. The δ 13 C curve obtained in Nirang can be correlated well with reference sections in other basins. OAE1b and 1c were identified as troughs in the δ 13 C profile in the lowermost and upper part of the section. Cyclostratigraphic analysis of MS, δ 13 C carb and TOC content from the Nirang Section reveals the imprint of the orbital cycles of eccentricity (∼100 kyr and ∼ 405 kyr) and a long-term amplitude modulation of either obliquity or eccentricity (∼1.2 Myr). The band-pass filters of the ∼100 kyr periodicity in MS provide the estimation of 563 kyr for the duration of OAE 1c and 677 kyr for that of the negative shift between OAE 1b and 1c. A detected ∼1.1 Myr periodicity is the most significant cycle, providing strong evidence for astronomically paced climate change in the eastern Tethys during the Albian. The band-pass filters of the ∼1.1 Myr periodicity in MS and TOC display a close correspondence, suggesting that the productivity and/or preservation potential of organic matter was likely controlled by orbitally forced changes in terrigenous input. Increasing δ 13 C values correspond to higher values of MS and TOC content and vice versa, indicating that the δ 13 C values of the eastern Tethys during the Albian were influenced by the intensity of the terrigenous flux and the subsequent burial of organic matter paced by orbital change. This work implies that cyclic changes in carbon reservoirs in the low latitudes of the Southern Hemisphere during the Albian were controlled by seasonal variations in terrigenous input driven by the influence of orbital cycles on regional hydrological processes. • A high-resolution δ 13 C curve of the Albian in the eastern Tethys. • A floating ATS built to estimate the duration of Albian CIEs. • The Albian carbon cycle in the eastern Tethys is paced by a ∼ 1.1 Myr cyclicity. • Terrigenous inputs and organic matter burial are responsible for δ 13 C changes in Tibet.