Late Jurassic paleoenvironmental reconstruction based on stable oxygen isotopes in bulk carbonates from the Qiangtang Basin, eastern Tethys

Abstract

A composite eastern Tethyan oxygen and carbon isotope curve reveals major climate changes through the Late Jurassic. Despite significantly lower values and different amplitudes in scale, the δ¹⁸O data from whole-rock carbonates present fluctuant temperature results similar with well-studied composite δ¹⁸O curves of diagenetically-screened biogenic calcites, and are possibly acceptable as a paleotemperature proxy. The paleoclimate trends imply a cool global Callovian-Oxfordian transition, a mid-Oxfordian warming, a late Oxfordian cooling, a turbulent Kimmeridgian climate, a warm earliest Tithonian and rapid early Tithonian cooling event. The climate shift from the earliest Tithonian warmth to the middle early Tithonian cool climate was up to 8 °C decrease in some regions. These paleoclimate changes are greatly consistent with the eustatic sea-level changes, biological evolutions and paleoatmospheric CO₂ reconstructions, and are recorded by coeval carbon isotope perturbations relating to the organic carbon accumulations in marine sediments. Coupled δ¹⁸O and δ¹³C chemostratigraphy evidence that higher temperatures lead to more rapid continental weathering, increased nutrient-rich runoff into the oceans, and intensified marine productivity, resulting in increased organic‑carbon burial and more positive δ¹³C values in limestones. The decrease in primary productivity and burial rates during cooling periods is, in turn, commonly accompanied by low δ¹³C values.