Astronomical pacing and impact of the Middle Maastrichtian warming event on the Maastrichtian upwelling system of the southern Neo-Tethys Ocean margin (Jordan)

Abstract. The southern NeoTethys Ocean margin was the site of one of the most organically rich Early Maastrichtian global upwelling systems, with organic matter concentrations reaching>20 % TOC, which came to an abrupt end in the Late Maastrichtian, when sedimentation changed to pure chalk deposits. The integration of biostratigraphy, climate and depositional environment proxies, and cyclostratigraphy demonstrated that this change from organic to carbonate-dominated productivity occurred around the Early-Late Maastrichtian and was time equivalent to a climatic change from cooler to warmer conditions. The smaller scale productivity variations were paced by the eccentricity modulated precession orbital cycles. The integration of calcareous nannofossil and dinoflagellate cyst biostratigraphy, radiolarian paleoecology, stable isotope geochemistry (δ¹³C_carb, δ¹³C_org, δ¹⁸O and δ¹⁵N_org), and organic geochemical proxies from two closely spaced shallow cores (139 m and 71 m thickness) in Central Jorden were used to reconstruct the evolution of the Maastrichtian upwelling system manifest along the Levant margin of the southern NeoTethys Ocean. Integrated biostratigraphic and chemostratigraphic data constrain deposition of the oil shale interval to the Early Maastrichtian (72.7–68.2 Ma), representing ~4.5 Myr of accumulation with sedimentation rates of ~1.5–2.2 cm kyr⁻¹. Pronounced lithological and geochemical cyclicity reveals a dominant precession signal modulated by short eccentricity (~100 kyr), suggesting that eccentricity-paced insolation forcing regulated migration of the Intertropical Convergence Zone (ITCZ), regional wind intensity, and coastal upwelling strength. These orbitally forced changes controlled nutrient delivery, marine productivity, as expressed in the calcareous nannofossil, dinoflagellate cyst, and radiolarian assemblages, and cyclic accumulation of organic-rich sediments. Combined δ¹³C_carb, δ¹³C_org, and calcareous nannofossil records place the Middle Maastrichtian Carbon Isotope Event within the upper part of the oil shale succession. δ¹⁸O trends and nannofossil assemblage variations indicate cooling during the Early Maastrichtian, followed by warming during the early Late Maastrichtian. Low total organic nitrogen values, elevated C/N ratios, depleted δ¹³C_org values, and enriched δ¹⁵N_org signatures indicate intense diagenetic recycling of nitrogen-rich organic matter under persistent oxygen-deficient conditions, likely involving denitrification within an expanded oxygen minimum zone. Our findings demonstrate the coupled influence of orbital forcing and climate change on upwelling dynamics, marine productivity, and biogenic sedimentation during the Early Maastrichtian.