Author:

Keywords:

iridium, stable isotopes, upper paleocene, benthic taxa, foraminifera, mass extinctions, carbon-isotope stratigraphy, tertiary boundary clays, eocene boundary, north-atlantic, south china, anomalies, mississippian, paleogene, caravaca, oklahoma, Science & Technology, Physical Sciences, Life Sciences & Biomedicine, Geography, Physical, Geosciences, Multidisciplinary, Paleontology, Physical Geography, Geology, upper Paleocene, CARBON-ISOTOPE STRATIGRAPHY, TERTIARY BOUNDARY CLAYS, EOCENE BOUNDARY, NORTH-ATLANTIC, SOUTH CHINA, ANOMALIES, MISSISSIPPIAN, PALEOGENE, CARAVACA, OKLAHOMA, 0403 Geology, 0602 Ecology, 0603 Evolutionary Biology, 3709 Physical geography and environmental geoscience, 4301 Archaeology

Abstract:

In the expanded upper Paleocene-lower Eocene section (approximate to 30 m of Zone P5 sediments) at Zumaya, northern Spain, the highest occurrence of many late Paleocene deep-sea benthic foraminifera species (approximate to 40% extinction), coincides with a transition from marl to calcite-free clay. Our high-resolution studies (chemical elements, delta(13)C, delta(18)O, calcareous nannofossils, planktic and benthic foraminifera) show that below the marl-clay transition there is a 40-50 cm thick interval (corresponding to 10-20 kyr) containing a detailed record of a gradual succession of faunal and geochemical events culminating in the benthic extinctions. Planktic foraminiferal and nannofossil changes (e.g., the onset of demise in Fasciculithus genus) occur a few meters below the marl-clay transition. In the limestone 50 cm below the base of the clay, a prominent glauconite maximum indicates that sea-floor oxygenation suddenly decreased. Glauconite continues to be common until the onset of clay deposition. A whole-rock negative delta(13)C Shift (1.6 parts per thousand), most likely reflecting an original sea-water trend, is gradually developed over the 40 cm of greenish brown marls immediately below the clay. Ar the base of these marls there is a small, significant iridium anomaly of 133 ppt Ir compared with an average background of 38 ppt. In the marls the demise of the Fasciculithus species accelerates, Gavelinella beccariiformis becomes extinct, and the abundance of Acarinina species begins to increase. The superjacent 4 m of clay is devoid of original calcite in its lower part and has a low calcareous content higher up. At calcareous levels in the clay an unusual planktic foraminifera fauna occurs, dominated by Acarinina species. When marl deposition returns, delta(13)C gradually increases and then stabilizes at values about 0.5 parts per thousand lower than before the isotopic excursion. The delta(13)C excursion spans in total 5 m, probably corresponding to 200-400 kyr. The fasciculiths disappear shortly after the stabilization of delta(13)C.