Mode and tempo of the Paleocene-Eocene thermal maximum in an expanded section from the Venetian pre-Alps

Abstract

The central part of the Piave River valley in the Venetian pre-Alps of NE Italy exposes an expanded and continuous marine sediment succession that encompasses the Paleocene series and the Paleocene to Eocene transition. The Paleocene through lowermost Eocene succession is >100 m thick and was deposited at middle to lower bathyal depths in a hemipelagic, near-continental setting in the central western Tethys. In the Forada section, the Paleocene succession of limestone-marl couplets is sharply interrupted by an ~3.30 m-thick unit of clays and marls (clay marl unit). The very base of this unit represents the biostratigraphic Paleocene-Eocene boundary, and the entire unit coincides with the main carbon isotope excursion of the Paleocene-Eocene thermal maximum event. Concentrations of hematite and biogenic carbonate, delta 13C measurements, and abundance of radiolarians, all oscillate in a cyclical fashion and are interpreted to represent precession cycles. The main excursion interval spans five complete cycles, that is, 105 ± 10 k.y. The overlying carbon isotope recovery interval, which is composed of six distinct limestone-marl couplets, is interpreted to represent six precessional cycles with a duration of 126 ± 12 k.y. The entire carbon isotope excursion interval in Forada has a total duration of ~231 ± 22 k.y., which is 5%–10% longer than previous estimates derived from open ocean sites (210–220 k.y.). Geochemical proxies for redox conditions indicate oxygenated conditions before, during, and after the carbon isotope excursion event. The Forada section exhibits a nonstepped sharp decrease in delta 13C (-2.35‰) at the base of the clay marl unit. The hemipelagic, near-continental depositional setting of Forada and the sharply elevated sedimentation rates throughout the clay marl unit argue for continuous rather than interrupted deposition and show that the initial nonstepped carbon isotope shift was not caused by a hiatus. A single sample at the base of the unit lacks biogenic carbonate. Preservation of carbonate thereafter improves progressively up-section in the clay marl unit, which is consistent with a prodigiously abrupt and rapid acidifi cation of the oceans followed by a slower, successive deepening of the carbonate compensation depth. Increased sedimentation rates through the clay marl unit (approximately the main interval of the carbon isotope excursion) are consistent with an intensified hydrological cycle driven by supergreenhouse conditions and enhanced weathering and transport of terrigenous material to this near-continental, hemipelagic environment in the central western Tethys. The sharp transition in lithology from the clay marl unit to the overlying limestone-marl couplets in the recovery interval and the coincident shift toward heavier delta 13C values suggest that the silicate pump and continental weathering, the cause of the enhanced terrigenous flux to Forada, stopped abruptly. This implies that the source of the light CO2 ceased to be added to the ocean-atmosphere system at the top of the cla...

Late Paleocene–early Eocene Tethyan carbonate platform evolution — A response to long- and short-term paleoclimatic change

“…In the Pyrenees, Spain, Schmitz andPujalte (2003, 2007) noticed a dramatic increase in seasonal rain and an increased intra-annual humidity gradient during the PETM that resulted in a megafan complex. Summarizing the global climatic situation for the PETM it can be noticed that this interval is characterized by enhanced humidity and thus an intensified hydrologic cycle, resulting in increased terrigenous input in hemipelagic regions, with exceptions in only few areas (Bolle and Adatte, 2001;Pagani et al, 2006b;Giusberti et al, 2007;Zachos et al, 2008). The intensified hydrologic cycle would have brought enhanced nutrients into marginal basins, whereas the open ocean may have remained oligotrophic (Gibbs et al, 2006b), which bears on a discussion of the trophic resource regimes.…”

“…In a former shelf setting (New Jersey, USA), oligotrophic nannofossil genera are reduced in abundance, while mesotrophic genera increased due to increased nutrient availability during the PETM (Gibbs et al, 2006b). Intensified weathering is also documented by an increase in kaolinite (Bolle and Adatte, 2001;Ernst et al, 2006), an osmium isotope excursion (Ravizza et al, 2001), and an increase in the rate of hemipelagic sedimentation in the northern Tethys (Egger et al, 2003;Giusberti et al, 2007).…”

Eustatic variations during the Paleocene‐Eocene greenhouse world

“…Increase in terrigenous sediment supply for Bass River and Wilson Lake is from Sluijs et al [2007b] and John et al [2008]. Numbers refer to the following sites: site 1, Lomonosov Ridge, Arctic Ocean (SL, TS ); site 2, Doel, North Sea (SL [Steurbaut et al, 2003]); site 3, Basque Region, Bay of Biscay (SL, TS Pujalte and Schmitz, 2006]); site 4, Forada, Central Northern Tethys (TS [Giusberti et al, 2007]); site 5, Turgay Straight (SL [Iakovleva et al, 2001]); site 6, Lodo Formation, California (SL [John et al, 2008]); site 7, Gebel Duwi, Central Southern Tethys (SL [Speijer and Morsi, 2002]); site 8, Tawanui, Southwestern Pacific (TS [Crouch et al, 2003b], SL [Crouch and Brinkhuis, 2005]); and site 9, Clarence River Valley, Southwestern Pacific (TS PETM [Hollis et al, 2005], TS other presumed hyperthermals [Nicolo et al, 2007]). …”

Magnetofossil spike during the Paleocene‐Eocene thermal maximum: Ferromagnetic resonance, rock magnetic, and electron microscopy evidence from Ancora, New Jersey, United States

“…The climatic event led to changes in the hydrologic cycle, which in turn altered the character of sediments deposited throughout the world. In many continental margin sections, the PETM is associated with thick, siliclastic deposits, presumably reflecting enhanced fluvial sediment delivery [e.g., Crouch et al, 2003;Gawenda et al, 1999;Giusberti et al, 2007;Schmitz and Pujalte, 2003]. In the Atlantic Coastal Plain of the northeastern United States, PETM sections are expanded, depleted in sand-sized particles and enriched in clay-sized kaolinite [Gibson et al, 1993[Gibson et al, , 2000Kent et al, 2003].…”