Unraveling the onset of Cretaceous Oceanic Anoxic Event 2 in an extended sediment archive from the Tarfaya‐Laayoune Basin, Morocco

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Abstract

We investigated the onset and development of Cretaceous Oceanic Anoxic Event 2 (OAE2) in a newly drilled core (SN°4) from the Tarfaya Basin (southern Morocco), where this interval is unusually expanded. High‐resolution (centimeter‐scale equivalent to centennial) analysis of bulk organic and carbonate stable isotopes and of carbonate and organic carbon content in combination with XRF scanner derived elemental distribution reveal that the ocean‐climate system behaved in a highly dynamic manner prior to and during the onset of OAE2. Correlation with the latest orbital solution indicates that the main carbon isotope shift occurred during an extended minimum in orbital eccentricity (~400 kyr cycle). Shorter‐term fluctuations in carbonate and organic carbon accumulation and in sea level related terrigenous discharge were predominantly driven by variations in orbital obliquity. Negative excursions in organic and carbonate δ ¹³C preceded the global positive δ ¹³C shift marking the onset of OAE2, suggesting injection of isotopically depleted carbon into the atmosphere. The main δ ¹³C increase during the early phase of OAE2 in the late Cenomanian was punctuated by a transient plateau. Maximum organic carbon accumulation occurred during the later part of the main δ ¹³C increase and was associated with climate cooling events, expressed as three consecutive maxima in bulk carbonate δ ¹⁸O. The extinctions of the thermocline dwelling keeled planktonic foraminifers Rotalipora greenhornensis and Rotalipora cushmani occurred during the first and last of these cooling events and were likely associated with obliquity paced, ocean‐wide expansions, and intensifications of the oxygen minimum zone, affecting their habitat space on a global scale.

Key Points

The onset of OAE2, which corresponds to a two‐stepped increase in δ ¹³C spanning ~100 kyr, is preceded by negative carbon isotope excursions
A three‐stepped transient climate cooling with intermittent brief anoxic episodes occurred in the latest stage of the main δ ¹³C increase
Two major extinction events of thermocline dwelling planktonic foraminifers were closely linked to intensifications of the OMZ

Related collections

Most cited references 103

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Southward migration of the intertropical convergence zone through the Holocene.

G H Haug, K A Hughen, D M Sigman … (2001)

Titanium and iron concentration data from the anoxic Cariaco Basin, off the Venezuelan coast, can be used to infer variations in the hydrological cycle over northern South America during the past 14,000 years with subdecadal resolution. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene "thermal maximum." Since approximately 5400 years ago, a trend toward drier conditions is evident from the data, with high-amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the "Little Ice Age." These regional changes in precipitation are best explained by shifts in the mean latitude of the Atlantic Intertropical Convergence Zone (ITCZ), potentially driven by Pacific-based climate variability. The Cariaco Basin record exhibits strong correlations with climate records from distant regions, including the high-latitude Northern Hemisphere, providing evidence for global teleconnections among regional climates.