Hadley circulation and precipitation changes controling black shale deposition in the Late Jurassic Boreal Seaway. (3rd August 2016)

• Record Type: Journal Article
• Authors: Armstrong, Howard A.; Wagner, Thomas; Herringshaw, Liam G.; Farnsworth, Alexander J.; Lunt, Daniel J.; Harland, Melise; Imber, Jonathan; Loptson, Claire; Atar, Elizabeth F. L.
• Is Part Of: Paleoceanography. Volume 31:Number 8(2016)
• Page Start: 1041
• Page End: 1053
• Publication Date: 2016-08-03
• Subjects: Hadley cell circulation -- Kimmeridge Clay -- black shale -- global climate; Paleoceanography -- Periodicals; 551.46
• DOI: 10.1002/2015PA002911
• Languages: English
• ISSNs: 0883-8305

Abstract

Abstract: New climate simulations using the HadCM3L model with a paleogeography of the Late Jurassic (155.5 Ma) and proxy‐data corroborate that warm and wet tropical‐like conditions reached as far north as the UK sector of the Jurassic Boreal Seaway (~35°N). This is associated with a northern hemisphere Jurassic Hadley cell and an intensified subtropical jet which both extend significantly poleward than in the modern (July–September). Deposition of the Kimmeridge Clay Formation (KCF) occurred in the shallow, storm‐dominated, epeiric Boreal Seaway. High‐resolution paleo‐environmental proxy data from the Kimmeridge Clay Formation (KCF; ~155–150 Ma), UK, are used to test for the role of tropical atmospheric circulation on meter‐scale heterogeneities in black shale deposition. Proxy and model data show that the most organic‐rich section ( eudoxus to mid‐ hudlestoni zones) is characterized by a positive δ 13 Corg excursion and up to 37 wt % total organic carbon (%TOC). Orbital modulation of organic carbon burial primarily in the long eccentricity power band combined with a clear positive correlation between %TOC carbonate‐free and the kaolinite/illite ratio supports peak organic carbon burial under the influence of very humid climate conditions, similar to the modern tropics. This reinterpretation of large‐scale climate relationships, supported by independent modeling and geological data, has profound implications for atmospheric circulation patterns and processes affecting marine productivity and organic carbon burial further north along the Boreal Seaway, including the Arctic. Key Points: Late Jurassic ITCZ at midtemperate latitudes Kimmeridge Clay deposition (35°N to 54°N) was controlled by tropical climate Organic carbon and clay patterns support strong orbital contrasts in humidity