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Title: Assessing the response of deep-marine macrofauna to the early Palaeogene hyperthermal events : an integrated ichnological, geochemical and stratigraphical approach in the Basque Basin, northern Spain
Author: Cummings, John Paul
ISNI:       0000 0004 2732 9359
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2011
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To understand the response of bathyal macrofauna to long-term climate change requires a multi-disciplinary approach (ichnology, sedimentology, stratigraphy, geochemistry), and an extensive integrated dataset. The deep-marine Basque Basin in northern Spain preserves a wide range of submarine fan-related environments of deposition in well exposed and easily accessible Cretaceous and Palaeogene outcrops. These outcrops contain exceptionally preserved deep-marine trace fossil assemblages, including the Zumaia section, one of the most expanded/continuous sections of early Palaeogene deposits in the world. In a detailed investigation to understand the control exerted by the environment of deposition on trace fossil assemblages in submarine fan "related environments, an increase in ichnodiversity and an increase in the ratio of pre- versus post-depositional forms occurs from lobe complex axis to lobe complex off-axis _ and fringe positions. In channel-related environments, diverse pre-depositional dominated assemblages are prevalent in marginal and overbank settings. These are replaced by low diversity post-depositional dominated assemblages in more axial positions within Jhe system. Diverse pre- and post-depositional assemblages are common in fan fringe deposits, with less diverse assemblages dominated by post-depositional ichnotaxa in basin floor deposits. The use of sub-ichnofacies is shown to have limited use in high resolution environmental interpretation in submarine fan related environments of deposition, but is still of value as an informal way of categorising a general position within the submarine fan system (e.g. proximal versus distal). Instead, it is proposed that ethology arid colonisation styles are the most powerful tool in complementing sedimentary facies and element geometry in the interpretation of depositional environments. The deep-water submarine fan deposits also span several major environmental perturbations associated with ancient episodes of climate change, namely the Danian-Selandian (O/S) transition, the mid-Palaeocene biotic event (MPBE), the Palaeocene Eocene Thermal Maximum and the early Eocene Climatic Optimum (EECO). This permits investigation into ichnological changes across major environmental perturbations. Low diversity, deep-tier fodinichnial dominated assemblages prevail throughout the Palaeocene, with the O/S transition and the MPBE having little impact on ichnodiversity and preserved ethologies. The extinction event that affected benthic microfauna at the PETM is found to have also affected macrofauna communities recorded in the ichnological record. Following the PETM, a gradual return to a tiered trace fossil community occurs but ichnodiversity remains relatively low. A vast increase in ichnodiversity, largely driven by diversification of the graphoglyptids is coincident with sedimentation in the basin becoming dominantly siliciclastic well into the early Eocene. Occurrences of Ophiomorpha (a crustacean trace) and Scolicia (an echinoid trace) also increase dramatically at this time. Analysis of clay minerals (utilising XRO) across the PETM, which represents a global highstand, and from EECO sediments, reveals several spikes of kaolinite. This is a phenomena recorded across the Atlantic, and is interpreted to represent the global increase in delivery of terrigenous material into the ocean over a prolonged period. Delivery of this material is associated with degradation of a mature regolith during elevated PETM and EECO temperatures. The incipient Pyrenean orogeny enhanced delivery of siliciclastic material into the basin. Benthic macrofauna were able to gradually adjust to fundamental changes in sediment delivery to the deep basin, and eventually were able to exploit this increase in terrigenous material. Several examples of Ophiomorpha group trace fossils are discussed in detail, including agrichnial forms, which are interpreted to represent an ethological response to climatically-driven changes in sediment supply.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral