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Title: Micro facies analysis of late Quaternary Peruvian upwelling sediments
Author: Brodie, Ian Raymond Alexander
ISNI:       0000 0001 3481 1686
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 1994
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This study examines the organic rich laminated sediments which have accumulated within the intense oxygen minimum zone of the Peruvian shelf under a coastal upwelling system. Sediment comes from three Ocean Drilling Program, Leg 112 sites (Sites 680, 681, and 161), and is examined in detail using the technique of backscattered electron microscopy. Within the diatomaceous mud, three different lamination styles have been identified; packet laminae, isolated laminae and triplet laminae. Packet laminae are characterised by decimetre scale alternations of laminated sediment and homogenous or bioturbated diatomaceous mud. The laminae are alternations between terrigenous sediment and diatom ooze bloom deposits. Rare examples of very thin ooze laminae occurring in close succession suggest that bloom events were more common than is generally recorded and that silica dissolution plays an important role in the occurrence of ooze laminae. Isolated laminae are several milimetre thick diatom ooze laminae within homogenous mud, and record very large blooms that either overcame dissolution effects in the water column or were not disrupted by bioturbation. Triplet laminae are characterised by a regular alternation between silt-rich and clay-rich laminae, with irregularly occurring diatom ooze laminae. The irregular occurrence of the diatom ooze laminae suggests that dissolution of the frustules in the water column occurred for all but the larger blooms. Two different types of pelletal structures have been identified; pellets and aggregates. Pellets can be classed into three groups, crushed diatom, intact diatom, and silt pellets. Crushed diatom pellets are benthic in origin. Intact diatom pellets, when associated with crushed diatom pellets are burrow infill structures, although isolated intact diatom pellets may be planktonic in origin. Silt pellets may be the remains of agglutinating forams. Aggregate structures are the bioturbated remains of laminated sediments. Their size suggests a meiofauna burrowing through the top few hundred microns of sediment. The presence of aggregate structures, even in well laminated sections, indicates that substrate oxygen levels rarely reached true anoxia.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Oceanography