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The AAPG/Datapages Combined Publications Database
Journal of Sedimentary Research (SEPM)
Sediments and Sedimentary Structures of the Astoria Submarine Canyon-Fan System, Northeast Pacific
Paul R. Carlson, C. Hans Nelson
Cores taken from the Astoria Submarine Canyon-Fan system illustrate the typical lithology and structure found in sediment deposited in these environments. The deposits include both postglacial and late glacial sediment. The postglacial sediment is mostly hemipelagic silty clay, except on the floor of Astoria Canyon and Channel where the clay is interbedded with some turbidity current deposits. The late glacial sediment, however, consists of numerous interlayered silty clay and turbidity current deposits. The turbidites range in grain size and thickness from micaceous silt laminae to thick beds of sand and gravel. In addition to these deposits, ice-rafted pebbles occur in glacial sediment and slump structure and burrows in the postglacial sediment of the canyon-fan system. The sediment and sedimentary structures of the Astoria Canyon-Fan system provide a basis for comparison with other modern and fossil canyon-fan systems.
Certain characteristics of the canyon and fan deposits that permit them to be identified as a related system include the laterally continuous contacts between postglacial and glacial sediment, distinctive mineral and faunal compositions, and rhythmically interbedded turbidites and hemipelagites.
Certain distinctions, however, can be made between deposits of the canyon and fan. Homogeneous silty clay beds dominate the canyon deposits, which also contain more organic material and glauconite and show more evidence of slumping than do the fan deposits. The deposits of the fan, in contrast, contain numerous thick, coarse, well-sorted sand and silt beds that exhibit well-developed internal structures.
Distinctions can also be made between deposits from different parts of the fan. Beds from the lower fan typically show features of the Bouma sequence of sedimentary structures (grading, parallel lamination, current ripple lamination). The beds themselves consist of moderately well-sorted sand and silt and are separated by clearly defined clayey interbeds. In contrast, deposits from the upper fan channels are characterized by poorly sorted, structureless muddy gravel, sand, and silt beds. Sediment from interchannel regions on the upper fan is mostly clay that contains poorly sorted silt laminae.
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