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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 5. (May)

First Page: 589

Last Page: 589

Title: Seismic Stratigraphy and Sedimentation, Magdalena Fan, Southern Caribbean Sea: ABSTRACT

Author(s): V. Kolla, R. T. Buffler, J. W. Ladd

Article Type: Meeting abstract

Abstract:

Multi- and single-channel seismic records from the Magdalena Fan reveal six seismic sequences in the entire sediment column (with thickness from > 5.5 to 2.5 secs two-way traveltime). Although sediments were deposited in the Magdalena Fan since about the Late Cretaceous, terrigenous sedimentation became important only in later Cenozoic time during the deposition of the upper three units following the Andean uplifts. However, the uppermost seismic sequence is the fan unit, most influenced by influx of terrigenous sediments and deposited subsequent to the major uplift of Andes in Pliocene time. The morphologic and shallow acoustic (3.5 kHz) characteristics of this fan unit are: (1) upper fan, 1/50 to 1/100 gradients, with channels having well-developed levees and with se eral subbottom reflectors; (2) middle fan, 1/100 to 1/200 gradients, occurrence of numerous channels with very subdued levees and several subbottom reflectors; and (3) lower fan, < 1/200 gradients having small channels and relatively smooth sea floor with few or no subbottom reflectors. Large irregular to regular hyperbolic echoes and sediment waves are very common in the upper, middle, and to some extent the lower fan, and have resulted from slumping and other downslope mass movements. On multichannel seismic records, the upper fan exhibits conspicuous channel-levee migration and onlapping and coalescing wedge-shaped reflection patterns (from levee deposits). The middle fan is characterized by the presence of chaotic and discontinuous reflection patterns which resulted from the prese ce of numerous channels and the hyperbolae and sediment waves of the type recorded on 3.5 kHz records. The lower fan region has continuous and smooth reflection patterns. Within the topmost seismic unit, several episodes of increased terrigenous sediment influx have resulted in a seaward progradation of different fan regions in Pliocene-Pleistocene times.

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