--> Abstract: Sedimentology And Sequence Stratigraphy Of The Caballos Formation, San Francisco Field, Upper Magdalena Valley, by J. C. Ramon and J. Pavas; #90928 (1999).

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RAMON, JUAN CARLOS, and JAIME PAVAS
HOCOL S.A., Bogota, Colombia

Abstract: Sedimentology and Sequence Stratigraphy of the Caballos Formation, San Francisco Field, Upper Magdalena Valley

Sedimentological and stratigraphical interpretation of 92 well logs calibrated with about 1070 feet of cored section, and 25 FMI logs allows a detail reconstruction of the sedimentary environments and the stratigraphic evolution during Aptian-Albian time.

The lower Caballos member consists of stacked fluvial and crevasse-splay sandstones locally intercalated with floodplain mudstones and siltstones. Stacking pattern of successive stratigraphic cycles shows onlap over a high relief paleo-topography. A local baselevel fall toward the top of the Lower Caballos resulted in amalgamated blanket sandstones. Progressive increase in base-level resulted in deposition of swamp mudstones that are covered by open bay mudstones and fossiliferous marls. These middle unit mudstones pass transitionally to inner bay and coastal plain mudstones and siltstones. Locally fluvial sandstone bodies occur toward the top of this middle Caballos member. This transition records the bay fill as the base-level falls.

A relative rise in sea level resulted in flooding of paleo-valleys and deposition of an heterolithic mix of sandstones and mudstones. Random alternation of through and planar cross-bedded, medium sandstones with ripple-laminated, finer sandstones indicate variable energy conditions. Lack of intraclasts at the base of thick ripple laminated sandstones indicate non-erosive contacts. Massive sandstones change laterally to gray mudstones with hematite-cemented "layers" deposited under brackish conditions. The progressive rise in sea level causes the flooding of the estuary. Open marine glauconite- and fossil-rich mudstones cover estuarine deposits.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas