PALAIOS
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PALAIOS; October 2003; v. 18; no. 4-5; p. 321-333; DOI: 10.1669/0883-1351(2003)018<0321:LCAALM>2.0.CO;2
© 2003 SEPM Society for Sedimentary Geology
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Late Cretaceous Anoxia and Lateral Microfacies Changes in the Tres Esquinas Member, La Luna Formation, Western Venezuela

MARIEN PARRA1, LORENA MOSCARDELLI2 and MARIA ANTONIETA LORENTE3

1 Petróleos de Venezuela, PDVSA, División Oriente, Apdo. 3426, Puerto La Cruz 6023, Venezuela parramo{at}pdvsa.com
2 University of Texas at Austin, University Station C1000, Austin, TX, 78712
3 GeoAmbio, Apdo 281, Jumilla 30520, Spain

ABSTRACT

The Tres Esquinas Member of the La Luna Formation is a glauconite-rich phosphorite unit associated with changes that took place in depositional environments in the Maracaibo Basin at the end of the Late Cretaceous. The unit marks the end of La Luna Formation sedimentary cycle. This paper presents results of petrographic studies of samples from two sections, one outcrop (Río Guaruries), and one well core (Perijá), and from seismic profiles across the Perijá and Colón areas in the Maracaibo Basin.

The Tres Esquinas Member is three meters thick in both locations. In the Río Guaruries outcrop, it contains an abundant foraminiferal fauna in addition to common allochemical material. Perijá core samples contain voluminous carbonate matrix, scarce allochemical materials, rare foraminifera, and poor definition of mineral facies, which may reflect higher-energy conditions on the sea floor.

The deposition of the Tres Esquinas Member resulted from altered sea-floor topography during an episode of intense tectonic activity in the eastern part of the Maracaibo Basin. The modified shelf configuration ended anoxic conditions on the sea floor and led to increased erosion characteristic of the Tres Esquinas Member.




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