TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 47 (No. 5), pp. 537-546, 2013

Geochemistry and chemostratigraphy of the Colón-Mito Juan units (Campanian-Maastrichtian), Venezuela: Implications for provenance, depositional conditions, and stratigraphic subdivision

L. A. Montilla,1 M. Martínez,2 G. Márquez,3 M. Escobar,4,5 C. Sierra,6 J. R. Gallego,6 I. Esteves7 and J. V. Gutiérrez2

1PDVSA, División Oriente, Gerencia de Exploración, Puerto La Cruz, Venezuela
2Instituto de Ciencias de la Tierra, Universidad Central de Venezuela, Caracas, 3895, 1010-A, Venezuela
3Departamento de Ingeniería Minera, Mecánica y Energética, Universidad de Huelva, Huelva, 21819 Huelva, Spain
4CARBOZULIA, Av. 2 No. 55-185, Casa Mene Grande, Maracaibo 4002 A, Venezuela
5Postgrado de Geología Petrolera, Facultad de Ingeniería, Universidad del Zulia, Maracaibo 4002, Venezuela
6Departamento de Exploración y Prospección de Minas, Universidad de Oviedo, Mieres, 33600 Asturias, Spain
7Fundación Instituto Zuliano de Investigaciones Tecnológicas (INZIT), Maracaibo 4001, Venezuela

(Received May 4, 2013; Accepted July 25, 2013)

Abstract: A geochemical and chemostratigraphical study was undertaken on Campanian-Maastrichtian sedimentary rocks (the Colón-Mito Juan sequence and the upper La Luna Formation) in the southwestern Maracaibo Basin, Venezuela. The objectives of this work were to determine the paleoenvironmental and physico-chemical characteristics of the Colón-Mito Juan sequence and its possible subdivision into chemofacies and to study the main chemical differences between the Colón, Mito Juan, and La Luna Formations within the study region. One hundred and ninety-one rock samples were collected, and bulk inorganic geochemistry (TiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, P2O5, C, S, Rb, Cs, Ba, Sr, Th, U, Y, Hf, Mo, V, Cr, Co, Cu, Ni, Sc, La, Ce, Nd, Sm, Eu, Yb, Lu, As, Sb, Zn, and Be) was analyzed by instrumental neutron activation analysis or inductively coupled plasma-atomic emission spectroscopy; total sulfur and carbon analyses were performed by a LECO SC-432 apparatus and coulometry, respectively. Multivariate statistical techniques were applied to evaluate correlations within this group of variables. Using cluster-constrained analysis, eight subdivisions, or chemical facies, were defined: two chemofacies differentiating the intervals controlled by biogenic deposition and by the predominant clastic contribution; three chemofacies correlating with the lithologic units (La Luna, Colón, and Mito Juan); and another three chemofacies related to changes in the paleoredox conditions along the stratigraphic column. All of the units studied were deposited under a relatively constant climate regime, and the composition of the sediment source showed no significant changes. The prevailing physico-chemical regime was disoxic-oxic, with a trend of increasing oxygen concentrations towards the top of the column.
Key words: geochemistry, chemostratigraphy, Colón-Mito Juan sequence, stratigraphic subdivision, Lake Maracaibo

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