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

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  • MONTILLA L. A.
    PDVSA, División Oriente, Gerencia de Exploración
  • MARTÍNEZ M.
    Instituto de Ciencias de la Tierra, Universidad Central de Venezuela
  • MÁRQUEZ G.
    Departamento de Ingeniería Minera, Mecánica y Energética, Universidad de Huelva
  • ESCOBAR M.
    CARBOZULIA Postgrado de Geología Petrolera, Facultad de Ingeniería, Universidad del Zulia
  • SIERRA C.
    Departamento de Exploración y Prospección de Minas, Universidad de Oviedo
  • GALLEGO J. R.
    Departamento de Exploración y Prospección de Minas, Universidad de Oviedo
  • ESTEVES I.
    Fundación Instituto Zuliano de Investigaciones Tecnológicas (INZIT)
  • GUTIÉRREZ J. V.
    Instituto de Ciencias de la Tierra, Universidad Central de Venezuela

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

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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.

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