LA VILLA, Formation

TERTIARY (upper Miocene or Pliocene)

State of Zulia, Venezuela

Author of name: A. H. Garner ( ? ).

Original reference: A. H. Garner, 1926, p. 683.

Original description: ibid.

Of the La Villa formation, Garner (1926, p. 683) gives the following description: "Type locality: around town of La Villa, western Perijá, State of Zulia. Massive, fine-grained, colored sandstones, and mottled white clays." Garner describes an "Arimpia formation", which is seemingly the underlying Los Ranchos unit. Considering that Garner's definition of the La Villa today remains essentially unchanged, and also the timeliness of Garner's article, it seems appropiate to credit Garner with authorship of the name. Yet, doubtlessly there were other, rather varied uses of the term in private reports concurrently and slightly prior to Garner's publication. Very likely the name developed gradually among numerous geologists during early phases of exploration in the District of Perijá. A private report dated February, 1926, uses the term rather loosely in a form that includes the Los Ranchos and La Villa formations, and evidently also the underlying El Fausto sediments, and states that "in the past, the names Llanos, Arimpia, Rodeo and La Villa have been used" for this sequence.

The type section defined by Liddle (1946, p. 508) (he interchangeably uses the terms "La Villa formation" and "La Villa beds") extends "westward for 10 kilometers to a point just west of the village of Arimpia where it is in normal contact with the underlying Los Ranchos formation." Photo-interpretation of this area reveals that the La Villa-Los Ranchos boundary passes through the village of Arimpia, where it tends to be mantled, however, by soil and alluvium. About one kilometer southwest of the village, the boundary is clearly evident at the east base of a somewhat discontinuous strike ridge. This ridge is coincident with the top sandstone member of the Los Ranchos type section, located 4 kilometers southward. The top of the La Villa formation is not evident in surface outcrops. Sporadic occurrences of the formation are found farther east from the type section, one of them on the Perijá highway about 10 kilometers northeast of La Villa del Rosario.

Good outcrops of the La Villa formation are somewhat infrequent because of the unconsolidated nature of the sediment. This accounts for the relatively sharp topographic break between the La Villa and more resistant Los Ranchos formation between Arimpia and the Río Apón. The La Villa generally erodes to gentle slopes and low, rounded hills. Sharply formed hills locally stand above this surface, and apparenty owe their presence to local resistance to erosion, induced by secondary hematite or silica cements. Exposures are mostly confined to the steep slopes of these hills, to gullies, and to road cuts.

In the type section, sandstones evidently prevail over claystones and siltstones. Light gray to pale yellowish-gray colors prevail in all lithologies except where mottling is present; the word "white" is sometimes (perhaps inappropiately) used in describing the color. Mottlings in hues of pale red purple, moderate red, and dusky or dark red, are irregularly distributed. Sandstones are poorly sorted, in places conglomeratic, and may be argillaceous or arkosic. Stratification is poor; cross-bedding is observed occasionally; jointing is prominently developed in the better outcrops. In well sections, carbonaceous shales and streaks of lignite are occasionally observed. The mineral suite includes ilmenite, leucoxene, zircon, rutile, tourmaline, and rarely garnet.

Reliable attitudes are so scarce that thickness values estimated at the type section are inherently unreliable. Sutton (1946, p. 1707), cites values from 900 to 1,200 meters (2,950 to 3,940 feet). In the Neopod-1 well, 2 kilometers south of La Villa del Rosario, the base of the formation is placed approximately at 4500 feet. Sediments logged as La Villa formation in this well grade downward into claystones that evidently belong to the Cuiba formation. The La Villa in the well contains less sand and more claystone than is evident in the surface section, and no recognition is made of the Los Ranchos which evidently grades eastward into the designated La Villa unit. Analogy is found in the Boscán oilfield area where La Villa type sediments, with high percentage of claystone, rest on claystones that are referred to the Upper La Rosa formation.

Transition of the La Villa formation toward claystone and silty claystone lithology is also noted toward the north and south from the vicinity of the type section, and is manifested by lower topography and fewer outcrops. An associated transition toward increasing claystone content occurs in the underlying Los Ranchos formation, and there is a corresponding loss in tangible boundary between the two units. Relationships of the La Villa and Los Ranchos, and transitions in lithology, are evidently dependent on variable conditions, like basinal position, proximity and character of source areas for sediments, and location of rivers or river mouths.

Overlying the La Villa formation is a sequence of beds which, by Sutton's interpretation, are grouped rather broadly into the El Milagro formation. Sutton (1946, p. 1708) indicates general unconformable conditions between the El Milagro and La Villa in the Districts of Páez, Mara, and Maracaibo, stating that the El Milagro "was deposited only after a long period of sub-aerial exposure of the La Villa, during which the red lateritic conglomerate cap was formed by weathering". In the Boscán oilfield area (District of Urdaneta) the unconformity, if present, is less conspicuous.

The name La Villa is generally restricted to the region west of Lake Maracaibo in the State of Zulia. The formation is correlated roughly, and corresponds in approximate lithology, to the La Puerta formation in eastern Zulia and Falcón; it is evidently a lateral equivalent of part of the El Guayabo group exposed in the Río de Oro area, southern Zulia. The age, assigned on the basis of stratigraphic associations, is evidently upper Miocene and Pliocene.

The La Villa formation is mostly unfossiliferous except for occasional reworked Cretaceous foraminifera, and scattered appearances of foraminifera with brackish water affinity that are otherwise non-diagnostic.

John B. Miller