LAKE MARACAIBO, Beds

See CHURUGUARITA, Formation

CHURUGUARITA, Formation

TERTIARY (upper Eocene)

State of Zulia, Venezuela

Author of name: A. H. Garner, 1926.

Original reference: A. H. Garner, 1926, p. 681.

Original description: ibid.

Garner (1926, p. 681) first employed the name Churuguarita limestone for a formation consisting of massive, grey foraminiferal limestone, which he assumed to be Oligocene in age. The name is derived from a small abandoned ranch in the southern part of the district of Miranda, state of Zulia.

The description by Sutton (1946, p. 1687) differs insofar as he also includes the clay shales in the Churuguarita formation.

According to Sutton, the dark gray to light bluish gray clay shales do not crop out but were observed in exploratory pits dug in the strike valleys between the ridge forming limestone members of which there are at least four of major importance. The clay shales contain here and there thin beds of tan to gray, fine to medium-grained, soft sandstones, and are locally sandy throughout. A few dense black shales occur, commonly near the limestone reefs. The latter form low strike ridges which locally develop into knobs where calcareous algae are most abundant.

The algae are commoner in the lower reefs than in the upper ones, where the orbitoids are more varied and more numerous. The reef limestones are massive and non-bedded, white in color and pitted on weathered surface. Above the highest limestone the clay shales become bleached, gypsiferous, and lignitic, indicating a change from marine to brackishwater and saline deposition.

The Churuguarita formation thickens from about 1,216 meters at the type locality to about 1,677 meters to the east. The interval of 976 meters between the base of the lowermost and the top of the uppermost limestone remains constant.

The formation crops out on the eastward-plunging Churuguarita anticline, of which the Las Flores formation forms the core. The Churuguarita formation is unconformable with the Las Flores. South and east of the structure the Churuguarita is overlain unconformably by the La Rosa formation, north of the structure by the La Victoria formation.

The bulk of the outcrop area of the Churuguarita formation lies in the southern part of the Miranda district, state of Zulia.

The age of the Churugarita is upper Eocene based on larger foraminifera as described by Hodson (1926, p. 1-46). For later changes in nomenclature see Vaughan and Cole (1941, p. 1-137) and Vaughan (1945, p. 1-175). The Lake Maracaibo beds of Maury (1925, p. 412) most likely are a synonym of the Churuguarita formation.

According to Schaub (1948, p. 227, table I) the Churuguarita formation correlates with the Paloma Alta formation.

W. A. Mohler