Type locality of the Santa Teresa Formation in Cundinamarca
The Santa Teresa Formation is the youngest unit outcropping in the
Jerusalén-
Guaduassynclinal, western
Eastern Ranges, covering the
San Juan de Río Seco Formation. The formation was formerly called La Cira Formation. In the Balú
quebrada, the formation shows a thickness of 118 metres (387 ft), while the maximum thickness could reach 150 metres (490 ft).[1]
The lower boundary of the formation is marked by the first occurrence of grey
claystones, covering the light brown claystones of the San Juan de Río Seco Formation. The formation comprises grey claystones intercalated by orange
quartzsiltstones and
sandstones of small to
conglomeraticgrain size. The
roundness of the sandstone grains has been characterized as angular to subangular by Lamus Ochoa et al. in 2013.[2] The claystones occur in thick layers with wavy lamination.[1]
In these thick packages of claystones, the formation has provided fossil leaves in various forms and sizes, and to a lesser extent the remains of
mollusks;
gastropods and
bivalves. The basal contacts of these beds are straight to transitional and most of the time are
coarsening upward towards
quartz arenites where the gastropods dominate. These
facies sequences have a thickness of about 2 metres (6.6 ft). Locally,
bioturbation,
siderite nodules and
coal beds occur in the formation. The sandstones occur in very thin to very thick beds, characterized by
plain parallel lamination, in lenses and very locally in
flasers. The cement of the arenites is
calcareous.[1] The grain composition of the lithic fraction comprises
zircon,[3]epidote,
zoisite,
clinozoisite and
pyroxenes, which at the top of the formation amounts to 86 percent.[4]
The age has been inferred to be
Late Oligocene. The
depositional environment has been interpreted as
lacustrine with marine influence in the form of channels. The abundance of
brackish and fresh water gastropods suggests these environmental conditions prevailed in the Oligocene of central Colombia.[1]
In the type section at the Balú quebrada, facies traits that confirm this interpretation can be observed. The lacustrine areas were probably shallow water environments with reducing conditions and a continuous supply of
siliciclastics by small
deltas. The many leaf imprints and coal layers support the presence of a lush vegetation at the time of deposition.[1] The abundance of lithic clasts near the top of the formation supports a renewed
provenance area to the east; the uplift of the Eastern Ranges of the Colombian Andes,[6] due to activity of the
La Salina Fault.[7]
Acosta Garay, Jorge, and Carlos E. Ulloa Melo. 2001. Geología de la Plancha 227 La Mesa - 1:100,000, 1–80.
INGEOMINAS.
Acosta Garay, Jorge Enrique; Rafael Guatame; Juan Carlos Caicedo A., and Jorge Ignacio Cárdenas. 2002. Geología de la Plancha 245 Girardot - 1:100,000, 1–101.
INGEOMINAS.
Caballero, Víctor; Mauricio Parra, and Andrés Roberto Mora Bohórquez. 2010. Levantamiento de la Cordillera Oriental de Colombia durante el Eoceno tardío – Oligoceno temprano: Proveniencia sedimentaria en el Sinclinal de Nuevo Mundo, Cuenca Valle Medio del Magdalena, 45–77. 32;
Boletín de Geología.
Lamus Ochoa, Felipe; Germán Bayona; Agustín Cardona, and Andrés Mora. 2013. Procedencia de las unidades cenozoicas del Sinclinal de Guaduas: implicación en la evolución tectónica del sur del Valle Medio del Magdalena y orógenos adyacentes, 1–42. 35;
Boletín de Geología.