The Santa Teresa Formation ( es, Formación Santa Teresa, Tist, Pgst) is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

of the western

Eastern Ranges The Eastern Ranges is an Australian rules football team in the NAB League, the Victorian statewide under-18s competition. The club is a founding member of the competition (1992) and has produced several players for the Australian Football Leagu ...

of the

Colombia Colombia (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as well as in the Pacific Ocean. The Colombian mainland is bordered by the Car ...

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

, west of the Bituima Fault, and the southern

Middle Magdalena Valley The Middle Magdalena Valley, Middle Magdalena Basin or Middle Magdalena Valley Basin ( es, Valle Medio del Magdalena, commonly abbreviated to VMM) is an intermontane basin, located in north-central Colombia between the Central and Eastern Ranges of ...

. The formation spreads across the western part of Cundinamarca and the northern portion of Tolima. The formation consists of grey claystones intercalated by orange

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

s and

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

s of small to conglomeratic

grain size Grain size (or particle size) is the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which refer ...

. The thickness at its type section has been measured to be and a maximum thickness of suggested. In the formation, dated on the basis of its fossil content to the

Late Oligocene The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene Epoch/Series. It spans the time between . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage ...

, many leaf imprints and mollusks were found, suggesting a

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

deltaic A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rarel ...

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be ...

with periodical marine incursions.

Etymology

The formation was defined by De Porta in 1966 and named after the vereda Santa Teresa, San Juan de Rioseco.Acosta & Ulloa, 2001, p.64

Description

The Santa Teresa Formation is the youngest unit outcropping in the Jerusalén-

Guaduas Guaduas () is a town in Colombia, in the Lower Magdalena Province department of Cundinamarca, about 117 km from Bogotá. It is an agricultural and tourist center of some importance with a population of about 41,000. Its name refers to a ...

synclinal, western

, covering the San Juan de Río Seco Formation. The formation was formerly called La Cira Formation. In the Balú

quebrada Quebrada may refer to: Places Argentina * Quebrada de Las Flechas, a valley in the province of Salta in northern Argentina * Quebrada de Humahuaca, World Heritage, a valley in the province of Jujuy in northern Argentina * Quebrada de Luna, vill ...

, the formation shows a thickness of , while the maximum thickness could reach . The lower boundary of the formation is marked by the first occurrence of grey

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than and are too sm ...

s, covering the light brown claystones of the San Juan de Río Seco Formation. The formation comprises grey claystones intercalated by orange

s and

s of small to conglomeratic

. The

roundness Roundness is the measure of how closely the shape of an object approaches that of a mathematically perfect circle. Roundness applies in two-dimensional space, two dimensions, such as the cross section (geometry), cross sectional circles along a c ...

of the sandstone grains has been characterized as angular to subangular by Lamus Ochoa et al. in 2013. The claystones occur in thick layers with wavy lamination. 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

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

s and

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

s. The basal contacts of these beds are straight to transitional and most of the time are coarsening upward towards

quartz arenite A quartz arenite or quartzarenite is a sandstone composed of greater than 90% detrital quartz. Quartz arenites are the most mature sedimentary rocks possible, and are often referred to as ultra- or super-mature, and are usually cemented by sili ...

s where the gastropods dominate. These

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...

sequences have a thickness of about . Locally,

bioturbation Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a pr ...

siderite Siderite is a mineral composed of iron(II) carbonate (FeCO3). It takes its name from the Greek word σίδηρος ''sideros,'' "iron". It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Zinc, magnesium and ...

nodules and

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...

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 Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an adje ...

. The grain composition of the lithic fraction comprises

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of the r ...

epidote Epidote is a calcium aluminium iron sorosilicate mineral. Description Well developed crystals of epidote, Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH), crystallizing in the monoclinic system, are of frequent occurrence: they are commonly prismatic in habi ...

zoisite Zoisite, first known as saualpite, after its type locality, is a calcium aluminium hydroxy sorosilicate belonging to the epidote group of minerals. Its chemical formula is Ca2 Al3( Si O4)(Si2O7)O(O H). Zoisite occurs as prismatic, orthorhombi ...

clinozoisite Clinozoisite is a complex calcium aluminium sorosilicate mineral with formula: Ca2Al3(Si2O7)(SiO4)O(OH). It forms a continuous solid solution series with epidote by substitution of iron(III) in the aluminium (m3 site) and is also called ''alumi ...

and

pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...

s, which at the top of the formation amounts to 86 percent.

Stratigraphy and depositional environment

The Santa Teresa Formation conformably overlies the San Juan de Río Seco Formation and is covered by subrecent

alluvium Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...

. The formation is part of the sequence after the

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

. The age has been inferred to be

. The

has been interpreted as

with marine influence in the form of channels. The abundance of

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

and fresh water gastropods suggests these environmental conditions prevailed in the Oligocene of central Colombia. 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

siliciclastic Siliciclastic (or ''siliclastic'') rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals. Siliciclasic rock types include mudrock, sandstone Sandstone is a clastic ...

s by small

deltas A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rarel ...

. The many leaf imprints and coal layers support the presence of a lush vegetation at the time of deposition. The abundance of lithic clasts near the top of the formation supports a renewed

provenance Provenance (from the French ''provenir'', 'to come from/forth') is the chronology of the ownership, custody or location of a historical object. The term was originally mostly used in relation to works of art but is now used in similar senses i ...

area to the east; the uplift of the Eastern Ranges of the Colombian Andes, due to activity of the La Salina Fault.Caballero et al., 2010, p.74

Paleontology

The Santa Teresa Formation has provided fossil

s, described by De Porta and Solé De Porta in 1962 and De Porta '' Anodontites laciranus'', '' Diplodon oponcintonis'', '' Diplodon waringi'',Acosta Garay et al., 2002, p.49 and '' Corbula sp.'', among other mollusks described by De Porta in 1966.

Regional correlations

Notes and references

Notes

References

Bibliography

''See also sources for the correlation table'' * * * *

Maps

* * * * {{cite LSA , last=Acosta , first=Jorge E. , last2=Guatame , first2=Rafael , last3=Torres , first3=Oscar , last4=Solano , first4=Frank , year=1999 , title=Plancha 245 - Girardot - 1:100,000 , url=https://drive.google.com/open?id=0BwFQPMJEi17QUmhEQTdMNmcxT28 , publisher=

INGEOMINAS The Colombian Geological Survey (CGS) ( es, Servicio Geológico Colombiano; formerly known as INGEOMINAS) is a scientific agency of the Colombian government in charge of contributing to the socioeconomic development of the nation through research ...

, pages=1 , accessdate=2017-06-06 Geologic formations of Colombia Paleogene Colombia Oligocene Series of South America Deseadan Chattian Stage Shale formations Sandstone formations Siltstone formations Coal formations Deltaic deposits Lacustrine deposits Fossiliferous stratigraphic units of South America Formations Formations