Navidad Formation ( es, Formación Navidad) is a marine

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago (Mya) to the beginning of the present Quaternary Period Mya. ...

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

ary

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

located in Central Chile. The formation is known for its diverse and abundant fossil record and is considered the reference unit for the marine Neogene in Chile. Originally described by

Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...

in 1846 the formation has attracted the attention of numerous prominent

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, alt ...

s and paleontologists since then. As a key formation Navidad has been subject to a series of differing interpretations and scientific disputes over time.

History

saw the formation in September 1834 during the

second voyage of HMS Beagle The second voyage of HMS ''Beagle'', from 27 December 1831 to 2 October 1836, was the second survey expedition of HMS ''Beagle'', under captain Robert FitzRoy who had taken over command of the ship on its first voyage after the previous capta ...

. He became the first to describe it 1846 when he published his book

Geological Observations on South America ''Geological Observations on South America'' is a book written by the English naturalist Charles Darwin. The book was published in 1846, and is based on his travels during the second voyage of HMS ''Beagle'', commanded by captain Robert FitzRoy ...

in 1846 and it was named by Darwin after the nearby town of Navidad. In this book Darwin calls the formation "Formation of Navidad" and "Sandstone Formation at Navidad". There are no signs of that Darwin would have attempted to make a formal definition of the formation. Early fossil descriptions from Navidad Formation were those of George Sowerby in ''Geological Observations on South America'' (1846) and by

Rodolfo Amando Philippi Rodolfo Amando (or Rudolph Amandus) Philippi (14 September 1808 – 23 July 1904) was a German–Chilean paleontologist and zoologist. Philippi contributed primarily to malacology and paleontology. His grandson, Rodulfo Amando Philippi Bañados ...

(1887). Gustav Steinmann redefined the Navidad Formation in 1895, then called Piso Navidad, by giving it a Lower Tertiary age and spanning much of south-central Chile. In 1934 Juan Brüggen separated Piso Concepción from Steinmanns Piso Navidad after showing there was a discordance between them. Humberto Fuenzalida published research on fossils of the formation in 1950–1951.Dr. Humberto Fuenzalida Villegas. Eusebio Flores S. Juan Tavera further narrowed the age of the formation in 1968 and 1979 by proposing a

Burdigalian The Burdigalian is, in the geologic timescale, an age or stage in the early Miocene. It spans the time between 20.43 ± 0.05 Ma and 15.97 ± 0.05 Ma (million years ago). Preceded by the Aquitanian, the Burdigalian was the first and longest war ...

(Lower Miocene) age for Navidad, Lincancheo and Rapel which were then the three subunits of Navidad Formation. Tavera's 1979 subdivision scheme for Navidad Formation remained popular until it was superseded in 2006 by a new one.

Outcrops and surface morphology

Navidad Formation is located in the Chilean Coast Range in Central Chile at the latitudes of 33°00' S–34°30' S. The formation crops out more-less continuously along coastal bluffs displaying well-preserved exposures. The coastal exposures extends from the vicinities of

San Antonio ("Cradle of Freedom") , image_map = , mapsize = 220px , map_caption = Interactive map of San Antonio , subdivision_type = Country , subdivision_name = United States , subdivision_type1= State , subdivision_name1 = Texas , subdivision_t ...

in the north to Boca Pupuya in the south over a length of 16 km. Morphologically the coastal zone near the formation has been divided into four distinct zones: a '' coastal platform'' of rocky outcrops and sand beaches, ''

marine terrace A raised beach, coastal terrace,Pinter, N (2010): 'Coastal Terraces, Sealevel, and Active Tectonics' (educational exercise), from 2/04/2011/ref> or perched coastline is a relatively flat, horizontal or gently inclined surface of marine origin, ...

s'' dipping gently towards the sea, ''dissected coastal plain'' at the mouth of Rapel River and ''

fluvial terrace Fluvial terraces are elongated terraces that flank the sides of floodplains and fluvial valleys all over the world. They consist of a relatively level strip of land, called a "tread", separated from either an adjacent floodplain, other fluvial ...

s'' in the northern and southern shores of Rapel River.

Stratigraphy and lithology

The formation rests above both an Upper

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

formation called Punta Tocopalma Formation and the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

granitic A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quart ...

basement A basement or cellar is one or more Storey, floors of a building that are completely or partly below the storey, ground floor. It generally is used as a utility space for a building, where such items as the Furnace (house heating), furnace, ...

. It lies below Licancheu Formation to which it has a concordant contact to. The formation has a thickness of 100 to 200 meters. The sedimentary rocks that make up the formation includes a basal

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** Co ...

stratigraphically followed by intercalated

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 ...

and

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, ...

with smaller occurrences of conglomerate and

coquina Coquina () is a sedimentary rock that is composed either wholly or almost entirely of the transported, abraded, and mechanically sorted fragments of the shells of mollusks, trilobites, brachiopods, or other invertebrates. The term ''coquina'' ...

. There are more than one subdivision scheme for the stratigraphy of the formation. A scheme made by Juan Tavera in 1979 that was by 2005 the most used compromises tree members ''Navidad'', ''Licancheo'' and ''Rapel''. A new scheme proposed in 2006 elevated Tavera's sub-units ''Licancheo'' (renamed Licancheu) and ''Rapel'' to formations leaving the new definition of Navidad Formation as the former sub-unit ''Navidad''. The rationale for subdividing Tavera's Navidad Formation was that the sub-units were separated by regional discontinuities. The stratotype of the formation is the coastal bluff west of Punta Perro. The stratopype does not coincide with the original description by Darwin. The sediments of the formation include

detrital Detritus (; adj. ''detrital'' ) is particles of rock derived from pre-existing rock through weathering and erosion.Essentials of Geology, 3rd Ed, Stephen Marshak, p G-7 A fragment of detritus is called a clast.Essentials of Geology, 3rd Ed, Steph ...

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) ...

amphibole Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different ...

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 th ...

and other

heavy minerals In geology, a heavy mineral is a mineral with a density that is greater than 2.9 g/cm3, most commonly referring to dense components of siliciclastic sediments. A heavy mineral suite is the relative percentages of heavy minerals in a stone. Heavy min ...

. Pyroxene is the most common heavy mineral in the lower sections of Navidad Formation. Part of the sediments are believed to have originated from the basement of the Chilean Coast Range based on the affinities of

with the coastal lithologies. Analysis of amphiboles and pyroxenes have led to the conclusion that they and other sediments originate from

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates ...

and

subvolcanic rock A subvolcanic rock, also known as a hypabyssal rock, is an intrusive igneous rock that is emplaced at depths less than within the crust, and has intermediate grain size and often porphyritic texture between that of volcanic rocks and plutonic ro ...

s from the Central Valley and the Andean Cordillera. Over-all three erosion-and-deposition events have been distinguished in Navidad Formation.

Fossil record

The formation contains a great variety of fossils. Among the macrofossils there are remnants from

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...

s and gastropods. Among microfossils there are ostracodes and

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

. In addition there are fossils of

leave Leave may refer to: * Permission (disambiguation) ** Permitted absence from work *** Leave of absence, a period of time that one is to be away from one's primary job while maintaining the status of employee *** Annual leave, allowance of time a ...

s and

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametop ...

. The teeth of the shark '' Odontaspis ferox'' have been identified in the formation.

Crustaceans

Fossils of the marine crab genera ''

Cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...

'', ''

Hepatus ''Hepatus'' is a genus of crabs in the family Aethridae, containing seven extant species, plus some fossil species: * '' Hepatus chiliensis'' H. Milne-Edwards, 1837 * ''Hepatus epheliticus ''Hepatus epheliticus'', known by various names, in ...

'', ''

Pilumnus In Roman mythology, Pilumnus ("staker") was a nature deity, brother of Picumnus. He ensured children grew properly and stayed healthy. Ancient Romans made an extra bed after the birth of a child in order to ensure the help of Pilumnus. He also ...

'', ''

Pinnotheres ''Pinnotheres'' is a genus of crabs, including the pea crab. Many species formerly in ''Pinnotheres'' have been placed in new genera, such as ''Zaops ostreus'' (formerly ''P. ostreus''), the oyster crab and ''Nepinnotheres novaezelandiae'' (form ...

'', '' Trichopeltarion'', '' Callianassa'', '' Pinnixa'' and '' Proterocarcinus'' have been reported from Navidad Formation. Navidad Formation host two of the first fossil crab species to be described from Chile: ''Cancer tyros'' and ''Pinnotheres promaucanus'' both described by

in 1887. Notably, the type specimen of ''Pinnotheres promaucanus'' has presumably been lost at the Chilean National Museum of Natural History.

Ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

species identified in Navidad Formation numbered 28 by 1978.

Molluscs

Gastropod shell The gastropod shell is part of the body of a Gastropoda, gastropod or snail, a kind of mollusc. The shell is an exoskeleton, which protects from predators, mechanical damage, and dehydration, but also serves for muscle attachment and calcium s ...

s are the most common macrofossils of Navidad Formation. A large number of these shells are remarkably well preserved. The mollusc fossil fauna of Navidad Formation is remarkably similar fossil faunas of the same age found in

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. Some of the gastropod species found in Navidad Formation are ''Miltha vidali'', '' Acanthina katzi'', '' Olivancillaria claneophila'', ''Testallium cepa'', '' Ficus distans'', ''Eucrassatella ponderosa'', '' Glycymeris ibariformis'' and '' Glycymeris colchaguensis''.

Flora

There are fossil

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of ligni ...

, cuticles and fresh water

algae Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from ...

in the formation. Pollen and spore associations are dominated by land species and reflect that land flora was of both

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final st ...

and

Neotropical The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropical terrestrial ecoregions of the Americas and the entire South American temperate zone. Definition In bi ...

affinities. In a 2011 study Barreda et al. identified a total of 65 morphospecies of pollen and spores. More specifically these consisted of at least 42

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. They include all forbs (flowering plants without a woody stem), grasses and grass-like plants, a vast majority of br ...

, 14

pteridophyte A pteridophyte is a vascular plant (with xylem and phloem) that disperses spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as " cryptogams", meaning that their means of reproduction is hidden. Ferns, ...

s, seven

gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...

s and two

bryophytes The Bryophyta s.l. are a proposed taxonomic division containing three groups of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. Bryophyta s.s. consists of the mosses only. They are characteristically limited i ...

. The dominant gymnosperms are the

Podocarpaceae Podocarpaceae is a large family of mainly Southern Hemisphere conifers, known in English as podocarps, comprising about 156 species of evergreen trees and shrubs.James E. Eckenwalder. 2009. ''Conifers of the World''. Portland, Oregon: Timber Pre ...

while the angiosperms lack any dominant family. Charcoal found together with

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...

is thought to indicate that

wildfire A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identi ...

s ignited by

volcanic eruption Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are ...

s were common on land where Mediterranean climate prevailed in the Miocene as well as today.

Trace fossils

The

trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

s representing the ichnogenera of '' Zoophycos'' isp. and '' Chondrites'' isp. can be found in Navidad Formation.

Scientific controversy

Over the years different age estimates for Navidad Formation have been proposed and led to a substantial debate. Based on a biostratrigraphic analysis Encinas et al. (2008b) suggested a

Tortonian The Tortonian is in the geologic time scale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma (million years ago). It follows the Serravallian and is followed by the Messinian. The Tort ...

Zanclean The Zanclean is the lowest stage or earliest age on the geologic time scale of the Pliocene. It spans the time between 5.332 ± 0.005 Ma (million years ago) and 3.6 ± 0.005 Ma. It is preceded by the Messinian Age of the Miocene Epoch, and ...

(Late

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...

–Early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but ...

–Early Miocene shark teeth that occur in basal

are reworked material originating at another formation that re–sedimented in Navidad Formation. The formation was interpreted as including both deep marine and shallow marine depositional environments. In 2013 Gutiérrez et al. published an article in ''

Andean Geology ''Andean Geology'' (formerly ''Revista Geológica de Chile'') is a peer-reviewed scientific journal published three times per year by the National Geology and Mining Service, Chile's geology and mining agency. The journal covers the field of geo ...

'' claiming an Early to Middle Miocene age for Navidad Formation. Further, Gutiérrez et al. (2013) disagreed with Encina et al.'s (2008b) suggestion of a deep marine depositional environment for Navidad Formation proposing a shallow marine environment instead. This prompted a response from Encina and his associates (Finger et al., 2013) contesting elements of these claims but stressing it is true that some of the formation is of shallow marine origin and that at least part of the formation is of Early Miocene origin. In their comment Finger et al. (2013) revealed that previous identification of foraminera was erroneous as was also the Late Miocene–Early Pleistocene age estimate based on incorrect identification of foraminifera. Gutiérrez and his associates defended their findings in a reply in 2013 and the exchange continued in 2014.

References

{{Geology of Chile Geologic formations of Chile Miocene Series of South America Neogene Chile Sandstone formations Siltstone formations Conglomerate formations Shallow marine deposits Fossiliferous stratigraphic units of South America Paleontology in Chile Geology of Valparaíso Region Geology of O'Higgins Region

History

Outcrops and surface morphology

Stratigraphy and lithology

Fossil record

Crustaceans

Molluscs

Flora

Trace fossils

Scientific controversy

See also

References