The La Toca Formation is a

geologic 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 ...

in the northern and eastern part of the

Dominican Republic The Dominican Republic ( ; es, República Dominicana, ) is a country located on the island of Hispaniola in the Greater Antilles archipelago of the Caribbean region. It occupies the eastern five-eighths of the island, which it shares with ...

. The formation, predominantly an alternating sequence of marls and turbiditic

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 ...

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

s and conglomerates, is renowned for the preservation of

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

s and other

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

s in

amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In ...

, known as

Dominican amber Dominican amber is amber from the Dominican Republic derived from resin of the extinct tree '' Hymenaea protera''. Dominican amber differentiates itself from Baltic amber by being nearly always transparent, and it has a higher number of fossil inc ...

. The formation is dated to the

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 w ...

Langhian The Langhian is, in the International Commission on Stratigraphy, ICS geologic timescale, an age (geology), age or stage (stratigraphy), stage in the middle Miocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between 15 ...

stages Stage or stages may refer to: Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly British theatre newspaper * S ...

of the

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

(

Hemingfordian The Hemingfordian on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 20,600,000 to 16,300,000 years BP. It is usually considered to overlap the lates ...

in the NALMA classification).La Toca Formation
at Fossilworks.org

Description

La Toca Formation was first defined by Redmond in 1982.Hoja de Esperanza - 6074-IV, 2010, p.20 The formation mainly consists of marls and turbiditic

s and conglomerates deposited in the northeastern part of Hispaniola.Díaz de Neira, 2017, p.663 The formation overlies the Los Hidalgos Formation and is overlain by the La Jaiba Conglomerate and in places by the Villa Trina Formation.Hoja de Puerto Plata - 6075-II, 2010, p.105 It is laterally and time-equivalent with the

Altamira Altamira may refer to: People *Altamira (surname) Places * Cave of Altamira, a cave in Cantabria, Spain famous for its paintings and carving *Altamira, Pará, a city in the Brazilian state of Pará * Altamira, Huila, a town and municipality in ...

and Luperón Formations and the Agua Clara Unit.Hoja de Esperanza - 6074-IV, 2010, p.18 ;Esperanza In the vicinity of

Esperanza Esperanza is the Spanish word for hope, and may refer to: Places Philippines * Esperanza, Agusan del Sur, a municipality * Esperanza, Masbate, a municipality * Esperanza, Sultan Kudarat, a municipality United States * Esperanza, Mississippi, ...

,Hoja de Esperanza - 6074-IV, 2010, pp.37-39 La Toca Formation is cropping out in the northeast of the geologic map, while it is also present in the neighboring municipalities of Imbert and San Francisco Arriba. The formation in this area comprises rhythmic alternations of ochre fine-to-medium-grained, locally grading to course-grained sandstones and greyish clayey and ochre marls. This succession is locally cut by meters thick microconglomerates and conglomerates with rounded and subrounded clasts. Analysis of the clasts in San Francisco Arriba shows the clasts consist of up to ten percent of volcanic rock fragments, mainly limestone fragments (23-42%),

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 ...

(8-33%),

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a ...

of up to five percent and minor

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, caus ...

fragments. The matrix which comprises about a quarter of the volume is micritic. The formation is in this area poor in

microfossil A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...

s, although

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 ...

of '' Catapsydrax af. dissimilis'', '' Globigerinoides trilobus'', '' Globigerina sp.'', '' Globorotalia sp.'', '' Cibicides sp.'', '' Brizalina sp.'', '' Reophax sp.'', '' ?Cassidulina sp.'' and '' Pirgo sp.'' have been found in the succession. Turbidite deposition moved to the northeast during the Miocene.Hoja de Esperanza - 6074-IV, 2010, p.99

Tectonics and depositional environment

La Toca Formation is in places inverted and put in contact with the San Marcos Formation along the Camú Fault.Hoja de Puerto Plata - 6075-II, 2010, p.100 The Septentrional Fault bounds the formation to the south.Díaz de Neira, 2017, p.662

Individual outcrops

The formation crops out in the

provinces A province is almost always an administrative division within a country or state. The term derives from the ancient Roman '' provincia'', which was the major territorial and administrative unit of the Roman Empire's territorial possessions ou ...

Puerto Plata and Hermanas Mirabal. ;Puerto Plata In Puerto Plata Province, two sections of La Toca Formation are visible. The type section along the Bajabonico River shows volcaniclastic

s with clasts originating from the Pedro García Formation. The breccias are poorly stratified and contain angular clasts of vesicular

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...

s and

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...

s, polymictic conglomerates of various provenance and chlorite-rich

feldspathic Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldsp ...

arenite Arenite ( Latin: ''arena'', "sand") is a sedimentary clastic rock with sand grain size between 0.0625 mm (0.00246 in) and 2 mm (0.08 in) and contain less than 15% matrix. The related adjective is ''arenaceous''. The equivalen ...

s. This sequence is overlain by bluish-grey marls and black

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel ...

y shales with conglomeratic intercalactions.Museo Virtual - Geositio Puerto Plata type section
- SGN A second outcrop in Puerto Plata shows a less typical debris flow setting, with a varied sedimentological character.Museo Virtual - Geositio Puerto Plata
- SGN ;Hermanas Mirabal The section of La Toca Formation in Hermanas Mirabal Province displays a thick series of matrix supported conglomerates. The clasts of these massively bedded conglomerates are characterized by two main lithology types;

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

and

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

. The limestone clasts are dark grey and white, where the light colored limestones contain carbonate platform fauna including

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and ...

s. The clasts are well-rounded and medium-sized. The succession increases upwards in bedding thickness where limestone clasts become more dominant, larger in size and more angular. The total visible thickness of the succession is approximately . The sequence of conglomerates and provenance of the clasts point to sedimentation in a

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 ...

to shallow marine environment, where the clasts were transported by fluvial systems in the

hinterland Hinterland is a German word meaning "the land behind" (a city, a port, or similar). Its use in English was first documented by the geographer George Chisholm in his ''Handbook of Commercial Geography'' (1888). Originally the term was associated ...

.Museo Virtual - Geositio Hermanas Mirabal
- SGN

Paleontological significance

Cephalotes integerrimus SMNSDO5689 dorsal

La Toca Formation is one of the formations of the Dominican Republic where Dominican amber is found. The amber is known for the many types of insects and other arthropods it contains and even mammalian hair, a leptodactylid

frog A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" ''Triadobatrachus'' is ...

and a gilled mushroom have been discovered in the Dominican amber.Henwood, 1992, p.902 Decades of study have led to an increased understanding of the invertebrate terrestrial fauna of the subtropical Early Miocene. Several genera have been described on the basis of these inclusions in

resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on n ...

from the fossil '' Hymenaea protera'' tree and the many fossils found in the amber provided a unique insight in the paleobiology of the Caribbean of the time. Of the 82 genera of spiders in Dominican amber, one third are extinct and about thirty percent are congeneric with extant taxa.Poinar, 2010, p.27

Fossil content

The following fossils have been found in the formation:

References

Bibliography

;General geology * ;Dominican amber * * * * * * * * * * * * * * * * *

Maps

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