La Toca Formation
# La Toca Formation

The La Toca Formation is a geologic formation in the northern and eastern part of the Dominican Republic. The formation, predominantly an alternating sequence of marls and turbiditic sandstones, breccias and conglomerates, is renowned for the preservation of insects and other arthropods in amber, known as Dominican amber. The formation is dated to the Burdigalian to Langhian stages of the Miocene period (Hemingfordian in the NALMA classification).

## Description

La Toca Formation was first defined by Redmond in 1982. The formation mainly consists of marls and turbiditic sandstones and conglomerates deposited in the northeastern part of Hispaniola. The formation overlies the Los Hidalgos Formation and is overlain by the La Jaiba Conglomerate and in places by the Villa Trina Formation. It is laterally and time-equivalent with the Altamira and Luperón Formations and the Agua Clara Unit.

### Esperanza

In the vicinity of Esperanza, 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 (8-33%), chert of up to five percent and minor metamorphic rock fragments. The matrix which comprises about a quarter of the volume is micritic.

The formation is in this area poor in microfossils, although foraminifera 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.

### Tectonics and depositional environment

La Toca Formation is in places inverted and put in contact with the San Marcos Formation along the Camú Fault. The Septentrional Fault bounds the formation to the south.

### Individual outcrops

The formation crops out in the provinces 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 breccias with clasts originating from the Pedro García Formation. The breccias are poorly stratified and contain angular clasts of vesicular basalts and andesites, polymictic conglomerates of various provenance and chlorite-rich feldspathic arenites. This sequence is overlain by bluish-grey marls and black silty shales with conglomeratic intercalactions.

A second outcrop in Puerto Plata shows a less typical debris flow setting, with a varied sedimentological character.

**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 and limestone. The limestone clasts are dark grey and white, where the light colored limestones contain carbonate platform fauna including corals. 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 100 metres (330 ft).

The sequence of conglomerates and provenance of the clasts point to sedimentation in a deltaic to shallow marine environment, where the clasts were transported by fluvial systems in the hinterland.

## Paleontological significance

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 and a gilled mushroom have been discovered in the Dominican amber. 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 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.

### Fossil content

The following fossils have been found in the formation:

| Group | Fossil | Location |
| - | - | - |
| Diptera | Brachypogon (Isohelea) dominicanus | El Valle |
| Diptera | Forcipomyia (Lepidohelea) sp. | El Valle |
| Diptera | Forcipomyia (Lepidohelea) antilleana | El Valle |
| Diptera | Forcipomyia (Lepidohelea) chrysosuccinea | El Valle |
| Diptera | Forcipomyia (Lepidohelea) domibicolor | El Valle |
| Diptera | Miomyia | El Valle |
| Diptera | Protortalotrypeta grimaldii | El Valle |
| Diptera | Archicratyna arcana | El Valle |
| Diptera | Procolobostema roseni | El Valle |
| Diptera | Forcipomyia (Forcipomyia) sp. | La Toca mine |
| Diptera | Procolobostema roseni | La Toca mine |
| Diptera | Antiquatortia histuroides | La Toca mine |
| Diptera | Culex malariager | La Toca mine (Poinar coll) |
| Diptera | Dominimyza tanyacaena | La Toca mine (Poinar coll) |
| Diptera | Diceratobasis worki | La Toca mine (Poinar coll) |
| Diptera | Feroseta prisca | La Toca mine (Poinar coll) |
| Diptera | Polyvena horatis | La Toca mine (Poinar coll) |
| Diptera | Enischnomyia stegosoma | La Bucara mine (Poinar coll) |
| Diptera | Archicratyna arcana | El Valle locality (Poinar coll) |
| Hemiptera | Leptopharsa evsyunini | El Valle |
| Hemiptera | Enicocephalus omen | La Toca mine |
| Hemiptera | Enicocephalus seniculus | La Toca mine |
| Hemiptera | Enicocephalus subvitreus | La Toca mine |
| Hemiptera | Amnestus electricus | La Toca mine |
| Hemiptera | Empiploiariola inermis | La Toca mine |
| Hemiptera | Prisciba dominicana | La Toca mine (Poinar coll) |
| Hemiptera | Apicrenus fossilis | La Toca mine (Poinar coll) |
| Hemiptera | Praecoris dominicana | La Toca mine (Poinar coll) |
| Hemiptera | Panstrongylus hispaniolae | La Toca mine (Poinar coll) |
| Hemiptera | Schizoptera dominicana | La Toca mine (Poinar coll) |
| Hemiptera | Electromyrmococcus abductus | La Toca mine (SMF coll) |
| Hemiptera | Acropyga sp. | La Toca mine (SMF coll) |
| Hemiptera | Minyscapheus dominicanus | La Bucara mine (Poinar coll) |
| Hemiptera | Prisciba serrata | La Bucara mine (Poinar coll) |
| Hemiptera | Hypselosoma dominicana | La Bucara mine (Poinar coll) |
| Hemiptera | Schizoptera hispaniolae | La Bucara mine (Poinar coll) |
| Hemiptera | Enicocephalus prius | La Vega group of mines (AMNH coll) |
| Hemiptera | Electrobates spinipes | El Valle locality (Poinar coll) |
| Coleoptera | Okamninus annae | La Toca mine |
| Coleoptera | Caulophilus ashei | La Toca mine |
| Coleoptera | Electroborus brighti | La Toca mine |
| Coleoptera | Bicalcasura maculata | La Bucara mine (Poinar coll) |
| Coleoptera | Dominibrentus leptus | Ron Cauble coll |
| Hymenoptera | Pseudomyrmex antiquus | La Toca mine (Poinar coll) |
| Hymenoptera | Wanderbiltiana wawasita | La Toca mine (Poinar coll) |
| Hymenoptera | Technomyrmex hispaniolae | El Valle locality (MCZ coll) |
| Hymenoptera | Proceratium gibberum | El Valle locality (MCZ coll) |
| Hymenoptera | Cephalotes integerrimus | El Valle locality (MCZ coll) |
| Orthoptera | Proanaxipha latoca | La Toca mine (Poinar coll) |
| Orthoptera | Anaxipha dominica | La Toca mine (Poinar coll) |
| Ephemeroptera | Borinquena parva | La Bucara mine (Manchester coll) |
| Enoplea | Palaeodiplogaster brentiphila | Ron Cauble coll |
| Symphypleona | ?Sphyrotheca sp. | La Bucara mine (Manchester coll) |
| Pterygota | Myopsocus arthuri | La Toca mine (Poinar coll) |
| Pterygota | Troctopsocoides gracilis | Los Cacaos (INHS coll) |
| Arachnida | Tityus geratus | La Toca mine (Poinar coll) |
| Arachnida | Habrotrocha sp. | La Toca mine (Poinar coll) |
| Arachnida | Bdelloidea indet. | La Toca mine (Poinar coll) |
| Arachnida | Dipoena dominicana | La Toca mine (SMF coll) |
| Phasmatodea | Clonistria dominicana | La Bucara mine (Poinar coll) |
| Funghi | Coprinites dominicana | La Toca mine (Poinar coll) |
