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).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 sandstones 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 and Luperón Formations and the Agua Clara Unit.Hoja de Esperanza - 6074-IV, 2010, p.18
Esperanza In the vicinity of Esperanza,Hoja de Esperanza - 6074-IV, 2010, pp.37-39 La Toca Formation is cropping out in the northeast of the geological 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.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 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. 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 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 .
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. Museo Virtual - Geositio Hermanas Mirabal - SGN
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.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 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:
Group Fossil Location Notes Diptera Brachypogon (Isohelea) dominicanus El Valle El Valle at Fossilworks.orgGolub & Popov, 2000 Forcipomyia (Lepidohelea) sp. Forcipomyia (Lepidohelea) antilleana Forcipomyia (Lepidohelea) chrysosuccinea Forcipomyia (Lepidohelea) domibicolor Miomyia Protortalotrypeta grimaldii Archicratyna arcana Procolobostema roseni Forcipomyia (Forcipomyia) sp. La Toca mine La Toca mine (AMNH coll) at Fossilworks.orgDavis & Engel, 2006 Procolobostema roseni Antiquatortia histuroides Heikkilä et al., 2018 Culex malariager La Toca mine (Poinar coll) Dominimyza tanyacaena Diceratobasis worki Feroseta prisca Poinar, 2006 Polyvena horatis Poinar & Brown, 1993 Enischnomyia stegosoma La Bucara mine (Poinar coll) Archicratyna arcana El Valle locality (Poinar coll) El Valle locality (Poinar coll) at Fossilworks.orgMohrig & Röschmann, 2005 Hemiptera Leptopharsa evsyunini El Valle Enicocephalus omen La Toca mine Enicocephalus seniculus Enicocephalus subvitreus Amnestus electricus Empiploiariola inermis Prisciba dominicana La Toca mine (Poinar coll) La Toca mine (Poinar coll) at Fossilworks.orgNel et al., 2006 Apicrenus fossilis Praecoris dominicana Panstrongylus hispaniolae Schizoptera dominicana Electromyrmococcus abductus La Toca mine (SMF coll) La Toca mine (SMF coll) at Fossilworks.orgJohnson et al., 2001 Acropyga sp. Minyscapheus dominicanus La Bucara mine (Poinar coll) La Bucara mine (Poinar coll) at Fossilworks.orgPoinar, 2011 Prisciba serrata Hypselosoma dominicana Schizoptera hispaniolae Enicocephalus prius La Vega group of mines (AMNH coll) La Vega group of mines (AMNH coll) at Fossilworks.orgGrimaldi et al., 1993 Electrobates spinipes El Valle locality (Poinar coll) Coleoptera Okamninus annae La Toca mine Caulophilus ashei Electroborus brighti Bicalcasura maculata La Bucara mine (Poinar coll) Dominibrentus leptus Ron Cauble coll Hymenoptera Pseudomyrmex antiquus La Toca mine (Poinar coll) Wanderbiltiana wawasita Technomyrmex hispaniolae El Valle locality (MCZ coll) El Valle locality (MCZ coll) at Fossilworks.orgWilson, 1985 Proceratium gibberum Cephalotes integerrimus De Andrade & Urbani, 1999 Orthoptera Proanaxipha latoca La Toca mine (Poinar coll) Anaxipha dominica Ephemeroptera Borinquena parva La Bucara mine (Manchester coll) Enoplea Palaeodiplogaster brentiphila Ron Cauble coll Ron Cauble coll at Fossilworks.orgPoinar, 2009 Symphypleona ?Sphyrotheca sp. La Bucara mine (Manchester coll) La Bucara mine (Manchester coll) at Fossilworks.orgPenney et al., 2012 Pterygota Myopsocus arthuri La Toca mine (Poinar coll) Troctopsocoides gracilis Los Cacaos (INHS coll) Los Cacaos (INHS coll) at Fossilworks.orgMockford & García Aldrete, 2014 Arachnida Tityus geratus La Toca mine (Poinar coll) Habrotrocha sp. Bdelloidea indet. Dipoena dominicana La Toca mine (SMF coll) Phasmatodea Clonistria dominicana La Bucara mine (Poinar coll) Funghi Coprinites dominicana La Toca mine (Poinar coll) Nel et al., 2006
See also
List of fossiliferous stratigraphic units in the Dominican Republic El Mamey Formation - Dominican amber formation of the Dominican Republic Yanigua Formation - Dominican amber formation of the Dominican Republic Thomonde Formation - Early Miocene formation of Haiti Lagunitas Formation - Burdigalian fossiliferous formation of Cuba Cucaracha Formation - Burdigalian to Langhian fossiliferous formation of Panama Castillo Formation - Burdigalian fossiliferous formation of Venezuela Honda Group - Langhian fossiliferous formation of Colombia
References
Bibliography General geology
Dominican amber
Maps
Further reading