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.

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 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, quartz, 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.
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:
GroupFossilLocationNotes
DipteraBrachypogon (Isohelea) dominicanusEl Valle
DipteraForcipomyia (Lepidohelea) sp.El Valle
DipteraForcipomyia (Lepidohelea) antilleanaEl Valle
DipteraForcipomyia (Lepidohelea) chrysosuccineaEl Valle
DipteraForcipomyia (Lepidohelea) domibicolorEl Valle
DipteraMiomyiaEl Valle
DipteraProtortalotrypeta grimaldiiEl Valle
DipteraArchicratyna arcanaEl Valle
DipteraProcolobostema roseniEl Valle
DipteraForcipomyia (Forcipomyia) sp.La Toca mine
DipteraProcolobostema roseniLa Toca mine
DipteraAntiquatortia histuroidesLa Toca mine
DipteraCulex malariagerLa Toca mine
DipteraDominimyza tanyacaenaLa Toca mine
DipteraDiceratobasis workiLa Toca mine
DipteraFeroseta priscaLa Toca mine
DipteraPolyvena horatisLa Toca mine
DipteraEnischnomyia stegosomaLa Bucara mine
DipteraArchicratyna arcanaEl Valle locality
HemipteraLeptopharsa evsyuniniEl Valle
HemipteraEnicocephalus omenLa Toca mine
HemipteraEnicocephalus seniculusLa Toca mine
HemipteraEnicocephalus subvitreusLa Toca mine
HemipteraAmnestus electricusLa Toca mine
HemipteraEmpiploiariola inermisLa Toca mine
HemipteraPrisciba dominicanaLa Toca mine
HemipteraApicrenus fossilisLa Toca mine
HemipteraPraecoris dominicanaLa Toca mine
HemipteraPanstrongylus hispaniolaeLa Toca mine
HemipteraSchizoptera dominicanaLa Toca mine
HemipteraElectromyrmococcus abductusLa Toca mine
HemipteraAcropyga sp.La Toca mine
HemipteraMinyscapheus dominicanusLa Bucara mine
HemipteraPrisciba serrataLa Bucara mine
HemipteraHypselosoma dominicanaLa Bucara mine
HemipteraSchizoptera hispaniolaeLa Bucara mine
HemipteraEnicocephalus priusLa Vega group of mines
HemipteraElectrobates spinipesEl Valle locality
ColeopteraOkamninus annaeLa Toca mine
ColeopteraCaulophilus asheiLa Toca mine
ColeopteraElectroborus brightiLa Toca mine
ColeopteraBicalcasura maculataLa Bucara mine
ColeopteraDominibrentus leptusRon Cauble coll
HymenopteraPseudomyrmex antiquusLa Toca mine
HymenopteraWanderbiltiana wawasitaLa Toca mine
HymenopteraTechnomyrmex hispaniolaeEl Valle locality
HymenopteraProceratium gibberumEl Valle locality
HymenopteraCephalotes integerrimusEl Valle locality
OrthopteraProanaxipha latocaLa Toca mine
OrthopteraAnaxipha dominicaLa Toca mine
EphemeropteraBorinquena parvaLa Bucara mine
EnopleaPalaeodiplogaster brentiphilaRon Cauble coll
Symphypleona?Sphyrotheca sp.La Bucara mine
PterygotaMyopsocus arthuriLa Toca mine
PterygotaTroctopsocoides gracilisLos Cacaos
ArachnidaTityus geratusLa Toca mine
ArachnidaHabrotrocha sp.La Toca mine
ArachnidaBdelloidea indet.La Toca mine
ArachnidaDipoena dominicanaLa Toca mine
PhasmatodeaClonistria dominicanaLa Bucara mine
FunghiCoprinites dominicanaLa Toca mine

Maps

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