Meetings Reports

MEETINGS REPORTS 1. Stratigraphy and correlation of Cretaceous volcanic-arc rocks, Dominican Republic (IGCP 364): July, 1997

489

THIS Field Workshop was attended by a group of 21 geologists from the Dominican Republic, Jamaica, Cuba, the USA, Canada, Italy and the UK. It. was co-sponsored by IGCP Project 364,

the Sociedad Geologica de Republica Dominicana, Falconbridge Dominicana, and the Direccion General de Mineria. The principal object of the Workshop was to document the fossiliferous limestones which are intercalated within the Cretaceous arc suite in the Cordillera Central and Oriental, and to correlate these units with possibly isochronous beds in Cuba, Puerto Rico and Jamaica. Particular attention was paid to the possible interruption of volcanic activity near the end of the Cretaceous as it is evidenced in Cuba (lturralde-Vinent, 1996). Fossils collected during the trip are to be studied by Edward Robinson (forams), Stephen Donovan (crinoids and echinoderms), Peter Skelton and Reinaldo Rojas (rudists and related taxa) . However, some preliminary conclusions are as follows:

The older part of the Cretaceous Volcanic Arc Suite in the Dominican Republic occurs both in the Cordillera Central and 01iental, and is known as the Los Ranchos Formation. These are primitive island-arc rocks represented by spilite-keratophyres, pillow basalts and andesite-basalts, and are interbedded with coarse- to fine-grained tuffaceous rocks. Earliest Cretaceous plant remains are known to occur .in fine-grained carbonaceous tuffites of the Los Ranchos Fm at the Rosario Dorninicana Golden Mine (Russel and Kesler, 1991), and represent the oldest evidence for subaerial exposure of the Cretaceous volcanic edifice. This unit has not been observed elsewhere in the Antilles (Table 1, fossiliferous bed 1).

The Los Ranchos Formation underwent Early Cretaceous deformation (Draper et al., 1977), and the unit is unconformably overlain by grey, shallow-marine limestones which contain an early to middle Albian fossil assemblage. J.-P. Masse identified the Albian rudist Coalcama sp., and Bourdon et al. (1995) reported Paracoskinolina sunnilandensis and Mesorbitolina subconcava from these beds (Table 1, fossiliferous bed 2). This limestone is known as the Rfo Hatillo Formation in the Dominican Republic, the Rfo Maton limestone in Puerto Rico (Labron and Perfit, 1993), and is probably present in south-central Cuba where limestones with Coalcomana ramosa have been reported (Rojas et al., 1995).

Overlying the Rfo Hatillo Formation is a thick calc-alkaline series of well-bedded to locally massive volcaniclastic and sedimentary rocks, with few volcanic flows , which is generally known as the Las Guayabas Formation. Additionally, some poorly-defined units have been named to account for lithological variations within the Late Cretaceous interval (Lebron and Mann, 1991). Another thick, fossiliferous limestone unit is interbedded with volcanic rocks just above the Rfo Hatillo limestone, not far from the Rosario Mine. This unit is known as the Las Canas (or Canas) Formation and was originally described by Bowin (GSA Mem. 98, 1966) as oflatest Cretaceous age. Preliminary observations of the limestone's fossil content at several localities during the Workshop suggest, however, a late Albian age, probably equivalent to the Tepeyacia corrugata limestone in Cuba (Rojas et al., 1995; Table 1, fossiliferous beds 3 and 3a). This age is more consistent with the stratigraphic position of the Las Canas Formation as observed in the field and on geological maps.

A Santonian interval of thin-bedded tuffites interbedded with thin, ammonite-bearing limestones was observed in the Cordillera Oriental. This unit seems to be the Rfo Chevon Formation (Lebron and Mann, 1991 ), equivalentto the Aguilar Formation in Central Cuba (Table 1, Santonian armnonites). A few grey, fos siliferous limestone boulders found within younger conglomerates yielded rudists (Barrettia monilifera and Macgillivryia sp.), and probably represent the "B. monilifera fauna" known from the early to middle Campanian of Cuba (Rojas et al. , 1995) (Table 1, fossiliferous beds 5 and Sa). From Table 1, it is evident that only the Santonian rudist-bearing limestone (Durania curasavica fauna) found in Cuba, Jamaica and Puerto Rico was not documented in the Dominican Republic during the Workshop.

An important finding was the depositional character and age of the Don Juan Formation. This coarse-grained, poorly-sorted, ill-bedded breccia-conglomerate contains a wide variety of clastic material, all derived from the underlying Cretaceous Volcanic Arc section. The composition of the clastic rocks suggests that the volcanic arc was deeply eroded; boulder-, cobble- and pebble­grade fragments of limestones and volcanic rocks were found in a single outcrop. These and other

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Table 1

CAMPANIAN

SANTONIAN

CONIACIAN

TURONIAN

CENOMANIAN

ALBIAN

APTIAN

Meetings Reports

East-Central Cuba (After Rojas et al ., 1995, lturralde-Vinent, 1996)

JJMAGUAYU Rudist biostromes, biorudites and rudist marls _ ~

_ ,:::: - - -- -~-- DURAN

5A (£l

AGUILAR Fine bedded tuffi­tes, tuffs, cherts and limestones.

Santonian • -ammonites·

Th. >150m.

PIRAGUA

Well bedded tuffs, . t1,1ffjt~s~ witb jnta~d.dQd.

andesitic and basaltic flows, tuffaceous sandstones

and conglomerates. Th. 500 m.

CAMUJIRO Calc-alkaline tuffs, agglomerate and

flows or traquibasalt, andesite-basalt shoshonite, trachyandesite and

Th. 3500-4000 m.

:-:-CENTRAL COLOMBIA-/ . 3A ~ Gray rudist-bearing - -

limestone .--~;80vvvvwvv -IIIJ!!!!IJ111,!@PI' Pillow basalts with interbedded minor llmestone and tuffites.

PRE-CAMUJIRO

CAOBILLA Acid tuffs

and tuffites,

SIERRA DE ROMPE

ANFIBOLITES

Metavolcanics of calc -alkaline composition

with intercalations of black fossiliferous rudist (?) marbles.

?

Well bedded black carbonaceous tuffites, tuffs, tuffaceous sandstones and conglomerates

with small bodies or dacites and microdiorttes. Radiolaria, Nannoconus spp., Globtoerinelloides sp.

Cordillera -Orlentelln O.R. (After IGCP -354 Field Meeting, 7197)

DON JUAN

s@ Poorly sorted breccias and conglotT'IefCDe:s with clastics derived from the erosior.

ot the Cretaceous volcanic arc

- - ~di;=-bea~g iimestone - > 5 @ found as pebbles and boulders · ~ · ~ the~~ich~n ~glo~ra~ '\ ·

"-

L

A

s RIOCHAVON / Well bedded tUffs and tuffites wih Santonian limestone intercalations • 'e.mmonites

- . .:__ · _:__ · :.._.:.. ............ - - ... . . - .

Well bedded to massive calc-alkaline vulcano-detritic series

with tuffs, tuffites and intercalations of cherts and some volcanic flows.

_WetJ Qe9Qe~ tp msts:siy~ calc-alkaline vulcano-detritic series with agglomerate, tuffs, tuffites and

Intercalations of some volcanic flows including shoshonite

- - LAS CANAs - / ..___ 3 ~ 11JCjist:_b:"ar!!}9 lms. -

Pillow basalts and tuffs

PIA basaltic to rhyolitic volcanic ftows interbedded with tuffs and black carbonaceous tuffites and sandstones with fossil plants.

1~

G

u

A

y

A

B

A

s

R 0 A S N

c H 0 s·

COnglomerates W' Plutonic Activity Unconformity

sedimentological features , such as the red colour of the clay matrix (where present), the poor horizontal and vertical sorting, the angularity of the clasts, etc., suggests that deposition occurred in terrestrial to shallow-marine intermontane basins.· Within this formation are found limestone clasts of the Rio Hatillo, Las Cafias, and "B. monilifera fauna". The discovery of eroded specimens of Titanosarcolites (rudist) suggests that the conglomerate is latest Campanian-Maastrichtian or younger; other stratigraphical considerations, however, indicated a Maastrichtian age.

Elsewhere in the Cordillera Oriental, the massive Maastrichtian limestones of the Lorna de Angelada Formation are present above the Cretaceous volcanics (Lebron and Mann, 1991). The occurrence of the Maastrichtian limestone and conglomerates suggest that volcanic activity in the Cretaceous Arc ended before the Maastrichtian (i.e. before deposition of the Don Juan and Lorna de Angelada Formations), an event recorded elsewhere in Jamaica, Puerto Rico and Cuba.

In conclusion, Workshop participants were able to identify major sedimentary and tectonic events affecting the evolution of the Caribbean volcanic arc during the Cretaceous, and to correlate these events between the Greater Antillean islands.

Meetings Reports 491

References Draper, G., et al. , 1997. Thrust emplacement of the Hispaniola peridotite belt: orogenic expression

of the mid-Cretaceous Caribbean arc polarity reversal? Geology. Iturralde-Vinent, M. (ed) ., 1996. Cuban ophiolites and volcanic arcs. Spec. Contrib. IGCP 364. Miami.

Fl., 254 pp. Lebron, M. C. and Mann, P., 1991. Geological map of Eastern Dominican Republic. In: Mann, P. et al., Geological and tectonic development of the North American-Caribbean plate boundary in

Hispaniola. GSA Spec. Paper 262. . Lebron, M.C. and Perfit, M. L. , 1993. Stratigraphical and petrochemical data support subduction

polarity reversal of the Cretaceous Caribbean volcanic arc. Journal of Geology, 101, 289-296. Rojas, R . M., lturralde-Vinent, P. W. and Skelton, P. W., 1995. Stratigraphy, composition and age

of Cuban rudist-bearing deposits. Rev. Mexicana de Ciencias Geologicas, 12 (2), 272-291. Russel, N. S. andKesler, S., 1991.Geology of the maar-diatremecomplex housing precious metal

mineralizaton at Pueblo Viejo, Dominican Republic. In: Mann, P. et at., (eds), GSA Spec. Paper 262, 213-215.

M. Itturalde-Vinent (Museo Nacional de Historia Natural, La Habana, Cuba)

Pmail: mnhnc@cenai.inf.cu