X CONGRESO CUBANO DE GEOLOGÍA (GEOLOGIA´2013) Estratigrafía y Paleontología GEO2-O10 PLANKTONIC FORAMINIFERS AND NANNOCONID ASSEMBLAGES FROM THE LATE APTIAN AND LATE ALBIAN LIMESTONES OF THE PONS FORMATION (SIERRA DE LOS ORGANOS, WESTERN CUBA) (1) (2) (2) Andrzej Pszczółkowski , Dora García Delgado , Santa Gil González 1. Institute of Geological Sciences, Polish Academy of Sciences, Warsaw Research Center, Twarda 51/55, 00-818 Warszawa, Poland, e-mail: [email protected] 2. Centro de Investigaciones del Petróleo, Churruca No. 481, Municipio Cerro, Habana 12000, Cuba, e-mail: [email protected]; [email protected] ABSTRACT The Pons Formation (Late Valanginian-Turonian) overlies the Guasasa Formation in the Sierra de los Organos (western Cuba). We have studied the planktonic foraminifera and nannoconids found in thin sections made from samples collected in outcrops from the Infierno tectonic unit. The samples taken at the new quarry near Pons locality contain planktonic foraminifers assigned to the Late Aptian Globigerinelloides ferreolensis Zone. The foraminiferal assemblage found in the sample CP-264a, collected in the old quarry, belongs to the Globigerinelloides algerianus Zone. Taxa reported from the sample CP-264b suggest the Hedbergella trocoidea Zone. The planktonic foraminifera identified in thin section MR-206 correspond to the Late Albian zones Pseudothalmanninella ticinensis-Thalmanninella appenninica and probably correlate with Zone K-17 in the scheme proposed for the western Gulf of Mexico region (Longoria, 1984). Three nannoconid assemblages have been found in the Late Aptian limestones of the Pons Formation. A major change related to disappearance of the narrow-canal taxa occurred between the Ferreolensis and Algerianus Zones. The last appearance of Nannoconus kamptneri kamptneri was registered in the Late Aptian below the Algerianus Zone. Late Albian was the time of enhanced productivity of siliceous zooplankton in the northwestern part of Proto-Caribbean Seaway. The Late Aptian-Albian limestones of the Pons Formation may be a distant facies equivalent of coeval pelagic sediments found at the DSDP Leg 77 Sites 537 and 538. RESUMEN La Formación Pons (Valanginiano Superior-Turoniano), sobreyace la Fm. Guasasa en la Sierra de Los Organos (Cuba occidental). Se expone el resultado del estudio de los foraminíferos planctónicos y Nannoconidos, encontrados en secciones delgadas de muestras colectadas en afloramientos de la Unidad Tectónica Infierno. Dichas muestras fueron tomadas de la cantera situada en las cercanías del poblado de Pons, y contienen foraminíferos planctónicos referidos al Aptiano Superior, Zona de Globigerinelloides ferreolensis. La asociación de foraminíferos encontrada en la muestra CP-264a, collectada en la parte vieja de la cantera, pertenece a la Zona Globigerinelloides algerianus. Taxones reportados de la muestra CP- 264b sugieren la Zona Hedbergella trocoidea. Los foraminíferos planctónicos identificados en la sección delgada MR-206 corresponden al Albiano Superior, Zonas Pseudothalmanninella ticinensis-Thalmanninella appenninica y son probablemente correlacionables con la Zona K-17 (Vraconiano) en el esquema propuesto para el oeste del Golfo de Mexico (Longoria, 1984). Tres asociaciones de Nannoconidos han sido encontradas en calizas del Aptiano Superior de la Formación Pons. El cambio más importante es el relacionado con la desaparición de los taxones con el canal estrecho entre las Zonas Ferreolensis y Algerianus. La última aparición del Nannoconus kamptneri kamptneri fue registrada en el Aptiano Superior debajo de la Zona Algerianus. El Albiano Superior fue un periodo de crecimiento de la productividad de zooplancton silíceo en la parte noroccidental del Proto-Caribe. Las calizas del Aptiano-Albiano Superior de la Formación Pons deben constituir una facies distal equivalente a sedimentos pelágicos coevos encontrados en las perforaciones del DSDP 77, pozos 537 y 538. INTRODUCTION The Pons Formation (Hatten, 1957) occurs in the Sierra de los Organos in western Cuba (Fig. 1A, B). This lithostratigraphic unit consists of Late Valanginian-Turonian pelagic limestones about 150m thick in the type section (Pszczółkowski, 1999a; Iturralde-Vinent, Pszczółkowski, 2011). The V CONVENCIÓN CUBANA DE CIENCIAS DE LA TIERRA, GEOCIENCIAS´2013 Memorias en CD-Rom, La Habana, 1 al 5 de abril de 2013. ISSN 2307-499X X CONGRESO CUBANO DE GEOLOGÍA (GEOLOGIA´2013) Estratigrafía y Paleontología GEO2-O10 Pons Formation overlies the Guasasa Formation and in a few sections occurs beneath the Peñas Formation, Campanian-Maastrichtian in age (Figures. 2). The Aptian-Albian planktonic foraminifers of the Pons Formation were occasionally mentioned in published and unpublished reports, only. The Pons Formation is important for its paleogeographic position south of the entrance to the south-eastern Gulf of Mexico and also from the point of view of oil exploration in the offshore area of western Cuba. We hope that our contribution will stimulate future detailed studies on microfossil stratigraphy of the Pons Formation and other Cretaceous lithostratigraphic units of the Guaniguanico megaunit in western Cuba (Figures. 2). Figures. 1. A – General map of Cuba; box shown northwest of Pinar del Río town denotes the studied Pons area in the Pinar del Río province (western Cuba). B – Simplified tectonic map of the Pons area in the Sierra de los Organos, Guaniguanico Mountains (partly after Piotrowska, in Puscharovsky et al., 1988): 1 - Valle de Pons tectonic unit; 2 - Infierno tectonic unit; 3 – Viñales tectonic unit; 4 -Ancón tectonic unit; 5 - Alturas de Pizarras del Sur (APS) and Alturas de Pizarras del Norte (APN), composed mainly of the San Cayetano Formation (?Lower Jurassic-Oxfordian sandstones and shales); 6 - overthrusts; 7 – Pons quarry at the southwestern termination of the Sierra Pan de Azúcar range; 8 – location of the MR-206 sample in the Sierra del Infierno section. Previous work From the Pons Formation, Hatten (1957) reported planktonic foraminifers of Albian-Turonian age, identified by M. A. Furrer. Moreover, Hatten (1967) recorded Globigerinelloides algeriana and Ticinella roberti from the Aptian to Albian sublithographic limestone. In his “Minas Formation” (=Pons Fm.), Herrera (1961) mentioned taxa identified by Seiglie (1961) in thin sections. Seiglie (1961, lam. VI, fig. 3) referred to Cenomanian-Lower Turonian identified taxa (Globigerina sp. type cretacica, Rotalipora cf. R. appenninica Renz, Ticinella roberti Gandolfi and Globigerinelloides sp.). According to Meyerhoff (in Khudoley, Meyerhoff, 1971, p. 76), the microfossils from the Pons Formation “prove the presence of Neocomian(?), Aptian, Albian, and Cenomanian”. De la Torre (1988) reported Albian-Maastrichtian taxa from limestones of the Pons Formation (together with the V CONVENCIÓN CUBANA DE CIENCIAS DE LA TIERRA, GEOCIENCIAS´2013 Memorias en CD-Rom, La Habana, 1 al 5 de abril de 2013. ISSN 2307-499X X CONGRESO CUBANO DE GEOLOGÍA (GEOLOGIA´2013) Estratigrafía y Paleontología GEO2-O10 Peñas Fm.). A presence of Ticinella spp. indicates Albian-Cenomanian (Torre, 1988). From other belts recognized in Cuba, Blanco-Bustamante (2001) reported planktonic foraminiferal assemblages studied in thin sections from limestones drilled by two wells located in the Cayo Coco zone (Iturralde-Vinent, 1994) in northern part of central Cuba. Figures. 2. Position of the Pons Formation in the stratigraphic scheme of the Los Organos succession and its relation to equivalent Cretaceous formations of the Rosario successions in the Guaniguanico megaunit (partly after Pszczółkowski, 1999a and Iturralde & Pszczółkowski, 2011 difi d) V i l d l k f d i ( iddii) Lithology and microfacies of studied limestones Pons quarry Figures. 3. Late Aptian limestones of the Pons Formation exposed in the old quarry at Sierra Pan de Azúcar, east of Pons locality: 1 - western part of the outcrop; 2 - eastern part of the outcrop containing medium- to thick-bedded nannofossil- foraminiferal biomicrites (photographs taken in 1983). V CONVENCIÓN CUBANA DE CIENCIAS DE LA TIERRA, GEOCIENCIAS´2013 Memorias en CD-Rom, La Habana, 1 al 5 de abril de 2013. ISSN 2307-499X X CONGRESO CUBANO DE GEOLOGÍA (GEOLOGIA´2013) Estratigrafía y Paleontología GEO2-O10 All limestone samples collected at the quarry belong to the Pons Formation from the Infierno tectonic unit, which is extensively exposed in the Sierra de los Organos (Piotrowska, 1978, fig. 3). Our samples from the Late Aptian limestones of the Pons Formation have been collected in the area situated in the central part of the Sierra de los Organos, 1.4 km east of Pons locality and north of the road from Viñales to Pons (Figures. 1B). In 1983, two samples (CP-264 a, b) have been taken from the limestones of the upper, but not the uppermost, part of the Pons Formation in an outcrop called here the “old quarry” (Figures. 3: 1, 2). At present, this outcrop is a part of the big Pons quarry. The gray micritic limestones consist of beds 0.1-0.5 m thick with lenses and nodules of black chert. Their total thickness is about 10 m (Figures. 3: 2). The sampled beds are located in the lower part of the outcrop, about 3 m apart. The limestones are foraminiferal biomicrites with relatively well preserved planktonic foraminifera (Figures. 4: 1). Figures. 4. LM micrographs of the studied limestones from the Pons Formation showing characteristic microfacies: 1 – radiolarian microfacies, sample PR-47-2, Late Aptian limestone exposed in the new quarry near Pons;