STUDIA GEOLOGICA POLO N I CA Vol. 114, Krakow· 1999, pp. 7- 33. Mesozoic stratigraphy of Cuba Edited by A. Pszczolkowski
Andrzej PSZCZOLKOWSKJ1
New data on the Lower Cretaceous microfossil and nannoconid stratigraphy in the Guaniguanico terrane of western Cuba2 (Figs 1-15)
Abstract. The age of some Lower Cretaceous lithostratigraphic units and their boundaries in the Guaniguanico terrane, western Cuba, is modified on the basis of calpionellids, forami nifers and nannoconids. In the Northern Rosario belt, the Artemisa/Polier formations boundary is diachronous (upper Lower Berriasian to Lower Valanginian). In the studied sites located in the Southern Rosario belt, the topmost part of the Sumidero Member of the Artemisa Formation is latest Valanginian to Hauterivian in age. Comparing this result with previous data, the Artemisa/Santa Teresa formations boundary ranges from Lower Valanginian to Hauterivian. The Late Valanginian to earliest Hauteri vian age of the lowermost part of the Pons Formation in the Rio Las Piedras section, Sierra de los Organos, is accepted on the basis of the planktonic foraminifers, calpionellids and nannoconids. The presence of Tintinnopsella cwpathica Murgeanu et Filipescu is characteristic for the Tintinnopsella Zone. ./llannoconus tru itti i Bronnimann, 195 5, subsp. iruilti iDeres et Acheriteguy, 1980, is present in the Barremian-Lower Aptian assemblages. Comparing the Lower Cretaceous stratigraphic record from the Guaniguanico terrane to that registered at the Southern Gulfof Mexico basin site (Hole 535), some sitnilarities, as well as differences, can be discerned.
Key words: Nannoconids, calpionellids, planktonic foraminifers, Lower Cretaceous, stratigraphy, Guaniguanico terrane, western Cuba.
INTRODUCTION During the past decades, the Lower Cretaceous formations of the Guaniguanico terrane in western Cuba (Fig. 1) have been studied mostly during the geological mapping (Myc:zyllski, 1977; Pszcz6!kowski, 1978, 1982; de Ia Torre, 1988). These studies allowed to elaborate a general stratigraphic scheme ofth e Mesozoic succes sions for the Guaniguanico terrane (Pszcz6lkowski, 1978, 1994). However, various
Institute of Geological Sciences, Polish Academy of Sciences, ul. Twarda 5 1/55, 00-818 Warszawa, Poland. 2 Manuscript accepted for publication June 25, 1999. 8 A. PSZCZOLKOWSKI LOWER CRETA CEO US STRA TlGRAPHY 9
define the age of Lower Cretaceous lithostratigraphic units in western Cuba. Pre Albian planktonic foraminifers were observed only occasionally in thin sections (de la Torre, 1988), usually without specific identification. The Lower Cretaceous nannofossils have not been investigated in the Gua niguanico terrane. Bronnimann (1955) defined the stratigraphic distribution of the species of Nannoconus in central Cuba (former Las Villas Province). Bronnimann (1955) distinguished three typical assemblages ofnannoconids: (1) N. steinmanni N. aff. g/obulus- N. colomi, associated with calpionellids, (2) N. steinmanni- N. co lomi- N. kamptneri- N. bermudezi- N. globulus (with rare "Globigerinas" in a sin gle section), (3) N. truittii- N. minutus - N. elongatus- N. bucheri- N. wassalli, as sociated with Orbitolina sp. and with the first "Globigerinas" of an undescribed GOLFO DE type. The age of the assemblage 1 has been determined as the Neocomian, the as semblage 2 has been tentatively assigned to the Barremian, while the assemblage 3 BATABANO was defined as Aptian to Albian (Bronnimann, 1955).
GEOLOGICAL SETTING 0 40 km The Guaniguanico terrane (lturralde-Vinent, 1994, 1996) consists of a number of tectonic units (thrust sheets) grouped in four belts: the Sierra de los Organos; Fig. 1. L?cation map showing sites sampled in the Guaniguanico terrane, western Cuba (inset Southern Rosario; Northern Rosario; and La Esperanza (Fig. 1). In general, these shows l ocan_o~ of the study area m Cuba). 1- Rio Las Piedras; 2 - San Vicente; 3 - Soroa; 4 _ Rancho Alto; 5-Chmno; 6-:- Ranch? Manetc; 7 - Los Cayos; 8-Lomas de Polier. The site 1 area outlined by belts differ in their stratigraphy and, partly, in their tectonic style (Pszcz6lkowski, the small rectan~le m the S1erra de los Organos belt is enlarged in Figure 2A. The area outlined by 1977, 1978). Nevertheless, the Northern Rosario and La Esperanza belts are similar ~~ger rectangle wlhe northeastern pan ofthe Guaniguanico terrane (dashed line) is enlarged in Figure and may be considered as equivalents. The Guaniguanico thrust sheets were em placed northwestvvard during the Early Eocene. The Pinar fault forms the southern boundary of the Guaniguanico terrane (Fig. 1). The Bahia Honda terrane is situated s~ati~aphic problems still remain to be resolved. The pelagic limestones and ra to the north of this tectonostratigraphic unit. The Upper Cretaceous and Paleogene dwlanan cherts predominate in the Lower Cretaceous sedimentary sequence of sedimentary sequences of the Bahia Honda terrane are underlain by an ophiolitic western Cuba. These rocks often lack macrofauna, hence the microfossils and nan complex and by Cretaceous (pre-Late Campanian) volcanic rocks. The Paleogene nofossils are the main source of biostratigraphic information. Los Palacios basin extends southeast of the Guaniguanico terrane (Fig. 1). The samples were collected at 8 sites in the Guaniguanico terrane of western The Guasasa Formation (Herrera, 1961) has been distinguished in the Sierra de Cuba during 1971-1990. All samples were studied in thin sections for microfossils los Organos belt of the Guaniguanico terrane (Figs 1, 2A). This formation com (calpionellids, foraminifers) and microfacies characteristics. The calcareous nan prises the ?Upper Oxfordian to Valanginian deposits subdivided into four mem nofossils were investigated in the limestone chips on scanning electron microscope bers. The Tumbitas Member consists of thick-bedded calpionellid-radiolarian and (SEM). The principal aims of thi s paper are: (1) to define the age of the lowermost nannoconid limestones of the Upper Berriasian to Lower Valanginian age (Fig. 3). part of the Pons Fonnation in the type section, and to document the lowennost fo One sample (AP-20) was taken from the topmost part of the Tumbitas Member raminiferal (planktonic) faunule in the Cuban Lower Cretaceous; (2) to precise the (Fig. 3). Tbe Pons Formation (Hatten, 1957), of the Late Valanginian to Turonian age of the bou~daries between the Artemisa, Potier and Santa Teresa formations; age, also occurs in the Sierra de los Organos belt. This unit, about 150 m in thick and (3) to contnbute to the knowledge of the stratigraphic ranoe of the Nannoconus ness, is composed of grey to black micritic limestones with chert intercalations. assemblages in the Caribbean region. o Four samples were collected from the limestones occurring in the lowermost part of the Pons F01mation in the Rio Las Piedras section (Figs 1, 2A, 3). PREVIOUS WORK The Artemisa Formation (Lewis, 1932), recognized in the Southern and North ern Rosario belts, is subdivided into three members: San Vicente, La Zarza and Su The Lower Cret~ceous ~alpionellids of western Cuba were studied by Pop midero (Pszcz6lkowski, 1978). The Lower Cretaceous Sumidero Member consti (1976, 1986). Pszcz6lk:owski (1978) and de Ia Torre (1988) used calpionellids to tutes the upper part of the Artemisa Formation (Fig. 3). This member consists of 11 10 A. PSZCZOLKOWSKI LOWER CRETACEOUS STRATIGRAPHY
-r------'crs Gayos
Northern • 7 0 Rosario be It ~ . q.'<>~ ~ 6 ------"-~"'~ Ch~rei nos I ' Southern Rancho o Mundito 1000 m
F?d}Jl !!mll2 - 3 _ , _4
Fig. 2. A - Detailed location ofthe Rio Las Piedras, southofPons (site I in Fig. 1). 1 - sampled area in the lowem10st pal1 of the Pons Formation; 2 - Guasasa Formation in the Sierra Chichoncs; 3 - roads; 4 - rivers. 8 - Sites 3-8 in Lhe Southern and Northern Rosari o belts (area outlined by dashed rectangle in Fig. I): 3 - Soroa; 4-Rancho Alto; 5-Chirino; 6-Rancho Mancte: 7-Los Cayos; 8 - Lomas de Polier biomicrites with intercalations of radiolarian cherts. The samples of the Sumidero Member limestones were collected at four sites (Fig. 1): Soroa; Rancho Alto; Chir ino; and on the Rancho Manete hill. The Potier Formation (Pszcz6lkowski, 1978) I occurs in the Northern Rosario belt. This formation, about 300m thick, includes pe lagic limestones with intercalations of turbiditic sandstones and shales. The Roble l z Member was distinguished in the uppermost part of the Polier Formation. Three => s samples were collected from the topmost beds of the Potier Formation (Figs 1, 2B, "' c 3~ 0 z;.." j Uz 8 0 Oo ~ u 3). ; D ~N z z ... DESCRIPTION OF SAMPLED SITES oil ;;; j - $ g. h tj"' ~w 1S,. ! ~~ .. l! Sierra de los Organos belt ;; ~ &E ~ii ~ i~ D V 2 1~ X <) x - i Rio Las Piedras (Fig. I: site 1) I This site is located south ofPons (Fig. 2A) in the type section ofthe Pons Forma I I tion (Hatten, 1957). This formation consists ofpelagic limestones interbedded with I I cherts. Their age was originally considered to be Albian to Turonian (Hatten, 1957; I Khudoley & Meyerhoff, 1971). Later, the age ofthe lowermost part ofthe Pons For I I mation was defined as ?Hauterivian (Pszcz6lkowski, 1978; de Ia Torre, 1988). The Joddn JSMOl •addn JIVI\Cl s:mns JaMCl I NVII"l3~~ve I N't'IAI~3J.n'<' H I N\fiN I ~NVl'o'A N'o'I S\fl~~38 Pons Formation occurs in the lowermost tectonic units of the Sierra de los Organos N'o'IJ.d'o'l belt, only. In the Rio Las Piedras section, the Pons Formation consists ofgrey bedded lime stones with occasional chert intercalations, lenses or nodules. The contact of the Pons Formation with the underlying Guasasa Formation (Fig. 3) is not exposed in this section. Four samples collected from the limestones occurring in the lowermost 12 A. PSZCZOtKOWSKI LOWER CRETACEOUS STRATIGRAPHY 13
(f) rite, that it was not possible to obtain light micrographs of 0 NANNOFOSSILS z -()~w - >- (f) ..J good quality. For this reason, computer drawing was made 0 (.9 Z LL ..J (/) (/) (f.) (f.) i= w 0- ::J ·- ::;:, ::;:, ::;:, ·- from a micrograph (Fig. 5). 0 ..J 1- Z w c::·i\j c::~ ·c:--··c:- <( ..J z c:: c:: ·~·i:: c::c::·- 0.. ~- 0(1) 0 0
Fig. 4. 1\annoconids and microfossils identified in the samples taken from limestones of the I Samolcs Nannofossil taxa lowermost part of the Pons Fonnation in the Rio Las Piedras section, south of Pons (Fig. 1: site I); 13365 6P-299 Ch-2 AP-20 PL-1 PL-2 LP-1 black intervals denote chert interbeds Nannoconus bemwdezii X X Nannoconus cf. bucheri X I I part of the Pons Formation (Fig. 4) have been investigated in the current study. The INannoconus colomii X X X samples PA-3 and PA-4 were taken from the lowermost beds of the Pons Formation Nannoconusglobulus globulus X X exposed in the river and south of it. The limestones are micrites and biomicrites Nannoconus kamptneri kamptneri X X I I X composed of calcareous nannofossils represented mainly by Nannoconus spp., Nannoconus steinmannii minor X X X X X while coccoliths are significantly less frequent in these limestones. Microfossils are I Nannoconus steinmannii steinmannii X X X I X X X present in some beds oftbe studied section. In the sample PA-4, the microfossil as Nannoconus minutus X semblage includes planktonic and benthic foraminifers, scarce calpionell ids and Nannoconus cf. minutus X frequent G/obochaete a/pina Lombard. The planktonic foraminifers belong to the X X X genus Hedbergella Bronnimann et Brown, 1958. Spirillina sp. occurs among the Nannoconus tmittii tntittii infrequent benthic foraminifers. Cyc/agelosphaera margerelii X I The calpionellids present in the samples PA-3, 151 / 1 and 15 1/2 belong exclu Lithraphidites carniolensis carniolensis X I sively to Tintinnopse/la carpathica Murgeanu et Filipescu (Fig. 4). The specimens Warznaueria barnesae X X I I classified to this taxon are so poorly preserved in the nannofossil-dominated mic- Watznaueria communis X 14 A. PSZCZOLKOWSKI LOWER CRETACEOUS STRATIGRAPHY 15
NANNOFOSSILS (/) z >- (/) 0 C) w :::J ::::; ~ :::J::::: ~::::: i= g ...J "' c:: c::c::"' c::c:: 4: a.. t::: ~ 0 ::2 8-o 8:ii 8:ii ::2 :r: 0 :::J §::::: 0:: 1- <( c:: E gE g E (5 0 ::J (/) ~ § C::.Q c:; .£; lii·~. s u.. ~~ ~8 ~~ <: (;) E
(/) HAUTERIVIAN o::o::J ww ~() - S-2 • • • • - S-1 • • • • • ...Jw0~ VALANGI 0:: ()
Fig. 6. annoconids identified in two samples taken from the limestone beds in the topmost part of the Artemisa Formation at Soroa, Southern Rosario belt (site 3 in Fig. 1); black intervals denote chert interbeds in the Artemisa Formation, as well as the radiolarian chertS with minor shale intercalations in the Santa Teresa Formation
San Vicente, the Tumbitas Member of the Guasasa Formation contacts directly with the Paleocene limestones of the Anc6n Formation, but in some other sections Fig. 7. Nannofossil biomicrite from the uppermost beds of the Sumidero Member {Artemisa Formation, Southern Rosario belt), with Nannoconus spp. and Lithraphidites carniolensis carnio this member passes into the Pons Formation (see Fig. 3). lensis Deflandre 1963 (in the center of the lower part of the scanning electron micrograph); sample Ch-2, Chirino (site 5 in Fig. 1); scale bar 10 ).lm Southern Rosario belt
Soroa (Figs 1, 2 B: site 3) Artemisa Formation. These limestones are radiolarian biomicrites containing fre The samples S-1 and S-2 (Fig. 6) have been collected from the topmost lime quent aptychi. The radiolarians are preserved as molds infilled by calcite. The stone beds of the Sumidero Member distinguished in the upper part of the Artemisa poorly preserved nannofossils are represented by nannoconids, while coccoliths Formation at Soroa (see Fig. 3). These samples were collected at the eastem side of are infrequent. The upper part ofthe Sumidero Member exposed at Rancho Alto site the road between Orquideario (orchidea garden) and the touristic centre of Soroa. may correspond to the limestones described earlier by some authors as "Aptychus At this site, the sampled limestones directly underlie the radiolarian cherts of the beds" (Housa, 1974). Santa Teresa Formation. There, the boundary between the Artemisa and Santa Teresa formations is perfectly transitional (Fig. 6). At Soroa, the Sumidero Member consists of grey, thin bedded micritic lime Chirino (Figs 1, 2B: site 5) stones with interbeds of black chert in the uppermost part of the section. The sam The uppermost part of the Artemisa Formation was also sampled at Chirino in pled limestones are radiolarian-nannofossi l biomicrites. Infrequent aptychi occur the Southem Rosario belt. At this site, located to the northwest of Rancho Mundi to, in the Sumidero Member below the sampled interval. Nannofossil assemblage is the Sumidero Member of the Arternisa Formation consists of thin-bedded biomic dominated by nannoconids (Fig. 6). rites containing aptychi. These biomicrites are greiysh-tan (beige) on weathered surfaces; elsewhere, the Sumidero Member limestones are invariably black in river Rancho Alto (Figs 1, 28: site 4) outcrops, and in drilling cores. The Rancho Alto site is situated to the southwest ofRancho Mundi to, relatively The sample Ch-2 was taken from the topmost bed of the Sumidero Member of close to the Pinar fault. Sample 6P-299 was taken from thin-bedded limestones with the Artemisa Formation, directly below the radiolarian cherts of the Santa Teresa chert intercalations occurring in the uppermost part of the Sumidero Member of the Formation. The sampled limestone of the Sumidero Member (Artemisa Formation) 16 A. PSZCZOI.KOWSKI LOWER CRETA CEO US STRATIGRAPHY 17 is a laminated radiolarian-nannofossi I biomicrite. The radiolarian tests are replaced PL-2 and LP-1), are listed in Tab. 1. by calcite. Nannoconids occur abundantly, while coccoliths are infrequent (Fig. 7). Lower Berr iasian nannofossil assemblage Northern Rosario belt The nannoconid assemblage found in the sample 13365 (Tab. 1) from the Ran cho Manete hill section (Fig. 1: site 6) contains Nannoconus steinmannii Kamptner, Rancho Manete hill (Figs 1, 2B: site 6) 1931 subsp. steinmannii Deres et Acheriteguy 1980, and Nannoconus steinmannii The sample 13365 was collected from the topmost limestone bed of the Ar Kamptner, 1931 subsp. minor Deres et Acheriteguy, 1980 (Fig. 8: 3). This nanno temisa Formation, below the overlying Polier Formation (see Fig. 3), at the eastern conid assemblage may correspond to the Nannoconus steinmannii steinmannii side of the hill named Rancho Manete. The uppermost part of the Artemisa Forma Zone (IC3) ofBralower et al. (1995), or may be slightly younger. A late Lower Ber tion exposed at this site, consists of micritic limestone with black chert interbeds. riasian age of this sample is based on the calpionellids. Therefore, at the studied site The sampled limestone is a radiolarian-nannofossil biomicrite with poorly pre the Sumidero Member of the Artemisa Formation is not younger than Lower Ber served calpionellids. The Rancho Manete section belongs to the Northern Rosario riasian (see Fig. 3). belt of the Guaniguanico terrane. The coccolith Watznaueria barnesae (Black, 1959) Perch-Nielsen, 1968 (Fig. 9: 4-7) was also identified in the sample 13365. Los Cayos (Figs 1, 2B: site 7) Two samples (PL-1 and PL-2) were taken from the black limestone exposed be Valanginian to lowermost Hauterivian nannoconid assemblages low the Santa Teresa Formation at the San Miguel River (Rio San Miguel), south west ofLos Cayos (Fig. 2B). At this site, turbiditic sandstones occasionally occur in The nannoconid assemblage identified in sample AP-20 (Tab. 1) is character black pelagic limestones and shaly marls. The presence of sandstones indicates that ized by abundant N. steinmannii steinmannii, the other taxa being less frequent. this sequence belongs to the uppermost part of the Polier Formation, and not to the Nannoconus steinmannii minor (Fig. 10: 3, 4) and N. bermudezii Bronnimann, Lucas Formation (cf Pszcz61kowski, 1994, fig. 2). The sampled limestone beds are 1955 are not uncommon, whileN kamptneri Bronnimann, 1955 subsp. kamptneri radiolarian-nannofossil biomicrites with infrequent calcareous dinoflagellate Bralower et Tbierstein 1989, is scarce. This Lower Valanginian to lower Upper cysts. The nannofossil assemblage is composed mainly of na1moconids, while the Valanginian assemblage is more diversified than the above-mentioned Lower Ber coccoliths are scarce and poorly preserved. Shales, silicified limestones and cherts riasian one identified in sample 13365 and, in general, is similar to the assemblage about 2m thick occur above the Potier Formation; these deposits belong to the low recorded in samples S-1, S-2 and Ch-2 (see below). ernlost part of the Santa Teresa Formation (see Fig. 3). Nannofossils identified in four samples collected at site 1 (see Fig. 1), in the limestones of the lower part of the Pons Formation (see Fig. 4), include taxa men Lomas de Po/ier (Figs 1, 2B: site 8) tioned by Bronnimann (1 955) in his assemblage 2 from central Cuba. Nannoconus The sample LP-1 was collected from the transitional beds between the Roble steinmannii steinmannii (Fig. 11: 5) is the most frequent taxon, while N. bonetii Member of the Potier Formation and the Santa Teresa Formation in the Lomas de Trejo, 1959 (Fig. 11: 4) is rare in all studied samples from the Lower Cretaceous Polier section (for detailed location see Pszcz6tkowski, 1978). The sampled lime limestones of western Cuba. The composition of the nannoconid assemblage ob stone bed is a green nannoplankton-radiolarian biomicrite, slightly silicified. The served in samples collected at site 1, suggests the Valanginian age of the studied nannofossil assemblage is composed of nannoconids, while coccal iths were not ob limestones ofthe Pons Formation, but a lowermost Hauterivian age cannot be ruled served in the studied sample. out. Nannoconids found in samples S-1 and S-2 (Fig. 6) at Soroa (Figs. 1, 2B: site 3) belong to the assemblage 2 ofBronnimann ( I 955). The age of these nannoconids is, NANNOFOSSIL ASSEMBLAGES however, older than that originally assumed by Bronnimann (1955) for his assem The Lower Cretaceous limestones of the Artemisa and Pons formations are blage 2 in central Cuba (Barremian). The nannofossil taxa suggest the Late Valang mostly Nannoconus-bearing nannofossil biomicrites. Coccoliths occur as a subor inian to earliest Hauterivian age of the S-1 and S-2 samples. This conclusion stems dinate component of these pelagic limestones and often are poorly preserved. The from the occurrence of Nannoconus bermudezii Bronnimann, 1955 (Fig. II: 3) nannoconids identified in samples collected at the sites I (Rio Las Piedras) and 3 with N. steinmannii minor (Fig. 8: 5), and lack of N bucheri Bronnimann, 1955. (Soroa) are shown in Figs 4 and 6, respectively. Nannoconids found in other sam Nannoconus steinmannii minor was originally reported from the Late Tithonian ples: from the Artemisa Formation (13365, 6P-299 and Ch-2), from the Tumbitas to Valanginian of Europe, Africa and North America (Deres and Acheriteguy, Member of the Guasasa Fonnation (AP-20), and from the Polier Formation (PL-1 , 1980). However, according to the present study, this taxon occurs in western Cuba 18 A. PSZCZOl:..KOWSKf LOWER CRETA CEO US STRATIGRAPHY 19 also in the limestones of post-Valanginian age. According to Thierstein (1973), Erba ( 1989) and Bralower eta/. (1995), the first specimens of N. bucheri Bronni mann appear in the Early Hauterivian (see Fig. 3). The nannofossil assemblage occurring in the sample Ch-2 (see Fig. 7) collected at site 5 (Figs I, 2B), includes 6 species (see Tab. 1): N steinmannii steinmannii, N steinmannii minor (Fig. 11: 1), Nannoconus bermudezii Bronnimann 1955 (Fig. 8: /), N globulus Bronnimann, 1955 subsp. globufus Bralower et Thierstein in Bra lower et al. (1989) (Fig. 8: 2), N. kamptneri Bronnimann 1955 subsp. kamptneri Bralower et Thierstein, 1989 (Fig. 8: 4), and scarce Nannoconus cf. minutus Bron nimann, 1955. The subspecies N. steinmannii steinmannii and N. steinmannii mi nor occur as the most common taxa. Specimens assigned to Nannoconus sp. cf. kamptneri kamptneri (Fig. 11: 2) were only occasionally observed in this sample. The species Nannoconus minutus was found by Bronnimann (1955) in the Ap tian to Albian nannoconid assemblages of central Cuba which included N truittii, N. elongatus and N. bucheri (all species erected by Bronnimann, 1955). According to this author, the above-mentioned assemblage appears there after the extinction of theN. colomii- N. globulus group. Deres and Acheriteguy (1980) reportedN. minu tus Bronnimann, 1955 from the Hauterivian-Cenomanian of Europe, Africa, and North and South America. This species was not reported, however, from the Italian sections of the Maiolica limestone studied by Erba and Quadrio (1 987), Bralower (1987) and Erba ( 1989). The occurrence ofNannoconus cf. minutus Bronnimann, 1955 may indicate the earliest Hauterivian age of the Ch-2 sample. The coccoliths identified in this sam ple: Lithraphidites carniolensis carniolensis Deflandre (Fig. 7), Watznaueria bar nesae (Black 1959) Perch-Nielsen 1968 (Fig. 9: I, 3), Watznaueria communis Re inhardt 1966 (Fig. 9: 2) and Cyclagelosphaera margereliiNoel (Fig. 9: 8) are long ranging taxa and cannot be used for the age detennination.
Fig. 8. Nannoconids from the Lower Cretaceous limestones oftl1e Guaniguanico terrane, western Cuba (scanning electron micrographs). / - Nannoconus bennude=ii Bro1mimann 1955; sample Ch-2 from the uppermost part of the Sumidero Member of the Arternisa Formation (Chirino, Southern Rosario belt); scale bar I J.liD; 2 - Nannoconus globulus Bronnimann 1955 subsp. globulus Bra lower et Thierstein 1989; sample Ch-2 from the uppermost part of the Sumidero Member of the Artcmisa Formation (Chirino, Southern Rosari o belt); scale bar I J.lm; 3 - Nannocomts sreimnannii Kamptner 1931 subsp. minor Deres et Acberiteguy 1980; sample 13365 from the uppermost part ofthe Sumidero Member ofthe Artemisa Formation (Rancho Manete hill, ~orthem Rosario belt); scale bar I J.lm; 4 - Nannoconus kamprneri Bronnimann 1955 subsp. kamptneri Bralower et Thierstein 1989; sample Ch-2 from the uppermost part ofthe Sumidero Member ofthe Artemisa Formation (Chirino, Southern Rosari o belt); scale bar I J.IID; 5 - Nannoconus steinmannii Kamptner 1931 subsp. minor Deres et Acheriteguy 1980: sample S-2 from the uppermost part of the Sumidcro Member of the Artemisa Formation (Soroa, Southern Rosario belt); scale bar I 0 J.lm 20 A. PSZCZOLKOWSKI LOWER CRETACEOUS STRATIGRAPHY 21
Hauterivian nannoconid assemblage The nannoconid assemblage found in the sample 6P-299 (see Tab. I) at site 4 (Fig. l) contains N steinmannii minor, N minutus (Fig. I 0: 2) and N. cf. bucheri (Fig. 10: 1). The latter two taxa suggest a Hauterivian age of the sample (cf Deres and Acheriteguy, 1980; Bra lower eta/., 1989). In western Cuba. Nannoconus stein mannii minor persisted during Hauterivian time.
Barremian- Lower Aptian nannoconid assemblages The assemblage found in the samples PL-1 and PL-2 (N. colomii, N. steinmannii steinmannii, N. steinmannii minor, N. globulus globulus, and N. truittii Bronni mann, 1955 subsp. truittii Deres et Acheriteguy, 1980) is Late Barremian to earliest Aptian in age. Nannoconus truittii truittii (Fig. 12: 1) is frequent in this assemblage, but the narrow-canal forms (N. colomii Lapparent, 193 I - Fig. 12: 1, N. steinmannii steinmannii, N. steinmannii minor) are also quite common. In Italy, the last occur rence of N. colomii was noted in the Early Aptian (Erba, 1989; Cobianchi eta/., 1997). Nannoconus truittii was described by Bronnimann (1955) from the Aptian-Al bian of central Cuba. Deres and Acberiteguy (1980) reported Nannoconus truittii truittii from the Early Aptian to the Early Campanian. According to Erba ( 1989), in the Italian sections N. truittii was first observed in the Late Aptian. However, Bra lower (1987) found this taxon in the Barremian, also in the Italian sections. In west ern Cuba, forms assigned toN. truittii truittii occur in the Lower Barremian lime stones of the Polier Formation (Pszcz6lkowski and Myczynski, 1999). In the sample LP-1 , N. truittii truittii (Fig. 12:2, 3) is more abundant thanN. ste inmannii steinmannii. Wide-canal forms (N. truittii truittii and N. kamptneri kampt neri) constitute about 70% and narrow-canal taxon (N. steinmannii sleinmannii) comprises about 30% ofthe nannoconid assemblage in this sample. By comparison with the Italian sections (see Erba, 1994), these proportions strongly suggest an Early Aptian age of the Cuban sample LP-1.
Fig. 9. Coccoliths from the Lower Cretaceous limestones of the Guaniguanico terrane (scanning electron micrographs, scale bar 1 ~lm). 1, 3- Watznaueria barnesae {Black 1959) Perch-Nielsen 1968, distal view; sample Ch-2 from the uppem10st part of the Sumidero Member of the Artemisa Fonnation (Chirino, Southern Rosario belt); 2 - Watznaueria communis Reinhardt 1966, distal view; sample Ch-2 from the uppennost part ofthe Sumidero Member of the Artemisa Formation (Cbirino locality, Southern Rosario belt); 4. 5 - Wacznaueria barnesae (Black 1959) Perch-Nielsen 1968, coccosphercs; sample 13365 from the uppermost part of the Sumidero Member of the Artemisa Fonnation (Rancho Manete hill. ·orthem Rosario belt); 6- Warznaueria barnesae (Black 1959) Perch-Nielsen 1968, proximal view; sample 13365 from the uppermost part ofth e Sumidero Member of the Artemisa Formation (Rancho Manete hill, Northern Rosario belt); 7 - Watznaueria bamesae (Black 1959) Perch-Nielsen 1968, distal view; sample 13365 from the uppermost part ofthe Sumidero Member of the Artemisa Formation (Rancho Manete bill, Northern Rosario belt); 8 - Cyclagelo sphaera margerelii Noel 1965, distal view; sample Ch-2 from the uppermost part of the Sumidero Yiember of the Artemisa Formation (Chirino, Southern Rosario belt) 22 A. PSZCZOLKOWSKI LOWER CRETACEO US STRATIGRAPHY 23
Erba (1994) studied the nannoconid abundance in the sections from central It aly. There, the Barremian nannoconid assemblage is dominated by narrow-canal forms \"\1ith minor contribution of wide-canal ones. The change in the proportion of narrow-canal versus wide-canal forms occurred in the latest Banemian to earliest Aptian, where the latter may make up to 50% of the nannoconids (Erba, 1994).
The Nannoconus biozones and age of two oaoooconid assemblages previously reported from central Cuba Deres and Acheriteguy (1980) distinguished three Nannoconus biozones in the earliest Cretaceous (Fig. 3): theN. steinmannii Zone (Berriasian), N. kamptneri Zone (Valanginian), and N. berrnudezii Zone (Hauterivian). The boundaries of these biozones were correlated with the boundaries of the stages (see Fig. 3). Later studies (Bralower, 1987; Erba & Quadrio, I 987; Bralower eta/., 1989; Erba, 1989) changed the ranges of the Nannoconus species important for biozonation proposed earlier by Deres and Acheriteguy (1980). Cun·ently, only the Early Berriasian Nan noconus steinmamlii steinmannii Zone is used in the calcareous nannofossil biozo nation for the Cretaceous (Bralower eta/., 1995). The present results from the Guaniguanico terrane (western Cuba) do not con firm the Barremian age tentatively assigned by Bronnimann ( 1955) to his assem blage 2 in central Cuba. In the Guaniguanico terrane, a similar assemblage com posed of N. steinmannii steinmannii, N. steinmannii minor, N kamptneri kampt neri, N. bermudezii with N colomii or N. globulus globulus, occurs in the Valangin ian to lowermost Hauterivian strata. The assemblage 3 ofBronnimann ( 1955) lacks such narrow-canal taxa as N. steinmannii steinmannii and N. coiomii. Therefore, the age of the assemblageN. truittii- N. minutus-N. elongatus-N. bucheri- N. was sa/Iii can be, rather late Early Aptian or Late Aptian to Albian than Aptian- Albian, as assumed by Bronnimann ( 1955). Erba ( 1989) reported the last occurrence ofN. steinmannii in the Late Aptian, whereas Cobianchi eta!. (1997) placed this event in the late Early Aptian.
CALPIONELLIDS The calpionellids occur in samples 13365, AP-20, PA-3, 151 / 1 and 15112. Their presence allows to verify age of these samples estimated by means of nannofossils. Two calpionellid zones (Remane eta/., 1986) can be identified in the studied sites: the Ca1pionella (C. elliptica Subzone- sample 13365) and the Calpionellites (sam ple AP-20) zones. Moreover, presence of the Tintinnopsella Zone (Borza, 1984; Pop, 1994; Grlin & Blau, 1997; Blau & Griin, 1997) is consistent with the occur Fig. I 0. annofossils from the Lower Cretaceous limestones of the Guaniguanico terrane, western rence ofT. carpathica Murgeanu et Filipescu in samples PA-3, 15lll and 15 112 Cuba (scanning electron micrographs). 1 - Nannoconus cf. bucheri Bronnimann 1955; sample (Fig. 4). In the Carpathians, the Tintinnopsella Zone spans Late Valanginian to Late 6P-299 from the uppermost part of the Sumidero Member of the Artemisa Formation (Rancho Alto, Hauterivian times but does not comprise the latest Hauterivian (Rehakova & Mi Southern Rosario belt); scale bar I 1-1m; 2 - Nannoconus minullls Bronnimann 1955; sample 6P-299; chalik, 1997). scale bar I J.im; 3, 4- Nannoconus steinmannii Kamptner 1931 subsp. minor Deres et AcheritehTUY 1980; sample AP-20 from the uppermost part ofthe Tumbitas Member of the Guasasa Fonnation (San The calpionellids found in sample 13365 indicate the Berriasian age of the Ar Vicente, Sierra de los Organos belt); scale bar l ~un ternisa/Polier formations boundary at the Rancho Manete hill (Fig. 1: site 6). At the 24 A. PSZCZOLKOWSKl LOWER CRETACEOUS STRATIGRAPHY 25
studied site, this lithostratigraphic boundary is placed below the Early Berria sian/Late BeJTiasian boundary. The calpionellid assemblage found in the sample AP-20 includes the following taxa: Calpione/lites darderi (Colom), Calpioneflites major (Colom), Tintinnopse/la cmpathica Murgeanu et Filipescu and Lorenziel/a hungarica Knauer et Nagy. Presence of Calpionellites darderi (Colom) and Calpi onellites major (Colom) in the topmost limestone beds of the Tumbitas Member (Guasasa Formation) at San Vicente section, SieJTa de los Organos belt, is distinc tive for the Calpionellites major Subzone of the Calpionellites Zone (Major Sub zone according to Pop, 1994, 1997). Lack of Calpionellopsis oblonga (Cadisch) in the studied sample is characteristic for the upper part of the C. major Subzone (Pop, 1994). This subzone is late Early Valanginian in age (Pop, 1997), but the uppermost part of the C. major Subzone was proposed to be as young as the basal Late Valang inian (Blau & Griin, 1997).
FORAMINIFERAL FAUNULE As stated above, planktonic foraminifers have been found in the sample PA-4 collected from pelagic limestone of the lower part of the Pons Formation in the Rio Las Piedras section (Figs 1, 2A: site 1). Two species of the genus Hedbergella Bronnimann et Brown, 1958, have been identified in thin sections, namely H. sigali Moullade (Fig. 13: I) and H. delrioensis (Carsey) (Fig. 13: 6). Other specimens have been determined asH. cf. siga/iMoullade(Fig. 13:2-4 and Fig. 14), H. cf. del rioensis (Carsey) (Fig.l3: 5, 8) andHedbergellasp. (Fig. 13: 7). This foraminiferal faunule belongs to the Hedbergella sigali- Hedbergella delrioensis Zone (Fig. 3) distinguished by Coccioni and Premoli-Silva ( 1994) in the Rio Argos area ofsouth em Spain, where this zone spans nearly the whole Late Valanginian, Hauterivian and earliest BaJTemian.
Fig. 11. Nannoconids from the Lower Cretaceous limestones of the Guaniguanico terrane, westem Cuba (scanning electron micrographs). I - Nannoconus steinmannii Kamptner I 931 subsp. minor Deres et Acheriieguy 1980; sample Ch-2 !Tom the uppermost part of the Sumidero Member of the Artemisa Formation (Chirino, Southern Rosario belt); scale bar I )lm; 2 - Nannoconus sp. cf. kampmeri Bronnimann I955subsp. kamptneri Bralower et Thierstein 1989 (specific identification uncertain due to oblique section); sample Ch-2 from the uppermost part of the Sumidero Member of the Artemisa Formation (Chirino, Southern Rosario belt); scale bar 1 ).lm; 3 - Nannoconus bennudezii Bronnimann I 955; sample S-1 from the uppermost pan of the Sumidero Member of the Artemisa Fonnation (Soroa, Southem Rosario belt); scale bar I 0 ~tm; 4- Nannoconus bonetii Trejo I 959; sample PA-4 from the lower part ofthe Pons formation (Rio Las Piedras, Sie1Ta de los Organos belt); scale bar I 11m; 5-Nannoconus steinmannii Kamptner 1931 subsp. steinmannii De reset Acheriteguy I 980: sample PA-4 from the lower part of the Pons formation (Rio Las Piedras, Sierra de los Organos belt); scale bar 1 11m 26 A. PSZCZOLKOWSKI LOWER CRETACEOUS STRATIGR.t\.PHY 27
AGE OF SOME LOWER CRETACEOUS LITHOSTRATIGRAPHIC Ul\'lTS AND THEIR BOUNDARIES IN THE GUAl'\TIGUAl'liCO TERRANE The stratigraphic position of the Guasasa!Pons formations boundary is close to the boundary of the Calpionellites and Tintinnopsella zones (see Fig. 3). The lower most part of the Pons Formation exposed at the Rio Las Piedras section (Figs 1, 2A, 4) con-elates with the lower part of the Tintinnopsella Zone, and includes also the Hedbergella sigali- Hedbergella delrioensis Zone. Considering together the fora minifers, calpionellids and nannoconids, the investigated part of the Pons Forma tion in the Rio Las Piedras section is Upper Valanginian to lowest Hauterivian in age. The base of the H. sigali- H. delrioensis Zone con-elates with the middle part of the ammonite Himantoceras trinodosum Zone (Coccioni & Premoli Silva, 1994), while the Calpionellites Zone (E) terminates earlier, that is, in the Busnardoites campylotoxus Zone (Allemann & Remane, 1979; Hoedemaeker & Leereveld, 1995). However, Blau and Grtin ( 1997) correlate the upper boundary of the Calpi onellites Zone with the (lower) Late Valanginian ammonite Inostranzewi Zone, while Rehakova and Michalik (1997) tenninate this calpionellid zone within the Late Valanginian Verrucosum Zone. As the topmost limestone beds of the Tumbi tas Member still belong to the Calpionellites Zone (see Fig. 3), an interval equiva lent to one or two ammonite zones (as a minimum) may separate the Guasasa/Pons formations boundary from the foraminiferal faunule found in the lower part of the Pons Formation at the Rio Las Piedras. At least in some sections located in the Southern Rosario belt (Soroa, Chirino, Rancho Alto), the topmost part of the Sumidero Member of the Artemisa Formation is uppermost Valanginian to Hauterivian in age. During the previous studies, the stratigraphic position of the upper boundary of the Sumidero Member was con-e lated in some sections with the Calpionellites Zone (Pszcz6lkowski, 1978, tab. 4). Thus, in the Southern Rosario belt, the Artemisa/Santa Teresa formations boundary is diachronous, ranging from the Lower-(lower) Upper Valanginian to Hauterivian (see Fig. 3). In the Northern Rosario belt, the boundary between the Artemisa and Potier for mations was placed in the Early Valanginian (Myczyflski, 1977; Pszcz6lkowski, 1978). In this study, the Artemisa/Polier fonnations boundary at the Rancho Ma nete (Figs I, 2B: site 6) is placed below the Early Berriasian/Late Berriasian age Fig. 12. Nannoconids from the Lower Cretaceous limestones of the Guaniguanico terrane, western boundary. Therefore, in the Northern Rosario belt the boundary between the Ar Cuba (scanning electron micrographs)./- Nannoconus rruirtii Bronnimann 1955 subsp.truittii Deres et Acheriteguy 1980; sample PL-1 from the uppermost part of the Polier Formation (Los Cayos, temisa and Potier formations is also diachronous (see Fig. 3). Northern Rosario belt); scale bar I J!m; 2 - Nannoconus truiuii Bronnimann 1955 subsp. truittii Deres The topmost limestone beds of the Potier Formation at site 7 (southwest of Los et Acheriteguy 1980; sample LP-1 from the transitional beds between the Roble Member ofthe Polier Cayos) are Upper Barremian to lowermost Aptian in age, according to the nonnoco Formation and the Santa Teresa Formation (Lomas de Polier, 1\ortbem Rosario belt); scale bar 1 J!ID: 3 nid assemblage found in the samples PL-1 and PL-2. The sample LP- 1 from the Lo - Nannoconus truittii Bronnimann 1955 subsp. truittii Deres et AcheritegliY 1980; sample LP-1 from the the transitional beds between the Roble Member of the Polier Formation and the Sama Teresa mas de Potier section (Figs 1, 2 B: site 8) contains a nannoconid assemblage which Fonnation (Lomas de Potier, Nonhem Rosario belt); scale bar I J.lm ; 4 - Nannoconus co!omii is probably Early Aptian in age (see Fig. 3). Consequently, the Roble Member of the Lapparent 193 1; sample PL-2 from th e uppermost part of the Polier Formation (Los Cayos, )/orthern Polier Formation in the Lomas de Potier section should be Upper Ban-ernian to Rosario belt); scale bar I ~1m Lower Aptian in age. 28 A. PSZCZOLKOWSKI LOWER CRETACEOUS STRATIGRAPHY 29
COMPARISON OF THE LOWER CRETACEO US MICROFOSSIL A.~D NAN~OFOSS IL DATA FROM THE GUANIGUANICO TERRANE WITH THOSE FROM THE SOUTHEASTERN GULF OF MEXICO Lower Cretaceous marine sediments have been drilled in the southeastern Gulf of Mexico (SGM) at 6 sites (Schlager eta/., 1984). The Upper Berriasian to Hau terivian sediments occur at the basin site 535 and at the basement site 537, while the uppermost Berriasian to Lower Valanginian sediments have been reached at site 538A (Premoli Silva & McNulty, 1984). Thin Barremian sediments have been cored at site 535, while incomplete Aptian succession was reported from sites 535, 536 and 537. At site 535, nannofossil biostratigraphy, based mainly on coccoliths, indicates almost complete record of sedimentation from Late Berriasian through Late Hau terivian (Fig. 15) to the earliest Barremian (Watkins & Bowdler, 1984). Comparing the stratigraphic record from the Guaniguanico terrane to that recognized at the SGM basin site, the following observations can be made: (I) The Upper Beniasian and Valanginian deposits are documented by calpi onellids both in western Cuba and in the SGM. The Tintinnopsella Zone is now rec ognized in western Cuba in the lower part of the Pons For mation. Although originally not distinguished in the SGM, the Tintinnopsella Zone may be present at the site 535 in ~ the upper part of the interval attributed there to the Calpi ,,1~~\.· ~ · ·ll.·...... ·.-. . ·.· ,.'1 ...·.. ;j .. . onellites Zone (Zone E), despite the absence of Calpionel ; :·:~;.. lites darderi (cf. Premoli Silva & McNulty, 1984). •.So: 1 (2) At site 535, foraminifers Favusella hauterivica (Subbotina), reported as Globuligerina hoterivica (Sub • botina), and Hedbergella spp. (with H. sigali Moullade ac - cording to Coccioni and Premoli Silva, 1994) were re Fig. 14. Hedbergella corded in the Lower Valanginian beds. ln western Cuba, cf. sigali Moullade 1966 Hedbergella sigali Moullade and H. delrioensis (Carsey) (computer drawing from a light micrograph); sample were found in the Upper Valanginian-lowermost Hau PA-4, Rio Las Piedras, terivian limestones (Fig. 15). Sierra de los Organos belt (3) Natmofossil assemblages found in the studied (for location see Figs l, 2 Lower Cretaceous limestones of western Cuba are domi and 4); scale bar 20 J.UTI nated by nannoconids, while infrequent coccoliths (Fig. 9: 1- 8) mainly belong to the dissolution-resistant taxa. By contrast, relatively rich, well-preserved coccolith nanno-
Fig. 13. Planktoni c foraminifers identi fied in thin sections from the limestone occurring in the lower part of the Pons Formation (sample PA-4, Rio Las Piedras, Sierra de los Organos belt). 1 - Hedbergella sigali Moullade 1966; x 200; 2 - Hedbergella cf. sigali Moulladc 1966; x 230; 3 - Hedbergella cf. sigali Moullade 1966; x 200; 4 - Hedbergella cf. sigali Moulladc 1966; x 300: 5 - Hedbergella cf. delrioensis (Carsey 1926); x 330; 6- Hedbergella delrioensis (Carsey 1926); x 200; 7 - Hedbergella sp.; x 200: 8 - Hedbergella cf. delrioensis (Carsey 1926); x 270 30 A. PSZCZOLKOWSKI LOWER CRETACEO US STRATIGRAPHY 31
GULF OF MEXICO GUANIGUANICO TERRANE C ONCLUSIONS SITE 535 (DSDP LEG 77) (WESTERN CUBA) (/) FORAMINIFERAL According to distribution of calpionellids, nannoconids and planktonic fora CALPIONELLID ZONES NANNOCONIDS w AND NANNOFOSSILS minifers, the age of some Lower Cretaceous lithostratigraphic units and boundaries <-' AND FOUND IN SAMPLES: <( CALPIONELLID in the Guaniguanico terrane, western Cuba, is modified in this study. In the North f- FORAMINIFER AP-20, PA-4. Ch-2 (/) ZONES (Watkins and ern Rosario belt the Artemisa!Polier formations boundary is diachronous (late (Premoli Silva BctNdler, 1984) FAUNULE AND 6P-299 Early Berriasian to Early Valanginian in age). In the studied sites, located in the and McNulty, 1984) (THIS PAPER) (THIS PAPER) z Southern Rosario belt (Soroa, Chirino, Rancho Alto), the topmost part of the Su <( G. hoterivica lithraphidites midero Member of the Artemisa Formation is uppermost Valanginian to Hau 5 ----? ----- bolli terivian in age. Comparing this result with previous data, the Artemisa/Santa 0:: w (?) ~~:N.N. cf.minutus bucheri Teresa formations boundary in the Southern Rosario belt appears diachronous, f- N. sleJnmannii ::l mmor ranging from Early Valanginian to Hauterivian. <( I ._J N. kamptneri Frequent plankton ic foraminifers have been found in the sample PA-4 collected 1 f------?----- ~rN. cf. minutus from the lower part of the Pons Fonnation in the Rio Las Piedras section, Sierra de ._j N. bermudezi Tintinnopsella N. kamptneri.. ,... .,. kamptneri los Organos belt. Hedbergella sigali Moullade and H. delrioensis (Carsey) have z A H. sigali ;I r--=: N. bermudezii been identified in thin sections. In other samples, Tintinnopsel/a carpathica Mur <( H. delrioensis PA-4 N. bonetii Calcicalathina N. sleinmannii geanu et Filipescu occurs indicating the Tintinnopsella Zone. Considering together z steinmannii 0 Calpionellites E oblongata the foraminifers, calpionellids and nannoconids, the lowermost part of the Pons z Formation at the studied site (Rio Las Piedras) is Late Valanginian to earliest Hau ::s N. bermudezii <( ._j H. siga/i AP-20 N. colomii terivian in age. Calpionellites N. kamptneri > kamptneri In western Cuba, Nannoconus steinmannii minor Deres et Acheriteguy appears N. steinmannii steinmannii to have persisted during the Hauterivian and Barremian times, at least. Nannoconus N. steinmannii truittii truittii is present in the Barremian-Lower Aptian assemblages. In another Calpio- D3 minor _Ill nellopsis nannoconid assemblage (sample LP-1), N. truittii truittii is more abundant than N. Calpionellopsis 0:: Cretarhabdus 0:: steinmannii steinmannii. By comparison with the Italian sections (Erba, 1994), w D D2 crenulatus m these proportions strongly suggest an Early Aptian age ofthis sample. Probably, the upper boundary of the Polier Formation is diachronous (Upper Barremian? to Fig. 15. Compa~is?n of microfossil and nannofossil data from the GulfofMexico (Hole 535, DSDP Lower Aptian). LEG 77 - Premoh S1lva and McNulty, 1984 and Watkins and Bowdler, 1984) and the Guaniguanico terrane, western Cuba (this paper) Comparing the Lower Cretaceous stratigraphic record from the Guaniguanico terrane to that recognized at the SGM basin site (535), some similarities, as well as differences, can be discerned. The contrasting composition of the nannofossil as flora from d~ r ker marly limestones provided important information on the Early semblages in both domains resulted, at least in part, by different methods used to c.retaceous history of the SGM, although nannoconids are also present there (Wat study the calcareous nannoplankton present in marly limestones (SGM) and in kms & Bowdler, 1984). Natmofossil assemblages from the lighter-colored lime well-indurated limestones (in the tectonically deformed successions of western stones were sparse and poorly preserved (Watkins & Bowdler, 1984). Cuba), respectively. (4) In the Guaniguanico terrane, Nannoconus bermudezii and Nannoconus kamptneri kamptneri occur in the uppermost part of the Calpionellites Zone. At the Acknowledgements site 535 (SGM), the first recorded occurrences of these taxa were reported close to the Valanginian/Hauterivian boundary (Watkins & Bowdler, 1984). The assistance of Mrs. Ewa Fila and Dr Ryszard Orlowski (Laboratory of Scanning Microscopy, (5) Nannoconus bucheri Bronnimann and Nannoconus minutus Bronnimann Institute of Geological Sciences, Polish Academy of Sciences) during preparation of scanning electron micrographs is appreciated. Prof. Andrzej Wierzbowski is gratefully acknowledged for hi s were not identified in the Lower Cretaceous (pre-Aptian) sediments of the SGM. constructive review. (6) N01~noconus truittii Bronnima1m was reported from the Lower Aptian sedi m~nts of s1te 537, but not from the coeval limestone of site 535. The Upper Barre REFERENCES ro tan sedi~ents are mi~sing there. Thus, it is difficult to ascertain the stratigraphic range of th1s nannocontd species in the southeastern Gulf of Mexico. Allemann, F. & Remane, J., 1979. Les faunes de Calpionelles du Berriasien superieurNalanginien. 32 A. PSZCZOLKOWSKI LOWER CRETACEOUS STRATIGRAPHY 33
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