paleogeographical and evolutionary implications - CiteSeerX

Journal of Foraminiferal Research, v. 31, no. 4, p. 287–293, October 2001

PALORBITOLINA LENTICULARIS FROM THE NORTHERN ADRIATIC REGION: PALEOGEOGRAPHICAL AND EVOLUTIONARY IMPLICATIONS ANTUN HUSINEC Institute of Geology, Sachsova 2, PO Box 268, HR-10000 Zagreb, Croatia

phaeric forms and progressive enlargement of microspheric individuals. Schroeder (1975) indicated gradual increase of the diameter of the embryonic areas from the Upper Barremian to the Lower Aptian/Upper Aptian boundary, with its maximum value reaching 200 ␮m. Cherchi and others (1978) pointed out that specimens with an embryonic chamber diameter of 240–300 ␮m belong to the latest Early Aptian. Very important research in this area was done by Gusˇic´ (1981). He used the increase in the size of the embryonic chamber in successive populations of P. lenticularis to distinguish different evolutionary stages within the phyletic line of the species, which enabled him to divide the Upper Barremian-Lower Aptian sequence in the absence of stratigraphically more indicative forms. Recently, Cherchi and Schroeder (1999) investigated the Late Barremian Palorbitolina from Northern Somalia. Their results exhibit embryonic chamber diameters ranging from 160 to 260 ␮m. The measured values of both the embryonic chamber and test diameters in this study agree with the age determined on the basis of microfossil association and clearly indicate the Lower Aptian.

ABSTRACT

Samples bearing Palorbitolina were obtained from three localities on the islands of Cres and Losˇinj in the northern Adriatic. Although a relatively small number (⬍60) of specimens were studied, the size of the embryonic chamber and test diameters of Palorbitolina lenticularis indicate a Lower Aptian age. This is confirmed for the Adriatic carbonate platform by the presence of Lower Aptian index taxa. Both embryonic chamber and test diameter variation are pronounced. No change was observed concerning the relationship between stratigraphic horizon and the embryonic chamber diameter. A proportional relationship between the size of the embryonic chamber and the test was determined. These data show that before it appeared on the Adriatic carbonate platform, Palorbitolina already colonized the predominantly mixed clastic-carbonate environments of the Mediterranean, as has been suggested by Velic´ & Sokacˇ (1978). Although an essentially westwards water circulation during the late Barremian and early Aptian probably aided Palorbitolina in colonization of the Tethyan realm, it can neither explain the simultaneous existence of Palorbitolina in different and remote parts of the Tethys nor its dispersal, which must have been very rapid.

DEPOSITIONAL ENVIRONMENT OF PALORBITOLINA LENTICULARIS Due to its eurytopic character, Palorbitolina lenticularis had a circum-global distribution during the Upper Barremian-Lower Aptian; hence, the species is found in various depositional environments. Rey (1975) concluded that it was living in the infralittoral zone, both in agitated reefal settings and backreef muds. Arnaud-Vanneau (1975) considered it as a form tightly linked to vegetation-covered substrates characteristic of clayey-to-carbonate muddy deposits. Alternatively, Masse (1976) has suggested that it reflected deeper circumlittoral conditions. Arnaud-Vanneau (1980) recorded occurrences in both infralittoral and circumlittoral environments. Three main settings were recognized by Arnaud (1981): circumlittoral (finely bioclastic limestones), open marine infralittoral (caprinid calcareous muds) and ‘‘marly channels’’. Velic´ (1988) defined its environment as lagoonto-subtidal-to-restricted shoals with patch reefs and backreef; i.e., shallow infralittoral. Banner and Simmons (1994) have suggested that the depth ranged from 5 to 60 m, with a preferred range of 10–60 m. Vilas and others (1995) pointed out five major distinctive depositional environments: littoral zone, coastal zone, platform interior, outer platform and outer shelf. In the study area of the northern Adriatic (the islands of Cres and Losˇinj), Palorbitolina is found within a protected, low-energy subtidal environment that was affected and modified by storm events.

INTRODUCTION In the Adriatic region, as in the wider Tethyan realm, the species Palorbitolina lenticularis is found at numerous localities, occasionally forming the bulk of the deposit. This study focuses on the northern Adriatic islands of Cres and losˇinj, where carbonate platform deposits range from the Early Neocomian to the Senonian (Fucˇek and others, 1995). Biozonation of the Aptian, Albian and Cenomanian platform carbonates in this area is based on the orbitolinids (Husinec and Velic´, 1998; Husinec and others, 2000). Although P. lenticularis is a well-known species, and in spite of the fact that for most fossil populations a relationship between size and age must be assumed (Brenchley and Harper, 1997), the relationship between its dimensions and age is poorly understood. Hofker Jr. (1963) was the first one who clearly showed gradual increase of the diameter of the deuteroconch from the Upper Barremian to the Lower Aptian. His measurements were made exclusively on axial sections of several specimens found in the same layer. The author reported minimum value of 110 ␮m for the Upper Barremian and maximum value of 350 ␮m for the Lower Aptian specimens. Arnaud-Vanneau (1968) studied five different populations of P. lenticularis and distinguished two architectural modifications: reduction in size of megalos-

METHODS Samples bearing Palorbitolina were obtained from three localities on the islands of Cres and Losˇinj in the northern

E-mail: [email protected]

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PLATE 1 Palorbitolina lenticularis (BLUMENBACH). (1–3) Axial and (4) oblique section through megalospheric embryonic apparatus, sample CK-4, magnification ⫻42.

Adriatic. The samples were cut to maximize the number of axial (vertical) sections of embryonic apparatuses (Plate 1). The embryonic chamber diameter of the species P. lenticularis was measured for 54 specimens, while test diameter measurements were made on 56 specimens. The limited number of measurements was a consequence of the very hard lithology (generally massive and compact limestones) from which it was difficult to obtain appropriate sections. Many of the tests were destroyed and some embryonic apparatuses were separated from their tests, which made it impossible to take both of the measurements on a single specimen. Samples were obtained at three sites: Dragozeticí – samples CDB-35 through CDB-38/4. Four samples were obtained from the wackestones (thickness 35 m) deposited in a protected, low-energy subtidal environment. The age of these samples is Lower Aptian. This can reliably be concluded due to the presence of Voloshinoides murgensis and Praeorbitolina cormyi in association with P. lenticularis. The embryonic chamber diameter of P. lenticularis was measured for 16 specimens (Table l, Fig. 1), TABLE 1. Embryonic chamber diameter (ECD) of P. lenticularis specimens from samples CDB–35-38/4, CK–1A-4 and LP–1-15.

and the test diameter was measured on 25 specimens (Table 2, Fig. 2). Kriz˘ice – samples CK-1A through CK-4. Five samples were taken from the 7.40 m thick sequence of wackestones, gastropod floatstones and grainstones (tempestites). The age of this sequence is Lower Aptian, which can be concluded from the association of the following species: Palorbitolina lenticularis, Praeorbitolina cormyi, and P. wienandsi. The embryonic chamber diameter of the species P. lenticularis was measured on 20 specimens (Table 1, Fig. 1), and test diameters were measured for 14 specimens (Table 2, Fig. 2). Losˇinj Punta – samples LP-1 through LP-15. Fifteen samples were collected from a very thick sequence (46.30 m) of massive wackestones-floatstones interbedded with rudstones and tempestites. The association of Palorbitolina lenticularis, Praeorbitolina cormyi, P. wienandsi, Orbitolina (Mesorbitolina) lotzei, and Voloshinoides murgensis reliably indicates early Aptian age. The embryonic chamber diameter of P. lenticularis was measured in 18 specimens (Table 1, Fig. 1), and the test diameter was measured for 17 specimens (Table 2, Fig. 2). RESULTS

Samples

CDB–35-38/4 CK–1A-4 LP–1–15 Total

Number

Mean ECD (␮m)

16 20 18 54

261.3 255.5 322.8 279.6

Standard deviation

Range (␮m)

40.48 35.0 32.7 46.9

200–330 200–320 260–370 200–370

Embryonic chamber diameter data are summarized in Table 1 and Fig. 1. Pronounced variation in the size of the embryonic chamber diameter occurred among specimens from each locality. The maximum value of embryonic chamber diameter was 42% larger than the minimum value

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FIGURE l.

Histogram of embryonic chamber diameters.

within the Losˇinj Punta samples (LP) and 65% larger than the minimum value in the Dragozeticí samples (CDB). Comparing all samples within the study area, the maximimum value for the embryonic chamber diameter was 85% larger than the minimum value. Similar observations were made by Gusˇic´ (1981) in his study of P. lenticularis from Bosnia-Herzegovina and Slovenia. Nevertheless, no change was observed concerning the relationship between stratigraphic horizon and size of the embryonic chamber diameter. The mean embryonic chamber diameter ranged from 255.5 ␮m for the specimens from the Krizˇice samples (CK) to 322.8 ␮m for the specimens from the Losˇinj Punta (LP) samples. The mean embryonic chamber diameter calculated from all sample specimens was 279.6 ␮m. The total range of the embryonic chamber diameter calculated from all sample specimens was 200–370 ␮m. Ac-

cording to Gusˇic´ (1981), both the range and value of the mean embryonic chamber diameter of P. lenticularis are characteristic of the late Early Aptian. The microfossil association observed in the investigated area, combined with the stratigraphy, also implies an Early Aptian age. Test diameter data are summarized in Table 2. The variation of the test diameter within specimens from each locality was even more pronounced than the embryonic chamber diameter. The maximum value of test diameter was 133% larger than the minimum value within the Dragozeticí samples (CDB) and 150% larger than the minimum value in the Losˇinj Punta samples (LP). Comparing all samples together within the studied area, the maximimum value for

TABLE 2. Test diameter of P. lenticularis specimens from samples CDB–35-38/4, CK–1A-4 and LP–1–15. Measured values are rounded to whole mm.

Samples

CDB–35-38/4 CK–1A-4 LP–1–15 Total

Number

Mean test diameter (mm)

Standard deviation

Range (mm)

25 14 17 56

4.0 3.4 4.8 4.1

1.1 0.9 1.1 1.2

1.8–6.4 2.1–5.3 3.0–6.5 1.8–6.5

FIGURE 2.

Histogram of test diameters.

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FIGURE 3. Geographic distribution of Palorbitolina lenticularis during the Lower Aptian (114–112 Ma). 1 ⫽ shallow platform, 2 ⫽ basin, 3 ⫽ slope or shelf-edge/slope boundary, 4 ⫽ palaeolatitude, 5 ⫽ present-day coastline, 6 ⫽ additional locating marks, 7 ⫽ Palorbitolina lenticularis. Palaoegeographical map simplified after Masse and others (1993a).

the test diameter was 250% larger than the minimum value. The mean diameter of all the tests was 4.1 mm and the measured values were predominately between 4 and 5 mm (Fig. 2). Although this measured character, unlike the embryonic chamber diameter, is strongly influenced by the environment (e.g., Vilas and others, 1995), the data yielded a proportional relationship between the diameter of the embryonic chamber and the diameter of the test. PALEOGEOGRAPHICAL AND EVOLUTIONARY IMPLICATIONS Although Hughes (1998) concluded that Heterostegina and Operculina possibly represent modern analogues for orbitolinids, it is most likely that such do not exist. Recent larger foraminifera are adapted to life in oligotrophic, nutrient-deficient conditions (Murray, 1991), where light and water energy are considered to be the most important factors controlling their distribution (Hottinger, 1980, 1983). However, as previously mentioned, Palorbitolina lenticularis is a eurytopic species. It is almost impossible to enumerate all the known localities in the Mediterranean region where P. lenticularis is found. It is known from the northwestern Atlantic (Sen Gupta and Grant, 1971; Schroeder and Cherchi, 1979), Mexico (Meza, 1980; Pantoja-Alor and others, 1994; Gonzalez-Arreola and others, 1996) and Venezuela (Arnaud-Vanneau, written communication, 1999). In Africa, besides the Mediterranean region, it is found in Ethiopia (Bosellini and others, 1999), Somalia (e.g. Bosellini, 1989; Luger and others, 1990; Cherchi and Schroeder, 1999) and Tanzania (Peyberne`s, 1982), which is the only locality in the present-day southern hemisphere. Palorbitolina lenticularis is also found in Israel, Lebanon and Syria (Saint-Marc, 1970), Yemen (Cherchi and others, 1998), Oman (e.g. Simmons, 1994; Simmons and Hart, 1987; Masse and others, 1998), and the United Arab Emirates (Witt and Gokdag, 1994; Vahrenkamp, 1996). It is also recorded from Iran (Mehrnusch, 1973; Ricou, 1976; Shakib, 1990), Afghanistan (Montenat

and others, 1982), Tibet (Marcoux and others, 1987; XZBGM, 1993), India (Cherchi and others, 1984), Borneo (Hofker, 1963; Yuwono and others, 1988) and the Phillipines (Wolcke and Scholz, 1988). Orbitolinids were perhaps the most significant larger foraminifera of the Lower Cretaceous Tethys. Paleogeographic factors were one of the host factors which limited their distribution (Moullade and others, 1985). Palorbitolina lenticularis, which is one of the most important species, has a world-wide distribution in Cretaceous carbonate platforms during the Lower Aptian (Fig. 3), when a global sea-level rise resulted in a series of transgressions in the wider periMediterranean area. The sea-level curves from Watts and Steckler (1979) and Watts (1982) in Williams (1988) suggest a global sea-level rise of nearly 10 m during this period, while Sahagian and Holland (1991) calculated it as up to 25 m. During this time carbonate platforms and warm seas occupied vast areas between palaeolatitudes 35⬚N and 35⬚S, except on the Pacific side of America where carbonate platforms are only documented from the northern hemisphere (Masse and others, 1993a, 1993b). Water temperature was approximately the same as or warmer than today (27–32⬚C), as suggested by Barron (1984, 1986), while overall salinities were 20% higher (Southam and Hay, 1981). The palaeogeographical reconstruction and the position of the equator imply an essentially westwards flowing circulation with a minor poleward deflection due to the land barriers from Southeast Asia and Africa (Masse and others, 1993b). Although P. lenticularis could have migrated with the help of the westward and poleward flowing currents, it cannot explain the dispersal of this species which must have been very rapid. Palorbitolina simultaneously existed in the Late Barremian, not only in what is today the Mediterranean region, but also in the Arabian Peninsula (Simmons and Hart, 1987; Scott, 1990; Witt and Gokdag, 1994; Simmons, 1994), Northern Somalia (Cherchi and others, 1993, 1998; Cherchi and Schroeder, 1999) and Venezuela (Arnaud-Vanneau, written communication, 1999).


Palorbitolina lenticularis originated from Valserina, a relatively small orbitolinid genus exhibiting an eccentrically situated embryonic apparatus (Schroeder, 1993), which was, according to Cherchi and Schroeder (1973), geographically restricted to SW Europe (Jura Mountains, Subalpine Chains, Provence, eastern Pyrenees and Sardinia). However, different species of Valserina have previously been found throughout the Tethyan realm: Hungary (Bodrogi, 1999), Oman (Simmons, 1994), Northern Somalia (Cherchi and others, 1993, 1998; Cherchi and Schroeder, 1999), and even as far as Venezuela (Arnaud-Vanneau, written communication, 1999). These widespread occurrences seem to exclude Palorbitolina evolution by allopatric speciation. During the Upper Barremian, P. lenticularis colonized most of the Mediterranean region. The data from the Apennines (e.g. Chiocchini and others, 1984; Luperto-Sinni and Masse, 1986; Raspini, 1998) and the Adriatic carbonate platform (e.g. Velic´ and Sokacˇ, 1978; this paper) show that Palorbitolina reached this region later than the rest of the Mediterranean, where mixed clastic-carbonate environments predominated. This environmental control is further suggested by findings of Palorbitolina in the mixed Upper Barremian environments of the neighboring area of Central and Eastern Bosnia in the Inner Dinarides (Gusˇic´, 1981; Velic´, 1988). Finally, according to Cherchi and Schroeder (1980), a direct descendant of the phylogenetical lineage Valserina primitiva–V. broenimanni–V. charollaisi–V. transiens–Palorbitolina turbinata – P. lenticularis (Schroeder, 1993; Schroeder and others, 1999; see also Caus and others, 1990) is Palorbitolinoides hedini. Previously it was found only in Ladakh (India), Afghanistan and Tibet (Cherchi and others, 1984; Marcoux and others, 1987), in the realm that corresponds to the ‘‘Cimmerian Continent’’ (S¸engo¨r, 1981). It is probably the result of the isolation of Palorbitolina lenticularis in these areas that produced the subsequent replacement by Palorbitolinoides hedini. ACKNOWLEDGMENTS The study greatly benefited from the numerous discussions held with Dr. I. Velic´ and Prof. Dr. I. Gusˇic´. Both also thoughtfully reviewed an early version of the manuscript and made valuable suggestions. The author gratefully acknowledges Prof. Dr. A. Arnaud-Vanneau and Prof. Dr. E. Caus for their constructive reviews and comments that have greatly improved the manuscript, and Dr. A. S. Henderson for improving the English. I thank Dr. R. E. Martin for his help in final preparation of the manuscript. This research was carried out during work on the geological map of the Republic of Croatia (scale 1:50.000), project No. 01810101, sponsored by the Ministry of Science and Technology of the Republic of Croatia. I thank the Institute of Geology, Zagreb, for financial support. REFERENCES ARNAUD H., 1981, De la plate-forme urgonienne au bassin vocontien: le Barre´mo-Be´doulien des Alpes occidentales entre Isere et Buech: Geólogie Alpine, v. 12, 804 p. ARNAUD-VANNEAU, A., 1968, Etude statistique et morphologique des Orbitolines du synclinal d’Autrans (Vercors septentrional): Geólogie Alpine, t. 44, p. 27–48.

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, 1975, Re´flexion sur le mode de vie de certain Orbitolinides (Foraminife`res) barre´mo-aptiens de 1’Urgonien du Vercors: Compte`s rendus des Sciences de la Socie´te´ de Physique et d’Histoire Naturelle de Gene`ve, v. 10, p. 126–130. , 1980, Micropaleóntologie, paleóecologie et se´dimentologie d’une plate-forme carbonateé de la marge passive de la Te´thys: L’Urgonien du Vercors septentrional et de la Chartreuse (Alpes occidentales): Geólogie Alpine, v. 11, 874 p. BANNER, F. T., and SIMMONS, M. D., 1994, Calcareous algae and foraminifera as water-depth indicators: an example from the early Cretaceous carbonates of north-east Arabia, in Simmons, M. D. (ed.), Micropalaeontology and Hydrocarbon Exploration in the Middle East: Chapman and Hall, London, p. 243–252. BARRON, E. J., 1984, Ancient climates: Investigation with climate models: Reports of Progress in Physics, v. 47, p. 1563–1599. , 1986, Physical paleoceanography: A status report, in Hsu¨, K. J. (ed.), Mesozoic and Cenozoic oceans: American Geophysical Union Geodynamics Series, v. 15, p. 1–9. BODROGI, I., 1999, Urgon limestone of inverse position in the SE foreland of the Villańy Mts, Transdanubia, Hungary: Annual Reports of the Geological Institute of Hungary, 1992/1993/II, p. 27– 52. BOSSELINI, A., 1989, The continental margins of Somalia: their structural evolution and sequence stratigraphy: Memorie di Scienze Geologiche, v. 41, p. 373–458. , RUSSO, A. & SCHROEDER, R. 1999, Stratigraphic evidence for an Early Aptian sea-level fluctuation: the Graua Limestone of south-eastern Ethiopia: Cretaceous Research, v. 20, p. 783–791. BRENCHLEY, P. J., and HARPER, D. A. T., 1997, Palaeoecology. Ecosystems, environments and Evolution: Chapman & Hall, London, 402 p. CAUS, E., GARCIA-SENZ, J., RODES, D., and SIMO, A., 1990, Stratigraphy of the Lower Cretaceous (Berriasian—Barremian) sediments of the Organya` Basin, Pyrenees, Spain: Cretaceous Research, v. 11, p. 313–320. CHERCHI, A., DE CASTRO, P., and SCHROEDER, R., 1978, Sull’eta` dei livelli a Orbitolinidi della Campania e delle Murge Baresi (Italia meridionale): Bolletino della Societa` Naturali di Napoli, v. 87, p. 1–17. , FANTOZZI, P. L., and ABDIRAHMAN, H., 1993, Micropalaeontological data on the Jurassic-Cretaceous sequences and the Cretaceous-Paleogene boundary in Northern Somalia (Bosaso region): Compte`s rendus de 1’Acade´mie des Sciences de Paris, t. 316, ser. II, p. 1179–1185. , and SCHROEDER, R., 1973, Sur la biogeógraphie de 1’association a Valserina du Barre´mien et la rotation de la Sardaigne: Compte`s rendus de 1’Acade´mie des Sciences de Paris, t. 277, ser. D, p. 829–832. , and , 1980, Palorbitolinoides hedini n. gen., n. sp., grand foraminife`re du Cre´tace´ infe´rieur du Tibet me´ridional: Compte`s rendus de l’Acade´mie des Sciences de Paris, t. 291, ser. D, p. 385–388. , and , 1999, Late Barremian orbitolinid Foraminifera from northern Somalia: Bolletino della Societa` Paleontologica Italiana, v. 38, p. 3–13. , , and BIN GNOTH, M., 1998, Early Aptian orbitolinid foraminifera from the Quishn Formation of Al Mukalla (Hadramawt, Southern Yemen). Comparisons with adjacent regions: Zeitschrift fu¨r Geologische Wissenschaften, v. 26, p. 610–622. , SEN GUPTA, V. J., and SCHROEDER, R., 1984, Late Aptian calcareous Algae and Larger Foraminifera from Khalsi, Ladakh, India: Bulletin of the Indian Geological Association, v. 17, p. 147– 157. CHIOCCHINI, M., MANCINELLI, A., and ROMANO, A., 1984, Stratigraphic distribution of benthic foraminifera in the Aptian, Albian and Cenomanian carbonate sequences of the Aurunci and Ausoni Mountains (southern Lazio, Italy), in Oertli, H. J. (ed.), Benthos ’83; 2nd International Symposium on Benthic Foraminifera (Pau, April 1983). Elf aquitaine, ESSO REP and Total CFP, Pau and Bordeaux, p. 167–181. FUCˇEK, L., VELIC´, I., VLAHOVIC´, I., OSˇTRIC´, N., KOROLIJA, B., and MATICˇEC, D., 1995, Novi podaci o stratigrafiji donje krede otoka Cresa, in Vlahovic´, I., Velic´, I. and Sˇparica, M. (eds.), l. hrvatski geolosˇki kongres, Opatija 1995, Zbornik radova 1 (The First Cro-

292

HUSINEC

atian Geological Congress, Opatija 1995, Proceedings 1), Zagreb, p. 167–172. GONZALES-ARREOLA, C., PANTOJA-ALOR, J., OLORIZ, F., VILLASENOR, A. B., and GARCIA-BARRERA, P., 1996, Lower Aptian ammonitina Pseudohaploceras liptoviense (ZEUSCHNER) in the Cumburindio Formation (southwestern Mexico): Geobios, no. 29, fasc. 1, p. 35–43. GUSˇIC´, I., 1975, Lower Cretaceous imperforate Foraminiferida of Mt. Medvednica, northern Croatia (Families Lituolidae, Ataxophragmiidae, Orbitolinidae): Palaeontologia jugoslavica, v. 14, p. 1–51. , 1981, Variation range, evolution, and biostratigraphy of Palorbitolina lenticularis (BLUMENBACH) (Foraminiferida, Lituolacea) in the Lower Cretaceous of the Dinaric Mountains in Yugoslavia: Palaöntologische Zeitschrift, v. 55, p. 191–208. HOFKER, J., Jr., 1963, Studies on the genus Orbitolina (Foraminiferida): Leidse Geologische Medelingen, v. 29, p. 181–253. HOTTINGER, L., 1980, Re´partition compareé des grands foraminife`res de la Mer Rouge et de l’Oceán Indien: Annali dell’Universita di Ferrara (NS Sez IV), Suppl. 6, p. 1–13. , 1983, Processes determining the distribution of larger foraminifera in space and time: Utrecht Micropaleontological Bulletin, v. 30, p. 239–253. HUGHES, G. W., 1998, Middle East Aptian rudist-foraminiferal-algal associations and their possible modern Arabian Gulf analogue, in Masse, J. P. and Skelton, P. W. (eds.), Quatrie`me Congre`s international sur les Rudistes: Geobios, Me´moire spećial 22, p. 147– 158. HUSINEC, A. AND VELIC´, I., 1998, Orbitolinid biostratigraphy of the Aptian and Albian carbonate deposits on the island of Cres (Adriatic Sea, Croatia), in Longoria, J. F. and Gamper, M. A. (eds.), International Symposium on Foraminifera FORAMS ’98, Proceedings of the Meeting and Abstracts with Programs: Sociedad Mexicana de Paleontologıá, Monterrey, p. 52. , VELIC´, I., FUCˇEK, L., VLAHOVIC´, I., MATICˇEC, D., OSˇTRIC´, N., and KORBAR, T., 2000, Mid Cretaceous orbitolinid (Foraminiferida) record from the islands of Cres and Losˇinj (Croatia) and its regional stratigraphic correlation: Cretaceous Research, v. 21, p. 155–171. LUGER, P., HENDRIKS, M., ARUSH, M., BUSSMANN, M., KALLENBACH, H., METTE, W. & STROUHAL, A., 1990, The Jurassic and the Cretaceous of northern Somalia: preliminary results of the sedimentologic and stratigraphic investigations: Berliner Geowissenschaftliche Abhandlungen, ser. A, v. 120, p. 571–594. LUPERTO-SINNI, E., and MASSE, J. P., 1986, Donneés nouvelles sur la stratigraphie des Calcaires de plate-forme du Cre´tace´ inferieur du Gargano (Italie me`ridionale): Rivista Italiana di Paleontologia e Stratigrafia, v. 92, p. 33–66. MARCOUX, J., GIRARDEAU, J., FOURCADE, E., BASSOULLET, J.-P., PHILIP, J., JAFFREZO, M., XUCHANG, X., and CHENGFA, C., 1987, Geology and biostratigraphy of the Jurrasic and Lower Cretaceous series to the north of the Lhasa Block (Tibet, China): Geodinamica Acta, v. 1, p. 313–325. MASSE, J. P., 1976, Les calcaires urgoniens de Provence (Valanginien– Aptien infe´rieur). Stratigraphie, Paleóntologie, les paleóenvironments et leur e´volution: The`se Sciences, Universite´ Aix-Marseille II, 445 p. , BELLION, Y., BENKHELIL, J., BOULIN, J., CORNEE, J. J., DERCOURT, J., GUIRAUD, R., MASCLE, G., POISSON, A., RICOU, L. E., and SANDULESCU, M., 1993a, Lower Aptian Palaeoenvironments (114–112 Ma), in Dercourt, J., Ricou, L. E. and Vrielynck, B. (eds.), Atlas Tethys Palaeoenvironmental Maps. Maps: BEICIPFRANLAB, Rueil-Malmaison. , , , DERCOURT, J., GUIRAUD, R., and RICOU, L. E., 1993b, Lower Aptian (114–112 Ma), in Dercourt, J., Ricou, L. E. and Vrielynck, B. (eds.), Atlas Tethys Palaeoenvironmental Maps. Explanatory Notes: Gauthier-Villars, Paris, p. 113–134. , BORGOMANO, J., and AL MASKIRY, S., 1998, A platform-tobasin transition for lower Aptian carbonates (Shuaiba Formation) of the northeastern Jebel Akhdar (Sultanate of Oman): Sedimentary Geology, v. 119, p. 297–309. MEHRNUSCH, M., 1973. Eine Orbitoliniden-Fauna aus der Unterkreide von Esfahan (Zentral Iran): Neues Jahrbuch fu¨r Geologie und Palaöntologie Monatshefte, 1973, p. 374–382. MEZA, J. G., 1980, El genero Orbitolina en Mexico y su distribucioń

estratigra´fica: Revista Instituto Mexicano del Petro´leo, v. 12, p. 4–33. MONTENAT, C., MOULLADE, M., and PHILIP, J., 1982, Le Cre´tace´ infe´rieur a` Orbitolines et Rudistes d’Afghanistan central: Geólogie Me´diterraneénne, t. 9, p. 109–122. MOULLADE, M., PEYBERNE`S, B., REY, J., AND SAINT-MARC, P., 1985, Biostratigraphic interest and paleobiogeographic distribution of early and mid-Cretaceous Mesogean orbitolinids (Foraminiferida): Journal of Foraminiferal Research, v. 15, p. 149–158. MURRAY, J. W., 1991, Ecology and Palaeoecology of Benthic Foraminifera: Longman Scientific and Technical, Avon, 397 p. PANTOJA-ALOR, J., SCHROEDER, R., CHERCHI, A., ALENCASTER, G., and PONS, J. M., 1994, Fossil assemblages, mainly Foraminifers and Rudists, from the Early Aptian of Southwestern Me´xico. Palaeobiogeographical consequences for the Caribbean region: Revista Espanõla de Paleontontologıá, v. 9, p. 211–219. PEYBERNE`S, B., 1982, Les Orbitolinide´s cre´tace´s d’Afrique: essai de synthe`se: Cahiers de Micropaleóntologie, v. 2, p. 13–28. RASPINI, A., 1998, Microfacies analysis of shallow water carbonates and evidence of hierarchically organized cycles—Aptian of Monte Tobenna, southern Apennines, Italy: Cretaceous Research, v. 19, p.197–223. REY, J., 1975, Observations sur l’ećologie des Orbitolines et des Choffatelles dans le Cre´tace´ infe´rieur d’Estremadura (Portugal): Compte`s rendus de l’Acade´mie des Sciences de Paris, v. 276, p. 2517– 2520. RICOU, L. E., 1976, E´volution structurale des Zagrides. La re´gion clef de Neyriz (Zagros iranien): Me´moires de la Societe Geólogique de France, t. 55, v. 125, 140 p. SAHAGIAN, D. L., and HOLLAND, S. M., 1991, Eustatic sea-level curve based on a stable frame of reference: preliminary results: Geology, v. 19, p. 1209–1212. SAINT-MARC, P., 1970, Contribution a` la connaisance du Cre´tace´ basal du Liban: Revue de Micropaleóntologie, v. 12, p. 224–233. SCHROEDER, R., 1975, General evolutionary trends in Orbitolinas: Revista Espanõla de Micropaleontologia, Numero Especial, p. 117– 128. , 1993, Evolution du genre Valserina SCHROEDER et al. 1968 et l’origine des Palorbitolines [Foraminiferida]: Palaöntologische Zeitschrift, v. 67, p. 245–251. , and CHERCHI, A. 1979, Upper Barremian-Lowermost Aptian Orbitolinid Foraminifers from the Grand Banks continental Rise, Northwestern Atlantic (DSDP Leg 43, Site 384), in Tucholke, B. E., Vogt, P. R. and others (eds.), Initial reports of the Deep Sea Drilling Project: v. 43, Washington, D.C. (U.S. Government Printing Office), p. 575–583. SCOTT, R. W., 1990, Chronostratigraphy of the Cretaceous carbonate shelf, southeastern Arabia, in Robertson, A. H. F., Searle, M. P. and Ries, A. C. (eds.), The Geology and Tectonics of the Oman Region: Geological Society Special Publication, no. 49, p. 89– 108. SEN GUPTA, B. K., and GRANT, A. C., 1971, Orbitolina, a Cretaceous larger foraminifera from Flemish Cap: Paleoceanographic implications: Science, v. 173, p. 934–936. S¸ENGO¨R, C. A. M., 1981, The evolution of the Palaeo-Tethys in the Tibetan segment of the Alpides, in Proceedings, Symposium Xinghai-Xizanq (Tibet) Plateau: v. 1, Beijing, p. 51–56. SHAKIB, S. S., 1990, The biostratigraphical aspects of Gadvan Formation (Barremian-Aptian) of southwest Iran: Rivista Italiana di Paleontologia e Stratigrafia, v. 96, p. 111–132. SIMMONS, M. D., 1994, Micropalaeontological biozonation of the Kahman Group (Early Cretaceous), Central Oman Mountains, in Simmons, M. D. (ed.), Micropalaeontology and Hydrocarbon exploration in the Middle East: Chapman & Hall, London, p. 177–206. , and HART, M. B., 1987, The biostratigraphy and microfacies of the Early to mid-Cretaceous carbonates of Wadi’aidin, Central Oman Mountains, in Hart, M. B. (ed.), Micropalaeontology of carbonate environments: Ellis Horwood, Chichester, p. 176–207. SOUTHAM, J. R., and HAY, W. W., 1981, Global sedimentary mass balance and sea level changes, in Emiliani, C. (ed.), The sea, Volume 7, The oceanic litosphere: Wiley Interscience, New York, p. 1617–1684. VAHRENKAMP, V. C., 1996, Carbon isotope stratigraphy of the Upper Kharaib and Shuaiba Formations: implications for the Early Cre-


taceous evolution of the Arabian Gulf region: American Association of Petroleum Geologists Bulletin, v. 80, p. 647–662. VELIC´, I., 1988, Lower Cretaceous benthic foraminiferal biostratigraphy of the shallow water carbonates of the Dinarides: Revue de Paleóbiologie, Volume Spećial No. 2 (Benthos ‘86), p. 467–475. , and SOKACˇ, B., 1978, Biostratigrafska analiza jure i donje krede sˇire okolice Ogulina (sredisˇnja Hrvatska) (Biostratigraphic analysis of the Jurassic and Lower Cretaceous in the wider region of Ogulin, central Croatia): Geolosˇki vjesnik, v. 30/l, p. 309–337. VILAS, L., MASSE, J. P., and ARIAS, C., 1995, Orbitolina episodes in carbonate platform evolution: the early Aptian model from SE Spain: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 119, p. 35–45. WILLIAMS, D. F., 1988, Evidence for and against sea-level changes from the stable isotopic record of the Cenozoic, in Sea-level changes—An integrated approach: Society of Economic Paleontologists and Mineralogists, Special Publication No. 42, p. 31–36. WITT, W., and GOKDAG, H., 1994, Orbitolinid biostratigraphy of the

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Shuaiba Formation (Aptian), Oman. Implications for reservoir development, in Simmons, M. D. (ed.), Micropalaeontology and Hydrocarbon exploration in the Middle East: Chapman & Hall, London, p. 221–234. WOLCKE, F., and SCHOLZ, J., 1988, Uber die palaöbiogeographische Bedeutung eines Vorkommens caprinider Rudisten aus der Unterkreide von Cebu (Philippinen): Mitteilungen aus dem Geologische-Palaöntologischen Institut in Hamburg, v. 67, p. 121–133. XZBGM (Xizang Bureau of Geology and Mineral Resources), 1993, Regional geology of Xizang Autonomous Region: Geological Publishing House, Beijing, 707 p. [in Chinese, English summary] YUWONO, Y. S., PRIYOMARSONO, S., MAURY, R. C., RAMPNOUX, J. P., SOERIA-ATMADJA, BELLON, H., and CHOTIN, P., 1988, Petrology of the Cretaceous magmatic rocks from Meratus Range, Southeast Kalimantan: Journal of Southeast Asia Earth Sciences, v. 2, p. 15–22.

Received 1 November 2000 Accepted 28 February 2001