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The Late Cretaceous planktonic foraminiferal distri- bution recorded at several drill sites (Deep Sea Drilling. Project and Ocean Drilling Program) in the South At-.
Journal of Foraminiferal Research, v. 33, no. 4, p. 330–337, October 2003

LATE CRETACEOUS PLANKTONIC FORAMINIFERAL BIOEVENTS IN THE TETHYS AND IN THE SOUTHERN OCEAN RECORD: AN OVERVIEW MARIA ROSE PETRIZZO1 Dipartimento di Scienze della Terra ‘‘Ardito Desio’’, Universita’ degli Studi di Milano, via Mangiagalli 34, I-20133 Milano, Italy

lowing a better biostratigraphic framework to be constructed for the southern high latitudes (Petrizzo, 2001). The main aim of this paper is to compare planktonic foraminiferal distributions recorded from several localities across latitudes in order to investigate the presence of a similar sequence of bioevents occurring in the low, middle and high latitudes. These bioevents are evaluated in terms of their value as zonal markers for a regional planktonic foraminiferal biostratigraphic zonation; some are shown to be possibly isochronous across many latitudes, and hence, useful for worldwide correlation.

ABSTRACT

The Late Cretaceous planktonic foraminiferal distribution recorded at several drill sites (Deep Sea Drilling Project and Ocean Drilling Program) in the South Atlantic and south Indian Ocean and from sediment outcrops in the Tethyan region (Gubbio and El Kef) have been analyzed in order to investigate the presence of a similar sequence of bioevents occurring at low, middle, and high latitude. Comparative analysis highlights the co-occurrence of several bioevents; some of them are isochronous bioevents occurring in the Tethys and in the Southern Ocean record, whereas others are diachronous across latitudes but can be used for correlation at regional scale, as they show the same stratigraphic distribution in the South Atlantic and Indian Ocean record. Isochronous bioevents are the first and the last occurrence of Helvetoglobotruncana helvetica, and the first appearance of Falsotruncana maslakovae in the lowermiddle Turonian. The first occurrence of Heterohelix papula in the Southern Ocean sites, correlated with the first occurrence of large heterohelicids in the Tethyan area, allows the Coniacian/Santonian boundary to be identified. The most reliable bioevents useful for correlation at a regional scale in the Southern Ocean record are the last occurrence of the marginotruncanids in the upper Santonian, the first and the last occurrence of Globigerinelloides impensus from the uppermost Santonian to upper Campanian, the first occurrence of Heterohelix rajagopalani in the middle-upper Campanian, and the appearance of Abathomphalus mayaroensis in the lower Maastrichtian.

BIOEVENTS The distribution of land and sea by Hay and others (1999) in their paleogeographic reconstruction of the Late Cretaceous is shown in Figure 1, with the inferred Late Cretaceous paleolatitudes for all locations analyzed in this study. In the Tethys area, the Gubbio and the El Kef sections were located at about 208N. In the Indian Ocean, the Exmouth and Kerguelen plateaus were located at 478S and 508S, respectively. In the South Atlantic the Rio Grande Rise was located at about 158S; a paleolatitude of 588S is inferred for the Northeast Georgia Rise and the Falkland Plateau, and a paleolatitude of 658S is assigned to the Maud Rise, the southernmost circum-Antarctic site analyzed in this study. As already mentioned, the sedimentary sequence in the Southern Ocean is characterized by poor recovery and incompleteness of the stratigraphic record, especially for the Cenomanian-Campanian interval, whereas the record is almost complete for the uppermost Campanian-upper Maastrichtian interval (Fig. 2). Nevertheless, a similar sequence of bioevents has been found in the middle and high southern latitudes after a detailed and comparative biostratigraphic analysis of planktonic foraminiferal distribution from the sites drilled during Leg 113 (Maud Rise; Huber, 1990), Leg 114 (Falkland Plateau; Huber, 1991a), Leg 119 (Kerguelen Plateau; Huber, 1991b), Leg 120 (southern Kerguelen Plateau; Quilty, 1992b), Leg 122 (Exmouth Plateau; Wonders, 1992; Zepeda, 1998; Petrizzo, 2000), and Leg 183 (Kerguelen Plateau; Petrizzo, 2001). Some of these bioevents were previously identified in sediments recovered at old drill sites (Deep Sea Drilling Project Legs 3, 26, 36 and 71) in the Southern Ocean area, but the incomplete record due to very poor recovery prevented construction of a biostratigraphic scheme valid even at a regional scale. The most significant Tethyan and Southern Ocean planktonic foraminiferal bioevents are here compared and discussed in stratigraphic order from the oldest to the youngest (Fig. 3): (1) The FO (first occurrence) and the LO (last occurrence) of Helvetoglobotruncana helvetica in the lower and middle Turonian, respectively, seem to be isochronous across latitudes, as they occur at the same stratigraphic level

INTRODUCTION Cretaceous planktonic foraminiferal assemblages from high latitudes typically exhibit low diversity and are mainly composed of long-ranging taxa of simple morphology, whereas Tethyan assemblages are characterized by an abundant and highly diverse fauna. Because of the absence of most Tethyan marker taxa in the Southern Ocean record, the Tethyan biostratigraphic scheme cannot be applied there. Moreover, the establishment of a detailed Late Cretaceous planktonic foraminiferal biozonation of the southern latitudes has been hampered by a rather incomplete record owing to overall poor recovery and the occurrence of several unconformities (Herb, 1974; Sliter, 1977; Krasheninnikov and Basov, 1983; Huber, 1992; Quilty, 1992a, b; Petrizzo, 2000, 2001). A comparative biostratigraphic analysis of planktonic foraminiferal distribution from the most recent Ocean Drilling Program (ODP) drill sites in the Southern Ocean has improved the Cretaceous deep-sea database, al1

E-mail: [email protected]

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FIGURE 1. Paleogeographic reconstruction for the Late Cretaceous (84.0 Ma) based on the data files used by Hay and others (1999), with the locations discussed in this study.

in the low latitude (Gubbio and Tunisia sections, Premoli Silva and Sliter, 1994; Robaszynski and others, 1990) and in the middle-high latitudes of the southern Indian Ocean at Exmouth Plateau (Wonders, 1992; Petrizzo, 2000). At the Kerguelen Plateau, H. helvetica first occurs after the appearance of the marginotruncanids. This reverse occurrence is interpreted as related to the small size of the ODP samples, H. helvetica always being rare in the lowermost part of its distribution. Fragments of H. helvetica have also been found by Herb (1974) at the Naturaliste Plateau (Site 258, Leg 26) in indurated residues yielding rare and poorly preserved planktonic foraminifera. No record of this species is documented in the southernmost area (Falkland Plateau, Northeast Georgia Rise, and Maud Rise) because of the lack of recovery of Turonian sediments. (2) The FO of the marginotruncanids falls slightly above the FO of H. helvetica in the middle Turonian in the Gubbio and El Kef sections (Premoli Silva and Sliter, 1994; Robaszynski and others, 1990), and in the middle-high latitudes at the Exmouth Plateau (Wonders, 1992; Petrizzo, 2000). As mentioned above, at the Kerguelen Plateau the occurrence of few to common specimens of marginotruncanids (see Petrizzo, 2001) precedes the appearance of H. helvetica owing to the small size of the samples. However, the hypothesis of a simultaneous appearance of H. helvetica and representatives of Marginotruncana at Kerguelen cannot be ruled out. (3) Falsotruncana maslakovae first occurs immediately after the extinction of H. helvetica in the middle Turonian at the Pont du Fahs type region in Tunisia (Caron, 1981). This first appearance in the low latitude area is in agreement with the record in the Exmouth and Kerguelen plateaus sequence, allowing extension of the biostratigraphic value of this bioevent into the Southern Ocean region. (4) In the Southern Ocean record, the disappearance of F. maslakovae coincides with the simultaneous extinction of all species of Falsotruncana at Exmouth and Kerguelen plateaus (Petrizzo, 2000, 2001). Moreover, the occurrence of a few specimens of F. maslakovae in one sample collected from the base of Hole 700B, drilled on the Northeast Georgia Rise (Leg 114, Petrizzo, 1999), allows the geographic distribution of this taxon in the South Atlantic Ocean to be extended. Based on correlation with nannofossil

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bioevents, the extinction of Falsotruncana in the southern sites occurs close to the FO of Micula staurophora (5 Micula decussata; see discussion in Persico and Villa, 2002) in the lower middle Coniacian (Crux, 1991; Bralower and Siesser, 1992; base of the UC10a Nannofossil Subzone, Burnett, 1998). The LO of F. maslakovae is not well documented in the Tethyan region, as the taxon becomes very rare at the end of its stratigraphic range. Therefore, further study on well preserved material from the Tethyan region is needed to verify the range of Falsotruncana at low latitudes. (5) Heterohelix papula first occurs in the Exmouth Plateau sedimentary sequence slightly below the base of the Dicarinella asymetrica Zone, and disappears in the lower part of the same zone (Petrizzo, 2000). Based on correlation with nannofossil bioevents, the FO of H. papula in the Exmouth Plateau (Sites 762C and 763B) occurs slightly below the appearance of Lithastrinus grillii (Bralower and Siesser, 1992; Petrizzo, 2000), close to the base of the Santonian (Erba and others, 1995). The distribution of H. papula observed at the Kerguelen Plateau (Petrizzo, 2001) and at the Northeast Georgia Rise Hole 700B (Petrizzo, 1999) appears to be consistent with that recorded from the Exmouth Plateau. The same stratigraphic range is documented from the Cretaceous successions outcropping in the Gingin and Kalbarri regions (Southern Carnarvon Basin, northwestern Australia; Rexilius, 1984; Haig, 2002). Moreover, the vertical range of H. papula is identical to that of H. rumseyensis (a junior synonym of H. papula; see discussion in Petrizzo, 2000) as documented by Douglas (1969) from Santonian deposits in the Great Valley Sequence of northern California. Subsequently, Douglas’s species was identified at Naturaliste Plateau Site 258 by Pessagno and Michael (1974) from a stratigraphic interval assigned to the upper Turonianlower Santonian, based on the planktonic foraminiferal assemblages; however, according to calcareous nannofossil data (Bukry, 1974), this interval can be dated to late Coniacian-early Santonian. The presence of H. papula (identified as H. rumseyensis) is also recorded in the South Atlantic Ocean (Site 511, Falkland Plateau; Krasheninnikov and Basov, 1983) from a stratigraphic interval that, in the absence of age diagnostic taxa, was assigned to the lower Campanian. The FO of Heterohelix papula in the Southern Ocean sites appears to be coeval to the FO of large heterohelicids (Sigalia and ventilabrellids) at low latitudes (Petrizzo, 2000, 2001). Taking into account that the FO of large heterohelicids slightly precedes the appearance of D. asymetrica (Sigal, 1977; Premoli Silva and Sliter, 1999), an event very close to the base of the Santonian (Robaszynski and Caron, 1995), the FO of H. papula seems to be an isochronous event useful in identifying the Coniacian/Santonian boundary in the Southern Ocean record (Petrizzo, 2001). (6) The FO of D. asymetrica in the Tethyan sections falls within the lower third of the texanus ammonite Zone, slightly above the base of the Santonian (Robaszynski and Caron, 1995). Dicarinella asymetrica disappears in the lowermost Campanian chron 33R just above the termination of the Cretaceous Normal Polarity Superchron, and above the FO of the nannofossil Aspidolithus parcus parcus (Erba and others, 1995; Bralower and others, 1995). The same stratigraph-

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FIGURE 2.

Recovery in the Southern Ocean (after Huber, 1992, and Petrizzo 2000, 2001).

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FIGURE 3. Stratigraphic distribution across latitudes of the planktonic foraminferal bioevents analyzed in this study plotted against magnetic chrons (Gradstein and others, 1994). Paleolatitudes according to Hay and others (1999). Tethyan and Austral biozonation follow Robaszynski and Caron (1995) and Huber (1992), respectively. Proposed Transitional biozonation modified after Petrizzo (2001).

ic range is observed in the Exmouth, but not in the Kerguelen Plateau and in other Southern Ocean sites (Petrizzo 2000, 2001) where D. asymetrica is absent and cannot be used as a zonal marker. (7) In the Tethyan sections, the marginotruncanids last occur above the extinction of D. asymetrica in the lower part of the Globotruncanita elevata Zone, close to the base of chron 33R (Premoli Silva and Sliter, 1994; Robaszynski

and Caron, 1995). By contrast, their disappearance in the Exmouth Plateau is older and falls in the upper part of the D. asymetrica Zone (uppermost Santonian, upper chron 34N), below the first occurrence of Globigerinelloides impensus (Petrizzo, 2000). This latter bioevent falls in the same position in the Kerguelen Plateau and in the Northeast Georgia Rise (Hole 700B; Petrizzo, 1999, 2001). The same sequence of bioevents is recorded in the southern Atlantic

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Ocean (Site 511, Falkland Plateau; Krasheninnikov and Basov, 1983), although the stratigraphic interval was assigned to the lower Campanian based on the assemblages, in the absence of age-diagnostic taxa. Therefore, the extinction of the marginotruncanids falls between the FO of H. papula and the FO of G. impensus in all the Southern Ocean sites. In spite of the absence of D. asymetrica in the southernmost sites, it could be dated as late (or latest) Santonian, based on the occurrence of D. asymetrica at Exmouth Plateau. (8) The FO of Globotruncana ventricosa in the Tethyan area is equated to the base of chron 33N in the mid-Campanian and is used to identify the base of the Globotruncana ventricosa Zone (Premoli Silva and Sliter, 1994; Robaszynski and Caron, 1995). However, the appearance of G. ventricosa slightly precedes the extinction of the marginotruncanids in the Exmouth and Kerguelen plateaus (Petrizzo, 2001), extending its vertical range down into the Santonian, as observed by Wonders (1992). Moreover, Rexilius (1984) identified G. ventricosa in lower Santonian sediments yielding H. papula and cropping out in the Kalbarri regions (Southern Carnarvon Basin, northwestern Australia). Thus, it appears that this bioevent is diachronous. An earlier FO of G. ventricosa at high latitudes is also recorded by Herb (1974), who reported many specimens morphologically very close to G. ventricosa from Coniacian deposits recovered at Naturaliste Plateau (DSDP Leg 26). (9) Globigerinelloides impensus, an endemic species of the Southern Ocean (Huber, 1992), first occurs in the uppermost part of the D. asymetrica Zone at Exmouth Plateau above the extinction of the marginotruncanids (Petrizzo, 2000); therefore, this event approximates the Santonian/ Campanian boundary. It appears in the same stratigraphic position on the Kerguelen Plateau and Northeast Georgia Rise (Petrizzo, 1999, 2001). At Falkland Plateau, G. impensus was recorded by Sliter (1977) at Site 327 and by Krasheninnikov and Basov (1983) at Site 511 from sediments assigned to the Campanian. Moreover, Herb (1974) reported it as G. ehrenbergi from Coniacian (?)-Santonian sediments drilled on the Naturaliste Plateau. At the Maud Rise, the southernmost site analyzed in this study, the FO of G. impensus was not detected because of the lack of recovery (Huber, 1992; Fig. 2). (10) The LO of G. impensus falls in the upper Campanian within the upper chron 33N at the Maud Rise (Huber, 1992) and is correlatable with its last occurrence at the Kerguelen Plateau. No data are available for the LO of G. impensus at Exmouth Plateau and from the other Southern Ocean sites. (11) Heterohelix rajagopalani first appears in the upper part of chron 33N before the extinction of Radotruncana calcarata (uppermost Campanian) at Site 356 drilled on San Paulo Plateau (DSDP Leg 39), as reported by Nederbragt (1990). The same position is recorded at the Exmouth Plateau (Zepeda, 1998; R. J. Campbell communication, 2002), whereas it first occurs at the base of chron 31R at the Kerguelen Plateau, slightly preceding the appearance of Abathomphalus mayaroensis (Petrizzo, 2001). At low latitudes, few specimens of H. rajagopalani have been found in the eastern Mediterranean (Hole 967E, Eratosthenes Seamont) in upper Maastrichtian assemblages yielding Contusotrun-

cana contusa (Premoli Silva and others, 1998). No record of this species is documented from the Maud Rise. (12) The FO of A. mayaroensis is a diachronous bioevent across latitudes. In fact, at Maud Rise and at Kerguelen Plateau, it first occurs in the lower 31R chron (Huber, 1992; Petrizzo, 2001), which is earlier than in the Tethyan sections and in the Exmouth Plateau, where it first appears at the base of chron 31N (Premoli Silva and Sliter, 1994; Robaszynski and Caron, 1995; Zepeda, 1998; R. J. Campbell communication, 2002) (13) The FO of Pseudoguembelina hariaensis in the El Kef section and at DSDP Sites 21 (Leg 3) and 357 (Leg 39) drilled on the Rio Grande Rise (Nederbragt, 1990) occurs in the upper part of chron 30N (Robaszynski and Caron, 1995; upper Maastrichtian) and extends up to the Cretaceous/Tertiary boundary. The same stratigraphic range is observed in the Kerguelen Plateau succession (Petrizzo, 2001). No data have been collected from the other Southern Ocean sites. DISCUSSION AND CONCLUSIONS Comparative analysis of planktonic foraminiferal distribution across latitudes highlights the succession of several biovents, some of them showing worldwide validity, others showing the basic importance in regional correlation. The most reliable of them are discussed below in stratigraphic order from low to high latitudes. In the lower-middle Turonian, the FO and LO of H. helvetica and the FO of F. maslakovae are isochronous bioevents occurring in the Tethys and in the Southern Ocean record, and hence are useful for worldwide correlation from 208N to 588S of paleolatitudes (Fig. 4). Besides the occurrence of the Tethyan taxa, the composition of the planktonic foraminiferal assemblages in Turonian successions throughout the middle and the mid-high latitudes sedimentary sequences also indicates strong affinities with the Tethyan fauna, suggesting that a warm climate characterized the earlymiddle Turonian worldwide. These data are in agreement with the highest sea level recorded in the Mesozoic (Hardenbol and others, 1998), and support evidence from stable isotopic analysis that indicate the ocean temperature maximum in the early Turonian at paleotemperature values close to 308C (Jenkyns and Wilson, 1999). The LO of F. maslakovae can be used to identify the lower (middle?) Coniacian only in middle and mid-high latitude sedimentary sequences from 478S to 588S (Fig. 4), as the species is rare in Coniacian Tethyan sediments. Such rarity in the Tethys is probably related to its ecology. Falsotruncana maslakovae is morphologically very close to A. mayaroensis, which is rare in the warmer Tethyan environment, and hence interpreted as preferring cold waters. Based on morphological resemblance, the same behavior is assigned to F. maslakovae; this is also supported by the composition of the planktonic fauna in the mid-high latitude area. In fact, from the late Turonian to the end of the Cretaceous, the planktonic foraminiferal assemblages progressively changed in composition, with a marked decrease in number of species until they resembled the Austral lowdiversity assemblages recovered in the circum-Antarctic site at Maud Rise.

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FIGURE 4. Summary of the most important bioevents with emphasis on degree of correlation between low and high latitudes. Paleolatitudes according to Hay and others (1999).

The FO of H. papula in the Southern Ocean sites, which correlates with the FO of large heterohelicids at low latitudes, allows identification of the Coniacian/Santonian boundary from 208N to 588S, and hence can be considered of worldwide value (Fig. 4). The total range of D. asymetrica allows correlation between the Tethys and the middle-high latitudes from 208N

to 478S in the Santonian-earliest Campanian (Fig. 4). The Dicarinella concavata-asymetrica group is absent in the high-latitude planktonic foraminiferal assemblages. Its absence at paleolatitudes higher then 478S could be related to the life-strategy presumed for this group. Dicarinellids are considered intermediate species close to the specialist taxa (k-strategist) occupying the most oligotrophic portion of the

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mesotrophic spectrum (i.e., Premoli Silva and Sliter, 1999; Petrizzo, 2002). In terms of the inferred vertical stratification of Cretaceous taxa, the dicarinellids are considered to have occupied ecological niches above the deeper specialist taxa (marginotruncanids and globotruncanids). However, based on their latitudinal distribution, this hypothesis can be applied to the dicarinellids in general but not to the D. concavata-asymetrica group, which is interpreted as having lived deeper in the water column (Hart and Bailey, 1979), as they are rare or absent in shallower water sediments. Therefore, the absence of D. asymetrica at high latitudes could be related to the general decrease in temperature through the Late Cretaceous (Jenkyns and Wilson, 1999; Barrera and others, 1997). Such a decrease in temperature caused the shallowing of the thermocline that resulted in the elimination of the ecological niches inhabited by the most specialized and deep-dwelling taxa. The FO of P. hariaensis in the upper Maastrichtian could be used for correlation between 208N and 508S, although other Southern Ocean sites should be searched for this species to confirm the isochroneity of this bioevent. Other Late Cretaceous bioevents are reliable for correlation in more restricted paleolatitudinal bands. Despite their diachronous first occurrence between low and high latitudes, some events occurred at the same time in the southern Atlantic and Indian Ocean. In stratigraphic order the events are (Fig. 4): 1) the LO of the marginotruncanids in the late Santonian, from 478S to 588S; 2) the FO of H. rajagopalani, which can be used to identify the Radotruncana calcarata Zone in the upper Campanian from 158S to 478S; 3) the total range of G. impensus, spanning the stratigraphic interval from the uppermost Santonian to the upper Campanian, which is useful for correlation from 478S to 658S; and 4) the total range of the Maastrichtian species A. mayaroensis, which allows the southernmost regions around Antarctica to be correlated from 508S to 658S. ACKNOWLEDGEMENTS I am grateful to I. Premoli Silva for reviewing earlier versions of the manuscript, and B. Walsworth-Bell for his beneficial advice on the English of the text. I warmly thank E. Erba for helpful discussions and advice on the nannofossil biostratigraphy. My sincere thanks to D. W. Haig and R. K. Olsson for carefully reviewing this paper. The research was supported by MIUR 2001, given to I. Premoli Silva. REFERENCES BARRERA, E., SAVIN, S. M., THOMAS, E., and JONES, C. E., 1997, Evidence for thermohaline-circulation reversal controlled by sealevel change in the latest Cretaceous: Geology, v. 25, p. 715–718. BRALOWER, T. J., and SIESSER, W. G., 1992, Cretaceous calcareous nannofossil biostratigraphy of Sites 761, 762 and 763, Exmouth and Wombat plateaus, northwest Australia: Proceedings of the Ocean Drilling Program, Scientific Results, v. 122, p. 529–556. BRALOWER, T. J, LECKIE, R. M., SLITER, W. V., and THIERSTEIN, H. R., 1995, An integrated Cretaceous microfossil biostratigraphy, in Berggren, W. A., Kent, D. V., Aubry, M-P, Hardenbol, J. (eds.), Geochronology, Time Scales and Global Stratigraphic Correlation: Society of Economic Paleontologists and Mineralogists, Special Publication, no. 54, p. 65–79. BUKRY, D., 1974, Cretaceous and Paleogene coccolith stratigraphy, Deep Sea Drilling Project, Leg 26: Initial Reports of the Deep Sea Drilling Project, v. 26, p. 669–673.

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Received 5 August 2002 Accepted 15 October 2002