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AAPG Bulletin

Abstract


Volume: 49 (1965)

Issue: 9. (September)

First Page: 1473

Last Page: 1484

Title: Paleocene--A Micropaleontologist's Point of View

Author(s): W. A. Berggren (2)

Abstract:

An historical summary is presented of the original definition, early and subsequent usage, and present conflicting concepts of the term Paleocene. Recent studies on planktonic foraminifers and coccolithophorids have resulted in a biostratigraphic zonation of the Paleocene which can be correlated with sufficient accuracy with the type localities of the classic stages of western Europe. The Paleocene is interpreted as consisting of the following units: Danian Stage (expanded to include the upper part of the Montian) and Landenian Stage (with lower Thanetian and upper Sparnacian Substages). The Paleocene-Eocene boundary is considered to be most appropriately drawn between the Landenian (Sparnacian) and Ypresian Stages (Globorotalia velascoensis/Globorotalia rex Zones).

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Text:

INTRODUCTION

What is the Paleocene? Since the term was first proposed by Schimper (1874), the Paleocene-its limits and, concomitantly, the limits of the stages commonly incorporated in it--probably has been subject to greater vicissitudes in interpretation and usage than any other of the well-known epoch-series terms (although the current Oligo-Miocene and Aquitanian debate threatens to eclipse this unenviable record; see Eames et al., 1962; Eames, 1953; Drooger, 1956; Stainforth, 1960, 1962; Bolli, 1957; Cole, 1963). This situation has developed despite the fact that Paleocene has been among the least popular of the time-stratigraphic terms in Europe (where it was first proposed)--having been only sparingly used there and, in general, not used in Belgium, France, and England. The Paleocene found eneral acceptance only in Scandinavia--Denmark and Sweden--through the works of Rosenkrantz, Harder, Brunnich-Nielsen, i. al., and in the Soviet Union through studies by Glaessner, Morozova, Shutskaya, Subbotina, Moskvin and Naidin, i. al. It was only during the second decade of the present century that Mathew revived the term in the United States for mammal-bearing strata of earliest Tertiary age in the montane-border basins of the Rocky Mountain province. In 1939 the United States Geological Survey formally recognized the Martinez Group of California as Paleocene.

Schimper (1874) applied the term Paleocene to denote the primitive appearance of the flora found in samples from the Sables de Bracheux, the travertine at Sezanne, and the lignites and sandstones of the Soissons district. He mentioned that the flora bore a striking resemblance to that now characteristic of the Northern Hemisphere and, in particular, to the modern European flora in contrast to the Cretaceous flora in which Southern Hemisphere types were predominant. There remains uncertainty to this day whether or not the flora which Schimper mentions having seen in the Lignites du Soissonais actually came from those beds or from the somewhat younger sandstones of the Cuisian (lower Eocene) (fide Savage, 1962, lecture notes). Yet these same Lignites du Soissonais are the type strata fo Dollfus' (1880) Sparnacian Stage. The lagoonal molluscan fauna of these beds is not directly comparable with either the subjacent Bracheux fauna or the overlying Ypresian. The mammalian fauna from the Sparnacian lignites at Epernay and various localities near Soissons is strikingly different from the underlying Cernaysian fauna, on the other hand.

Von Koenen (1885) monographed the foraminiferal fauna of the glauconitic sands and clays at Copenhagen and vicinity and said it had its closest affinity with the microfauna found in the Thanet sands of England and the Bracheux sands of the Paris Basin, France. The Thanet sands were first described by Prestwich (1852), but it was not until nearly half a century later that Burrows and Holland (1897) presented the first monograph of the foraminiferal fauna. Thus the marine microfauna of the glauconites at Copenhagen has come to serve for many workers as the reference guide (for comparative purposes) for marine Paleocene, although reference is more often made to the microfauna of the Thanet sands as "typical" for the Paleocene.

Because the overlying Woolwich and Reading beds (Sparnacian) are of lagoonal and fluviatile

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nature in England, as are their counterparts in the Paris basin and Belgium, the upper part of Schimper's Paleocene remained an enigma to invertebrate paleontologists. However, because the terms Thanet and Sparnacian generally were applied in the sense of facies development of the rock units rather than in a time-stratigraphic sense, and because they came to be considered as the transgressive and regressive phase, respectively, of the first sedimentary cycle of the Tertiary, the top of the Paleocene was drawn at the top of the Sparnacian. It has remained there for most invertebrate paleontologists to this day, the Eocene generally being considered to begin with the transgression of the Ypresian, as represented in its type area.

Vertebrate paleontologists have cited the marked difference in the mammalian fauna of the Sparnacian lignites at Epernay and localities near Soissons (which are more closely related to the Eocene fauna above) and the underlying Cernaysian fauna which belongs to the Thanetian, and have used this argument in placing the Paleocene-Eocene boundary between the Thanetian and Sparnacian. Thus a gradual dichotomy in the determination of the Paleocene-Eocene boundary has developed between vertebrate and invertebrate paleontologists with no rational solution in sight. A considerable amount of work remains to be done before this difference can be resolved, but it would seem that dispassionate inquiry, factual presentation, and interdisciplinary discussion are

Fig. 1. Regional correlation of some Paleocene-lower Eocene stratigraphic sequences by planktonic Foraminifera and coccolithophorids.

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the logical sequence before the subject is taken up for recommendation by an international commission of stratigraphic nomenclature. In the following pages the writer will consider, from the point of view of historical perspective, some of the ways in which the term Paleocene has been used and some recent studies bearing directly on the formulation of a unified time-stratigraphic subdivision of the Paleocene. A discussion and evaluation are presented of various alternatives in the use of stage names in the Paleocene and the determination of the Paleocene-Eocene boundary, several recommendations are made.

HISTORICAL SUMMARY

The Paleocene Epoch of Schimper (1874) embraces the marine Bracheux sands (Bracheux quarry, Butte de la Justice, near Beauvais, northwest of Paris), the travertine of Sezanne (east of Paris), and the lignites and sandstones of Soissons (northeast of Paris)--all in the classic Paris Basin. The Bracheux sands of the Paris Basin generally are considered age-equivalent to the Thanet sands on the Isle of Thanet, London Basin, and the lower part of the Landenian s.s., on the basis of the foraminiferal and molluscan faunas. The microfauna of the so-called Heersian Stage in Belgium indicates that its separation from the Landenian s.s. is superficial; it has distinct affinities with the fauna in the lower part of the Landenian s.s. and the Thanet sands of the London basin. An interesting and s gnificant discovery

Fig. 1. Continued. See caption on page 1474.

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of a Cernaysian-type mammalian fauna in the Bracheux sands at Chalons on the Vesle River (about 10 miles west of Cernay and 25 miles east-southeast of Soissons) recently has been reported by Savage (1962, lecture notes) in direct association with the marine and littoral foraminiferal and molluscan assemblage. The age relationships between the two faunas appear to be well documented.

The upper part of the Paleocene--the lignites and sands of Soissons--type of the Sparnacian of Dollfus (1880)--generally is regarded as approximately age-correlative with the Woolwich and Readings beds of England and the upper lagoonal-fluviatile Landenian of Belgium.

Subsequent usage by geologists of the late nineteenth and early twentieth centuries of the terms Thanetian and Sparnacian gave these units a facies connotation, i.e., they were interpreted as representing distinct phases in the normal cycle of sedimentation. In Belgium the Landenian was considered to be the first cycle of the Eocene seas and to comprise the Thanetian and Sparnacian, as interpreted in England and France. Interpreted in this sense, it is apparent that these units have lost some of their time-stratigraphic significance. The writer will review the concept and application of the Paleocene in stratigraphy in the past half century, before considering the various alternative solutions to the apparent dilemma.

Haug (1911) expanded Schimper's (1874) concept of the Paleocene by extending its upper boundary to include the Cuisian Stage above and its lower boundary to include the Montian Stage below. In doing so, he drew the Cretaceous-Tertiary boundary between the Danian and Montian Stages, assigning the latter to the lowermost Tertiary (his Eonummulitique; Paleogene of Naumann) and the former to the uppermost Cretaceous. He stated that the Danian in Denmark is overlain by beds which all authors consign to the Paleocene and which, "without doubt," correspond with the Montian of Belgium. But he did not explain why these beds correspond "without doubt" with the Montian; indeed Von Koenen (1885) had shown earlier that they were probably correlative with the Thanet beds of England, and Brotzen (19 8) and Haynes (1958) have corroborated this. It was Haug's considerable influence which led to general acceptance of this basic dichotomy between Danian and Montian and which has influenced most French and Belgian geologists to the present time (see Lex. strat. internat., 1957, v. 1, fasc. 4a, VIII, p. 134). For additional information on this problem the reader is referred to Haug's (1911) original discussion and to Yanshin's (1953) and Berggren's (1964) summary comments.

Stamp (1921) presented a comprehensive discussion of the cyclical depositional sequence in the Eocene of the Anglo-Franco-Belgium basin. In a series of figures he correlated the various lithologic units in the different parts of this widespread basin. With Prestwich he regarded the Cyprina scutellaria Zone of the Paris Basin (upper part of the lower or marine Landenian) to be represented by the Bottom Bed of the Woolwich Series (just above the Thanet sands) in the London Basin; thus, he recommended dropping the term Thanetian. The Sparnacian of France, in turn, was considered not wholly contemporaneous with the Woolwich and Reading Beds of England.

Rosenkrantz (1924) erected the Selandian Stage in Denmark for the glauconitic sands and clays above the Danian. The peculiar molluscan fauna of this unit made its correlation with other supposedly Paleocene equivalents difficult, but Rosenkrantz believed that the Selandian might one day prove to be equivalent to the Thanetian Stage. The supposition now appears fully justified.

Haynes (1955, 1958) discussed the distribution of foraminifers in the type Thanet beds and their role in determining the place of the Thanetian in the Paleocene. He suggested that the Thanetian be reduced to the rank of substage = lower Landenian, in as much as the small faunal changes in the various supposedly equivalent formations in Europe were not significant enough to be distinguishable from the effects of local facies changes, nor significant enough to justify the Thanetian as a time-stratigraphic unit of stage rank.

Nakkady (1957, 1959) has discussed the nature of the Paleocene in the Mediterranean region, particularly with reference to Egypt. However, his concepts of the limits of the various stages within the Paleocene reveal that he has misinterpreted the nature of these stages as defined and expressed in their type areas. Basically his usage of the stage terms Danian and Montian encompasses strata commonly assigned to Danian through lower Ypresian (= upper part of the Ilerdian of Hottinger and Schaub, 1960). For example, Nakkady (1957, p. 434; 1959, p. 455) has expanded the concept of the Danian Stage in Egypt to include

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strata containing both the "Globigerina zone" and keeled Globorotalia as well. The Montian Stage, on the other hand, is denoted by the first appearance of Nummulites deserti de la Harpe, Operculina libyca (Schwager), Discocyclina nudimargo (Schwager), i.al., and typified by the Eponides lotus assemblage-zone of Leroy's Unit II in the Maqfi section at Farafra Oasis. But by ignoring the first appearance of these forms in Leroy's Unit III at Maqfi within the Globorotalia pseudomenardii Zone, i.e., within the upper Paleocene (Said, 1961, p. 325), his concept of Montian is completely different from the original definition. Indeed, the Eponides lotus assemblage-zone is, in part, equivalent to the Globorotalia rex (= G. subbotinae) Zone in Egypt and Libya and is early Eocene (Ypresian) in ag . Said (1961, p. 325) has shown that Nakkady's interpretation of the Danian and Montian Stages in Egypt does not correspond with the time-stratigraphic boundaries as defined in the type areas, and has discussed the stratigraphic units at Farafra Oasis in their proper frame of reference, although it is believed that the Paleocene-Eocene boundary should be drawn at the base of the Eponides lotus Zone, rather than at its upper junction with the Alveolina decipiens Zone.

Nakkady (1957) thus leaves no room for the Landenian in his stratigraphic scheme. But he suggested that the Selandian deposition may have occurred before the type Montian, "with a slight vertical extension to the base of the Thanetian" (Nakkady, 1957, p. 433), giving ample justification to Haynes' (1958, p. 90) remark that "There is thus a good possibility that the stage terms Zeelandian (sic!), Montian and lower Landenian, as used, are at least partially synonymous."

The confusion which was introduced by Nakkady's concept of the "Paleocene" finally led Mangin (1957b) to suggest the abolition of the term Paleocene altogether and the use, in its place, of lower Eocene, i.e., all strata from and including the Danian to and including the Cuisian. (Mangin believes in the stratigraphic independence of the Danian and Montian Stages, at least the upper part of the Montian = Calcaire du Mons = Montian s.s. and equivalent strata; 1957a, b, 1960, and personal communication; cf. Moskvin and Naidin, 1960; Berggren, 1963.) In their original definitions, based on flora, the Paleocene stages Thanetian and Sparnacian are meaningless, he maintains. In terms of micropaleontology the stages of the "lower Eocene" are difficult to separate; no significant faunal "break separates the Sparnacian and Cuisian, which stratigraphers have previously united under the term Londinian, so that a time-stratigraphic subdivision at this horizon is artificial. Mangin's views are interesting but are judged erroneous and based on insufficient data. There would appear to be considerable evidence for distinguishing between the Paleocene and Eocene stage and substage units with the help of a biostratigraphic zonation based on planktonic organisms.

An auspicious beginning in this direction was made by the investigations of Loeblich and Tappan (1957a, b). They claimed that the Danian and Montian are time-stratigraphically equivalent and that the Paleocene should be expanded to include the Danian Stage at its base. They admit that incomplete information on the Sparnacian Stage makes it possible that the Sparnacian may represent both late Paleocene and early Eocene. This was based on their acceptance of Haynes' (1956) record of Globorotalia velascoensis (Cushman) aff. var. acuta Toulmin in the upper part of the Reculver silts (upper part of the Thanetian) which indicated to them that the Thanetian was the youngest known planktonic foraminiferal zone of the Paleocene, the Globorotalia velascoenis-acuta-spiralis Zone. Thus there appe red to be little room for the Sparnacian in the Paleocene (in the sense in which Schimper first defined it), but this appearance was illusory because Haynes' (1956) G. velasocensis aff. acuta actually is a reworked upper Campanian juvenile globotruncanid (Berggren, 1963) and Loeblich and Tappan's G. velascoensis-acuta-spiralis zone would appear to be no younger than Bolli's (1957) Globorotalia pseudomenardii Zone. Loeblich and Tappan (1957a, p. 1113) settled on the Landenian Stage for strata between the Danian and Ypresian and used the local designations as rock-stratigraphic terms (and did not relegate the Thanetian and Sparnacian to substage status as erroneously attributed to them by Berggren, 1963).

Bolli (1957) formulated a biostratigraphic zonation of the Paleocene-lower Eocene based on planktonic foraminifers. This zonation has since found widespread utility and has served as a standard of reference in the recognition of zones based on other pelagic groups, such as the nannoplankton.

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An interesting and informative discussion of the stages of the Paleocene and Eocene is given by Kaasschieter (1961). He notes that the stage names, such as those applied by Dumont, originally were conceived for rock units. Subsequently a vague facies connotation was applied to them, each stage corresponding to a cycle of sedimentation. Such a subdivision was developed in Belgium by Rutot (1883), by others in France, and later in England by the vertebrate paleontologists.

The first subdivision of the Belgium Tertiary was made by Dumont (1839) into: Landenian, Bruxellian, Tongrian, Diestian, Campanian, and Hesbayan. Later (1849) he subdivided the Landenian into Ypresian and Landenian. The Heersian was subsequently added (1851) below the Landenian. Kaasschieter (op. cit.) notes that the Limestones of Rilly with Physa gigantea and the conglomerate of Cernay with the oldest known mammalian fauna of the European Tertiary, as well as marine mollusks, probably are lateral equivalents of the Sands of Bracheux (as previously mentioned), but that they are regarded commonly as lowermost Sparnacian. This illustrates how the terms Thanetian and Sparnacian commonly have been used because of the facies of the sediments only. "As time-stratigraphic units they had bett r to be neglected" (Kaasschieter, 1961, p. 8). (Berggren 1963, p. 142, erroneously attributed to Kaasschieter the opinion to reduce Thanetian and Sparnacian to substage rank.) Kaasschieter, in contrast to most of his continental colleagues, retains the distinction between the Paleocene and Eocene; the Eocene begins with the Ypresian and in this northern region is generally thought to be characterized by the first appearance of the genus Nummulites. However, a species of Nummulites recently has been found in the type Landenian strata of Belgium by F. T. Barr and currently is undergoing study by H. Schaub.

Bramlette and Sullivan (1961) made a basic contribution to the further understanding of the Paleocene with their biostratigraphic subdivision of the Paleocene and Eocene of California by means of coccolithophorids. In the beginning, they make the pertinent observation that their biostratigraphic zones are range-zones in that they are based on "the overlap in the ranges of a considerable number of species. Few of them are apt to be restricted to the zone, and the zone is recognized primarily by the association of those species having their highest (latest) occurrence in the zone with some others having their lowest (earliest) occurrence in the zone" (1961, p. 134). Among the most significant results of this investigation we may cite the following.

(a) Biostratigraphic Unit I, the Heliolithus riedeli Zone, belongs "to that part of the Paleocene represented by the type Thanetian Stage in England" (op. cit., p. 136). "The distinctive Heliolithus riedeli and Discoaster helianthus of Unit I occur in the type Thanetian and are as yet unknown in European strata of earlier or later ages" (loc. cit.). The Heliolithus riedeli Zone occurs in the Globorotalia pseudomenardii Zone of Bolli in lower Lizard Springs strata of Trinidad.

(b) Biostratigraphic Unit II, the Discoaster multiradiatus Zone, is well developed in upper Paleocene strata of many parts of the world and its equivalence with the largely non-marine Sparnacian Stage of Europe is suggested from the following lines of evidence: many species characteristic of Unit II are found in the upper part of the Paleocene of southwestern France; these strata overlie beds with H. riedeli (Thanetian) and underlie Cuisian strata; thus the D. multiradiatus Zone in France lies in a stratigraphic position equivalent to the Sparnacian. D. multiradiatus and some of its associated species also occur in the Globorotalia velascoensis Zone of Bolli in Trinidad.

(c) Biostratigraphic Unit III, the Discoaster tribrachiatus Zone, correlates well with the Ypresian. Characteristic faunal elements were found in the London Clay and the Rosnaes Clay of Rogle Klint, Denmark. The D. tribachiatus Zone seems to be well represented in the Globorotalia aragonensis Zone of Bolli in Trinidad. The Bashi Formation of Alabama may contain the basal part of the D. tribrachiatus Zone, but it also bears a close similarity to the upper Paleocene Unit II, D. multiradiatus Zone. (Based on the occurrence in the Bashi Formation of Globorotalia rex = G. subbotinae, G. wilcoxensis, G. triplex, G. pseudotopilensis, and Pseudohastigerina eocenica = P. wilcoxensis, i.al., this formation probably is most accurately correlated with the Globorotalia rex Zone of Bolli (1957); cf Berggren, 1960.) A marked change in the fauna occurs between Units II and III.

Although Bramlette and Sullivan (1961) do not discuss the coccolithophorids of the Danian, they note that Danian faunas have much greater affinities with the Paleocene than with the Cretaceous.

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The Paleocene thus consists for these authors of Danian, Thanetian, and Sparnacian; no mention was made of Montian.

Bolli and Cita (1960a, b) have described the planktonic foraminiferal fauna of the Paleocene of the Paderno d'Adda section of Italy. Although the planktonic zonation proposed earlier by Bolli (1957) was not altered, fundamental changes in the time-stratigraphic subdivision of the Paleocene were made. The Globorotalia uncinata Zone was placed at the top of the Danian Stage s.s. Although no reason was given for this, it would appear that this was merely an accommodation, because the Globorotalia pusilla pusilla and G. pseudomenardii Zones were placed in the lower and upper Montian, respectively, based on Hofker's (1959) record of these species in the Montian of Belgium. Accepting Haynes' (1956) record of Globorotalia velascoensis acuta in the type Thanetian of England, the G. velascoens s Zone was correlated with the Thanetian Stage. However, these conclusions are considered erroneous here (see also Gohrbandt, 1963; Berggren, 1963, Barr and Berggren, 1964), as may be judged from the discussion.

Hottinger and Schaub (1960) pointed out that it has been difficult to ascertain at what place in the Paleocene the nummulites, assilinas, and alveolinids made their first appearance. As continous depositional successions in the Tethyan region have shown, this appearance and early development apparently occupied a rather considerable period of time, probably between the marine phase of the Montian and the Cuisian. The question, as the authors framed it, was with which part of the Landenian did this appearance correspond. They proposed the term Ilerdian Stage as a new stage of the Mediterranean Paleogene to include the upper part of the "Paleocene with Nummulites" and lower half of the "lower Ypresian" (op. cit., p. 457); the upper Ypresian was equated with the Cuisian s.s. But the Alve lina corbarica Zone of the type Ilerdian corresponds with the Discoaster multiradiatus Zone of Bramlette and Sullivan (1961) and the Globorotalia velascoensis Zone of Bolli (1957), and the upper Ilerdian of the Schlierenflysch in Switzerland to the Discoaster (= Marthasterites) tribrachiatus Zone (Hay and Schaub, 1960; Hay, 1962), which in turn has been correlated with the Globorotalia rex Zone (Bramlette and Sullivan, 1961). Thus the authors include strata of both Paleocene and Eocene age in their concept of the Ilerdian Stage.

It appears that the authors have confused biostratigraphic and chronostratigraphic terminology in their definition of the Ilerdian Stage and that a "stage" erected on the basis of the appearance and evolution of a specialized and strongly ecologically controlled group of foraminifers is a misinterpretation of the time-stratigraphic denotation of the term stage and will lead only to further confusion in the stratigraphic terminology of the Paleocene.

In his study of the Paleogene of the Helvetikum north of Salzburg, Austria, Gohrbandt (1963) established five zones in the Paleocene (A-E) and a basal lower Eocene one (F) based on planktonic foraminifers. By integrating data from the larger foraminifers (Papp) and nannoflora (Stradner) in this area, he was able to present some interesting conclusions with regard to the relationships of his zones to the type areas of the Paleocene stages. The Paleocene is interpreted as consisting of strata from Danian through Sparnacian; the Ypresian (Globorotalia rex Zone) is basal Eocene. Zone A, with a typical Danian planktonic fauna and a nannoflora which differed markedly from that in the underlying Maestrichtian, was correlated with the Danian Stage. Zone B, characterized by Globigerina spirali Bolli and Globigerina? uncinata (Bolli) and with a nannoflora essentially the same as that in Zone A, was placed in the Montian Stage. Gohrbandt (op. cit., p. 37) points out that, although it is difficult to substantiate the assignation of the G. uncinata Zone to the Montian Stage, a suggestion for this is found in the fact that the Oichinger beds in Zone C above contain a rich Thanetian invertebrate fauna (particularly mollusks; Traub, 1938, 1953). Because his Zones D and E above contained planktonic foraminifers reported by Haynes (1956) from the upper part of the Thanetian, Gohrbandt (op. cit., p. 38) placed his Zone C, characterized by Truncorotalia angulata angulata (White), in the lower part of the Thanetian. The nannoflora of Zones A and B continued up into Zone C. Zone D was cor elated with the Thanetian Stage based on the first appearance in it of the Truncorotalia velascoensis group (T. velascoensis occlusa). Haynes (1958) had reported G. velascoensis acuta, Globigerina pseudobulloides, and G. triloculinoides in the Thanet beds of England, but the first two have been re-identified as

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Globotruncana sp. (juvenile) and Rugoglobigerina or Globotruncana sp. ex. gr. cretacea (d'Orbigny) (Berggren, 1963) and are reworked from the upper Campanian in the vicinity. Zone D was correlated with the lower part of the Globorotalia pseudomenardii Zone of Bolli (1957a). Further support of the correlation of Zone D with the Thanetian was offered in the form of the first appearance in Zone D of Fasciculithus involutus Bramlette and Sullivan; this species was also cited by its authors in the type Thanetian in their Heliolithus riedeli Zone. It will be recalled that Bramlette and Sullivan (1961) considered the H. riedeli Zone to be restricted to the Thanetian Stage. Zone E was subdivided informally into two parts: a lower part without Nummulites and an upper part with Nummulites. The lanktonic foraminiferal fauna continued unmodified through the zone, but a moderate change in the nannoflora was noted at the boundary denoting the appearance of the nummulitids. Zone E was shown to be characterized by the appearance of Globorotalia pseudomenardii. Heliolithus riedeli and Discoaster gemmeus appeared for the first time in Zone E, and thus the lower part of Zone E was correlated with the H. riedeli Zone (= Unit 1) of Bramlette and Sullivan (1961) and the upper part of the Thanetian Stage. The upper part of Zone E is characterized by the first appearance of nummulites (Nummulites nitidus nitidus, N. fraasi, N. cf. fraasi) in the deeper part of the facies equivalent of the Lithothamnium limestone. This lower part of the Zone E was correlated with the lower Ilerdian of Hottin er and Schaub (1960). The upper part of Zone E was correlated with the middle Ilerdian on the basis of Hay's (1962) demonstration that Discoaster multiradiatus occurs in the stratotype of the Ilerdian in the Alveolina corbarica Zone (middle Ilerdian); D. multiradiatus also occurs in the upper part of Zone E. Zone F (characterized by Globorotalia rex and the appearance of Discoaster tribrachiatus) was correlated with the basal part of Unit 3 of Bramlette and Sullivan (1961) and the Cuisian Stage (lower Eocene). Although it was realized that the nannoflora of Zone F was similar to that in the upper Ilerdian (upper Paleocene of Hottinger and Schaub, 1960), the subdivision based on planktonic foraminifers was taken as definitive in assigning Zone E to the lowermost Eocene.

Thus we see that there is positive evidence for considering that the Thanetian is approximately equivalent to the Globorotalia pusilla pusilla (or G. angulata) Zone and the lower half of the Globorotalia pseudomenardii Zone. The Sparnacian is approximately equivalent to the upper half of the Globorotalia pseudomenardii Zone and the G. velascoensis Zone.

The planktonic foraminiferal fauna of the type Thanet beds has recently been described by Barr and Berggren (1964) and the essentially similar planktonic foraminiferal fauna of the type Landenian currently is under investigation. Luterbacher and Premoli Silva (1964) have recently made a detailed study of the planktonic Foraminifera at the Cretaceous = Tertiary boundary in the central Appennines, Italy. A new biostratigraphic unit, the Globigerina eugubina Zone, was defined and described. It was said to lie directly above the uppermost Cretaceous (Maestrichtian), to be characterized by Globigerina fringa Subbotina, G. sabina n. sp., G. minutula n. sp., G. umbrica n. sp., G. anconitana n. sp., and G. eugubina n. sp., and to correspond to the time-stratigraphic interval between the Stevn ian and Danian in southern Scandinavia, i.e., to the lowermost Danian. It was shown to be questionably older than Zone I (Globigerina (Eoglobigerina) taurica) in the Danian of the southwestern Crimea which Morozova (1960, 1961) considered to be the oldest Danian yet recorded. Their Globigerina pseudobulloides/G. daubjergensis Zone above was correlated with the major part of the G. (E.) taurica Zone of the southwestern Crimea, the G. pseudobulloides/G. daubjergensis Zone of Leonov and Alimarina (1962), and the major part of the type Danian; the G. eugubina and G. pseudobulloides/G. daubjergensis Zones were correlated questionably with the Rzehakina epigona Zone of Bolli (1957a).

The G. trinidadensis Zone above was correlated with its name-sake in Trinidad, the lower part of the Zone of rotaliid-like globorotaliids in the northern Caucasus (Subbotina, 1953), the lower part of the G. inconstans/G. angulata Zone of Leonov and Alimarina (1962), and the upper half of Zone II (G. (G.) microcellulosa) and lower half Zone III (G. daubjergensis/A. schachdagica Zone) of the southwestern Crimea (Morozova, 1960, 1961).

The recognition of two distinct units, the G. trinidadensis and G. pseudobulloides/G. daubjergensis Zones in succession within the Danian, appears questionable to this writer. All three species

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characterize the Danian in the Tethyan region and the G. trinidadensis Zone of Trinidad and the Tethyan areas can be correlated with the G. pseudobulloides/G. daubjergensis Zone of the boreal regions. The G. uncinata Zone would appear correlatable with the upper Montian (Calcaire de Mons, Montian s. str.) (see Moskvin and Naidin, 1960; Berggren, 1963, 1964, 1965).

The occurrence of the G. eugubina Zone, if correct, is an important link in the understanding of the development of planktonic foraminiferal faunas at the Cretaceous-Tertiary boundary. It would enable a revision of the concept of the Danian Stage by a lowering of its base. However, this writer retains some reservations for the moment. The specimens illustrated by Luterbacher and Premoli Silva (1964) apparently are fairly poorly preserved. The definitive morphologic characters of the test are not described in detail. Indeed the extremely small size of the material would appear to preclude this. There would appear to be some resemblance of some of the illustrated forms to Upper Cretaceous (Maestrichtian) elements. For instance, Globigerina umbrica n. sp. (op. cit., pl. 2, Figs. 2a-c) be rs a resemblance to Rugoglobigerina hexacamerata Bronnimann (= R. pennyi Bronnimann) and might well be a juvenile specimen. Globigerina anconitana n. sp. (op. cit., pl. 2, Figs. 3a-c) resembles Rugoglobigerina pustulata Bronnimann. If the material covering the umbilici in these two species (G. umbrica and G. anconitana) is not a true tegillum, specimens with open umbilici should have been more appropriately chosen as holotypes.

Globigerina minutula n. sp. (op. cit., pl. 2, Figs. 5a-c) bears a resemblance to both Globoconusa daubjergensis (Bronnimann) and Rugoglobigerina macrocephala, and could be a juvenile specimen of either.

The thin section of a planispiral form (op. cit., pl. 2, Fig. F) is suggestive of Globigerinelloides; no planispiral planktonic species is known in the Tertiary until the lower Eocene (Globanomalina wilcoxensis (Cushman and Ponton) = Pseudohastigerina eocenica (Berggren)).

It may be that these illustrated forms are juveniles whose definitive morphologic characters have not yet developed. Juvenile similarity and morphologic overlap are common features among different genera of planktonic foraminifers. The taxonomic implications are far-reaching. Globigerina eugubina n. sp. (op. cit., pl. 2, Figs. 8a-c) bears a resemblance to Hedbergella monmouthensis Olsson. In the absence of an opportunity to make direct comparison with type material, this writer would only caution that the Cretaceous-Tertiary boundary is fraught with problems in regard to the nature of the planktonic foraminiferal fauna. The Globigerina eugubina Zone may well be a significant biostratigraphic entity (cf. Lehmann, 1964), but it may actually contain a mixed (i.e., transitional) fauna wit both Maestrichtian and Danian faunal elements in a stratigraphic interval which straddles the Maestrichtian-Danian boundary as is now recognized. It is also possible that the minute forms which characterize this stratigraphic level also could be an upper Maestrichtian stratigraphic condensate as a result of winnowing action by weak currents.

UPPER PALEOCENE STRATIGRAPHIC NOMENCLATURE AND PALEOCENE-EOCENE BOUNDARY

It is apparent from the foregoing summary that the various stage names of the upper Paleocene have been used in a variety of ways, e.g., as chronostratigraphic units and as lithostratigraphic (facies) units within cycles of sedimentation. In view of the previous discussion there appear to be two problems, inextricably linked together, which should be considered. The problems involve: (a) usage or abandonment of terms Landenian, Sparnacian, and Thanetian and (b) the placement of the Paleocene-Eocene boundary. A discussion of several alternatives and some informal recommendations follow.

With regard to problem (a), three alternatives appear possible: (1) abandonment of the term Landenian and substitution of Thanetian and Sparnacian with stage rank; (2) retention of the Landenian Stage to comprise the time-stratigraphic interval between Dano-Montian and Ypresian, and elimination of Thanetian and Sparnacian as chronostratigraphic units (Loeblich and Tappan, 1957a, b; Kaasschieter, 1961); and (3) retention of the Landenian Stage as comprising the time-stratigraphic interval between Dano-Montian and Ypresian and the Thanetian and Sparnacian as lower and upper substage units respectively (Haynes, 1956).

Because the Thanetian and Sparnacian generally have been used to denote marine and non-marine facies, respectively (although both actually have corresponding non-marine and marine

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counterparts), their elevation to stage rank appears unwise. The difficulty of accurate correlation of the type strata with the standard planktonic foraminiferal zonation makes the determination of chronostratigraphic limits between the two units difficult. Thus, the first alternative is regarded as unsatisfactory. The elimination of the Thanetian and Sparnacian as chronostratigraphic units (alternative 2) and the retention of the term Landenian can be defended. The time-stratigraphic interval represented by the Landenian is large enough to allow a detailed biostratigraphic subdivision based on distinct evolutionary changes in planktonic foraminifers, coccoliths, discoasterids, and other groups. The upper and lower time-stratigraphic limits of the Landenian Stage can be determined wit a reasonable degree of accuracy and recognized outside of the type area. However, in view of the usefulness of the terms Thanetian and Sparnacian in the type areas as well as in western Europe in general, their complete elimination as time-stratigraphic units would appear unwise. This brings up alternative 3; it is recommended that the Landenian be considered to comprise all strata between the Dano-Montian and Ypresian with the Thanetian and Sparnacian as lower and upper substages of the Landenian.

Several alternatives also are possible regarding the question of the position of the Paleocene-Eocene boundary: (1) abandonment of term Paleocene and replacement of time-stratigraphic interval represented by Danian-Ypresian by lower Eocene (Mangin, 1957); (2) placing boundary between Thanetian and Sparnacian; and (3) placing boundary between Sparnacian and Ypresian.

The term "lower Eocene" is a vague term when used in the sense suggested by Mangin (1957). It would nullify the really significant evolutionary changes which take place within various fossil groups (not the least among them the planktonic forms) which make possible a time-substratigraphic subdivision of a higher order (epoch-series). The term "Paleocene" is a very useful one from the paleontologic point of view, and it is, in the last analysis, on evolutionary changes in fossil faunas that chronostratigraphic subdivision of earth history is based. Further, the use of "lower Eocene" in this sense gives it a connotation far out of proportion to the Eocene as a whole.

Emplacement of the Paleocene-Eocene boundary between the Thanetian and Sparnacian has been advocated for many years by vertebrate paleontologists because of the Eocene affinities of the Sparnacian vertebrate faunas (Hyracotherium-Coryphodon fauna). This is not Schimper's (1874) original definition, which includes the Sparnacian strata in his definition of Paleocene. If it is granted, for sake of argument, that there is a significant change in the vertebrate mammalian fauna between the Thanetian and Sparnacian, it must nevertheless be borne in mind that this is the evidence from but one discipline. Few would argue that the biostratigraphic and chronostratigraphic subdivision of the geologic column, on the basis of marine invertebrate faunas (particularly planktonic and nektonic forms), does not provide recognition of more finely and subtly defined intervals of time and allows more satisfactory accurate intercontinental stratigraphic correlation of smaller time-stratigraphic and biostratigraphic units than do vertebrate faunas. Although continuous stratigraphic sections across the Sparnacian-Ypresian boundary (the Globorotalia velascoensis and G. rex Zones of Bolli) in various parts of the world reveal a gradual transition in the planktonic foraminiferal fauna, the appearance of several new species, as well as the genus Pseudohastigerina, is considered significant, as is the marked change in the nannoflora; this brings us back to Schimper's original definition of the Paleocene.

Schimper (1874) included beds of Sparnacian age in his original definition of Paleocene, admittedly on rather weakly documented paleontologic grounds. But invertebrate paleontologists can muster as many arguments in favor of retaining the Paleocene-Eocene boundary above the Sparnacian as vertebrate paleontologists can for drawing it at the base of the Sparnacian. If a body of scientifically informed opinion wishes to change the customarily accepted Paleocene-Eocene boundary, let the evidence be submitted, considered dispassionately, and weighed against evidence from other fields. Discussion, eventual legislation, and execution can be performed through the official channels of an international subcommission on stratigraphic nomenclature. The burden of disproof appears to rest on the ve tebrate paleontologists.

References:

Barr, F. T., and Berggren, W. A., 1964, Lower Tertiary planktonic Foraminifera from the Thanet Formation of Kent, England: XXII Internatl. Geol. Cong. (New Delhi) (in press).

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Berggren, W. A., 1963, Some problems of Paleocene stratigraphic correlation: Rev. Inst. Franc. Petrole, v. 18, no. 10, p. 134-143, 2 figs., Paris.

Berggren, W. A., 1964, The Maestrichtian, Danian and Montian Stages and the Cretaceous-Tertiary boundary: Stockholm Contr. Geol., v. 11, no. 5, p. 103-176.

Berggren, W. A., 1965, The recognition of the Globorotalia uncinata Zone (lower Paleocene) in the Gulf Coast: Micropaleontology, v. 11, no. 1, p. 111-113.

Bolli, H. M., 1957a, The genera Globigerina and Globorotalia in the Paleocene-lower Eocene Lizard Springs Formation of Trinidad, B.W.I.: U. S. Natl. Mus. Bull. 215, p. 61-81, pls. 15-20.

Bolli, H. M., 1957b, Planktonic Forminifera from the Oligocene-Miocene Cipero and Lengua Formations of Trinidad, B.W.I.: U. S. Natl. Mus. Bull. 215, p. 97-123, pls. 17-21.

Bolli, H. M., 1960a, Upper Cretaceous and lower Tertiary planktonic Foraminifera from the Paderno d'Adda section, northern Italy: XXI Internatl. Geol. Cong., pt. 5, sect. 5, p. 15-161, 3 figs., Copenhagen.

Bolli, H. M., 1960b, and Cita, M. B., 1960a, Globigerine e Globorotalie del paleocene di Paderno d'Addo (Italia): Riv. Ital. Paleont., v. 66, no. 3, p. 361-402, 3 pls., Milan.

Bramlette, M. N., and Sullivan, F. R., 1961, Coccolithophoroids and related nannoplankton of the early Tertiary in California: Micropaleontology, v. 7, no. 2, p. 129-180, 1 fig.

Brotzen, F., 1948, The Swedish Paleocene and its foraminiferal fauna: Sver. Geol. Unders., ser. C, no. 493 (Arsb. 4, 1948), 140 p., 19 pls., 41 figs., Stockholm.

Cole, W. S., 1963, Illustrations of conflicting interpretations of the biology and classification of certain larger Foraminifera: Bull. Am. Pal., v. 46, no. 205, 157-185, 14 pls.

Dollfus, G., 1880, Terrains tertiares dans le bassin anglo-parisien: Bull. Soc. Geol. Normandi, p. 55.

Drooger, C. W., 1956, Transatlantic correlation of the Oligo-Miocene by means of Foraminifera: Micropaleontology, v. 2, no. 2, p. 183-192, 1 pl., 1 fig.

Dumont, A., 1839, Rapport sur les travaux de la carte geologique en 1839, avec une carte geologique des environs de Bruxelles: Bull. Acad. R. Belg., v. 6, pt. 2, p. 464-485, Brussels.

Dumont, A., 1849, Rapport sur la carte geologique de la Belgique: ibid., v. 16, pt. 2, p. 351-373.

Eames, F. E., 1953, The Miocene/Oligocene boundary and the use of the term Aquitanian: Geol. Mag., v. XC, no. 6, p. 388-392, London.

Eames, F. E., et al., 1962, Fundamentals of mid-Tertiary stratigraphical correlation: Cambridge Univ. Press, 163 p., 17 pls.

Gartner, S., and Hay, W. W., 1962, Planktonic Foraminifera from the type Ilerdian: Eclogae Geol. Helv., v. 55, no. 2, p. 553-572, 2 pls.

Gohrbandt, K., 1963, Zur Gliederung des Palaogen im Helvetikum nordlich Salzburg nach planktonischen Foraminiferen. Erste Teil, Paleozan und tiefstes Untereozan mit Beitragen von Adolf Papp (Grossforaminiferen) und Herbert Stradner (Nannofloren): Mitt. geol. Ges., Wien, Band 55, Heft 1, 116 p., 11 pls., 1 chart.

Hay, W. W., 1962, Zonation of the Paleocene and lower Eocene utilizing discoasterids: Colloque Paleogene, Bordeaux, 4 p. (Pre-print).

Hay, W. W., and Schaub, H. H., 1960, Discoasterids from the Schlierenflysch, Switzerland (abs.): Geol. Soc. America Bull., v. 71, p. 1885.

Haynes, J., 1955, Pelagic Foraminifera in the Thanet beds and the use of Thanetian as a stage name: Micropaleontology, v. 1, no. 2, p. 189.

Haynes, J., 1956, Certain smaller British Paleocene Foraminifera. Part I. Nonionidae, Chilostomellidae, Epistominidae, Discorbidae, Amphistegenidae, Globigerinidae, Globorotaliidae, and Gumbelinidae: Contr. Cushman Found. Foram. Research, v. 7, pt. 3, p. 79-101, pls. 16-18, text-figs. 1, 2.

Haynes, J., 1958, Certain smaller British Paleocene Foraminifera, Part V. Distribution: Contr. Cushman Found. Foram. Research, v. 9, pt. 4, p. 83-92, 1 chart.

Hofker, J., 1959, Arguments for a lower Paleocene age of the section above the upper Md in the Quarry of Curfs, near Houthem: Natuurhist. Maandblad, anno 48°, n. 1-2, p. 18-30, figs. 1-5.

Hottinger, L., and Schaub, H., 1960, Zur Stufenteilung des Paleocaens und des Eocaens. Einfuhrung des Ilerdien und des Biarritzien: Eclogae Geol. Helv., v. 53, p. 454-479.

Kaasschieter, J. P. H., 1961, Foraminifera of the Eocene of Belgium: Inst. Roy. Sci. Nat. de Belgique, mem. 147, 271 p., 16 pls.

Koenen, A. von, 1885, Uber eine palaocane Fauna von Kopenhagen: Abh. kgl. Ges. Wiss., v. 32, Gottingen.

Lehmann, E. P., 1964, Tertiary-Cretaceous boundary facies in the Sirte basin, Libya: XXII Internatl. Geol. Congress (New Delhi) (in press).

Leonov, G. P., and Alimarina, V. P., 1961, Problema V. Granitsa melovoi i paleogenovoi sistem: Sb. Trudov geol. fak. MGU, p. 29, 7 pls., Moscow.

Lex. Strat. Internat., v. 1, Europe (P. Provost, director), fasc. 4a VII, Tertiare, 217 p.

Loeblich, A. R., Jr., and Tappan, H., 1957a, Correlation of the Gulf and Atlantic Coastal Plain Paleocene and lower Eocene formations by means of planktonic Foraminifera: Jour. Paleontology, v. 31, no. 6, p. 1109-1136.

Loeblich, A. R., Jr., and Tappan, H., 1957b, Planktonic Foraminifera of Paleocene and early Eocene age from the Gulf and Atlantic Coastal Plains: U. S. Natl. Mus. Bull. 215, p. 173-198, pls. 40-64.

Luterbacher, H. P., and Premoli Silva, I., 1964, Biostratigrafia del limite Cretaceo-Terziario nell'appennino centrale: Riv. Ital. Paleont., v. LXX, no. 1, p. 67-128, pl. 2-7, Milan.

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Prestwich, J., 1852, On the structure of the strata between the London Clay and the Chalk in London and Hampshire Tertiary systems: Part III, Thanet Sands:

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Yanshin, A. L., 1953, Nekotorye voprosy stratigraficheskogo raschleneniya i stratigraficheskoi nomenklatury paleogenovykh otlozhenii (Some problems of stratigraphical subdivision and stratigraphical nomenclature of Paleogene deposits), in Geologiya severnogo Priaraliya (Geology of northern Aral-Land): Press of Moscow Society of Naturalists, Moscow, p. 180-243.

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Acknowledgments:

(2) Oasis Oil Company of Libya, Inc. Published with permission of Oasis Oil Company.

Copyright 1997 American Association of Petroleum Geologists

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