- © The Mineralogical Society
Clay mineral associations of Palaeocene and Eocene age, with special attention to the late Palaeocene thermal maximum, have been examined in ten sections from the Tethys (Egypt, Israel, Tunisia, Spain and Kazakhstan) and Atlantic (England). A widespread abundance of kaolinite in marine sediments at all locations suggests a warm and humid climate with high rainfall in the Tethys region during the early Palaeocene. In the coastal basins along the southern margin (Israel and southern Tunisia), kaolinite disappears gradually giving way to palygorskite and sepiolite, suggesting the progressive development of arid climatic conditions in this part of the Tethys from the late Palaeocene to the early Eocene. Remarkably, kaolinite increases strongly throughout most of the Tethys during the late Palaeocene thermal maximum (LPTM) reflecting an episode of humidity and warmth and coincident with a global maximum warmth of seawaters inferred from oxygen isotopic data.
Beginning during the late Palaeocene, a climate-warming trend culminated at the end of the Palaeocene epoch (referred to as the late Palaeocene thermal maximum or LPTM) (e.g. Zachos et al., 1993), which was probably the warmest period of the entire Cenozoic. During this period, oceanic deep waters and high-latitude surface waters warmed worldwide by 6 to 8°C. Coincident with the warm pulse was an abrupt negative δ13C isotopic excursion (e.g. Kennett & Stott, 1991), the presence of sub-tropical to temperate faunas and floras in subpolar regions of both hemispheres (e.g. Estes & Hutchison, 1980; Wolfe, 1980), a dramatic extinction of deep-sea benthic foraminifera (e.g. Thomas, 1990) and a radiation of planktonic foraminifera (e.g. Lu & Keller, 1995; Pardo et al., 1999) and terrestrial vertebrates and plants (e.g. Gingerich, 1980).
During the LPTM, the abundance of kaolinite in oceanic sediments indicates a time of high humidity with enhanced chemical weathering in the South Atlantic and Antarctica (Robert & Chamley, 1991; Robert & Kennett, 1992, 1994) and in New Zealand (Kaiho et al., 1996). Such a period of warming and increased precipitation has also been interpreted in the Central North Sea (Knox, 1996), the New Jersey continental margin (Gibson et al., 1993), northern Spain (Gawenda et al., 1999), southern Spain (Lu et al., 1998) and northern Tunisia (Bolle et al., 1999). In contrast, from the late Palaeocene to the early Eocene, low latitudes experienced intensive aridity and evaporation, especially in the coastal areas from West and North Africa and the Arabian Peninsula (Robert, 1982; Robert & Chamley, 1991; Oberhänsli, 1992; Bolle et al., 1999). However, humid conditions may have prevailed on the continental hinterland, as suggested by laterization processes and the presence of bauxite on the African craton (Millot, 1970; Hendricks et al., 1990; Strouhal, 1993).
The purpose of this paper is to synthesize information gained from studies of clay mineral associations, from lower latitudes (12°) to higher latitudes (39°) in the Tethys (Egypt to Kazakhstan, Fig. 1⇓), and to increase the knowledge of climate evolution not only during the LPTM but also during the periods preceding and following this remarkable short-term (~50,000 years) climatic warm pulse. This synthesis is based mainly on sections detailed in Bolle (1999) and complemented by clay mineral data from sections studied by Adatte & Lu (1995), Lu et al.(1998), Gawenda et al.(1999), Bolle et al.(1999), Adatte et al.(2000). Clay mineral data from two English sections located in the Atlantic Realm at about the same latitude as Kazakhstan (Bolle, 1999) are also presented.
Ten sections located in Spain (Lu et al., 1998; Gawenda et al., 1999; Adatte & Lu, 1995; Adatte et al., 2000), Tunisia (Bolle et al., 1999), Israel, Egypt, Kazakhstan and England (Bolle, 1999) were considered for this synthesis. Planktonic foraminiferal and nanofossil biostratigraphy in these sections are based on the revised zonation by Berggren et al.(1995), modified by Pardo et al.(1999) and Martini (1971). X-ray diffraction (XRD) analyses of 1500 clay mineral samples were conducted at the Geological Institute of the University of Neuchâtel, Switzerland, using a SCINTAG XRD 2000 Diffractometer with standard errors varying between 5 and 10%. Clay mineral analyses followed the analytical method of Kübler (1987) described in Adatte et al.(1996). We present here data from the <2 μm fraction. Clay minerals are given in relative percent abundance and the kaolinite/smectite index is calculated from the ratio of the 001 kaolinite (7 Å) and smectite (16.9 Å) peaks, measured on the X-ray pattern obtained after saturation with ethylene glycol.
At Gebel Duwi, smectite (62%) and kaolinite (31%) dominate the clay mineral fraction in the first 8 m (Subzone P4c, Fig. 2a⇓). Illite, chlorite and palygorskite are minor components. The onset of the LPTM event is marked by a high kaolinite/smectite ratio (>1; Fig. 3⇓); the increase in kaolinite to 58% coincides with a decrease in smectite to a mean value of 28%. In the uppermost 8 m, kaolinite averages 70% whereas smectite, illite and chlorite decrease to 22%, 4% and 3% respectively.
At Ben Gurion, kaolinite (50%) and smectite (42%) in the lowermost 11 m dominate the clay mineral fraction (Subzones P1b to P2, Fig. 2a⇑). Between 11 and 22 m, kaolinite disappears gradually (Figs 2a⇑, 3⇑). This decrease coincides with a gradual increase in smectite (40 to 60%), illite (3 to 6%) and palygorskite (1 to 8%). Between 22 and 39 m, palygorskite increases to 35% and sepiolite is found at the base of Zone P4 (Fig. 2⇑). Smectite (49%), illite (14%) and chlorite (4%) complete this clay mineral association. Between 39 and 49 m, smectite increases to reach a maximum of 85% above the LPTM interval (Subzone P6a; Fig. 2a⇑). This increase coincides with a general decrease in other minerals (illite, chlorite, palygorskite and sepiolite). In the uppermost 6 m, smectite decreases to 50%, coincident with increased palygorskite from 10 to 40%.
At Foum Selja (southern Tunisia), kaolinite is the major component in the first 15 m (60%, Fig. 2a⇑). The dramatic decrease in kaolinite coincides with an increase in smectite (34 to 75%) and illite (20 to 50%). The NP4/5 to NP9 interval is characterized by large amounts of smectite (37% to 95%) and the occurrence of palygorskite and sepiolite (2 to 40%). In the uppermost 10 m (Zone NP10) palygorskite reaches a peak abundance of 60% and smectite decreases. At Elles (northern Tunisia), in the Zone P4b/c interval, smectite is the major component, averaging 76% (Fig. 2a⇑). Kaolinite (11%), illite (9%) and chlorite (4%) are minor components. The lower part of Zone P5 is marked by increased kaolinite, with maximum values (50%) reached during the LPTM (Figs 2a⇑, 3⇑). The upper part of Zone P5 (22–28 m) and lower part of Zone P6a lack kaolinite. Its absence corresponds with an increase in smectite to 92% and illite from 4 to 7%.
At Alamedilla (southern Spain), smectite (75%) is the major component in the lower 12 m (part of Zone P5, Fig. 2a⇑). Kaolinite (10%), illite (12%) and palygorskite (3%) complete the clay mineral association in this interval. The onset of the LPTM is marked by an increase in kaolinite to a maximum of 33% (Fig. 2a⇑). The rapid decrease in kaolinite to 5% during the LPTM coincides with a strong increase in palygorskite to 40% and illite from 7 to 45%. In the upper 14 m (Subzones P6a and P6b), palygorskite and smectite dominate the clay mineral fraction, with values varying from 5% to 50% and from 26% to 84% respectively. At Zumaia (northern Spain), illite, chlorite and smectite are present in varying proportions in the entire section (Fig. 2b⇑) and reach ~40–100% of the clay mineral fraction. Kaolinite is present at two distinct periods, in the early Palaeocene and in the latest Palaeocene to earliest Eocene (Gawenda et al., 1999). The LPTM interval (NP9-NP10) is marked by a high kaolinite/smectite ratio (Fig. 3⇑) which corresponds to a strong increase in kaolinite up to 75% (Fig. 2b⇑). From NP11 upwards, illite and chlorite dominate the clay mineral fraction whereas kaolinite only sporadically exceeds 2%.
At Kaurtakapy, smectite (55%) dominates the clay fraction in the lower 18 m (Zones P4 to P6a) and decreases to 0% in P6b (Fig. 2b⇑). This decrease coincides with increased illite and chlorite contents up to 65% and 20% respectively. Kaolinite is sporadically present in the first 15 m (P4 to P5b), increases gradually in P6a (2%) and reaches a maximum of 10% in P6b. Irregular mixed-layered illitesmectite is a minor component (3%) throughout the profile (Fig. 2b⇑).
At Herne Bay (southeastern England), smectite (52%) and illite (34%) dominate the clay mineral fraction in the entire section (NP9 and NP10; Fig. 2b⇑). Kaolinite is sparse in the first 15 m (4%) and increases gradually to reach a maximum value of 18% in NP10 (Fig. 2b⇑). Chlorite is present throughout the section, varying between 3.8 and 20%. At Alum Bay (southern England), NP9 (Thanet Formation), the lower part of NP10 (Woolwich and Reading Formation) and the middle part of NP10 (London Clay Formation, divisions 1 and 2) intervals are missing (Fig. 2⇑). The upper part of NP10 is marked by the dominance of kaolinite (41%) and illite (44%). Smectite and chlorite are minor components, averaging 7 and 8% respectively.
SIGNIFICANCE OF THECLAY MINERALS
Clay minerals and their relative abundance may record information on climate, eustasy, burial diagenesis, or reworking.
The thickness of the Tertiary deposits within the Tethyan sections does not exceed 1500 m, indicating that sediments did not suffer deep burial diagenesis. Actually, modifications affecting clay minerals usually occur at burial depths exceeding 2 km (Chamley, 1998). This low diagenetic overprint due to burial throughout the sections is documented by the following: (1) the constant but variable presence of smectite; (2) the co-existence of smectite with high kaolinite content in some sections and with palygorskite and sepiolite in other sections; and (3) the scarcity of mixed-layered illitesmectite. This clay mineral assemblage corresponds roughly to zones 1 and 2 defined by Kübler et al.(1979).
Despite the absence of a deep burial, it has been demonstrated convincingly that clay minerals, typically kaolinite, can crystallize diagenetically in permeable sandstone (Weaver, 1989; Chamley, 1998) and also, but more rarely, in some mudrocks (Weaver, 1989). However, the sections studied here consist mainly of marls and shales, in particular in the LPTM where the maximum level of kaolinite was observed. Although we cannot completely exclude a diagenetic origin for at least part of the kaolinite, it would be difficult to explain the large amounts of this clay mineral observed worldwide during the LPTM as resulting from diagenetic recrystallization only, a mechanism which is rare in shales and marls (Weaver, 1989; Chamley, 1998).
In this study, detrital input is the dominant factor responsible for the clay mineral distribution in marine sediments. Illite, chlorite, associated quartz and feldspars typically constitute terrigenous species (Chamley, 1998). These clay minerals develop generally in areas of steep relief where active mechanical erosion limits soil formation, particularly during periods of enhanced tectonic activity (Millot, 1970; Chamley, 1998). They can also form in cold and/or desert regions where low temperatures and/or low rainfall reduce the chemical weathering (Millot, 1970; Chamley, 1998).
Palygorskite and sepiolite have been observed in southern Tunisia (Bolle et al., 1999), southern Spain (Lu et al., 1998; Adatte et al., 2000) and in Israel (Bolle, 1999). These two fibrous clay minerals may have three main origins. (1) They can form in situ as a result of hydrothermal weathering of Mg-bearing rocks, especially those of volcanic origin combined with the influence of seawater (Karpoff et al., 1989; Hillier, 1995). However, no hydrothermal activity has been reported at the southern margin of the Tethys which was relatively stable from the late Palaeocene to the early Eocene (Oberhänsli, 1992; Charisi & Schmitz, 1995). (2) Palygorskite may also form along coastal and peri-marine environments where continental alkaline waters are concentrated by evaporation, leading to solutions enriched in Si and Mg which favour the formation of palygorskite and/or smectite (Millot, 1970; Robert & Chamley, 1991; Pletsch, 1996). This process of authigenic neoformation by chemical precipitation is accelerated in warmer temperature zones (Millot, 1 970; Ch amley, 1989). (3) Palygorskite and, to a much lesser extent, sepiolite are frequently found on land in calcrete soils in arid to semi-arid climatic zones (Chamley, 1989; Robert & Chamley, 1991). It is difficult to determine the origin (continental or marine) of the palygorskite and sepiolite observed in southern Spain, southern Tunisia and in Israel (Fig. 2⇑). The existence of shallow Palaeogene restricted basins between emerged land areas in Tunisia (Bolle et al., 1999) and in the Negev area (Arkin et al., 1972), favourable to the neoformation of palygorskite and sepiolite, suggests that most of the fibrous clay minerals present in this part of the Tethys could have been formed in these coastal basins (Bolle, 1999). However, for suggested origins 2 and 3 of palygorskite and sepiolite, warm and arid climatic conditions are required to form the two fibrous clay minerals. Thus, in the different sections (Lu et al., 1998; Bolle et al., 1999; Bolle, 1999; Adatte et al., 2000), the presence of palygorskite and sepiolite has been considered as an indicator of aridity.
Although smectites can form locally in deep sea from the hydrothermal weathering of volcanic rocks (Karpoff et al., 1989; Chamley, 1998), the Palaeogene smectites are not considered to result from this process in this study. Actually, as noted previously, it has been shown that the southern margin of the Tethys corresponded to a relatively stable period, with no hydrothermal or volcanic activity (Oberhänsli, 1992; Charisi & Schmitz, 1995). Moreover, no volcanoclastic components were observed throughout the sedimentary columns of the sections presented here (Bolle, 1999). Thus, this clay mineral appears to be mostly of detrital origin and can issue from soils developed under a warm to temperate climate characterized by alternating humid and dry seasons (Chamley, 1998).
In Antarctica, as in the South and North Atlantic (see introduction for references), the LPTM is marked by the appearance, or a significant increase in, kaolinite. This greater kaolinite content, coincident with the warm pulse and the negative δ13C excursion, has been interpreted as marker of humidity. Kaolinite typically develops in tropical soils which are characterized by warm, humid climates, well-drained areas with high precipitation and accelerated leaching of parent rocks (Robert and Chamley, 1991). However, increased kaolinite may result from increased erosion, which could be caused by sea-level falls (Robert & Kennett, 1994). This clay mineral may also be introduced in significant amounts into oceanic sediments through erosion of older sediments and soils during sea-level transgressions (Thiry, 1989; Chamley, 1998). However, the deposition of kaolinite and its disappearance in southern Tunisia (Bolle et al., 1999) and in Israel (Figs 2a⇑, 3⇑; Bolle, 1999) during the early Palaeocene coincide with a period of relatively stable high sealevel (Haq et al., 1988). During the global sea-level transgression which took place at the end of the Palaeocene, the absence of kaolinite at Foum Selja (southern Tunisia) and the abundance of this clay mineral at Elles (northern Tunisia; Fig. 2a⇑) show no correlation between variations in the abundance of kaolinite and in sea-level fluctuations during the period of time studied. This suggests that kaolinite records regional qualitative climatic changes and not erosion due to sea-level fluctuations. Thus, the kaolinite/smectite index shown in Fig. 3⇑ is considered as reflecting climate variations from humid/warm to more seasonal conditions.
CLIMATICEVOLUTION IN THE TETHYSREGION
During the early Palaeocene (Zones P1 to P3), the adjacent coastal and continental areas of the southern and southeastern Tethys margins (Tunisia, Israel and Egypt) were influenced by a warm and humid climate with high rainfall as indicated by the abundance of kaolinite in deep-sea sediments of this region (Fig. 2a⇑). Abundant kaolinite suggests perennial rainfall and minimum soil temperatures of 15°C during at least part of the year (Robert & Kennett, 1994). Southern (Adatte et al., 2000) and northern Spain (Gawenda et al., 1999) experienced similar humid climatic conditions during the same period of time as suggested by the high kaolinite content (>50%) observed in the sediments of the Spanish sections (Gawenda et al., 1999; Adatte et al., 2000). This climatic trend is in agreement with the generally humid and warm climate that marked the end of the Cretaceous and the early Danian (P1a to P1c) in the southern Tethys region (Arkin et al., 1972; Keller et al., 1998). From the late Cretaceous to the late Palaeocene (mid-Zone P3), the climate appears to have been relatively uniform in the Tethys region with the dominance of warm, perennially wet conditions which favoured intensive leaching of the parent rocks and formation of kaolinitic soils (Fig. 4⇓).
From the late Palaeocene (mid-Zone P3) to the early Eocene (Zone P6), the different areas of the Tethys were marked by different clay mineral patterns which suggest climatic variations (Fig. 2a,b⇑). In southern Tunisia and in the Negev area (Israel) the gradual disappearance of kaolinite coincident with the gradual increase in smectite, palygorskite and sepiolite, as well as illite and chlorite, suggests the progressive development of aridity in the coastal basins or peri-marine environments of the southeastern margin of the Tethys and on the Saharan Platform. In the Negev, kaolinite disappeared in the middle of Zone P3 whereas palygorskite and sepiolite increased markedly. At Foum Selja (southern Tunisia) kaolinite disappeared at approximately the same period of time (Fig. 2a⇑; Bolle et al., 1999). This simultaneous disappearance of kaolinite in sections located at about the same palaeolatitude (~20°N), but separated by more than 2700 km suggests a latitudinal change from humid and warm to more arid climatic conditions (Fig. 4⇑). In the coastal basins of the Negev area, these arid climatic conditions were already initiated in the Danian (based on Zone P2) and developed largely in the Selandian (middle of Zone P3) whereas in southern Tunisia, arid climatic conditions dominated later in Zone NP6 (Zone P4). In both regions, aridity persisted through the late Palaeocene reaching a maximum in the early Ypresian (NP10) as indicated by high palygorskitesepiolite content observed at Foum Selja (Bolle et al., 1999) and at Ben Gurion (Bolle, 1999). These arid climatic conditions inferred from the distribution of the clay minerals is confirmed by palynological analyses which reveal that samples from Ben Gurion lack spores and pollens, suggesting the absence of vegetation (Bolle, 1999). Similar climatic conditions have been observed in the coastal basins and peri-marine environments of West Africa, from Morocco to Benin where palygorskite deposition started to increase in the late Palaeocene associated with smectite (Robert, 1982). This fibrous clay mineral almost dominates the clay fraction in the lower Eocene indicating that low latitudes and especially their coastal areas experienced intensive dryness and evaporation (Robert & Chamley, 1991). As a result of enhanced evaporation, gypsum deposits accumulated over vast areas of the southeastern Arabian Peninsula (Oberhänsli, 1992).
During the time of increased aridity on the coastal basins of the southeastern Tethys margin, the continental hinterland (Arabia-Nubian massive) experienced a quite different climatic pattern. Similar to peri-marine environments, this emerged area was first subjected to warmth and humidity during the early Palaeocene as indicated by the high kaolinite content observed in the sediments of western Sinai (Bolle, 1999). However, from Subzones P4a to P5a (late Palaeocene) the abundance of smectite and the relatively low kaolinite content in the marine sediments of central Eastern Desert (Gebel Duwi, southern Egypt) suggest a climate dominated by wet seasons on the hinterland (Fig. 2a⇑). Similar to southern Egypt, the southwestern Tethys margin (northern Tunisia and southern Spain), the marginal northeastern Tethys (Kazakhstan) and the Atlantic Realm (northern Spain) experienced seasonal climatic conditions during the late Palaeocene (Zones P4 and P5) as indicated by the abundance of smectite and the low kaolinite content (Fig. 2a,b⇑).
During the LPTM, an episode of strong humidity indicated by high kaolinite influx affected the Tethys region except the coastal basins of the Arabian Peninsula and the Saharan Platform where dry climatic conditions continued (Figs 2a⇑, 4⇑). This humid episode, not restricted to the Tethys, has been observed in the central North Sea (Knox, 1996), New Jersey continental margin (Gibson et al., 1993), northern Spain (Gawenda et al., 1999) and in high-latitude sections (Robert & Chamley, 1991; Robert & Kennett, 1992, 1994; Kaiho et al., 1996). The duration of this subtropical event varies from one region to another. On the southwestern Tethyan margin, as well in northern Spain, the change to tropical non-seasonal climatic conditions was initiated before the LPTM as suggested by the occurrence or the strong increase in kaolinite several metres below the LPTM event (Figs 2⇑, 3⇑). In New Zealand, kaolinite started to increase ~3 kyr before the carbon isotope excursion (Kaiho et al., 1996) whereas in the South Atlantic and eastern North Atlantic, the amount of kaolinite increased rapidly in the latest Palaeocene, with the highest occurrence during the LPTM (Robert & Chamley, 1991). In Antarctica, the kaolinite episode seems to be restricted to the duration of the LPTM changes (Robert & Kennett, 1994). The development of a humid perennial climate before the short-term thermal maximum appears to be diachronous, varying from one region to another. However, the high humidity indicated by the kaolinite maximum correlates better on the southwestern Tethys margin with the major LPTM changes (Fig. 3⇑) than is the case in the Atlantic Realm or in Antarctica. The kaolinite peak observed in the marine sediments on a vast geographical distribution might be a response to the terrestrial warming and increased precipitation, which affected continental areas during the latest Palaeocene. These subtropical climatic conditions coincide with the dispersion of primate specimens living in rain forest into Europe and between North America and Europe through the North Atlantic land bridge (Godinot, 1999).
In northern Tunisia, kaolinite disappears abruptly just above the LPTM giving way to smectite (Bolle et al., 1999) whereas at Caravaca (southern Spain) the disappearance of kaolinite coincides with an important increase in palygorskite, sepiolite and smectite (Adatte et al., 2000), suggesting increased aridity in both regions. At Alamedilla, kaolinite also decreases abruptly giving way to the palygorskite and sepiolite but earlier, during the LPTM (Figs 2a⇑, 3⇑, 4⇑; Lu et al., 1998). In northern Spain, kaolinite disappears also, but later into Zone NP11 (P6b) (Gawenda et al., 1999) (Figs 2b⇑, 3⇑, 4⇑) indicating the persistence of warmth and high precipitation in the source areas of this region during the early Eocene.
At the same time, the warm and humid climate persisted into the Arabo-Nubian massive as indicated by the high kaolinite/smectite ratio at Gebel Duwi (Fig. 3⇑), lateritization processes, the presence of bauxite in the African craton (Millot, 1970; Hendricks et al., 1990; Strouhal, 1993) and the development of a subtropical to tropical flora onshore (Abou-Ela, 1989).
Compared to lower-latitude Tethys sections (southern Spain: Lu et al., 1998; and northern Tunisia: Bolle et al., 1999) and North Atlantic sections (Gibson et al., 1993; Knox, 1996; Gawenda et al., 1999), the marginal northeastern Tethys (Kaurtakapy) does not appear to be affected during the LPTM by a major humid episode marked by strong kaolinite influx (Figs 2b⇑, 3⇑). A humid perennial climate gradually developed into Zone P6a and extended fully during Zone P6b (NP10) on the adjacent land areas of the marginal northeastern Tethys. During the late Palaeocene (NP9), southern and southeastern England experienced a seasonal climate probably relatively cool and/or dry as indicated by high illite, chlorite and smectite contents (Fig. 2b⇑; Bolle, 1999). However, part of these two typical terrigenous clay minerals (illite and chlorite) could be related to the extensive uplift which affected the central North Sea and England during the late Palaeocene (Knox, 1996; Nadin & Kusznir, 1996). In the English sections, kaolinite started to increase in the Oldhaven Formation (NP10) and high kaolinite content persisted during the deposition of the London Clay Formation (top of NP10; Division A3) suggesting that humid and warm climatic conditions affected the northwestern part of Europe at this time (Fig. 4⇑). This climatic interpretation inferred from clay minerals is consistent with the palynological data collected in southern England (Collinson, 1999). The LPTM floras imply coastal vegetation of herbs, lianas and few trees, probably an open wooded habitat with freshwater plants colonizing mires and channels. This vegetation includes few exclusively megathermal taxa but contains a range of megathermal to mesothermal families. However, LPTM floras indicate a cooler climate than floras found in the London Clay. Nypa, a typical indicator of mangrove, ranging from the London Clay Formation Division A2 (early Ypresian) to the late Lutetian is associated with flora specimens, which indicate a dense megathermal rain forest extending throughout the London and Hampshire Basins (Collinson, 1999) and thus indicates warm and humid climatic conditions.
Similarly, the northwestern part of Europe (England; Atlantic Realm) and the marginal northeastern Tethys (Kazakhstan) located at about the same latitude, were late subjected to a subtropical climate (top NP10) suggested by increased kaolinite, compared to the humid episode which affected the southwestern Tethys margin (southern Spain and northern Tunisia) and the northern part of Spain (Zumaia; Atlantic Realm) during the LPTM (Figs 2⇑, 4⇑).
Except for the Arabo-Nubian massive, which experienced humid climatic conditions during the early Eocene, the humid perennial episode characteristic of the LPTM seems to shift from lower to higher latitudes (Fig. 3⇑) leading to progressively more arid climatic conditions. Kaolinite disappears in Zone P5b at Elles, in the early part of Zone P6a at Caravaca and in the later part of Zone P6a at Zumaia (Fig. 3⇑). The increase in the aridity in northern Spain coincides roughly with the extension of this subtropical belt on higher-latitude sections (England and Kazakhstan) (Figs 3⇑, 4⇑).
During the early Palaeocene, the Tethys region was influenced by a warm and humid climate with high rainfall as suggested by the abundance of kaolinite in marine sediments. This uniform Tethys climate differentiated during the late Palaeocene. Whereas coastal basins along the south and southeastern Tethyan margins (southern Tunisia and Israel) were progressively affected by warm and arid climatic conditions indicated by the gradual increase in palygorskite and sepiolite, a seasonal climate dominated on the southwestern margin (southern Spain and northern Tunisia) and in the marginal northeastern Tethys (Kazakhstan). During the late Palaeocene thermal maximum (LPTM), an episode of humidity and warmth indicated by a strong increase in kaolinite affected the Tethys region. However, in the coastal basins along the southern margin, warm and arid conditions associated with enhanced evaporation continued. Except for the Arabo-Nubian massive where humid conditions persisted into the early Eocene, the humid perennial episode characteristic of the LPTM shifted from lower to higher latitudes leading to progressively more arid conditions during the early Eocene.
We thank José Richard for preparing material for X-ray analysis at the laboratory of mineralogy and petrology, University of Neuchâtel, Switzerland. We also thank Gerta Keller of the Department of Geosciences, Princeton University, USA and Alfonso Pardo of the Departamento de Ciencas de la Tierra, Universidad de Zaragoza, Spain for providing the planktonic foraminiferal biostratigraphy and Katharina von Salis, Geologisches Institut, ETH-Zurich, Switzerland for providing the calcareous nanofossil biostratigraphy for the sections studied in the PhD thesis by Bolle (1999). This study was supported by the Swiss National Fund, N°2100-043450.95/1.
This paper was presented at a colloquium held at the University of Lausanne on 20th May 1999 in honour of Professor Bernard Kübler, who subsequently died on 16th September 2000
- Received November 22, 1999.
- Revision received June 30, 2000.