Biostratigraphy of the Late Campanian–Maastrichtian of the Duwi Basin, Red Sea, Egypt

4.1 Globotruncana aegyptiaca zone (CF8)

The Globotruncana aegyptiaca zone is subdivided into two subzones (CF8a and CF8b) to yield a higher resolution time control [2].

4.2 Gansserina gansseri zone (CF7)

Authors of ref. [33] divided the Gansserina gansseri zone into three subzones: the Late Campanian Rugoglobigerina rotundata subzone CF7a, and the two Early Maastrichtian Rugoglobigerina scotti CF7b subzones and Planoglobulina acervulinoides CF7c subzones (Table 2).

Table 2

Comparison of the most relevant planktonic foraminiferal biozonations across the upper-Campanian and Maastrichtian biozonations proposed in this study

Definition: According to several authors in the published literature, the FAD of Rugoglobigerina rotundata slightly postdates the FAD of Gansserina gansseri [27,34,35,36], in this case, the Rugoglobigerina rotundata subzone could be correlated to the lower part of the Gansserina gansseri zone.

4.3 Contusotruncana contusa (CF6)

Author: Ref. [48].

Definition: It is defined by the first appearance of the nominate taxon C. contusa (Cushman) at the base of 70.15 Ma [4,49] and the last appearance of Globotruncana linneiana (d’Orbigny) at the top. This zone is equal to the CF6 zone of refs [2,3,24].

Age: Early Maastrichtian.

Thickness: 6.80 m (samples 12–18)

Remarks: An overflow of faunal turnover characterizes this zone as commented by authors of refs [2,3]. According to ref. [4], the first appearance of Pseudotextularia intermedia (De Klasz) was at 69.83 Ma level and Pseudotextularia elegans (Rzehak) at 69.55 Ma. The presence of Globotruncana linneiana (d’Orbigny) marks the Early Maastrichtian zone CF6. In the present material of the Gebel Duwi section, the Pseudotextularia intermedia (De Klasz) taxon is completely absent as a marker taxon after Contusotruncana contusa (Cushman) as investigated by the authors of refs [2,3], but it was noticed within the Late Maastrichtian interval of the Duwi section (CF3 zone).

4.4 Pseudotextularia intermedia (CF5)

Author: Ref. [50].

Definition: Pseudotextularia intermedia (De Klasz) is absent in the present study, so the definition by authors of refs [2,3] is used to define zone CF5 in the present work. The biostratigraphic interval extended from the last appearance datum (LAD) of the Globotruncana linneiana (d’Orbigny) at the base to the FAD of Racemiguembelina fructicosa (Egger) at the top.

Age: Late Early Maastrichtian.

Thickness: 6.40 m (samples 19–23)

Remarks: The authors recommended renaming this zone due to the absence of Pseudotextularia intermedia (De Klasz) in the study area. On the other hand, Authors of ref. [51] recorded P. intermedia (De Klasz) in Campanian rocks (zone CF10) in the Jorband section (north Iran). The interval of the CF5 zone [2,3] is represented by a community barren of Pseudotextularia intermedia (De Klasz) taxon through Maastrichtian of the Dakhla Formation of Central Egypt and Western Desert [29].

4.5 Racemiguembelina fructicosa (CF4)

Author: Ref. [45].

Definition: Authors of ref. [45] defined this zone by the first appearance of Racemiguembelina fructicosa (Egger) at the base and Abathomphalus mayaroensis (Bolli) at the top. In the present study, the authors follow the definition given in refs [2,3,24], the first appearance of Racemiguembelina fructicosa (Egger) marks the base of this zone and the first appearance of Pseudogumbelina hariaensis Nederbragt marks the top. The first occurrence of Racemiguembelina fructicosa (Egger) was at 69.02 Ma level, just slightly above the first occurrence of Abathomphalus mayaroensis (Bolli) taxon at 69.33 Ma. Racemiguembelina fructicosa zone marks the Early/Late Maastrichtian stage [4].

Age: Latest Early Maastrichtian

Thickness: 12.50 m (samples 24–32)

Remarks: The boundary between Racemiguembelina fructicosa zone (CF4) and the overlying Pseudoguembelina hariaensis zone (CF3) is marked by abrupt thin layers of some dark gray shales represented by the majority of very small (dwarfed) planktic species of compressed tests and impregnated by reddish colors as Globigerinelloides spp., mostly decrease in the number of globotruncanids except Globotruncana esnehensis Nakkady and flooding of heterohelicids which they considered more opportunistic taxa.

Several Late Campanian species disappeared in the late boundaries of this zone, such as Archaeoglobigerina cretacea (d’Orbigny) and others. Globotruncanita conica (White) appeared through this zone at a level of 68.75 Ma, and Racemiguembelina powelli at level 69.14 Ma [4].

Pseudotextularia elegans (Rzehak) indicates a connection of the basin with the warm Tethys [7]. The dark grey shales towards the upper interval of zone CF4 record the beginning of the decrease in P/B in globotruncanids, rugoglobigerinids, Globigerinelloides, and heterohelicids (Figures 7 and 8) implying a fall in sea level and development of black shale in a regressive regime.

4.6 Pseudoguembelina hariaensis (CF3)

Author: Ref. [50]

Definition: This zone is defined by the FAD of the Pseudoguembelina hariaensis Nederbragt at the base and the FAD of Pseudogumbelina palpebra Brönnimann and Brown at the top. Also, the top of this zone is defined as the LAD of G. gansseri (Bolli) [2,3,24] and is equal to the CF3 zone.

Age: Late Maastrichtian.

Thickness: 8.90 m (samples 33–39)

Remarks: Authors of refs [52,53,54,55] recorded that the world’s major sea-level fall hiatus coinciding with the CF4/CF3 boundary interval may cause common dwarfed specimens in several horizons and extinctions of Globotruncana bulloides Vogler at level 67.87 Ma and Planoglobulina carseyae (Plummer). The smaller size fractions <63 µm contain the first occurrence of common Pseudoguembelina hariaensis Nederbragt, a new generation of heterohelicids, Globigerinelloides, absent of Guembelitria cretacea and rare Globotruncanita stuarti (de Lapparent) and Globo. conica (White). This zone is characterized by declined Gansserina gansseri (Bolli), which is a very rare or absent taxon.

The faunal changes indicate continued and even increasing high-stress environments during the CF3 zone [56,57]. The top of the CF3 zone is marked by the extinction of Globotruncana linneiana (d’Orbigny) (at level 66.96 Ma) according to ref. [4]. Authors of ref. [6] recorded Globotruncana esnehensis Nakkady with Pseudoguembelitria hariaensis Nederbragt in the subtropical North Atlantic. The observed low abundance of planktic specimens between zones CF4 and CF3 (Figure 7) may be due to the presence of pyrite with black shale interval suggesting low oxygen condition. This event coincides with global environmental perturbations of sea-level fall at ∼ 66.25 Ma [52,58] and is recognized in the Indian and Tethyan oceans [53,54,55,59,60].

4.7 Pseudoguembelina palpebra (CF2)

Author: Refs [2,3].

Definition: In the present study, it is defined as a biostratigraphic interval extended from the FAD of the Pseudoguembelina palpebra Brönnimann and Brown at the base and the FAD of Plummerita hantkeninoides (Brönnimann) at the top of the biozone.

Age: Late Maastrichtian.

Thickness: 0.70 m (samples 40–43)

Remarks: Unfortunately, new species have stopped appearing through this zone interval, and thereby we have used the last appearance and occurrence (i.e., complete extinction) of Globotruncana linneiana (d’Orbigny) and Pseudoguembelina palpebra Brönnimann and Brown and Gansserina gansseri (Bolli) and the only first appearance of Plummerita hantkeninoides (Brönnimann) with an estimated duration of ∼180 at the top limit of this zone [55,61].

Zone CF2 summarizes the faunal diversity and species abundance data related to high-stress environments of Deccan volcanism phase 2 (Late Maastrichtian). During the Late Maastrichtian stage, the warm water Tethyan planktic foraminifera Pseudotextularia elegans (Rzehak) occurs in the Racemiguembelina fructicosa zone (zone CF4), and Pseudoguembelina palpebra zone (zone CF2). The absence of P. elegans (Rzehak) in the Pseudoguembelina hariaensis zone (zone CF3) is related to tectonic cause whereas its absence in the Plummerita hantkeninoides zone (zone CF1) was due to regression.

4.8 Plummerita hantkeninoides (CF1)

Author: Ref. [62]

Definition: This zone is defined by the total range of the nominated taxon, Plummerita hantkeninoides (Brönnimann). This zone is equal to the CF1 zone of ref. [24].

Age: Latest Maastrichtian.

Thickness: 0.70 m (samples 44–45)

Remarks: The biggest surprise is the lack of “Guembelitria blooms” [63], which are present in several sections of Al-Kef, Elles (in Tunisia, [55,64,65], Israel, Spain, Italy, Brazos (Texas), northern Mexico, Bulgaria, Kazakhstan, Denmark, Madagascar, southern middle latitudes, high latitudes, southern ocean, and others [63] and in the Indian Ocean. In the Qareiya area in Central Egypt, authors of refs [56,63] recorded low Guembelitria abundance indicating that the Late Maastrichtian of Egypt experienced similar high-stress conditions as Danian data. The high content of small heterohelicids indicates highly abundant blooms in the Duwi section. Like the case of the Gebel Duwi section, authors of ref. [66] recorded no abundance of Guembelitria cretacea in the Late Maastrichtian of SW Iran.

The maximum Maastrichtian cooling at 66.25 Ma is followed by rapid warming of 3–4°C in the oceans and 7–8°C on land in zones CF2 and CF1 [2,3,67,68,69] correlative with Deccan phase 2 [70]. The climate warm events in zones CF2 and CF1 are accompanied by decreased planktic foraminiferal diversity and increased dissolution effects [57,71,72,73].

5.1 Species richness

The major increase in species richness had no significant effect on the relative abundance of long-ranging species of Globigerinelloides and caused no significant extinctions. Globotruncanita stuarti (de Lapparent) and Globotruncana orientalis El-Naggar are common in Late Maastrichtian but do not exceed 3% of each of the total population. Species diversification of the planktic foraminifera during the Late Maastrichtian (CF4), which results in the highest species richness characterizing the studied section is more than 50 species (Table 1) (Figure 8).

The Latest Campanian species richness varies from 30 to 20% in zone CF8a to CF8b respectively, the Latest Maastrichtian ranges from 15% in zone CF7 and CF6 to 13% in zone CF5 and 40% in zone CF4. The Late Maastrichtian ranges from 16 to 13% in zones CF2 and CF1 (Figure 8).

Species diversification of the planktic foraminifera during the Late Maastrichtian (CF4), which results in the highest species richness characterizing the studied section is more than 50 species, also in the interval between C8a and C8b, species diversification of the planktic foraminifera is very high and nearly equal to those in CF4, so there are two important intervals of highest diversification.

5.2 Species population changes

5.3 Early Maastrichtian (CF7–CF4)

Through the event of the CF6 zone, a gradual increase in the relative abundance of Gublerina rajagopalani Govindan ranging between 0.03 and 6.7%, Planoheterohelix planata (Cushman) ranging between 2.7 and 9.3%, and other heterohelicids to 30% (Figure 8) have been shown the tolerate and thrive in a wide range of environmental conditions as in high-stress environments affected by temperate, salinity, nutrients, and oxygen variations due to sea-level fluctuations and receiving more meteoric water. These conditions may increase the population, abundance, and stability of life of different organisms [56,57].

CF6 zone is characterized by the last appearance of Globotruncana linneiana (d’Orbigny) at the top marking the base of CF5 with the first appearance of Racemiguembelina fructicosa (Egger) coincident with another sea-level fall at CF6 zone and the overlying CF5 boundary marking a major sequence boundary dated 69.4 Ma [52,58] with minor extinctions at the end of warming climate which is called Middle Maastrichtian Event (MME).

The first occurrence of Pseudotextularia intermedia (De Klasz) (CF5) must be recorded at 69.83 Ma level [4], meanwhile, it is only recorded partially through the Pseudoguembelina hariaensis (CF3). We think that the disappearance of Pseudotextularia intermedia (De Klasz) may be interpreted as due to ecological reason. The same observation was noticed by refs [7,29,55,59,67,73,80]. Authors of ref. [79] in Tunisia considered CF5 as a gap or partially representing a hiatus interval.

The latest zone CF4 records a sharp decrease in P/B, globotruncanids, rugoglobigerinids, and heterohelicids implying a fall in sea level and the development of dark grey shales in a regressive regime. Authors of ref. [55] recognized that ocean acidification and reduced water mass stratification are contributors to the high-stress environments of the planktic foraminiferal assemblages except for the opportunistic species during the Late Maastrichtian CF4–CF2 zones.

The high-stress environments induced by the Deccan eruption prevented the normal growth in some Late Maastrichtian planktic foraminifera such as Guembelitria [56,63,80,81]. The Deccan eruption occurred in two phases: the first phase happened during CF4 (normal chron C30N ∼ 66.5–67 Ma), and the authors of ref. [82] aged that to be during 66.6 Ma. The most vigorous second eruption occurred during CF2 (65.4–65.2 Ma) [83,84,85].

The sediment deposition began in the Late Maastrichtian with global cooling and a sea-level fall at ∼66.8 Ma (CF4 and CF3) showing warm temperatures and rapid cooling before the CF4/CF3 hiatus. The climate warmed to 2–3°C before and after this cooling and appears correlative with the onset of Deccan volcanism (phase 1) [86]. During the CF4 and CF3 zones, the climate warm events are accompanied by decreased planktic foraminiferal diversity and increased dissolution effects [57,71,72,73].

Pseudotextularia elegans (Rzehak) flourished in the unusual environment and developed morphological diversities implying that the environment had influenced this species, and other planktic foraminifera reduced test size to avoid the strike of the Deccan volcanism. Some other associated planktic foraminifera also shows abnormalities in these environments [87]. Thus, the reduction in the size of the planktic foraminifera is produced by major environmental factors including warming of climate, volcanogenic factors such as aerosols (acid rain), CO₂ emissions related to Deccan volcanism, and/or sea-level changes provoked by local tectonic changes. Zone CF1 largely represents a regressive regime and the general absence of P. elegans (Rzehak) in the zone indicates that the warm water of the sea could not sustain the species [72].

Many authors noted test irregularity, dwarfing, and unusual variation in a species of Late Maastrichtian planktic foraminifera as an effect of environmental stress [72,88,89,90]. While authors of ref. [91] mentioned that the biotic effects of Chicxulub impact and “Lilliput Effect” [92] in some Late Maastrichtian planktic foraminifera were accounted for environmental stress [57,91,93]. Environmental factors caused a change in test size and population density in Pseudotextularia elegans (Rzehak) during the Late Maastrichtian [7,72].

5.4 Late Maastrichtian interval (CF3–CF1)

The globotruncanids appear in low diversity (only seven species) and are detected throughout the Duwi section. Due to more environmental changes and shallowing basin than in west-central Sinai, the most tolerant species such as Globotruncana aegyptiaca Nakkady, G. bulloides Vogler, G. rosetta (Carsey), and G. dupeublei have thrived under shallowing conditions at different levels of gray shales which reduced water mass stratifications [55].

The foraminiferal species richness began to decline dramatically, and diversity decreased gradually from the interval of the P. hariaensis zone (CF3) affecting the complex subsurface and thermal intermediate dwellers (Figure 8) leading to marked richness of dwarfed heterhelicids as Planoheterohelix globulosa (Ehrenberg), Planoheterohelix planata (Cushman), Gublerina rajagopalani Govindan, and Planoglobulina riograndensis. Pseudoguembelina palpebra zone (CF2) is associated with the development of “photosymbiotic” species Racemiguembelina powelli Smith and Pessagno and Plummerita reicheli, as reported by refs [66,94].

The cooler ecosystem at the Late Maastrichtian time (CF3) and a new sequence of high sea levels between 68.33 Ma and slightly to 66.0 Ma associated with new species of Racemiguembelina fructicosa (Egger), R. powelli Smith and Pessagno, Globotruncana esnehensis Nakkady, and Abathomphalus mayaroensis (Bolli) are originated through this interval. The cosmopolitan Abathomphalus mayaroensis (Bolli) is very rare in tropical, subtropical, and Tethyan paleogeographic provinces. The Globigerinelloides, Rugoglobigerina, and Heterohelicids reached maximum relative abundance through this interval, while the globotruncanids gradually decreased up-section (Figure 7). Minor extinction event is marked by the last occurrence of Contusotruncana contusa (Cushman), Globotruncana bulloides Vogler, and Globotruncanita pettersi and the disappearance of Archaeoglobigerina cretacea (d’Orbigny).

The latest biozones CF2 and CF1 spanning from 67.87 Ma to 66.0 Ma are generally characterized by heterohelicids blooms specially Planoheterohelix globulosa (Ehrenberg), gradual decreasing of diversity associated with the warming phase before the K/Pg boundary event, indicating highly biotic stress [53,54,56,63,89,95].

The Guembelitria cretacea is not registered possibly because of eutrophic conditions [96] or may result from high terrigenous runoff, upwelling of nutrient-rich water, phosphorus input of pre-existing phosphatic Duwi Formation, indicating environmental instability as recorded by refs. [97,98].

5.5 Dwarfism of species

Authors of ref. [99] recorded the foraminiferal size reduction and termed it as the “Lilliput effect.” This effect may report the aftermath of mass extinctions and rarely pre-extinction due to a highly stressful environment. The dwarfism of the planktic foraminifera species was observed and documented from the uppermost Maastrichtian sediments in Egypt, Israel, Madagascar, and South Atlantic [53,54,55,59,79,80].

In the Duwi section, dwarfed planktic foraminiferal species were observed at CF8b with some small lower levels of relatively high organic materials. The CF5/CF4 boundary or so-called MME includes dwarfed species of Rugoglobigerina, Heterohelix, Globotruncana bulloides Vogler, and Globotruncanella compressiformis.

Another example is a very small (dwarfed) stress-tolerant species of some Pseudoguembelina which may be adapted to warm temperatures at low latitudes as observed at CF4/CF3 boundary and even through CF3. The dwarfed specimens amounting to an average of 70% in CF2, while 40% in CF1 may be due to a sharp diversity drop. These indicate an upward Maastrichtian interval. There are more stressed environmental conditions globally or locally due to sea-level regression, which may be associated with increased competition and possibly carbonate dissolution pointing to high biotic stress [55,73,94].

5.6 Depth ranking

The recent study by authors of refs [55,94] for determining the depth ranking enables us to recognize the following concepts in the Duwi section.

5.6.1 Deep dwellers

The deep dwellers contain Abathomphalus mayaroensis (Bolli), Globotruncanita stuartiformis (Dalbeiz), Gublerina cuvillieri Kikoine, and Gublerina rajogopalani compared with that cited by refs [55,94], the following points can be noted (Figure 9).

1. Duwi material contains rare to very rare deep dwellers faunal group, it ranges between 0 and less than 5% maximum.

2. The Gublerina rajogopalani rarely reaches 5% of all the intervals, it seems to be endemic species to the deepest and coldest habitat [94].

3. Despite the “cosmopolitan Late Maastrichtian,” Abathomphalus mayaroensis (Bolli) is very rare or even absent through the present material indicating its endemism to the deepest seas.

Figure 9

Life habit distribution of surface dwellers, deep dwellers, subsurface dwellers, and thermocline dwellers in the studied section.

5.6.4 Surface dwellers

This is a group of Pseudoguembelina spp. of the Maastrichtian age that reflects the warm temperatures of the oceans as a “mixed layer” as reported in ref. [94]. It reaches 12% as the maximum abundance of the Duwi section planktic species represented by Pseudoguembelina costillifera, P. costulata (Cushman), P. excolata (Cushman), P. kempensis Esker, P. palpebra Brönnimann and Brown, and P. hariaensis Nederbragt. Authors of ref. [94] suggested that they inhabited the warmest or shallowest parts of the mixed layer (Figure 8). Rugoglobigerina spp. are observed in more common abundance than the Pseudotextularia spp. The Rugoglobigerina spp. range between 12 and 30% and returns to 20% through the lower Maastrichtian and exceeds the maximum through the CF4 zone (Figure 10).

Figure 10

Deccan phase 2 and phase 3 volcanism is correlative with global warming events in the Late Maastrichtian zones CF1 and CF2 and the early Danian. Dan-C2 event in Zone P1b. KTB-Cretaceous-Tertiary boundary; API-American Petroleum Institute units; VPDB-Vienna Peedee belemnite (ref. [72]).

During the Maastrichtian age, surface dwellers, subsurface dwellers, thermocline dwellers, and a low abundance of deep dwellers are populated by Planoheterohelix globulosa (Ehrenberg) and even Planoheterohelix planata (Cushman). This indicated that low water ranking through different climates with high action of upwelling currents which implies the majority of planktic foraminifera inhabited through different depth levels and sea-level fluctuation with a relatively warm climate period. This conclusion in the Duwi section is greatly in agreement with refs [2,3,55,73,94,100] across different localities of the Tethys, Indian and Atlantic oceans.

5.7 Opportunistic species

The low oxygen tolerant Planoheterohelix globulosa (Ehrenberg) and its associated Planoheterohelix planata (Cushman) significantly increase in relative abundance from the Latest Campanian to the Latest Maastrichtian. P. globulosa (Ehrenberg) ranged between 10 and 18% in abundance through zones CF8a to CF4 and abruptly increase in abundance by about 20% in zone CF3 to more than 45% in both CF2 and CF1 zones. Planoheterohelix planata (Cushman) started its abundance from CF4 to CF1 zones to reach a 10% maximum at different levels. The global warming documented in CF2 and CF1 zones worldwide is recorded in the Duwi Basin by a high decrease or even absence of the global Guembelitria cretacea and high relative abundance of Planoheterohelix globulosa (Ehrenberg) and robust index species Globotruncana esnehensis Nakkady and Globotruncana aegyptiaca Nakkady.

The heterohelicids reach abundance abruptly between 35 and 60% through the CF3 zone and exceed more than 60% in CF2 and CF1 zones. The dominance of heterohelicids has also been recorded in Tunisia, Israel, Italy, Spain, Texas, Denmark [101], and others indicating decreased water mass stratification and expanded low oxygen environments as ecological stress.

The Planoheterohelix globulosa (Ehrenberg) only shared 45% of this high abundance. The robust index species Globotruncana esnehensis Nakkady increased to 15% in the CF3 zone and returned to 5% at both CF2 and CF1 zones, while the other robust Globotruncana aegyptiaca Nakkady species was 2% in CF3 and returned to less than 1% in CF2 and CF1 zones.

Not only the heterohelicids are considered opportunistic groups but also, Globotruncana aegyptiaca Nakkady and Globotruncana esnehensis Nakkady must be grouped as the most tolerant species. The Duwi Basin in CF2 and CF1 zones became shallower with some organic material, warm humid climate, high rainfall, low salinity and oxygen, and low primary production in a basin of very shallow marginal environment.