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Abstract
Three sections represent the Upper Cretaceous-Lower Paleogene successions at Eastern Desert, Egypt, between Latitude 26° 06` to 26° 30` N and Longitude 33° 04` to 34° 05` E., are investigated for the benthonic foraminifera to follow their distribution and determine their turnover across the warming events during this interval. Also paleoenvironmental conditions and paleobathymetric settings have been discussed.
To achieve these objectives; 327 samples were collected from the three sections (Gebel. Duwi, G. Serai, G. Um El-Huetat) and micropaleontologically investigated.
Lithostratgraphically, the studied sections have been subdivided into three mappable rock units: arranged from base to top as follow: Dakhla, Tarawan, and Esna formations. Dakhla Formation is subdivided into two members; Hamama at the base and Beida at the top. Esna Formation is subdivided into four members: Hanadi (at base), Dababiya Quarry, Mahmiya and Abu Had members (at top).
In general foraminifera from G. Serai, G. Duwi sections are well preserved (except at the critical intervals). The benthonic foraminifera are diverse, heterogenous and dominated by calcareous taxa. On the contrary to G. Um El-Huetat section which show less preservation at many intervals.
The Maastrichtian benthonic foraminifera from Duwi and Um El-Huetat sections show low diversity with high abundance of infaunal morphotypes. The assemblage composed mainly of Elhasaella allanwoodi, Siphogenerinoide oveyis, Reussella. aegyptiacus, Bulimina reussi, beside the epifaunal Anomalinoides acuta, A. praeacutus, A.welleri.
The Paleocene assemblage from the three sections was generally dominated by epifaunal morphotypes like Anomalinoides midwayensis, A.acuta, A.praeacuta, Cibicidoides alleni, Eponides plummerae, Neoepondes duwi, Frondicularia
phosphatica, F. nakkadyi beside the less dominant infaunal species like Siphogenerinoides eleganta, loxostomoides applinae., Siphogenerinoides brevispinosa, Stilostomella spp.
Due to the unconformity at the K/Pg boundary (minor at Duwi section and large magnitude at Um El-Huetat section) the absolute faunal turnover at this boundary could not be detected but it was clear that main uni, bi, and tri serial Maastrichtain species did not pass K/Pg boundary like Reussella. aegyptiacus, Siphogenerinoides oveyi, Bulimina reussi, and Elhasaella allanwoodi.
D/S event was completely represented at G. Serai section by the four alternating grey and brown organic-rich phosphatic shale of Qreiya Beds, while record short range hiatus at Duwi section which retained some criteria characteristic of D/S event, but Danian interval was completely absent at Um El-Huetat due to large magnitude hiatus. No true extinction of benthonic foraminifera was recorded at the D/S boundary except for temporary disappearance of deep water taxa (Angulogavelinella avnimelechi, Nuttallides truempyi) and high abundance of opportunistic Neoeponides duwi. This mostly caused by migration of deeper taxa from this site after regression while Neoeponides duwi could adapt this shallow, high productivity, disturbed conditions.
The five beds of DQM are all represented at G. Serai and G. Duwi sections while the beds nos 4 and 5 are missing at Um El-Huetat section. The high abundance (230 specimen/sample) of agglutinated taxa (Bathysiphon spp., Haplophragmoides spp.) with the beginning of CIE (PETM interval) is recorded only from G. Serai section but did not detected from the other two sections. The PETM is characterized by benthonic extinction event (BEE) of deep sea benthonic foraminifera. The largest extinction is recorded from G. Serai section due to it’s higher content of deep water taxa, while the extinction is limited at G. Duwi because of it’s shallow setting and it’s rare content of deep water taxa, since the extinction of benthonic foraminifera with the PETM is less pronounced through midway-type fauna (shallow settings). The responsible factor for absence of calcareous benthonic foraminifera at beds nos. 1 and 2 and 3 at the three sections is not the dissolution only because of high abundance of planktonic Acarinina, morozovella through the PETM.
The last occurrence of deep water Angulogavelinella avnimelechi, Neoflabellina jarvisi have been recorded from the latest Paleocene at the three sections and Coryphostoma midwayensis at G. Serai and Um El-Huetat. Other deep water taxa like; Nuttallides truempyi, Gaudryina pyramidata passed the PETM and reappeared during the Early Eocene. Also certain shallow water taxa disappeared locally at certain sections while continued in normal or rare abundance at other sections. Bulimina midwayensis recorded last occurence within Hanadi Member at G. Duwi section. Anomalinoides midwayensis, Cibicidoides succedens recorded last occurrence at the top of Hanadi Member at G. Serai section.
High abundance of infaunal taxa was recorded from the Maastrichtian interval (especially at G. Duwi section) suggesting eutrophic conditions during the deposition of Hamama Member. The main infaunal species were Reussella. aegyptiacus, Siphogenerinoides oveyi, Bulimina reussi, Elhasaella allanwoodi).
The benthonic foraminifera during the Paleocene interval is dominated by epifaunal morphotypes, especially various Cibicidoides, Anomalinoides suggesting oligotrophic, oxygen rich sea floor during most the Paleocene time but it may reach mesotrophic condition at the upper part of Beida Member (P4b Zone).
Mesotrophic conditions were suggested for the deposition of Early Eocene sediments at both Serai and Um El-Huetat sections due to the high abundance of the infaunal taxa, while the low infaunal content at Duwi section suggests oligotrophic conditions for the Early Eocene sediments at Duwi section.
Certain peaks in the agglutinated percentage were recorded from the middle part of Beida Member (just above D/S unconformity) at G. Duwi section and top of Tarawan Formation which may be related to shallowing. Nearly two synchronous peaks in abundance of agglutinated foraminifera was recorded from the middle part of Mahmiya Member at Duwi section (biostratigraphicaly spanning E3 and lower part of E4) and Um El-Huetat section (span E4 hence E3 is missing). This may be related to shallowing or tectonic event.
The Paleocene sediments of G. Serai section record high abundance of velasco-type Angulogavelinella avnimelechi, Nuttallides truempyi, Gaudryina pyramidata, less abundance of coryphostoma midwayensis beside rare occurrence of Anomalinoides rubignosus, and Gavelinella beccariiformis. The dominated midway-type fauna was mainly of epifaunal morphotypes (various Cibicidoides, various Anomalinoides, and Gyroidinoides subangulata) which suggest outer neritic-upper bathyal setting (150-400m) through most Paleocene and retreated to inner-middle neritic setting during D/S regression event which was dominated by shallow water taxa Neoeponides duwi, Siphogenerinoides esnehensis, Siphogenerinoides eleganta, and Haplophragmoides spp.
The occurrence of velasco-type species at G. Duwi section is rare and represented by Angulogavelinella avnimelechi, Neoflabellina jarvisi, Nuttallides truempyi and high abundance of midway-type fauna like Anomalinoides midwayensis, A. acuta, A. praeacuta, Cibicidoides alleni, Eponides plummerae, Frondicularia phosphatica, F. nakkadyi, Neoepondes duwi, Bulimina farafraensis, B. strobila, B. callahani, and Valvulineria scrobiculata. So middle-outer neritic (50-150m) setting is suggested for most Paleocene of Duwi section. The lower part of the Maastrichtian sediments was deposited at middle-outer neritic (50-150m depth) and changed upward into inner neritic (30-50m depth) setting at the upper part of Hamama Member.
At Um El-Huetat section despite of the bad preservation and high diagenetic alteration of fauna, the occurrence of Angulogavelinella avnimelechi and Nuttallides truempyi is recorded. So middle-outer neritic (75-200m) setting is suggested for the Paleocene from Um El-Huetat section while the Maastrichtian part of Um El-Huetat section was deposited at inner-middle neritic setting (30-70m depth). The Early Eocene sediments recorded relatively high P/B ratio and low abundance of the velasco-type taxa suggesting middle-outer neritic setting for the deposition of Mahmiya Member (Early Eocene) at the three studied sections while Abu-Had Member was deposited at inner-middle neritic (30-100m depth) setting at Um El-Huetat section and was barren at Duwi section.
Based on data from the studied sections became obvious that the extinction rate of benthonic foraminifera at K/Pg boundary was higher than that at P/E boundary. The most Maasstrichtian benthonic foraminiferal taxa are not recorded within the Paleocene sediments. On the other hand the extinct species at the P/E boundary were rare components with abundance do not exceed 5%. (e.g. Neoflabellina jarvisi, Gavelinella beccariiformis and coryphostoma midwayensis) except Angulogavelinella avnimelechi that is represented main component of the foraminiferal assemblage. It is known that the studied sections was deposited in epicontinental basin in southern Tethys and they are shallow sections mainly ranging between inner-outer neritic (except G. Serai sometimes record bathyal setting), so the studied benthonic assemblage was mainly of midway-type or shallow water fauna.
The D/S event is considered one of the Early Paleogene hyperthermals so it is similar to P/E event in many aspects (Speijer 2003). The sediments of Qreiya Beds, which mark the D/S event are very similar to those in the lower part of the earliest Eocene Dababiya Beds in Egypt (Soliman and Obaidalla 2010). The organic rich- phosphatic shale layer of the D/S boundary at G. Serai section is similar to beds nos. 2 and 3 at the P/E boundary from the three sections. This layer suggests highly reducing conditions at the sea floor that allowed preservation of this organic matter. High P/B ratio is recorded from beds nos. 2 and 3 (fish skeleton and coprolite rich-phosphatic shale) at the three sections and from brown layers (2 and 4) of Qreiya Beds at Serai section.
The benthonic foraminiferal assemblage during the D/S event composed mainly of opportunistic Neoeponides duwi at G. Serai and recorded incursion at G. Duwi section despite the occurrence of the unconformity. At the boundary beds nos. 2 and 3, calcareous benthonic foraminifera is nearly absent. The opportunistic taxa followd the D/S event compose of Siphogenerinoides esnehensis, Siphogenerinoides eleganta, Haplophragmoides spp., in addition to Neoeponides duwi reflecting shallow inner-middle neritic environment with high productivity and disturbed conditions at sea floor. The opportunistic taxa followed PETM event was similar at the three sections and consisted mainly of Valvulineria scrobiculata, Anomalinoides aegyptiacus, A.acuta, Lenticulina midwayensis reflecting the organic-rich, oxygen depleted sea floor after PETM.