چكيده لاتين :
One of the first works about Cretaceous deposits in eastern part of the Lut Block is done by Stocklin et al. (1972). They reported Orbitolina limestones in Shah Kuh area and Maasterichtian siliciclastic and limestone beds which have overlaid the older deposits with a gap. In geological maps of the east of Iran, Upper Cretaceous deposits have been reported (Berthiaux et al., 1990; Eftekharnejad, 1991; Berberian and Soheili, 1992; Alvai Naini, 1983; Guillou et al., 1981 that they have been mostly referred to shallow and relatively deep facies. Moreover, Gorgich (2002), Gorgich et al. (2009) and Motie (2010) reported Maastrichtian deposits in the east of Iran.
The study area is located at Geological Quadrangle Map of Qayen (Berthiaux et al., 1990) and Geological Sheet Map of Roum (Shahidi et al., 2000). The measured section is geographically situated at 33o 05? north latitude and 59o 02? east longitude.
Aims and Method:
This paper aims to study lithostratigraphy, identification of foraminifera assemblage, age determination, and biostratigraphy and biozonation of the measured section. The authors hope this research lead to a better understanding of the regional geology and distribution of Cretaceous foraminifera that might describe the degree of lithostratigraphic and biostratigraphic precision.
In this research 160 samples have been collected which 130 samples were cut and thin sections were prepared. The other samples were disaggregated in dilute H2O2 (10% vol.) and washed. The washed residues were dried and picked the isolated forams. Thin sections studied under Olympus microscope and the foraminifera were identified and photographed. The isolated forms were photographed with Scanning Electronic Microscope (SEM) device model XL30 Philips in Technical Faculty of Tehran University.
Discussion and results (Lithostratigraphy and biostratigraphy):
From point of view of lithostratigraphy, the lower contact of the succession is faulted and the sequence could be divided into two informal members. The lower member is formed by intercalation of marl, shaly marl, thin bedded limestone and sandstone. The upper member includes medium to thick bedded limestone, medium bedded sandy limestone that changes to red sandstone. Moreover, in the upper part medium bedded limestone and sandy limestone are predominant. The upper boundary with Eocene deposits is unconformable.
In the lower member, the following assemblage is identified; Abathomphalus sp., Bolivinoides draco draco, Dentalina granti, Gavelinella sp., Globotruncanita conica, Globotruncana arca, Globotruncana sp., Globotruncanita stuarti, Heterohelix sp., Heterohelix globulosa, Marssonella turris, Neoflabellina cf. permutata, Pseudotextularia sp., Pseudotextularia elegans, Pseudotextularia nuttalli, Planomalina sp., Schackonia sp.
The following assemblage is also recognised in the upper member; Bolivinita planate, Goupilloudina iranica, Goupilloudina shirazensis, Globotruncanita stuarti, Heterohelix globulosa, Iranites ornatus, Lepidorbitoides socialis, Lepidorbitoides sp., Nezzazzata sp., Orbitoides media, Omphalocyclus macroporus, Orbitoides tissoti, Orbitoides apiculata. Pseudorotalia persica, Pseudotextularia elegans, Sulcoperculina sp., Siderolites calcitrapoides, Sirtina sp., Textularid.
Globigerinelloides sp., Globotruncanita stuarti, Iranites ornatus, Lepidorbitoides socialis, Lepidorbitoides sp., Nezzazzata sp., Omphalocyclus macroporus, Orbitoides media, Pseudorotalia persica.
Above the deposits that attributed to Cretaceous with a basal conglomerate, there is a sequence that the following foraminifera are identified; Alveolina pasticillata, Alveolina leupoldi, Alveolina aragonensis, Alveolina aff. pisella Alveolina (Glomalveolina) primaeva, Alveolina aff. rutimeyeri, Alveolina (Glomalveolina) sp., Biloculina sp., Miscellanea aff. iranica, Miscellanea sp., Nummulites convexa, Nummulites cf. guettardi.
Based on the identified benthic and palnktonic foraminifera, three biozones are suggested as follows
1- Globotruncanita stuarti Interval Zone: this biozone is defined by first appearance of Globotruncanita stuarti to first appearance of Bolivinoides draco draco. The foraminifera assemblage includes Neoflabellina cf. permutata, Pseudotextularia elegans, Gavelinella sp., Globotruncana arca, Marsonella turris. The Globotruncanita stuarti is not reported as an index foraminifera in previous presented biozonations, but is known as one of well known foraminifera of the Globotruncana havanensis and Globotruncana aegyptica biozones (Robaszynski & Caron 1995; Sliter 1989).
A Late Campanian to Maastrichtian is attributed to Globotruncanita stuarti biozone (Darvishzadeh and Abdolalipour, 2009 ;Abdelghany, 2003; Bertle and Suttner, 2005).
2- Bolivinoides draco draco Interval Zone: this biozone is defined by first of Bolivinoides draco draco appearance to first appearance of Omphalocyclus macroporus. The assemblage fauna including Heterohelix globulosa, Heterohelix sp., Pseudotextularia nuttalli, Pseudotextularia sp., Globotruncanita conica, Dentalia granti, Schackonia sp., Planomalina sp. This biozone is comparable with Akimets et al. (1991), Beniamovski and Kopaevich (1998), Olfer’ev and Alekseev (2005) and Beniamovski (2011). A Maastrichtian age is suggested for this biozone.
3- Siderolites-Omphalocyclus Assemblage Zone: this biozone is correlateable with biozone number 37 (Wynd, 1965) and also is reported by Maghfori Moghaddam (2005). The assemblage fauna including Omphalocyclus macroporus, Orbitoides media, Siderolites calcitrapoides, Textularids, Nezzazzata sp., Lepidorbitoides socialis, Orbitoides tissoti, Orbitoides apiculata. Based on the previous works such as Mitchell (2005) from Jamaica, Rosales-Domingoes (1997) from Mexico and Abd-El-Gawad (2010) from United Arab Emirates, the suggested biozone is similar to the mentioned areas. A late Maastrichtian age is suggested for this biozone. A Late Campanian–Late Maastrichtian age is suggested for the measured section.
Conclusion:
In the studied area, the following foraminifera are reported for first time; Abathomphalus sp., Bolivinoides draco draco, Dentalina granti, Gavelinella sp., Globotruncanita conica, Globotruncana arca, Heterohelix globulosa, Marssonella turris, Neoflabellina cf. permutata, Pseudotextularia elegans, Pseudotextularia nuttalli, Goupilloudina iranica, Goupilloudina shirazensis, Orbitoides tissoti, Orbitoides apiculata, Pseudorotalia persica,
Based on the identified assemblage fauna, three biozones including Globotruncanita stuarti Interval Zone, Bolivinoides draco draco Interval Zone and Siderolites-Omphalocyclus Assemblage Zone are suggested. The assemblage fauna confirms a Late Campanian-Maastrichtian age.
Moreover, the following assemblage fauna including Alveolina pasticillata, Alveolina leupoldi, Alveolina aragonensis, Alveolina aff. pisella Alveolina (Glomalveolina) primaeva, Alveolina aff. rutimeyeri, Biloculina sp., Miscellanea aff. iranica, Miscellanea sp., Nummulites convexa, Nummulites cf. guettardi, are identified in the uppermost part of the succession. The assemblage suggests an Eocene age and therefore an unconformity is determined in the upper boundary of the sequence.
It seems Laramid Orogenic phase has effected on facies changes at the east of Iran. It led gaps in the Upper Cretaceous deposits in some parts of the basin due to ophiolites emplacement. In adjacent areas, sedimentation continued in two flych-flychoid and calcareous facies. Presence of an unconformity in Cretaceous-Tertiary boundary is another result of Late Cretaceous Orogenic movements in the studied area that is proofed by basal conglomerate.
