زیست ‌چینه نگاری نهشته های ائوسن شرق بلوک لوت در برش چینه‌شناسی آلنج بر اساس نانوفسیلهای آهکی

در این پژوهش زیست چینه نگاری نهشته های ائوسن حاشیه شرقی بلوک لوت، برمبنای نانوفسیل‌های آهکی در برش چینه شناسی آلنج بررسی شده است تا زیست‌زونها و نهایتا بر اساس آنها سن دقیق این نهشته‌ها تعیین شود. نهشته‌های ائوسن در این برش چینه‌شناسی حدود 633 متر ضخامت دارد و ترکیب سنگ شناسی عمدتا شامل واحدهای شیل و مارنی با میان‌لایه‌های ماسه‌سنگی و واحدهای ماسه سنگ می باشد. براساس مطالعات تاکسونومیکی، 45 گونه نانوفسیلی متعلق به 20 جنس در برش چینه‌شناسی آلنج شناسایی و عکسبرداری شد. بر اساس گونه‌های نانوفسیلی شناسایی شده، در برش چینه‌شناسی آلنج زونهای ‌زیستی زیر تفکیک گردیده است: discoaster binodosus zone (np11), tribrachiathus orthostylus zone (np12), dicoaster lodoensiszone (np13), discoaster sublodoensis zone (np14), nannotetrina fulgens zone (np15), discoaster taniinodifer zone (np16), discoaster saipanensis zone (np17), chiasmolithus oamaroensis zone (np18), isthmolithus recurvus zone (np19)بر اساس این زون‌های‌ زیستی، سن توالی مورد مطالعه در این برش چینه‌شناسی، ائوسن پیشین تا ائوسن پسین( ایپرزین تا پریابونین) پیشنهاد می شود.

nannostratigraphy of the eocene deposits in east of lut block in alanj stratigraphic section

lut block in the eastern part of the subcontinent of central iran and a stretched structural zone with a north-south trend that is 900 km long and about 150 to 200 km wide. lut blocks east to nehbandan fault; it ends in nayband fault from the west and the daruneh fault from the north, and the southern border of this structural zone is the jazmourian depression.the characteristic features of the lut block are the presence of intense magmatic activity and the presence of intrusive masses, the presence of many faults and joints and different metamorphic facies in different rock units, which shows the similarity of the stratigraphic history of lut block with other subcontinent areas of central iran. moreover, sedimentary rocks such as lime, marl, sandstone are also more limited in this structural zone.the paleogene sediment sequence is exposed in areas of the lut block sedimentary basin. however, due to the tectonic dynamics of the lut block, especially in its eastern margin in this area, faulting, drift, fragmentation, and metamorphism are significant. in many places, due to these special tectonic conditions, the existing sequences are not thoroughly studied. therefore, most of the studies conducted in the lut block are related to the preparation of geological maps or tectonic studies.therefore, to complete previous studies and conduct bio-stratigraphic studies, sampling and study of deposits in this area seems necessary. therefore, the present study aimed to identify calcareous nanofossils, determine nanozones based on the presence of indicator species and finally determine the exact age of some eocene deposits of lut block in the stratigraphic section alanj (northeast of ghaen).it is worth mentioning that according to aghanbati (2004) segmentation, the study area is located in the eastern margin of the lut block in eastern iran.the studied sequence is located in south khorasan province, northeast of qaen city, and three kilometres north of alanj village.the thickness of the sequence studied in the stratigraphic section of alanj is 633m and includes marl deposits with interbedded sandstone and shale layers and sandstone units. the sampled sequence with a normal boundary is located on the andesitic unit in the map attributed to the paleocene, and at the upper boundary of this sequence is a conglomerate unit that is normal to it.2- materials and methodssampling is often from shale and marl layers and takes samples without weathering from a depth of 50cm. it should be noted that the sandstone units of the mentioned section were also sampled, but they did not contain nanofossils.the collected samples were prepared by the smear slide method. bown and young (1998) studied and photographed with olympus polarizing microscope model bh2 with 100 lenses. in order to investigate the properties of nanofossils, the prepared samples were studied under ppl and xpl light.3-results and discussionthe factors influencing how nanofossils are preserved, according to bown and young (1998); andruleit (1997); honjo (1976), includes dissolution, the incidence of diagenesis and secondary growth. therefore, the nanofossil species identified in the alanj stratigraphic section have relatively good to good preservation.