پديد آورندگان :
مناني، مريم دانشگاه پيام نور - گروه زمين شناسي، تهران، ايران , سعادت نژاد، جواد دانشگاه فردوسي مشهد - دانشكده علوم - گروه زمين شناسي، مشهد، ايران , علامه، محسن دانشگاه فردوسي مشهد - دانشكده علوم - گروه زمين شناسي، مشهد، ايران
كليدواژه :
فسيل گياهي , سازند نايبند , ترياس پسين , اصفهان
چكيده فارسي :
سازند نايبند در شمال شرق اصفهان از پايين به بالا به پاره‌سازند‌هاي گلكان (ماسه‌سنگ و مارن)، بيدستان (ماسه‌سنگ و سنگ‌آهك ريفي)، حوض شيخ (ماسه‌سنگ و مارن)، حوض خان (سنگ‌آهك ريفي با ميان لايه‌هايي از مارن) و قدير (ماسه‌سنگ، شيل و مارن) قابل تفكيك است. در پاره‌سازند قدير يك لايه كليدي ماسه‌سنگ خاكستري داراي فسيل گياهي وجود دارد كه در اين پژوهش دو جنس و چهار گونه از فسيل‌هاي گياهي شامل Clathropteris meniscoides، Clathropteris obovata، Nilssonia pseudobrevis و Nilssonia sp از اين واحد سنگي شناسايي گرديدند. بر اساس سن اين گونه‌ها و موقعيت چينه‌شناسي اين طبقات، اين رسوبات در طي زمان رتين ته‌نشين شده‌اند. با توجه به حضور فراوان جنس Clathropteris مي‌توان به رطوبت بالا و هواي گرم منطقه شمال اصفهان در رتين اشاره داشت
چكيده لاتين :
The extent of the Shemshak group with Late Triassic-Middle Jurassic age in Iran can be divided into two structural-sedimentary zones of Iran and Zagros, which are separated by the main thrust of Zagros. The first zone is divided into two areas of Alborz and Central Iran (Moin-o-Sadat & Zade-Kabir, 1991). After the Early Cimmerian orogeny, a sedimentary sequence consisting of marl, sandstone, and reef limestone was deposited in Central Iran, called Nayband Formation. The Nayband Formation type section is located near the Naybandan village, 220 km south of Tabas city (Douglas, 1929). Its thickness reaches 3000 m in type locality (Kluyver et al., 1983; Seyed-Emami, 2003; Fürsich et al., 2005). The study area of the current research is located 74 km northeast of Isfahan, 15 km northwest of Chahriseh village (33°04’10’’N, 52°01’40’’E). This region is located in the western margin of the central Iran zone and south of Kashan. The thickness of the Nayband Formation in the north and northeast of Isfahan reaches a maximum of 660 meters, divided into five members (Mannani & Yazdi, 2009).
Material and Methods
Upper Triassic succession in the northeast of Isfahan (Chahriseh section) was studied using Kashan's quadrangular geological map (Zahedi et al., 1991). Characteristics of sedimentary sequences such as stratification, lateral expansion and sedimentary structures were recorded. Sampling was taken systematically and regularly at one-meter intervals. Twenty-two plant macrofossils of Nayband Formation from the Qadir member have been collected.
Discussion and Conclusion
A key bed of gray sandstone with plant macrofossils, up to 15 m thick, is identified in the Qadir member. Two genera and four species have been found in the section, include Clathropteris meniscoides (Brongniart 1825) Brongniart 1828 (Age: Carnian- Early Lias), Clathropteris obovata Oishi 1932, emend. Harris 1961 (Age: Norian- Middle Jurassic), Nilssonia pseudobrevis (Barnard 1967b) Corsin & Stampfli 1977 (Age: Norian- Rhaetian) and Nilssonia sp.
Based on the Clathropteris meniscoides, Clathropteris obovata, and Nilssonia pseudobrevis in Qadir member (Nayband Formation) and their in situ stratigraphic position, these strata are deposited in Rhaetian. In this study, Clathropteris obovata is reported from Late Triassic age in Iran for the first time. Before this, Clathropteris obovata in Iran has been reported from only Jurassic (Late Liassic-Early Dugger); however, this species has a wider range from Late Triassic to Late Dugger succession in the other parts of the world. So, its record in the Nayband Formation (Late Triassic) is not unexpected. Moreover, the record of Clathropteris in the northeast of Isfahan is its first occurrence in an area outside of Kerman in Central Iran. Due to the low presence of plant macrofossils and the abundant presence of Clathropteris in the northeastern region of Isfahan, high humidity and warm weather of the Late Triassic may be suggested.
