سیستماتیک و جغرافیای دیرینه سرخس‌ها در گروه شمشک، ناحیه غزنوی، البرز شرقی

سرخس‌ها از جمله ماکروفسیل های گیاهی هستند که با فراوانی و تنوع زیاد در گروه شمشک واقع در شمال البرز شرقی یافت می‌شوند. هدف از این مطالعه بررسی بخش‌های مختلف سرخس‌ها از جمله فروند و اندام زایای منتسب به این ماکروفسیل های گیاهی در ناحیه غزنوی (بین شاهرود و آزاد شهر) است. در این تحقیق، هفت جنس و چهارده گونه سرخس از جمله: korallipteris yipinglagensis, cladophlebis nebbensis, cladophlebis australis, cladophlebis sp., cladophlebis haiburnensis, cladophlebis raciborskii, cladophlebis cf. scoresbyensis, cladophlebis denticulata, clathropteris meniscioides, dictyophyllum exile, dictyophyllum nathorsti, thainguyenopteris, parvipinnulata, osmundopsis sturiiو marattia intermediaشناسائی گردید که به سه راسته از سرخس‌ها به اسامی filicales،osmundales و marattiales تعلق دارند.گونه‌های فوق با نمونه‌های همزمان آن‌ها از سایر نقاط جهان مقایسه گردید. این مقایسه نشان می‌دهد که بیشترین شباهت بین گونه‌های ناحیه مورد مطالعه با کشورهای کره، ژاپن، چین، ویتنام، گرین لند، ایتالیا، آلمان و آرژانتین وجود دارد. از سوی دیگر، همراهی گونه‌های سازگار با آب و هوای گرم و مرطوب و گرم و نسبتا خشک‌تر، می‌تواند حاکی از آن باشد که گونه‌های مورد بررسی همگی در محیط lowland دلتایی، اما در زیر محیط‌های مختلف می‌زیسته‌اند.

Systematic and paleogeography of the ferns in Shemshak group, Ghozanavi area, eastern Alborz mountain

Introduction The eastern Alborz contains a rich assemblage of plant macrofossils studied previously by several authors (e. g. Corsin and Stampfli, 1977; VaezJavadi, 2006; Najafi, 2009 and VaezJavadi, 2016). Ferns are the most dominant plant macrofossils in the Shemshak Group (Kalariz formation) in the eastern Alborz Mountains. Accordingly, this study focuses on the ferns and the habitat of this group. In addition, paleogeographic distribution and the range of extension of encountered species are discussed, and the composition of ferns in the studied flora was compared to those of other Rhaetian assemblages in other parts of the world.Materials and methodsThe samples containing Triassic fern macroremains were collected through systematic sampling during the measurement of stratigraphic section in the Ghoznavi area (116 Km NE of Shahroud, 22 Km SE of Azadshahr). The specimens were studied using binocular microscopy. The identification and classification followed Taylor et al., 2009; Nagalingum and Cantrill, 2006; and Vera and Passalia, 2012.Results and discussionsThe aim of this study is to establish a systematic investigation of Triassic fern macrofossils including fronds and reproductive organs from Shemshak Group (Kalariz Formation) in the Ghoznavi area. The encountered specimens comprise of fern macroremains referable to three orders (Marattiales, Osmundales and Filicales) including 7 genera, 14 species: two Pterophyta incertae sedis species (Korallipteris yipinglagensis and Thainguyenopteris parvipinnulata); three Filicale species belonging to the Dipteridaceae (Dictyophyllum exile, Dictyophyllum nathorsti and Clatheropteris meniscioides); eight species of Osmundales and their reproductive organ (Cladophlebis nebbensis, Cladophlebis australis, Cladophlebis sp., Cladophlebis haiburnensis, Cladophlebis raciborskii, Cladophlebis scoresbyensis, Cladophlebis denticulata and Osmundopsis sturii); and one species of Marattiales (Marattia intermedia).Although certain encountered species are longranged, extending through the Jurassic period (i.e. Cladophlebis denticulata and Clathropteris meniscioides), others (i.e. Dictyophyllum exile, and Thainguyenopteris parvipinnulata) are indicative of Rhaetian.The encountered fern species in the studied area show the affinities with other Rhaetic flora from both Laurasia and Gondwana landmasses. The similarities between the fern species of the studied area and those of Korea, Germany and Argentina (each one having 5 common species); China and Japan (each one having 6 common species); and finally, Greenland, Italy and Vietnam (each one having 4 common species) support the cosmopolitan nature of these taxa during the Late Triassic.The presence of large and mature fern fragments, preserved parallel to bedding in gray shale and sandstone, indicates the lowland of deltaic environments (swamp, marsh, levee, flood plain). Most of the encountered Osmundaceae ferns are indicative of wetter lowland environment and warm conditions, although the osmundaceous genus, Cladophlebis denticulata, with narrow pinnules and denticulate margin, suggests drier conditions in drier parts of delta lowland (i.e. levee and flood plain). The large fronds of understory fern family, Dipteridaceae, (three species of Dictyophyllum and Clatheropteris) reflect a humid climate with low levels of light in lowland of delta (i.e. marsh and river bank), and the presence of Marattialean fern species (Marattia intermedia) suggests warm and moist environments in deltaic lowland (i.e. marsh and swamp).ConclusionA comparison was made between the Triassic ferns of the studied area and those of other parts of the World. This indicates broad similarity with the Late Triassic of Korea, Japan, China, Vietnam, Greenland, Sweden, Germany, Italy and Argentina. On the other hand, the cooccurrence of hydrophilic and xerophilic species reveals that these plants lived in the lowland of deltaic environment, but in different microhabitats.