فهرست مطالب

مجله پژوهش های دانش زمین
پیاپی 43 (پاییز 1399)

  • تاریخ انتشار: 1399/06/05
  • تعداد عناوین: 14
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  • معصومه ظاهری، بهروز رفیعی*، رضا علی پور صفحات 1-20

    اشکال تافونی در ماسه سنگ های نیوژن اشتهارد (جنوب باختری کرج)، واقع در بخش شمال باختری پهنه ساختاری ایران مرکزی، منظره قابل توجهی را در این گروه از سنگ ها به وجود آورده اند. مطالعه این اشکال فرسایشی در دو برش شمال اشتهارد و مردآباد به ترتیب با ضخامت تقریبی 820 تا 1080 متر بر روی نهشته های ماسه سنگی صورت گرفت. طی بررسی های میدانی مشخص شد که در برش شمال اشتهارد ضخامت لایه های ماسه سنگی، ابعاد و گستردگی تافونی ها (به ویژه در دامنه جنوب خاوری لایه های ماسه سنگی) و درزه های پرشده با ژیپس، بیشتر می باشد. بررسی های سنگ نگاری نشان داد که ماسه سنگ های برش شمال اشتهارد از نوع فلدسپاتیک ولکارنایت (Q11 F35 RF54) و برش مردآباد از نوع ولکارنایت (Q5 F12 RF83) می باشند. در ماسه سنگ های برش اشتهارد مقادیر فلدسپات و میزان دگرسانی بیشتر و مقادیر سیمان کلسیتی و دولومیتی کمتر از برش مردآباد است که می تواند ناشی از انحلال سیمان کربناتی باشد. آنالیز XRD بر روی مواد هوازده در داخل تافونی ها، حضور کانی های رسی ایلیت و کایولینیت را برای نمونه برش اشتهارد و کانی رسی ایلیت را برای نمونه برش مردآباد نشان می دهد. همچنین داده های بادسنجی، جهت باد غالب در منطقه مورد مطالعه را باختری و شمال باختری نشان می دهد. در مجموع ضخامت زیاد لایه های ماسه سنگی، وجود درزه های پرشده با ژیپس، فراوانی کانی های نامقاوم از قبیل فلدسپات های (ارتوز و پلاژیوکلاز) دگرسان شده، انحلال سیمان کربناته طی هوازدگی، تخلخل بین دانه ای بالا و نیز وزش بادهای غالب (به ویژه در جهت باختر)، باعث گسترش و پراکندگی بیشتر تافونی ها در برش شمال اشتهارد نسبت به برش شمال مردآباد گردیده است.

    کلیدواژگان: اشتهارد، تافونی، ماسه سنگ‌های نئوژن، مردآباد
  • محمدامین جعفری، علی کنعانیان*، احد نظرپور صفحات 21-34

    کمربند فلززایی ملایر-الیگودرز-اصفهان با طولی افزون بر 400 کیلومتر و عرض 90 کیلومتر بزرگترین کمربند فلززایی سرب و روی در ایران است. با توجه به اینکه یکی از مهم ترین فلزات همراه با زون های سرب و روی، مس می باشد، در این پژوهش، به منظور جدایش جوامع آنومالی ژیوشیمیایی از زمینه این فلز از روش های فرکتال عیار- مساحت (C-A) و شاخص سینگولاریتی (SI) استفاده شده است. لذا تجزیه و تحلیل 19974 نمونه از رسوبات آبراهه ای با استفاده از روش های نام برده در زون فلززایی ملایر- الیگودرز- اصفهان، منجر به تفکیک مناطق آنومال عنصر مس گردید. در نقشه های حاصل از مدل فرکتال عیار- مساحت (C-A)، قسمت های شمال غرب و جنوب شرق زون بیشترین میزان آنومالی را از خود نشان می دهد. در نقشه های حاصل از روش شاخص سینگولاریتی (SI)، آنومالی های پنهان بهتر نمایش داده شده و انطباق خوبی بین آنومالی ها و موقعیت فعلی معادن مس در زون مورد نظر وجود دارد. با تطبیق آنومالی های به دست آمده از هر دو روش با نقشه زمین شناسی محدوده مورد نظر، مشخص گردید که آنومالی های به دست آمده هم پوشانی بالایی با واحد آهک کرتاسه در منطقه نشان می دهد و لذا این واحد می تواند راهنمای اکتشافی مناسبی برای پی جویی عناصری نظیر سرب، روی و مس در این منطقه محسوب شود.

    کلیدواژگان: فرکتال، عیار-مساحت، شاخص سینگولاریتی، مس، ملایر-الیگودرز-اصفهان
  • بهزاد سعیدی رضوی*، علیرضا گنجی، سپهر ضرابی صفحات 35-52

    در این پژوهش ریزرخساره ها، محیط رسوبی و پالیواکولوژی سازند آسماری با تکیه بر مطالعه 105 مقطع نازک (شامل مغزه های حفاری) تهیه شده از 132 متر توالی های برش تحت الارضی یکی ازچاه های میدان نفتی کرنج انجام شده است. 12 ریزرخساره شناسایی و تفسیر شد که شامل: 1) انیدریت، 2) مادستون-دولومادستون، 3) باندستون استروماتولیتی، 4) ماستون کوارتزدار، 5) بیوکلاستیک بنتیک فرامینیفرا (بدون منفذ) پکستون-گرین استون، 6) بنتیک فرامینیفرا (منفذ دار و بدون منفذ) وکستون-پکستون-گرین استون، 7) بایوکلاست گرینستون، 8) اایید گرینستون، 9) کورالیناسه آ کورال فلوتستون، 10) لپیدوسیکلینا کورالیناسه آ نیوروتالیا پکستون-گرین استون، 11) لپیدوسیکلینا نومولیتیده پکستون-وکستون، 12) پلاژیک فرامینیفرا وکستون هستند، که می توان به 5 محیط رسوبی شامل: پهنه جذر و مدی، لاگون محصور، لاگون نیمه محصور، دریای باز تقسیم کرد. به طور کلی این رسوبات تحت 3 نوع متفاوت از شوری در دریایی باز(psu 40-34)، لاگون نیمه محصور (psu 50-45) و لاگون محصور (بیش از (psu 50 با زون نوری افوتیک، الیگوفوتیک، مزوفوتیک تا یوفوتیک و تحت 4 نوع رژیم غذایی: الیگوتروفی، مزوتروفی، یوتروفی و هایپرتروفی در یک پلاتفرم کربناته از نوع رمپ هموکلینال در زمان چاتین تا بوردیگالین رسوب گذاری نموده است.

    کلیدواژگان: پالئواکولوژی، ریزرخساره‌ها، سازند آسماری، محیط رسوبی، میدان نفتی کرنج
  • زهرا فرهمندفر، محمدرضا جعفری، پیمان افضل*، افشین اشجع اردلان صفحات 53-72

    هدف از این پژوهش، شناسایی ناهنجاری های عنصری با استفاده از ترکیب مدل فرکتالی1 (فرکتال، ساختاری هندسی است که با بزرگ کردن هر بخش از این ساختار به نسبت معین، همان ساختار نخستین به دست آید؛ به بیان دیگر، فرکتال ساختاری است که هر بخش از آن با کل آن همانند است. فرکتال در بسیاری از ساختارهای طبیعی مثل سنگ ها، برف، رسوب گذاری، برگ و تنه درختان، DNA و غیره دیده می شود. هندسه فرکتال یا هندسه بعد چهارم یا هندسه طبیعت در تضاد کامل با هندسه اقلیدسی بعدهای اول تا سوم می باشد. درواقع هندسه فرکتال تعریفی از نظریه بی نظمی یا آشوب است). عیار-تعداد و آنالیز فاکتوری مرحله ای نمونه های رسوبات آبراهه ای با داده های ژیوفیزیک هوابرد برگه 1:100،000 لاهرود بود. منطقه مورد مطالعه در نوار آتش فشانی البرز-آذربایجان واقع است. تمام عناصر اخلال کننده (مولیبدن، برلیوم، جیوه، سرب، نقره، استرانسیوم، سلنیوم و بیسموت) پس از اعمال چهار مرحله آنالیز فاکتوری حذف شدند و عناصر ارسنیک، آنتیموان، قلع، تنگستن، کبالت، منگنز، روی، تیتانیوم، باریوم، نیکل، کروم، طلا، مس و بور در پنج گروه طبقه بندی شدند؛ مس و طلا در گروه چهار از مرحله چهارم قرار گرفتند. نمودار عیار-تعداد امتیازهای فاکتوری ترسیم و مقادیر آن ها به منظور تهیه نقشه های جوامع ژیوشیمیایی، تعیین شد. مناطق ناهنجار عناصر فلزی در بخش های شمال غرب، مرکز و جنوب غرب منطقه قرار دارند که نشان دهنده هم بستگی با مناطق دگرسان شده، گسل ها و توده های نفوذی می باشد. با استفاده از داده های ژیوفیزیک هوایی و تهیه نقشه های مربوط به آن، توده ژرف سنگ در جنوب غربی، که توجیه کننده دگرسانی ها و در نتیجه، ناهنجاری هاست و هم چنین مناطق قابل پی جویی منطقه لاهرود شناسایی شد.

    کلیدواژگان: پتانسیل عنصری، ژئوشیمی(زمین‌شیمی)، ژئوفیزیک(زمین‌فیزیک) هوایی، شمال‌غرب ایران
  • محمد گودرزی*، حسن زمانیان، علیرضا جوانشیر، محمدرضا رضوانیان زاده، محمدرضا قادری صفحات 73-88

    منطقه مطالعاتی در خاور شهر بم و در بخش جنوبی بلوک لوت واقع شده است. با هدف بررسی مقدار و رفتار اورانیوم و عناصر همراه در منطقه ای به وسعت 10 کیلومتر مربع تعداد 616 نمونه لیتوژیوشیمیایی برداشت و جهت انجام آنالیز ICP-MS به آزمایشگاه لب وست استرالیا فرستاده شدند. مطالعات آماری مختلف از قبیل تحلیل ضرایب همبستگی، آنالیز خوشه ای و تجزیه تحلیل عاملی به شناسایی دو نوع مجموعه ژیوشیمیایی مرتبط با حضور اورانیوم در سنگ های منطقه منجر گردید که عبارتند از مجموعه های مرتبط با سنگ های اسیدی و حدواسط دگرسان شده (آرژیلیک) شامل U-W-As-Mo-S-Cu-Ag و مجموعه های مرتبط با سنگ های آذرین بازیک که شامل U-Ni-V-Ag-Co-W-Mo-Cr-Cu-S. همچنین چهارگروه عنصری به دلیل داشتن همبستگی ژیوشیمیایی با اورانیوم می توانند مورد توجه قرار گیرند که عبارتند از: عناصر نادر خاکی: Ce, La, Y عناصر پلی متال: As, Sb, Ba, Cu, Pb, Zn, Mn, Fe, Se Sr, عناصر مرتبط با آتشفشان های اسیدی: Be, Mo, W, Zr عناصر مرتبط با فعالیت های ماگمایی مافیک: Co, Cr, Ni, V. براساس بررسی نقشه های آنومالی ژیوشیمیایی عناصر ردیاب اورانیوم در منطقه مشاهده می شود که عناصر Mo, W, As, Sb, Tl, Pb, Be و Cd دارای روند غنی شدگی منطبق بر آنومالی های اورانیوم می باشند و در میان عناصر ردیاب در درجه اول اولویت قرار دارند. با انطباق منحنی های هم تراز اورانیوم بر روی نقشه زمین شناسی منطقه، مشاهده می شود که آنومالی های یاد شده منطبق با زون های خردشدگی و روند گسل های منطقه می باشند و منطبق بر واحدهای توف ریولیتی (داسیت توف، توف های ریولیتی )، واحدهای حد واسط، همراه با دگرسانی های آرژیلیتی، اکسیدها و هیدروکسیدهای آهن و در بعضی نقاط همراه با دگرسانی کربناتی و کانی زایی منگنز می باشند.

    کلیدواژگان: آمار، اورانیوم، بم، زمین‌شناسی ژئوشیمی، عنصر
  • اکرم مهدیزاده، فاطمه واعظ جوادی*، علیرضا عاشوری، عباس قادری صفحات 89-112

    سازند هجدک در منطقه چاه رخنه، جنوب غرب طبس دربر دارنده ماکروفسیل های گیاهی به نسبت خوب حفظ شده ای می باشد به طوری که تعداد 33 گونه ماکروفسیل گیاهی متعلق به 21 جنس از راسته های مختلف شناسایی شدند. براساس اولین و آخرین حضور مشاهده شده گونه های شاخص، یک زیست زون تجمعی با نامConiopteris hymenophylloides- Klukia exilis Assemblage zone و سه زیر زیست زون غیررسمی شامل: زیر زیست زون Equisetites beanii- Ptilophyllum harrisianum Interval zone (I)، زیر زیست زونPtilophyllum harrisianum- Elatides thomasii Interval zone (II) و زیر زیست زون Elatides thomasii - Nilssonia macrophylla Interval zone (III) به ترتیب از پایین به بالا تعیین گردیدند. این زیست زون ها با سایر زیست زون های هم ارز بازه زمانی ژوراسیک میانی در منطقه طبس قابل مقایسه و تطابق می باشند. حضور گونه های Klukia exilis و Elatides Thomasii نشان دهنده سن آالنین- باژوسین برای این مجموعه می باشد. مطالعات آماری نشان می دهد که راسته های فیلیکال ها، سیکادال ها، پاینال ها و اکویی ستال ها به ترتیب با فراوانی نسبی 31/46 %، 50/23 %، 12 % و 26/9 % و جنس های Nilssonia، Klukia، Coniopteris و Equisetites به ترتیب با فراوانی نسبی 81/22 %، 38/13 %، 40/8 % و 40/8 % بیشترین حضور را در منطقه چاه رخنه داشته اند. بدین ترتیب، براساس فراوانی نسبی فیلیکال ها و سیکادال ها، حضور گونه های شاخص آب و هوایی و بوم شناختی نظیر Equisetites beanii و میانگین عددی تراز گیاهی فلورای چاه رخنه (81/41)، آب و هوای مرطوب و نیمه گرمسیری در این منطقه در بازه زمانی آالنین- باژوسین غلبه داشته است.

    کلیدواژگان: آب و هوای دیرینه، زیست چینه‌نگاری، ژوراسیک میانی، سازند هجدک، ماکروفسیل‌های گیاهی، طبس
  • مریم فرهی منش، محمد قویدل*، عباس صادقی صفحات 113-132

    سرخس ها از جمله ماکروفسیل های گیاهی هستند که با فراوانی و تنوع زیاد در گروه شمشک واقع در شمال البرز شرقی یافت می شوند. هدف از این مطالعه بررسی بخش های مختلف سرخس ها 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 intermedia شناسایی گردید که به سه راسته از سرخس ها به اسامی Filicales،Osmundales و Marattiales تعلق دارند. گونه های فوق با نمونه های همزمان آن ها از سایر نقاط جهان مقایسه گردید. این مقایسه نشان می دهد که بیشترین شباهت بین گونه های ناحیه مورد مطالعه با کشورهای کره، ژاپن، چین، ویتنام، گرین لند، ایتالیا، آلمان و آرژانتین وجود دارد. از سوی دیگر، همراهی گونه های سازگار با آب و هوای "گرم و مرطوب" و "گرم و نسبتا خشک تر"، می تواند حاکی از آن باشد که گونه های مورد بررسی همگی در محیط Lowland دلتایی، اما در زیر محیط های مختلف می زیسته اند.

    کلیدواژگان: البرز شرقی، تریاس پسین، سرخس‌ها، گروه شمشک، ماکروفسیل های گیاهی
  • عاطفه نیمروزی، غلامرضا قدمی*، جمشید حسن زاده، محمد پوستی صفحات 133-148

    تاریخچه تکاملی زون سنندج-سیرجان، تحت تاثیر دو رژیم کششی و فشارشی بوده که باعث ایجاد بازشدگی، فرورانش، تصادم و بسته شدن نهایی آن شده است. این پژوهش با استناد به مطالعات پتروگرافی، ژیوشیمی و همچنین داده های سن سنجی سنگ های آتشفشانی منطقه اسفندآباد یزد، شواهدی از باز شدگی و ولکانیسم حاصل از آن را در اختیار قرار می دهد. توالی مورد مطالعه شامل گدازه های تیره رنگ آندزیتی، ریولیتی و بازالتی همراه با میان لایه های آذرآواری همراه با واحدهای رسوبی است. در مقاطع میکروسکوپی، کانی های اصلی تشکیل دهنده در سنگ های آندزیتی به ترتیب فراوانی شامل پلاژیوکلاز، پیروکسن و کوارتز، در سنگ های ریولیتی پلاژیوکلاز، فلدسپار آلکالن و کوارتز و در بازالت ها شامل پلاژیوکلاز، اولیوین و پیروکسن است. براساس داده های ژیوشیمیایی، سنگ های مورد مطالعه دارای ترکیب شیمیایی بازالتی و تراکی داسیتی با گرایش کالک آلکالن و توله ایتی می باشند. همچنین نمودارهای تعیین جایگاه تکتونیکی محیط درون صفحه ای را در تشکیل آنان تایید می نماید. مطالعات ژیوشیمیایی نشان داد که سنگ های تراکی داسیتی حاصل 5% ذوب بخشی یک منشا گارنت-لرزولیت و سنگ های بازالتی حاصل20 % ذوب بخشی یک منشا اسپینل-لرزولیتی می باشند. مطالعات سن سنجی براساس زیرکن های موجود در سنگ های تراکی داسیتی به روش اورانیوم-سرب سن 6/6 +240 معادل با تریاس زیرین را برای این بازشدگی ارایه داده است که با بازشدگی و تشکیل اقیانوس نیوتیس در پرموتریاس مطابقت می کند.

    کلیدواژگان: اسفندآباد، سنندج-سیرجان، باز شدگی، نئوتتیس، یزد
  • محمدحسین جهانگیر*، سیده مهسا موسوی رینه، مهناز ابواقاسمی صفحات 149-166

    بررسی خشکسالی به عنوان یکی از مخاطرات طبیعی، که زندگی اکثر مردم به آن گره خورده است، بسیار حایز اهمیت است. جهت آماده سازی در مقابله با خشکسالی و کاهش خسارات ناشی از آن از روش های شبیه سازی، مدل سازی و تهیه مقدمات احتمال وقوع خشکسالی، استفاده می شود. در این مطالعه برای فراهم آوردن یک دید کلی از شرایط خشکسالی آینده از دو شاخص خشکسالی SSI و SPI استفاده گردید. در گام اول داده های مربوط به دبی و بارش با استفاده از مدل CanESM2 تحت سناریو انتشار RCP4.5 و مدل ریزمقیاس SDSM برای دوره 2050-2020 پیش بینی شد سپس با توجه به موقعیت جغرافیایی هر ایستگاه مناسب ترین تابع توزیع تجمعی برای هر شاخص در هر ایستگاه انتخاب گردید و امکان محاسبه شاخص های خشکسالی SSI و SPI فراهم گردید. نتایج نشان داد در دوره آتی براساس شاخص SSI، ایستگاه شریف آباد بیشترین مقدار خشکسالی (74/2-) را داراست و همچنین براساس شاخص SPIبیشترین مقدار شاخص خشکسالی (17/2-) مربوط به ایستگاه لتیان است. لازم به ذکر است که تطابق دو شاخص در ایستگاه های نمرود و لتیان نیز با ترسیم متناظر منحنی تغییرات در طی دوره مطالعاتی نشان داد که اختلاف مقادیر عددی این دو کمیت، تنها برای 5 سال از انطباق مناسبی برخوردار نیست.

    کلیدواژگان: پیش‌بینی خشکسالی، شاخص SPI و SSI، SDSM، استان تهران
  • مهدی صدیقی، بهارک معتمدوزیری*، حسن احمدی، ابوالفضل معینی صفحات 167-182

    در این تحقیق، سه مدل داده کاوی شامل شبکه عصبی مصنوعی، ماشین بردار پشتیبان و بیشینه آنتروپی برای ارزیابی حساسیت زمین لغزش در حوزه آبخیز تجن استان مازندران انتخاب گردید. نتایج مدل ها با شش شاخص کارایی مدل شامل: 1) روند توزیع مساحتی کلاس های حساسیت، 2) روند توزیع عددی زمین لغزش ها در کلاس-های حساسیت، 3) خطای نوع یک مدل سازی (مثبت کاذب)، 4) خطای نوع دو مدل سازی (منفی کاذب)، 5) مساحت زیر منحنی نرخ موفقیت و 6) مساحت زیر منحنی نرخ پیش بینی بررسی گردید و براساس آن ها مدل ها رتبه بندی شدند. نتایج حاکی از آن بود که براساس شاخص اول، مدل های بیشینه آنتروپی، ماشین بردار پشتیبان و شبکه عصبی مصنوعی به ترتیب بهترین تا ضعیف ترین کارایی را نشان دادند. براساس شاخص دوم، به ترتیب مدل های ماشین بردار پشتیبان، بیشینه آنتروپی و شبکه عصبی مصنوعی بهترین تا ضعیف ترین عملکرد را ارایه نمودند. شاخص سوم با اشاره به پتانسیل خسارات اقتصادی ناشی از خطای مدل سازی بیانگر عملکرد مناسب مدل ماشین بردار پشتیبان بود و مدل های بیشینه آنتروپی و شبکه عصبی مصنوعی مشترکا در درجات بعدی اهمیت قرار گرفتند. همچنین، شاخص چهارم با اشاره به پتانسیل تلفات جانی و مالی ناشی از خطای مدل سازی نشانگر عملکرد خوب مدل شبکه عصبی مصنوعی بود و مدل های بیشینه آنتروپی و ماشین بردار پشتیبان به ترتیب در رتبه دوم و سوم قرار گرفتند. نتایج حاصل از شاخص های پنجم و ششم بیانگر قدرت بالای یادگیری و تعمیم نتایج در مدل ماشین بردار پشتیبان بود و مدل های بیشینه آنتروپی و شبکه عصبی مصنوعی در درجات بعدی اهمیت قرار گرفتند.

    کلیدواژگان: بیشینه آنتروپی، شبکه عصبی مصنوعی، ماشین بردار پشتیبان، مثبت کاذب، منفی کاذب
  • سیده آزاده آقاجان زاده، محسن تابان* صفحات 183-202

    با افزایش جمعیت، شهرها با رشد روز افزون بلند مرتبه سازی و همچنین تراکم بالای جمعیتی و ارتفاعی روبه رو شده اند. توریستی بودن و افزایش جمعیت در شهر بابلسر در سال های اخیر باعث افزایش بی رویه ساخت و ساز و بلند مرتبه سازی شده است. دلیل استقرار این ساختمان ها در این محدوده ها، دید بصری مناسب به دریا، وجود دسترسی با عرض مناسب، وجود زیرساخت ها و امکانات می باشد که استقبال سرمایه گذاران برای ساخت و ساز را به دنبال داشته است. شهر بابلسر در اقلیم معتدل و مرطوب واقع شده است و رطوبت نسبی آن نسبتا بالاست، شرجی بودن و احساس گرمای بیش از حد واقعی از نتایج بالا بودن رطوبت است. از این رو، مهم ترین عامل ایجاد آسایش در این مناطق، برقراری و تداوم کوران در فضاست. با توجه به تغییر در تراکم ارتفاعی و نوع چیدمان و توده های جدید، جهت و سرعت جریان باد دچار تلاطم شده است که به لحاظ بیولوژیکی و احساس آرامش برای ساکنین مشکلاتی را در پی دارد. در این پژوهش اثرات بلند مرتبه سازی و تغییرات در دو بلوک شهری، در محدوده شمالی شهر بابلسر با نرم افزارFlow-3d شبیه سازی و مورد ارزیابی قرار گرفته است. در گرم ترین روزهای تابستان تاثیر تراکم ارتفاعی و چیدمان توده ها بر دمای بلوک ها و سرعت جریان باد بین آنها بررسی شده است. با افزایش ارتفاع، افزایش محصوریت و جهت گیری نا مناسب توده ها، کوران باد اتفاق نمی افتد در این صورت دمای بین توده ها افزایش می یابد و باعث سلب آسایش ساکنین این محدوده شده است. برای بهبود وضعیت نیاز به تغییر در شرایط کالبدی با توجه جهت و توزیع جریان باد است.

    کلیدواژگان: بلوک شهری، بلندمرتبه‌سازی، سرعت باد، رطوبت، شبیه‌سازی سیال، بابلسر
  • خه بات درفشی*، صارم امینی، ولی جهانی، ناصر رضایی صفحات 203-222

    در زمین باستان شناسی با تشخیص و بررسی محتوای رسوبی و چینه نگاری لایه ها و مواد باستان شناسی، می توان درک کامل و صحیحی از پیشینه های باستانی به دست آورد. نوشتار حاضر گزارشی از مطالعات زمین شناختی و رسوب شناختی در محل برش رسوبی - باستانی گسکرک واقع در شهرستان رودبار است که به منظور بازسازی شرایط محیطی دیرینه انجام گرفته است. برش گسکرک شامل دو لایه رسوب آبرفتی - واریزه ای ریزدانه، با تمایز رنگ مشخص می باشد که مرز زیرین آن ها محدود به سنگ بستر رسوبی و مرز بالایی آن ها توسط نهشته های استقراری جدیدتر پوشیده شده است. رسوبات طبیعی تشکیل دهنده این دو لایه را ذرات در حد سیلت شامل می شود که تراکم بالایی را نشان می دهد. لایه پایینی (لایه I) عمدتا از رسوبات ریزدانه سیلتی با ناخالصی مواد آهکی تشکیل شده است که درون آن قطعات آهکی به صورت پراکنده مشاهده می شود. لایه II که در مرز بالایی خود توسط نهشته های طبیعی فرهنگی عصر مفرغ پوشیده شده است با وجود خرده های زغالی مشخص می شود که آن را از لایه زیرین خود متمایز می کند. مطالعه نمونه های عهد حاضر شرایط آب و هوایی خشک تا نیمه خشک را برای تشکیل افق های کربناتی شده در خاک پیشنهاد می کند. محتوای کم مواد کربناتی، رنگ قرمز- قهوه ای و همچنین وجود خرده های زغالی در لایه II که متمایز از لایه I می باشد، شرایط دیرینه محیطی متفاوتی را برای لایه II پیشنهاد می کند که به نظر می رسد با تغییر شرایط آب و هوایی، افزایش بارندگی و رطوبت و گسترش پوشش گیاهی جنگلی در منطقه همزمان بوده است.

    کلیدواژگان: زمین‌باستان‌شناسی، میکرومورفولوژی، رسوب‌شناسی، قطعات آهکی، برش رسوبی- باستانی گسکرک، رودبار
  • مهرداد کیانی، حسن لشکری*، هوشنگ قائمی صفحات 223-244

    وقوع بارش های روزانه فرین نقش مهمی در سامانه اقلیم و هیدرولوژی غرب ایران دارد. در زمستان با نفوذ سامانه های بارشی به غرب ایران شرایط برای رخداد بارش های شدید فراهم می شود. در این مطالعه شدیدترین رخداد فرین های بارشی زمستان غرب ایران در دوره آماری 1996 تا 2017 مورد بررسی قرار گرفت. هدف از این پژوهش تحلیل همدیدی سامانه های عامل رخداد شدیدترین فرین های بارشی زمستان بوده است. ابتدا با پردازش های آماری بیشینه بارش های روزانه مشخص شد و با تعیین آستانه بارش روزانه 41 میلی متر، شدیدترین رخداد فرین بارشی هر ماه مورد تحلیل قرار گرفت. نتایج تحلیل نشان داد که در شرایط رخداد فرین ها، پرفشار روی ایران تضعیف شده و سامانه های کم فشار در تراز دریا جایگزین آن شده اند. در تراز میانی جو جریانات جنوبی و غربی در قسمت جنوب شرقی ناوه مدیترانه همگرا شده و به بخش غربی ایران نفوذ کرده اند. بیشینه محتوای رطوبتی سامانه ها از طریق دریای سرخ و با کمک سامانه واچرخندی مستقر روی عربستان تامین شده است. در ماه دسامبر عمیق شدن ناوه مدیترانه ای و جذب رطوبت از دریای سرخ عامل وقوع فرین بارشی بوده است. در ماه های ژانویه و فوریه استقرارسامانه بلوکینگ کم ارتفاع بریده در تراز میانی جو شرایط مناسب برای وقوع بارش سنگین در سطح زمین را فراهم نموده است. بهره گیری همزمان از رطوبت دریاهای سرخ و مدیترانه، موجب رخداد فرین ماه ژانویه و رخداد بارش سنگین در بیشتر ایستگاه ها شده است. اما در جریان رخداد فرین ماه فوریه فقط ایستگاه های دامنه غربی به دلیل نزدیکی به مسیر رطوبت دریای سرخ شاهد بارش سنگین بوده اند.

    کلیدواژگان: بارش فرین، سامانه، همدید، نم ویژه، فشار
  • محمود احمدی*، محمد آزادی مبارکی صفحات 245-262

    یکی از مهم ترین جنبه های رشد سریع و بدون برنامه ریزی شهری، کاهش سطح پوشش گیاهی است که اغلب با سطوح غیرمجاز مانند ساختمان ها و سایر سطوح نفوذ ناپذیر جایگزین می شود. کلانشهر تبریز، یکی از مناطق شهری مهم است که با رشد سریع در شمال غرب ایران واقع شده است. در این مطالعه، تغییرات زمانی- مکانی دمای سطح زمین (LST) با استفاده از داده های ماهواره LANDSAT7 سنجنده ETM+برای یک دوره 15 ساله (2013-1999) با هدف زیست پذیری شهر تبریز و دسته بندی جزایرحرارتی شهری مطالعه شد. برای محاسبه UHI از رویکرد تکاملی فرکتال ویژه (FNEA) و همچنین برای وضعیت زیست محیطی شهری از روش قیاسی وضع بحرانی زیست محیطی (ECI) براساس LST و NDVI استفاده شد. نتایج نشان داد متوسط LST در کلان شهر تبریز بین 30 تا 43 درجه سلسیوس است و از سال 2010 به بعد بر مقدار انحراف معیار دمای سطح زمین افزوده شد؛ به طوری که مقدار بیش از 4 درجه سلسیوس نیز برای LST مشاهده شد. تحلیل منطقه ای دما و پارامترهای موثر آن در کلان شهر تبریز نشان از همبستگی معنی داری بین LST با NDVI (منفی) و مناطق ساخته شده شهری (مثبت) وجود دارد. مهم ترین جزایر حرارتی شهری تبریز که با استفاده از روش FNEA آشکار شدند در فرودگاه تبریز، مناطق مسکونی پر تراکم همچون ملازینال، مناطق صنعتی جنوب غربی و پایانه های شهری تبریز دیده می شوند. شاخص ECI نشان داد سال های 2002، 2003 و 2009 بیش ترین مناطق طاقت فرسا را دارند؛ مقادیر SUHI و ECI در کلان شهر تبریز دارای تطابق مکانی هستند؛ لذا فضاهای سبز می توانند به بهبود پایداری محیطی کلان شهر تبریز برای زیست پذیری شهری کمک شایان توجهی کنند.

    کلیدواژگان: جزایر حرارتی شهری، دمای سطح زمین، روش FNEA، زیست پذیری شهری، کلان شهر تبریز
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  • Masoomeh Zaheri, Behrouz Rafiei*, Reza Alipoor Pages 1-20
    Introduction

    Tafoni weathering refers to large cave-like holes ranging from a few decimeters to several meters wide. They develop often in the medium and coarse-grained silicate rocks such as sandstones, conglomerates and granites in various areas, under arid and semi-arid climate condition

    Materials and Methods

    To identify the tafoni forms, we measured the morphological features (such as the dimensions and extent) of the tafoni in the sandstone layers in the north of Eshtehard and Mardabad sections. A total of ten medium to coarse-grained sandstone samples were selected from the lens-liked channel deposits. Framework mineral composition (modal analysis) was quantified using the point-counting method (300-500 point) of Gazzi and Dickinson, as described by Ingersoll et al. (1984).

    Results and discussion

    Field survey To calculate the dimensions of the tafoni in the sandstone layers, the width (W), height (H) and depth (D) of the ninety eight tofoni were measured in different parts of two sections. The higher average values of W than the mean values of H and D and also the higher W/D values than H/D indicate that the tafoni forms in the sandstone layers are more elliptical and semicircular (W> H> D).

    Petrography


    Based on the petrographical and modal analysis, the mean grain size in the sandstone samples are about 0.5 mm with weak to moderate sorting and rounded to subrounded grains. Sandstone samples from the Eshtehard section include high amount of the igneous, sedimentary and metamorphic rock fragments (average 53.8%), and the feldspar (orthoclase and plagioclase) (average 35.4%), and low amount of mono-and poly-crystallin quartz grains (average 10.8%) with point, straight to concavo-convex grain contacts. In turn, the Mardabad sandstone samples show higher proportion of the igneous and sedimentary rock fragments (average 83%) and lower proportion of the feldspar (average 12%) and quartz (average 2.5%). The average amount of calcium carbonate in the Eshtehard and Mardabad sandstone samples are 6.4% and 10.4%, respectively.

    Dissolution

     of unstable grains such as feldspars (plagioclase and orthoclase) and carbonates (microcrystalline and fossil particles) and rock fragments due to the infiltration of acidic waters, promotes the development of porosity in the rock and reduces its resistance during chemical and physical weathering (Hamblin and Christiansen 2008). The Eshtehard sandstones include higher feldspar amount (Q11 F35 RF54) than that of the Mardabad sandstones (Q5 F12 RF83). According to microscopic studies, the Eshtehard sandstones have higher propotion of feldspar and in turn, higher chemical alteration. The development alteration in the feldspar grains can cause the weakness or loose texture and finally physical destruction of rock zones. Dissolution of calcite and dolomite cement Low proportion of calcite and dolomite cement due to dissolution have caused an increased amount of porosity of grains in the process of tofoni formation in the Eshtehard sandstones. The relatively high amounts of calcite cement and calcium carbonate rock fragments, low intergranular porosity and also point, straight to concavo-convex grain contacts created a relatively strong texture in the sandstones of the north of Mardabad section.

    Conclusions

    The presence of feldspar grains (in high amounts) and low amounts of calcite and dolomite cement, and consequently the increase of intergranular porosity (due to the alteration of feldspars and dissolution of calcite and dolomite cement) are important factors in the formation of tafoni in sandstone layers of the Eshtehard compared to the Mardabad sections. In general, the high thickness and extent of sandstone layers, chemical alteration of feldspars, and patch carbonate cement due to dissolution, control the formation and development of tafoni in the Eshtehard section.

    Keywords: Eshtehard, Tafoni, Neogene sandstone, Mardabad
  • MohamadAmin jafari, Ali Kananian*, Ahad Nazarpour Pages 21-34
    Introduction

     Malayer-Aligudarz-Esfahan metal belt with a length of more than 400 km and a width of 90 km is located in the active zone of Sanandaj-Sirjan and is the largest lead and zinc metal belt in Iran. Considering that one of the most important metals with Pb and Zn zones is Cu, in this study, in order to separate geochemical anomalies from background anomaly of the Cu metal, we used fractal methods of concentration-area (C-A) and Singularity Index (SI).

    Materials and Methods

    Multifractal Fractal and multifractal models have also been applied to separate anomalies from background values. These methods are gradually being adopted as an effective and efficient means to analyze spatial structures in metallic geochemical systems. The concentration-number (C-N), concentration-area (C-A) multifractal methods have been used for delineation and description of relations among mineralogical, geochemical and geological features based on surface and subsurface data. Fractal/multi-fractal models consist of the frequency distribution and the spatial self-similar or self-affine characteristics of geochemical variables and have been demonstrated to be effective tools for decomposing geological complexes and mixed geochemical populations and to recognize weak geochemical anomalies hidden within strong geochemical background.Singularity Index (SI) The Singularity technique is another important method developed for fractal/multifractal modeling of geochemical data. It is defined as the characterization of the anomalous behaviors of singular physical processes that often result in anomalous amounts of energy release or material accumulation within a narrow spatial–temporal interval. The Singularity can be estimated from observed element concentration within small neighborhoods based on the following equation:(1) The Singularity Index is a powerful tool to identify weak anomalies, but it is influenced by the selection of the window size.

    Results and Discussion

    In general, 19974 stream sediment geochemical samples were analyzed using the ICP-MS and XRF method. The geochemical anomalies of the Cu metal were separated using fractal methods concentration-area (C-A) and according to the fitting line Cu metal on the logarithmic graph. The singularity index was estimated through a large window and mainly reflects regional changes but it does not focus on the local weak anomalies. In maps derived from fractal method of concentration-area (C-A), the North-West and South-East parts of the zone showed the highest anomaly. In maps that were obtained from the Singularity Index method, the hidden anomalies are better represented and there is a good overlap between the anomalies and the current position of the Cu deposits in the target zone.

    conclusions

    By matching the anomalies obtained from both methods with the geological map of the target area, it was determined that the obtained anomalies showed high overlap with the cretaceous limestone unit in the region. So this unit can be a good guide of exploration for identifying elements such as Pb, Zn and Cu in this area.

    Keywords: Fractal, Concentration-Area, Singularity index, Cu, Malayer-Aligudarz-Esfahan
  • Behzad Saeedi Razavi*, Alierza Ganji, Sepehr Zarrabi Pages 35-52
    Introduction

    The Asmari Formation (Oligo-Miocene) is spread in the Zagros region. The Formation was first identified in Tang-Gel-Torsh, located on Mount Asmari. In a sample type section, the thickness of this formation is 314 meters. Kranj oil field is one of the most important oil fields in the North of the restricted embayment of Dezful. The Karanj anticline structure, one of the most important oil fields in Iran, is located in the southwest of the Zagros sedimentary basin and in the southern part of the north of restricted Dezful embayment adjacent to the Persian fields.

    Material and methods

    The study section is located 115 km east of Ahvaz. In this study, 105 thin sections of core drilling, belonging to Asmari Formation wells, were prepared in Karanj oil field. They were prepared with the help of a microscope equipped with a camera and carefully examined in lithology and fossiles studies. In the study of microfacies, the naming of limestones was done by Dunham and Amberi and Calvan methods and the identification of microfacies was based on the Flogel model. Asmari Formation is 132 meters thick in this well.

    Resultes and Discussion

    In this study, microfacies, depositional environment and paleoecology of Asmari Formation have been performed based on the study of 105 thin sections (including Core drilling) prepared from 132 m of subsurface cutting sequences from one of the wells of Karanj oil field.12 microfacies related to the environments, tidal flat, lagoon, shoal and open marine were identified and interpreted, including: 1) Anhydrite, 2) Mudstone-Dolomudstone, 3) Stromatolitic boundstone, 4) Quartz mudstone, 5) Bioclastic benthic foraminifera (perforate and imperforate) packstone-grainstone, 6) Benthic foraminifera (perforate) wackestone-packstone-grainstone, 7) Bioclastic grainstone, 8) Ooid grainstone, 9) Corallinacean coral floatstone, 10) Lepidocyclina corallinacean Neorotalia packstone-grainstone, 11) Lepidocyclina Nummulitids wackestone-packstone, 12) planktonic foraminifera wackestone, which can be grouped into five depositional environments: tidal flat, restricted lagoon, open lagoon, shoal and open marine.Investigating the important factors in the distribution of large benthic Foraminifera in this well The following factors play a role in the distribution of large benthic Foraminifera in the study period: 1- Salinity, 2- Distribution of food, 3- Temperature, 4- Water mobility, 5- Water depth, 5- Light.

    Conclusion

    In deposits of Asmari Formation in this well in Karanj oil field, aging from chattian to Burdigalin, with 132 meters in thickness, 12 microfacies were identified. The microfacies identified in this section belong to four ancient environments, including the tidal flat, lagoon, shoal, and open marine. Based on these microfacies and how to expand them, a hemoclinical ramp is recommended for sedimentation of this Formation. .Based on the presence of benthic and other components of sediments and how they are distributed in the carbonate platform, these sediments were formed with normal salinity in aphoic, oligophic and oligophic to mesophotic zones and under low nutritional (oligotrophy) and medium (mesotrophy) food conditions in chatian age. In Aquitanian-Burdigalian age, in the study section, high salinity conditions in the uphotic zone with high (uphotic) feeding conditions were present. Within the studied profile, the Asmari Formation was deposited during the Chattian period in the open marine with normal salinity (Psu 40-34) in the aphotic, oligophic to mesophotic light zone, and under the oligotrophic to mesotrophic nutrient.  At the time of Aquitanian to Burdigalian, it was deposited in a restricted lagoon environment with a psu 50-45 salinity and in an open lagoon with a salinity of more than 50 psu, in the uphotic light zone, under a uphoty nutrient.

    Keywords: Paleoecology, Microfacies, Asmari Formation, Depositional environment, Karanj oil field
  • Zahra Farahmandfar, MohammadReza Ja'fari, Peyman Afzal*, Afshin Ashja Ardalan Pages 53-72
    Introduction

    Lahrud is situated in NW Iran, between 47º 30´ to 48º longitudes and 38º 30´ to 39º latitudes, based on the structural units this area is part of the Eocene age trending  Alborz-Azerbaijan magmatic belt .The volcanic rocks of Eocene age mainly comprise of alkaline series.

    Materials and Methods

     Fractal modeling has been widely used in various fields of earth sciences and mineral exploration since the 1980s. One of the most important methods is the Concentration-Number fractal method; this method is based on the inverse relationship between the concentration and the cumulative frequency of each concentration and higher concentrations. In 2003, about 600 samples of Lahroud 1: 100,000 sheet stream sediments were randomly sampled by the National Geological and Mineral Exploration Organization and analyzed by ICP-MS. In this study, classical statistics operations, factor analysis, fractal Concentration-Number of operations and element geochemical anomaly maps were prepared. Classical statistics have a structural weakness for not taking into account the spatial position of the data which causes systematic errors. Factor analysis is one of the most popular multivariate analyses, which is used as a powerful tool for visualizing large three-dimensional spatial data based on the variance and covariance matrices. In this method, a large set of geochemical variables are combined with several factors. The basis of the factor analysis work is, that after the initial stages of data preparation, at each stage, the elements that have a number higher than 0.6 should be selected and the rest of the elements should be removed.

    Results and Discussion

     Factor analysis was performed in SPSS software and had four stages; All disruptive elements (Mo, Be, Hg, Pb, Ag, Sr, Se, and Bi) were removed after four stages of factor analysis, and As, Sb, Sn, W, Co, Mn, Zn, Ti, Ba, Ni, Cr, Au, Cu and B were classified into five groups. Graph diagram of the C-N of invoice points was drawn and their values determined the maps of geochemical communities. The interpretation of airborne geophysical data is done both qualitatively and quantitatively. In interpreting this data, geological structures such as the location of intrusive masses, faults or hidden faults, contacts, special structures such as folds, various alteration zones and various lithologies and their changes are considered. The Oasis Montaj geophysical software offers a variety of filters and applications for analyzing and, interpreting aerial magnetic data. Geophysical surveys of the Lahrud area were performed on 48 flight lines, including longitude, latitude, and magnetic field for each point.

    Conclusion

    The presence of Andesite and Andesite-basalt rocks on the surface (geological study of area) reinforces the possibility of the presence of dioritic intrusive mass. This, has caused some of the rocks around the intrusive mass and fractures to rise through the weak points around it, and it has flowed as lava on the earth's surface. Finally it has formed the Andesite rocks of the region. Due to the size, depth and alterations of the rocks around the southern intrusive mass of the region, this, type of rooted batolite was detected with a slope to the south. The presence of Sb in the southwestern region confirms the performance of a hydrothermal system; the system, rises through the existing faults and affects the alteration rocks, creating Alunitization, Kaolinitiezation and Silicification alterations in the southwest and center of the sheet. Most of the anomalies are around the intrusive mass south of the region, where hydrothermal fluids have caused alterations, followed by mineralization. Concentration-Number fractal calculations, step-by-step factor analysis, preparation of geochemical anomalies of Gold, Antimony and Copper elements, studies and preparation of geophysical maps indicate that the anomalies of the elements are significant. They correspond to alteration areas and intrusions. This, indicates a close and notable connection between the alterations, faults and, intrusive masses of the Lahrud 1:100,000 sheet with the anomaly of the elements, especially Au and Cu. Therefore, the best exploration items in this sheet are Gold and Copper.

    Keywords: Elemental anomalies, Geochemistry, Airborne geophisics, NW Iran
  • Mohammad Goudarzi, Hasan Zamanian, Alireza Javanshir, Mohammadreza Rezvanianzadeh, Mohammadreza GhaderI* Pages 73-88
    Introduction

    The study area is located at east of Bam city and southeast of Kerman province. This area is located at 45 km from the Bam-Zahedan Road. From the main asphalt road of Bam - Zahedan it has 15 km of dirt and car accessible road. It is part of the NW-SE trending volcanic belt east of Bam.

    Materials and methods

    This study aims to geochemically investigate the behavioral pattern of hydrothermal mineralization elements in the region in order to determine local and regional uranium enrichment at 1: 5000 scale. For this purpose 616 lithogeochemical samples were collected and analyzed. The study area is located southwest of Allahabad 1: 250000 Map. The Eocene outcrops are divided into two classes of pyroclastic and lava based on 1: 5000 scale studies. These deposits are cut by numerous dykes with an approximate northwest-southeast trend. These basaltic-diabase dykes can actually be attributed to the Eocene. The most important statistical parameters used in interpretation of area data are mean, median, mode, variance, standard deviation, coefficient of variation, skewness and kurtosis which were calculated for all data.

    Results and discussion

    After normalizing and eliminating outlier values data, the data were analyzed using Pearson correlation matrix method to identify the correlation coefficients of the elements that accordingly, the highest correlation of uranium was observed with Be, Cd, Co, Cu, Mn, Mo, Na, Ni, Sc, Se, Tl, V, Y, Zn, Zr, Ga, Ge, and Hf. It indicates the paragenetic relationship of these elements with each other.Based on data clustering, four groups of chemical elements can be of particular interest due to their strong association with uranium, which include:Rare earth elements: Y, La, Ce Polymetallic elements: As,Sb, Ba, Cu, Pb, Zn, Mn, Fe, Se, Sr Related to acidic volcanism: Be, Mo, W, Zr Related to basic magmatic activities: Co, Cr, Ni, V The pattern of uranium paragenesis element groups in this diagram is roughly consistent with previous studies in the field of uranium volcanogenic deposits. Based on factor analysis, an 8-factor model with 78.6% variance was obtained for 43 elements. The second factor with a variance coverage of about 12.5% contains As, Mo, Sb elements with high factor loadings and Ag, Be, Ce, La, Pb, Tl, U, W, Y elements with average factor loadings. This factor is related to uranium mineralization in the region. Based on the results of the statistical analysis and interpretation of the geochemical map of the uranium element, the enrichment limit for this element is considered to be 5.67 ppm and background and threshold values were 2.39 ppm and 4.3 ppm, respectively.

    Conclusion

    The impact of hydrothermal solutions is strongly observed on the volcanics of the area, resulting in geochemical imbalances. Mo in the region forms large lithogeochemical haloes that are highly consistent with U elemental haloes and are generally concentrated at high U concentrations. Due to the Mo mineralization in the deeper regions, probability of U mineralization also exists in the deeper parts of the region and it is anticipated that subsurface studies will show significant results in terms of the occurrence of U compounds. Much of the southern half of the region, except for abnormal areas, is consistent with fault trends and concentrated along fault lines. There is widespread argillic alteration in the Eocene units of the region, with enrichment of the REEs, especially associated with lanthanum. Increasing the intensity of alteration and increasing joints and fractures allow the fluid to move, thereby increasing the fluid / rock ratio and facilitating migration of anomalies. The trend of uranium anomalies is often consistent with the cerium, yttrium, and lanthanum anomalies, and is usually in the margins of the basic dykes which indicates the convection of these elements from a mineralized fluid. This indicates the mobility of rare earth elements during alteration processes and their concentration by geochemical dams, including basic dykes. By comparing the obtained paragenesis for the uranium element in the region and the geochemical pattern observed with different types of known uranium deposits in the world, the most likely option for the type of mineralization in the region, is volcanogene uranium type.

    Keywords: Statistics, Uranium, Bam, Lithogeochemistry, Element
  • akram mehdizadeh, Fatemeh Vaez Javadi*, Alireza Ashouri, Abbas Ghaderi Pages 89-112
    Introduction

    Early and Middle Jurassic, continental sediments of considerable thickness are widespread in the northern, central, and central-eastern Iran (Kilpper, 1964, 1968, 1971, Barnard and Miller, 1976, Sadovnikov, 1976, 1984, 1991, Corsin and Stampfli, 1977, Fakhr, 1977, Schweitzer and Kirchner, 1995, 1996, 1998, 2003, Schweitzer et al., 1997, 2000, 2009, Vaez-Javadi and Pour-Latifi, 2004, Vaez-Javadi and Mirzaei-Ataabadi, 2006, Vaez-Javadi, 2008, 2011, 2012, 2014, 2015a, b, 2018, Saadatnejad et al., 2010, Vaez-Javadi and Abbasi, 2012, 2018, Vaez-Javadi and Allameh, 2015). For a more detailed study, plant macrofossils from Chah-Rekhneh were considered here.
    Material, metho

    ds and geological setting

    The plant fossils have been driven from a borehole in Chah-Rekhneh, 62km of SW Tabas city, 33˚17´56ʺ North latitude, 56˚24´01ʺ East longitude. A total of 84 specimens have been collected from a 240 m stratigraphic-core section. Some specimens yielded more than one fossil. The flora from this locality here is introduced for the first time. Material cited in this work (prefixed MJHCh; acronym for Mehdizadeh, Javadi, Hojedk, and Chah-Rekhneh) is held in the collection of the Palaeobotany Laboratory of the Department of Geology at the University of Ferdowsi, Mashhad. Biostratigraphy of the Chah-Rekhneh The Hojedk Formation consists of shale, siltstone, and fine-sandy silt alternating with thick medium-grained sandstone at the base of column. Several coal seams are present at the middle and upper part of the core column. One assemblage biozone was established in this section with lower and upper boundaries identified by FOO (First Observed Occurrence) and LOO (Last Observed Occurrence) of Coniopteris hymenophylloides and Klukia exilis, respectively. Furthermore, three informal subzones were recognized which are upward: I- Equisetites beanii- Ptilophyllum harrisianum Interval zone; II- Ptilophyllum harrisianum- Elatides thomasii Interval zone, III- Elatides thomasii - Nilssonia macrophylla Interval zone.Palaeoclimate Analysis In order to recognize palaeoclimate of the Chah-Rekhneh area during the Middle Jurassic, plant macrofossils relative abundance analysis and floral gradient method were used. Ziegler et al. (1996) assigned all Jurassic leaf genera to ten coarser morphological categories (or 'morphocats'). Rees et al. (2000) explained "Floral gradient" analysis. They show how this analysis can be used to interpret phytogeographic patterns based on the axis 1 scores of individual leaf genera and corresponding plant localities, due to their relative degrees of association. Then the climatical distribution in terms of the basic morphological characteristics of individual leaf genera and the palaeogeographic distribution of plant localities can be understood. By calculating the average of the scaled (0 to 100) axis 1 scores of the 32 genera common to all three intervals, a Jurassic 'floral gradient' has been derived. Floral gradient score of this flora in Chah-Rekhneh is 41.81. It shows that the flora assigned to the middle part of Floral Gradient table and suggests a humid and sub-tropical climate during early Middle Jurassic.

    Conclusion

    The Hojedk Formation in the Chah-Rekhneh area, south west Tabas contains 33 plant macrofossil species (21 genera) of various orders. On the basis of FOO and LOO of index species, one assemblage zone- Coniopteris hymenophylloides-Klukia exilis Assemblage zone and three informal subzones were recognized. These subzones are upward: I- Equisetites beanii- Ptilophyllum harrisianum Interval zone, II- Ptilophyllum harrisianum- Elatides thomasii Interval zone, and III- Elatides thomasii - Nilssonia macrophylla Interval zone. The occurrence of index fossils such as Klukia exilix and Elatides thomasii, Aalenian-Bajocian are assigned for this assemblage. Statistical analysis studies reveal that Order Filicales, Cycadales, Pinales and Equisetales with relative abundance of 46.31%, 23.50%, 12% and 9.26%, and Nilssonia, Klukia, Coniopteris and Equisetites were the most abundant genera with 22.81%, 13.38%, 8.40% and 8.40%, respectively in the Chah-Rekhneh area. Therefore, based on relative abundance of Filicales and Cycadales, the occurrence of Equisetites beanii as index species of climatic and ecologic, and average floral gradient score (41.81), a humid sub-tropical palaeoclimate was dominant in this area during the Aalenian-Bajocian interval.

    Keywords: Palaeoclimate, Biostratigraphy, Middle Jurassic, Hojedk Formation, Plant macrofossils, Tabas
  • maryam farahimanesh, mohammad ghavidel syooki*, abbas Sadeghi Pages 113-132
    Introduction

    The eastern Alborz contains a rich assemblage of plant macrofossils studied previously by several authors (e. g. Corsin and Stampfli, 1977; Vaez-Javadi, 2006; Najafi, 2009 and Vaez-Javadi, 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 methods

    The samples containing Triassic fern macro-remains 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 discussions

    The 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 macro-remains 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 long-ranged, 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).

    Conclusion

    A 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 co-occurrence of hydrophilic and xerophilic species reveals that these plants lived in the lowland of deltaic environment, but in different microhabitats.

    Keywords: E Alborz mmuntain, Late Triassic, Ferns, Shemshak group, Plant fossils
  • Atefeh Nimroozi, gholamreza ghadami*, Jamshid Hassanzadeh, Mohammad Posti Pages 133-148
    Introduction

    The evolutionary history of the Sanandaj-Sirjan zone has been influenced by two extensional and compressional regimes that have caused rifting, subduction, collision and its final closure.The study area is located in Esfandabad city of Yazd province. The sequence contains dark colored andesitic, rhyolitic and basaltic lava with interlayers of volcanoclastic and sedimentary units. The volcanic rocks detected contain aphanitic textures and have dark gray to black color with oxidized surface, fractures and pores. These volcanic rocks have a layered flow and are mostly seen as dome-shaped structures and are sometimes in the form of dikes. Another characteristic of this group of rocks is the green color obtained from the secondary minerals of chlorite and epidot, as a result of the alteration applied to them. The volcanoclastic rocks are mainly fine-grained and welded purple tufts.

    Materials and methods

    In order to achieve the aim of this study, after descriptive studies, field operations were performed in three stages and 100 samples were taken from the desired outcrops and thin sections were prepared. After petrographic studies, less altered samples were selected and sent to the GeoLeb Laboratory in Canada for geochemical analyzing using XRF, ICP-MS and ICP-IAS methods. Age studies have been conducted at the Caltech Institute in California.

    Results and discussion

    In microscopic studies, the dominant texture in basaltic rock is porphyry, consisting of plagioclase, olivine and pyroxene in a fine-grained matrix composed of plagioclase, epidote, chlorite, sphene and opaque minerals. Andesitic rocks have microporphyric and seriate textures consisting of plagioclase, in a fine grained matrix consisting of plagioclase, pyroxene, quartz, epidote, carbonate and chlorite alteration products and opaque minerals. Rhyolite rocks have a microcrystalline to hyalline texture consisting of quartz, alkali feldspar and plagioclase. Evidence such as sosoritization of plagioclase, filling of cavities by chlorite and zeolite, idingitizated or chlorinated olivine and uralite pyroxene crystals indicate the performance of metamorphic phenomena in the studied rocks.

    Conclusion

    Based on geochemical data, the studied rocks have basaltic and trachydacite composition with tholeitic and calcalkaline affinity. The pattern of spider diagrams in the study area are almost the same but with a different frequency. The enrichment of Th and U in these diagrams can be attributed to crustal contamination and enrichment of LREE to low melting rates of mantle source (less than 15%), or contamination of magma with crustal materials. The negative Eu anomaly is related to the differentiation of plagioclase during magmatic crystallization or its persistence at the source when H2O activity is low. In the tectonic setting diagrams, which are used to separate the intra-plate basalts from other tectonic environments, the samples are located in the intra-plate field (WPB). Geochemical studies show an asthenospheric mantle source that has been affected by crustal contamination and crystalline differentiation. Petrographic evidence, such as the presence of porphyric texture in volcanic rocks in the area, indicate that magma has stopped in crustal chambers and contaminated it. Geochemical studies showed that trachydacite rocks form from5% melting of garnet-lorzolite and basaltic rocks produced compose from 20% melting of a spinel-lerzolite origin. U-Pb dating studies of trachydacite presents 240+ 6.6 ma age equivalent to the lower triassic which match the opening and formation of neotethys ocean in permotriass.

    Keywords: Esfandabad, Sannandaj-Sirjan, Opening, Neotethys, Yazd
  • MohammadHossein Jahangir*, Seyedeh Mahsa Mousavi Reineh, Mahnaz Abolghasemi Translator: Drought forecast, SPI, and SDI index, SDSM, Tehran province Pages 149-166
    Introduction

    In the present study, to monitor droughts, the RCP4.5 scenario of the CanESM2 model of the Fifth IPCC Report and the most appropriate distribution functions of drought indicators were used to assess the current climate change and drought conditions in the present and future. Since the drought in an area can be affected by various climatic parameters, in this study, in addition to using SPI as a practical index, the important SSI index was also used to assess drought.

    Materials and Methods

    In the present study, the following steps were performed to monitor, evaluate, and inform the occurrence of droughts in Tehran province.
    1.Quality control of precipitation and  water flow parameters during the period 1986-2018
    2.Prediction of these parameters during the period 2020-2050 based on daily output data of CanESM2 model under the RCP4.5 scenario using SDSM model
    3.Selecting the most appropriate distribution function with time series for both SPI and SSI index
    4.Drought detection and simulation using SPI and SSI drought characteristics during the next period (2050-2050).

    Conclusion

    The results for future showed that Sharifabad station has the highest drought index (-2.74) based on SSI, and according to SPI, the highest drought index (-2.17) is for Latian station. It should be noted that the matching of the two indicators at Namroud and Latian stations was also studied and the results showed that the difference in the numerical values of these two quantities did not fit well for a 5 year period.

  • Mehdi Sadighi, Baharak Motamedvaziri*, Hasan Ahmadi, Abolfazl Moeini Pages 167-182
    Introduction

    Landslides are isolated processes which may not be very large, but they can occur frequently and cause sizable damages. In most areas, there is a vivid pattern of irrational reaction while confronting such events. Nonetheless, such actions as avoidance, prevention, or restoration are more feasible for landslides than all other natural hazards because many discernable morphological symptoms appear months and even years before landslide occurrences. To the date, inherent driving forces of terrain processes have been identified quite well. Therefore, if we optimistically identify the landslide-prone areas, we would be able to reduce the landslide driven accidents through landslide susceptibility zonation. Nowadays, landslide susceptibility assessment endeavors have made great progress. Nevertheless, concurrent with advancements in developing susceptibility models, end-users have had many challenges selecting the superior model.

    Materials and methods

    This study is focused on the determinant role of the modeling goal and end-user’s need in opting for the superior model in the context of landslide susceptibility assessment and generally any endeavor with a spatial connotation. Hence, three widely used data mining models including artificial neural network (ANN), support vector machine (SVM), and maximum entropy (MaxEnt) were adopted for landslide susceptibility assessment in one of the pilot subbasins of the Tajan Watershed in Mazandaran Province. Models’ results were assessed using six performance criteria including 1) areal distribution of the susceptibility classes in each model, 2) distribution of landslides within the susceptibility classes in each model, 3) Error Type I (false positive), 4) Error Type II (false negative), 5) area under the success rate curve and 6) area under the prediction rate curve, based on which models were ranked.

    Results and discussion

    The first criterion showed that the MaxEnt, SVM, and ANN, respectively, have the highest to the lowest performance. The second criterion showed that the SVM, MaxEnt, and ANN, respectively, have the highest to the lowest performance. The third criterion with economic losses connotation often associated with the modeling errors, indicated a good performance of the SVM model, while the MaxEnt and ANN were concurrently second-ranked. The fourth criterion with a connotation of casualties and economic losses often associated with the modeling errors indicated a good performance of ANN, followed by MaxEnt and SVM. The results regarding the fifth and sixth criteria both revealed a great learning and prediction power of the SVM model, followed by MaxEnt and ANN.

    Conclusion

    The findings of this study attests for the notion that models superiority is rather a relative matter and despite the fact that landslide susceptibility results are resultant of local properties and cannot be generalized to other areas. Therefore opting for the superior model should be also carried out on the basis of engaging a wide range of performance criteria as well as acknowledging the modeling goal and end-user’s need.

    Keywords: Maximum entropy, Artificial neural network, Support vector machine, False positive, False negative
  • seyedeh azadeh aghajanzadeh, mohsen taban* Pages 183-202
    Introduction

    Plans should improve the urban spaces quality in order to create access to a sustainable place for the residents’ comfort in the environment. For this reason, studies are essential on the micro-urban climate and in optimizing the urban structure for achieving this goal. Nowadays, the cities and population growth has disturbed nature and altered the original structure of the city. In recent years, the high-rise buildings idea has been raised in the cities of the world in order to prevent the horizontal growth of cities. One of the high-rise buildings negative effects is the change in urban wind flow. Our cities are now witnessing the growth and expansion of high-rise buildings and this issue occurs when there is no proper understanding of the subject and no laws and regulations are in place. The concerns existence and the need regulation for The correct application of the high-rise building phenomenon, conducting various research and studies in this field is necessary.In this study, the effects of elevation and changes in two urban blocks in the northern area of Babolsar were evaluated by Flow-3d software. In the warmest days of summer, the effect of altitude and mass arrangement on the blocks temperature and the wind flow velocity between them have been investigated. Increasing height, enclosure, and inappropriate orientation of the masses will not occur in the wind. This will increase the temperature between the masses and disappoint the inhabitants of comfort area. In order to improve the situation, it is necessary to change the physical conditions according to the wind direction and distribution.

    Materials and Methods

    The study area has two urban blocks with the total area of 111315 m2. The length of the area is 466 m and the width is 258 m. Comparing block A and B it is perceived that in block A density and setting of buildings has been changed relative to the nearby fabric while block B has maintained its traditional physical condition. Demand for construction is going to change morphology of block B and transform it into high-rise buildings. Minimum height of buildings is 4 m in block B, and the maximum height of buildings is 39 m in block A. The wind speed is measured using a hot wire anemometer st-3880 at 32 points in two blocks at a height of 1.75 (pedestrian level) and synoptic center meteorological information. The wind measurement data were obtained from 32 points carried out in two blocks site setting based on actual buildings/local neighborhood in northern part of Babolsar. These 32 points have been selected by their difference in height, enclosure, orientation and width between masses in this area. Their information has been surveyed in 5 times intervals of 2 hours a day in chart 3. Measurement is performed in normal street activity mode of neighborhood. For validation purposes, the wind velocity magnitude was done in-field on August 8, 2017. The research area has been computationally modeled in order to evaluate wind flow in Flow-3d (V11.2) software. The two blocks were studied as part of a small urban model, to simplify of modelling the experiments in CFD codes. The wind simulations data - at two blocks - were determined based on the time-series results, and subsequently compared with the measured wind data.

    Discussion of Results

    The validation for real urban areas is typically performed with data from infield measurements. This part of study was to provide experimental data for the validation of CFD simulations. Some special aspect of the flow between buildings setting were observed from the measurements. For further analysis of the flow aspect, CFD simulations could be used to attachment the present data and provided that these simulations are carefully validated. Velocity measured in in-field and computed in simulations are compared. Comparison between wind velocities extracted from 32 points in CFD simulation and infield wind measurements are shown. The mean correlation coefficient is 0.6563 that respectively represent a positive relation. Some low inconsistencies existed in certain points locations and this error rate is readily apparent due to unpredictable environmental factors.The velocity contours and streamlines were studied using the CFD method around the buildings. The results were presented for the annual wind velocity at a pedestrian height of 1.75 m from ground level. The basic results from the CFD simulations are presented for the proposed new building in Figures below. These figures show plan and section views of velocity streamlines for prevailing wind speeds varying from 0 m/s to 1.4 m/s. Evaluation of wind flow’s simulation:- Winds are driven by the prominence of masses in urban environment and are not randomly distributed.-The wind speed decreases by encountering the exterior of the existing masses (the form of the buildings) in the urban area.-The form of the masses increases and decreases the velocity and change the direction and streamlines of wind flow.-The wind speed increases in low density areas due to low prominence, simple form of the masses, low height and then low enclosure. But wind speed decreases by the new high-rise buildings in front of these masses.-When the buildings are rotated vertically and horizontally to the wind streamlines, the wind will be reduced behind the row buildings. In this case, the number of buildings will fall under the shadow of the wind, because the wind continuously hits the walls, and the wind moves around and above the buildings. These buildings are located on the street, so the air flow is also reduced in the street.-tall buildings have a lot of effects on the wind flow in the city. When the wind flows hit into high-rise buildings, there will be more flow around them. A pressure packet is created at the back of these buildings, which causes the air to flow downwards and on the ground.-tall buildings such as towers deflect a large part of the wind flow toward around.- When the width of the masses increases, the deviation rate of the velocities contours increases toward the surrounding. Therefore, the wind flow is more behind the buildings with high width than tower buildings with low width.-The acceleration of the wind movement is high near the edges and corners of the building.- Leeward is created in front of the building.- Wind turbulence occurs behind high-rise buildings.-The wind streamline rises in narrow spaces.- Creation rotational flow between buildings.-The inflow wind, which moves at 90 ° to the masses, causes collision and deviation of the wind and reduces the velocity.- The horizontal masses, along the wind direction, reduce the wind going up and down in the opposite of the vertical masses.

    Conclusions

    According to the results of the specified area simulation in Amir Mazandarani street, the type of the masses arrangement to the wind flow and other masses, height and low width between them changes the wind flow direction and velocity. In general, the enclosure increase between masses or barriers to wind, the velocity and wind direction distribution increase. The important point is that the shape and wind shades range of the masses change according to the enclosure and the masses orientation to the wind. Finally, the north-south streets have lower wind velocity than the east-west streets. the reason is that the north-south corridors are perpendicular to the wind and the masses, they have some continuity, and eventually the main air flow will flow over the building masses. Due to the low wind velocity is not able to climb above the buildings. At east-west streets, there is high wind velocity. The main reasons of the increasing velocity in these passages can be Same direction of wind flow and these passages, low width and canalization them. The high wind velocity in the range causing these conditions have inversely correlated with the amount of humidity between the masses, so that the optimum occurrence in this range is due to climatic conditions and high relative humidity.

    Keywords: Urban block, High-rise buildings, Wind velocity, Humidity, CFD simulation, Babolsar
  • Khabat Derafshi*, Sarem Amini, Vali Jahani, Naser Rezay Pages 203-222
    Introduction

    Geoarchaeology is a new and interdisciplinary concept that studies the past of human history using geological methods. In geoarchaeology, a complete and accurate understanding of ancient records can be obtained by identifying and examining the sedimentary content and stratigraphy of archeological layers and materials. Geology has been available to archaeologists over the past two decades as a basic tool for reconstructing ancient environments and understanding the long-term climatic and anthropogenic conditions and interactions of pre-historic human and surrounding environments. These studies are particularly influential in understanding the Pleistocene and Holocene archaeological and geological backgrounds and materials. Meanwhile, geoarchaeological studies of Iran are practically linked to Paleolithic observations and exploration and the use of geological methods such as sedimentology to describe the details of ancient records in caves and rock shelters. Geoarchaeology is an interdisciplinary specialty between geological sciences and archeology that examines the role of geological factors in the formation, continuation, and weakening of ancient settlements. In this field, techniques and methods common in earth science such as aerial photography and satellite imagery, sampling, microscopic studies, chemical analysis, etc. are used to solve archaeological problems. On the other hand, often referred to as archaeo-geology, archaeological data are used to solve geological problems, particularly in relation to dating of Quaternary deposits, ancient seismological studies, and ancient mining. Large-scale archaeologists study most of the natural landforms and anthropogenic structures and small-scale archaeologists study the soil, natural sediments, and anthropogenic deposits. Archaeo-geology also occasionally covers other interdisciplinary studies such as pottery petrography, ancient mineralogy, ancient metallurgy, dating, etc. and so-called archaeometry.

    Materials and methods

    In order to determine the frequency of sediment grains based on their size and to investigate the pattern of particle size distribution to determine the textural properties, the sorting of grains and the sedimentary abundances of two natural sediment layers I and II were extracted from Gaskarak section and analyzed by laser particle size analyzer. Organic matter and carbonate bind the sediment particles to each other and therefore, to determine the true distribution of particle size, they must be removed prior to analysis of the samples to separate the sediment particles. The mixing and rotating system of the device will cause the particle to move and be exposed to the laser beam. So after the laser light from a high voltage source is exposed to the sample, the laser beam will reflect from the sample surface and then pass through it. The size of the deposited particles is directly proportional to the magnitude of the reflected laser light and to the angle of refraction of the laser beam to the surface of the particle, so that with increasing diameter of the deposited particles, the intensity of the reflected laser light increases, but its angle of failure decreases.

    Results and discussion

    Gaskarak section consists of two layers of fine-grained alluvial-debris sediment, with distinct color which their lower boundary is confined to the sedimentary bedrock and their upper boundary is covered by more recent deposits. The natural sediments that form these two layers are silty particles that show high density. The lower layer (I) is mainly composed of silty fine-grained sediments with calcareous fragments. Layer II, covered at its upper bound by the natural and cultural deposits of the Bronze Age is characterized by a charcoal inclination that distinguishes it from its lower layer. Study of the recent samples suggests dry to semi-arid climatic conditions for the formation of carbonated horizons in the soil. Low carbonate content, reddish-brown color, as well as the presence of charcoal fragments in layer II, which is distinct from layer I, suggest a different environmental condition for layer II that seems it has been facing simultaneous climate changes, such as increasing rainfall and humidity and expanding forest vegetation in the region.

    Conclusion

    Field evidence and results of laboratory studies indicate that the natural deposits of the Gaskarak section probably formed as abnormal sediments on ancient hillslope surfaces of sedimentary bedrock. As the morphology and slope of the sedimentary layers show a valley-like position, the eroded material accumulates from sections with higher topography within it. The natural sediments of the Gaskarak section are distinguished by two distinct layers (I and II) that show distinct differences in color, carbonate content, and mineral and organic fragments.

    Keywords: Geoarchaeology, Micromorphology, Sedimentology, Calcareous fragments, Ancient - sedimentary section of Gaskarak, Roudbar
  • mehrdad kiani, Hasn Lashkari*, Houshang Ghaemi Pages 223-244
    Introduction

    Rain and snow occurrences on Zagros topography in the winter, provide groundwater resources, soil moisture, and surface water current on slopes, valleys and plains. Western Iran is covered by Zagros topography. The Zagros Mountains are one of the highest mountains in Iran and Western Asia. The maximum height of Zagros Mountains in western Iran reaches 4000 meters. These mountains are located in the form of a barrier in the direction of the entrance of the dominant western winds to the region. The width of these mountains in western Iran is relatively wide and about 300 km. The Zagros topography is a series of high mountain ranges, folds, valleys and plains. In this study, the effects of severe winter rainfall in the Zagros topography in western Iran have been investigated.

    Materials and methods

    In the present study, the extreme rainfalls for the three months of December, January and February as winter months (DJF) for 1996-2017 were reviewed from synoptic and statistical points of view. Three extreme rainfall patterns were determined for the three winter months (DJF). In this way, the rainfall days of each month were divided into 10 categories based on maximum rainfall of each day. But the frequency of winter precipitation systems in western Iran have led to the occurrence of extreme daily rainfalls over the course of a specified statistical period. Due to the role of these systems in the occurrence of daily winter precipitation, the arrangement of synoptic patterns, moisture content, temperature fluctuations and airflow paths were analyzed simultaneously, with the occurrence of the most severe extremes in the current study. The tenth category included the highest averages and first category included the lowest. Daily rainfall maximums in the tenth category were selected as extreme rainfall patterns of that month. These three patterns included December 21, 2002, January 9, 1999 and February 3, 2006.

    Results and discussion

    Extreme is an intense and unusual event in observations that may exceed a certain threshold. The most severe of extreme rainfalls occurred in the region at the end of the winter season. In other words, the intensity of the extreme rainfalls were respectively at February, December and January. This trend has been observed for stations located in Kurdistan and Ilam provinces. While in Hamadan province stations, the reverse mode has formed, and the maximum rainfall occurred in December, January and February, respectively. This trend for the stations of Kermanshah province has changed to January, February and December, respectively. But in Lorestan province it was observed as December February and January.

    Conclusion

    The results of the synoptic analysis showed that during extreme daily precipitations, high pressure systems were weakened in Iran and Mediterranean and Sudanese pressures were deployed in western Iran. The synoptic arrangement of the December precipitation occurred in the form of a deepening of the Mediterranean Trough over the Red Sea at a level of 500 hPa and directing lower levels moisture flow as a convergence flow from the south and west winds to Iran. Whereas the deployment of a cut-off low blocking system in January and February played an important role in the event of low rainfall. During these months, the merger of two Mediterranean and Sudanese sea-level systems over western Iran has brought heavy rainfall to most stations. At 850 and 700 hPa, the warm and cold air flow resulting from the establishment of the Saudi anticyclonic system beyond the northeastern boundaries of Iran caused a deep cold northward wind flow, to the west of Iran. This resulted the cold precipitation of January. In February, the deployment of a blocking system on Turkey and Syria affected the northwestern parts of Iran, and the Red Sea moisture stream to north. Because of this, heavy precipitations formed due to proximity to the path of moisture in the western slopes of Zagros, such as Ilam, and the rest of the stations had little precipitation due to the long distance from the moisture path.

    Keywords: Extreme rainfall, System, Synoptic, Specific humidity, Pressure