رسوب‌شناسی، محیط‌های رسوبی و ژئوشیمی آلی در بخش جنوبی حوضه خزر جنوبی

نوع مقاله: مقاله پژوهشی

نویسندگان

مدیریت زمین‌شناسی دریایی، سازمان زمین‌شناسی و اکتشافات معدنی کشور، تهران

چکیده

به منظور بررسی رسوب­شناسی، محیط­های رسوبی و ژئو­شیمی­آلی در بخش جنوبی حوضه خزر جنوبی، تعداد 124 نمونه رسوب سطحی  (نواحی کم­ژرفا تا ژرف) با نمونه­گیر فکی برداشت شده و از نظر کربن آلی کل و s2 (پیرولیز راک-اول)، محتوی زیستی (موجودات آشفته کننده)، اندازه ذرات و کانی­شناسی تحت آنالیز قرار گرفتند. بر پایه داده­های لرزه­ای کم­ژرفا و مشاهدات میدانی، محیط­های دلتا، سکوی قاره، شیب قاره و دشت حوضه شناسایی گردیدند. ذرات تشکیل­دهنده این ناحیه به سه گروه آواری (کوارتز، خرده­سنگ کربناته و غیر کربناته، فلدسپات، مسکویت و کانی­های رسی اسمکتیت، کائولینیت، ایلیت و کلریت)، آلی- زیستی (پوسته موجوداتی نظیر دوکفه­ای، استراکود و گاستروپود) و قطعات غیر اسکلتی (پلوئید­های آهکی گلی) تقسیم شده است. چندین شاخص نظیر میزان کربن آلی کل، نوع مواد آلی و محتوی زیستی نشان­دهنده شرایط متفاوت اکسیدان (رسوبات سکو و شیب قاره) و فقیر از اکسیژن (رسوبات ژرف دشت حوضه) می­باشد. رسوبات فقیر از اکسیژن، غنی از مواد آلی نوع II و حاوی کربن آلی کل بیش از 1 درصد وزنی می­باشند، در حالی­که رسوبات مناطق اکسیدان، غنی از پوسته موجودات ساکن در بین رسوبات (نظیر گاستروپودا و استراکودا)، حاوی مواد آلی نوع III و کربن آلی کل کم­تر از 1 درصد وزنی می­باشند. این موارد نشان­دهنده حفظ بهتر مواد آلی در مناطق ژرف­تر (دشت حوضه) می­باشد. مواد آلی نوع III نشان­دهنده ورود مواد آلی خشکی­زی (قاره­ای) به رسوبات سکو و شیب قاره می­باشد.

کلیدواژه‌ها


عنوان مقاله [English]

Sedimentology, depositional settings and organic geochemistry in the southern part of the South Caspian Basin

نویسندگان [English]

  • r behbahani
  • a karim khani
  • gh hosseinyar
چکیده [English]

In order to study sedimentology, depositional settings and organic geochemistry in the southern part of the South Caspian Basin, 124 surface samples were taken from shallow to deep water with utilizing Van Veen Grab. All samples were analyzed for total organic carbon (TOC), S2 (Rock-Eval Pyrolysis), biota content (bioturbating organisms), particles size and mineralogy. Based on shallow seismic data, a range of depositional settings were distinguished including delta, shelf, slope, and basin plain. Composition of samples revealed detrital particles (quartz, feldspar, muscovite, carbonate and non-carbonate rock fragments and clay minerals (illite, chlorite, kaolinite, smectite)), as well as organic/biogenic components (i.e. bivalves, gastropods, ostracods) and non-skeletal particles (i.e. mud peloids). Several factors (e.g. TOC, organic matter type, biota content) suggest that these sediments were deposited under markedly different redox conditions, namely: (1) shelf and slope settings (oxic sediments), (2) basin plain settings (dysoxic sediments). The dysoxic sediments are enriched in type II organic matter (OM) with high TOC content (>1wt. %) while the oxidized sediments are enriched in infaunal organisms (i.e. ostracods and gastropods), and contain type III OM with low TOC content (<1wt. %). These evidences suggest better preservation of OM in the basin plain setting (deeper areas). Type III OM implies terrestrial input to the shelf and slope.

کلیدواژه‌ها [English]

  • Organic geochemistry
  • depositional setting
  • total organic carbon
  • terrestrial organic matter
  • South Caspian Basin

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