نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه تحقیقات مهندسی رودخانه ها و سواحل ، پژوهشکده حفاظت خاک و آبخیزداری کشور

2 عضو هیئت علمی مرکز تحقیقات کشاورزی و منابع طبیعی استان هرمزگان

3 گروه زمین شناسی، دانشگاه آزاد اسلامی واحد بندرعباس

چکیده

منطقه ساحلی استان هرمزگان جایگاه شکل‌گیری بیش از دوازده سری سواحل پس‌رونده است. هدف این تحقیق، دستیابی به روند تکاملی خطوط ساحلی در سواحل استان هرمزگان از هولوسن میانی است. از این‌رو، از متدولوژی فراگیر شامل پهنه‌بندی خطوط ساحلی دیرینه، پیمایش‌های میدانی و سن‌سنجی به روش کربن‌14 استفاده شد. نتایج نشان از وجود سطح پیشروی (TS) و سری رخنمون سطحی افق‌های افت تراز دریا (FSST) در هر یک از مناطق شناسایی شده دارد. نمونه‌های فسیل برجای از مناطق کریان و بندمعلم جهت سن‌سنجی به روش کربن14 انتخاب و به‌دقت مساحی و آنالیز شد. سن مطلق خطوط ساحلی دیرینه 24S، 4S (منطقه کریان) و 1B (منطقه بند معلم) به ترتیب BP 64±4329، BP 43±1787 و BP 14±1306 به‌دست آمد. این خطوط ساحلی در تراز ارتفاعی 10.21، 5.58 و 3.76 متر از سطح دریا و در فواصل 4570، 500 و 244 متری از نوار ساحلی کنونی واقع شده‌اند. بر این اساس، روند نسبی توسعه سواحل پس‌رونده از 24S، 4S و 1B به ترتیب1.05، 0.28 و 0.186 متر در سال به‌دست آمد. نتایج نشان از تشکیل این سواحل پس‌رونده در محیط رسوبی ساحلی آواری داشت که شرایط تکتونیکی، هیدرودینامیکی و بودجه رسوب آن‌ها از 4000 تا 2000 سال گذشته ثابت بوده است. 

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Evolution of trend and paleoshoreline mobility since the late-Holocene in the Hormozgan Province (Northern Persian Gulf)

نویسندگان [English]

  • Mohammad Reza Gharib Reza 1
  • Saeed Shoupani 2
  • Hamid Reza Maasoumi 3

1 Research Department of Rivers and Coastal Engineering, National Soil Conservation and Watershed Research Institute

2 Faculty member of Hormozgan Province Agriculture and Natural Resources Research Center

3 Department of Geology, Islamic Azad University, Bandar Abbas branch

چکیده [English]

Introduction
Paleoshorelines are the most important key landforms for studying evolutionary trend of coastal sedimentary environments. Hormozgan province is one of the Iranian coastal provinces at the north of the Persian Gulf and the Oman Sea representing high variety of geological settings influenced by regional and local geological events. According to large scale coastal landmarks, sedimentary environments have been formed mainly since the late-Quaternary. Intrusion of the Precambrian salt domes, structural development of rocky coasts, and the Quaternary glacial and interglacial events have contributed in shaping of Hormozgan province’s coastal area. Fossil beaches as landmarks of regression coasts can be observed at 12 large coastal dune fields. They demonstrate superficial evidences of sea level fall tracts especially since the late-Quaternary. Recognition of the mid-Holocene mechanism of land progradation and rate of shoreline mobility is required for interpretation of regional coastal sedimentary environments. Therefore, main aim of this research was determination of evolutionary trend of paleoshorelines along the Hormozgan province.
Materials and Methods
The research method was included application of geographic information system (GIS), surveying of geo-indicators, and dating of fossils using 14C. Therefore, digital topographic maps (1:25,000 scales) and satellite image (IRS, 2006) of spatial resolution 6 m, and numerous aerial photos (flown in 1967 at an approximate scale of 1:20,000) as materials in order to obtain the research objectives were used. Thus, mapping of paleoshorelines and fossil beaches was carried out using GIS tools. Additionally, survey of coastal features, check of maps accuracy, and collect of in-situ fossils from paleoshorelines were implemented during field observations. The Kerian and Band-e-Moalem were chosen as master areas for 14C dating from east and west of the study area, respectively. The 14C dating (Ultra Low Level Liquid Sintillation Counting on Benzene) of fossil samples was conducted using a Quantulus 1220 instrument calibrated with oxalic acid I with a detection limit of DL = 1-2 pMC at the Laboratory of Gamma Spectrometry of Iran’s Atomic Energy Organization. Resulting data was calibrated by using CalPal-2007-HULU software, Cologn radiocarbon calibration & paleoclimate research pacage, Germany.
Results and Discussion
Paleoshorelines and their distribution were identified at 12 dune fields where superficial evidences of sea transgression (TS) and falling stage system tract (FSST) have been formed since the mid- Holocene. Details of the most reliable landmarks of shoreline mobility at Kerian and Band-e- Moalem areas were obtained. As results, S4, S24 and B1 were dated 4329±64 BP, 1787±43 BP, and 1306±14 BP, respectively. Height of paleoshorelines was calculated to be 10.21, 5.58, and 3.76 m using DGPS where they are located at 4570, 500, and 244 m far from the present coastline.
Therefore, the mean rate of shoreline mobility of S4, S24 and B1 were calculated to be 1.05, 0.28, and 0.186 m yr-1, respectively.
Conclusion
Present research has concluded that rate of sediment supply, tectonic movements, and hydrodynamic condition had been relatively constant between 4000 BP and 2000 BP. Accordingly, coastal ridges have been distributed parallel to the shoreline uniformly without considerable disruption. Results confirmed that regression coasts at the eastern coasts have been created wider and completed than the western coasts. Superficial evidences of the mid-Holocene sea level fall in the study area have provided opportunity to find out regional evolutionary trend of paleoshorelines and to sketch sea level curve for the Persian Gulf and the Oman Sea. Therefore, importance of Quaternary landmarks along the north of the Persian Gulf and the Oman Sea was highlighted by present research for further investigation of coastal zones formation.

کلیدواژه‌ها [English]

  • 14C dating
  • Hormozgan Province
  • Holocene
  • plaeoshorelines
  • retrograssive coasts