نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه جغرافیای طبیعی، ژئومورفولوژی، دانشگاه محقق اردبیلی، ایران

2 گروه جغرافیای طبیعی، ژئومورفولوژی، دانشگاه تهران، ایران

چکیده

160 سانتی­متر از توالی لایه­های گوانو خفاش و رسوبات غار کوله­تاریکه واقع در شهر دیوان­دره، استان کردستان مورد آزمایشات ژئوشیمی و مطالعات آماری قرار گرفت، تعداد چهار نمونه به روش کربن14 تعیین سن گردید که سن توالی لایه ­های رسوبی و گوانو خفاش را بین 5686 سال قبل تا سال 1955 میلادی نشان می­دهد. نتایج نشان داد که بین 5513 الی 5814 سال قبل منطقه دارای آب و هوای گرم و مرطوب و بین 4400 الی 5513 سال قبل دارای آب و هوای گرم و خشک بوده است، خفاش­ها از حدود 4399 سال قبل با بهتر شدن شرایط محیطی در غار ساکن شده­اند، بیشترین میزان تجمع آ­ن­ها مربوط به 608 الی 1122 سال قبل منطبق با دوره­ی ناهنجاری آب و هوایی سده­ی میانی (MCA) است که نشان از وجود آب و هوای گرم و مرطوب ­ بوده است بعد از این دوره یعنی در حدود 380 الی 191 سال قبل منطبق با عصر یخبندان کوچک (LIA) به تدریج به دلیل سرد شدن هوا از تجمع خفاش­ها در غار کاسته شده است. کمترین تجمع آن­ها 291 سال قبل با دوره­ی حداقلی ماندر  همزمان است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Reconstruction of paleoenvironment changes from bat Guano and sediment deposits in Kolatarika Cave, Divandarreh, Kurdistan, from mid to late Holocene.

نویسندگان [English]

  • Fariba Esfandiyari Darabad 1
  • Mehran Maghsoudi 2
  • Omid Rahimi 1

1 Department of Natural Geography, Geomorphology, Mohaghegh Ardabili University, Iran

2 Department of Natural Geography, Geomorphology, University of Tehran, Iran

چکیده [English]

Introduction
Bat Guano and sediment deposition in caves have been used as an important source of information for reconstructing paleoenvironment and climate changes. Environmental conditions and climate have been mentioned as the most important factor in the economic-social change, migration and even the collapse and decline of civilizations (DeMenocal, 2001), although this is a global issue, some semi-arid regions of the world, similar to Southwest Asia, where water is a key source of civilized activity, it is more important (Kelley et al., 2015). In caves throughout the world, bats in sufficient populations produce copious amounts of fecal droppings (guano) reported at rates up to 10 cm/year (Hutchinson, 1950). These deposits have been used to examine palaeoenvironments reconstruction for example, the guano geochemical studies, speleothem and cave sediments for reconstruction of paleoenvironment reconstruction, including stable  isotopes  δ18O, δ13C, , δ15N  pollens and micro-charcoal radiocarbon age determination of guano, paleology and paleoecology, bat fossils (Forray et al., 2015,  Royer et al., 2015,  Wurster et al., 2017, Onac et al., 2015,  Stoetzel et al., 2016, Widga and Colburn, 2015, Campbell et al., 2017).
The purpose of this study was to reconstruct environmental change and climate change in Kurdistan province using multi-proxy data derived from  geochemical studies (LOI, Oxides, major and trace elements and statical data) derived from a precisely 14C-dated bat guano and cave sediment recovered from kolatarika Cave.
Materials and methods
Study site
Kolatarrika (mean dark cave) Cave, located in the Ghalojeh Village (Divandarreh city, Kurdistan province). The cave is located at 1910 m a.s.l. in a small karst area. Kolatarrika Cave develops in Oligo-Miocene limestones (Qom Formation), has a total length of 56 m, and no water flows along its passages.
Sampling
A 160-cm guano and sediment core were taken by manually pushing an aluminium tube into a vertical wall deposit in the main guano accumulation is located in the Bat Room towards the end of the cave. The core was sampled at 2 cm ± 2mm intervals for geochemical analysis (73 samples) Samples for 14C dating were collected at irregular intervals based on changes of the guano and sediment texture.
Chronology
Four accelerator mass spectrometry (AMS) 14C measurements on bulk guano and bulk sediment samples was obtained from the Poznan Radiocarbon Laboratory (Poland) (Goslar et al., 2004),. The AMS 14C dates were then calibrated into The calendar Year Anno Domini (Cal AD) and Before Present (Cal BP) using OxCal4.3.1 software (Ramsey et al., 2013) using the IntCal13 (Reimer et al., 2013) a calibration curve. In the current study, we established the age-depth models using The Bacon2.2 code (Blaauw, 2010, 2011, 2013) running in an R software environment (Team, 2010).
Geochemical analysis
X-ray fluorescence (XRF) method was used to determine the Major oxides,  trace elements and loss on ignition (LOI).
Statistical analysis
 Basic statistics including, Correlation coefficient, Cluster analysis, Principal Component Analysis was carried out by using the Paleontological Statistics software (Hammer et al., 2001).
Results and discussion
Based on the age-depth model supported by four AMS radiocarbon dates, the sediment layers (85-160 cm) deposited between 4399 yr cal BP and 5686 yr cal BP and the guano deposit (85-0 cm) accumulated between 4399 yr cal BP and the present. The results of statistical studies show that there is a positive correlation between LOI in guano layers with Na2O, MgO, K2O, MnO oxides and Cl, As, Cu, Ni, Pb, and Zn, indicating that these oxides and elements are biological and originated from guano and there is a negative correlation between LOI with SiO2, Al2O3, Fe2O3, CaO, TiO2, P2O5 oxides and Ba, S, Zr, Y, V, Rb elements, indicating that these elements originated either outside of the cave or weathered by surrounding environments.
In the sedimentation layers there is a positive correlation between SiO2, Al2O3, K2O, TiO2, Fe2O3, Ba, Co, Cr, Nb, Pb, Rb, Sr, V, Y, Zr, all of these elements and oxides Have a negative correlation with CaO.
The results of cluster analysis for guano layers show that the two groups of elements can be detected; in group1: (As, LOI, Pb, Cl, MnO, K2O, MgO, Na2O, Ni, Zn) and in group2: (Nb, S, CaO, Sr, Mo, Cu, Ce, Cr, Co, Fe2O3, SiO2, Rb, V, TiO2, Zr, Al2O3, Ba, Y, P2O5). The results of cluster analysis for sedimentary layers show that the two groups of elements can be detected; in the group1 (Mo, MnO, MgO, Zn, Cl, As, Na2O, CaO, P2O5 Ni, S, LOI) and in the group2: (Nb, Sr, Cu, Ce, Cr, Co, Fe2O3, SiO2, Rb, V, TiO2, Zr, Al2O3, Ba, Y, Pb, K2O).
Conclusion
The results of four AMS radiocarbon dates, The age of the sequence of sedimentary layers and bat guano in Kolatarika Cave shows between 1955 cal yr AD and 5686 cal yr BP. The result of this study shows that between 5513 and 5814 yr cal BP, the region had a warm and humid climate and warm and dry climate between 4400 and 5513 yr cal BP. The bats have been gradually settled in Kolatarika Cave with the improvement of the environmental conditions, that is, the increase in humidity and temperature around 4399 cal yr BP. The highest bat accumulation was from 608 to 1122 cal yr BP (828-1342 cal yr AD), linked to the medieval climate anomaly (MCA) or the medieval warm period (MWP), which peaked at 835 cal yr BP (1115 yr cal AD), it coincided with the Seljuq dynasty in Iran. This indicates that the area has a warm and humid climate during this period. After this period, about 380 to 191 yr cal BP, linked to the Little Ice Age period (LIA), the bat accumulation in the cave has gradually diminished due to the cold climate. The lowest accumulation was 291 yr cal BP (1659 yr cal AD), which indicates that the area has a cold and humid climate. This phase, also linked to the Maunder Minimum period when sunspots became exceedingly rare and it has coincided with the Safavid dynasty in Iran. After this period gradually increasing the bat accumulations in the cave when local temperatures increased. The results show that bat guano is a very useful archive for reconstructing paleoenvironments similar to other proxies (tree rings, ice cores, lake and river sediments, loess, and glacier evidence) and are valuable resources in areas where no other paleo proxies are available.

کلیدواژه‌ها [English]

  • Bat guano
  • Cave sediments
  • Holocene
  • Little ice age
  • Medieval climate anomaly