پديد آورندگان :
باوي ، هدي نويسنده دانشجوي كارشناسي ارشد گروه زمين شناسي دانشگاه فردوسي مشهد , , محبوبي، اسدالله نويسنده استاد گروه زمينشناسي دانشگاه فردوسي مشهد , , موسوي حرمي، رضا نويسنده , , زند مقدم، حامد نويسنده استاديار گروه زمينشناسي دانشگاه شهيد باهنر كرمان ,
چكيده لاتين :
Introduction
Carbonate deposits of the Derinjal Formation in the eastern Zarand, Kerman Province, with the Late Cambrian age (Huckriedeh et al. 1962; Wolfart 1974) overlies the carbonate deposits of Kuhbanan Formation and underlies the open marine deposits of Shirgesht Formation (e.g. Lasemi, 2001). Huchrideh et al. (1962), for the first time stated that these deposits are the upper member of Kuhbanan Formation. These carbonate deposits can be equivalent to the Derinjal Formation in Tabas area or correlated with the lower units of the Mila Formation in the Alborz Mountains. In the study area, the Derinjal Formation is composed of three lithostratigraphic parts (lower, middle and upper) with different thickness at the studied sections. The lower part is composed mainly of dolomite and stromatolitic boundstone with thinly interbeds of marl. While the middle and upper parts are composed of calcarenite with interbeds of marl and dolomite and stromatolitic boundstone with thinly interbeds of sandstone, respectively. The aims of this study are to interpret the sedimentary history, sequence stratigraphy and reconstruction of paleogeography during the Late Cambrian time in the study area.
Material and Methods
In this study, we measured, described, and sampled (210 samples) three sections of the Derinjal Formation at Dahueih (160m), Gatkueih (140m) and Gazueih (130m). For petrography studies, 202 thin sections were stained with red alizarin solution in order to differentiate calcite and dolomite minerals based on Dickson (1966). Based on Grabau (1904), the carbonate rocks described in the field and microfacies are classified and described on the basis of Dunham’s (1962) and Embry and Klovan’s (1971) classification in the laboratory. The identified petrofacies are based on Folk (1980) classification scheme. We interpreted the sequence stratigraphy for the studied sections based on standard classification of Catuneanu (2006) and Catuneanu et al. (2009) that considered three standard system tracts (LST, TST,HST) as the 3rd order.
Discussion and Conclusion
Generally, two petrofacies and nine microfacies have been identified in the field and laboratory for the Derinjal Formation deposits at the studied sections. Petrofacies (S association) consists of quartzarenite and mudstone with structural and textural characteristics such as symmetrical ripples, cross bedding, flaser and wavy beddings as well as high textural and compositional maturity that show these petrofacies have been deposited in tidal environments so that, quartzarenite petrofacies related to intertidalwhile the mudstones have been deposited in subtidal lagoon (e.g. Klein 1971; Lasemi et al. 2012; Zand-Moghadam et al. 2013). Despite an extensive dolomitization within the carbonate microfacies, the microfacies are easily describable and recognizable due to the well preservation of their original textures. The microscopic analysis led to recognition of nine carbonate microfacies. These microfacies are related to subenvironments such as intertidal, subtidal lagoon and bar of a tidal environment. Dolomudstone and stromatolitic boundstone with evidences such as lack of fossil, very fine crystalline, present of evaporate crystal, fenestral fabrics and mud cracks show that these microfacies are related to upper intertidal to supratidal subenvironments (T association) (e.g. Warren 2000; Alsharhan and Kendall 2003; Preto and Hinnov 2003; Riding 2006; Bachmann and Harsch 2006; Flugel 2010). The subtidal lagoon microfaces (L association) including peloidal packstone, bioclastic wackestone, ooid-intraclastic packstone and intraclastic floatstone (e.g. Tucker and Wright 1990; Bosence and Wilson 2003; Scholle and Ulmer-Scholle 2003; Adachi et al. 2004; Bevington Penneya and Racey 2004). Ooid grainstone, ooid-intraclastic grainstone and intraclastic rudstone with evidences such as wavy and current ripples, flaser-wavy bedding and herringbone cross beds show that these microfacies have been deposited in high energy subenvironments such as a bar (B association) and tidal channels (e.g. Geel 2000; Masse et al. 2003; Shanmugam 2003; Palma et al. 2007; Davis 2012; Hughes 2012). Generally, all identified facies have been deposited in the inner ramp of the Cambrian ramp model (e.g. Lasemi, 2001). Due to the lack of index fossils in the identified facies, and according to our objectives in this research, sequence stratigraphic analysis of the Derinjal Formation was done based on petrofacies and microfacies characteristics and interpreted sedimentological processes. According to the Cambrian paleogeography of Iran (Berberian and King 1981; Husseini 1989; Sharland et al. 2001; Abed 2005), the sediments of the Derinjal Formation were deposited in a passive margin setting at the southern margin of the Proto-Paleotethys Ocean (Lasemi, 2001). Rising of global sea level during the Middle Cambrian to Late Ordovician (Vail et al., 1977; Gradstein et al., 2012) resulted deposition of Top quartzite, Kuhbanan, Derinjal and Shirgesht formations in the study area (e.g. Husseini 1989), that are equivalent to transgressive facies of Sak Megasequence (Sloss 1963; Gradestein et al. 2012). Sequence stratigraphic analysis of the studied sections indicates that the basal layers (conglomerates) of the Derinjal Formation were deposited unconformably above the upper most layers of the previously deposited the Kuhbanan Formation: therefore the lower boundary is erosional and is type one (SB1) sequence boundary. The LST in the Dahueih and Gatkuieh sections consists of 4 and 2 meters conglomerates whereas in the Gazueih section, the LST is not formed and sequence boundary is composite type (SB+TS). The carbonate facies that overlies the conglomerates was deposited under intertidal and subtidal conditions and belongs to the TST. Thickness of TST deposits in the Dahueih, Gatkuieh and Gazueih sections are 87, 112, and 77 meters, respectively. In the three measured sections, the TS surface is located in the basal part of dolomudstone or peloeidal packstone of lagoon deposits. Progradation of the TST deposits developed and stacked patterns of peritidal in meter scale cycles that was most likely generated by intrabasinal autocyclic and allocyclic processes. In TST deposits, these cycles were considered as parasequences in 4 or 5 orders (Hardie 1986; Catuneanu 2006; Lasemi et al. 2012). Since the lateral accretion is small, it seems that peritidal cycles of the studied deposits were often formed due to the intrabasinal processes such as lateral migration of tidal channels and progradation of shore line. Falling relative sea level results in reduced accommodation space for HST deposits. Thus, HST deposits including intertidal deposits that overlie the subtidal and bar facies and MFS surface located in the last layer of the bar deposits. In the three studied sections, the end of the HST sediments is placed at the top of the Derinjal Formation, which is overlain by carbonate deposits of the Shrigesht Formation. Thus, HST deposits are continuing into Shirgesht Formation and top of the Derinjal Formation is not coinciding with sequence boundary.
