Identifying and naming of studied sections components and surveys of diagenetic
processes are important in the determination and study of microfacies and sedimentary
environment interpretation (Flugel, 2010).
On the other hand, the clay minerals can were used in determine the sedimentary
environment and deposits diagenetichistoric (Jackson, 1979).
Clay minerals, hydreous aluminum silicates is layer structure and they are classified
as sheet silicates (Hardy and Tucker, 2004).
A unique characteristic of these minerals are including formed of the surface
and subsurface different conditions. XRD analysis is important in determining
the exact of clay minerals type and the semi-quantitative analysis of clay minerals
(Jeong et al., 2004).This study investigated
depositional environment and a digenetic conditions of the Lar formation depositions
based on study of clay minerals and microfacies in the Haft-Cheshmeh anticline
section in southwest of Azarshahr.
MATERIALS AND METHODS
Study area: The Haft-Cheshmeh is located in 45°42' 43" E and 37°41'
80" N in east Azarbaijan province with 7495 km2 in about 18 km the
south west of Azarshahr (Fig. 1). This area is part of the
western Alborz-Azarbaijan (Aghanabbati, 2005). There
are deposits of belonging to the Jurassic, Cretaceous and Quaternary outcrops
in this study area (Assereto, 1966). Jurassic deposits
is include of marl (Delichay formation, middle Jurassic), marl and limestone
(Lar formation, late Jurassic), Cretaceous deposits are consist of limestone
(Tizkuh formation, early Cretaceous), shale and deposits are not named (late
Cretaceous) and Quaternary deposits are include of alluvial terraces of ancient,
travertine and alluvial terraces of young (Steiger, 1966)
Methods: This study was investigated based on fields and laboratory studies which these are one of the commonly methods in sedimentary geology. In the field studies, sampling of the formations are done with change of fancies and vertical of along the layers.
Hereby, eighty samples prepared of lower, middle and upper parts from the formations
of study area and then the formation lithostratigraphy column has been plotted.
|| Study area in Iran, west Azarbaijan province
Moreover, seventy thin sections were prepared and studied. Ten thin sections
was used by Red Alizarin (Red-s) to determine of calcite and dolomite mineral
also detection of iron in carbonate cement was paint during burial and then
thin sections petrographic of formation carbonate parts were named by Dunham
(1962). Finally, carbonate parts microfacies were determined based on Flugel
facies belt and the Lar formation deposition environment was determined based
on existing facies. Twenty samples for X-ray diffraction (ten samples from the
lower marl and ten samples from upper marl) were selected according to the lowest
carbonate amount (value). Samples analysis in laboratory was done by Simense-Difractometr
500 device in Geology Organization and Mineral Exploration of Tabriz.
RESULTS AND DISCUSSION
Lar formation lithostratigraphy: Lar formation according to late Jurassic
age has large out crops in area of the Alborz-Azerbaijan and it has in traduced
rich of the Ammonites and Foraminifer. According to present of fossils its age
has been determined of Late Jurassic (Oxfordian-Kymbrjyn) (Aghanabbati,
In field studies, the Lar formation thickness was determined about 250 m. Its lower boundary is located on Delichay formation gradually and it the upper boundary is an erosion unconformable with Tizkoh formation. Lar formation sections are consists of three facies as follows.
The lower marl section thickness is about 70 m. The middle limestone with red marls section thickness are about 80 m. Gray limestone to upper milky section thickness is about 100 m.
Clay minerals: According to the XRD obtained results (Table 1) samples of related to the middle marl, peaks of smectite, illite and chlorite is observed and the lower marls are detect able peaks of smectite, illite and silica (Fig. 3).
As Fig. 3 shows, climate and depth of deposition of smectite
in sedimentary environments is directly related to the high level of water,
sea water as well as warm and mode rate climates conditions with alternating
grey and wet seasons that it changes frequently. Also, chlorite and illite with
origin of detrimental is formed in low leaching condition and weathering in
cold and temperate climate or cold and dry rarely. Adatte
et al. (2002) believes that the simultaneous presence of the smectite
and illite in the depositional environment may be representing of sediments
in temperate climates.
According to this simultaneous presence of the smectite minerals in the lower
marl Lar formation can be concluded that the early Jurassic period is low to
mode rate leaching amount (value) and the weather is warm and humid (Mees
et al., 2007).
||Amount of clay minerals in removal samples that represent
of smectite relative increasing and relative decreasing of illite toward
low of Lar formation
|| Semi-quantitative analysis of the clay minerals in Lar formation
Smectite compared with illite and chlorite deposits in the deeper parts of
the bas in in which sediment action environment (Adatte
et al., 2002).
According to smectite decreased and illite relative increase the upwards parts
sedimentary basins in studied section, it can be concluded that the depth of
the sedimentary basin has decreased upward parts of the formation (Stuben
et al., 2002). The high rate (amount) of smectite in the lower part
of the Lar formation in studied section can be attributed to uplifting sea water
level in the early Jurassic period (Razmara, 2005). This
issue is confirmed by considering of the global and regional changes of sea
water level (Vail et al., 1977).
Microfacies: Main components Lar formation deposits can be classified in the two components of the non-carbonate and carbonate. The most important carbonate allochemes in thin section of study identified bioclasts the type of planktonic foraminifera.
The non-carbonate components Lar formation can be pointed to detrimental quartz, charted iron oxide which detrimental quartz particles is observed in the lower marl and iron oxide, chert nodules are observed in limestone upper and low part. According to components type and quantify were identified three microfacies of bioclastic packstone, bioclastic wackstone and mudstone.
Bioclastic packstone: Components of Bioclastic dominant skeletal in
this microfacies is type of planktonic foraminifers which they are in a micrite
matrix. This microfacies is observed in the upper part of the formation. There
are others bioclastics in this microfacies that maybe pointed to parts of the
Ammonites. This microfacies is equivalent to facies of No. 2 (RMF2) infacies
belts Flugel (Flugel, 2010) which represents the least
deep of Lar formation part (Fig. 4a).
Bioclastic wackstone: This microfacies allocates 20% of bioclastics (planktonic foraminifera predominantly) that it is a micrite matrix. The planktonic foraminifera in this microfacies can be pointed to milolida and the non-carbonate components in this facies can be pointed to chert fragments. This microfacies is observed mainly in the middle and upper Lar formation. This microfacies is equivalent to facies of No. 3 (RMF3) in facies belts Flugel (Fig. 4b).
Mudstone: Bioclastics is less than 10% of the sample volume in this microfacies and it has a floating micrite matrix. Over all, this microfacies makes the deepest of formation carbonate part.
Limited bioclastics facies in this microfacies are include of planktonic foraminifera
and there are rich ammonite facies within the Marl. This microfacies is equivalent
to facies of No. 3 (RMF3) in facies belts Flugel (Fig. 4c).
||(a) Bioclastic wackstone, (b) Bioclastic packstone, (c) Mudstone
and (d) Iron oxide of developing into fractures that it is the latest
Depositional environment: According to the evidence of petrography and facies and clay minerals studies of the Lar formation marl part has deposited in the open marine and carbonate platform.
According to the Lar formation in the study area is located between two Tizkoh
and Delichay formations (Berberian and King, 1981) and
its also important to remember that both are introduced in the western
Alborz region with an open marine and carbonate ramp (Aghanabbati,
2005). The Lar formation deposition in the study area can be called related
to an open marine and carbonate platform that its schematic model is shown in
|| Lar formation depositional environment model in area study
Based on Flugel facies, facies of No. 2 is represents the deposition of the
formation in the middle and interior ramp and open marine basin part. Facies
of No. 3 is related to the middle and outer ramp from carbonate ramp. Deposits
of this formation have been in traduced in Kopetdagh (Mozdoran formation) as
a carbonate ramp (Adabi and Rao, 1991).
Diagenesis: Diagenetic processes of a limited is done because of semi-deep of Lar formation deposition bas in that it is based on event includes.
The cement action which is consist of equal calcite cement at ion veincalcite cementation, dissolution and porosity of the inter-granular fracture and channel, finally processing of iron stain into the fractures chert nodules formation.
Studies of sections shows which processor being is occurred in the study area and also it has been filled in to the fractures (Fig. 6).
The others of digenetic processes are including the primary and secondary porosities.
An inter-granular porosity is the types of primary porosity that generally,
it has been filled by cement and in the case of; also, shelter porosity is observed
(Hardy and Tucker, 2004).
Porosity due to fracture in the late diagenetic stage (Late diagenesis) occurred
in the dissolution process can cause it spread and cause to be channel porosity
that this process is observed clearly. Finally, it should be noted that the
Lar formation is having ferro occurrence in the late condition. The process
considering to filling the fractures with constructing of chert nodules is last
diagenetic processes (Grassman and Milet, 1961).
||Lar formation diagenetic events, (a) Cementation into fractures,
(b) Channel fractures that it is caused of permeability increasing, (c)
Diagenetic step iron oxide of developing in to fractures that it is the
latest and (d) Equalcalcite cementation that it has been advanced into fracture
According to the presence of illite, chlorite, smectite with detrital origin in the samples can be identified constructing of alogenic smectite related to change and con version of others clay minerals.
According to study on microscopic thin sections showed that Lar formation has three microfacies of bioclastic including the packstone, wackstone and mudstone which representing of deposition in the middle part of this formation, as well as it is an open marine of carbonate ramp typein sedimentary basin of Alborz-Azarbaijan.
The survey of clay minerals showed due to presence to smectite and cholorite as well as probability of alogenic smectite in this formation and their changes upward are representing the decrease of depth and climate warming.
Diagenetic processes that it is observed in the Lar formation sequence of events including: the cementation (equal calcite cement and a vein cement calcite), the appearance of chert nodules in fluencing of environment changes, dissolution and appearance of porosities of the inter-granular, middle-granular and shelter fracture, finally, the process of ferro occurred within the fractures. To sum up these fractures have prepared the suitable groundwater aquifer in area of study.