Facies analysis of the Middle to Late Cambrian tidalites in Zarand area - Central Iran Dr. Nader Kohansal Ghadimvand1 Abstract The Middle to Late Cambrian deposits have several outcrops in Kerman Province - Central Iran. These deposits have been introduced as Kuhbanan Formation. This formation has a thickness of about 330 meters in east of Zarand city and has been studied for tidal facies analysis. The Kuhbanan Formation is disconformably overlain with Ordo-Silurian clastic deposits and also the formation is disconformably underlain by the Top Quartzites of the Early Cambrian Dahu Formation. Based on stratigraphic studies, the Kuhbanan Formation is devided into 4 members in Zarand area. All deposits in members 1 and 3 and some deposits of member 4 were formed in tidal flats. Field and petrographic studies of the Kuhbanan tidalites led to recognization of carbonate, siliciclastic, and mixed carbonate-siliciclastic facies groups. Detailed facies analysis of the Kuhbanan Formation resulted in recognition of three sequences (3rd order cycles) equivalent to the second half of the Sauk Sequence. After a global sea-level rising in the Late Early Cambrian and during the expanding of shallow seas, these deposits were formed on the northern margin of the Gondwana Super Continent in a rift basin as homoclinal ramp facies. Keywords: Kuhbanan Formation, Cambrian, Tidalites, Ramp, Zarand, Central Iran Introduction1 a persistent marker in the wider Kerman- The first Cambrian fossils discovered in Kuhbanan-Ravar area. The Cambrian beds Central Iran were identified by King of Kuhbanan seem to correlate with the among the material collected near Kalshaneh Formation of the Tabas area Kuhbanan by R. C. Jennings and K. and with some members of the Mila Washington Gray (in Hukriede et al., Formation of Northern Iran. 1962). The fauna included Redlichia chinensis Walcott, Anomocare megalurus, Methods of study Obolus (?) sp., and Hyolithes sp., To determine facies types and their indicating late EarlyArchive Cambrian to Middle oflateral andSID vertical variations of the Cambrian age. The beds containing these Kuhbanan Formation in Zarand area, one fossils from a 20-40 m thick zone of black outcrop section was studied (Fig.1). A total platy limestone, shale and dolomite of 280 thin sections and polished surfaces reaching a thickness of about 200 meters of representative lithofacies were studied and unconformably overlying the top to provide petrographic details quartzite of the Dahu Formation. Hukriede (composition, texture, fabrics and et al. (1962) found the fossil-horizon to be structures) to enhance the field descriptions. Grains and matrix 1 percentages were estimated using visual Department of Geology, Faculty of Sciences, percentage chart in Flügel (1982). The Islamic Azad University, North Tehran Branch, Tehran, Iran textural scheme of Dunham (1962) was E-mail: [email protected] used to classify carbonate rocks, but here www.SID.ir 2 J. Earth, Vol. 4, No. 2, Summer 2009 the upper size limit for matrix was based on compositional, textural, fabrics considered to be 60 microns. The and structural (field and petrographic) siliciclastic facies classified according to criteria and comparison with modern and Folk’s ideas (Folk, 1974). Facies types and ancient environments (e.g., Purser, 1973; their depositional settings are determined Tucker and Wright. 1990; Flügel, 2004). Fig.1 Simplified map of the study area in northeast of Zarand City, Kerman Province Regional stratigraphy Facies analysis and depositional The Kuhbanan Formation (Middle - Late environ-ments Cambrian) has several outcrops in Kerman Field and petrographic studies of the Province-Central Iran. Huckriede et al. Kuhbanan Formation led to recognition of (1962) introduced the same deposits for the a wide spectrum of facies that are grouped first time. This formation has a thickness into the following facies associations: of about 330 meters in east of Zarand city 1- Carbonate facies association: This (Fig.1) and has been studied for tidal facies facies association consists of four facies analysis. The Kuhbanan Formation is groups that belong to (A) tidal flat, (B) disconformably overlain with Ordo- lagoon, (C) bioclastic/ ooilitic barrier and Silurian clastic deposits and also the (D) open marine. These groups consist of formation is disconformably underlain by the following facies: the Top QuartzitesArchive of Early Cambrian of SID Dahu Formation (Fig.2). Based on A- Tidal flat facies: stratigraphic studies, the Kuhbanan A1) Laminated dolomudstone with Formation is devided into 4 members in evaporite casts and birdseyes (supratidal Zarand area (Fig3). Members 1 and 3 environment) (Fig. 5A). mostly consist of sandstones, clastic A2-1) Sandy dolomitic lime mudstone mudstones and some dolomite layers. (upper intertidal sub-environment) . Members 2 and 4 consist of limestones and A2-2) Dolomitic lime mudstone (upper dolomites (Fig.4). All deposits in members intertidal sub-environment) (Fig. 5B) . 1 and 3 and some deposits of member 4 A2-3) Dolomitic peloid lime mudstone/ were formed in tidal flats. wackestone (middle intertidal sub- environment). www.SID.ir Facies analysis of the Middle to Late Cambrian ….. 3 A2-4) Oncoidal, undulatory, columnar B1) Sandy peloid packstone (shallow and domal dolomitized stromatolite lagoon) (Fig. 5D). boundstone (intertidal environment and B2) Dolomitized ooid peloid tidal channel sub-environment) (Fig. 5C) . wackestone (deeper lagoon). B3) Sorted bioclast peloid grainstone B- Lagoonal facies: (back barrier logoon) (Fig. 5E) . Ordo- Silurian Kuhbanan Fm. Dahu Fm. Fig.2 A complete section of the Kuhbanan Formation in Zarand area- view to the west. Archive of SID Fig.3 Stratigraphic column of the Kuhbanan Formation in Zarand area www.SID.ir 4 J. Earth, Vol. 4, No. 2, Summer 2009 Fig.4 A) ErosionalArchive contact between purple shales (right)of and theSID Top Quartzite (left) of the Dahu Formation, view to the southeast. B) Alternation of carbonate and siliciclastic rocks of the Kuhbanan Formation members, view to the west. There is an erosional contact between Dahu and Kuhbanan Formations. C) Tidal carbonates in member 4 of the Kuhbanan Formation, view to the east. D) Upper erosional contact of the Kuhbanan Formation (down) and Ordo-Silurian rocks (up), view to the northeast C- Barrier facies: C4) Unsorted fossiliferous/oolitic C1) Sorted ooid grainstone (oolitic bar). intraclast grainstone (barrier tidal channel). C2) Sorted echinoderm grainstone (bioclastic bar) . D- Open marine facies: C3) bioclast ooid grainstone (oolitic/ D1) Bioclast packstone (fore barrier bioclastic bar) (Fig. 5F). sub-environment). www.SID.ir Facies analysis of the Middle to Late Cambrian ….. 5 D2) Bioclast wackestone (Shallow are those related to exposure and include marine) (Fig.6A). desiccation cracks, fenestrae, evaporate D3) Bioturbated lime mudstone (deeper mineral growth, soils and related features. marine). Lamination is a distinctive feature in intertidal deposits and reflects alternations 2- Siliciclastic facies association: This of sediment input and microbial activities. facies association mostly consists of some Sediment transported on to intertidal flats terrigenous mudstones/shales with mud from adjacent subtidal areas, principally cracks. These facies were deposited in during storms, is commonly deposited as intertidal environment. millimeter alternations of mud and silt to 3- Mixed carbonate-siliciclastic facies sand-grade carbonate material. Coarser association: This group of facies has layers are commonly rippled or graded and almost equal amounts of detrital grains and mostly peloid-rich (Davies, 1970b; Park, carbonate matrix. Detrital grains are 1977; Hardie & Ginsburg, 1977; Wanless, bimodal in origin and are found as eolian Tyrell et al.. 1988). Where tidal flats are rounded coarse sands and fluvial angular overgrown by mats of cyanobacteria and fine sands. These mixed facies can be algae (most common in elevated salinities), found as dolomitic subchertarenites to these trap and bind fine material to sandy dolomites (Fig.6B). Sedimentary generate a laminated sediment (microbial structures such as bioturbation and Wavy, laminate; also called criptalgal laminate, lenticular and flaser beddings are common fenestral laminate or loferite). Microbial in mixed carbonate-siliciclastic tidal facies. communities on tidal flats produce flat The mixed facies with abundant sands mats, or ones with tufted, crinkled or were formed in lower intertidals, but the pustular surface morphology (e.g. Logan, carbonate rich mixed facies were deposited Hoffman & Gebelin, 1974; Kinsman & in upper intertidals. Park, 1976). Under suitable conditions microbial mats can form domal structures Facies interpretation and depositional or stromatolites; those with relief of more model than a few centimeters generally appear to In this section, only tidal deposits of the have formed in lower intertidal to subtidal Kuhbanan Formation have been explained. areas (Tucker & Wright, 1990). Laminated dolomudstones with evaporite Irregularities in mat morphology can also casts, anhydrite/gypsum pseudomorphs be caused by desiccation, mat expansion and mud cracks are common supratidal during growth, evaporate mineral facies in the Kuhbanan Formation. precipitation, or blisters and fenestrae Presently, these dolomite types are formed caused by gas generated during in the Bahamas and the Florida supratidal decomposition. Mat morphology is less flats and in sabka areas in the Persian Gulf regular