Depositional environment and sequence stratigraphy of siliciclastic - carbonate deposits of Parvadeh Formation (Middle Jurassic) in Tabas block, East Central of Iran

Abstract

Parvadeh Formation (Bathonian) in Tabas block is formed of mixed siliciclastic-carbonate deposits. Six stratigraphic sections have been selected in this formation which dominantly composed of conglomerate, sandstone, shale and limestone. Integration of field and microscopic studies resulted in identifying two facies association including 4 siliciclastic and 10 carbonate facies in this formation. Analyzing facies and sea level fluctuations caused identification of two 3rd order sedimentary sequences in each of the sections. The low-stand system tracts of the recorded sequences are characterized by tidal flat and lagoon facies and shallowing-upward para-sequences. Highstand and transgressive systems tracts are generally both represented by dominantly intertidal and sub-tidal lagoon, shoal and open marine facies. The upper and lower boundaries in all stratigraphic sections of middle Jurassic successions are SB1 that are distinguished by erosional evidences and sometime red conglomerate and sandstone horizons. On the basis of detailed facies and depositional sequences analysis, global sea level fluctuations and tectonic events are the most important factors that affected system tracts and depositional sequences in the Tabas block. Local tectonic activities (mostly related to Kalmard and Nayband Faults) also have an effective role on the thicknesses of siliciclastic and carbonate deposits in different parts of study areas.