Controls on Hierarchy of Miocene Buildups within a High Resolution Cycle Stratigraphic Framework of Dam Formation, Lidam Area, Saudi Arabia

Abstract

The Trucial coast is considered a unique geological setting in the Arabian Gulf with the distribution of facies from supratidal to subtidal zones. Multiple factors were the controllers for the distribution of the facies. The analogy of the Miocene rocks into some extent with the modern makes the Dam formation in Lidam Area an example that completes the full picture, in which to understand the results of the same strong controlling factors. Dam Formation is a mixed carbonate / siliciclastic succession deposited during the Middle Miocene in a closed embayment. Dam Formation in the studied outcrop is divided into three Composite Sequences: Composite sequence 1 (CS1) is made up of four meter scale cycles. Composite Sequence 2 and 3 (CS2, and CS3), each is made up of two High Frequency Sequences (HFS1, HFS2, HFS3, and HFS4). For Composite Sequence 2 and 3, High Frequency Sequence 1 (HFS1) and High Frequency Sequence 3 (HFS3) are made up of a TST flooding on incised Type 1 sequence boundary. The HST is of prograding bioclastic grainstone channels dominated facies tracts. High Frequency Sequence 2 (HFS2) and High frequency sequence 4 (HFS 4) are made up of a TST flooding a type 2 sequence boundary. The HST is of prograding banks and bioclastic channels. Within the High Frequency Sequences, skeletal and microbial banks tend to form as buildups during the TST, whereas skeletal grainstone channels (broad and shallow) dominated the late HST. Cross-bedded, burrowed, unconsolidated quartz sandstone (estuarine fill), forms during the earliest flooding phase of the TST. This is on top of the incised Type 1 sequence boundary in High Frequency Sequence 1 and 3. Due to the prolific microbial deposits (sheets, digitates, heads, and bioherm/ biostrome buildups), there are extensive mud-cracked stromatolites tidal flats, red beds, ooid grainstone, dominantly mono-specific skeletal banks, and adjacent continental eolian facies at the Lidam escarpment. The climate is interpreted as arid. The arid climate coupled with observed Miocene eolinites at the Lidam escarpment, suggest that the dominate transport mechanism for the quartz sandstone facies was eolian during sea-level drop of the low stand systems tracts. This is expressed at the study area in the preserved incisions filled with quartz sandstone. Possibly it was reworked during subsequent base level rises of the Transgressive System Tracts in the cases of HFS 1 and HFS3.