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Mixed Carbonate-Siliciclastic Sequence Development on a Distal Fore-Land During Miocene Glaciation, Eastern Saudi Arabia

Abstract

The Miocene of the Lidam area, Eastern Province, Saudi Arabia, was studied to examine the interaction of glacio-eustasy during moderate Antarctic glaciation, within a small back bulge basin on the slowly subsiding distal Arabian foreland, distal from the active Zagros fold-thrust belt. The Aquitanian Hadrukh Formation (∼60 m thick) is dominated by non-marine siliciclastics and minor palustrine carbonates. The late Aquitanian to early Langhian Dam Formation (up to 80 m thick) is a mixed carbonate-siliciclastic with updip sections dominated by siliciclastics, grading downdip into carbonates. The Langhian to Serravallian Hofuf Formation (90 m thick) is a non-marine sequence with a lower siliciclastic unit. The middle and upper units of the Hofuf Formation were not examined in this study. Subsidence rates of the studied sequences were 1 to 4 cm/k.y and are considerably slower than those in the proximal foredeep in Iran. This together with long-term sea level changes generated the accommodation space, which produced the observed depositional sequences. Differential warping during the Oligocene-Miocene generated a structurally controlled embayment within the study area. Deposition of Hadrukh siliciclastics was driven by low sea levels in a moderately humid to arid climate. The siliciclastics were brought into the area by ephemeral streams and eolian processes. Arid phases are marked by gypseous quartz sands. Rising sea levels pushed the siliciclastics updip allowing Dam mixed siliciclastics and carbonates to form downdip, under a semi-arid climate and locally hypersaline conditions. Falling sea levels triggered Hofuf siliciclastic deposition under a semi-arid climate. The Miocene sequences were generated by glacio-eustatic sea level changes. Sequences seem to relate to long-term obliquity (∼1.2 m.y. cycles) and long term eccentricity (400 k.y.) cycles. The succession contains numerous missing beats, reflecting the updip position of the study area, and sea level changes of tens of meters that frequently exposed the platform. These conditions resulted in numerous paleosols formed on redbeds near sequence boundaries in the Hadrukh and the Dam formations. Siliciclastic units commonly incised into muddy sediments beneath sequence boundaries, as well as multiple exposure surfaces within Hadrukh brecciated palustrine carbonates.