Sequence Stratigraphy of the Jurassic Hanifa Supersequence: A Stratigraphic Framework for Understanding the Distribution of Marine Restricted Source Rocks in the Hanifa Intrashelf Basin

Abstract Deposits of the Hanifa Supersequence represent the filling of the restricted-marine, intra-shelf Hanifa Basin during Jurassic time. The Hanifa Supersequence is a distinctive source rock-bearing section bounded by prominent regional unconformities that includes the Hanifa Formation along with the Tuwaiq Mountain Formation. This Hanifa/Tuwaiq Mountain section can be subdivided into four sequences (Figure 1).In ascending stratigraphic order, these sequences are the 1) Tuwaiq Mountain Sequence, 2) Hadriya Sequence, 3) Lower Hanifa sequence, and 4) Upper Hanifa Sequence. Each of the sequences has a similar distribution of depositional thickness. Thickest deposits are located in the western part of the study area in Saudi Arabia and thin to the east in the central part of the study area in Qatar. Although not shown in Figure 1, the deposits thicken again in the eastern part of the study area in Abu Dhabi. An important exception to this general trend in the distribution of the deposits is truncation of section due to erosion at the unconformity that caps the supersequence. Significant amounts of the youngest two sequences are removed by this truncation over much of the study area. The youngest sequence, the Upper Hanifa Sequence is particularly impacted by this truncation and is only preserved in the northeast part of the study area. Each of the four sequences represents a discrete episode of carbonate platform development and progradation into the Hanifa Basin. Each sequence consists of thick platform deposits of skeletal/oolitic grainstone, packstone and wackestone that grade basinward into organic-rich mudstone (Figure 2).The thick accumulation of grainstone, packstone and wackestone represent stacked carbonate shoal complexes that individually grade off the platform into organic-rich mudstone which characterizes deposition in the restricted basin adjacent to the platform. The sequences can be further subdivided into a lower Transgressive Systems Tract and an upper Highstand Systems Tract with the boundary between the two marking the maximum flooding surface of a sequence. The Transgressive Systems Tract section is relatively thin forming a gentle ramp from platform to basin.