Enigmatic Kilometric Scale Diagenetic Structures of the Haushi-Huqf High, Central Oman

In this study, we present enigmatic exposures of suspected Cambrian age deposits of the Haushi-Huqf High, Central Oman. The present study area is an uplifted horst-block bounded by north-south oriented normal faults, with onlapping Mesozoic carbonate deposits on its western and eastern flanks, covering an outcrop area of ~1 km². This exposure reveals decameter to kilometer-scale concentric, nested and coalescing ring-like structures superimposed within a clastic host rock, forming regularly spaced structural highs with lateral thicknesses and heights of one to several meters bounded by several meter wide troughs infilled with recent sediments. The host rock comprises fine to coarse grained, cross stratified quartz arenites, with basal pebbly lags, and with paleocurrents indicating a W-SW paleo-transport direction. The significant textural/mineralogical maturity of these sandstones suggests extensive recycling of older sediments, with the presence of frosted, well rounded grains signifying aeolian input. Establishing the stratigraphic position of the deposit within the regional context is challenging, owing a lack of body fossils, datable strata or correlatable stratigraphy proximal to the study site. However, Uranium-Lead Zircon dating of the host rock does reveal two geochronological populations: Neoarchaean to Paleoproterozoic (2.8-2.5 Ga), likely sourced from Precambrian basement rocks of Northern and Eastern Yemen, and Early Cambrian (~530 Ma), likely sourced from Cambrian-aged alkaline magmatism located within close proximity to the study site. Based upon the above, coupled with the observed textural, mineralogical and depositional characteristics of the deposit, we postulate that a Lower Paleozoic origin (esp. Amin Fm. Of the Haima Supergroup) is likely.

Interpreted as fluivial-plain / fluvio-deltaic in origin, these rocks exhibit bioturbation within a select interval in the form of large horizontal/vertical calcite cemented burrows, indicating marine influence and colonization by benthic macrofauna. Furthermore, a thin, laterally continuous deposit of botryoidal calcite is observed, which commonly pinches out between reactivation surfaces. We interpret this deposit as recrystallized bacterially induced precipitates of calcium carbonate, signifying the presence of microbial mats developed during a short-lived period of marine incursion. Petrographic analysis reveals that there is a strong association between the pronounced diagenetic overprint of the study area and the occurrence of this deposit. Ridges structural highs exhibit major chemical compaction and porosity collapse via the development of quartz overgrowths. Conversely, topographic lows between these structures are generally porous and poorly consolidated, being characterized by the presence of calcite cementation and hematite grain coatings. The contrasting mechanical competence of the sandstones forming the topographic highs and lows offer spatial controls over differential weathering and erosion of the study area, resulting in the remarkable diagenetic architecture observed therein. It is proposed that spatially disparate early calcite cementation associated with microbial mat colonization protected the pore system from pervasive chemical compaction, which was extensively removed by meteoric dissolution post-exhumation. The pronounced spatial organization of calcite precipitation and cementation controlling these structures poses fascinating questions regarding the self-organization of microbial mat communities during the Cambrian substrate revolution, hinting at the influence of internal feedback and environmental controls in their nucleation and propagation.