Abdulrahman Al-Harthy

Late Cretaceous Conglomerates of the Qahlah Formation, north Oman

Abstract Conglomerate sequences over 700 m thick were deposited subsequent to ophiolite emplacement during Late Cretaceous time in north Oman. The conglomerates were deposited by streams draining the allochthonous ophiolite and Hawasina complex after their obduction onto autochthonous Mesozoic and older Oman shelf sequences and subsequent uplift. The conglomerates belong to the Qahlah Formation of Late Cretaceous age, which is sandwiched between the Semail Ophiolite/Hawasina complex and Maastrichtian–Palaeogene carbonate rocks. The siliciclastics of the Qahlah Formation are the first sediments deposited over the obducted oceanic crust sequence of ophiolite and Hawasina lithologies. In five locations studied in north Oman, the thickness of the formation varies from 140 m to over 700 m and comprises interbedded conglomerate, sandstone and siltstone. The sediments were deposited in isolated segmented depressions each characterized by its source terrain depending on lithologies exposed in the source area. Lithofacies associations, clast sorting and grain roundness suggest deposition in stream-dominated alluvial fans. Clasts in the conglomerates range from subangular to subrounded pebbles to boulders with both grain and matrix (sandstone) support. Cross-bedded fining-upwards sequences in channelized conglomerate and sandstone suggest deposition by high-energy flows in the proximal to distal reaches of alluvial fans. High proportions of chert and ophiolite fragments in the conglomerates suggest rapid erosion of obducted oceanic crust. The presence of Loftusia-bearing carbonate beds and bivalve-bearing conglomerate beds in different sections indicates occasional interruption of alluvial deposition by marine transgressions.

Stratigraphic evolution and depositional system of Lower Cretaceous Qishn Formation, Dhofar, Oman

Abstract The Barremian(?)–Aptian Qishn Formation of Dhofar (Oman) is represented by eastward (landward) thinning strata that onlap Marbat palaeohigh basin margin. The formation includes Shabon, Hinna and Hasheer members, in ascending order. The Shabon Member consists of massive and cross-bedded, locally conglomeratic arkose and quartzarenite. The Hinna Member has a lower part of rhythmically arranged bioclastic wackestones/mudstones that grade to fine crystalline dolomudstone and an upper part of cyclic units of nodular, marly, rudistic floatstone/rudstone lithofacies capped by normally grading, intraclastic, bioclastic packstone/grainstone lithofacies. Mudcracks, teepee structures and microbial laminations occur in the lower part. The member terminates with 10-m-thick discoidal orbitolinid- and rudist-bearing marls envisaged as the deepest facies of the formation. The Hasheer Member consists of partly dolomitized strata of bioclastic packstones, grainstones and rudstones. Cross-bedding and erosional surfaces are present. The overall depositional system of the formation evolved from high-energy clastic-dominated, marginal marine environment through tidal carbonate mudflat and lagoonal setting to high-energy carbonate sand shoals. The overall stratigraphic arrangement of the formation suggests a third-order transgressive-regressive system with superimposed fourth- and fifth-order cycles. Shabon and Hinna members represent lowstand to transgressive systems tracts whereas Hasheer Member represents highstand to falling stage systems tracts. Terminal platform-wide exposure resulted in an unconformity at the Qishn–Kharfot contact.

Rare earth element mobility during laterization of mafic rocks of the Oman ophiolite

Eleven samples representing a sequence of progressive alteration through a laterite profile of Upper Cretaceous age developed on a layered gabbro from the Oman ophiolite have been analyzed for their rare earth element (REE) contents. The results provide new insights into the fractionation and vertical movement of REEs during the laterization of mafic parent rocks. Compared to the fresh parent rock, from the same section nearly flat chondrite-normalized REE patterns are observed in the saprolite zone, while light REE (LREEs: La-Nd)-enriched patterns characterize the oxide and clay zones. The altered gabbro shows a depletion in middle REEs (MREEs: Sm-Ho) compared to its unaltered counterpart. A negative cerium (Ce) anomaly is observed in the upper part of the altered gabbro, while the lower part appears to be depleted in Ce. The similarity in the LREE-enriched fractionation patterns throughout the alteration profile suggests that the REE fractionation process is independent of the total REE content of the parent rock.

Diversity in the later Paleogene proboscidean radiation: a small barytheriid from the Oligocene of Dhofar Governorate, Sultanate of Oman

Despite significant recent improvements to our understanding of the early evolution of the Order Proboscidea (elephants and their extinct relatives), geographic sampling of the group’s Paleogene fossil record remains strongly biased, with the first ~30 million years of proboscidean evolution documented solely in near-coastal deposits of northern Africa. The considerable morphological disparity that is observable among the late Eocene and early Oligocene proboscideans of northern Africa suggests that other, as yet unsampled, parts of Afro-Arabia might have served as important centers for the early diversification of major proboscidean clades. Here we describe the oldest taxonomically diagnostic remains of a fossil proboscidean from the Arabian Peninsula, a partial mandible of Omanitherium dhofarensis (new genus and species), from near the base of the early Oligocene Shizar Member of the Ashawq Formation, in the Dhofar Governorate of the Sultanate of Oman. The molars and premolars of Omanitherium are morphologically intermediate between those of Arcanotherium and Barytherium from northern Africa, but its specialized lower incisors are unlike those of other known Paleogene proboscideans in being greatly enlarged, high-crowned, conical, and tusk-like. Omanitherium is consistently placed close to late Eocene Barytherium in our phylogenetic analyses, and we place the new genus in the Family Barytheriidae. Some features of Omanitherium, such as tusk-like lower second incisors, the possible loss of the lower central incisors, an enlarged anterior mental foramen, and inferred elongate mandibular symphysis and diminutive P2, suggest a possible phylogenetic link with Deinotheriidae, an extinct family of proboscideans whose origins have long been mysterious.