ABSTRACT The unit previously mapped as the lower Upper Devonian Okse Bay Formation in the Yelverton Pass area of northern Ellesmere Island, considered indicative of syn-orogenic foreland (Devonian clastic wedge) basin deposition along the apex of the Ellesmerian Orogen, is in fact Early Carboniferous (Serpukhovian) in age and belongs to the Borup Fiord Formation of the successor Sverdrup Basin. The principal lines of evidence in favor of the original Okse Bay formational assignment were: (1) the presence of late Middle (Givetian) or early Late (Frasnian) Devonian palynomorphs; (2) a set of lithofacies presumably different from that of the Borup Fiord Formation; and (3) an angular unconformity between the so-called Okse Bay strata and overlying Pennsylvanian carbonates of the Nansen Formation. Here we demonstrate that the Devonian palynomorphs were eroded from the Devonian clastic wedge, transported for some distance, and deposited into the Sverdrup Basin in the Early Carboniferous. We also show that the units mapped as Okse Bay and Borup Fiord formations share the same clastic lithofacies assemblages, albeit in different proportions. We report the presence of Early Carboniferous palynomorphs in the uppermost part of a section assigned to the Okse Bay Formation, and show that detrital zircons contained in the middle part of the Okse Bay Formation yield dates as young as 358 Ma, thus demonstrating that the rocks that contain them are considerably younger than the assumed youngest age (Frasnian) based on palynology. We conclude that the Okse Bay Formation is the same unit as the Borup Fiord Formation and should be remapped as such. Both units are part of the same unconformity-bounded syn-rift Serpukhovian sequence that was rotated and differentially eroded prior to the widespread Pennsylvanian transgression. The Serpukhovian sequence comprises three lithofacies assemblages: meandering stream clastic, braided stream/alluvial fan clastic, and shallow marine carbonate. These lithofacies assemblages were deposited as part of a differentially subsiding rift system likely bounded to the south by one or more master listric faults and associated footwall uplift, and to the north by hanging wall ramp uplift. The Serpukhovian sequence comprises three fourth-order sequences, each interpreted as corresponding to a rift pulse. Relatively coarse terrigenous sediments derived from the erosion of the Franklinian basement (Laurentia margin) and the Devonian clastic wedge entered the rift basin at a high angle through broad alluvial fans and braided river systems. These streams fed into a NE-flowing basin-axial meandering system, which met a shallow sea to the northeast. An additional source of sediments is Crockerland to the north, including syn- to post-Ellesmerian intrusions that shed detrital zircons of latest Devonian age once sufficient unroofing of these had occurred during the Serpukhovian.

ABSTRACT The Devonian System in the Kingdom of Saudi Arabia (KSA) forms a significant part of the Paleozoic succession on the Arabian plate and was deposited on an extensive coastal plain to shoreline to shallow continental shelf, dipping slightly to the north and east. The Devonian succession attains a thickness of nearly 2.5 km (8200 ft), though a significant part of this thickness is from the reconstructed Jubah Formation in deep basins to the east and north of KSA. The Devonian Jauf Formation is an important siliciclastic gas-bearing and producing reservoir in eastern Saudi Arabia, and it formed within a second-order progradational megasequence, lasting from the latest Ordovician to the culmination of the Hercynian orogeny in the very early Carboniferous. It also includes proven source-rock intervals related to plate-wide flooding events. We recommend that the top of the Jauf Formation, in the subsurface of the Eastern Province, be raised approximately 120–130 m (390–430 ft) higher than the currently adopted top by Saudi Aramco staff, to include all strata that are considered as part of Jubah by Saudi Aramco current usage. The present Jauf top (Saudi Aramco’s operational Jauf top) is picked at the top of a biostratigraphic zone (D3A), a practice not recommended by the code of stratigraphic nomenclature for formational tops. The contact this chapter proposes coincides with a prominent lithological change that marks a third-order sequence boundary (SB70). We believe that this distinct disconformable contact is of regional significance. We reconstruct the Jauf depositional systems using subsurface and outcrop data, emphasizing key regressive deltaic and transgressive estuarine shorelines as well as and associated fluvial, paralic, and shelf deposits. We demonstrate the importance of the fundamental fourth-order shelf-transiting sequences and larger third-order host sequences in the very extensive Devonian Arabian shelf building. We also draw contrasts between the Jauf Formation development in the outcrops of northwest KSA (including carbonate embayments) and those in the subsurface of the east and southeast parts of the KSA (wave-dominated strandplains and deltas and tide-influenced estuaries), where there was stronger fluvial supply. The Devonian Jauf shorelines show truly spectacular regressive and transgressive transits for hundreds of kilometers across the wide shallow shelf that sloped gently off the Arabian shield. In eastern KSA’s producing fields, the revised Jauf Formation thickens toward the east-northeast from 170 m (557 ft) to 343 m (1125 ft) and comprises three third-order sequences, referred to as SQ55, SQ60, and SQ65. Five new paleogeographic maps are presented for these three sequences. Each of the third-order sequences consists of several fourth-order sequences. Sequence SQ55 is dominated by a spectacular falling stage systems tract (forced regressive shoreface), which prograded from west to east across a distance of over 200 km (125 mi). The overlying sequences SQ60 and SQ65 each have a thick transgressive systems tract (TST) and a thinner highstand systems tract (HST). Depositional environments were mostly coastal plain and nearshore and ranged from wave-dominated shorefaces to tidally influenced estuarine embayment fills with tidal channels and bars to tidal and fluvial-dominated coastal-plain channels. Reservoir quality rocks are preferentially those deposited during the TST of SQ60 in tidal estuarine environments as channel-fills, bars, and bay-fill deltas. In these reservoirs, porosity was protected by grain-rimming clays from subsequent quartz cementation. The well-sorted shoreface facies, which dominates SQ55, tends to be of lower reservoir quality because of finer grain size and pervasive silica cementation.

There was a new focus on “processes” within sedimentary geology from the 1960s. It was initially driven by alluvial-channel and flow-regime experiments, but led to the concept of facies succession for all depositional environments and eventually, on the larger scale, to a new stratigraphy in which base-level change was the key ingredient. Systematic study of modern environments led to a marked improvement in our knowledge of alluvial to deepwater sedimentary systems and how they are linked. New access to seismic data, especially on shelf margins and deep marine environments, was critical for further great changes in our understanding of marine processes and basin-scale products. Integration of new knowledge on rates and time scales in tectonics, climate dynamics, and sea-level change has been important for gleaning the signals of these drivers from the accumulated sedimentary successions. Current research, not least from geomorphic and stratigraphic experiments, is suggesting that autogenic responses in stratigraphy are more common and occur on longer time scales than formerly thought and will cause a rethink in sequence stratigraphy. The past half-century of work in siliciclastic petrology has benefited from a broad consensus on classifications for sandstones and limestones that provided clarity on the roles of detrital and diagenetic components in compositional heterogeneity. Subsequent advances in provenance and diagenetic studies have both been driven by the availability of microanalytical tools for imaging and analysis of elements and isotopes. A petrographically based appreciation of the role of pervasive non-equilibrium and chemical kinetics underpins our current capabilities to make predictions of siliciclastic rock properties in the subsurface, creating a strong link between siliciclastic petrology and the global petroleum industry. Community consensus has yet to converge on classification for fine-grained siliciclastic rocks (shales, mudrocks, mudstones), but the compelling need for prediction of rock properties in unconventional reservoirs is presently driving much research into the causes of heterogeneity in this great class of sedimentary materials.