Resolving stratigraphic architecture and constraining ages of paralic strata in a low‐accommodation setting, Firebag Tributary, McMurray Formation, Canada

Abstract

The McMurray Formation in McMurray Depocentre, Canada, is typically subdivided into stratigraphic units based on regionally mappable marine mudstones, the bases of which define flooding surfaces (bottom to top: Lower McMurray, C2, C1, B2, B1, A2, A1 depositional unit). However, the McMurray Formation comprises a variety of palaeoenvironments, with the north-eastern Firebag Tributary hosting significant delta-plain deposits in the Lower McMurray and B1 depositional units. Facies analysis of 60 cores and 4763 wireline logs was used to resolve the palaeoshoreline trajectory and stratigraphic architecture in Firebag Tributary. Of 14 identified facies, three delta-plain facies reveal: (1) eluviated palaeosols, interpreted as shrublands and woodlands formed during base-level fall; (2) gleyed palaeosols, interpreted as tidal marshes; and (3) coals formed in coastal mires, the two latter facies are interpreted to accumulate during base-level rise. Eluviated palaeosols occur below the Lower McMurray coal seam, implying valley incision and a maximum regressive surface. Gleyed palaeosols underlying the coal seam atop the B1 depositional unit do not record base-level fall. Wettingupward coals overlying either palaeosol facies indicate base-level rise (i.e. major flooding surface). B1 depositional unit coals and gleyed palaeosols are overlain by shallow-marine facies or are eroded by wave ravinement during transgression. Consequently, the tops of coals or gleyed palaeosols correlate to the bases of regional marine mudstones elsewhere in McMurray Depocentre. Stratigraphic cross sections showcase palaeoshoreline regression and transgression. During the Lower McMurray and B1 depositional units, widespread coals and palaeosols indicate the palaeoshoreline resided near the western edge of Firebag Tributary.Regression during C2 through B2 depositional units and A2 and A1 depositional units resulted in palaeoshorelines near the Alberta-Saskatchewan border.To complement a previously dated Lower McMurray ash (121.39 ± 0.2 Ma), a new high-confidence maximum depositional age from ash in the B1 coal seam

Carbonate Stable Isotope Data Suggest Freshwater Environment for the McMurray Formation (Aptian), Alberta, Canada

“…The McMurray Formation has long been considered to be Aptian in age [29]. This interpretation is supported by new high-precision thermal ionization mass spectrometry (TIMS) detrital zircon U-Pb ages from isolated zircon grains [30,31], which show that McMurray Formation deposition included the period ca. 121-115 Ma, and by lower precision detrital zircon U-Pb maximum depositional ages from laser ablation inductively coupled mass spectrometry (LA-ICPMS) techniques, which place deposition from ca.…”

Coastal Depositional Responses to Relative Sea-Level Rise: Insights from a Superimposed Sandstone–Shale–Coal Reservoir in the Linxing Gas Field, China

“…Lithofacies mSm with faint and/or spaced planar lamination indicates deposition of within-channel turbidites originated by breach failures in the channel margin [59]. Lithofacies mSx is interpreted to have been formed in the channel thalweg and/or on the lower point bar [60,61].…”

“…Lithofacies Sm or mSm with spaced planar and/or faint lamination are interpreted as within-channel turbidite sequences generated by breach failures in the channel margin [59]. Lithofacies Sx, mSx Sxd, Sbx, mSbx, Sbd, and mSs are all interpreted to have been formed in the channel thalweg and/or on the lower intertidal point bar [14,60,62,63]. The basal and/or intervening mMh layers are interpreted as channel-bottom fluid mud deposits [64].…”