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TitreTuronian to Santonian paleoenvironmental changes in the Cretaceous Western Interior Sea: The Carlile and Niobrara formations in southern Alberta and southwestern Saskatchewan, Canada
AuteurNielson, K S; Schröder-Adams, C J; Leckie, D A; Haggart, J W; Elberdak, K
SourcePalaeogeography, Palaeoclimatology, Palaeoecology vol. 270, 2008 p. 64-91,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20070474
ÉditeurElsevier BV
Documentpublication en série
Mediapapier; en ligne; numérique
ProvinceAlberta; Saskatchewan
SNRC72F; 72K; 72N; 82H; 82I; 82J; 82O; 82P
Lat/Long OENS-118.0000 -108.0000 52.0000 49.0000
SujetsTuronien; Santonien; paléoenvironnement; paléogéographie; faciès; faciès sédimentaires; milieu sédimentaire; sédiments marins; sédiments marins; milieux marins; mudstones; grès; roches sédimentaires; lithostratigraphie; biostratigraphie; Formation de Carlile ; Formation de Niobrara ; Groupe d'Upper Colorado ; Formation de White Specks ; paléontologie; stratigraphie; Crétacé; Mésozoïque
Illustrationslocation maps; stratigraphic columns; stratigraphic charts; tables
Résumé(disponible en anglais seulement)
The Upper Cretaceous Upper Colorado Group, including the Carlile and Niobrara formations, reveals a complex and dynamic marine basin system in southern Alberta and southwestern Saskatchewan. An integrated study of the lower offshore to shelf environment, including sedimentology, geochemistry, petrophysics and micropaleontology demonstrates how sea-level fluctuations played a major role in the facies distribution and paleogeography of the Interior Seaway.
Paleogeographic maps, depicting seven time slices covering the Late Turonian to Santonian, illustrate general lithologies and their distribution in the north-central part of the Interior Seaway of NorthAmerica. Thesemaps are based on data fromsouthern Alberta and southwestern Saskatchewan integratedwith studies of time-equivalent strata in neighboring regions inwestern Canada and northwestern U.S. The Interior Seaway reached itsmaximum extent during the peak transgression of the Greenhorn Cycle (Early Turonian) and the basinwas gradually infilled starting in the Late Turonian with the Carlile Formation. The boundary between the Carlile and Niobrara formations is an angular unconformitywhere up to 20mof the upper Carlile Formationwas eroded. At this time (late Late Turonian), the Interior Seaway was a narrow strait of a few hundred kilometers with its basin axis in eastern Alberta. Marginalmarine sandstones were deposited inwestern Alberta (CardiumFormation) and central Saskatchewan/north-central Montana (Bowdoin sandstone).
The overlying transgressive part of theNiobrara Cycle showsmultiple dramatic basin changes,with two examples of relative lowstand and complete basin drainage implied by the Verger Member (Coniacian). These rapid lowstand events occurred within periods of marine mudstone deposition, which indicate shelfal to offshore conditions. During deposition of the Medicine HatMember (Early toMiddle Santonian), changes froma shaly to a sandy shelf took place with deposition of thirteen sandstones in the vicinity of the Bow Island Arch of southern Alberta. During lowstand periods with low accommodation, the Bow Island Arch affected sedimentation,whereas during high accommodation, the arch had no influence.A subtle syncline in the northwest part of the study area is the primary reason for deposition of the main gas producing sandstone of the Medicine Hat Member. The maximum extension of the Interior Seaway during the Niobrara Cycle occurred in the late Santonian with the deposition of the First White Specks Member.