Linking Stratigraphic Architecture and
Petroleum
System
Elements of the Niobrara Formation to Oceanographic and Far-Field Tectonic Events
Abstract
The Niobrara Formation was deposited in the Western Interior Seaway
(WIS), which filled an active foreland basin during the Upper Cretaceous. The
WIS experienced important oceanographic variations and tectonic events
during Niobrara time, and resolving their influence is critical to mapping
petroleum
system
elements of the greater Denver-Julesburg (D-J) Basin area.
To unravel stratigraphic complexity through time, sequence stratigraphic
surfaces suited to the distal carbonate ramp, and in the context of biozone and
isotope geochronology data, were correlated through basin-scale well control
to create a series of age-constrained isochore maps. At a WIS scale, thickness
patterns suggest that the basin’s flexural forebulge had migrated eastward to a
position along trend with the future Rocky Mountains where it defined the
western edge of the distal carbonate ramp that developed in the backbulge of
the basin. At the D-J Basin scale, early Niobrara deposition (Upper Turonian -
Lower Santonian) was dominated by patterns of differential sediment
accumulation with compensational infilling in the form of systematic reversals
of stratigraphic thicks and thins through time. This pattern was interrupted in
the Lower Santonian by the development of sublinear basement uplifts along
the trend of the emergent Transcontinental Arch. As a result, sediment
accumulation became dominated by patterns of draping over the long-lived
seafloor paleohighs. Absolute timing of architectural changes in the Niobrara
suggests a link between Sevier thrusting episodes, a migrating flexural
forebulge, and uplifts along reactivated basement shear zones in the distal
foreland. The well-known transgressive-regressive cycles of the Niobrara in
the D-J Basin appear to be broadly overprinted by two distinct influences:
circulation-related bottom currents and deposits and the later interference of
tectonic uplifts. This dynamic paleoseafloor morphology was a first-order
control that shaped the depositional patterns of Niobrara source rock and
reservoir rock intervals.
AAPG Datapages/Search and Discovery Article #90357 ©2019 AAPG Rocky Mountain Section Meeting, Cheyenne, Wyoming, September 15-18, 2019