Mass-Balance Constraints On Stratigraphic Interpretation of Linked Alluvial-Coastal-Shelfal Deposits From Source To Sink: Example From Cretaceous Western Interior Basin, Utah and Colorado, U.S.A

Abstract

Experimental work suggests that the rate of upstream-to-downstream loss of sediment from an active depositional system to permanent storage exerts a fundamental control on stratigraphic architecture. This rate of sediment (mass) loss is determined by the spatial distribution of tectonic subsidence and rate of sediment supply. The character of input sediment (grain-size distribution and composition) is the third parameter that affects stratigraphic architecture. We apply this concept in a mass-balance framework to linked alluvial-coastal-shelfal deposits of the Upper Cretaceous Castlegate Sandstone, Blackhawk Formation, Star Point Sandstone, and Mancos Shale (Western Interior Basin, Utah and Colorado, USA). Facies partitioning and sediment budgets are estimated for eight stratigraphic intervals, in order to compare temporal dynamics of the sediment routing system from erosional source to depositional sink. Mapping of each stratigraphic interval and its constituent segments, from upsystem to downsystem, was achieved along a representative, dip-oriented 2D cross section over a distance of c. 350 km using extensive outcrop exposure and densely spaced subsurface wells. The cross section provides time-averaged estimates of the spatial distribution of deposition. Grain-size data show that there is limited downsystem fining of any particular facies within the Castlegate Sandstone, but that the proportion of facies changes systematically downsystem to accommodate an overall fining trend. Therefore, it is reasonable as a first approximation to use facies proportions as a ''textural replacement'' for grain size. Sediment supply characteristics for each of the eight stratigraphic intervals are constrained by total facies proportions in each interval. For each stratigraphic interval, we assess the level of interaction between alluvial and coastal-to-shelfal segments of the routing system.Comparison of the downsystem mass-balance characteristics of the eight stratigraphic intervals suggests that there were depositional gains and losses of shallow-marine shale in the five youngest intervals, which can be attributed to along-strike sediment transport. This result is consistent with increased interaction through time with vigorous wave-and tide-driven circulation in the seaway, as the sediment-routing system advanced out of a sheltered embayment in response to decreasing tectonic subsidence. In the youngest stratigraphic interval, the upstream-unconformable base of the Castlegate Sandstone is marked by a pronounced increase in the sand-to gravel-grade mass fraction of the fluvially supplied depositional volume. This marked increase can be attributed to hinterland unroofing and/or cannibalization of wedge-top basins, leading to import of coarse-grained sediment into the Castlegate fluvial system. Our results demonstrate the value of analyzing downsystem sediment loss (i.e., downsystem mass extraction) within a mass-balance framework as a simple and practical tool to quantify the relationship between accommodation and sediment supp...

Towards a sequence stratigraphic solution set for autogenic processes and allogenic controls: Upper Cretaceous strata, Book Cliffs, Utah, USA

“…4a), but additional southward-directed, longshore sediment transport occurred in shallow-marine sandstone tongues (e.g. Hampson 2010;Hampson et al 2014). This latter, southward-directed component of sediment transport is more pronounced in the upper part of the Star Point-Blackhawk-lower Castlegate wedge (e.g.…”

“…1. Schematic illustration of the Star Point-Blackhawk-Castlegate sediment routing system and its deposits as preserved in a typical stratigraphic interval (after Hampson et al 2014), with principal controls on stratal architecture of the deposits of the routing system and its segments listed underneath. The delta comprising the distal segments of the sediment routing system had a 'compound clinoform' geomorphology, in which an inner, sand-rich, wave-dominated clinofom was separated by a subaqueous topset from an outer clinofom containing sand-poor, 'shelf' or 'ramp' turbidites (Hampson 2010).…”

“…3. Correlation panels illustrating stratal architecture through (a) the Book Cliffs outcrop belt and adjacent areas, and (b) the Wasatch Plateau outcrop belt (after Horton et al 2004;Hampson 2010;Hampson et al 2011Hampson et al , 2012Hampson et al , 2014, and references therein). Interpreted major flooding surfaces and sequence boundaries (e.g.…”

“…In this paper, we follow the nomenclature of Hampson (2010) and Hampson et al (2014), who subdivided the Star Point-Blackhawk-lower Castlegate wedge into eight parasequence sets or genetic sequences (sensu Galloway 1989) bounded by major flooding surfaces (Fig. 3).…”

“…3): (a) Kenilworth Member, Blackhawk Formation, and middle part of the Prairie Canyon Member, Mancos Shale (between major flooding surfaces FS200 and FS100); (b) lower Castlegate Sandstone and upper part of Desert Member, Blackhawk Formation (between base-Castlegate unconformity and top-lower Castlegate surface, and between major flooding surfaces FS600 and FS500) (after Hampson et al 2014, and references therein). The palaeoshoreline in each map is positioned at the boundary between coastal plain (green) or fluvial (orange) and shoreline-shelf (yellow) facies belts.…”