Mesa Rica Research Articles

Using delta channel width to estimate paleodischarge in the rock record: geometric scaling and practical sampling criteria

Abstract Quantifying paleodischarge from geological field observations remains a key research challenge. Several scaling relationships between paleodischarge and channel morphology (width, depth) have been developed for rivers and river deltas. Previous paleodischarge scaling relationships were based on discharge–catchment-area scaling and an empirical flow-velocity estimate (e.g., the Chézy equation, the Manning equation) multiplied by channel cross-sectional area to derive discharge. In deltas, where marine (wave, tide) energy causes bidirectional flow in distributary-channels, the available paleodischarge scaling relationships are not applicable due to their unidirectional-flow assumption. Here, the spatial variability of distributary-channel widths from a database of 114 global modern river deltas is assessed to understand the limit of marine influence on distributary-channel widths. Using measured 6,213 distributary-channel widths, the median channel widths of distributary-channels for each delta were correlated with bankfull discharge for river-, tide- and wave-dominated deltas, the latter two including the effect of bidirectional flow. Statistically significant width–discharge scaling relationships are derived for river- and wave-dominated deltas, with no significant relationships identified for tide-dominated deltas. By reverse bootstrapping the channel widths measured from modern deltas, the minimum number of width measurements needed to apply width–discharge scaling relationships to ancient deltaic deposits is estimated as 3 and 4 for the upstream parts of river- and wave-dominated deltas, respectively, increasing to 30 in the downstream parts of river-dominated deltas. These estimates will guide sedimentological studies that often have limited numbers of distributary-channel widths exposed in the rock record. To test the reliability of these alternative width–discharge scaling relationships in the rock record, paleodischarges were estimated for the well-studied Cretaceous lower Mesa Rica Sandstone Formation, USA. Comparison of these results with the more complex Chézy-derived method suggests that these new scaling relationships are accurate. Hence, it is proposed that the scaling relationships obtained from modern deltas can be applied to the rock record, requiring fewer, and easier-to-measure, data inputs than previously published methods.

Low‐accommodation and backwater effects on sequence stratigraphic surfaces and depositional architecture of fluvio‐deltaic settings (Cretaceous Mesa Rica Sandstone, Dakota Group, USA)

AbstractThe adequate documentation and interpretation of regional‐scale stratigraphic surfaces is paramount to establish correlations between continental and shallow marine strata. However, this is often challenged by the amalgamated nature of low‐accommodation settings and control of backwater hydraulics on fluvio‐deltaic stratigraphy. Exhumed examples of full‐transect depositional profiles across river‐to‐delta systems are key to improve our understanding about interacting controlling factors and resultant stratigraphy. This study utilizes the ~400 km transect of the Cenomanian Mesa Rica Sandstone (Dakota Group, USA), which allows mapping of down‐dip changes in facies, thickness distribution, fluvial architecture and spatial extent of stratigraphic surfaces. The two sandstone units of the Mesa Rica Sandstone represent contemporaneous fluvio‐deltaic deposition in the Tucumcari sub‐basin (Western Interior Basin) during two regressive phases. Multivalley deposits pass down‐dip into single‐story channel sandstones and eventually into contemporaneous distributary channels and delta‐front strata. Down‐dip changes reflect accommodation decrease towards the paleoshoreline at the Tucumcari basin rim, and subsequent expansion into the basin. Additionally, multi‐storey channel deposits bound by erosional composite scours incise into underlying deltaic deposits. These represent incised‐valley fill deposits, based on their regional occurrence, estimated channel tops below the surrounding topographic surface and coeval downstepping delta‐front geometries. This opposes criteria offered to differentiate incised valleys from flood‐induced backwater scours. As the incised valleys evidence relative sea‐level fall and flood‐induced backwater scours do not, the interpretation of incised valleys impacts sequence stratigraphic interpretations. The erosional composite surface below fluvial strata in the continental realm represents a sequence boundary/regional composite scour (RCS). The RCS’ diachronous nature demonstrates that its down‐dip equivalent disperses into several surfaces in the marine part of the depositional system, which challenges the idea of a single, correlatable surface. Formation of a regional composite scour in the fluvial realm throughout a relative sea‐level cycle highlights that erosion and deposition occur virtually contemporaneously at any point along the depositional profile. This contradicts stratigraphic models that interpret low‐accommodation settings to dominantly promote bypass, especially during forced regressions. Source‐to‐sink analyses should account for this in order to adequately resolve timing and volume of sediment storage in the system throughout a complete relative sea‐level cycle.

Internal mouth‐bar variability and preservation of subordinate coastal processes in low‐accommodation proximal deltaic settings (Cretaceous Dakota Group, New Mexico, USA)

AbstractMouth bars are the fundamental architectural elements of proximal deltaic successions. Understanding their internal architecture and complex interaction with coastal processes (fluvial, tide and wave‐dominated) is paramount to the interpretation of ancient deltaic successions. This is particularly challenging in low‐accommodation systems, because they are commonly characterized by thin, condensed and top‐truncated sections. This study analyses the exhumed Cenomanian Mesa Rica Sandstone (Dakota Group, Western Interior Seaway, USA), a fluvio‐deltaic system covering a ca 450 km depositional dip‐parallel profile. The study targets the proximal deltaic expression of the system, using 22 sedimentary logs (total of 390 m) spatially correlated within a ca 25 km2 study area at the rim of the Tucumcari Basin. Analysis of facies distributions, depositional architecture and spatial extent of stratigraphic surfaces reveals a 6–10 m thick, sharp‐based and sand‐prone deltaic package, comprising several laterally extensive (>1.4 km width) mouth bars. Composite erosional surfaces infilled with multi‐storey fluvial and marine‐influenced channel deposits (12–20 m thick, 100–250 m wide) scour locally into the deltaic package. Based on differences in sedimentary structures, bed thicknesses, occurrence of interflood beds and bioturbation indexes, four different sub‐environments within single mouth bars were distinguished. These range from mouth‐bar axis, off‐axis, fringe to distal‐fringe deposits, which reflect waning depositional energy with increasing distance from the distributary channel mouth. The interpreted mouth‐bar components also show internal variability in dominant process regime, with overall river dominance but local preservation of tide influence in the fringe and distal fringe components. Mouth‐bar deposits amalgamate to form an extensive sand‐rich sheet body throughout the study area, in which interflood mudstone to very‐fine grained sandstone beds are nearly absent. These features reflect successive coalescence of mouth bars in a low accommodation/supply (A/S) setting. These conditions promoted recurrent channel avulsion/bifurcation and thus the potential reworking of previously deposited mouth‐bar fringe and distal‐fringe sediments, where time and background processes are better recorded. Results of this study evidence internal process‐regime variability within mouth‐bar components. They also caution against the possible loss of preservation of subordinate coastal processes (e.g. tidal indicators), and consequent underestimation of the true mixed influence in low‐accommodation deltaic settings.

Coalesced Delta-front Sheet-like Sandstone Bodies from Highly Avulsive Distributary Channels: The Low-accommodation Mesa Rica Sandstone (Dakota Group, New Mexico, U.S.A.)

AbstractLow-accommodation deltaic systems are often challenging to interpret due to their condensed, low-gradient nature, which often results in extensive, sheet-like sandstone bodies. As a result, detailed studies of such systems are scarce, and their internal depositional architecture is still poorly understood. We analyze one such system, the Cenomanian deltaic Mesa Rica Sandstone (Dakota Group), which was deposited in the Western Interior Seaway, in east-central New Mexico, USA. A > 20-km-long escarpment, subparallel to the main delta progradation direction, allows a detailed analysis of facies distribution, depositional architecture, and the spatial extent of stratigraphic surfaces. Results reveal an arrangement of laterally variable shallowing-upward facies successions with three depositional cycles preserved. The first cycle is characterized by deltaic sheet-like sandstone bodies that are consistently overlain by sand-filled amalgamated distributary-channel deposits. The two successive cycles record a progressive reduction of sediment supply into the basin. Vertical and lateral relationships between facies associations and architectural geometries allow the recognition of regional key stratal surfaces, incised-valley fills, and the presence of lagoonal deposits at a sub-regional scale.The Mesa Rica deltaic system represents a river-dominated delta with multiple distributary channels. The sheet-like delta-front sandstone bodies are interpreted as the result of the combined effect of high sandy-sediment supply and low accommodation. The latter acted as an accelerator for autogenic depositional mechanisms such as mouth-bar deposition and abandonment, and for the highly avulsive character of distributary channels. After deposition, minor wave reworking facilitated lateral sand redistribution and favored bioturbation. This study demonstrates that sheet-like delta-front sandstone geometries from low-accommodation systems can be formed without the dominance of wave redistribution processes. This cautions against interpretations of amalgamated shoreline systems based solely on apparent sandstone geometries, without taking into account the preservation potential and postdepositional modification of primary deltaic characteristics.

Complex Fluvial Response to Low Gradients at Maximum Regression: A Genetic Link Between Smooth Sequence-Boundary Morphology and Architecture of Overlying Sheet Sandstone

ABSTRACT The Mesa Rica Sandstone is an extensive fluvial sandstone sheet that is separated from underlying marine strata throughout northeastern New Mexico by a regionally smooth and laterally continuous sequence-bounding unconformity. The Mesa Rica Sandstone consists mostly of channel-fill elements, with lesser proportions of lateral-accretion elements, and almost everywhere is of the same thickness as the largest channel fills. This broad sandstone sheet reflects deposition on a coastal plain by frequent avulsion and minor lateral migration of straight and low-sinuosity streams under nearly stable base-level conditions, which are here attributed to rapid progradation of the adjacent Mesa Rica deltaic shoreline relative to change in relative sea level during maximum Kiowa-Skull Creek regressi n. Rapid deltaic shoreline progradation under such conditions caused seaward extension and gradient reduction in the adjacent Mesa Rica coastal plain. Overextension and resultant loss of power in Mesa Rica rivers crossing this coastal plain forced both stream straightening and storage of nontransportable coarser sediment in coastal-plain channels. Because base level was stable, Mesa Rica channels could aggrade only minimally, and were forced to spread excess sediments mostly laterally by avulsion. Frequent avulsion and minor lateral migration of Mesa Rica channels under these conditions caused both regional scouring of a smooth sequence-bounding unconformity and deposition of a sheet sandstone with minimal channel stacking. The Mesa Rica Sandstone and the sequence boundary that underlies it represent a distinctive genetic association of single-story fluvial sheet sandstone and smooth sequence-boundary morphology that is probably not unique to the Lower Cretaceous of northeastern New Mexico. Such unincised sequence boundaries are also implied in conceptual models and flume experiments of previous authors.

Cretaceous Stratigraphy and Biostratigraphy, Sierra Blanca Basin, Southeastern New Mexico: ABSTRACT

The Sierra Blanca basin of Otero and Lincoln counties, New Mexico contains a Lower (upper Albian)-Upper (Santonian) Cretaceous section of marine and nonmarine strata as much as 700 m thick which represent the upper part of a regressive cycle followed by two transgressive-regressive deposition cycles. The lower 55 m of the Cretaceous section are the same tripartite Dakota Group units recognized in Guadalupe and San Miguel counties: basal Mesa Rica Sandstone (late Albian), medial Pajarito formation (late Albian) and upper Romeroville sandstone (earliest Cenomanian). The Mesa Rica and Pajarito represent a regression and are overlain disconformably by the transgressive Romeroville sandstone. Overlying transgressive marine clastics and minor carbonates of the Mancos Shale are as much as 73 m thick and include the early Turonian Greenhorn Limestone. The overlying Tres Hermanos formation (up to 91 m thick) consists of the (ascending order) Atarque sandstone and the Carthage and Fite Ranch sandstone members. These strata represent a mid-Turonian regression in response to regional tectonism (Atarque and Carthage), followed by a transgression (Fite Ranch sandstone) that ended in the deposition of the D-Cross Tongue of the Mancos Shale and Fort Hays Member of the Niobrara Formation during the late Turonian. The subsequent regressionmore » began with the Coniacian Gallup Sandstone (55 m) followed by coal-bearing Crevasse Canyon Formation (up to 244 m thick). The Coniacian-Santonian Crevasse Canyon Formation, the youngest Cretaceous unit in the basin, is disconformably overlain by middle Eocene conglomerates and red-bed siliciclastics of the Cub Mountain formation. Dakota Group age determinations in the Sierra Blanca basin are those of well-dated sections to the north, but ammonites and inoceramid bivalves from the Sierra Blanca basin provide precise age control for Cenomanian-Santonian marine and marginal marine strata and palynology and megafossil plants for nonmarine strata.« less

Depositional history of Lower Cretaceous strata in northeastern New Mexico: Implications for regional tectonics and depositional sequences

Lower Cretaceous strata in northeastern New Mexico reflect deposition during marine transgression and regression associated with the Kiowa-Skull Creek cycle. Development of regionally significant unconformities can be directly related to shoreline shifts during this cycle. Topography related to Early Cretaceous tectonic activity on crystalline basement structures, including the Dalhart Basin, Tucumcari Basin, and the intervening Bravo Dome, also had a direct effect on Early Cretaceous deposition and is reflected by thickness trends in marine strata. The Kiowa-Skull Creek transgression was preceded by infilling of paleovalleys represented by the Long Canyon and Campana sandstone beds of the Glencairn Formation and Tucumcari Shale, respectively. The Long Canyon and Campana sandstone beds are equivalent to the Plainview Formation of central Colorado, and together they represent an extensive drainage network, developed over a correlative unconformity, that is preserved throughout most of the southern Western Interior. Glencairn and Tucumcari marine shales represent clastic deposition during Kiowa-Skull Creek transgression and early regression. Base-level drop associated with Kiowa-Skull Creek regression resulted in dramatic shoreline regression and deposition of fluvial channel sandstone in the Dalhart Basin, which maintained a low offshore gradient. This produced an erosional unconformity at the base of Mesa Rica channel sandstone that correlates with the well-documented erosional surface at the base of the Muddy Sandstone in central Colorado. The Tucumcari Basin, which maintained a steeper offshore gradient, accumulated marine-deltaic Mesa Rica Sandstone at this time. Marine strata in both the Tucumcari and Dalhart Basins thin toward the Bravo Dome. Mesa Rica and upper Tucumcari strata represent the only extensive marginal-marine lowstand deposits found on the High Plains to date, associated with the southern arm of the Kiowa-Skull Creek sea. Major Mesa Rica deposition was followed by transgression that infilled only those Mesa Rica fluvial channels that were active at that time and, also, that deposited marine-influenced strata of the basal Pajarito Formation. This event most likely represents onset of the Greenhorn cycle in northeastern New Mexico. Other crystalline basement structures in the northern part of the United States Western Interior Basin were active during Early Cretaceous time. Tectonism in these areas may be related to structures in northeastern New Mexico and thus may be expressions of broad-scale crustal strain in the Early Cretaceous Western Interior that is undocumented by present tectonic models.

Sequence Stratigraphic Interrelationship of Lower Cretaceous Dakota and Purgatoire Formations in Northeast New Mexico/Southeast Colorado and Correlative Strata (Muddy, Skull Creek, Plainview) of the Denver Basin

The Albian Glencairn Member (Purgatoire Formation) and underlying Dakota Sandstone of southeastern Colorado and northeastern New Mexico are related depositionally to the Tucumacari, Mesa Rica, and Pajarito formations of east-central New Mexico and to the Plainview, Skull Creek, and Muddy formations of central Colorado. Depositional interrelationships of these strata are best understood when placed in a sequence-stratigraphic framework. The Plainview Formation, Long Canyon sandstone bed (basal Glencairn) and Campana sandstone bed (basal Tucumcari) overlie a correlative lowstand surface of erosion (LSE) and represent backfilling of valleys during Kiowa-Skull Creek transgression. These strata are separated from overlying marine transgressive shale deposits of the lower Skull Creek, Glencairn, or Tucumcari, respectively, by a correlative transgressive surface of erosion. Fluvial incision during maximum Kiowa-Skull Creek regression is manifest as an LSE atop Skull Creek and Glencairn marine deposits. Southward-flowing streams debouched into the maximum regressive sea forming a lowstand wedge, the remnants of which are represented by the Mesa Rica, Pajarito, and uppermost Tucumcari formations. Stable base level conditions developed near the maximum regressive shoreline resulting in widening of paleovalleys and deposition of a fluvial lowstand sheet sandstone in southeastern Colorado and northeastern New Mexico. Transgression followed lowstand deposition and resulted in backfillingmore » of paleovalleys represented by portions of the Muddy and Dakota sandstones.« less

Type and reference sections of the Tucumcari, Mesa Rica and Pajarito Formations, Cretaceous of east-central New Mexico

Type and reference sections of the Tucumcari, Mesa Rica and Pajarito Formations, Cretaceous of east-central New Mexico

Facies Relationships in Mesa Rica Sandstone (Lower Cretaceous), Tucumcari Basin, East-Central New Mexico: ABSTRACT

The Mesa Rica Sandstone, a Lower Cretaceous (Albian) cliff-forming unit in east-central New Mexico, represents a progradational fluvial-dominant deltaic system. On Mesa Rica, south of Conchas Lake, the formation is underlain by the marine (prodelta.) Tucumcari Shale, and is overlain by upper and lower delta-plain deposits of the Pajarito Shale. Clear facies interfingering between the Mesa Rica and Pajarito formations documents a direct genetic link between the two. Whether the Mesa Rica Sandstone lies unconformably on the Tucumcari Shale or is transitional to it is as yet unresolved. Three major sandstone bodies exist within the Mesa Rica formation, each capped by a thin (less than 2-m) mudstone interval. The two basal sandstone bodies record deposition of separate delta lobes; the bottom unit represents progradation toward the south-southeast (215/sup 0/), whereas the upper sandstone exhibits progradation toward the east-southeast (106/sup 0/). For each unit, lobe development was followed by abandonment, often marked by wave reworking. The third major sand body in the Mesa Rica overlies the lower units and records interdistributary deposition. Subenvironments recognized within the marine part of the delta include distal bar, bar front, bar crest, bar back, distributary channel, and beach. Intervening mudstones are similar in lithology tomore » the overlying Pajarito Shale. These units grade southward from nonmarine upper delta plain, containing overbank and levee deposits, to marine-influenced lower delta plain.« less

Paleogeographic and Stratigraphic Constraints on Lower Cretaceous Mesa Rica Delta System, East-Central New Mexico: ABSTRACT

The Mesa Rica Sandstone of east-central New Mexico undergoes facies transition from nonmarine fluvial distributary channels to fluvial-dominated deltaic strata over an outcrop distance of approximately 40 km. The underlying Tucumcari Shale contains equivalent prodelta deposits, and the overlying Pajarito Shale represents the delta-plain environment. The delta contains two major progradational lobes, each directly traceable into its correlative distributary channel system. Paleoflow within the older distributary system is toward the south-southwest (206/sup 0/), and progradation of its corresponding delta lobe is also in that direction (215/sup 0/). Eastward shift in fluvial transport (to 107/sup 0/) resulted in delta-lobe abandonment and established a younger lobe that prograded toward the east-southeast (106/sup 0/). Mesa Rica distributary sandstones correlate westward with alluvial strata of unknown age that have been assigned to the lower braided interval of the Dakota Formation or to the Mesa Rica Sandstone. Results of their study clearly link these fluvial deposits to the Mesa Rica delta front, which is of Albian age based on the presence of the index ammonoid Mortoniceras equidistans. They support assignment of these fluvial strata to the Mesa Rica Sandstone and reserve use of the name Dakota Formation for the overlying Cenomanian marine transgressive sandstone.

Sedimentology of Cretaceous Mesa Rica Sandstone, Tucumcari Basin, New Mexico: ABSTRACT

Sedimentology of Cretaceous Mesa Rica Sandstone, Tucumcari Basin, New Mexico: ABSTRACT

Revisions in Stratigraphic Nomenclature in Tucumcari-Sabinoso Area, Northeastern New Mexico: GEOLOGICAL NOTES

It is proposed to revise the stratigraphic nomenclature of rocks in the Tucumcari-Sabinoso area in Guadelupe, Harding, San Miguel, and Quay counties in northeastern New Mexico. The following terminology for the Triassic, Jurassic, and Cretaceous units are proposed: Cretaceous (3 formations) -- Pajarita shale, Mesa Rica sandstone, Tucumcari shale; Jurassic (3 formations) -- Morrison formation, Bell Ranch formation, Entrada sandstone (latter two are part of the San Rafael group); Triassic (3 formations) -- Redonda formation, Chinle formation, Santa Rosa sandstone (latter two are part of the Dockum group).