Integration of the geological and archaeological perspectives into a unified geoarchaeological approach has been impeded by differences in the temporal scales of analysis used by the two disciplines. These disparities reflect (1) the chronological scope of the events or processes to be explained and (2) the sensitivity with which variation on this dimension is measured. Because geologic processes and human behavioral processes commonly operate at different rates, the chronological information inherent in these processes is incapable of resolving the different scales. Therefore, reconciliation of these temporal perspectives depends primarily on the application of independent dating techniques to both geologic and archaeological phenomena. Recent research in northeastern Arizona integrates geological and archaeological scales of time measurement in a unified attack on problems of human behavioral adaptation to environmental variability. Correlation of the various time scales employed (1) independent chronometry (radiocarbon and tree-ring dating), (2) intrinsic dating (stratigraphic relationships and ceramic placement), and (3) direct association between geological, archaeological, and chronometric samples. This degree of chronological integration delineated differential behavioral responses to low- and high-frequency environmental fluctuations.

Detailed analysis of three sections of the Late Cretaceous Mancos Shale at Black Mesa in northeastern Arizona demonstrates that sufficient data are preserved within the thick, seemingly monotonous, fine-grained clastic sequences of the western foreland basin to develop a conceptual framework comparable to that developed for the carbonate-dominated central Western Interior Seaway. The Mancos Shale ranges from 146 m in southwestern Black Mesa to form 200 to 210 m in northern and eastern Black Mesa and is herein divided into four members in ascending order: lower shale member, middle shale member, Hopi Sandy Member, and upper shale member, of which only the Hopi Sandy Member is formally described. In addition, a prominent sandstone tongue of the overlying Toreva Formation at Blue Point in southwestern Black Mesa is herein designated the Blue Point Tongue of the Toreva Formation. Based on recovered fauna, a total of 13 biostratigraphic subdivisions are recognized, in ascending order: the upper Cenomanian Metoicoceras mosbyense Zone, Sciponoceras gracile Zone divided into the Vascoceras diartianum and Euomphaloceras septemseriatum subzones, and Neocardioceras juddii Zone divided into the Euomphaloceras irregulare, Neocardioceras juddii, and Nigericeras scotti subzones; the early Turonian Watinoceras coloradoense Zone divided into the Pseudaspidoceras flexuosum and Vascoceras birchbyi subzones and the Mammites nodosoides Zone; the Middle Turonian Collignoniceras woollgari Zone divided into the Collignoniceras woollgari woollgari/Mytiloides hercynicus, Collignoniceras woollgari woollgari, and Collignoniceras woollgari regulare subzones and the Prionocyclus hyatti Zone. Within this lithostratigraphic and biostratigraphic framework, 77 chronostratigraphic marker beds (BMI, BM2, . . . BM77) have been recognized, consisting mainly of bentonites along with laterally continuous concretion horizons, bioturbated marlstones, and sediment bypass intervals (calcisilts). The Mancos Shale disconformably overlies the Dakota Formation, recording the partial to complete destruction of a series of northwest- to southeast-trending barrier coastlines. The development and preservation of these barrier systems were tectonically controlled by subtle movements of northwest- to southeast-trending folds developed over deep-seated basement structures. The seaway transgressed across Black Mesa from the northeast to the southwest during the Metoicoceras mosbyense Zone through the Sciponoceras gracile Zone. Water depth increased rapidly through the early Turonian, with the lower shale member recording the greatest influence of pelagic sedimentation at Black Mesa. The lower shale member ranges from 54 to 67 m thick, being thickest in the northwest toward the area of maximum development of the western foreland basin proximal to the Sevier Orogenic Belt. The middle shale member thins from 55 m in the southwest to 42.5 m in the northeast and records the first demonstrable effects of regression at Black Mesa, marked by a decrease in carbonate content and an increase in silt and fine sand content representing distal storm deposits. Significant quantities of sand were first transported across the shelf during deposition of the Hopi Sandy Member (uppermost Collignoniceras woollgari woollgari subzone) by a combination of delta progradation from the southwest and storm-induced reworking. The Hopi Sandy Member ranges from 12 to 22 m in thickness, being thickest to the north and northeast. Sandstone abundance and thickness increase in the southwestern shoreward direction, indicating winnowing and offshore reworking of much of the clay. Renewed subsidence is indicated by a rapid decrease in silt and sand content in the lower part of the upper shale member. The upper shale member measures 34 m in the southwest (including the interval of the Blue Point Tongue) and thickens rapidly to the northeast, where it is 85 m thick. Regression of a wave-dominated shoreline complex across the area of southwestern Black Mesa during the Collignoniceras woollgari regulare subzone led to the development of the shallow coastal shoals of the Blue Point Tongue and beach sequences of the lower sandstone member of the Toreva Formation. Continued fine clastic sedimentation offshore reflects dominantly longshore sediment transport. Regression of the sea continued with the final progradation of wave-dominated delta systems across northern and eastern Black Mesa during the Prionocyclus hyatti Zone.

The study area at Blue Point is the southwesternmost exposure of upper Cretaceous strata in Black Mesa, Arizona. The Mancos Shale at Blue Point was deposited in an embayment along the western margin of the Greenhorn Seaway during late Cenomanian-early Turonian time. Foraminifera from the Mancos Shale were investigated to interpret their biostratigraphic and paleoecological significance. Most species of foraminifera identified are long-ranging taxa of limited biostratigraphic value. Nevertheless, foraminiferal assemblages reflect the interaction between oceanic circulation in the Greenhorn Seaway and local paleoenvironmental controls. Foraminifera indicate the existence of a shallow marine environment in the study area during the late Cenomanian and the influence of warm Tethyan waters. Depths were above wave base, substrates were oxygenated, and the water column was periodically hyposaline due to freshwater influx. During the Turonian, the study area became a deeper, more normal marine, offshore environment. This increase in depth continued into the basal 14 m of the middle Turonian Collignoniceras woollgari ammonite zone, although waters were probably less than 100 m deep during peak transgression. Peak transgression at Blue Point postdates the onset of regression at the axis of the seaway near Pueblo, Colorado. The anomalous depth increase may indicate a period of basin subsidence at Black Mesa or may suggest that eustatic highstand in the Greenhorn Seaway occurred during C. woollgari time. After peak transgression, the water column was periodically hyposaline, and salinity and depth at Blue Point decreased with regression of the Greenhorn Seaway. Increasing hyposalinity may have been caused by the retreat of Tethyan waters, an increase in freshwater influx associated with strandline progradation, the influence of boreal waters, or some combination of these factors. Before disappearing in upper strata of the Mancos Shale, foraminiferal assemblages indicate a hyposaline, marginal marine environment.

The coal-bearing upper carbonaceous member of the Wepo Formation (Upper Cretaceous) at Black Mesa in northeastern Arizona represents the landward segment of a regressive-transgressive sequence deposited along the southwestern margin of the Western Interior foreland basin. A detailed field investigation of the unit near the northeastern escarpment of Black Mesa resulted in the recognition of six lithofacies (Facies A through F). Facies A includes scour-based, predominantly trough-crossbedded sandstones that are interpreted as distributary, fluvial, and crevasse channel deposits. Facies B consists of rooted, heterolithic sandstone, siltstone, and mudstone sequences that are interpreted as levee deposits. Facies C includes sharp-based, predominantly ripple-laminated sandstones and siltstones that are interpreted as crevasse splay deposits. Facies D consists of rooted mudrocks that are interpreted as well-drained marsh or backswamp deposits. Facies E includes coals, carbonaceous shales, and organic mudrocks that are interpreted as poorly drained marsh or backswamp deposits. Facies F consists of burrowed sandstones and mudrocks that are interpreted as fluvial or interfluvial pond, interfluvial lake, or interdistributary bay deposits. Vertical trends in the distributions and spatial relations of depositional subenvironments suggest that the upper carbonaceous member can be vertically subdivided into lower, middle, and upper stratigraphic intervals, representing deposition on a deltaic plain, backswamp-dominated alluvial plain, and lake-dominated alluvial plain to marginal marine coastal plain, respectively. The vertical succession of depositional environments records a deltaic to fluvial sequence produced by regression of the shoreline followed by a fluvial to marginal marine sequence produced by a rising base level associated with transgression. The depositional model developed from the vertical succession assists in defining depositional controls on both coal occurrence and geometry and suggests that the thickest and most laterally extensive coal deposits formed on a backswamp-dominated alluvial plain during regression and early transgression and possibly during a stillstand of the shoreline, with the proliferation of vegetation in protected, poorly drained interfluvial backswamps.