Abstract The Sivas Basin in central-eastern Anatolia is a north-verging salt-bearing fold-and-thrust belt including synorogenic salt tectonics. It formed between the northern leading edge of the Taurides platform and the Kırşehir block since Late Cretaceous time. We have constructed five regional cross-sections supported by field data and 2D seismic to constrain the structure of the basin and its evolution. The area is divided into three tectonic domains from south to north: (1) a Maastrichtian to Eocene north-verging fold-and-thrust belt, which terminates by a regional Eocene evaporitic level; (2) an Oligo-Miocene salt domain which contains two generations of minibasins separated by a salt canopy, forming a salt-and-thrust belt; and (3) a late Miocene to present day foreland basin. The cross-sections show the along-strike variations and the increasing shortening in the fold-and-thrust belt from west ( c. 15 km) to east ( c. 25 km). The thick salt allows for the intracutaneous propagation of the fold-and-thrust belt below a domain of salt withdrawal minibasins, decoupled as the initial salt thickness increases. In that case, the salt domain is thrusted both frontward and backward. Efficient exhumation followed by erosion of the fold-and-thrust resulted in synorogenic salt tectonics in the foreland and thus increased the mechanical resistance between them.

Abstract Cripple Creek is among the largest epithermal districts in the world, with more than 800 metric tons (t) Au (>26.4 Moz). The ores are associated spatially, temporally, and genetically with ~34 to 28 Ma alkaline igneous rocks that were emplaced into an 18-km 2 diatreme complex and surrounding Proterozoic rocks. Gold occurs in high-grade veins, as bulk tonnage relatively low-grade ores, and in hydrothermal breccias. Pervasive alteration in the form of potassic metasomatism is extensive and is intimately associated with gold mineralization. Based on dating of intrusions and molybdenite and gangue minerals (primarily using 40 Ar/ 39 Ar and Re-Os techniques), the region experienced a protracted but intermittent history of magmatism (over a period of at least 5 m.y.) and hydrothermal activity (intermittent over the final ~3 m.y. of magmatic activity). Key factors that likely played a role in the size and grade of the deposit were (1) the generation of alkaline magmas during a transition between subduction and extension that tapped a chemically enriched mantle source; (2) a long history of structural preparation, beginning in the Proterozoic, which created deep-seated structures to allow the magmas and ore fluids to reach shallow levels in the crust, and which produced a fracture network that increased permeability; and (3) an efficient hydrothermal system, including effective gold transport mechanisms, and multiple over-printed hydrothermal events.

The Eocene-Oligocene transition in the eastern Gulf Coastal Plain of Alabama and Mississippi occurs within a sequence of marine clastic rocks making up the Jackson Group and the lower Vicksburg Group. The placement and the nature of the Eocene-Oligocene boundary remain controversial after more than 20 yr of detailed study. In Alabama, the Eocene-Oligocene boundary is placed within a condensed section at the contact between the Shubuta Member of the Yazoo Clay and the Red Bluff Clay. In eastern Mississippi, the Eocene-Oligocene boundary is recognized through the use of planktonic foraminifera and calcareous nannofossils as also occurring at the Yazoo–Red Bluff contact, but this surface is considered an unconformity representing a sequence boundary. In the Mossy Grove core of western Mississippi, planktonic foraminifera, in conjunction with radiometrically dated bentonites, place the Eocene-Oligocene boundary within the upper Yazoo Clay. There is a pronounced turnover in benthic foraminiferal species between the Yazoo Clay of the Jackson Group and the Red Bluff Clay of the Vicksburg Group. This turnover does not occur at the biostratigraphic Eocene-Oligocene boundary within the Yazoo Clay in western Mississippi. Rather, it occurs above the unconformity associated with the base of the Vicksburg Group throughout the Gulf Coastal Plain. This unconformity was produced by a fall in relative sea level, possibly associated with the oxygen isotope event Oi-1. In some sections in the eastern Gulf Coastal Plain (Little Stave Creek, Saint Stephens Quarry, and the Mossy Grove core), the Eocene-Oligocene boundary as defined at the Massignano global stratotype section and point can be recognized. In most sections in the region, however, such as those in the Chickasawhay River valley of Mississippi, subaerial erosion associated with the basal Vicksburg unconformity has removed the latest Eocene and earliest Oligocene (pre–Oi-1) rocks. This means that in most cases in the eastern Gulf Coastal Plain, the Eocene-Oligocene boundary is coincident with a lithostratigraphic and allostratigraphic surface associated with the Oi-1 event rather than the highest occurrence of Hantkenina. The Jackson Group—Vicksburg Group contact, with its associated turnovers in benthic foraminifera, is important in identifying the Eocene-Oligocene boundary in the eastern Gulf Coastal Plain. Work currently under way by Charles Betz at Ball State University on stable isotopes in both the Yazoo Clay and Red Bluff Clay will help to further characterize this boundary in the Gulf Coastal Plain and enhance understanding of this important transition.