1. Acquisition of new data.--Over the last two decades, regional and local geologic mapping, drilling and coring, and seismic reflection profiling have vastly increased our structural and tectonic database. It is now clear that these basins are predominantly half-graben, with generally synthetic intrabasinal faults and fault-perpendicular folds that in many cases are related to fault segmentation.

2. Role of preexisting structures.--The rift system is located within the Appalachian orogen, and thus the border fault systems of the rift basins consist of reactivated structures. The attitude of the reactivated fault with respect to the rift-related extension direction controlled the nature of the reactivation (dip-slip dominated vs. strike-slip dominated), which affected the amount of basin subsidence and types of associated structures. The uniform dip-direction of preexisting faults over large areas accounts for the lack of half-graben polarity reversals within rift zones (e.g., Newark-Gettysburg-Culpeper rift zone).

3. Application of fault-population studies.--In the last 10 years, considerable progress has been made in our understanding of the geometry and scaling relationships of populations of normal fault systems. This information is directly applicable to rift-basin structural geology in that half graben are large normal-fault-bounded basins. The most relevant features of normal fault systems to basin geometry are: (a) Displacement is greatest at or near the center of a normal fault and decreases systematically to the fault tips; displacement also decreases with distance perpendicular to the fault. (b) Normal fault systems are segmented, and many fault segment boundaries are areas of (at least temporary) displacement deficits. (c) As displacement builds up on a normal fault, the fault increases in length. Consequently, rift basins consist of scoop-shaped depressions that grow longer, wider, and deeper through time. In the case of segmented border fault systems, the scoop-shaped depressions are separated by intrabasinal highs.

4. Integrating stratigraphy and structural geology.--The sedimentary deposits of half-graben are, of course, influenced by basin geometry; consequently, we can use stratigraphy to infer aspects of basin evolution and structural geology. On a local scale, thickness variations of fixed-period Milankovitch cycles are particularly useful for assessing variations in basin subsidence and for determining whether of not structures formed syndepositionally. On a regional scale, (a) the lack of Jurassic strata in the southern basins likely indicates that they stopped subsiding before the northern basins did; (b) high accumulation rates in Early Jurassic strata in the northern rift basins indicate accelerated basin subsidence during eastern North American magmatism; and (c) the presence of a tripartite stratigraphy (basal fluvial unit, middle deep-water lacustrine unit, upper shallow-lacustrine and fluvial unit) in most basins indicates that they share a similar evolutionary trend, most likely related to the infilling of basins growing larger through time.

5. Recognition of inversion structures.--Although post-rift contractional structures have long been recognized, recent works shows that the magnitude of post-rift shortening was greater than previously thought and the initiation of shortening and basin inversion was diachronous. In particular, shortening in the southern basins began after synrift deposition and prior to the eastern North America magmatic event (~201 Ma), while rifting and subsidence continued in the northern basins. Inversion in the northern basins occurred between early Middle Jurassic and Early Cretaceous time. Post-rift shortening is attributed to ridge-push forces and continental resistance to plate motion during the initiation of seafloor spreading, which itself was diachronous along the North American margin.

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