Although much is known about the interaction of faulting and sedimentation within the basins of active segmented continental rift systems, little is known about these processes within the interaction zones of varying geometries that separate the young interacting segments. We address this problem by exploring the non-volcanic rift interaction zones (RIZ) along the humid, magma-poor juvenile western branch of EAGE KOLAWOLE Et AL. F I G U R E 1Cartoon illustrating the growth of propagating rift segments along active continental rift systems (updated and modified after Nelson et al., 1992). Note that this cartoon only features collinear and underlapping parallel rift segments. For each zone of rift segment interaction, the cartoon illustrates the pre-and post-linkage geometries of the rift segments. Also, note that cartoon represents rift segmentation and interaction at the early stages (stretching stage) of continental rifting F I G U R E 4 Eastern Africa rift basins and the major rift interaction zones. (a) Map of eastern Africa showing the different segments of the Cenozoic Western Branch (WBEARS) of the East African Rift System (and some of the Eastern branch segments). Also shown are the Mesozoic rift segments that are reactivated (e.g. LR, RR, SRZ) and unreactivated (e.g. LmR, MnR, RuR, ZR) during the current phase of Cenozoic extension.
Although much is known about the interaction of faulting and sedimentation within the basins of active segmented continental rift systems, little is known about these processes within the transfer zones of varying geometries that separate the young interacting segments. We address this problem in the humid, magma-poor juvenile western branch of the East African Rift System (WB-EARS). First, we present a broader classification of rift transfer zone geometries that accommodate both the plan-view geometries and border fault polarity patterns of the interacting rift segments. Within the framework of the transfer zone geometries, we explore the large-scale cross-over relief profiles, and the relationships with the spatiotemporal development of rift-linking faults (breaching faults) and axial stream patterns. Our results show that: 1.) distinct long-wavelength 2-D cross-over topographic relief shapes, directionality of axial stream flow (sediment routing patterns), and breaching fault patterns characterize rift transfer zones at the various stages of the linkage of interacting rift basins, 2.) these stages include unbreached, partially-breached, recentlybreached, and breached transfer zones, 3.) deforming transfer zones exhibit different styles of directionality of breaching, including a unidirectional (distinct propagator and receiver segments) and bi-directional propagation (both segments act as propagators and receivers) which may also modulate the cross-over relief shape, 4.) transfer zone breaching is facilitated by rift-flank deformation, and/or rift tip propagation structures in the form of rift splaying, border fault rotation, and fault cluster networks, 5.) the lateral propagation of breaching faults at the rift tips and flanks may be modulated by the extension direction and inherited basement structures. Our findings offer a broader insight into the geometries and structural evolution of rift transfer zones, and provide first-order predictions of large-scale sedimentation patterns of humid early-stage continental rift environments. Our models provide testable hypotheses for linking rift architecture and patterns of early-stage sedimentation applicable to ancient rift basins.
Patterns of recent seismogenic fault reactivation in the granitic basement of north-central Oklahoma necessitates an understanding of the structural characteristics of the inherited basement-rooted faults. One area is the Nemaha Uplift and Fault Zone (NFZ) in north-central Oklahoma. We have analyzed the top-basement and intrabasement structures in eight poststack time-migrated 3D seismic reflection data sets. Overall, our results reveal 115 fault traces at the top of the Precambrian basement with dominant trends of west-northwest–east-southeast, northeast–southwest, and north–south. We observe that proximal to the NFZ, faults dominantly strike north–south, are fewer (<10), and have the lowest areal density and intensity, while displaying the maximum vertical separation. However, farther away from the NFZ, faults exhibit predominantly northeast–southwest trends, fault areal density and intensity increases, and max. vertical separation decreases steadily. Of the analyzed faults, approximately 49% are limited to the intrabasement, approximately 28% terminate within the Arbuckle Group, and approximately 23% transect units above the formation. These observations suggest that (1) proximal to the NFZ, deformation is dominantly accommodated along a few but longer fault segments, most of the mapped faults cut into the sedimentary rocks, and most of the through-going faults propagate farther up-section above the Arbuckle Group and (2) with distance away from the NFZ, deformation is diffuse and distributed across relatively shorter fault segments and most basement faults do not extend into the sedimentary cover. The existence of through-going faults suggests the potential for spatially pervasive fluid movement along faults. Further, observations reveal pervasive, subhorizontal intrabasement reflectors (igneous sills) that terminate at the basement-sediment interface. Results have direct implications for wastewater injection and seismicity in north-central Oklahoma and southern Kansas. Additionally, they provide insight into the characteristics of basement-rooted structures around the NFZ region and suggest a means by which to characterize basement structures where seismic data are available.
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