Detrital modes of sandstone suites primarily reflect the different tectonic settings of provenance terranes, although various other sedimentological factors also influence sandstone compositions. Comparisons of sandstone compositions are aided by grouping diverse grain types into a few operational categories having broad genetic significance. Compositional fields associated with different provenances can then be displayed on standard triangular diagrams.

Interpreting Provenance Relations from Detrital Modes of Sandstones

Several previous studies have shown that sandstones from different tectonic settings possess characteristic chemistry, particularly $$SiO_{2}$$ content and $$K_{2}O/Na_{2}O$$ ratio. Systematic vari...

Determination of Tectonic Setting of Sandstone-Mudstone Suites Using $SiO_{2}$ Content and $K_{2}O/Na_{2}O$ Ratio

Provenance signatures of sandstone-mudstone suites determined using discriminant function analysis of major-element data

Geochemical and NdSr isotopic composition of deep-sea turbidites: Crustal evolution and plate tectonic associations

Relationships between Lu–Hf and Sm–Nd isotopic systems in the global sedimentary system

Framework modes of terrigenous sandstones reflect derivation from various types of provenance terranes that depend upon plate-tectonic setting. Triangular QFL and QmFLt compositional diagrams for plotting point counts of sandstones can be subdivided into fields that are characteristic of sandstone suites derived from the different kinds of provenance terranes controlled by plate tectonics. Three main classes of provenance are termed “continental blocks,” “magmatic arcs,” and “recycled orogens.” Sandstone suites from each include three variants, of which the subfields lie within the larger subdivisions. Average modes for sandstone suites can be classified provisionally according to tectonic setting using the subdivided QFL and QmFLt plots. To test the validity of the classification, average modes for 233 Phanerozoic sandstone suites from North America were plotted on the triangular compositional diagrams and accompanying paleotectonic maps. Paired maps and ternary diagrams were prepared for eight different time slices, for each of which the tectonic setting of each major region within the continent remained relatively unchanged. Time slices are unequal in length but are controlled by the timing of major orogenic and rifting events that affected North America during the Phanerozoic. Comparison of the sandstone compositions with inferred tectonic setting through the Phanerozoic indicates that the proposed classification scheme is generally valid and yields satisfactory results when applied on a broad scale. Its application, together with other approaches, in regions of the world where over-all trends of geologic history are less well known could lead to important conclusions about the timing and nature of major tectonic events.

Provenance of North American Phanerozoic sandstones in relation to tectonic setting

The real eastern california shear zone

Basin and Range extension in the Lake Mead region, Nevada, is unique in that strike-slip faulting exerts major control on extensional processes. The south Virgin Mountains (SVM) in eastern Lake Mead are cut by multiple NE-striking faults that form the Lake Mead left-lateral fault system (LMFS). Here, details of early basin formation and the onset of left-normal oblique faulting of the LMFS are well preserved because they are not overprinted by younger deformation as is the case to the west. In the 1980s, Bob Bohannon defined the Oligo-Miocene Horse Spring Formation for the Lake Mead region, and in the 1990s Beard focused within the SVM on the interaction between lower basin strata and onset of faulting. Starting in the 2000s, an NSF-funded university research group, led by the highly enthusiastic team of Paul Umhoefer, Lisa Lamb, Tom Hickson, Bill McIntosh, Nelia Dunbar, along with Sue Beard (USGS), began a new effort in the Lake Mead area. Within the SVM, Lamb et al. (2018) elevated the Rainbow Gardens Member to formation status, and MS students of Umhoefer’s (Matt Schmidt, 2014; Lane Tucker, 2017; Daniel Conrad, 2018) as well as undergraduate students led by Lamb and Hickson, focused on detailed stratigraphic and structural studies of Oligo-Miocene geology. These NSF-funded studies are being used to update USGS 100k and 24k geologic maps from the 1980s to the 2000s. In particular, the eastern termination and stepover structures of the individual LMFS strands are key structural features of the SVM. The interaction of sedimentation and faulting at the NE end of the Lime Ridge fault (LRF) strand was mapped originally by Beard and improved upon by Schmidt, using higher precision Ar-dating and detailed facies mapping. Schmidt determined that extension initiated ~17–16.3 Ma along east-side down normal faults within a stepover zone between the LRF and the Piedmont fault, a LMFS strand to the NNE. As displacement progressed, deformation shifted to left normal oblique faulting along the LRF ~15.4 Ma. By ~14 Ma, most deformation had shifted westward and the SVM were uplifted, such that basins were inverted and cannibalized into younger basins to both the east and west (Beard, 1996). In honor of Paul Umhoefer, who encouraged us for years to do this, we present the melding of mapping and ideas along the eastern LMFS as they evolved through the decades. 

The lake mead fault system and oligo-miocene basins in the virgin mountains: collaboration between dr. paul umhoefer, his students, and colleagues

Recognition of large-scale Tertiary extensional tectonics of the Basin and Range can be credited to Ernie Anderson, iconoclastic and legendary geologist. This session is dedicated to his science and influence on generations of geologists. Ernie had a distinguished career with the USGS beginning with mapping at the Nevada Test Site and Lake Mead areas. His early study of tilted fault blocks bounded by low-angle faults due to spreading above a shallow pluton made him widely recognized with the classic publication ‘Thin-skin distension in Tertiary Rocks of Southeastern Nevada’ (1971). Paradoxically, Ernie spent the last 20 years trying to dispel some of the later research in which disparate low-angle fault segments were linked as evidence of crustal scale detachment faults. Based on intensive field work, he promoted south-directed shortening and westward tectonic escape as important mechanisms for the complex deformation he observed widely and that to him was not easily explained by the detachment fault paradigm. In GSA Special Paper 463, dedicated to his Lake Mead work, he and Sharon Diehl described widespread dissolution fabrics in breccias, suggesting many features interpreted as fault-related were instead caused or strongly altered by fluid flow, dissolution, and collapse. He argued that estimates of extension magnitude could be significantly too large. This hypothesis remains controversial—and that was the wonder of Ernie as a geologist, as he was compelled to think beyond models when his mountain-goat style field-based studies warranted it. He said once: “The older I get, the more I see, the less I understand”. He told us of his Lake Mead quadrangle mapping: “Those are just cartoons”, even while they were excellent maps. Ernie and Vera moved to Kernville in the southern Sierra, living on the banks of the Kern River with kayaking, rafting, and swimming out the back door. Retiring in 2008, he continued his research on tectonic escape and the influence of dissolution on extension. As a team, they travelled widely, with research-focused adventures to the Italian and Greek Islands, western Mojave Desert, Lake Mead, and lower Colorado River corridor. Ernie was born on Christmas Day, 1932, and passed away peacefully on June 13, 2020, leaving a gaping hole in his family, the Kernville hamlet, and the greater geologic community. 

L. Sue Beard

Papers

Provenance of North American Phanerozoic sandstones in relation to tectonic setting

The real eastern california shear zone

The lake mead fault system and oligo-miocene basins in the virgin mountains: collaboration between dr. paul umhoefer, his students, and colleagues

Remembering r. ernest anderson: a pioneer in basin and range extensional tectonics

Preliminary bedrock geologic map of the Blythe 30' x 60' quadrangle, California and Arizona