Post-Paleozoic activity - Lamont-Doherty Earth Observatory ...

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340 W. Manspeizer and Others U S G S . OFFSHORE EAST COAST 1978 LINE USGS - 28 Figure 17. Seismic section of buried Mesozoic basin as recorded on offshore USGS Line 28. Unmigrated data. Arrows at 1.55 and 1.85 sec mark Jurassic drift sequence. STATION M 0 0 CULPEPER LINE 1 lo I I I I I 0 Figure 18. Seismic section (Line l), eastern Culpeper basin, Virginia. CDP data are 24-fold acquired by Virginia Tech. Display is an automatic line drawing (Coruh and others, 1987). " B marks reflection from bottom of basin as interpreted from seismic data.
Post-Paleozoic activity CULPEPER LINE 2 STATION Figure 19. Seismic section (Line 2), western Culpeper basin, Virginia. CDP data are 24-fold acquired by Virginia Tech. Display is an automatic line drawing (qoruh and others, 1987). J, Jurassic strata of the Culpeper basin. The bottom of the basin (B) is sharply defined by the contact with the underlying late Precambrian to Cambrian metamorphosed basalts and sandstones. BRMD, Blue Ridge master dkcollement as interpreted from the seismic data. D, deepest regional dkcollement in Paleozoic parautochtho- nous shelf strata. the area of Summerville, South Carolina, northwest of Charleston (Coruh and others, 1981; Belcher and others, 1986). At this locality, about 770 m of Cretaceous and Cenozoic Coastal Plain sediments are underlain by about 250 m of subaerial basalt flows (Gohn, 1983). High velocities typical of Triassic-Jurassic rocks are indicated by reflections from beneath the lower velocity (2,000 m/sec) sediments of the Coastal Plain from 0.6 sec (700 m) to approximately 1.6 sec (3 km) below CDP station 100. Numerous diffractions in the basin suggest the presence of diabase sills or faults. Seismic reflection surveys, especially multifold coverage with vibrator energy sources, provide some of the best geophysi- cal data, but seismic refraction surveys have also been selectively used with good results (Ackermann, 1983) to solve specific problems. DEEP ELECTRICAL RESISTIVITY The direct-current electrical resistivity method has been used to explore onshore eastern U.S. early Mesozoic basins because the Mesozoic sedimentary rocks form a prism of relatively porous, water-saturated conductive rocks that produce a good resistivity contrast with the enclosing less conductive Piedmont metamor- phic rocks (Ackermann and others, 1976). The measured resistivity of Triassic rocks in the Durham-Wadesboro basin is between 30 and at least 350 ohm-m (Ackermann and others, 1976). In contrast, the resistivity of the Piedmont crystalline rocks exceeds 1,000 ohm-m. Vertical electrical soundings in the Durham-Sanford basins of North Carolina indicate that not only are large resistivity con- trasts present between Triassic rocks and the enclosing Piedmont
Page 1 and 2: The Geology of North America Vol. F
Page 3 and 4: Post-Paleozoic activity SIBERIAN Fi
Page 5 and 6: DETRITAL BASINS :'->: SALT BASINS 0
Page 7 and 8: similar orientations and/or lie alo
Page 9 and 10: Post-Paleozoic activity NEWARK BASI
Page 11 and 12: Strata within these Mesozoic basins
Page 13 and 14: Post-Paleozoic activity USGS LINES
Page 15 and 16: sic marine tongue was speculated to
Page 17 and 18: contours in red are over Jurassic d
Page 19 and 20: crust. A pronounced north-northeast
Page 21: for relative contributions from iso
Page 25 and 26: the basins and also corresponding w
Page 27 and 28: tons (1963), Thayer and others (197
Page 29 and 30: ank 0 6 I I Post-Paleozoic activity
Page 31 and 32: the north side of the basin. Accord
Page 33 and 34: - 46' - 42O Post-Paleozoic activity
Page 35 and 36: activity was initiated. The initial
Page 37 and 38: percent pyroxene (chiefly augite),
Page 39 and 40: have formed under higher conditions
Page 41 and 42: lines an elongated north-south patt
Page 43 and 44: Several studies of the intrusions w
Page 45 and 46: 0 100 200 300 Miles ^ Figure 27. Ma
Page 47 and 48: tomac Formation. They also report t
Page 49 and 50: REFERENCES CITED ' Post-Paleozoic a
Page 51 and 52: Galton, P. M., 1976, Prosauropod di
Page 53 and 54: - , 1988, Triassic-Jurassic rifting
Page 55 and 56: Bulletin, v. 95, p. 1176-1 187. Res

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