The Chesapeake Bay Crater

by Poag, C. Wylie; Koeberl, Christian; Reimold, Wolf Uwe; Koeberl, Christian; Reimold, Wolf Uwe

• ISBN13: 9783540404415
• ISBN10: 3540404414
• Edition: CD
• Format: Hardcover
• Copyright: 2003-11-01
• Publisher: Springer Verlag

Summary

This volume synthesizes 16 years of geological and geophysical studies which document an 85-km-wide impact crater buried 500 m beneath Chesapeake Bay in south eastern Virginia, USA. The authors integrate extensive seismic reflection profiling and deep core drilling to analyze the structure, morphology, gravimetrics, sedimentology, petrology, geochemistry, and paleontology of this submarine structure. Of special interest are a detailed comparison with other terrestrial and extraterrestrial craters, as well as a conceptual model and computer simulation of the impact. The extensive illustrations encompass more than 150 line drawings and core photographs. An accompanying CD-ROM includes selected seismic profiles, scaled cross sections, detailed maps, and downhole geophysical logs.

Table of Contents

Introduction	1	(40)
Geological Framework of Impact Site	41	(32)
Crystalline Basement Rocks	41	(6)
Regional Tectonostratigraphy	41	(2)
Crystalline Basement Rocks in Boreholes	43	(2)
Regional Configuration of Crystalline Basement Surface	45	(2)
Coastal Plain Sedimentary Rocks	47	(10)
General Stratigraphic Framework	47	(1)
Preimpact Deposits	48	(1)
Potomac Formation	48	(2)
Unnamed Upper Cretaceous Beds	50	(1)
Brightseat Formation	50	(1)
Aquia Formation	50	(1)
Marlboro Clay	50	(1)
Nanjemoy Formation	51	(1)
Piney Point Formation	51	(1)
Unnamed Upper Eocene Deposits	51	(1)
Postimpact Deposits	51	(1)
Chickahominy Formation	52	(1)
Delmarva Beds	52	(1)
Old Church Formation	52	(2)
Calvert Formation	54	(1)
Choptank Formation	54	(1)
St. Marys Formation	54	(1)
Eastover Formation	54	(1)
Yorktown Formation	54	(1)
Chowan River Formation	55	(1)
Quaternary Formations	55	(2)
Sequence Stratigraphy	57	(1)
Paleogeography of Impact Site	57	(7)
Subsidence of Virginia Continental Margin	64	(1)
Initial Evidence of East Coast Impact	64	(5)
Onshore Borehole Evidence	69	(4)
Noncored Boreholes	69	(1)
Cored Boreholes	69	(4)
Geophysical Framework of Impact Site	73	(18)
Seismic Investigations of Virginia Coastal Plain	73	(1)
Seismic Signature of Crystalline Basement Rocks	73	(4)
Chesapeake Bay Seismic Reflection Profiles	77	(8)
Depth Conversion of Seismic Two-way Traveltimes	85	(1)
Gravity Evidence	86	(5)
Database	86	(1)
Interpretation	87	(4)
The Primary Crater	91	(62)
Crater Structure and Morphology	91	(62)
Seismic Interpretation	91	(1)
Outer Rim	91	(29)
Annular Trough	120	(1)
Peak Ring	120	(19)
Inner Basin	139	(1)
Central Peak	140	(6)
Gravity Interpretation	146	(7)
Secondary Craters	153	(18)
Location and Identification	153	(2)
Secondary Craters on Profile T-1-CB	155	(3)
Secondary Craters on Profile T-11-PR	158	(5)
Implications of Secondary Crater Record	163	(8)
Synimpact Crater-Fill Deposits	171	(84)
Oldest Breccia Unit	171	(1)
Displaced Megablocks	171	(14)
Seismic Signature and General Lithic Composition	171	(13)
Expression on Downhole Geophysical Logs	184	(1)
The Exmore Breccia	185	(70)
Seismic Signature and General Geometry	185	(3)
Distribution and Thickness	188	(5)
General Lithology	193	(11)
Sedimentary Structures	204	(8)
Expression on Downhole Geophysical Logs	212	(1)
Windmill Point Corehole	212	(1)
Newport News Corehole	213	(1)
NASA Langley Corehole	213	(1)
Exmore Corehole	214	(1)
North Corehole	215	(1)
Bayside Corehole	215	(1)
Kiptopeke Corehole	216	(1)
Petrography	216	(1)
Shock Fractures	216	(1)
Planar Deformation Features (PDFs)	216	(8)
Impact Melt Rocks	224	(1)
Glassy Microspherules	224	(9)
Geochemistry	233	(22)
Initial Postimpact Deposits	255	(24)
Depositional Setting	255	(1)
Dead Zone	255	(4)
Chickahominy Formation	259	(20)
Lithology of Cores	259	(1)
Expression on Downhole Geophysical Logs	259	(7)
Seismic Signature	266	(1)
Geometry	266	(4)
Faults and Fault Systems	270	(9)
Age of Chesapeake Bay Impact Crater	279	(8)
Biochronology	279	(4)
Radiometric Chronology	283	(1)
Magnetochronology	283	(1)
Correlation with Other Craters and Impactites	283	(4)
Geological Consequences of Chesapeake Bay Impact	287	(14)
General Nature of Consequences	287	(1)
Reconfigured Basement Structure and Morphology	287	(5)
Central Peak	289	(1)
Inner Basin	289	(1)
Peak Ring	290	(1)
Normal Faults	290	(1)
Reverse Faults	291	(1)
Compression Ridges	291	(1)
Disruption of Preimpact Sedimentary Column	292	(2)
Source of North American Tektite Strewn Field	294	(4)
General Distribution of Distal Ejecta	294	(3)
Correlation Problems	297	(1)
Far-Field Seismic Effects	298	(3)
Comparisons with Other Impact Craters	301	(42)
Terrestrial Craters	301	(25)
Subaerial Craters	301	(6)
Submarine Craters	307	(19)
Extraterrestrial Craters	326	(6)
Comparison with Chicxulub Multiring Impact Basin	332	(11)
Comparisons Between Impactites	343	(22)
Terrestrial Impactites	343	(18)
Ries Breccias	343	(5)
Manson Breccias	348	(2)
Lockne Breccias	350	(1)
Popigai Breccias	351	(3)
Montagnais Breccias	354	(1)
Sudbury Breccias	354	(3)
Chesapeake Bay Breccias	357	(4)
Flowin, Fallout, and Dead Zone	361	(1)
Other Intrabreccia Bodies	361	(1)
Continuous Ejecta Blankets	362	(1)
Secondary Breccias	362	(1)
Strewn Fields	363	(1)
Impact Melt Rocks	363	(2)
Implications for Impact Models	365	(22)
General Conceptual Models and Scaling Relations	365	(7)
Subaerial Cratering	365	(3)
Submarine Cratering	368	(4)
Conceptual Model for Chesapeake Bay Crater	372	(5)
Stage 1 -- Contact and Compression	373	(1)
Stage 2 -- Excavation	373	(3)
Stage 3 -- Modification	376	(1)
General Conceptual Model of Crater-Fill Deposition	377	(4)
Intracrater Regimes and Lithofacies	377	(4)
Extracrater Regimes and Lithofacies	381	(1)
Differentiating Crater-Fill Lithofacies at Chesapeake Bay	381	(3)
Comparison of Models	384	(3)
Biospheric Effects of Chesapeake Bay Impact	387	(46)
Local Paleoenvironmental Effects	387	(32)
Sediment Accumulation Rates	387	(2)
Stratigraphic Attributes of Benthic Foraminiferal Community	389	(1)
Preimpact Benthic Foraminiferal Community	389	(1)
Postimpact Benthic Foraminiferal Community	390	(11)
Bathysiphon Subassemblage	401	(1)
Community Structure of Benthic Foraminiferal Associations	402	(1)
Predominance and Equitability	402	(5)
Species Richness	407	(1)
Paleoenvironmental Interpretations	407	(12)
Possible Global Paleoenvironmental Effects	419	(14)
Hypothetical Short-Term Effects	421	(2)
Possible Long-Term Effects	423	(1)
Implications of δ18O Data	424	(7)
Implications of δ13C Data	431	(2)
Residual Effects of Chesapeake Bay Impact	433	(14)
Hypersaline Groundwater	433	(7)
Near-Surface Compaction Faults	440	(1)
Surface Expression of Crater	440	(4)
Altered River Courses	444	(1)
Relative Change of Sea Level	444	(3)
Summary and Conclusions	447	(6)
Appendix	453	(8)
References	461	(28)
Index	489