chesapeake bay impact crater

In The ICDP-USGS Deep Drilling Project in the Chesapeake Bay Impact Structure: Results from the Eyreville core holes, edited by Gohn G. S., Koeberl C., Miller K. G., Reimold W. U. Geological Society of America Special Paper 458. 4a). Figure 1. The Kiptopeke corehole may be located over the crater's peak ring, which the seismic data shows as an area that has thinning and truncation of early post-impact deposits. Poag, C.W., and Ward, L.W., 1993, Allostratigraphy of the U.S. middle Atlantic continental margin--Characteristics, distribution, and depositional history of principal unconformity-bounded Upper Cretaceous and Cenozoic sedimentary units: U.S. Geological Survey Professional Paper 1542, 81 p. Powars, D.S., Bruce, T.S., Poag, C.W., and Mixon, R.B., 1994, Virginia's Coastal Plain inland salt water wedge--A geohydrological response to the Chesapeake Bay bolide impact [abs. Even the courses of the modern rivers in the lower bay region point to the continued influence of differential subsidence over the crater. The contrast in lithology and color between the Marlboro Clay and the underlying and overlying glauconitic units facilitates identification. The deep crater, 24mi (38km) across, is surrounded by a flat-floored terrace-like ring trough with an outer edge of collapsed blocks forming ring faults. In the MW4-1 corehole, only the upper Cenomanian beds were encountered (pl. The Delmarva beds appear to be the first post-impact unit preserved across the disruption boundary south of the crater. According to Mazanek, NASAs NEO Observation Program has been responsible for a vast majority, about 99 percent, of all NEO discoveries since 1998. The thickness of the Delmarva beds ranges from 2 to 26 ft outside the outer rim of the crater and from 2 to 60 ft inside the crater. Another explanation offered by Back (1966) and followed by Richardson (1994) was that the higher inland salinity resulted from low topographic altitude of the recharge area located along the Fall Line. The Exmore tsunami-breccia is the upper syn-impact deposit and overlies either the CBIC megablock beds (lower syn-impact deposit) or the crystalline basement (pls. It should be noted that until a sonic velocity log is obtained from a borehole inside the crater, there is uncertainty about correlation between the seismic data and the corehole and borehole data. Powars D. S., Johnson G. H., Bruce T. S. (1998) Stratigraphic, structural, and hydrogeological complexities related to the outer rim of the Chesapeake Bay impact crater (abstract). Its presence also limits the availability of freshwater. Griscom D.L. (2012) In plain sight: the Chesapeake Bay crater ejecta blanket, Solid Earth Discuss., Volume 4, pp. pp. "Mind-Blowing" Discovery: Oldest Body of Seawater Found in Giant Crater The crater's structural depression and subsequent structural adjustments since burial have controlled post-impact environmental depositional settings and stratigraphic relations within and among formations and are responsible for the higher subsidence rates in and adjacent to the crater. The fluvial-deltaic deposits are primarily made up of fining-upward sequences that consist of light-gray to pinkish to greenish-gray to green (in part mottled red, brown, and yellow), poorly sorted, fine to coarse, quartzose and feldspathic sand and gravel, with accompanying silt and clay. Focazio, M.J., Speiran, G.K., and Rowan, M.E., 1993, Quality of ground water in the Coastal Plain physiographic province of Virginia: U.S. Geological Survey Water-Resources Investigations Report 92-4175, 20 p., 5 pls. These profiles are based on 96-channel, 48-fold, common depth point (CDP), digital seismic data that are recorded in two-way travel time (twt). The unit is characteristically intensely burrowed (including clay-filled, clay-lined, and sand-filled types) and contains a few to several fining-upward sequences that are generally capped with a sandy clay-silt. PALAIOS, Volume 18, No. South of the James River and the Chesapeake Bay, relatively thick Upper Cretaceous marine and fluvial-deltaic deposits overlie Lower Cretaceous fluvial-deltaic deposits. Robbins, E.I., Perry, W.J., Jr., and Doyle, J.A., 1975, Palynological and stratigraphic investigation of four deep wells in the Salisbury embayment of the Atlantic Coastal Plain: U.S. Geological Survey Open-File Report 75-307, 120 p. Russnow, Kane and Associates, Inc., 1995, City of Newport News Waterworks, Brackish Groundwater Development (BGD) Project Phase II, report on the hydrogeologic framework and well construction activities, Lee Hall Water Treatment Plant Test Site: [about 100] p. Russnow, Kane and Associates, Inc., 1997, City of Newport News Waterworks, Brackish Groundwater Development (BGD) Project Phase III, report on the hydrogeologic framework and well construction activities, Harwood Drive (LH-1) and Lee Hall (LH-2) well sites: Appendix G, [about 100] p. Schultz, P.H, and Anderson, R.R., 1996, Asymmetry of the Manson impact structure--Evidence for impact angle and direction, in Koeberl, C., and Anderson, R.R., eds., The Manson impact structure, Iowa--Anatomy of an impact crater: Geological Society of America Special Paper 302, p. 397-417. Some flat-floored rimless depressions with chaotic infill in these terrains are impact craters that expanded by collapse farther than expected for similar-sized complex craters in solid targets. Despite the fact that the structure is deeply buried, it is one of the better studied impact craters in the United States, through drilling and geophysical survey. 7, p. A119., Johnson G. H., Powars D. S., Bruce T. S., Vaughn A. W, Lucey J. K., Kruse S. E. (1998) Relationship of Yorktown Formation lithofacies to post-impact deformation on the terrace zone, southeastern Virginia (abstract). As is typically found in continental deltas, these deposits primarily consist of fining-upward sequences that are highly variable in their lithology and thickness. Official websites use .gov North of the crater and beneath the Delmarva Peninsula, the unit consists of a relatively thick (up to twice as thick as the clayey facies), predominantly sandy, shelly facies. ), 2009. "Recent Research on the Chesapeake Bay Impact Structure, USA - Impact Debris and Reworked Ejecta." These deposits are interpreted as representing stacked deposits of meandering streams, braided streams, and river- and wave-dominated delta-plain and delta-front facies (Glaser, 1969; Reinhardt and others, 1980; Owens and Gohn, 1985; Meng and Harsh, 1988). Drilling into the Chesapeake Bay crater . These deposits have progressively filled in the crater and blanket the entire region. In the Exmore corehole, the Delmarva beds (zones P18-20) consist of 41 ft of olive-gray to grayish-olive, micaceous, clayey, silty, very fine glauconitic quartz sand, containing scattered patches of pyrite and marcasite (Powars and others, 1992). Much of the work was summarized in a major volume, Gohn et al. 469-479.doi:10.1130/2009.2458(21), Plescia J. Chesapeake Bay impact structure: Morphology, crater fill, and relevance Gerald Johnson, Professor Emeritus of Geology at the College of William and Mary, spoke during an August presentation at the Hampton History Museum about the Chesapeake Bay Crater impact and its effect on the geology of Hampton Roads. The inner basin includes a central uplift surrounded by a series of concentric valleys and ridges. ?85 km in diameter. The Chesapeake Bay impact structure is associated with the North American tektite strewn field. A distinctive suite of microfossils and macrofossils is found in the Nanjemoy Formation, indicating an early Eocene age (Powars and others, 1992). This report documents the highly variable structure, stratigraphy, and buried topography of the outer rim of the Chesapeake Bay impact crater created by its impact and burial. The "older Foraminifera" on which Cederstrom based his interpretations belong to the Aquia (upper Paleocene) and Brightseat (lower Paleocene) Formations. 7, p. A-119. The thinning and variable thickness of the Piney Point strata to the east, closer to the disruption boundary, reflects the immense erosional power of the impact blast and subsequent train of tsunamis that largely shaped the upper surface of the Piney Point. 4). Figures 17 and 18 graphically show this report's geological framework in relation to the cross sections of Meng and Harsh (1988) and Laczniak and Meng (1988) that traverse the lower York-James Peninsula. Differentiation of the Delmarva beds from the Old Church is not always possible and, therefore, the two units are undifferentiated and labeled as Oligocene deposits in plates 3 and 4. For this investigation, the thin Delmarva beds are grouped together with the overlying Old Church Formation and lower Miocene beds of the Calvert Formation into a single seismic stratigraphic unit and labeled as lower Miocene and Oligocene deposits on plates 2 and 3. The first hint was a 8-inch-thick (20cm) layer of ejecta found in a drilling core taken off Atlantic City, New Jersey, about 170 miles (274km) to the north. The CBIS formed in a layered target of water, weak clastic sediments, and hard crystalline rock. They theorized that a huge rock or chunk of ice slammed . Borehole geophysical logs were interpreted by establishing geophysical signatures for the various units defined in several continuously cored test holes. Borehole geophysical signature typical of undisturbed stratigraphic units outside the disruption boundary that separates pre-impact from syn-impact deposits; Jamestown (A) and MW4-1 (B) coreholes. The St. Marys-Choptank aquifer, an important aquifer to the north in the Maryland Coastal Plain, is not present in this area (Laczniak and Meng, 1988), and the Virginia Beach aquifer is present only south of the James River and Chesapeake Bay (Hamilton and Larson, 1988). This is similar to the lithology assigned to the Old Church Formation (upper Oligocene) in the Exmore corehole (Powars and others, 1992) and suggests that the lower 17 ft of this section, as Poag's Foraminifera data had indicated, belong in the Delmarva beds (P21a). These interpretations were influenced, in part, by the thick sections of the St. Marys Formation strata encountered in the Jamestown corehole (app. Granules of quartz, glauconite, and phosphate are scattered throughout, with minor amounts of pyrite, carbonaceous material (including wood), and very small sharks' teeth. In this huge new reservoir, pore spaces are filled with briny water that is 1.5 times saltier than normal seawater. The clasts are fragments ripped from previously deposited beds that underlie southeastern Virginia. Geological Society of America, Abstracts with Programs, Volume 25, p. A-378., Pusz A. E., Miller K. G., Wright J. D., Katz M. E., Cramer B. S., and Kent D. V. (2009) Stable isotopic response to late Eocene extraterrestrial impactsGeological Society of America Special Papers, Volume 452, p. 83-95, doi:10.1130/2009.2452(06), http://specialpapers.gsapubs.org/content/452/83.abstract, Riddle P. C., Vaughn A. W, Lucey J. K., Kruse S. E., Johnson G. H., Hobbs C. H. (1996) Geophysical studies of near-surface deformation associated with the Chesapeake Bay impact structure, southeastern Virginia (abstract). Boulder, Colorado: Geological Society of America. (2009) A petrographic and fluid inclusion assessment of hydrothermal alteration of some impactites and crystalline rocks in the Chesapeake Bay impact structure, ICDP-USGS Eyreville B coreGeological Society of America Special Papers, Volume 458, p. 543-557, doi:10.1130/2009.2458(23), http://specialpapers.gsapubs.org/content/458/543.abstract, Wittmann A., Reimold W. U., Schmitt R. T., Hecht L., Kenkmann T. (2009) The record of ground zero in the Chesapeake Bay impact crater - Suevites and related rocks. This water is too salty to drink or to use in industry. Differentiation between the Aquia and the Exmore tsunami-breccia also is difficult because of similarities in lithologic and borehole signatures. was formed during the late Tertiary from deposition by the Pensauken fluvial-deltaic complex into the northern end of the Salisbury tectonic low by the ancestral Hudson-Delaware River system. The finer grained beds range from gray to dark gray, finely laminated, carbonaceous clays interbedded with thin, sandy clay beds to highly oxidized, multicolored (reds, browns, purples, and yellow), laminated to thick-bedded clays. Catchings, R.D., Saulter, D.E., Powars, D.S., Goldman, M.R., Dingler, J.A., Gohn, G.S., Schindler, J.S., and Johnson, G.H., 2001, High-resolution seismic reflection/refraction images near the outer margin of the Chesapeake Bay impact crater, York-James Peninsula, southeastern Virginia: U.S. Geological Survey Open-File Report 01-407, 18 p. Edwards, L.E., Horton, J.W., Jr., and Gohn, G.S., 2004, ICDP-USGS Workshop on deep drilling in the central crater of the Chesapeake Bay impact structure, Virginia, USA, September 22-24, 2003: U.S. Geological Survey Open-File Report 2004-1016, CD. The latter is considered . [5] The sedimentary walls of the crater progressively slumped in, widened the crater, and formed a layer of huge blocks on the floor of the ring-like trough. Gohn, G.S., Clark, A.C., Queen, D.G., Levine, J.S., McFarland, E.R., and Powars, D.S., 2001, Operational summary for the USGS-NASA Langley corehole, Hampton, Virginia: U.S. Geological Survey Open-File Report 01-87-A, 21 p. Powars, D.S., Bruce, T.S., Bybell, L.M., Cronin, T.M., Edwards, L.E., Frederiksen, N.O., Gohn, G.S., Horton, J.W., Jr., Izett, G.A., Johnson, G.H., Levine, J.S., McFarland, E.R., Poag, C.W., Quick, J.E., Schindler, J.S., Self-Trail, J.M., Smith, M.J., Stamm, R.G., and Weems, R.E., 2001, Preliminary geologic summary for the USGS-NASA Langley corehole, Hampton, Virginia: U.S. Geological Survey Open-File Report 01-87-B, 20 p. Prepared in cooperation with the Hampton Roads Planning District Commission and the NASA Langley Research Center. Six air guns providing 984 in3 at 2,000 psi (pounds per square inch) were used as the energy source and hydrophone groups were 41 ft apart. Drillers' logs use a variety of lithic descriptions for this unit, such as a "black sand," "black pepper sand," "marl," "clay and shell," or "shell rock." 5C ). This section contains calcareous material in the top 10 ft. Bio-stratigraphic data from these beds indicate a late Oligocene to early Miocene age (Powars and others, 1992). Electrical cross sections based on audio-magnetotelluric (AMT) soundings image a nearly vertical zone of high resistivity at the outer margin of the annular trough, possibly indicating fresh ground water at that location, and they show impedance trends that match the curvature of thestructure. Prepared in cooperation with the International Continental Scientific Drilling Program (ICDP). These deposits form an eastward-thickening wedge ranging from about 10 ft thick updip to 348 ft thick at the Fentress corehole downdip (Powars and others, 1992). The borehole-numbering system in this report refers to a location number on plate 1 (printed in bold in the text, for example, 65) and a local reference number, such as the USGS ground-water storage inventory (GWSI) number or the well number assigned in other reports (Cederstrom, 1945a, b, 1957). 5). Timing of the impact is relatively well constrained by multiple studies, to 35.3 to 35.4 Ma (e.g. Bybell, USGS, oral commun., 1998) (see pl. 349376., Wittmann A., Schmitt R. T., Hecht L., Kring D. A., Reimold W. U., Povenmire H. (2009) Petrology of impact melt rocks from the Chesapeake Bay crater, USA. Within the crater, the seismic data suggest that the syn-impact deposits can roughly be divided into two principal depositional units (Poag, 1997a; D.S. Various structural and stratigraphic complexities related to the CBIC and its burial have altered the hydraulic characteristics of the aquifers and confining units inside and adjacent to the crater and have apparently retarded the flushing of salt water from inside the crater. GSA Special Paper 458. Because of the lack of shallow seismic data, the Eastover Formation is lumped with the upper Miocene to Quaternary post-impact deposits. It was formed by a bolide that struck the eastern shore of North America about 35.5 0.3 million years ago, in the late Eocene epoch. data, 1995). A comprehensive effort to understand the crater's materials, architecture, geologichistory, and formative processes, as well as its influence on ground water, includes the drilling of coreholes accompanied by high-resolution seismic-reflection and seismic-refraction surveys, audio-magnetotelluric surveys, and related multidisciplinary research. One of the keys for differentiation is that these basal sands are at the base of the Eastover Formation's overall coarsening-upward trend. The channels exit across the eastern side of the crater, which subsided at a faster rate, probably because of an underlying tectonic hinge zone. These Aquia microfossil and macrofossil assemblages also are found in the Exmore tsunami-breccia deposits. Until more definitive age resolutions for the Popes Creek Sand and Fairhaven Members are available, we will name the lower Miocene deposits found in Virginia the Newport News unit of the Calvert Formation. These crater-fill materials are preserved beneath a 235.6-m-thick (773.12-ft-thick) blanket of postimpact sediments. A lock () or https:// means youve safely connected to the .gov website. The discovery of the crater disrupted this scenario and raises many questions concerning the crater's possible effects on eastern Virginia's ground-water system, such as effects on the aquifer system's flow system, hydraulic properties, and geochemistry. The distribution of Lower and Upper Cretaceous and lower Paleogene deposits documents the existence of a pre-impact, east-west structural zone, approximately located along the James River, which represents the north flank of the Cape Fear-Norfolk block. Dinocyst data from the Jamestown corehole also indicate an equivalence to the Windmill Point beds (see app. 12, p. 149, 156-157. Copyright 2011, 2012, 2013, 2014, 2015, 2016 United States Meteorite Impact Craters. Clay analysis of core samples from the top 54 ft of Exmore tsunami-breccia found in the Kiptopeke corehole indicate that the clayey matrix is dominated by montmorillonite (greater than 80 percent), with lesser amounts of illite and kaolinite (less than 10 percent each); one sample was nearly 100 percent montmorillonite. Laczniak, R.J., and Meng, A.A., III, 1988, Ground-water resources of the York-James Peninsula of Virginia: U.S. Geological Survey Water-Resources Investigations Report 88-4059, 178 p. Larson, J.D., 1981, Distribution of saltwater in the Coastal Plain aquifers of Virginia: U.S. Geological Survey Open-File Report 81-1013, 25 p., 2 pls. Though we have learned much from the geology of the Chesapeake Bay crater, Dan Mazanek, a near-Earth object (NEO) expert at NASA Langley, explained that there is still much left to learn. 7). Conflicting data were encountered most often around the outer edge of the CBIC, especially for the boreholes located far from one of the continuously cored test holes. The nannofossil data indicate an NP 16 nannofossil zone (see app. Johnson, About 35 million years ago, a large comet or meteor slammed into the shallow shelf on the western margin of the Atlantic Ocean, creating the Chesapeake Bay impact crater. It provides an accessible analog for studying impact processes in layered and wet targets on volatile-rich planets. 1) and thus provide the best correlation possible at this time and the most probable range of depth equivalence for the seismic data. The middle Miocene beds show the widest variation in thickness of all the post-impact deposits and generally thicken and prograde into the crater, especially from the north side, which suggests a northern source. The crater's structural depression has determined the post-impact depositional history and stratigraphic relations among formations beneath the lower York-James Peninsula. Dinocyst data (L. DeVerteuil, University of Toronto, written commun., 1994; Verteuil and Norris, 1992, 1996) from the St. Marys clayey facies encountered in the Exmore corehole suggest an equivalence to the Windmill Point beds (Ward, 1984) and are extrapolated to upper zone N16 to lower zone N17 (planktonic foram zones). The high relief of the peak ring on the south side of the crater and the apparent underplating of the peak ring on the north side indicates an angled impact trajectory from the northeast (D.S. The first evidence of this impact crater came from the identification of shocked quartz in cores (G. Izett and L. Poppe, USGS, written commun., 1993) and structure contour and isopach mapping of the upper Eocene "Exmore beds" (herein named the Exmore tsunami-breccia) and the overlying upper Eocene Chickahominy Formation (D.S. In 1996, the USGS and the National Geographic Society collected more than 497 mi of seismic-reflection profiles in and around the CBIC; however, the authors of this report did not have access to those data. (Chesapeake Bay in Virginia). 4a). data, 1995). Seismic sections north and northwest of the crater show that the Aquia strata have long, unbroken, parallel, relatively high-amplitude reflectors typical for marine deposits. Today, that 25-mile-wide (40 kilometers) crater is buried half a mile below the rocky basement of Chesapeake Bay the 200-mile-long (320 km) estuary linking Virginia and Maryland on the East. Geology, Volume 31, No. Powars, unpub. It is one of the best preserved craters in the world and the largest to be found in America. The outer rim of the crater, characterized by a zone dominated by normal-faulted slump blocks, forms a buried, 1,000- to 4,000-foot escarpment. The target region was on the marine continental shelf at the time of impact, and most of the region is still or again underwater today. TheLangleycorehole is locatedinthe southwestern part of the crater's annular trough. A summary of the chronostratigraphic data is included on the MW4-1 and Jamestown corehole stratigraphic columns (pl. Because of the lack of shallow seismic data, the Yorktown strata are combined into the upper Miocene to Quaternary seismic stratigraphic unit. Differentiation of the Lower Cretaceous fluvial-deltaic deposits from the overlying Aquia Formation or the Exmore tsunami-breccia deposits is difficult when using only geophysical logs. The location, however, of the preserved limit of the Exmore tsunami-breccia somewhere beneath the river is uncertain. An official website of the United States government. Similar to the St. Marys Formation, the Eastover is deep enough inside the crater to be resolved and is represented by long, thin, parallel marine reflectors. The Old Church Formation is overlain by lower Miocene beds of the Calvert Formation and by the middle Miocene beds of the Calvert Formation or St. Marys Formation in updip areas (pls. In Virginia, downdip areas outside the CBIC include beds of earliest Late Cretaceous age. Satellite image of the Chesapeake Bay impact structure in Virginia. Edwards, L.E., 1989, Dinoflagellate cysts from the lower Tertiary formations, Haynesville cores, Richmond County, Virginia, chap. The study area encompasses the central to eastern part of the Virginia Coastal Plain (fig. Clay analysis of core samples from the 220-ft-thick section encountered in the Kiptopeke corehole indicates the clays consist primarily of a mixture of illite/smectite (50-75 percent), illite (10-20 percent), and kaolinite (0-30 percent; pl. 317348., http://specialpapers.gsapubs.org/content/458, Collins G. S., Wnnemann K. (2005) How big was the Chesapeake Bay impact? The Chesapeake Bay Bolide: Modern Consequences of an Ancient Cataclysm USGS Coastal & Marine Geology Program, Chesapeake Bay Ecosystem History and Change USGS, The Chesapeake Bay: Geologic Product of Rising Sea Level - USGS Fact Sheet 102-98 USGS Coastal & Marine Geology Program, Earth Impact Database University of New Brunswick Department of Geology, National Aeronautics and Space AdministrationU.S. A narrow band of preserved Exmore tsunami-breccia deposits surrounds the crater's outer rim; these deposits also are offset by the bounding fault zone and other faults apparently produced or reactivated by the impact. Chesapeake Bay Impact Crater | U.S. Geological Survey - USGS.gov 4), and the structure contour and isopach maps (pls. Wylie Poag, U.S. Geological Survey (USGS), identified the Chesapeake Bay Crater, which was formed when an object hit the Atlantic Ocean over 35 million years ago in the late Eocene and is largely responsible for creating the Chesapeake Bay and surrounding area. Poag assembled an international team to investigate its characteristics and consequences. Edwards, L.E., 1986, Late Cenozoic dinoflagellate cysts from South Carolina, U.S.A., in Wrenn, J.H., Duffield, S.L., and Stein, J.A., eds., Papers from the first symposium on Neogene dinoflagellate cyst biostratigraphy: American Association of Stratigraphic Palynologists, Contribution Series Number 17, p. 47-58. ]: Geological Society of America Abstracts with Programs, v. 28, no. 726, doi:10.1016/S0022-3093(03)00304-1. http://www.sciencedirect.com/science/article/pii/S0022309303003041, Horton, J. W., Jr., J. N. Aleinikoff, M. J. Kunk, G. S. Gohn, L. E. Edwards, J. M. Self-Trail, D. S. Powars, and G. S. Izett. The older beds have sagged over the subsiding breccia, and the younger rocks have been deposited in the resulting topographic depression. The Marlboro Clay (upper Paleocene and lowermost Eocene) consists of 8 to 18 ft of light-gray to pinkish-gray and reddish-brown kaolinitic clay and is found consistently outside of the crater between the glauconitic Aquia and Nanjemoy Formations (fig. Nannofossil data from the Jamestown corehole (55) also indicate a late Oligocene to early Miocene age (see app. As ground-water use increases in the Hampton Roads region and public water utilities increasingly tap into brackish-water aquifers as sources of drinking water, additional information about the CBIC will be needed for future management of these ground-water resources. Powars D. S., Bruce T. S. (1999) The effects of the Chesapeake Bay impact crater on the geological framework and correlation of hydrogeologic units of the lower York-James Peninsula, Virginia. The Old Church Formation also has a distribution pattern similar to the Delmarva beds, except that the Old Church Formation extends farther west and northwest outside the disruption boundary (fig. Dingler, G. S. Gohn, J. S. Schindler, G.H. Wherever there are no seismic profiles that traverse the outer rim, the location of the outer rim is only approximate. Until the late 1980's, knowledge of this region's subsurface geology was derived primarily from studies of water well cuttings and geophysical logs (Sinnott and Tibbitts, 1968; Brown and others, 1972; Meng and Harsh, 1988; Laczniak and Meng, 1988). 3 and 5) and northern part of the crater (Exmore corehole) and because of uncertainty in correlating these similar-looking sequences, a "?" The Chesapeake Bay Bolide Impact: A New View of Coastal Plain Evolution These fine-grained sediments contain abundant microfauna, which give a white-speckled appearance to some intervals; abundant finely crystalline iron sulfide; and variable amounts of fine-sand to silt-sized glauconite, shells (including solitary corals), and pyrite. Its like a coin toss. Even though its a 50-50 heads or tails on average, it could be heads ten times in a row or tails ten times in a row.. The entire circular crater is about 53mi (85km) in diameter and 0.81mi (1.3km) deep, an area twice the size of Rhode Island, and nearly as deep as the Grand Canyon. The geological framework must be refined in order to produce a new hydrogeological framework. Interpretation of these lithic descriptions and geophysical logs provides the basis for the lithostratigraphic cross section presented in this report. Poag (1997a) offers an alternative interpretation of this "fuzzy" seismic boundary as the contact between sediment-clast breccia overlying a crystalline-clast breccia.
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