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Impact Database
v. 2009.2
The data folder includes:
Complete data in an Excel file – separate sheets for impact sites, impact deposits and a calculator of a number of structures to be expected in an area over a period of time.
.kmz file for uploading to Google Earth. Just double click on the file. Once opened in Google Earth, clicking on each data point will bring up all information about the site, EXCEPT the notes will be trimmed. For full notes and references the user must refer to the Excel spreadsheet file. If you don't have the software download Google Earth here...
Maps – confirmed+most probable structures
Explanation of data attributes:
Classification
Confirmed – an impact site with shock features and/or meteoritic material documented in a geological and geophysical context, which does not allow any alternative explanation. The evidence must be documented in a peer-reviewed publication. Although it is difficult to quantify the probability of impact origin, common statistical practice is to consider a scientific hypothesis valid if it passes a test within >95 % confidence limits. This compares well to the history of the Earth Impact Database (http://www.unb.ca/passc/ImpactDatabase/faq.html) with 174 confirmed structures listed (as of 12 April 2007), 3 structures removed during previous ~5 years and at least 1 structure not considered confirmed in this database. In fact following the outlined criteria these structures should have never been included in the confirmed list, thus one can assume that the structures in this category have an impact origin with >>95 % probability.
Most probable – an impact site where shock features and/or meteoritic material have not been documented sufficiently but various lines of geological, geophysical, modeling, historical and other evidence convincingly support impact origin as the only viable interpretation. This is, in fact, a common practice in geosciences as few geologic processes leave behind such a strong evidence as the shock features associated with impacts. For example, although seismic evidence has traditionally been considered insufficient due to its poor resolution, the modern 3D seismic data over the Praia Grande structure leave little room for arguments against impact origin. The evidence should be documented in a peer-reviewed journal. Analogous to the “Confirmed” class, the impact origin can be expected with at least 95 % probability but logically lower than for the confirmed structures.
Probable – some structural, geological and/or geophysical evidence exists but the impact origin is still uncertain. The evidence may be published in a non peer-reviewed publication. Estimating the probability of impact origin for these structures is even more difficult than for the “Confirmed” and “Most probable” structures. Calling something probable commonly implies >50 % probability. Dence (1972) listed 39 possible impact structures, which compared to “Probable” and “Possible” structures combined in this database, and 20 (51 %) of them are confirmed as of 2009.
Possible – proposed impact site, for which there is little evidence for impact origin (e.g. breccia occurrence, circular lake). The structure was reviewed by a geologist using at least satellite remote sensing data and this review failed to reject the impact origin. Highly relaxed criteria for this class make the probability of impact origin much smaller then 50 %.
Improbable – observations of the structure and/or geological context suggest non-impact origin but a single alternative interpretation has not been well established.
Rejected – non-impact origin has been well documented.
Proposed – Any proposed impact site not evaluated by a geologist within the context of this database.
Inherited classification
Indicated with an “x” for structures, for which impact evidence has not been reviewed within the context of this database and the structures remain classified according to the source work.
Structure name
The most common name. Other used names appear in the notes. Craters that are part of a field are named individually, usually the one or several most prominent craters. This approach was adopted to allow precise localization of individual craters and is different from most other databases, which quote names of the whole field. For structures in countries using Latin alphabet, spelling in respective language is adopted. Note that diacritics (a mark added to a letter to indicate a special pronunciation) can be destroyed when saving as .txt file.
Crater field
Indication of whether the structure is a part of a crater field.
Region, Country, Continent/Ocean
Mostly taken from the referenced literature source, but not always. This may also be derived by the database contributor from Lat/Lon data as those are considered the primary way of the structure location.
Latitude/Longitude
Shown in decimal degrees format, where N and E are positive, and S and W are negative. Number of shown digits depends on precision of available data and circumstances. For example, showing a center of a 1-km structure with 1-minute precision is inadequate as the location may end up outside of the structure. Precision of 1 second for an 80-km structure is clearly irrelevant. Beware that underlying number may show many more digits; this is a result of a deg/min/sec conversion to decimal degrees and does not reflect actual precision. When saving in different format or copying and pasting the numbers the formatting may be lost, i.e. zeros at the end will be omitted effectively decreasing precision and irrelevant digits will be shown increasing precision unreasonably.
Diameter
Original rim-to-rim diameter is preferred. If not available, diameter of observed feature is used. In any case, the diameter should be explained in “Notes”. Please refer to Turtle E. P., Pierazzo E., Collins G. S., Osinski G. R., Melosh H. J., Morgan J. V. and Reimold W. U. (2005) Impact structures: What does crater diameter mean? In Large meteorite impacts III, edited by T. Kenkmann, F. Hörz and A. Deutsch. Geological Society of America Special Paper 384. Boulder, Colorado, USA: Geological Society of America. pp. 1-24.
For some of the structures, original rim-to-rim, present day and limit of deformation diameters are listed.
Age
The age is recorded in original format and with a range of uncertainty. The stratigraphic names are translated in number in the columns “Youngest age”, “Best age”, and “Oldest age” and the note explains how the age was calibrated. For ages indicated with a range, e.g. 100-300 Ma, the “Best age” is left blank as it would be meaningless. “Age uncertainty” is filled in only if explicitly indicated in original data. “Age uncertainty type” shows whether the uncertainty represents 1σ, 2σ, 95% confidence interval, MSWD, stratigraphic range, etc. For cases of approximate ages without an indication of uncertainty an arbitrary 10% uncertainty has been chosen. Note that 2σ and 95% confidence intervals are not necessarily the same.
Representation of age data in several columns allows searching and ranking. Initially, stratigraphic ages were converted to numerical ages for some structures and the original format does not appear in the database. This practice has been later abandoned with a realization that the numerical ages will change according to evolving stratigraphic charts.
Overburden
The thickness of the rocks (in meters) covering the structure above its rim.
Present water depth
The thickness of water layer (in meters) covering the entire structure. Lakes filling the structures do not count.
Drilled
This information can be provided with certainty if the answer is “yes”. As one cannot be sure about the negative answer for drilling of many of the structures, “no” should be entered with care.
Target
Indication of the target rocks assuming impact origin of the structures. Target types: W – water, M – metamorphic, I – igneous, S – sedimentary with indexes s – siliciclastic, c – carbonate, e – evaporite. The rock types are presented in the order of decreasing volume in the target (if that is possible to judge).
Target water depth
Indication of the target water depth presented assuming impact origin of the structures.
Impactor
Indication of the projectile type.
Notes
The notes should:
Accurately capture literature sources for each individual data entry
Describe the basis of impact origin proposal, particular attention should be paid to reports of shock features and meteoritic material.
Explain methods used to obtain the data (e.g., step-heating Ar/Ar on K-feldspar separates) and uncertainties. Sometimes a brief discussion of other conflicting data is useful (e.g., older ages with different methods).
Describe competing hypotheses, at least by referring to who advocated what.
Provide at least a list of other references not discussed any further. However, the focus of the notes is to document collected data and impact evidence, not to provide complete bibliography for the particular structure.
Pay attention to information about drilling (where, who, location of cores …)
The notes should be kept brief but clear and specific.
Compiled by
Recognition is given to those persons who contributed information to a particular structure in “ready format”. Throwing an abstract at me does not count towards your recognition.
