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dc.contributor.advisor Fritsche, A. Eugene en Ocampo, Adriana C. en 2016-09-28T18:07:17Z en 2016-09-28T18:07:17Z en 1997 en 1997-08 en
dc.identifier.uri en
dc.description Includes bibliographical references (leaves 61-67) en
dc.description California State University, Northridge. Department of Geology. en
dc.description.abstract In 1980 Alvarez and others proposed that the mass extinction that marks the end of the Mesozoic Era (Cretaceous/fertiary or K/T boundary) was triggered by the impact of an asteroid at least 10 kilometers in diameter. In 1991 the Chicxulub crater in the Yucatan Peninsula of Mexico was identified as the K/T impact site with gravity and magnetic data and satellite imagery. K/T deposits with meteoritic iridium (Ir) anomalies, shocked quartz, and tektites have since been identified throughout the world, confirming the theory of the impact postulated by Alvarez and others. Two new K/T sites in Belize, Central America, here in identified, contain the most proximal Chicxulub ejecta exposures yet known. Chicxulub ejecta found in these two new Belize locations are: 1) on Albion Island in northern Belize, 364 km from the center of the crater, and 2) in the Cayo District, 475 km from the crater. The Albion deposit unconformably overlies Late Cretaceous dolomite of the Barton Creek Formation. The basal Albion unit is a 1-m-thick bed of clay-rich dolomite and calcite silt containing abundant 1- to 15-mm-diameter spheroids of dolomite, and spheroidal to angular clasts of clay containing relict vesicles. Both the dolomite and clay spheroids are flattened near the basal contact. The base of this Spheroid Bed is slightly enriched in Ir. The Spheroid Bed is overlain by 15 m of Albion Diamictite that contain millimeter- to meter-sized clasts (maximum 7.5 m) floating in a matrix of dolomite silt. The clasts are mostly dolomite, but include limestones with Early to Late Cretaceous rudists and foraminifera. Clasts are commonly fractured and range from well rounded pebbles and cobbles to very angular flakes. Polished facets, multiple sets of striations on single clasts, and penetrating rock chips occur on some dolomite clasts. The Diamictite bed also contains abundant clay clasts with relict vesicles, as well as mudballs, pockets of calcite spherules, and authigenic quartz. Granite, schist, and detrital qua11z are restricted to rare sand-size chips found in insoluble residues. One shocked quartz grain was found out of several kilograms of material dissolved from the Albion Diamictite. In the Cayo District a diamictite deposit directly overlies the Barton Creek Formation. This Cayo Diamictite is similar in composition to the Albion Diamictite, but in three locations (Pook' s Hill, Mount Hope, and San Antonio Cayo) it contains abundant pink limestone cobbles and pebbles with surface polish, striations, and penetrating rock chips (called Pook's Pebbles). The Albion Spheroid bed is similar to K/T spherule beds described from elsewhere in the Gulf Coast and Caribbean region, but the dolomite spheroids are thus far unique and may be the tektite-equivalent of vaporized carbonates. The only correlate for the Albion and Cayo Diamictites is the coarse ejecta unit drilled on the rim of the Chicxulub crater, however the latter contains abundant granitic clasts, nearly absent in Belize. The Albion and Cayo Diamictites share many characteristics with the Bunte breccia of the Ries crater, Germany. The Ries crater was also f01med in carbonate target rock, but is only about 30 km in diameter. The Spheroid Bed may have been deposited by the vapor plume and the diamictites by ballistic sedimentation coupled with debris flow processes. The abundance of Pook's Pebbles in Cayo, interpreted as ballistic ejecta, suggests that ballistic sedimentation may be more important in this area. Models show that Pook's Pebbles were ejected to altitudes of about 100 km before they were deposited in Cayo, in this way overtaking the debris flow deposits and reaching greater distances of deposition such as the Pook's Pebbles found in the Cayo District. en
dc.description.statementofresponsibility by Adriana C. Ocampo en
dc.format application/pdf en
dc.format.extent ix, 67 pages en
dc.language.iso en en
dc.publisher California State University, Northridge en
dc.rights.uri en
dc.subject.other Dissertations, Academic -- CSUN -- Geology. en
dc.title The geology of Chicxulub impact ejecta in Belize en
dc.type Thesis en 2016-09-28T18:07:17Z en
dc.contributor.department Geological Sciences en M.S. en
dc.contributor.committeemember Fischer, Peter en
dc.contributor.committeemember Sloan, Jon R. en
dc.contributor.committeeMember Fischer, Peter en
dc.contributor.committeeMember Sloan, Jon R. en
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