Authigenic “spherules” in K-T boundary sediments at Caravaca, Spain, and Raton Basin, Colorado and New Mexico, may not be impact derived

Research Article| July 01, 1987 Authigenic "spherules" in K-T boundary sediments at Caravaca, Spain, and Raton Basin, Colorado and New Mexico, may not be impact derived GLEN A. IZETT GLEN A. IZETT 1U.S. Geological Survey, M.S. 913, Denver Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information GLEN A. IZETT 1U.S. Geological Survey, M.S. 913, Denver Federal Center, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 99 (1): 78–86. https://doi.org/10.1130/0016-7606(1987)99<78:ASIKBS>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation GLEN A. IZETT; Authigenic "spherules" in K-T boundary sediments at Caravaca, Spain, and Raton Basin, Colorado and New Mexico, may not be impact derived. GSA Bulletin 1987;; 99 (1): 78–86. doi: https://doi.org/10.1130/0016-7606(1987)99<78:ASIKBS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The K-T boundary interval at Barranco del Gredero, Caravaca, Spain, consists of three units: a light gray Cretaceous marl, a 1- to 3-mm-thick ferruginous clay called the "K-T boundary impact layer" because of its content of shock-metamorphosed quartz grains, and an overlying greenish-gray clay. A conspicuous feature of the impact layer is its content of potassium-feldspar particles called "sanidine spherules" by some authors. The particles consist of a porous mesh-work of prismatic potassium-feldspar crystals clearly of authigenic origin. Their shape, distribution, and texture suggest that they are not altered basaltic melt droplets formed during impact of an extraterrestrial object as advocated by some proponents of the impact-extinction theory of Alvarez. Moreover, authigenic spherules also occur in a thin kaolinitic claystone layer at the K-T boundary in continental sedimentary rocks of the Raton Basin, Colorado and New Mexico. This layer is overlain by another claystone (5–8 mm thick) that records the abrupt appearance of shock-metamorphosed quartz grains in the local stratigraphic section. Four compositional types of spherules (kaolinite, goyazite, layered goyazite/kaolinite, and jarosite) occur in the lower of the two claystone layers. Because the spherules are (1) not in a bed containing shock-metamorphosed minerals, (2) common at some and rare at other localities, and (3) hollow and form peculiarly shaped intergrown masses suggest that they are not altered microtektites or melt droplets. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.