Quench textures in altered spherules from Cretaceous-Tertiary boundary at Agost and Caravaca, SE Spain

Abundant spherules are observed in a well preserved Cretaceous-Tertiary boundary (KTB) layer at the Agost and Caravaca sections (Betic Cordilleras, SE Spain). These spherules have been diagenetically altered to goethite or K-feldspar. Different morphologies are observed ranging from perfect spheres to droplet shapes. This is the first time that dendritic and fibroradial textures are reported in goethite spherules with clearly splash-form morphology. This morphology suggests that they originated from melt in the hot vapour piume and not as condensate. As unaltered KTB spherules are composed of clinopyroxene, this could be the probable precursor of part of the altered spherules at Agost and Caravaca, which may have been derived from an expanding vapour plume with a significant contribution of extraterrestrial materiai. In addition C-rich cores have been detected in K-feldspar which are enriched in Ir, Pt, Pd and Ni. Although postdepositional processes and microbial activity could have led to severe modification of the original element concentrations, the high content of noble metals and Ni suggests extraterrestrial contamination.