The Blake Geomagnetic Field Event recorded in a sequence of marine and continental facies outcropping in the coast of Buenos Aires province, Argentina

AZCUY, CARLOS; RODRIGUEZ AMENABAR, CECILIA; BRAÑA CARREÑO, CLARA; VIZÁN, HAROLDO; GEUNA, SILVANA; RENDA, EMILIANO; CASTRO, LILIANA; TOFALO, OFELIA RITA; ORGEIRA. MARÍA JULIA; PANARELLO, HÉCTOR

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2019 p. 506 - 522

0895-9811

Different authors have suggested that there is a relationship between Quaternary geomagnetic field events andclimate variability. Considering that in a recent paper a detailed stratigraphic study in a section of the coast ofClaromecó (Buenos Aires province) indicates Late Pleistocene paleoclimatic changes, a paleomagnetic study wasperformed in the same stratigraphic succession. The analyzed sedimentary section belongs to ?Belgranense? unitthat is composed of continental and marine deposits. According to previously published dates and stable isotoperesults presented in this paper, it is proposed that 6 facies (sedimentary units) of the Claromecó section developedduring the interglacial Marine Isotope Stage 5 (MIS 5). These units are presumably coeval with one ofthe best known geomagnetic field events, the Blake Event, occurred during the MIS 5, between ca. 120 and ca.115 ka. The studied units from the base to the top are: 1) diagenetic wackestones with clasts of sand, 2) pedogenizedloessian deposits, 3) lower marine wackestones, 4) lower tidal channel deposits, 5) upper marinewackestones and 6) upper tidal channel deposits. The section is capped by a continental gravity flow muchyounger than MIS 5. Different facies record distinct characteristic remanent magnetizations (ChRM) suggestingthat these have a not modern origin. Low-field thermomagnetic curves and hysteresis loops were performed forall the sedimentary facies that provide magnetic remanences. Special sediment magnetism experiments weremade for the units with reverse and/or oblique reverse components including isothermal remanent magnetizationand anhysteretic remanent magnetization to perform the Lowrie-Fuller test. In these units opaque mineralswere identified using polished and thin sections together with scanning electron microscopy analysis.According to all the results it is interpreted that the Blake Geomagnetic Field Event was recorded in the pedogenizedloessian deposits with magnetite crystals generated during pedogenetic processes, and in extracellularbiogenic magnetite crystals in the lower marine wackestones. The reverse and/or oblique reverse ChRM componentswere recorded before the lower tidal channel deposits, which have normal polarity directions. The BlakeGeomagnetic Field Event was recorded in Claromecó during last interglacial MIS 5, however a direct correlationcannot be made between the recorded transitional polarity and a marine transgression corresponding to animportant melting of ice sheets during this marine isotope stage. The magnetic components recorded in thestudied sequence could be used as a stratigraphic tool to help identify ?Belgranense? unit in Argentina or correlativesedimentary facies outcropping in South America.