Applicability of the authigenic 10 Be/ 9 Be dating to deltaic deposits: Preliminary results from the Slanicul de Buzau section, Pliocene, Romania.
Authors: Aherwar Kishan , Šujan Michal , Šarinová Katarína , Braucher Régis , Leeuw Arjan de , Chyba Andrej , Team Aster 
Published: March 2021

&lt;p&gt;&lt;strong&gt;Abstract&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;br&gt;The authigenic &lt;sup&gt;10&lt;/sup&gt;Be/&lt;sup&gt;9&lt;/sup&gt;Be dating method utilizes the ratio of cosmogenic radionuclide &lt;sup&gt;10&lt;/sup&gt;Be produced in the atmosphere and of stable &lt;sup&gt;9&lt;/sup&gt;Be derived from chemical erosion of rock massifs.Different origin of both nuclides points to difficulty in determination of the initial isotopic ratio, which radioactive decay is the base of age calculation using the equation N&lt;sub&gt;1&lt;/sub&gt;=N&lt;sub&gt;o&lt;/sub&gt;e&lt;sup&gt;-&amp;#955;t&lt;/sup&gt;. The initial ratio could be affected by several factors and might change through time. Mixing of riverine and basinal (lacustrine or marine) waters appear to be one of the significant effects, since surficial streams are the major source of the dissolved &lt;sup&gt;9&lt;/sup&gt;Be and its relative content is expected to decrease towards the open basinal environment due to the continuous growth of authigenic rims around particles (Wittmann et al., 2017: Geophys. Res. Lett.). This effect should be traceable when analyzing different facies from open shelf through prodelta and delta front up to the delta plain environments, however, a study focusing on the mentioned issue is missing.&lt;/p&gt;&lt;p&gt;This study aims to examine, how change in sediment source proximity across a deltaic parasequence affects the applicability of the authigenic &lt;sup&gt;10&lt;/sup&gt;Be/&lt;sup&gt;9&lt;/sup&gt;Be dating method. Two early Pliocene deltaic parasequences D and E were selected for this purpose from the Slanicul de Buzau section in the Dacian Basin (Romania), with an established robust geochronological model based on magnetostratigraphy (Jorissen et al., 2018: Sed. Geol.). Hence, the parasequences are of known age of 4.46&amp;#8211;4.44 Ma (D) and 4.39&amp;#8211;4.36 Ma (E). The authigenic &lt;sup&gt;10&lt;/sup&gt;Be/ &lt;sup&gt;9&lt;/sup&gt;Be ratio of 19 samples was compared to granulometric and geochemical analyzes in order to trace and interpret the variability of the data.&lt;/p&gt;&lt;p&gt;In our study it was found that &lt;sup&gt;10&lt;/sup&gt;Be/ &lt;sup&gt;9&lt;/sup&gt;Be ratios are relatively stable for both parasequences without significant different trend from distal to proximal facies. Grain size of all samples are generally comparable, indicating silt (71.45&amp;#8211;82.64 vol. %) with content of clay (8.09&amp;#8211;23.78 vol. %) and low content of sand (1.5&amp;#8211;13.32 vol. %). There are three significant outliers regarding &lt;sup&gt;10&lt;/sup&gt;Be/ &lt;sup&gt;9&lt;/sup&gt;Be ratio. One sample in the parasequence D exhibit increase of &lt;sup&gt;10&lt;/sup&gt;Be correlating with high carbonate wt. % and an increase of CIA index. The carbonate content appears to be a good proxy for a decrease in riverine sediment input and lower accumulation rate, which favors higher relative content of &lt;sup&gt;10&lt;/sup&gt;Be. Both parasequences exhibit almost identical weighted mean authigenic &lt;sup&gt;10&lt;/sup&gt;Be/ &lt;sup&gt;9&lt;/sup&gt;Be ratio after excluding the outliers, what is an expected result considering analytical uncertainty of the method in ca 4.5 Ma old sediments. The low variability of &lt;sup&gt;10&lt;/sup&gt;Be/ &lt;sup&gt;9&lt;/sup&gt;Be ratios within parasequences and in their comparison is encouraging for the method applicability.&lt;/p&gt;&lt;p&gt;This research was financially supported by the Slovak Research and Development Agency under contract No. APVV-16-0121.&lt;/p&gt;