STUDIES ON THE GEODIVERSITY OF THE NORTHERN SECTOR OF THE SAN MATIAS GULF, RIO NEGRO, ARGENTINA.

MEDINA WALTER; CHARO MELISA

Oxford

Conferencia; Oxford Geoherintage Virtual Conference; 2022

University Museum of Natural History

IntroductionThis work deals with the study of the geodiversity of the northern of the northern San Matías Gulf, between Baliza San Matías (40°54'S/64°27'W) to the south of Piedras Coloradas (40º50'S/ 65º06'W), following the coastline of the following the coastline of the province of Río Negro (Figure 1). The area of analysis is relatively small, where important geological coexist important geological features that allow us to describe the events that occurred in the Cenozoic that led to the formation of the gulf.Currently there are several meanings of the term geodiversity in use, but one of the most cited is that of Gray (2004) who considers it as "the natural range of diversity of geological (rocks, minerals and fossils), geomorphological (landforms and processes) and soil features, including their relationships, properties, interpretations and systems". The objective of this work is to analyze and assess the geodiversity of the northern coast of San Matias Gulf. MetodologyThe methodology used was based on the sum of partial numerical indices, calculated on different maps that represent the greatest number of geodiversity elements. The Geodiversity Index is obtained from the sum of these partial indices, the latter being the the result of the sum of units and occurrences in units in areas defined by a grid, adapted from Pereira et al, 2013. In order to carry out this methodology, as a first step, they were georeferenced under the same reference system (POSGAR 2007, Faja 3) served as input for the different indexes that make up the geodiversity index. These are the geological, geomorphological, geotectonic, edaphic and paleontological maps.It should be noted that the base maps come from various sources, and in some cases, they aresome cases, they are made at different scales. Subsequently, a 5x5 km grid at a scale of 1:200,000, which will be the scale for the representation of the maps. As result, 45 squares of 5x5 km each were created. From this grid, the number of structures present in each square was number of structures present in each square, and thus the partial indices were partial indexes. Finally, the partial was summed to generate a single geodiversity index in the study area. As a result, a geodiversity map with a minimum value of 1 and a maximum of 10, ordered in three intervals: Low (1-5), Medium (5-8) and High (8-10).In addition, this analysis takes the study of Medina and Charó (2019) based on 3 sites of geologic-paleontological interest; the proposed names for each site are names proposed for each of the sites are formed by the marine deposits and the fossil species that characterize it: 1-Paleocliff -Tegula atra; 2- Littoral ridges-Anomalocardia brasiliana and 3- "beachrocks"- Chama iudicai (Figure 2).Figure 3.One of the base maps used. The three coastal deposits that preserve the fossil molluskspecies analyzed are located. Image Google Earth Pro 2018 base. (Medina and Charó, 2019).ResultsAs preliminary results, based on the four maps used, the geological, geomorphological, edaphic, and paleontological maps, from which partial indexes are then added to build the Geodiversity Index, it can be seen that, following the coastal zone, it is the highest index that predominates in the study area, it is also noted that, on the other hand, the zones with the lowest indexes cover the areas with the lowest indices cover less areal extension even smaller than those with average index values. The appreciation of these first results of a work that aims to analyze geodiversity and its geodiversity and its distribution in the northern San Matías Gulf based on indexes results in an area of significant geological diversity, in an area that, in the last decades, has consolidated as a tourist corridor in the Patagonian coast.The Geodiversity Index Map of the northern San Matias Gulf (Figure 4) shows high values in areas coinciding with the littoral and the Pleistocene littoral ridges associated with the fossil mollusks of the Tegula atra and Anomalocardia brasiliana and a smaller stretch to the east and a smaller section located to the east where eolian deposits (dunes) of fine sands with beachrocks associated by Chama iudica. The sectors of medium values coincide with the tidal plains and and edaphically correspond to aridisols. Finally, the areas with the lowest values of the Geodiversity Index are located in the sectors where the tidal plains of the estuarial system.Figure 4.Map Geodiversity Index in Northern San Matias Gulf, where it contains low, medium and high values. Source based on Google Earth 2021 satellite image, and Qgis.