Análise de Palinofácies da Formação Fox Bay (Devoniano), Ilhas Malvinas

M A Carvalho,H Costa,C G Gonçalves,V S F Trindade

doi:10.11137/2019_1_07_19

M A Carvalho, H Costa + Show 2 more

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https://doi.org/10.11137/2019_1_07_19

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Abstract

The Falkland Islands are an archipelago consisting two main islands (West and East) that show contrasts in their sedimentary history. The palynofacies analysis was applied as tool for reconstructing the history of sedimentary organic matter deposition during the Devonian. The material derives from the Fox Bay Formation that crops out in the East and West Falklands. Spore Color Indices (SCI) and Total Organic Carbon (TOC) also were conducted. Seven kerogen categories were identified: amorphous organic matter (AOM), opaque phytoclasts, Spongiophyton, acritarchs, prasinophycean algae and spores. In general, the samples are carbonized, in particular the AOM that is most abundant, and are distinguished into two subgroups: amorphous organic matter (AOM) and amorphous organic matter carbonized (AOMc). Four palynofacies associations were identified: Palynofacies A, which is composed of prasinophycean algae and acritarchs, Palynofacies B of spores and AOMc, Palynofacies C of phytoclasts and Spongiophyton; and Palynofacies D only of AOM. The results confirm a differentiation between the West and East islands. In fact, this reflects the abundance of AOM and AOMc, respectively. In West Falkland the sedimentary organic matter is not completely carbonized indicated by a lower abundance of AOMc as a result of a lesser thermal influence caused probably by movement of the Hornby Mountains Fault.

Highlights

The Falkland Islands are an archipelago consisting two main islands (East Falkland, ca. 6700 km2, and West Falkland, ca. 5300 km2), and several hundred islands in the South Atlantic Ocean, lying 600 km east of Argentina between latitudes 51o00’ S and 52o30’ S, and longitudes 57°30’ W and 61°30’W (Figure 1).According to Hyam et al (2000), the sedimentary history, thermal maturity and kerogen facies allow to distinguish between the East and West Falkland Islands.Palynofacies analysis is an interdisciplinary approach where the palynomorphs in the palynological slides are investigated, but the entire organic content of the slides
The palynological organic matter or kerogen was deined by the same author as “the particulate organic matter residue isolated from a sedimentary rock after complete dissolution of the rock matrix by HCl and HF acids.”
The particulate organic matter typically consisted of seven categories of kerogen: amorphous organic matter (AOM), amorphous organic matter carbonized (AOMc), opaque phytoclasts, Spongiophyton, acritarchs, prasinophycean phycomata and spores (Figure 2)

Summary

Introduction

The Falkland Islands are an archipelago consisting two main islands (East Falkland, ca. 6700 km, and West Falkland, ca. 5300 km2), and several hundred islands in the South Atlantic Ocean, lying 600 km east of Argentina between latitudes 51o00’ S and 52o30’ S, and longitudes 57°30’ W and 61°30’W (Figure 1).According to Hyam et al (2000), the sedimentary history, thermal maturity and kerogen facies allow to distinguish between the East and West Falkland Islands.Palynofacies analysis is an interdisciplinary approach where the palynomorphs in the palynological slides are investigated, but the entire organic content of the slides. According to Hyam et al (2000), the sedimentary history, thermal maturity and kerogen facies allow to distinguish between the East and West Falkland Islands. Combaz, 1964; Boulter & Riddick, 1986; Oboh, 1992; Traverse, 1994; Tyson, 1995, Oboh-Ikuenobe & De Villiers, 2003). This is the irst time that such a palynofacies approach has been applied in Falkland Islands. Special attention was paid to the comparison, based on sedimentary organic matter (SOM), between the two main islands of the Falkland Islands

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