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Facies, Sedimentary Characteristics, and Seismic Geometry of a Carbonate Delta Drift (Miocene, Maldives, Indian Ocean)

Abstract

The facies and sedimentary characteristics of a Miocene carbonate delta drift is presented, based on seismic and well data from IODP Expedition 359 to the Maldives. In contrast to siliciclastic drift bodies, this carbonate sediment drift system has an important contribution from shallow water in-situ carbonate production. The internal stratal architecture of the delta drift consists of sigmoidal clinoforms that thin out towards proximal and distal settings. The outer shape of the delta drift is lobate. Diagnostic criteria of the delta drift deposits are as follows: Proximal settings are characterized by coarse-grained facies with abundant shallow-water components; Proximal facies belts are grain-supported in contrast to the distal, micrite-rich facies; The main shallow-water components of the deposits are large benthic foraminifera (Amphistegina, Cycloclypeus, Lepidocyclina, Operculina, Heterostegina), fragmented red algae and bryozoans, equinoid debris, and Halimeda plates; Fragmentation of bioclasts is intense; Large channels and bigradational intervals are representative sedimentary structures. The delta drift presents signatures of tractive bottom currents and from gravity flows with development of cyclic steps. Condensed intervals in the succession may result from winnowing by enhanced bottom-current activity. We propose that our study object in the Maldives archipelago is not a singular case. Similar settings and situations are given in many carbonate platforms, such as for example seaways between individual banks, where current reworked sediments accumulate on the downcurrent sides of the passages. We therefore propose to critically test cases where similar platform configurations were described. For example, in absence of a three-dimensional control of the depositional geometries, a two-dimensional section of a carbonate delta drift may be mistaken to present a ramp depositional system.