Sedimentary evolution and chemostratigraphy of the post-Sturtian cap carbonate-like Dolomie Tigrée Formation (Katanga Supergroup) in the Democratic Republic of the Congo

This study provides new constraints on the paleoenvironmental, eustatic and carbon isotopic models of the cap carbonate-like rocks of the Dolomie Tigrée Formation in the Katanga region, Democratic Republic of the Congo. The study integrates detailed lithofacies analysis combined with sequence stratigraphy to reveal the high-resolution architecture framework of deposition. Eight lithofacies types are defined: shale, siltstone and sandstone (LF1), dolosiltite (LF2), dolarenite (LF3), massive dolomudstone (LF4), laminated dolomudstone (LF5), intraclastic dolopackstone (LF6), laminar dolomudstone (LF7), and fenestral dolopackstone (LF8). These lithofacies types show that the Dolomie Tigrée carbonate succession accumulated on a distally steepened slope to proximal carbonate ramp setting. The sequence stratigraphy analysis revealed 17 elementary parasequence sets (5th order) that are grouped into 3 distinct successive marine transgressive cycles (PSQ1 to PSQ3) of 4th order magnitude. Each cycle records, from the base to the top, a dominant transgressive system tract, vertically-upward evolving to short time highstand and lowstand system tracts bounded by a sequence boundary. PSQ1 records an early marine transgression marked by the negative shift in δ13C values near −5‰ at the base, then returned to positive values in the upper part of PSQ1 and PSQ2. This carbon isotopic excursion is here interpreted as the hydrological and tectonic reorganizations of outer-ramp-derived allopadic materials from deeper to shallow carbonate-oversaturated reservoirs, coupled with a glacial-isostatic rebound, which enhanced the development of biogenic carbonates in a proximal carbonate ramp setting. Our results show that the changes of sea level triggered the carbonate deposition occurring during the marine transgression. This trangression was related to extensional tectonics of the Nguba rift basin, which were possibly enhanced by the isostatic deglacial rebound in the aftermath of the Sturtian glaciation event.