Late Triassic to Late Jurassic evolution of the Adriatic Carbonate Platform and Budva Basin, Southern Montenegro

Abstract

Southeastern Montenegro is the only part of the Adriatic Carbonate Platform (AdCP) that bears record of its evolution from a ramp, through a distally steepened ramp to a platform. In this paper we present the sequence stratigraphy of the Late Triassic to Late Jurassic rocks from this part of Tethys for the first time in the literature. We discovered and described three new facies: hardground and cerebroid oolites of the Livari Supersequence, and black pebble conglomerate of the Tejani Supersequence. The mid-ramp and lower ramp cherty oolite, wackestone and mudstone facies of the Livari Supersequence, as well as Oolite Conglomerate facies of the Stari Bar Supersequence were partially or completely reinterpreted. The Middle and Late Triassic rifting separated the AdCP from the other South Tethyan carbonate platforms and created the intraplatform Budva Basin. The AdCP evolved through three morphologic stages: a detached ramp (Livari Supersequence; Rhaetian–Early Toarcian), a distally steepened ramp (Tejani Supersequence; Early Toarcian–Middle Callovian) and an accretionary rimmed platform (Stari Bar Supersequence; Oxfordian to Neogene). The Rhaetian regression is marked by a regional unconformity surface that represents a type S sequence boundary at the base of the Livari Supersequence. Lowstand Wedge of the Halobia Limestone was the oldest sediment in the Budva Basin. TST and HST of the Livari Supersequence include: supratidal and intertidal inner ramp sediments, ooid shoals, and cyclic shallowing-up parasequences of the mid-ramp. Sedimentation rates were high in the inner ramp, while Budva Basin received relatively thin accumulation of siliceous plankton. A brief exposure of supratidal flats and ooid bars represents a type P sequence boundary between the Livari and the Tejani Supersequences, which was flooded by the Early Toarcian transgression. TST and HST of the Tejani Supersequence consist of supratidal, lagoon, and shoal sediments in the inner ramp, and deeper water carbonates of the mid- and outer ramp. Highstand shedding of the sediment from the steepened ramp left thick deposits in the Budva Basin. The Bathonian regression is marked by a regional unconformity that represents a type S sequence boundary between the Tejani and Stari Bar Supersequences. Stari Bar Oolite Conglomerate is a Lowstand Wedge of the Stari Bar Supersequence. The Middle Callovian transgression induced aggradation of ooid shoals deep into the platform interior. Oxfordian coral reefs created a rimmed platform and restricted export of the shallow carbonates into the Budva Basin.