A Neoproterozoic multi-phase rift sequence: the Grampian and Appin groups of the southwestern Monadhliath Mountains of Scotland

Abstract

The Grampian and Appin groups of the southwestern Monadhliath Mountains form the earliest known syn-rift sequences of the Scottish central Highlands. They were likely to have formed in an intracontinental setting and represent deposition of mixed clastic and carbonate shallow and deep marine strata. The Grampian Group of the southern Monadhliath Mountains was deposited during a period of initial basin rifting (NW–SE extension) followed by a phase of thermal subsidence. Syn-rift sediments comprise a 2.5–6 km thick turbidite system. Thermal subsidence brought about the basinward progradation of shallow marine shelf sediments resulting in the infilling of pre-existing basin topography. The overlying Appin Group commenced with deposition of a shallow marine sequence alternating between nearshore tidal sand and offshore mud deposition. This formed in response to renewed rifting and concomitant subsidence. Accelerated rifting resulted in localized footwall uplift and erosion while sedimentation continued in the hanging-wall areas. Resultant subsidence, perhaps partly thermally driven, caused gradual basin widening and produced an onlapping marine sequence. There followed a period of progressive clastic deprivation when carbonates were precipitated, and at the onset of anoxic conditions, deposition of organic muds. The fundamental structural elements responsible for the formation of the Grampian and Appin group basins were also influential in the orogenic evolution of the basin-fill. Half-graben fills were deformed to produce regionally extensive folds such as the Stob Ban–Craig a’ Chail Synform.

87 Sr/ 86 Sr chemostratigraphy of Neoproterozoic Dalradian limestones of Scotland and Ireland: constraints on depositional ages and time scales

“…The Dalradian is divided into four Groups (oldest to youngest): Grampian, Appin, Argyll and Southern Highland. The Grampian Group is dominated by fluvial to marine siliciclastic rocks with very rare limestone units (Glover et al 1995). The base of the Grampian Group beneath the oldest lithostratigraphical unit (Glen Shirra Subgroup) is nowhere exposed and its relationship to gneissose metasedimentary rocks that may constitute basement is unknown ).…”

Laurentian margin evolution and the Caledonian orogeny—A template for Scotland and East Greenland

“…6) after a flooding event (Banks, 2005). Reduced subsidence and relative tectonic stability at this time is interpreted to represent a postrift thermal subsidence phase (Glover et al, 1995). The lithological associations of the Glen Spean Subgroup, combined with well preserved sedimentary structures, indicate deposition in shallow (tidally influenced) marine shelf environments with intensive sediment recycling and winnowing of the underlying turbiditic rocks (Banks, 2005).…”

“…A reduction in sand grade sediment supply and development of shelf conditions along the tectonically active basin margins and intrabasinal highs is recorded by lateral thickness and facies changes to striped semipelite and psammite. This is followed by a renewed influx of sanddominated turbidites (Plate 2B) deposited by fan-lobe systems derived from the 11-Feb-09 northwest, passing south and eastwards into shelf environments (Glover et al, 1995;Robertson and Smith, 1999;Banks, 2005).…”

The Dalradian rocks of the northern Grampian Highlands of Scotland

“…Since then, application of the techniques of basin analysis to the lithostratigraphy of the Northern Grampian Highlands has made important contributions to an evolutionary model for the Grampian and Appin group depocentre in that region (Glover et al, 1995;Smith et al, 1999;Robertson and Smith, 1999).…”

“…A return to sand-dominated turbidites (the Creag Meagaidh Psammite Formation) marks deposition in extensive turbidite fan-lobe systems, derived from the north-west and extending southwards and eastwards into shelf environments in the Glen Roy and Drumochter areas (Glover et al, 1995).…”