DETERMINING FLUID SOURCE AND POSSIBLE PATHWAYS DURING BURIAL DOLOMITIZATION OF MARYVILLE LIMESTONE (CAMBRIAN), SOUTHERN APPALACHIANS, USA

Detailed petrographic analyses along a depositional transect from a ca rbonate platform to shale basin reveals that dolomite is the principal burial diagnetic mineral in the Mayville Limestone. This study examin es the role of burial dolomitization of subtidal carbonates. Dolomite occurs as a replacement of precursor carbonate and as inter- and intra particle cements. Four different types of dolomite are identified base d on detailed petrographic and geochemical analyses. Type I dolomite o ccurs as small, irregular disseminations typically within mud-rich fac ies. Type II dolomite typically occurs as inclusions of planar-euhedra l rhombs (ferroan), 5-300 mum in size, in blocky clear ferroan calcite (meteoric) spar. Type II dolomite is non-luminescent. Type I and II d olomite formed during shallow to intermediate burial diagenesis. Type III dolomite consists of subhedral to anhedral crystals 10-150 mum in size occurring as thin seams along stylolites and as thick bands a few millimetres in width. This dolomite consists of dominantly non-lumine scent rhombs and, less commonly, orange luminescent and zoned rhombs. Type IV dolomite consists of baroque or saddle-shaped, 100-1500 mum cr ystals, and is non-luminescent. Type IV dolomite formed during the per iod of maximum burial. Types III and IV dolomite increase in abundance downslope. Type III dolomite contains 1.2-2.6 wt% Fe and a maximum of 1000 ppm Mn. The distribution of these elements displays no distinct vertical or lateral trends. In contrast, Fe and Mn distributions in Ty pe IV dolomite exhibit distinct spatial trends, decreasing from 3.5-4. 5 wt% Fe and 0.1-0.3 wt% Mn in the west (slope/basin) to 1.5-2.5 wt% F e and less than 600 ppm Mn in the east (shelf margin), a distance of a pproximately 60 km. Spatial trends in Fe and Mn distributions in Type IV saddle dolomite, suggest a west-east fluid flow during late burial diagenesis. Types III and IV dolomite have a mean deltaO-18 value of - 7.8% and a mean deltaC-13 value of +1.1% (relative to the PDB standard ). Based on a range of assumed basinal water composition of 2-8% SMOW, temperatures calculated from deltaO-18 values of Types III and IV dol omite range between 75 and 160-degrees-C. Sr-87/Sr-86 data for Types I II and IV dolomite range from 0.7111 to 0.7139. These values are radio genic when compared to Cambrian marine values and are consistent with the presence of a diagenetic fluid that interacted with siliciclastic sediments. The distribution of Palaeozoic facies in the southern Appal achians indicates a Cambrian shale source for the fluids, whilst buria l curves suggest a Middle Ordovician age for burial fluid movement.