Lithostratigraphy and sedimentology of the Khao Khad Formation in the vicinity of Khao Chan, Ban Saphanhin, Amphoe Muak Lek, Changwat Saraburi

Abstract

The Khao Khad Formation of Saraburi Group in the vicinity of Khao Chan area is repetitive sequence of limestone, dolomitic limestone, and silt-shale with nodular and banded cherts. Eleven measured rock sections, totally 8,603 metres long, are conducted to determine the lithological characteristics of sedimentary sequences. Altogether 269 rock samples, stratified sampling type, are obtained from all measure sections to examine the petrographical characteristics in order to supplement the rock identification. The lithofacies analysis of the sedimentary sequence is undertaken on the basis of lithological characteristics and sedimentary structures. Nine lithofacies can be distinguished from the sedimentary sequence indicating the depositional environments of shallow restricted marine, barrier bar, and foreslope with some alternating of calm and storm conditions. There are seven members subdivided on the basis of lithological characteristics and depositional environments in ascending order as follows: 1) KC1 member is characterised by dark grey, thin- to medium-bedded, sparse biomicrite, algal biomicrite, and packed biomicrudite with some dark grey chert nodule, 251 to 294 metres thick; 2) KC2 member is characterised by light grey to dark grey, medium-bedded sorted biosparite, crinoidal biosparite, and unsorted biosparudite with some dark grey chert nodule and slightly dolomitic, 181 to 446 metres thick; 3) KC3 member is characterised by grey to dark grey, thinbedded, graded bedding poorly-washed intrasparudite, poorly-washed biosparite, packed biomicrite, and fossiliferous micrite with abundant reddish brown, thinly-laminated to thin-bedded silt-shale between limestone beds, 20 to 81 metres thick; 4) KC4 member is characterised by light grey to pinkish grey, and dark grey, medium- to thick-bedded, poorly-washed biosparite and unsorted biosparite, 25 to 122 metres thick; 5) KC5 member is characterised by dark grey, thinand thick-bedded, packed intramicrite and biomicrite with some elongated chert nodules, dolomite patches, and laminated silt-shale, 267 to 273 metres thick; 6) KC6 member is characterised by grey to dark grey, thin-bedded, poorly-washed biosparite, intramicrudite, intramicrite, packed biomicrite, and micrite, associated with yellowish brown to reddish brown, thin-bedded, silt-shale, and silty sand, 300 to 448 metres thick; 7) KC7 member is characterised by grey to dark grey, thin to thick-bedded, cross-lamination in the lower part, poorly-washed biosparite, and packed biomicrite, 300 to 365 metres. All members have the tendency to be thinning eastwardly. The lithostratigraphy of Khao Khad Formation at Khao Chan area can be correlated with the Khao Khad Formation at the type location using several similarities of lithological characteristics of each member with difference in thickness. The sedimentary sequences of both locations are quite similar in the lower and middle parts. However, the KC7 member is absent in the upper part of the type location.