Fusiline foraminiferal biostratigraphy and carbonate facies of the Permian Ratburi Limestone, Saraburi, central Thailand

A succession of Permian carbonates outcropping along the highway north of Saraburi, central Thailand, has yielded a prolific and diverse fusiline-algal assemblage of Early Permian (Sakmarian) to early Late Permian (Midian) age. Six major units representing dominantly carbonate platform environments are recognised: turbidite and basin slope deposits, a platform margin algal reef, a back reef, an interior platform with patch reefs, a protected lagoon inner platform, and supratidal, dolomitised algal mats. Archaeolithoporella and Tubiphytes form major reef frameworks analogous to those described from the Middle Permian reefs of Trogkofel (southern Austria) and El Capitan (western Texas). The associated dasycladacean floras are assignable to the Eastern Circum-Pacific Realm, whilst the fusiline fauna has Arctic-Tethyan affinities in the Early Permian and Tethyan affinities in the Middle Permian. Eight fusuline assemblage zones are recognised and the Robustoschwagerina-Nagatoella Zone, representing the Sakmarian (early Artinskian) stage, is recorded for the first time from central Thailand. Phylogenetic studies of the fusulines, coupled with an examination of the diagenetic fabrics and field observations, indicate the presence of an unconformity during the late Early Permian-early Middle Permian, which may be correlatable with a worldwide eustatic sea-level fall or may be due to local tectonic movements.

Dawson microcrystalline limestones with occasional chert nodules. Dark argillaceous chert and microcrystalline siliceous limestone dominate the lower part of the unit. Layers of chert nodules and chert bands appear to have formed through the replacement of lime mud. Some bioclasts are entirely siliceous and are encompassed within a black bituminous matrix. Traces of sponge spicules are common. The upper part of the facies (3m) consists of thin-bedded bioclastic wackestones / packstones. Shell fragments and fusuline tests show abrasion and grading and many features indicative of calciturbidites, as described by Helmke and Kraikhong (1982).
Misellina, Schubertrlla, Mesoschubertella, Pseudofusilina, ?Neothailandina and Neofusulinella are among the few fusulines that are present in this facies, which is similar in age to the middle part of Facies 2 (see below).
Facies 2: Archaeolithoporella-Tubiphytes boundstones and skeletal grainstones: Platform margin algal biostrome (Sakmarian-Bolorian). This facies is exposed as a limestone pavement in a paddy field and occurs structurally and in part, stratigraphically above Facies 1. It has a minimum thickness of 630m. The limestone is medium to light grey, massive to thick-bedded and comprises dense microcrystalline skeletal grainstones and boundstones and lacks any mud matrix. The facies is characterised by its diverse macro-and microfauna, common algal boundstone, and an abundance of fibrous and sparry cements. The grainstone is locally dolomitised, particularly towards the top of the unit. Fusuline-algal grainstones and boundstones dominate the entire facies, whilst brachiopods, gastropods, and cephalopods are common. A few metres of a black, argillaceous bioclastic packstone occurs near the top of the section, above the dolomitised bed and has yielded a Middle Permian belemnite-like aulacocerid (Dawson, 197813).
The lowest part of this facies contains 1.5m of fusulinerich grainstones containing abundant Robustoschwagerina, Nagatoella, Toriyamaia and dasycladacean algae in the lower part; this unit represents the oldest marker bed in the section. Skeletal grains are not in contact and are bounded by Tubiphytes and other encrusting algae with masses of columnar and fibrous cements. Locally, dense micrite envelopes and Tubiphytes coat skeletal grains and are followed by syntaxial drusy and fibrous calcites in optical continuity (Pl. 9, Figs 1, 2). These cement fabrics are typical of early marine cements as described from other Permian reef frameworks (Toomey & Babcock, 1983, Fliigel, 1981and Fliigel et al., 1984. The grain sorting and depositional fabrics indicate a high energy open shelf environment. Meniscus cements suggest early vadose diagenesis (Dawson, 1978a).
Robustoschwagerina is considered to be a derivative of Pseudoschwagerina (and by some authors to be a subgenus of Paraschwagcrzna). Facies 2 is therefore presumably younger than the Pseudoschwagerina Zone, said to be the lowest part of the Permian within the Ratburi Limestone . These beds represent the earliest dateable horizon in the limestone sequence of the Saraburi area.
The beds overlying the fusiline-rich grainstones are massive and are dominated by algal boundstones containing Archaeolithopovella and Tubiphytes together with an abundant radiaxial cement. Archaeolithoporella intergrowths with fibrous calcite and botryoidal cements may represent an altered encrusting or dome-shape organic biostromal structure. Later, radiaxial and blocky cements fill the remaining voids. These features are very similar to structures described and illustrated from the El Capital Reef, as a cemented reef framework, by Toomey & Babcock (1983). Edwards & Riding (1988) pointed out similar fibrous calcites from the Trogkofel reef of Austria which they interpreted as having formed through neomorphism of earlier algal skeletons. The occurrence of Archaeolithoporella and Tubiphytes boundstones, early marine cements and associated grainstones all indicate a wave-swept shelf area, as described by Toomey & Babcock (1983) and Fliigel(l981) from the El Capital limestone of the Guadalupe Mountains and the Trogkofel Limestone of the Carnic Alps, respectively. The Saraburi boundstones formed localised biostromal buildups at the platform margin and did not develop into a reef-rimmed margin to the carbonate platform (Dawson et al. in press

Dawson
The dasycladacean algal diversity in this facies is similar to that described from Trogkofel (Fliigel, 1985), Japan and Thailand (Endo, 1969), and indicates the presence nearby of shelf lagoons with both protected and open marine areas (Fliigel, 1985). The dasycladaceans Antkracoporella, Vermiporella, Gyroporella, Clavaporella and Mizzia are commonly associated with textulariids and fusuline foraminifera.
Above these boundstones the rest of Facies 2 grades into grainstones, packstones and rudstones with fusulines, dasycladacean algae and echinoderm fragments as the main bioclasts. Occasionally, Tubiphytes and Arckaeolitkoporella occur as stabilising binding elements.
Pseudofisulina vulgaris (Schellwien) and l? padangensis  Facies 3 outcrops as small hills of thin bedded subhorizontal limestone at KmlO west of the highway and has a minimum thickness of 56m. A brecciated limestone with a reddish silty matrix appears at the base. The limestone clasts contain species of Misellina, Sckubertella and Armenina, which are probably derived from the Facies 2 fauna (Yahtashian-Bolorian).
The limestone contains enormous (up to 1.5m long) bivalves referable to Alatyoconcha (= cf. Tanckintongia). Shells replaced by sparry calcite are common and occur with waagenophyllid coral colonies in growth position. This mixed fauna floatstone is interbedded with fusulinedasycladacean packstones 1 grainstones. Large bioclasts are commonly silicified and large chert nodules are common throughout the section. This particular deposit is similar to the mixed fauna back-reef interior platform facies reported from the Ratburi area by Baird (1990).
The facies is dominated by an assemblage of Parafusulina gigantea (Deprat), Chusenella and its associated species. Neosckwagerina simplex Ozawa and Afgkanella megaspherica Sheng are common in the lower part, whilst Neoschwagerina craticulifera (Schwager) and Afgkanella pesuliensis (Ozawa & Tobler) are abundant in the upper part. The smaller foraminifera Hemigordius, Cribrogenerina and Climacammina are also common as finer bioclasts. The occurrence of N. simplex and A. megaspkerica suggests that this facies can be correlated with the Neoschwagerina simplex Zone of the early Murgabian (Middle Permian). The upper part of Facies 3 (Fig. 6), however, also ranges up into the middle Murgabian, as evidenced by an association of Neoschwagerina craticulifera (Schwager) and Afgkanella pesuliensis (Ozawa & Tobler). The representative fusuline assemblages of Facies 3, together with those of Facies 4, are given in Fig. 4.

Facies 4 Coral-bryozoan boundstoneslpackstones: Interior platform with patch reefs (late Kubergandian-late Murgabian).
These limestones outcrop along the road section between Km7 and 9, in a NE-SW striking anticline structure with dips at 30° -45O S-N. Faulting and folding has led to a repetition of part of Facies 4 (Fig. 2), however, the biostratigraphy has helped minimise correlation problems. The limestones are dark grey, thick-bedded bioclastic wacke 1 packstones with a carbonaceous-rich lime-mud matrix. Coral and sponge colonies are common, occasionally forming l m to 3m high mounds or patch reefs. Brachiopods and gastropods are also abundant throughout the facies. Its minimum thickness is approximately 280m.
Facies 4 comprises at least three microfacies arranged in shallowing upwards cycles. Each cycle starts with a bioclastic limestone which grades upwards from wackestone to packstone, to grainstone, passing up into floatstone with a microlaminated algal stromatolite capping each cycle. Waaganophyllids, lonsdaloids and solitary corals occur in growth position in the floatstones together with bryozoan fragments. Dasycladacean algae and  encrusting Tubipkytes are common in the boundstones and packstones, suggesting deposition in an inner platform environment. Brachiopod, gastropod, echinoid and crinoid fragments are locally present. Large botryoids of replacive sparry calcite are believed to be due to the replacement of dome-shaped algal mounds (cf. Edwards & Riding, 1988), suggesting the presence of algal bioherms in this inner platform environment.
The upper part of Facies 4 has a dark carbonaceous matrix and is often associated with algal mats and algal peloids, suggesting deposition in a restricted, peritidal environment. The presence of carbonaceous-rich material also suggests a rather restricted shallow marine environment and this is supported by the occurrence of Permian plant fossils nearby (Campbell & Ingavat, 1972). In contrast, the rich biotas in the lower part of this facies suggest deposition mainly in a shallow, open marine platform environment. Fusulines are diverse and abundant in grainstones and boundstones, but show low diversity in the wacke/ packstones with a carbonaceous matrix. Verbeekina and some species of Pseudodoliolina and Afgkanella seem to survive into the restricted shallower marine environment of Facies 5. Overall, this facies represents shallowing from a bioherm inner platform, to restricted lagoonal and peritidal environments.
Two fusuline assemblages can be recognised: Facies 5: Interbedded shales, skeletal peloidal wacke/packstones: Protected lagoon inner platform (Murgabian-early Midian). The facies outcrops as a small hill forming part of the Khao Khiero range (Fig. 2) extending east-west to Phra Phuttabat at Kmll on the western side of the highway. The road cut is 20m high and 800m long. Beds strike at 125O and dip south at about 50°. Faults occurring in the middle of the outcrop cause bedding dips to become more gentle (15O). The minimum tectonic thickness of this unit is about loom.
It comprises beds of dense, dark grey medium to coarse-grained carbonaceous rich bioclastic-peloidal wacke I packstone, with argillaceous patches, interbedded with yellowish shale beds. There are four calcareous shale beds, 3 to 8m, apart, in the section. Slabs of waagenophyllid coral occur one metre above the third shale bed from the bottom. Based on the fusuline assemblages, the waagenophyllids can be correlated with the corals of Facies 3 and 4. Productids, rhynchonellids and gastropods occur sparsely throughout this facies. Phylloid algae occasionally formed small mounds which have a peloidal matrix.
Parafusulina, Verbeekina, Ckusenella, Pseudodoliolina and Afgkanella form the main assemblage and occur in abundance throughout the facies, permitting correlation with Facies 3 and 4, as mentioned above. Near the top, species of Pseudodoliolina show signs of abrasion, suggesting some transportation and the tests of associated species of V. verbeeki are often crushed. These features also occur within the equivalent assemblage in Facies 6 and have been reported from Khao Khao, to the southwest of the area (Toriyama, 1978) and from molasse-type Pseudodoliolina-Verbeekina limestones, south of Phetchabun, NE Thailand (Helmcke & Kraikhong, 1982 the lower part of this facies, is a significant horizon for correlation with Facies 3 and 4. The same fusuline assemblage and crushed specimens of Verbeekina also reappear in Facies 6, which is considered to be contemporaneous with Facies 5. Representative fusuline assemblages of Facies 5 are given in Fig. 4. Facies 6 Dolomitised algal mats: Intertidal-supratidal flats (late Murgabian-Early Midian). This facies is 69m thick and outcrops in small hills to the south of Km7, near a quarry with red shale. The limestones are thick bedded bioclastic and peloidal wacke 1 packstones with bedding striking 280° and dipping 40°-50° to the west. The top of the hills comprise red siliceous shale beds which cap the underlying Facies 6. The lower and upper part of this facies contains 0.5m of laminated algal dolomite, containing abundant birds eye structures and algal filaments. In the middle part of the facies, the limestones comprise bioclastic peloidal wackestones and packstones Verbeekinid foraminifera dominate this part of the section. Verbeekina verbeeki (Geinitz), Pseudodoliolina pseudolepida (Deprat), Afghanella schencki Thompson and A . sumatrinaeformis (Gubler) are common whilst advanced species of Parafusulina occur sparingly throughout the facies. V. verbeeki becomes more abundant towards the top, together with Metadoliolina and Colania. Globivalvulina also appears towards the top of this facies. Verbeekina occurs in packstones associated with Pseudodoliolina and shows signs of crushing during compaction (as noted in Facies 5, above). This horizon can probably be correlated with the similar horizon of crushed Verbeekina described by Toriyama (1978) from the Khao Khao section.
The faunal assemblage of Verbeekina verbeeki-Pseudodoliolina-Metadoliolina of Facies 6 is similar to that of Facies 5 and belongs to the Neoschwagerina Zone, probably the N . craticulifera-N. margaritae zones (late Murgabian). The presence of Metadoliolina lepida (Schwager), Colania douvillei (Ozawa) and Globivalvulina suggests that the top of this facies may extend into the lower part of the Yabeina Zone, early Midian (Late Permian).

DISCUSSION
The Permian carbonates in this area can be divided into six major carbonate facies, from north to south, namely: slope-turbidites, platform margin algal reef, back-reef, open marine interior platform, protected shelf and intertidalsupratidal (peritidal) environments. The younger beds indicate progressively shallower environments, suggesting that the Saraburi section represents a regressive Early to Late Permian sequence. Unfortunately, the outcrops are not large enough to postulate oceanward and basinward directions or the possible direction of progradation associated with this regressive sequence. Diagenetic fabrics suggest that the limestones have undergone early and subaerial diagenesis as well as subsequent subsurface diagenesis. The sections range in age from Sakmarian (Early Permian) to early Midian (Late Permian) in age. The evidence of a disconformity between Facies 2 and Facies 3 and 5 during the early Mid-Permian (Figs. 2 and 6) is supported by diagenetic and palaeontological criteria, which are discussed later in this paper.

FUSULINE ASSEMBLAGE ZONES
There have been several previous studies of the fusuline foraminifera from Thailand and Malaysia. In the "Carboniferous and Permian systems in Thailand and Malaysia" Toriyama et al. (1975) compiled a list of 197 species of fusulines belonging to 50 genera and subgenera. Ingavat et al. (1980) and Toriyama (1984) summarised the fusuline zonation and characteristics of the Ratburi Limestone in Thailand and its equivalents in Malaysia, in which 265 species belonging to 70 genera were described. The fusuline fauna from Khao Phlong Phrab, Khao Khao, and Khao Imot, Saraburi, west of my study area (Fig. l), have been described in detail by Pitakpaivan (1965), Ozawa (1970b), Toriyama (1976;, Toriyama & Kanmera (1977;1979) and Toriyama & Pitakpaivan (1973). Consequently, taxonomy will be omitted in this paper. The dasycladacean algae from Khao Phlong Phrab and Khao Khao have been described by Endo (1969) and the identification of the algae in the present article is based on his descriptions.
The three-fold division of the Permian, based on the Permian Tethys scale for the Mediterranean-Alpine fold belt was revised by Leven (1981) and is now widely accepted by workers in Southeast Asia (Toriyama et al., 1975;Toriyama, 1984;Ingavat, 1984;Ingavat-Helmcke & Helmcke, 1986;Fontain et al., 1986). Correlation of fusuline assemblages of overlapping facies, such as these, is best Explanation of Plate 7 All figures x40, except where stated. achieved by using the stage of phylogenetic evolution and extinction of the mid-Permian Verbeekinoidea, as already demonstrated by Ozawa (1970a), Kanmera et al. (1976), Toriyama et al. (1978), Ingavat et al. (1980), Ingavat-Helmcke & Helmcke (1986) and Ingavat (1988). The Tethyan Verbeekinoidea evolved independently from primitive species of Misellina into five bioseries in the early Middle Permian (Bolorian) (Fig.5). The evolutionary trends of the verbeekinoidean foraminifera are characterised by the modification and reduction of the keriothecal layer, increased development of the parachomata, multiplication of septa and septula, and enlargement of the test (Kanmera et al., 1976;Ozawa, 1970a;Ross, 1979).
Eight fusuline zones are proposed as an aid to correlating the Saraburi section (Fig.6). The age ranges of the individual species found in Facies 1-6 are shown in Fig. 4.

Robustoschwagerina-Nagatoella Zone
(Thickness 8m; lower part of Facies 2). This zone forms the base of Facies 2 in the lowest part of the section and is characterised by an abundance of Robustoschwagerina (Pl.1, figs 1-3) and Nagatoella (Pl. 1, figs 4-7). The fusuline genera Toriyamaia, Pseudofusulina, Pseudoendothyra and Pseudoreichelina, together with the dasycladacean algae Vermiporella and Anthracoporella are also common in this assemblage zone. The Robustoschwagerina species from Saraburi are extremely large (10-12mm in diameter), and have a spherical test with deep umbilici (PI. 1, figs 1-3) which readily distinguishes them from other schwagerinids.
Pseudoschwagerina mouonthensis (Deprat) and was referred by Igo (1972) to the (older) Pseudoschwagerina Zone of the Asselian (Early Permian). The Sakmarian index fauna appears to be absent, especially in the central part of Thailand (Toriyama, 1976;Ingavat et al., 1980;Fontaine et al., 1986), although Ingavat (1984;1988) has proposed a zone of Robustoschwagerina tumida for the Sakmarian, based on specimens reported from the north of Thailand, as mentioned above. My Saraburi species of Robustoschwagerina occurs with an associated fauna (Nagatoella and Toriyamaia), which indicates it must be younger than the Pseudoschwagerina Zone; it is probably a derivative of R. tumida and for this reason is kept in open nomenclature.
Sakmarian fusuline faunas have been reported from various localities in Thailand by recent workers, but none of the index fauna of the Sakmarian-Yahtashian stages has been reported from continuous sections from central Thailand, until now. If this is supported by subsequent work it would provide the answer to the question set by Toriyama et al. (1975) as to whether the latest part of the Early Permian is missing in central Thailand or has just not been found. The Robustoschwagerina-Nagatoella Assemblage

Dawson
Zone, it is hoped, can now be used as the standard for the correlation of Sakmarian carbonates in Thailand.
Above this zone lie Archaeolithoporella-Tubiphytes beds which occur as algal buildups 25m thick. Overlying these, in turn, are algal-fusuline limestones of ArtinskianIYahtashian age (see below).
Advanced species of Pseudofusulina, and primitive species of Parafusulina, appear in this zone and become common through the rest of Facies 2. Pseudofusulina vulgaris (Schellwien) has a close affinity with Cuniculinella globosa (Skinner & Wilde), as noted by Igo et al. (1979). The faunal assemblage of this zone can be placed withn the Yahtashian Stage, or the early Artinskian (late Early Permian). This association of Pseudofusulina vulgaris, P. padangensis, Cuniculinella, Nagatoella, Minojapanella and Toriyamaia is closely comparable with the fauna found by Igo et al. (1979) from the Sungei Sedili area, Johore, Malaysia. They described 26 species and in correlating the assemblage with that of the Pamir, South China and Japan, considered it to be older than the fauna of the Ratburi Limestone from the Khao Phlong Phrab section (Misellina Zone). My P. vulgaris-Chalaroschwagerina Zone can also be considered coeval with the Monodiexodina shiptoni Zone designated by Ingavat & Douglass (1981) from Mae Sariang in the north of Thailand.
The occurrence of Pseudofusulina species, together with the associated schwagerinids, declines towards the top of the facies, in parallel with the increasing numbers of primitive members of the verbeekinoidean group, Misellina, Armenina and Brevaxina.
Facies 1, although more restricted in thickness, has a faunal association essentially the same as the later part of Facies 2, and can probably be placed within the P. vulgaris-Chalaroschwagerina Zone, Yahtashian Stage of the Early Permian (D. Vachard, pers. comm.). These assemblages occur in association with advanced schwagerinids, together with species of Schubertella, Mesoschubertdla, Neofusulinella, Minojapanella, Ozawainella, Nankinella, Sphaerulina and Pseudoreichelina. A few specimens of Neothailandia, Maklaya and Pseudodoliolina, which also occur in the Misellina and Maklaya zones in the Khao Phrong Phrab sections (Toriyama et al., 1974), appear towards the top of this zone. The fusuline assemblages occur in association with abundant dasyclad algae, encrusting algae, and smaller foraminifera.
In contrast to the exposures of this zone of Facies 2, which occur as karstic limestone pavements, the outcrop of Facies 5 rises abruptly to form a small hill (Fig. 2). The boundaries between Facies 2, 3 and 5 are obscured, but are probably disconformable and subsequently faulted. The faunal assemblage of Facies 5 appears to represent a higher Explanation of Plate 9 All figures x10, except where stated.  Fig. 2 Nagatoella sp. and Anthracoporella spectabilk Endo, encrusted by Tubiphytes within a fibrous cement. Facies 2, platform margin algal buildup. Sakmarian, Early Permian. Dawson stratigraphic horizon than that in Facies 3, but is equivalent in age to that of Facies 6 (see Figs 4 and 6). A brecciated limestone with a reddish matrix occurs at the base of Facies 3, which contains a Misellina, Nankinella and Armenina Facies 2 fauna in the limestone clasts. The fauna in Facies 3 and 4 seems to have no direct association or lineage continuity with that in Facies 2. Although the age ranges of the fusulines do not show a significant time gap, the sudden change of the faunal assemblages and the absence of the Misellina bioseries lineages, Maklaya, Cancellina and Armenina (Fig. 5) indicate an abrupt change in environment, unfavourable for the verbeekinoidean evolution and their particular ecological niche. This may correspond with the abrupt marine regression during the late Early Permian and, early Middle Permian, postulated by Vail et al. (1977) (See Fig. 6). Ingavat-Helmcke & Helmcke (1986) and Ingavat (1988) suggest that this may correspond to the Ural Orogeny.
Faunal characteristics allow this zone to be divided into This zone, although it lacks the endemic index species of Maklaya and Cancellina of the Kubergandian stage can, however, be correlated with the Maklaya zones of the Khao Phlong Phrab section (Fig. 6), by reference to the flourishing assemblage of Parafusulina-Ckusenella and their allies, and is assignable to the Cancellina Zone, Middle Permian, of Tethyan terminology (Toriyama et al., 1974;Ingavat et al., 1980 andIngavat, 1984).
The absence of endemic species of Maklaya and Neotkailandia, which are otherwise abundant in the Khao Phlong Phrab section, is of ecological and stratigraphical significance. Maklaya, Cancellina and Armenina are derived directly from Misellina (Fig. 5), which occurs in abundance in the zone below (in Facies 2), as mentioned previously. Their absence suggests that the environment changed unfavourably for the verbeekinoidean fusulines in this area during Bolorian-Kubergandian times. In the Khao Phlong Phrab area, only 7km to the west, the verbeeknid bioseries seems to have flourished without disruption from the Misellina phase into the Neosckwagerina simplex phase (early Murgabian), then there is an unconformity (Toriyama et al., 1974). In our area, this appears to be earlier and would seem to mark the onset of a regression during late Early Permian (Vail et al., 1977, see also Fig. 6) which corresponds with the Ural Orogeny and the beginning of tectonic activity in the Phetchabun Belt in the northeast (Helmcke et al., 1985, Ingavat-Helmcke & Helmcke, 1986.
This zone covers the middle part of Facies 3 and 4 and the lower part of Facies 5. The fusuline assemblages now change considerably. The limestones in Facies 3 and 4 have a dominant assemblage of Neosckwagerina-Parafusulina-Afgkanella, while the limestones and interbedded shales of Facies 5 contain a dominant assemblage of Pseudodoliolina-Verbeekina-Afghanella. Although Parafusulina and Verbeekina are common to these two biofacies, the former genus seems to decrease in importance, while the latter becomes increasingly dominant towards the top of the zone.
In more detail, Afgkanella megaspkerica Sheng, Verbeekina verbeeki (Geinitz) and Parafusulina gigantea (Deprat) are species common to both these biofacies. Parafusulina kaerimizensis (Ozawa) and P. japonica (Ozawa)  The faunal assemblages of this zone have the same stratigraphic age range as the Neosckwagerina simplex Zone and the lowest part of the Presumatrina schellwieni Zone in the upper part of the Khao Phlong Phrab section (Toriyama et al., 1974), and with the lowest part of the Khao Khao section (Toriyama & Kanmera, 1979) (see Fig. 6).

correlated these zones with the Neosckwagerina simplex
Zone of Afghanistan and southeast Pamir, belonging to the early part of the Murgabian stage of the Middle Permian, in worldwide correlation.
This zone occupies the upper part of Facies 3 and 4, middle part of Facies 5 and the lower part of Facies 6. In  (Toriyama et al., 1974;Toriyama & Kanmera, 1979); their distribution would also probably range high into the Afghanella schencki Thompson occurs abundantly throughout the zone; this species, together with PseFdodoliolina pseudolepida (Deprat) have long ranges, more or less throughout the Murgabian (Toriyama & Kanmera, 1979). P. pseudolepida and Xeoschwagerina simplex Ozawa occur together with Verheekina verbeeki (Geinitz) in Facies 6. Afghanella sumatrinaeforinis (Gubler), the advanced member of the Afghanella (megaspherica-pesuliensis-schenckisunzatrinaeforrnis) bioseries appears towards the top of this zone in Facies 5 & 6. Parafusulina gigantea (Deprat) still occurs in the lower part of the zone while Chusenella finally dies out. Metadoliolinn cf. lepida (Schwager) and M . multiseptata (Ozawa) appear towards the top.
In this zone, Neoschwagerina is represented by advanced members of the simplex-craticulifera-margaritae bioseries. N . cf. haydeni (Doutkevitch & Khabkov), which is considered to be a subspecies of N. craficulifera (Deprat), and N. cheni Sheng, an advanced member of the N. margaritae phase (Toriyama & Kanmera, 1979), appear towards the top of the zone. Colania also occurs in the upper part of the zone in Facies 4. The faunal assemblages allow a correlation with the upper part of the A. schencki and the N . haydeni zones in the Khao Khao section (Fig. 6), corresponding, in the most part, to the N. maragariiae Zone, late Murgabian, of world correlation . 8. Metadoliolina lepida-Vevbeekina verbeeki Zone (Thickness 4m; uppermost part of Facies 6).
This assemblage dominates the upper part of Facies 6 over a narrow interval. Pseudodoliolina becomes rare, Metadoliolina cf. lepida (Schwager) and Verbeekina verbeeki (Geinitz) more common, the shells of the latter at one horizon being so crowded together so as to form a Verbeekina-bed. The smaller foraminifera Bradyina and Globivalvulina occur in dolomitised algal mats above the Verbeekina horizon. A correlation can be made with a similar horizon of crowded Verbeekina in the V. verbeeki Zone at Khao Imot (Fig. l), west of the present area, described by Ozawa (1970b). There, it occurs together with Colania douvillei (Ozawa). Ozawa (1970b) (Fig 6).
Above the M. lepida-V. verbeeki Zone the carbonates are overlain by siliceous red shales although the boundary is not seen (Fig. 2).
A summary of the Fusuline Assemblage Zones is shown in Fig. 6. The characteristic foraminifera and algae are illustrated in Plates 1-9.

PALAEOECOLOGY
Fusuline foraminifera are abundant and diverse in the algal buildups, shoal and transition zone, and open platform margin environments of Facies 2, where they occur with common Archaeolithoporella, Tubiphytes and a diverse dasycladacean microflora. Algae could have constituted an important food supply as well as providing symbionts to the fusulinid community (Ross, 1974). Abundant schwagerinid, schubertellid, boultonid, staffelld, and some primitive verbeekinoidean species occur in association with encrusting, branching, and tubulate algae forming boundstones, rudstones and grainstones. The dasyclad algae mainly occur in bioclastic packstones. Although the dasycladacean algae are abundant, species diversity varies and this suggests a range from low energy to rather agitated water environments. Dasycladaceans are common in the Sakmarian (Early Permian) within the extended shelf platforms and margin buildups of the TrogkofelLimestone in the Southern Alps and Shakhtau Limestone of Central Asia (Flugel, 1985). Fusulinids appear to have thrived best in shallow warm tropical to subtropical, well oxygenated open marine environments in association with algae.
The advanced schwagerinids with large fusiform, subcylindrical tests, thick walls and fluted septa, may have favoured reef margins, or shoal areas. The minute schubertellids and the verbeekinids seem to have preferred relatively lower energy, transition zone or back reef environments where they occur with encrusting and branch algae. For a more detailed discussion see Dawson & Racey, in press. In the Middle Permian, the environment changed from platform margin algal buildups and open platform to inner platform and protected lagoon, with common bioherms; corals, calcisponges and algae form much of the bioherm framework. Energy levels were lower and lime mud accumulated. This suggests shallowing of the carbonate platform in the Middle Permian. Neoschwagerinids and verbeekinids are diverse and occur with some advanced schwagerinids, whilst smaller fusulinids are less common, being replaced by smaller foraminifera. Dasycladacean algae are common to abundant in the wacke / packstones. The smaller foraminifera1 assemblages are similar to those described by Vachard (1990b) from west Sumatra.
The neoschwagerinids, with their thick porous keriothecal wall, thick septa, septula and parachomata seem to have favoured algal-rich environments and may have used these algae as symbionts (Ross, 1974), in lower energy back reef, inner platform and lagoon environments. In general, the verbeekinids, with their thin wall, short and thin septa and septula and dense parachomata, seem to have thrived in calmer, more protected lagoon and inner platform environments. Afghanella with its thin wall, thin septa, septula seems to have been more adapted to both conditions than the associated Pseudodoliolina and Neoschwagerina. Verbeekina, with its rounded shape, delicate wall and thin, long septa occurs in both low energy wacke/packstones and in intertidal/ supratidal environments (Dawson & Racey, in press). Verbeekina may have had a semipelagic, rather than benthonic sessile lifestyle and was transported into intertidal-supratidal environments by currents.

CONCLUSIONS
The Saraburi Limestone, of the Ratburi Limestone Group from Saraburi, represents a variety of carbonate platform environments including turbidite and slope deposits, platform margin algal buildups, inner platform with patch reefs, protected lagoon, intertidal and supratidal (peritidal). Two regressive sequences, ranging in age from Early Permian (Sakmarian) to early Late Permian (Midian) are recognised.
In the Early Permian (Sakmarian), Archaeolithoporella and Tubiphytes form major carbonate buildups (Dawson et al., in press) resembling those described from the Trogkofel reef (Sakmarian), of the southern Alps (Edwards & Riding, 1988), the Capitan Reef (Guadalupian) of Texas (Toomey & Babcock, 1983), the Wolfcampian Boundstone from west Texas (Wahlman, 1985) and the Late Permian Reef from Sichuan, China (Guo & Riding, 1988). It represents an expanded platform margin liable to wave surges (Toomey & Babcock, 1983). The diversity of dasycladacean algae within these Early Permian buildups of the East Circum-Pacific Realm (Endo, 1969), suggests deposition in a warm, tropical open marine, shelf /platform environment. The high and fluctuating microfloral diversity of this facies is similar to those described from Khao Phlong Phrab by Endo (1969) and to the Sakmarian shelf margin and shelf lagoon of the Trogkofel Limestone, southern Alps and of the Akiyoshi Limestone in Japan (Fliigel, 1985).
In the Early Permian the fusuline fauna shows mixing of Arctic and Tethyan faunas; Robustoschwagerina-Nagatoella-Pseudofusulina assemblages are regarded as Arctic elements Ingavat, 1988), whilst the verbeekinoidean fauna belongs to the Tethyan realm. This suggests that the Tethys seaway was still linked with the Arctic until at least the late Early Permian (Yahtashian). This suggestion is supported by the occurrence of a Permian aulacocerid found in the upper part of Facies 2, which has also been found in Belgium and Greenland (Dawson, 1978b). The disappearance of an Arctic fauna and increasing dominance of a Tethyan fauna, together with the absence of the Misellina-Maklaya-Neoschwagerina bioseries (Figs 5 and 6) during the Bolorian and Kubergandian, supports the idea of a disconformity between Facies 2 and 3 (see Fig. 2). Environmental change thus effected the evolutionary development of the Verbeekinoidea. This period (Yahtashian to Bolorian) coincides with the worldwide marine regression of Vail et al. (1977); see Fig. 6. Ingavat-Helmcke & Helmcke (1986) and Ingavat (1988) suggest that tectonic activity during the late Early Permian caused the disappearance of the Arctic fauna and appearance of a dominantly Tethyan fauna during the Middle Permian; this, in turn, had an effect on the provincialism of the fusuline faunas of central Thailand. Diagenetic fabrics, including meniscus and vadose cements (Dawson, 1978a), support this theory by indicating uplift and resubmergence of the lithified limestone during this time period. This may have been caused by an eustatic sea level fall and/or tectonic activity associated with the Ural Orogeny in the Phetchabun belt during the late Early and early Middle Permian (Yahtashian-Bolorian) (Helmcke, 1984;Helmcke et al., 1985;Ingavat-Helmcke, 1986;Ingavat 1988). This event may have created the disconformity between Facies 2 and 3 in this area. Wielchowsky & Young (1985) also suggest that the distribution of Permian lithofacies in the Phetchabun Fold Belt was largely controlled by eustatic sea level variation and regional tectonic events.
The Conglomerate Formation described by Toriyama & Kanmera (1977) from the Khao Khao section, lies with angular unconformity on the Mid-Permian Presuinutriiia schellwieni Zone. The conglomerate clasts contain a Verbeekina-Pseudodolioliiiu-Chuseizella assemblage of the Khao Khao fauna which is also found in Facies 5 of the present study area. Unconformities in this area are therefore to be expected and are generally only of local significance.
During the Middle Permian, the carbonate platform in this region comprised a rather calm, inner platform lagoon, indicating a shallowing of the platform. Coral, algae and calcisponges form patch reef frameworks and occur with dasycladacean algae and phylloid algal mounds. The Tethyan Verbeekinoidea dominate the fusuline assemblages together with some cosmopolitan species of Parufusuliira and Schzoagerina, and can be correlated with the southern Pamirs, Afghanistan (Vachard, 1990), Turkey, Eastern Europe, Russia, southern China, western Japan , Johore, Malaysia (Igo et al., 1979), west Sumatra and western Kampuchea (Vachard, 1990b).
In the late Murgabian-early Midian a crushed Verbeekiimrich horizon is overlain by dolomitised algal mats and red shales in the uppermost part of the section, suggesting a sea level fall which can be correlated with an early Late Permian marine regression (Fig. 6). The crushed Verbeekim