JOURNAL GEOLOGICAL SOCIETY OF Vol. 26, June 1985, pp. 422 to 425

THE OCCURRENCE OF TRACE FOSSILS IN THE DELHI SUPERGROUP OF NORTHEASTERN

S. P. SINGH 1 AND UTPAL BOSE 2

123 1 Commerce College, Professors' Colony, Chitragupta Nagar, Patna 800020 2 B-16 (A), House, 302001

Abstract Trace fossils of trail markings and burrows are reported from the and Ajabgarh metasediments of the Proterozoic Delhi Supergroup from several localities of northeastern Rajasthan.

Introduction Occurrence of algal stromatolites and probable fucoid markings have been re­ ported earlier from the otherwise unfossiliferous Delhi Supergroup of rocks (Sen and Hore, 1976 : Negi and Ravindra, 1981 ; Verma and Burman, 1981). Dutt and Sri­ vastava (1975) have reported fossil flora from Firozpur Jhirka ridge, Haryana. Singh (1982a, b) has reported trace fossils from the Bayana sub-basin. In the course of recent investigations in the Delhi basin of northeastern Rajas­ than, presence of trace fossils have been recorded at several places. Among these Bhasawar, Sita, Alapuri (in the Bayana sub-basin), Dago, Bairat and Jaipur localities are worth mentioning. Stratigra phy The litho-assemblage of the Delhi Supergroup along with its trace fossil occur­ rences is shown in Table 1.

Description of trace fosS1ts Trail marks: Crawling traces (Fig. 1) or Bairat area have smooth, curved and coiled groove-like forms with about 2 mm depth, 5-8 mm width: and a few tens of centimetres in total length. These traces are sinuous, cross-cutting and overprinted on rippled surface in Jaipur and Bayana areas, They are shallower and shorter in length as compared to those of the Bairat area, but are more densely populated and have comparatively much larger areal extent. Apart from ripples, wrinkle marks and desiccation cracks are also associated with them. Total sediment column con­ taining bioturbated shale layers is more than 40 m near A1apuri in Bayana area. BurJ'ow.~: Burrows of Dago area are normally vertical, of simple type, and have affected only 5-10cm sediment column. The primary sedimentary structures have been totally destroyed and the bedding surface has a mottled look. In Bhasawar area, these structures occur either in the form of grooves and ridges or as shafts and tunnels (Fig. 2) and probably belong to the Thalassinoid genera. Some of these grooves are internally connected and separated on the surface by thin septa. They appear to be the surface manifestation of interpenetrating burrows affecting a sedi­ ment column of about 30cm. Burrow systems consisting of shafts and tunnels show simple as well as branching f,?rms. Most of the shafts are connected by hori~ zontal or indined tunnels. Burrow nucleus and burrow halo (Reineck and Singh, 1975) can be recognized in most of the cases. These structures show medium

0016 -7622/85/26-6-422/$ 1.00 © Geo!. Soc. India. RESEARCH NOTES 423

Figure 1. Rippled Alwar quartzite with crawling traces near Bairat.

Figure~. Ferruginous quartzite showing bioturbation structures south of Bhasa\~ar. 424 RESEARCH NOTES

TABLE I. Stratigraphic Sequence and occurrence of Trace Fossils of the Delhi Supergroup in Northeastern Rajasthan.

Group Formation Lithology Trace fossils

Arauli - Mandhah Carbon phyllite, schist and quartzite Bharkol Quartzite-schist-phyllite- carbon phyllite Thana Ghazi Carbon phyllite-quartzite­ marble-schist. Ajabgarh Seriska/Weir Quartzites with thin bands of Burrows are common in the phyllite, chert-breccia) and ferruginous quartzites to the also tectonic breccia south of Bhasawar. Kushalgarh Impure marble) quartzite­ phyllite-schist calc. schist­ gneiss) amphibole quartzite.

I?ratabgarh/Bayana Massive quartzite) conglome­ and Damdama rates Kankarhi/ Quartzite-phyllite, schist, Trail marks in shale-sandstone­ lBadalgarh marble. sequence around Alapuri. Alwar Rajgarh/Jogipura Feldspathic quartzite-arkose­ Trail marks in quartzite and conglomerate. Thick poly­ phyl1ite near Bairat, Galtaje~ mictic conglomerates. (Jaipur) and Sita. Burrows in quartzite along foot-track leading to the Matajeeka Temple (Dago).

Tehle/Jahaj Lava flows, volcanic breccias, Govindpura agglomerates, tuffs, quartzite, Volcanics phyllite, schist, marble. Raialo Serra te/Qua rtzite Quartzite-schist, conglomerate. Nithar Dogeta Mar ble-q ua rtzl te-phy llite­ schist

Pre·Delhi . Granite and metasediments.

degree of bioturbation with 30-50 per cent destruction of bedding. More bio­ turbated zones are separated by less bioturbated zones and there is upward increase in the degree of bioturbation.

Environmental interpretations The above discussions reveal that two types of lebensspUi are present in the Delhi Supergroup. The first type is trail markings - the crawling trace~ produced by the moving organisms on a soft sediment surface (Singh, ] 982b). The other type is burrows which are produced by dwelling organisms. RESEARCH NOTES 425 Trail markings show similar morphology and· wide coverage in space and time, and so is the case with burrows of the Delhi rocks. And, hence these structures cannot be used for stratigraphic correlation. However, burrow forms and degree of bioturbation can directly be used for palaeoenvirO'nmental interpretation (Seilacher, 1967). Presence of vertical burrows in the W.eir Formation of the Bayana area and Jogipura Formation of the Dago area indicate its intertidal depo­ sitional environment. The medium degree of bioturbation indicates rather slow sedimentation in low energy zone. Change in the degree of bioturbation in a verti­ cal column may be attributed to the fluctuating rate of sedimentation or alterna­ tively it may suggest sedimentation during alternate periods of agitated and quieter environments (Reineck and Singh, 1975). Similar depositional environments have been interpreted from the studies of sedimentary structures and facies assemblages (Singh, 1982b).

References DUTT, G. N. and SHRIVASTAVA, R. N., (1975) Fossil flora in the Alwar Quartzite, pjrozpur Jhirka, Gurgaon district, Haryana. In: Precambrian Geology of the Peninsular Shield, Part 2. Misc. Pub/. Geol. Surv. India, no. 23, pp. 149.156. NEGI, R. S. and Ravindra, R., (1980) On the occurrence of stromatolites in Kushalgarh Forma­ tion of Delhi Supergroup from Baraud, , Rajasthan. Misc. Publ. Geo/. Surv. India, no. 44, pp. 90-95. REINECK, H. E. and SINGH, 1. B., (1975) Depositional Sedimentary Environment. Springer-Ver- lag, Berlin, pp. 439. . SEILACHER, A., (1967) Bathymetry of trace fossils. Marine Geology, v. 5, pp. 413·428. SEN, T. K. and HORE, M. K .. (J976) Investigation for basemetals in Pratabgarh anticline, Alwar and Jaipur districts, Rajasthan. Indian Minerals, v. 30, no. 4, pp. 13-22. STNGH, S. P., (1982a) Stratigraphy of the Delhi Supergroup in the Bayana sub-basin, northeastern Rajasthan. Rec. Geol. Surv. India, v. J J 2, pt. 7, PP. 46-62. -- (I982b) Palaeogeography and sedimentation history of the Delhi Supergroup....,...A study from the Bayana sub-basin (Ph.D. Thesis, the University of Rajasthan). VF.RMA, K. K. and BURMAN, G., (1980) On the discovery of algal stromatolites from Delhi Supergroup, Rajasthan, India. Misc. Publ. Geol. Surv. India, no. 44, pp. 86-89.

(Received: Nov. 23, 1984; Revised/orm accepted: Jan. 7, 1985 )