84 RESEARCH REPORTS Copyright  2002, SEPM (Society for Sedimentary Geology) 0883-1351/01/0017-084/$3.00 Coniform Stromatolites from Geothermal Systems, North Island, New Zealand BRIAN JONES Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada ROBIN W. RENAUT Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada MICHAEL R. ROSEN* Wairakei Research Centre, Institute of Geological and Nuclear Sciences, Wairakei Research Centre, Private Bag 2000, Taupo, New Zealand KEVIN M. ANSDELL Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada PALAIOS, 2002, V. 17, p. 84–103 Coniform stromatolites are found in several sites in the To- kaanu and Whakarewarewa geothermal areas of North Is- land, New Zealand. At Tokaanu, silicification of these stro- matolites is taking place in Kirihoro, a shallow hot spring- fed pool. At Whakarewarewa, subfossil silicified coniform stromatolites are found on the floor of ‘‘Waikite Pool’’ on the discharge apron below Waikite Geyser, and in an old sinter succession at Te Anarata. The microbes in the coniform stromatolites from Tokaanu, Waikite Pool, and Te Anarata have been well preserved through rapid silicification. Nev- ertheless, subtle differences in the silicification style in- duced morphological variations that commonly mask or al- ter morphological features needed for identification of the microbes in terms of extant taxa. The coniform stromatolites in the New Zealand hot- spring pools are distinctive because (1) they are formed of upward tapering (i.e., conical) columns, (2) neighboring col- umns commonly are linked by vertical sheets or bridges, (3) internally, they are formed of alternating high- and low-po- rosity laminae that have a conical vertical profile, and (4) Phormidium form more than 90% of the biota. As such, they are comparable to modern coniform mats and stromatolites found in the geothermal systems of Yellowstone National Park and ice-covered lakes in Antarctica. Formation of the coniform stromatolites is restricted to pools that are characterized by low current energy and a microflora that is dominated by Phormidium. These deli- cate and intricate stromatolites could not form in areas characterized by fast flowing water or a diverse microflora. Thus, it appears that the distribution of these distinctive stromatolites is controlled by biological constraints that are superimposed on environmental needs. INTRODUCTION Fossil coniform stromatolites, commonly termed Cono- phyton, have attracted much attention because of their * Present Address: Nevada Basin and Range Study Unit, US Geolog- ical Survey, 333 W. Nye Lane, Carson City NV 89706 abundance in Precambrian (especially Proterozoic) sedi- mentary rocks wherein they may form large mounds sev- eral meters high (Walter, 1983). In contrast, modern coni- form stromatolites are rare. They have, however, been re- corded from settings that range from the hot-spring sys- tems of Yellowstone National Park (e.g., Walter et al., 1976; Brock, 1978; Farmer et al., 1997) to ice-covered lakes of Antarctica (Love et al., 1983; Wharton, 1994). These dis- tinctive stromatolites are characterized by their conical external morphology, their nested, conical internal lami- nations with upward-pointing apices, vertical ridges or bridges that connect neighboring columns and, in recent examples, their Phormidium-dominated microbial popu- lations (Walter et al., 1976; Brock, 1978; Love et al., 1983; Wharton, 1994; Farmer et al., 1997). This paper focuses on coniform stromatolites found in parts of the Tokaanu and Whakarewarewa geothermal systems in the Taupo Volcanic Zone on the North Island of New Zealand (Fig. 1). At Tokaanu, these stromatolites are being actively silicified in Kirihoro hot pool (Fig. 2; Table 1). In the Whakarewarewa geothermal area (Fig. 3), coni- form stromatolites are present on the floor of an artificial pool (informally named here ‘‘Waikite Pool’’) on the dis- charge apron below Waikite Geyser. These stromatolites are less than 100 years old. Other examples in a subfossil sinter succession at Te Anarata (Fig. 3) lie  4 m above an alluvial deposit of reworked ignimbrite and tephra (Orua- nui Formation) that is  22,500 years old (Ashley Cody, pers. commun., 2000). The coniform stromatolites from New Zealand are de- scribed in terms of (1) their morphology, (2) their microbial components, and (3) the preservation style of the mi- crobes. This information is then used to explore the specif- ic factors that may control the distribution and develop- ment of coniform stromatolites in the hot-spring systems of New Zealand. The New Zealand coniform stromatolites are then compared to similar coniform mats and stromat- olites elsewhere in the world in order to explore the possi- bility that they grow under similar environmental and bi- ological constraints despite disparate geographic loca- tions. Finally, following the lead of Walter et al. (1976), we