Abstract The geology of lake basins was a popular subject in the 19th century, fired by interest in the discoveries during the exploration of the American west. This book builds on the experience of an international group of limnogeology enthusiasts. The science of limnogeology is of importance to petroleum geology. Although not every limnic deposit is an exploration target, a comprehensive understanding of diverse lacustrine environments of deposition can help exploration strategies. The volume presents 60 new basin summaries, a few of which are Mongolia, southeastern Kazakhstan, southern Scotland, northwest China, the U.S. southwest, southern France, northeastern Spain, central Italy, and northwestern Mexico.

Abstract Rocks associated with lakes probably account for more than 20% of current worldwide hydrocarbon production (Kulke, 1995;Calhoun, 1999),and lacustrine organic-rich rocks are significant sources of these hydrocarbons. Lacus-trine sources and reservoirs are important in many areas of current and future exploration opportunities: Africa, South America, southeast Asia, China ( Hedberg, 1968;Powell, 1986;Smith, 1990;Katz, 1995). The years since the last AAPG lake Memoir (Katz,1990) have seen both an expansion of work on modern and ancient lake systems and a focusing on their hydrocarbon potential. Through the efforts of individual workers and teams in academia and industry, along with collaborative efforts (e.g. ,IGCP-GLOPALS, International Association of Limnogeology),we have significantly increased our knowledge of lake systems on two fronts: key processes and sedimentary response-record(e.g., Anadon et al., 1991;Gierlowski-Kordesch and Kelts,1994; Katz, 1995). Particularly enlightening have been the increase in (1)basin-scale studies of ancient systems that integrate stratigraphy, sedimentology, biofacies, and inorganic and organic geochemistry, (2) the use of reflection seismic data to gain large-scale 3-D perspectives on basin-fill history, (3) studies by petroleum-industry scientists that benefit from this large-scale perspective and physical, chemical, and biological processes and responses, and (4) studies of modern lakes and closely associated Quaternary deposits focused on key elements of sediment delivery and dispersal, organic production and preservation, and temporal evolution of lake hydrology (again aided by seismic-scale perspective, especially in east Africa) (e.g., Johnson et al., 1987;Scholz, 1995). Analytical advances and a broader experience base integrated into geological context have also contributed; geochemists have better tools for difficultnonmarine organic-matter mixtures

Abstract The Mongolian People's Republic in central Asia(frequently called Mongolia, but often referred to in the past as Outer Mongolia in English language literature)encompasses some 2 million km2 of steppe, desert, and mountains. Knowledge and understanding of Mongolian geology is limited, and in particular very little is known outside of Mongolia and Russia. The purpose of this paper is to highlight the development of lake basins, lakes, and lacustrine sequences during the geologic evolution of Mongolia and thereby stimulate further interest and research. Many characteristic features and apparent key controls on lake basin and lacustrine sequence development are described. Lake sediment scan be identified in all geologic periods from the Carboniferous to Quaternary. Collectively, they include examples of all the principal types of tectonically formed lake basins and lacustrine depositional environments. The geology of Mongolia is not known in any detail in western literature, partly due to the country's remoteness and inaccessibility. Pioneering work reported by Berkey and Morris (1927) remains the single most important source of documentation in the English language. Following the changes in Mongolia and the former Soviet Union during the late 1980s,geoscientists can now access the remotest areas of the country. Mongolian and Soviet surface geology maps, made from the 1950s onward, are a key source of data. Most of the stratigraphic units and nomenclature in this paper are based on these maps. The maps, most of which are not officially published, do notably contain some inconsistencies in the use of terms such as "early" vs. "lower"

Abstract The Ili basin (Figures 1 and 2) is one of the smaller Cenozoic successor basins associated with the Tien Shan ranges of southeastern Kazakhstan and western China (Allen et al., 1991; Graham et al., 1993). Nonmarine Cenozoic strata deposited in the IIi basin are best exposed at and around Aktau Mountain in the southern foothills of the Dzhungarian Alatau of southeastern Kazakhstan (Figures 1 and 2). The Cenozoic section exposed at Aktau Mountain is about 2.5 kmthick and mostly of Neogene age (e.g., Lavrov and Rayushkina, 1983); however, the lower third of this section has yielded fossil mammals of late Eocene, late Oligocene, and early Miocene age (e.g., Russell and Zhai, 1987; Abdrakhmanova et al., 1989; Tleuberdinaet al., 1993). The Aktau Mountain section preserves sedimentary rocks deposited in an array of lacustrine and fluvial environments. Here, we present a preliminary overview of these strata, including their lithostratigraphy, paleontology, and depositional systems.

Abstract During the Late Carboniferous to Early Permian, a large lowland desert developed over the whole of southern Scotland. Several desert basins were eroded into softer Carboniferous sediments preserved in post depositional grabens within the lower Paleozoic Southern Uplands massif (Figure 1) (Brookfield, 1978, 1980; Glennie,1982). Early Permian eruptions of basaltic lavas occurred in the Thornhill basin where they were accompanied by pediment formation and the deposition of thin pediment and desert floor stream and lake sediments. These interfinger with, and are overlain by, thick eolian sands. Northwesterly directed faulting then formed the isolated grabens of the Moffat, Lochmaben, and Dumfriesbasins to the south and east. In these grabens, marginal alluvial fan sequences are dominated by immature streamflood and sheetflood breccias and sandstones with interbedded eolian sandstones that pass basinwardinto massive dune sandstones. Depositional facies are those of very arid intermontane basins summarizedin Figure 2 (Brookfield, 1980;Nilsen 1982). The fan deposits have angular, poorly sorted clasts and often contain abundant well-rounded, reworked, coarse eolian sand and reworked ventifacts derived from the fan surfaces. Silt and clay are rare and probably were mostly removed by the wind; nevertheless ,rare silt and clay beds are occasionally interbedded with the pediment, alluvial fan, and eolian deposits. These fine-grained sediments were deposits inephemeral ponds and lakes and provide additional data on paleoenvironments. Such deposits are rarelydescribed from sections of ancient arid desert deposits because the most impressive units are the alluvial and eolian deposits (cf. Brookfield, 1984).The purpose of this paper is to record the facies

Abstract The Southern Permian basin of central Europe (Figure1) was superimposed on the Late Carboniferous Variscan foredeep. This elongated depocenter comprises several interconnected en echelon sub-basins (Silverpit/Dutch, North German, and Polish basins),where maximum thicknesses of >2000 m of German Rotliegende red beds and halites coincide with areas of Late Carboniferous-Early Permian volcanism(Ziegler, 1982, 1988). Superimposed on regional thermal subsidence, a post-Variscan dextral shear system is widely recognized, inferred from basin subsidencepatterns (Ziegler, 1990). Early Permian extrusive magmatism, located mainly at intersections of fault systems, resulted from deep crustal fracturing (Plein,1978). Related to this magmatic event, Early Permian thermal uplift apparently caused rifting and a regional stratigraphic hiatus generally referred to as the Saalian unconformity. After magmatic activity hadterminated, the central portions of this future SouthernPermian basin began to subside thermally and Rotliegende deposition was initiated within grabensystems (Drong et al., 1982; Gast, 1988). Acceleratedthermal subsidence during the Late Permian wasaccompanied with an increasing depositional area, sedimentation on lapping, and overstepping of the southern and western margins of the large basin. With a basin floor that was below global sea level, rapid flooding of this large intracontinental closed basin occurred during the Zechstein marine transgression(Glennie and Buller, 1983). Both biostratigraphy (Schneider, 1988; Hoffmannand Kamps, 1989;Gebhardt et al., 1991;Gebhardt, 1988,1994; Gebhardt and Plein, 1995; Schneider et al., 1995)and magnetostratigraphy (Lutzner and Menning, 1980;Menning, 1986, 1994; Menning et al., 1988) indicate a Tatarian age for the upper Rotliegende (Figure 2) of the North German basin (NGB), designated as the centralpart of the Southern Permian

Abstract The separation of South America from Africa during the Early Cretaceous isolated equivalent stratigraphic sequences on both continents. This is well established for rock sequences, including flood basalts, which were deposited prior to oceanic onset; however, earlier extensional events are also recorded by the resulting intracontinental basins. Of these, the depositional area containing the Late Permian-earliest Triassic Gai-As Lake is a prime example. The aims of this paper are (1) to record facies generated within and outside the lake body and (2) to compare them with correlative bodies on the other side of the present-day South Atlantic Ocean, and (3) to record the controls of fault structures on facies architecture and lake margins. The advantages of good exposures produced by river dissection of the continental margin in northern Namibia allows good access for identifying synsedimentary fault controls on theGai-As Lake. We suggest that these can be extrapolated to correlative sequences at the conjugate South American side where exposure and thus the potential for recognition of synsedimentary structural activity is limited; consequently, the Parana "basin," commonly dealt with as an intracratonic sag basin, may be underlain by a complex of stacked rift and thermal subsidence-controlled depositional centers.

Abstract The Junggar basin is one of the most important oil producingareas in China. It is located in the northern part of Xinjiang Province and occupies an area of about140,000 km-, Commercial production comes mainly from the giant Karamay and associated oil fields at the northwest margin of the basin (Figure 1). Extensive exploration since 1980 has resulted in a series of new discoveries in other regions of the basin. The purpose of this paper is to document the lacustrine deposits of the Upper Permian Pingdiquan Formation in the eastern Junggar basin, which serves as both source and reservoir for the Huoshaoshan oil field (Figure 1). In the eastern part of Junggar basin, the thrust faulted Kelameili mountains are composed of Devonian and Carboniferous volcanic rocks plus derivativevolcaniclastic sedimentary rocks (Carroll et al., 1990).To the southwest, Permian and Mesozoic strata are exposed, forming several broad, gentle anticlines and synclines. Quaternary sands and gravels compose the dry river channels derived from the foothills of Kelameili. Zou (1984) first reported on the fan-deltadeposits of Pingdiquan Formation. In 1986/ ZhaoXiafei, together with his students, describedand measuredtwo lithologic sections in outcrop (Figure 2). At the same time, we did seismic stratigraphic studies toreveal the subsurface features of the Pingdiquan Formation.Liu and Zhao (1992) discussed the gravelly fandelta of Figure 2a and Wang et al. (1992) published the microfacies of the six producing horizons of the Pingdiquan Formation in the Huoshaoshan oil field. This paper documents the sedimentary paleo environment of the formation and examines the delta

Abstract Permian deposits of the Junggar and Turpan-Hamibasins of the Xinjiang Uygur Autonomous Region of northwest China preserve some of the thickest and mostareally extensive lake strata on Earth. In the south Junggar depocenter, these nonmarine deposits are up to 5 kmthick and organic-rich facies rank among the thickestand richest petroleum source rocks in the world (Grahamet al., 1990; Lawrence, 1990; Demaison and Huizinga, 1991;Carroll et al., 1992).In addition, Permianlacustrine deposits are estimated to span 1000km along strike, indicating that widespread lakes represented amajor paleogeographic feature of central Asia (Figure 1).Unfortunately, the remote location of these deposits has hindered detailed studies, and the western literature contains only sparse reference to this important record of continental sedimentation. The purpose of this paperis to briefly review the Permian nonmarine stratigraphyand report on recent field-based studies documentingthe Permian lacustrine stratigraphy exposed along the north and south flanks of the Bogda Shan (Figure 2).

Abstract The Tanzhuang Formation represents the uppermost Triassic unit in the Iiyuan-Yima basin. It is well exposed southwest of Jiyuan City, western HenanProvince, central China (Figure 1). The Jiyuan-Yimabasin, which is part of the Ordos megabasin, containsabout 1500 m of Middle Triassic-Middle Jurassic continentalsediments. This basin is divided into two subbasins, Jiyuan and Yima, located north and southof the Yellow River, respectively. Stratigraphy and paleontologic content of the deposits have beensummarized by Zhou and Li (1980), Kang et a1.(1984, 1985), and Hu (1991) (Figure 2). Sedimentologic and stratigraphic evidence suggest that Jurassic sedimentation took place in a pull-apart basin(Buatois et aI., 1994a, this volume); however, the Triassictectonic framework is still poorly understood.Triassic deposits of the northern Jiyuan area andsouthern Yima area show significant changes in facies associations. These facies variations may have resulted from asymmetry of the basin. Triassic lacustrine sediments were most likely developed within apost-collisional intracratonic downwarp basin that formed as a result of early Indo-Sinian tectonic movements during the Middle Triassic. Strike-slip tectonismoccurred in the study area coincident with the Triassic-Jurassic boundary (cf. Wang, 1985; Manganoet aI., 1994; Buatois et aI., 1994a).

Abstract The occurrence and distribution of Early and MiddleJurassic lake systems in northwest China (Figure 1)are poorly represented in the lacustrine literature. This is surprising because lacustrine environments would appear to have flourished in this geologic setting: intracontinental foreland-style, internally drained basins, with rapid, periodic basin floor subsidence,and a thriving humid climate supplying abundant fresh water into the many available basins. Although the Chinese literature reports mostly coaly, swamp/marsh, fluvial/ alluvial, fan delta, deltaic, and marginallacustrine environments for Lower and Middle Jurassic strata, the areal extent and descriptive sedimentology of the lacustrine systems are virtually unknown (Wang et al., 1994; Qiu et al., 1997;Wu and Zhao, 1997;Wu et al., 1997). This study will briefly describe one of the many Middle Jurassic lacustrine systems contained within northwest China: the Qiketai Formation (J2q) of the Turpan-Hami basin (Figures 1-3). Based on measured outcrop stratigraphic sections, detailed borehole core descriptions, and well log data, Qiketai Formation141deposits covered an area of nearly 300 km x 40 km along depositional strike and dip, respectively (Figure4). Facies represent littoral to profundal freshwater to saline lacustrine and lake-plain environments and reach a maximum thickness of 250 m in the basin center(Figure 4). The finer grained facies are organic-rich,ranging from 2 to 21% total organic carbon (TOe),with hydrogen indices (HI) reaching 811 mg hydrocarbons/gram rock (Table 1). The data presented here represent the first documentation of this large lake system outside the Chinese literature, and emphasize the importance of future detailed studies of Jurassic lake deposystems throughout northwest China.

Abstract One of the most distinctive Jurassic lithostratigraphic units in the American Southwest is the Todilto Formation of northern New Mexico and southwestern Colorado (Figure 1). This relatively thin (>75 m) unit is mostly carbonates and evaporates in a thick section otherwise dominated by siliciclastic eolianites (Figures 2, 3). The To dilto Formation is extremely significant economically as a source rock for petroleum (Vincelette and Chittum, 1981)and uranium (Chenoweth, 1985); it also provides all the gypsum mined in New Mexico (Weber and Kottlowski,1959).Some earlier workers regarded the Todilto as having been deposited in a marine embayment of the Middle Jurassic Curtis seaway (e.g., Harshbarger etal., 1957; Ridgley and Goldhaber, 1983), but morerecent studies of stratigraphy, paleontology, and geochemistry indicate that any marine connection tothe Todilto Basin was short-lived or intermittent(Lucas et al., 1985; Kirkland et al., 1995). Todilto deposition took place in a paralic salina culminated by a gypsiferous evaporitic lake.

Abstract The Fundy rift basin, comprising the contiguous Minas, Fundy, and Chignecto structural subbasins (Figure 1), is filled by terrestrial redbed siliciclastics, minor carbonates, and tho leiitic basalts of the Fundy Group, Newark Super group. The Minas subbasinis a shallow transtensional basin formed by left-oblique slip (Olsen and Schlische, 1990) on there activated Minas fault zone, a transform along which the Meguma and Avalon terranes were superimposed during the late Paleozoic. Outcrops of Fundy Group strata occur almost exclusively asseacliffs along the shores of the Bay of Fundy. In the Minas subbasin, a maximum of approximately 1 km of Fundy Group section is exposed along the northern and southern shores of the geographic Minas Basin and the eastern side of the Blomidon Peninsula(Figure 1). The Fundy and Chignec to subbasins are simplehalf-grabens formed when regional extension caused reactivation of Paleozoic thrusts as southeast dipping normal faults with displacement locally exceeding 10 km (With jack et al., 1995).Fundy Group strata are exposed along the Nova Scotia shore of the Bay of Fundy, forming the Fundy subbasin margin. A rider block along the faulted northwestern margin of the Fundy sub basinat Point Lepreau in New Brunswick exposes nearly2.5 km of strata. Over 3.5 km of Mesozoic strata were penetrated in the Chinampas N-37 well (Figure1) drilled offshore in the Fundy subbasin, and interpretation of seismic data suggests that thethickness of the Mesozoic section may exceed 8k min the Fundy subbasin depocenter (Brown and Grantham, 1992; Wade et al., 1996). The Chignectosubbasin is bounded to

Abstract The lake sediments are preserved as two separate layers interleaved with Early Jurassic Kalkrand flood basalts (Duncan et al., 1984; Cerschutz, 1996) and are best exposed around Hardap reservoir, 15 km north of Mariental town in southwestern Namibia (Figure1). The 55-300 m thick volcano-sedimentary sequenceun conformably oversteps underlying Triassic(Stormberg) and latest Carboniferous-Early Permian(Dwyka and Ecca) sediments in the east onto latest Proterozoic-Early Cambrian (Nama) basement toward the west (Heath, 1972; Schalk and Germs,1980). The top of the sequence is defined by the erosive Cretaceous land surface with continental sediments of the Cenozoic Kalahari thermal sag basin draped thinly over the top. The 183.0 0.6 Ma to 186.0 0.8 Ma dated olivine-tholeiitic basalts (Duncanet al., 1997) of the Kalkrand Formation were extruded during extensional rifting between South America and Africa (Miller, 1992; Dingle, 1993). This was one of a series of early rifting episodes from the Permian onward (Figure 2) prior to ultimate extensional rift phases during the Early Cretaceous. The latter caused extrusion of the Etendeka-Parana flood basalts and onset of South Atlantic oceanic opening(Hawkesworth et al., 1992; Renne et al., 1996; Gladczenkoet al., 1997). Extensional tectonism was experienced in the study area along a northerly trending set of extensional167faults dipping toward the east. This is inferred (Stollhofenet al., 1998) to be conjugate to a westerly dipping break-away detachment system that connected with the more major detachment toward the west,along which oceanic opening was eventually effected(Maslanyj et al., 1992; Light et al., 1992, 1993).The Hardap area is therefore characterized by

Abstract Siliciclastic- and carbonate-dominated lacustrine systems are present within the Morrison Formation (Upper Jurassic), Western Interior basin, U.S.A. The siliciclastic dominated systems, common on the Colorado Plateau ,have been studied intensely in association with the extensive Lake T' 00'dichi' complex, an alkaline-salinelake in the Brushy Basin Member of the Morrison Formation(Bell, 1983, 1986; Peterson and Turner-Peterson,1987; Turner and Fishman, 1991). Conversely, the carbonate-dominated lacustrine systems prevalent in east central Colorado, New Mexico, Kansas, and Wyoming have received limited attention (Frazier et al., 1983;Sweet 1984; Lockley et al., 1986; Sweet and Donovan,1988; Johnson, 1991), with few regional-scale and even fewer detailed sediment logic and stratigraphic investigations(exceptions include West, 1978; Jackson, 1979;Dunagan et al., 1996, 1997; Dunagan, 1997, 1998). This study describes the initial results of a systematic, regional scale investigation of lacustrine carbonate deposits in the Morrison Formation focusing on the well-developed lacustrine complex in east-central Colorado, which willultimately provide important insights into one of the most poorly understood depositional environments in the Morrison paleoeco system. Detailed results are forthcoming in other publications.

Abstract The Lower Jurassic Anyao Formation crops out southwest of Jiyuan city, western Henan Province, central China (Figure 1). It represents part of the infill of the Late Triassic-Middle Jurassic [iyuan-Yima Basin, which hosts more than 2000 m of non marine sedimentary rocks. The east-west Yellow River fault separates the northern Jiyuan sub-basin from the southern Yimasub-basin. Jurassic sedimentation is thought to represent deposition in a pull-apart basin. This type of sedimentary basin is common in many different areas of China (Hsu, 1989; Lin et a1., 1991). The Jiyuan-YimaBasin is characterized by an asymmetric fill, a limited lateral extent, and extreme lateral facies changes, as well as coal seams and oil reservoirs. Data for the[iyuan-Yima Basin come from both outcrops and boreholes. Stratigraphy of the Jurassic units of the [iyuan Yima Basin was summarized by Zhou and Li (1980)/Kang et a1. (1984/ 1985)/ and Hu (1991). In particular, the sedimentology and ichnology of the Anyao Formation were previously discussed by Wu (1985). The Anyao Formation is about 100 m thick and consists of light greenish-grey, medium to very fine grained sandstones and mudstones (Figure 2). Thelower part of the formation is well-exposed southwest of [iyuan city, but the upper part is covered in mostplaces. The Anyao Formation overlies the Triassic Tanzhuang Formation, which consists of fluvial andshallow lacustrine deposits (Mangano et a1., 1994) an dis overlain by the Middle Jurassic Yangshuzhuang Formation of deltaic origin. The Jurassic succession culminates with alluvial deposits of the Mawa Formation.The age of the Anyao Formation is

Abstract During the Late Jurassic and Early Cretaceous, a series of aborted extensional rift basins developed in northeastern Brazil as a consequence of the separation of South America and Africa. This basin series occursin a southwest-northeast-trending depression (Figure1)/ called the Araripe-Potiguar Depression (Mabesoone,1994). From southwest to northeast, these basins are the Araripe, composed of two fault-limited depressions; the Rio do Peixe with three subbasins; Iguatu-Ico with four sub basins; and the onshorePotiguar or Pendencia graben composed of three depressions, as well as a number of intermediate smalleroutcrops. Table 1 presents the stratigraphy of the basin fill for this series of basins; two extensive lacustrinephases are recorded: one in the latest Jurassic-Barremian and the other in the late Aptian-early Albian. During the first phase (latest Jurassic-Barremian), a chiefly finegrained section accumulated during rather humid climate sin a slowly subsiding area. Record of the second phase (late Aptian-early Albian) is only found in the Araripe Basin, represented by laminated limestones and shales deposited under fairly dry climatic conditions. This latter sequence is extremely rich in fossils(Viana et al., 1994).

Abstract Hydrocarbon exploration in rift basins increased during the 1980s mainly because of (1) the recognition of lacustrine shales as good source rocks and (2) notable exploration successes (Begawan and Lambiase, 1995).Petroleum production from rift basins is particularly important for Brazil (Bruhn et a1., 1988), Indonesia(Williams and Eubank, 1995), and China (Desheng,1995) and for African margins. In addition to good source rocks, rift basins commonly contain sandy reservoirs including turbidites, deltaic, and fluvial types. A typical vertical succession for nonmarine rift basins includes basal syn-rift lacustrine strata overlain by deltaic deposits, then fluvial sediments. Basin fill follows from the interplay between tectonics and short-term climatic fluctuations (Cohen, 1990; da Silva,1993; Lambiase and Bosworth, 1995; and others).These two mechanisms control important parameter sregulating basin evolution like basin-floor subsiden cerates, main sediment entry points, and lake level fluctuations. Cohen (1990) recognized three typical associations of margins and drainage zones for rift basins: (1) flexural or shoaling margin, related to more stable, low subsiden ceareas, (2) axial margin, running parallel to the main elongation of the rift basin (usually) draining axial depocenters ,and (3)escarpment margin, related to the a symmetry of the main fault system. Generally, shoaling and axial margins deliver a higher sediment load. During early rifting, subsidence rates may overcome sediment input and starve the rift basin of coarse-grainedsediments. If climate is adequately wet, a perennial lake209may develop. During early phases, main rivers may be impounded behind structural barriers with coarsegrained sediments derived from the uplifted foot wall region and/or from elevated

Abstract Lower Cretaceous lacustrine basins occur rather continuously along about 3500 km (from Pelotas to Sergipe-Alagoas Basins) of the eastern Brazilian margin(Figure 1). Because these basins accumulated large volumes of organic-carbon-rich sediments, they form source rocks for much of the Brazilian oil discovered to date. Economic and scientific interest in these lacustrine basins has resulted in numerous publications(e.g., Ponte and Asmus, 1978; Ojeda, 1982; Estrella etal., 1984; Bertani and Carozzi, 1985; Baumgarten et al.,1988; Guardado et al., 1989; Van der Ven et al., 1989;Aquino and Lana, 1990; Cupertino, 1990; Mello and Maxwell, 1990; Santos and Braga, 1990; Castro, 1992;Horschutz and Scuta, 1992; Mato et al., 1992; Rangel etal., 1993a, b; Caixeta et al., 1994; Dias et al., 1994; Feijo,1994a, b; Pereira and Feijo, 1994; Rangel et al., 1994a, b;Santos et al., 1994; Teixeira Net to et al., 1994; Vieira etal., 1994; da Silva et al., this volume). Several of these studies have attempted comparative syntheses. They emphasize differences in each basin system dependent on the tectonic evolution. For example, continental breakup is accompanied bybasaltic extrusions during initial stages of rifting, such as in the Campos Basin (Rangel et al., 1994a, b), orbasins may lack basaltic extrusions, such as in the Reconcavo Basin. Based on tectonic evolution, the eastern Brazilian Atlantic margin can be organizedinto basically two types of rift lake environments: (1)deep-water lakes, in which tectonism outpaced sedimentation,with the Reconcavo Basin, northeastern Brazil, for example, and (2) shallow water lakes in which tectonism and sedimentation maintain a balanced pace, such as in