Submarine fan and channel levee deposits in the Lower Cretaceous Bogota trough, Colombian Andes

Sedimentary Geology, 86 (1993) 229-246

229

Elsevier Science Publishers B.V., Amsterdam

Submarine fan and channel levee deposits in the Lower Cretaceous Bogota trough, Colombian Andes Christo Pimpirev

a, Gustavo Sarmiento

b

a Sofia University, Department of Geology, 15 Ruski btd, Sofia 1000, Bulgaria b Ingeominas, Diagonal 53, No. 34-53, Bogota, Colombia Received November 11, 1991; revised version accepted October 27, 1992

ABSTRACT

Pimpirev, C. and Sarmiento, G., 1993. Submarine fan and Channel level deposits in the Lower Cretaceous Bogota trough, Colombian Andes. Sediment. Geol., 86: 229-246. Bogota trough in the Cordillera Oriental of Colombia was an elongate N E / S W oriented Lower Cretaceous basin. It was one of the main depocentres in the northern Andes during earliest Cretaceous time. Six lithofacies and three facies associations are recognised, based on four detailed stratigraphic sections situated in the western portion of the trough. Sedimentation in the basin comprised channel levee, fan lobe and outer fan-basin plain (?) depositional environments. Channel-levee complexes without a well-developed fan-growth pattern were more proximal to the sediment supply. In more distal settings, the migrating channels evolved into suprafan lobes. Their sediments were covered by outer fan-basin plain (?) deposits at a time of retrogradation of the fan system. The evolution in the basin continued with progradation and development of depositional lobes and channel-fill middle fan environments. The western portion of the trough was situated near to the zone of convergence between the Nazca and the South American plates and the main sediment supply derived from the Paleo-central Cordillera, which in early Cretaceous time consisted of an uplifted Jurassic plutonic arc. This active margin defined the coexistence of small sand-rich radial fans and channel-levee complexes. In the eastern portion of the basin main source area, the stable Guayana shield determined the existence of a larger fan system of a hybrid type between radial and elongate fans. Despite the differences between the two fan systems in eastern and western portions of the trough, the observed retrogradational and progradational sequences are similar.

Introduction

Bogota trough in the Cordillera Oriental of Colombia and Uribante trough in the Merida Andes of Venezuela were the main depocentres during the Lower Cretaceous in the northern Andes of South America (Fig. 1). Shallow-water genesis is supposed for the sedimentation in Uribante trough (Renz, 1959; Fabre, 1985; Macellari, 1988), while the sediments in Bogota trough are predominantly turbidites (Campbell, 1962; Thompson, 1966; Villamil, 1988, 1990; Moreno, 1991a, b; Pimpirev et al., 1992). A sub-

Correspondence to: Christo Pimpirev, Sofia University, Department of Geology, 15 Ruski bul, Sofia 1000, Bulgaria.

marine fan model is proposed for the sedimentation in the eastern part of the trough (Pimpirev et al., 1992), while the data for the depositional environments in the western part are very scarce. For that reason the sedimentological observations in this paper are concentrated on the western part of the Bogota area where Moreno (1991a, b) divided the rocks in the base of Lower Cretaceous into two lithostratigraphic units: Murca Formation (formal) and Utica Sandstone (informal) (Fig. 2). Without detailed sedimentological investigations he suggested that the sedimentation of the Murca Formation took place in a submarine fan environment and the Utica Sandstone was deposited in shallow-marine conditions. The last opinion does not correspond to the conclusions of Villamil (1988, 1990) who per-

0037-0738/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved

230

(:. P I M P I R E V A N D G. S A R M I E N T O

suasively shows that the terrigenous rocks with shallow-marine bivalves of the Utica Sandstone were formed by turbidity flows. The aims of the present study were to undertake detailed palaeontological (G.S.) and sedimentological (C.P.) observations in the Murca Formation and the Utica Sandstone, as well as to unravel the depositional environments of the Lower Cretaceous turbidites in the Cordillera Oriental (C.P.), and to introduce a new palaeogeographic model for the geological evolution in Bogota trough during earliest Cretaceous time as an ancient example of complex, coexisting turbidite systems dependent on different source areas (C.P.). Geological setting

The study area is located about 100 km northwest of Bogota in the western central part of the

Cordillera Oriental of Colombia (Fig. 2). In four stratigraphic sections nine details were chosen for defining the different lithofacies and their relationships in the facies associations (Figs• 3-6). The section Utica-Tobia is located along the railroad between the villages of Utica and Tobia in the core of the Utica anticline (Figs. 2 and 3). The section La Magdalena-Villeta begins 500 m east of La Magdalena village on the scarp of the road to Villeta (Figs• 2 and 4). The rock sequence corresponded to the upper part of the section Utica-Tobia. The section T o b i a - L a Vega is located 6 km north of Villeta along the new road to the village of La Vega in the Caquero area (Figs. 2 and 5). The section P a c h o - L a Palma begins 25 km northwest of the village of Pacho at the confluence of the Murca river and the Rio Negro and continues along the road to the Village of La Palma (Figs. 2 and 6). It cuts through the core and the west limb of the Murca anticline. The I ?~O

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Fig. 2. Generalized geological map of the study area showing location of measured sections (after Suarez, 1991).

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stone (Alto de Caqueza Formation), the upper Formation of the Caqueza Group (Burgl, 1961; Thompson, 1966; Gallo, 1977; Acosta and Obando, 1984; Ulloa, 1988). Moreno (1991a, b) defined the Utica Sandstone as an informal lithostratigraphic unit and we prefer to use this name, but this unit is related to the Caqueza Group. The Utica Sandstone consists of thick packets of pebbly and coarse sandstones often with coquina lenses, interbedded with mudstones, siltstones and fine-grained sandstones. Moreno (1991b) characterizes petrographically the sandstones as arkosic wackes. In our paper detailed stratigraphic sections and sedimentological observations of these sediments are shown in (Figs. 3 and 4). The Utica Sandstone is dated as ranging

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from the Tithonian to the Hauterivian according to Thompson (1966), Gallo (1977), Villamil (1988) and Moreno (199]a). Murca Formation. This lithostratigraphic unit was formally defined by Moreno (1991a). He set the type section along the road Pacho-La Palma. It consists of an about 800-m thick sequence of alternating packets of sandstones and mudstones with variable thickness and common turbidite origin. According to Moreno (1991b) the sandstones are lithograywackes and arkosic wackes. In our paper we present detailed stratigraphic sections and facies analyses of the whole formation (Fig. 6). The stratigraphic section Villeta-La Vega reveals a sequence with similar sedimentological characteristics as the type section, but with some

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Lower Cretaceous rocks cropping out at the Utica-Tobia and the La Magdalena-Villeta sections belong to the Utica Sandstone, an informal lithostratigraphic unit proposed by Moreno (1991a). The sediments building up the Tobia-La

Vega and the Pacho-La Palma sections correspond to the Murca Formation, defined by Moreno (1991a). Utica Sandstone. In previous works Utica Sandstone was referred to as the Caqueza Sand-

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Fig. 5. (a) Stratigraphic section along the road Tobia and La Vega, Murca Formation (?). (b) Details o f subassociation lB. (c) Detail of subassociation IIA. (d) Detail of association llI.

massive sandstones

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Chaotic deposits

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A

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Dominant in middle fan mouth channel and outer fan lobe Dominant in outer fan

Remaining in middle fan braided channel and middle fan mouth channel

Normally graded channeled bases Channeled, erosional bases, structureless, dish and flame structures Graded, parallel and crosslamination, complete or partial Bouma division Bouma sequence with base missing, ripples, flaser Slump structures

Very thick, thick, massive amalgamated

laterally

Thick

Thick, medium, continuous

Very thin, laminae, lenticular or irregular and flaser Coherent and contorted

Pebbly sand

Coarse to medium sand

Fine to medium sand, mud

Fine, very fine sand, silt, mud

Medium, fine sand, mud

D2 E

A

Muttiand Ricci Lucchi (1972, 1975)

Facies association

Dominant in inner fan

Features

Disorganized organized erosional bases

Boulder, cobble and pebbly conglomerates

Breccia-conglomerates and conglomerates

Bedding

Very thick, thick, massive amalgamated

Grain size

Lithofacies

Lithofaciees scheme in the eastern part of the trough

TABLE 1

F2.1

D2.1 D2.2

C2.3

ll.1 B2A

A2.7

ALl A2.2 A2.3

Pickering et al. (1986)

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>

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III dominant

Structureless mudstones, ripples, flasers, rare- Td~,

Very thin and lamin, of silt and sandstones, mudstones variable thickness

fine sand, silt, s a n d : m u d ratio

Very mud, 1:4

Mudstones interbedded with siltstones and very fine sandstones

6.

II dominant, IA, IB, IC, III subordinate

Bouma sequences with base missing ripples

Thin to very thin laminae, lenticular or irregular and flaser

Fine to very fine sand, silt, mud, s a n d : m u d ratio 1:1

Fine sandstones and siltstones interbedded with mudstones

5.

I1 dominant, IA, IB, IC, III rare

Graded complete or partial B o u m a sequence

Medium, laterally continuous

Medium to fine sand

Medium to fine sandstones with B o u m a sequences

4.

E or G

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Pickering et al. (1986)

or E

C 1, C 2

B1

IC dominant IA, IB, II rare

Channel fill, structureless, dish and flame structures

Very thick to thick and medium sharp and erosional bases, amalgamated

Corase to fine sand

Massive sandstones without Bouma sequences

C1

IB dominant, IA rare

Channel fill, m u d chips, normal graded Ta, Tab

Very thick to thick, rare medium, irregular, amalgamated

Coarse to medium sand

Graded coarse and medium sandstones

3.

A1

IA dominant

Channel fill, m u d chips, coquina lenses, normal and inverse graded

Very thick to thick, irregular, amalgamated

Very coarse to coarse sand, m e d d i u m to fine pebble

Graded coarse and pebbly sandstones

Mutti and Ricci Lucchi (1972, 1975)

Facies association

Features

Bedding

Grain size

Lithofacies

Lithofacies scheme in the western part of the trough

TABLE 2

Z .-q O

7 (7

O0

F4

F5

F6

III. Outer fanBasin plain (?)

F3

F4, F5

liB

thickening

up-

No clear thickening upward

Clear ward

Outer fan-basin plain

Low-density turbidity currents, mud suspension

Transitional high- to low-density turbidity currents

Transitional high- to low-density turbidity currents

Suprafan lobe

No clear thickening upward

Depositional lobe

Transitional high- to low- and low-density turb. currents

Fan lobes

F3 Thickening upward

Debris flows, high-density turbidity currents

Channels and their levees without well developed fan growth pattern

High-density turbidity currents

Debris flows, high-density turbidity currents

processes

Main depositional

Channels and their levees

Environment

Middle fan channelized areas

Clear thinning upward

F3, F4

F3

F5

No clear thinning upward

F2, F3, F4

F4, F5

F2

IB

F5

Thinning upward

Depositional cycles

F4

IIA

F1

IA

F5

F4, F5

F1, F2, F3

Channel-levee

rare

II. Fan lobe

I.

subasociations

dominant

ciations and

subordinate

Composed facies

Facies asso-

Facies association scheme in the western part of the trough

TABLE 3

t-O

240

differences such as coarser material and lesser thickness. Probably these sediments are transitional facies between Utica Sandstone and Murca Formation (Figs. 5). Data for the age of the Murca Formation are scarce (Moreno, 1991a), but our conclusion is that the unit is ranging from the late Tithonian to the Early Hauterivian. The Lower Cretaceous turbidites in the eastern part of Bogota trough are formally subdivided in the Buenavista Formation. Macanal Formation and Alto de Caqueza Formation included in the Caqueza Group (Pimpirev et al., 1992). The age of the Caqueza Group according to ammonite assemblages is late Tithonian-Hauterivian (Fig. 7).

Facies analysis The facies analysis of the turbidites in the eastern part of Bogota trough was done by Pimpirev et al. (1992). The characteristics of the divided lithofacies are summarized in Table 1. The facies analysis of the turbidites in the western part of Bogota trough is based on four stratigraphic sections and on detailed measurements in nine outcrops of these sections (Figs. 3-6). Six lithofacies and three facies associations are recognized (Tables 2 and 3). Two of the facies associations are subdivided into subassociations. The different lithofacies are defined using bedding style and thickness, grain size, sedimentary structures, composition and texture of the beds. They are compared with Mutti and Ricci Lucchi (1972, 1975) and Pickering et al. (1986)--wellestablished facies classification schemes.

Characteristics of lithofacies Facies 1. Graded coarse and pebbly sandstones. This facies is found predominantly in the stratigraphic sections Utica-Tobia and La Magdalena-Villeta (Figs. 3 and 4). It occurs generally as thick and very thick beds of very coarse and pebbly sandstones with common channelized bases. The sandstones are inversely and normally graded. Amalgamation is observed. The presence of coquina lenses of bivalves (trigoniids) is a distinctive feature of this lithofacies. These shal-

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Fig. 8. Scheme of the deposition of bivalves in one pebble sandstone bed in the section La Magdalena-Villeta. VL = left valves, VR= right valves.(Modifiedafter Viliamil, 1990.)

low-water fossils are resedimented from highdensity sandy flows (Villamil, 1990). The differential energies of the flow have sorted the left from the right valves in each sandstone bed, according to the differences in weight and the presence of a wide central tooth on the left valve (Villamil, 1990) (Fig. 8). This facies is similar to facies A2. 7 (normally graded pebbly sand) of the classification scheme of Pickering et at. (1986) and to facies A~ of Mutti and Ricci Lucchi (1972, 1975). Facies 2. Graded coarse and medium sandstones. This facies is quite common at the base of all described stratigraphic sections, but it is predominant in the sections T o b i a - L a Vega and P a c h o - L a Palma (Figs. 5a and 6a). It consists chiefly of very thick to thick, rarely medium bedded coarse to medium-grained sandstones with common channelized bases, especially in the section P a c h o - L a Palma (Fig. 6b). The beds are usually normally graded and it is possible to observe T a and Tab divisions of Bouma. Their upper portions are structureless or parallel laminated. The amalgamation is common. Coquina lenses of bivalves are infrequently observed in these sanstones (Fig. 5b). This facies is similar to facies C2.1 (very thick/thickbedded s a n d - m u d couplets) of Pickering et al. (1986) and to facies C l of Mutti and Ricci Lucchi (1972, 1975). These turbidites indicate transport processes of high density turbidity currents. Facies 3. Massive sandstones without Bouma sequence. This facies is dominant in the upper parts of the stratigraphic sections Utica-Tobia, La Magdalena-Villeta and P a c h o - L a Palma (Figs. 3a, 4a, 6a and 6d). It consists of coarse to fine-grained sandstones forming very thick, thick and medium beds. Amalgamation is common. Bases are generally sharp and erosional. The

SUBMARINE

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DEPOSITS

IN THE

BOGOTA

sandstones are disorganized and the Bouma sequence is usually not applicable. In some cases it is possible to observe dish and flame structures. The facies has characteristics very similar to facies B1.1 (thick/medium-bedded disorganized sands) of Pickering et al. (1986) and to facies B 1 of Mutti and Ricci Lucchi (1972, 1975), and is interpreted as a result of sedimentation from high-density turbidity currents. Facies 4. Medium to fine sandstones with Bouma sequence. This facies is dominant in the middle portions of the stratigraphic sections Tobia-La Vega and Pacho-La Palma (Figs. 5a, 5c, Utico - Tobio

320

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6a and 6c), but occurs less often in all the sections described. It consists of medium- to finegrained sandstones forming generally laterally continuous medium beds. Each sandstone bed is typically graded and shows complete or partical Bouma sequences (Tae, Tabe, Tace, T~). The sandstones are interbedded with mudstones and amalgamation is rare. The facies is comparable to facies C 1 and C 2 (classical turbidite) of Mutti and Ricci Lucchi (1972, 1975) and to facies C2. 2 (medium bedded sand-mud couplets) of Pickering et al. (1986). It is interpreted as a result of sedimentation from transitional high- to low-den-

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Fig• 9• The relationships between the facies associations in the stratigraphic sections• IA, IB and IC--subassociations of association I (channel-levee)• IIA and IIB--subassociations of association II (fan lobe)• III--association III (outer fan-basin plain ?).

242

sity turbidity currents or low-density turbidity currents. Facies 5. Fine sandstones and siltstones interbedded with mudstones. The facies is dominant in the middle parts of the sections T o b i a - L a Vega and P a c h o - L a Palma (Figs. 5a, 5c, 6a and 6c), but occurs as a subordinate facies in all sections. It is represented by sand-mud couplets with a sand : mud ratio of 1 : 1. The sand portion is built up of thin to very thin beds and laminaes of fine-grained sandstones and siltstones. The sandstone beds are generally continuous, rarely discontinuous and it is possible to observe the upper part of the Bouma sequence: Tcde, Tde , Tee. The siltstones occur as lenticular or irregular laminae with flaser bedding and climbing ripples. The mudstones are quite homogeneous. This facies is comparable to facies D 2, D 3 and E of Mutti and Ricci Lucchi (1972, 1975) and to facies D2. p D2. 3 of the Pickering et al. (1986) classification scheme. Sedimentation is from low-density turbidity currents. Facies 6. Mudstones interbedded with siltstones and very fine sandstones. The facies is dominant in the middle parts of the sections T o b i a - L a Vega and P a c h o - L a Palma (Figs. 5a, 5d and 6a). It is represented by s a n d - m u d couplets with a sand : mud ratio much less than 1 : 1, commonly 1:4. The mudstones are structureless and graded with variable thickness. They are interbedded with laminae and very thin beds of siltstones and very fine sandstones. The sandstones and siltstones from lenticular or irregular beds with internal features including flaser bedding, climbing ripples and rarely observable Tde or Teae Bouma sequences. The facies is similar to facies E or G of Mutti and Ricci Lucchi (1972, 1965) and to facies El. ~, E2.1 according to the Pickering et al. (1986) classification scheme. The s a n d - m u d couplets are probably deposited by low-density turbidity currents and mud suspension. Facies associations

The stratigraphic sections show three distinctive facies associations formed in different submarine depositional environments: distributary

C. P I M P I R E V A N D G . S A R M I E N T O

channels and their levees, fan lobes and outer fan-basin plain (?) (Table 3). In each facies association one or two of the facies are dominant and the others are subordinate, or occur rarely. Two of the facies associations are subdivided into subassociations. Association 1 (channel-levee association). This facies association builds the entire stratigraphic section of Utica-Tobia and La Magdalena-Villeta and occurs in the lower and upper parts of the sections T o b i a - L a Vega and P a c h o - L a Palma (Fig. 9). It consists of the facies 1, and 3 (dominant), facies 5 (subordinate) and facies 4 (rare). The association is composed almost entirely of thick channelized amalgamated sandstone units separated by sandstone-mudstone levee deposits. The variation in the vertical relationships between the facies allows the subdivision of this association into three subassociations (IA, IB and IC). Subassociation 1,4. This subassociation occurs in the stratigraphic sections Utica-Tobia (sequences up to 250 m thick) and La MagdalenaVilleta (sequences up to 30 m thick) (Figs. 3b, 3e, 4b, 4e and 9). It consists of facies 1 (dominant), facies 5 (subordinate) and the rare facies 4, 2 and 3. The vertical variations of the facies do not show clear thinning or thickening upward trends and they form packets of thick coarse or pebbly channelized sandstones covered with thin-bedded turbidites. We suggest that the deposition of the sediments took place in the channel-levee complex close to the source area. Subassociation lB. This subassociation builds up the lower part of the section P a c h o - L a Palma (sequence up to 270 m thick) and 25 m of the b a s e and the top of section T o b i a - L a Vega (Fig. 9). It consists of facies 2 (dominant), facies 5 (subordinate) and facies 3 and 4 rare. The sequences show clear thinning upward trends (Figs. 5b and 6b). This subassociation was probably formed in the inner-middle fan channelized areas. Subassociation IC. This subassociation occurs at the top of all stratigraphic sections, except section T o b i a - L a Vega where, in its place, subassociation IB is to be found (Fig. 9). The thickness of the sequence is variable, from 30 m in the

SUBMARINE FAN AND CHANNEL LEVEE DEPOSITS IN THE BOGOTA T R O U G H

section Utica-Tobia to 200 m in the section Pacho-La Palma. The main characteristic of this subassociation is the occurence of thick bodies of massive sandstone (facies 3) with thin-bedded turbidites (facies 5). Facies 4 occurs rarely. Thinning upward sequences are typical for the section Pacho-La Palma (Fig. 6d). We suggest that this subassociation probably was formed in channel-fill middle-fan environments. Association H (fan-lobe association). This association occurs in the middle parts of the sections Tobia-La Vega and Pacho-La Palma where it forms sequences about 50 m thick (Fig. 8). The facies association is defined by a series of thickening upward sequencies from 3 to 12 m thick, where facies 4 and facies 5 are dominant and facies 3 occurs rarely (Figs. 5c and 6c). Mediumbedded, medium- to fine-grained sandstones are separated from each other by the thin-bedded levee facies 5. The differences in sedimentary structures, composition and texture of the beds allow the subdivision of this association into two subassociations. Subassociation IIA. This subassociation overlies subassociation IB in the sections Tobia-La Vega and Pacho-La Palma (Fig. 9). Besides the medium beds of facies 4, it is possible to observe thick beds (40-70 cm) of medium- to fine-grained, rarely coarse-grained sandstones with erosional bases (facies 3). In this subassociation cycles of thickening upward trends might be defined, though not quite clearly (Fig. 5c). Subassociation liB. This subassociation occurs only in the section Pacho-La Palma, where it overlies association III (outer fan-basin plain (?)) (Fig. 9). Cycles of thickening-upward trend are well represented (Fig. 6c). The beds of the dominant facies 4 are laterally continuous and show an absence of basal channeling. Association III (outer fan-basin plain (?) association). This facies association is observed in the sections Tobia-La Vega and Pacho-La Palma with sequences from 25 to 50 m thick (Figs. 5d and 9). In the section La Magdalena-Villeta it is poorly preserved. The association occurs above or between the fan-lobe association. Facies 6 is dominant, facies 5 is subordinate and facies 4 is rare. The character of the association is more or

243

less homogeneous and repetitive sequences were not observed. Depositional environment and progression of facies associations The relationships between the former facies associations described above show that the sedimentation in the western part of the basin was realized in channel-levee, fan lobe and outer fan-basin plain (7) depositional environments. In the sections Utica-Tobia and La Magdalena-Villeta a channel-levee complex without well developed fan-growth pattern is preserved. The only relationships observed between the associations are the passing from subassociation IA to subassociation IC in the top of the sequences (Fig. 9). In the sections Tobia-La Vega and Pacho-La Palma the interrelations between the facies associations show development of submarine fan environments. Here the channel-levee complex (association I) evolved into a fan with lobes (association II). These lobes may be classified as suprafan (sensu Shanmugan et al., 1988, and Shanmugan and Moiola, 1991) and were developed in small radial active-margin fans. As a result of retrogradation of the fan system suprafan lobe deposits (subassociation IIA) covered distal outer fanbasin plain (?) sediments (association III) (Fig. 9). In a vertical development of the sequences in the stratigraphic section Pacho-La Palma over the outer fan-basin plain (?) deposits in a time of progradation of the fan system, depositional lobes (sensu Shanmugan and Moiola, 1991) with cycles of thickening-upward trend and laterally persistent beds without channelized bases (subassociation IIB) are well represented (Figs. 6c and 9). The progradational sequence of the turbidite system finishes with the development of middle fan channel deposits represented by subassociations IC and IB (Fig. 9). Sedimentation in the eastern part of the trough took the form of inner, middle, outer fan and depositional and suprafan-lobe environments (Pimpirev et al., 1992). The progression of the fan facies associations shows two main cycles of retrogradation and progradation in the turbidite basin.

244

Discussion and conclusions Bogota trough was an elongate N E / S W - o r i ented Lower Cretaceous basin situated between the Guyana shield to the east and the PaleoCentral Corillera to the west. In Early Cretaceous time the Paleo-Central Cordillera was an uplifted Jurassic plutonic arc (Aspden et al., 1987). The petrographic and provenance analyses by Moreno (1991b) show that the main sediment supply for the deposition of the Murca Formation and Utica Sandstone derived from the west, probably corresponding to the Paleo-Central Cordillera, formed by calc-alkaline Jurassic volcano-plutonism. The sandstone samples from the Utica Sandstone contain higher amount of igneous fragments and feldspar. Many of the feldspars are plagioclase and occur as separate clasts and as components of the volcanic clasts (Moreno, 1991b). Samples from the Murca Formation are characterized by abundant feldspar and volcanic lithics (Moreno, 1991b). The lithic-rich nature of the sandstones of the Murca Formation and Utica Sandstone (Moreno, 1991b) suggests a magmatic arc provenance for the turbidites (Dickinson and Suczek, 1979). The position of the western portion of the trough near to the zone of convergence between the Nazca and South American plates predetermined the coexistence of small sand-rich radial fans and channel-levee complexes in this region (Fig. 10). A channel-levee complex was developed in areas situated closer to the sediment supply, with steep gradients on the slope, and narrow canyons. The combination of erosional and depositional features led to the formation of thick, coarse channelized sandstone bodies from high-density sandy flows, while thin-bedded levee deposits were the result of overbank suspension flows (Nelson and Maldonado, 1988). In the areas of deposition of the Murca Formation suprafan lobes were developed in the time of retrogradation of the turbidite system (Figs. 10 and 11). The evolution of the basin continue with progradation, and depositional lobes were deposited over the outer fan-basin plain (?) environments (Fig. 11). Coexisting channel-levee complexes and radial fans probably were fed by river systems whose terrigenous sediments are preserved in the north-

C PIMPIREV AND G. SARMIENTO

ern part of the area investigated (Renzoni, 1985). Recent analogues of this turbidite system are difficult to find, but some distinctive features may be correlated with the Ebro turbidite system in the Mediterranean Sea, as described by Nelson and Maldonado (1988). In the eastern part of Bogota trough a different turbidite system with a well-expressed fangrowth pattern was developed (Pimpirev et al., 1992) (Fig. 12). The Quetame Massif, built up of Palaeozoic metamorphic rocks (Quetame and Farallones Groups) was the main source of sediment during the Late Tithonian and the begining of the Berriasian. 80% of the clasts in the conglomerates of the Buenavista Formation, deposited in the areas near to the sediment supply, are from the Quetame Group (boulders and cobbles of unstable metamorphic rocks). In the areas situated farther from the sediment supply, 90% of the clasts in the conglomerates belong to the Upper Palaeozoic orthoquartzites of the Farallones Group (Pimpirev et al., 1992). The petrographic analysis made by Aalto (1972) suggests stable source areas such as the Guyana shield for the deposition of the orthoquartzitic sandstones from the Macanal and Alto de Caqueza Forma-

I~G

~

NE

Fig. 10. Schematic model of the depositional environments during earliest Cretaceous time in the western portion of Bogota trough: 1 = channel-levee, 2 = submarine fan in area Tobia-La Vega, 3 = submarine fan in area Pacho-La Palma, A = Utica Sandstone, B = Murca Formation.

245

S U B M A R I N E F A N A N D C H A N N E L L E V E E D E P O S I T S IN T H E B O G O T A T R O U G H

WESTERN

MARGIN

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MIDDLE FAN

z

MARGIN

Cdquezo turbidite system

-~

~-

-,t-

,~

~

W~_=

MIDDLE

'~

FAN

z

z

O.

O

z

:=

z

I,~

OUTER ~N BASIN PLAIN(?)

1"4

_

OUTER FAN

I-

DE POSI TIONAL

<~ :>

:S Q:: o LL

LOBES

(.9

LOBES

O

I

o

z

--

DEPOSITIONAL

Q:

SUPRAFAN LOBES

z

¢_) r~ :E

g zoo

MIDDLEINNER

(?)

(.~

N ILl

7, o ~.. .< wJ

OUTER .-I

<

FAN

g

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<

~i; zoo

m

MOUTH OF THE CHANNELS [SUPRAFAN LOBES ;))

FAN ._?--

=

i

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Fig. 11. Scheme of the depositional environments and their progression in the turbidite systems developed in the western and eastern portions of Bogota trough (eastern portion after Pimpirev et al., 1992).

tions during the Valanginian and Hauterivian. The eastern margin of the trough, situated near to the stable Guyana shield determined the existence of larger fan systems of a hybrid type between radial and elogate fan (Fig. 12). Despite the differences between the two fan systems in the eastern and western margins of the

trough, the observed retrogradational and progradational sequences are similar (Fig. 11). The retrogradation is compared with the major flooding events during the Berriasian in northwestern South America and the progradation probably coincided with the short period of minor flooding events during the Valanginian (Macellari, 1988; Pimpirev et al., 1992). Acknowledgements This work was supported by INGEOMINAS, Bogota. We would like to thank C. Ulloa and T. Villamil for the discussions before the field work. Thanks are also due to the journal referees and A.D. Miall for useful criticism and fruitful comments on the manuscript. V. Minev helped with computerized wordprocessing.

g~,,..'2'f~

o-,,

Fig. 12. Schematic paleogeographic model of the Bogota trough with different source areas in eastern and western margin and complex coexisting turbidite systems during the earliest Cretaceous time.

References Aalto, K.R., 1972. Diagenesis of orthoquartzites near Bogota, Colombia. J. Sediment. Petrol. 42: 330-340.

246 Acosta, F.E. and Obando, E., 1984. Desarrollo estructural del extremo sur del Valle Medio del Magdalena. XXIII reconocimiento Geologico, Colombian Society of Petroleum Geologists and Geophysicists, Bogota, 14 pp. Aspden, J., McCourt, W. and Brook, M., 1987. Geometrical control of subduction-related magmatism: the Mesozoic and Cenozoic plutonic history of western Colombia. J. Geol. Soc. London, 144: 893-905. Burgl, tt., 1961. Sedimentation ciclica en el geosinclinal Cretaceo de la Cordillera Oriental de Colombia. Bol. Geol., Ingeominas, Bogota, 8: 85-118. Campbell, C.J., 1962. A section trough the Cordillera Oriental of Colombia between Bogota and Villavicencio. Fourth Annu. Field Conference, Colombian Society of Petroleum Geologist and Geophysicists, Bogota, pp. 89-118. Dickinson, W.R. and Suczek, C.A., 1979. Plate tectonics and sandstone compositions, Bull. Am. Assoc. Pet. Geol., 63: 2164-2182. Fabre, A., 1985. Dinamica de la sedimentacion cretacica en la region de la Sierra Nevada del Cocuy (Cordillera Oriental de Colombia). In: F. Etayo-Serna and F. Laverde, (Editors), Proyecto Cretacico, Ingeominas, Bogota, 16: XIX.1XIV.20. Gallo, J., 1977. The environmental facies analysis of selected Tertiary and Cretaceous outcrops along the Vitleta-Honda road. Seventheenth Field Conference, Colombian Society of Petroleum Geologists and Geophysicists, Bogota, pp. 473-487. Irving, E., 1971. La evolucion estructural de los Andes mas septentrionales de Colombia. Bol. Geol., 19 (2): 1-90. Macellari, C.E., 1988. Cretaceous paleogeography and depositional cycles of western South America. J. S. Am. Earth Sci., 1 (4): 373-418. Moreno, M., 1991a. Stratigraphy of the Lower Cretaceous Rosablanca and Cumbre Formations, Utica Sandstone and Murca Formation, west flank Eastern Cordillera, Colombia. Geol. Colomb., 17, in press. Moreno, M., 1991b. Provenance of the Lower Cretaceous sedimentary sequences, central part, Eastern Cordillera, Colombia. Rev. Acad. Colomb. Cienc. Exact., Fis. Nat., 69, in press. Mutti, E. and Ricci-Lucchi, F., 1972. Le tobiditi dell Appennino settentrionales: introduzione all' analisi di facies. Mem. Soc. Geol. Ital., 11: 161-189. Mutti, E. and Ricci Lucchi, F., 1975. Turbidite facies and facies associations. In: E. Mutti, G. Parea, F. Ricci Lucchi, M. Sargi, G. Zanzucchi, G. Chibaudo and S. Laccarino, Examples of Turbidite Facies and Associations from Selected Formations of the Northern Apennines. Guide of Excursion 11, 9th International Congress of Sedimentology, Nice, pp. 21-36.

c. PIMP1REVAND G. SARMIENTO Nelson, H. and Maldonado, A., 1988. Factors controlling depositional patterns of Ebro turbidite systems, Mediterranean sea. Bull. Am. Assoc. Pet. Geol., 72: 698-716. Pickering, K., Stow, D., Watson, M. and Hiscott, R., 1986. Deep-water facies, process and models: a review and classification scheme for modern and ancient sediments. Earth Sci. Rev., 23: 75-179. Pimpirev, C., Patarrovo, P. and Sarmiento, G., 1992. Stratigraphy and facies analysis of the Caqueza Group a sequence of Lower Cretaceous turbidites in the Cordillera Oriental of Colombian Andes. J. S. Am. Earth Sci., 5 (3/4): 295306. Renz, O., 1959. Estratigrafia del Cretaceo en Venezuela Occidental. Bol. Geol., Caracas, 5(10): 3-48. Renzoni, G., 1968. Geologia del Macizo de Quetame. Rev. Geol. Colomb., Bogota, 5: 75-127. Renzoni, G., 1985. Paleoambientes en las Farmaciones Arcabuco y Cumbre de la Cordillera de Los Cobardes. In: F. Etayo-Serna and F. Laverde (Editors), Proyecto Cretacico. Publ. Espec., lngeominas, Bogota, 16: X.1-X.14. Shanmugan, G. and Moiola, R., 1991. Types of submarine fan lobes models and implications. Bull. Am. Assoc. Pet. Geol., 75: 156-173. Shanmugan, G., Moiola, R., McPherson, J, and O'Connell, S. 1988. Comparision of turbidite facies associations in modern passive-margin Mississippi fan with ancient activemargin fans. Sediment. Geol., 58: 63-77. Suarez, M., 1991. Mapa Geologico del departamento de Cundinamarca, Colombia, 1:250,000. Ingeominas, Bogota, in press. Thompson, A.V., 1966. A geological sections from Bogota to the Central Cordillera. Seventh Field Conference, Colombian Society of Petroleum Geologists and Geophysicists, Bogota, pp. 201-219. Ulloa, C., 1988. Guia de excursion Bogota-Honda. Geologia Colombiana, No. 16, anexo, Universidad Nacional de Colombia, Departamento de Geociencias. Ulloa, C. and Rodriguez, E., 1979. Geologia del Cuadrangulo K-12 Guateque. Bol. Geol., lngeominas, Bogota, XXII (1) 84 pp. Villamil, T., 1988. Estudio del potencial bioestratigrafico de tres especies de Trigonia de Cretacico Inferior de Colombia. Tesis, Universidad Nacional de Colombia, Departamento de Geociencias, 120 pp. Villamil, T., 1990. Concideraciones tafonomicas de una concentracion de bivalvos en una secuencia turbiditica del Cretacico Basal de occidente de Cundinamarca, Colombia. Revista Facies Colombia, 1: 26-31.