Good Dates and Bad Dates in Ecuador Radiocarbon Samples and Archaeological Excavation: a Commentary Based on the "Valdivia Absolute Chronology"

Jorge G. Marcos Universidad Autónoma de Barcelona Departemento de Geologia, Edificio CS 08193 Bellaterra Barcelona, España.

Adam Michczynski Gliwice Radiocarbon Laboratory Institute of Physics Silesian Technical University ul. Krzywoustego 2 44-100 Gliwice, Poland.

Summary

The cultural chronology of Ecuador is based on several hundreds radiocarbon determinations. Most of the dated samples, which come from coastal sites, are charcoal, however a good number were shell and few were the collagen of human bone. Some dates were obtained by other methods. Early in the fifties, obsidian hydration dates served to complete the 14C sequence, and more recent Thermoluminescence assays have not only completed some missing dates for a more refined sequence, but have served to validate some 14C calibrations and to explain some aberrant determinations. In the following commentary, we will refer mostly to Valdivia dates, since they were obtained by the most varied field methods, during the forty years Valdivia sites have been under excavation.

This paper has two parts: firstly, an archaeological discussion of the Valdivia absolute chronology by Jorge Marcos; and secondly, the presentation of the calibration of the Valdivia dates in the Gliwice Radiocarbon Laboratory, by Adam Michczynski. Marcos, discusses the importance of selecting a 14C sample in order to obtain a secure date, and the most common errors that have affected the Valdivia absolute chronology. The necessity to calibrate dates, and the importance of publishing them properly. (1)

The results of calibration of individual 14C dates by Adam Michczynski are presented in Table 1 and Figure 1. Finally, as a corollary, a commentary on the problems presented in the combined presentations is provided by the senior author.


Introduction

When Willard Libby published the first radiocarbon age determinations in 1949, a rapid growing and widely accepted impression, that at last a direct scientific procedure to determine absolute chronologies had been discovered, invaded the archaeological discipline. Most archaeologists became “true believers” of the “Radiocarbon Revolution”, and it took nearly thirty years before the discipline accepted a different reality.

We know now that radiocarbon determinations can not be translated into BC/AD calendar years by the simple addition or subtraction of 1950 years. We also know of the existence of an effect, which not only registers different atmospheric concentrations of 14C for different periods, causing determinations not always to agree with real dates; but it can also happen that one particular radiocarbon determination may represent more than one true date.

Libby, had assumed that 14C atmospheric concentrations had been constant in the past; but now we know that it was variable, and that this was mainly due to changes in the earth magnetic field. Dendrochronology, the method that demonstrated 14C dating inexactitudes, also provided us with a way to correct, calibrate and thus to convert 14C assays into real calendar years. Since then, several methods for correction and calibration of radiocarbon assays have been offered, the most recent by Stuiver, Long and Kra (1993). Recently, the methodological advance experimented in radiometric analysis has been enormous. These advances not only refer to 14C dates calibration, and statistical correction of radiocarbon assays, but also to the development of more precise ways to treat the organic samples and to determine the concentration of 14C, like the introduction of the accelerator mass spectrometer (AMS), which allows the direct measurement of smaller samples. This has been called the “second radiocarbon revolution.”


The “Radiocarbon Revolution”

As a result of this conception of the “Radiocarbon Revolution”, up to 1974, all organic samples used for 14C determinations of the Valdivia chronology in coastal Ecuador were gathered by “artificial” metric levels of excavation (Meggers, Evans and Estrada 1965: 15-21, 147-156). A good number of these samples were sea and estuarine shells, while a lesser number corresponded to wood charcoal samples. Most of the metric levels used, were 30 cm. thick taken from 5 x 5 m. units. This “artificial stratigraphy” disregarded visible cultural deposits and intrusions, like erosion channels, hearths, postmolds, storage pits, etc., as Bischof and Viteri noted in 1972.

During this period, in Ecuador (like in most of Latin America) not only the majority of 14C determinations came from excavations such as this, but a good number of them were published without their laboratory reference number. Even today, this convention is hardly followed, as well as the unconventional practice of publishing uncalibrated dates followed by B.C. and A.D, and not in lower case, as it should be, misleading readers, and making of any chronological comparison a deceitful effort.

As an example of the problems introduced in the past, and in some present cases, the Valdivia cultural is especially valuable. Bischof and Viteri (op.cit.) not only demonstrated a that at the type site (G-31) 14C assays were discordant with their purportedly stratigraphic position, but showed that clear stratigraphic deposits, that could have allowed to precisely define the depositional history of the site, were ignored. The problems with the generalised “artificial stratigraphic” method of excavation used then, became more apparent during the early months of excavation at Real Alto.

In 1974, NSF awarded the Illinois archaeological team, headed by D. W. Lathrap, funds for the excavation of Real Alto. The major literature on Valdivia, at that time, indicated that such sites did not allow to clearly determine stratigraphic deposits. Most reviewers of the project considered that the Midwestern, Mississippian Bottom-Lands, excavation procedure, proposed by the Illinois team of archaeologists was not applicable to the excavation of Real Alto. As a result, the grant contract provided a restriction on the excavation procedure, it forced us to excavate the site by metric levels. Since we were convinced that we would be able to identify different soil deposits, as well as cultural features such as wall-trenches, house-floors, food-preparation, ovens and storage pits, a compromise was reached. We were allowed to excavate in alternate units. Even numbered units were excavated removing cultural deposits in the way done by most Mississippian archaeologists, as we had planned, and in the odd numbered units we had to use the artificial metric-level method, imposed by the grant.

We had only to excavate metrically five odd units before it became obvious that such method was destroying important retrievable information, and it was dropped. We found out that after excavating thirty centimetres, removing all deposits and intrusive fills, only about 30% to 40% of the next 10 cm. layer remained to be excavated. From then, a 60% to 70% intrusions remained as a constant throughout the sequence, even below 120 cm. deep where the undisturbed geological strata began to emerge. Meaning, that if we had followed the traditional method of excavation and ceramic type serration used in Ecuador during the fifties and early sixties, we would have been treating as contemporaneous, materials with a with only 30% to 40% probability, with an added 360 to 480 years margin of error beyond that implied by the 14C method itself (see Appendix 3).


Sampling for Radiocarbon dates

Thus the first Valdivia “dates”, from samples taken in the late fifties, served to confirm the antiquity of that phase in Coastal Ecuador. And although, such samples dated also some Late Formative, Regional Developmental and Integration Period episodes. Valdivia, being the better dated and studied Early Formative Culture in Coastal Ecuador, allows for a more detailed commentary on the 14C dating problems.

The 14C determinations from the type-site (G-31), and from other Valdivia sites excavated by Meggers, Evans and Estrada (op. cit.) in the fifties, due to the excavation strategy used, which disregarded contexts, could only roughly date the grossly estimated four sub-phases proposed by these authors.

In the early sixties a Columbia University team of archaeologists, headed by Edward Lanning (1964), surveyed the Santa Elena Peninsula, and surface collected ceramic samples from several thinly occupied sites, defining the late preceramic Vegas occupation. This exploration of the Santa Elena Peninsula sites allowed Betsy Hill to refine the Valdivia sequence into eight phases. Alison Paulsen, did likewise with Guangala for which she identified nine phases, and three for the Integration Period occupation, which had been defined as Manteño by Bushnell, and she now called Libertad. During the late sixties, Henning Bischof (1972) refined the Engoroy and Machalilla (2) sequences obtaining a good number of 14C dates which included some for early Guangala.

In the seventies, Presley Norton and Felipe Cruz excavated the Loma Alta site 19 km. inland, deep into the Valdivia river valley. They improved on the excavation procedure used up to then, by being able to separate an Engoroy level covering two Valdivia occupations. With the aid of B. Hill, Norton (1972) identified the deeper cultural deposits as Valdivia phases 1 and 2. However, the greyish dusty midden did not allow them to identified some features, like Valdivia 2 storage pits, whose contents were interpreted as ’cairns’. The several wood charcoal samples obtained correspond nicely with such phases, with the exception of those gathered from the ’cairns’, which date to Valdivia phase 2.


Proper Excavation, the validation of 14C and TL determinations.

The quality of excavation reflects on the validity of the increasingly more precise physical methods of chronological determination. The earlier Valdivia dates, which samples were obtained form metric levels served to date periods, but not events. Today, the appropriate selection of the sample is of great importance to validate closed contexts and micro-stratigraphic relationships. Ideally, we should date no less than five 14C samples per event, to select against on-site and laboratory contamination and error. However, the availability of organic material, and cost, are a constrain. This can be offset by the use of less expensive comparative methods, like TL chronological determinations. We have done so successfully at Real Alto, Punta Tintina, Loma de Los Villones, and San Lorenzo del Mate (3) (see Appendix 2).


Excavations at Real Alto

Research at Real Alto began with a non random surface collection by the senior author (Marcos, 1978, 1988). This collection was analysed during 1972 and 1973 to plan an excavation strategy for the 1974/75 excavations at Real Alto. In the process of analysing material samples a lump of ’terracotta’ with two textile imprints was discovered (Marcos, 1974). The associated material were Valdivia phase 7 sherds. To compare this event with other cotton textile bearing contexts from coastal Peru, a preliminary attempt at correction for isotopic fractionation of 14C shell determination and an statistical calibration for existing Valdivia determinations were attempted by Gary Vescellius (ibidem) (4).

Since 1974, during excavations at Real Alto, a more refined method of excavation was introduced, for the first time, to a Formative site in coastal Ecuador. House floors and public building floors, were identified and excavated, together with associated burials, hearths, food preparation pits, ritual paraphernalia disposal pits, and bell-shape storage pits, etc. Samples for 14C determinations were obtained from these closed contexts, and their stratigraphic correlation was verified. Although some 14C determinations correlated nicely with microstratigraphic deposits, others obtained from wall-trenches and from food-preparation pits, appeared not to correlate with the stratigraphic sequence. However, once calibrated, some of these dates became acceptable, but others were simply wrong.

Excavations conducted since the mid eighties at Real Alto and San Lorenzo del Mate have shown some site formation peculiarities, and have permitted refined observations of the manner of building and rebuilding public edifices and households, which could explain some of the chronological aberrations.
• All Valdivia buildings were placed on top of a prepared platform mound, which were reworked and reshaped when a major rebuilding of the structure took place. This became more obvious at San Lorenzo del Mate where the limonite-rich soils clearly showed the forming of house platforms throughout the stratigraphy. This is also evident in Real Alto deposits, clearly showing in Mound A (Marcos, 1988).
• In most of the wall-trenches it was evident that wall posts were removed and replaced from time to time.
• Surface hearths similar to those found ethnographically among Amazonian groups are common in Valdivia house floors, as well as bell-shaped food preparation pits (see Zeidler, 1984:327, Map 49; Marcos 1988:48).
• Bell-shape storage pits generally contained manos and metates, or rests of them. These sacrificial rites filled to capacity some storage-pits with broken manos and metates (Marcos, 1978; 1988:144-145).

Building activity, could explain some wood charcoal sample up-mix, especially in wall trenches. But well defined bell-shaped food-preparation pits should contain only charcoal from the cooking activity performed there, and aberrant dates could not be explained by up-mixture. On the other hand, re-use and replacement of wall-posts activity, could indicate that a good percentage of the wood burnt in hearths and oven-pits were old, discarded, building material. Long-lasting wood, like algarrobo and guasango, would date to several centuries before, when the tree was cut, and not when it ended as fuel.

Our recent excavations on the north-east sector of Real Alto, have shown that the so-called cairns found at the bottom of the excavation in that sector of the site, are actually the bottom of, Valdivia 2b, bell-shape storage-pits where manos and metates where stored, or sacrificed before filling the pit with rubble (5). This is coherent with some of the dates associated with cairns, which date to Valdivia 2b and not to Valdivia 1a.


Calibration of Radiocarbon Dates from Valdivia Culture

The results of calibration of individual dates are presented in Appendix 2, Table 1 and Figure 1. All dates were calibrated using the Gliwice Calibration Program GdCALIB (Pazdur & Michczynska 1989). The calibration curves used for the calculation were taken from Radiocarbon - Calibration 1993 (Stuiver, Long and Kra, 1993). Due to irregular multimodal shapes of probability distributions of the major part of these dates it was decided to present the results in a form of 95% confidence intervals of the highest probability (narrowest 95% confidence intervals) - the same form, which was used in ANDES catalogue (Ziólkowski et. al. 1994). The intervals presented in Table 1 were rounded to 5 years and corrected (after analysis of the shape of probability distribution of calendar age obtained for each date) in order to remove unimportant information. There are some dates with 95% confidence intervals divided into two or three parts. For these dates the probability of each part of interval is placed in brackets. Especially, dates SI-81 (Valdivia) and ISGS-446 (Real Alto) give after calibration two clearly separated parts with equal probability.

The obtained results agree very good with appropriate TL dates. For almost all radiocarbon dates TL date is inside 95% confidence interval of calibrated radiocarbon age. Only three dates from San Isidro (Valdivia Phase 8) are exceptional, but even for them the 95% confidence intervals of calibrated radiocarbon age and ±1s intervals (intervals of standard error) of TL dates are abutting.

The results of calibration of selected dates related to succeeding phases are presented in Figures 2. Table 2 contains a list of dates included in the calibration. Its important to accent that the number of dates included to analysis is not enough for delimitation of time intervals of individual phases with high reliability, but it is sufficient for approximate estimation.

Figure 2 shows composite probability distributions of calibrated radiocarbon dates for succeeding phases of Valdivia obtained from sites Real Alto, Loma Alta, Colimes, Ayalán and San Isidro (see Table 2). We can note, that chronological succession is evident, although the distribution is partially overlapping. All distributions (Except phase 1a) have a shape with the highest part in the middle. We can assume, that limits of these middle parts show presumable limits of appropriate phases.

The time intervals of individual phases specified as 50%, 68% and 95% confidence intervals of appropriate composite probability distribution are presented in table 3. It is not straightforward task to decide, which of these intervals is the best image of time interval of specified phase. We suggest to use the 68% confidence interval, which corresponds ±1s interval of radiocarbon dates, or 50% confidence interval, which conform to conception of the floruit of a culture, proposed by Barbara Ottaway (Ottaway, 1973; Atchinson et. al., 1991).


Concluding Remarks

Early use of 14C dating in Ecuadorian archaeology, was undoubtedly of great importance to substantiate the antiquity of the Formative process there. The method of excavation employed, which disregarded the history of site formation and its cultural deposits, did not allow for a precise dating of archaeological events. Unfortunately, this has been a widely used method of excavation not only in Ecuadorian, but in South American Archaeology in general. In the middle seventies, although new methods of excavation began to be used, the high cost of 14C assays, did not allow for a sufficient number of organic samples to be dated, and in this way, validate the results of the more precise, forms of event-oriented excavations now in use. The chronic lack of sufficient-funds, since the nineteen eighties, made new advances in 14C, like dating (like AMS) unavailable to most archaeological projects in Ecuadorian archaeology. Many of the few dates obtained are based on any available samples, without selecting them for the least possible form of intrinsic error. Charcoal samples are best, when they come from closed contexts like shards sealed in refuse pits, grains or straw inside adobe bricks, or bits of charcoal in the bake clay of burnt wattle-and-daub walls, or from bone covered with stones or inside a vessel. It is important to be sure that samples had a short life, and that they were not too old at the time they were buried. For this reason such samples like small branches, twigs of brushwood, charred cereal grains, are best. Large charcoal samples, although they appear to give “good dates” to most archaeologists, could “derive from roof timbers -posts or other large pieces of construction material (6) - that might themselves have been centuries old when destroyed by fire, then one is dating some early construction, not the context of destruction.” (Renfrew and Bahn, 1991:126-127).

It is important for archaeologists not only to be aware of the various forms of contamination a sample might have been subjected to, in the past (7). They should also make sure, themselves and their action in the field and in the laboratory are not a major source of contamination (8). The assays, and the calibration should be discussed critically with the physicists at the 14C laboratory in order to obtain a good date for the event. It has been mentioned above that the best way to secure a valid sequence of dates, is to date at least five samples from each clearly-stratified context that needs to be dated. However, because it is difficult to obtain sufficient datable organic materials at most sites, other dating methods such as thermoluminescence of potsherds should be undertook. Yet, because we are dealing with methods, it is not a straightforward procedure. It is necessary to compare, both 14C and TL dates with respect to the relative rate of deposition apparent in the site stratigraphy. This has been done for the Valdivia sequence based on the 14C calibrated dates for Real Alto and Loma Alta, and on the TL dates for Real Alto, Punta Tintina, Loma de los Villones, San Lorenzo del Mate, in relation to the stratigraphic deposits in Real Alto, and San Lorenzo del Mate. Ceramic modal-analysis and the study of changes in paste composition and firing temperature (9), have also served to refine the ceramic phase indicators proposed by Betsy Hill (1972/1974), which have served to substantiate the ceramic phases presented in Table 4.

There are enough radiocarbon dates for all Phases of the Valdivia chronological sequence (see Marcos, 1988 (1):78-81). However, these were measured before Hill’s (op.cit.) refinement of the sequence into 8 phases, were taken from artificial stratigraphical contexts, and refer to the A, B, and C sequence initially setup by Meggers, Evans and Estrada (op.cit.). The few assays that exist, taken from Valdivia Phases 4, 5, 6 and 7 deposits, present various problems, and therefore were not taken into consideration. Acceptable dates for these phases were provided by direct TL measurement of diagnostic ceramic shards from closed contexts at Real Alto. A dating 14C program of the complete Valdivia sequence, using the most modern methods is hereto a pending assignment.


REFERENCES
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TABLE 1

GdCALIB REPORT: calibration of set of unrelated radiocarbon dates
No	Site	Labcode	Radiocarbon age BP	95% confidence interval [calendar year BC]
VALDIVIA PHASE 1
1	Real Alto	GX-5269	6195±215	5520-4610
2	Loma Alta	GX-7704	5275±175	4455-3710
3	Real Alto	ISGS-448	5260±256	5065-3940
4	Real Alto	GX-5267	5495±200	4785-3940
5	Valdivia	M-1320	5150±150	4260-3655
6	Loma Alta	I-7076	5010±120	4045-3615 (91%) 3595-3520 (4%)
7	Loma Alta	ISGS-142	5000±190	4240-3360
8	Loma Alta	I-7075	4920±120	3965-3500 (92%) 3425-3380 (3%)
9	Real Alto	GX-5268	4900±170	4045-3310
10	P.Concep.	L-1042D	4700±100	3695-3295 (87%) 3240-3105 (8%)
11	Real Alto	ISGS-452	4700±300	4050-2615
12	Valdivia	ISGS-275	4700±75	3650-3335
13	Valdivia	ISGS-274	4680±75	3640-3315 (92%) 3225-3190 (2%)
14	Valdivia	HV-4674	4510±95	3500-3455 (3%) 3380-2915 (92%)
15	Valdivia	HV-4840	4495±100	3500-3455 (3%) 3380-2910 (92%)
16	Valdivia	M-1322	4620±140	3645-2925
17	P.Concep.	I-7167	4460±90	3355-2915
18	P.Concep.	L-1042C	4450±100	3365-2890
19	Valdivia	SI-84	4540±150	3630-2895
20	Valdivia	SI-83	4530±55	3370-3040
VALDIVIA PHASE 2
21	Real Alto	ISGS-468	4760±75	3665-3365
22	Loma Alta	ISGS-146	4750±120	3785-3295 (89%) 3235-3105 (6%)
23	Real Alto	ISGS-452	4700±300	4050-2615
24	Loma Alta	GX-7699	4630±160	3695-2920
25	Loma Alta	ISGS-192	4590±120	3630-3020 (91%) 2985-2930 (4%)
26	Colimes	ISGS-477	4525±75	3495-3465 (2%) 3375-3020 (88%) 2990-2925 (5%)
27	Colimes	ISGS-478a	4510±100	3500-3430 (5%) 3380-2915 (90%)
28	Colimes	ISGS-478b	4460±100	3370-2890
29	Real Alto	GX-5266	4495±160	3635-2870
30	Valdivia	M-1317	4480±140	3535-2870
31	Loma Alta	HV-4673	4335±100	3335-2855 (80%) 2820-2665 (15%)
32	Valdivia	SI-22	4450±90	3350-2910
33	Valdivia	W-631	4450±200	3635-2610
34	El Encanto	SI-1311	4405±90	3340-2885
35	Real Alto	ISGS-466	4390±75	3330-3155 (20%) 3135-2885 (75%)
36	Valdivia	HV-4838	4260±100	3100-2565
37	El Encanto	SI-1184	4370±85	3335-2875
38	Loma Alta	SI-1055	4370±65	3305-3230 (8%) 3120-2875 (86%)
39	Colimes	GX-5271	4365±245	3645-2390
40	Valdivia	SI-81	4270±60	3030-2855 (53%) 2820-2660 (45%)
41	Real Alto	ISGS-446	4265±75	3035-2835 (47%) 2825-2620 (48%)
42	Real Alto	ISGS-439	4110±75	2875-2490
43	Loma Alta	ISGS-190	3765±85	2450-1950
VALDIVIA PHASE 3
44	Valdivia	SI-18	4230±100	3085-2560 (93%) 2530-2500 (2%)
45	Valdivia	HV-4675	4075±110	2890-2325
46	Valdivia	W-632	4190±200	3345-2205
47	Valdivia	SI-85	4170±90	2915-2495
48	Valdivia	M-1318	4170±140	3040-2320
49	Valdivia	SI-16	4220±100	3035-2495
50	Real Alto	ISGS-467	4140±190	3310-3225 (3%) 3125-2175 (92%)
51	Valdivia	SI-80	4140±60	2880-2570
52	Valdivia	SI-82	4120±65	2880-2560 (89%) 2535-2495 (6%)
53	Valdivia	M-1321	4100±140	2925-2205
54	Real Alto	GX-7429	4050±185	3040-2035
55	Real Alto	GX-7430	3845±240	2910-1680
VALDIVIA PHASE 4
56	Valdivia	W-630	4050±200	3095-2015
57	Buenavista	SI-71	4040±55	2865-2810 (9%) 2745-2455 (86%)
58	P.Concep.	L-1232H	3900±150	2870-2805 (3%) 2770-1950 (92%)
59	Valdivia	SI-78	3970±65	2620-2280
VALDIVIA PHASE 5
60	Real Alto	GX-7437	4157±165	3310-3225 (3%) 3130-2280 (92%)
61	Real Alto	GX-7436	4145±170	3300-3235 (2%) 3105-2195 (93%)
VALDIVIA PHASE 6
62	Real Alto	GX-7438	4204±160	3330-3220 (4%) 3135-2340 (91%)
63	Real Alto	GX-7334	4015±170	2920-2030
VALDIVIA PHASE 7
64	Real Alto	GX-7439	4050±185	3040-2035
65	La Emerenciana	SMU-4259	4109±215	3330-2040
66	Anllula	P-2761	4020±220	3095-2895
VALDIVIA PHASE 8
67	Ayalan	N-2908	3665±95	2290-1750
68	Ayalan	N-2909	3630±105	2285-1650
69	San Isidro	ISGS-1221	3630±70	2190-1860 (86%) 1845-1775 (9%)
70	San Isidro	ISGS-1222	3620±70	2140-1760
71	San Isidro	ISGS-1223	3560±70	2115-2085 (3%) 2040-1690 (92%)
72	San Isidro	ISGS-1220	3500±70	1970-1630
73	San Isidro	PIT-426	3545±135	2205-1520
74	Anllula	N-2909	3630±105	2285-1690
75	Anllula	N-2908	3660±95	2295-1750
76	La Emerenciana	SMU-2263	3775±165	2620-1740
77	La Emerenciana	SMU-2225	3707±148	2485-1690
78	La Emerenciana	SMU-4549	3629±303	2875-1300
79	La Emerenciana	SMU-2226	3400±220	2305-1130
80	La Emerenciana	SMU-2241	3361±246	2305-1010

TABLE 2

Composite probability distribution of calibrated radiocarbon dates from Valdivia Culture. Dates included to calibration:
No	Site	Labcode	Radiocarbon age BP
PHASE 1a
1	Real Alto	ISGS-448	5260±256
2	Real Alto	GX-5267	5495±200
3	Loma Alta	I-7076	5010±120
4	Loma Alta	ISGS-142	5000±190
5	Loma Alta	GX-7704	5275±175
PHASE 1b
1	Real Alto	GX-5268	4900±170
2	Real Alto	ISGS-452	4700±300
3	Loma Alta	I-7075	4920±120
PHASE 2a
1	Colimes	ISGS-477	4525±75
2	Colimes	ISGS-478a	4510±100
3	Colimes	ISGS-478b	4460±100
4	Real Alto	GX-5266	4495±160
5	Real Alto	ISGS-452	4700±300
6	Real Alto	ISGS-468	4760±120
7	Loma Alta	ISGS-192	4590±120
8	Loma Alta	ISGS-146	4760±120
9	Loma Alta	GX-7699	4630±160
PHASE 2b
1	Real Alto	ISGS-466	4390±75
2	Real Alto	ISGS-439	4110±75
3	Real Alto	ISGS-446	4265±75
4	Valdivia	HV-4838	4260±100
5	Loma Alta	SI-1055	4370±65
6	Loma Alta	HV-4673	4335±100
7	Colimes	GX-5271	4365±245
PHASE 3
1	Real Alto	GX-7429	4050±185
2	Real Alto	ISGS-467	4140±190
PHASE 8
1	Ayalan	N-2908	3665±95
2	Ayalan	N-2909	3630±105
3	San Isidro	ISGS-1221	3630±70
4	San Isidro	ISGS-1222	3620±70
5	San Isidro	ISGS-1223	3560±70
6	San Isidro	ISGS-1220	3500±70
7	San Isidro	PIT-426	3545±135

TABLE 3

	50% confidence interval [calendar years BC]	68% confidence interval [calendar years BC]	95% confidence interval [calendar years BC]
Phase 1a	4340 to 3830	4460 to 3755	4820 to 3515
Phase 1b	3780 to 3455	3860 to 3340	4020 to 2835
Phase 2a	3475 to 3135	3555 to 3065	3765 to 2905
Phase 2b	3030 to 2765	3090 to 2695	3335 to 2510
Phase 3	2810 to 2455	2870 to 2360	3205 to 2080
Phase 8	2030 to 1830	2090 to 1790	2240 to 1665

TABLE 4. VALDIVIA CHRONOLOGY

Valdivia phases	14C dates 68%CI	TL chronology	BC chronology (10)
Phase 8b			1600-1450 BC (11)
Phase 8	2090-1790 BC	1700-1500 BC	1800-1600 BC
Phase 7		1900-1700 BC	1950-1800 BC
Phase 6		2100-1900 BC	2100-1950 BC
Phase 5		2400-0100 BC	2250-2100 BC
Phase 4		2600-2400 BC	2400-2250 BC
Phase 3	2870-2360 BC	2900-2400 BC	2800-2400 BC
Phase 2b	3090-2695 BC	3200-2900 BC	3300-2800 BC
Phase 2a	3555-3065 BC		3300-3000 BC
Phase 1b	3860-3340 BC	3600-3200 BC	3800-3300 BC
Phase 1a	4460-3755 BC		4400-3800 BC

APPENDIX 1

Valdivia 14C Determinations Loma Alta (12) 14C determinations according to Archaeological Phase and Stratigraphic Association
Laboratory	BP determination	Archaeological stratigraphic association
Valdivia 2b
ISGS-190	3765± 85 BP	Unit J-III 2.10m. bs.
HV-4673	4335±100 BP	Unit J-II 1.60m. bs.
SI-1055	4370± 65 BP	Unit J-II 1.70m. bs.
Valdivia 2a
ISGS-192	4590±120 BP	Unit J-III 2.20m. bs. associated with Cairn (13) N_8
GX-7699	4630±160 BP	From hearth in Valdivia 2a house floor
ISGS-146	4750±120 BP	Associated with Cairn N_1 Top of Cairn 1.90m. bs.
Valdivia 1b
I-7075	4920±120 BP	14C sample taken below levels of Cairns
Valdivia 1a
ISGS-142	5000±190 BP	Below Cairn N_6 2m. bs.
I-7076	5010±120 BP	14C sample taken below levels of Cairns
GX-7704	5275±175 BP	Hearth below Valdivia cultural deposits
Real Alto 14C determinations according to Archaeological Phase and Stratigraphic Association
Laboratory	BP determination	Archaeological stratigraphic association
Valdivia 7
GX-7439	4050±185 BP	Charcoal Sample from feature F-197 bell shaped food preparation pit (14).
Valdivia 6
GX-7434	4015±170 BP	Charcoal Sample from Wall Trench Structure S-13. (15)
GX-7438	4204±160 BP	Charcoal Sample from feature F-108 large “Fiesta” refuse pit. (16)
Valdivia 5
GX-7436	4145±170 BP	Charcoal Sample from Wall Trench Structure S-38 (17)
GX-7437	4175±165 BP	Charcoal Sample from feature F-101 “Fiesta” refuse pit. (18)
Valdivia 4
No Valdivia 4 Radiocarbon Samples were collected at Real Alto
Valdivia 3
GX-7430	3845±240 BP	Charcoal Sample from Structure S-1, level (19)
GX-7429	4050±185 BP	Charcoal Sample from Structure S-1, level 2 (20)
Valdivia 2b
ISGS-439	4110± 75 BP	Valdivia 2 Mound burnt wattle and daub
ISGS-446	4265± 75 BP	Top of Valdivia 2 Mound
ISGS-466	4390± 75 BP	Trench C 0.70-0.80m. bs.
Valdivia 2a
GX-5266	4495±160 BP	Trench B bottom of Valdivia 2 Mound
ISGS-452	4700±300 BP	Trench B bottom of Valdivia 2 Mound
ISGS-468	4760±120 BP	Trench C 0.80-0.90m. bs. first Valdivia 2 occupation.
Valdivia 1b
GX-5268	4900±170 BP	Trench C Structure S-2-77 0.90-0.98m. bs.
Valdivia 1a
ISGS-448	5620±250 BP	Trench C 0.90-1.00m. bs.
GX-5267	5495±200 BP	Adjacent to S-2-77 0.95-1.02m. bs.
GX-5269	6195±215 BP	Bottom of Structure S-2-77
Radiocarbon Determinations for San Isidro, Anllulla and La Emerenciana, San Isidro (Northern Manabí)
Laboratory	BP determination	Archaeological stratigraphic association
Valdivia 8
ISGS-1220	3500± 70 BP	San Isidro Valdivia 8 occupation
PIT-426	3545±135 BP	San Isidro Valdivia 8 occupation
ISGS-1223	3560± 70 BP	San Isidro Valdivia 8 occupation
ISGS-1222	3620± 70 BP	San Isidro Valdivia 8 occupation
ISGS-1221	3630± 70 BP	San Isidro Valdivia 8 occupation
Anllulla
Valdivia 8
N-2909	3630±105 BP	Valdivia 8, below the Jambelí occupation
N-2908	3660± 95 BP	Valdivia 8, below the Jambelí occupation
Valdivia 7
P-2761	4020±220 BP	San Isidro Valdivia 7 stratum below the Valdivia 8 occupation
La Emerenciana
Valdivia 8
SMU-2241	3361±246 BP	Transition Valdivia 8/ Machalilla, ceramic content similar to Valdivia 8b from San Lorenzo del Mate
SMU-2226	3400±220 BP	Transition Valdivia 8/ Machalilla, ceramic content similar to Valdivia 8b from San Lorenzo del Mate
SMU-4549	3629±303 BP	Valdivia 8, below Valdivia 8b occupation
SMU-2225	3707±148 BP	Valdivia 8, below Valdivia 8b occupation
SMU-2563	3775±165 BP	Valdivia 8, below Valdivia 8b occupation
Valdivia 7
SMU-4259	4109±215 BP	Valdivia 7, below Valdivia 8 occupation

APPENDIX 2

Thermoluminescence Age Determinations from Real Alto, Punta Tintina, Loma de los Villones, and San Lorenzo del Mate Ceramics.
Sample Number	Provenience (21)	Formal Class	TL determination
Valdivia 8
7248d	LV-U4-25 cmbs	18 deep carinated bowl	1620±289 BC
7248c	“	35 carinated rim olla wm	1602±329 BC
7248b	“	8 deep incurved bowl	1596±296 BC
7248e	“	Too small to reconstruct	1523±310 BC
SLM-24-38	SLM-U2-45 cmbs	36 carinated rim olla cn	1446±265 BC
SLM-24-41	“	6 deep hemispheric bowl	1422±245 BC
SLM-24-40	“	36 carinated rim olla cn	1410±260 BC
Valdivia 7 and Thin Orange Engraved and Punctated Ware (Protomachalilla)
SLM-53-a	SLM-U2-65 cmbs	36 carinated rim olla cn	1916±265 BC
7240a	RA-U2-30 cmbs	6 deep hemispheric bowl	1894±328 BC
SLM-53-64	SLM-U2-65 cmbs	42 Top for 36	1857±324 BC
7249e	LV-U4-45 cmbs	27 S-shaped neck olla	1834±331 BC
7249d	“	7 m. deep incurved bowl	1819±375 BC
7240b	“	7 hemispherical bowl	1811±333 BC
7240d	“	34 short curved neck olla	1874±303 BC
SLM-53-59	SLM-U2-65	40 carinated rim olla wm	1763±286 BC
7259a	LV-U4-45 cmbs	3 flaring-wall deep plate	1700±384 BC
Valdivia 6
SLM-56-76	SLM-U2-100 cmbs	40 carinated rim olla wm	2167±331 BC
SLM-56-84	“	33 short neck globular olla	2081±344 BC
7220b	RA-U1-45 cmbs	25 shallow bowl	2052±353 BC
SLM-62-21	SLM-U2-100 cmbs	16 shallow carinated bowl	2048±338 BC
7220c	RA-U1-45 cmbs	29 bell-shp. long neck olla	2042±427 BC
7220d	“	”	2039±411 BC
7220e	“	32 short bell-neck jar	2037±300 BC
Valdivia 5
7241c	RA-U2-40 cmbs	16 shallow carinated bowl	2321±301 BC
7241b	“	16 shallow carinated bowl	2306±347 BC
7241e	“	4 shallow hemisph. bowl	2292±352 BC
7220a	RA-U1-60 cmbs	20 neckless olla	2287±315 BC
7241a	RA-U2-40 cmbs	27 S-shaped neck olla	2243±324 BC
Valdivia 4
7243d	RA-U2-55 cmbs	Undiagonistic body sherd	2541±378 BC
7243b	“	35 carinated rim olla wm	2524±358 BC
7243a	“	Unidagonostic body sherd	2458±331 BC
7243c	“	6 deep hemispheric bowl	2405±358 BC
Valdivia 3
7222e	RA-U1-80 cmbs	23 folded rim l-neck olla	2897±409 BC
7222c	“	33 short-neck globular olla	2829±404 BC
7223a	“	25 S-shaped neck olla	2829±381 BC
7223e	“	17 deep carinated bowl	2740±391 BC
Valdivia 2b
7245b	PT-U3-18 cmbs	22 folded rim olla	3154±440 BC
7245a	“	23 long neck f-rim olla	3024±410 BC
7245e	“	23 long neck f-rim olla	2958±433 BC
7246b	“	33 short neck globular olla	2904±524 BC
7246a	“	33 short neck globular olla	2888±483 BC
7245c	“	23 long neck f-rim olla	2727±476 BC
Valdivia 2a
7235a	RA-U1-100 cmbs	19 deep neckless olla	3270±426 BC
7235b	“	32 short bell-necked jar	3093±407 BC
7234a	“	21 short-neck f-rim olla	3052±436 BC
Valdivia 1b
7238b	RA-U1-140 cmbs	19 deep neckless olla	3673±439 BC
7238a	“	21 short-neck f-rim olla	3577±454 BC
7236a	“	33 short-neck globular olla	3524±487 BC
7238c	“	9 deep tetrapod bowl	3388±424 BC
7238d	“	9 deep tetrapod bowl	3284±375 BC
7236b	“	9 deep tetrapod bowl	3149±496 BC
7236c	“	33 short-neck globular olla	3099±578 BC
7236d	“	23 folded rim l-neck olla	3078±435 BC

NOTES
1 The 14C assay, with its margin of error, and the laboratory reference number, should be followed by B.P. (before present). When calendar years are reported, these should be followed by b.c. or a.d. (in lower case) if the dates are not calibrated. Calibrated dates should always be indicated by B.C. or A.D. (in capital letters).

2 Ronald Lippi (1983) in his unpublished doctoral dissertation at the Department of Anthropology, University of Wisconsin, Madison La Ponga and the Machalilla Phase of Coastal Ecuador, offered a new Machalilla sequence.

3 The project CERAMIC DATING BY THERMOLUMINESCENCE AND GEOLOGICAL DETERMINATION OF ARCHAEOLOGICAL MATERIALS SOURCE AREAS, provided a excellent validation of the Valdivia Chronology, complementing and expanding the scope of the existing 14C determinations(Alvarez, Marcos and Spinolo, 1995).

4 Since then, more precise methods of 14C dates calibration have been described by various authors. Several 14C/tree-ring dendrochronological calibration tables have been proposed by Suess (1967, 1970 ) Damon et. al (1974 ) Struiver, et. al.(1993).

5 See J. Marcos 1988, Real Alto. La Historia de un centro ceremonial Valdivia. (Primera Parte) Biblioteca Ecuatoriana de Arqueología Vol 4, pp. 144-145, fig. bottom page 144. ESPOL/CEN, Quito.

6 Addition by J. G. Marcos

7 Forms of contamination before sampling are water logged sites where water dissolves the carbon from a samples and deposits it elsewhere, also the formation of mineral concretions around the carbon sample can be a problem. However the latter can be solved in the laboratory.

8 In order not to contaminate the sample this should be sealed within a clean container, such as a plastic bag, and its should be labeled outside the container. Carboard or paper labels should not be put inside the container.

9 These studies have been carried out by Aureli Alvarez and Jorge G, Marcos at the Archaeological Materials Service of the Universidad Autónoma de Barcelona, Bellaterra, Barcelona. See Alvarez, A., Marcos, J. And Spinolo G. (1995).

10 The BC chronology has been established through the comparative study of radiocarbon dates and TL dates, in relationship with the relative rate of deposition at Real Alto and San Lorenzo del Mate.

11 Phase 8b is proposed based on ceramic sequence at San Lorenzo del Mate, and the TL dates from the upper deposit of Unit 2b. The appearance of pedestal plates and compoteras in this context suggests that there is a distinct assemblage after the Valdivia Phase 8 proposed by Hill. We are provisionally referring to it as phase 8b, although in the future, after a close comparison with the Vlaidivia-Machalilla transitional phase defined by Staller (1994), it may be better to refer to it as Valdivia Phase 9.

12 Loma Alta is a Valdivia 1a-2b occupation covered by an Engoroy phase occupation.

13 The so called Cairns, both at Loma Alta and Real Alto, proved to be Manos and Metates kept (or sacrificed) at the bottom of Valdivia 2a bell-shaped storage pits. Sometime these sacrifices contained vessels and burials. (see foot note 3)

14 This determination is too old for Valdivia 7 even when calibrated it is closer to Valdivia 4 dates. This could be due to reuse of long lasting building material as firewood.

15 This determination is again too old for Vakdivia 6, it may be due to reuse of long lasting building material.

16 This aberrant date may result from the use of old building material as firewood

17 Although expected date falls within the lower part of this determination interval, it may also be due to the reuse of old building material.

18 Date falls within lower part of the calibration interval. However reuse of building material for cooking fires might account for slightly older than expected date

19 This date falls on the upper part of the calibration interval.

20 This date is more in alignment with Valdivia 3 expected dates.

21 SLM = San Lorenzo del Mate; RA = Real Alto; LV = Loma de los Villones; PT=Punta Tintina


Figure 1A

Figure 1B

Figure 2